How to cite: Couespel, D., Tjiputra, J., Johannsen, K., Vaittinada Ayar, P., and Jensen, B.: Machine learning-based drivers of present and future inter-annual variability in air-sea CO2 fluxes, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-824, https://doi.org/10.5194/egusphere-egu23-824, 2023.

Over the past decade, the number of high-quality measurements of the sea surface partial pressure of CO2 (pCO2) has rapidly increased and large-scale community efforts have led to the compilation of these measurements into uniform quality-controlled databases. Moreover, the development of different robust interpolation techniques allowed one to circumvent the limitation of these datasets that remain discontinuous in time and space to create continuous spatiotemporal pCO2 maps. While significant progress has been made regarding the development of several global data-products for the global ocean, most of these products omit the coastal ocean and/or their spatial resolution is too coarse to fully capture the highly heterogeneous spatiotemporal pCO2 dynamics that occurs in these regions. As a result, the evaluation of the interannual variability and the long-term trends of the coastal air-sea CO2 exchange using a continuous CO2 flux (FCO2) product dedicated to the shallow portion of the global ocean has not yet been attempted and, hence, remains poorly understood. To address these limitations, this study updates the global coastal data-product of Laruelle et al. (2017) based on the coastal version of the Self Organizing Map and Feed Forward Network method and uses ~ 32 million observations to cover the longest period available for the coastal ocean (1982-2020). The good performance in space and time of this new data-product using several evaluation methods allows us to reconstruct the temporal evolution of the global coastal FCO2 sink based on observations. Our results indicate that today’s coastal ocean acts as a CO2 sink and that it has been a CO2 sink since the beginning of our study period (1982). This CO2 sink has however increased over time from a value of -0.25 Pg C yr-1 (for a total shelf surface area of 77 million km2) in the early 1980s to a current value of -0.6 Pg C yr-1. Our new product provides a new constraint for closing the global carbon cycle and its temporal evolution as well as for establishing regional carbon budgets requiring high resolution coastal flux estimates.

How to cite: Roobaert, A., Laruelle, G. G., Landschützer, P., and Regnier, P.: An updated sea surface pCO2 data-product for the global coastal ocean, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15678, https://doi.org/10.5194/egusphere-egu23-15678, 2023.

Observational networks monitoring marine carbon variables are established to meet the critical need to estimate ocean CO2 uptake, as well as assessing its consequences on ocean health through changes in carbonate chemistry (ocean acidification). Despite considerable efforts over the past decades, data coverage is still sparse over large ocean regions, prompting the implementation of mapping methods to gap-fill carbon datasets over the globe. Different statistical approaches have been proposed with the aim to generate reconstructions of the complete marine CO2 system at high spatial-temporal resolutions. Following this goal, we first introduce a global reconstruction of surface ocean partial pressure of CO2 (pCO2) at monthly and 0.25-degree resolutions over the period 1985-2021. This high-resolution pCO2 product is derived from ensemble neural network models interpolating monthly gridded observation-based data from Surface Ocean CO2 ATlas (SOCAT). We will assess the ability of the proposed pCO2 ensemble (1) to derive long-term time series of pCO2 and associated 1-sigma uncertainty per 0.25-degree grid cell for each month, (2) to reproduce temporal and horizontal gradients of coastal pCO2 observations in comparison with a coarser spatial resolution, (3) to estimate surface ocean pH and air-sea CO2 fluxes. Furthermore, we will present an extension of the ensemble neural network models, which is referred to as a new module extrapolating pCO2 to several years ahead. The extended ensemble-based approach will ultimately be used to project global ocean CO2 uptake and ocean acidification with low latency.

How to cite: Chau, T.-T.-T., Chevallier, F., and Gehlen, M.: A seamless coastal to global ocean pCO2 and pH reconstruction at a 0.25-degree resolution with extrapolation to the near future, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14024, https://doi.org/10.5194/egusphere-egu23-14024, 2023.

