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The Role of North Atlantic Deep Water Formation in an OGCM’s Ventilation and Thermohaline Circulation

Abstract Two coarse-resolution model experiments are carried out on an OGCM to examine the effects of North Atlantic Deep Water (NADW) formation on the thermohaline circulation (THC) and ventilation timescales of the abyssal ocean. An idealized age tracer is included to gauge the ventilation in the model. One experiment is forced with the present-day climatology, the other has a negative salinity anomaly imposed on the North Atlantic surface to eliminate the formation of NADW. The Atlantic branch of the THC is reversed and the ventilation of the deep Atlantic basin is severely reduced when NADW formation is prevented. The Southern Ocean forms bottom water in both experiments, but downwelling and upwelling in the Southern Ocean are both reduced when NADW is included due to increased stratification of the water column. The Indian and Pacific basins are upwelling regions in both experiments and upper-level upwelling is stronger there when NADW is included; this change leads to cooler temperatures and reduced...