Quaternary ostracoda from the Arctic Ocean: sea ice and ocean circulation variability over orbital timescales

Abstract

The Arctic is experiencing major changes in sea-ice cover, ocean temperature and marine ecosystems that many hypothesize are caused by anthropogenic influence on polar climate. In order to understand the impacts of climatic change on the Arctic Ocean, it is instructive to examine past climate changes and their impacts. We analyzed ostracode assemblages from six piston cores from the Northwind and Mendeleev Ridges in the Amerasian Basin and the Lomonosov Ridge in the central Arctic to reconstruct paleoceanographic history during Quaternary glacial-interglacial cycles. These cores come from water depths ranging between 700 and 2000 meters and the sediments recovered represent glacial-interglacial cycles of the past 700 ka (kiloannum) including the mid-Brunhes climatic transition ( 700-300 ka). The most important ostracode taxa (and their paleoceanographic significance) include Acetabulastoma arcticum and Pseudocythere caudata (perennial sea ice), Polycope spp. (productivity and sea ice), Krithe glacialis and Henryhowella asperrima (partially sea-ice free conditions, deep water formation), Pterygocythereis vannieuwenhuisei (warm interglacial conditions). Results indicate a seasonally sea-ice free western Arctic during an exceptionally warm interglacial period 400 ka (Marine Isotope Stage 11, MIS 11) and a major faunal turnover at approximately 300 ka when P. vannieuenhuisei became extinct. During this faunal and climatic transition, ostracode assemblages characteristic of interglacial and interstadial periods (MIS 9, 7, 5, 3, 1) first appeared in the Arctic. These changes signify the initial development of interglacial periods characterized by perennial sea ice, such as existed during thelate Holocene interglacial. In addition to orbital-scale paleoceanographic variability, ostracode assemblages vary over millennial timescales, which signify changes in ocean circulation during the glacial, deglacial and interglacial periods.