Mid to Late-Holocene environmental dynamics recorded in Lake Pup Lagoon, East Antarctica: Insights from environmental magnetism and biogeochemical proxies

Abstract

Paleoenvironmental archives in East Antarctica have revealed significant changes during the Holocene, marked by ice sheet retreat leading to the isolation of submarine basins. These basins offer valuable insights into past climate, glaciology, and oceanography shifts that impact sedimentary processes. In this study, environmental magnetism and biogeochemical proxies to investigate the Mid-to-Late-Holocene transitions in Pup Lagoon, a coastal isolation basin is presented. Our findings reveal distinct stratigraphic zones reflecting shifts from marine to lacustrine environments. The results reveal predominant mechanical weathering in the Stornes region, producing coarse-grained “soft” ferrimagnetic minerals. Notably, a period of warm oceanographic conditions between 6000 and 4722 cal. yr BP was characterized by mixed magnetic grain sizes and ultrafine superparamagnetic grains, indicating relatively oxic open waters in the basin. Subsequent shifts to reducing conditions coincide with persistent marine sea ice cover from 4722 to 2634 cal. yr BP, favoring the retention of coarse-grained ferrimagnets. Finer magnetic grain sizes between 2634 and 2185 cal. yr BP was attributed to the increased freshwater inputs associated with the Mid-Holocene Hypsithermal. Further, diagenetic changes under persistent sea ice cover between 2185 and 1970 cal. yr BP led to the selective dissolution of fine-grained ferrimagnets. Transitioning to freshwater isolated basin conditions between 1970 and 588 cal. yr BP, fine ferrimagnet precipitation indicate oxic to suboxic conditions alongside drier conditions. Biogenic productivity increased post-isolation, which was reflected in increased (Total Organic Carbon) TOC and (Total Nitrogen) TN percentages. Additionally, the presence of greigite in the isolated phase sediment indicates reducing conditions owing to organic matter decomposition. Notably, χfd% exhibits an inverse trend to sea ice concentration, potentially indicating anoxic-dysoxic conditions due to the presence of sea ice. These observations align with broader regional sea ice concentration changes, emphasizing the interconnected behavior of local and regional factors shaping Antarctic coastal environments.