New findings have uncovered how a significant Antarctic ice shelf has experienced increased melting from warmer ocean waters over the past 40 years. Researchers believe that this trend will likely intensify as climate change continues to warm the oceans.
New findings have uncovered how a significant Antarctic ice shelf has experienced increased melting from warmer ocean waters over the past 40 years.
Researchers from the University of East Anglia (UEA) have linked their observations to an incident where their autonomous Seaglider became unintentionally trapped beneath the Ross Ice Shelf. This suggests that the rate of melting may increase as climate change progresses.
The glider, named Marlin, was sent out in December 2022 from the edge of the sea ice into the Ross Sea. Equipped with various sensors designed to gather data essential for understanding climate processes, Marlin was programmed to head north into open waters.
Unfortunately, the glider got caught in a southward current and was pulled into an ice shelf cavity, where it remained for four days while taking measurements. During its time trapped, it made 79 dives, measuring water temperatures in the cavity down to a depth of 200 meters, right at the bottom of the ice shelf above.
Researchers from UEA’s School of Environmental Sciences detected a 50-meter-thick layer of relatively warm water entering the cavity from the open sea, with temperatures ranging from -1.9°C to a warmer -1.7°C under the ice.
Further analysis of all data available indicates that the amount of heat transferred into this cavity has risen over the past 45 years, likely due to the warming of the Ross Sea resulting from climate change. These findings have been published in the journal Science Advances.
“While the annual temperature increase of four thousandths of a degree may seem minimal, it could result in an extra ice loss of approximately 20 to 80 centimeters each year over the 45 years we studied,” explained lead author Dr. Peter Sheehan.
“We discovered that the warmer waters were sufficient to melt the bottom of the ice shelf, contrasting with the freezing-point waters they likely replaced. What is significant is that we can now trace the warm water from the open Ross Sea all the way back into the cavity. This is the first time we’ve observed such an intrusion firsthand.”
Dr. Sheehan continued: “Our trip into the cavity under the Ross Ice Shelf was unexpected and typically unfeasible for measurement due to the risks associated with sending instruments so close to the underside of an ice shelf.”
The ice shelves surrounding Antarctica are continually subjected to ocean warmth beneath them, leading to melting at their bases, which is the largest contributor to the loss of Antarctic ice mass.
While the melting of floating ice does not significantly influence sea levels, ice shelves play a crucial role in slowing the flow of land ice into the sea, thus stabilizing the Antarctic ice sheet. Their thinning and eventual collapse could greatly accelerate the influx of land ice into the ocean, contributing to global sea-level rise.
One factor that can push warmer surface water beneath the Ross Ice Shelf is wind. Certain wind patterns can cause a southward flow in the surface ocean, directing it into the ice shelf cavity.
These wind-driven surface flows, known as Ekman currents, carry heat and are particularly relevant to climate scientists, as they have immediate implications for melting the ice above. Unlike deeper ocean currents, this heat can melt the ice shelf without needing to mix upward.
Understanding Ekman heat transport is important because the oceans absorb a significant amount of Earth’s heat and redistribute it. Changes to this system can lead to substantial impacts on weather, sea levels, and global temperatures.
Dr. Sheehan and co-author Prof. Karen Heywood utilized long-term data on wind patterns and ocean temperatures, combined with modeling to address gaps in the dataset, to estimate the strength of southward Ekman heat transport over the last 45 years. They concluded that the amount of heat transported into the cavity by these currents has been increasing.
Variability from year to year is driven by wind patterns. However, the overall upward trend in heat transport is likely tied to the warming of the Ross Sea—warmer water means that contemporary winds carry more heat energy into the cavity compared to similar wind conditions in the past.
Prof. Heywood stated: “It seems likely that the Ekman heat flux and the melting it causes will continue to grow as climate change progresses and oceans warm further. This trend itself is troubling.”
“It’s critical to integrate the effects of surface-water intrusions and the changing dynamics of Ekman currents into climate models, especially considering the ongoing uncertainty regarding how Antarctica’s land-based ice will respond to climate change.”
This study marks the first time that this phenomenon has been examined using a comprehensive, multi-decadal dataset. Previous understandings of surface-water intrusions primarily came from comparisons of hydrographic data in open waters through ship observations, tagged seal research, or mooring deployments within a cavity.
This research was supported by the UK Natural Environment Research Council, the US National Science Foundation, and the European Research Council’s Horizon 2020 program.