The Impact of Melting Ice on Ocean Waters

Ice melts when it is in contact with ocean waters that have temperatures above the in situ freezing point. The product is a mixture of meltwater and seawater having properties intermediate between those of the two components. Density is one of the properties that is affected, and this has important implications for how the melt-induced changes are eventually manifested. Although the direct impact of melting is to cool and dilute the ocean, subsequent convection can carry the products of melting to parts of the water column where they are comparatively warm and salty. These principles are illustrated with a set of observations from the continental shelf of the Amundsen Sea. Measurements made near a floating glacier are used to calculate the concentration of meltwater in the water column. Concentrations approaching 2% are associated with comparatively high temperatures, low dissolved oxygen concentrations, and negligible stable isotope anomalies. The impact of drifting icebergs on the Southern Ocean is discussed. Over most of the area to the south of the Polar Front, melting effects a transfer of heat from the Circumpolar Deep Water to the overlying winter water. The resultant net heat flux over the entire area is small, but locally it may exceed 100 W m−2.