MEPS prepress abstract  -  DOI:

Carbon and nitrogen isoscapes in West Antarctica reflect oceanographic transitions

Emily K. Brault*, Paul L. Koch, Kelton W. McMahon, Kyle H. Broach, Aaron P. Rosenfield, Wilson Sauthoff, Valerie J. Loeb, Kevin R. Arrigo, Walker O. Smith Jr


ABSTRACT: Antarctic marine ecosystems are spatially and temporally dynamic. Regional climate change is significantly altering the patterns and magnitudes of this dynamism with cascading impacts on biogeochemistry, productivity, and food web architecture. Isoscapes (or isotopic maps) provide a valuable analytical framework to characterize ecosystem processes and address questions about trophic dynamics, animal movement, and elemental cycling. Applications of stable isotope methods to Antarctic ecosystems are currently limited by a paucity of information on geospatial isotope characteristics within the Southern Ocean. In response, we have created the first empirically derived zooplankton isoscapes for West Antarctica based on analysis of bulk nitrogen and carbon isotope values (δ15N and δ13C, respectively) in 94 zooplankton specimens from the Drake Passage, West Antarctic Peninsula (WAP), and Amundsen and Ross Seas. The zooplankton δ15N values increased by 3 ‰ from north of the Polar Front (3.3 ± 0.6 ‰) to the Ross Sea (6.2 ± 0.8 ‰), reflecting a productivity gradient across this region. Abundant open water polynyas in the Amundsen and Ross Seas exhibit strong nitrate drawdown, resulting in more 15N-enriched phytoplankton and zooplankton relative to those from the generally less productive WAP and Drake Passage. Zooplankton δ13C values decreased by 3 ‰ from north of the Polar Front (–24.2 ± 0.9 ‰) to the Ross Sea (–27.5 ± 1.6 ‰), likely driven by decreasing sea surface temperatures with increasing latitude. Our isoscapes are a valuable first step in establishing isotopic spatial patterns in West Antarctica and are critical for addressing numerous ecosystem questions.