Semi-quantitative reconstruction of early to late Holocene spring and summer sea ice conditions in the northern Barents Sea

Abstract

Semi-quantitative estimates of early to late Holocene spring sea ice concentration (SpSIC) andoccurrence of summer sea ice for the northern Barents Sea have been obtained by analysing the biomarkers IP₂₅,brassicasterol and a tri-unsaturated highly branched isoprenoid lipid in a Holocene marine sediment core.Sub-surface water mass variations were derived from planktic foraminiferal assemblages and stable isotopes (d¹⁸O,d¹³C). The record indicates paleoceanographic changes over three intervals. During Period I (ca. 9500–5900 cal aBP), the study location experienced the lowest recorded SpSIC (ca. 25%) with short spring seasons and longproductive summers, resulting partly from increased Atlantic Water inflow that caused a stronger ocean–atmosphere heat exchange. Throughout Period II (ca. 5900–2700 cal a BP), the winter sea ice margin migratedsouthwards and an overall cooling trend resulted in higher SpSIC (ca. 60%) and increased delivery of cold ArcticWater. During Period III (ca. 2700 cal a BP to present), SpSIC increased further (ca. 75%) and some sea iceremained during summer months. A sub-surface warming probably indicates a decoupling of heat exchangebetween the ocean and the atmosphere. Longer springs and shorter summers were accompanied by the mostsoutherly location of the winter sea ice margin.