PICO
Bioluminescence, the light emitted naturally by marine organisms, is the main light source in the mesopelagic zone. Nearly 75% of marine organisms, from the surface to the deep sea, use this capability for communication with diverse ecological goals (predation, repulsion...). Bioluminescence detection thus offers an indirect way of tracking the presence, distribution and migrations of organisms (ranging from zooplankton, dinoflagellates to fishes). Such detection can lead for example to a better understanding of vertical migrations of organisms and consequently of a better quantification of the active carbon export in the mesopelagic ocean. However, current technologies still limit large deployments, and high frequency observations of in situ bioluminescence.
To overcome these limitations, the CEMSOR2 project aims to develop an innovative, low cost, compact, multi-instrumented sensor capable of measuring bioluminescence in situ. The CEMSOR2 is designed to be easily deployable on a wide range of vectors (such as underwater gliders, CTDs, buoys, trawls, living organisms). The sensor being easy to deploy will enable us to collect a wide range of bioluminescent data with high spatiotemporal resolution, while recording environmental and behavioral variables related to the organisms.
A series of controlled tests is essential to validate the sensor's robustness under diverse marine conditions (pressure, salinity, light, etc.) and to characterize its performance in capturing subtle bioluminescent events. This process includes specification and calibration steps to ensure the sensor’s sensitivity to required wavelengths, sampling frequencies, and intensity levels, while accounting for operational limits, such as the maximum detectable intensity and baseline noise level.
The analysis of bioluminescence data involves several key steps to enhance data quality. First, background noise (sensor dark noise and other artifacts) is filtered out, through measurements taken in a dark chamber. Next, ambient light interference is minimized to prevent contamination of bioluminescent signals. Bioluminescent flashes are identified using a peak-detection algorithm based on frequency and threshold filters, distinguishing true bioluminescent signals from background light.
Once detected, each flash undergoes detailed analysis, with characteristics such as Flash Duration (FD), Peak Intensity (PI), Rise Time (RT), Decay Time (DT), and Integrated Flash Energy (IFE) evaluated. Deconvolution techniques further separate overlapping flashes, allowing for a clearer understanding of multi-peak events. This analysis helps classify bioluminescent events by their spatio-temporal dynamics, intensity, and form, which are crucial for linking bioluminescence patterns with specific species' behaviors and environmental variables, especially in relation to migratory and behavioral patterns of marine organisms.
By advancing bioluminescence detection and interpretation, the CEMSOR2 project contributes essential tools and insights for marine biology, enhancing our understanding of the role bioluminescent organisms play in oceanic ecosystems.
How to cite: Maingot-Lépée, J., De Knyff, L., Caillat, A., Benoit, J., Soulier, F., Azais, F., Mahiouz, K., Louber, D., Gojak, C., Fourmond, J.-J., Bonhommeau, S., Bernard, S., and Martini, S.: Analysis, quantification and identification of in situ bioluminescence signals by an innovative sensor (CEMSOR2), EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-85, https://doi.org/10.5194/egusphere-egu25-85, 2025.
We ask (i) what sets the vertical stratification in the abyssal ocean, and (ii) what sets the upwelling in the bottom boundary layer of the abyssal ocean?
We restrict attention to the bottom-most, densest, 2000m of the ocean and analyse the buoyancy budget in buoyancy coordinates. The bottom-intensified nature of diapycnal mixing means that the diapycnal velocity in the ocean interior is downwards towards denser fluid, and all the diapycnal upwelling occurs in the first ~50m above the sea floor, with the upwelling transport in this Bottom Boundary Layer often being two or three times the net diapycnal upwelling needed to balance the sinking transport of Antarctic Bottom Water.
The rate of sinking of dense Antarctic Bottom Water and the area-integrated diffusive buoyancy flux across the upper-most buoyancy surface are both regarded as known, which gives the buoyancy contrast between the sinking Antarctic Bottom Water and the value of buoyancy on this upper-most surface. We show that the vertical stratification in the interior abyssal ocean is then entirely determined by knowledge of the rate of detrainment (or entrainment) of plume fluid out of (into) the sinking plume and into (out of) the ocean interior. Importantly, the vertical stratification cannot be determined from knowledge of oceanic diapycnal mixing alone.
How to cite: McDougall, T., Holmes, R., and Gunn, K.: How much Upwelling occurs in the Abyssal Bottom Boundary Layer? , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-187, https://doi.org/10.5194/egusphere-egu25-187, 2025.
Primary productivity and respiration form the foundation of the ocean's food web and life and drive oxygen's biogeochemical cycling. Oxygen and phytoplankton abundance are two essential ocean variables (EOV) in monitoring the state of the ocean and in the study of the impact of climate change on the marine ecosystem. To estimate primary productivity and respiration in the sea, ocean gliders deployed in the Northeast Atlantic are equipped with oxygen optodes and chlorophyll fluorescence sensors to obtain critical data in the upper water column at a much larger spatial and temporal scale than is possible with research vessels.
During the first missions near the ESTOC Station in the Canary Islands led by PLOCAN, oxygen, turbidity and chlorophyll fluorescence data was measured with sensors installed on SeaExplorer gliders. We used this dataset to provide estimates of primary productivity and respiration in the medium term. Short deployments of Slocum Gliders with the Marine Institute in the Celtic Sea and along the continental shelf provide much higher temporal resolution data of the phytoplankton diel cycle. This also allowed for the study of the potential for gliders to detect phytoplankton thin layers and/or vertical migration of HAB species as part of an integrated operational oceanography platform for the early warning system for HABs.
How to cite: Burin, C., Fennell, S., Moran, R., Caudet, E., and Croot, P.: Applications of ocean gliders for climate change monitoring of Essential Ocean Variables (EOVs) in the Northeast Atlantic, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-263, https://doi.org/10.5194/egusphere-egu25-263, 2025.
