1 The Influence of Shelf Processes in Delivering Dissolved Iron to the HNLC waters of the Drake Passage, Antarctica

Dissolved trace element distributions near Elephant Island in the Drake Passage show extremely high levels of dissolved Fe and Mn in waters above the shelf. The entrainment of this enriched shelf water by the Fe-poor ACC as it passes through the Shackleton Gap delivers an estimated 5 x 106 moles dissolved Fe to the offshore waters of the Drake Passage. The magnitude and spatial distribution of dissolved Fe, Mn and Al over the shelf are consistent with a diagenetically-produced sedimentary source, but are inconsistent with eolian or upwelling sources. In our limited geographical sampling region, the spatial distribution of the dissolved Fe and Mn was predominantly controlled by simple mixing between ACC and enriched shelf end member(s), as a result of rapid flushing of the shelf waters and relatively slow growth rates of phytoplankton. Some stations though did show clear evidence of biological removal of Fe. The export of the large amounts of Fe from the shelf are likely responsible for the extensive regions of enhanced primary production downstream of the Drake Passage. It is suggested though that during glacial periods the shelves could play a more important biogeochemical role by supplying fine-grained, Fe-rich, particulate material that strong glacial winds could deliver to more remote parts of the Southern Ocean