Impact of Mesoscale Eddies on Deep Chlorophyll Maxima.

Deep Chlorophyll Maxima (DCM) are ubiquitous features in stratified oceanic systems. Their establishment and maintenance result from hydrographical stability favoring specific environmental conditions with respect to light and nutrient availability required for phytoplankton growth. This stability can potentially be challenged by mesoscale eddies impacting the water column's vertical structure and thus the environmental parameters that condition the subsistence of DCMs. Here, data from the global BGC‐Argo float network are collocated with mesoscale eddies to explore their impact on DCMs. We show that cyclonic eddies, by providing optimal light and nutrient conditions, increase the occurrence of DCMs characterized by Deep Biomass Maxima for phytoplankton. In contrast, DCMs in anticyclonic eddies seem to be driven by photoacclimation as they coincide with Deep Acclimation Maxima without biomass accumulation. These findings suggest that the two types of eddies potentially have different impacts on the role of DCMs in global primary production. Plain Language Summary: In the global ocean, phytoplankton can be found at depths where their growth is limited by their access to light from the surface and nutrient supply from below. Depending on the combination of environmental conditions, phytoplankton at depth can either accumulate in densely populated layers or deploy adaptive survival strategies such as multiplying their internal light sensors. Given their dependence on environmental variations, phytoplankton can be affected by physical disturbances that alter the vertical structure of the water column's properties. Among these are mesoscale eddies, large water structures dominated by rotation on the horizontal plane which also induce vertical physical movements. In this study, we associate data from autonomous robots that drift with ocean currents and sample physical and biological properties down to a depth of 2,000 meters, with mesoscale eddies detected by satellite. We show that on a global scale, cold mesoscale eddies promote the growth of phytoplankton at depth. Key Points: Deep Chlorophyll Maxima are key biological features of stratified environments that escape satellite ocean‐color detectionThe impact of mesoscale eddies on DCM is assessed by matching a global BGC‐Argo database with eddies detected from satellite altimetryWhile cyclonic eddies increase biomass maxima occurrences, anticyclonic eddies favor the presence of maxima resulting from photoacclimation [ABSTRACT FROM AUTHOR]