Sea surface temperatures and ice rafting in the Holocene North Atlantic: climate influences on Northern Europe and Greenland

The oceanographic conditions in the high-latitude North Atlantic ocean during the Holocene were reconstructed through analyses of sea surface temperature (SST; alkenone unsaturation ratios) and ice rafting (mineralogy and grain size) from two sediment sequences, one recovered from the Reykjanes Ridge at 59°N and the other from the Norwegian Sea at 68°N. Comparison of our records to published ice core and terrestrial proxy-climate data sets suggests that atmospheric temperature changes over Northern Europe and Greenland were coupled to SST variability and ice rafting. The records outline four major climatic phases: (i) an early-Holocene Thermal Maximum that lasted until approximately 6.7 kyr BP, (ii) a distinctly cooler phase associated with increased ice rafting between 6.5 and 3.7 kyr BP, (iii) a transition to generally warmer, but relatively unstable climate conditions between 3.7 and 2 kyr BP and (iv) a second distinct SST decline that took place between 2 and 0.5 kyr BP. In contrast to the dominant control of Northern Hemisphere summer insolation on early-Holocene climate development (via strong seasonality), the trigger for the onset of relatively unstable climatic conditions in the North Atlantic at 3.7 kyr BP is not straightforward. However, it is possible that this change was triggered by late-Holocene winter insolation increase at high northern latitude and/or by inter-hemispheric changes in orbital forcing. The late-Holocene Neoglaciation trend, which is characteristic of numerous terrestrial archives in northern Europe, may not only be attributed to a gradual decrease in orbitally forced summer temperature, but also to increase snow precipitation at high northern latitudes during generally milder winters.