Dissolved iron in the Southern Ocean (Atlantic sector)

We report a comprehensive dataset of dissolved iron (Fe) comprising 482 values at 22 complete vertical profiles along a 1° latitudinal section at the Zero meridian. In addition a shorter high resolution (∼00°09′) surface section of the southernmost part of the transect (66°00′–69°35′S) is presented. Within the upper surface mixed layer the concentrations of dissolved Fe vary between 0.1 and 0.3 nM. An inverse trend versus fluorescence suggests significant Fe removal by plankton blooms. Vertical mixing and upwelling are the most important supply mechanisms of iron from deep waters to the upper surface mixed layer. At lower latitude (42°S) there is a distinct maximum of 0.6–0.7 nM in the 2000–3000 m depth range due to inflow of North Atlantic Deep Water. In one region (55°S) elevated dissolved Fe found in the surface mixed layer is ascribed to the recent deposition of aeolian dust originating from South America. Close to the Antarctic continent there is an indication of Fe supply in surface waters from icebergs. In the deep waters there is a strong indication of a hydrothermal plume of dissolved Fe and Mn over the ridge in the Bouvet region (52–56°S). In the Weddell Gyre basin the dissolved Fe in the deep water is 0.47±0.16 nM in the eastward flow at ∼56–62°S and is lower with a value of 0.34±0.14 nM in the westward flow at high ∼62–69°S latitude. At the edge of the continental ice-sheet on the prime meridian, the continental margin of the Antarctic continent appears to be lesser source of dissolved Fe than in any other place in the world; this is likely because it is unique in being overlain by the extending continental ice-sheet that largely prevents biogeochemical cycling.