NSIDC Artic Sea Ice News

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A recent slowdown

Tue, 2017-07-18 10:14

Arctic extent nearly matched 2012 values through the first week of July, but the rate of decline slowed during the second week. Weather patterns were unremarkable during the first half of July.

Overview of conditions

Figure 1. Arctic sea ice extent for July 17, 2017 was 7.88 million square kilometers (3.04 million square miles). The orange line shows the 1981 to 2010 average extent for that day. Sea Ice Index data. About the data

Credit: National Snow and Ice Data Center
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As of July 17, Arctic sea ice extent stood at 7.88 million square kilometers (3.04 million square miles). This is 1.69 million square kilometers (653,000 square miles) below the 1981 to 2010 average, and 714,000 square kilometers (276,000 million square miles) below the interdecile range. Extent was lower than average over most of the Arctic, except for the East Greenland Sea (Figure 1). Hudson Bay was nearly ice free by mid July, much earlier than is typical, but in line with what has been observed in recent years.

Conditions in context

Figure 2a. The graph above shows Arctic sea ice extent as of July 17, 2017, along with daily ice extent data for five previous years. 2017 is shown in blue, 2016 in green, 2015 in orange, 2014 in brown, 2013 in purple, and 2012 as a dotted brown line. The 1981 to 2010 median is in dark gray. The gray areas around the median line show the interquartile and interdecile ranges of the data. Sea Ice Index data.

Credit: National Snow and Ice Data Center
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Figure 2b. This map compares sea ice extent for July 11 in 2017 and in 2012. White shows where ice occurred only in 2012, medium blue is where ice occurred only in 2017, and light blue is where ice occurred in both years.

Credit: National Snow and Ice Data Center
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Through the first week of July, extent closely tracked 2012 levels. The rate of decline then slowed, so that as of July 17, extent was 169,000 square kilometers (65,300 square miles) above 2012 for the same date (Figure 2a). The spatial pattern of ice extent differs from 2012, with less ice in the Chukchi and East Siberian Seas in 2017, but more in the Beaufort, Kara, and Barents Seas and in Baffin Bay (Figure 2b).

Visible imagery provides up close details  RESEARCHER'S NAME/ORGANIZATION *or * National Snow and Ice Data Center| High-resolution image

Figure 3a. This image from the NASA Moderate Resolution Imaging Spectroradiometer (MODIS) shows sea ice in the Canadian Archipelago on July 3, 2017. The blue hues indicate areas of widespread melt ponds on the surface of the ice.

Credit: Land Atmosphere Near-Real Time Capability for EOS (LANCE) System, NASA/GSFC
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sea ice floes

Figure 3b. The Sentinel-2 satellite captured this image of large sea ice floes in Nares Strait on July 8, 2017.

Credit: European Space Agency
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MODIS image of arctic

Figure 3c. This false-color composite image of the Arctic is based on NASA MODIS imagery from July 4 to 10. Most clouds are eliminated by using several images over a week, but some clouds remain, particularly over the ocean areas.

Credit: NASA/Canadian Ice Service
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NSIDC primarily relies on passive microwave data because it provides complete coverage—night and day, and through clouds—and because it is consistent over its long data record. However, other types of satellite data, for example visible imagery from the NASA MODIS instrument on the Aqua and Terra satellites or from the European Space Agency Sentinel 2 satellite, can sometimes provide more detail. When skies clear, details of the ice cover can be seen, including leads, individual ice floes and melt ponds. For example, on July 3 in the Canadian Archipelago, 1-kilometer resolution MODIS imagery shows that the ice surface has a distinctive blueish hue due to the presence of melt ponds on the surface (Figure 3a). Higher resolution Sentinel-2 imagery (10 meters, Figure 3b) on the other hand provides up close detail on individual melt ponds on the ice floes.

The Arctic is a cloudy place, and generally, it is difficult to obtain a clear-sky image of the entire region. However, if images are compiled, or composited, over several days, most of the region may have at least some clear sky. This approach can yield a composite image that is mostly cloud-free. The Canadian Ice Service uses this approach to create a weekly nearly cloud-free composite image of the Arctic (Figure 3c). However, because the ice cover moves (typically several kilometers per day) and melts (during the summer), over the week-long composite period, fine details that can be seen in the daily imagery are not as evident because they have been “smeared” out over the week.

An ice-diminished Arctic

In response to diminishing ice extent, the US Navy has been holding a semi-annual symposium to bring together scientists, policy makers, and others to discuss the sea ice changes and their impacts. The seventh Symposium is taking place this week in Washington, DC, and will be attended by NSIDC scientists Mark Serreze, Walt Meier, Florence Fetterer, and Ted Scambos.

Tendency for warmer winters is increasing

A new study published this week in Geophysical Research Letters by Robert Graham at the Norwegian Polar Institute shows that warm winters in the Arctic are becoming more frequent and lasting for longer periods of time than they used to. Warm events were defined by when the air temperatures rose above -10 degrees Celsius (14 degrees  Fahrenheit). While this is still well below the freezing point, it is 20 degrees Celsius (36 degrees Fahrenheit) higher than average. The last two winters have seen temperatures near the North Pole rising to 0 degrees Celsius. While an earlier study showed that winter 2015/2016 was the warmest recorded at that time, the winter of 2016/2017 was even warmer.

