Melt Expanding into East Antarctica as Nansen Ice Shelf Crack Produces 20 Kilometer Long Iceberg

Ever since 1999 a gigantic crack has been growing in the Nansen Ice Shelf in East Antarctica. By 2014, expansion of the crack accelerated. As of early 2016, the crevice had grown to 40 kilometers in length. Flooded by melt along the Ice Shelf’s warming surface and weakened by the heating of ocean waters from below, on April 7th, according to ESA reports, this East Antarctic Ice Shelf produced an immense 20 kilometer long iceberg. A towering block of ice covering an area larger than Manhattan floating on out toward the world’s shipping lanes.

Nansen Ice Shelf Fracture

(Surface melt water flooding into a great crack along the Nansen Ice Shelf. Large volumes of melt water flooding into ice shelf cracks forces them to widen even as they dive toward union with the warming waters below. Image source. ESA.)

The Nansen Ice Shelf, before this most recent very large iceberg calving event, was a 10 mile wide and 30 mile long ice shelf that buttressed the Presley and Reeve Glaciers of East Antarctica. It abuts the north side of the Drygalski Ice Tongue, and runs out from Mount Nansen just inland of the coast of Victoria Land, Antarctica. And it’s yet another large shelf of ice that appears to be facing severe weakening as global average temperatures are driven above 1 C warmer than those experienced during the late 19th Century by an ongoing and reckless fossil fuel emission.

Nansen occupies a region of the world that has come under increasingly intense observation due to a number of scientific studies highlighting its accelerating rates of melt and a related risk of rapidly rising global sea levels.  Human-forced heating of the world’s ocean has caused waters warm enough to accelerate glacial melt to encroach upon Antarctica from the Southern Ocean. These warmer waters are drawn along beneath the floating ice shelves as fresh melt water flooding out along the ocean surface generates a landward-moving bottom current. These warmer waters eventually push beneath the ice shelves — eating away at their undersides.

Nansen Ice Shelf Fracture

(Massive ice berg breaks away from the Nansen Ice Shelf on April 7th in this ESA satellite shot.)

In West Antarctica, glaciers are seen as especially vulnerable. One region containing the Pine Island and Thwaites glaciers — alone capable of increasing global sea levels by 3-6 feet — is experiencing 3-4 meters of melt along the undersides of ice shelves each year. Meanwhile, the Pine Island Glacier’s grounding line — the point upon which the floating ice shelf is anchored — has retreated more than 31 kilometers further into Antarctica.

As ice shelves and glaciers melt from below, more of the glacial mass is floated away from the main ice mass. And since West Antarctica has a retrograde slope, more warm ocean water comes flooding in beneath the glaciers. As more ice calves off the glacial faces, ice fronts along the ocean become taller. The brittle ice cannot retain structural integrity for long and ever taller ice faces produce swifter and swifter rates of collapse into the ocean. On the surface, warmer conditions cause rivers of melt water to flow into cracks. The extreme weight of the water flooding these cracks serves as a kind of wedge — widening the cracks and shoving sea-facing sections along the cracks into the ocean.

Antarctic glacial melt

(Though the most rapid rates of glacial melt dominate the Antarctic Peninsula and the region near the Pine Island and Thwaites glaciers, increasing rates of volume loss from Antarctic ice shelves have been creeping into a section of East Antarctica near the Nansen Ice Shelf along the coastline of the Ross Sea [just below where the abbreviation DRY for Drygalski Ice Tongue appears on the map]. With global average temperatures now exceeding 1 C above pre-industrial, we can expect melt and net volume loss to expand along the Antarctic coastline. Image source: Science.)

East Antarctica, a region occupied by Nansen, has been seen as less vulnerable to melt from human-forced warming than West Antarctica and the Antarctic Peninsula. That said, increasing melt rates have progressed on into much of the Ross Sea coastal region. Though the current very large calving event at Nansen appears to have taken place within the expected time-frame (once every 30 years), a context of melt is beginning to encroach. For almost all glaciers along this section of East Antarctica show increasing rates of ice loss.

Links:

Nansen Gives Birth to Two Icebergs

Widespread, Rapid Grounding Line Retreat at Pine Island Glacier

Volume Loss From Antarctic Ice Shelves is Accelerating

The Nansen Ice Shelf

The Drygalski Ice Tongue

Hat Tip to Colorado Bob

 

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 basin

(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 meltingWarm 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:

totten_glacier_labeledpaths

(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:

NASA six meter sea level rise SE

(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

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