Sea ice

Influence on climate

Sea ice influences the Earth's climate in many ways: its high albedo affects the planet's heat budget; its thermal insulation controls heat and mass fluxes between the atmosphere and the polar oceans, and its role in destabilising the water column through brine rejection may drive deep convection. In addition, variations in the seasonal pattern of sea ice distribution are likely to be sensitive indicators of changes in the heat content of the upper ocean, itself a key marker for climatic change. The area of the planet's surface involved is enormous: the sea ice extent in the Antarctic alone varies from a minimum of 4 million sq km at the end of summer to a maximum of nearly 20 million sq km in winter (see NASA image left). However, the processes governing ice formation, especially in the outer part of the pack, are not well understood. Moreover, young ice is not well imaged by satellites, thus placing increased reliance on in situ studies.

Archives of sea ice data

Much historical data on sea ice extent is now available via the Internet. These data include satellite and ship observations and analyses spanning several decades. (Image: Young pancake ice, by courtesy of the Scott Polar Research Institute.)
 
 
 
 
 
 
 
 
 
 
 
 
 
 

A hazard to navigation

Increasingly, marine transportation, fishing and oil exploration activity are occurring in ice-covered waters in polar and sub-polar regions. In polar waters, ice and sometimes icebergs present a substantial obstacle to navigation by even ice-strengthened vessels. Thus, forecasts of ice formation, behaviour and decay make an important contribution to the safety of navigation. This has led to growing requirements for sea ice information services and WMO and national Meteorological Services have risen to the challenge. Very significant advances have been made since the loss of the SS Titanic. The collision with an iceberg provided the impetus which led to the development of the International Ice Patrol in the North West Atlantic Ocean. Today, regular provision of sea ice maps, forecasts and bulletins is an integral part of the operational programmes of national Meteorological Services whose nations conduct activities in the polar seas. To compound the concerns of mariners regarding pack ice and icebergs, the accumulation of ice on vessel superstructures due to spray freezing on contact (and to a lesser extent due to ice fog and freezing rain) is an added hazard in higher latitudes. Freezing spray occurs in conditions of strong winds, cold water and below freezing air temperatures. The build-up of ice from freezing spray can severely diminish a vessel's stability and, in the worst circumstances, ships have overturned and been lost due to this phenomenon. Consequently, warnings of freezing spray and ice accretion are an important component of marine weather forecasts in cold ocean regions. (Image: RV Polarstern in the ice, by courtesy of Alfred Wegener Institute.)

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