| Summary: | The micropaleontological study (radiolarians and foraminifera) of the sediment core AMK-340, Reykjanes Ridge, North Atlantic, combined with the radiocarbon dating and oxygen and carbon isotopic record, provided data for the reconstruction of the summer paleotemperature across the upper 100 meters water depth range, and paleoenvironments during the Termination I in the age interval of 14.5–8 ka. The response of the main microfossil species to the paleoceanographic changes within the Bølling-Allerød (BA) warming, the Younger Dryas (YD) cold event and final transition to the warm Holocene, was different. The BA warming was well captured by the radiolarian and benthic foraminiferal records, but not the planktic one. The high abundances of the cold-water radiolarian species Amphimelissa setosa as a Greenland/Iceland Sea indicator marked a cooling at the end of the BA and at the start of the YD at 13.2–12.3 ka. The micropaleontological and isotopic data together with the paleotemperature estimates for the Reykjanes Ridge at 60°N document that, after the warm BA, the middle YD ca. 12.5–12.2 ka was the next significant step toward the Holocene warming. The start of the Holocene interglacial conditions was reflected in large representation of the microfossils being indicators of the open boreal North Atlantic environments indicating increasing warmth.
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