Tag: Sea Ice

High Levels of Molecular Chlorine Found in Arctic Atmosphere

 

By Brett Israel | Georgia Tech

January 13, 2014 Alaska Native News

Scientists studying the atmosphere above Barrow, Alaska, have discovered unprecedented levels of molecular chlorine in the air, a new study reports.

Molecular chlorine, from sea salt released by melting sea ice, reacts with sunlight to produce chlorine atoms. These chlorine atoms are highly reactive and can oxidize many constituents of the atmosphere including methane and elemental mercury, as well activate bromine chemistry, which is an even stronger oxidant of elemental mercury. Oxidized mercury is more reactive and can be deposited to the Arctic ecosystem.

Jin Liao checks the instrumentation in Barrow, Alaska, during a research trip to measure molecular chlorine in the atmosphere. Image-Georgia Tech
Jin Liao checks the instrumentation in Barrow, Alaska, during a research trip to measure molecular chlorine in the atmosphere. Image-Georgia Tech

The study is the first time that molecular chlorine has been measured in the Arctic, and the first time that scientists have documented such high levels of molecular chlorine in the atmosphere.

“No one expected there to be this level of chlorine in Barrow or in polar regions,” said Greg Huey, a professor in the School of Earth and Atmospheric Sciences at the Georgia Institute of Technology in Atlanta.

The study was published January 12 in the journal Nature Geoscience and was supported by the National Science Foundation (NSF), part of the international multidisciplinary OASIS program.

The researchers directly measured molecular chlorine levels in the Arctic in the spring of 2009 over a six-week period using chemical ionization mass spectrometry. At first the scientists were skeptical of their data, so they spent several years running other experiments to ensure their findings were accurate.

The level of molecular chlorine above Barrow was measured as high as 400 parts per trillion, which is a high concentration considering that chlorine atoms are short –lived in the atmosphere because they are strong oxidants and are highly reactive with other atmospheric chemicals.
Molecular chlorine concentrations peaked in the early morning and late afternoon, and fell to near-zero levels at night. Average daytime molecular chlorine levels were correlated with ozone concentrations, suggesting that sunlight and ozone may be required for molecular chlorine formation.

Previous Arctic studies have documented high levels of oxidized mercury in Barrow and other polar regions. The major source of elemental mercury in the Arctic regions is coal-burning plants around the world. In the spring in Barrow, ozone and elemental mercury are often depleted from the atmosphere when halogens — chlorine and bromine — are released into the air from melting sea ice.

“Molecular chlorine is so reactive that it’s going to have a very strong influence on atmospheric chemistry,” Huey said.

Chlorine atoms are the dominant oxidant in Barrow, the study found. The area is part of a region with otherwise low levels of oxidants in the atmosphere, due to the lack of water vapor and ozone, which are the major precursors to making oxidants in many urban areas.

In Barrow, snow-covered ice pack extends in every direction except inland. The ultimate source of the molecular chlorine is the sodium chloride in sea salt, Huey said, most likely from the snow-covered ice pack. How the sea salt is transformed into molecular chlorine is unknown.

“We don’t really know the mechanism. It’s a mystery to us right now,” Huey said. “But the sea ice is changing dramatically, so we’re in a time where we have absolutely no predictive power over what’s going to happen to this chemistry. We’re really in the dark about the chlorine.”

Scientists do know that sea ice is rapidly changing, Huey said. The sea ice that lasts from one winter to the next winter is decreasing. This has created a larger area of melted ice, and more ice that comes and goes with the seasons. This seasonal variation in ice could release more molecular chlorine into the atmosphere.

“There is definite climate change happening in the Arctic,” Huey said. “That’s changing the nature of the ice, changing the volume of the ice, changing the surface area and changing the chemistry of the ice.”

This research is supported by the National Science Foundation under award number ATM-0807702, ARC-0806437 and ARC-0732556. Any conclusions or opinions are those of the authors and do not necessarily represent the official views of the NSF.

