Alaskan Glaciers Are Melting Twice as Fast as Models Predicted

Scientists from the University of Oregon recently found that the underwater section of a glacier in southeast Alaska is melting at rates up to two orders of magnitude greater than those predicted by theory.  The results, published in the journal Science, challenge the current models used to predict the melting of tidewater glaciers worldwide.

Tidewater glaciers play an important role in maintaining glacier stability, and their melting is accelerating overall ice loss in Greenland and in Antarctica. According to the study, no one has yet directly measured the melting of the underwater portion of a tidewater glacier. Instead, scientists have relied on untested theoretical models.

This diagram of a typical marine-terminating glacier in Greenland is from Oceans Melting Greenland (OMG), a project to investigate the extent to which the ocean is melting Greenland’s glaciers from below. (Source: NASA Jet Propulsion Laboratory)

Glaciers that terminate in the ocean come in two forms: Ice shelves, which are horizontal slabs of ice that extend into the ocean, and tidewater glaciers, which end in relatively vertical ice faces, Rebecca Jackson, one of the study’s authors, told GlacierHub.

Jackson explained that observing tidewater glaciers from below is difficult. Ice shelves retreat horizontally, and this can be seen by satellites and other remote sensing techniques. But the horizontal retreat of a tidewater glacier’s vertical face is too slight to be detected with remote sensing.

With funding from the National Science Foundation, the University of Oregon scientists used a new method to directly observe tidewater glacier melt: creating and comparing sonar images of the glacier over time. They studied the melting of Alaska’s LeConte Glacier, mainly because of its accessibility, Dave Sutherland, the lead author of the study, told GlacierHub. The physics of the interactions between glacier and ocean at LeConte are the same as in other systems around the world, including tidewater glaciers in Greenland, Patagonia, and the west Antarctic, he said.

They made observations at the glacier six times from 2016 to 2017, Sutherland told GlacierHub.

The glacier-ocean boundary at LeConte. (Source: Dave Sutherland, University of Oregon)

The results were striking. “We have direct observations that show melt rates are much higher than we we expected,” Jackson told GlacierHub.

This doesn’t change the amount of glacier ice currently being lost to the ocean, she explained. “Right now we know, to a pretty good degree, how much glaciers are losing ice and raising sea level,” Jackson said. “That’s a pretty well-documented quantity and our results don’t change that.”

Instead, the study illuminates what portion of the glacier ice being lost to the ocean is the result of underwater ice melting as opposed to calving—the process by which chunks of the glacier break off and float into the ocean as icebergs. “The sub-marine melt rates are higher than we expect, which means that the amount calving off is slightly less,” said Jackson.

That means that the ocean is playing a larger role than expected in the loss of water-terminating glacial ice, Sutherland told GlacierHub.

With a warming ocean, this news suggests that tidewater glaciers could disappear quicker in response to climate change than previously thought, Jackson explained. “There’s a hypothesis that ocean warming can increase submarine melting and then that triggers a glacier acceleration that deposits more ice overall into the ocean,” she said.

In other words, if the portion of glacier submerged in ocean water melts quicker, then the rate at which the glacier flows toward the ocean will increase, and the rate of calving will increase as well.

“You could imagine that if sub-marine melting was depth-dependent, you could undercut the glacier and destabilize it, leading to increased calving,” Sutherland told GlacierHub. And indeed their study found that the melt rates of the glacier were depth-dependent.

A picture of LeConte Glacier taken during the study. (Source: Dave Sutherland, University of Oregon)

“Ultimately what we want to be able to do is start answering questions like, if the ocean warms by one or two degrees, how will that affect the glacier?” said Jackson. And in order to do that, the faulty model must be replaced by a more accurate theory. The same team of scientists is currently working on that new model, Jackson said.

Although the Science study does not address why the previous theory might be incorrect, the scientists involved have a hypothesis, Jackson said. The velocity of the water touching a tidewater glacier face affects its melting rate: A higher velocity means a higher melt rate, just as pouring hot coffee over an ice cube melts the ice cube faster than placing it into the hot coffee. The current theory takes into account how freshwater that seeps out from the bottom of the glacier increases the water velocity as it rises to the top of ocean along the surface of the ice. However, it doesn’t take into account other drivers of ocean currents near the glacier, including wind, tide, and waves. “Those can also enhance the velocity along the ocean ice boundary, and that can also enhance melt rate,” Jackson told GlacierHub.

