Abstract
ABSTRACTSurface mass balance (SMB) is the net input of mass on a glacier's upper surface, composed of snow deposition, melt and erosion processes, and is a major contributor to the overall mass balance. Pine Island Glacier (PIG) in West Antarctica has been dynamically imbalanced since the early 1990s, indicating that discharge of solid ice into the oceans exceeds snow deposition. However, observations of the SMB pattern on the fast flowing regions are scarce, and are potentially affected by the firn's strain history. Here, we present new observations from radar-derived stratigraphy and a relatively dense network of firn cores, collected along a ~900 km traverse of PIG. Between 1986 and 2014, the SMB along the traverse was 0.505 m w.e. a−1on average with a gradient of higher snow deposition in the South-West compared with the North-East of the catchment. We show that along ~80% of the traverse the strain history amounts to a misestimation of SMB below the nominal uncertainty, but can exceed it by a factor 5 in places, making it a significant correction to the SMB estimate locally. We find that the strain correction changes the basin-wide SMB by ~0.7 Gt a−1and thus forms a negligible (1%) correction to the glacier's total SMB.
Highlights
Surface mass balance (SMB), the net mass flux arriving at the ice-sheet surface per unit area, is an important component of ice-sheet mass balance because respective observations or modelling output are used to (i) calculate mass change using the input–output method (Rignot and others, 2008; Medley and others, 2014), (ii) to force firn compaction models (Ligtenberg and others, 2012) that can be used to correct altimetry measurements of elevation change (McMillan and others, 2016) and (iii) to identify and partition dynamic ice mass loss when mass change time series are compared against the snowfall deficit into the basin (Hogg and others, 2017)
The chronologies of the firn cores were evaluated at these respective depths (Table 1), and the respective reflector was found to stem from 1986, approximately coinciding with the main reflector tracked by Medley and others (2014) who examined SMB based on a reflector from 1985
Using ground-penetrating radar (GPR) radar stratigraphy and chemical analysis of shallow firn cores, we have shown that in the regions sampled by the ice sheet stability programme (iSTAR) traverse, Pine Island Glacier (PIG) received an average 0.505 m w.e. a−1 of SMB over the period 1986–2014, a value that is likely not representative for the whole PIG basin due to oversampling of high-accumulation areas
Summary
Surface mass balance (SMB), the net mass flux arriving at the ice-sheet surface per unit area, is an important component of ice-sheet mass balance because respective observations or modelling output are used to (i) calculate mass change using the input–output method (Rignot and others, 2008; Medley and others, 2014), (ii) to force firn compaction models (Ligtenberg and others, 2012) that can be used to correct altimetry measurements of elevation change (McMillan and others, 2016) and (iii) to identify and partition dynamic ice mass loss when mass change time series are compared against the snowfall deficit into the basin (Hogg and others, 2017). While some of these products are able to provide reliable estimates of the magnitude of surface mass input at the basin scale, none are able to resolve the fine spatial pattern of SMB, with the highest resolution continent-wide dataset produced at 27 km resolution (van Wessem and others, 2018), and a regional product generated at 5.5 km (Lenaerts and others, 2018). The spatial resolution of SMB data is important, because it has been demonstrated that lower resolution model output systematically underestimates the rate of snowfall, in relatively mountainous regions (van Wessem and others, 2016), which may lead to an estimate of the total mass balance that is biased towards more negative values for a glacier catchment. SMB models are notoriously poorly constrained by independent observations (Lenaerts and others, 2018), due to the logistical effort necessary for collecting measurements for one season in Antarctica, let alone over longer time periods, so that the total amount of snow deposition across the full range of spatial scales remains uncertain
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