On the relationship between fronts of the Antarctic Circumpolar Current and surface chlorophyll concentrations in the Southern Ocean

[1] We reexamine the relationship between circulation, bathymetry, and surface chlorophyll in the Southern Ocean, using new high-resolution maps of the frontal structure of the Antarctic Circumpolar Current (ACC) derived from satellite altimetry. The maps reveal that the ACC consists of multiple filaments or jets. By averaging surface chlorophyll measurements along streamlines, we show that the fronts define the limits of zones with similar concentrations and seasonality of surface chlorophyll. The overall pattern of surface chlorophyll is consistent with strongest upwelling of nutrient-rich deep water south of the Polar Front (PF). However, the distribution of chlorophyll in the Southern Ocean is concentrated in a number of persistent blooms, observed downstream of islands and bathymetric features. In contrast to previous studies, we find little evidence that the fronts of the ACC are associated with enhanced productivity, at least where the fronts are distant from topography. Rather, we find that most regions of elevated chlorophyll in the open Southern Ocean can be explained by upwelling of nutrients (both macronutrients and micronutrients) where the ACC interacts with topography, followed by downstream advection. The upwelling is shown to be the consequence of the bottom pressure torque established by the large-scale flow, rather than being due to small-scale instabilities of the jets. The interaction of the flow with the topography therefore establishes both the large-scale dynamical balance of the ACC and determines the productivity of the open Southern Ocean.