Abstract
Iceberg discharge is a major component of the mass balance of the Greenland Ice Sheet (GrIS). While bulk estimates of discharge variation over time exist, inferred remotely from measurements of grounding line ice velocities or surface mass balance calculations, few detailed measurements of discharge itself from individual marine-terminating glaciers existed until recent years. Recently, it has been shown, through a combination of ocean–iceberg modelling and non-linear system identification, that the century-long record of iceberg numbers crossing 48oN in the West Atlantic is a good first-order proxy for discharge from at least south and west Greenland. Here, we explore the varying relative importance of ice sheet, oceanic and climatic forcing of iceberg discharge from these areas over the twentieth century, by carrying out sensitivity studies of a non-linear auto-regressive mathematical model of the 48oN time series. We find that the relationships are mainly non-linear, with the contribution of the GrIS surface mass balance to iceberg discharge likely to be dominant in the first half of the century. This period is followed by several decades where oceanic temperature effects are most important in determining the model variation in iceberg discharge. In recent decades, all physical processes play a non-negligible part in explaining the iceberg discharge and the model suggests that the glacial response time to environmental changes may have decreased.
Highlights
The total mass balance of the Greenland Ice Sheet (GrIS) comes from the net mass balance between surface accumulation/runoff, basal melting, and ice discharge through calving
Because some selected terms may involve more than one input variable, the sum of ERRCui for all input variables can be greater than SERR
Using a control engineering approach to data analysis that has not been used for environmental data before, we have shown that NIFR modelling provides strong statistical relationships between a plausible set of large-scale physical variables and icebergs crossing 48oN (I48N), a proxy for western Greenland iceberg flux
Summary
The total mass balance of the Greenland Ice Sheet (GrIS) comes from the net mass balance between surface accumulation/runoff, basal melting, and ice discharge through calving. Box, 2013; Fettweis et al, 2008; Hanna et al, 2011; Van den Broeke et al, 2009), but with considerable interannual variability (e.g. Fig. 1). This recent trend is part of a longer-term SMB decrease, starting around 1930 (Hanna et al, 2011). While D inferred from grounding line discharges has shown a distinct upward trend in the last decade, in contrast to the SMB time series it is characterised by a lack of interannual variability
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