Multidecadal pre- and post-collapse dynamics of the northern Larsen Ice Shelf

Abstract

Rapid retreat of Antarctic ice shelves in a warmer climate remains challenging to predict, contributing to uncertainties in projections of sea level rise. The collapse of the Larsen B Ice Shelf on the Antarctic Peninsula in 2002 was perhaps the most dramatic example of ice shelf retreat on record. Despite a general consensus that regional climate warming is associated with ice shelf collapse, knowledge of the precise details leading to and following collapse is limited. Here we examine a comprehensive set of satellite observations, modeling experiments, and climate reanalysis data to elucidate calving behavior, flow dynamics, and mechanical conditions of the northern Larsen Ice Shelf since the mid-1960s. Our analysis reveals that the Larsen B collapse in March 2002 was the last phase of a calving sequence that began in 1998, and was controlled by both atmospheric and oceanic anomalies that weakened the ice shelf structure over time. The collapse was preceded by a transition from infrequent calving of large tabular-icebergs and localized flow acceleration to frequent calving of small-icebergs and ice-shelf-wide acceleration. The intermittent pulses of the calving sequence were triggered by failure of the northern shear margin, most likely due to ocean-driven weakening by incision of sub-ice-shelf channels, and were further controlled by the location of effective buttressing sources and preexisting crevasses. The limited observational data indicate a similar process for the Larsen A ice shelf. These calving events corresponded with warm anomalies associated with a La Niña / positive Southern Annular Mode teleconnection pattern. The results suggest that warm climate anomalies control the occurrence of calving, while the extent and speed of calving are governed by ice shelf geometry and mechanical conditions, in particular, the sturdiness of the “weakest” shear margin. Sudden widespread flow acceleration and frequent small-iceberg calving may serve as quantifiable precursors for ice shelf destabilization.