Volcano Discovered Beneath World’s Fastest Melting Glacier

West Antarctica’s Pine Island Glacier (PIG) is the fastest melting glacier in Antarctica, making it the single biggest contributor to global sea-level rise. The main driver of this rapid loss of ice is the thinning of the PIG from below by warming ocean waters due to climate change. However, a recently published study in Nature Communications discovered a volcanic heat source beneath the PIG that is another possible driver of the PIG’s melting.

Photo of the Pine Island Glacier from icebreaker.
On the icebreaker RSS James Clark Ross looking toward the Pine Island Glacier on the 2014 expedition (Source: University of Rhode Island/Twitter).

The study was a result of a larger project funded by the National Science Foundation and the U.K. National Environmental Research Council to “examine the stability of the Pine Island Glacier from the terrestrial and the ocean side,” according to the lead author Brice Loose, who spoke with GlacierHub about the research.

The West Antarctic Ice Sheet (WAIS), which includes the PIG, sits on top of the West Antarctic Rift System that includes 138 known volcanoes. It is difficult, however, for scientists to pinpoint the exact location of these volcanoes or the extent of the rift system, because most of the volcanic activity occurs below kilometers of ice.

Pine Island Glacier from Landsat
The Pine Island Glacier from above taken by Landsat (Source: NASA/Twitter).

Warming ocean temperatures due to climate change have long been identified as the primary contributor to the extensive melting of the PIG and other glaciers that transport ice from the WAIS. This melting is largely driven by Circumpolar Deep Water (CDW), which melts the PIG from below and leads to the retreat of its grounding line, the place where the ice meets the bedrock.

To trace CDW around coastal Antarctica, the scientists used helium isotopes, specifically He-3, because CDW is widely recognized as the principal source of He-3 in the waters near the continent. For this study, the scientists used historical data of helium measurements from the Weddell, Ross, and Amundsen seas around Antarctica. They looked at the 3 seas, all of which have CDW, and examined differences in He-3, which could have come from volcanic activity.

By tracing the glacial meltwater produced by the CDW, the researchers discovered a volcanic signal that stood out in their data. The helium measurements utilized were expressed by the percent deviation of the observed data from the atmospheric ratio. For the observed CDW in the Weddell Sea, this deviation was 10.2 percent. In the Ross and Amundsen Seas, it was 10.9 percent. However, HE-3 values gathered by the team during expeditions to the Pine Island Bay in 2007 and 2014 differed from the historical data.

Map of elevated He-3 samples in 2007 and 2014.
Map of elevated He-3 samples in 2007 and 2014 (Source: Loose et. al).

For this data, the percent deviation was considerably higher at 12.3 percent, with the highest values being near the strongest meltwater outflow from the PIG’s front. Additionally, these high helium values coincided with raised neon concentrations, which are usually an indication of melted glacial ice. The helium was also not uniformly distributed. This suggests it originated from a distinct meltwater source and not from across the PIG’s entire front.

With this knowledge in hand, the team of scientists endeavored to identify the source of the HE-3 production. The Earth’s mantle is the largest source of HE-3, although it is also produced in the atmosphere and during past atmospheric tests of nuclear weapons through tritium decay. These two sources, however, could only account for 0.2 percent of the 2014 data.

Another potential source was a fissure in the earth’s crust directly below the PIG, where He-3 could rise from the mantle. However, this source was ruled out as it would have a strong thermal signature, something that was not discovered by mapping expeditions.

Map of He-3 samples around Antartica.
Map of He-3 samples around Antartica (yellow = 2007, red = 2014) (Source: Loose et. al).

The researchers then considered another source: a volcano beneath the PIG itself, where He-3 escapes from the mantle in a process known as magma degassing. The He-3 could be transported by glacial meltwater to the PIG’s grounding line, where the ice meets the underlying bedrock. At this line, the ice shifts due to the ocean tides, allowing the meltwater and the He-3 to be discharged into the ocean.

