Characteristics of surface physical and biogeochemical parameters within mesoscale eddies in the Southern Ocean

Abstract. Using satellite sea surface temperature (SST) and chlorophyll a (Chl a) as well as observation-based reconstruction of dissolved inorganic carbon (DIC) and partial pressure of CO2 (pCO2) from 1996 to 2015, we investigate the modulation mechanisms of eddies on surface physical and biogeochemical parameters in the Southern Ocean (SO). About one-quarter of eddies are observed to be “abnormal” (cold anticyclonic and warm cyclonic eddies) in the SO, which show opposite SST signatures to “normal” eddies (warm anticyclonic and cold cyclonic eddies). The study finds that the modification of abnormal eddies on physical and biogeochemical parameters is significant and differs from normal eddies due to the combined effects of eddy pumping and eddy-induced Ekman pumping. Normal and abnormal eddies have opposite DIC anomalies, contrary to the SST anomalies. Moreover, the contributions of abnormal eddies to pCO2 are about 2.7 times higher than normal eddies in regions where abnormal eddies dominate. Although Chl a anomalies in normal and abnormal eddies show similar patterns and signals, eddy-induced Ekman pumping attenuates the magnitudes of Chl a anomalies within abnormal eddies. In addition to the variation of the same parameter within different eddies, the dominant eddy-driven mechanisms for different parameters within the same kind of eddies also vary. The strength of the eddy stirring effect on different parameters is the primary factor causing these differences, attributed to variations in the magnitudes of horizontal parameter gradients. Understanding the role of abnormal eddies and the complexity of eddy-driven processes is crucial for accurately estimating the influence of mesoscale eddies on physical and biogeochemical processes in the SO, which is essential for simulating and predicting biogeochemical dynamics and carbon cycling in the region.