How Does Our Ocean "Pass the Salt"? Ask ECCO

Time evolution of globally averaged deep ocean salinity
Time evolution of globally averaged deep ocean salinity calculated as deviations from the temporal means from January 1993 to December 2014. Credit: Liu et al., 2019, Fig. 1b; image modified from open-source article.
Time evolution of globally averaged deep ocean salinity
Time evolution of globally averaged deep ocean salinity calculated as deviations from the temporal means from January 1993 to December 2014. Credit: Liu et al., 2019, Fig. 1b; image modified from open-source article.
[01-Aug-2019] When compared to the variable flux of freshwater at the ocean's surface, the amount of dissolved salt in our ocean basins is relatively stable. Thus, understanding changes in salinity is key to estimating the global net freshwater input into our ocean. Moreover, processes related to climate warming ­- such as ocean freshening from the melting of glaciers and ice sheets, and salt rejection during sea ice formation - have affected the vertical distribution of salt of in our seas.
To understand these types of connections, salinity and related dynamical processes must be reliably represented, both globally and over the ocean's full depth. So, investigators have used ECCO global state estimates, in which salt and heat budgets are explicitly closed, to examine how salinity has changed over two decades.
Horizontally averaged, the salt budget reveals trends within distinct ocean layers: some depths have freshened over time while others have become saltier. The study also focuses on the vertical redistribution of salt in the upper mile of the ocean, within the range of Argo profiling floats. These salt transport processes are parsed among ocean motion (e.g., currents and eddies), diffusion, and brine rejection, and knowing them permits more robust inferences about surface freshwater fluxes from observed salinity changes. Study results also reveal regional patterns including the essential role of vertical salt fluxes at high latitudes.

Reference

Liu, C., Liang, X., Ponte, R., Vinogradova, N., and Wang, O. (2019). Vertical Redistribution of Salt and Layered Changes in Global Ocean Salinity, Nat. Commun., 10, 3445, doi: 10.1038/s41467-019-11436-x.
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