| Summary: | Under present-day conditions no deepwater is formed in the North Pacific. There is however evidence that a weakening of the Atlantic meridional overturning circulation (AMOC) consecutive to meltwater discharge during the deglaciation resulted in a switch of deepwater formation between the North Atlantic and the North Pacific [ Okazaki et al. , 2010]. Earlier model studies already put in evidence a link between a weakened AMOC and the establishment of a Pacific meridional overturning circulation (PMOC) (e.g., [ Mikolajewicz et al. , 1997]).We address the potential establishment of a PMOC and its impact on biogeochemical cycles with the help of LOVECLIM, a global three-dimensional Earth system model of intermediate complexity [ Goosse et al. , 2010]. In the present work, key physical or biogeochemical parameters of LOVECLIM are varied within their range of uncertainty in order to obtain an ensemble of parameter sets resulting in contrasted climate and global carbon cycle sensitivities. We then analyze the results of experiments in which the model is constrained with freshwater discharge in the North Atlantic.While a weakening of the AMOC is obtained with each of the parameter sets the development of a PMOC only occurs with a few of them. The establishment of a PMOC leads to an enhanced ventilation with major changes in oxygen and radiocarbon deepwater content as well as in primary production. A significant increase in atmospheric CO 2 also occurs. The mechanisms leading to the different responses are examined and discussed.
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