Variability in North Pacific intermediate and deep water ventilation during Heinrich events in two coupled climate models

Chikamoto, Megumi O.; Menviel, Laurie; Abe-Ouchi, Ayako; Ohgaito, Rumi; Timmermann, Axel; Okazaki, Yusuke; Harada, Naomi; Oka, Akira; Mouchet, Anne (2012). Variability in North Pacific intermediate and deep water ventilation during Heinrich events in two coupled climate models. Deep-sea research. Part 2 - topical studies in oceanography, 61-64, pp. 114-126. Kidlington, UK: Elsevier Science 10.1016/j.dsr2.2011.12.002

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The responses of North Pacific intermediate and deep water ventilation and ocean biogeochemicalproperties to northern North Atlantic glacial freshwater perturbations are evaluated with a coupledatmosphere–ocean general circulation model MIROC and an earth system model of intermediatecomplexity LOVECLIM. When the Atlantic meridional overturning circulation (AMOC) is weakened as aresult of the North Atlantic freshwater discharge, both models simulate subthermocline and inter-mediate water warming in the Pacific Ocean. The sensitivities of the Pacific meridional overturningcirculation (PMOC) to AMOC weakening differ significantly between the two models. MIROC simulatesa small enhancement of the deep sinking branch of the PMOC in the North Pacific. On the contrary, theLOVECLIM freshwater experiment exhibits intensified deep water formation in the North Pacific,associated with a maximum transport change of 19 Sv. Despite the significant differences in oceancirculation response, both models successfully reproduce high-oxygen and low-nutrient conditions ofintermediate and deep waters, in accordance with sediment core based paleoproxy reconstructionsfrom the North Pacific and Bering Sea during Heinrich event 1. Emergence of younger intermediate anddeep water in the North Pacific can be partly attributed to an overall enhanced mixing as well asintensified overturning circulation of the subpolar North Pacific. Our models simulate broad featuresobserved in several paleoproxy data of the Pacific Ocean: biological production decrease in northernJapan, cooling in the western North Pacific Ocean, and the southward shift of the Pacific intertropicalconvergence zone.

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