Arctic ice pack

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NOAA projected Arctic changes Arctic Ice Thickness.gif
NOAA projected Arctic changes
This animation shows the Arctic Ocean melt during the summer of 2011.
This visual shows the Arctic sea ice change and the corresponding absorbed solar radiation change during June, July, and August from 2000 through 2014.

The Arctic ice pack is the sea ice cover of the Arctic Ocean 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 is about 50% of winter cover. [1] Some of the ice survives from one year to the next. Currently, 28% of Arctic basin sea ice is multi-year ice, [2] thicker than seasonal ice: up to 3–4 m (9.8–13.1 ft) thick over large areas, with ridges up to 20 m (65.6 ft) thick. Besides the regular seasonal cycle there has been an underlying trend of declining sea ice in the Arctic in recent decades as well.

Contents

Climatic importance

Energy balance effects

Sea ice has an important effect on the heat balance of the polar 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 when bare and about 80% when covered with snow. This is due to a feedback known as the albedo effect. [3] 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. [4] [5]

Hydrological effects

The sea ice cycle is also an important source of dense (saline) "bottom water." 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 masses such as North Atlantic Deep Water. This production of dense water is essential in maintaining the thermohaline circulation, and the accurate representation of these processes is important in climate modelling.

Odden

In the Arctic, a key area where pancake ice forms the dominant ice type over an entire region is the so-called Odden ice tongue in the Greenland Sea. The Odden (the word is Norwegian 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, which diverts some water eastward from the East Greenland Current 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 and pancake in the rough seas.

Location of the weather station Alert. Extension of the ice at 15 September 2008 (36 Mpx). Une partie de l'hemisphere nord de la Terre avec la banquise, nuage, etoile et localisation de la station meteo en Alert.jpg
Location of the weather station Alert. Extension of the ice at 15 September 2008 (36  M px).
Photo from on board the
MS Hanseatic, 27 August 2014:
Polar ice limit
(Record position 85deg40.7818' N, 135deg38.8735' E) Nordpolarmeer 1 2014-08-27.jpg
Photo from on board the
MS Hanseatic , 27 August 2014:
Polar ice limit
(Record position 85°40.7818 N, 135°38.8735 E)
In this animation, the Earth rotates slowly as the Arctic sea ice advances over time from 21 March 2014 to 3 August 2014.
Extent of Arctic ice
Arctic ice March 1946 20%25.jpg
Extent of Arctic ice, March 1946 (U.S. Navy)
Arctic ice October 1946 20%25.jpg
Extent of Arctic ice, October 1946 (U.S. Navy)

Records of Arctic Sea ice from the United Kingdom's Hadley Centre for Climate Prediction and Research 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 (SMMR) on Seasat (1978) and Nimbus 7 (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 (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.

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. [6]

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. [7] Climate models simulated this trend in 2002. [8] The September minimum ice extent trend for 1979–2011 declined by 12.0% per decade during 32 years. [9] In 2007, the minimum extent fell by more than a million square kilometers, the biggest decline since accurate satellite data has been available, to 4,140,000 km2 (1,600,000 sq mi). 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 in preparing its 2007 assessments. [10] In 2012, a new record low of about 3,500,000 km2 (1,400,000 sq mi) was reached. [11] [12]

In the overall mass balance, the volume of sea ice 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 cyclones resulting in extensive fractures of sea ice. [13]

Sea Ice Extent over the Arctic (OSI SAF data) [14] [15]

See also

Related Research Articles

<span class="mw-page-title-main">Cryosphere</span> Those portions of Earths surface where water is in solid form

The cryosphere is an all-encompassing term for the portions of Earth's surface where water is in solid form, including sea ice, lake ice, river ice, snow cover, glaciers, ice caps, ice sheets, and frozen ground. Thus, there is a wide overlap with the hydrosphere. The cryosphere is an integral part of the global climate system with important linkages and feedbacks generated through its influence on surface energy and moisture fluxes, clouds, precipitation, hydrology, atmospheric and oceanic circulation.

<span class="mw-page-title-main">Sea ice</span> Outcome of seawater as it freezes

Sea ice arises as seawater freezes. Because ice is less dense than water, it floats on the ocean's surface. Sea ice covers about 7% of the Earth's surface and about 12% of the world's oceans. Much of the world's sea ice is enclosed within the polar ice packs in the Earth's polar regions: the Arctic ice pack of the Arctic Ocean and the Antarctic ice pack of the Southern Ocean. Polar packs undergo a significant yearly cycling in surface extent, a natural process upon which depends the Arctic ecology, including the ocean's ecosystems. Due to the action of winds, currents and temperature fluctuations, sea ice is very dynamic, leading to a wide variety of ice types and features. Sea ice may be contrasted with icebergs, which are chunks of ice shelves or glaciers that calve into the ocean. Depending on location, sea ice expanses may also incorporate icebergs.

