Observations of diatoms, dinoflagellate cysts and highly branched isoprenoid lipids within the sea ice, water column, sediment traps, and sediment surface in the Belcher Islands Archipelago, Hudson Bay throughout spring 2019

This project sought to obtain direct observations of the seasonal distribution and habitat of algal species widely used as sedimentary sea-ice proxies. The ongoing rapid reductions of sea-ice area, persistence and thickness have motivated increasing efforts to resolve past sea-icechanges and their climatic causes. This study was done to address a major challenge with sea-ice reconstructions, namely deficient knowledge of the habitats, environmental controls, and vertical transport of many protist species and biomarkers commonly associated with sea ice. In this study, we focused on the three groups of biogenic sea-ice proxies: diatoms, dinoflagellate cysts and highly branched isoprenoid lipids (HBIs), which are biomarkers selectively synthesized by some diatom species. We collected and analyzed samples from the landfast sea ice, the under-ice water column, an automated sequencing sediment trap suspended about 40m beneath the ice cover, and the surface sediment. We chose to conduct the study near Sanikiluaq, on the Belcher Islands in southeastern Hudson Bay, where University of Manitoba researchers Jens Ehn and Zou Zou Kuzyk have been working in partnership with the Arctic Eider Society and Inuit since 2014. The baseline knowledge of the oceanography around the Belcher Islands developed through this research partnership and knowledge shared by Inuit partners informed the design of the study and enabled its successful execution. The study was conducted by the team over spring-summer 2019, and included deploying a Baker-style sequential sediment trap through a hole cut in the landfast ice cover. Valuable insights into sea-ice proxies were gained from the study. We demonstrated previously unstudied species-specific temporal and habitat sources for diatoms, dinoflagellate cysts and HBIs. The results support the notion that these sedimentary proxies are particularly valuable when used jointly. We also showed that sediment core diatom and dinoflagellate cyst assemblages from seasonally ice-covered environments can be dominated by species not directly affiliated with sea ice.