Five decades of strong temporal variability in the flow of Brunt Ice Shelf, Antarctica

Abstract

ABSTRACT. Data showing velocity changes on the Brunt Ice Shelf (BIS), Antarctica, over the last 55 years are presented and analysed. During this period no large-scale calving events took place and the ice shelf gradually grew in size. Ice flow velocities, however, fluctuated greatly, increasing twofold between 1970 and 2000, then decreasing again to previous levels by 2012 after which velocities started to increase yet again. In the observational period, velocity changes in the order of 10% a −1 have commonly been observed, and currently velocities are increasing at this rate. By modelling the ice flow numerically, we explore potential causes for the observed changes in velocity. We find that a loss of mechanical contact between the BIS and the McDonald Ice Rumples following a local calving event in 1971 would explain both the increase and the subsequent decrease in ice velocities. Other explanations involving enlargement of observed rift structures are discounted as the effects on ice flow are found to be too small and the spatial pattern of velocity change inconsistent with data. The most recent phase of acceleration remains unexplained but may potentially be related to a recent re-activation of a known rift structure within the BIS.

Recent rift formation and impact on the structural integrity of the Brunt Ice Shelf, East Antarctica

“…1). In concurrence with these changes, Gudmundsson et al (2017) reported on a new phase of ice-shelf-wide acceleration as surface velocities have increased by up to 10 % per year since 2012. Detailed measurements of these changes have been facilitated by the presence of the Halley 6 Research Station, now located at Halley 6a (see Fig.…”

“…8b. In subsequent decades, the BIS gradually readvanced and reestablished contact with the bedrock at the MIR, whilst velocities decreased to pre-1970 levels (Gudmundsson et al, 2017). This cycle of internal dynamical change controlled by calving-induced unpinning and subsequent regrounding at the MIR is arguably not a unique phenomenon, as many ice shelves around Antarctica, and in particular in Dronning Maud Land, are controlled by the presence of one or several pinning points (Matsuoka et al, 2015;Fürst et al, 2015;Favier et al, 2016;Berger et al, 2016).…”

“…1. It is a dynamic environment, characterized by alternating decades of fast and slow flow (Thomas, 1973;Simmons and Rouse, 1984a, b;Simmons, 1986;Gudmundsson et al, 2017) and a number of large rifts that penetrate the full thickness of the ice shelf and stretch deep into its interior (Anderson et al, 2014). These rifts are indicators of historical and recent glaciological activity and are long-lived features that form as the ice shelf goes through phases of steady growth followed by rapid ice loss through calving.…”

“…These rifts are indicators of historical and recent glaciological activity and are long-lived features that form as the ice shelf goes through phases of steady growth followed by rapid ice loss through calving. Observational evidence for the episodic changes in ice shelf configuration has been obtained from a unique 57-year velocity record measured at several Halley Research Stations that have occupied locations on the BIS since 1956 (Gudmundsson et al, 2017) and from regular shipborne and satellite-derived outlines of the ice front dating back to 1915 (Anderson et al, 2014).…”

“…Using an ice dynamics model to investigate the relationship between flow velocities and ice shelf geometry, Gudmundsson et al (2017) concluded that the observed changes in velocities can be explained by a calving-induced (un)pinning of the ice shelf at the McDonald Ice Rumples (MIR; Fig. 1).…”