Photo Credit: NASA

A NASA satellite caught this image on March 16 of the Mawson Coast of East Antarctica. At left, iceberg B-15T floats near the Emory Ice Shelf, far from the Ross Ice Shelf where it calved off 13 years earlier as part of the world's largest iceberg known simply as B-15.

Bergy bits

Remnants of mighty iceberg B-15 still floating around 13 years later

A NASA satellite recently spied a remnant piece of the mighty B-15 iceberg — 13 years after it first calved off the Ross Ice Shelf.

The Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Aqua satellite found B-15T last month floating along the Amery Ice Shelf nearly halfway around the continent from where it started.

Iceberg B-15 was the world’s largest recorded iceberg, with a surface area of 11,000 square kilometers, nearly the size of the state of Connecticut. It calved off the Ross Ice Shelf in March 2000. It spawned a number of smaller icebergs as it began to break apart, with B-15A accounting for more than half of its original size.

The resulting icebergs were so large that they choked the channel to McMurdo Sound, which leads to McMurdo Station . That caused the sea ice to remain locked into McMurdo Sound for a number of years, complicating the re-supply of the station via the sea. It also caused ecological challenges for top predators like penguins and seals because of the changes in the extent and thickness of sea ice. [See previous article — After the icebergs: Royds penguins just 'treading water' while nearby Beaufort Island supports new sub-colony.]

The sea ice dam finally broke at the end of the 2010-11 austral summer when the sound cleared out all the way to the southerly McMurdo Ice Shelf for the first time in more than a decade. [See previous article — Open water: Break-up of sea ice in McMurdo Sound welcomes wildlife, nears airfield road.]

Glaciologist Doug MacAyeal , a professor at the University of Chicago, is a leading expert on ice dynamics who was one of the first scientists to study the calving event with funding from the National Science Foundation . He and colleagues installed instruments on several of the icebergs in the early 2000s to track their progress and collect meteorological and other data.

MacAyeal said none of the instrument stations that were installed are still working except one on a site dubbed “Nascent Iceberg,” an area near the front of the Ross Ice Shelf that scientists expected to calve before now.

MacAyeal said his team tracked B-15A and B-15J until late 2010 when the GPS stations failed. They were south of New Zealand at the time.

Another iceberg tracked by MacAyeal, C16, is south of South Georgia Island after circumnavigating the continent from the Ross Sea to the Weddell Sea.

It had calved in September 2000 when B15 collided with the most northerly portion of the Ross Ice Shelf and caused a large chunk to break away, according to a NASA news story.

C-16 ended up being “trapped” with several other icebergs — B-15K, B-15A and B-15J — near the Ross Ice Shelf and Ross Island for at least five years. For part of that time, C-16 was grounded in the shallow shoal area between Lewis Bay and Beaufort Island, where it was a target for other icebergs transiting the region — what MacAyeal has referred to as the iceberg equivalent of a mosh pit.

All the icebergs were fitted with several instruments: GPS receivers, magnetic compasses and automatic weather stations. In addition, a seismometer used to study calving, drift, break-up and collisions, was placed on C16, as was a camera.

“We have data to recover from C-16,” MacAyeal noted, “so if anybody gets out there near it (a cruise ship), we’d be happy to tell them where the data recorders are [located].”

The icebergs and calving events have offered researchers a wealth of information about ice dynamics. MacAyeal’s own work has suggested that the eventual break-up of B-15A in 2005 was caused by a large storm in the Gulf of Alaska that generated a trans-Pacific ocean swell. However, other scientists have argued that the iceberg broke apart after repeatedly grounding near the coast.

Research on the bergs continues to this day.

A poster presented by University of Chicago undergraduate student Sarah U. Neuhaus at last December’s American Geophysical Union meeting showed “remarkable fidelity between the drift of B-15A, B-15J and C-19 with sea-floor spreading features, like transform faults and mid-ocean ridges,” MacAyeal noted.