October 5th, 2021 by Logan Berner and Patrick Burns (Northern Arizona University), and Roman Dial (Alaska Pacific University)
Following caribou and brown bear trails when possible, a small NASA-supported research team trekked 800 miles across Alaska’s Brooks Range last summer. With additional support from NSF, the Alaska Space Grant Program, and the Explorers Club/Discover, the research team is collecting extensive ecological field data that will be linked with satellite observations to better understand long-term changes in vegetation, including impacts of climate warming. The Arctic is warming nearly twice as rapidly as the rest of the planet and the impacts are becoming increasingly evident as glaciers melt, permafrost thaws, and tundra greens.
Arctic greening and browning
Earth-observing satellites have detected widespread increases in tundra greenness in the Arctic over the last four decades. The phenomena is caused, in part, by increases in vegetation growth as summers have become warmer and longer, and has been termed “Arctic greening.” On the other hand, satellite observations have also detected localized declines in tundra greenness attributed to surface flooding, extreme weather, and other disturbances. This has been termed “Arctic browning.” Satellite observations of greening and browning show that extensive changes are occurring in the Arctic, but much remains unclear about why specific regions have greened or browned in recent decades.
To better understand recent greening and browning in northern Alaska, Professor Roman Dial’s team from Alaska Pacific University (APU) has been collecting extensive ecological observations while trekking throughout Alaska’s Brooks Range. For nearly forty years, Dial has studied and traversed the Alaskan wilderness, including nearly 2,000 miles by foot and packraft throughout the Brooks Range during the last three field seasons. For 11 days last summer, Dial’s team was joined by Dr. Logan Berner and Patrick Burns who are research ecologists from Northern Arizona University (NAU) and members of NASA’s Arctic-Boreal Vulnerability Experiment (ABoVE). While Dial is an expert in field ecology and wilderness travel, Berner and Burns are experts in satellite remote sensing and ecological informatics. By combining their expertise, these researchers hope to shed light on the extent, nature, and causes of vegetation changes during recent decades in the Brooks Range.
Trekking through the Brooks Range
The Brooks Range forms a natural barrier that separates the boreal forest of Alaska’s interior from the arctic tundra of Alaska’s North Slope. This mountain range includes the largest complex of protected wilderness in the United States, including 21,000,000 acres among the Arctic National Wildlife Refuge, Noatak National Preserve, and Gates of the Arctic National Park. Berner and Burns joined Dial’s research team as they trekked from the northern edge of boreal forest into the Noatak Wilderness where trees give way to thickets of shrubs, wetlands, and barren rocky ridges. During the course of 11 rain-soaked days, the team followed caribou and brown bear trails through verdant valley bottoms and over cloud-choked mountain passes as they traversed about 80 miles from the Ambler River to the Cutler River. While trekking, the researchers collected ecological field data to be linked with measurements of vegetation greenness from NASA Earth-observing satellites.
Ecological research often involves establishing field plots and then meticulously characterizing the composition and other attributes of the plant community in each field plot. Plot sampling provides valuable information, but the time consuming nature of the approach limits the spatial extent over which measurements can be made. Dial recognized that to better understand recent greening and browning, there is a need for more spatially extensive information on plant community composition than can be provided by field plots alone. He thus has pioneered an alternative approach that involves continuously documenting plant community composition and other attributes while trekking across the landscape. Termed “pixel-walking”, this approach harnesses the multifunctionality of smartphones to record and geolocate visual observations of vegetation composition and density for the overstory, midstory, and understory. While pixel-walking, researchers record a new observation every time they visually detect a change in vegetation composition or density at about a 30 meter spatial scale, corresponding to one pixel from the Landsat satellites. These spatially extensive field observations are thus collected with the explicit goal of being linked to decades of Landsat satellite observations.
During summer 2021, Dial’s research team pixel-walked over 800 miles from east to west through the Brooks Range, collecting data on vegetation composition for about 100,000 Landsat pixels. Over the coming year, Dial’s team will work with Berner, Burns, and Professor Scott Goetz (ABoVE Science Team Lead) at NAU to link these extensive field data with several decades of Landsat satellite observations provided by NASA. This collaboration will help unravel the mysteries of Arctic greening and browning by shedding light on where, how, and why plant communities changed in recent decades. NASA’s Earth-observing satellites provide long-term observations that are crucial for monitoring and understanding ongoing environmental changes in the rapidly-warming Arctic, especially when complemented by field data collected across large regions.
A sign at the the Inupiat Heritage Center in Barrow, AK.
