NSFGEO-NERC: Collaborative Research: Accelerating Thwaites Ecosystem Impacts for the Southern Ocean (ARTEMIS)

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The Amundsen Sea hosts the most productive polynya in coastal Antarctica, with its vibrant green waters visible from space, and an atmospheric CO2 uptake flux density 10x higher than average for the Southern Ocean. The region is vulnerable to climate change, with rapid losses in sea ice, episodic shifts in the coastal icescape, and the fastest melting glaciers in the adjacent West Antarctic Ice Sheet (WAIS). In an ecosystem experiencing such dramatic change, it is critical to resolve the climate-sensitive drivers and feedbacks of the meltwater-associated iron (Fe) delivery, which underpins productivity in this otherwise high-nutrient, low chlorophyll region. Our previous field research (ASPIRE) identified a clear link between the melting WAIS and the delivery of micronutrient Fe to the polynya ecosystem, and its role in rapid CO2 drawdown. Our recent numerical modeling effort (INSPIRE) suggests several pathways for Fe delivery, ways to optimize fieldwork, and guidance for improving mechanistic understanding of Fe supply and cycling. An ongoing physical oceanographic field program (TARSAN, part of the International Thwaites Glacier Collaboration, ITGC) offers an ideal physical framework for our next research effort. We propose here to collaborate with TARSAN-supported UK scientists, providing significant value added to both teams. TARSAN explored the eastern Amundsen Sea by ship in Feb-Mar 2019 and expects to operate in the Thwaites region again in Feb-Mar 2021. They will use a full suite of physical oceanographic techniques, including 2 under-ice-shelf AUVs, gliders, surface vehicles, a microstructure profiler, shipboard CTD, seal tags, noble gases, and underway sensors to characterize the ice-ocean interactions responsible for rapid glacial melting. During 2019, TARSAN and THOR (also ITGC) collected detailed bathymetric, sedimentary, and ice-shelf cavity information (available Sept 2019) that will immediately improve and update the INSPIRE model to present-day boundary conditions. Our combined NSFGEO-NERC project (ARTEMIS) will facilitate collaboration between ASPIRE/INSPIRE team members and TARSAN/ITGC, add biogeochemical measurements to the funded 2021 expedition, and build on existing glider infrastructure and seal tag expertise (adding biogeochemical sensors to autonomous vehicles) at modest additional logistical cost. Numerical runs with ARTEMIS's updated model will inform TARZAN's 2021 field effort. Observations made will improve our understanding and our model, allowing a more sophisticated assessment of the role of Fe in present and future scenarios. Our team (ARTEMIS) would add shipboard biogeochemical observations (trace metals, carbonate system, nutrients, organic matter, microorganisms) and autonomous vehicle biogeochemical observations (nitrate, Chl a, optical backscatter) to gather knowledge critical to understanding the impact of WAIS melting on both the polynya ecosystem and the regional carbon (C) cycle. ARTEMIS combines the expertise of a US component comprising a carbonate system and microbial ecologist (Yager), a trace metal biogeochemist (Sherrell), a trace metal isotope geochemist (Fitzsimmons), an organic geochemist (Medeiros), an ice-ocean-atmosphere interactions expert (Stammerjohn), and a numerical ocean modeler (St-Laurent), with a UK component comprising 3 physical oceanographers: TARSAN lead PI (Heywood), a biogeochemically savvy autonomous vehicle expert (Queste), and an oceanographer whose vehicles are marine mammals (Boehme). This international team will work together at sea and with shore-based analyses to address a set of interconnected questions arising from the findings of ASPIRE/ INSPIRE.