The Arctic ice pack is the
sea ice
Sea ice arises as seawater freezes. Because ice is less dense than water, it floats on the ocean's surface (as does fresh water ice, which has an even lower density). Sea ice covers about 7% of the Earth's surface and about 12% of the world's oce ...
cover of the
Arctic Ocean
The Arctic Ocean is the smallest and shallowest of the world's five major oceans. It spans an area of approximately and is known as the coldest of all the oceans. The International Hydrographic Organization (IHO) recognizes it as an ocean, a ...
and its vicinity. The Arctic ice pack undergoes a regular seasonal cycle in which ice melts in spring and summer, reaches a minimum around mid-September, then increases during fall and winter. Summer ice cover in the
Arctic
The Arctic ( or ) is a polar regions of Earth, polar region located at the northernmost part of Earth. The Arctic consists of the Arctic Ocean, adjacent seas, and parts of Canada (Yukon, Northwest Territories, Nunavut), Danish Realm (Greenla ...
is about 50% of winter cover. Some of the ice survives from one year to the next. Currently, 28% of Arctic
basin sea ice is
multi-year ice
Sea ice arises as seawater freezes. Because ice is less dense than water, it floats on the ocean's surface (as does fresh water ice, which has an even lower density). Sea ice covers about 7% of the Earth's surface and about 12% of the world's oc ...
, thicker than seasonal ice: up to thick over large areas, with ridges up to thick. The regular seasonal cycle there has been an underlying trend of
declining sea ice in the Arctic in recent decades as well.
Climatic importance
Energy balance effects
Sea ice
Sea ice arises as seawater freezes. Because ice is less dense than water, it floats on the ocean's surface (as does fresh water ice, which has an even lower density). Sea ice covers about 7% of the Earth's surface and about 12% of the world's oce ...
has an important effect on the heat balance of the
polar
Polar may refer to:
Geography
Polar may refer to:
* Geographical pole, either of two fixed points on the surface of a rotating body or planet, at 90 degrees from the equator, based on the axis around which a body rotates
* Polar climate, the c ...
oceans, since it insulates the (relatively) warm ocean from the much colder air above, thus reducing heat loss from the oceans. Sea ice is highly
reflective of solar radiation, reflecting about 60% of incoming
solar radiation
Solar irradiance is the power per unit area (surface power density) received from the Sun in the form of electromagnetic radiation in the wavelength range of the measuring instrument.
Solar irradiance is measured in watts per square metre (W/m ...
when bare and about 80% when covered with snow. This is due to a feedback known as the albedo effect. This is much greater than the reflectivity of the sea (about 10%) and thus the ice also affects the absorption of sunlight at the surface.
Hydrological effects
The sea ice cycle is also an important source of dense (saline) "
bottom water
Bottom water is the lowermost water mass in a water body, by its bottom, with distinct characteristics, in terms of physics, chemistry, and ecology.
Oceanography
Bottom water consists of cold, dense water near the ocean floor. This water is charac ...
." When sea water freezes it leaves most of its salt content behind. The remaining surface water, made dense by the extra salinity, sinks and produces dense
water mass
An oceanographic water mass is an identifiable body of water with a common formation history which has physical properties distinct from surrounding water. Properties include temperature, salinity, chemical - isotopic ratios, and other physical ...
es such as
North Atlantic Deep Water
North Atlantic Deep Water (NADW) is a deep water mass formed in the North Atlantic Ocean. Thermohaline circulation (properly described as meridional overturning circulation) of the world's oceans involves the flow of warm surface waters from the s ...
. This production of dense water is essential in maintaining the
thermohaline circulation
Thermohaline circulation (THC) is a part of the large-scale ocean circulation that is driven by global density gradients created by surface heat and freshwater fluxes. The adjective ''thermohaline'' derives from '' thermo-'' referring to temper ...
, and the accurate representation of these processes is important in
climate model
Numerical climate models use quantitative methods to simulate the interactions of the important drivers of climate, including atmosphere, oceans, land surface and ice. They are used for a variety of purposes from study of the dynamics of the cl ...
ling.
Odden
In the Arctic, a key area where
pancake ice
Pancake ice is a form of sea ice that consists of round pieces of ice with diameters ranging from 30 centimetres (12 in) to 3 metres (9.8 ft) and thicknesses up to 10 centimetres (3.9 inches), depending on the local conditions. It forms as a resu ...
forms the dominant ice type over an entire region is the so-called
Odden ice tongue in the
Greenland Sea
The Greenland Sea is a body of water that borders Greenland to the west, the Svalbard archipelago to the east, Fram Strait and the Arctic Ocean to the north, and the Norwegian Sea and Iceland to the south. The Greenland Sea is often defined as p ...
