ALBERT

Description: The configuration of the Arctic Ocean as a mediterranean sea, surrounded by continents, gives a particular importance to the few connections that exist to the world ocean. In this manuscript critical cases are examined when the Arctic Ocean played an important role in climatic changes occurring over long and short geological timescales. By presenting three examples of published research results it is shown that in particular the water mass exchange through Bering Strait and the Fram Strait has varied in direction and volume. These variations have caused significant changes in the environments in the Arctic Ocean itself, on the surrounding continents, and – in cases – even hemisphere-wide. Owing to the prominent role of the Arctic Ocean in the global ocean circulation system, studies of the role of Arctic gateways are key to a better understanding of past, present, and future changes.

Description: The variability of Atlantic Water advection to the Arctic Ocean is described for the last about 50 million years based on available published sources. Until the opening of the Fram Strait as a deep-water passage at about 17 million years before present the inflow of Atlantic Water may have occurred through gaps in morphologic barriers, but results from microfossil findings are in part contradictory and difficult to interpret. After the opening, brownish deep-sea Arctic sediments reflect well-oxygenated deep-sea conditions and an improved exchange with the North Atlantic. The build-up of first ice sheets on northern Eurasian continental and shelf areas in the Late Tertiary may have resulted in intensive brine formation at the ice sheet margins and a significantly weaker influence of Atlantic Water on the Arctic intermediate waters. The history of Quarternary glacial-interglacial variability in the central Arctic is not well understood for most of the last 2 million years due to the lack of carbonate microfossils. For the last 200,000 years, however, short intervals of intensive Atlantic Water advection during interglacials and interstadials can be clearly identified in a number of sediment cores. Seasonally open water conditions (i.e., reduced sea ice) during these periods and even during maximum glaciation at Arctic continental margins probably made additional moisture available for the (re)growth of adjacent ice sheets. After the last deglaciation, Atlantic Water quickly returned to the Arctic and established conditions close to the modern ones. High-resolution records from the Fram Strait, however, indicate a rapid temperature rise of the Atlantic Water layer during the last 100 years, which most probably reflects on-going global warming and the so-called “Arctic Amplification“.

Description: Geological records from Tertiary and Quaternary terrestrial and oceanic sections have documented the presence of ice caps and sea ice covers both in the Southern and the Northern hemispheres since Eocene times, approximately since 45 Ma. In this paper focussing on Greenland we mainly use the occurrences of coarse ice-rafted debris (IRD) in Quaternary and Tertiary ocean sediment cores to conclude on age and origin of the glaciers/ice sheets, which once produced the icebergs transporting this material into the adjacent ocean. Deep-sea sediment cores with their records of ice-rafting from off NE Greenland, Fram Strait and to the south of Greenland suggest the more or less continuous existence of the Greenland ice sheet since 18 Ma, maybe much longer, and hence far beyond the stratigraphic extent of the Greenland ice cores. The timing of onset of glaciation on Greenland and whether it has been glaciated continuously since, are wide open questions of its long-term history. We also urgently need new scientific drilling programs in the waters around Greenland, in particular in the segment of the Arctic Ocean to the north of Greenland.