Tracer transport timescales and the observed Atlantic-Pacific lag in the timing of the Last Termination

Type Article
Date 2012-09
Language English
Author(s) Gebbie Geoffrey
Affiliation(s) Woods Hole Oceanog Inst, Dept Phys Oceanog, Woods Hole, MA 02543 USA.
Source Paleoceanography (0883-8305) (Amer Geophysical Union), 2012-09 , Vol. 27 , N. PA3225 , P. 1-14
DOI 10.1029/2011PA002273
WOS© Times Cited 21
Abstract The midpoint of the Last Termination occurred 4,000 years earlier in the deep Atlantic than the deep Pacific according to a pair of benthic foraminiferal delta O-18 records, seemingly implying an internal circulation shift because the lag is much longer than the deep radiocarbon age. Here a scenario where the lag is instead caused by regional surface boundary condition changes, delays due to oceanic transit timescales, and the interplay between temperature and seawater delta O-18 (delta O-18(w)) is quantified with a tracer transport model of the modern-day ocean circulation. Using an inverse method with individual Green functions for 2,806 surface sources, a time history of surface temperature and delta O-18(w) is reconstructed for the last 30,000 years that is consistent with the foraminiferal oxygen-isotope data, Mg/Ca-derived deep temperature, and glacial pore water records. Thus, in the case that the ocean circulation was relatively unchanged between glacial and modern times, the interbasin lag could be explained by the relatively late local glacial maximum around Antarctica where surface delta O-18(w) continues to rise even after the North Atlantic delta O-18(w) falls. The arrival of the signal of the Termination is delayed at the Pacific core site due to the destructive interference of the still-rising Antarctic signal and the falling North Atlantic signal. This scenario is only possible because the ocean is not a single conveyor belt where all waters at the Pacific core site previously passed the Atlantic core site, but instead the Pacific core site is bathed more prominently by waters with a direct Antarctic source.
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