The ocean is a critical component of the global carbon budget. With a carbon reservoir substantially larger than the atmosphere's and an air-sea carbon flux absorbing approximately 25% of anthropogenic carbon annually, understanding and quantifying the air-sea carbon dioxide (CO₂) flux and ocean carbon storage is essential for climate research. With this in mind, we developed a two-step neural network approach (SOM-FFN) to reconstruct the partial pressure of carbon dioxide (pCO₂) at a 1°x1° resolution, providing an important global observational resource. Uncertainties in neural network and other interpolation techniques are, however, still substantial and remain poorly quantified, especially for remote or infrequently sampled regions. These uncertainties, which include mapping or extrapolation uncertainties as well as uncertainties in wind and gas transfer formulations, have a significant effect on our ability to balance regional and global carbon budgets. Therefore, we are reporting on the development of a two dimensional (longitude and latitude) gridded uncertainty product, available publicly alongside our standard neural network air-sea CO₂ flux output from the SOM-FFN method. This dataset will pave the way for a better guided use of the computed air-sea CO₂ fluxes and their regional uncertainties, taking into account major sources of air-sea CO₂ flux uncertainty. Early analysis presented here allows for identification of regions of higher uncertainty, such as high latitude open ocean, and points to areas within the flux calculation where uncertainty must be further constrained in order to contribute to improving balance of regional carbon budgets in support of the UN stocktake.

How to cite: Jersild, A. and Landschützer, P.: A spatially explicit uncertainty analysis of the air-sea CO2 flux from observations, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4184, https://doi.org/10.5194/egusphere-egu23-4184, 2023.

We present year-long, vertically-resolved, high-resolution observations of phytoplankton community and primary productivity in the Bornholm Basin of the Baltic Sea. Sustained high-resolution monitoring reveals how the small-scale environmental dynamics regulate the phytoplankton community composition and primary productivity in the Bornholm Basin. We combine data from the Swedish National Monitoring Program, collecting phytoplankton (abundance, biomass and productivity) and environmental  (e.g. nutrients concentration) samples with remote sensing data and sustained observations from an Ocean Glider Observatory from March 2021 to 2022.

The Ocean Glider Observatory continuously collected high-resolution physical (e.g.temperature, salinity) and biochemical (chlorophyll a, dissolved oxygen) data (vertical resolutions at 10-centimetre scale and vertical profiles with a mean temporal resolution of ~37 min). Glider data are calibrated against remote sensing data, while in situ measurements of photosynthetic yield and community composition allow us to model community composition and primary productivity across the dataset.

Accurate estimation of primary productivity reveals the importance of short term and rapid changes in near-surface stratification and the deep chlorophyll maximum for the Bornholm ecosystem. Vertically resolved glider estimates also highlight limitations of remote sensing methods in this cloud covered region. As phytoplankton plays a crucial role in the transfer of energy through the food web via zooplankton up to fish, the importance of sustained, continuous high-resolution observations is required to fully capture the magnitude and variability of ecosystem processes and consequences to productivity.

How to cite: Paczkowska, J., Queste, B. Y., Monforte, C., and Biddle, L. C.: Seasonal changes in phytoplankton community composition and primary production in the southern Baltic Sea based on monitoring, ocean glider and satellite data, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15673, https://doi.org/10.5194/egusphere-egu23-15673, 2023.

Coastal ocean is more vulnerable to ocean acidification (OA) than open ocean due to high inputs of nutrients from land, large biological production, and various human activities. We started coastal acidification monitoring at three coastal (Busan, Jeju, and Ulleung) and one offshore (3km away from the Busan site) sites in Korea to examine long-term trends of the OA and their effects on coastal ocean environment. Discrete surface seawater samples for measurement of total dissolved inorganic carbon and total alkalinity were collected at the Busan, the Jeju and the Ulleung, and the offshore sites on a weekly, biweekly, and monthly basis, respectively. Here, we report changes in pH and saturation state of seawater with respect to aragonite (Ω) at the four sites for the period of 2019–2022. At the Busan and the Ulleung sites, both pH and Ω showed significant decreases, but there were no trends at the other two sites. The change rates of deseasonalized pH and Ω (-0.011 ± 0.005 yr^-1 for pH and -0.049 ± 0.024 yr^-1 for Ω) found at the Busan site were similar to those (-0.010 ± 0.005 yr^-1 for pH and -0.058 ± 0.025 yr^-1 for Ω) of the Ulleung site. These rates are about six times greater than the global long-term mean rates (-0.016 per decade for pH and -0.07 per decade for Ω). Sea surface temperature and salinity did not show any significant trends for the same period. Continuous monitoring of carbonate parameters at these sites is necessary to get robust long-term OA trends and understand coastal OA processes by finding their drivers.

