Doctor of Oceanography and Coastal Sciences (POCS)


Oceanography and Coastal Sciences

Document Type



The Southern Ocean ecosystem has experienced short- and long-term physical change, affecting sea ice dynamics, biogeochemical cycling, and ocean productivity. Recent, rapid warming in the past century due to human-caused climate change further aggravates these environmental changes and altered ecosystem dynamics. Also, between 1820-1970 humans over-harvested Antarctic krill predators including seals and baleen whales, potentially creating a ‘krill-surplus’ for other krill predators, such as penguins. Together, these climatic and ecosystem shifts impact ecosystem structure and function, including shifts in the foraging ecology of upper trophic organisms. Past studies using bulk tissue stable isotope analysis identified a dietary shift in Adélie penguins (Pygoscelis adeliae) coinciding with the proposed krill surplus, while other studies found relationships between carbon isotope values and climate variability. Understanding the underlying mechanisms driving these shifts is necessary to predict future ecosystem responses but disentangling these often-confounding effects of human exploitation and human-caused and long-term climate change on ecosystem dynamics remains a challenge.

My dissertation examines the relative importance of the proposed krill surplus and long-term natural climate variability as drivers of change in Adélie penguin trophic ecology and Southern Ocean ecosystem dynamics over the Holocene using compound-specific stable isotope analysis of individual amino acids (CSIA-AA). Analysis of Adélie penguin eggshell identified a gradual decline in trophic position over the Holocene, likely driven by solar insolation and sea ice dynamics. The significant decrease in δ15Nbulk values seen in past studies was largely attributed to baseline biogeochemical cycling that significantly shifts around the Little Ice Age. Analyzing the same eggshell samples for δ13C CSIA-AA, I identify sea-ice algae as a consistent dominant carbon source supporting the Southern Ocean food web through the Holocene. Finally, using modern and archived museum feathers, I found that Adélie penguin trophic position did not vary over the last 175 years. This indicated that Adélie penguin diet was inflexible relative to the proposed krill surplus in the early and mid-20th century. My dissertation reconciles the differing conclusions made by previous studies, provides greater insights in the trophic ecology of Adélie penguins, and identifies drivers underlying past ecosystem shifts in Southern Ocean food web.

Committee Chair

Polito, Michael



Available for download on Monday, January 10, 2028