Effects of atmosphere-ocean interactions on late Holocene climate in the Arctic-Subarctic region

After the last glaciation numerous temperature sensitive climate proxies from around the Arctic – ice cores, terrestrial and marine archives alike – show a tight connection to northern insolation with highest temperatures noted in the early Holocene. However, until the mid-Holocene (5-6ka; start of neoglaciation) all environmental change and reorganization occurred under circumstances still caused by deglaciation and global sea-level rise. Thus, the situation observed since then is interpreted to be mainly driven by a kind of ocean-atmospheric system that has little in common with the time before. In the Arctic the flooding of the vast shelves ended thereby massively expanding the area of winter sea-ice. And in the Nordic Seas water fronts were established which caused intensification of the gyre systems leading to the modern-like circulation pattern during the past 4kyrs. In several records these past 4 millennia were relatively cool. In the largest Arctic delta (Lena) peat-based island accumulation started at 4ka and another major change in growth occurred after 2.5ka in both, accumulation and species composition.

Neoglacial cooling in the colder Nordic Seas is witnessed by a persistent sedimentation of ice-rafted debris (IRD) after 6 ka, a trend which continued until recent time. Although within the eastern, Atlantic-influenced sector warm conditions persisted until about 1 ka, as seen in both planktic and benthic O-isotopes, variability among foraminiferal species would indicate major surface changes, as the abundance of the polar species increased to 70 % since then (in the Little Ice Age). That drastic increase was associated with highly variable O-isotope values throughout the entire water column. Thus, for the Little Ice Age the particular situation caused a rerouting of polar water masses and sea-ice far into the eastern Nordic seas. The major force behind such centennial-long climatic events must be sought in a complex atmosphere-surface ocean interaction rather than in the often-mentioned meridional ocean overturning circulation. Thus, spatial expansion of sea-ice impacts both the polar vortex and the temperature gradient between the high and low latitudes thereby exerting climate pressure on regions well beyond the Arctic realm.