{1} Lamont-Doherty Earth Observatory of Columbia
University, Palisades, N.Y., 10964, USA
{2} Institute of Marine Research, PO Box 1870 Nordnes, N-5024
Bergen, Norway
{3} National Oceanic and Atmospheric Administration, Pacific
Marine Environmental Laboratory, 7600 Sand Point Way, N.E., Seattle, WA
98115
{4} Department of Earth and Environmental Sciences, Columbia University,
New York, USA
{5} Oceanographic and Atmospheric Sciences Division, Department of
Applied Science, Brookhaven National Laboratory, P.O. Box 5000,
Upton, NY 11973-5000
We present long-term observations of temperature, salinity, tritium/, chlorofluorocarbon-11 (CFC11) and chlorofluorocarbon-12 (CFC12) for the central Greenland Gyre. The time series span the periods between 1952 and 1994 (temperature), 1981 and 1994 (salinity), 1972 and 1994 (tritium/), and 1982 and 1994 (CFCs). The correlation between hydrographic and transient tracer data indicate that decreasing and cold temperatures in the deep water in the early 1950s and between 1960 and 1980 reflect periods of higher deep water formation rates, whereas periods of increasing temperatures in the late 1950s and between 1980 and 1994 are related to low deep water formation rates. However, the transient tracer observations obtained in the 1980s and early 1990s indicate that even during periods of low deep water formation some water from the upper water column contributed to deep water formation between 1980 and 1994. In 1994, the deep water reached temperatures and salinities of -1.149 and 34.899, respectively, and does no longer fit the classical definitions of Greenland Sea Deep Water (). The temperature increase in the water column between 200m and 2000m depth between 1980 and 1994 corresponds to an average heating rate of about 5 Wm over this period, resulting in a decrease in density. The 13-year warming could be balanced by intensive cooling in 2 winters. The surface salinity steadily increased from 34.50 in 1991 to 34.85 in 1994.