Iron fluxes from the shelf regions near the South Shetland Islands in the Drake Passage during the austral-winter 2006

Abstract

Spatial distributions of dissolved iron (Fe), manganese (Mn) and aluminum (Al) in the upper 500m of the water column near the Antarctic Peninsula (AP) during the 2006 austral-winter are consistent with diagenetically-produced sedimentary sources and are somewhat higher than data obtained in this region during the 2004 austral-summer. In contrast, surface phytoplankton abundances were 6–7 times lower relative to the 2004 austral-summer. Near the South Shetland Islands elevated levels of dissolved Al, Fe and Mn were found corresponding to high loads of resuspended material above the shelf as indicated by the transmissometer signal. Despite these high levels of trace metals, phytoplankton abundances in this area were lower than in the offshore Antarctic Circumpolar Current (ACC) waters. Offshore ACC stations had low concentrations of Fe, but up to five times greater abundance of phytoplankton. The difference in phytoplankton abundance between the regions seems largely driven by light availability, as indicated by mixed layer depths. The elevated trace metal concentrations near King George Island in the Bransfield Strait (BS) correspond to the flow path of the Bransfield Current. This enriched plume can also be seen exiting the BS, between Clarence and Elephant islands into the Ona Basin where it mixes with high nutrient low trace metal concentration ACC waters leading to high productivity in this region and further downstream in the Scotia Sea during the growing season.