Mapping steric sea level from satellite altimetry, GRACE/GRACE-FO, and Argo.
Event: 2023 Ocean Surface Topography Science Team Meeting
Session: Synergies between Argo, GRACE and Altimetry
Presentation type: Type Oral
Contribution: PDF file
Two major components of sea level rise are changes in steric sea level (eg. density changes) and changes in mass (eg. water additions due to ice melt). Recent studies have derived steric sea level primarily from in situ observations from the Argo Program. One limitation to this method is the statistical mapping of sparse Argo float data, especially in eddy-rich regions. Here we conduct an initial study of combining satellite altimetry, GRACE/GRACE-FO, and Argo data to estimate monthly maps of steric sea level anomalies from January 2005 through December 2019. A consistent optimal interpolation method is used to recover the longest wavelength correlated patterns (while accounting for the eddy- and other mesoscale signals in the covariance function). Individual Argo profiles of temperature/salinity are used to compute density and vertically integrated steric sea level anomalies (as well as thermosteric and halosteric components) for the exact time and location of the Argo float. These are then optimally interpolated into monthly maps of steric sea level anomalies, using the altimetry-GRACE/GRACE-FO estimate as a first guess. An examination of the Argo updates to the initial guess reveal several areas with anomalously large updates away from eddy-rich regions. A further examination of the thermosteric/halosteric anomalies reveal significant departures from other floats in several regions after 2014. These are tied to a handful of Argo floats. Although flagged as “good” in the standard Argo climatology, removing these floats leads to a significant reduction in misfit between Argo and the initial guess, and a significant rise in global steric sea level since 2014.