Is the Artctic Ice Shelf Growing Again

Sea ice in the Southern Ocean defies predictions.

by Natasha Vizcarra

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On the prowl for nutrient, Adelie penguins scan the water ice ceiling. They peck at silverfish and hunt for polynyas, gaping holes in the sea ice where shoals of krill and bug-like copepods graze on clouds of algae. When bound comes, the huge plates of ocean ice showtime to cook and later in the brief Antarctic summer all but disappear. And so, algae blooms unfurl: a bacchanalian feast for krill and critters all the way up the Antarctic nutrient chain. Sea water ice, sunlight, and nutrient—they all come and go with the seasons in the Antarctic ocean.

Paul Holland, a climate modeler with the British Antarctic Survey, has spent the last ten years studying Antarctica'southward sea ice and the Antarctic ocean. Lately, he has been scrutinizing the seasons of Antarctica and how fast the ice comes and goes. Holland thinks these seasons may exist a key to a puzzler: If Earth's temperatures are getting warmer and ocean water ice in the Arctic has been shrinking fast, why then is sea water ice in the Antarctic slowly increasing?

A Weddell seal hunts for nutrient nether the ocean ice near McMurdo Sound in Antarctica. (Due south. Rupp/National Science Foundation)

Contrary poles

Ocean ice is simply frozen seawater. Although found only in the Arctic and the Antarctic, information technology influences Globe'south climate in big ways. Its bright surface reflects sunlight dorsum into infinite. Icy areas absorb less solar energy and remain relatively cool. When temperatures warm over fourth dimension and more than sea ice melts, fewer vivid surfaces reverberate sunlight dorsum into infinite. The water ice and exposed seawater absorb more solar energy and this causes more than melting and more warming.

This scene shows a mixture of ocean ice types commonly seen in the Southern ocean. The different thicknesses of sea ice form a spectrum of colors and shapes ranging from dark black open h2o, a thin grease-similar covering called grease ice, and thicker greyness water ice. Older sea ice has a bright white covering of snowfall and many chaotic deformation features visible as ridges and rubble fields caused by the continuous motion of the ice pack. (Courtesy M. Studinger/NASA)

Scientists have been watching this feedback loop of warming and melting in the Arctic. To them, Arctic sea ice is a reliable indicator of a changing global climate. They pay the virtually attending in September when Arctic sea ice shrinks to its smallest extent each yr. Measured by satellites since 1979, this minimum extent has been decreasing by every bit much as xiii.7 percent per decade. Antarctic bounding main ice, on the other hand, has non been considered a climatic change indicator. Whereas Arctic sea water ice generally sits in the middle of country-locked sea—which is more sensitive to sunlight and warming air—Antarctic sea ice surrounds state and is constantly exposed to high winds and waves.

According to climate models, rising global temperatures should cause sea ice in both regions to shrink. But observations show that ice extent in the Arctic has shrunk faster than models predicted, and in the Antarctic it has been growing slightly. Researchers are looking much closer at Antarctica, saying, "Wait, what is going on down in that location?" The netherlands is i of those intrigued.

"The Antarctic case is as interesting as the Arctic case," Holland said. "Y'all tin can't sympathise ane without understanding the other."

Minding the models

To The netherlands, the discrepancy calls parts of the climate models into question. Modeling groups from around the world interact on the Coupled Model Intercomparison Projection Phase five (CMIP5), which simulates Earth'due south climate and predicts how it will change in the near future. World leaders and policy makers rely on it to decide how much countries should limit carbon emissions, known to cause some aspects of climate change.

"About all of the CMIP5 models produce a subtract in Antarctic bounding main ice," The netherlands said. "In that location is a trouble in the bit that reproduces the concluding 30 years of sea ice variability." The netherlands was searching for data to amend and verify his own modeling of trends in Antarctic water ice when he noticed that other researchers were finding that the trends varied in forcefulness in the different seasons.

Nearly studies on Antarctic bounding main water ice trends focus on changes in water ice extent. For Holland, it was more important to wait at how fast the ice was growing or shrinking from flavor to flavor. "Changes in climate forcing directly affect the rate of ice growth," he said, "not the amount of ice." Year to yr cooling in fall, for example, may cause faster ice growth during fall, but non necessarily an increase in the amount of autumn ice.

A pressure ridge forms on the sea ice well-nigh Scott Base in Antarctica. These form when divide ice floes collide and pile upwardly on each other. Lenticular clouds are seen to a higher place. (Courtesy M. Studinger/NASA)

Jump surprise

Holland used data from NASA's National Snow and Ice Data Center Distributed Active Archive Center (NSIDC DAAC) to summate the water ice concentration rate of growth for each unmarried twenty-four hours, which he called intensification; and the total ice surface area rate of growth, which he called expansion. "I did that for all thirty years of data and plotted the trends," he said. Holland'due south plots showed that the different regions in the Southern Ocean contributed to the overall increment, but they had very diverse trends in bounding main ice growth. This suggested that geography and different wind patterns played a role. And so to gain more insight Holland looked at seasonal wind trends for the different regions.

Holland found that winds were spreading sea water ice out in some regions and compressing or keeping it intact in others and that these furnishings began in the spring. It contradicted a previous study in which, using ice drift data, Holland and Ron Kwok from the NASA'due south Jet Propulsion Laboratory (JPL) found that increasing n winds during the autumn acquired the variations.

