Sea Ice and Icebergs Overview

Sea ice is frozen seawater that floats on the ocean's surface and is produced when saline ocean water is cooled below its freezing temperature of approximately -1.5°C.

The two types of ice encountered at sea are sea ice, and icebergs.

Icebergs originate from the frigid zone in the North Atlantic area and in both the frigid and temperate zones in the Antarctic.

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<p>Sea Ice interacts with the climate system. It helps with the heat exchange between the atmosphere and the polar regions as the white surface colour of the sea ice, which has a high reflective index. The high reflective index causes most of the sun's incoming solar radiation to be reflected back out to space, thus keeping the polar regions cool. Sea Ice also interacts with ocean currents and this interaction occurs when the cooling of surface water increases its density, and it sinks, and warmer, less dense surface water flows to replace sinking water.</p> Signup and view all the answers

<p>The development of sea ice begins with the formation of needle-shaped crystals called frazil ice. These crystals tend to float with their long axis vertically, and they give the sea an oily appearance. The Frazil ice crystals then thicken and congeal to form a greasy or soupy layer on the sea surface known as grease ice. Alternatively, falling snow crystals can produce slush. In the next stage, Shuga ice develops, consisting of spongy lumps a few centimetres across. All the above are classified generally as new ice. Nilas is a thin, elastic crust of ice, easily bending on waves or swells, or under pressure, thrusting in a pattern of interlocking fingers. It has a matt surface and is up to 10 cm in thickness. Nilas ice can be subdivided into dark nilas and light nilas; ice rinds. This is followed by pancake ice, consisting of flat pieces, roughly circular in shape, often with a rim around the edge due to rubbing against adjacent pieces. The pancakes gradually join to form a more or less continuous ice sheet, called young ice; this can also be broken up by wave action. Young ice eventually thickens and becomes field ice or pack ice, which is a generic term for all fully developed sea ice floating on the ocean and not attached to the shore; it varies in thickness from a few inches to several feet. Individual pieces of pack ice more than 20 metres across are called floes and the pack is termed 'open', 'very open', 'close' or ‘very close' depending on the distance between the floes. Very close pack leaves little or no water visible. Pack ice originating in Arctic or Antarctic waters may be several feet thick and very uneven due to hummocking (piling up) by the waves. Fast ice is sea ice that is &quot;fastened&quot; to the coastline, to the sea floor along shoals or to grounded icebergs. Fast ice may either grow in place from the seawater or by freezing pieces of drifting ice to the shore or other anchor sites. Unlike drift (or pack) ice, fast ice does not move with currents and winds.</p> Signup and view all the answers

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<p>The main preventative measures include: reduction in speed, change of heading, ship's officers to be made aware of the potential dangers of ice accretion and heading into warmer waters.</p> Signup and view all the answers

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<p>Some of the causes of shipboard ice accretion include: Sea spray hitting the vessel with the air temperature being at least minus 2°C. Fog freezing on the structure of your vessel. Rain Freezing on the structure of your vessel. Seas entering your vessel and freezing up. Freshwater leaking or being discharged from a pipe on your vessel.</p> Signup and view all the answers

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<p>A full icing allowance is defined as an additional pressure of 1 kN/m² (100 mm of ice) applied to all exposed horizontal or near horizontal surfaces and 0,25 kN/m² (25 mm of ice) applied to all exposed vertical surfaces.</p> Signup and view all the answers

<p>A half icing allowance is defined as an additional pressure of 0,5 kN/m² (50 mm of ice) applied to all exposed horizontal or near horizontal surfaces and 0,18 kN/m² (18 mm of ice) applied to all exposed vertical surfaces.</p> Signup and view all the answers

<p>For vessels operating in areas where ice accretion IS likely to occur, the following Icing allowance should be made in the stability calculations: 30 kg per square metre on exposed weather decks and gangways; 7.5 kg per square metre for projected lateral area of each side of the vessel above the water plane; The projected lateral area of discontinuous surfaces of rail, sundry booms, spars (except masts) and rigging of vessels having no sails and the projected lateral area of other small objects should be computed by increasing the total projected area of continuous surfaces by 5% and the static moments of this area by 10%.</p> Signup and view all the answers

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<p>Other icing allowances may apply in the areas defined above in 1., 3., 4. and 5. known to have icing conditions significantly different from those described in 6.3.1, ice accretion requirements of one-half to twice the required allowance may be applied; and Within the area defined in 2., where ice accretion in excess of twice the allowance required by 1. may be expected, more severe requirements than those given in 1 may be applied.</p> Signup and view all the answers

<p>The diminution of ice takes place in the following ways: Calving is the breaking of ice from a glacier or iceberg, ice front, ice shelf, crevasse. Melting: caused by warm air and or sunlight. Warm ocean currents, such as underwater melting will result in toppling and calving. Erosion: caused by the erosive action of wind and waves.</p> Signup and view all the answers