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Breakup of the Arctic's Ward Hunt Ice Shelf

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  • Patrick Neuman
    January 20, 2004 http://earthobservatory.nasa.gov/Study/wardhunt/ In the summer of 2002, graduate student Derek Mueller made an unwelcome discovery: the
    Message 1 of 1 , Jan 21, 2004
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      January 20, 2004

      http://earthobservatory.nasa.gov/Study/wardhunt/

      In the summer of 2002, graduate student Derek Mueller made an
      unwelcome discovery: the biggest ice shelf in the Arctic was breaking
      apart. The bad news didn't stop there. Lying along the northern coast
      of Ellesmere Island in northern Canada, the Ward Hunt Ice Shelf had
      dammed an epishelf lake, a body of freshwater that floats on denser
      ocean water. This epishelf lake, located in Disraeli Fiord, was host
      to a rare ecosystem, and it was the largest and best-understood
      epishelf lake in the Northern Hemisphere. When the Ward Hunt Ice
      Shelf fractured, the epishelf lake suddenly drained out of Disraeli
      Fiord, spilling more than 3 billion cubic meters of fresh water into
      the Arctic Ocean.

      Mueller and his graduate advisor Warwick Vincent, both of Laval
      University in Quebec City, realized something unusual was happening
      to the ice shelf when they found unexpected fractures while doing
      fieldwork on the ice and during helicopter overflights. They
      contacted geophysics professor Martin Jeffries at the University of
      Alaska Fairbanks. Fortunately, Jeffries had planned ahead.

      "Knowing that Derek and Warwick would be doing fieldwork, I'd already
      placed data acquisition requests with the Canadian Space Agency
      through the Alaska Satellite Facility DAAC," Jeffries said. Jeffries
      requested data from the agency's RADARSAT-1 satellite. Equipped with
      a Synthetic Aperture Radar (SAR) sensor, RADARSAT-1 can acquire
      imagery in almost any kind of weather, with or without sunlight. "I
      had almost real-time RADARSAT data on my computer in a very short
      time, and I could confirm Derek's observation."

      In their final flight over the Ward Hunt Ice Shelf on August 11,
      2002, Mueller and his party learned something else: new icebergs had
      just calved from the front of the ice shelf. Using the RADARSAT data
      again, Jeffries confirmed that the icebergs had calved sometime
      between August 6 and August 11, 2002. "We made an almost real-time
      detection through a combination of field observations and RADARSAT
      data," he explained.
      January 20, 2004

      Title graphic image credits: Warwick Vincent, Université Laval (left)
      Vicki Sahanatien, Parks Canada (center) Mueller et al. 2003 (right)

      By September 2002, the Ward Hunt Ice Shelf had split several times.
      By looking at historical RADARSAT data, Mueller, Vincent, and
      Jeffries determined that the ice shelf actually beganto crack as
      early as April 2000, culminating a century-long decline in the
      shelf's extent. Though the Ward Hunt is very small compared to
      Antarctic ice shelves, its breakup and the resulting drainage from
      Disraeli Fiord concerned the researchers for several reasons.

      When the Ward Hunt Ice Shelf originally formed, it blocked the mouth
      of Disraeli Fiord, cutting it off from the Arctic Ocean. In the
      process, the ice shelf trapped driftwood inside the epishelf lake and
      kept other pieces of driftwood from entering. Pieces of driftwood
      found along the shores of Disraeli Fiord have been there since the
      ice shelf formed, and by radiocarbon dating the wood, researchers
      have been able to estimate the minimum age of the ice shelf. "There
      simply are no radiocarbon dates more recent than 3,000 years before
      present," said Jeffries. This ice shelf, in existence for at least
      three millennia, has now encountered conditions it can no longer
      survive.

      In just the last century, scientists have discovered dramatic changes
      in the Ward Hunt Ice Shelf. Changes became apparent in the 1950s when
      ice-shelf investigators examined early 20th-century records of Arctic
      explorer Robert Peary. "It was already clear there was a vast region —
      much greater than today — of thick, ancient ice floating on the
      ocean. We estimate that this ice has now retreated by about 90
      percent relative to Peary's observations," said Vincent.

      Drainage of the epishelf lake worries Jeffries and Vincent as much as
      the loss of the ice shelf. Although the fresh water in Disraeli Fiord
      floated on top of denser salt water, a small amount continually
      flowed out of the fiord under the ice shelf. Because the Ward Hunt
      Ice Shelf is not fed by glaciers, its existence depends on snow and
      ice accumulation on top and freshwater freezing on the bottom. "Some
      of our earlier studies indicated that the most likely source of
      freshwater freezing was water flowing out of Disraeli Fiord,"
      Jeffries explained. "The freshwater freezing was important because it
      was happening at the same time that ice was melting off the top, but
      now that source of fresh water is gone." Without the freshwater
      freezing on the bottom of the ice shelf, Jeffries fears that the
      shelf may start to thin, or thin at a faster rate.

