Iceberg B15G offshore from Casey station.

Information collated by Dr. Neal Young, Australian Antarctic Division.

Background:

Iceberg B15G is part of the immense iceberg B15 which broke away from the Ross Ice Shelf in Antarctica in March 2000, and which within a few weeks broke into six still large sections: B15A, B15B, …, B15F. The largest, B15A, is still in the Ross Sea, and now moving slowly northwards along the coast of Victoria Land.

The other sections (B15B, etc) drifted out of the Ross Sea as a group and then began to move counter-clockwise around the Antarctic coast. After the largest of those sections, B15B, rounded Cape Adare into the Southern Ocean in April 2001, another three icebergs progressively calved from it. One of these is B15G. All sections drifted in towards the coast of George V Land (approximately longitude 150 E) to the east of Mertz Glacier. B15D soon drifted on around the continent and in May 2005 is located at about longitude 50 E off the coast of Enderby Land.

B15G and several other bergs started drifting west from the area, where they had been stranded for several years in fast-ice east of Mertz Glacier, in about mid-2004.

Size of B15G:

Shape: Wedge-shape
Length: 49-50 km
Width: Max overall, 23 km, typical 12-20 km
Area: 775-795 sq km
Thickness: Estimated average for whole iceberg about 270 m, range 150-300+ m
Ice volume: 220 cu km
Mass: 200 Gt (Giga-tonnes)
Water volume 200,000,000,000,000 L

Comparative sizes:

Area approximately:
2.5 times area of island of Malta,
similar to area of island of Domingo,
one third area of ACT.

Water volume equivalent to approximately 5% of annual global water usage
(that includes all of agriculture, industry, and domestic usage).

Mass is more than 200 times total world shipping tonnage, and
about 30 times total cargo tonnage of annual world shipping trade.

Current situation:

B15G has been drifting slowly from east to west with the ocean current known as the East Wind Drift. It passed the French Antarctic station of Dumont D’Urville (longitude 140 E) in August 2004. In April/May 2005 it drifted west past Law Dome, and then south into Vincennes Bay. It came to rest a few kilometres from Vanderford Glacier, and some 25-30 km offshore from Casey station and clearly visible from the station as a long ice cliff stretching along the horizon .

B15G is measured on satellite images to be 50 km long and 12 to 20 km wide and a wedge shape.

ACE / AAD glaciologists say the iceberg appears to have moved quite quickly into Vincennes Bay possibly being transported on an ocean gyre, and reached its southern position on 26/27 April 2005. Since then, it has exhibited negligible movement. It appears that the southern end of the berg is aground in relatively shallow water along the south-west flank of the deep channel off-shore from the Vanderford Glacier. The few bathymetric surveys in that area indicate water depths around 300 m.

The berg could stay in its present location for days, weeks, or even months. However it is expected to eventually work its way back out from the coast to continue its westward drift around the continent. There is no particular concern about damage to land forms as was the case recently with another of the icebergs which calved from B15 – B15A – and which made contact with the Drygalski Ice Tongue in April 2005, and later with Aviator Glacier tongue in May 2005.

B15G is the first massive iceberg to be observed to enter Vincennes Bay. It has moved about 150 km south over the continental shelf, well south of the typical drift path expected to be followed by these icebergs. Icebergs do move onto the continental shelf at various locations around the continent, for instance the area to east of Mertz Glacier. They may become grounded for periods from days to years. The first of the offspring of B15 to drift west around the coast, B15D with a similar size and shape to B15G, drifted past Casey / Law Dome in April 2003, and subsequently spent about 6 months grounded on “Four Ladies Bank” on the edge of the continental shelf in Prydz Bay north of Davis in 2003/4. It has now drifted well to the west to about longitude 50 E

For more information contact Dr.Neal Young