Faster than Predicted! Upside-Down 'Rivers' Threaten Antarctic Ice Shelves

Of all the glaciological processes that comprise the massive Antarctic Ice Sheet, it is the ice shelf that is the most at risk due to climate change. Because, as the most seaward extension of a glaciological system, ice shelves are in contact with both the air above and the underlying ocean. As a result, ice shelves are constantly adjusting to aggressive forcing from multiple sources: the advancing glaciers, the bedrock to which they are attached, the atmosphere such as the temperature, pressure and wind, as well as underlying ocean conditions such as temperature, currents and waves.

Antarctica.org​​ describes the role of an ice shelf and how it can collapse.

Ice shelves are floating tongues of ice that extend from grounded glaciers on land. Snow falls on glaciers, which flow downstream under gravity. Ice shelves are common around Antarctica, and the largest ones are the Ronne-Filchner, Ross and McMurdo Ice Shelves.

Ice shelves surround 75% of Antarctica’s coastline, and cover an area of over 1.561 million square kilometres (a similar size to the Greenland Ice Sheet). Ice shelves gain mass from ice flowing into them from glaciers on land, from snow accumulation, and from the freezing of marine ice (sea water) to their undersides[1]. They lose mass by calving icebergs, and basal melting towards their outer margins, along with sublimation and wind drift on their surfaces. Ice shelves are important, because they play a role in the stability of the Antarctic Ice Sheet and the ice sheet’s mass balance, and are important for ocean stratification and bottom water formation; this helps drive the world’s thermohaline circulation. Melting from beneath ice shelves is one of the key ways in which the Antarctic Ice Sheet loses mass[1].

 A new study led by researchers at the National Snow and Ice Data Center and co-authored by researchers at Scripps Institution of Oceanography found that warm ocean water is carving “upside-down rivers” into the underside of the ice shelves, weakening and rotting them from below and making them vulnerable to collapse. This phenomenon is occurring on all the ice shelves of Antarctica and according to the study the channels can be tens of miles long, and up to 800-feet “deep.”

Scripps Institution of Oceanography reports: 

“This paper is the first inventory of these basal channels all around Antarctica,” said Matthew Siegfried, a postdoctoral scholar at Scripps Oceanography, and co-author of the study. “We show that these channels are extremely dynamic features that can change rapidly. Our observations demonstrate that they can deepen, they can lengthen, and, perhaps most importantly, they can cause the larger regions of the ice shelf to crack.”

When a channel is carved into the base of an ice shelf, the surface of the ice shelf sags, leaving a visible depression in the relatively smooth ice surface. Alley and her colleagues mapped the locations of these depressions all around the Antarctic continent using satellite imagery, as well as radar data that images the channels through the ice, mapping the shape of the ice-ocean boundary.

Researchers at Scripps were able to document how quickly some of the channels were growing through the use of satellite laser altimetry, which measures the height of an ice shelf surface with high accuracy. The data show that growing channels on the rapidly melting Getz Ice Shelf in West Antarctica can bore into the ice shelf base at rates of approximately 10 meters (33 feet) each year.

The mapping shows that basal channels have a tendency to form along the edges of islands and peninsulas, which are already weak areas on ice shelves. The team observed two locations where ice shelves are fracturing along basal channels, clear evidence that basal channel presence can weaken ice shelves to the point of breaking in vulnerable areas.

The study shows that basal channels are associated with the development of new areas of crevassing, suggesting that these channels may cause the ice to fracture. In conclusion, it found that ”basal channels can form and grow quickly as a result of warm ocean water intrusion, and that they can structurally weaken ice shelves, potentially leading to rapid ice shelf loss in some areas.”

NASA Emeritus Scientist  Robert Bindschadler, who worked for 35 years as a glaciologist at NASA's Goddard Space Flight Center, reacts to a question from Truthout.org​​ on how best to get the point across that heating of the southern hemisphere’s air conditioner is causing tectonic shifts in the atmospheric and ocean current circulatory systems of Earth.

Speaking about what is impacting Antarctica, the basics of it are that the atmospheric winds influence the ocean and the ocean affects the ice. These are all at play in Greenland, too. In the Antarctic, you have the circumpolar winds rotating clockwise around the continent, and these isolate the continent.

Two things result from this: The first is that the Antarctic is isolated from other weather patterns, so as the rest of the world has warmed, the Antarctic hasn't warmed as much. So that causes an increased isolation, as the temperature gradient of the warm tropics and the cold Antarctic increases, that causes an increase in pressure. That pressure has increased the speed of the circumpolar winds.

The second thing that results from this is the winds drag the ocean along with it. So there is a huge, strong, powerful, broad current, the Antarctic circumpolar current, that is spun up and drug along by the winds. So now we have the ocean going around faster and faster because the air is dragging it faster. In the Southern Hemisphere, because of the rotation of the planet, the faster ocean water is turning a little more to the left, and that steers it away from the continent of Antarctica, so that is forcing water from a greater depth to upwell high enough for it to spill onto the continental shelf. And this is warm water because in the tropics you have warm water on top and cold water down deep. In the polar oceans, you have three layers, a cold surface, then a warm layer, then the cold deep waters, because sea ice freezes and melts every year, hence the creation of the cold surface layer. So it's the surface layer being pushed away, and the upwelling is warm.

So once it does that, the continental shelf is tilted down toward the ice sheet, so the warm, dense, salty water gets onto the shelf, and hugs the shelf, and flows down toward the ice sheet, contacting it at the grounding zone where the ice is, melting the ice very, very rapidly. Every degree of heat increase melts an additional 30 feet of ice, each year. So that is a powerful heat gun.

Although the West Antarctic Ice Sheet has passed the point of no return and is in irreversible melt, new research has found that if co2 levels in the atmosphere continue increasing as predicted,  East Antarctica will melt as well.

The below raw footage videos were filmed by Scripp researchers studying the “ocean waves that impact the front of the Ross Ice Shelf that sends vibrations throughout the ice shelf, much like the beating of a heart sends a detectable pulse throughout the body. As with a pulse, these vibrations can be used to help assess the health — the stability and structural integrity — of the ice shelf.”