Iron Isotope Biogeochemical Cycling in the Western Arctic Ocean

Abstract

AbstractThe Arctic Ocean is unique, connecting the Atlantic and Pacific basins and being especially vulnerable to the impacts of a changing climate. Iron stable isotopes (δ56Fe) provide a unique window into the biogeochemical cycling of Fe in the Arctic. Here we present the first seawater δ56Fe for the Western Arctic Ocean, from the 2015 U.S. GEOTRACES GN01 transect. Samples analyzed for δ56Fe include seawater dissolved (<0.2 μm), soluble (<∼0.003 μm), and leachable particulate phases. Several key processes were explored using Fe isotopes, each characterized by a distinct combination of δ56Fe and Fe concentrations. Input of Fe from reducing continental shelf sediments was characterized by high dissolved Fe concentrations (6.18 ± 4.84 nmol kg−1) and low δ56Fe (−1.57 ± 0.66‰). Riverine Fe input observed in the Transpolar Drift Current was characterized by high Fe concentrations corresponding to a riverine end‐member Fe concentration of 19 nM, and near‐zero δ56Fe (0.02 ± 0.23‰) that was similar to that of average crustal material. The deep Arctic was mostly characterized by low Fe concentrations (0.33 ± 0.14 nmol kg−1) and slightly higher δ56Fe (0.05 ± 0.30‰), except for samples taken near continental slopes that were affected by sedimentary Fe input with lower δ56Fe, and in the Amundsen Basin which showed possible hydrothermal Fe input. Our data thus illuminate Fe biogeochemical cycling processes in the modern Arctic Ocean, and serve as a baseline for understanding how the Arctic Fe cycle responds to climate change.