A new study shows that the loss of Arctic sea ice has a detrimental effect on polar bear reproduction. As ice breaks up earlier in the year, females are less likely to give birth to twins and triplets due, in part, to food scarcity, according to the study. Photo: AP Photo/The Canadian Press,Jonathan Hayward

Scientists have found that polar bear litter size is decreasing and it appears to be correlated with melting Arctic sea ice, according to a new study published Feb. 8, 2011 in the journal Nature Communications. If the melting trend continues as is predicted, polar bear reproduction could be imperiled.

Population decline

“Polar bear litter size is decreasing,” study lead author Peter Molnar of the University of Alberta, now a post-doc at Princeton University, told USA Today. Specifically, the scientists analyzed a group of polar bears near western Hudson Bay in Canada, the population of which dropped from 1,200 to 900 in the past 20 years.

Twins and triplets less common

“There were lots of triplets and twins in the 1990s, and now there are more females with just a single cub or twins,” says Molnar.

Earlier ice break up means drastic reproduction declines

According to the study, 28 percent of the females were not reproducing in the early 1990s. Using computer models to predict what will happen in 2050, the study found that if the ice breaks up just one month earlier, then 40 to 70 percent will not reproduce.

Surviving on the ice

For eight months, polar bears live on sea ice and hunt for seals. During the warmer months, they live on land and fast, surviving off their fat stores. Photo courtesy NSIDC

Arctic ice is critical for polar bears. For eight months out of the year the bears live on the ice and feed on seals. During the warmer months the bears fast on land. As the ice melts, the bears have less time at sea which means less time to eat and store fat. This can affect the bears’ fertility.

Food scarcity results in lower reproductive rates

“When little food is available,” the study states, “polar bears are known to rely on stores of energy for survival and reproduction. The reliance on energy stores in pregnant females however, limits the survival rates of their cubs.”

Arctic ice has been breaking up earlier and earlier each year, says Molnar. Just last week, the National Snow and Ice Data Center reported that Arctic sea ice was at its lowest January level on record.

Current litter size indicates future populations

“The litter size predictions provided in this study serve as another indicator that the western Hudson Bay population will probably not remain viable under predicted climatic conditions,” the authors write in the study.

“Outside western Hudson Bay, over one-third of the global polar bear population follows similar patterns of seasonal on-ice feeding and on-shore fasting.”

Thus, the study concludes, similar litter size declines may occur in over one-third of the global polar bear population.  —Rachel Walker

Comments (1) Feb 09 2011

Obama assigns Arctic Science Policy to White House

In July, the White house announced that Arctic science policy oversight will now fall under a White House council organized by President Obama’s science adviser, John Holdren. Under the new organization, the council’s environment and natural resources committee will oversee activities of the federal Interagency Arctic Research and Policy Committee. The move underscores the significance of the committee, which was originally created by Congress in 1984. It surveys arctic research to help set federal priorities in natural resources, physical and biological sciences and social and behavioral sciences. The same act of Congress established the Arctic Research Commission, a presidentially appointed group that recommends broad arctic policy goals. The commission has seats for four scientists, two private industry representatives and an indigenous leader.

Jakobshavn Isbrae Glacier Loses 2.7 Square Mile Ice Chunk

Satellite images show a major calving event on the Jakobshavn Isbrae glacier, July 6 and 7. Photo: Courtesy of NASA via DigitalGlobe

NASA-funded researchers monitoring Greenland’s Jakobshavn Isbrae glacier report that a 7 square kilometer (2.7 square mile) section of the glacier broke up on July 6 and 7, causing the calving front—where the ice sheet meets the ocean—to retreat nearly 1.5 kilometers (a mile) in one day. The chunk of lost ice is roughly one-eighth the size of Manhattan Island, New York.

Research teams led by Ian Howat of the Byrd Polar Research Center at Ohio State University and Paul Morin, director of the Antarctic Geospatial Information Center at the University of Minnesota have been monitoring satellite images for changes in the Greenland ice sheet and its outlet glaciers. While this week’s breakup itself is not unusual, Howat noted, detecting it within hours and at such fine detail is a new phenomenon for scientists.

