The Expedition of the Research Vessel "Polarstern" to the Arctic in 2008 (ARK-XXIII/1)

The first leg of the 23rd Polarstern expedition to the Arctic started on 12 June 2008 from Bremerhaven. The ship headed directly to the east Greenland coast at 74N and entered ice covered waters close to the Greenland coast. Due to an engine fault, spare parts for the ship's engine were collected by a helicopter from Bergen, Norway while we were steaming. The first research activities were geodetic works on Greenland. GPS receivers were installed on land with the use of helicopters. The receivers determine the vertical movement of the land masses which are caused by the decreasing ice load. At three latitudes between 74N and 76N receiver pairs were installed, one close to the coast, and the second about 100 km inland. The instruments need a measuring period of some weeks and were to be recovered during the next cruise leg. In addition to this, already existing Danish GPS fixpoints were re-evaluated or serviced. Owing to favourite weather conditions it was possible to comply with the tight time schedule despite the still dense ice cover related to the relatively early season. After the geodetic work a hydrographic transect across the Greenland Gyre was performed. This transect extends from the Greenland coast to Bear Island. It serves as a mean to record and explain ongoing changes in the Greenland Basin and its rim currents. In this basin a globally unique recent structure modification has been observed which is caused by a fresh water input pulse during the early 90s. The formerly present cold water dome was superseded by a persistent two-layer structure which prevails until today and which effectively inhibits the ventilation of the lower storey. As the two-storey structure is changing continously, a long-term project has been established for its observation. The highly dynamic changes, the complex modifications by convection, and the exchange with the surrounding waters can be correctly explained only with the aid of quality consistent long-term time series. During recent years, an increased input of Atlantic waters has been perceived which has far reaching implications. This increased input of Atlantic waters essentially contributes to the fact that nowadays the Greenland Sea remains usually ice-free in winter and it continued in 2008. Another issue on the working plan of the project was the exchange of autonomously profiling deep sea moorings and of a shallow water profiling mooring which is specifically designed to assess the fresh water introduction