A comparison of Arctic Ocean sea-ice conditions during interglacials MIS 5e and MIS 1 based on biogenic sedimentary structures

Modeling results and proxy data both suggest that sea-ice conditions in the Arctic Ocean were less severe during the last interglacial (MIS 5e) compared to the present interglacial (MIS 1), but spatial variability of the sea-ice cover is still poorly constrained. In this study, variations in the intensity and composition of biogenic sedimentary structures (bioturbation and trace fossils) are used to address spatial differences in sea-ice distribution between the two interglacials. The presence or absence of trace fossils and bioturbated sediment have long been used to separate interglacial and glacial and intervals in central Arctic Ocean sediment cores based on the premise that interglacial conditions with less sea ice and more open waters led to higher food flux to the benthic communities, and vice versa. However, spatial differences in sea-ice cover during the individual interglacials also led to differences in primary productivity and consequently to spatial variations in the intensity of bioturbation and the composition of trace fossils. Areas characterized by perennial sea ice and few open leads or polynyas have a lower food flux than areas close to the sea-ice margin or with abundant polynyas. Consequently, the areas with more severe sea-ice conditions display fewer trace fossils and less intensely bioturbated sediments than areas characterized by open leads, polynyas, or areas situated close to the ice margin where primary productivity is higher. The spatial pattern shows a clear decrease in bioturbation intensity and trace fossil diversity from areas today characterized by relatively open waters, towards areas characterized by thick perennial sea ice. There is also a general pattern of more diverse trace fossil communities and more intense bioturbation observed from MIS 5e sediments compared to MIS 1, suggesting that sea-ice conditions during MIS 5e were generally less severe than during the present interglacial. The application of trace fossils and bioturbation for the reconstruction of sea ice conditions is particularly viable because of the large number of cores with X-ray radiographs available from data repositories such as www.pangaea.de. The main limitation of the method comes from the generally poor age control of Arctic sediments beyond the range of radiocarbon dating.