The Human-Warmed Southern Ocean Threatens Major Melt For East Antarctica

Totten Glacier. A mountainous expanse of ice in the very heart of the greatest accumulation of frozen water on Earth. A bastion of cold containing 11.5 feet worth of sea level rise if it were to melt in total. An accumulation roughly equal to half of all the frozen water in the whole of the Greenland Ice Sheet.

According to a new scientific report out this week, Totten Glacier is under threat of melt. Warm water is swelling up through troughs in the Continental Shelf zone, approaching the ice shelf locking Totten and a vast swath of interior East Antarctic glaciers. As with West Antarctica, this warm water upwelling has the potential to rapidly destabilize an already fast-moving glacier.

(Totten glacier outflow zone covers a massive region of East Antarctica. An area about equivalent in size to the entire US Southeast region. Warm water is starting to encroach upon an ice shelf locking this great ice mass into its Continental Catchment Basin. Image source: Australian Antarctic Division.)

Totten already hosts one of the most rapid thinning rates in East Antarctica. And, in fact, it was a satellite detection of this very thinning that set off a recent scientific investigation of the glacier’s stability. What the new scientific report identified was a threat that enhanced warm water upwelling from a human-heated circumpolar current would collide with an ice structure that is already vulnerable to melt.

The net result would mean a destabilization and acceleration of one of the greatest ice masses on the planet. Such an event would have far-reaching implications, especially relating to the pace and end state of warming-related global sea level rise.

From the abstract of Ocean Access to A Cavity Beneath Totten Glacier:

Totten Glacier… has the largest thinning rate in East Antarctica. Thinning may be driven by enhanced basal melting… Warm modified Circumpolar Deep Water, which has been linked to glacier retreat in West Antarctica, has been observed in summer and winter on the nearby continental shelf beneath 400 to 500 m of cool Antarctic Surface Water…We identify entrances to the ice-shelf cavity below depths of 400 to 500 m that could allow intrusions of warm water if the vertical structure of inflow is similar to nearby observations. Radar sounding reveals a previously unknown inland trough that connects the main ice-shelf cavity to the ocean. If thinning trends continue, a larger water body over the trough could potentially allow more warm water into the cavity, which may, eventually, lead to destabilization of the low-lying region between Totten Glacier and the similarly deep glacier flowing into the Reynolds Trough. (emphasis added)

At issue are two pathways for this upwelling, warm, deep water to follow:

(Topographic map of the Totten Glacier outlet region and nearby seabed. Note the vulnerable water inlets [orange lines], the inland troughs and basins [red highlights and blue topographic signature] and the rather advanced inland extent of the grounding line [white line]. Image source: Ocean Access to a Cavity Beneath Totten Glacier.)

The pathways are identified by the orange lines in the topographic image above. The lines identify underwater valleys that run out to the deeper, warmer waters accumulating on the edge of the Antarctic Continental Shelf region. As the waters rise, scientists are concerned that these troughs will act like channels, funneling a flood of much warmer than normal water beneath the belly of the great glacier.

The result is an instance of ‘global consequence.’ The authors note:

We estimate that at least 3.5 m of eustatic sea level potential drains through Totten Glacier, so coastal processes in this area could have global consequences.

Indeed. If we add in all the other destabilized glaciers around the world to Totten, should it destabilize, you end up with about 26 feet of sea level rise locked in. And that has some pretty staggering consequences when you look at impacts to the world’s coastlines.

This is what 20 feet of sea level rise impact looks like for the US Southeast and Gulf Coasts:

(Six meters of sea level rise would permanently inundate many of the major cities along the US Gulf and Southeastern coasts. Areas inundated shown in red. Image source: NASA.)

But, perhaps worst of all, is the fact that some of the world’s longest lasting and most stable accumulations of frozen water are now under threat of melt.

In essence, what we are witnessing is possible initiation of the end of the greatest and oldest ice province on Earth. East Antarctica glaciated 35 million years ago, when atmospheric CO2 levels fell below a range of 500-600 parts per million, and has been mostly stable or growing ever since. Now that region of ice, the most ancient remaining in the memory of Earth, is under threat. With human greenhouse gasses in the range of 484 ppm CO2e (CO2 equivalent) and 400 ppm CO2 and rising, it appears that even the oldest glaciers are under existential threat.

To this point, Eric Rignot noted in a recent interview:

“..the stage is set. You have a submarine glacier and a deep trough. The warm water is not too far from that frontal region and we’ve seen some changes in the glaciers that suggest that something is happening at their base.”

Links:

Ocean Access to A Cavity Beneath Totten Glacier

Hidden Channels Beneath East Antarctica Could Cause Massive Melt

Australian Antarctic Division

NASA

A Glacier Area the Size of the Entire South is Melting Away

Posted by robertscribbler on March 20, 2015

https://robertscribbler.wordpress.com/2015/03/20/the-human-warmed-southern-ocean-is-threatening-to-melt-east-antarctica/