Accurate and precise measurements of total dissolved inorganic carbon (DIC) in seawater are essential for evaluating key ocean carbon cycle processes such as ocean acidification, carbon storage, air-sea fluxes, and carbon dioxide removal (CDR) monitoring, reporting, and verification (MRV). Although calibration procedures for instrumentation used to measure seawater DIC are available, their adoption by many oceanographic laboratories has been limited due to perceived complexity or lack of technical support. As a result, single-point calibration with CO2-in-seawater Reference Material (RMs) from Andrew Dickson’s laboratory at Scripps Institution of Oceanography has become a prevailing practice. While the use of these RMs has substantially improved the repeatability and reproducibility of DIC measurements, reliance on single-point calibration can significantly increase measurement uncertainty, especially for samples with DIC values far from the typical RM values of surface Pacific water (1950–2100 μmol kg-1; https://www.ncei.noaa.gov/access/ocean-carbon-acidification-data-system/oceans/Dickson_CRM/batches.html). This practice leaves no way to assess measurement accuracy over the typical DIC measurement range (1800-2300 µmol kg-1).
To address these challenges, an International Association for the Physical Sciences of the Oceans (IAPSO) Best Practice Study Group was established in late 2023. The study group aims to improve DIC measurement accuracy by facilitating and promoting the adoption of instrument calibration procedures. Enhancing the accuracy of DIC measurements will improve the reliability of ocean carbon cycle assessments and contribute to better-informed climate change mitigation strategies.
We will present the state-of-the-art calibration techniques for seawater DIC measurements employed in oceanographic laboratories worldwide, based on findings from a public survey conducted by our study group. We will also outline our planned activities, which include: (1) the preparation and dissemination of updated Standard Operating Procedures (SOPs) for DIC instrumentation calibration, (2) the development of practical calibration solutions and exploration of potential commercial opportunities, and (3) the evaluation of the broader impact of adopting the updated SOPs for calibration.
How to cite: García-Ibáñez, M. I., Álvarez, M., Cantoni, C., Easley, R., Fisicaro, P., Humphreys, M. P., Ishii, M., Jenkins, A., Knockaert, M., Metzl, N., Seitz, S., Steinhoff, T., and Williams, R.: Advancing calibration practices for total dissolved inorganic carbon measurements in seawater, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-293, https://doi.org/10.5194/egusphere-egu25-293, 2025.
The concept of density or isopycnal sufaces forms the backbone of our understanding of numerous aspects of the ocean circulation. It is central to the study of quasi-geostrophic motions, potential vorticity, lateral stirring, and the Atlantic meridional overturning circulation, among others. It is well known, however, that the identification of such surfaces is greatly complicated by the thermobaric nonlinearity of the equation of state. So far, the prevailing paradigm has been that isopycnal surfaces should be empirically constructed to be as neutral and material as feasible. Because these two properties cannot be simultaneously and exactly satisfied, isopycnal surfaces constructed in such a way necessarily include subjective elements related to the cost function necessary to define proximity to neutrality and materiality. In this work, I argue that the most natural and objective way to define isopycnal surfaces in the oceans is as the iso-surfaces of the reference pressure of fluid parcels in their state of minimum potential energy entering Lorenz theory of available potential energy. This claim will be supported by a few illustrative examples ranging from the specification of lateral stirring directions in Redi rotated diffusion tensors to the study of the meridional overturning circulation in density coordinates.
How to cite: Tailleux, R.: An objective definition of isopycnal surfaces, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3485, https://doi.org/10.5194/egusphere-egu25-3485, 2025.
The concentration of particulate matter is a critical ocean variable for understanding biogeochemical processes across diverse spatial and temporal scales. It plays a key role in refining ocean productivity estimates, which are essential for constraining coupled physical-biogeochemical numerical models. However, direct measurements are often challenging to obtain. A reliable alternative is the optical backscattering coefficient of marine particles (bbp), which serves as a robust proxy for particulate matter concentration and can be estimated from space. Traditionally, most in-situ multi-spectral bbp measurements are conducted using ship-based or moored systems, limiting their spatial and temporal coverage.
To address these limitations, we have integrated bio-optical sensors into Lagrangian Surface Velocity Programme (SVP) drifters, resulting in the Backscatter-Optical (BO)-SVP drifter. These systems enable continuous data collection in challenging marine environments by adopting a water-following approach and high-frequency sampling. Such measurements can validate satellite estimates, bridge observational gaps when satellite data is unavailable and capture small-scale variability that cannot be resolved by satellite observations or other sampling strategies. By crossing multiple satellite pixels within a single day, these drifters significantly enhance satellite validation efforts to ocean color missions, such as Sentinel-3/OLCI and PACE/OCI. Furthermore, BO-SVP drifters offer a unique perspective for studying surface bio-physical dynamics critical to ocean ecosystem functioning, spanning a continuum of spatial (sub-mesoscale to basin scale) and temporal (hours to weeks) resolutions.
Here, we detail the integration of a commercially available multispectral optical backscatter sensor into an SVP drifter to perform near-surface bbp measurements. The collected data demonstrated high reliability across a range of environmental conditions, showing strong agreement with independent datasets. These results highlight the potential for deploying a global network of BO-SVP drifters, offering new opportunities to monitor and understand the world’s oceans.
The high-frequency observations obtained from BO-SVP drifters could be impactful across ongoing and future hyperspectral ocean color satellite missions (e.g., NASA GLIMR, ESA Sentinel Next Generation, and ESA CHIME), and lidar mission (e.g., ASI CALIGOLA). In the next future, multiple deployments are planned in the Mediterranean Sea and on a global scale through the support of the INSPIRE and ITINERIS projects. These deployments will facilitate measurements of ocean processes across broad and fine spatial and temporal scales. Some of these deployments will be coordinated with BGC-Argo floats and other autonomous platforms, providing complementary surface and subsurface data at multiple temporal, spatial, and spectral scales. These efforts are expected to yield new insights into oceanic ecosystem functioning by enabling more comprehensive assessments of biogeochemical cycles, plankton dynamics, and carbon fluxes.