Reference

Graham, R. M., L. Cohen, A. A. Petty, L. N. Boisvert, A. Rinke, S. R. Hudson, M. Nicolaus, and M. A. Granskog. 2017. Increasing frequency and duration of Arctic winter warming events, Geophys. Res. Lett., 44, doi:10.1002/2017GL073395.

Categories: Climate Science News

Arctic ice extent near levels recorded in 2012

Wed, 2017-07-05 13:00

Contrasting with the fairly slow start to the melt season in May, June saw the ice retreat at a faster than average rate. On July 2, Arctic sea ice extent was at the same level recorded in 2012 and 2016. In 2012, September sea ice extent reached the lowest in the satellite record. As a new feature to Arctic Sea Ice News and Analysis, NSIDC now provides a daily updated map of ice concentration in addition to the daily map of ice extent.

Overview of conditions Figure 1. Arctic sea ice extent for June 2017 averaged 11.06 million square kilometers (4.27 million square miles).

Figure 1. Arctic sea ice extent for June 2017 averaged 11.06 million square kilometers (4.27 million square miles). The magenta line shows the 1981 to 2010 average extent for that month. Sea Ice Index data. About the data

Credit: National Snow and Ice Data Center
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Arctic sea ice extent for June 2017 averaged 11.06 million square kilometers (4.27 million square miles), the sixth lowest in the 1979 to 2017 satellite record. The average June 2017 extent was 900,000 square kilometers (348,000 square miles) below the 1981 to 2010 long-term average, and 460,000 square kilometers (178,000 square miles) above the previous record low set in 2016.

Continuing the pattern seen in May, sea ice extent at the end of the month remained below average in the Chukchi Sea and in the Barents Sea. Ice extent was at average levels in the Greenland Sea. Areas of low concentration ice have developed along the ice edge and coastal seas.

Based on imagery from the Moderate Resolution Imaging Spectroradiometer (MODIS) aboard the NASA Terra and Aqua satellites, summer melt ponds atop the ice cover were somewhat slow to develop. However, there is now widespread melt pond coverage in the Canadian Archipelago and the Laptev and East Siberian Seas. Data from the Advanced Microwave Scanning Radiometer 2 (AMSR-2) instrument analyzed by the University of Bremen, as well as MODIS imagery, indicate that melt ponds have also developed over the Central Arctic Ocean. Researchers in Dease Strait in Northern Canada have observed melt ponds forming about two weeks earlier than average. Melt ponds are important as they decrease the albedo or reflectivity of the ice surface, which hastens further melt.

Conditions in context Figure 2. The graph above shows Arctic sea ice extent as of July 4, 2017, along with daily ice extent data for five previous years. 2017 is shown in blue, 2016 in green, 2015 in orange, 2014 in brown, 2013 in purple, and 2012 in dashed red. The 1981 to 2010 median is in dark gray. The gray areas around the median line show the interquartile and interdecile ranges of the data.

Figure 2. The graph above shows Arctic sea ice extent as of July 4, 2017, along with daily ice extent data for five previous years. 2017 is shown in blue, 2016 in green, 2015 in orange, 2014 in brown, 2013 in purple, and 2012 in dashed red. The 1981 to 2010 median is in dark gray. The gray areas around the median line show the interquartile and interdecile ranges of the data. Sea Ice Index data.

Credit: National Snow and Ice Data Center
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The rate of decline in ice extent was fairly steady through the month, and the average rate of decline of 81,800 square kilometers (31,600 square miles) per day was slightly faster than the 1981 to 2010 long-term average of 56,300 square kilometers (21,700 square miles) per day. On July 2, extent was the same as that recorded in 2012 and 2016. The year 2012 ended up with the lowest September extent in the satellite record.

June air temperatures were modestly above average (1 to 3 degrees Celsius or 2 to 5 degrees Fahrenheit) in a band spanning the Arctic Ocean roughly centered along the date line and the prime meridian. This contrasts with below-average temperatures over the eastern Beaufort Sea and Canadian Arctic Archipelago and the Barents and Laptev Seas (1 to 3 degrees Celsius, 2 to 5 degrees Fahrenheit). Atmospheric pressures at sea level were below-average over the Kara Sea and extending north of the Laptev Sea.

June 2017 compared to previous years Figure 3. Monthly June ice extent for 1979 to 2017 shows a decline of 3.7 percent per decade.

Figure 3. Monthly June ice extent for 1979 to 2017 shows a decline of 3.7 percent per decade.

Credit: National Snow and Ice Data Center
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The linear rate of decline for June is 44,300 square kilometers (17,100 square miles) per year, or 3.7 percent per decade.

Ice thickness  University of Washington Pan-Arctic Ice Ocean Modeling and Assimilation System

Figure 4. This figure shows that sea ice thicknesses for May 2017 were below the 2000 to 2015 average over most of the Arctic Ocean (areas in blue) except for the region north and west of the Svalbard archipelago (areas in red).

