Sea Ice and Icebergs Overview

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Questions and Answers

What is sea ice?

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.

Name two types of ice encountered at sea.

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

Where do icebergs originate?

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

What are the terms for small and larger icebergs?

<p>Growler (A), Bergy Bit (D)</p> Signup and view all the answers

What is the importance of sea ice to the atmosphere?

<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

What are the stages of sea ice development, without the aid of diagrams?

<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

How can ice accretion affect the stability of a ship?

<p>All of the above (D)</p> Signup and view all the answers

How can ice accretion affect a ship's equipment?

<p>All of the above (F)</p> Signup and view all the answers

What are the main preventative safety measures to avoid ice accretion?

<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

What are some precautions to be taken prior to sailing into an ice area?

<p>All of the above (P)</p> Signup and view all the answers

Which of the following are indications of ice?

<p>All of the above (I)</p> Signup and view all the answers

What are five causes of shipboard ice accretion?

<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

How to remove ice accumulation from the upper works of a vessel?

<p>All of the above (E)</p> Signup and view all the answers

What does Full Icing allowance mean?

<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

What does Half Icing allowance mean?

<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

Name three (three) Icing Allowances that should be applied in the stability calculations applicable to vessels operating in areas where shipboard ice accretion is likely to occur?

<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

Which regions require a full icing allowance?

<p>All of the above (F)</p> Signup and view all the answers

In which areas do other icing allowances apply?

<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

Name three ways in which the diminution of ice takes place.

<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

Flashcards

Sea Ice

Frozen seawater that floats on the ocean's surface, formed when saline water cools below -1.5°C.

Icebergs

Pieces of ice that break off glaciers and ice shelves.

Growler

A small iceberg, less than 1 meter above water.

Bergy bit

A medium-sized iceberg, 1-5 meters above water.

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Frazil Ice

Needle-shaped ice crystals that float on the water surface.

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Grease Ice

A soupy layer of thickened frazil ice on the surface.

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Slush

Sea ice formed from falling snow on water

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Shuga Ice

Spongy lumps of sea ice, a few centimeters across.

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Nilas

Thin, elastic crust of ice, easily bending on waves.

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Pancake ice

Flat, roughly circular pieces of ice, often with rims.

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Young Ice

A more or less continuous sheet of ice formed from joined pancakes.

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Field Ice

Thickened young ice, also called pack ice.

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Pack Ice

A large area of interconnected sea ice floes (pieces).

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Floes

Individual pieces of ice in pack ice, more than 20 meters across.

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Fast Ice

Sea ice attached to the coastline, sea floor, or shoals.

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Importance of Sea Ice to Atmosphere

Sea ice reflects solar radiation, helping to cool polar regions and influencing heat exchange between atmosphere and ocean.

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Study Notes

Sea Ice

  • Sea ice is frozen seawater that floats on the ocean's surface.
  • Sea ice forms when saline ocean water cools below -1.5°C.
  • It forms in frigid zones and parts of temperate zones (particularly Antarctica) during winter.
  • Sea ice breaks up and spreads into temperate waters in spring.

Types of Sea Ice

  • Two types of floating ice are encountered at sea: sea ice and icebergs.
  • Icebergs break off glaciers and shelf ice.

Iceberg Origin

  • Icebergs originate in the frigid zones of the North Atlantic and Antarctic.
  • They can drift into temperate zones during the springtime.
  • Ice shelves have cracks and crevasses that cause ice to break off, forming icebergs.

Growler and Bergy Bit

  • Growlers are small icebergs, less than 1 meter above the waterline.
  • Bergy bits are larger icebergs, with 1 to 5 meters above the waterline.

Sea Ice and Atmosphere

  • Sea ice helps regulate heat exchange between the atmosphere and polar regions.
  • Its high reflectivity (white color) reduces the absorption of solar radiation, keeping the polar regions cool.
  • Sea ice interacts with ocean currents, with cooling surface water becoming denser and sinking, replaced by warmer, less dense water.

Stages of Sea Ice Development

  • Frazil Ice: Needle-shaped crystals float with their long axis vertical, giving the sea an oily appearance.
  • Grease Ice: Frazil ice thickens and congeals, forming a greasy layer on the sea surface.
  • Slush Ice: Falling snow crystals can form slush.
  • Shuga Ice: Consists of spongy lumps, generally as new ice.
  • Nilas Ice: Thin, elastic ice, easily bending on waves.
  • Pancake Ice: Flat pieces, roughly circular, joined to form continuous sheets.
  • Young Ice: Further thickening of pancake ice forms a more or less continuous sheet.
  • Pack Ice: Fully developed, unattached sea ice, varying in thickness.
  • Fast Ice: Sea ice attached to coastlines, shoals, or icebergs.

Ice Accretion Damage

  • Ice accretion significantly affects vessel operations and safety.
  • Added weight shifts the center of gravity, potentially causing capsizing or listing.
  • Increased stress on structures can lead to fatigue cracking or brittle fracture, especially in frigid conditions.
  • Icing on lifeboats, equipment, etc., threatens crew safety and impedes operations.
  • Deicing needs careful consideration and execution.

Preventing Ice Accretion

  • Reducing speed and changing direction is a crucial preventative measure against ice accretion.
  • Crew awareness of ice accretion hazards and its potential consequences.
  • Moving into warmer waters.

Ice Region Precautions

  • Precautions to take before sailing into an ice region include checking firefighting equipment (sprinkler system, extinguishers), ensuring adequate heating, and having appropriate personnel on duty (like lookouts).

Ice Indicators

  • Six indications of ice include iceblink, fog near the ice edge, dramatic temperature drops, seal herds and bird flocks away from land, ice cracking noise, and radar use.

Ice Accretion Causes

  • Sea spray freezing on the ship.
  • Rain freezing on the ship.
  • Seawater freezing inside the ship.
  • Leaks from freshwater pipes are a source of freezing water.

Removing Ice Accretion

  • Cold and hot water pressure.
  • Using ice-removing tools (axes, scrapers).
  • Heating.

Icing Allowance

  • Full icing allowance: 1 kN/m² (100 mm ice) on horizontal and 0.25 kN/m² (25 mm ice) on vertical exposed surfaces.
  • Half icing allowance: 0.5 kN/m² (50 mm ice) horizontal and 0.18 kN/m² (18 mm ice) vertical surfaces.
  • Icing in areas may also vary.

Ice Diminishment Mechanisms

  • Calving: Breaking off of ice from glaciers, icebergs, or ice shelves.
  • Melting: Due to warm air or sunlight.
  • Erosion: Due to wind and waves.

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