Millenial Scale Variability of the Arctic Ocean and Northern North Atlantic during the Holocene

Abstract:

In the Arctic and northern North Atlantic, the relationships between ocean and climate are complex as sea-surface temperatures (SST) are intimately related to salinity, water mass stratification and sea-ice cover. From this viewpoint, the assemblages of dinoflagellate cysts (dinocysts), whose distribution is dependent upon all the above mention parameters, yield proxies of sea-surface conditions and reveal particularly useful for the reconstruction of past ocean conditions in such environments. Analysis of dinocyst assemblages and application of the modern analogue technique in more than 30 sediment cores were used to document the surface ocean changes in the northern North Atlantic and Arctic oceans during the Holocene. Among salient features, we note little variations in the Canadian Arctic Archipelago Channels. In contrast, relatively large amplitude variations in the Chukchi Sea and the Barents Sea are recorded and suggest millennial type oscillations with amplitude exceeding long-term trends (e.g., up to 4°C in summer SST). Data also indicate an almost opposite pacing between the western and eastern Arctic. Another important feature is the major SST-increase and sea-ice cover reduction in eastern Baffin Bay and along the south-east Greenland margins at about 7.5 ka ago, linked to the penetration of warmer and more saline North Atlantic water. This led to production of the Labrador Sea Water through winter cooling and convection and was followed by a reorganisation of water masses in the Nordic seas around 7.0 ka. The ~ 7.5-7.0 ka transition thus marks the actual onset of “interglacial” conditions in the subpolar North Atlantic. Whereas a more or less diachronic “thermal optimum” might be recorded at some sites during the early-mid Holocene, a strong regionalism in trends and millennial-scale instabilities persisted throughout the postglacial. Finally, one should mention that last decade variations of ocean conditions in these basins exceed those of the mid-late Holocene, notably for what concerns the sea ice cover.