Sea surrface density is derived from Aquarius science products and generated by the NASA Goddard Space Flight Center's Aquarius Data Processing System. It is very important because sea surface density drives formation of ocean water masses and three-dimensional ocean circulation. As water parcels sink and move through the ocean, their densities will be modified by mixing with other parcels of seawater. However, if the density signatures of all the end member water masses are known, this mixing can be "unraveled" to determine the proportions of their various source waters. This animation shows the changes of sea surface density from September 7, 2011 to May 20, 2015.