WINTER CONVECTIVE EVENTS AND BOTTOM WATER WARMING IN THE GREENLAND SEA

From observations on yearly cruises to the central Greenland Sea betwe en 1993 and 1996, conclusions are drawn with respect to winter convect ion and bottom water renewal. The data indicate that winter convection was extremely weak after 1993, not even ventilating the intermediate waters. This is remarkable, since the salinities in the upper layers i ncreased considerably between 1993 and 1995, thus providing presumably favorable conditions for winter convection. With the absence of deep reaching winter convective events, the temperatures in the deeper wate rs of the Greenland Gyre increased steadily by about 0.03 K between 19 93 and 1996. We conclude from the development of mainly the thermal st ructure on a zonal transect that an explanation for the temperature in crease can be given by a large-scale downward water movement of about 150 m/yr in the central Greenland Sea. The data indicate that this pro cess is independent of changes in the dynamically induced density dist ribution. It is therefore possible that a downward movement, perhaps m asked by other processes, may continue for many years. If this is the case, resulting flushing times would be of the order of 20-30 years on ly. The presence of a large-scale circulation cell with downward movem ent in the central Greenland Gyre would explain the observed warming o f the bottom waters without the demand for an actually active heat sou rce. It is also in accordance with the observed increase of chemical t racer concentrations in the deep waters.