The last glacial period was marked by pronounced millennial-scale climate changes that were first documented in Greenland ice core records and thereafter in numerous ocean and climate records from around the world. This so-called Dansgaard-Oeschger (D-O) climate variability comprises one of the most pronounced and puzzling examples of abrupt climate change. The D-O climate changes and in particular the associated abrupt warming transitions by up to 15°C over Greenland happening within years or decades might have been linked to shifts in sea ice cover in the Nordic Seas. However, the coupled ocean-sea ice-climate dynamics and feedbacks underlying the abrupt D-O climate variability have remained largely unresolved.
In this talk, I will present high-resolution sea ice records from two Norwegian Sea sediment cores covering four D-O cycles at ~32–40 ka. Sea ice proxy records are based on the sea ice diatom biomarker IP25, open-water phytoplankton biomarkers (sterols and alkenones) and semi-quantitative phytoplankton-IP25 (PIP25) sea ice estimates. These sea ice records, a tephra-assisted chronology and integration of other marine and ice core proxy records allow to resolve and constrain the nature, timing and role of sea ice changes during abrupt Greenland climate changes. The results suggest that previously unresolved changes in sea ice cover: (1) contributed to regime shifts between surface ocean stratification and convective deep-water formation in the Nordic Seas, and (2) acted as feedback mechanism for abrupt Greenland climate change during D-O cycles.