Greenland Something Less than Snow White

12 August 2005, 8 PM local time, Photo from a helicopter flying over the ice sheet surface at ~1500 feet altitude. This is how much darker the Greenland ablation area is than a fresh snow surface that blankets it in wintertime. Along much of the southwestern ice sheet at the lowest 1000 m in elevation, impurities concentrate near the surface and produce this dark surface. Not all of the ice sheet is this dark, only the lower ~1/3 of the elevation profile of the ice sheet is. However, as melting increases on the ice sheet, so does the area exposed that is this dark.

The following provides detail to a story run by NOAA entitled Greenland Ice Sheet Getting Darker…

Freshly fallen snow under clear skies reflects 84% (albedo= 0.84) of the sunlight falling on it (Konzelmann and Ohmura, 1995). This reflectivity progressively reduces during the sunlit (warm) season as a consequence of ice grain growth, resulting in a self-amplifying albedo decrease, a positive feedback. Another amplifier; the complete melting of the winter snow accumulation on glaciers, sea ice, and the low elevations of ice sheets exposes darker underlying solid ice. The albedo of low-impurity snow-free glacier ice is in the range of 30% to 60% (Cuffey and Paterson, 2010). Where wind-blown-in and microbiological impurities accumulate near the glacier ice surface (Bøggild et al. 2010), the ice sheet albedo may be extremely low (20%) (Cuffey and Paterson, 2010). Thus, summer albedo variability exceeds 50% over parts of the ice sheet where a snow layer ablates by mid-summer, exposing an impurity-rich ice surface (Wientjes and Oerlemans, 2010), resulting in absorbed sunlight being the largest source of energy for melting during summer and explaining most of the inter-annual variability in melt totals (van den Broeke et al. 2008, 2011).

The photo below shows how dark the ice sheet surface can become in the lowest ~1000 m elevation in the “ablation area” after the winter snow melts away and leaves behind an impurity-rich surface. This dark area is where the albedo feedback with melting is strongest.

 Dirty ice surrounds a meltwater stream near the margin of the ice sheet. Compared to fresh snow and clean ice, the dark surface absorbs more sunlight, accelerating melting. © Henrik Egede Lassen/Alpha Film, from the Snow, Water, Ice, and Permafrost in the Arctic report from the U.N. Arctic Monitoring and Assessment Programme.

Satellite observations from the NASA Moderate-Resolution Imaging Spectroradiometer (MODIS)  indicate a significant Greenland ice sheet albedo decline (-5.6±0.7%) in the June-August period over the 12 melt seasons spanning 2000-2011. According to linear regression, the ablation area albedo declined from 71.5% in 2000 to 63.2% in 2011 (time correlation = -0.805, 1-p=0.999). The change (-8.3%) is more than two times the absolute albedo RMS error (3.1%). Over the accumulation area, the highly linear (time correlation = -0.927, 1-p>0.999) decline from 81.7% to 76.6% over the same period also exceeds the absolute albedo RMS error.

Greenland ice sheet average reflectivity or albedo (multiply by 100 to get % units) for 12 summer (June-August) periods.

NOAA Climate Watch:

According to Jason Box, the lead author of the Greenland chapter of the 2011 Arctic Report Card and the analyst of the reflectiveness data, the darkening in the interior is just as remarkable than the changes at the margins. The interior is the high-point of the dome-shaped ice sheet, rising to nearly two miles above sea level. There is no visible melting there in the summer, so why is the area becoming darker?

Map of changes in the percent of light reflected by the Greenland Ice Sheet in summer (June-July-August) 2011 compared to the average from 2000-2006. Virtually the entire surface has grown darker due to surface melting, dust and soot on the surface, and temperature-driven changes in the size and shape of snow grains. Map by NOAA’s climate.gov team, based on NASA satellite data processed by Jason Box, Byrd Polar Research Center, the Ohio State University.

The darkening in the non-melting areas, says Dr. Box, is due to changes in the shape and size of the ice crystals in the snowpack as its temperature rises. Snow grains clump together, and they reflect less light than the many-faceted, smaller crystals. Additional heat rounds the sharp edges of the crystals. Round particles absorb more sunlight than jagged ones do.

A freshly fallen snow crystal has numerous facets to reflect sunlight (left). Warming causes the grains to round at the edges and clump together (right). Scanning electron microscope photos courtesy the Electron and Confocal Microscopy Laboratory, USDA Agricultural Research Service.

Climate Denial Crock of the Week 

On the Kangerdlugssuaq Glacier -- one of Greenland's largest ice fields -- scientists measure the movement of the ice sheet as it transports frozen water to the ocean. They discover that the speed of the glacier's march to the sea has tripled in just ten years. Alarm bells sound because at the current melt rate, within a few decades rising seas will have a profound effect on the low-lying countries of the world.

Once considered an inexhaustible source of food, the oceans are now in danger of being significantly depleted. Matt Damon hosts "The State of the Planet's Oceans" as award-winning filmmakers Hal and Marilyn Weiner investigate the health and sustainability of the world's oceans and the issues affecting marine preserves, fisheries, and coastal ecosystems worldwide.

