Abstract's details
Studying the physical-biogeochemical coupling at fine scale with SWOT : first results of the BioSWOT-Med campaign.
Event: 2025 SWOT Science Team Meeting
Session: Oceanography: Regional Validation
Presentation type: Oral
The oceanic fine scales (1-100 km) have relatively short lifetimes (days to weeks) but crucially affect ocean physics and ecology up to the climate scale, due to intense gradients created by their energetic dynamics. These gradients can be associated with enhanced vertical transport connecting the ocean's upper layer to its interior. Moreover, the temporal scale associated with the fine-scale dynamics is similar to that of many important oceanic processes including biogeochemical cycles, biodiversity, fish distribution, and even foraging strategies of mega-fauna.
Over the past few decades, numerical studies with physical and biophysical configurations for km-scale processes allowed significant progress in characterizing this regime. However, in situ observations of the physical-biogeochemical coupling at fine scales are particularly challenging to obtain due to the ephemeral nature of the dynamical structures and the complexity and multidisciplinarity of the processes. A few in situ surveys have shown the structuring role of fine-scale dynamics on plankton communities, but most of these studies were conducted in highly productive and energetic regions.
During the BioSWOT-Med cruise (21/4 – 14/5 2023, R/V L'Atalante, https://doi.org/10.17600/18002392) we targeted a moderately energetic front (the North-Balearic Front) in an oligotrophic region (the Western Mediterranean Sea).
Guided by the first bidimensional altimetry data transmitted by the novel SWOT satellite, we used an adaptive Lagrangian strategy to conduct high-resolution multi-disciplinary sampling and deploy several autonomous platforms.
The front consisted of a strong meandering jet, separating cold, salty and more productive waters in the north from warmer, fresher and more oligotrophic waters in the south.
Within a region approximately 50 kilometers wide we performed a series of 24-hour stations in three distinct dynamical features: a cyclonic circulation to the north, an anticyclonic eddy to the south, too small to be clearly detected by conventional altimetry, and the front itself.
Two consecutive northerly wind events created challenging conditions for shipboard operations but allowed us to observe and characterize the generation and propagation of strong near-inertial waves. Microstructure measurements revealed how trapping mechanisms of those waves lead to enhanced turbulence mixing within the anticyclone.
Drifters revealed the significant role of wind and sea-surface height in driving local surface circulation and showed an alternating pattern of vertical velocities within the anticyclone.
Innovative methods allowed us to estimate nutricline depths and nutrient concentration gradients at high resolution and precision. Significant variability of nutricline depths and nutrient gradients across the front, equivalent to basin-scale variability, were observed.
A 24-hour continuous water sampling within the front with automated high frequency flow cytometry was crucial to unveiling a distinct frontal phytoplankton community, where the relative contribution of non-dominant phytoplankton groups increased relative to the one of the adjacent water masses.
Within the frontal area total mesozooplankton abundance and biovolume had values lower than adjacent waters. Within the upper 100 meters the taxonomic composition of the front waters differed from the adjacent ones. Then, with depth, a progressive homogenization of community structure was observed.
Multidisciplinary analyses of the large dataset collected are in progress to explain underlying mechanisms of these observations.
The BIOSWOT-Med campaign showcases the new opportunities for biophysical experiments opened by the combination of SWOT observations and dedicated sampling strategies. Moreover, as the Mediterranean sea shares several physical and biogeochemical conditions with several other regions of the world ocean where fine scale activity is mostly undocumented, this research acquires a global significance.
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(*,*) BioSWOT-Med Collaboration Members:
https://people.mio.osupytheas.fr/~doglioli/BioSWOT-Med_MailingList.png
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Cruise Report:
https://doi.org/10.13155/100060
Cruise Metadata: https://people.mio.osupytheas.fr/~doglioli/BioSWOT/BioSWOT-Med_2023/BioSWOT-Med_metadata.pdf
Popularization Book: Doglioli A., Ballerini T. (eds), 2025. People, science and instruments of the BioSWOT-Med Campaign. https://doi.org/10.13155/105690
Back to the list of abstractOver the past few decades, numerical studies with physical and biophysical configurations for km-scale processes allowed significant progress in characterizing this regime. However, in situ observations of the physical-biogeochemical coupling at fine scales are particularly challenging to obtain due to the ephemeral nature of the dynamical structures and the complexity and multidisciplinarity of the processes. A few in situ surveys have shown the structuring role of fine-scale dynamics on plankton communities, but most of these studies were conducted in highly productive and energetic regions.
During the BioSWOT-Med cruise (21/4 – 14/5 2023, R/V L'Atalante, https://doi.org/10.17600/18002392) we targeted a moderately energetic front (the North-Balearic Front) in an oligotrophic region (the Western Mediterranean Sea).
Guided by the first bidimensional altimetry data transmitted by the novel SWOT satellite, we used an adaptive Lagrangian strategy to conduct high-resolution multi-disciplinary sampling and deploy several autonomous platforms.
The front consisted of a strong meandering jet, separating cold, salty and more productive waters in the north from warmer, fresher and more oligotrophic waters in the south.
Within a region approximately 50 kilometers wide we performed a series of 24-hour stations in three distinct dynamical features: a cyclonic circulation to the north, an anticyclonic eddy to the south, too small to be clearly detected by conventional altimetry, and the front itself.
Two consecutive northerly wind events created challenging conditions for shipboard operations but allowed us to observe and characterize the generation and propagation of strong near-inertial waves. Microstructure measurements revealed how trapping mechanisms of those waves lead to enhanced turbulence mixing within the anticyclone.
Drifters revealed the significant role of wind and sea-surface height in driving local surface circulation and showed an alternating pattern of vertical velocities within the anticyclone.
Innovative methods allowed us to estimate nutricline depths and nutrient concentration gradients at high resolution and precision. Significant variability of nutricline depths and nutrient gradients across the front, equivalent to basin-scale variability, were observed.
A 24-hour continuous water sampling within the front with automated high frequency flow cytometry was crucial to unveiling a distinct frontal phytoplankton community, where the relative contribution of non-dominant phytoplankton groups increased relative to the one of the adjacent water masses.
Within the frontal area total mesozooplankton abundance and biovolume had values lower than adjacent waters. Within the upper 100 meters the taxonomic composition of the front waters differed from the adjacent ones. Then, with depth, a progressive homogenization of community structure was observed.
Multidisciplinary analyses of the large dataset collected are in progress to explain underlying mechanisms of these observations.
The BIOSWOT-Med campaign showcases the new opportunities for biophysical experiments opened by the combination of SWOT observations and dedicated sampling strategies. Moreover, as the Mediterranean sea shares several physical and biogeochemical conditions with several other regions of the world ocean where fine scale activity is mostly undocumented, this research acquires a global significance.
-----
(*,*) BioSWOT-Med Collaboration Members:
https://people.mio.osupytheas.fr/~doglioli/BioSWOT-Med_MailingList.png
-----
Cruise Report:
https://doi.org/10.13155/100060
Cruise Metadata: https://people.mio.osupytheas.fr/~doglioli/BioSWOT/BioSWOT-Med_2023/BioSWOT-Med_metadata.pdf
Popularization Book: Doglioli A., Ballerini T. (eds), 2025. People, science and instruments of the BioSWOT-Med Campaign. https://doi.org/10.13155/105690