Ross Sea Ecosystem Responses to Climatic Changes during the Mid-to-Late Holocene as Indicated by Bulk Stable Isotope Analyses of Antarctic Seals
Emily Brault1, Paul L. Koch2, Matthew McCarthy3, Brenda L Hall4, A. R. Hoelzel5, Andreanna J Welch5, Jonathan W Nye6 and Aaron P Rosenfield1, (1)University of California, Santa Cruz, Ocean Sciences, Santa Cruz, CA, United States, (2)University of California Santa Cruz, Santa Cruz, CA, United States, (3)University of California Santa Cruz, Ocean Sciences Department, Santa Cruz, CA, United States, (4)University of Maine, School of Earth and Climate Sciences and Climate Change Institute, Orono, ME, United States, (5)Durham University, School of Biological and Biomedical Sciences, Durham, United Kingdom, (6)University of California, Merced, Merced, CA, United States
Abstract:
Substantial environmental changes occurred in the Ross Sea during the Holocene, with sea ice likely significantly increasing around 1,000 years before present (YBP). We are investigating the effects of these environmental changes on the biological community. Previous work demonstrates that the southern elephant seal (
Mirounga leonina) colonies in the region began to collapse ~1,000 YBP and disappeared from the area by 250 YBP. Ecosystem shifts are also evident in isotopic records. Carbon and nitrogen isotope data from Adélie penguins (
Pygoscelis adeliae) differ from animals in the region today, and our isotopic values of fossil southern elephant seals are inconsistent with foraging in the current Ross Sea ecosystem. The dating of these isotopic shifts is uncertain, ranging from 1,000 to 250 YBP.
We examined trends in the bulk carbon and nitrogen isotope values of Weddell (Leptonychotes weddellii) and crabeater (Lobodon carcinophagus) seals over the last ~5,500 years to clarify the timing of the ecosystem shift, and further explore its effects on top predators. Crabeater seals have stable mean carbon and nitrogen isotope values through the late Holocene period, suggesting stable foraging behavior. However, isotopic data from this species are more variable before ~750 YBP, indicating a more diverse foraging ecology. Weddell seals show a clear transition in isotopic values around 500 YBP, similar to that previously observed in penguins. This shift may indicate a change in Weddell seal diet (to lower trophic level prey in more recent times), a changed ecosystem (with the Ross Sea becoming less productive later in the Holocene), or both. Overall, our data shows that the ecology of top predators shifted substantially in response to changes in the Ross Sea around 1,000-500 years ago.
