Heart Lake, Adak, central Aleutian Islands. Photo: Darrell Kaufman

Next time you consider whacking the tiny, bloodthirsty mosquito persistently singing in your ear, consider for a moment that he and his kind may hold the key to past climate change. Mosquitoes are relatives to the diverse “non-biting midge” family, chironomids, small, two-winged flies that spend much of their life cycle in and around water. Yarrow Axford (Northwestern University) is looking to the mosquito’s relatives, preserved in lake mud, to help quantify western Alaska’s climate during the Holocene epoch, over the last 11,000 years. 

Small lakes form in the topographic lows carved by Alaska’s ancient glaciers. The lakes collect sediments during warm interglacial intervals like the Holocene. With funding from the National Science Foundation, Axford and Darrell Kaufman (Northern Arizona University) are collecting and studying sediment cores from these lakes in a transect across southern Alaska between Adak, one of the Aleutian Islands midway between Alaska and Russia, and Valdez. 

Back in the lab, Axford hunts for chironomids preserved in the lake sediments. During their larval stage these tiny flies molt four times. Chironomids shed the outer part of their entire bodies, but the head capsule, which looks like a teeny tiny helmet with teeth, is the part that allows Axford to identify the midges. The head capsules fall to the lake floor where they are preserved in the sediment. 

Yarrow Axford says hello to a chironomid. Photo: Darrell Kaufman

“Chironomids are very abundant in fresh water lakes across the Arctic and subarctic regions,” explains Axford. “So, this equates to lots and lots of larvae remains raining down on the lake floor. Their abundance makes them very useful” 

Under a microscope, Axford identifies midge species by examining minute features including each larva’s teeth: teeth patterns and shape; the number of teeth and whether that number is odd or even; and tooth positioning—all of these factors provide clues to the species. One benefit of using chironomids in paleoclimate studies is their sheer abundance. In only a gram of lake mud, Axford can find a statistically representative sample of chironomids—tens to hundreds of helmet-heads representing many different species. Since chironomids’ habitats are partly temperature-dependent, the different types of chironomids present in lake sediments can help constrain past temperatures and climate variability. 

Teeny tiny teeth. Photo: Yarrow Axford

A geologist by training, Axford first studied chironomids as part of her Ph.D. research at the University of Colorado, Boulder. With training from paleoclimatologist Donna Francis (University of Massachussets) Axford looked to midge assemblages to help reconstruct ecosystems and climate changes on Baffin Island, in the Canadian Arctic, and Iceland. Axford has found midge remains in 200,000-year-old lake sediments from Baffin Island and says that chironomids would probably be found in even older sediments 

Axford finds deep satisfaction from spending a day looking under the microscope. She admits she enjoys “the tedious, time-consuming work of identifying chironomids. The process is a bit old-fashioned when compared to black-box-ish geochemical methods, but concrete.” 

Coring takes a lot of stuff! Anne Krawiec and Dave Vaillencourt are up for it. Photo: Yarrow Axford

Meanwhile, Alaska’s Adak Island is a unique research location for a couple of reasons. First, there were no mosquitoes or bears complicating field work on Adak, which made it different than most other Alaska field locales (the tradeoff: wondering whether the field party would come across any “unexploded ordnance,” as signs posted at Adak’s decommissioned military base warn). 

“Adak is also likely to be biologically interesting. As an isolated north-Pacific Island which was completely ice-covered during the last glacial maximum, the chironomids were likely wiped out and then returned following glacial retreat and lake development,” says Axford. “I look forward to finding out what flies returned and where they were from. Which species showed up first, and were they from Asia or North America?” 