Credit: University of Washington Pan-Arctic Ice Ocean Modeling and Assimilation System
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The University of Washington Seattle Pan-Arctic Ice Ocean Modeling and Assimilation System (PIOMAS) regularly produces maps of ice thickness anomalies (departures from the long-term average). PIOMAS is based on a coupled ice-ocean model that is driven by data from an atmospheric reanalysis, and also assimilates data on observed ocean conditions and ice thickness (e.g., from NASA IceBridge). The PIOMAS analysis suggests that, relative to the average over the period 2000 to 2015, ice thickness for May 2017 (when the melt season was just beginning) was below average over most of the Arctic Ocean, especially in the Chukchi Sea and north of the Canadian Arctic Archipelago. A small region with above-average ice thickness is depicted over the Atlantic side of the Arctic north and west of the Svalbard Archipelago, and in the Greenland Sea. Starting the melt season with below-average ice thickness raises the likelihood of having especially low September ice extent.

Freezing degree days and ice thickness Figure 5. The figure shows departures from average in cumulate freezing degree days, extending from July 1 for a given year through July 1 of the next year, along with the range, 15th through 85th percentile and 30th to 70th percentile values over the base period 1981 through 2010.

Figure 5. The figure shows departures from average in cumulate freezing degree days, extending from July 1 for a given year through July 1 of the next year, along with the range, 15th through 85th percentile and 30th to 70th percentile values over the base period 1981 through 2010.

Credit: National Snow and Ice Data Center
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Cumulative Freezing Degree Days (FDD) is a simple measure of how cold it has been and for how long. Cumulative FDD is the sum of daily mean temperatures below zero from some start date. Here we start on July 1. Cumulative FDD is related to ice thickness because, on average, years with longer periods of temperatures below freezing will have more ice growth. A simple empirical model that has been used by scientists relates ice thickness to the square root of cumulative FDD.

Anomalies (departures from the average) in cumulative FDD illustrate the coldness of a given period relative to the long-term average (1981 to 2010). Figure 5 shows that most of the period from July 2016 to July 2017 was extremely mild and was milder (less cold) than both 2006 to 2007 and 2011 to 2012. September of both 2007 and 2012 ended up with very low September sea ice extent. This is consistent with below-average ice thickness seen in the PIOMAS data. Although conditions cooled in May and June, this likely had little impact on ice thickness. This is because ice in the Arctic reaches its maximum thickness earlier in the season during March or April. As noted earlier, ice retreated at a fast rate throughout June. This is likely linked to a thinner than average ice cover as seen in the PIOMAS analysis.

Sudden Antarctic sea ice decline in late 2016

A slight decrease in the rate of sea ice growth at the end of June brought Antarctic sea ice extent back to daily record lows. Sea ice extent in the Bellingshausen, eastern Amundsen, and western Ross Seas was below average.

Our post on December 2016 ice conditions highlighted a precipitous drop in Antarctic sea ice extent in the Weddell and Ross Sea sectors during September, October, and November of 2016. A recent study by John Turner and colleagues links this pattern of sea ice decline to a series of strong storms, marked by long periods of warm winds from the north. These changing weather conditions are associated with large shifts in the Southern Annual Mode index (SAM index).

Further reading

Turner, J., T. Phillips, G. J. Marshall, J. S. Hosking, J. O. Pope, T. J. Bracegirdle, and P. Deb. 2017. Unprecedented springtime retreat of Antarctic sea ice in 2016, Geophysical Research Letters, 44, doi:10.1002/2017GL073656.

Categories: Climate Science News

Sluggish ice retreat, except in the Chukchi Sea

Wed, 2017-06-07 11:30

After setting satellite-era record lows during winter, Arctic sea ice extent declined at a steady but somewhat sluggish pace during May. However, ice has retreated at a record rate in the Chukchi Sea, and open water extended to Barrow, Alaska. In the Southern Hemisphere, ice extent continues its seasonal expansion, but extent remains well below the long-term average for this time of year.

Overview of conditions n_extn_hires

Figure 1. Arctic sea ice extent for May 2017 was 12.74 million square kilometers (4.92 million square miles). The magenta line shows the 1981 to 2010 average extent for that month. Sea Ice Index data. About the data

Credit: National Snow and Ice Data Center
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Arctic sea ice extent for May 2017 averaged 12.74 million square kilometers (4.92 million square miles), the fourth lowest in the 1979 to 2017 satellite record. This contrasts strongly with the past several months, when extent tracked at satellite-era record lows. May 2017 extent was 710,000 square kilometers (274,000 square miles) below the 1981 to 2010 long-term average, and 660,000 square kilometers (255,000 square miles) above the previous record low set in 2016. Sea ice extent remained below average in the Pacific sector of the Arctic and in the Barents Sea, but was slightly above average in Baffin Bay and Davis Strait towards the Labrador Sea. Ice extent was at average levels in the Greenland Sea. In the Chukchi Sea, extent was at record low levels for May.

Conditions in context time series graph

Figure 2a. The graph above shows Arctic sea ice extent as of June 6, 2017, along with daily ice extent data for five previous years. 2017 is shown in blue, 2016 in green, 2015 in orange, 2014 in brown, 2013 in purple, and 2012, the record low year, as a dashed line. The 1981 to 2010 median is in dark gray. The gray areas around the median line show the interquartile and interdecile ranges of the data. Sea Ice Index data.

