OS3.1 | Understanding ocean ecosystems, biogeochemical cycles and their responses to climate change
EDI
Understanding ocean ecosystems, biogeochemical cycles and their responses to climate change
Convener: Alessandro Tagliabue | Co-conveners: Charlotte Laufkötter, Fanny Monteiro, Nicola Wiseman
Orals
| Thu, 18 Apr, 08:30–12:25 (CEST), 14:00–15:40 (CEST)
 
Room 1.61/62
Posters on site
| Attendance Wed, 17 Apr, 16:15–18:00 (CEST) | Display Wed, 17 Apr, 14:00–18:00
 
Hall X4
Posters virtual
| Attendance Wed, 17 Apr, 14:00–15:45 (CEST) | Display Wed, 17 Apr, 08:30–18:00
 
vHall X5
Orals |
Thu, 08:30
Wed, 16:15
Wed, 14:00
Climate induced alterations to net primary production act alongside changes to biogeochemical cycling of oxygen and nutrients to affect marine ecosystem structure and function, as well as the ocean carbon cycle. Climate change is driving alterations to these key components of ocean health, both via long-term changes and the emergence of extremes. The 6th Climate Model Intercomparison Project provides new opportunities to analyze the long-term changes in biogeochemistry under different emissions scenarios, as well as to explore the emergence and potential impacts of extremes. Additionally, historical variability linked to climate oscillations such as ENSO and the Southern Annular Mode provide an opportunity to bring insights from observed changes and impacts, as well as developing fundamental understanding of the marine ecosystem-biogeochemical system.

This session invites submissions, from both observations and modelling efforts, that address the impact of historical variability and climate change on net primary production, biogeochemical cycling of nutrients and oxygen, and the ocean carbon cycle, including cascading effects for marine ecosystems to modulate biodiversity and ecosystem services.

Orals: Thu, 18 Apr | Room 1.61/62

Chairpersons: Nicola Wiseman, Charlotte Laufkötter
Session 1
08:30–08:35
08:35–08:45
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EGU24-16428
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On-site presentation
Ana C. Franco, Debby Ianson, Raffaele Bernardello, and Adam H. Monahan

The Northeast Pacific is an important net sink of atmospheric CO2. However, substantial natural variability modulates the long-term increase of seawater partial pressure of CO2 (pCO2), potentially influencing the magnitude of the CO2 sink. In addition to the seasonal cycle, the Pacific Decadal Oscillation (PDO) is known to play a role in driving a large fraction of the non-seasonal variability in the region. Yet, the magnitude of this natural variability, especially periods of high surface dissolved inorganic carbon (DIC), are not well constrained. Here we quantify the seasonal and non-seasonal variability in DIC and pCO2 using observations from the Line P program, the longest marine carbonate system time-series transect in the NE Pacific (1990-2019), as well as an ensemble of historical simulations with an Earth system model (EC-Earth-CC). Preliminary results show that the mean amplitude of the DIC seasonal cycle is similar across our NE Pacific transect (23-30 µmol kg-1) and decreases with depth to less than 5 µmol kg-1 at 60 to 70 m. In contrast, the non-seasonal variability remains approximately constant with depth, ranging between 10 – 20 µmol kg-1. We quantify the role of the PDO in driving this residual non-seasonal variability, and analyse the contrasting impact of temperature and DIC changes in controlling surface pCO2 during opposite phases of the PDO.

How to cite: Franco, A. C., Ianson, D., Bernardello, R., and Monahan, A. H.: Seasonal and interannual inorganic carbon dynamics in the Northeast Pacific, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16428, https://doi.org/10.5194/egusphere-egu24-16428, 2024.

08:45–08:55
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EGU24-17424
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ECS
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On-site presentation
Freya E. Sykes, Julie Meilland, Adele Westgård, Thomas B. Chalk, Melissa Chierici, Gavin L. Foster, and Mohamed M. Ezat

Planktic foraminifera are calcifying marine protists living in the upper water column of the world’s oceans. As they grow, the composition of their calcite shells is influenced by their local environment. Thus, by analysing the geochemical signature of their fossil shells, a record of past changes in temperature, pH and salinity of the seawater can be reconstructed. Globigerina bulloides is a spinose planktonic foraminifera species that tolerates sub-tropical to sub-polar conditions and is present in high concentrations in the southern Norwegian Sea. It is of ecological interest as it encroaches into previously ‘cold water’ territories due to climate warming and Nordic Seas “Atlantification”. The relative abundance and shell geochemistry of fossil specimens of G. bulloides are also widely used for palaeoceanographic reconstructions in the region. Despite the widespread use of G. bulloides for these reconstructions, biological, metabolic, and behavioural observations are scarce, leaving large knowledge gaps regarding the impacts of these ‘vital effects’ on its calcification and preserved geochemical signature. One way to fill this gap is via the study of the species in controlled culture conditions, however to date, all reported culturing studies have been carried out in a temperate to warm water setting (>14oC), and using sub-tropical specimens. This reduces the applicability of these studies to G. bulloides inhabiting the high latitudes.

We cultivated over 250 individual specimens of G. bulloides from the Norwegian Sea across a range of temperatures (6 - 13o C), salinities (30.4 – 37.8), pHs (7.7 - 8.3) and carbonate ion concentrations (70 – 230 µmol/kg). Experimental conditions were chosen relative to ambient seawater at the collection site(s) and were intended to reflect a plausible range of past and future scenarios.

After several weeks in culture, we observed that G. bulloides was tolerant of environmental conditions well outside their natural range, with no significant difference in mortality or final size. This was corroborated by a high percentage of spine regrowth and/or maintenance (~65% for most treatments) after the first week. Many individuals thrived in culture, with some surviving up to three months. Two alternative strategies appeared to be employed; specimens opted either for rapid growth shortly followed by death, or for a prolonged lifespan with minimal size increase. Longer living specimens developed ectoplasmic structures on multiple occasions. Our observations suggest G. bulloides can exhibit considerable adaptability to shifting environmental conditions with implications to its tolerance to ongoing ocean changes.

How to cite: Sykes, F. E., Meilland, J., Westgård, A., Chalk, T. B., Chierici, M., Foster, G. L., and Ezat, M. M.: The response of planktic foraminifera Globigerina bulloides to changing environmental parameters through extensive culturing experiments, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17424, https://doi.org/10.5194/egusphere-egu24-17424, 2024.

08:55–09:05
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EGU24-7699
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ECS
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On-site presentation
Hanfeng Wen

Seasonal-interannual climate change is an important component of Earth’s climate system and has a significant impact on ecosystems and social systems. However, the scarcity of modern observational data limits our understanding of the seasonal-interannual climates in long-term timescales. The natural archives can provide information on climate change before the industrial period, but most of their temporal resolution is too low to capture the seasonal-interannual climate signals. Tridacna spp. is the largest marine bivalve, and its shell has the potential to trace climatic/environmental changes on a daily to interannual scale. In this study, we have investigated the daily growth pattern of modern Tridacna gigas shell (PL-1) from Palau based on laser scanning confocal microscopy images. The results showed that the growth pattern of PL-1 was affected by OLR primarily on the seasonal timescale. On the interannual timescale, the growth rate of the shell was modulated by ENSO through the changing OLR, SLH, and upwelling, which affect the effective solar radiation and nutrients accepted by Tridacna. The growth rate of Tridacna PL-1 is accelerated during the ENSO positive phase, and vice versa. This study indicates that the daily growth rate of Tridacna shells in equatorial regions may have the potential to reconstruct seasonal-interannual climate/environment variations.

How to cite: Wen, H.: Seasonal to interannual variations of daily growth rate of Tridacna shell from Palau Island, western Pacific, and their paleoclimatic implication, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7699, https://doi.org/10.5194/egusphere-egu24-7699, 2024.

09:05–09:15
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EGU24-4689
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ECS
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On-site presentation
Lotta Ternieten, Martina Preiner, Peter Kraal, and Oliver Plümper

Motivated by the goal to increase our knowledge of the impact of hydrothermal iron (Fe) nanoparticles on ocean chemistry and to explore their unique catalytic capabilities, we sampled suspended and dissolved matter in the water column above the Rainbow (36°-33°N) hydrothermal vent field at the Mid-Atlantic Ridge. Innovative sampling techniques were used to constrain the (trans)formation of hydrothermal iron-based nanoparticles. Instead of filtration of plume particles, freezing, and later resuspension, which is commonly used to separate particles from their surrounding solution and preserve them1, we immediately drop cast small amounts of the fluid on transmission electron microscopy (TEM) grids and plunge-freeze them, resulting in vitrification of dissolved compounds and preservation of containing nanoparticles. Using an array of (micro)spectroscopic techniques, TEM, and a machine learning approach, we can characterize the Fe nanoparticles and unravel their fate in the ocean biogeochemical cycle.

Initial results show that the new sampling approach allows us to successfully collect Fe colloids with minimal artifacts – specifically avoiding aggregation of various suspended phases during filtration, which can result in spurious spatial correlations. The hydrothermal plume samples collected closest to an active vent show crystalline spherical Fe-nanoparticles that predominantly consist of poorly-ordered Fe-oxyhydroxide and are in parts enriched in P, S, Ni, and/or Cu. Using the machine learning model SIGMA2 further allows us to explore the distribution of distinct Fe phases and reveals the local occurrence of reduced Fe as chalcopyrite and pyrite. On the outside, the Fe-nanoparticles are covered with an amorphous phase enriched in Mg, Cl, ± P, and S. Amorphous silica clusters are omnipresent and often co-occur with the Fe colloids. Notably, our results do not show associations of Fe with (organic) carbon.

These observations suggest that a higher local concentration of P within the Fe-colloids is potentially a crucial component affecting the Fe-nanoparticle's properties and environmental fate. Furthermore, this shows that C-rich phases do not significantly affect, at least in the early stages, the particles at the Rainbow vent field, contrasting previous studies, which suggest that organic compounds play a key role in stabilizing and transporting hydrothermal Fe1,3. While Si is abundant in the hydrothermal fluid and often interacts with Fe precipitates similar to P, we show spatial decoupling suggestive of a distinct precipitation mechanism. Neither in the hydrothermal plume away from the active vent nor in the sediment did we observe much transformation of the poorly-ordered Fe-colloids, suggesting that these were stable early on. However, we do observe an enrichment in organic compounds associated with the Fe-colloids further up in the buoyant plume.