How to cite: Bellacicco, M., Busatto, J., Lacorata, G., Pitarch Portero, J., Organelli, E., Falcini, F., Volpe, G., Marullo, S., Centurioni, L., Santoleri, R., and Zoffoli, M. L.: Leveraging Lagrangian drifters to validate satellite particulate backscatter estimates and unravel ocean bio-physical dynamics, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3578, https://doi.org/10.5194/egusphere-egu25-3578, 2025.
Eddies are common mesoscale features known to impact regional ocean biogeochemistry and water mass exchange. In 2022-2023, we deployed two gliders in the southern Ross Sea, Antarctica, carrying sensors to measure temperature, salinity, chlorophyll fluorescence, dissolved oxygen, optical backscatter, and acoustic backscatter for biomass. The glider survey revealed five sub- to mesoscale features, likely eddies, during the spring season: three cold core rings and two warm core rings with radii of approximately 1-2 km. Most noteworthy of these was a shallow, warm core ring that caused isopycnal doming, bringing in cold, salty water to the surface (upper 100 m) ocean from depth. This feature substantially altered the biogeochemistry of the surface waters, inducing declines in concentrations of carbon (derived from optical backscatter) and krill (derived from acoustic backscatter), with chlorophyll exhibiting the most dramatic decline within the ring. Chlorophyll concentrations of ring waters averaged <1 – 2% of deployment average concentrations. The biogeochemical impacts of the ring may in turn impact carbon export, penguin foraging, and energy transfer to higher trophic levels. This feature serves as a characteristic example of warm core rings in the Ross Sea and illustrates the important role of mesoscale, physical features on regional biogeochemistry and foodweb dynamics.
How to cite: Meyer, M. G., Portela, E., Saenz, B., Smith Jr., W. O., and Heywood, K.: Impacts of a Warm Core Ring on the Biogeochemistry and Food web in the Ross Sea, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4532, https://doi.org/10.5194/egusphere-egu25-4532, 2025.
The settling velocity of suspended particles is of importance for sediment transport modelling, e.g. in coastal zones or the bottom boundary layer, as well as for carbon and particle flux export calculations in the open ocean. In this presentation we compare two new instruments that have recently been commercialized by Sequoia for these purposes. One, the LISST-RTSSV is a camera system designed for measuring suspended sediment size, concentration and settling velocity in the deep sea down to 6,000 m depth. The other, LISST-OST is an optical sediment trap designed to measure particle flux on Argo floats.
Here, we present the first results from a laboratory intercomparison between the two instruments. In a controlled environment, the two sensors were installed together, and a range of different particle types were allowed to settle through their sensing zones. We show that the particle flux from a camera system like the LISST-RTSSV is highly sensitive to the appearance (or not!) of a few large particles in the field of view. Because the particle concentration in the open ocean is very low, camera methods will not necessarily work well for settling velocity or settling flux measurements. The LISST-OST measures the diffuse attenuation flux from which we derive equations for the mass settling flux. The diffuse attenuation can be measured with high accuracy and precision and is thus suitable for settling flux measurements in low concentration environment like the open ocean. Because our laboratory experiments concerned settling of dense, dis-aggregated sediment grains, and because particles in the open ocean are of organic origin and/or aggregated into marine snow, the equations we present constrain upper limits to the settling flux from the LISST-OST.
How to cite: Mikkelsen, O. and Simon, K.: Intercomparison of Instrumentation for Settling Velocity and Settling Flux Measurements in the Deep Sea and Open Ocean, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5506, https://doi.org/10.5194/egusphere-egu25-5506, 2025.
Marine dissolved inorganic carbon (DIC) is the largest pool of carbon in the Earth surface system, so measurements of DIC are essential for understanding the changing global carbon cycle. The most accurate widely-used method for measuring DIC is coulometric titration. DIC is extracted from a water sample as CO2 and delivered to a coulometric cell, where it reacts, and an electrical current applied across the cell reverses the reaction. There is also a quasi-continuous background current (termed the ‘blank’). The total integrated current (termed ‘counts’) minus the blank is directly proportional to the amount of CO2 in the sample. Here, we show how determining the blank on a per-sample basis can reveal changes through time that would not be noticed with the SOP-recommended approach of a single blank determination at the start of each analysis session. If not accounted for, these changes in the blank lead to an apparent drift in the DIC results and reduced accuracy. We show how the per-sample blanks can be best computed and the results applied across an analysis session, an approach which we have implemented in an open source Python package (Koolstof). We quantify the improvement in the reproducibility of DIC measurements when using this approach by application to several different measurement datasets from our laboratory.
How to cite: Humphreys, M.: Blank variability in coulometric measurements of dissolved inorganic carbon, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6194, https://doi.org/10.5194/egusphere-egu25-6194, 2025.
Mode water acts as a barrier layer controlling surface-to-interior fluxes of key climatic properties. In the Arabian Sea, mode water provides an oxygen-rich layer for rapid remineralization, and its subduction is a direct pathway for oxygen into the upper oxygen minimum zone. Using observations from underwater gliders and argo floats, alongside numerical models (GOTM CVmix and MOM4p1-TOPAZ), we characterize the Arabian Sea mode water across temporal and spatial scales, ranging from submesoscale variability to seasonal climatologies.