Credit: National Snow and Ice Data Center
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temperature difference plot

Figure 2b. The plot shows differences from average for Arctic air temperatures from May 1 to 27, 2017 at the 925 hPa level (about 2,500 feet above sea level) in degrees Celsius. Yellows and reds indicate higher than average temperatures; blues and purples indicate lower than average temperatures.

Credit: NSIDC courtesy NOAA ESRL Physical Sciences Division
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For the Arctic as a whole, the rate of decline in Arctic sea ice extent through May was relatively slow. The May 2017 rate of decline was 42,800 square kilometers (16,500 square miles) per day, compared to the 1981 to 2010 average of 46,990 square kilometers (18,143 square miles) per day.

Sea ice was especially slow to retreat in the Atlantic sector of the Arctic, with little change in the ice edge in Baffin Bay and Davis Strait. The ice edge expanded in the Barents and Greenland Seas until the end of May, when the ice finally started to retreat. Most of the ice retreat in May occurred within the Pacific sector, particularly within the Sea of Okhotsk, and the Bering and Chukchi Seas.

Overall, air temperatures at the 925 hPa level were 2 to 4 degrees Celsius (4 to 7 degrees Fahrenheit) below average over Eurasia and extending over the Barents, Kara and Laptev Seas, and 1 to 4 degrees Celsius (2 to 7 degrees Fahrenheit) above average over the East Siberian, Chukchi, and Beaufort Seas (Figure 2b).

May 2017 compared to previous years monthly_ice_05_NH_v2.1

Figure 3. Monthly May ice extent for 1979 to 2017 shows a decline of 2.5 percent per decade.

Credit: National Snow and Ice Data Center
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The linear rate of decline for May is 33,900 square kilometers (13,100 square miles) per year, or 2.5 percent per decade.

Low ice in the Chukchi Sea

Fig. 4a. This map shows sea ice concentration in percent coverage for the Alaska area on May 22, 2017.

Credit: NOAA National Weather Service Alaska Sea Ice Program
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Figure 2d.

Figure 4b. The plot shows daily May sea ice extent, in square kilometers, in the Chukchi Sea region for 2012 to 2017.

Credit: J. Stroeve/ NSIDC
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Figure 4c. The graph shows cumulative temperature departures from average for each year, in degrees Fahrenheit, for Barrow, Alaska from 1921 to May 2017.

Credit: Blake Moore, Alaska Climate Research Center
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Notably, sea ice within the Chukchi Sea retreated earlier than seen at any other time in the satellite data record. By the third week in May, open water extended all the way to Barrow, Alaska (Figure 4a). Figure 4b shows daily ice extent for May from 2012 onward in the Chuckchi Sea. The rapid retreat in 2017 stands out. A recent report by the National Oceanographic Atmospheric Administration (NOAA) indicates that the amount of open water north of 68o N at this time of year is unprecedented.

Part of the explanation for earlier open water formation in the Chukchi Sea is the unusually high air temperatures in that region during the previous winter. It is instructive to look at the cumulative temperature departure from average for Barrow, Alaska (Figure 4c). From 1921 until about 1989, conditions at Barrow actually got progressively cooler. However, since that time, temperatures have markedly increased.

Consistent with warm conditions, extensive open water in the Chukchi Sea region persisted into December; the delayed ice growth potentially led to thinner ice than usual in spring. In addition, strong winds from the north occurred for a few days at the end of March and early April, pushing ice southward in the Bering Sea, breaking up the ice in the Chukchi Sea, and even flushing some ice out through the Bering Strait. At the same time further east near Barrow, winds helped to push ice away from the coast. Based on recent work by NSIDC and the University of Washington, the pattern of spring sea ice retreat also suggests a role of strong oceanic heat inflow to the Chukchi Sea via Bering Strait.

Impacts of low Chukchi Sea on Alaskan communities

The ARCUS Sea Ice for Walrus Outlook (SIWO) provides weekly reports from April to June on sea ice conditions in the northern Bering Sea and southern Chukchi Sea regions of Alaska to support subsistence hunters and coastal communities. While the reports are not intended for operational planning or navigation, they provide detailed ice and weather observations for the region, some made by local community members, others from operational forecast centers. The most recent update on June 2nd discusses the continued rapid deterioration of sea ice between Wales and Shishmaref, Alaska. Nearly ice-free conditions around Nome, Alaska reflect warmer waters from the Bering Sea moving into the region. Some sea ice remains attached to the shore along the northeast coast of St. Lawrence Island, but the Bering Sea is essentially ice free. Prime walrus hunting for these communities is typically in May. However, when the ice retreats early, the walrus go with it, reducing the number of walrus the local communities can hunt.

Sea ice data and analysis tools

NSIDC has released a new set of tools for sea ice analysis and visualization. In addition to Charctic, our interactive sea ice extent graph, the new Sea Ice Data and Analysis Tools page provides access to Arctic and Antarctic sea ice data organized in seven different data workbooks, updated daily or monthly. Animations of September Arctic and Antarctic month average sea ice and concentrations may also be accessed from this page.

Further Reading

Serreze, M.C., Crawford, A., Stroeve, J. C., Barrett, A.P. and Woodgate, R.A. 2016.  Variability, trends and predictability of seasonal sea ice retreat and advance in the Chukchi Sea.  Journal of Geophysical Research, 121, doi:10.1002/2016JC011977.