Our research presents the first indications that during the early formation of hydrothermal Fe colloids, the properties of the Fe-based nanoparticle and, subsequently, the environmental fate and impact are more likely affected by P and Si than by organic carbon compounds.

 

1. Toner, B. M., et al. Acc. Chem. Res. 49, 128–137 (2016).

2. Tung, P., et al. Geochem., Geophys., Geosystems 24, (2023).

3. Bennett, S. A. et al. Deep Sea Res. Part : Oceanogr. Res. Pap. 58, 922–931 (2011).

How to cite: Ternieten, L., Preiner, M., Kraal, P., and Plümper, O.: The early fate of hydrothermal Fe nano-colloids at the Rainbow Hydrothermal Vent Field, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4689, https://doi.org/10.5194/egusphere-egu24-4689, 2024.

09:15–09:25
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EGU24-2725
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On-site presentation
Jiwei Li, Xiyang Dong, and Xiaotong Peng

Seafloor cold seepage systems are environments known for their high levels of arsenic, a prevalent and toxic metalloid in nature. However, the biogeochemical mechanisms of arsenic enrichment remain poorly understood. In this study, sediment cores recovered from the active, inactive, and reference areas of the Hama cold seep in the South China Sea were examined using geochemical and metagenomic analyses. Geochemical data revealed evident enrichment of total arsenic, sulfide-bound arsenic, and organic arsenic in the seep site sediments compared to the reference area. Metagenomic analyses identified genes involved in arsenic oxidation (aoxA and arxA) primarily present in the upper zone, while arsenic reduction genes (arrA) were predominantly detected in the deeper zone of the sediment cores in the active area. Moreover, 25 metagenome-Assembled Genomes possessing arsenic reduction genes were affiliated with the Desulfobacterota, possibly syntrophic partners of the Anaerobic Methane Oxidizing Archaea. Furthermore, a strong linear correlation was observed between the dissolved arsenic and DIC (R2=0.64, p<0.01) and δ13CDIC values (R2=0.86, p<0.01) in the active area. These results suggest a synergistic relationship between arsenate reduction and methane oxidation, possibly indicating the occurrence of AsR-AOM, within the sediment column of the active seep site. Combining this with the Fe and Mn geochemistry, we propose that arsenic was efficiently transported from the seawater column to the sediment column through rapid and continuous redox cycling of Mn and Fe, then stored in the sediment columns by HS-, which is produced by bacterially mediated sulfate reduction. In summary, these findings indicate that cold seepage systems function as crucial sink for arsenic in the deep ocean, which would create arsenic-deficient seawater environments during the large-scale methane release events in earth histroy.

How to cite: Li, J., Dong, X., and Peng, X.: Seafloor Cold Seeps as Crucial Mediators of Arsenic Enrichment in Deep Sea, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2725, https://doi.org/10.5194/egusphere-egu24-2725, 2024.

09:25–09:35
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EGU24-1273
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On-site presentation
Xuan Lu

Typhoons can significantly change marine biogeochemical processes. The organic matter (OM) decomposition (carbon source) plays an important role in biogeochemical process in coastal waters after typhoons. However, more field investigations are needed to quantify the contributions of particulate organic matter (POM) and dissolved organic matter (DOM) to OM decomposition triggered by typhoons. To address this issue, the stable isotopes of particulate OM (POM) and the spectral properties of dissolved OM (DOM) were investigated before and after Typhoon "Barija" in Zhanjiang Bay, northwestern South China Sea. High-salinity seawater intruded from the lower bay to the upper bay due to the external forces of clockwise wind stress, thereby forming an ocean front in the middle bay during the typhoon. The POM decomposition induced by the typhoon in the upper bay (inventory 72%) was substantially higher than in the lower bay (inventory 5%) due to the barrier effect of ocean front in the middle bay. However, the decomposition removed only 1–4% DOM in the upper bay, and a net addition of DOM occurred in the lower bay due to phytoplankton growth and POM decomposition. More importantly, although the quantity of DOM is much larger than that of POM in the water, the inventory of POM in the upper bay removed by typhoon-induced decomposition (20.19 g m-2) is much higher than that of DOM (16.08 g m-2). Overall, our study suggests that POM decomposition is more critical than DOM decomposition after typhoons, mainly controlled by the strong ocean front and vertical mixing.

How to cite: Lu, X.: Using stable isotopes and spectral properties to quantify the contributions of particulate organic matter and dissolved organic matter to organic matter decomposition triggered by typhoons, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1273, https://doi.org/10.5194/egusphere-egu24-1273, 2024.

09:35–09:45
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EGU24-1951
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On-site presentation
Fajin Chen and Qibin Lao

Typhoons are extreme whether events that can not only affect marine dynamics, but also change marine biogeochemistry, which greatly impact on the marine eco-environment and climate. Recently, we reported that decomposition (as a carbon source) of organic matter (OM) is the dominant process in coastal waters after typhoons, which is contrary to phytoplankton blooms (as a carbon sink) in previous studies. The decomposition directly affects the global carbon and nitrogen cycles, and the efficiency of the biological pump and global climate change. Yet, the mechanisms of OM decomposition after typhoons and the question of whether the decomposition is mainly of particulate organic matter (POM) or dissolved organic matter are still unclear. To address these issues, more than ten typhoons with different intensity, moving speed, and path of the typhoon were chosen, and physicochemical parameters and multiple isotopes in the coastal waters were measured before and after typhoons. The results showed that not all typhoons can trigger phytoplankton blooms in the oceans, which mainly depends on the supply of nutrients after typhoons. However, a positive apparent oxygen utilization value occurred in the coastal waters, suggesting that decomposition of OM was the dominant biogeochemical process regardless of whether phytoplankton blooms occurred after the typhoon. Despite the overall larger DOM in the water column, the amount of POM removed by typhoon-induced decomposition is much greater than that of DOM. Our study suggests that typhoon-induced decomposition might be dominated by POM, which is not conducive to the storage of OM in sediments. It means that the capacity of sediments as a carbon sink will be weakened under global warming (increasing typhoon events).

How to cite: Chen, F. and Lao, Q.: Characteristics and Mechanisms of Typhoon-Induced Decomposition of Organic Matter and Its Implication for Climate Change, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1951, https://doi.org/10.5194/egusphere-egu24-1951, 2024.

09:45–09:55
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EGU24-11752
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On-site presentation
Lorenzo Mentaschi, Tomas Lovato, Momme Butenschön, Jacopo Alessandri, Leonardo Aragao, Giorgia Verri, Roberta Guerra, Giovanni Coppini, and Nadia Pinardi

The Adriatic Sea is home to diverse marine ecosystems, showing rich biodiversity and distinctive ecological dynamics. Its complex coastal habitats and waters support a variety of species, playing a crucial role in the region's ecology and economy. Understanding the impact of ongoing climate changes on this delicate environment is vital for the basin's future preservation. To address this, we developed a comprehensive biogeochemical model for the entire basin, featuring a horizontal resolution of approximately 2 km and 120 vertical levels. This model is driven by atmospheric, hydrological, and ocean circulation projections from 1992 to 2050, downscaled from one Med-CORDEX model under the RCP8.5 emission scenario, developed within the AdriaClim project. The projected changes between 1992-2011 and 2031-2050 were evaluated in distinct trophic ecoregions identified by means of a k-medoid classification. The results reveal a strong oligotrophication tendency, particularly pronounced in the northern estuarine area. This trend can be largely attributed to a significant decrease in river discharge projected by our modelling system for the rivers of the Po Plain. This scenario of unproductive resources, ongoing warming, salinization, and acidification poses concerns about the long-term resilience of the Northern Adriatic food web structure, adapted to thrive in high trophic conditions. Our study provides the stakeholders with insights into how potential long-term decreases in Northern Adriatic river regimes might impact the marine ecosystem and its future goods and services.

How to cite: Mentaschi, L., Lovato, T., Butenschön, M., Alessandri, J., Aragao, L., Verri, G., Guerra, R., Coppini, G., and Pinardi, N.: Projected extreme oligotrophication of the marine ecosystems of the Adriatic Sea, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11752, https://doi.org/10.5194/egusphere-egu24-11752, 2024.

09:55–10:05
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EGU24-1811
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On-site presentation
Oligotrophic Trend following surface freshening in the western Arctic Ocean basin    
(withdrawn)
Yanpei Zhuang, Haiyan Jin, Di Qi, and Jianfang Chen
10:05–10:15
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EGU24-13505
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ECS
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On-site presentation
Investigating the Impact of Changing Ocean Ventilation, due to Climate Change, on the Biological Carbon Pump
(withdrawn)
Elisavet Baltas, Anna Katavouta, and Hugh Hunt
Coffee break
Chairpersons: Alessandro Tagliabue, Fanny Monteiro
Session 2
10:45–11:05
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EGU24-7894
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solicited
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On-site presentation
Lester Kwiatkowski, Laurent Bopp, Olivier Torres, James Orr, and Alessandro Tagliabue

Net primary production (NPP) by marine phytoplankton transfers organic matter and energy to higher tropic levels, supporting ocean food webs, as well as enhancing ocean carbon sequestration. Conversely, ocean acidification is a consequence of anthropogenic carbon uptake and alongside wide-ranging ecosystem impacts, reduces the capacity of the ocean to absorb future anthropogenic emissions. Multi-model projections of NPP (including those of CMIP exercises) have typically had very high associated uncertainty, with model uncertainty generally exceeding scenario uncertainty and limited confidence in even the sign of twenty-first century change. In contrast, projections of acidification have often been portrayed as having almost no associated uncertainty for a given emissions scenario. Here I will reassess these divergent characterizations. Can we say anything about projected changes in ocean NPP with confidence? And do we have any novel insights into projected ocean acidification? Efforts to constrain model projections of NPP have been challenging, with a dramatic increase in global projection uncertainty in CMIP6. Past efforts, which used the observable sensitivity of NPP to ENSO variability to constrain the multi-model NPP response to climate change, have been shown to have their limitations. Notably, parameterizations of marine diazotrophy and phytoplankton iron requirements can both limit the applicability of such emergent constraints. Nonetheless, at regional scales there is often broad agreement across multi-model NPP projections. With respect to acidification, the apparent lack of projection uncertainty is often a result of focusing on the annual mean global surface ocean. Numerous recent advances have been made in understanding regional and subsurface acidification as well as characterizing how the temporal variability of the ocean carbonate system is likely to respond. Particularly notable is the Arctic Ocean, where the amplitude and phasing of the seasonal cycle of CO2 partial pressure are projected to modify in response to both the geochemical and radiative impacts of anthropogenic emissions.

