Multiple proxies needed to reconstruct the Atlantic Water Masses and AMOC during the Last Glacial Maximum

Sifan Gu, Ocean University of China, Qingdao, China, Zhengyu Liu, The Ohio State University, Department of Geography, Columbus, United States, Delia Oppo, WHOI, Geology and Geophysics, Woods Hole, United States, Jean Lynch-Stieglitz, Georgia Institute of Technology, School of Earth and Atmospheric Sciences, Atlanta, GA, United States, Alexandra Jahn, University of Colorado at Boulder, Atmospheric and Oceanic Sciences and INSTAAR, Boulder, CO, United States, Jiaxu Zhang, Los Alamos National Laboratory, Los Alamos, NM, United States and Lixin Wu, Key Laboratory of Physical Oceanography and Frontiers Science Center for Deep Ocean Multispheres and Earth System, Ocean University of China, Qingdao, China
Abstract:
Reconstructing the Atlantic Meridional Overturning Circulation (AMOC) during the Last Glacial Maximum (LGM) is essential for understanding glacial-interglacial climate change and the carbon cycle. However, uncertainties remain about the AMOC strength and the water mass distributions in the Atlantic during the LGM. Here we simulate the LGM ocean with an isotope (d13C, eNd, 231Pa/230Th, and ∆14C) enabled ocean model. The simulated LGM AMOC shows an intensity comparable to that of the present day (PD) but with a 600-m shallower upper cell and AABW is dominating the Atlantic below 3000 m. With this ocean circulation, the tracer distributions simulated by the model are consistent with the general features of the observations from glacial Atlantic sediments. A sensitivity experiment with similar AMOC geometry but much weaker strength suggests that the correct AMOC geometry is more important than the AMOC strength to simulate the glacial water mass tracers such as d13C and eNd in agreement with observations. The simulated 231Pa/230Th suggest that the glacial AMOC strength is not weaker than PD. Furthermore, the decomposition of the Atlantic water masses by calculating water mass fraction using the air-sea gas exchange signature of water masses (d13C_as) and eNd suggests that the LGM water mass distributions can be correctly reconstructed with d13C_as in the model, but eNd overestimates the percentage of the North Atlantic Deep Water (NADW) in the deep Atlantic because of the boundary source of Nd. Therefore, multiple proxies should be combined to reconstruct the past ocean circulation accurately.
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