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Abstract:
The overarching goal of MSM58 was to gain knowledge about the natural variability of the Subtropical Gyre (STG) and Azores Front (AF) system as well as of changes in the deepwater composition and geometry in the eastern and western North Atlantic Basins, particularly during warm periods and during times of significant warming and ice sheet melting as during the last 25,000 years. For this purpose a sediment and water column sampling program was carried out along the Mid Atlantic Ridge (MAR) from 32° to 41°N and in four E-W depth transects on the MAR flanks. Prior to sediment sampling with multi corer/box corer and gravity corer, small interridge basins were hydroacoustically mapped using the onboard multibeam swath bathymetry and sediment echosounder systems to identify proper locations for coring sequences of Last Glacial to Holocene sediments with high sedimentation rates. After hydroacoustic surveys, sediment sampling was carried out in 6 working areas at 30 stations between 1300 and 4100m water depth. In total 205 m of sediment were gathered. Water column sampling for plankton and seawater took place at 16 stations. Preliminary sediment inspection indicates that the cores contain the Holocene and up to three glacial-interglacial cycles. As expected, sedimentation rates decrease from North to South and from East to West following the decline in nutrient supply from the subpolar to subtropical North Atlantic. This was also evident in decreasing abundances of planktonic foraminifera and increasing numbers of denitrifying cyanobacteria Trichodesmium in the water column.
