Antarctic ice sheet was more dynamic than previously thought

Deep beneath the West Antarctic Ice Sheet, lies a frigid, dark subglacial lake filled with tales yet to be discovered. More enigmatic than even the planets of our solar system, these mysterious lakes have remained largely unexplored due to their inaccessibility. 

However, scientists have made a groundbreaking discovery in one such lake, known as Mercer Lake, by studying the chemical fingerprint of the water, microbes, and sediments found there. This has led to a surprising revelation about the geologic history of the region, as well as new insights into the carbon cycle of these extreme ecosystems.

In the journal AGU Advances, the researchers describe how they examined the carbon cycle within Mercer Lake to determine the sources of energy for the lake’s resilient microbial inhabitants. 

The findings provide the first-ever description of how these hardy microbes obtain and utilize carbon, the energy source of choice for most life forms, in such a hostile environment.

The data obtained from the sediment, microbes, and carbon cycle also allowed the scientists to infer the geological history of the region, with results that defied their expectations. Previously, it was believed that the ice covering Mercer Lake had been stable for hundreds of thousands of years. 

However, the new findings confirm that the lake was connected to the ocean around 6,000 years ago, when the West Antarctic Ice Sheet was significantly smaller than it is today. This period marked a time of relative climate stability following the last ice age, and even compared to the ongoing anthropogenic climate change.

Ryan Venturelli, lead author of the study and assistant professor at the Colorado School of Mines, stated: “This is the first time we have unequivocal geologic proof that the grounding line of the West Antarctic Ice Sheet, which is like its shoreline where the ice meets the ocean, was at least 250 kilometers further inland than it is today – possibly more.” 

How the study was done

Venturelli conducted the research alongside her former PhD advisor, marine geologist Brad Rosenheim from the University of South Florida College of Marine Science.

Their research indicates that the West Antarctic Ice Sheet retreated approximately 155 miles (about 250 kilometers) just a few thousand years ago, only to regrow to its current size. This information is crucial for validating ice sheet models and improving our understanding of the dynamic nature of these ice formations.

The samples analyzed in the study were collected during the historic Subglacial Antarctic Lake Scientific Access (SALSA) expedition, funded by the National Science Foundation. The 25-member team, including Venturelli and Rosenheim, worked tirelessly in the challenging conditions of Mercer Lake, located a few hundred miles from the South Pole. 

Utilizing a clean-access, custom hot water drill, they managed to retrieve the longest sediment core ever taken from a subglacial lake, measuring approximately seven feet in length. This feat required drilling through more than half a mile of ice, all the while racing against time as the water-filled hole began to refreeze.

This achievement marks only the second time in history that a sediment core has been extracted from a subglacial lake, with the first occurring in 2013 at Lake Whillans. 

Rosenheim believes that their work represents a significant advancement in our understanding of these mysterious ecosystems. “We’d thought the glacier retreated back to where it is now, but it went back well beyond that, which indicates the ice is a lot more dynamic than we realized. Now we need to incorporate this new understanding into models so we can better predict what may happen in the future as the planet warms.”

What the researchers discovered

The scientists have combined geochemistry tools, including isotopes and radiocarbon dating, to understand how carbon cycles through this extraordinary ecosystem. The findings not only shed light on the resilience of microbial life in these hidden lakes but also provide valuable insights into the geological history of the region.

Venturelli noted that the research has finally confirmed the maximum extent of the last deglaciation.

The team discovered that microbes in the lake are feeding off carbon that is 6,000 years old, a time when the region was still connected to the ocean. This evidence challenges previous assumptions about the stability and extent of the West Antarctic Ice Sheet.

In the absence of sunlight, the microbial life in these subglacial lakes relies on alternative sources of energy. Brent Christner, a study co-author and microbe expert from the University of Florida, explained that in Mercer Lake, microbes utilize chemical energy from physical processes associated with the ice sheet itself. 