 

 

Categories: Climate Science News

Warm Arctic, cool continents

Wed, 2017-05-03 12:00

Arctic sea ice extent for April 2017 tied with April 2016 for the lowest in the satellite record for the month. Warm weather conditions and lower-than-average sea ice extent prevailed over the Pacific side of the Arctic, while relatively cool conditions were the rule in northern Europe and eastern North America. In the Southern Hemisphere, Antarctic sea ice extent remained lower than average.

Overview of conditions Figure 1. Arctic sea ice extent for April 2017 was 13.83 million square kilometers (5.34 million square miles). The magenta line shows the 1981 to 2010 average extent for that month.

Figure 1. Arctic sea ice extent for April 2017 was 13.83 million square kilometers (5.34 million square miles). The magenta line shows the 1981 to 2010 average extent for that month. Sea Ice Index data. About the data

Credit: National Snow and Ice Data Center
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Arctic sea ice extent for April 2017 averaged 13.83 million square kilometers (5.34 million square miles), and tied with April 2016 for the lowest April extent in the 38-year satellite record. The April 2017 extent is 1.02 million square kilometers (394,000 square miles) below the April 1981 to 2010 long-term average. The largest reductions in ice extent through the month occurred on the Pacific side of the Arctic, within the Bering Sea and the Sea of Okhotsk. Little change in extent occurred in the Atlantic sector of the Arctic.

Conditions in context Figure 2a. The graph above shows Arctic sea ice extent as of May 2, 2017, along with daily ice extent data for four previous years. 2017 is shown in blue, 2016 in green, 2015 in orange, 2014 in brown, and 2013 in purple, and 2012 in dashed brown. The 1981 to 2010 median is in dark gray. The gray areas around the median line show the interquartile and interdecile ranges of the data.

Figure 2a. The graph above shows Arctic sea ice extent as of May 2, 2017, along with daily ice extent data for five previous years. 2017 is shown in blue, 2016 in green, 2015 in orange, 2014 in brown, and 2013 in purple, and 2012 in dashed brown. The 1981 to 2010 median is in dark gray. The gray areas around the median line show the interquartile and interdecile ranges of the data. Sea Ice Index data.

Credit: National Snow and Ice Data Center
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Figure 2b. These figures show April 2017 Arctic air temperature difference at the 925 hPa level (about 2,500 feet above sea level) in degrees Celsius (left) and sea level pressure (right). Yellows and reds indicate higher than average temperatures and pressure; blues and purples indicate lower than average temperatures and pressure.

Figure 2b. These figures show April 2017 differences from average for Arctic air temperatures at the 925 hPa level (about 2,500 feet above sea level) in degrees Celsius (left) and for sea level pressure (right). Yellows and reds indicate higher than average temperatures and pressure; blues and purples indicate lower than average temperatures and pressure.

Credit: NSIDC courtesy NOAA Earth System Research Laboratory Physical Sciences Division
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Figure 2c. These maps show Arctic sea ice motion for April 13 to 15, 2017, which is representative of the general pattern seen throughout the month. Black arrows represent sea ice drift. The purple arrows represent "filled" values, data gaps that have been interpolated from surrounding data.

Figure 2c. These maps show Arctic sea ice motion for April 13 to 15, 2017, which is representative of the general pattern seen throughout the month. Black arrows represent sea ice drift. The purple arrows represent “filled” values, data gaps that have been interpolated from surrounding data.

Credit: EUMETSAT
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The decline in ice extent through the month was fairly steady, at a rate similar to what was observed over the previous two Aprils (2016 and 2015). Throughout the month, sea ice extent was either at daily record lows for the period of satellite observations, or within 100,000 square kilometers (~38,600 square miles) of record low values. At the end of the month, extent was below average in the Barents Sea, the Sea of Okhotsk, and the western Bering Sea, similar to the pattern seen in March. Despite fairly warm conditions, sea ice extent was slightly above average in Baffin Bay.

Unusually warm conditions were observed across the Pacific side of the Arctic Ocean, with temperatures at the 925 hPa level (about 2,500 feet above sea level) north of the Bering Strait ranging from 6 to 8 degrees Celsius (11 to 14 degrees Fahrenheit) above the 1981 to 2010 average. Western Alaska and easternmost Siberia also saw warm conditions. However, below average temperatures ruled across a broad swath of northern Canada. Of particular note, cooler-than-average conditions also prevailed over Greenland, leading to relatively little surface melting on the ice sheet in April (unlike the preceding two years).

The overall temperature pattern is consistent with the average sea level pressure pattern for the month, which had large areas of low and higher-than-average pressure in the Eastern and Western Hemispheres, respectively. This pattern produces a cross-Arctic airflow, with southerly winds from the Bering Sea blowing into the Chukchi Sea and central Arctic, and cool winds blowing from the north over Scandinavia and other areas of northern Europe. This cross-Arctic wind pattern is also evident in the sea ice motion field for April 2017. Sea ice motion is determined by tracking patterns in the sea ice in both visible imagery and in passive microwave data from satellites.

April 2017 compared to previous years Figure 3a. Monthly April ice extent for 1979 to 2017 shows a decline of 2.6 percent per decade.

