Novosilski Glacier is a large tidewater outlet glacier on the west (cloudier) coast of South Georgia, terminating in Novosilski Bay. It shares a divide with the rapidly retreating Ross and Hindle Glacier on the east coast.
Gordon et al. (2008) observed that larger tidewater and calving outlet glaciers generally remained in relatively advanced positions from the 1950’s until the 1980s. After 1980 most glaciers receded; some of these retreats have been dramatic.
The change in glacier termini position that have been documented by Cook et al (2010) at British Antarctic Survey in a BAS retreat map identified that 212 of the peninsula’s 244 marine glaciers have retreated over the past 50 years and rates of retreat are increasing.
Pelto (2017) documented the retreat of 11 of these glaciers during the 1989-2015 period.
Here we examine Landsat images from 2001-2018 and the British Antarctic Survey GIS of the island to identify the magnitude of glacier change.
In 2001 Novosilski Glacier terminated in shallow water just east of a small island that acted as a pinning point (red arrow). By 2009 the glacier had retreated only a minor amount from this island into deeper water.
A rapid retreat ensued, and by 2016 the glacier had retreated into a narrower fjord reach. The north and south margins featured remnant ice that was based above tidewater (pink arrows). The blue arrows in the 2016 Landsat image indicate the large accumulation area feeding Novosilski.
By 2018 the 2-kilometer-wide calving front had retreated 2.5 km from the 2001 position. There is little evident thinning upglacier of the terminus, and there is a significant increase in surface slope suggesting that unless calving rate increases the terminus can remain near its current position.
The snowline is below 500 meters in each of the satellite images of the glacier. This is not a particularly hospitable section of coastline and the BAS has only identified gentoo penguins having colonies in the area.
This article originally appeared on From a Glacier’s Perspective, a blog published by the American Geophysical Union.
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.
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.
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.
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.
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.
The vast, unpopulated landscape of Ryder Bay, West Antarctica gives the impression of complete isolation. However, despite its barren, cold exterior, Antarctica plays an important role in regulating the Earth’s climate system. Located along the southeast coast of Adelaide Island, Ryder Bay is helping mitigate impacts of climate change by removing greenhouse gases from the atmosphere to the ocean, where these gases can remain for centuries. This repurposing is being done by benthos, microorganisms like phytoplankton that bloom during summer months and provide critical food supplies that maintain the marine ecosystem in Ryder Bay. Quietly residing on the floor of the Southern Ocean, benthos are encountering increased risks due to a changing climate. While the potential carbon recycling capacity of local marine ecosystems remains significant, the collapsing glaciers and ice shelves in Ryder Bay may threaten this productivity, according to an article in the journal of Global Change Biology.
The carbon recycling process in the marine ecosystems is one of the strongest mechanisms helping to reduce the impacts associated with historic carbon emissions. Located along the continental shelf, benthos absorb carbon through photosynthesis; when these organisms die and fall to the ocean floor, this carbon is then stored in sediments. Undisturbed, the ocean can help thwart warming due to an enhanced greenhouse effect by removing carbon from the atmosphere and storing it in the ocean. David Barnes, a Marine Benthic Ecologist with the British Antarctic Survey and an author of the article, pointed out to GlacierHub, “Trends in carbon accumulation and immobilization, which occur on the seabed, could be considered most important as these involve long-term carbon storage. [These trends] are perhaps the largest negative feedback on climate change.” However, because of shifting land dynamics, the increased frequency of iceberg creation is having a direct impact on the ability of the marine ecosystems to recycle carbon.
As the Earth continues to warm, ice sheets and glaciers in Antarctica advance and become thinner, causing cracks and crevasses to form. These fissures, in turn, lead to unpredictable, large-scale breaks which create icebergs that discharge into the ocean. At the time of detachment, ice formations hit the ocean floor, obliterating the marine ecosystems below. Icebergs can continue to impact the benthos as they travel on the ocean.
Barnes described this problem to GlacierHub: “At places like Ryder Bay, it would be very difficult to provide forecasting, because it is very frequent and a bit chaotic. The direction an iceberg travels depends on its shape, how deep its keel is, wind, and current speed. A smaller iceberg with a vertically flat side above water will easily catch wind like a sail, so if the wind is strong it will mainly follow wind direction. Conversely, a bigger iceberg with a deep vertical flat side might more easily catch current.”
According to NOAA, these icebergs— typically rising 5 meters above the sea surface and covering 500 square meters in area— are large enough to inflict significant destruction. Dubbed “iceberg killing fields,” these places of impact can cause extensive disruption to the beneficial marine ecosystems along the ocean floor.
David Barnes works with the British Antarctic Survey to study the iceberg killing fields and measure the impact of iceberg-seabed collisions on marine ecosystems. The British Antarctic Survey has been monitoring the local marine ecosystems in Ryder Bay due to their sensitivity to environmental change and the surprisingly large role benthos play in removing carbon from the atmosphere. According to the report, “The scour monitoring has probably become the longest continuously running direct measurement of disturbance on the seabed anywhere in the world.” With roughly 93 percent of carbon dioxide being stored in our oceans, it is necessary to monitor how these potential carbon sinks may fluctuate, according to the Worldwatch Institute.
According to Barnes’ findings, the benthos in Ryder Bay are experiencing high mortality rates due to the frequent and powerful collisions between collapsing ice shelves and the sea floor, often referred to as ice scour. “Since 2003, when it was first measured in Ryder Bay, ice scour has been less predictable and more variable (than many other environmental variables),” according to Barnes and the British Antarctic Survey. The heightened unpredictability of ice scour makes predicting and preventative measures challenging.
Collisions between icebergs and the ocean floor are frequent and damaging, with the “potential to halve the value of benthic immobilized carbon in the Ryder Bay shallows,” says Barnes. These measurements show a very high frequency of scouring in the shallows because of its proximity to the ocean floors in Ryder Bay, according to the article. In fact, on average, ice scour affected 29 percent of the seabed study area yearly, from 5 to 25 meters deep. In the past decade, Barnes found that only seven percent of the shallows had not been hit by icebergs. This scouring accounts for nearly 60 percent of total benthic fatality at a 5m depth. The high frequency and fatality rates associated with iceberg scour make it one of the “most significant natural disturbance events,” according to Barnes.
Weekly ocean measurements of temperature, salinity and size-fractionated (micro, nano and pico) phytoplankton have been collected since 1997, says Barnes. The field work conducted by the British Antarctic Survey set up 75 ice scour markers gridded at 5, 10 and 25m. These grids are surveyed and replaced by researchers using scuba gear, allowing for the different scour depths to be calculated. Frequency of collisions is then calculated through the recording of disturbances for each meter squared in order to establish a detailed history and provide insight into potential future trends. Annual collection of faunal remains and boulders are integrated into the disturbance data sets. These collections will help further quantify the damages inflicted upon marine ecosystems and their abilities to sequester carbon.
While glaciers in polar regions seem inconsequential to our everyday experiences with climate, they have the ability to significantly influence the biological systems which remove greenhouse gasses from the atmosphere. Continued support of scientific endeavors in the polar regions are critical in order to understand the places and processes that play such a vital role in the Earth’s climate system. As Barnes states, “We have a huge and powerful ally [in the polar regions] in the fight against climate change, so let’s make sure we look after it.”