Glacial–interglacial carbonate preservation records in the Nordic Seas

A combination of weight and reflectance measurements as well as scanning electron microscope (SEM) analyses on planktic foraminiferal tests from two sites in the Nordic Seas were used to investigate the pelagic carbonate preservation during the last five glacial–interglacial cycles. In general, a pattern showing good preservation during glacial times and enhanced corrosion during interglacial times can be observed. Marine Isotope Stage 11 (MIS 11) reveals the strongest corrosional features with an estimated 45% total loss of the foraminiferal carbonate before shell fragmentation. One reason for the enhanced interglacial corrosion may be a high regional surface productivity during these intervals, which led to increased dissolution rates in the deep sea driven by metabolic carbon dioxide. However, the carbonate preservation changes may also be linked to global changes in the marine carbonate system. Although the reason for the observed dissolution pattern in the Nordic Seas remains speculative, it seems to be in phase with the rhythm of glacial–interglacial carbonate preservation in the Pacific Ocean but out of phase with the rest of the Atlantic. The data further support the hypothesis that much of the glacial decrease in the atmospheric CO2 may be attributed to the changes in the alkalinity of the oceans.