New Analysis of the 2002 Larsen B Ice Shelf Collapse

A new paper has been published which examines the factors involved in the 2002 collapse of the Larsen B ice shelf in Antarctica.

The lead author, Professor Neil Glasser of Aberystwyth University (Wales, UK) was interviewed about the findings in the Western Mail on 7th February:

'Antarctic ice shelf did not just melt away'

Excerpt: Prof Glasser told the Western Mail, “Climate change may have been the last straw, but it was not the only straw.”

“Ice shelf collapse is not as simple as we first thought,” said Prof Glasser, lead author of the paper."

“Because large amounts of meltwater appeared on the ice shelf just before it collapsed, we had always assumed that air temperature increases were to blame."

“But our new study shows that ice-shelf break-up is not controlled simply by climate. A number of other atmospheric, oceanic and glaciological factors are involved."

“The location and spacing of fractures on the ice shelf such as crevasses and rifts are very important too, because they determine how strong or weak the ice shelf is.”

Prof Glasser pointed out that he is not a climate change sceptic.

The full paper entitled, 'A structural glaciological analysis of the 2002 Larsen B ice shelf collapse' is currently available for free download from the Journal of Glaciology.

The Abstract reads:

This study provides a detailed structural glaciological analysis of changes in surface structures on the Larsen B ice shelf on the Antarctic Peninsula prior to its collapse in February–March 2002. Mapped features include the ice-shelf front, rifts, crevasses, longitudinal linear surface structures and meltwater features. We define domains on the ice shelf related to glacier source areas and demonstrate that, prior to collapse, the central Larsen B ice shelf consisted of four sutured flow units fed by Crane, Jorum, Punchbowl and Hektoria/Green/Evans glaciers. Between these flow units were ‘suture zones’ of thinner ice where the feeder glaciers merged. Prior to collapse, large open-rift systems were present offshore of Foyn Point and Cape Disappointment. These rifts became more pronounced in the years preceding break-up, and ice blocks in the rifts rotated because of the strong lateral shear in this zone. Velocity mapping of the suture zones indicates that the major rifts were not present more than about 20 years ago. We suggest that the ice shelf was preconditioned to collapse by partial rupturing of the sutures between flow units. This, we believe, was the result of ice-shelf front retreat during 1998–2000, reducing the lateral resistive stress on the upstream parts of the shelf and glacier flow units, ice-shelf thinning and pre-shelf-break-up glacier acceleration.

While we are on the subject of the Larsen B (and A) ice shelf, I am reminded of a paper from 2006, published in QUATERNARY SCIENCE REVIEWS, entitled: 'Ice shelf history from petrographic and foraminiferal evidence, Northeast Antarctic Peninsula'

This paper suggests that there was "widespread ice shelf breakup in the mid-Holocene." This finding is harmonious with the earlier finding of Pudsey and Evans (2001) that the adjacent Prince Gustav Channel ice shelf also retreated in mid-Holocene time, but that subsequent colder conditions, in their words, "allowed the ice shelf to reform." It is also in harmony with the finding of Vaughan et al. (2001) that from 6000 to 1900 years ago the Prince Gustav Channel ice shelf, as they describe it, "was absent and climate was as warm as it has been recently." Consequently, and most recently, Pudsey et al. concluded that "the maximum ice shelf limit may date only from the Little Ice Age," which they report is "widely recognized" to have held sway in that part of the world between 700 and 150 years ago.

A large body of data makes it pretty clear that the greatest extent of the Larsen ice shelf during the current interglacial likely occurred only a few hundred years ago, and that the portions of it that recently disintegrated (Larsen-A and Larsen-B) were probably created about that same time. In addition, it would appear that some 2000 years ago the Larsen-A and B ice shelves likely were altogether absent, and that temperatures of that time were likely as warm as, or even warmer than, they have been recently. Furthermore, there was approximately 100 ppm less CO2 in the air of that time than there is in the air of today; and this fact suggests that something other than anthropogenic CO2 emissions was the cause of the earlier "balmy" conditions of northeast Antarctica, which implies that that same something else, or something different yet, could well be responsible for the current warmth of the region.
(CO2Science.org, December 2006)

The Abstract reads:

A detailed record of late Pleistocene deglaciation followed by mid-Holocene ice shelf breakup and late Holocene re-growth is contained in continental shelf sediments in the northern Larsen area, northeast Antarctic Peninsula. The zero age of core tops is confirmed by new and published 210Pb profiles, and 70 accelerator mass spectrometer (AMS) 14C dates on bulk organic carbon define sedimentation rates of 7.6–92 cm/ka. The varied geology in the local ice drainage basins facilitates the use of ice-rafted debris (IRD) provenance in determining the presence or absence of ice shelves. All inshore cores contain an interval of non-local IRD in the post-glacial section, demonstrating widespread ice shelf breakup in the mid-Holocene. Both breakup and re-growth may have taken centuries and there are no widespread debris layers associated with breakup. Cores beyond and up to 30 km inside the historical ice shelf limit exhibit a varied IRD provenance throughout the Holocene, suggesting the maximum ice shelf limit may date only from the Little Ice Age. Benthic foraminiferal assemblages are related to water masses and position on the continental shelf and have been modified by taphonomic processes. Nevertheless we discern a deglaciation signal in Prince Gustav Channel of a calcareous spike in predominantly agglutinated assemblages, and this is repeated at the time of mid-Holocene ice shelf breakup. The inferred mid-Holocene warm period occurred later in the northern Larsen area than on the west coast of the Antarctic Peninsula.

The above papers suggest that the collapse of the Larsen B ice shelf in 2002 wasn't simple or unprecedented.