Figure 3a. Monthly April ice extent for 1979 to 2017 shows a decline of 2.6 percent per decade.

Credit: National Snow and Ice Data Center
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Figure 3b. This shows April 2017 Arctic sea ice concentration anomalies (left) and Arctic sea ice concentration trends (right).

Figure 3b. These images show April 2017 Arctic sea ice concentration anomalies (left) and Arctic sea ice concentration trends (right). Sea Ice Index data. About the data

Credit: National Snow and Ice Data Center
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The linear rate of decline for April is 38,000 square kilometers (15,000 square miles) per year, or 2.6 percent per decade.

Declining ice extent in the Barents Sea, Sea of Okhotsk, and off the coast of southeastern Greenland is a part of the long-term pattern of sea ice decline. Below-average ice extent in the western Bering Sea has to date not been a part of the long-term trend for April.

A report from the field Figure 4. This photo shows broken up sea ice and some multi-year floes at Alert, on the northern tip of Ellesmere Island, Canada. A researcher and a Twin Otter aircraft are obscured in the background.

Figure 4. This photo shows broken up sea ice and some multi-year floes at Alert, on the northern tip of Ellesmere Island, Canada on April 2017. A researcher and a Twin Otter aircraft are obscured in the background.

Credit: J. Stroeve/NSIDC
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NSIDC scientist Julienne Stroeve continued her Arctic field work into early April, moving from Cambridge Bay, Canada to Alert in Ellesmere Island. In Alert, Stroeve focused on sampling ice thickness and snow pack characteristics along a CryoSat-2 flight track within the Lincoln Sea. This is an area between northernmost Greenland and Ellesmere Island where thick, old ice remains. The scientists flew by Twin Otter each day, out onto the sea ice between latitudes 83°N and 87.1°N. The field campaign was also supported by an aircraft from the British Antarctic Survey carrying a Ka band radar, LiDAR, and a broadband radiometer. A NASA Operation IceBridge flight also flew over the same track.

The group noted that the ice was unusually broken up and reduced to rubble, with few large multi-year floes, forcing the pilots to land on refrozen leads that at times were only 70 centimeters (28 inches) thick. Pilots remarked that they had never seen the ice look like this. Preliminary estimates suggest mean thicknesses ranging from 2 to 3.4 meters (6.6 to 11 feet), with the thickest ice found between an ice bridge in the Lincoln Sea and mobile pack ice to the north. Modal thickness, a representation of thermodynamically-grown level ice, ranged between 1.8 and 2.9 meters (6 and 10 feet), including 0.25 to 0.4 meters (10 to 16 inches) of snow. Second- and first-year modal ice thicknesses ranged between 1.8 and 1.9 meters (6 and 6.2 feet), about 0.2 meters (8 inches) thinner than previous airborne measurements indicated. More details can be found at the European Space Agency’s Campaigns at Work blog.

Arctic sea ice age Figure 5. These maps shows 2016 (top left) and 2017 (top right) Arctic sea ice age for the end of March and the time series of percent coverage for the Arctic Ocean (bottom).

Figure 5. These maps shows 2016 (top left) and 2017 (top right) Arctic sea ice age for the end of March and the time series of percent coverage for the Arctic Ocean (bottom).

Credit: National Snow and Ice Data Center, courtesy M. Tschudi, C. Fowler, J. Maslanik, R. Stewart/University of Colorado Boulder; W. Meier/NASA Cryospheric Sciences
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Sea ice age is a proxy for ice thickness, with older ice generally meaning thicker ice. Though ice can pile up into rubble fields when the motion of the ice pushes up against the coast or thicker ice, level ice generally increases in thickness as it ages through more winter freeze cycles. Thus, ice age is a reasonable indicator of the sea ice thickness.

At the end of March, ice age data show only a small remaining coverage of old (5+ years) ice. Since 2011, the oldest ice has comprised less than 5 percent of the total ice cover. During the mid-1980s, such ice made up nearly a third of the ice.

The next oldest ice category, four-year-old ice has also dropped from about 8 to 10 percent to less than 5 percent. The coverage of intermediate age ice categories (2- and 3-year-old ice) has stayed fairly consistent through time. The oldest ice has essentially been replaced by first-year ice (ice that has formed since the previous September). First-year-ice has risen from 35 to 40 percent of the Arctic Ocean’s ice cover during the mid-1980s to about 70 percent now.

Comparison of March 2016 conditions to this year shows a similar percentage coverage for the different ice ages. However, the spatial distribution is different. In March 2016, bands of the oldest ice extended through the Beaufort Sea and into the Chukchi, with scattered patches north of the Canadian Archipelago and Greenland. This year, the oldest ice is consolidated against the coast of Greenland and the archipelago except for a short arm extending north to the region around the pole. Most of the third year ice is between Fram Strait and the pole, which means it is likely to exit the Arctic Ocean during the coming months.

Antarctic ice extent low, but not lowest Figure 6. The graph above shows Antarctic sea ice extent as of May 2, 2017, along with daily ice extent data for four previous years. 2017 is shown in blue, 2016 in green, 2015 in orange, 2014 in brown, and 2013 in purple, and 2012 in dashed brown. The 1981 to 2010 median is in dark gray. The gray areas around the median line show the interquartile and interdecile ranges of the data.

