ICE DEVELOPMENT

METEOROLOGY LEVEL II: Ice Formation and Vessel Icing

Main Types of Floating Ice

  • Freezing Point of Seawater:

    • Decreases as salt concentration increases.

    • At typical salinity, it freezes at approximately -2 °C.

    • The coldest recorded seawater was -2.6 °C, measured in 2010 under an Antarctic glacier.

  • Freezing Point of Fresh Water:

    • Defined as 0 °C for the liquid to solid phase transition.

Sea Ice Observations

  • Parameters of Sea Ice:

    • Concentration: Fraction of the sea surface covered by ice, reported in tenths.

    • Stage of Development: Characteristics inferred from visible features, age, and conditions prior to observations.

    • Form: Horizontal shape and dimensions; freeboard is the height above sea surface.

Arctic and Antarctic Regions

  • Differences in Climate and Ice Regimes:

    • Arctic: Basin approximately 3,000 m deep, ice thickness of about 4 m. Annual mean temperature is -20°C.

    • Antarctic: Covered by a continent with an ice cap up to 3,000 m thick and an annual mean temperature of about -49°C.

Antarctic Ice Cap

  • Comprises over 90% of the Earth's permanent ice, covering nearly 14 million square km.

  • Calving results in thousands of icebergs, mostly melting during summer.

Greenland Ice Cap

  • Covers 1,710,000 square kilometres, approximately 80% of Greenland's surface.

  • Second largest ice body globally, nearly 2,400 km long, 1,100 km wide at northern margin.

Glaciers

  • Definition: Dense, persistent moving ice body formed by snow accumulation exceeding melting over years.

  • They deform, flow, and create features like crevasses and moraines, distinct from sea or lake ice.

Types of Glaciers

  • Inland ice sheets, ice shelves, ice streams, ice caps, ice piedmonts, cirque glaciers, mountain (valley) glaciers.

Floating Ice Overview

  • Definitions:

    • Sea Ice: Ice formed at sea.

    • Lake Ice: Ice formed on lakes.

    • River Ice: Ice formed on rivers.

    • Ice of Land Origin: Ice that originates from land or ice shelves.

Sea Ice Stages of Development

  • Frazil Ice: Fine ice needles or plates in water.

  • Grease Ice: Thin skin of frazil crystals on the sea surface.

  • Slush: Snow mixed with water.

  • Shuga: Accumulation of spongy lumps.

  • Nilas: Thin, elastic crust under 10 cm thick.

  • Ice Rind, Young Ice, Grey Ice (10-15 cm thick), Grey-White Ice (15-30 cm thick).

Old Ice

  • Characteristics: Survived at least one summer's melt.

  • 2 types:

    • Second Year Ice: Survived one summer, thicker and higher above water.

    • Multi-Year Ice: Survived multiple summers, almost salt-free, develops intricate drainage systems.

Lake Ice Stages of Development

  • Thickness Categories:

    • New Lake Ice: <5 cm.

    • Thin Lake Ice: 5-15 cm.

    • Medium Lake Ice: 15-30 cm.

    • Thick Lake Ice: 30-70 cm.

    • Very Thick Lake Ice: >70 cm.

Ice of Land Origin: Terminology

  • Firn: Dense old snow.

  • Glacier Ice: Ice from glaciers, including that found in icebergs.

  • Ice Wall: Cliff-like seaward margin of a glacier.

  • Ice Stream: Inland ice sheet segment that flows rapidly.

Iceberg Types

d- Iceberg Features:

  • Tabular, Domed, Pinnacled, Wedged, Dry-docked, Blocky.

  • Sizes: Small (<5 m), Medium (5-15 m), Large (16-45 m), Very Large (>75 m).

Ice Motion Processes

  • Diverging: Ice fields moving apart, reducing concentration.

  • Compacting: Ice pieces coming together, increasing concentration.

  • Shearing: Different directional ice motion causing rotational forces.

Ice Surface Features

  • Types:

    • Rafted Ice, Ridge, New Ridge, Weathered Ridge, Humock.

    • Distinct features based on aging and displacement due to pressure.

Ice and Shipping

  • Safety Terms:

    • Beset: Vessel surrounded by ice. Unable to move.

    • Ice-Bound: Navigation prevented by ice except w/icebreaker assistance.

    • Nipped: Ice pressing forcibly against a ship - danger to shipping

    • Difficult Area: Severity of ice condition where navigation is difficult.

    • Easy Area: Ice conditions in an area are not difficult to navigate.

    • Iceport: Safe area for a vessel - temporary, ships can moor alongside and unload directly onto ice itself.

Icebergs in the North Atlantic

  • Origin from West Greenland glaciers, producing 10,000-15,000 annually, with only about 1% reaching the Atlantic.

Monitoring Icebergs

  • The International Ice Patrol (IIP) coordinates iceberg advisories in North Atlantic shipping lanes, providing critical safety information.

  • Icebergs spotted in various regions including Atlantic and around Antarctic ice shelves.

Indications of Ice