Dynamical ocean response to projected changes of the global water cycle

Abstract

AbstractOver the next century substantial changes will occur in the ocean as a consequence of an accelerated global hydrological cycle and the associated net surface freshwater flux change is projected to result from global warming. This paper is concerned with the dynamical response to the associated surface volume flux anomalies. Based on ocean model runs driven by RCP8.5 surface freshwater flux anomalies over the period 2081–2100 relative to 1986–2005, we show that the adjustment of the circulation involves a barotropic circulation response as predicted from the Goldsbrough‐Stommel theory. The corresponding barotropic circulation intensifies by approximately 20% with a stronger intensification of about 50% in the Southern Ocean, comparing to the present‐day Goldsbrough‐Stommel Circulation. The barotropic circulation anomaly induced by intensified freshwater flux reaches to 0.6 Sv in the Antarctic Circumpolar Current region. The adjustment also involves changes in the meridional overturning circulation mirroring the basin‐wide averages of changes in the convergence and divergence of the mass transport driven by the surface volume flux. The subsequent pathways of fresh water match with the spreading of volume flux in the shallow cells but diverge substantially with depth. Associated with changes of the flow field are the changes in meridional heat and freshwater transports. Changes in the circulation also lead to a redistribution of temperature and salinity from which a significant contribution results in form of regional steric sea level changes. These changes are of the order of 0.5 cm and can be largely attributed to the displacement of the isopycnals.