Trace Element Dispersal by an Antarctic Subglacial Sediment Plume

Subglacial environments are distinct cryospheric sources of dissolved nutrients to the euphotic zone, yet their contributions to trace element biogeochemistry remain uncertain. Additionally, the speciation of key bio-limiting micronutrients, such as iron, present within sediment plumes arising from subglacial meltwater discharge is unknown. Enhanced microbial respiration, high weathering rates, and limited diffusion of oxygen increase the solubility of redox sensitive elements such as iron (Fe) and manganese (Mn), which enter the ocean within buoyant turbid plumes. Here we characterize the signature, dispersion and physicochemical speciation of bioactive trace metals in a glacial sediment plume and speculate on the geochemical setting beneath west Antarctic Peninsula glaciers. This work reveals that sediment plumes arising from subglacial meltwater discharge are important subsurface sources of dissolved and labile particulate Fe (82-100% of total particulate Fe) to resident phytoplankton communities. Our analyses reveal strong co-variation between dissolved and labile particulate pools at plume depths (70-150m), indicating exchange over short length scales. Given that Antarctic glaciers are susceptible to rapid changes in the warming climate, the interface between glaciers and the coastal ocean is poised to be an important control on the quantity and quality of micronutrients transported to downstream nutrient-limited phytoplankton communities.