How to cite: Kwiatkowski, L., Bopp, L., Torres, O., Orr, J., and Tagliabue, A.: Reevaluating progress and uncertainties associated with projections of ocean net primary production and acidification , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7894, https://doi.org/10.5194/egusphere-egu24-7894, 2024.

11:05–11:15
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EGU24-14377
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On-site presentation
Nathaelle Bouttes, Lester Kwiatkowski, Elodie Bougeot, Manon Berger, Victor Brovkin, and Guy Munhoven

Coral reefs are currently under threat due to climate change and ocean acidification. However, future atmospheric CO2 levels, climate change and associated impacts on coral reefs remain uncertain. Critically, corals not only respond to atmospheric and climatic conditions but modify them. The calcification of corals modifies the concentration of dissolved inorganic carbon and total alkalinity in the upper ocean, impacting air-sea gas exchange, atmospheric CO2 concentrations, and ultimately climate. These feedbacks between atmospheric conditions and coral biogeochemistry can only be accounted for with a coupled coral-carbon-climate model.

To simulate coral-mediated climate-carbon interactions, we have implemented a coral reef calcification module into the iLOVECLIM Earth system model of intermediate complexity. We then performed an ensemble of 210 parameter perturbation simulations to derive carbonate production parameter values that optimise the simulated distribution of coral reefs and associated carbonate production rates. The tuned model simulates the presence of coral reefs and regional-to-global carbonate production values in good agreement with data-based estimates. We have used this new coupled model to project future changes in coral reef carbonate production. The use of a computationally efficient intermediate complexity model allows us to cover a large range of possible futures that encompass different emissions scenarios (SSPs), climate sensitivities (hence different levels of warming) as well as the possibility of coral reefs adapting to higher SSTs which would reduce the risk of bleaching. We found a high sensitivity of the simulations to the ability of corals to adapt to thermal changes and to climate sensitivity, with the possibility of 20 to 100% coral extinction in scenario SSP1-2.6 depending on these parameters. This highlights the importance of improving the constraints on these factors in models and observations.

How to cite: Bouttes, N., Kwiatkowski, L., Bougeot, E., Berger, M., Brovkin, V., and Munhoven, G.: Future evolution of coral reef carbonate production from a global climate-coral reef coupled model, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14377, https://doi.org/10.5194/egusphere-egu24-14377, 2024.

11:15–11:25
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EGU24-9341
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ECS
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On-site presentation
Stéphane Doléac, Marina Lévy, and Laurent Bopp

Human-induced climate change is expected to have a significant impact on primary production in the world's oceans, affecting marine ecosystems and the biological carbon pump. The sixth phase of the Coupled-Models Intercomparison Project (CMIP6) provides a common tool for investigating this impact. However, the extent and direction of the impact can vary widely among these models, partly due to the diverse representations of oceanic biogeochemistry. A comprehensive analysis of the biogeochemistry component in each model is therefore crucial for understanding the origins of diverse responses to similar environmental forcings. In this context, we focused on primary production projections in the subtropical North Atlantic Ocean under the RCP5-8.5 scenario in eight CMIP6 models. To ensure comparability across models with different ocean dynamics, a subtropical region was constructed in the observations using satellite and in-situ measurements from 2000 to 2020. A classification procedure based on a Self-Organizing Maps algorithm was applied to the entire North Atlantic Ocean, and the resulting classification was then used to identify the closest subtropical region in each model. While the eight regions obtained were similar in terms of location and physical boundaries, their surfaces varied from 19.1 to 24.1 million km². Among the eight models, three projected an increase in primary production in the region (up to +19.5 g-C/m2/yr), while the remaining five predicted a decrease (down to -33.4 g-C/m2/yr), despite a consistent decrease of nitrate concentrations across models. Nitrogen fixation, a crucial source of nitrogen in the area, emerged as a key differentiating factor among these models. Three of them (IPSL-CM6A-LR, CanESM5-CanOE, CanESM5) featured an implicit representation of diazotrophy, with no effective control from other nutrients. This led to a substantial increase in nitrogen fixation under the influence of rising temperatures. In IPSL-CM6A-LR and CanESM5-CanOE, the heightened nitrogen fixation sustained ammonium concentrations, enabling an increase in primary production with NH4 serving as an alternative nitrogen source. However, in CanESM5, where only one nitrogen pool was represented, the increase in nitrogen fixation was insufficient to offset the nitrogen decrease, resulting in a decline in primary production. In the models with an explicit representation of diazotrophs (MPI-ESM1-2-LR, CESM2, CESM2-WACCM), primary production was limited by declining phosphate concentrations, leading to a decrease in both nitrogen fixation and primary production. Finally, in models without any representation of nitrogen fixation, primary production decreased when nutrients were initially limiting (UKESM1-0-LL) and increased if they were not (ACCESS-ESM1-5). In conclusion, biogeochemical models with a more realistic representation of diazotrophy consistently projected a decline in primary production in the subtropical North Atlantic Ocean throughout the 21st century. The increases observed in some models were attributed to the absence or inadequate representation of interactions between phosphate, ammonium, and diazotrophy, making such scenarios unlikely. Consequently, an explicit representation of diazotrophs seems necessary for projecting the primary production response to climate change in the subtropical North Atlantic Ocean.

How to cite: Doléac, S., Lévy, M., and Bopp, L.: Nitrogen fixation as a key diverging factor of primary production projections in the subtropical North Atlantic Ocean in CMIP6 models, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9341, https://doi.org/10.5194/egusphere-egu24-9341, 2024.

11:25–11:35
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EGU24-5943
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ECS
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On-site presentation
Lana Flanjak, Aaron Wienkers, and Charlotte Laufkötter

Dissolved organic carbon (DOC) is a substantial pool of bioreactive carbon in the ocean, comparable in quantity to the atmospheric inorganic carbon reservoir. DOC plays an important role in the marine carbon cycle; its contribution to total organic carbon export corresponds to about 20%. Current modeling studies suggest a broad range of DOC surface concentration estimates, and the response of DOC concentration and export to climate change is unclear and has not yet been described in an Earth System Model. To address this knowledge gap, we make use of the ocean biogeochemistry and ecosystem model COBALTv2. We analyze DOC dynamics and export under the present and future climate conditions within the high-emission scenario. The COBALTv2 model, coupled to the GFDL’s ESM2M Earth System Model, enables us to trace DOC from its primary sources, including phytoplankton activity and grazer-prey dynamics, to its sinks such as bacterial remineralization. We also account for the physical processes such as advection that influences DOC distribution. Preliminary findings suggest that the current distribution of DOC in the ocean may undergo significant changes, contingent upon the biological sources and sinks that are sensitive to ocean temperature increases. The relative contributions of different phytoplankton groups to DOC production are expected to shift across various ocean regions, along with the magnitude of heterotrophic respiration, which is the predominant DOC sink. This study contributes to understanding and forecasting of potential shifts in oceanic DOC dynamics under current and future climate conditions.

How to cite: Flanjak, L., Wienkers, A., and Laufkötter, C.: Dissolved organic carbon dynamics in a changing ocean: A COBALTv2 Earth System Model analysis, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5943, https://doi.org/10.5194/egusphere-egu24-5943, 2024.

11:35–11:45
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EGU24-16901
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ECS
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On-site presentation
Rebecca Wright, Joe Guest, Tereza Jarníková, Marie-Fanny Racault, Erik Buitenhuis, Nicolas Mayot, Philip Townsend, and Corinne Le Quéré

Understanding how climate variability and climate change affects marine ecosystem dynamics and its cascading implications for the carbon cycle is a “known-unknown” that was highlighted in the past four Assessment reports of the IPCC. We present results from a novel set of global ocean biogeochemistry model branches which were designed to explore the role of marine ecosystem structure for carbon dynamics both globally and regionally, with a focus on the Southern Ocean.

PlankTOM12 is a global ocean biogeochemistry model based on the representation of marine microorganisms grouped into twelve Plankton Functional Types (PFTs) as a function of their importance for the carbon cycle. PlankTOM12 uniquely represents explicitly heterotrophic bacteria/archaea, six types of phytoplankton , and five types of zooplankton . We build three distinct branches of PlankTOM12, with identical ecosystem framework and identical physical environment, but each branch with its own set of ecosystem parameters allowing different ecosystem formations. Branch 1 (called GCB) is the historical branch that  underpinned much prior research on the carbon cycle using this model and contributed to the Global Carbon Budget 2023. Branch 2 (ECO) is optimised to reproduce the observed mean, seasonal cycle, and interhemispheric distribution of surface chlorophyll-a (Chla). Branch 3 (CO2) is optimised to reproduce the observed mean and seasonality of the partial pressure of surface ocean carbon dioxide (pCO2). Even though the parameterisations are optimised globally, many of the substantial differences between the three branches occur in the Southern Ocean. In particular, it was not possible to reproduce a good mean and seasonality for both Chla and pCO2 simultaneously in the Southern Ocean. Strikingly, each of the three PlankTOM12 model branches offers a different perspective on marine ecosystem dynamics. The branches differ most distinctly in the relative fraction of biomass that is distributed among PFTs: the GCB branch distributes most of its biomass in small phytoplankton PFTs and large zooplankton PFTs, the ECO branch distributes its biomass relatively evenly among PFTs, and the CO2 branch is intermediate with most biomass in the small phytoplankton PFTs and large zooplankton PFTs, but also substantial biomass in the medium-sized PFTs for both phyto- and zooplankton. We show how the differences in these ecosystem structures transfer through to differences in carbon dynamics, including primary and secondary production, sinking fluxes of organic carbon, calcium carbonate, and silica, and how they propagate to carbon export to the deep ocean and export efficiency. We present the response of the three branches to recent climate change and variability using hindcast simulations over 1948-2022, and discuss model evaluation based on available biogeochemistry and ecosystem observational data. Finally, we suggest future applications and questions which may be best addressed by each model branch.

How to cite: Wright, R., Guest, J., Jarníková, T., Racault, M.-F., Buitenhuis, E., Mayot, N., Townsend, P., and Le Quéré, C.: Community structure matters: diverse ecosystem structure shapes carbon dynamics in a model system., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16901, https://doi.org/10.5194/egusphere-egu24-16901, 2024.

