Vorrath, Maria-Elena; Müller, Juliane; Rebolledo, Lorena; Cárdenas, Paola; Shi, Xiaoxu; Esper, Oliver; Opel, Thomas; Geibert, Walter; Muñoz, Praxedes; Haas, Christian; Lange, Carina B; Lohmann, Gerrit; Mollenhauer, Gesine (2020): Sea Ice dynamics in the Bransfield Strait, Antarctic Peninsula, during the past 240 years: a multi-proxy intercomparison study [dataset publication series]. PANGAEA, https://doi.org/10.1594/PANGAEA.918808

In the last decades, changing climate conditions have had a severe impact on sea ice at the Western Antarctic Peninsula (WAP), an area rapidly transforming under global warming. To study the development of spring sea ice and environmental conditions in the pre-satellite era we investigated three short marine sediment cores for their biomarker inventory with particular focus on the sea ice proxy IPSO25 and micropaleontological proxies. The core sites are located in the Bransfield Strait, in shelf to deep basin areas characterized by a complex oceanographic frontal system, coastal influence and sensitivity to large-scale atmospheric circulation patterns. We analyzed geochemical bulk parameters, biomarkers (highly branched isoprenoids, glycerol dialkyl glycerol tetraethers, sterols), as well as diatom abundances and diversity over the past 240 years, and compared them to observational data, sedimentary and ice core climate archives as well as results from numerical models. Based on biomarker results we identified four different environmental units characterized by (A) low sea ice cover and high ocean temperatures, (B) moderate sea ice cover with decreasing ocean temperatures, (C) high but variable sea ice cover during intervals of lower ocean temperatures and (D) extended sea ice cover coincident with a rapid ocean warming. While IPSO25 concentrations correspond quite well with satellite sea ice observations for the past 40 years, we note discrepancies between the biomarker-based sea ice estimates and the long-term model output for the past 240 years, ice core records and reconstructed atmospheric circulation patterns such as the El Niño Southern Oscillation (ENSO) and Southern Annular Mode (SAM). We propose that the sea ice biomarker proxies IPSO25 and PIPSO25 are not linearly related to sea ice cover and, additionally, each core site reflects specific, local environmental conditions. High IPSO25 and PIPSO25 values may not be directly interpreted as referring to high spring sea ice cover because variable sea ice conditions and enhanced nutrient supply may affect the production of both the sea-ice associated and phytoplankton-derived (open marine, pelagic) biomarker lipids. For future interpretations we recommend to carefully consider individual biomarker records to distinguish between cold, sea ice favoring and warm, sea ice diminishing environmental conditions.