Changing Atlantic Freshwater Transports in Response to Future Climate Projections

Abstract

Changes in Atlantic meridional freshwater transports have been hypothesized to play an important role in Atlantic Meridional Overturning Circulation (AMOC) stability, redistributing precipitation and evaporation and dynamic sea level changes.  Freshwater transports can be altered by both changes in ocean circulation and changes in salinity.  In this study CMIP5 and CMIP6 models are analyzed to investigate how salinity and velocity changes impact the freshwater transports in the ScenarioMIP future projections.  In the multi-model means of CMIP5 and CMIP6 data there is only a slight increase (< 0.1Sv) in southward freshwater transport across the Atlantic basin.  This slight increase comes from a balance of changes in overturning (zonal mean) and azonal freshwater transports.  The changes in overturning and azonal freshwater transports are largest in the subtropical Atlantic where the salinity driven azonal changes drive an increase in southward freshwater transport which are almost completely counteracted by a velocity driven overturning freshwater transport.  Changes in these freshwater transports are larger in CMIP6 relative to CMIP5, which is especially noticeable in the velocity driven overturning changes (due to the larger AMOC weakening in CMIP6) and salinity driven azonal changes (due to a comma shaped freshening pattern in the North Atlantic, typically associated with a weakening of the AMOC).