Penguins as ecosystem proxies? Identifying millennial-scale shifts in carbon sources and phytoplankton regimes in the Antarctic marine ecosystem

Chantel Michelson1, Kelton McMahon2, William Paul Patterson3, Steven D Emslie4 and Michael J Polito1, (1)Louisiana State University, Department of Oceanography and Coastal Sciences, Baton Rouge, LA, United States, (2)University of Rhode Island, Graduate School of Oceanography, Narragansett, United States, (3)University of Saskatchewan, Department of Geological Sciences, Saskatoon, SK, Canada, (4)University of North Carolina Wilmington, Department of Biology & Marine Biology, Wilmington, NC, United States
The Southern Ocean is undergoing recent rapid physical and biological change. A rise in sea-surface temperature and significant losses in sea ice extent affect phytoplankton community composition, food web dynamics, and biogeochemical cycling. For example, recent anthropogenic climate change in the Antarctic Peninsula is related to decreases in large-celled diatoms in favor of small-celled phytoplankton, which has significant implications for CO2 drawdown and carbon transfer to higher trophic organisms. Pygoscelis penguins serve as a sensitive indicator for ecosystem change. Prior studies of bulk tissue stable carbon isotope values in preserved eggshell (δ13Cbulk) from Adélie penguin (P. adeliae) colonies around Antarctica show an abrupt shift from higher to lower values within the last 200 years. This has been hypothesized as indicative of increased consumption of krill over fish. However, dietary, environmental, and physiological processes alter δ13Cbulk values and their relative influences are difficult to disentangle. Here, we use compound-specific stable isotope analysis (CSIA) of essential amino acids (EAAs) in a Holocene time series of Adélie penguin eggshells to re-interpret prior δ13Cbulk studies and trace carbon flow and relative importance of basal carbon sources in the Antarctic food web over time. EAA δ13C values provide unique isotopic fingerprints of primary producers that are transferred through a food web unmodified, preserving a record of the baseline plankton source in the tissues of higher trophic consumers. Using a fingerprinting approach with Adélie penguin eggshells, we determined the contribution of key primary producers to the Antarctic food web throughout much of the Holocene to identify changes in plankton regimes and carbon sources linked to climate regimes. This novel approach improves past environmental reconstructions and may provide mechanisms driving ecosystem change to facilitate future predictions of Antarctic ecosystem health.