. The Odden (the word is
Norwegian
Norwegian, Norwayan, or Norsk may refer to:
*Something of, from, or related to Norway, a country in northwestern Europe
* Norwegians, both a nation and an ethnic group native to Norway
* Demographics of Norway
*The Norwegian language, including ...
for ''the headland'') grows eastward from the main East Greenland ice edge in the vicinity of 72–74°N during the winter because of the presence of very cold polar surface water in the
Jan Mayen Current
Jan, JaN or JAN may refer to:
Acronyms
* Jackson, Mississippi (Amtrak station), US, Amtrak station code JAN
* Jackson-Evers International Airport, Mississippi, US, IATA code
* Jabhat al-Nusra (JaN), a Syrian militant group
* Japanese Article Numb ...
, which diverts some water eastward from the
East Greenland Current
The East Greenland Current (EGC) is a cold, low- salinity current that extends from Fram Strait (~80N) to Cape Farewell (~60N). The current is located off the eastern coast of Greenland along the Greenland continental margin. The current cuts th ...
at that latitude. Most of the old ice continues south, driven by the wind, so a cold open water surface is exposed on which new ice forms as
frazil
Frazil ice is a collection of loose, randomly oriented ice crystals millimeter and sub-millimeter in size, with various shapes, e.g. elliptical disks, dendrites, needles and of an irregular nature. Frazil ice forms during the winter in open-wate ...
and pancake in the rough seas.
Extent and volume of sea ice and their trends
Records of Arctic Sea ice from the United Kingdom's
Hadley Centre for Climate Prediction and Research
The Met Office Hadley Centre — named in honour of George Hadley — is one of the United Kingdom's leading centres for the study of scientific issues associated with climate change. It is part of, and based at the headquarters of the Met Of ...
go back to the turn of the 20th century, although the quality of the data before 1950 is debatable. Reliable
measurements of sea ice edge begin within the satellite era. From the late 1970s, the
Scanning Multichannel Microwave Radiometer The Scanning Multichannel Microwave Radiometer (SMMR) ronounced ''simmer''was a five-frequency microwave radiometer flown on the Seasat and Nimbus 7 satellites. Both were launched in 1978, with the Seasat mission lasting less than six months until ...
(SMMR) on
Seasat
Seasat was the first Earth-orbiting satellite designed for remote sensing of the Earth's oceans and had on board one of the first spaceborne synthetic-aperture radar (SAR). The mission was designed to demonstrate the feasibility of global sa ...
(1978) and
Nimbus 7
Nimbus 7 (also called Nimbus G) was a meteorological satellite. It was the seventh and last in a series of the Nimbus program.
Launch
Nimbus 7 was launched on October 24, 1978, by a Delta rocket from Vandenberg Air Force Base, California, Uni ...
(1978–87) satellites provided information that was independent of solar illumination or meteorological conditions. The frequency and accuracy of passive microwave measurements improved with the launch of the DMSP F8
Special Sensor Microwave/Imager The Special Sensor Microwave/Imager (SSM/I) is a seven-channel, four-frequency, linearly polarized passive microwave radiometer system.Hollinger, J.P. 1989: ''DMSP Special Sensor Microwave/Imager Calibration/Validation''. Final Report, Vol. I., Spac ...
(SSMI) in 1987. Both the
sea ice area and
extent are estimated, with the latter being larger, as it is defined as the area of ocean with at least 15%
sea ice
Sea ice arises as seawater freezes. Because ice is less dense than water, it floats on the ocean's surface (as does fresh water ice, which has an even lower density). Sea ice covers about 7% of the Earth's surface and about 12% of the world's oce ...
.
A modeling study of the 52-year period from 1947 to 1999 found a statistically significant trend in Arctic ice volume of −3% per decade; splitting this into wind-forced and temperature forced components shows it to be essentially all caused by the temperature forcing. A computer-based, time-resolved calculation of sea ice volume, fitted to various measurements, revealed that monitoring the ice volume is much more significant for evaluating sea ice loss than pure area considerations.
The ice extent trends from 1979 to 2002 have been a statistically significant Arctic sea ice decrease of −2.5% ± 0.9% per decade during those 23 years.
[Cavalieri et al. 2003.] Climate models simulated this trend in 2002.
The September minimum ice extent trend for 1979–2011 declined by 12.0% per decade during 32 years.
