Abstract
Surface melting has been contributing to the surface lowering and loss of firn air content on Larsen C Ice Shelf since at least the mid‐1990s. Where the amount of melting and refreezing is significant, the firn can become impermeable and begin to support ponds of surface meltwater such as have been implicated in ice shelf collapse. Although meteorological station data indicated an increase in melt on the Antarctic Peninsula over the second half of the 20th century, the existing Ku‐band Quick Scatterometer (QuikSCAT) time series is too short (1999–2009) to detect any significant 21st century trends. Here we investigate a longer 21st century period by extending the time series to 2017 using the C‐band Advanced Scatterometer (ASCAT). We validate our recent observations with in situ weather station data and, using a firn percolation model, explore the sensitivity of scatterometry to water at varying depths in the firn. We find that active microwave C‐band (5.6‐cm wavelength) instruments can detect water at depths of up to 0.75 m below a frozen firn layer. Our longer scatterometry time series reveals that Larsen C Ice Shelf has experienced a decrease in melt season length of 1–2 days per year over the past 18 years consistent with decreasing summer air temperatures. Only in western inlets, where föhn winds drive melt, has the annual melt duration increased during this period.
Highlights
Since the advent of satellite altimetry in the early 1990s, volume losses from west Antarctic and Antarctic Peninsula (AP) ice shelves have generally accelerated but have exhibited a large amount of spatial and temporal variability (Paolo et al, 2015)
Note that even though QuikSCAT noon detects more melt than QuikSCAT morning, there are places where it detects less than Advanced Scatterometer (ASCAT)
A better agreement is found between ASCAT and QuikSCAT morning, where ASCAT generally exceeds QuikSCAT morning over the northern part of the ice shelf and most strongly in the south-western inlets where the difference can be up to 30 days (Figures 2c)
Summary
Since the advent of satellite altimetry in the early 1990s, volume losses from west Antarctic and Antarctic Peninsula (AP) ice shelves have generally accelerated but have exhibited a large amount of spatial and temporal variability (Paolo et al, 2015). Superimposed on the north-south gradient is a concentration of melt and firn densification within the north-western inlets in the lee of the Peninsula Mountains (Holland et al, 2011; Luckman et al, 2014) In these inlets, most notably in Cabinet Inlet, repeated years of melt/refreeze cycles have left the ice shelf surface sufficiently impermeable to support ponds of surface melt water (Alley et al, 2018; Kuipers Munneke et al, 2014; Scambos et al, 2000), a phenomenon which preceded, and may have led to, the collapse of Larsen A, Larsen B, and Wilkins Ice Shelves (Sergienko & Macayeal, 2005; van den Broeke, 2005). Melt ponds have been observed on LCIS, they are confined to the western inlets where they occupy shallow surface troughs originating at the grounding line (Hubbard et al, 2016; Luckman et al, 2014)
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