A Continent of Ice on the Wane

 

 

A whale-watching platform made of and sitting on sea ice north of Barrow. Photo by Ned Rozell.
A whale-watching platform made of and sitting on sea ice north of Barrow. Photo by Ned Rozell.

Despite taking up as much space as Australia, the blue-white puzzle of ice floating on the Arctic Ocean is an abstraction to the billions who have never seen it. But continued shrinkage of sea ice is changing life for many living things. A few Alaska scientists added their observations to a recent journal article on the subject.

 

By Ned Rozell | Geophysical Institute

08/26/2013

 

Since 1999, the loss of northern sea ice equal to the size of Greenland is a “stunning” loss of habitat for animals large (polar bears) and small (ice algae and phytoplankton that feed a chain of larger creatures leading up to bowhead whales). So write the 10 authors that teamed to write “Ecological Consequences of Sea-Ice Decline,” featured in the August 2, 2013 issue of Science.

Eric Post of Penn State University, a former graduate student who studied caribou at the University of Alaska Fairbanks, is the lead author on the paper. When sea ice hit its minimum extent in the satellite era about a year ago, it got him thinking about how the loss of ice affects living things. That’s when Post, now the director of the Polar Center, rallied other contributors, from polar bear biologists to atmospheric scientists, to bring their results together.

“I think all of us as authors learned quite a bit about the importance of sea ice loss,” he said by email. “Individually, we each had a pretty clear idea of the implications of sea ice loss for certain parts of the arctic system, but none of us really grasped the full scope of the problem.”

Starting at the smaller end of things, the scientists point out that freshening of the Arctic Ocean caused by melting of sea ice may cause smaller types of plankton to thrive.

Arctic foxes, great wanderers of sea ice, will be limited by less of it, which would decrease the spread of rabies they sometimes carry from Russia’s mainland to Svalbard.

Walrus, which suck clams out of their shells with piston-like tongues, use sea ice as a resting spot between dives to the ocean floor. In recent years, people have seen more walruses using shorelines as haul-out spots; U.S. Geological Survey scientists counted 131 carcasses at one of these sites in September 2009. They wrote that the deaths, perhaps because of exhaustion or trampling, “appear to be related to the loss of sea ice over the Chukchi Sea continental shelf.”

In Canada’s arctic, “later freeze-ups and increased shipping traffic should shift or prevent the annual migration of the Dolphin and Union caribou herd,” the Science authors wrote. Parasites that feed off the caribou might increase because of this, but diseases spread by wandering caribou might decrease.

Polar bears need sea ice to hunt their favorite food, seals. As the sea ice shrinks, polar bears may be driven to land, where brown bears might outcompete them or hybridize with them.

The two UAF scientists who added to the report are Uma Bhatt, who studies the atmosphere, and Skip Walker, an expert on tundra plants. They have both done work to prove that the loss of sea ice has made the Arctic a greener place.

How might that happen? With less ice acting as a mirror for sunlight, the darker ocean absorbs more heat, which in turn warms the coastlines touching the Arctic Ocean. That warm air encourages plants to convert sunlight into growth at a higher rate and lengthens the growing season. Woody shrubs are becoming more numerous and taller, shouldering out smaller tundra plants. And the most extreme region of far north plants — a swath of bryophytes, lichens, blue-green algae and a few other non-woody species that make up what Russians call “polar desert” — seems to be headed for extinction.

The study helped lead-author Post envision northern sea ice as he would a great boreal forest or caribou herd scattered across an arctic plain.

“Sea ice is a living system,” Post said. “And not only does it harbor and sustain life, which is obviously affected by its loss, its disappearance influences the climate systems that affect life on other parts of the planet. We’ve come a long way in understanding how the loss of vast areas of mature tropical rainforest affects everything from indigenous cultures to species to ecosystems; our views of sea ice loss need to catch up with that understanding.”

Since the late 1970s, the University of Alaska Fairbanks’ Geophysical Institute has provided this column free in cooperation with the UAF research community. Ned Rozell is a science writer for the Geophysical Institute.

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