Pleistocene calcite lysocline and paleocurrents of the central Arctic Ocean and their paleoclimatic significance

Abstract

Most previous references to the depth of the Arctic Ocean calcite lysocline have been based on comparison with the known North Atlantic carbonate compensation depth. Foraminifera from cores taken at depths ranging from 2316 to 3956 m provide the first firm calcite lysocline constraints for the central Arctic Ocean. These data suggest progressive lowering of the calcite lysocline to at least 3956 m during the past ˜1.5 m.y., interrupted by 300‐m rises of the lysocline level that apparently correspond with interglacial and early glacial climate conditions. Most cores from less than 2450 m indicate variable foraminifera abundance but continual presence of foraminifera for the past ˜1.5 m.y. Low abundances commonly occur in coarse‐textured sediment and are interpreted to represent low productivity during major deglaciations. Within certain equivalent lithostratigraphic units representing the past ˜1.5 m.y. there is an absence of foraminifera in cores from depths greater than 2450 m. This absence of foraminifera is interpreted to be due to dissolution. Dissolution intervals are associated with fine‐grain sediments interpreted to represent interglacial and early glacial climate conditions. The interpretation of a rise in the lysocline level during interglacials is in apparent disagreement with studies reported from lower latitudes in the Atlantic Ocean but is complementary with the hypothesis that formation of Norwegian‐Greenland Sea Deep Water (NGDW) and cold Canada Basin Deep Water occurs during interglacials. Paleocurrent data from the Lomonosov Ridge and the adjacent Makarov Basin are interpreted to indicate that during periods of increased glacial ice influx into the Arctic Ocean system there was reduced current activity in the bottom and intermediate water masses relative to periods when little glacial ice was present. This is in accord with the idea that NGDW affects intermediate and deep water circulation in the central Arctic Ocean and hence the calcite lysocline level.