Figure 6. The graph above shows Antarctic sea ice extent as of May 2, 2017, along with daily ice extent data for four previous years. 2017 is shown in blue, 2016 in green, 2015 in orange, 2014 in dashed brown, and 2013 in purple. The 1981 to 2010 median is in dark gray. The gray areas around the median line show the interquartile and interdecile ranges of the data. Sea Ice Index data.

Credit: National Snow and Ice Data Center
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Antarctic sea ice grew at a slightly faster-than average pace in April, but was still setting daily record lows until about April 10, after which extent rose above the 1980 ice extent. The April 2017 sea ice extent is lower than average in the Amundsen Sea and slightly lower than average in the Ross Sea and easternmost Weddell Sea. However, an area of above average extent is present in the north-central Weddell. Temperatures on the continent were above average over West Antarctica and western Wilkes Land, and considerably below average over the central Weddell sea.

Categories: Climate Science News

Another record, but a somewhat cooler Arctic Ocean

Tue, 2017-04-11 08:21

Arctic sea ice extent for March 2017 was the lowest in the satellite record for the month. The decline in ice extent has been uneven since the seasonal maximum was reached on March 7, 2017, with a modest period of expansion towards the end of the month.

Overview of conditions extent map

Figure 1. Arctic sea ice extent for March 2017 was 14.43 million square kilometers (5.57 million square miles). The magenta line shows the 1981 to 2010 average extent for that month. Sea Ice Index data. About the data

Credit: National Snow and Ice Data Center
High-resolution image

Arctic sea ice extent for March 2017 averaged 14.43 million square kilometers (5.57 million square miles), the lowest March extent in the 38-year satellite record. This is only 60,000 square kilometers (23,000 square miles) below March 2015, the previous lowest March extent, and 1.17 million square kilometers (452,000 square miles) below the March 1981 to 2010 long-term average. This month continues the record low conditions seen since October 2016.

Conditions in context timeseries graph

Figure 2a. The graph above shows Arctic sea ice extent as of April 9, 2017, along with daily ice extent data for five previous years. 2017 to 2016 is shown in blue, 2015 to 2016 in green, 2014 to 2015 in orange, 2013 to 2014 in brown, 2012 to 2013 in purple, and 2011 to 2012 in dashed brown. The 1981 to 2010 median is in dark gray. The gray areas around the median line show the interquartile and interdecile ranges of the data. Sea Ice Index data.

Credit: National Snow and Ice Data Center
High-resolution image

air temperature plot

Figure 2b. The plot shows Arctic air temperature differences at the 925 hPa level (about 2,500 feet above sea level) in degrees Celsius for March 2017. Yellows and reds indicate temperatures higher than the 1981 to 2010 average; blues and purples indicate temperatures lower than the 1981 to 2010 average.

Credit: NSIDC courtesy NOAA/ESRL Physical Sciences Division
High-resolution image

sea level pressure plot

Figure 2c. The plot shows Arctic sea level pressure (in millibars) for March 2017 expressed as departures from average conditions. The dominant feature is a large area of below average pressure covering most of the Arctic Ocean.

Credit: NSIDC courtesy NOAA/ESRL Physical Sciences Division
High-resolution image

The decline in sea ice extent following the March 2017 seasonal maximum was interrupted by a brief period of expansion from about March 11 to 15, a decline extending through about March 26, then another period of growth through the end of the month into early April. On April 4th, the extent was greater than on the same day in 2016. This type of behavior is not unusual for this time of year when declines in extent in warmer, lower latitudes can be countered by periods of expansion in the still-cold higher latitudes. Shifts in wind patterns also lead to variability. Regions that experienced slight ice advance were at the end of the month in the Barents Sea and in the Bering Sea. Nevertheless, by early April, extent remained below average in the Barents Sea and in the Sea of Okhotsk and the western Bering Sea. Interestingly, ice extended further south than usual in the eastern Bering Sea.

March saw continued warmth over the Arctic Ocean. The warmest conditions for March 2017 as compared to average were over Siberia. While temperatures were still well above average along the Russian coastal seas (6 to 7 degrees Celsius, or 11 to 13 degrees Fahrenheit), those over the northern North Atlantic and the Canadian Arctic Archipelago were near average.

The dominant feature of the sea level pressure field for March 2017 was an area of below average pressure covering most of the Arctic Ocean. Locally, pressures were more than 15 millibars below the 1981 to 2010 average. This pattern points to a continuation of the stormy conditions that prevailed over the past winter and is broadly consistent with the positive phase of the Arctic Oscillation, a large-scale mode of climate variability. When the Arctic Oscillation is in its positive phase, sea level pressure is below average over the Arctic Ocean. The Arctic Oscillation has generally been in a positive phase since December. The unusually high Siberian temperatures for March 2017 are consistent with persistent winds from the south and east along the southern side of the low pressure.

March 2017 compared to previous years trend graph

Figure 3. Monthly March ice extent for 1979 to 2017 shows a decline of 2.74 percent per decade.

Credit: National Snow and Ice Data Center
High-resolution image

The linear rate of decline for March is 42,700 square kilometers (16,500 square miles) per year, or 2.74 percent per decade.

