Deep Convection-Driven Chlorophyll Blooms Revealed by Bgc-Argo Floats and Satellites Observations

Abstract

Deep convection in the Antarctic Circumpolar Current influences biogeochemical cycles, yet its link to chlorophyll bloom remains understudied. Analysis of time series of mixed layer depth (MLD) based on over 3 years of BGC-Argo datasets highlights the occurrence of deep convection, characterized by very deep MLDs. Ocean color data derived by satellite observations are extracted to evaluate surface CHL concentrations at two floats positions, providing evidence for deep convection. The cross-correlation analysis between the time series of surface CHL and the MLDs for the year in which the MLDs reached their maxima indicates that the bloom of surface CHL lags the maxima of the MLDs by 20 days. Analysis of wind field data and observed profiles from two floats suggest that deep convection events are attributed to the strengthened positive anomalies of wind stress curl and mesoscale activities, where the MLDs reach their maxima and the turbulent diffusion coefficient reach their maxima. Analysis of the observed profiles from the two BGC-Argo floats indicates that the deepest MLDs associated with deep convection trigger CHL bloom. The impact of MLD on CHL changes helps to improve the comprehension of the interaction between physical and biological dynamics.

Keywords: Deep convection, Chlorophyll bloom, Mixed layer depth, Turbulence mixing, Antarctic Circumpolar Current