The iceberg also may drag its keel on the continental shelf. Each of these processes has impacts for surface and deep-water animals[6]. The surface phytoplankton increases by up to one third in the wake of a large iceberg. Tracking icebergs provides information on ocean currents. Scientists can assess whether the number of icebergs is increasing[7, 8]. The input of freshwater may affect surface water currents and even sea ice formation[9]. Sea ice surrounds the polar regions. On average, sea ice covers up to 25 million km 2 , an area 2.
Sea ice is frozen ocean water. The sea freezes each winter around Antarctica. Each year, the extent of sea ice varies according to climate variability and long-term climate change. In the Arctic , sea ice extent is steadily decreasing, with a trend of Year-on-year variations reflect normal variability.
Because removal of sea ice changes the reflectivity of the Arctic, a diminishing sea-ice extent amplifies warming. Sea ice in the Antarctic is currently increasing[9]. This is associated with cooling sea surface temperatures in the Southern Ocean, in particular near the Ross Ice Shelf. Causes of this increasing Antarctic sea ice, which are contrasted with shrinking glaciers and ice shelves and warming deeper ocean current temperatures and atmospheric air temperatures, include changes to the Southern Annual Mode due to intensification and migration of the predominant Southern Ocean Westerlies, and cooler sea surface temperatures as a result of increased glacier and ice-shelf melting[9].
Glasser, N. Kulessa, A. Luckman, D. Jansen, E. King, P. Sammonds, T. Scambos, and K. Jezek, Journal of Glaciology , 55 : Gudmundsson, Longitudinal surface structures flowstripes on Antarctic glaciers. The Cryosphere , 6 : Scambos, J. Bohlander, M. Truffer, E. Pettit, and B. Davies, Journal of Glaciology , 57 : Cook, A. Vaughan, Overview of areal changes of the ice shelves on the Antarctic Peninsula over the past 50 years. The Cryosphere , 4 1 : Schwarz, J. Schodlok, Impact of drifting icebergs on surface phytoplankton biomass in the Southern Ocean: Ocean colour remote sensing and in situ iceberg tracking.
Long, D. Ballantyn, and C. Bertoia, Is the number of Antarctic icebergs really increasing? Eos, Transactions American Geophysical Union , 83 42 : Ice that forms each winter and melts each summer is known as annual ice, and is usually about six feet thick.
In the central Arctic, the ice never thaws completely in summer, and thus it is known as multi-year ice. This ice ranges in thickness from 15 feet to 25 feet. Why doesn't it just keep getting thicker and thicker? Multi-year ice eventually enters an equilibrium where the amount of new ice being formed on the bottom of the layer in winter is exactly balanced by the loss due to melting off the top in summer.
Mariners have adopted a number of different names for icebergs and pack ice. The following glossary of ice terms is from Bowditch's Glossary of Marine Navigation. Anchor ice. Submerged ice attached or anchored to the bottom, irrespective of the nature of its formation.
Bergy bit. A large piece of floating glacier ice, generally showing less than 5 meters above sea level but more than 1 meter and normally about to square meters in area. A typical bergy bit is about the size of a small house. Blue ice. The oldest and hardest form of glacier ice, distinguished by a slightly bluish or greenish color.
Brash ice. Accumulations of floating ice made up of fragments not more than 2 meters across, the wreckage of other forms of ice. Close pack ice. Compact pack ice. Consolidated pack ice. Fast ice. Sea ice which forms and remains attached to the shore, to an ice wall, to an ice front, between shoals or grounded icebergs.
Vertical fluctuations may be observed during changes of sea level. Fast ice may be formed in situ from the sea water or by freezing of pack ice of any age to the shore, and it may extend a few meters or several hundred kilometers from the coast.
Fast ice may be more than 1 year old and may then be prefixed with the appropriate age category old, second-year or multi-year. Fast-ice boundar y. The ice boundary at any given time between fast ice and pack ice. Fast-ice edge. The demarcation at any given time between fast ice and open water. First-year ice. Sea ice of not more than one winter's growth, developing from young ice, with a thickness of 30 centimeters to 2 meters.
Any relatively flat piece of sea ice 20 meters or more across. Floes are subdivided according to horizontal extent. A giant flow is over 5. A massive piece of sea ice composed of a hummock, or a group of hummocks frozen together, and separated from any ice surroundings. It may float showing up to 5 meters above sea level. Old snow which has recrystallized into a dense material.
Unlike snow, the particles are to some extent joined together; but, unlike ice, the air spaces in it still connect with each other. Frazil ice. Fine spicules or plates of ice, suspended in water. Glacier ice. Ice in, or originating from, a glacier, whether on land or floating on the sea as icebergs, bergy bits, or growlers.
A coating of ice, generally clear and smooth but usually containing some air pockets, formed on exposed objects by the freezing of a film of super cooled water deposited by rain, drizzle, fog, or possibly condensed from super cooled water vapor. Grease ice. Ice at that stage of freezing when the crystals have coagulated to form a soupy layer on the surface.
Grease ice is at a later stage of freezing than frazil ice and reflects little light, giving the sea a matte appearance. Grounded ice. Floating ice which is aground in shoal water. It extends less than 1 meter above the sea surface and its length is less than 20 feet 6 meters. Land ice can be labelled as ice sheets whereas sea ice can be labelled as ice shelves. An increase in global temperature caused by anthropogenic warming influences the quantity of polar ice.
Sea ice forms in the winter months and melts in the summer months, however in certain regions it remains year round. Sea ice is white which means it has a highly reflective surface, thus it has a high albedo.
This absorption heats up the ocean causing further more melting of ice. Both types of ice range over vast areas of the polar regions. Global sea ice on average covers nearly 25 million km 2 , the same size as the North American continent. Glaciers are land ice. Which can become sea ice when chunks of ice that break off and fall into the ocean and become icebergs. Lake ice is also considered land ice. Frigid, low density fresh water stays at the surface of a lake or river, forming a layer of ice on the surface.
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