After identifying a subglacial volcano as the most likely source of the elevated He-3 levels near the PIG’s front, the scientists next calculated the heat released by the volcano in joules per kilogram of sea water at the front of the glacier. It turned out that the heat given off by the volcano constitutes a very small fraction of the overall mass loss of the PIG compared to the CDW, according to Loose.  

In total, the volcanic heat was 32 ± 12 joules kg-1, while the heat content of the CDW was much larger at 12 kilojoules kg-1. Nevertheless, if the volcanic heat is intermittent and/or concentrated over a small surface area, it could still have an impact on the overall stability of the PIG by changing its subsurface conditions, said Loose. There is also the possibility that the continued melting of the PIG could lessen the pressure and weight on the volcano, spurring more volcanism and subsequent melting.

The presence of an active volcanic heat source beneath the world’s fastest-melting glacier is a disturbing discovery that threatens to accelerate the PIG’s contribution to future sea-level rise. To develop a better understanding of how the volcano might impact the PIG, Loose stated that future studies should examine how the volcanic signal varies from year to year and attempt to pinpoint the likely location of the volcano itself beneath the ice.

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Loss of Contact with Ridges Below Likely Triggered Pine Island Glacier’s Retreat

The Pine Island Glacier (PIG) is losing ice rapidly. During the past 25 years, the ice of the PIG and its neighboring glaciers in west Antarctica’s Pine Island Bay thinned between 3.9 and 5.3 meters a year, accounting for about 5 to 10 percent of observed global mean sea-level rise. Before 2015, however, the front of the PIG had been at a relative standstill since the 1940s, not retreating as one might expect of a melting glacier. Why? To account for this unique situation, a recently published study in The Cryosphere points to ridges below the ice that likely held the PIG’s ice front in place despite its rapid melting.

In August 2015, the long steady front of the PIG changed significantly when large sections of ice broke off during a calving event when the glacier retreated upstream and its orientation shifted. This change presented an exciting opportunity in 2017 for researchers from the Alfred Wagner Institute for Polar and Marine Research to map the seafloor formerly covered by the PIG.

Photo of the Pine Island glacier
A front section of the Pine Island Glacier (Source: BAS_News/Twitter).

To complete this mapping project, the researchers employed an echo sounder mounted to the hull of the research vessel RV Polarstern, in addition to complementing remote sensing data acquired by satellite. The information acquired by the expedition through echo sounding showed the seafloor features that were present below the PIG. With this data in hand, the researchers had the idea to correlate this information with satellite data from the past to the present to better understand the role of these features for the calving behavior of PIG, according to lead author Jan Erik Arndt, who spoke with GlacierHub about the study.

These survey methods revealed a complex, underwater landscape once covered by the PIG. The discoveries included a 10-kilometer long ridge and two other high points. At its deepest point, Pine Island Bay reaches down over 1,000 meters, while the submarine ridge peaked at 375 meters below the ocean’s surface and the two downstream high points peaked at 350 and 250 meters below the surface

How did these sub-surface features impact the PIG? Satellite data from January 1973 until March 2005 showed a rumple in the PIG’s ice above the location of shallowest section of the underlying ridge. A glacial rumple is similar to a bump on a beach towel that suggests there is a beach toy or pile of sand below it. In the case of the PIG, the ridge below the ice acts as an obstacle in the the way of the ice, leading to a raised section of the glacier directly above the point of contact between it and the ridge. This rumple is not observed after March 2005 in the satellite data, indicating that the ice after this date had thinned to such a degree that it either was no longer in contact with the ridge or was too light to produce a signature on the surface.

Satellite photo of the PIG's calving front.
The evolving calving front of the Pine Island glacier (Source: J. E. Arndt et al.).

The loss of contact with the ridge was consequential. In the time before this separation when the PIG was in contact with the underwater ridge, the ridge acted as a “pinning point,” holding it in place. However, after the ice had thinned considerably, the ridge no longer acted as a restraint on the PIG. As a result, in the time since there was evident contact between the two, four major calving events occurred.

