Publication Date:
2022-05-25
Description:
Author Posting. © The Author(s), 2017. This is the author's version of the work. It is posted here under a nonexclusive, irrevocable, paid-up, worldwide license granted to WHOI. It is made available for personal use, not for redistribution. The definitive version was published in Proceedings of the National Academy of Sciences of the United States of America 114 (2017): 11075-11080, doi: 10.1073/pnas.1704512114.
Description:
The large-scale reorganization of deep-ocean circulation in the Atlantic involving changes in North
Atlantic Deep Water (NADW) and Antarctic Bottom Water (AABW) played a critical role in
regulating hemispheric and global climate during the last deglaciation. However, changes in the
relative contributions of NADW and AABW and their properties are poorly constrained by marine
records, including δ18O of benthic foraminiferal calcite (δ18Oc). Here we use an isotope-enabled
ocean general circulation model with realistic geometry and forcing conditions to simulate the
deglacial water mass and δ18O evolution. Model results suggest that in response to North Atlantic
freshwater forcing during the early phase of the last deglaciation, NADW nearly collapses while
AABW mildly weakens. Rather than reflecting changes in NADW or AABW properties due to
freshwater input as suggested previously, the observed phasing difference of deep δ18Oc likely
reflects early warming of the deep northern North Atlantic by ~1.4°C while deep Southern Ocean
temperature remains largely unchanged. We propose a thermodynamic mechanism to explain the
early warming in the North Atlantic, featuring a strong mid-depth warming and enhanced
downward heat flux via vertical mixing. Our results emphasize that the way ocean circulation
affects heat, a dynamic tracer, is considerably different than how it affects passive tracers like
δ18O, and call for caution when inferring water mass changes from δ18Oc records while assuming
uniform changes in deep temperatures.
Description:
This
work is supported by the U.S. NSF P2C2 projects (1401778 and 1401802) and OCE projects
(1600080 and 1566432), China NSFC 41630527, and the Wisconsin Alumni Research Foundation
Keywords:
Atlantic water masses
;
Last deglaciation
;
Oxygen isotopes
;
Deep ocean warming
Repository Name:
Woods Hole Open Access Server
Type:
Preprint
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