Global ocean freshwater budget ($\dot{M}=R+I+P-E$)

With positive freshwater runoff $R$, net sea ice melt $I$ and precipitation $P$, and evaporation loss $E$, the ocean water-mass budget is $\dot{M}=R+I+P-E$. With salt-free ice and fixed total dissolved salt mass, mean salinity satisfies $\dot{S}/S=-\dot{M}/M$. Gross regional ice melt must not be substituted for net global melt without accounting for ice formation elsewhere and the averaging period.