      The Ward Hunt Ice Shelf breakup comes at the same time as news of
      unprecedented melting of sea ice in the Northern Hemisphere. "Sea ice
      cover has been shrinking about 3 percent per decade over the past few
      decades. We saw a record minimum in September 2002, and the summer of
      2003 almost set a new record," said Mark Serreze, a research
      scientist at the National Snow and Ice Data Center in Boulder,
      Colorado.

      Loss of sea ice can have major implications for global climate.
      Because of its light appearance, sea ice reflects most of the Sun's
      energy back into space, whereas darker seawater absorbs most of the
      incoming radiation and could potentially warm Earth's climate. As sea
      ice continues to melt, more radiation will be absorbed by the ocean.

      This Canadian RADARSAT image, acquired in August 2002, shows the
      central crack in the Ward Hunt Ice Shelf running down the center of
      the image. (Image courtesy of the Alaska Satellite Facility,
      Geophysical Institute, University of Alaska Fairbanks)

      Additional images of the Ward Hunt Ice Shelf are available in News
      and Natural Hazards.

      Biodiversity loss concerns Vincent as much as potential climate
      change. Both the ice shelf and the epishelf lake it dammed hosted
      uncommon microenvironments. "As you fly over in a helicopter, you see
      these beautiful Mediterranean-blue lakes on the ice. Within these
      lakes are remarkable microbial communities. A lot of them are bright
      orange because they're rich in carotenoids, the same pigments found
      in carrots, which protect them from UV radiation. They look like
      alien life forms, but they're actually micro-worlds of bacteria, and
      microscopic plants and animals. As we're losing sections of the ice,
      we're losing portions of these communities," he said.

      Another type of community also disappeared with the epishelf lake.
      Disraeli Fiord's combination of fresh, brackish, and salt water
      created a rare ecosystem of cold-adapted, salt-tolerant organisms.
      According to Vincent, further research on the epishelf lake's
      microbial community might have discovered brand new
      species. "Unfortunately, we didn't have enough time for the molecular
      techniques needed to identify new species," he said.

      Scientists study a luxuriant microbial mat on the Markham Ice
      Shelf, one of the last remaining ice ecosystems on the northern coast
      of Ellesmere Island. (Image courtesy of Warwick Vincent, Université
      Laval)

      Beyond improving knowledge of modern biodiversity, polar
      communities may help scientists understand Earth's past. A hypothesis
      that has gradually developed since the 1960s postulates that between
      800 and 600 million years ago, the Earth underwent a series of global
      glaciations, a time nicknamed the Neoproterozoic "Snowball Earth." It
      was after this period of worldwide freezing that multicellular life
      forms began leaving a rich fossil record. "One of the arguments
      against the Snowball Earth hypothesis is that life might not have
      survived the massive freeze-ups," said Vincent. "But those of us
      working in the polar regions see incredible opportunities for life in
      surprising places."

      Unfortunately, researchers may not get the chance to test their
      hypotheses by examining modern life forms. "We're really running out
      of time to understand these unique environments and their biota
      before they disappear," Vincent said.

      Understanding the impact of declining sea ice on marine wildlife may
      be easier to assess, though the news is not encouraging. Microbial
      ecosystems in sea ice comprise the base of much of the food chain in
      the Arctic Ocean. Directly or indirectly, zooplankton, fish, whales,
      seals, and polar bears depend on the energy provided by those
      microbial ecosystems. "In western Hudson Bay, satellite data reveal a
      significant change in sea ice cover, and we know from studies by the
      Canadian Wildlife Service that polar bears have been adversely
      affected by changes in their habitat that limit their access to
      seals," said Jeffries.

      Ice shelf decline may affect humans as well as wildlife. During its
      breakup in 2002, the Ward Hunt Ice Shelf calved a number of ice
      islands, and the heavily fractured ice shelf now has the potential to
      release many more. Ranging in sizes up to tens of kilometers, these
      ice islands could eventually drift into the Beaufort Sea and
      jeopardize shipping and offshore development, such as oil rigs. "An
      ice feature of this size could exert tremendous force on an offshore
      structure, and there wouldn't be much we could do to divert it," said
      Jeffries.

      Although researchers wouldn't be able to divert ice islands, they
      could use satellite data to track ice island movement. RADARSAT data
      was instrumental in tracking the movement of the giant B-15 iceberg
      that calved from the Ross Ice Shelf in Antarctica in March 2000, and
      the data may have similar applications in the Northern Hemisphere.