Report from the field research photo

Figure 4. The team prepares to measure snow thickness over sea ice in Cambridge Bay, Canada on April 5, 2017, during an AltiKa field validation campaign. NSIDC researcher Andrew Barrett is in a red jacket; Julienne Stroeve holds a magna probe.

Credit: Isobel Lawrence
High-resolution image

As of the publication of this post, NSIDC scientists Julienne Stroeve and Andrew Barrett are in Cambridge Bay, Canada on a satellite validation campaign. Efforts focus on ground measurements of snow depth over sea ice, ice thickness, and snow structure in order to validate the joint French/Indian AltiKa Ka band radar altimeter. Coincident aircraft Ka band and LiDAR measurements allow researchers to connect measurements on the ground with those made by the satellite. Air temperatures have ranged from -20 to -5 degrees Celsius (-4 to 23 degrees Fahrenheit), with wind chills from -40 to -20 degrees Celsius (-40 to -4 degrees Fahrenheit). Dr. Stroeve will then join another field campaign operating out of Alert, Canada for further validation of AltiKa and CryoSat2 over the Lincoln Sea.

Arctic sea ice thickness sea ice volume plot

Figure 5. The graph shows sea ice volume from the PIOMAS model/observations for each year from 2010 through March 2017, and the 1979 to 2016 average (black line) and one (dark gray) and two (light gray) standard deviation ranges.

Credit: NSIDC courtesy University of Washington Polar Science Center
High-resolution image

A key early indicator for the upcoming melt season is the thickness of the sea ice. An assessment of available information suggests a fairly thin ice cover, not surprising given the warm temperatures over much of the Arctic Ocean during the winter.

Satellite data from the European Space Agency (ESA) CryoSat-2 radar altimeter, which is processed into sea ice thickness estimates at the University College London’s Center for Polar Observing and Modeling (CPOM) indicates ice along much of the Siberian coast with thicknesses of 1.5 to 2.0 meters (4.9 to 6.6 feet) or less. This is not atypical for seasonal ice; however this band of <2.0 meters of ice covers a much larger region and extends much farther north than it used to—well north of 80 degrees N latitude on the Atlantic side of the Arctic. NASA’s Operation IceBridge has also been collecting data over the past month. That data will not be available for a few weeks; a key focus of some flights has involved collaboration with ESA to collect coincident data with CryoSat-2 to help validate the satellite estimates.

Another way to estimate thickness and total ice volume is with a combination of observations and a model, which is done by the University of Washington Polar Science Center’s University of Washington Polar Science Center’s Pan-Arctic Ice Ocean Modeling and Assimilation System (PIOMAS). The model uses observed sea ice concentration fields to constrain the model and estimates thickness and total volume via physical simulations in the model. It shows that sea ice volume has been at record low levels throughout 2017 so far (Figure 5).

Sea ice loss and Atlantic layer heat

For many years, scientists have pondered how much of the sharp decline in summer sea ice extent and volume is due to “top down” forcing—a warmer atmosphere leading to more summer melt and less winter growth, versus “bottom up” forcing, in which ocean heat is brought to bear on the underside of the ice. There is a great deal of heat in the Arctic Ocean from waters that are imported from the Atlantic. As fairly warm and salty Atlantic water enters the Arctic Ocean it dives underneath the relatively fresh Arctic Ocean surface layer. Because the fresh surface layer has a fairly low density, the vertical structure of the Arctic Ocean is very stable. As such, it is hard to mix this Atlantic heat upwards to melt ice or keep it from forming in the first place. However, new work by an international team led by Igor Polyakov of the University of Alaska Fairbanks provides strong evidence that Atlantic layer heat is now playing a prominent role in reducing winter ice formation in the Eurasian Basin, which is manifested as more summer ice loss. According to their analysis, the ice loss due to the influence of Atlantic layer heat is comparable in magnitude to the top down forcing by the atmosphere.

Antarctic ice extent low, but on the rise antarctic timeseries plot

Figure 6. The graph above shows Antarctic sea ice extent as of April 9, 2017, along with daily ice extent data for four previous years. 2017 is shown in blue, 2016 in green, 2015 in orange, 2014 in brown, and 2013 in purple. The 1981 to 2010 median is in dark gray. The gray areas around the median line show the interquartile and interdecile ranges of the data. Sea Ice Index data.

Credit: National Snow and Ice Data Center
High-resolution image

Following the record-low seasonal sea ice minimum, Antarctic sea ice extent has sharply risen, but extent is still far below average, and set daily record low values throughout the month of March. Regionally, sea ice recovered to near average conditions in the Weddell Sea and around much of the coast of East Antarctica. The primary region of below average extent was in the Ross, Amundsen, and Bellingshausen Sea regions, as has been the case throughout the spring and summer. This appears to be related to warmer-than-average sea surface temperatures.

Additional reading

Polyakov, I., A.V. Pnyushkov, M.B. Alkire, I.M. Ashik, T.M. Baumann, E.C. Carmack and 10 others. 2017. Greater role for Atlantic inflows on sea-ice loss in the Eurasian Basin of the Arctic Ocean. Science, doi:10.1126/science.aai8204.

 

 

Categories: Climate Science News