Characterizing Submesoscale Frontal Dynamics and their Ecological Impact in the Peruvian Upwelling System

Alice Pietri1, Cristhian Asto1,2, Anthony Bosse3, Mathieu Gentil4, Pedro Diaz2, François Colas5
1LOCEAN-IPSL, Sorbonne Université, IRD, CNRS, MNHN, Paris, France
2Dirección General de Investigaciones Oceanográficas y Cambio Climático (DGIOCC), Instituto del Mar del Peru (IMARPE), Callao, Peru
3Aix Marseille Université, Université de Toulon, CNRS, IRD, MIO, Marseille, France
4LEGOS, Université de Toulouse, UPS, IRD, CNRS, Toulouse, France
5LOPS (IRD/UBO/CNRS/Ifremer), IUEM, Technopôle Brest-Iroise, Plouzané, France

Eastern Boundary Upwelling Systems (EBUS) are global hotspots of ocean productivity and sustain some of the world's most significant fisheries. In the Northern Humboldt Upwelling System off Peru, the combination of strong wind-driven upwelling and sharp horizontal density gradients creates an environment highly conducive to the development of submesoscale dynamics. These processes, typically acting at spatial scales of O(10km) and time scales of days, are increasingly recognized as key drivers of vertical exchanges and ecosystem functioning, yet their spatial and temporal variability, and their subsequent effects on biogeochemistry, remain poorly documented due to historical sampling limitations.

Here we investigate the characteristics, dynamics and impacts of submesoscale fronts in the Peruvian upwelling system using repeated high-resolution glider transects collected off central Peru, complemented by satellite observations and a high-resolution regional numerical model. Using a specialized detection algorithm for vertical sections, submesoscale fronts are identified from along-track density gradients and their dynamical nature is examined through a suite of metrics including Richardson and Rossby numbers, two-dimensional potential vorticity, and estimates of ageostrophic vertical velocities. Statistical analyses are used to document the spatial distribution and seasonality of frontal occurrences.

Observations reveal that submesoscale fronts are preferentially located near the base of the mixed layer and within the pycnocline, with a marked seasonal modulation characterized by enhanced frontal activity during winter. Model simulations reproduce the observed frontal characteristics and extend the analysis in space and time. Using glider-based oxygen and chlorophyll data, we find that these fronts can modulate the vertical structure of the oxycline and are associated with enhanced chlorophyll concentrations, suggesting an active role in ventilation and biological productivity. These findings highlight the importance of submesoscale frontal dynamics in shaping physical–biogeochemical interactions in the Humboldt system, with potential implications for ecosystem productivity and fisheries.