The first of these events took place in 2007 when the PIG advanced and made contact with one of the subsurface downstream high points (A in figure 3). This impact placed what is known as “back stress” on the glacier upstream from the point of contact, causing rifts to form in the ice and ultimately leading to the calving event.

The process leading to the 2011 calving event was similar, the researchers state. In this instance, the second subsurface high point (B in figure 3) trapped a dense cluster of icebergs between it and the PIG ice shelf, placing back stress on the upstream ice leading to the calving event.

Photo of the 2007, 2011, and 2015 calving events in relation to the underlying topography
Before or after the 2007, 2011, and 2015 calving events and the PIG’s position in relation to the underlying topography (Source: J. E. Arndt et al.).

The 2015 event was different: The ice-flow velocity of the northern edge of the PIG’s ice shelf was nearly at a stand still, whereas the velocity of the ice shelf’s central and southern edges increased. Further, the direction of the northern edge’s ice flow shifted around 3 degrees clockwise, while the direction of the central and southern edges did not change (C in Figure 3). The reason? The northern edge of the ice-shelf was likely making slight contact with the submarine ridge, according to the authors.

As a result, the calving line that had not changed orientation in decades finally did change due to the loss of contact between the ice and its previous pinning points as well as from melting from below driven by warm ocean waters. The most recent calving event which occured in 2017 happened along the same orientation, which aligns with a new pinning point to the north near Evans Knoll, a small snow-covered hill that rises above sea level. The point near the knoll is likely one of the last anchors acting on the PIG, according to Arndt.

This new calving line and loss of contact with past pinning points could have grave implications for PIG. A 2017 study on the PIG and a number of other glaciers in the area found that changes to a glacier’s ice shelf propagate upstream within just a few years. For the PIG, this likely means the glacier’s flow will speed up and thinning will increase, leading to further melting.

Photo of Pine Island Glacier rift in 2017
The rift in the Pine Island Glacier that led to the 2017 calving event (Source: American Geophysical Union/Twitter).

It is unlikely the PIG’s calving line will retreat much further over the next few years thanks to the new pinning point stabilizing the glacier near Evans Knoll. However, the authors note that there is continued thinning due to melting. This thinning has the potential to destabilize the glacier and unfortunately may have already started, according to Arndt. The large icebergs produced by the recent calving events have broken up into smaller icebergs much more quickly due to the thinner ice than events in the past, when they remained stable for longer. This ongoing breakup and subsequent melting of calved icebergs will contribute to already rising global sea-levels, threatening the millions of people who live along the coast. And unlike the ridges that held the front of the PIG for decades, many coastal communities will not have anything to hold back the sea.

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Below the Ice: Subglacial Topography in West Antartica

When traversing the broad white expanses of West Antarctica’s Pine Island Glacier (PIG) by snowmobile, you might think the main attraction would be the surface of the rapidly receding river of ice. However, for the authors of a recently published study in Nature Communications, the real draw was not the surface but the rock beneath—the subglacial topography of Antarctica’s most rapidly melting glacier.

Photo of snowmobile pulled radar
Snowmobile pulling survey radar on Pine Island Glacier (Source: Damon Davies/British Antarctic Survey).

Utilizing ice penetrating radar towed by snowmobile, the study’s authors were able to compile the first high-resolution maps of PIG’s underlying bed topography. What sets these maps apart from previous surveys is the detail and diversity of the rugged underlying landscape according to Ted Scambos of the National Snow & Ice Data Center who was not one of the authors of the study. Where previously conducted airborne studies found relatively level topography, this work showed more varied, and often rugged topography—findings that earlier studies had missed, because of the inability of planes to conduct very close parallel surveys.