Jun. 1, 2016 — We started our last day of the camp with a morning visit to the Inupiat Heritage Center to learn more about the indigenous local culture. Many of the Inupiat in Barrow still live their traditional subsistence lifestyle – hunting, trapping, and fishing for food. They do however take advantage of modern technology to make their way of life a bit easier and safer. For example, now machines have replaced dogsleds and rifles have replaced harpoons. But for some things, the old ways did not need to be modernized: the sealskin umiaq kayaks are lighter (easier to carry across the ice) and more navigable in the narrow leads of open water common to the area than anything manufactured today. And the fur-lined coats, pants, and boots are lighter, warmer, and repel moisture better than any modern outdoor gear.
A painting of whale hunting at the Inupiat Heritage Center.
The Inupiat way of life is governed by the seasons. There is a season for whale hunting, for seal hunting, for polar bear hunting. The dark, cold winter season is a time to stay indoors and sew new clothes or repair old clothes. Festivals mark the seasons where the community comes together to celebrate and reinforce the bonds between families.
After visiting the heritage center, we headed back to our base for a final meal. Several times during the week, our field leader, Don Perovich, said that the key for a successful field expedition is “to eat as much as you can as often as you can.” And we were certainly well fed throughout, with plentiful sandwiches, instant soups, chips and crackers, and all-important chocolate for our typical mid-day meals. But our final meal in Barrow was a step above, thanks to Elizabeth Hunke at Los Alamos National Laboratory. She proved herself not only a top-notch sea ice modeler but also a great chef, putting together a delicious meal of spaghetti, garlic bread, and salad.
Last meal in Barrow.
Then it was time for our final sessions, presenting the data we collected and discussing our Grand Challenge efforts. Unfortunately, the data collection the previous day did not go as smoothly as we had hoped. We couldn’t collect albedo measurements because the instrument didn’t work yesterday. But this type of things is not at all unusual in field work. As Don said: “In Arctic field research, it’s important to make a plan; it’s also important to not become too enamored of that plan” because something inevitably will go awry and you have be prepared to adapt.
So we couldn’t directly compare one of the key surface features between the two sites. However, we had other data we could look at. The new site to the north was 10-20 centimeters (4-8 inches) thicker than the original southern site. So there was less melt there and the ice was likely to last longer there. And while we lacked some data, we had models we could use. Many people think of modeling simply as predicting the future – and indeed models are used for that purpose (e.g., weather forecasts), but models, particularly climate ones, are also used to investigate processes and learn how climate responds to different parameters. Though we didn’t have albedo data, we could adjust albedo in the model and see how that affected how the modeled sea ice evolves in the future.
Grand Challenge results.
Several folks worked late into the previous night to process data and run the sea ice model. We obtained climatological weather data, input the data into the model and run it for the first two weeks in June. The results showed that the melt was strongly affected by the albedo of the surface and the amount of incoming sunlight, and that there will likely be substantial differences between the two sites. In a sense this isn’t terribly surprising, but to see such variation over such a small distance (the two sites were separated by only a couple miles) and within such short time periods (two weeks) is sobering. Large-scale complex models and satellite data cannot (yet) resolve such variability. There is still much research to do, and those of us at the camp have come away a greater appreciation for the challenge.
We finished up by discussing future plans. The goal of this camp wasn’t simply to get everyone together for one week, but to start new collaborations between modelers, satellite folks, and field researchers. We discussed several ideas to build upon the start we’ve made, keep momentum going, and convey what we learned to the broader sea ice research community. With that, it was time to head to the airport and begin our long journeys home.
Another tradition Don has is to bring a lollipop to each field expedition. When the expedition is done, he pulls it out as a reward for a job well done. At the beginning of our camp, he gave each of us a lollipop. It was up to us to decide when we were done. Some pulled theirs out after we wrapped up the meeting; some enjoyed theirs at the airport. I waited until the plane left the ground.
And so my adventure on the ice has come to an end. I can’t say I’m an expert in the field or ever will be. But it has been a rewarding week for me. I’ve gained a lot of knowledge about what it takes to do field work. I’ve gained an even greater appreciation of the value of field observations, as well as modeling studies. Hopefully I was able to give participants a greater understanding of satellite data. And finally, now when someone asks me if I’ve been on the sea ice, I can say “Indeed I have!” I still have the taste of the lollipop in my mouth to prove it.
