Glacial-to-Interglacial Changes in NADW Fluxes? 
Alan C. Mix and Richard G. Fairbanks 
Lamont-Doherty Geological Observatory 
Palisades, NY 10964 
Interglacial gradients in 613¢ between Atlantic and Pacific deep waters reflect differences 
between low-nutrient, 13C-enriched North Atlantic Deep Water (NADW) and high-nutrient, 
13¢-depleted Pacific Deep Water. Reduced Atlantic-Pacific 613C and cadmium gradients at the 
last glacial maximum have been used to suggest substantial replacement of NADW with nutrient- 
rich Antarctic Bottom Water (Boyle and Keigwin, 1982; Shackleton et al., 1983). We show that 
the Atlantic 613C signal is linked directly to North Atlantic polar-front migration, as reflected 
by planktonic foraminiferal faunas (Fig. 1). 
Three possible scenarios may explain the glacial pattern. First, if NADW formation 
stopped entirely, the deep Atlantic would be flooded with a single southern-source water mass. 
Our 6180 data argue against this (Mix and Fairbanks, in press). Tropical Atlantic cores record 
deep-water temperatures higher (and/or salinities lower) than in the high-latitude North Atlantic. 
At least two deep-water masses were present in the glacial Atlantic. 
Second, NADW flux may have been reduced, but not eliminated, with no charge in pre- 
formed nutrients of NADW. Third, NADW flux may have remained constant, but its preformed 
nutrients may have increased in glacial time as a response to heavy sea-ice cover and southern 
position of the polar front. A modern analogue for this scenario is the Weddell Sea. 
V30—-97 K708—-1 
618-0 Benthics 613—-C Benthics % N.pachyderma (left) 
ease e ee $$ & fF FE § @ 
$'$$3:3388 3 8 8 38 8 5 8 » 
(ada 44) FOV 
Fig. 1. Comparison of North Atlantic benthic isotope records from core V30-97 (41°00'N, 
32°56'W, 3371m) to polar front migration recorded by % N. pachyderma (left-coiling) in core 
K708-1 (50°00'N, 23°45'W, 4053m). LEFT: For 6180, which records mostly ice volume, +=U. 
peregrina and X=C. wuellerstorfii + 0.64. CENTER: For 613C, which records both changes in 
global carbon budget and water-mass nutrients, +=U. peregrina + 0.90 and X=C. wuellerstorfii. 
RIGHT: High % N. pachyderma (left-coiling) indicates a southern position for the North Atlantic 
polar front in glacial time. Strong correlation between polar front position (right) and benthic 
613c¢ (center) suggests a direct link between surface- and deep-water oceanographic changes. 