Mode water forms when surface buoyancy gain and weak winds cap dense, deep mixed layers beneath a stratified surface layer. This process occurs annually in the northern Arabian Sea during winter and biannually south of 20°N following the monsoons. Atmospheric forcing primarily drives mode water formation, except in regions influenced by advective processes (e.g., freshwater influx from the Bay of Bengal via the WICC), or biological modulation of heat uptake at seasonal timescales. Our findings show that mode water contributes up to 30% of the upper ocean (0-250 m) oxygen content in the Arabian Sea, emphasizing its critical role in regulating oxygen storage. On timescales of days to weeks, we demonstrate the significance of mesoscale eddies in eroding the mode water layer leveraging high-resolution glider observations. These results underline the multifaceted drivers shaping mode water dynamics and their pivotal role in regional climate and biogeochemical processes at different temporal and spatial scales.
How to cite: Font, E., Queste, B., Swart, S., Vinayachandran, P., and Portela, E.: Arabian Sea Mode Water: A Key Player in Surface-to-Interior Exchange, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6198, https://doi.org/10.5194/egusphere-egu25-6198, 2025.
Diurnal warming (DW) at the ocean surface occurs when there is sufficient solar heating in the absence of vertical mixing. Observations of a DW event of 1.5 °C confined to the upper 2 m in the Labrador Sea at ~55°N were conducted with an upwardly-rising microstructure profiler. DW has been well described using satellite and in-situ observations, but there are very few reports at northerly latitudes. Contemporaneous satellite observations indicate a region that is largely obscured by clouds thereby preventing spaceborne detection of this DW event. Combining our in-situ observations with the ERA5 reanalysis product, we derive a set of conditions for potential DW in the Labrador Sea: shortwave radiation above 600 W/m2; total cloud cover less than 30%; and 10-m windspeed lower than 4 m/s. Based on this analysis, DW events in the Labrador Sea have the potential to occur more frequently than satellites can observe. A first look at microstructure profiler data from other regions of the North Atlantic indicates that such conditions can also be derived for these regions.
How to cite: Hauser, S., ten Doeschate, A., Ward, B., and Esters, L.: A Significant In-Situ Diurnal Warming Event in the Labrador Sea Unobserved by Satellite Observations, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6921, https://doi.org/10.5194/egusphere-egu25-6921, 2025.
Phytoplankton communities, shaped by complex water dynamics, are vital to ecosystem structure and play a key role in oceanic productivity and the biological carbon pump. Previous studies suggest that fine-scale O(1-100km, day-week) physical features significantly influence phytoplankton production, distribution and diversity in highly productive and dynamic regions. However, in oligotrophic and moderate energy conditions, representing a significant part of the global ocean, how fine-scale dynamics impact phytoplankton dynamics and diversity remains a key open question. Observations of fine-scale fronts are particularly challenging due to the difficulties in tracking their spatial and temporal evolution. Using a multidisciplinary, adaptive Lagrangian approach that integrated novel SWOT altimetry data with high-resolution in situ observations, we conducted fine-scale physical and biological sampling of the North-Balearic Front in the oligotrophic Mediterranean Sea (BioSWOT-Med, doi.org/10.17600/18002392). We found that specific biomass proportions of phytoplankton functional types were associated with distinct water masses separated by the front. Furthermore, we performed high-resolution sampling within the front itself to demonstrate that the front hosts a distinct community, where dominant phytoplankton groups display intermediate or decreased biomass proportions relative to water masses on either side but non-dominant phytoplankton groups display increased biomass proportions. Overall, these results suggest that frontal systems drive biological heterogeneity by promoting the existence of a distinct frontal community. This highlights the crucial role of fine-scale features in maintaining community diversity in oligotrophic and moderate energy regions and represents an initial step toward understanding the global ecological response to fine-scale structuring.
How to cite: Oms, L., Doglioli, A., Messié, M., d'Ovidio, F., Izard, L., Rousselet, L., Barrillon, S., Bellacicco, M., Lévy, M., Martellucci, R., Moutin, T., Petrenko, A., and Grégori, G.: ”Living on the edge”: Fine-scale observations of frontal phytoplankton communities, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8487, https://doi.org/10.5194/egusphere-egu25-8487, 2025.
The mesopelagic zone plays a crucial role in the global carbon cycle and supports a key area for developing sustainable mesopelagic fisheries due to its significant fish biomass. Active acoustic scattering techniques are particularly well-suited for synoptic studies of fish and zooplankton distribution given that organisms scatter sound differently as the frequency changes. We estimated the distribution of sound scattering layers, the diel vertical migration (DVM) and the abundance of Mueller's pearlside (Maurolicus muelleri), a key mesopelagic fish in the Whittard Canyon deep-sea submarine canyon system in the NE Atlantic using established active acoustic techniques (EK60 echosounder). Environmental data were collected from 50 CTD stations. Environmental DNA samples were obtained at various depths at each CTD station to address a ground truth component of backscatter and to explore potential interactions between deeper scattering layers and other mesopelagic species. EK60 backscatter data was processed using Echoview 14 and unique multi-frequency acoustic discrimination algorithms. The most pervasive phenomenon observed acoustically was a regular DVM evident along a series of stationary and transects throughout the canyon and the interfluve/channel system. Two strong backscatter signals were encountered in mesopelagic (650-700 m, average Nautical Area Scattering Coefficient Sa =~2568 nmi2/m2) and pelagic (45 -70 m, average Sa = ~59 nmi2/m2) at 18kHz and 38kHz in nighttime transects. Moreover, stationary data illustrate a prominent signal at nighttime in pelagic waters (25-75 m, average Sa = ~716 nmi2/m2). Non-migratory scattering layers were noticeable in deep mesopelagic zones between 800-1000 m. However, a significant inter-canyon variability of deep scattering layers was observed, with stronger layers found in two of the four canyons surveyed. The characterisation of the sound scattering layer variability probably reflected the heterogeneity in hydrographic regimes within the multi-channel canyon system. The present study will advance our understanding of the function of migrating mesopelagic fish in carbon cycling and their ramifications on carbon fluxes and sequestration. A comparison of the dynamic Whittard Canyon system and the adjacent non-canyon shelf-edge areas (based on historical acoustic data) has identified the canyon region as a possible hotspot for continental margin carbon cycling.