11:45–11:55
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EGU24-21938
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On-site presentation
Christopher Follett, Barbara Duckworth, and Stephanie Dutkiewicz

Understanding the relative importance of top-down vs. bottom up controls for setting plankton populations is an open challenge in marine ecology. Recent work has focused on the sharp spatial decline in Prochlorococcus biomass when moving northward in the North Pacific transition zone. This work has argued against bottom up controls like temperature and for top down mechanisms like apparent competition or viruses setting the location of the collapse. However, as temperature and light modify the underlying rates in the system we would expect them to play some role in the temporal dynamics. Here, we seek to unify bottom up and top down controls to make predictions about the seasonal progression of the ‘Propocalypse’ and the associated predators of Prochlorococcus. Observations suggest that the Propocalypse occurs further poleward in the summer and about 10 degrees further south in the winter. Here, we use models to confirm that ecological interactions allow for the existence of the transition, and that the meridional movement is determined by growth rate changes due to light and temperature in the spring, and by mixed layer depth changes during the fall and early winter. We go on to seek a diversity-mortality relation for Prochlorococcus connecting viral mortality to the seasonal motion of the Propocalypse. 

How to cite: Follett, C., Duckworth, B., and Dutkiewicz, S.: Do Temporal Diversity Dynamics Reconcile Viral and Grazer Based Theories for the Propocalypse?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-21938, https://doi.org/10.5194/egusphere-egu24-21938, 2024.

11:55–12:05
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EGU24-11441
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On-site presentation
Emilio Marañón, Cristina Fernández-González, Solange Duhamel, and Mariona Segura

We have conducted experiments with both laboratory cultures and natural plankton assemblages, together with basin-scale observations across the Atlantic Ocean, to investigate the interactive effects of temperature and nutrient supply on phytoplankton across multiple levels of biological organization, including molecules, cells, populations and communities. Laboratory data indicate that nutrient supply has a stronger effect than temperature on photosynthetic protein abundance, C:N stoichiometry, photosynthesis and growth. Due to changing resource allocation into photosynthetic machinery, the chlorophyll a (chl a) content of cells is strongly dependent on both temperature and nutrient availability, which has implications for the use of chl a concentration as a proxy for phytoplankton biomass in the ocean. Across the tropical and subtropical Atlantic, experimental nutrient enrichment consistently causes an increase in chl a concentration, picoeukaryote abundance and the contribution of small nanophytoplankton to total biomass, all of which take place irrespective of temperature. Light-harvesting capacity is synergistically stimulated by warming and nutrient addition in both picocyanobacteria and picoeukaryotes. The latitudinal variability in elemental composition of different phytoplankton groups, determined on single cells with X-ray microanalysis across the temperate, subtropical and tropical Atlantic, reveals the effect of changing temperature and nutrient supply on C:N:P stoichiometry. Our experimental and observational results suggest that while changes in nutrient supply have a stronger effect than temperature on growth, metabolic rates, community structure and elemental stoichiometry, the warming of the surface ocean may increase the ability of tropical phytoplankton assemblages to exploit events of enhanced nutrient availability. Across multiple levels of biological organization, nutrient limitation tends to reduce the effects of temperature on phytoplankton ecophysiology.

How to cite: Marañón, E., Fernández-González, C., Duhamel, S., and Segura, M.: Role of temperature and nutrients as drivers of resource allocation, elemental stoichiometry, metabolism and growth in marine phytoplankton, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11441, https://doi.org/10.5194/egusphere-egu24-11441, 2024.

12:05–12:15
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EGU24-15355
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On-site presentation
Thomas Hermilly, Elodie Martinez, Julia Uitz, Marin Cornec, and Catherine Schmechtig

The South Pacific Ocean stands out as a dynamical region with contrasted biogeochemical (BGC) regimes. Among others, it encompasses mesotrophic areas as well as the most oligotrophic waters of the global ocean. Within these regions, the existing thousands of islands can locally or regionally disrupt the oceanic circulation and, thereby, thus the nutrient availability in the upper sunlit layer and the phytoplankton growth. Yet, the phytoplankton seasonal dynamics in these contrasted BGC regions remain largely unknown and understood. Indeed, most existing studies on phytoplankton seasonal variability from observations are either dedicated to the global ocean or based on remotely sensed data due to a lack of in-situ observations in the water column, preventing the consideration of 3D processes.

Here we took advantage of in situ observations from 13 BGC-Argo profiling floats that have drifted from 2015 to 2023 in five subregions of the South Pacific Ocean: the Tasman and Coral Seas, the Fiji island region, the oligotrophic and equatorial mesotrophic areas. We used measurements of temperature, salinity, chlorophyll-a fluorescence (Chl), particulate backscattering at 700 nm (bbp) used as a proxy of particulate organic carbon and Photosynthetically Active Radiation. The seasonal variations of Chl and bbp vertical distributions are characterized among the subregions and physical and biogeochemical processes likely involved have been investigated. To do so, we considered isolume and nutricline depths, the Mixed Layer Depth (MLD) as well as the maximum Brunt-Vaissala depth as an indicator of the ocean stratification stability. The latter appears more suitable than the MLD when related to the phytoplankton seasonal dynamics. 

How to cite: Hermilly, T., Martinez, E., Uitz, J., Cornec, M., and Schmechtig, C.: Seasonal variability of the phytoplankton biomass and its underlying processes in contrasted regions of the South Pacific Ocean based on BioGeoChemical-Argo observations, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15355, https://doi.org/10.5194/egusphere-egu24-15355, 2024.

12:15–12:25
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EGU24-2748
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On-site presentation
Alakendra Roychoudhury, Kayla Buchanan, and Saumik Samanta

In the South Atlantic HNLC regions, productivity limitation is largely attributed to light in combination with the unavailability of micro-nutrients, mainly dissolved iron (dFe). Many of these regions fall within the dynamic marginal ice zone (MIZ), which are highly vulnerable to future change in climate where in the past decades Southern Ocean is absorbing more heat than the polar north. It is hypothesized that sea-ice formed in winter concentrates macro- and micro-nutrients and serves as their source, on melting, to surface waters in spring to support phytoplankton blooms, where dFe concentrations can be less than 0.1 nM. For the logistical difficulties in accessing these remote areas, especially in winters, and analytical challenges, sea ice as a source or sink of micro-nutrients in these remote regions has remained understudied and only ~78 dFe usable data is available for the entire Southern Ocean sea-ice.

Sea-ice cores were collected in winter and spring from South Atlantic MIZ and analyzed for dissolved and particulate iron (pFe) along with other ancillary data. Ice-core depth profiles of dFe show a typical C-shape with higher dFe concentrations at the top and bottom of the core. dFe profiles did not follow the salinity profiles, suggesting external input of Fe at the top and bottom of the core and not brine drainage. The average concentration of dFe (0.53 ± 0.64 nmol kg-1; n = 34) in sea-ice remained consistently lower than pFe (3.82 ± 2.42 nmol kg-1; n = 11) and there was considerable heterogeneity even in replicate cores collected from the same floe. The measured concentrations translate into a total iron flux (TFe) of 38.05 ± 27.49 mol y-1 (n = 45) in South Atlantic MIZ. Both measured species show regularly lower concentrations than what has been measured from other regions of the Southern Ocean, resulting in the calculated flux from the studied MIZ being 30 times lower than what has been calculated from melting of near shelf ice. 

Experiments conducted in the laboratory show that majority of the dissolved iron accumulated in sea-ice is released within the first 10% of melting but with complete melting and mixing, resulting net dFe concentrations fall within the Fe-limiting conditions. pFe, although available at higher concentrations in sea-ice, had lower Fe/Al ratio compared to the typical crustal ratio. That is, a more refractory phase is released on melting of sea-ice, which is not ideal for uptake by phytoplankton. 

How to cite: Roychoudhury, A., Buchanan, K., and Samanta, S.: Marginal sea-ice is not a major source of iron to support spring blooms in the South Atlantic, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2748, https://doi.org/10.5194/egusphere-egu24-2748, 2024.

Lunch break
Chairpersons: Charlotte Laufkötter, Fanny Monteiro
Session 3
14:00–14:10
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EGU24-19854
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On-site presentation
Tatiana Ilyina, Hongmei Li, Lennart Ramme, and Chao Li

CO2 emission-driven simulations are becoming a priority way of running Earth system model simulations of climate change as they directly link Earth system responses to climate policies. Also large ensemble simulations have been identified as a key tool to quantify effects of internal climate variability in the Earth system. We ran a large ensemble of emission-driven climate change projections in MPI-ESM with various CMIP6 emission scenarios. Our simulations produce a realistic temporal and spatial evolution of atmosphric CO2, as well as ocean and land carbon sinks. An increased seasonal cycle in all carbon cycle compartments is projected in future simulations. Ongoing work focuses on discerning responses of the ocean and land carbon sinks to changing emissions. Thereby, we find that changes in atmospheric carbon are asymmetric to CO2 emissions across various scenario pathways. Furthermore, temperature continues to increase after CO2 emission mitigation. In our simulations, under negative emissions, the ocean and land shift from being sink to source after 2100. In particular, for the ocean carbon sink evolution, the regions which acted as a sink for anthropogenic CO2 in the 20th century, remain sinks also during the 21st century. However, the major carbon uptake shifts from the North Atlantic to the Southern Ocean and much of the additional carbon is then stored in the south-west Pacific. In the 22nd century, it is mostly the North Atlantic that shifts towards less uptake of CO2 and from which dissolved inorganic carbon is transported away, while the Barents Sea and WeddelSea keep taking up more CO2 than during pre-industrial times, and parts of the ocean in the southern hemisphere keep accumulating carbon. Air-land CO2 fluxes overlap among different scenarios emphasizing the substantial role of internal climate variability.

How to cite: Ilyina, T., Li, H., Ramme, L., and Li, C.: Unfolding responses in the global ocean and land carbon sinks and atmospheric CO2 to changing emissions with the large ensemble future projections with interactive carbon cycle., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19854, https://doi.org/10.5194/egusphere-egu24-19854, 2024.

