The impact of landfast sea ice buttressing on ice dynamic speedup in the Larsen-B Embayment, Antarctica

Abstract

Abstract. We observe the evacuation of 11-year old land-fast sea ice in the Larsen-B Embayment on the East Antarctic Peninsula in January 2022, which was in part triggered by warm atmospheric conditions and strong offshore winds. This evacuation of sea ice was closely followed by major changes in the calving behaviour and dynamics of the ocean-terminating glaciers in the region. Following a decade of gradual slow-down, satellite measurements show that Hektoria, Green and Crane Glaciers have sped up by approximately 20–50 % since February 2022, each increasing in speed by more than 100 m a-1. Circumstantially, this is attributable to the loss of floating ice/mélange tongues and their transition into tidewater glaciers. However, a question remains as to whether the landfast sea ice itself could have acted to provide direct buttressing to the glaciers prior to its disintegration. We use diagnostic model simulations to estimate the buttressing effect of the land-fast sea ice in the Larsen-B Embayment and its impact on the speed of Hektoria, Green, Evans and Crane Glaciers. The results show that direct sea ice buttressing had a negligible impact on the dynamics of the grounded ice streams. Additionally, our results show that the loss of sea ice buttressing likely produced noticeable changes to the flow speeds of the rheologically weak ice tongues, which could have diminished their stability over time. However, as the accompanying changes in viscous stress were small compared to local spatial variation, this loss of buttressing is likely to have been a secondary process in the disintegration of the ice tongues compared to, for example, increased ocean melting or swell.

Change in grounding line location on the Antarctic Peninsula measured using a tidal motion offset correlation method

“…The GL change observed in the Larsen-A and -B Embayments is particularly noteworthy given the ongoing dynamic evolution of these glaciers in response to the collapse of Larsen-A Ice Shelf in 1995, Larsen-B in 2002, and more recent changes which have been observed through to, and after, the 2019/20 period (Ochwat et al, 2023;Surawy-Stepney et al, 2023). In the Larsen-B Inlet, Crane Glacier and the HGE system have differing evolutions since the collapse of the Larsen-B Ice Shelf.…”

“…Finally, modelling studies also require the GL position as an input dataset for the initialisation of model domains when assimilating observational datasets. In the AP region there are a number of examples where modelling studies depend on accurate GL locations, including glaciological processes case studies (Surawy-Stepney et al, 2023), projections of future change under different warming scenarios (Barrand et al, 2013), and calculating glacier bed topography by modelling ice thickness (Huss and Farinotti, 2014).…”

“…Since the 2019/20 period, for which our TMOC GL is dated, the glaciers of the Larsen-A and -B Embayments have continued to evolve, and our grounding line measurements provide insight into the causes of these changes. In January 2022, the multi-year landfast sea-ice in Larsen B embayment disintegrated and this event was followed by a major retreat and acceleration of Crane and the Hektoria-Green-Evans glacier system (Ochwat et al, 2023;Surawy-Stepney et al, 2023). The largest retreat was observed on Hektoria Glacier, which retreated by approximately 25 km between March 2022 to April 2023.…”

Determining the Freshwater Fluxes from Antarctica with Earth Observation Data, Models, and In Situ Measurements: Uncertainties, Knowledge Gaps, and Prospects for New Advances

“…For example, following Larsen B collapse, fast ice formed in the Larsen B embayment and remained there for a decade, eventually reaching thickness of order 10 m, until it broke up in February 2022. Subsequent but delayed acceleration of the glacier ice behind suggests that land fast sea ice affects the dynamics of grounded glaciers (Ochwat et al, 2023), but the slow response (Sun et al, 2023) and lack of modelled speed up (Surawy-Stepney et al, 2023a) suggests that sea ice did not provide buttressing in the same manner as an ice shelf. Instead, fast ice may have permitted glacier advance and ice tongue formation by resisting rotational forces at the terminus and delaying calving.…”

High-resolution elevation models of Larsen B glaciers extracted from 1960s imagery

“…Crane Glacier alone lost ~ 13 km 3 of grounded ice in the period 2001–2009 related to the collapse 18 . Thinning continues upstream in former LBIS tributaries despite sea surface cooling and the development of land-fast sea ice that buttressed glacier outlet flow between 2011 and 2021 9 , 24 , 25 . While detailed observations and models of retreat exist for post-collapse changes to these glaciers, information for glacier configurations decades before the removal of the LBIS is sparse.…”