PREFACE 
A miniworkshop on North Atlantic Deep Water Formation was held on ‘June 4-5, 1984 at 
Lamont-Doherty Geological Observatory, based on financial support from the Goddard Space Flight 
Center Director's Discretionary Fund. The workshop is expected to be the first in a series on 
key problem areas in the earth sciences. The objective is to contribute to improved definition 
of a scientific approach for understanding each problem, including data and measurement require- 
ments. This should also help define contributions that NASA could make as part of its Global 
Habitability program. 
The workshop approach is to bring together scientists from different disciplines that might 
not usually interact, particularly researchers who think across disciplinary boundaries. Prior 
to the workshop a focused question is identified within the broader scientific problem area. 
The broad issue of concern for the first workshop was: How will ocean circulation 
respond to climate change at the ocean surface, and what are the effects of ocean variability on 
climate? The focused question which the workshop addressed was: What controls the rate of 
deep water formation in the North Atlantic Ocean and what repercussions would there be from 
changes in this rate? 
North Atlantic Deep Water (NADW) forms near the end of at least some winters, after 
cooling and evaporation at the ocean surface have created water of sufficient density that it 
sinks to the ocean bottom somewhere in the Greenland/Norwegian/Labrador Sea _ region. 
Eventually this deep water spreads through and ventilates the deep global ocean; the process of 
NADW formation is the principal mechanism causing the exchange of heat, nutrients, CO»), and 
other trace substances between the deep ocean and the surface layers and atmosphere. It is 
thus apparent that any major changes in deep water formation could have important implications 
for climate, ocean productivity, atmospheric CO, and related issues. 
It can be said that deep water forms in the North Atlantic because it is the saltiest of the 
high latitude ocean basins. But why is it the saltiest ocean and how subject is this to change? 
Deep water formation itself probably helps create the high salinity by drawing north warm waters 
which are subject to high rates of evaporation. Is such a self sustaining mechanism for 
creating dense deep water stable to climate fluctuations, natural or man-made, at the ocean sur- 
face? Are other source regions for North Atlantic water, such as the Arctic and Mediterranean 
Seas, subject to climate fluctuations sufficient to influence the rate of deep water formation in 
the North Atlantic? Since conditioning of the surface water which sinks to form NA™™ occurs in 
the upper layer of the ocean, it seems possible that climate changes at the ocean surface could 
modify deep water formation on short time scales. 
Evidence for rapid changes of climate in the North Atlantic region, in fact, has been found 
in studies of isotopic abundances in Greenland ice cores by Dansgaard, Oeschger and others, in 
studies of North Atlantic sediment cores by Ruddiman, McIntyre and others, and in studies of 
pollen records throughout Europe. Several climate fluctuations from near glacial to near 
interglacial conditions appear to have occurred in periods not longer than a few decades. 
Recent measurements by Oeschger and colleagues of the CO,g content of a Greenland ice core 
suggest similarly rapid fluctuations of atmospheric CO9. If more complete analysis shows these 
apparent changes in atmospheric CO, to be real, they may be difficult to explain other than 
through changes in ocean circulation, because of the limited magnitude of COg reservoirs on 
land. 
Oeschger interprets the rapid climate changes as an indication that the climate system may 
shift between two quasi-stable states. Broecker et al. suggest that these climate states may be 
one in which NADW formation is 'on' and one in which it is 'off'. Climate models predict large 
increases in temperature and precipitation at high latitudes in the coming century as a result of 
the greenhouse effect of increasing atmospheric CO» and trace gases. Could this climate change 
shut off or reduce deep water formation? If so, the North Atlantic and European regions may 
actually become colder while the global climate warms. In any case, the paleoclimate data indi- 
cates that current perceptions of long-range climate issues are probably too simple. In par- 
ticular: 1) climate changes can happen more suddenly than presently anticipated, and 2) the 
geographical distribution of climate changes may be much more complex than suggested by current 
climate models, which assume that the ocean will continue to operate in the future in the same 
way as at present. 
Wallace Broecker served as scientific chairman for the workshop, James Hansen as co- 
organizer and Theodore Bennett as recorder. Participants are listed in an Appendix. 
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