Properties and Dispersal of a Hydrothermal Plume in a Weakly Stratified Under‐Ice Environment

Abstract The Aurora vent field (82°53.83′N, 6°15.32′W) is located in the weakly stratified Arctic Ocean under perennial ice cover at the western edge of the ultraslow‐spreading Gakkel Ridge, the slowest spreading mid‐ocean ridge on Earth. Here, we report data on the dispersal of the proximal hydrothermal plume in this extreme environment. The hydrothermal plume is of unusual dimensions, with a small horizontal, but large vertical extent, which is caused by the hydrography of the Arctic Ocean. Water column parameters such as turbidity and redox potential show a highly variable but horizontally confined non‐buoyant plume. Dissolved iron (dFe), manganese (dMn), δ 3 He, and methane (CH 4 ) all show distinct enrichment in the hydrothermal plume relative to background deep‐water, but relatively low peak concentrations due to the dilution over a vertical extent of over 500 m. Plume particle samples exhibit elevated Fe/Al ratios consistent with Fe‐oxyhydroxide precipitation close to the vent, whereas particulate Mn/Al ratios do not reveal any complementary pMn enrichment in the proximal plume. The positive correlation between Fe/Al, and several other element/Al ratios (e.g., P, V, As) is consistent with scavenging of these elements onto Fe‐hydroxide plume particles and removal into the underlying sediments. Surface sediment samples collected close to Aurora reveal highly elevated concentrations of hydrothermally sourced elements in the immediate vicinity of the vent‐site. For example, proximal surface sediments contained up to 8,222 mg kg −1 Cu, whereas Cu concentrations in core tops a few kilometers away from the site were much lower (<50 mg kg −1 ).