How to cite: Weerasinghe, K. D. I., White, M., and Reid, D.: Distribution of deep-water sound scattering layers and diel vertical migration of mesopelagic fish in the Whittard Canyon, NE Atlantic, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8842, https://doi.org/10.5194/egusphere-egu25-8842, 2025.
There is growing concern that global warming will lead to declining oxygen levels and the expansion of so-called "dead zones”. This endangers local ecosystems. Model-based projections are essential for assessing the impact of respective political management strategies and for implementing early warning systems. However, simulating dissolved oxygen dynamics in the oceans remains challenging. While the underlying processes are well understood, their representation in contemporary coupled biogeochemical-ocean models crucially depends on poorly constrained model parameters. This parameter uncertainty can map onto to diverging projections. In a step forward to more robust projections we advocate the use of abiotic tracers to assess the effects of different parameter choices among models. In addition to common tracers, such as artificial “clocks” that measure residence times and the timescales of (surface) ventilation, we propose to introduce of argon saturation as an additional tracer to the ocean models to diagnose ocean mixing, which is key to setting oxygen concentrations in the interior. We provide illustrative examples from the Baltic Sea and the North Atlantic Ocean off Mauretania.
How to cite: Löptien, U., Schneider, B., Renz, M., and Dietze, H.: Projections of hypoxia: Abiotic tracer-based insights into model parameter uncertainty, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9127, https://doi.org/10.5194/egusphere-egu25-9127, 2025.
Between the years 2002 and 2023, seawater pH was determined in more than 20,000 samples within the biennial Franco-Spanish framework of oceanic observations in the North Atlantic (OVIDE-BOCATS), during 11 cruises along the transoceanic A25 line of the GO-SHIP programme. The OVIDE-BOCATS pH measurements were regularly carried out using a spectrophotometric technique based on the pioneering article by Clayton and Byrne (1993), which allows for the total scale pH (pHT) determination at 25ºC by using a seawater-prepared solution of m-cresol (Sigma Aldrich; 2mM) dye or indicator. Although this methodology provides very high reproducibility (<0.001 pH units), it has been updated since 2007 (Yao et al., 2007) in various articles to improve the problems associated with indicator impurities. Despite this, the same methodology has been used throughout the OVIDE-BOCATS series, but during the oceanographic expeditions of 2018, 2021 and 2023, samples have been replicated using the habitual pHT determination with a non-purified indicator, and a purified indicator, not commercially available. For the purified indicator samples, we determined two different pHT values following the functions proposed by Liu et al. (2011) and DeGrandpre et al. (2014) that allow obtaining the pHT from the absorbances. Beyond the comparison of the resulting pHT values between the use of pure and impure indicators, we also tested the differences that arise when applying the correction for the effect of impurities in pHT measurement proposed by Douglas and Byrne (2017). Our methodology has also been contrasted against reference materials (TRIS buffers) determining an average bias of +0.006 ± 0.003 pH units. We found the same bias when comparing replicate samples measured with pure and impure dyes, thus attributing the bias to the use of an unpurified dye. Our results suggest that the best correction using the TRIS buffer is obtained in samples measured with purified dye and using the equation of DeGrandpre et al. (2014). These experiments, carried out on more than 178 samples, allowed us to correct the bias and standardize the entire series of two decades of pH measurements in the North Atlantic.
How to cite: Pérez, F. F., López-Mozos, M., Fontela, M., García-Ibáñez, M., Padín, X. A., Fajar, N., Castaño, M., Álvarez, M., Lherminier, P., and Velo, A.: Two decades of spectrophotometric pH measurements along the Atlantic GOSHIP-A25 section, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9869, https://doi.org/10.5194/egusphere-egu25-9869, 2025.
Interactions between physical and biogeochemical processes have traditionally been studied at ocean basin scales or in in regions with by large mesoscale features. At finer scales, such as fronts and small eddies, modeling studies have offered valuable insights into how physical features influence biogeochemistry. However, these interactions remain understudied using empirical data due to the challenges of identifying and sampling these dynamic structures. In oligotrophic regions, the vertical distribution of nutrients plays a crutial role in shaping phytoplankton diversity. Nutrient profiles typically exhibit near-zero concentrations in the upper water column and higher concentrations at depth, separated by the nutricline – a transitional zone marked by sharp or gradual changes in nutrient concentrations. The depth of the nutricline (defined as its upper limit) and its strength (reflected in the associated concentration gradient) are closely linked to nutrient fluxes into the photic layer, which are critical for sustaining new primary production.
In spring 2023, the BioSWOT-Med campaign (doi.org/10.17600/18002392) investigated the influence of fine-scale circulation on biogeochemical processes and phytoplankton biodiversity in the North Balearic Front (Western Mediterranean Sea). Coordinated with the initial CalVal phase of the SWOT (Surface Water and Ocean Topography) satellite mission, the campaign leveraged the high spatial resolution of SWOT, capable of detecting circulation features as small as 7–10 km and used an adaptive Lagrangian sampling strategy. Three distinct fine-scale features within a region approximately 50 kilometers wide were targeted: a frontal zone separating an anticyclonic eddy from a cyclonic eddy, encompassing contrasting water masses. A comprehensive dataset of nitrate and phosphate concentrations was collected using a Niskin bottle carousel (discrete profiles down to 500 m), a high-resolution pumping system (sampling every 2–4 m down to 50 m) and one BGC-Argo float (sampling of nitrates down to 400 m).
