French Research Institute for Exploitation of the Sea
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Response of phytoplankton to eddy dipole structure in the Mozambican channel: An automated underway evaluation
No full textFine-scale oceanographic structures such as eddies, fronts, and filaments strongly influence biogeochemical and ecological processes. So far, the characterization of phytoplankton communities of the Mozambique Channel (MZC) was limited to in-situ sampling and satellite monitoring of chlorophyll-a biomass estimation. Few studies have looked at phytoplankton community composition. During the RESILIENCE cruise in 2022, three structures were sampled; an anticyclonic eddy, a frontal area and a cyclonic eddy. Phytoplankton functional groups (PFGs) were studied at small-scale (1 km) in subsurface (about 5m depth) waters using automated underway measurements. A multispectral fluorometer (FLP) and an automated pulse shape-recording flow cytometer (AFCM). The oceanographic mesoscale features clearly structured the phytoplankton groups with distinct patterns observed in each of the three areas studied. A relatively high concentration of brown pigmentary group (groups containing xanthophyll and carotenoids-like pigments) was observed in the cyclonic eddy. High abundance of nano-microeukaryotes and of prokaryotic phytoplankton (Synechococcus spp. and Prochlorococcus spp.) were identified in the cyclonic eddy. These differences could potentially affect higher trophic levels such as zooplankton, micronekton, large pelagic fish, mammals, and seabirds. Finally, this phytoplankton community differentiation could also impact biogeochemical processes such as carbon sequestration and nutrient dynamics in the MZC
The nutritional quality of zooplankton in the sub-antarctic Southern Ocean during late austral summer
No full textKnowledge of the trophic ecology of zooplankton is essential for evaluating their functional roles in marine food webs and nutrient cycling since they represent the link between primary producers and higher trophic levels. Here we investigated the fatty acid (FA) composition of different zooplankton size classes and selected species collected in the vicinity of the sub-Antarctic Kerguelen Islands in late austral summer 2018 as part of the MOBYDICK research project. The analysis revealed that zooplankton FA composition varied significantly across size classes and species but not among stations. Larger zooplankton (>1000 μm) generally had higher total FA (TFA) amounts per dry weight than smaller classes (22.1 ± 3.0 vs. 61.9 ± 11.8 mg g−1). Essential FAs (EFA) accounted for 40.5 ± 0.8 % of TFA, with 22:6n-3 (DHA) and 20:5n-3 (EPA) being the most prominent. Diatom trophic markers (TM) were abundant in larger zooplankton size classes, while non-diatom TM were more prevalent in smaller size classes. The FA-based nutritional quality index (NQI) of zooplankton was positively correlated with EFA and DHA, and it was higher than the NQI of phytoplankton concurrently collected, indicating that zooplankton has a better nutritional quality than primary producers. This study highlights the importance of size and species-specific dietary preferences in determining zooplankton FA profiles and the high nutritional quality of this group collected during late austral summer, which significantly contributes to our understanding of zooplankton's ecological role in sub-Antarctic pelagic food webs
MPsizeBase: a database for particle size distributed environmental microplastic data
No full textUnderstanding the sources, dispersion, and health impacts of microplastic (MP) pollution requires quantitative observations in terms of MP number and/or mass concentrations. Measurements of environmental MP fragments or fibers typically target variable size spans within the formal 1 to 5000 µm range, due to different sampling and detection techniques, and are therefore not directly comparable. In addition, the majority of measurements by microscopy techniques are number based, whereas life cycle analysis, numerical models for MP dispersion and policy evaluation, and plastic additive exposure estimates are mass based. Data analysis frameworks, based on measured MP particle number size distribution (PSD), have been developed to align and extrapolate measurements to a common MP size range (e.g. 1-5000 or 1-300 µm), which in turn allows direct data inter-comparison. In this study we present the MPsizeBase, a database of published MP number concentrations and PSD in the environment, including land, ocean and atmosphere. MPsizeBase uses the power law to fit observed MP cumulative number PSDs, and extrapolate and align observations over a common size range of choice. Assuming MP shape and volume approximations, MPsizeBase also estimates size-aligned MP mass concentrations. We illustrate how the MPsizeBase can be used for inter-comparison studies, and end with recommendations on MP size, shape, and PSD reporting, including length, width and surface area. We invite scientists to contribute old and new data to MPsizeBase for additional environmental compartments, including soils, sediment and biota
Mesoscale processes in the northern Arabian Sea: Linking in situ observations to remote-sensing
No full textThe PHYSINDIEN2019 campaign occurred in the Northwestern Arabian Sea, during the spring intermonsoon, between 16 and 25 °N. Along its 3000 km transect, it sampled 5 anticyclones, 3 cyclones and 2 cyclonic submesoscale coherent vortices (SCV) with continuous hydrological and velocity measurements. Remarkably, the two cyclonic SCV were located beneath surface mesoscale anticyclones. Also, a water mass analysis shows that small anticyclones with Persian Gulf Water (PGW) are found in the Gulf of Oman, while anticyclones further south are shallower vortices containing Arabian Sea High Salinity Water (ASHSW). Comparison of in situ data with the META atlas, a state-of-the-art eddy detection and tracking atlas based on altimetry, reveals that eddy radii are often underestimated by remote sensing. In this atlas, eddy tracks are often discontinuous due to missing detections. Both hydrological measurements and remote-sensing tracking are however consistent in indicating that along the southern Omani coast anticyclones are formed offshore during the spring intermonsoon, near the center of the Arabian Sea. These results underline the diversity of surface and subsurface eddies in the sparsely explored Arabian Sea, and provide insight on the potential bias of their remote detections
