Assessing storm impacts on Southern Ocean primary production using an observation-based Copernicus Marine Service biogeochemical product

The Southern Ocean is a major sink of atmospheric carbon dioxide (CO₂) and a key component of the global carbon cycle. Phytoplankton primary production modulates air-sea CO₂ exchange, yet its response to ongoing climate-driven changes in storm intensity and storm-track position remains poorly constrained. A major challenge is that most primary production estimates rely on satellite observations restricted to the ocean surface, thereby missing subsurface production and limiting interpretation of storm-driven variability and long-term changes. Here we use the Copernicus Marine Service 3D biogeochemical product derived from in situ and satellite observations to reconstruct depth-resolved primary production over 1998–2023. Weekly three-dimensional fields of phytoplankton biomass and light-related variables are used as inputs to a depth- and phytoplankton-group-resolved bio-optical primary production model. Storm occurrence is characterized using the ERA5 atmospheric reanalysis. This approach allows us to examine how storms influence the vertical distribution of primary production and its partitioning among major phytoplankton groups. We evaluate how these effects vary across Southern Ocean regions and seasons.