Southern Ocean mesoscale eddies play an important role in ocean circulation and biogeochemical cycling, but their biological characteristics have not been well quantified at the basin scale. To address this, we combined a 15‐year tracked eddy data set with satellite observations of ocean color, sea surface temperature, and autonomous profiling floats to quantify the surface and subsurface properties of eddies. Anomalies of surface temperature and chlorophyll were examined in eddy‐centric composite averages constructed from thousands of eddies. Normalized surface chlorophyll anomalies (chl_norm) vary seasonally and geographically. Cyclones typically show positive chl_norm, while anticyclones have negative chl_norm. The sign of chl_norm reverses during late summer and autumn for eddies between the Subtropical and Polar Fronts. The reversal is most obvious in the Indian sector, and we attribute this to a combination of eddy stirring (deformation of surface gradients by the rotational velocity of an eddy) and deeper winter mixing in anticyclones. Both chl_norm and sea surface temperature anomalies transition from dipole structures north of the Subtropical Front to monopole structures south of the Subantarctic Front. Sea surface temperature and chl_norm composites provide evidence for eddy trapping (transporting of anomalies) and eddy stirring. This research provides a basin‐scale study of surface chlorophyll in Southern Ocean eddies and reveals counterintuitive biogeochemical signals.

The Antarctic Circumpolar Current has highly energetic mesoscale phenomena, but their impacts on phytoplankton biomass, productivity, and biogeochemical cycling are not understood well. We analyze satellite observations and an eddy‐rich ocean model to show that they drive chlorophyll anomalies of opposite sign in winter versus summer. In winter, deeper mixed layers in positive sea surface height (SSH) anomalies reduce light availability, leading to anomalously low chlorophyll concentrations. In summer with abundant light, however, positive SSH anomalies show elevated chlorophyll concentration due to higher iron level, and an iron budget analysis reveals that anomalously strong vertical mixing enhances iron supply to the mixed layer. Features with negative SSH anomalies exhibit the opposite tendencies: higher chlorophyll concentration in winter and lower in summer. Our results suggest that mesoscale modulation of iron supply, light availability, and vertical mixing plays an important role in causing systematic variations in primary productivity over the seasonal cycle.

Satellite-tracking of mature white sharks (Carcharodon carcharias) has revealed open-ocean movements spanning months and covering tens of thousands of kilometers. But how are the energetic demands of these active apex predators met as they leave coastal areas with relatively high prey abundance to swim across the open ocean through waters often characterized as biological deserts? Here we investigate mesoscale oceanographic variability encountered by two white sharks as they moved through the Gulf Stream region and Sargasso Sea in the North Atlantic Ocean. In the vicinity of the Gulf Stream, the two mature female white sharks exhibited extensive use of the interiors of clockwise-rotating anticyclonic eddies, characterized by positive (warm) temperature anomalies. One tagged white shark was also equipped with an archival tag that indicated this individual made frequent dives to nearly 1,000 m in anticyclones, where it was presumably foraging on mesopelagic prey. We propose that warm temperature anomalies in anticyclones make prey more accessible and energetically profitable to adult white sharks in the Gulf Stream region by reducing the physiological costs of thermoregulation in cold water. The results presented here provide valuable new insight into open ocean habitat use by mature, female white sharks that may be applicable to other large pelagic predators.