Organohalogen contaminants of emerging concern in common dolphins (Delphinus delphis) from the Bay of Biscay (NE Atlantic): Occurrence and 2000–2023 temporal patterns
No full textThe contamination of marine mammals by legacy pollutants has been largely studied in oceans worldwide. However, international regulations have given rise to the replacement of legacy substances by alternative compounds, which represent a potential additional threat to marine mammal health and conservation. In this study, we investigated the occurrence and temporal trends of contaminants of emerging concern (CECs) in the blubber of common dolphins (Delphinus delphis) from the Bay of Biscay, North-East Atlantic, and in their major prey. Alternative brominated flame retardants were below the limits of quantification in all samples, while dechlorane-related compounds were identified as the major CECs, at levels of 4.6 ± 5.9 ng g−1 lw, i.e. similar to or higher than those reported in various marine mammals from other oceanic regions. The concentrations of 3,6-dichlorocarbazole (3,6-CCZ), the major polyhalogenated carbazole, and of methyl-triclosan were one order of magnitude lower. The halogenated natural products, methoxylated polybrominated diphenyl ethers (MeO-BDEs), were also investigated and showed substantially higher concentrations than all CECs, i.e. 322 ± 214 ng g−1 lw. Declorane-602, anti-monohydro dechlorane plus and MeO-BDEs were the only compounds showing biomagnification between small pelagic fish and dolphins. No significant differences in most CEC concentrations were found over the studied time period, indicating that these compounds are still emitted in the environment and/or have long residence times in the dolphins’ blubber. Conversely, methyl-triclosan concentrations significantly decreased over the studied period. An increase in MeO-BDE concentrations in the last two decades might reveal a change in algal production in relation to global warming
On the cyclogeostrophy of mesoscale eddies as revealed by in situ observations
No full textMesoscale eddies are persistent and dynamic structures that are ubiquitous across the global ocean. Most of these eddies are observed to be in geostrophic equilibrium, where the Coriolis force is balanced by the horizontal pressure gradient. However, a subset exhibits more nonlinear behaviors, requiring a more complex framework for describing their azimuthal flows. To account for the curvature of the streamlines, several studies have applied the cyclo-geostrophic velocity, incorporating not only the Coriolis and pressure gradient forces but also the centrifugal acceleration. Despite this correction, the equilibrium solution often diverges near the eddy core, failing to accurately represent the velocity field in these regions. This study evaluates the geostrophic and cyclo-geostrophic characteristics of nine mesoscale eddies sampled in various regions. A theoretical analysis is provided to explain why the cyclo-geostrophic adjustment can lead to divergences in eddy cores. Our results show that while geostrophy remains a robust approximation for the overall dynamics of mesoscale eddies, it does not fully capture the three-dimensional structure. Additionally, the ageostrophic components of eddy flows are not solely attributable to cyclostrophic effects, suggesting the need to consider other factors influencing eddy behavior
Mean Kinetic Energy and Its Projected Changes Dominate Over Eddy Kinetic Energy in the Arctic Ocean
No full textAs sea ice retreats in a warming climate, the Arctic Ocean is becoming more energetic; yet little is known about this additional energy's distribution in the water column. We use a high‐resolution (3–4 km) pan‐Arctic ocean‐sea ice model forced by present day and future scenarios to examine changes in mean kinetic energy (MKE) and eddy kinetic energy (EKE). Our study suggests that both the mean and eddy fields are becoming more energetic under anthropogenic forcing but changes in the mean circulation dominate the increase, concurrent with a spin‐up of the large‐scale circulation, concentrated in the top 200 m and along boundaries. The increase in EKE is strongest in the upper 50 m and is linked to enhanced baroclinic instability within the mean boundary currents. A better grasp of the distribution of this energy surplus helps to understand projected changes to stratification, mixing, and circulation in a future Arctic Ocean
Waterscape dataset of the municipality of Girona
No full textThis dataset presents a detailed cartographic and classification of freshwater body types within the Girona’s municipality territory to support integrated urban planning and ecological conservation strategies. The data were collected through a systematic spatial analysis of water bodies, combining GIS mapping and field validation techniques to characterize the water bodies and cartography aquatic systems across the urban and peri-urban landscape. The resulting database, that was converted to a grid with 100 × 100 m cells, categorizes each water body according to four key typologies: type of aquatic system (F1: lentic or lotic), degree of urbanization (F2: urban or peri-urban), water permanence (F3: permanent or temporary), and geographical location (F4: central or peripheral). Each water body is also georeferenced and quantified by surface area (m²), enabling comparative analysis across categories. Griona’s waterscape is dominated by lotic water bodies and permanent hydroperiods. Lotic water bodies are more distributed on the peri-urban area contrasting with lentic ones, which are located more within the urban area. The distribution pattern of the waterscape over the geographical location shows a similar pattern to the degree of urbanization, with a small difference on lentic water bodies. This dataset provides a resource for understanding the structure and characteristics of urban and peri-urban freshwater systems. Through integrating hydrological and spatial data into a cohesive framework, it can support decision-making in land-use planning, conservation prioritization, and sustainable urban development, while also serving as a valuable tool for further research and applied modelling