Jakobshavn Isbrae is located on the west coast of Greenland at latitude 69°N and has retreated more than 45 kilometers (27 miles) over the past 160 years, 10 kilometers (6 miles) in just the past decade. As the glacier retreated, it broke into a northern and southern branch. The breakup this week occurred in the north branch.

Scientists estimate that as much as 10 percent of all ice lost from Greenland is coming through Jakobshavn, which is also believed to be the single largest contributor to sea level rise in the northern hemisphere. Scientists are more concerned about losses from the south branch of the Jakobshavn, as the topography is flatter and lower than in the northern branch.

July Melting Sea Ice Data Released

The National Snow and Ice Data Center in Boulder, CO., reported that the ice extent for July 2010 was 8.39 million square kilometers, the second lowest on record. Although this year’s melting is significant, it likely won’t set a new record. The report also reveals that older, thicker multi-year ice continues dramatic declines.

Meteorite May Affect Beaufort Sea Probe

The U.S. Coast Guard Cutter Healy is probing deep in the Beaufort Sea to map the Arctic shelf. Photo: U.S. Coast Guard

Canadian and U.S. scientists aboard two government research vessels must navigate around a two-million-year old meteorite deep in the high Arctic as they attempt to probe the depths of the northern Beaufort Sea. The meteorite is believed to be lodged in the submerged peaks of Alpha Ridge — a 2,000-km-long undersea mountain chain off of Canada’s northernmost shores, about 300 kilometers beyond Ellesmere Island. Both Canada and the U.S. are trying to prove that parts of the Arctic seabed are extensions of the North American landmass, key to asserting political authority over those areas under provisions of the UN Convention on the Law of the Sea (UNCLOS).

To that end, the U.S. Coast Guard cutter Healy and the Canadian Coast Guard icebreaker Louis S. St-Laurent are heading north in early August to continue the two nations’ collaborative Arctic mapping mission in the shadow of Alpha Ridge.

Navy Subs Help Scientists Expand Study of Arctic Thaw

The New York Times reports that scientists who study Arctic ice have signed an agreement with the U.S. Navy to use nuclear powered marine subs to collect information on parts of the Arctic’s ice and ocean that normally lie beyond scientists’ reach. The agreement revives a program called SCICEX — short for “Science Ice Exercise” — that began in 1993, and which went dormant after six years.

Now, with data documenting Arctic warming that led to a historic low in summer sea ice in 2007, the shortening of the region’s snow season, rising land surface temperatures and warmer permafrost, and changes in the population and habitat of polar bears, walruses, seabirds and other Arctic wildlife, scientists and the Navy are collaborating to restart the SCICEX program.

SCICEX will allow scientists to use submarines that can travel at high speed and operate even in areas that are covered by ice instead of icebreaking ships to collect data. The subs will also provide data to help “ground-truth” satellite measurements. The submarines can also collect data on ocean chemistry that satellites cannot.

The renewed SCICEX program will operate under a memorandum of understanding inked in 2000 between the National Science Foundation and parts of the Navy. The new science plan calls for collection of baseline data on the Arctic’s ice canopy and seafloor and the physical, chemical and biological properties of Arctic seawater.

Comments (0) Aug 06 2010

At the edge of the sea ice, a Barrow resident awaits the return of a seal-skin whaling boat. Photo: Faustine Mercer

Here’s a really interesting story on Shari Gearheard’s NSF-funded people and sea-ice study. Gearheard, a glaciologist from U Colorado’s National Snow and Ice Data Center, combined scientific sea-ice studies with the traditional knowledge of Inuit collaboraters who’ve spent their lives on or near the ice.  The aim: to gain a better understanding of how sea ice is changing in the Arctic–and how community lifeways around the Arctic may be changing in response.  

Gearheard and her collaborators speak extensively in the piece, and what they have to say about the changes they’ve seen in sea-ice conditions is compelling.   

“‘I’m a scientist so when I look at sea ice I see what its properties are. How dense it is. But I remember sitting with the hunters when we were all in Qaanaaq. They looked at the sea ice and the first thing they said they saw was ‘freedom’.  

‘(Sea ice) meant they could hunt for food. It meant they could travel to see relatives on the other side of the water, that they hadn’t seen all year.  

