Long-term sea-level change revisited: the role of salinity

Abstract

Of the many processes contributing to long-term sea-level change, little attention has been paid to the large-scale contributions of salinity-driven halosteric changes. We evaluate observed and simulated estimates of long-term (1950-present) halosteric patterns and compare these to corresponding thermosteric changes. Spatially coherent halosteric patterns are visible in the historical record, and are consistent with estimates of long-term water cycle amplification. Our results suggest that long-term basin-scale halosteric changes in the Pacific and Atlantic are substantially larger than previously assumed, with observed estimates and coupled climate models suggesting magnitudes of ∼25% of the corresponding thermosteric changes. In both observations and simulations, Pacific basin-scale freshening leads to a density reduction that augments coincident thermosteric expansion, whereas in the Atlantic halosteric changes partially compensate strong thermosteric expansion via a basin-scale enhanced salinity density increase. Although regional differences are apparent, at basin-scales consistency is found between the observed and simulated partitioning of halosteric and thermosteric changes, and suggests that models are simulating the processes driving observed long-term basin-scale steric changes. Further analysis demonstrates that the observed halosteric changes and their basin partitioning are consistent with CMIP5 simulations that include anthropogenic CO _2 forcings ( Historical ), but are found to be inconsistent with simulations that exclude anthropogenic forcings ( HistoricalNat ).

Keywords

• oceanography
• sea level
• salinity
• climate model
• CMIP5
• global change