Estimating nutricline depths and concentration gradients at this unprecedented scale was constrained by uncertainties associated with near-zero phosphate concentrations in the upper water column and the discrete sampling methods. To address these challenges, innovative data processing techniques were employed. Statistical approaches to reconstruct continuous nutrient profiles enabled more precise estimates of nutricline depths and gradients, while facilitating the application of functional data analysis. Significant variability across the front appeared: concentration gradients (nitracline depths) were highest (shallowest) in the cyclonic feature and lowest (deepest) in the anticyclonic feature, emphasizing the link between fine-scale oceanic structures and distinct vertical nutrient distributions. The underlying processes driving the observed variability remain to be elucidated. This study opens interesting perspectives on nutrient supply to the photic layer driven by fine-scale oceanic circulation in oligotrophic regions, and their role in shaping phytoplankton community dynamics.
How to cite: Joël, A., Doglioli, A., Berline, L., Bosse, A., Buniak, L., d'Ovidio, F., Grégori, G., Martellucci, R., Mauri, E., Menna, M., Moutin, T., Nunige, S., Pacciaroni, M., Petrenko, A., and Pulido-Villena, E.: Oceanic Fine-Scale Circulation and Nutricline: Unveiling Uncertainty and Variability., EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9945, https://doi.org/10.5194/egusphere-egu25-9945, 2025.
By giving a highly resolved 2D view of sea level (down to submesoscales), the recently launched SWOT altimetric satellite is revealing a brand new view on upper ocean dynamics. The signatures of ageostrophic processes (e.g. submesoscale, internal gravity waves) on SWOT SSH is nevertheless expected to complicate the estimation of the upper ocean circulation from SWOT altimetry. An improved knowledge of the relative importance of these signatures is thus required. From April to July 2023, SWOT flew over the Western Mediterranean sea daily. Meanwhile, three different in-situ campaigns of the SWOT-Adac Consortium (C-SWOT-2023, FaSt-SWOT and BIOSWOT-Med) deployed numerous in situ instruments, including drifters, to sample the upper ocean underneath the satellite tracks. We combine here these in-situ observations with wind reanalysis and SWOT sea level data to reconstruct the near-surface horizontal momentum balance. For given observation sources, an original statistical method enables us to not only quantify contributions from the different dynamical terms involved (e.g. inertial acceleration, coriolis acceleration, pressure gradient and wind stress vertical divergence) but also identify different dynamical regimes. This analysis reveals in particular limits of the geostrophic approximation and the dominance of inertial balance. We also present a detailed error budget including SWOT noise and comparisons between analyses with Pre-SWOT L4 gridded and SWOT sea levels.
How to cite: Demol, M., Ponte, A., and Garreau, P.: Diagnosis of near-surface horizontal momentum balance from SWOT altimetry, drifter trajectories and wind reanalysis in the Western Mediterranean Sea., EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10704, https://doi.org/10.5194/egusphere-egu25-10704, 2025.
This research uses hybrid machine learning technique to show the regional trends of sea level change along the Australian coastline. The study uses a combination of machine learning algorithms to capture regional heterogeneity in sea level changes by combining data from 43 tidal gauge stations and grid satellite altimetry solutions covering the years 1993–2023. A robust regional evaluation is provided by the hybrid modeling framework, which combines spatial interpolation approaches with algorithms such as Random Forest (RF), Decision Tree (DT), Support Vector Machines (SVM), and Gaussian Process Regression (GPR).
The results show that the hybrid approach is able to effectively capture both temporal trends and spatial patterns in sea level variations, especially when DT is combined with spatial analysis. Regional variations in sea level trends were identified, and the northern regions exhibit slightly different patterns compared to the southern coastal areas. The model explained up to 76% of the variance in the tide gauge data while giving very accurate predictions of regional trends with average rates of 3.55-4.06 mm/year for tide gauge data and 3.13-3.99 mm/year for satellite altimetry data.
A new regional classification is proposed, which is based on the patterns of sea level behavior and delineates well-defined coastal zones characterized by similar features of the trend. This is a very useful regional categorization for local coastal management strategies and also pinpoints areas that need special attention in climate adaptation planning. These results clearly show the importance of regional variation in sea level trends and hybrid machine learning methods for efficient monitoring of coastal environments.
How to cite: Erkoç, M. H.: Integrating Machine Learning Models for Regional Sea Level Monitoring: The Australian Coastal Experience, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11469, https://doi.org/10.5194/egusphere-egu25-11469, 2025.
How to cite: Gray, P., Boss, E., Bourdin, G., and Lehahn, Y.: Physical and planktonic properties in the ocean exhibit different patterns of patchiness, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13532, https://doi.org/10.5194/egusphere-egu25-13532, 2025.
Over the last years we have a developed an open-source python package and accompanying instructional materials that are being used in graduate education as the Virtual Ship Classroom. The python tool can be used to extract reanalysis data and thereby simulate o.a. open-ocean physical oceanograpic research missions. The tool is actively being developed and will be extended with bio-geochemical measurements and gliders in the next two years.
The Virtual Ship Classroom has been developed as an authentic learning environment and is purposely suitable for students, early-career scientist and staff who want to practice planning and conducting expeditions. Plan an expedition using the MFP Cruise Location Planner[1], and run VirtualShip to virtually measure ocean fields. The data is extracted so that the output closely resembles the datafiles that are generated by the equipment onboard research vessels.
Additionally VirtualShip can for example be used to assist in observing system simulation experiments as it easily extracts data to compare to ship based or stationary observations, from e.g. landers or moorings. The tool integrates part of the open-access Copernicus Marine Service API[2] to automate data download, saving you time.
All material is open source and available online: github.com/OceanParcels/virtualship. We welcome anyone in the world to use and contribute to the Virtual Ship Classroom.