‘That was a very powerful thing for me as a person, not just as a scientist.’”–Shari Gearheard  

* * *

“‘When I was a boy, the ice used to hover around Barrow all year,’ 51-year-old Leavitt said. ‘Now when the ice takes off it doesn’t want to come back. So our hunting is very limited.’”–Joe Leavitt, Barrow resident and whaling captain  

* * *

“‘We used to live as nomads in those days,” Sanguya continued. “After Christmas, when there was enough snow, we’d go out on the sea ice and make igloos.  

‘In those days I didn’t have any math or measurements … or anything like that. But I remember looking down through seal breathing holes and the ice was so thick, they looked like they were tapering away.  

‘Today you don’t see that very much. You’ll probably see 4 feet or 5 feet (down) and that’s it.’”–Joelie Sanguya, Elder and hunter, Clyde River, Nunavut

Hunters in Qaanaaq, Greenland traditionally travel over the sea ice on dog-powered sledges like these. Photo: Hans Jensen

Comments (0) May 13 2010

A recent study found that polar bears predating 1950 that ate a phytoplankton-based diet have higher concentrations of mercury in their systems than bears that eat diets based from the ice algae food web. Photo: Jerzy Strzelecki

The looming threat of melting sea ice has raised awareness about climate change’s impact on polar bears, an endangered species. Also relevant—and less studied—is how changes to the earth—and melting sea ice—could affect the species’ diet. 

Which may be why a recent study in the December issue of the journal Polar Research that establishes two different primary food webs for polar bears and documents surprisingly higher mercury levels in bears that eat from one specific web garnered interest from both the scientific community and science journalists. 

Mercury concentrations can be poisonous to humans and other members of the food chain; currently scientists do not know what levels of mercury are dangerous to polar bears. 

(Note: mercury is not a greenhouse gas, nor is it associated directly with global warming. However, high concentrations of mercury in polar bears is significant to scientists for complex reasons outlined below.) 

Diet Details 

 The study confirmed that polar bears got their food from two primary food webs: 

• Phytoplankton-based, which begins with single-celled plants inhabiting the top layer of the ocean 

• Ice algae-based, which begins with microscopic plants living within and below the sea ice 

The research went further, analyzing mercury concentrations in the bears’ fur. 

They found that polar bears chowing down on the phytoplankton-based food chain, which originates in the open ocean in the absence of sea ice, had greater concentrations of mercury in their bodies than bears whose diet traced back to the ice algae. 

Dr. Joel Blum, principal investigator, collects snow samples to test for mercury concentrations near Barrow, AK. Photo: Joel Blum

Mercury Investigations 

One of the study’s authors, Joel Blum, the John D MacArthur Professor of Geological Sciences, and Professor of Ecology at the University of Michigan, said the findings are significant as scientists strive to learn more about mercury, an inorganic element whose presence in the atmosphere has tripled since the industrial revolution. 

“Very little is known about how mercury moves around the globe,” said Blum. “But we know humans have increased the amount of mercury in the environment.” 

Mercury can stay in the atmosphere for up to a year and travel to far reaches of the globe, and scientists have documented a considerable amount of mercury deposited in the Arctic. Studying the bears provides important background data on earlier mercury levels, Blum said. 

Factory emissions are a major source of mercury pollution. Photo: courtesy Air Resources Laboratory, NOAA

Museum Bears 

Blum and his colleagues analyzed mercury concentrations in polar bears that predated 1950, before the major influx of mercury from coal-burning power plants and other industrial activities that send mercury into the atmosphere. 

Specifically, they analyzed the late-19th- and early-20th-century polar bear hair for the chemical signatures of nitrogen isotopes, carbon isotopes, and mercury concentrations, looking back in time to a period before man-caused mercury emissions escalated. 

“We know that due to human inputs mercury distribution in the Arctic is currently heterogeneous (multi-faceted and complex), so we decided to take a step back and understand the fundamental processes, pre-1950,” said Blum. 

Phytoplankton Diets = High Mercury Concentrations 

 The discovery that bears that eat on the phytoplankton food chain have significantly higher mercury concentrations suggests that as sea ice melts and bears eat more phytoplankton-based diets, their mercury concentrations could increase, said Blum. 

Moving Through The Food Web 

 And, he added, if concentrations of mercury are increasing in polar bears, which are at the top of the food chain, “this is an indication that they are also increasing lower in the arctic food chain.” 

That means human populations that rely on subsistence hunting could also be experiencing an increase of mercury exposure as well. 

