Geostrophic Transport and Biological Productivity in Southern Drake Passage
Sarah Gille (1), Marina Frants, Mati Kahru, Greg Mitchell, Scripps Institution of
Oceanography
(1) Scripps Institution of Oceanography
The Shackleton Fracture Zone in southern Drake Passage separates low chlorophyll water
to the west from high chlorophyll, biologically productive water in the Ona Basin to the
east. Measurements collected in two research cruises in the region indicate that the
difference in chlorophyll concentrations most likely occurs because iron-rich shelf water
is entrained into the water as it flows eastward within the southern Antarctic Circumpolar
Current Front at the southern edge of the Shackleton Fracture Zone. Satellite altimeter
data provide information needed to place these research cruise findings in a broader
context. Using sea surface height measurements in comparison with time varying
chlorophyll measurements, we explore two possible mechanisms that might explain how
iron mixes into the Ona Basin. First, changes in transport of the SACCF could drive
changes in the supply of iron to the Ona Basin. Second, changes in the off-shore
meandering of the SACCF on the eastern side of the Shackleton Fracture Zone may
determine the extent to which iron can be stirred into the Ona Basin. The first hypotheses
is not supported by the satellite data, since geostrophic transport into the southern portion
of the Ona Basin is uncorrelated with chlorophyll. However, the second shows some skill
in explaining the observed spatial and temporal variability in chlorophyll concentrations
in the Ona Basin.