Biological and geochemical proxies in sediment cores reveal shifts in marine predator population dynamics relative to historic anthropogenic exploitation and recent climate change at South Georgia Island sub-Antarctic

Historical climate change and human exploitation are thought to have played important roles in shaping population dynamics of sub-Antarctic marine predators, such as king penguins (Aptenodytes patagonicus) and Antarctic fur seals (Arctocephalus gazelle). For example, Antarctic fur seals on the sub-Antarctic South Georgia Island were nearly hunted to extinction by humans before the early 1900s. However, records of occupation history pre- and post-anthropogenic stress are often sporadic and challenging to interpret. In this study, we investigated paleoecological proxies in sediment cores from South Georgia Island to examine past marine predator population dynamics in the face of climate change and exploitation pressure. Sediment cores representing 1854 CE to present were collected from two sites on South Georgia Island in the South Atlantic and analyzed for geochemical (total carbon, total nitrogen, delta C-13 and delta N-15 values) and biological (e.g., seal hairs, penguin feathers) proxies. Proxies in both cores indicated the onset of the recovery of penguin and fur seal populations in the early to mid-1900s, following the cessation of hunting. Additionally, our results suggest marked increases in both penguin and seal populations beginning around 1950 CE. Between the 1950s and 2019, 97% of South Georgia Island's glaciers retreated associated with recent climatic warming. This warming increased the availability of local breeding areas for king penguins, which likely explains the population rise during that time. This study deepens our understanding of the response of sub-Antarctic marine predator populations to past climate change and human exploitation, which may aid in predicting future ecosystem responses to environmental disturbance.

Automated summary

This study examines the population dynamics of sub-Antarctic marine predators, including king penguins and Antarctic fur seals, in response to historical climate change and human exploitation. The results show that the populations of these animals started to recover after hunting ceased and experienced significant growth after 1950, which may be attributed to the increased availability of breeding areas due to recent climatic warming.