[1] https://nioz.marinefacilitiesplanning.com/cruiselocationplanning#
[2] https://data.marine.copernicus.eu/products
How to cite: Daniels, E. and van Sebille, E.: Introducing the VirtualShip tool for virtual fieldwork and e.g. observing system simulation experiments, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15730, https://doi.org/10.5194/egusphere-egu25-15730, 2025.
Oceanic adjustment processes in response to local changes in atmospheric or buoyancy forcing play a crucial role in understanding how the global climate responds to both short-term variability and long-term changes. Whilst studies show global teleconnections in this context, highly simplified models aiming to explain the fundamental processes at play lack important ingredients in their description. In particular, the effects of continuous stratification, bottom topography, background currents, and realistic coastlines are often neglected. This study aims to provide insight into how the adjustment takes place and which mechanisms are most important, focusing on the timescale of days to weeks. For this purpose, a realistic global ocean general circulation model (FESOM2) is used to apply localized perturbations in temperature, salinity, and freshwater flux in the shelf-slope area of the western North Atlantic and eastern South Pacific. An eddy-permitting mesh (horizontal resolution up to 4 km) is compared with a > 20 km mesh to capture the effect of grid resolution on the modeled adjustment process.
The perturbations are found to generate local anomalies in both salinity and temperature, regardless of the perturbed quantity. Only in limited cases do they propagate as a classical coastal trapped wave of a fixed sign. The strongest anomalies remain close to the perturbation region and are found to propagate advectively after reaching a presumed geostrophic balance. Waves in sea surface height (SSH) originate from the perturbation site and are found to travel at about 1 m s−1 to 6 m s−1 for O(1000 km) along the coast before fading away. In most of the observed cases, the baroclinic response consists of weak coastally confined anomalies with wavelengths of O(100 km) that also propagate with advective speeds after being excited by the waves in SSH. Indications of coastal adjustment through two distinct physical restoring mechanisms are found: Internal Kelvin waves and topographic waves with an offshore sign change.
The high-resolution mesh simulates narrower and faster currents with finer structure resulting in highly complex patterns in the primary (advective) temperature and salinity response. Background currents as well as changing topography along propagation pathways are known to significantly influence propagation velocities. The resolution dependency of adjustment processes in terms of signal velocities is likely to mainly enter through these processes rather than through the direct influence of discretization. Still, high spatial resolution is found to be necessary to resolve baroclinic Poincaré waves.
The observed wide range of different processes involved in adjustment including (complex) advection patterns needs to be considered when seeking explanations for teleconnections in realistic models and observations.
How to cite: Thorneloe, A. and Lohmann, G.: Adjustment Processes in an Unstructured Ocean Circulation Model at Different Resolutions, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17147, https://doi.org/10.5194/egusphere-egu25-17147, 2025.
This study conducted various sensitivity experiments to assess and improve the performance of low-resolution global ocean circulation models. The MOM6 (Modular Ocean Model Version 6), developed by the Geophysical Fluid Dynamics Laboratory, was utilized. We focused on analyzing the effects of implementing the ePBL (energetics based planetary boundary layer) mixed layer scheme, including tidal simulation, and applying hybrid vertical coordinate system on the simulation accuracy of ocean circulation. The results revealed that the ePBL scheme effectively mitigated excessive mixed layer thickness and high temperature biases in the equatorial Pacific, while tidal simulations contributed to improving the oceanic structures in the Yellow Sea and the East Sea. Additionally, the hybrid vertical coordinate system enabled more accurate simulations of the vertical structure of temperature and salinity, enhancing model performance. This study proposes specific approaches to enhance the accuracy of ocean circulation models, contributing to global ocean and climate modeling efforts.
How to cite: Park, H. C., Chang, I., Jin, H., Pak, G., Park, Y., and Kim, Y. H.: Optimizing a low-resolution global ocean circulation model using MOM6, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18298, https://doi.org/10.5194/egusphere-egu25-18298, 2025.
Robust detection of climate change is crucial to assess the influence of anthropogenic forcing on the status of the marine biogeochemical system. The sparse and varied quality of time series data can hinder long-term trend detection. The traditional linear regression to estimate trend assumes that the series consist of a stationary random noise. However, time series are data collected sequentially over time, so the assumption of noise independence is not guaranteed. This noise consists of red noise, linked to fluctuations due to internal processes or recurring natural cycles, and white noise, indicating random noise which may include data quality. Thus, accurate trend analysis requires to establish the effect of the autocorrelation of the noise (serial correlation between each sequential sampling) on the detectability of the trend.
In the framework of EuroGO-SHIP project, the Trend Detection Time (TDT) method was used to determine years required for detecting statistically significant trends, considering the signal-to-noise ratio and noise autocorrelation. High autocorrelation indicates red noise, while near zero suggests white noise. This method was performed using complete temporal and spatial reanalysis data to assess how data quality and coverage affect TDT of the seawater carbonate system, dissolved inorganic nutrients, and dissolved oxygen, in the Mediterranean, Black and Baltic Seas; regions with a high anthropogenic footprint. In addition, subsampling three random months and each season yearly, with and without adding varying levels of noise based on GLODAPv2 (Global Data Analysis Project version 2) adjustment limits, simulate noncontinuous data conditions and best-to-worst expected data quality, respectively. This approach advances a key application of understanding noise nature to gauge trend uncertainty.
TDT averages well over 20 years varying greatly with seawater properties and regions included in this study, as well as local factors like meso-scale eddies, which are responsible for high variability and may even double the TDT. Random subsampling provides knowledge on the nature of the noise. It may increase the randomness by less capturing the cyclic record of the noise, which reduces its magnitude, thus shortening TDT. Mimic the data quality changes is even more enlightening. Adding perturbations increases noise magnitude, combining with inherent white and red noise, which lengthens TDT despite raised randomness. However, in case of large magnitude and high autocorrelation of the inherent noise, the additional perturbation fails to mask the inherent cyclicity of the noise and TDT is unchanged. Exception remains when this perturbation yields decrease in the autocorrelation which lead to underestimate the overall magnitude of the noise.
