Ocean variability beneath the Filchner-Ronne Ice Shelf inferred from basal melt rate time series

<p>We deployed multiple phase-sensitive radars (ApRES) on Filchner-Ronne Ice Shelf (FRIS) to measure and characterize variability in its basal melt rate under present-day climatic conditions.<br aria-hidden="true" />Sites along the western portion of the ice shelf show primarily seasonal variations, consistent with the propagation dynamics of seasonal dense water from the western FRIS front into the cavity.<br aria-hidden="true" />Fifteen years of melt rate estimates from instruments moored beneath the ice at sites further from the western Ronne Ice Front are remarkably uniform in that melting is bounded between 0 and 1 m/a throughout the record. Here, inter-annual melt rate variability is expressed as a suppression or delay in the arrival of a seasonal melt rate minimum, which can be understood in terms of inter-annual stratification changes and variable inflow pathways towards the western Ronne sites.<br aria-hidden="true" />Elsewhere in the cavity, along a direct flow pathway connecting the western FRIS front and the southwestern tip of Berkner Island, the lower frequency inter-annual signal is superimposed on a regular seasonal signal, with year-to-year melt rate variations as high as 1 m/a. Anomalously low summer sea-ice concentrations in front of the ice shelf, such as in 1998 and 2017, cause higher melting along this pathway with a year's delay.<br aria-hidden="true" />Long term mean ApRES melt rates agree with estimates from satellite data over eastern FRIS. However, the satellite estimates overstate the area of active basal freezing in the western part of the ice shelf. The temporal melt rate variability from the satellite estimates dramatically overstates the range of variability at both seasonal and inter-annual time scales and only one site, on the eastern Ronne Ice Shelf, shows any correspondence between the in-situ and remotely derived inter-annual variability.</p>