Collecting data from glaciers with different fjord conditions and glacier characteristics will provide the scientists with the information needed to model tidewater glacier melt as a function of the physical properties of the glacier and adjoining ocean. Since ocean conditions vary from season to season, the team is continuing to collect data at LeConte Glacier throughout the year, with the same goal of discovering how oceanic properties affect glacier melt. “One thing we’re excited about is what we present is the new method for directly measuring sub-marine melting that hopefully can be used at many other glaciers around the globe,” said Jackson.

In the mean time, estimates of sea level rise might need adjustment.

Footage of LeConte Glacier taken during the study. (Source: Dave Sutherland, University of Oregon)

Polar Bears and Ringed Seals: A Relationship in Transition

Disconnected sea-ice during the Svalbard summer (Source: Allan Hopkins/Creative Commons).

Along the tidal glacier fronts of Svalbard, an archipelago halfway between Norway and the North Pole, polar bears have changed their hunting practices. A recent study published in the Journal of Animal Ecology indicates the new behavior is a response to rapidly disappearing sea ice. Charmain Hamilton and other researchers from the Norwegian Polar Institute mapped changes in the spatial overlap between coastal polar bears and their primary prey, ringed seals, to better understand how the bears are responding to climate change. The results don’t bode well for the long-term survival of polar bear populations: as sea ice continues to shrink in area, ringed seals—calorie-rich prey that are high in fat— have become increasingly difficult to catch during the summer and autumn. The bears are now finding sources of sustenance elsewhere: in the archipelago’s thriving bird colonies.

The Arctic is warming at a rate three times the global average, and the sea ice in the Svalbard region is experiencing a faster rate of decline than in other Arctic areas. As Charmain Hamilton reported in an interview with GlacierHub, the findings could demonstrate what the future holds for the top predator elsewhere. “The changes that we are currently seeing in Svalbard are likely to spread to other Arctic areas over the coming decades,” she said.

A polar bear steps across a gap in the sea ice near Spitsbergen, Svalbard (Source: Thomas Nilsen/The Barents Observer).

Svalbard’s polar bears exhibit one of two annual movement patterns: some follow the sea ice as it retreats northward during the summer, while others stay local, inhabiting coastal areas throughout the year. Both groups of bears depend on sea ice as a platform to hunt ringed seals. Given a rapid decline of sea-ice levels that began in 2006, Hamilton and other researchers wanted to know if the coastal bears were still hunting ringed seals under the deteriorating conditions.

The researchers compared satellite tracking data for both polar bears and ringed seals from the periods 2002-2004 and 2010-2013 to assess whether the predator-prey dynamic had shifted. The data was analyzed according to season, with researchers paying careful attention to the dynamics of spring, summer and autumn.

In spring, access to fat-rich ringed seals is critical, particularly for mothers weakened from nourishing their young in winter dens. The study shows that coastal polar bears continued to spend the same amount of time near tidal glacier fronts in spring as they did when sea ice was more abundant. The authors conclude that the declines in sea ice in Svalbard have not yet reached the stage at which bears must find alternative hunting methods during the spring. This could help to explain why cub production is not currently declining.

A calving glacier in Svalbard (Source: Geir Wing Gabrielsen/Norwegian Polar Institute).

However, during summer and autumn, bears are spending less time in the areas around tidal glacier fronts. The study shows a significant decrease in the amount of time bears spent within 5 km of glacier fronts and a sharp increase in the distances they traveled in search of food per day. The ringed seals, on the other hand, have remained near the glacier fronts. As Hamilton reported to GlacierHub, “The reduced spatial overlap between polar bears and ringed seals during the summer indicates that the reductions in sea ice have made it much more difficult for polar bears to hunt their primary prey during this season.”

