Description of the data set

As part of this study, we evaluate previously unpublished data collected in the center of the Greenland Sea during four cruises of the Norwegian research vessel JOHAN HJORT between 1991 and 1994. All JOHAN HJORT cruises were carried out in November. The center of the Greenland Gyre is defined as the area between 0 W and 8 W in the southern sector (74 N to 75 N) and between 0 W and 5 W in the northern sector (75 N to 76 N, Fig. 1; Koltermann and Lüthje [1989]). We have restricted the selection of the stations to this area to minimize the influence of boundary effects. For evaluation of long-term trends we combine our data collected during the 1990s with historical data from the same area. The stations used for this purpose are listed in Table 1. In the context of this study, long-term trends are defined as changes that occur on time scales of several years to decades. The amplitude of the seasonal cycle in the surface layer of the Greenland Sea is large. The data set presented here, collected at various points during the annual cycle over a number of years, is too sparse to adequately resolve the seasonal cycle, or to detect systematic long-term trends in the surface layer over the study period.

	Fig. 1: Map of the Greenland Sea, all stations used in this study are located in the marked area.

A concern in identifying trends in oceanographic time-series is the separation of temporal from spatial variability. Spatial variability in the temperature field in our restricted study area was evaluated by examining data from years in which multiple stations were occupied, covering a significant portion of the central Greenland Sea. Mean values, standard deviations, and 95% confidence intervals for all observations taken during a particular year in two narrow depth intervals (900m - 1100m and 2900m - 3100m) were calculated and are listed in Table 2. These depth intervals were chosen, because they are in the middle of the intermediate and deep layers used for a quantitative evaluation in Section 4. The standard deviations of the mean values of the potential temperature are usually < 0.008 in the deeper water column, and < 0.03 in the intermediate waters. For comparison, long-term trends of potential temperature that we identify are of the order of 0.08 per decade in deep water and 0.2 per decade in intermediate water. Therefore, year to year changes can not be addressed by the data set, however, long-term trends occuring on time scales of several years to decades are larger than the uncertainties associated with the sometimes limited spatial sampling and can therefore be evaluated.

Table 2: Mean values, standard deviations and 95 % convidence intervals of temperature observations between 1900m and 2100m and between 2900m and 3100m depth from years in which 3 or more stations were occupied and contained observations in the apropriate depth intervals.

• Hydrographic data
• Tracer data