"I always thought, and as far every bit I can tell anybody else thought, that the biggest changes must be in fall," Holland said. "But the big result for me now is we need to look at spring. The tendency is bigger in the autumn, only it seems to be created in spring."

"Paul has created 2 more bounding main ice metrics that nosotros can use to appraise how Antarctic body of water ice is responding," said researcher Sharon Stammerjohn, referring to the measures of intensification and expansion. The new metrics assist assess how the organisation is responding as opposed to just monitoring the state of the system. "Say your temperature is at 99.2 degrees Fahrenheit," Stammerjohn said. "You lot don't have any insight to that temperature unless you take it again an hour later and you come across that it inverse to 101 degrees. And then you tin say, okay, my system is responding to something."

The panels above show seasonal variations of body of water ice quantities for each region and the whole Southern Body of water. The mean monthly full ice expansion (b) peaks in autumn, and hateful monthly total ice surface area (a) peaks in the winter. Interannual trends in monthly total water ice area (c) evidence that for the last thirty years, Antarctic sea ice has tended to expand during the autumn. Interannual trends in monthly total water ice expansion (d) show that changes in water ice growth in the spring produced the change in the ice the following summer and autumn. (Courtesy P. R. Holland)

Partial explanations

Kingdom of the netherlands continues to study the Antarctic jump to better understand why Antarctic ocean water ice is irresolute. While Holland's work helps researchers begin to see the problem in more detail, scientists continue to develop ideas almost why the ice is expanding.

One study paradoxically suggests that ocean warming and enhanced melting of the Antarctic ice canvas is causing the small simply statistically pregnant bounding main water ice expansion in the region. Another report suggests that rain caused by a warmer climate has been causing an influx of fresh water into the Southern ocean, making it less dense and inhibiting oceanic rut from reaching bounding main ice in the Antarctic. To date, there is no consensus on the reason for the expansion.

"Fractional explanations accept been offered, merely we don't take the complete picture," said Ted Scambos, a scientist at NSIDC DAAC. "This may just be a case of 'nosotros don't know yet.'"

Emperor penguins balance near the coast in Antarctica and hunt for food in the nearby bounding main ice. (Courtesy K. Watson)

References

Bintanja, R., G. J. Van Oldenborgh, S. S. Drijfhout, B. Wouters, and C. A. Katsman. 2013. Of import part for ocean warming and increased ice-shelf melt in Antarctic bounding main-ice expansion. Nature Geoscience six: 376–379, doi:10.1038/ngeo1767.

Cavalieri, D. J., C. Fifty. Parkinson, P. Gloersen, and H. Zwally. 1996, updated yearly. Sea Ice Concentrations from Nimbus-seven SMMR and DMSP SSM/I-SSMIS Passive Microwave Data. Southern Hemisphere. Boulder, Colorado USA: NASA National Snow and Ice Information Center (NSIDC) DAAC.

Holland, P. R. 2014. The seasonality of Antarctic sea water ice trends. Geophysical Inquiry Letters 41, doi:10.1002/2014GL060172.

Holland, P. R. and Kwok, R. 2012. Wind driven trends in Antarctic sea-ice migrate. Nature Geoscience 5: 872–875, doi:10.1038/ngeo1627.

Holland, P. R., N Bruneau, C. Enright, M. Losch, North. T. Kurtz, R. Kwok. 2014. Modeled trends in Antarctic sea ice thickness. Journal of Climate 27: 3,784–three,801, doi:ten.1175/JCLI-D-13-00301.i.

Kirkman, C. H., C. Chiliad. Bitz. 2011. The effect of the body of water water ice freshwater flux on Southern Body of water temperatures in CCSM3: Deep-ocean warming and delayed surface warming. Journal of Climate 24: 2,224–2,237, doi:10.1175/2010JCLI3625.1.

Scambos, T. A., R. Ross, T. Haran, R. Bauer, and D.Thousand. Ainley. 2013. A camera and multisensor automated station pattern for polar physical and biological systems monitoring: AMIGOS. Journal of Glaciology 59(214): 303–314, doi:x.3189/2013JoG12J170.

Stammerjohn, Due south., R. Massom, D. Rind, and D. Martinson. 2012. Regions of rapid sea ice modify: An interhemispheric seasonal comparison. Geophysical Research Messages 39, L06501, doi:10.1029/2012GL050874.

For more information

NASA National Snow and Ice Data Center Distributed Active Archive Center (NSIDC DAAC)

Well-nigh the remote sensing data
Satellites	Nimbus 7 and Defense Meteorological Satellite Program (DMSP) F8, F11, F13, F17
Sensors	Scanning Multichannel Microwave Radiometer (SMMR), Special Sensor Microwave/Imager (SSM/I), Special Sensor Microwave Imager/Sounder (SSMIS)
Information set	Ocean ice concentrations from Nimbus-vii SMMR and DMSP SSM/I-SSMIS Passive Microwave Data
Resolution	25 kilometers
Parameter	Ocean ice concentration
DAAC	NASA National Snow and Ice Data Center Distributed Active Archive Center (NSIDC DAAC)

The photo in the title graphic shows sea ice in the Bellingshausen Bounding main, off the coast of Antarctica, equally seen from a NASA Operation IceBridge flight on Oct xiii, 2012. (Courtesy M. Studinger/NASA)

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Source: https://earthdata.nasa.gov/learn/sensing-our-planet/unexpected-ice

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