U.S. Dept. of Commerce / NOAA / OAR / PMEL /Publications
During June 1987 we obtained a series of hydrographic sections in the Greenland Sea from the R/V Polarstern. The emphasis was on the relatively undersampled southwestern portion of the sea, together with the northern source waters in Fram Strait. Figure 1 shows those stations extending below 500 m. Other, shallower stations primarily supported the biological programs on board, and these provide no information on the deep water issues of interest here.
Figure 1. Hydrographic stations extending below 500 m, June 1987. The reference station for Norwegian Sea deep water characteristics shown in Figure 3 is denoted by the solid circle marked I. Mooring locations during 1987-1988 used to define the eastward recirculation of water from the East Greenland Current are shown by the three triangles labeled GS, and locations of moorings during 1987-1989 used to estimate transport in the saline core over the Greenland slope are shown by the two unlabeled triangles.
At each of the deep stations, conductivity-temperature-depth (CTD) profiling was accompanied by discrete sampling for nutrients and dissolved oxygen, using a 24-bottle rosette. The CTD, a Neil Brown Instrument Systems (NBIS) Mark III, was calibrated for temperature and pressure at the Scripps facility before and after the cruise. In situ calibration was done at each station using a full set of discrete salinity samples spanning the depth of the cast and 3-4 racks of deep-sea reversing thermometers. The salinities were determined with a Guildline Autosal standardized against standard seawater batch P-105 before and after the analysis of the samples from each station. These bottle salinities have a precision and accuracy of about 0.001 and 0.002, respectively. The time- and pressure-corrected CTD profiles are accurate to about 0.003 in salinity and 0.003°C. In regions of strong gradients the time constant mismatch between the temperature and conductivity sensors reduces the accuracy significantly further; however this is not a problem in the deep water sphere we consider here.
Dissolved oxygen and nutrients were determined by standard methods using a
Manostat titration system and a Technicon autoanalyzer, with due attention being
paid to the analysis standards and to temperature control. We judge the precision
to be 0.02 mL L
for
oxygen and 0.1-0.2, 0.01-0.02, and 0.1-0.2 µmoL L,
respectively, for nitrate, phosphate, and silicate.
We shall also refer briefly to CTD data from Polarstern cruises in 1988 and 1989. The calibration procedures were similar to those in 1987, and the overall data quality is fully as good.
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