NADW formation as a branch of the hydrological cycle



The wide interest in the nature and evolution of deep ocean circulation as a key factor to understanding climate change set the stage for a conference devoted to North Atlantic Deep Water (NADW) formation held at Lamont-Doherty Geological Observatory (LDGO), Palisades, N.Y., from November 11 to 12, 1991. Sponsored by the LDGO Climate Center and hosted by Wally Broecker, about seventy scientists attended. Twenty-seven invited papers were presented at the 2-day conference.

The rates and paths of NADW formation were the focus of the first day. Bob Dickson, Lowestoft, U.K., summarized the present state of the “northern end” of global thermohaline circulation. In contrast to the view one obtains from many existing numerical models, especially the simpler ones, NADW derives, in reality, from a mixture of distinctly different water masses before it spreads into the world ocean. At most, 50% of the estimated 20 Sv (1 sverdrup = 106 m3/s) of North Atlantic overturning actually comes from the Arctic via the overflows east and west of Iceland; the rest is thought of as recirculating water from the Labrador Sea. The Greenland-Iceland ridge overflow conspicuously lacks both seasonal and interannual variability in the transport. This is an important constraint for future modeling efforts.