ALBERT

Description: During summer 2014 and summer 2015 two autonomous Seagliders were operated over several months close to the ice edge of the East Greenland Current to capture the near-surface freshwater distribution in the western Greenland Sea. The mission in 2015 included an excursion onto the East Greenland Shelf into the Norske Trough. Temperature, salinity and drift data were obtained in the upper 500 to 1000 m with high spatial resolution. The data set presented here gives the opportunity to analyze the freshwater distribution and possible sources for two different summer situations. During summer 2014 the ice retreat at the rim of the Greenland Sea Gyre was only marginal. The Seagliders were never able to reach the shelf break nor regions where the ice just melted. During summer 2015 the ice retreat was clearly visible. Finally, ice was present only on the shallow shelves. The Seaglider crossed regions with recent ice melt and was even able to reach the entrance of the Norske Trough. The data processing for these glider measurements was conducted at Alfred Wegener Institute (AWI). The first part consists of the Seaglider Toolbox from the University of Each Anglia; the second was exclusively composed for the data from the Greenland Sea. The final hydrographic, position and drift data sets can be downloaded from https://doi.org/10.1594/PANGAEA.893896 (Latarius et al., 2018).

Description: During summer 2014 and summer 2015 two autonomous Seagliders were operated over several months close to the ice edge of the East Greenland Current to capture the near-surface fresh water distribution in the western Greenland Sea. The mission 2015 included an excursion onto the East Greenland Shelf into the Norske Trough. Temperature, salinity and drift data were obtained in the upper 500 to 1000 m with high spatial resolution. At AWI the data processing for these glider measurements was conducted. The first part consists of the Seaglider Toolbox from the University of Each Anglia, the second was exclusively composed for the data from the Greenland Sea. The final hydrographic, position and drift data sets can be downloaded from https://doi.org/10.1594/PANGAEA.893896.

Description: Within the Arctic Mediterranean the inflowing warm and saline Atlantic Waters are transformed into cold and relatively fresh, dense overflow waters, which flow back into the North Atlantic at depth. The major part of the transformation takes place in the ice-free areas of the Nordic Seas. This investigation examines the contribution of the deep basins in the Nordic Seas to the overall transformation. Since 2001 hydrographic measurements with profiling floats were conducted in the Nordic Seas. This data set provides insight into the temporal development of the hydrography in the four deep basins (Norwegian Basin, Lofoten Basin, Greenland Sea and Icelandic Plateau). In the study on hand the data are used to describe the variability of the hydrography on seasonal and inter-annual to decadal time scales. In combination with sea surface flux data heat and freshwater budgets for the basins are established. Based on the budgets the relative importance of the deep basins for the water mass transformation is estimated. Time series of temperature and salinity for the basins are dominated by the seasonal signal in the upper 500 to 750 m. Amplitudes are up to 2.5°C. A harmonic analysis is used to separate it from the signals on longer time scales. The detailed knowledge of the seasonal signal can be used for the analysis of longer-term variability on the basis of historical data. Without a seasonal correction there is a risk of misinterpretation due to aliasing, because data were mainly taken in the summer month. With a maximum total length of the time series of 11 years the separation of inter-annual and decadal variability is mathematically not possible. However the temperature and salinity development in the Greenland Sea and the Norwegian Basin is interpreted in relation to the propagation of decadal to multi-decadal anomalies in the properties of the inflowing Atlantic water around the Nordic Seas, which was analyzed in other studies. Furthermore the time series from the Greenland Sea demonstrate the decay of the intermediate temperature maximum in the time span of float-observations and the inter-annual variability of the near-surface (0-50m) freshwater content, which in turn influences the convection depth in the following winter. Heat and freshwater budgets give insight into the interplay of lateral exchange between the basins and the boundary currents, the sea-surface heat and freshwater fluxes and the development of heat and freshwater content inside the basins. The development inside the basins is derived from the float-observations. Surface fluxes are taken from a corrected NCEP data set. The data set was selected in a detailed examination as the most realistic one. The lateral exchange is given by the residuum of the two other components and is identified with the contribution of the basins to the total transformation. The most striking result is that more heat is imported laterally into the basins below 50 m than the basins release back to the atmosphere, because they additionally release heat laterally in the near-surface layer. Furthermore the basins gain more freshwater laterally in the near-surface layer than from the atmosphere. That means the water mass transformation is underestimated when taking only surface fluxes into account. The four basins contribute 17% to the total water mass transformation of the Arctic Mediterranean in terms of heat and 7% in terms of freshwater although they account for only 4% of the total area of the Arctic Mediterranean. Within the Nordic Seas the contribution from the eastern basins is most important. Increasing input of freshwater, caused by climate change, will foremost influence the transformation in the west. Therefore a future decrease, but no break-down, of the transformation seems realistic, which may result in a slow-down of the Atlantic Meridional Overturning Circulation. In relation to examinations of the transformation in the whole Nordic Seas it becomes obvious, that the deep basins are particularly important. Although they account for only one fifth of the total area they contribute 40% to the total transformation in the Nordic Seas.

Description: Polarer Atlantik zwischen Island, Grönland, Spitzbergen und Nordnorwegen

Description: In the Arctic Mediterranean a transformation of Atlantic Water, flowing in near the surface, into overflow water, which leaves the area at depth, takes place. For this transformation the Nordic Seas are of particular importance, as they are largely ice-free and thus heat loss to the atmosphere during winter is strong. Since 2001 Argo-type profiling float measurements have been carried out in the region and enable the observation of hydrography during the whole year. The measurements concentrate on the deep basins, the Norwegian Basin, Lofoten Basin, Greenland Sea and Icelandic Plateau. They are analysed with special emphasis on the seasonal cycle in hydrography. Based on the mean seasonal cycle of temperature and salinity and atmospheric fluxes from reanalysis products for the first decade of this century heat and freshwater budgets are calculated. The residuum in the budgets gives the lateral exchange of water between the inner basins and the boundary current, circumnavigating the whole area. This lateral exchange is identified with the contribution of the deep basins to the water mass transformation within the Nordic Seas. Budget calculations, using atmospheric flux data from NCEP with corrections for high latitudes, yield a contribution of 18% to the total temperature decrease and 6% to the total salinity decrease in the Arctic Mediterranean, although the basins account for only 4% of the total area. The density increase nearly exclusively takes place in the eastern basins, whereas the Greenland Sea plays an important role in matching the temperature and salinity characteristic of the overflow water. An increasing amount of freshwater in the surface layer will have only minor effects on the strength of the overflows across the Greenland-Iceland-Scotland Ridge.