14:10–14:20
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EGU24-7254
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ECS
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On-site presentation
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Amber A. Boot, Jeroen Steenbeek, Marta Coll, Anna S. von der Heydt, and Henk A. Dijkstra

Marine ecosystems provide several important services for the Earth System and society in the form of, for example, carbon export, food and income. These ecosystems, and the functions they provide, are under threat from anthropogenic climate change, pollution and overfishing.  Besides being a large risk for marine ecosystems, anthropogenic climate change might also lead to passing tipping points in the Earth System, leading to relatively fast and strong additional changes to the climate system.  A tipping element in the Earth System is the Atlantic Meridional Overturning Circulation (AMOC). Tipping of the AMOC will disrupt the climate system and lead to changes in temperature, precipitation, wind fields, ocean circulation and the carbon cycle. In this study, we look at the effect of a strong AMOC weakening on global marine ecosystems. We do this by forcing a state-of-the-art model, the Community Earth System Model v2 (CESM2), with low (SSP1-2.6) and high (SSP5-8.5) emission scenarios, and with an additional freshwater flux in the North Atlantic from 2015 to 2100. Since the ecosystem component of the CESM2 is limited, we use the CESM2 output in a marine ecosystem model, EcoOcean v2. EcoOcean simulates 52 functional groups including mammals, birds, zooplankton, benthic species and fish on a 1° horizontal grid, and reconciles food web dynamics with a dynamic niche model. EcoOcean is forced with phytoplankton biomass and temperature fields from the CESM2 simulations and this enables us to determine the effect of the AMOC weakening in CESM2 on marine ecosystems. In CESM2, the weakening of the AMOC has a large impact on phytoplankton biomass and temperature fields through various mechanisms including changes in stratification and mixed layer depth, changes in sea-ice cover, and changes in upwelling velocities. Through these mechanisms, the three dimensional distribution of nutrients in the ocean is altered which directly affects the primary producers in CESM2. In EcoOcean, we see that almost all functional groups are negatively impacted by an AMOC weakening. The strongest net effect is seen in the high emission scenario, but the relative effect of the AMOC weakening is larger in the low emission scenario.  There are some functional groups, e.g. pinnipeds, that show a strong decrease that closely follows the AMOC weakening. These results show that marine ecosystems will be under increased threat if the AMOC strongly weakens. Furthermore, the results show how tipping in the climate system can negatively impact marine ecosystems and thereby put an additional stress on socio-economic systems that are dependent on fishery industries as a food and income source.  

How to cite: Boot, A. A., Steenbeek, J., Coll, M., von der Heydt, A. S., and Dijkstra, H. A.: Global marine ecosystem response to a strong AMOC weakening under low and high emission scenarios, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7254, https://doi.org/10.5194/egusphere-egu24-7254, 2024.

14:20–14:30
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EGU24-19449
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ECS
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On-site presentation
Joost de Vries, Fanny Monteiro, and Levi Wolf

For many ecosystems, biodiversity promotes productivity. Global biodiversity loss due to anthropogenic climate change has thus raised concerns about its resulting impact on productivity since ecosystem services like carbon sequestration are key in limiting climate change. Our oceans are especially important in this context, as they sequester more carbon than terrestrial ecosystems. Nonetheless, our understanding of how biodiversity relates to productivity in oceanic ecosystems is limited and hitherto undescribed for coccolithophores, a main ocean calcifier which plays a key role in the ocean carbon cycle. Here, by combining a new comprehensive coccolithophore abundance data set and species distribution models we illustrate that biodiversity is decoupled from standing stocks for coccolithophores. We show this is because the processes driving coccolithophore diversity do not influence coccolithophore standing stocks. Our results contribute new knowledge about the relationship between productivity for a key marine planktonic microorganism, highlighting that diversity loss due to anthropogenic carbon emission does not necessitate reduced ocean standing stocks and productivity. This result is important for climate models, suggesting that they do not need to capture our ocean’s full diversity to capture key biogeochemical processes such as calcification and carbon fixation.  

 

How to cite: de Vries, J., Monteiro, F., and Wolf, L.: Unexpected decoupling between biodiversity and standing stocks in marine calcifying phytoplankton , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19449, https://doi.org/10.5194/egusphere-egu24-19449, 2024.

14:30–14:40
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EGU24-17453
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Virtual presentation
What determines the simulated strength of the future North Atlantic carbon uptake?
(withdrawn)
Nadine Goris, Jerry Tjiputra, Klaus Johannsen, Are Olsen, Jörg Schwinger, Siv Lauvset, and Emil Jeansson
14:40–14:50
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EGU24-2739
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ECS
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On-site presentation
Hyung-Gyu Lim, John Dunne, Charles Stock, Paul Ginoux, Jasmin John, and John Krasting

The El Niño-Southern Oscillation (ENSO) strongly influences phytoplankton in the tropical Pacific, with El Niño conditions suppressing productivity in the equatorial Pacific (EP) and placing nutritional stresses on marine ecosystems. The Geophysical Fluid Dynamics Laboratory's (GFDL) Earth System Model version 4.1 (ESM4.1) captures observed ENSO-chlorophyll patterns (r = 0.57) much better than GFDL's previous ESM2M (r = 0.23). Most notably, the observed post-El Niño “chlorophyll rebound” is substantially improved in ESM4.1 (r = 0.52). We find that an anomalous increase in iron propagation from western Pacific (WP) subsurface to the cold tongue via the equatorial undercurrent (EUC) and subsequent post-El Niño surfacing, unresolved in ESM2M, is the primary driver of chlorophyll rebound. We also find that this chlorophyll rebound is augmented by high post-El Niño dust-iron deposition anomalies in the eastern EP. This post-El Niño chlorophyll rebound provides a previously unrecognized source of marine ecosystem resilience independent from the La Niña that sometimes follows.

How to cite: Lim, H.-G., Dunne, J., Stock, C., Ginoux, P., John, J., and Krasting, J.: Oceanic and Atmospheric Drivers of Post-El-Niño Chlorophyll Rebound in the Equatorial Pacific , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2739, https://doi.org/10.5194/egusphere-egu24-2739, 2024.

14:50–15:00
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EGU24-12177
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ECS
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On-site presentation
Lucas Casaroli, Tatiana Ilyina, Nuno Serra, and Fatemeh Chegini
Within the oceanic mesoscale and submesoscale spectral ranges, energetic phenomena unfold which include eddies, fronts, filaments and internal waves. Those intricate features significantly impact the biogeochemical cycles. For instance, they contribute to the vertical transport of nutrients to the euphotic zone, modify the mixed layer depth through vertical displacement of isopycnals, and play a pivotal role in shaping the patchiness of phytoplankton. Many ocean biogeochemical models are constrained by computational resources, limiting their ability to resolve the complex details of high-resolution processes. In this study, we introduce a state-of-the-art ocean biogeochemical model (ICON-O/HAMOCC) with a uniform 10-km resolution. Our results show the impact of vortical structures on oxygen, phytoplankton, and carbon. The model solution highlights a robust signal of Tropical Instability Waves (TIW) in biogeochemical tracers in the Equatorial Pacific. We assess the seasonal and interannual variability of this signal, demonstrating the significant role of eddies in ocean oxygenation and in the carbon cycle.

How to cite: Casaroli, L., Ilyina, T., Serra, N., and Chegini, F.: Mesoscale and submesoscale biogeochemical signatures in a high-resolution ocean model (ICON-O/HAMOCC), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12177, https://doi.org/10.5194/egusphere-egu24-12177, 2024.

15:00–15:10
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EGU24-6435
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ECS
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On-site presentation
Jens Terhaar

The ocean and land biosphere are the two major natural sinks of carbon at present and the ocean is projected to become the dominant sink on centennial timescales when anthropogenic carbon emissions become zero and temperatures stabilize, and. Despite the ocean’s importance for the carbon cycle and climate, uncertainties of the decadal variability of this carbon sink and the underlying drivers of this decadal variability remain uncertain. The main tools to assess the ocean carbon sink over the last decades are global observation-based pCO2 products that extrapolate sparse pCO2 observations in space and time and global ocean biogeochemical models forced with atmospheric reanalysis data. However, these tools (i) are limited in time over the last 3 to 7 decades, which hinders statistical analyses of the drivers, (ii) are all based on the same internal climate state, and (iii) cannot assess the robustness of the drivers in the future, especially when carbon emissions decline or cease entirely. Here, I use an ensemble of 12 Earth System Models (ESMs) from phase 6 of the Coupled Model Intercomparison Project (CMIP6) to understand drivers of decadal trends in the past, present and future ocean carbon sink. The simulations by these ESMs span a period of 251 years and include 4 different future Shared Socioeconomic Pathways, from low emissions and high mitigation to high emissions and low mitigation. Using this ensemble, I show that 80% of decadal trends in the multi-model mean ocean carbon sink can be explained by changes in decadal trends of atmospheric CO2 as long as the ocean carbon sink remains smaller than 4.5 Pg C yr-1. The remaining 20% are due to internal climate variability and ocean heat uptake, which results in a loss of carbon from the ocean. When the carbon sink exceeds 4.5 Pg C yr-1, atmospheric CO2 rises faster, climate change accelerates, and decadal trends in the ocean carbon sink are substantially smaller than estimated based on changes in atmospheric CO2 trends. The breakdown of this relationship under high emission scenarios, also implies that the increase in the ocean carbon sink is effectively limited, even if the trend in atmospheric CO2 continues to increase. This limit of decadal trends in the ocean carbon sink is here estimated to be 1 Pg C yr-1 dec-1.Previously proposed drivers, such as the atmospheric CO2 or the growth rate of atmospheric CO2 can explain trends in the ocean carbon sink for specific time periods, for example during exponential atmospheric CO2 growth, but fail when emissions start to decrease again. The robust relationship over a large Earth System Model ensemble also suggests that very large  positive and negative decadal trends of the ocean carbon sink by some pCO2 products are highly unlikely, and that the change in the decadal trends of the ocean carbon sink in 2000 is likely substantially smaller than estimated by these pCO2 products.

How to cite: Terhaar, J.: Decadal trends of the ocean carbon sink in Earth System Models in the past, present and future, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6435, https://doi.org/10.5194/egusphere-egu24-6435, 2024.

