Abstract's details
The Role Of Fine-Scale Circulation In Shaping The Nutricline Unveiled At The SWOT Era. Insights From BioSWOT-Med.
Event: 2025 SWOT Science Team Meeting
Session: Oceanography: Regional Validation
Presentation type: Oral
The SWOT satellite mission, during its CalVal phase, provided a unique opportunity to study oceanic fine-scale circulation and its interactions with biogeochemical processes. In low-to-moderate energy systems and oligotrophic regions—representing the majority of the global ocean—numerical models have suggested how physical features such as eddies, fronts, and filaments influence the vertical distribution of nutrients, playing a key role in shaping phytoplankton diversity and distribution. Until SWOT, these interactions remained poorly characterized empirically due to the transient nature of fine-scale structures and the challenges associated with tracking and sampling them in situ.
In spring 2023, as part of the SWOT-AdAC consortium, the BioSWOT-Med campaign (doi:10.17600/18002392) investigated the influence of fine-scale circulation on biogeochemical processes and phytoplankton biodiversity in the North Balearic Front located in the Western Mediterranean Sea. The campaign leveraged the unprecedented spatial resolution of sea surface height measurements provided by SWOT, combined with an adaptive Lagrangian sampling strategy. Within a ~50 km-wide area, three distinct fine-scale features were targeted, including a frontal zone separating an anticyclonic eddy from a cyclonic circulation structure, encompassing contrasting water masses. A comprehensive dataset of nitrate and phosphate concentrations was generated based on Niskin bottle rosette samples (nitrate and phosphate profiles down to 500 m) and automated measurements performed in situ by a BGC-Argo float (nitrate profiles down to 400 m).
Nutrient profiles typically exhibit near-zero concentrations in surface waters and increasing concentrations with depth, separated by the nutricline—a transition layer marked by sharp or gradual changes in nutrient concentrations. The depth of the nutricline and its strength (vertical concentration gradient) are key factors controlling nutrient fluxes into the photic layer, which are critical for sustaining new primary production. Estimating these parameters at an unprecedented spatial scale was complicated by uncertainties related to near-zero nutrient concentrations in surface waters and the discrete nature of the sampling. To address these limitations, statistical approaches and innovative data processing techniques were applied.
For the first time at this scale, a significant variability across the front was observed with in situ data: concentration gradients were steepest within the cyclonic feature, which exhibited the shallowest nutricline depths, and weakest within the anticyclonic feature, where the nutricline was deepest. These results highlight the strong coupling between fine-scale oceanic structures—detectable thanks to SWOT—and distinct patterns in vertical nutrient distribution. Ongoing investigations aim to disentangle the contributions of biological activity, episodic wind forcing, and near-inertial wave dynamics to the observed variability. This study opens promising perspectives on nutrient supply to the photic layer driven by fine-scale circulation in oligotrophic regions, and its implications for structuring phytoplankton communities in the SWOT era.
Back to the list of abstractIn spring 2023, as part of the SWOT-AdAC consortium, the BioSWOT-Med campaign (doi:10.17600/18002392) investigated the influence of fine-scale circulation on biogeochemical processes and phytoplankton biodiversity in the North Balearic Front located in the Western Mediterranean Sea. The campaign leveraged the unprecedented spatial resolution of sea surface height measurements provided by SWOT, combined with an adaptive Lagrangian sampling strategy. Within a ~50 km-wide area, three distinct fine-scale features were targeted, including a frontal zone separating an anticyclonic eddy from a cyclonic circulation structure, encompassing contrasting water masses. A comprehensive dataset of nitrate and phosphate concentrations was generated based on Niskin bottle rosette samples (nitrate and phosphate profiles down to 500 m) and automated measurements performed in situ by a BGC-Argo float (nitrate profiles down to 400 m).
Nutrient profiles typically exhibit near-zero concentrations in surface waters and increasing concentrations with depth, separated by the nutricline—a transition layer marked by sharp or gradual changes in nutrient concentrations. The depth of the nutricline and its strength (vertical concentration gradient) are key factors controlling nutrient fluxes into the photic layer, which are critical for sustaining new primary production. Estimating these parameters at an unprecedented spatial scale was complicated by uncertainties related to near-zero nutrient concentrations in surface waters and the discrete nature of the sampling. To address these limitations, statistical approaches and innovative data processing techniques were applied.
For the first time at this scale, a significant variability across the front was observed with in situ data: concentration gradients were steepest within the cyclonic feature, which exhibited the shallowest nutricline depths, and weakest within the anticyclonic feature, where the nutricline was deepest. These results highlight the strong coupling between fine-scale oceanic structures—detectable thanks to SWOT—and distinct patterns in vertical nutrient distribution. Ongoing investigations aim to disentangle the contributions of biological activity, episodic wind forcing, and near-inertial wave dynamics to the observed variability. This study opens promising perspectives on nutrient supply to the photic layer driven by fine-scale circulation in oligotrophic regions, and its implications for structuring phytoplankton communities in the SWOT era.