Why is improved glacier bed delineation crucial for analyzing and predicting glacial retreat rates? It has to do with basal traction or, simply, bottom ice flow. Although we might imagine a glacier sliding as smoothly as an ice cube on a table on a hot summer day, in fact glacial movement is often slowed by two factors, friction and drag. The first of these components is the friction where ice meets the bed below. This factor is highly dynamic, changing as ice melts, flows, and refreezes; friction is also affected by subglacial till, sediment in the glacier bed which was eroded by the glacier, as it moves and freezes.

The second factor, drag, is the more static component of glacial movement. It reflects the size and orientation of undulations in the bedrock below. The net result is the sum of the first, more variable component and the second, more constant component. But earlier work had measured only the sum of the two—making it difficult to predict how the sum might vary. This study marks a major step in removing this limitation. Researchers were able to estimate the two components separately and come up with more precise predictions.

Ariel view of Pine Island Glacier meeting the sea (Source: NASA Ice/Creative Commons).

The glaciers of remote Pine Island Bay (PIB) have received a good deal of attention lately. In May, Rolling Stone published an article examining the Thwaites glacier, West Antarctica’s other rapidly shrinking glacier, and its contribution to rapid sea level rise. Then, in November, Grist published a piece titled “Ice Apocalypse” on the possibility of a rapid glacier collapse in PIB.

Pine Island Glacier, one of the most rapidly retreating glaciers in Antarctica, is estimated to have contributed up to 10 percent of observed global sea level rise, according to the study’s authors. Because of already problematic sea level rise and the societal threats posed by the rapid collapse of these glaciers, many studies have attempted to project the PIG’s future retreat. However, despite all of the focus on the PIG’s retreat, one condition has remained uncertain: the slowing of the glacier’s seaward movement, due to the forces deep below the surface where ice meets terrain.

Photo of figure showing Pine Island subglacial topography
Pine Island subglacial topography derived from study observations (Source: Bingham et al.).

Previous survey methods were unable to separately resolve glacial friction and drag. They could only measure the sum of the two, leading to inaccuracies in ice sheet models that predict retreat rates. These inaccuracies contributed to high variability in bottom ice flow predictions. Given the improved clarity of bed topography observed in this study, the authors were able to conclude that previous inconsistencies must be associated with an incomplete picture of topography beneath glaciers.

The study’s observations of the PIG painted a detailed picture of the landscape beneath the ice. Utilizing these observations, the authors were able to compare them to satellite data outlining the glacier’s recent movements and shrinkage. The comparisons revealed an interesting relationship, the movement of the glacier differed in its tributaries. What was the reason for this variation? It turns out that the slower advancing tributaries corresponded to rougher bottom terrains, with the coarse tributaries, for example, advancing toward the coast where melting occurs, two to three times slower than their smoother counterparts. These findings indicate that bedrock undulations under the PIG impact the glacier’s flow considerably more than changes in friction, a result not previously observed.This discovery allows researchers to make more precise predictions, by summing each of the different tributaries of PIG.

Photo of Thwaites glacier.
Thwaites Glacier, the other rapidly shrinking glacier in Pine Island Bay (Source: NASA’s Marshall Space Flight Center/Creative Commons).

The study shows the large influence of subglacial topography on the retreat of PIG, a topic of great importance to society for its potential disastrous impacts. While the results reveal the importance of these landscapes for glacial recession, the authors note that more research is needed to better measure terrain beneath glaciers. Specifically, they underscore the significance of these needed improvements for PIG’s counterpart, the Thwaites glacier. Like PIG, Thwaites appears to have similar diversity in underlying topography. Nonetheless, the glacier has exhibited a rapid recent retreat, faster than that of even the smoothest PIG tributaries. This is a disturbing fact given that the study’s authors state that the glacier has the “potential for rapid and irreversible retreat, and a considerable contribution to sea-level rise.”

How fast the glaciers of PIB and West Antarctica retreat in the future is still difficult to predict. Nevertheless, as exemplified by this study, scientists continue to develop better methods and models in the face of extreme conditions in one of the most remote and inhospitable places on Earth. But while remote, what happens in the coming years to the ice in PIB has the potential to change the world.

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