15:10–15:20
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EGU24-15731
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On-site presentation
Yohei Takano and the Ocean Biogeochemistry Modelling Group

   This study presents an analysis of the historical upper ocean (0-700m) dissolved oxygen (O2) and heat content changes from a suite of  the Coupled Model Intercomparison Project phase 6 (CMIP6) ocean biogeochemistry simulations. The simulations include both forced ocean-only models (the Ocean Model Intercomparison Project, OMIP1 and OMIP2) and coupled historical simulations from Earth System Models (ESMs)  (CMIP6 Historical). Simulated changes in the O2 inventory and ocean heat content (OHC) over the past five decades spatially and temporally diverge across the models. The multi-model mean and spread of the upper ocean global O2 inventory trend for each of the simulations is 0.03 ± 0.39 × 1014 [mol/decade] for OMIP1,  -0.37 ± 0.15 × 1014 [mol/decade] for OMIP2, and -1.06 ± 0.68 × 1014 [mol/decade] for CMIP6 Historical simulations, respectively. The latest observational trend based on the World Ocean Database 2018 is -0.98 × 1014 [mol/decade],  in line with the CMIP6 Historical multi-model mean, though this recent observations-based trend estimate is weaker than previously reported trends.  A comparison between OMIP1 and OMIP2 simulations suggests that differences in atmospheric forcing such as surface wind explain the simulated divergence across simulations in O2 inventory and OHC changes. An additional comparison between OMIP and CMIP6 Historical simulations indicates that differences in background mean states due to differences in spin-up strategy and equilibrium states result in substantial differences in the climate change response of O2. In this presentation, we will discuss gaps and gaps and uncertainties in both ocean biogeochemistry simulations and observations and explore possible future coordinated ocean biogeochemistry simulations to fill in gaps and unravel the mechanisms controlling the O2 and changes in associated ocean biogeochemical cycles. This presentation is based on the recently published work (Takano et al., 2023).

Reference

Takano Y., Ilyina T., Tjiputra J., Eddebbar Y.A., Berthet S., Bopp L., Buitenhuis E., Butenschön M., Christian J.R., John  J.P., Gröger M., Hayashida H., Hieronymus J., Koenigk T., Krasting J.P., Long M.C., Lovato T., Nakano H., Palmieri J., Schwinger J., Séférian R., Suntharalingam P., Tatebe H., Tsujino H., Urakawa S., Watanabe M., and Yool A.: Simulations of ocean deoxygenation in the historical era: insights from forced and coupled models, Front. Mar. Sci., 10:1139917, doi: 10.3389/fmars.2023.1139917.

How to cite: Takano, Y. and the Ocean Biogeochemistry Modelling Group: What are the challenges simulating historical ocean deoxygenation?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15731, https://doi.org/10.5194/egusphere-egu24-15731, 2024.

15:20–15:30
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EGU24-11155
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ECS
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On-site presentation
Yousheng Li, Alexander Farnsworth, and Paul Valdes

Projections for the future under high scenarios using state-of-the-art Earth System Models suggest a warmer climate for both the land and the ocean, and this leads to ocean acidification globally and ocean deoxygenation. Strengthened denitrification and anammox from Oxygen Minimum Zones (OMZs) or hypoxic coastal areas would possibly enhance nitrous oxide emissions which is one of the main greenhouse gases (GHGs). However, the global dynamics of nitrous oxide are largely uncertain. Considering current emission rates, revisiting past warm periods (e.g., the Paleocene-Eocene Thermal Maximum and the Mid-Miocene Climatic Optimum) would improve our understanding of the biogeochemical-climate feedback. One of the uncertainties in such studies is the paleogeographic boundary condition which is shown to have significant impacts on the global climate and the ocean circulations. However, to date, few studies have been able to explore how paleogeographic features could impact the ocean biogeochemical processes during past warm periods. We applied a suite of sensitivity simulations with modifications only to the topographic features based on three sets of paleogeographies for the mid-Miocene, namely the Getech, the Scotese, and the Robertsons. We found there are huge differences in the ocean circulation patterns, with the strength of the Atlantic Meridional Overturning Circulation (AMOC) ranging from 0Sv to over 12Sv. We will likely see apparent biogeochemical responses accordingly, especially in tropical upwelling regions and the North Atlantic. Results TBC.

How to cite: Li, Y., Farnsworth, A., and Valdes, P.: Paleogeographic impacts on the ocean biogeochemistry during the mid-Miocene, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11155, https://doi.org/10.5194/egusphere-egu24-11155, 2024.

15:30–15:40
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EGU24-11030
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ECS
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On-site presentation
Ruby Barrett, Ann Power, Paul Halloran, and Daniela Schmidt

The Cenozoic shift from a hothouse to icehouse provides a natural experiment to explore how a changing climate and macroevolutionary trends control marine pelagic carbonate production and burial. In the modern ocean, the key components of pelagic carbonate burial — planktic foraminifera and coccolithophores — contribute approximately evenly. However, in the past, coccolithophores dominated open ocean inorganic carbon burial. Exactly when and why this shift away from a coccolithophore dominated ooze occurred is unresolved. To this end, we reconstructed a 65Myr record of foraminifer to nannofossil ratios from sites covering the Pacific, Southern, Indian, and Atlantic Ocean. To better understand the climate and macroevolutionary controls on carbonate production, we move away from the commonly reported bulk changes and instead investigate the individual components of carbonate production:  foraminiferal and coccolithophore size, weight and abundance. We use a suite of methodologies to extract these data, including the novel application of imaging flow cytometry to rapidly and digitally reconstruct the fossil record of coccolithophore size and abundance. Our ratio data shows a shift towards calcareous zooplankton during the Neogene. Initial qualitative analysis reveals that coccolithophore size is relatively smaller in the modern part of the record, whilst automated microscopy shows that modern subtropical and tropical foraminiferal size is greater than recorded in the previous 65Myr. Foraminiferal size-normalised weight (SNW) is expected to be higher in the modern ocean than in the past due to its suggested carbonate system control (i.e. higher carbonate ion concentrations being conducive to heavier tests). However, SNW data from a high latitude site during the Palaeogene are similar to modern values for extant species – potentially implying something other than a carbonate system control on SNW.

How to cite: Barrett, R., Power, A., Halloran, P., and Schmidt, D.: Co-evolution of the oceans and inorganic carbon cycle, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11030, https://doi.org/10.5194/egusphere-egu24-11030, 2024.

Posters on site: Wed, 17 Apr, 16:15–18:00 | Hall X4

Display time: Wed, 17 Apr 14:00–Wed, 17 Apr 18:00
Chairpersons: Fanny Monteiro, Nicola Wiseman, Alessandro Tagliabue
X4.19
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EGU24-2243
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ECS
Shangjun Cai, Qibin Lao, Chunqing Chen, Xin Zhou, Sihai Liu, Guangzhe Jin, and Fajin Chen

The algae bloom in the bay can lead to a large amount of N2O in situ production. However, the coupling relationship between N2O and algae bloom and their mechanism in the bay remains unclear. To address this issue, N isotope culture experiment and qPCR experiment were measured in Zhanjiang Bay during the normal period and algae bloom period. The results showed that the in situ N2O production in algae bloom is 3 times than normal period. Stable isotope rate cultivation experiments also indicated that denitrification and nitrification-denitrification were promoted in the water during algae bloom period, but the increase in nitrification-denitrification is more significant. In addition, the main way for in situ N2O production, shifted from denitrification in the normal period to nitrification-denitrification during algae bloom period. The increase of denitrification and nitrification-denitrification during algae bloom period was attributed from the increase  of fresh particulate organic matter (POM) from algae bloom organisms. The increase of fresh POM enhanced the degradation, providing the necessary anaerobic and hypoxic environment for denitrification and nitrification-denitrification. Additionally, a positive linear correlation between N2O concentrations and ammonia-oxidizing bacteria (AOB) and denitrifying bacteria (nirK), provided further evidence of significant nitrification-denitrification and denitrification processes occurring in the water during algae bloom. Our findings contribute to a clearer understanding of mechanism of in situ N2O emission during algae bloom period.

How to cite: Cai, S., Lao, Q., Chen, C., Zhou, X., Liu, S., Jin, G., and Chen, F.: Promoting effect and mechanism of algae bloom on in situ N2O emission: a case from Zhanjiang Bay, China, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2243, https://doi.org/10.5194/egusphere-egu24-2243, 2024.

X4.20
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EGU24-2295
|
ECS
Helen Stewart, Rin Irie, Tsuneko Kura, Masaki Hisada, and Keiko Takahashi

Projections from CMIP6 Earth System Models forecast a decline in net primary production (NPP) as the ocean warms up due to climate change. However, for coarse model resolutions of O(105) m, there is still roughly a 2-fold disagreement between models for the magnitude and distribution of NPP in the contemporary era [1]. A recent study using the coupled NEMO-LOBSTER ocean physics-biogeochemistry model projected decline in net primary production halving at an eddy-resolving resolution O(103) m compared to an eddy-parameterized coarse resolution O(105) m in response to ocean warming [2]. In this study, we build on our previous work [3] and simulate changes in biogeochemical parameters using the MITgcm Ocean Physics Model coupled with the Simple Global Ocean Biogeochemistry with Light, Iron, Nutrients and Gas (BLING) Model [4] and examine the reproducibility of the results from the previous study [2].

The ocean physics model in this work uses the hydrostatic primitive equations for an implicit free surface, as described in [5], with a bi-linear equation of state. The simulation domain is a closed basin of size (30 × 30)° with a depth of 4000 m,  representing an idealized portion of the North Atlantic Ocean on a spherical polar grid. Analytical profiles of zonal wind, SST forcing and freshwater flux are applied to fluctuate periodically between summer and winter extrema. Temperature and salinity profiles and are initialized using the 2018 World Ocean Atlas reanalyzed climatologies [6]. Monthly atmospheric iron deposition rates are taken from global chemical transport model estimates from a previous work [7]. Biogeochemical tracer concentrations are initialized from interpolated values from MITgcm tutorial experiments [8]. These initial values are spin-up for each resolution until tracer distributions reach equilibrium.

For an ocean warming scenario of +2.8°C over 70 years, roughly corresponding to the SSP8.5 scenario [9], mechanisms for changes in NPP, plankton biomass and nutrient distributions at resolutions of O(105) m, O(104) m, and O(103) m are examined and compared with the previous study [2]. In the future we plan to extend experiments to examine the effect of changing ocean winds and rainfall on ocean biogeochemistry.

Acknowledgements
This work used computational resources of supercomputer Fugaku provided by the RIKEN Center for Computational Science through the HPCI System Research Project (Project ID: hp230382).

