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 basin-scale contributions of salinity-driven halosteric changes. We evaluate simulated against observed 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 Pacific and Atlantic basin-scale halosteric change contributions 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 models Pacific basin-scale freshening leads to a density reduction that augments thermosteric expansion whereas in the Atlantic halosteric changes partially compensate strong thermosteric expansion through 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 sea-level change. Further analysis demonstrates that the observed halosteric changes and their basin partitioning are consistent with CMIP5 simulations that include anthropogenic CO₂ forcings (Historical), but are found to be inconsistent with simulations that exclude anthropogenic forcings (HistoricalNat). This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. IM release number is: LLNL-JRNL-653602