As sea ice recedes, ringed seals are increasingly relying on calved pieces of glacier ice as shelters and resting places. Since these pieces of calved ice are no longer connected to land-fast ice, polar bears can no longer walk up to the seals or wait by their breathing holes, but have to attack from the water. This involves swimming surreptitiously up to seals resting on calved glacier ice and bursting onto the platform to make a kill. But this specialty hunting technique has only been observed in a minority of bears.

A Svalbard polar bear eats a ringed seal on a calved piece of glacier ice (Source: Kit Kovacs and Christian Lydersen/Norwegian Polar Institute).

So where are the coastal bears getting their calories during summer and autumn? The study shows that along with the marked decline in sea ice, the coastal bears were spending more of their time around ground-nesting bird colonies. At present, these tactics seem to be working. The bears are benefiting from a large increase in the populations of several avian species in the region, which Hamilton attributes to ongoing international conservation efforts along migration routes. While an increase in the amount of time polar bears spend on land is considered a cause of deteriorating health in other bear populations, the adult bears and cubs of Svalbard have not shown marked signs of decline.

Have the bears found a lasting alternative? Jon Aars, a research scientist and one of the co-authors on the paper, doesn’t think so. In an interview with GlacierHub, Aars emphasized that while birds and eggs provide the bears with an alternative to burning fat reserves as they wait for the sea ice to return, the dynamic is not permanent. “It is not likely that switching to eating more birds and eggs is something that can save polar bears in the long run if sea ice is gone for the whole of, or most of, the year,” he said. “We do think the bears are still dependent on seals to build up sufficient fat reserves. And it is limited how many bears can utilize a restricted source of eggs and birds on the islands.”

A mother and her cubs look out across an ice-free stretch of bay as they hunt for birds and eggs (Source: Thomas Nilsen/The Barents Observer).

The bears have adapted to the current change in their environment but may not be able to adapt as well in the future. The authors of the paper point out that the increased rates of movement required to hunt avian prey increases the bears’ energy needs. Additionally, as more bears rely on avian prey, their high rate of predation means that bird populations on the archipelago will likely decline, causing bears to alter their hunting strategies again. Ringed seals have not changed their own spatial practices, and the authors propose that more bears could learn, or be forced to learn, the aquatic hunting method.

However, ringed seal populations are in decline due to the loss of sea ice, according to Hamilton. Thus, the future of both species in the region is uncertain. In sensitive environments like the Arctic, predator-prey dynamics are fragile, particularly for species of such high trophic positions. In the future, Hamilton would like to include other Arctic marine top predators in similar studies to better understand how Arctic marine mammal communities are being impacted.

Roundup: Everest, Subglacial Microbiomes, and Tidewater Glaciers

Roundup: Everest, Anaerobes & Fjords

 

China Tries to Conquer Everest

From Bloomberg: “Earlier this year, China opened a new paved road that winds 14,000 feet up the slope [of Mount Everest] and stops at the base camp parking lot. Plans are in the works to build an international mountaineering center, complete with hotels, restaurants, training facilities, and search-and-rescue services. There will even be a museum… What’s bad for Nepal will likely turn out to be a boon for tourists. Instead of fencing off Everest as a pristine wilderness, much as the U.S. has done with its national parks, China is approaching the Himalayas as the Europeans have the Alps… And if China sticks to it, it may well become the world’s new gateway to the Himalayas.”

Interested in learning more? Read the latest news here.

China opened a new paved road to Mount Everest (source: Mudanjiang Regional Forum).
China’s new paved road to Mount Everest (Source: Mudanjiang Regional Forum).

 

Implications for the Subglacial Microbiome

From Microbial Ecology: “Glaciers have recently been recognized as ecosystems comprised of several distinct habitats: a sunlit and oxygenated glacial surface, glacial ice, and a dark, mostly anoxic [absence of oxygen] glacial bed. Surface meltwaters annually flood the subglacial sediments by means of drainage channels. Glacial surfaces host aquatic microhabitats called cryoconite holes, regarded as ‘hot spots’ of microbial abundance and activity, largely contributing to the meltwaters’ bacterial diversity. This study presents an investigation of cryoconite hole anaerobes [organisms that live without air] and discusses their possible impact on subglacial microbial communities.”

Learn more about this study here.