NASA Mission, Led by Stanford Biologist, Finds Massive Algal Blooms Under Arctic Sea Ice

The NASA-sponsored ICESCAPE expedition that discovered the bloom was led by Stanford 

environmental Earth system science Professor Kevin Arrigo. (Photo: Gert van Dijken)

A massive phytoplankton bloom has been found underneath the Arctic pack ice in the Chukchi Sea. The under-ice bloom, previously thought impossible, will require a complete rethinking of Arctic ecosystems – and is a potent indicator of global warming's effects on the far north.

The 2011 NASA-sponsored ICESCAPE expedition that discovered the bloom was led by Stanford environmental Earth system science Professor Kevin Arrigo. The paper announcing the find appeared today in Science.

 

 

Under-ice discovery

Unlike most Arctic research teams, ICESCAPE headed deep into the Chukchi Sea ice pack, north of the Bering Strait. The research cruise, consisting of prominent scientists in the fields of oceanography, biology, chemistry and optics, was intended to improve NASA's remote monitoring of the Arctic's changing conditions.

"Suddenly, the fluorometer" – the fluorescence-measuring device used to estimate the algal content of water – "went nuts," Arrigo said. "We thought there was something wrong with the instrument."

Most models of biological production in the Arctic Ocean assume a value of zero below pack ice. Sea ice and snow cover have historically reflected incoming solar radiation, leaving no sunlight for plankton in the water below.

"Not only was the value not zero," said Arrigo, "production was higher there than it was in open water."

Based on samples from surrounding water and on the species of algae in the bloom, the scientists confirmed that the phytoplankton had not drifted under the ice from elsewhere.

Instead, changing ice conditions now allow light to penetrate large swaths of Arctic sea ice. 

Thick "multi-year" ice, which requires several seasons to accumulate, is on the decline, while warming temperatures favor thinner "first-year ice." Additionally, the melt pools that now commonly form on top of Arctic sea ice decrease the ice pack's ability to reflect light.

The resulting under-ice environment is ideal for Arctic phytoplankton. The thin ice lets in light while protecting the algae from ultraviolet radiation.

"Grow rates under the ice are higher than I thought was possible for Arctic phytoplankton," Arrigo said. Algal cells that would normally take three days to divide were doubling more than once a day.

 

A shifting Arctic

While the discovery marks the first direct observation of an under-ice bloom, the conditions that allow for it in the Chukchi Sea exist over a large area of the Arctic.

"We suspect that this is a lot more widespread than we realize," said Arrigo.

The appearance of under-ice blooms may presage wholesale shifts in the ecosystem of the Arctic. Colder-water phytoplankton production, as with under-ice algae, may cause organic matter to drop to the ocean floor sooner. The effect would benefit bottom-feeding species, to the detriment of species that feed in the water column.

And, as algal blooms are able to occur earlier in the year, animals that depend on timing their behavior to "pulses" in algal productivity may be left out in the cold.

One piece of seemingly good news is an increase in the Arctic's ability to sequester carbon. As the Arctic Ocean's productivity increases, so should its carbon capture rate. But, Arrigo says, the effect is unlikely to make much difference.

"Even if the amount of CO₂ going into the Arctic Ocean doubled, it's a blip on a global scale," he said.

Written by Max McClure@News Stanford University

Warming Climate Sets Evolution Within Ice to High

Microbes frozen in ice for eons are evolving as they thaw. 

 

While they pose little threat to humans now, they could force out existing microbial populations, with unknown effects.

 

Don't expect to see strange, cobbled-together creatures like miniscule Frankenstein's monsters climbing out onto a shore near you.

The world's ice sheets, scientists now say, are a gigantic reservoir of microbial life – some of which are relics hundreds of thousands of years old. Most of what has melted out and been identified appears related to common soil and marine bacteria. But scientists see evidence that these bugs are evolving within the ice.

Scientists think it’s unlikely that any off-the-wall organisms will turn up. "I think whatever we've been exposed to at this point won't be terribly different from things that are melting out now," said Scott Rogers, an evolutionary biologist at Bowling Green State University in Ohio. "The chances of something really bizarre coming out now are very, very slim."

A warming climate could set the speed of evolution to high, however. University of Wisconsin, Madison, biologist Jonathan Klassen and a colleague have identified five new species of a common bacterium from Antarctica's Victoria Upper Glacier. The new strains, found in 4,000-year-old ice, are bright pink and have acquired new traits that show the organisms are exchanging DNA.

"Bacteria can be fairly promiscuous in terms of trading genes with each other," Klassen said. By moving snippets of genetic information directly from cell to cell, these ice-bound microbes are "creating a whole bunch of diversity that wasn't there before." Recombining in ice is a particularly good mechanism for microbial evolution because it involves individual cells, which can then melt out and introduce new traits into the existing population. 

"You'll get new combinations of organisms that have the ability to take advantage of modern conditions," Klassen added. In an altered climate, many existing types of microbes will be unable to adapt and will end up going extinct. The environmental niches they inhabited will be available to opportunists.

"And that's where these [new] organisms come in," he said.

By Cheryl Katz@The Daily Climate