Iceberg B-34 frees itself from Antarctica’s Getz ice sheet and proceeds to scour the sea floor.

Apr 29, 2015 by

‘It’s catastrophic, really. They kill 99 per cent of things they come in contact with”.
David Barnes, British Antarctic Survey

An iceberg 17 miles long,  now named B-34,  cracked and broke loose from Antarctica’s Getz Ice Shelf. The Getz ice shelf is roughly 300 miles long and up to 60 miles wide. Ice shelves in Antarctica have an average thickness of between 1,300 to 1,600 feet and some can extend out hundreds of miles off the coast. The Amundsen shelves are grounded on a bed that lies below sea level and several large islands are partially or wholly embedded in the ice shelf.  The Amundsen Sea ice shelves are weak and more prone to climate change. It is thought to be melting at a rate triple of what it had 10 years ago. NASA notes:

“Why is the Amundsen Sea region more at risk than other parts of West Antarctica?

In addition to the ice sheet being grounded below sea level, there are three main reasons. First, the glaciers here lack very large ice shelves to stem ice flow. Second, they aren’t “pinned” by obstructions in their beds except in a few small places, unlike the Ronne and Ross shelves which are pinned down by large islands. Third, as first observed in the 1990s, the area is vulnerable to a regional ocean current, ushered in by the shape of the sea floor and the proximity of the circumpolar deep current. This current delivers warm water to grounding lines and the undersides of ice shelves in the region.”

NASA reports on the recent finding that B-34 has separated from the ice shelf:

B-34 is the 34th iceberg from the “B” quadrant of Antarctica (located between 90 degrees East and 180 degrees) to be tracked by the NIC. The newberg is still smaller, however, than the much older B-15T—a fragment of B-15 that initially broke off from the Ross Ice Shelf in March 2000.Large icebergs can have large-scale impacts on the Southern Ocean. For example, as the bergs melt, the addition of cold, fresh water to the saltwater ocean can affect ocean currents and circulation. Researchers have shown, however, that even more fresh water comes from the melting of smaller and much more numerous bergs.

In just 17 years, icebergs have decimated the sea life near western Antarctica. In 1997 a 500 square mile section of sea bottom was studied and discovered to have colorful coral like creatures called “moss animals”. These creatures filter the water for food. Upon return in 2013, the researchers discovered that all but one of these species had vanished.CBC news reports:

As the glaciers retreat and the ice shelves collapse on the West Antarctic Peninsula, they break off into floating chunks of ice, some of them extremely massive.Fifty years ago, icebergs couldn’t move around much because most years, the sea surface was frozen for much of the year. But recently, Barnes said, most years, the sea is frozen for less than 50 days a year. That leaves the icebergs free to drift and blow in the wind until they crash boulders on the sea floor, pounding and scraping away everything that lived on them.

The animals that live on the sea floor are called benthos. Species can include sea anemones, sponges, corals, sea stars, sea urchins, worms, bivalves, crabs, and many more. These organisms grow very slowly in the ice cold water, have low levels of reproduction, colonization and growth. Ice shelves and ice bergs scour the bottom killing everything in its path. This is not good news for the southern ocean food web.From Current Biology:

Life on Antarctica’s coastal seabed rollercoasters between food-rich, open-water, iceberg-scoured summers and food-sparse winters, when the sea surface freezes into ‘fast-ice’, locking up icebergs, reducing their seabed collisions (scouring). In the last half century, there have been massive losses of winter sea ice along the Antarctic Peninsula, as well as retreat of glaciers and disintegration of ice shelves coincident with rapid recent regional warming [1] . More calving from glaciers and ice shelves coupled with less winter ice should increase scouring of the seabed — which is where most Antarctic species live (http// Polar benthos are considered highly sensitive to change, slow growing and all endemic. However, the only published effect of increased scouring on benthos has been increased mortality of the pioneer species Fenstrulina rugula, adjacent to Rothera Research station, West Antarctic Peninsula [2] (Supplemental information; Figure S1 ). It is likely that the recent increase in mortality in this species reflects the mortality of other species on hard substrata. A 2013 survey dive at a nearby locality (Lagoon Island) revealed large areas where no live mega- or macro-fauna could be found, the first time this has been observed there despite being regularly visited by scientific divers since 1997. Here, we report the first assemblage level changes coincident with increased scouring.

Originally posted to Pakalolo on Wed Apr 29, 2015 at 01:38 AM PDT.

Also republished by Climate Change SOS.


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