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Title: Asynchronous warming and δ 18O evolution of deep Atlantic water masses during the last deglaciation

Abstract

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 δ 18O of benthic foraminiferal calcite (δ 18Oc). 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 δ 18O 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 δ 18O c 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 oceanmore » circulation affects heat, a dynamic tracer, is considerably different from how it affects passive tracers, like δ 18O, and call for caution when inferring water mass changes from δ 18O c records while assuming uniform changes in deep temperatures.« less

Authors:
ORCiD logo [1];  [2];  [3]; ORCiD logo [4];  [5]; ORCiD logo [6];  [7];  [3]
  1. 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)
  2. 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
  3. National Center for Atmospheric Research, Boulder, CO (United States). Climate and Global Dynamics Division
  4. Woods Hole Oceanographic Inst., Woods Hole, MA (United States). Dept. of Geology and Geophysics
  5. Oregon State Univ., Corvallis, OR (United States). College of Earth, Ocean, and Atmospheric Sciences
  6. 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
  7. Univ. of Wisconsin, Madison, WI (United States). Dept. of Geoscience
Publication Date:
Research Org.:
Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Sponsoring Org.:
USDOE Office of Science (SC); National Science Foundation (NSF); USDOE Laboratory Directed Research and Development (LDRD) Program
OSTI Identifier:
1412877
Report Number(s):
LA-UR-17-28261
Journal ID: ISSN 0027-8424
Grant/Contract Number:  
AC52-06NA25396; SC0006744; 41630527
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Proceedings of the National Academy of Sciences of the United States of America
Additional Journal Information:
Journal Volume: 114; Journal Issue: 42; Journal ID: ISSN 0027-8424
Publisher:
National Academy of Sciences, Washington, DC (United States)
Country of Publication:
United States
Language:
English
Subject:
54 ENVIRONMENTAL SCIENCES; Earth Sciences; Atlantic water masses; last deglaciation; oxygen isotopes; deep ocean warming

Citation Formats

Zhang, Jiaxu, Liu, Zhengyu, Brady, Esther C., Oppo, Delia W., Clark, Peter U., Jahn, Alexandra, Marcott, Shaun A., and Lindsay, Keith. Asynchronous warming and δ18O evolution of deep Atlantic water masses during the last deglaciation. United States: N. p., 2017. Web. doi:10.1073/pnas.1704512114.
Zhang, Jiaxu, Liu, Zhengyu, Brady, Esther C., Oppo, Delia W., Clark, Peter U., Jahn, Alexandra, Marcott, Shaun A., & Lindsay, Keith. Asynchronous warming and δ18O evolution of deep Atlantic water masses during the last deglaciation. United States. doi:10.1073/pnas.1704512114.
Zhang, Jiaxu, Liu, Zhengyu, Brady, Esther C., Oppo, Delia W., Clark, Peter U., Jahn, Alexandra, Marcott, Shaun A., and Lindsay, Keith. Mon . "Asynchronous warming and δ18O evolution of deep Atlantic water masses during the last deglaciation". United States. doi:10.1073/pnas.1704512114. https://www.osti.gov/servlets/purl/1412877.
@article{osti_1412877,
title = {Asynchronous warming and δ18O evolution of deep Atlantic water masses during the last deglaciation},
author = {Zhang, Jiaxu and Liu, Zhengyu and Brady, Esther C. and Oppo, Delia W. and Clark, Peter U. and Jahn, Alexandra and Marcott, Shaun A. and Lindsay, Keith},
abstractNote = {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.},
doi = {10.1073/pnas.1704512114},
journal = {Proceedings of the National Academy of Sciences of the United States of America},
number = 42,
volume = 114,
place = {United States},
year = {Mon Oct 02 00:00:00 EDT 2017},
month = {Mon Oct 02 00:00:00 EDT 2017}
}

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