Spatial distribution of n-alkanes and GDGTs in the central Arctic Ocean during Marine Isotope Stages 1, 2 and 3

Abstract

Arctic sea ice affects Earth's albedo, marine productivity and organic matter (OM) transport. Lipid biomarkers have been used to trace OM transport in the Arctic Ocean, but uncertainties remain regarding their spatiotemporal variations and sources over the last glacial cycle. Our study addresses these gaps by analyzing glycerol dialkyl glycerol tetraethers (GDGTs), n-alkanes, and total organic carbon (TOC) in nine central Arctic sediment cores spanning the Marine Isotope Stages (MISs) 3-1. Elevated IIIa/IIa values of branched GDGTs (brGDGTs) in the central Arctic throughout the studied interval suggest a marine origin, contrasting to the #ringstetra ratios which indicate a terrigenous brGDGT source. We propose that the IIIa/IIa ratio may be a more sensitive indicator of in situ brGDGT production in the central Arctic marine sediments. TOC and biomarker concentrations in the Central Lomonosov Ridge (CLR) cores were higher compared to those from the Lomonosov Ridge off Greenland (LRG) and Morris Jesup Rise (MJR) cores. Low productivity in the central Arctic, along with similarity in the spatial patterns of marine-derived brGDGTs and isoprenoid GDGTs, as well as terrestrial longchain n-alkanes, suggests that these biomarkers are primarily transported to the central Arctic from the Siberian shelves. This spatial pattern persisted throughout MISs 3-1, suggesting continued sea ice drift during glacial periods, albeit with weakened intensities. Meanwhile, the spatiotemporal variations of the Branched Isoprenoid Tetraether (BIT) index in the region plausibly reflect the relative changes in the crenarchaeol and brGDGT production on the shelf and/or selective degradation of crenarchaeol during its transport.