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Study shows increasing snow-free season on Slope

August 18th | Shady Grove Oliver Print this article   Email this article  

Snow is melting sooner and coming in later on the North Slope, and that, in turn, is having an affect on other ecological variables.

"So, we want to understand what about this location, the atmosphere, the sea ice conditions, might be influencing the snow here around Utqiaġvik and what that means for the environment, like the growing season or the local seabird population," said Christopher Cox, a research scientist at the University of Colorado.

Through a partnership between the university's Cooperative Institute for Research in Environmental Sciences (CIRES) and the National Oceanic and Atmospheric Administration (NOAA), researchers have been diving deep into long-term data sets and observations to learn more about the causes and effects of the longer annual snow-free season.

Some of their findings are the subject of a paper recently published in the Bulletin of the American Meteorological Society.

Researchers have been collecting data in the Utqiaġvik area for more than a century, with the first snow record dating back to 1901 from a National Weather Service station. The records are a bit touch-and-go through the early 20s, when the service installed its first weather observatory.

"We end up with a snow record from this location that goes back pretty continuously to 1920," said Cox. "Most of the past 115 years are captured, so this is an extraordinarily long record of surface observations for the Arctic."

What that data shows is that the snow-free season in the area, meaning the time between spring melt and fall ice-in, has been trending longer since the 1970s.

"Not having the snow impacts substantially the surface energy budget, or the surface radiation budget, [meaning] how much energy is being absorbed at the surface rather than reflected, which affects the temperature," he explained.

That same cycle is often talked about in terms of sea ice — the more white ice there is, the more it reflects energy (sunlight) back from the water. The more water (which is darker than ice) is exposed, the more energy is absorbed, increasing temperatures and in turn, thawing more ice.

Along with temperature, the annual freeze-thaw cycle affects a multitude of other ecological factors as well, such as river flow and runoff, and the life cycles of plants and animals.

One of the types of animals included in the study is the black guillemot, a seabird found on Cooper Island, several miles outside Utqiaġvik.

Observations from the local Friends of Cooper Island group allowed researchers to learn that these birds were mating and laying their eggs sooner than they previously had been. They nest on the ground, so they don't mate until the snow melts. An earlier melting season means an earlier start to their cycle, as well.

While those are some of the effects of the longer snow-free seasons, researchers were also interested in the causes.

They found there are a few important variables to take into consideration for both the spring melt and the autumn ice.

"In spring, one of the things we think is particularly important is atmospheric circulation in the North Pacific, specifically the Aleutian Low," Cox said.

He described the Aleutian Low as a quasi-stationary area of low pressure in the Gulf of Alaska region. If the low is deeper and shifted more to the west in April and May, it sends warm, moist air from the North Pacific across Alaska. It's a driving force behind the heat waves the state saw in 2015 and 2016 and the snow melt that followed.

In the fall, sea ice is a key factor.

"Over the past couple of decades, we've had a decrease in sea ice in the western Arctic during summer. At this time of year, now, the ice edge is much further out than it used to be so there's much more open water. The timing of the freeze-up is getting much later," Cox said.

The wind that reaches the northern coast at that time of year circulates around an area of high pressure in the Beaufort Sea and then blows in off the ocean, he explained. That means, the more open water there is, the more the temperature is regulated by the sea, and kept warmer. Blowing in off the ice, the air is colder, which encourages the onset of snowpack. So, the less sea ice there is, the warmer the air will be coming off the coast, and the less likely snow is to set.

"The Arctic is in a state of change right now," he said.

That means, on top of the long-term observable trends, there are also short-term anomalies researchers have to grapple with. While 2015 and 2016 had some of the longest snow-free seasons on record, 2017 is proving to have one that is much shorter.

"The difference between 2016 and 2017 was about a month, so that's a really big change between two years and we don't really know what that means yet. I think we need to collect more data and study this moving forward to understand what this really means," he said. "Five years doesn't give you climatological perspective; it gives you five years. Five decades gives you something that allows you to statistically look at climate and to look at recent years and how they fit into the picture of multiple decades."

Looking back over the decades, researchers are able to see that the annual freeze-thaw cycle is tipping toward thaw rather than freeze. Consequently, they can see how that is affecting the land, animals, and people of the North Slope.

However, Cox said, they won't have a complete picture of the changes happening now, in historical context, until they're able to see what the next several years bring.

Shady Grove Oliver can be reached at sgoarctic@gmail.com.

 

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