Influence of oceanic mesoscale eddies on the deep chlorophyll maxima.

The deployment of the biogeochemical Argo network significantly enhances our understanding of the ecological effects of mesoscale eddies at different ocean depths. In this study, satellite data and more than one hundred thousand biogeochemical Argo float profiles were used to analyze the responses of the deep chlorophyll maximum (DCM) to mesoscale eddies. The DCM profiles were categorized into two types: DAM (adaptation maximum) and DBM (biomass maximum), based on their adaptation to light and maximum biomass characteristics. The variabilities in the DCM profiles in terms of latitude, seasonality, and their response to mesoscale eddies were subsequently investigated on a global scale. Our analysis demonstrates that light and nutrient availability explain a significant portion of the variability in the phytoplankton distribution across different regions and seasons. Statistical analysis reveals that cyclonic (anticyclonic) eddies enhance (weaken) the intensity of the DCM. The magnitude of this enhancement or weakening exhibits regional differences. Specifically, high-latitude regions are more influenced by eddies in terms of light-adapted DCM intensity, while in mid-latitude regions, eddies exhibit a stronger effect on the maximum biomass-driven DCM intensity. Moreover, our findings suggest that eddies in the North Atlantic Subtropical Gyre contribute to a downward shift in the euphotic zone depth, leading to an increased DCM depth and strengthened DCM intensity. However, in the equatorial region, eddies impact the DCM depth by influencing the nitracline (a layer in a body of water in which the nitrate concentration changes rapidly with depth). Similar patterns are frequently observed in different regions at the same latitude, providing a foundation for further detailed investigations of the DCM in specific areas.