Anne Krawiec and Darrell Kaufman study a core. This beauty has a bonus volcanic ash layer! Photo: Yarrow Axford

Finally, as the westernmost location in Axford and Kaufman’s Alaska transect, this site will help them meet their goal of reconstructing southern Alaska’s Holocene climate, specifically in the context of the Aleutian Low, an area of low pressure that is centered on the Aleutian Islands in winter. The Aleutian Low is a major component of Northern Hemisphere circulation. Through detailed studies of lake sediments across many different sites, Kaufman and his students Anne Kraweic and David Vaillencourt hope to track the strength and position of a changing Aleutian Low as it migrated over time. This, says Axford, will help scientists identify important regional differences in Arctic climate. — Marcy Davis

Comments (1) Nov 29 2010

“Every day is different. We start each morning with oatmeal and coffee and a meeting in the cook tent and go from there.” – Jason Briner on field work in the western Brooks Range

Mapping Upper Kurupa Lake by Zodiac. Coring "cataraft" in the background. Photo: Darrell Kaufman

In July, Jason Briner (State University of New York, Buffalo) and Darrell Kaufman (Northern Arizona University) spent three weeks working in the Kurupa Valley in the western Brooks Range as part of a pilot study funded by the National Science Foundation to assess how Alaska’s climate and glaciers have changed over the last 10,000 years.

Remote Studies

Kurupa Valley basecamp. Photo: Jason Briner

Briner, Kaufman, and graduate students Mike Badding (SUNY Buffalo) and Brandon Boldt (NAU) put in by float plane and established a base camp in the Kurupa Valley. Using a fish-finder mounted on a Zodiac inflatable boat, they zig-zagged back and forth across the Upper Kurupa and Kurupa Lakes, mapping the lake bottom topography.

After choosing coring locations, the scientists anchored their “cataraft,” two rubber pontoons bridged by a plywood coring platform, to hold steady in often windy conditions. Using Briner’s trusty “percussion system,” corers spent an hour or two hammering a core tube into the lake bottom through a tripod and a hole in the platform.

Kaufman examines a core in less than perfect conditions. Photo: Jason Briner

Ordinarily, cores tubes are three meters, but this year, the team acquired seven meter cores using a custom-made corer extension dubbed the “Kaufman Kontraption” (or KK for short) for its designer.

Briner (right) and Kaufman get ready to kore using the Kaufman Kontraption. Photo: Darrell Kaufman

Kurupa Lake core collection (graduate student for scale). Photo: Darrell Kaufman

Once the core was pulled up, the team capped it, carried it ashore, and split it lengthwise for inspection before packing it for eventual shipment to the universities.

Reading the Cores

Back in the lab, the team is examining cores for organic content (preserved vegetation can be used for radiocarbon dating) and for volcanic ash layers, which can be chemically dated and correlated to other Alaskan lake cores.

Dating The Region With Geology

Hiking to Fireweed Glacier. Photo Jason Briner

The group also worked in the upper Kurupa Valley, collecting hand-sized rock samples for Beryllium 10 exposure dating, a chemical method that will help Briner decipher when and how quickly Kurupa Valley glaciers retreated.

Looking for hand samples on the Little Ice Age Moraine. Photo: Jason Briner.

As glaciers advance and retreat they deposit piles of rock debris, called glacial moraines, which are often reworked during younger and larger glacier advances. Consequently, glacial landscapes are not often preserved for longer than 500 years. The Kurupa Valley is unique because younger glaciations—those that came later than the one under study—covered less area, leaving moraines as old as 5000 years preserved in the valley.

Reconstructing History

Kaufman and Briner will reconstruct the glacial history of the western Brooks Range by correlating data obtained from rocks in the upper part of the valley with details teased from lake cores. The two-method approach will help the duo build on previous studies in which they examined north Pacific atmospheric circulation over the last 10,000 years.  —Marcy Davis

Comments (0) Oct 26 2010

Jason Briner samples for exposure dating in southern Alaska, 2006. Photo: Darrell Kaufman

Darrell Kaufman (Northern Arizona University) and Jason Briner (State University of New York, Buffalo) are at it again. This month, the climate scientists are working in the western Brooks Range for an NSF-funded pilot study aimed at assessing seasonal factors that contribute to changes in mountain glaciers. The research builds upon previous studies by Briner and Kaufman, which examine the response of north Pacific oceanic and atmospheric circulation to Arctic and Subarctic climate change over the last 10,000 years.

