Ocean-Ice Shelf Interaction

The accelerating rate of mass loss of the Antarctic and Greenland ice sheets, responsible for global sea level rise, is closely linked to warming of the polar oceans.

Driven by gravity, ice streams transport inland (meteoric) ice towards the ocean. As they encounter coastal embayments, they spread out like a dough. This causes a thinning often up to the point where the ice starts to float – an ice shelf is born. Meteoric ice floats on sea water because of its density being smaller (910 kilograms per cubic meter) compared to the density of sea water (1028 kilograms per cubic meter).

An ice shelf is part of an ice sheet and floats on the ocean, but it rests on the sea floor at its fringes and on embedded islands. Contact with the sea floor slows down the seaward movement of shelf ice and thus the ice streams draining the ice sheet. Enhanced melting at the ice shelf base relaxes the braking force, e.g., if the ice detaches from embedded rumples and islands.

Only ice transported from inland to the ocean contributes to sea level rise as it replaces the volume of water of equal weight (Archimedean principle). A floating ice shelf already replaced the ocean water.  Thus, melting ice shelves as well as icebergs do not contribute to sea level rise. Keep an eye on the water level while an ice cube melts in a glass of water.

Photo: Yannick Kern



Dr. Hartmut Hellmer