How Mercury Becomes Poison 

 Relatively harmless in its inorganic state, mercury becomes extremely poisonous to humans when it is converted into methylmercury and passed up the food chain. 

Mercury in its methylated state is considered by many to be “public enemy number one,” said Blum. Its prevalence in the Arctic and potential to spread through the food chain is a very real concern and could be exacerbated by climate change. 

Recent discoveries about mercury’s biochemical properties have unlocked mysteries about the element and enabled scientists to probe deeper into the question of how a relatively inert element (mercury) can transform into a menacing poison. 

Scientists know that at times there can be extremely high concentrations of mercury in the Arctic snow pack and are working to understand where it is coming from and what unique chemical reactions take place in the Arctic that lead to rapid deposition of mercury from the atmosphere to the snowpack. 

Next Steps 

Sunrise on the flats near Barrow. Blum and his colleagues hope to better understand how mercury travels to and deposits in the Arctic. Photo: Joel Blum

Now that his team better understands the Arctic food web, pre-1950, the logical next step would be to examine mercury levels and nitrogen and carbon isotopes in bears from 1950 to present day, he said. 

In addition, much remains to be understood regarding mercury in the Arctic. Specifically, scientists want to better understand where it comes from, how it travels to northern latitudes, what mechanisms cause it to be deposited, and where it is converted to methylmercury. 

“We want to better understand what’s going on in the arctic mercury cycle, to see if we can help mitigate the problem,” said Blum.  —Rachel Walker

Comments (0) Jan 26 2010

Retreating sea ice leaves the Alaskan coast vulnerable to the full force of the ocean. Photo: Benjamin Jones, USGS

Rapid erosion of the northern coastline of Alaska midway between Point Barrow and Prudhoe Bay is accelerating at a steady rate of 30 to 45 feet a year, according to CPS-supported scientists presenting a study at the annual American Geophysical Union meeting this week in San Francisco. As the coast erodes, frozen blocks of silt and peat that contain 50 to 80 percent ice topple from bluffs into the Beaufort Sea during the summer.

The acceleration is caused by a combination of large waves pounding the shoreline and warm seawater melting the base of the bluffs, said CU-Boulder Associate Professor Robert Anderson, a co-author on the study. Once the blocks fall they melt within days and sweep silt material out to sea.

Anderson, along with collaborators Cameron Wobus of Stratus Consulting and Irina Overeem of CU’s Institute of Arctic and Alpine Research (INSTAAR) have studied the coastline for the past two summers with Office of Naval Research support. Equipped with two meteorology stations, a weather station, time-lapse cameras, detailed GPS and wave sensors outfitted with temperature loggers, they documented the summer ocean/shore dynamic.

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Triple Whammy

Declining sea ice, warming sea water, and increased waves create a “triple whammy” that expedites erosion. For the majority of the year, the Beaufort Sea is covered with sea ice that disconnects from the coast during the summer. These ice-free summer conditions are lasting for longer periods of time, allowing warmer ocean water to lap the coast and weaken the frozen ground. And the longer that sea ice is not connected to the coastline, the further the distance grows between the ice and the shore.  This open-ocean distance between the sea ice and the shore, known as “fetch,” increases both the energy of waves crashing into the coast and the height to which warm seawater can come into contact with the frozen bluffs, said Anderson.

The shoreline bluffs are made up of contiguous, polygon-shaped blocks, primarily made of permafrost and measuring roughly 70 to 100 feet across. Ice “wedges” (created by seeping summer surface water that annually freezes and thaws) are driven deep into the cracks between individual blocks each year. The blocks closest to the sea are undermined as warm seawater melts their base, and eventually split apart from neighboring blocks and topple during stormy conditions, said Anderson.

Impacts of Erosion

As the coastline submits to the ocean, old whaling stations, military and oil related infrastructure and entire towns threaten to fall into the sea. In addition, the loss of sea ice alters ocean systems and diminishes habitat for creatures like the polar bear.

According to a 2009 CU-Boulder study, Arctic sea ice during the annual September minimum is now declining at a rate of 11.2 percent per decade. This year, only 19 percent of the ice cover was more than two years old — the least ever recorded in the satellite record and far below the 1981-2000 summer average of 48 percent.

Comments (0) Dec 16 2009