Photomicrograph of Gram-stained enrichment culture, showing several cell morphotypes (source: Implications for the Subglacial Microbiome).
Photomicrograph of Gram-stained enrichment culture, showing several cell morphotypes (Source: Microbial Ecology).

 

Analysis of Icebergs in a Tidewater Glacier Fjord

From PLOS ONE: “Tidewater glaciers are glaciers that terminate in and calve icebergs into the ocean. In addition to the influence that tidewater glaciers have on physical and chemical oceanography, floating icebergs serve as habitat for marine animals such as harbor seals. The availability and spatial distribution of glacier ice in the fjords is likely a key environmental variable that influences the abundance and distribution of selected marine mammals… Given the predicted changes in glacier habitat, there is a need for the development of methods that could be broadly applied to quantify changes in available ice habitat in tidewater glacier fjords. We present a case study to describe a novel method that uses object-based image analysis (OBIA) to classify floating glacier ice in a tidewater glacier fjord from high-resolution aerial digital imagery.”

Read more about this study here.

Map of Johns Hopkins Inlet study area (source: Quantification and Analysis of Icebergs in a Tidewater Glacier Fjord Using an Object-Based Approach).
Map of Johns Hopkins Inlet study area (Source: PLOS ONE).

Photo Friday: Project Pressure’s Greenland Journey

Project Pressure is a glacier photography project that has been documenting glaciers and partnering with photographers since 2008. Last year, photographers Mariele Neudecker and Klaus Thymann journeyed to southwest Greenland for the project. The team traveled by boat from the settlement of Narsarsuaq around a peninsula to  Quoroc Bay. The purpose was to record the place where the glaciers extend to the Denmark Strait, a part of the Atlantic Ocean. Such glaciers are referred to as  tidewater glaciers. The team also captured images of striking intersections between land and the Eqalorutsit Glacier. In one image, a red “path” consisting of blueberry bushes leads to the glacier. Another image shows how sunlight marks a contrast on the glacier surface. More images from the recent trip and other Project Pressure journeys can be found on the group’s Instagram page.

Neudecker wrote via email, “The most challenging part was walking and clambering in rough terrain endlessly and relentlessly in the thickest fog, where quite often we lost contact between the three of us. The fog seemed to subsume sound, space and time.” The artists relied completely on compass and GPS to get to shelter and safety from freezing overnight temperatures. They stayed in a remote hut in the area.  The photos part of an exhibition opening today and running through April at the Zeppelin Museum in Germany.
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Roundup: Tidewater Glaciers, North Cascades, Antarctic Bacterium

The Culprit for Greenland Ice Sheet Mass Loss

Source: Christine Zenino/Flickr
Greenland Ice Sheet. Source: Christine Zenino/Flickr

“Overall mass loss from the Greenland ice sheet nearly doubled during the early 2000s resulting in an increased contribution to sea-level rise, with this step-change being mainly attributed to the widespread frontal retreat and accompanying dynamic thinning of tidewater glaciers. Changes in glacier calving-front positions are easily derived from remotely sensed imagery and provide a record of dynamic change […] In this study multiple calving-front positions were derived for 199 Greenland marine-terminating outlet glaciers with width greater than 1 km using Landsat imagery for the 11-year period 2000–2010 in order to identify regional seasonal and inter-annual variations. Our results suggest several regions in the south and east of the ice sheet likely share controls on their dynamic changes, but no simple single control is apparent.”

Read more here.

Area Changes of North Cascades Glaciers

North Cascades Glaciers. Source: Sean Munson/Flickr
North Cascades Glaciers. Source: Sean Munson/Flickr

“We present an exhaustive spatial analysis using the geographic, geometric, and hypsometric characteristics of 742 North Cascades glaciers to evaluate changes in their areal extents over a half-century period. Our results indicate that, contrary to our initial expectations, glacier change throughout the study region cannot be explained readily by correlations in glacier location, size, or shape. Our statistical analyses of the changes observed indicate that geometric data from a large number of glaciers, as well as a surprisingly large amount of spatial change, are required for a credible statistical detection of glacier-length and area changes over a short (multidecadal) period of time.”

