The radiolarian Amphimelissa setosa is one of the prominent species of the Pleistocene radiolarian assemblages in the Seaof Okhotsk below the marine isotope stage (MIS) boundary 5/4, and it represents one of the most abundant radiolarianspecies in Holocene and modern environments of the Nordic Seas. We studied the A. setosa distribution in six cores fromthe Sea of Okhotsk and established morphometric measurements on A. setosa specimens from two cores of the Sea ofOkhotsk and one core from the Labrador Sea. We further compared our data with other available studies from theSubarctic Pacific, the Labrador Sea, the North Atlantic, the Norwegian Sea, and the Iceland/Greenland Seas in order todiscuss the possible settling of the species from the North Pacific via the Arctic Ocean into the Iceland/Greenland Seas. A.setosa exhibits a stable abundant population in the Sea of Okhotsk during most of the last ca. 0.7 m.y. and mightrepeatedly extend its population into the North Atlantic through the Arctic Ocean during the Pleistocene interglacialoptima. The species declines from the Sea of Okhotsk and from the Subarctic Pacific at the end of MIS 5. Its finaldocumented settling into the North Atlantic is during MIS 5, when A. setosa appears in low numbers in sediments of theLabrador Sea, however reaching significant percentages at the boundary of MIS 5/4. Based on the available information,we propose that A. setosa could migrate from the North Pacific into the Arctic Ocean during the interglacial optimum MIS5e and then through the channels of the Canadian Arctic Archipelago into the Baffin Bay and Labrador Sea. A furthermigration step of A. setosa occurs at the boundary of MIS 5/4, when A. setosa migrated from the Labrador Sea into theNorth Atlantic, probably related to a southward expansion of cold waters at the end of the MIS 5. During the warming atTermination I, A. setosa moved from the North Atlantic into the Nordic Seas. The abundant occurrence of A. setosa insediments south of Iceland, the Norwegian and North Seas within the Younger Dryas period points to a marked coolingand a southward movement of polar water masses restricted to this time interval.
Helmholtz Research Programs > MARCOPOLI (2004-2008) > POL6-Earth climate variability since the Pliocene