Sea Ice (Ice Bergs)

Primary reference(s)

WMO, 2015. Manual on the Global Observing System: Volume 1 – Global aspects: Annex V to the WMO Technical Regulations: WMO No. 544. World Meteorological Organization (WMO). Accessed 5 December 2019.

Additional scientific description

The presence of sea ice in polar and subpolar oceans is a defining environmental factor that interacts with weather and climate and impacts on the ecology and human activities in these regions. Sea ice is also a significant natural hazard, both through direct interaction with assets and infrastructure and through the indirect impacts of variability and rapid changes in its distribution, in particular in Arctic and subarctic regions.

There are three types of sea-ice hazard: broad, long-term hazards and risks associated with a rapid reduction in (summer) ice volume and extent; near-term hazards resulting from changes in sea-ice extent and dynamics such as increased coastal erosion and threats to coastal infrastructure; and immediate risks and the potential for disasters derived from the combination of sea-ice hazards and human activities such as shipping or offshore resource development (Eicken and Mahoney, 2015).

Owing to a wide range of possible causes, preventing disasters and mitigating hazards requires approaches that address a multitude of factors. Hazard and risk maps are one option to help in the long-term planning and coordination of emergency response assets. Such maps do not appear to be available at the regional scale in the Arctic, although national ice forecasting services may generate local maps that indicate ice severity as a hazard indicator. For example, the Chinese Marine Environmental Forecasting Center’s Ice Severity Zones (Zhang et al., 2013) or the Barnett Ice Severity Index used in the United States (Eicken et al., 2009; Eicken and Mahoney, 2015).

Ice crystals form at the surface of the ocean mixed layer. Under sustained heat loss these ice crystals aggregate and can form a solid layer and up to several metres thick. During this process the solid ice expels salt (brine rejection), which increases the salinity of the underlying water and can initiate convective mixing in the ocean. In a few places where this cold, salty water is dense enough, it can sink via overflowing plumes along the bottom topography to reach the ocean abyss. This newly formed dense water generally flows slowly at depth towards the equator.

A thick sea-ice layer restricts wind and wave action near coastlines, lessening coastal erosion and protecting ice shelves. Sea ice also creates an insulating cap across the ocean surface, which reduces evaporation and heat loss to the atmosphere. As a result, the weather over ice-covered areas tends to be colder and drier than it would be without ice (Scott and Hansem, 2016).

Metrics and numeric limits

Not available.

Examples of drivers, outcomes and risk management

Sea Ice Trackers and Analysis: The Norwegian Meteorological Institute gives access to the latest products and information about sea ice via its website. It provides satellite imagery, operational ice charts, automatic sea ice analysis, and sea ice trackers, etc (Norwegian Meteorological Institute, no date).