Salty, Saltier, and Saltiest: A Tale of Two Ocean Basins

Hansi Singh, University of Washington

Why is the Atlantic Ocean saltier than the Pacific Ocean? And why do most global climate models (GCMs) predict that the Atlantic will get saltier as the Earth warms while the Pacific will get fresher? We address these questions using a state-of-the-art GCM equipped with numerical water-tracing capability, which permits tracking of atmospheric moisture from evaporation to precipitation. Our control GCM experiment reveals that in the preindustrial climate, a large fraction of the moisture that's evaporated from the subtropical Atlantic precipitates in the equatorial eastern Pacific, thereby sustaining a steady-state interbasin salinity difference. We show that this finding is consistent with two independent lines of observational data. Furthermore, a second water-tracking GCM experiment in which carbon dioxide has been doubled projects intensified aerial moisture transport from the Atlantic to the Pacific as the Earth warms, a finding consistent with a suite of GCM simulations from the fifth phase of the Climate Model Intercomparison Project. We utilize results from both heuristic models and GCMs to show that these hydrological cycle predictions are robust because they reflect simple, yet fundamental, shifts in the aerial hydrological cycle in a warming world. We conclude by considering implications of these salinity projections for the oceanic global meridional overturning circulation.

Abstract Author(s): H.K.A. Singh, A. Donahoe, C.M. Bitz, J. Nusbaumer, D.M. Noone