The team of four put in via float-plane from Bettles a week or so ago and established a base camp in the Kurupa Valley. During their three-week stint, they will map the lake bottom and collect sediment cores in the Upper Kurupa and Kurupa Lakes from a motorized inflatable boat. Briner and Kaufman will evaluate sediments for vegetation content (used for radiocarbon dating) and for the volcanic ash layers that may be time-correlated to layers in other Alaskan lake sediment cores. They will also visit the upper reaches of the valley to collect rocks from moraine deposits thought to record the last 5000 years of glacial history in the valley. Briner plans to use the hand-sized samples for Beryllium 10 exposure dating, a method that will yield a date and a rate at which glaciers retreated in the Kurupa Valley. From these data, Briner and Kaufman hope to produce a well-constrained glacial history for the western Brooks Range.

Christie Haupert, who manages CPS support to the project, herself an extreme sports woman, wrote about the Briner/Kaufman team’s stop in Fairbanks enroute to the field. “Darrell Kaufman and Jason Briner arrived on Wednesday. In a short three hours they managed to collect all gear, shop, shop, shop, and get onto a chartered caravan. Their plan was to make a single push from Anchorage to Kurupa Lake (north of Brooks Range) in one day. This meant three flights and collecting bits and pieces at each layover. As someone learning about endurance events, I highly respect this style of logistics.” 

*In other words, “Get up offa that thing!”

–Marcy Davis

Comments (1) Jul 19 2010

Cascade Lake, Alaska, during a 2009 coring trip. Photo: Darrell Kaufman

Darrell Kaufman jotted an email last week to report that his team was back from a ten-day excursion to Cordova, Alaska, to collect sediment samples from a group of area lakes. Their field work went well. “We recovered over 350 lb of mud from four different lakes and discovered some really interesting new records of environmental changes,” Kaufman wrote. For more on Kaufman’s work, click here.

Comments (0) Mar 25 2010

If all goes according to plan, Darrell Kaufman is coring lake sediments in southern Alaska. Of course, hardly anything ever goes according to plan.

Darrell Kaufman

One of the busiest researchers we know, paleoclimatologist Darrell Kaufman from Northern Arizona University, has started a long research season with a truck and snowmachine trip in southeastern Alaska’s Copper River Valley. He travelled there earlier this week to core a couple of lakes around Cordova.

After flying in to Anchorage a few days ago and picking up a truck with a trailer and two snowmachines, Kaufman and team drove down the gorgeous Richardson Highway to Valdez, and then travelled by ferry over to Cordova—or such was the plan. The Valdez area has received over five feet of snow in the past few days, but we suspect Kaufman’s team had already reached Cordova before the storm hit, and that all is proceeding roughly according to plan. Basing in Cordova, they will use snowmachines to travel to nearby lakes, still capped with winter ice—or so we hope. In this El Nino year, there’s been speculation that lake ice might be a bit thin.

The plan is to set a small drilling rig on the frozen lake and then to bore a hole in the ice in which to deploy the sediment coring equipment.  Cores harvested from the lake bottoms will be shipped to the Kaufman lab at NAU for analysis. Researchers will look for evidence in the sediments–tiny bugs, pollen spores, and dust, for example–that they can use to understand what climate was like when the particles drifted down to the lake bottom.

A Kaufman researcher examines deformed sediments pulled from beneath Tonsina Lake (one of the lakes Kaufman plans to revisit this trip). Photo courtesy D. Kaufman Web site: http://jan.ucc.nau.edu/~dsk5/

As we mentioned, Kaufman is busy this year. He’s leading a giant international collaboration of scientists who are looking at lake cores to better understand how unusual events, say, large volcanic eruptions, can trigger abrupt changes in climate—and what those abrupt changes look like in the sediment record, as well as what types of climate phenomenon may follow.  Understanding the “signatures” these events leave can help scientists improve the models we use to predict future climate.

Kaufman will also work in the Brooks Range this summer with collaborator Jason Briner; and he’ll revisit Adak Island in the Aleutian chain and Allison Lake to collect more lake cores. 

We caught up with Kaufman to learn more about his work last fall. Click here to find out about lake core science—straight from Kaufman himself.

We discovered this recent Kaufman article in the Arizona Republic, a statement about the so-called “Climategate” folly resulting from illegally-obtained emails.

Comments (0) Mar 11 2010