<span class="mw-page-title-main">Drift ice</span> Sea ice that is not attached to land

Drift ice, also called brash ice, is sea ice that is not attached to the shoreline or any other fixed object. Unlike fast ice, which is "fastened" to a fixed object, drift ice is carried along by winds and sea currents, hence its name. When drift ice is driven together into a large single mass, it is called pack ice. Wind and currents can pile up that ice to form ridges up to dozens of metres in thickness. These represent a challenge for icebreakers and offshore structures operating in cold oceans and seas.

<span class="mw-page-title-main">National Snow and Ice Data Center</span> U.S. information and referral center

The National Snow and Ice Data Center (NSIDC) is a United States information and referral center in support of polar and cryospheric research. NSIDC archives and distributes digital and analog snow and ice data and also maintains information about snow cover, avalanches, glaciers, ice sheets, freshwater ice, sea ice, ground ice, permafrost, atmospheric ice, paleoglaciology, and ice cores.

<span class="mw-page-title-main">Byrd Polar and Climate Research Center</span>

The Byrd Polar and Climate Research Center (BPCRC) is a polar, alpine, and climate research center at The Ohio State University founded in 1960.

<span class="mw-page-title-main">Polar ice cap</span> High-latitude region of an astronomical body with major parts covered in ice

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.

<span class="mw-page-title-main">Greenland Sea</span> Body of water

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 part of the Arctic Ocean, sometimes as part of the Atlantic Ocean. However, definitions of the Arctic Ocean and its seas tend to be imprecise or arbitrary. In general usage the term "Arctic Ocean" would exclude the Greenland Sea. In oceanographic studies the Greenland Sea is considered part of the Nordic Seas, along with the Norwegian Sea. The Nordic Seas are the main connection between the Arctic and Atlantic oceans and, as such, could be of great significance in a possible shutdown of thermohaline circulation. In oceanography the Arctic Ocean and Nordic Seas are often referred to collectively as the "Arctic Mediterranean Sea", a marginal sea of the Atlantic.

<span class="mw-page-title-main">Climate change in the Arctic</span> Impacts of climate change on the Arctic

Major environmental issues caused by contemporary climate change in the Arctic region range from the well-known, such as the loss of sea ice or melting of the Greenland ice sheet, to more obscure, but deeply significant issues, such as permafrost thaw, as well as related social consequences for locals and the geopolitical ramifications of these changes. The Arctic is likely to be especially affected by climate change because of the high projected rate of regional warming and associated impacts. Temperature projections for the Arctic region were assessed in 2007: These suggested already averaged warming of about 2 °C to 9 °C by the year 2100. The range reflects different projections made by different climate models, run with different forcing scenarios. Radiative forcing is a measure of the effect of natural and human activities on the climate. Different forcing scenarios reflect things such as different projections of future human greenhouse gas emissions.

<span class="mw-page-title-main">Polar amplification</span>

Polar amplification is the phenomenon that any change in the net radiation balance tends to produce a larger change in temperature near the poles than in the planetary average. This is commonly referred to as the ratio of polar warming to tropical warming. On a planet with an atmosphere that can restrict emission of longwave radiation to space, surface temperatures will be warmer than a simple planetary equilibrium temperature calculation would predict. Where the atmosphere or an extensive ocean is able to transport heat polewards, the poles will be warmer and equatorial regions cooler than their local net radiation balances would predict. The poles will experience the most cooling when the global-mean temperature is lower relative to a reference climate; alternatively, the poles will experience the greatest warming when the global-mean temperature is higher.

<span class="mw-page-title-main">Climate of the Arctic</span>

The climate of the Arctic is characterized by long, cold winters and short, cool summers. There is a large amount of variability in climate across the Arctic, but all regions experience extremes of solar radiation in both summer and winter. Some parts of the Arctic are covered by ice year-round, and nearly all parts of the Arctic experience long periods with some form of ice on the surface.

<span class="mw-page-title-main">Global Energy and Water Exchanges</span>

The Global Energy and Water Exchanges Project is an international research project and a core project of the World Climate Research Programme (WCRP).