In general, original high noise’s autocorrelation or lowering it due to data strategy and quality would engender an erroneous sens of confidence in the ability to detect a trend. Consequently, failing to consider noise characteristics and magnitude may mislead trend precision, and its standard deviation shall understate true uncertainty. This study provides concrete examples that underpin the falsely accurate estimation of trends due to misestimating the autocorrelation of the noise.
How to cite: Beghoura, H., Olsen, A., McDonagh, E., Fransner, F., and Sanders, R.: Assessing statistical features of time series through Trend Detection Time method, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19691, https://doi.org/10.5194/egusphere-egu25-19691, 2025.
The ocean’s biological pump (BCP) exerts a major control on global carbon cycling, maintaining atmospheric CO2 100-200 ppm lower than it would otherwise be. The BCP’s primary vehicle that transfers organic carbon to depth is a diverse assemblage of sinking of organic particles collectively called ‘marine snow’. It is thought that the morphological characteristics of marine snow (e.g. size, compactness, and shape) govern the efficiency with which sinking carbon is transferred to the deep ocean. With the rapid advance of in situ camera systems, we are now in the position to collect images of marine snow at high temporospatial scales. As in-situ imaging approaches become more widespread in the study of the BCP, classifying marine snow and relating marine snow morphology to biogeochemical functioning will form a crucial lens through which to view the BCP. With the large amount of images, the challenge is to categorise marine snow particles into a practical number of ecologically meaningful groups, reducing complexity whilst maintaining nuance.
Here we explore the vertical and spatial patterns in marine snow composition across an Atlantic meridional transect. We classified non-organism particles into 8 groups and used manual expert classification for the zooplankton. We found that primary production appears to drive particle composition in the upper 100 m, while temperature strongly constrains Rhizaria distribution and diversity both with depth and along the transect. Our approach provides an elegant way to explore marine snow characteristics across the Atlantic. However, though they show that marine snow types vary - as expected - considerably across the Atlantic, the drivers of this variability appear unexpectedly complex. Determining the key drivers and their interactions that govern BCP efficiency on basin scales will be crucial for mechanistically explaining and predicting how climate changes may impact BCP function.
How to cite: Williams, J., Couret, M., Contreras-Pacheco, Y., Elineau, A., Major, W., Masoudi, M., Takeuchi, M., and Giering, S.: Drivers of Marine Snow Morphology along an Atlantic Meridional Transect, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19746, https://doi.org/10.5194/egusphere-egu25-19746, 2025.
In the context of ocean deoxygenation and increase of hypoxia events (e.g. in coastal zones), many questions exist about the analytical performances of optodes and electrodes used to measure dissolved oxygen in high gradient zones (lakes, estuaries, Oxygen Minimum Zones in open ocean), i.e. between fully oxygenated environments and hypoxic, or even anoxic, environments. Comparing the performance of commercial sensors has become essential to harmonize their implementation and estimate the overall in situ measurement uncertainty.
Tests were carried out on Lake Pavin (Massif central, France) in June 2024 using optodes commonly used by 10 laboratories for measurements in lakes, groundwater, rivers, estuaries, coastal and oceanic waters. Lake Pavin is a meromictic lake which presents in early summer three zones of interest for dissolved oxygen measurements:
- an oxygenated surface layer between 0 and 25 m (at the top of the mixolimnion) in which is observed a peak of supersaturated oxygen concentrations related to the photosynthetic activity of highly productive phytoplankton.
- a transition zone between 50 and 60 m presenting a strong negative gradient (oxycline within the mesolimnion layer),
- an anoxic zone between 60 and 90 m depth which corresponds to the monimolimnion.
Several dissolved oxygen profiles were carried out using a frame on which were mounted 22 portable meter instruments (multiparameter or dissolved oxygen only) from various manufacturers, including 8 identical ones, in order to:
(1) quantify measurement uncertainties in gradient zones,
(2) identify and quantify the most significant interferences in terms of bias,
(3) estimate the detection limit in anoxic zones,
(4) evaluate the minimum stabilization time in the gradient zones and in the anoxic zone,
(5) compare measurements collected during downcast and upcast,
(6) evaluate the influence of sensors response times on results.
The profiles were carried out with different downcast/upcast speeds and with various stop durations at depths of interest. Continuous measurements were also taken overnight at a fixed point in the anoxic layer. Water samples were collected using a Niskin bottle for dissolved oxygen cross-calibration using the Winkler reference method.
Two statistical treatments were implemented to estimate the standard deviation of reproducibility between optodes (EN ISO 5725-2 standard and algorithm A of the EN ISO 13528 standard). Furthermore, an estimation of the overall measurement uncertainty was carried out for the 8 identical optodes using the RANOVA4 software.
The results showed significantly better performances during upcast, with slow speed and when stops of 5 min are carried out at depths of interest. These results will enable us to propose recommendations (1) for choosing optodes according to measurement objectives and expected dissolved oxygen concentration ranges, and (2) for carrying out profiles under conditions that limit the measurement uncertainties to monitor with confidence trends and extreme events in changing aquatic environments.
How to cite: Daniel, A., Guigues, N., Billard, H., Caradec, F., Gal, F., Jézéquel, D., Lefèvre, D., Lejeune, A.-H., Paulmier, A., Pérrière, F., Quétin, P., Rautureau, C., Rétho, M., and Viollier, E.: Assessment of optodes analytical performances in high dissolved oxygen gradient zones, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-20025, https://doi.org/10.5194/egusphere-egu25-20025, 2025.