May 31, 2016 — The morning sessions this week have been inside in a classroom setting. It’s been like being back in school, which has been quite fun (believe it or not). For the first four days I’ve been a student, but today I got to be the teacher. I gave the class a lab exercise working with satellite data. The “students” went through several days of imagery and calculated sea ice extent, first for the entire Arctic and then for a region around Barrow, Alaska. One of things this showed is that there are different methods to calculate sea ice extent, each with some advantages and limitations, each giving a slightly different answer. No data is perfect, so this variation in the data gives an indication of the uncertainty of the estimate.
One of the reasons for the differences is that the resolution of the satellite data varies, from 25-kilometer (15.5-mile) grid cells down to 1-kilometer (0.6-mile) cells. This makes a big difference in how well we can resolve ice features. The lower resolution data obviously does not provide the detail of the higher resolution, but in turn it has more complete coverage. So there is a trade-off one has to make. For conditions immediately around Barrow, higher resolution is better, but such data is not always available. For the entire Arctic, having complete data is useful, even if the resolution is lower.
The scientists prep to go on their Grand Challenge.
In the afternoon, we did our last day in the field and it was a “Grand Challenge” activity. Last night, we were challenged by the leaders of the workshop to use what we learned the first four days to come up with a science question and attempt to answer it by collecting data on the ice. We needed to develop a plan and then implement it today. The question we came up with was to try to determine if the ice would break out from the Barrow coast earlier than normal this year. To help answer that question, we realized we needed data from a different site than what we had used the first four days. Field observations are really valuable, but because they are limited to a small area, it’s hard to tell if they are representative of the larger area. During our snow machine morphology activities, the groups noticed that the ice conditions seemed to change as they headed north. The ice seemed more solid and uniform, with fewer ponds.
Out on the ice.
Laying out the sampling line.
So this afternoon we set out a new site a couple miles farther north. The ice was quite different; it was more uniform in appearance, with a white crust of large crystals of crumbly ice on top. We found the ice to be about 10 centimeters (4 inches) thicker than at the southern site and more uniform in thickness. That data and other measurements will be put together tonight and tomorrow. Then we’re going to enter that data into a simple model and run the model with typical weather conditions to see when the ice may become thin enough to break up.
An ice core.
Tonight, the workshop organizers, Don Perovich of CRREL and Marika Holland of NCAR, gave a public talk to the community at the Inupiat Heritage Center in town. Don talked about observations of sea ice and how it has changed over the years, both around Barrow and throughout the Arctic. Then Marika discussed climate models and their projections for the future. The room was full of local residents and the community was quite engaged – there were many questions afterward. The residents here know first hand that the climate is changing because their community is already being affected by the warming: the earlier opening of sea ice is necessitating adaption of their hunting practices, lack of ice is allowing more storm surges and coastal erosion, and warming temperatures are starting to thaw the tundra.
May 30, 2016 — This morning we did another modeling exercise, led by Jen Kay of the University of Colorado. A question a sea ice scientist inevitably gets asked is “so, when is the Arctic Ocean going to become ice free?” I can understand the interest, but answering it is quite difficult. One reason of course is that the sea ice models are not perfect – we don’t know exactly how the sea ice will respond to warming temperatures in the future. But the main reason is that the climate naturally varies from year to year and over many years, just due to randomness in the climate system. Jen and others have found that the natural variation in sea ice is quite large. The implication is that even under warming temperatures, variations in the climate system may result in many years where the extent doesn’t decrease and may even increase for several years.
The Red Team in the classroom.
This means that we can’t extrapolate from current trends to estimate the year ice-free conditions occur because the current trends may well be interrupted by natural variations. It also means that even if we have several years where the extent doesn’t drop, it doesn’t mean the warming isn’t having an effect – it just means the warming effect is overwhelmed, temporarily, by a natural cooling effect. It’s like driving a car down a mountain – eventually you’ll get to the bottom, but on the way there may be many flat spots or even sections of the road that go uphill.
In the afternoon, our group did the sea ice properties activity. This involved drilling a core through the ice and analyzing it. Sea ice is not simply frozen water – it is frozen salt water. Although most of the salt escapes during the freezing process, some salt gets trapped in the ice in briny pockets of very high salinity water. Over time, these pockets begin to drain (especially during the summer melt), leaving little channels within the ice. In the core, we noticed the brine already starting to drain after we lifted it out of the hole. These brine pockets are important in determining how the ice melts and interacts with the ocean.
Slicing a sea ice core.
A section of a sea ice core.
