Significant Biological Uptake of Trace Metals in the Mertz Glacier Polynya, East Antarctica

David Janssen1, Matthias Sieber2, Michael Joseph Ellwood3, Tim M Conway4, Pamela M Barrett5, Christel Hassler6 and Sam Jaccard1, (1)University of Bern, Institute of Geological Sciences & Oeschger Center for Climate Change Research, Bern, Switzerland, (2)ETH Swiss Federal Institute of Technology Zurich, Earth Sciences, Zurich, Switzerland, (3)Australian National University, Research School of Earth Sciences, Canberra, ACT, Australia, (4)University of South Florida, St. Petersburg, FL, United States, (5)The Australian National University, Research School of Earth Sciences, Canberra, ACT, Australia, (6)Department F. -A. Forel for Environmental and Aquatic Sciences, University of Geneva, Switzerland., Geneva, Switzerland
Polynyas along the Antarctic coast are areas of high biological productivity, supporting communities at higher trophic levels and acting as important sinks of CO2. Additionally, through their role in Antarctic Bottom Water formation, Antarctic polynyas can impact deepwaters on a basin-wide scale. Elevated primary productivity in polynyas can be sustained by local Fe sources in the otherwise Fe-limited, high-nutrient low-chlorophyll Southern Ocean. Despite the importance of trace metal availability for biological productivity in the Southern Ocean, and the role of biological uptake and export in the Southern Ocean in shaping dissolved trace metal and macronutrient distributions in the global ocean, trace metal data from Antarctic coastal polynyas are limited. We present the first trace metal concentrations (dissolved Fe, Ni, Cu, Zn, Cd, Pb) from the Mertz Glacier Polynya, on the East Antarctic continental shelf, from samples collected during the 2016-2017 Antarctic Circumnavigation Expedition. These data show significant surface depletions of trace metals and macronutrients compared to open ocean surface waters. The observed depletions cannot be explained solely by freshwater dilution and correspond with high chlorophyll fluorescence, indicating metal depletions are most likely due to increased biological uptake. Inferred biological uptake ratios for metals relative to phosphate (Me:PO4) compare well with previously reported metal to phosphorus ratios in Southern Ocean phytoplankton from single cells and incubation experiments. Inferred Ni:PO4, Zn:PO4 and Cd:PO4 uptake ratios also compare well with metal-PO4 slopes in the Southern Ocean as a whole, reflecting the established role of biological uptake in the Southern Ocean and of exported Southern Ocean waters in shaping global metal-macronutrient correlations. These data highlight polynya systems as promising but understudied natural environments for process studies of the supply, biological uptake and export of trace metals and macronutrients.