In 2007, the minimum extent fell by more than a million square kilometers, the biggest decline since accurate satellite data has been available, to . New research shows the Arctic Sea ice to be melting faster than predicted by any of the 18 computer models used by the
Intergovernmental Panel on Climate Change
The Intergovernmental Panel on Climate Change (IPCC) is an intergovernmental body of the United Nations. Its job is to advance scientific knowledge about climate change caused by human activities. The World Meteorological Organization (WMO) a ...
in preparing its 2007 assessments. In 2012, a new record low of about was reached.
In the overall mass balance, the volume of
sea ice
Sea ice arises as seawater freezes. Because ice is less dense than water, it floats on the ocean's surface (as does fresh water ice, which has an even lower density). Sea ice covers about 7% of the Earth's surface and about 12% of the world's oce ...
depends on the thickness of the ice as well as the areal extent. While the satellite era has enabled better measurement of trends in areal extent, accurate ice thickness measurements remain a challenge. "Nonetheless, the extreme loss of this summer's sea ice cover and the slow onset of freeze-up portends lower than normal ice extent throughout autumn and winter, and the ice that grows back is likely to be fairly thin". As more and more of the sea ice is thinner
first-year ice the greater effect storms have on its stability with turbulence resulting from major
extratropical cyclone
Extratropical cyclones, sometimes called mid-latitude cyclones or wave cyclones, are low-pressure areas which, along with the anticyclones of high-pressure areas, drive the weather over much of the Earth. Extratropical cyclones are capable of ...
s resulting in extensive fractures of sea ice.
File:2012 Arctic Ice Extent-aug25.png, alt=Ice extent as of August 25, 2012. Gray area indicates ± two standard deviations from 1979 to 2000 averages., Ice extent as of 25 August 2012. Gray area indicates ± two standard deviations from 1979 to 2000 averages.
File:Arctic Extent 1978-2007.png, alt=Arctic sea ice extent, 1978 to 2007., Arctic sea ice extent, 1978 to 2007
File:Plot arctic sea ice volume.svg, The development of Arctic sea ice volume as determined by measurement corrected numerical simulation shows probability of total sea ice loss in summer for the near future.[Zhang, Jinlun and D.A. Rothrock]
Modeling global sea ice with a thickness and enthalpy distribution model in generalized curvilinear coordinates
Mon. Wea. Rev. 131(5), 681–697, 2003.
File:Ice-floe params hg.png, alt=Scientific parameter to quantify the extent of sea ice., Scientific parameter to quantify the extent of sea ice
File:2015 Cycle Arctic.png, alt=Cycle plot of Arctic sea ice area and extent by month, 1979 to 2015., Cycle plot of Arctic sea ice area and extent by month, 1979 to 2015
See also
*
Arctic sea ice ecology and history
The Arctic sea ice covers less area in the summer than in the winter. The multi-year (i.e. perennial) sea ice covers nearly all of the central deep basins. The Arctic sea ice and its related biota are unique, and the year-round persistence of th ...
*
Global warming
In common usage, climate change describes global warming—the ongoing increase in global average temperature—and its effects on Earth's climate system. Climate change in a broader sense also includes previous long-term changes to E ...
*
Iceberg
An iceberg is a piece of freshwater ice more than 15 m long that has broken off a glacier or an ice shelf and is floating freely in open (salt) water. Smaller chunks of floating glacially-derived ice are called "growlers" or "bergy bits". The ...
*
Polar ice cap
A polar ice cap or polar cap is a high-latitude region of a planet, dwarf planet, or natural satellite that is covered in ice.
There are no requirements with respect to size or composition for a body of ice to be termed a polar ice cap, nor a ...
*
Polynya
A polynya () is an area of open water surrounded by sea ice. It is now used as a geographical term for an area of unfrozen seawater within otherwise contiguous pack ice or fast ice. It is a loanword from the Russian полынья (), which re ...
*
Shelf ice
Shelf ice is ice that forms when a portion of a lake surface freezes. It is often then washed upon the shore. The phenomenon is common within the Great Lakes.
Formation
Shelf ice forms from float ice. Float ice is like drift ice, but seldo ...
*
Antarctic sea ice
Antarctic sea ice is the sea ice of the Southern Ocean. It extends from the far north in the winter and retreats to almost the coastline every summer, getting closer and closer to the coastline every year due to sea ice melting. Sea ice is froze ...
References
External links
Global Sea Ice Extent and Concentration (NSIDC)Sea ice extent graphs since 1979 (NSIDC)Sea Ice Index (NSIDC)NOAA Arctic Program"Ice-free Arctic could be here in 23 years" (2007)
{{Arctic topics
Sea ice
Glaciology
Arctic Ocean
Earth phenomena
Articles containing video clips
Climate change and the environment