Massive icebergs on the move

Massive icebergs that calved during 2000–2002 are now spread around the Antarctic coastline. Of these, B22 remains within a few kilometres of its source — the Thwaites Glacier. Of the bergs that calved from Ronne Ice Shelf in March 2000 (A42 and A43), small sections of A43 remain in the Weddell Sea, while the others have drifted out into the South Atlantic and dissipated.

Iceberg B15 created a lot of interest when one of its progeny, B15A, drifted west across the front of Ross Ice Shelf, ultimately blocking the entrance to McMurdo Sound, affecting wildlife in the area and hindering shipping movements (see figure). During 2004 another two sections (B15J and B15K) broke off B15A, allowing its northern end to clear Franklin Island and swing into the northern part of McMurdo Sound. Here it became temporarily grounded, blocking movement of sea ice out of the sound. Some months later it began moving slowly north, giving a glancing blow to the outer end of the Drygalski Ice Tongue and then almost colliding with the Aviator Glacier Tongue. On October 28 2005, as B15A was exiting the Ross Sea round Cape Adare, it broke into several more sections. The list of progeny now extends to B15N.

Almost all of the massive icebergs coming from Ross Ice Shelf have drifted westwards out of the Ross Sea and onto the continental shelf east of the Mertz Glacier, where they have been either grounded or locked in by fast ice (sea ice that is joined to the coast, islands, or grounded icebergs) for some time. B9B, which calved in 1987 is still there. B15D is now off Dronning Maud Land, a half circumnavigation from its calving site. B15G followed, but then drifted into the coast near Casey station, where it became grounded for some weeks and made a prominent sight on Casey station’s horizon. It is now adjacent to the Shackleton Ice Shelf. B15B, which is now the largest of the B15 progeny, as of November 2005, is passing just north of Law Dome.

NEAL YOUNG, Antarctic Climate and Ecosystems Cooperative Research Centre and Ice, Oceans, Atmosphere and Climate Programme, AAD