      Big as the ice islands are, the Ward Hunt Ice Shelf breakup does not
      approach the scale of ice shelf deterioration observed in
      Antarctica. "The Ward Hunt Ice Shelf is a fairly small feature, and
      in terms of global climate impact, the breakup of this ice shelf is
      trivial. Yet it's another indication of what's happening in the
      Arctic," said Serreze. Among the changes in the Northern Hemisphere
      that Serreze has recently reported are earlier spring breakups of
      river ice, increased freshwater runoff, shrinking glaciers, and trees
      and shrubs invading Arctic tundra. "The Arctic is changing. This is
      fact," he said.


      One of the oldest fossils of multicelluar oganisms is Dickinsonia.
      Estimated at 560 million years old, Dickinsonia may have evolved
      after the end of the last Neoproterozoic global glaciation. (Image
      Copyright © University of California Museum of Paleontology, 1994-
      2004. All rights reserved.)

      Some paleontologists suspect that the extreme conditions of the
      Snowball Earth may have jump-started evolution, ultimately giving
      rise to complex organs like this calcite-crystal eye of the trilobite
      Phacops. (Image courtesy of An Enlightened View of Calcite in the
      Ocean with MODIS from the GES Earth Sciences DAAC)

      Changes observed in the Arctic confirm climate model predictions. "We
      know from global circulation models — the results of which are
      broadly accepted among the polar climate and global climate
      community — that if global change is occurring, the effects will be
      felt first and amplified in the polar regions, particularly the
      Arctic," said Jeffries. "We've seen changes in the Arctic, and in
      recent years, the changes seem to be occurring faster."

      Vincent agrees. Prior to the Ward Hunt Ice Shelf breakup, his team
      monitored Disraeli Fiord for five years. Though he had observed
      gradual decreases in the lake's fresh water, its sudden disappearance
      caught him off guard. "I think it underscores a fundamental problem
      we have in climate change research," he said. "Climate change models
      usually predict gradual, continuous change, but real-life impacts are
      not continuous. Changes can be relatively small, and then suddenly
      you can move to a new threshold. This ice shelf survived 3,000 years
      of human civilization, but now it's gone."

      An ice island about 1.5 kilometers long, 250 meters wide, and 30
      meters thick moves into the Arctic ocean after the fracturing of the
      Ward Hunt Ice Shelf in August 2002. (Image courtesy of Warwick
      Vincent, Université Laval)

      How much change can be attributed to human activity is difficult to
      estimate. "We know the climate can vary on many different time scales
      due to natural processes," said Serreze. "But when we look at the
      longer-term record of paleoclimate information, the warming we're
      seeing does appear to be very unusual. Carbon dioxide concentrations
      in ice cores today are probably the highest they've been in 400,000
      years. There's a growing consensus between the things we're observing
      and climate model projections of change. I'm still a fence-sitter,
      but I'm leaning more to the side of human causes for at least some of
      what we're seeing."

      Jeffries and Vincent plan to continue monitoring the Ward Hunt Ice
      Shelf and Ellesmere Island. "It's at the northern limit of North
      America, right in the bull's-eye of the region that climate models
      predict will change most rapidly, most abruptly, and most severely,"
      said Vincent. RADARSAT data will continue to play a role in that
      monitoring. "We have been especially impressed with RADARSAT imagery
      resolution. In combination with our field measurements, it's provided
      an unprecedented time series showing the magnitude of change."

      "I think this ice shelf breakup is another example of how valuable
      remote sensing is, and how important it is that scientists have easy
      access to these data on a frequent basis," said Jeffries. "Otherwise,
      we miss things we really need to know."


      Reductions in sea ice cover have put polar bear populations at risk.
      Here, two orphaned cubs await transport to a zoo. (Image courtesy of
      the NOAA Photo Library)

      References:
      Mueller, Derek R., Warwick F. Vincent, and Martin O. Jeffries. 2003.
      Break-up of the largest Arctic ice shelf and associated loss of an
      epishelf lake. Geophysical Research Letters. 30(20):2031.
      doi:10.1029/2003GL017931.
      Sturm, Matthew, Donald K. Perovich, and Mark C. Serreze. 2003.
      Meltdown in the north. Scientific American. 289(4):60-67.
      Hoffman, Paul F. and Daniel P. Schrag. 2000. Snowball Earth.
      Scientific American. 282(1):68-75.
      RADARSAT-1 Antarctic Mapping Project. Accessed November 25, 2003.
      RADARSAT-1. Accessed January 13, 2004.
      For more information, visit the Alaska Satellite Facility DAAC.

      This article contributed from Distributed Active Archive Center
      (DAAC) Alliance: Supporting Earth Observing Science 2004 (to be
      released in the fall of 2004)

      The NASA Distributed Active Archive Center (DAAC) Alliance provides
      data and user services in support of the Earth observing sciences.
      For other articles about DAAC Alliance data, visit the DAAC Alliance
      features list.

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