Seaice ice shelves

Sea-ice ice shelves are normally formed by a combination of thickening by snow accumulating on the surface, and freezing of seawater. Movement and deformation in such a shelf is entirely determined by the weight of the ice mass. Sea-ice ice shelves exist where annual temperatures are sufficiently low for ice to form and where embayments and islands

Figure 4.1 Tentative temperature profiles through polar, subpolar and temperate glaciers. (Adapted from Skinner and Porter, 1987)

Temperature (°C)

Temperature (°C)

Temperate Glaciers

Figure 4.1 Tentative temperature profiles through polar, subpolar and temperate glaciers. (Adapted from Skinner and Porter, 1987)

provide anchor points for sea ice to thicken. Examples of sea-ice ice shelves are found in the Canadian and Greenland High Arctic.

4.2.1.13 Composite ice shelves

Composite ice shelves are formed where floating glaciers and sea ice are protected from currents and wave disruption. A good example of such an ice shelf is that at Cape Alfred Ernest on the NW coast of Ellesmere Island in the Canadian Arctic. Composite ice shelves are also present in Antarctica.

4.2.1.14 Ice rises

Ice rises form where floating ice shelves thicken sufficiently to be grounded on offshore shoals and islands. Ice rises are normally formed either by thickening due to surface accumulation or by overriding by the ice shelf. In the first case the ice rise will have a radial flow pattern independent of the general flow direction of the surrounding ice shelf. Where glacier ice shelves override offshore shoals, they normally become heavily crevassed, forming ice rumples. Several examples exist within the Antarctic ice shelves, for example, Roosevelt Island in the Ross ice shelf, and the Gipps Ice Rise in the Larsen ice shelf.

4.2.2 Classification based on physical properties (temperature distribution)

The ice temperature is an important factor for a variety of glacial processes, such as glacier flow, meltwater drainage, and subglacial erosion and deposition. An important distinction is therefore made between temperate ice (at the pressure melting point) and polar ('cold') ice (below the pressure melting point) (Fig. 4.1). In addition, subpolar or polythermal glaciers are glaciers which are temperate in their inner and deeper parts, but with cold-based margins (Paterson, 1994). As more information on temperature distribution in glaciers and ice sheets becomes available, it is now recognized that this classification is too simple, and many glaciers are difficult to classify according to this scheme. The terms temperate or wet-based ice and cold or cold-based ice are now widely used for ice at and below the pressure melting point, respectively.

In polar/cold glaciers, the entire ice mass is below the pressure melting point. The term 'pressure melting point' may be misleading, because the ice may contain 'impurities' (glacier ice consists normally of ice, water, air, salts and carbon dioxide) and therefore there may not be a single distinct melting point determined only by pressure. In subpolar/ polythermal glaciers, the temperature in the ice mass is either below or at the pressure melting point. In temperate glaciers, the major part of the ice mass is at the pressure melting point during the summer season.

There is, however, no clear boundary between the different glacier types. On several glaciers all three temperature conditions may be present simultaneously. Expressions like dynamically/climatically, active/inactive glaciers as a result of movement and mass exchange are also used. Maritime and continental glaciers may also be utilized to classify glaciers according to their proximity to the coast and the amount of precipitation falling upon them.

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