Natural iron fertilization of the Atlantic sector of the Southern Ocean by continental shelf sources of the Antarctic Peninsula

Abstract

In large parts of the Southern Ocean, primary production is limited due to shortage of iron (Fe). We measured vertical Fe profiles in the western Weddell Sea, Weddell‐Scotia Confluence, and Antarctic Circumpolar Current (ACC), showing that Fe is derived from benthic Fe diffusion and sediment resuspension in areas characterized by high turbulence due to rugged bottom topography. Our data together with literature data reveal an exponential decrease of dissolved Fe (DFe) concentrations with increasing distance from the continental shelves of the Antarctic Peninsula and the western Weddell Sea. This decrease can be observed 3500 km eastward of the Antarctic Peninsula area, downstream the ACC. We estimated DFe summer fluxes into the upper mixed layer of the Atlantic sector of the Southern Ocean and found that horizontal advection dominates DFe supply, representing 54 ± 15% of the total flux, with significant vertical advection second most important at 29 ± 13%. Horizontal and vertical diffusion are weak with 1 ± 2% and 1 ± 1%, respectively. The atmospheric contribution is insignificant close to the Antarctic continent but increases to 15 ± 10% in the remotest waters (>1500 km offshore) of the ACC. Translating Southern Ocean carbon fixation by primary producers into biogenic Fe fixation shows a twofold excess of new DFe input close to the Antarctic continent and a one‐third shortage in the open ocean. Fe recycling, with an estimated “fe” ratio of 0.59, is the likely pathway to balance new DFe supply and Fe fixation.

Sedimentary and atmospheric sources of iron around South Georgia, Southern Ocean: a modelling perspective

“…8) are also in agreement, especially at depths below the surface layer influenced by the seasonal biological uptake of iron. Both upstream and downstream of South Georgia, modelled dFe concentrations increase with depth and fall in the range of measurements reported by Nielsdóttir et al, 2012, but also by de Jong et al (2012) in other regions of the Southern Ocean.…”

“…Our model results clearly show that the South Georgia island mass effect can reach regions located far away from the island (> 1000 km), where dFe concentrations may still be above background concentrations. A comparable long-range influence of coastal regions has been previously suggested in other open-ocean regions of the world ocean, including the Southern Ocean (Elrod et al, 2004;Lam et al, 2006;de Jong et al, 2012;Moore and Braucher, 2008).…”

The winter pack-ice zone provides a sheltered but food-poor habitat for larval Antarctic krill

“…Our findings imply that if, due to climate change, present habitats for larval krill overwintering and nursery in the South Scotia Ridge and southern Scotia Sea 1 become ice free in winter, there may be an increase in food for larval krill development and growth [32][33][34][35][36][37] . If, however, the seasonal sea-ice cover does not extend as far north in future, then larvae that are released from under the sea ice in spring will be farther south in the Weddell Sea (south of the South Scotia Ridge in spring) and will take longer to reach the Scotia Sea 17 ( Supplementary Fig.…”

The significant inputs of trace elements and rare earth elements from melting glaciers in Antarctic coastal waters

“…Ardelan et al (2010) also suggested that this supply of Fe by lateral transport contributes significantly to high phytoplankton biomass in the Scotia Sea region. More recently, de Jong et al (2012) showed that almost a half (54%) of the total Fe flux to the Atlantic sector of the Southern Ocean is transported through horizontal advection. Recent studies have also shown that global warming may have caused an increase in the disintegration of the ice shelves along the Antarctic Peninsula by up to 13% during the last two decades (Rignot et al 2011).…”