How to cite: Park, G.-H. and Lee, S.-E.: Significant changes in pH and saturation state of calcium carbonate in coastal ocean waters in Korea, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12184, https://doi.org/10.5194/egusphere-egu23-12184, 2023.

As the largest oceanic sink of anthropogenic CO₂, the Southern Ocean (SO) plays a key role for climate and climate change, absorbing between 5 and 10 percent of the global CO₂ emissions from human activities each year. Factors influencing the efficiency of the Southern Ocean CO₂ sink include, for example, the rate and level of change of CO₂ in the atmosphere and the associated changes in climate, including warming and winds. In particular, winds in the Southern Ocean have been observed to increase in the past 50 years, with this increase linked both to the change of stratospheric ozone and to the observed increase in greenhouse gasses. Here, we use a set of model simulations with the UKESM1 model run from 1950 to the end of the 21st century, we explore the relative contribution of changing greenhouse gases and ozone recovery in driving the evolution of the Southern Ocean carbon sink. Our runs encompass three sets of forcing: one with no ozone, one with ozone but no ozone recovery, and one with best estimated ozone recovery. This set therefore bookends possible evolution of ozone this century and thus the response of the ocean carbon state. Our results demonstrate the critical role of changes in wind distribution in the likely evolution of the SO carbon sink over the course of the 21st century.  

How to cite: Jarnikova, T., Le Quéré, C., Rumbold, S., and Jones, C.: The Changing Role of Stratospheric Ozone and Greenhouse Gasses in Modifying the Southern Ocean Carbon Sink, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-591, https://doi.org/10.5194/egusphere-egu23-591, 2023.

The Indian Ocean experienced an extremely anomalous carbon flux with a magnitude of 0.1 PgC/yr in 2015-2016 according two pCO₂-based data products and MOM6 model simulations. However, the Indian Ocean Dipole (IOD) climate mode cannot well explain the anomalous interannual variability. We show that the Indian Ocean carbon flux anomaly is remotely driven by the extreme 2015-2016 El Niño which is the strongest El Niño in the 21st century. The El Niño is able to drive a basin-scale warming and high dissolved inorganic carbon (DIC) anomaly in the southeastern tropical Indian Ocean which increase ocean pCO2 and weaken the ocean carbon sink in the Indian Ocean. The basin-scale warming is induced by a more shortwave radiation and less latent heat flux loss in the Indian Ocean which is originated from El Niño through cloud-radiation-SST feedback and wind-evaporation-SST (WES) feedback. The high DIC in the southeastern tropical Indian Ocean is induced by a less dilution of weakened the fresh Indonesia Through Flow (ITF) and reduced freshwater flux associated with El Niño. The ocean carbon response to El Niño remote effect is different from IOD. This study complements the understanding of air-sea CO2 flux interannual variability in the Indian Ocean.

How to cite: Liao, E. and Lu, W.: Exceptional decrease of Indian Ocean carbon uptake in 2015-2016 due to a remote effect of El Niño, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4202, https://doi.org/10.5194/egusphere-egu23-4202, 2023.

Planktonic foraminifera are a critical component of global pelagic biogeochemistry, export fluxes, and seawater properties. Calcifying foraminifera cells are profoundly important to biogeochemistry also due to their mass and strong ballasting of particulate organic matter that drives the biological carbon pump and to carbon cycling because of the biochemistry of calcite formation that both removes carbon towards the geological record in the form of carbonate and also produces CO₂ for every molecule of CaCO₃ produced. My research shows that ocean density exerts a role on planktonic foraminifera biomineralization. Since foraminifera are non-motile plankton glacial/interglacial ocean density fluctuations may cause shell weight changes for buoyancy regulation if foraminifera tend to always maintain certain depths. This newly described mechanism may help to further elucidate the marine carbon cycle. The decreased plankton calcification needs that it foresees during warm periods of lighter waters would remove less alkalinity from the surface interglacial ocean thus leaving it capable to absorb more atmospheric carbon. Furthermore, it is found that foraminifera species calcification intensifies with depth habitat following the increase in water density, offering new hints about the control of the different ocean strata to the carbon cycle.

How to cite: Zarkogiannis, S.: Influence of seawater density on pelagic carbonate production, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10098, https://doi.org/10.5194/egusphere-egu23-10098, 2023.