Asynchronous warming and δ18O evolution of deep Atlantic water masses during the last deglaciation
Brady, Esther C.
Oppo, Delia W.
Clark, Peter U.
Marcott, Shaun A.
MetadataShow full item record
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.
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.
Suggested CitationPreprint: 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", 2017-08-21, https://doi.org/10.1073/pnas.1704512114, https://hdl.handle.net/1912/9300
Showing items related by title, author, creator and subject.
Coherent response of Antarctic Intermediate Water and Atlantic meridional overturning circulation during the last deglaciation : reconciling contrasting neodymium isotope reconstructions from the tropical Atlantic Gu, Sifan; Liu, Zhengyu; Zhang, Jiaxu; Rempfer, Johannes; Joos, Fortunat; Oppo, Delia W. (John Wiley & Sons, 2017-10-24)Antarctic Intermediate Water (AAIW) plays important roles in the global climate system and the global ocean nutrient and carbon cycles. However, it is unclear how AAIW responds to global climate changes. In particular, ...
Cook, Mea S.; Keigwin, Lloyd D.; Sancetta, Constance A. (2005-07-31)The lithology of deglacial sediments from the Bering Sea includes intervals of laminated or dysaerobic sediments. These intervals are contemporaneous with the occurrence of laminated sediments from the California margin ...
Inferring surface water equilibrium calcite δ18O during the last deglacial period from benthic foraminiferal records : implications for ocean circulation Amrhein, Daniel E.; Gebbie, Geoffrey A.; Marchal, Olivier; Wunsch, Carl (John Wiley & Sons, 2015-11-12)The ocean circulation modifies mixed layer (ML) tracer signals as they are communicated to the deep ocean by advection and mixing. We develop and apply a procedure for using tracer signals observed “upstream” (by planktonic ...