Sensitivity of marine heatwaves metrics to SST products, focusing on the Tropical Pacific
No full textMarine heatwaves (MHWs) are increasingly studied in climate sciences for their ecological impacts, for which accurate real-time bulletins and forecasts are essential. Yet, methodological choices in their detection affect metric estimates, underlining the need to better assess these sensitivities. This study provides a thorough assessment of the impact of Sea Surface Temperature (SST) product choice on MHW statistics, focusing on the tropical Pacific. MHW detection was performed on six daily gridded SST datasets: four widely used blended satellite observational products, one ocean reanalysis, and a multi-dataset ensemble mean computed from the four observational products. Sensitivity to SST products was evaluated for six MHW metrics (MHW days per year, number of events per year, duration, maximum intensity, cumulative intensity and onset rate) and for the Degree Heating Weeks (DHW), a widely used proxy for coral bleaching. Inter-product comparisons revealed a significant dispersion among MHW metric estimates, with the reanalysis GLORYS12v1 detecting fewer, longer and less intense MHWs while OISST detected more MHWs of shorter duration and higher intensity, likely related to their weak and strong high-frequency SST variability (periods shorter than 2 weeks) respectively. The sensitivity analysis showed that the onset rate was the most sensitive metric to SST product choice and the maximum intensity the most robust. Metrics uncertainties were quantified inside seven regions of the basin and were largest in the western Pacific Warm Pool. Co-occurrence analyses of MHWs revealed that, over the basin, 10 to 80 % of MHW days were detected simultaneously by all products, with the western Pacific Warm Pool showing the lowest agreement (10–40 %). Filtering MHWs by size also revealed that the detection of large-scale MHWs (> 5°x5°) was more consistent across products than smaller ones. Finally, over the studied period, inter-product differences tend to decrease with time. The DHW also revealed to be sensitive to SST products, with inter-product differences on DHW annual maximum reaching more than 1°C.weeks-1 and percentages of bleaching alert days (DHW ≥ 4°C.weeks-1) in common across products reaching 70 % at most across much of the basin. These findings contribute to a better understanding of how methodological choices affect the characterization of MHWs and DHW, and their associated uncertainties
Paleoproductivity and coccolith carbonate export in the northern Bay of Bengal during the late Pleistocene
No full textThe Bay of Bengal (BoB) is a unique oceanographic and sedimentary environment because of the influence of the South Asian monsoon, which causes seasonal reversals of wind-driven ocean circulation and results in massive inputs of freshwater and sediment into the northern margins. Monsoon dynamics also control primary productivity in the Bay of Bengal, causing nutrient inputs that stimulate productivity when wind-driven or eddy mixing is intense but also limiting oceanic productivity when salinity stratification resulting from runoff and precipitation is intense. In the modern Bay of Bengal, coccolithophores (calcifying unicellular phytoplankton) are an important component of primary productivity, in particular in the deep photic zone, and are a key contributor to organic and inorganic carbon export. Here, we present a revised age model and new high-resolution (mean 1200 years) calcareous nannofossil records from core MD12-3412 in the central northern Bay of Bengal, drilled in the Bengal Fan (18° N, 89° E; 2368 m water depth), spanning the last 279 000 years. We document significant orbital timescale variations in total coccolith accumulation rates (ARs) and coccolith carbonate mass accumulation rates (MARs), suggesting a strong influence of monsoon dynamics on coccolithophore productivity on both glacial–interglacial and precessional timescales. We find that productivity (coccolith accumulation rates) maxima in the northern Bay of Bengal generally coincide with South Asian monsoon minima as inferred from other independent proxies. This pattern is opposite to that observed in the southern Bay of Bengal and likely results from a weakening of salinity stratification in the north during periods of weaker monsoon, allowing entrainment of nutrients into the mixed layer fueling coccolithophore productivity. The abundance of Florisphaera profunda coccoliths, a species typically inhabiting the deep photic zone in the tropical ocean, is high in core MD12-3412 sediments (mean 80 % of total coccoliths and > 60 % of coccolith mass accumulation rates, cMARs), suggesting an important role of deep photic zone productivity in carbon and carbonate export. Significant precession-scale variance in F. profunda accumulation rates is resolved; however, peaks in this species' accumulation rates are in phase with maximum accumulation rates of Noelaerhabdaceae coccoliths (the dominant upper-photic-zone group), and no clear variations in the relative percent of F. profunda are observed. This suggests that percent F. profunda cannot be universally applied as a paleoproductivity proxy in the Bay of Bengal