Sedimentary sea-ice proxies in the Arctic: seasonal production, vertical export and taxonomic insights

• Main Author: Luostarinen, Tiia
• Other Authors: Caissie, Beth, University of Helsinki, Faculty of Biological and Environmental Sciences, Doctoral Programme in Interdisciplinary Environmental Sciences, Helsingin yliopisto, bio- ja ympäristötieteellinen tiedekunta, Ympäristöalan tieteidenvälinen tohtoriohjelma, Helsingfors universitet, bio- och miljövetenskapliga fakulteten, Doktorandprogrammet i tvärvetenskaplig miljöforskning, Heikkilä, Maija, Ribeiro, Sofia
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: Helsingin yliopisto 2023
• Subjects: ympäristötieteet; Arctic; albedo; Sea ice
• Online Access: http://hdl.handle.net/10138/357635

Arctic sea-ice cover is decreasing at an alarming rate with severe consequences for ecosystems across the Arctic and the climate system globally. The changes observed in the ice cover amplify global climate warming by decreasing the ice-albedo effect and may alter ocean circulation and weather patterns. The loss of sea ice is likely to increase primary production in the Arctic, leading to drastic changes in marine food webs and biodiversity at all trophic levels. For over four decades, satellite imagery has provided high-resolution spatial and temporal understanding of changing Arctic sea-ice cover. However, the paucity of any human observations of Arctic sea ice beyond a few centuries limits our understanding of the current trajectory and its implications for ecosystems and the global climate. Marine sediments provide a natural archive of past sea-ice variability over timescales from centuries to millions of years. Commonly used sedimentary sea-ice proxies are biogenic: (sub)fossil remains and biogeochemical tracers originating from micro-organisms inhabiting sea ice (sympagic), or ice-associated under-ice and ice-edge ecosystems. State-of-the-art sea-ice reconstructions typically use diatoms, resting stages (cysts) of dinoflagellates and the highly branched isoprenoid (HBI) lipids IP25, IPSO25, HBI III and HBI IV, which are synthetized by certain diatom species. Current understanding of the associations of these proxies with sea ice is largely based on their relative abundances in surface sediment assemblages with respect to sea-ice cover, as well as limited ecological field and laboratory studies. Each of these proxies has some advantages over others, but there are important limitations to consider, largely stemming from the lack of adequate understanding of their behaviour in modern environments seasonally with respect to habitat source (sea-ice, under-ice, ice-edge or open-water) and factors controlling proxy production, vertical transport and deposition on the sediment. While certain diatom species are ...