<span class="mw-page-title-main">Arctic Ocean</span> Ocean in the north polar region

The Arctic Ocean is the smallest and shallowest of the world's five major oceans. It spans an area of approximately 14,060,000 km2 (5,430,000 sq mi) and is known as one of the coldest of oceans. The International Hydrographic Organization (IHO) recognizes it as an ocean, although some oceanographers call it the Arctic Mediterranean Sea. It has also been described as an estuary of the Atlantic Ocean. It is also seen as the northernmost part of the all-encompassing World Ocean.

<span class="mw-page-title-main">Polar seas</span> Collective term for the Arctic Ocean and the southern part of the Southern Ocean

Polar seas is a collective term for the Arctic Ocean and the southern part of the Southern Ocean. In the coldest years, sea ice can cover around 13 percent of the Earth's total surface at its maximum, but out of phase in the two hemispheres. The polar seas contain a huge biome with many organisms.

<span class="mw-page-title-main">Ice–albedo feedback</span> Positive feedback climate process

Ice–albedo feedback is a positive feedback climate process where a change in the area of ice caps, glaciers, and sea ice alters the albedo and surface temperature of a planet. Ice is very reflective, therefore it reflects far more solar energy back to space than the other types of land area or open water. Ice–albedo feedback plays an important role in global climate change. For instance, at higher latitudes, warmer temperatures melt the ice sheets. However, if warm temperatures decrease the ice cover and the area is replaced by water or land, the albedo would decrease. This increases the amount of solar energy absorbed, leading to more warming. The change in albedo acts to reinforce the initial alteration in ice area leading to more warming. Warming tends to decrease ice cover and hence decrease the albedo, increasing the amount of solar energy absorbed and leading to more warming. In the geologically recent past, the ice–albedo positive feedback has played a major role in the advances and retreats of the Pleistocene ice sheets. Inversely, cooler temperatures increase ice, which increases albedo, leading to more cooling.

<span class="mw-page-title-main">Measurement of sea ice</span> Records made for navigational safety and environmental monitoring

Measurement of sea ice is important for safety of navigation and for monitoring the environment, particularly the climate. Sea ice extent interacts with large climate patterns such as the North Atlantic oscillation and Atlantic Multidecadal Oscillation, to name just two, and influences climate in the rest of the globe.

Sea ice concentration is a useful variable for climate scientists and nautical navigators. It is defined as the area of sea ice relative to the total at a given point in the ocean. This article will deal primarily with its determination from remote sensing measurements.

Sea ice thickness spatial extent, and open water within sea ice packs can vary rapidly in response to weather and climate. Sea ice concentration are measured by satellites, with the Special Sensor Microwave Imager / Sounder (SSMIS), and the European Space Agency's Cryosat-2 satellite to map the thickness and shape of the Earth's polar ice cover. The sea ice volume is calculated with the Pan-Arctic Ice Ocean Modeling and Assimilation System (PIOMAS), which blends satellite-observed data, such as sea ice concentrations into model calculations to estimate sea ice thickness and volume. Sea ice thickness determines a number of important fluxes such as heat flux between the air and ocean surface—see below—as well as salt and fresh water fluxes between the ocean since saline water ejects much of its salt content when frozen—see sea ice growth processes. It is also important for navigators on icebreakers since there is an upper limit to the thickness of ice any ship can sail through.

<span class="mw-page-title-main">Arctic sea ice decline</span> Sea ice loss observed in recent decades in the Arctic Ocean

Sea ice in the Arctic has declined in recent decades in area and volume due to climate change. It has been melting more in summer than it refreezes in winter. Global warming, caused by greenhouse gas forcing is responsible for the decline in Arctic sea ice. The decline of sea ice in the Arctic has been accelerating during the early twenty‐first century, with a decline rate of 4.7% per decade. It is also thought that summertime sea ice will cease to exist sometime during the 21st century.

<span class="mw-page-title-main">Antarctic sea ice</span> Sea ice of the Southern Ocean

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. Sea ice is frozen seawater that is usually less than a few meters thick. This is the opposite of ice shelves, which are formed by glaciers; they float in the sea, and are up to a kilometre thick. There are two subdivisions of sea ice: fast ice, which are attached to land; and ice floes, which are not.

<span class="mw-page-title-main">Julienne Stroeve</span> American climatologist

Professor Julienne Christine Stroeve is a polar climate scientist known for her research on remote sensing of ice and snow. She is Professor of Polar Observation & Modelling at the Centre for Polar Observation and Modelling, University College London, Senior Canada-150 Research Chair in Climate Forcing of Sea Ice at the University of Manitoba, and a senior research scientist at the National Snow and Ice Data Center within the Cooperative Institute for Research in Environmental Sciences (CIRES). She is also a member of the American Geophysical Union and an ISI highly cited researcher.

References

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