References
[1] Tagliabue, A. et al (2021). Frontiers in Climate 3. doi: 10.3389/fclim.2021.738224
[2] Couespel, D. et al. (2021). Biogeosciences 18.14, pp. 4321–4349. doi: 10.5194/bg-18-4321-2021.
[3] Stewart, H. et al (2023). EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11212, https://doi.org/10.5194/egusphere-egu23-11212, 2023.
[4] Dunne, J. P. et al. (2020) Journal of Advances in Modeling Earth Systems 12.10, e2019MS002008. doi: 10.1029/2019MS002008.
[5] Marshall, J. et al. (1997). Journal of Geophysical Research: Oceans 102.C3, pp. 5733–5752. doi: 10.1029/96JC02776.
[6] Garcia, H.E. et al. (2019). World Ocean Atlas 2018.
[7] Fan, S-M et al. (2006).  Geophysical Research Letters 33.7. doi: 10.1029/2005GL024852.
[8] MITgcm User Manual: 4.10 Biogeochemistry Simulation. (Accessed Jan 2024). http://mitgcm.org.
[9] Tokarska, K. B. et al. (2020). Science Advances 6.12, eaaz9549. doi: 10.1126/sciadv.aaz9549.

How to cite: Stewart, H., Irie, R., Kura, T., Hisada, M., and Takahashi, K.: Changes in net primary production in a warming ocean: Examining model projections from coarse resolution to the submesoscale , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2295, https://doi.org/10.5194/egusphere-egu24-2295, 2024.

X4.21
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EGU24-4257
Response of the Yellow and East China Seas ecosystems to two typhoons with different translational speeds in the northwestern Pacific
(withdrawn)
Yucheng Wang and Jing Zhang
X4.22
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EGU24-6464
Fatemeh Chegini, David Nielsen, Mariana Salinas, Lucas Casaroli, Nils Brüggemann, Cathy Hohenegger, and Tatiana Ilyina

Tropical cyclones (TCs) and oceans are a tightly coupled system. On the one hand, the ocean physical conditions such as stratification and eddies can change the intensity of TCs. On the other, TCs can strongly affect the physical and biochemical structure of the upper ocean by e.g. increasing mixing and primary production and impacting the ocean pCO2.

While previous studies have explored the impact of TCs on the global upper ocean biogeochmistry using observational data or coarse resolution stand-alone ocean models, their effect on ocean pCO2 and primary production remain unexplored within Earth system models. In this study, we investigate the response of ocean biogeochemistry to TCs through a high resolution simulation using the ICON-ESM model. The simulation features a spatial resolution of 5km for both the atmosphere and the ocean, resolving mesoscale eddies in the ocean and convective storms in the atmosphere. We quantify the contribution of TCs to changes in air-sea CO2 flux and primary production globally and in different basins.

How to cite: Chegini, F., Nielsen, D., Salinas, M., Casaroli, L., Brüggemann, N., Hohenegger, C., and Ilyina, T.: Impact of tropical cyclones on ocean biogeochemistry in a high resolution Earth system model, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6464, https://doi.org/10.5194/egusphere-egu24-6464, 2024.

X4.23
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EGU24-7817
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ECS
|
Martin Vodopivec, Janja France, Nenad Jasprica, Nika Pasković, Mirna Batistić, and Patricija Mozetič

The phenology of phytoplankton blooms holds significant implications for marine ecosystems as it shapes pelagic food webs. The onset, intensity, and duration of phytoplankton blooms, along with their synchronization with zooplankton cycles, can impact the survival rates of these species and overall community production. In this study, we employ a combination of in situ and satellite-derived chlorophyll concentrations, utilizing various statistical methods to discern the presence and timing of spring and autumn blooms in different regions of the Adriatic Sea. The northern Adriatic (NA) represents a coastal, river-dominated ecosystem influenced by anthropogenic nutrient enrichment, with a recent decline observed in chlorophyll concentration and primary production. Conversely, the southern Adriatic (SA) is characterized as a true pelagic ecosystem with minimal influence from coastal waters on nutrient levels. Here, primary production is primarily controlled by meteorological conditions that dictate convective mixing and nutrient availability for autotrophic uptake. Our analysis reveals that the northern Adriatic predominantly experiences both spring and autumn blooms, whereas the southern Adriatic witnesses only autumn blooms, peaking in late autumn or winter. We investigate trends in the timing of the onset and peak of phytoplankton blooms, searching for environmental factors influencing these shifts. As anticipated, the onset of the autumn bloom is found to be delayed, with statistically significant trends observed in specific areas. It is worth noting that the lack of statistical significance in some instances may be attributed, at least in part, to the relatively short period of available satellite data (from 1997 onwards).

How to cite: Vodopivec, M., France, J., Jasprica, N., Pasković, N., Batistić, M., and Mozetič, P.: Changes in the timing of phytoplankton blooms: comparison between northern and southern Adriatic, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7817, https://doi.org/10.5194/egusphere-egu24-7817, 2024.

X4.24
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EGU24-10594
Solveig Olafsdottir, Alice Benoit-Cattin, and Jon Olafsson

We present spatial and temporal patterns of nutrients concentrations from February observations from two hydrographically different regions in the high latitude North-Atlantic: The northern Irminger Sea and the Iceland Sea. Our observations are from two time-series stations located off the continental shelf and from stations on the shelf. The Irminger Sea, southwest of Iceland, is primarily in the realm of Atlantic Water derived from the North Atlantic Current. The Iceland Sea is north of the Greenland-Iceland-Faroe Ridge separating the Nordic Seas from the sub-arctic North Atlantic. Both regions undergo strong seasonal variations and winter mixing is induced by strong winds and loss of heat to the atmosphere. The winter mixed layer depth is found to be variable in the Irminger and Iceland Seas, but it reaches much deeper in the Atlantic Water of the Irminger Sea as a halocline limits the vertical convection in the Arctic Waters of the Iceland Sea. Consequently, the winter mixed layer depths in the two regions range from or 300-700 m and 150-250 m respectively. The nutrient concentrations in the surface layer that result from the winter vertical mixing vary interannually and there is a significant spatial difference between the two regions where the long term (1991-2020) average for the nitrate concentration is 14.4 µmol kg-1 in the Atlantic Water and 10.3 µmol kg-1 in the Arctic Waters. Higher spatial differences are in the silicate concentration, in the Atlantic Water the long-term average concentration is 6.8 µmol kg-1 and 4.0 µmol kg-1 in the Arctic Water. The interannual variations in the relative abundance of nitrate and silicate, the Si/N ratio, are likely to influence the productivity of silicious diatoms in the spring bloom. Nutrient concentrations at the end of winter on the shelf are also high, they reflect the state of the offshore waters. Our observations show hydrographic changes that have induced significant biogeochemical changes in these regions.

How to cite: Olafsdottir, S., Benoit-Cattin, A., and Olafsson, J.: Interannual and regional variability in winter nutrient concentrations in Icelandic Waters, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10594, https://doi.org/10.5194/egusphere-egu24-10594, 2024.

X4.25
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EGU24-12796
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ECS
Kunal Madkaiker and Ambarukhana Devendra Rao

This study employs a high-resolution MITgcm-DIC model at 5 km spatial resolution with climatological forcing to investigate the biogeochemical dynamics of surface dissolved inorganic carbon (DIC) and alkalinity (ALK) over the northern Indian Ocean. The physico-chemical parameters of the model are validated against available observational data to ensure its accuracy. The DIC biogeochemical module is integrated within the model framework, considering multiple DIC sources and sinks, including air-sea CO2 exchange, biological production, and carbonate mineral dissolution. To analyse the influences of various processes within our domain, we focussed on the surface DIC and ALK budgets. This investigation helps us understand the intricate interplay of drivers impacting the budgets. The DIC and ALK budgets are found to be significantly influenced by the counterbalancing effects of advective and diffusive terms. We also assessed the role of biological activity and observed that productivity causes a continuous uptake of CO2, which leads to a reduction in surface DIC. Since freshwater intrusion is an important factor governing the surface dynamics of waters in north Indian Ocean, we examined the impact of freshwater dilution on surface DIC and ALK concentrations. The surface ALK budget is predominantly governed by freshwater flux. The dilution of ALK and DIC is attributed to the influence of both precipitation and river runoff. Regions where evaporation exceeds precipitation and river runoff exhibit an increase in the concentration of these variables. The findings shed light on the regional variations along the north Indian Ocean, providing valuable insights into the dominance and interactions of these mechanisms. This study is valuable for enhancing our understanding of regional carbon cycling dynamics in our domain with implications for global carbon cycle models and climate-related predictions. The findings are relevant not only for the scientific community but also for policymakers and stakeholders concerned with oceanic and environmental health.

How to cite: Madkaiker, K. and Rao, A. D.: Variability and budgets of Dissolved Inorganic Carbon and Alkalinity over the north Indian Ocean using a high-resolution model , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12796, https://doi.org/10.5194/egusphere-egu24-12796, 2024.

X4.26
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EGU24-16108
Marta Gluchowska, Weronika Patula, Kaja Balazy, and Emilia Trudnowska

One of the fundamental challenges in modern studies of zooplankton ecology at high latitudes is to understand the processes that promote co-existence of morphologically and ecologically related species with different origin and that maintain high overall zooplankton diversity in a warming Arctic. The increased inflow of warm Atlantic Water into the Arctic Ocean is making marine ecosystems increasingly resemble those of the North Atlantic. Consequently, a mixture of resident and advected species coexist over large areas of the European Arctic. In this study, pairs of taxonomically and ecologically related species (small-sized copepods, large calanoid copepods, amphipods, euphausiids, and chaetognaths), essential for the functioning of Arctic ecosystems were thoroughly studied with regard to their existence and degree of niche separation of studied pairs. Individual species within each pair are characterized by different centers of distribution (Arctic or boreal). The design of our study, covering three core hydrographical regions of the Polar Front on the West Spitsbergen Shelf, was set up to study the pairs of sibling species that either co-occur in the same water (Hornsund fjord, Spitsbergen) or thrive in the water mass they originate from (Arctic and Atlantic domains). Our results demonstrate that vertical abundance distributions in each pair of species differ when species occur separately (waters from each particulate species originate) or from the vertical distribution patterns  when they co-exist. This supports the hypothesis that environmental niche separation exists in sibling species of marine zooplankton sharing the same environment and highlights its role as a mechanism reducing interspecific competition.

How to cite: Gluchowska, M., Patula, W., Balazy, K., and Trudnowska, E.: When co-existence means separation – environmental niche partitioning of ecologically similar zooplankton species in the warming Arctic, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16108, https://doi.org/10.5194/egusphere-egu24-16108, 2024.