Read more here.

 

The Small Tough Organisms

Growth of cold-sensitive mutants on Antarctic Bacterial Media containing stressor. Source: D. Sengupta et al (2015).
Growth of cold-sensitive mutants on Antarctic Bacterial Media containing stressor. Source: D. Sengupta et al (2015).

“A population of cold-tolerant Antarctic bacteria was screened for their ability to tolerate other environmental stress factors. Besides low temperature, they were predominantly found to be tolerant to alkali. Attempt was also made to postulate a genetic basis of their multistress-tolerance […] A number of multistress-sensitive mutants were isolated. The mutated gene in one of the mutants sensitive to low temperature, acid and alkali was found to encode citrate synthase. Possible role of citrate synthase in conferring multistress-tolerance was postulated.”

Read more here.

High schoolers get “hands on” with Alaska glacier

 

A program for high school students in Alaska brings 16 and 17 year olds up close and personal to glaciers. (Vic Trautman/LeConte Survey Program)
A program for high school students in Alaska brings 16 and 17 year olds up close and personal to glaciers. (Vic Trautman/LeConte Survey Program)

In an age when satellite images are often the only source of data you could need about a glacier, few people will still strap on ice cleats and lug a theodolite up to a calving ice front. What’s even more unusual is finding a group of 16 and 17 year olds who do just that.

For over 30 years, students from the high school in Petersburg, a town in southeastern Alaska, have been taking part in the LeConte Survey Program, a two-year training course where they spend their lunch break gaining the skills they need to produce reliable survey data from the LeConte Glacier. In their first year, they focus on the basics of surveying and mathematics, while in the second year, they, and two supervisors, visit the glacier as a group to survey it.

The LeConte Glacier is the southernmost tidewater glacier in the northern hemisphere. Tidewater glaciers are unconfined ice streams that stretch down from mountains, reach the coast and extend into open sea. The bottoms of tidewater glaciers rest on the sea floor, at elevations below sea level. These glaciers lose ice by calving, often creating copious numbers of icebergs.

(https://flic.kr/p/2Jb6tF)
Alaska’s LeConte Glacier is the southernmost tidewater glacier in the northern hemisphere. (JBrew/Flickr)

On the day of the survey the group splits into two, with each hiking to a different ledge. Each group measures as many points on the glacier as possible (usually between 15 and 20) before a helicopter takes each group to the other ledge, where they cross-measure the other group’s points. They end the day with a “math night” of intensive trigonometry and data validation.

The LeConte Survey Program was founded in 1983 by geology teacher Paul Bowen. Trautman has been running the it since in the late 1990s, when Bowen retired. The LeConte Survey Program has given students a new perspective on the environment they grew up in and contributed to the science of glaciology. The student-collected data has used by professional scientists and published in academic papers.

In 1993, the students discovered very significant retreat of the glacier, half a mile in 6 months. Scientists became very interested in the Survey Program’s data. “That was way before we had any of the other, quote, unquote, huge recessions of glaciers,” said Vic Trautman, who runs the program. This discovery prompted researchers to collection additional data, particularly the height of the glacier’s terminus above the water level.

Tidewater glaciation is found both above and below the water's surface. (via the National Park Service, http://www.nps.gov/glba/naturescience/glaciers.htm)
Tidewater glaciation is found both above and below the water’s surface. (via the National Park Service, http://www.nps.gov/glba/naturescience/glaciers.htm)

Researchers from the University of Alaska Southeast suggested to the students that the rapid retreat might indicate a thinning trend. Additional years of steady data collection proved this hypothesis to be correct. Their earliest records showed the glacier to be 250 to 260 feet above water level, but currently they are measuring it at 190 feet. “The face falls off continuously, but we have a map and we plot each point, so every year we get a new line,” Trautman said. “We can compare this year’s line to last year’s line, all the way back.”

Through measurement and monitoring of glaciers is often automated, direct field research can still be of value. It is satisfying to know that glaciers are providing young people with research skills, with direct experience of environmental change, and with the sense of participating in a community effort that has lasted for decades. Perhaps the dedicated efforts of two teachers to support this activity will inspire others to such establish such programs as well.