How Salty Is the Global Ocean: Weighing It All or Tasting It a Sip at a Time?

Global ocean mean salinity S over bar is a key indicator of the Earth's hydrological cycle and the exchanges of freshwater between land and ocean, but its determination remains a challenge. Aside from traditional methods based on gridded salinity fields derived from in situ measurements, we explore estimates of S over bar based on liquid freshwater changes derived from space gravimetry data corrected for sea ice effects. For the 2005-2019 period analyzed, the different S over bar series show little consistency in seasonal, interannual, and long-term variability. In situ estimates show sensitivity to choice of product and unrealistic variations. A suspiciously large rise in S over bar since similar to 2015 is enough to measurably affect halosteric sea level estimates and can explain recent discrepancies in the global mean sea level budget. Gravimetry-based S over bar estimates are more realistic, inherently consistent with estimated freshwater contributions to global mean sea level, and provide a way to calibrate the in situ estimates.

Automated summary

The determination of global ocean mean salinity remains a challenge, with different estimation methods showing little consistency in seasonal, interannual, and long-term variability. In situ measurements are sensitive to product choice and exhibit unrealistic variations, while gravity-based measurements are more realistic and provide a way to calibrate in situ estimates.