Effects of sea ice coverage on sedimentary iron and manganese cycling at the Eurasian Arctic Margin

Allyson Tessin, University of Southern Mississippi, Stennis Space Center, United States, Christian März, University of Leeds, Leeds, United Kingdom, Hans-J Brumsack, University of Oldenburg, Oldenburg, Germany, Jens J Matthiessen, Alfred Wegener Institute, Bremerhaven, Germany, Marie-Amélie Blais, Université Laval, QC, Canada, Matt O'Regan, Stockholm University, Department of Geological Sciences, Stockholm, Sweden and Bernhard Schnetger, University of Oldenburg, ICBM Microbiogeochemistry Research Group, Oldenburg, Germany
The Arctic Ocean is currently undergoing rapid change in response to anthropogenic climate warming, and the most striking evidence of this is the rapid retreat of Arctic sea ice. Sea ice retreat will have complicated effects on Arctic Ocean biogeochemistry, including how nutrients and metals are cycled across the sediment-water interface. Here, we investigate Fe and Mn cycling within the Eurasian margin region of the Arctic Ocean that separates the archipelago of Svalbard from the open Arctic Ocean basin. We use paired sediment and pore water geochemistry to investigate spatial and downcore patterns of Fe and Mn in nine locations spanning the northern Svalbard continental slope, the Sophia Basin, and the Yermak Plateau from materials collected on the TRANNSIZ cruise (PS92) in 2015. Our results indicate that Mn and Fe are remobilized in northern Svalbard slope sediments underlying seasonally ice-free waters. In contrast, Fe and Mn is not remobilized from Yermak Plateau and Sofia Basin sediments, which experience more permanent ice coverage. These regional patterns are best explained by the spatial distribution of primary productivity and organic carbon flux, which are controlled by sea ice cover. As sea ice continues to retreat and the Yermak Plateau becomes seasonally ice-free, productivity is expected to increase following reduced light limitation and an earlier start/longer duration of the growing season. This increase in productivity would increase the flux of organic carbon to the sediments, thereby increasing oxidant demand, and eventually the reduction of Fe and Mn mineral phases. Our results suggest that as Arctic sea ice continues to retreat, the Yermak Plateau may become a source of Fe, Mn, and associated trace metals to the Arctic water column.