As the ice moves, the rock beneath it is ground into fine particles, which are then mobilized in the water. Microbes, primarily bacteria and Archaea, access these minerals for energy during a process called chemosynthesis. Archaea are unique microorganisms that thrive in extreme environments, such as hot springs and deep-sea hydrothermal vents.

Venturelli explained that the pool of carbon in the sediment at the bottom of Mercer Lake is at least 100 times larger than any other carbon pool in the cycle, and the microbes use it efficiently. 

In addition, they also utilize carbon introduced into the system from water bodies upstream. The subglacial lakes, connected by a network of water and sediment transport, function more like a braided subglacial river system than isolated lakes.

Why the results of this study are important

Understanding the fate of the Antarctic ice sheet has significant implications for global sea-level rise. If the entire West Antarctic Ice Sheet were to melt, some estimates suggest that coastlines worldwide could see an increase of more than nine feet. 

Despite the alarming potential consequences of climate change, Venturelli remains hopeful, stating that their work highlights the dynamic nature of ice sheets and the need to investigate the reversibility of these processes. By probing the mechanisms that caused the ice sheet to re-advance to its current state, scientists can better predict future scenarios.

With over 650 subglacial lakes estimated to exist in Antarctica, scientists have only just begun to explore their mysteries. Venturelli emphasizes the importance of examining the base of the glacier, particularly the water and sediment in these subglacial lake systems, to unearth exciting findings. 

This study demonstrates that sometimes a new perspective is needed to unlock the secrets hidden within some of the most remote and enigmatic ecosystems on Earth.

As scientists continue to unravel the secrets of subglacial lakes and the dynamic history of the West Antarctic Ice Sheet, these discoveries will undoubtedly prove invaluable in informing our understanding of climate change and the future of our planet.

More about the West Antarctic Ice Sheet

The West Antarctic Ice Sheet (WAIS) is an enormous mass of ice covering approximately 1.9 million square kilometers of Antarctica. It is considered one of the most vulnerable ice sheets on Earth due to its marine-based nature and the presence of underlying warm ocean currents. 

As climate change intensifies, the WAIS is experiencing significant ice loss, leading to concerns about its future stability and the potential consequences for humanity and the environment.

One of the primary drivers of ice loss in the WAIS is the warming of ocean waters, which has accelerated the melting of the ice sheet from below. In addition, warmer air temperatures have led to increased surface melting and a higher frequency of ice-shelf disintegration events. 

These processes contribute to the destabilization of the WAIS, with several glaciers – such as the Pine Island, Thwaites, and Smith glaciers – experiencing rapid retreat and thinning.

The potential collapse of the West Antarctic Ice Sheet carries severe implications for humanity and the environment, primarily due to its impact on global sea levels. If the entire WAIS were to melt, it is estimated that sea levels could rise by more than nine feet (around 3 meters). 

Such a rise in sea levels would have catastrophic consequences for coastal communities, infrastructure, and ecosystems worldwide. Millions of people living in low-lying areas would be displaced, while countless plant and animal species would face the risk of extinction due to habitat loss.

Issues other than rising sea levels caused by the loss of WAIS

Beyond sea-level rise, the loss of the WAIS would also have implications for global ocean circulation and weather patterns. The influx of freshwater from the melting ice sheet could disrupt ocean circulation, potentially affecting regional climate systems and marine ecosystems. 

This, in turn, could have far-reaching consequences for agriculture, fisheries, and the overall functioning of Earth’s climate system.

The recent discoveries in subglacial lakes, such as Mercer Lake, have highlighted the dynamic nature of the WAIS and the need for a better understanding of the processes that drive its behavior. 

As scientists continue to study these enigmatic ecosystems and the history of the WAIS, it is crucial to improve our ability to predict its future evolution and develop strategies to mitigate the impacts of its potential collapse.

Addressing climate change by reducing greenhouse gas emissions, transitioning to renewable energy sources, and implementing sustainable development practices will be key to slowing down the melting of the West Antarctic Ice Sheet and preserving the delicate balance of Earth’s climate system.

 By taking action now, we can help safeguard our planet for future generations and protect the rich biodiversity of our world’s coastal regions.

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