X4.27
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EGU24-22229
Meriel Bittner, Naomi Levine, Benjamin Twining, Mak A. Saito, Maria Teresa Maldonado, and Alessandro Tagliabue

Global biogeochemical cycles in which essential elements are transformed and recycled are governed by microbial processes. Despite international efforts of studying these important cycles, fundamental questions remain especially regarding fluxes and regulation. The international BioGeoSCAPES initiative aims to unravel the intricacies of these interconnected biogeochemical cycles and improve our understanding of the microbial biogeochemistry of the oceans from regional to ocean basin-scale on a changing planet. The community envisions a more quantitative and predictive understanding of ocean biogeochemical cycles and metabolism by combining detailed information of nutrient/metabolite fluxes, plankton and biochemical processes. The program has an integrative and multidisciplinary approach, by combining state-of-the-art methods in biochemistry, omics, physiology and modeling. Within the scope of BioGeoSCAPES standardized best practices will be established and intercalibration efforts carried out to create an international interoperable data system that nations around the world can contribute to and participate in.
Currently, a globally-supported science plan is being developed, in which key scientific interests are identified such as mapping key metabolisms over space and time, measuring rates to connect microbial metabolisms to biogeochemical cycles, and predicting interactions with environmental change. In the near future, the BioGeoSCAPES community will work towards integrating modeling efforts across a range of scales and to develop the infrastructure to support this global initiative. Initial objectives of the science plan will be presented to discuss with the Ocean Sciences community and to receive feedback.

How to cite: Bittner, M., Levine, N., Twining, B., A. Saito, M., Maldonado, M. T., and Tagliabue, A.: BioGeoSCAPES: Ocean metabolism and nutrient cycles on a changing planet, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-22229, https://doi.org/10.5194/egusphere-egu24-22229, 2024.

X4.28
|
EGU24-20714
Fanny Monteiro, Joost de Vries, Nicola Wiseman, Alex Poulton, Rosie Sheward, and Levi Wolf

Coccolithophores are a main marine calcifier critical to ocean carbon pumps (via organic matter ballast and the carbonate pump), ultimately controlling atmospheric CO2 and climate. However, their contribution to the global carbon cycle is still very uncertain, limiting our understanding of their impact and response to climate change. One major issue is that most coccolithophore studies rely solely on one outlier species (Emiliania huxleyi), which is relatively small and lightly calcified. Here, we apply novel machine-learning techniques to determine the global distribution of the top 52 species and the total calcite production of coccolithophores. These techniques build predictive models of coccolithophore carbon stocks and calcite production based on newly compiled datasets of coccolithophore abundance and calcification rates, which we combined with environmental data. Our species predictive model shows that a handful of species, including Emiliania huxleyi, are responsible for the global calcite standing stock, with subtropical species being a significant contributor. Our rate predictive model also supports this finding, showing large calcification rates in the subpolar and subtropical regions. This result revisits the traditional view that coccolithophore calcification primarily occurs in sub-arctic bloom-like events and that other species besides Emiliania huxleyi should be considered to resolve coccolithophore’s subtropical contribution. 

How to cite: Monteiro, F., de Vries, J., Wiseman, N., Poulton, A., Sheward, R., and Wolf, L.: New global machine-learning estimates of coccolithophore standing stocks and calcification rate accounting for biodiversity , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20714, https://doi.org/10.5194/egusphere-egu24-20714, 2024.

X4.29
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EGU24-1928
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ECS
Qibin Lao and Fajin Chen

Since offshore waters are less affected by human activities and nutrient-rich water masses, existing theories on periodic offshore blooms (POB) consider that the POB is proportional to the intensity of ocean fronts (nutrient supply from enhancing vertical mixing), ignoring external nutrient supply and external forcing (climatic oscillations). This study proposes an external dynamic mechanism of the POB on the basis of field observations and long-term satellite remote sensing data (1981–2022) in Beibu Gulf, which is influenced by remarkable external forcing. Three water masses, coastal current (CC), West-Guangdong coastal current (WGCC), and South China Sea water (SCSW), were identified using dual water isotopes. The seawater in the gulf mainly originated from CC in summer and fall, while it changed to the SCSW in winter. The nutrient in the gulf was mainly from the CC in summer and fall, while it shifted to the WGCC in winter. Notably, a strong thermal front with an inverted-V structure was found in the central gulf every winter due to the strong wind stress and change of water mass mixing. The intensity of the front on the east side is weaker due to the intrusion of WGCC. However, Chlorophyll-a concentrations in the eastern (nutrients supplied by WGCC) and northern (nutrients supplied by vertical mixing) were obviously higher than that in the western front (limited nutrient supply) in winter. On an interannual scale, the intensity of POB in La Niña years is remarkably stronger than in El Niño years due to the stronger WGCC supplying more nutrients in La Niña. This study suggests that the intensity and range of POB are not proportional to the frontal intensity in the gulf, but are directly driven by the internal forcing (fronts and nutrient supply from WGCC), which is controlled by the external forcing.

How to cite: Lao, Q. and Chen, F.: External Dynamic Mechanisms Controlling the Periodic Offshore Blooms in Beibu Gulf, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1928, https://doi.org/10.5194/egusphere-egu24-1928, 2024.

X4.30
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EGU24-2765
|
ECS
Frequency of enhanced food availability controlled the growth of bamboo corals in the Northwestern South China Sea
(withdrawn after no-show)
Haozhuang Wang, Zhimin Jian, Xiaoli Zhou, Haowen Dang, Yue Wang, Xingxing Wang, and Haiyan Jin
X4.31
|
EGU24-5020
|
ECS
Hwa-Jin Choi, Jong-Yeon Park, and Charles Stock

Climate change has caused shifts in the abundance, geographic distribution, and phenology of marine species. Spatial shifts of species due to global warming will cause a high local extinction rate and decrease fisheries catch and species richness at tropical latitudes. Predicting the migration of marine organisms in response to climate change holds significance not just from an ecological perspective, but also from an economic standpoint in terms of effectively managing marine living resources. This study investigates the predictability of metabolically viable habitats by utilizing an Earth system model (ESM) that incorporates a coupled physical-biogeochemical prediction system. The metabolic index, previously defined with dissolved oxygen and temperature, has a higher predictability compared to temperature, particularly in the subsurface tropics. The primary factor contributing to the high predictability of the metabolic index is the longer persistency of lateral oxygen advection at the boundary of the tropical oxygen minimum zone. Further investigations indicate that the interannual fluctuations in the catch of bigeye tuna within the exclusive economic zones (EEZs) in tropical regions can be predicted based on the metabolic index forecasted one year ahead, implying the potential application of ESM-based physiological prediction to dynamic management of marine living resources.

How to cite: Choi, H.-J., Park, J.-Y., and Stock, C.: Predictability of Metabolic index and its application to fish catch prediction, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5020, https://doi.org/10.5194/egusphere-egu24-5020, 2024.

Posters virtual: Wed, 17 Apr, 14:00–15:45 | vHall X5

Display time: Wed, 17 Apr 08:30–Wed, 17 Apr 18:00
Chairpersons: Charlotte Laufkötter, Fanny Monteiro, Nicola Wiseman
vX5.26
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EGU24-18162
|
ECS
|
Anjaneyan Panthakka and Jayanarayanan Kuttippurath

Global temperatures and atmospheric carbon dioxide (CO2) have been rising since the industrial period due to increased anthropogenic activities. The adverse impact of this warming and changing climate systems significantly reflects on Eastern Boundary Upwelling Systems (EBUS) in the global ocean. Here, we investigate the influence of climate change on EBUS by analysing the long-term changes in upwelling and productivity within these ecologically crucial regions. Based on the Bakun's (1990) hypothesis, which suggests that modifications in land-sea thermal gradients affect atmospheric pressure cells and subsequently influence upwelling patterns in EBUS, we analyse the daily time series data of wind and sea surface temperature (SST). Furthermore, we assess the impact of changes in these upwelling patterns on productivity.

We employ a set of matrices to objectively characterise upwelling dynamics, focusing on frequency, intensity and duration across four EBUS. Our findings reveal a compelling relationship between SST changes and upwelling events, demonstrating a decrease in SST associated with increased upwelling frequency and reduced intensity. Interestingly, variations emerge among EBUS and regions within them, notably an intensification of upwelling in the Humboldt Current systems. Despite this observed response, clear evidence supporting the associated changes in wind dynamics that drive upwelling remains elusive.

This study enhances our understanding of how shifts in global temperatures impact EBUS, which are crucial systems in regulating fisheries and marine ecosystems. Consistent changes in the timing, intensity and spatial heterogeneity of coastal upwelling are evident in most EBUS. The spatially variable yet subtle changes are observed in accordance with climate change patterns. These findings provide valuable insights into the complex interplay between climate-driven shifts and the dynamic nature of EBUS, suggesting implications for marine ecosystems and coastal communities.

How to cite: Panthakka, A. and Kuttippurath, J.: Dynamic shifts in eastern boundary upwelling systems: climate-change driven impacts on frequency, intensity and spatial patterns of upwelling., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18162, https://doi.org/10.5194/egusphere-egu24-18162, 2024.

vX5.27
|
EGU24-14657
Moritz Mathis, David Nielsen, Stefan Hagemann, Tatiana Ilyina, and Corinna Schrum

Arctic permafrost thaw and sea ice retreat lead to enhanced coastal erosion and a contemporary increase in the transport of terrestrial carbon to the Arctic Ocean. However, the influence of this carbon supply on the marine carbon cycle and the CO2 uptake of the broad Arctic shelves is poorly understood. We use the global ocean-biogeochemistry model ICON-Coast with a dedicated representation of coastal carbon dynamics to investigate the impacts of erosive coastal carbon input during the 20th century and quantify its partitioning into burial, transport and air-sea gas exchange in the Arctic Ocean. Anthropogenic climate change increased the carbon supply from coastal erosion by 1.5 Tg C yr-1. We find that about 50% of this increase is remineralized on the shelves and released to the atmosphere. Another 30% get deposited in near-shore sediments, whereas 10% are exported to the open ocean via advection, and 10% reside in the shelf waters as accumulating DIC. This means that the anthropogenically induced increase in coastal erosion reduced the CO2 uptake during the past century by 0.8 Tg C yr-1 (3% of the total uptake by Arctic shelves) and may further weaken the CO2 sink of the Arctic Ocean as global warming continues.

How to cite: Mathis, M., Nielsen, D., Hagemann, S., Ilyina, T., and Schrum, C.: The fate of terrestrial carbon in the Arctic Ocean supplied by increasing coastal erosion, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14657, https://doi.org/10.5194/egusphere-egu24-14657, 2024.