We also measured the salinity and temperature in the water near the base of the core. The water was near freezing throughout, as expected. But the salinity was quite low just beneath the bottom of the ice. Normally, the ocean salinity should be around 30 ppt (parts per thousand), but below the ice, the salinity was only about 2 ppt. This is because the fresh surface melt water was draining through the ice. Several centimeters lower, we saw the salinity increase rapidly to near 30 ppt.
Today was Memorial Day, so it’s worth noting that Barrow has a long history of being involved in defense activities. We are staying and working at the Naval Arctic Research Laboratory, which as the name implies was a military research station. We can also see nearby the DEW (Distant Early Warning) Line station, which was an early warning defense system to detect ballistic missiles that could’ve been launched by the Soviets. The soldiers that served in the DEW Line stations were literally on the front lines of the Cold War. So it seems appropriate to be here in Barrow on the day honoring those that have served and made the ultimate sacrifice for their country.
May 29, 2016 — This morning, we had our second modeling exercise, led by Ian Eisenman of the University of California, San Diego, where we investigated whether sea ice loss is irreversible – i.e., is there a tipping point for sea ice, a point of no return? In the simple models, like the one we used yesterday, once the sea ice disappears under warming temperatures, the ice does not come back even if temperatures cool back down to where they started. This means the loss is irreversible. However, the ice loss is reversible in more sophistical models such as those used for most future climate projections. So are the simple models missing something essential, or do the more sophisticated models get it wrong?
We examined an in-between Goldilocks model –not too simple, not too complicated– and found that the simpler models do miss important processes, such as the fact that heat diffuses into larger regions. This spreads out and slows down the ice-albedo feedback so that if the temperatures cool, the sea ice will come back.
In the afternoon, my group did an optics exercise out on the ice. This primarily involved measuring albedo of the ice. Albedo is basically the proportion of sunshine that gets reflected by the surface. At its simplest, it can be thought of as the whiteness of the surface. A perfectly white surface reflects all of the sun’s energy and has an albedo of 1 and a perfectly black surface will absorb all of the sun’s energy and has an albedo of 0. Albedo is key for sea ice because the ice has a much higher albedo than the ocean. So as temperature rises, the ice decreases, the albedo drops and more energy is absorbed. This added energy warms things further and you get what is called the sea ice albedo feedback, which amplifies the effects of warming temperatures. But the ice doesn’t need to disappear to have the sea ice albedo feedback. Changes on the ice surface – such as melting and ponding – also reduce the albedo.
Measuring sea ice albedo.
Our goal for the day was to measure albedo along a 100-meter (328-feet) line across the ice. It was our first day here with substantial sunlight; we had blue skies interspersed with clouds. Unfortunately, this was a bad day for albedo: to get good measurements, consistent light is desired. So the intermittent clouds make things difficult. Don told us that normally, if he were in the field in such conditions, he would skip the albedo measurements and drill some thickness holes instead. But we went out and gave it our best effort.
In the evening, we had a visit from two native Inupiat whale hunters, Billy and Joe. They told us how hunting bowhead whales is a fundamental part of their culture. The hunters go out onto the ice to the edge of fast ice (ice attached to the coast) and wait for the whale to surface. When they catch a whale, they bring it up onto the ice and share it with the rest of the community. Sharing is part of the fabric of their society – though the hunters make the kills, they are supported by the entire community. At the end of the whale-hunting season in June, there is a big celebration throughout the town with food, music, and dancing.
Because they use the ice to hunt, the Inupiat have intimate knowledge of the ice cover. They have shared this knowledge with scientists; this provides a valuable complement to our scientific data because they see things that satellites, models, and even scientific field observations don’t. For example, they can sense the softness of the ice, indicating a weaker ice cover. They also provide a long record from their personal observations and oral histories passed down over generations. The hunters mentioned how the fast ice used to extend at least 4 miles from shore, but now it only about half that distance. The ice moves out earlier as well, which affects their seal hunting. Also, there used to be a lot of multiyear ice in the area, but now it is rare.
The Inupiat work with the scientists to better understand the changes in the sea ice and their changes on the community. The scientists also help Inupiat by providing data and scientific guidance. With the changing ice conditions, going out on the ice has become more dangerous for the Inupiat – ice floes can break off without warning, stranding hunters. They now can use the Barrow sea ice radar to see how the ice is moving to get a sense of when and where it is safe to go out onto the ice. It was really interesting to hear the perspective from the local community, an essential source of knowledge that provides a view of sea ice that we scientists don’t get in the field, in our models, or in our satellite data.