Magnetic susceptibility, radiocarbon and Polarella glacialis data for core KH21-234-34GC

Description

Here we present a magnetic susceptibility dataset from marine sediment core KH21-234-34GC , for its age model. Core KH21-234-34GC was retrieved from the Yermak Plateu (81.2199280 ˚N, 2.3710955˚E ) with a gravity corer at 1011m water depth during cruise KH21-234 . We measured the magnetic susceptibility at 1 cm resolution using a Bartington MS2C loop sensor (Ø 125mm) with a Geotek Multi-Sensor Core Logger (MSCL-S). Gene copies of the sympagic dinoflagellate Polarella glacialis were determined by droplet digital PCR on samples from marine sediment core KH21-234-34GC collected from the Yermak Plateu (81.2199280 ˚N, 2.3710955˚E ) with a gravity corer at 1011m water depth during cruise KH21-234. DNA from gravity core sediments was extracted in the NORCE ancient DNA laboratory using the DNeasy PowerMax Soil Kit (Qiagen). Primers targeting the ITS1 region of P. glacialis were used in ddPCR reactions to determine gene copies per g of sediment. Radiocarbon dates were determined by picking shells of Neogloboquadrina pachyderma at four depths from marine sediment core KH21-234-34GC collected from the Yermak Plateu (81.2199280 ˚N, 2.3710955˚E ) with a gravity corer at 1011m water depth during cruise KH21-234. Accelerator mass spectrometry (AMS) 14C dates from the radiocarbon lab at ETH Zurich, and calibrated ages were calculated used the functions BchronCalibrate:sampleAges and Bchronology:PredictAges from the statistical package BChron (version 4.7.7). We trace P. glacialis quantitatively using droplet digital PCR (ddPCR), alongside biomarkers of sea-ice-associated and open-water phytoplankton. We utilise these proxies in combination to reconstruct past sea ice conditions in a sediment core from the Yermak Plateau (Arctic Ocean) dating back to MIS 3 (ca. 50,000 years ago). Our results indicate perennial and extensive sea ice coverage from MIS 3 until the end of the Last Glacial Maximum. We show that first-year sea ice, and seasonal sea ice were very variable during the Bølling-Allerød and Younger Dryas periods, including periods of open ocean during the Bølling-Allerød and permanent sea ice during the Younger Dryas. Within the Holocene we observe an increasing trend of P. glacialis DNA from the warm early Holocene to the cool late Holocene, suggesting an increase in first-year sea ice extent.

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