Review of North Atlantic Source Waters 
James H. Swift 
Scripps Institute of Oceanography 
La Jolla, California 92093 
North Atlantic Deep Water (NADW) ventilates the deep World Ocean. It not only carries 
relatively well-oxygenated waters, but also other substances derived from recent sea-surface 
exchanges. There are five regional sources for NADW (Fig. 1): 1) derivatives of the salty 
Mediterranean Sea outflow, 2) products of open-ocean convection in the Labrador Sea, 3) 
Iceland-Scotland Overflow Water from the Norwegian Sea - salty by virtue of mixing with saline 
water near the sills, 4) Denmark Strait Overflow Water from the Iceland and Greenland Seas - 
which retains a high-density, relatively low-salinity signal, and 5) remnants of deep water from 
the Antarctic circumpolar region - freshest of the bottom waters. Despite the differences of 
characteristics of the source waters, the NADW is relatively uniform (e.g., cf. Fig. 1). 
Because the formation of each of the five source waters may be viewed as a response to a 
complex series of events, it is difficult to examine the sensitivity of NADW to environmental 
fluctuations. It is known that the deep northern North Atlantic is relatively closely coupled to 
the sea surface in the Greenland and Iceland seas. The most recent studies indicate a minimum 
response time of only two years between the introduction of a passive signal north of Iceland 
f 
W 
O 
247 348 349 350 351 
SALINITY X 10° 
POTENTIAL TEMPERATURE (°C) 
Nm 
Fig. 1. Potential temperature - salinity diagram for North Atlantic deep waters colder than 4°C, 
adapted from Worthington and Wright (1970). The solid line encloses all of Worthington and 
Wright's ¢-S classes containing at least 100 km® of cold deep water. The hatched #-S classes 
are the largest classes enclosing 51% of the total deep water volume, i.e., the principal volu- 
metric mode (NADW: North Atlantic Deep Water). Regional water mass nomenclature is intro- 
duced by shading near the appropriate e-S ranges: LSW (Labrador Sea Water), NEADW 
(Northeast Atlantic Deep Water, fed by the Iceland-Scotland overflow), and NWABW (Northwest 
Atlantic Bottom Water, fed by the Denmark Strait overflow). The waters of the cold, fresh 
"arm" are derived from the Antarctic. The Mediterranean Sea outflow waters are too warm and 
salty to appear distinctly within these e-S ranges. The 6-S correlation at a single northern 
North Atlantic location may show influences of each of these deep water masses, but would not 
pass through all the shaded areas. (From Swift, 1984b) 
