Asynchronous warming and δ18O evolution of deep Atlantic water masses during the last deglaciation
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- Univ. of Wisconsin, Madison, WI (United States). Center for Climatic Research; Univ. of Wisconsin, Madison, WI (United States). Dept. of Atmospheric and Oceanic Sciences; Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
- Univ. of Wisconsin, Madison, WI (United States). Center for Climatic Research; Univ. of Wisconsin, Madison, WI (United States). Dept. of Atmospheric and Oceanic Sciences; The Ohio State Univ., Columbus, OH (United States). Dept. of Geography, Atmospheric Science Program
- National Center for Atmospheric Research, Boulder, CO (United States). Climate and Global Dynamics Division
- Woods Hole Oceanographic Inst., Woods Hole, MA (United States). Dept. of Geology and Geophysics
- Oregon State Univ., Corvallis, OR (United States). College of Earth, Ocean, and Atmospheric Sciences
- Univ. of Colorado, Boulder, CO (United States). Dept. of Atmospheric and Oceanic Sciences; Univ. of Colorado, Boulder, CO (United States). Inst. of Arctic and Alpine Research
- Univ. of Wisconsin, Madison, WI (United States). Dept. of Geoscience
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 in this study, 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 caused by 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 middepth warming and enhanced downward heat flux via vertical mixing. Our results emphasize that the way that ocean circulation affects heat, a dynamic tracer, is considerably different from 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.
- Research Organization:
- Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC); National Science Foundation (NSF); USDOE Laboratory Directed Research and Development (LDRD) Program
- Grant/Contract Number:
- AC52-06NA25396; SC0006744; 41630527
- OSTI ID:
- 1412877
- Report Number(s):
- LA-UR-17-28261
- Journal Information:
- Proceedings of the National Academy of Sciences of the United States of America, Vol. 114, Issue 42; ISSN 0027-8424
- Publisher:
- National Academy of Sciences, Washington, DC (United States)Copyright Statement
- Country of Publication:
- United States
- Language:
- English
Web of Science
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