An exploratory modelling study of perennial firn aquifers in the Antarctic Peninsula for the period 1979-2016

Abstract

In this study, we focus on the model detection in the Antarctic Peninsula (AP) of so-called perennial firn aquifers (PFAs) that are widespread in Greenland and Svalbard and are formed when surface meltwater percolates into the firn pack in summer, which is then buried by snowfall and does not refreeze during the following winter. We use two snow models, the Institute for Marine and Atmospheric Research Utrecht Firn Densification Model (IMAU-FDM) and SNOWPACK, and force these (partly) with mass and energy fluxes from the Regional Atmospheric Climate MOdel (RACMO2.3p2) to construct a 1979–2016 climatology of AP firn density, temperature, and liquid water content. An evaluation using 75 snow temperature observations at 10m depth and density profiles from 11 firn cores shows that output of both snow models is sufficiently realistic to warrant further analysis of firn characteristics. The models give comparable results: in 941 model grid points in either model, covering _ 28000km2, PFAs existed for at least 1 year in the simulated period, most notably in the western AP. At these locations, surface meltwater production typically exceeds with accumulation for most locations > 1000mmw:e: yr1. Most persistent and extensive are PFAs modelled on and around Wilkins Ice Shelf. Here, both meltwater production and accumulation rates are sufficiently high to sustain a PFA on 49% of the ice shelf area in (up to) 100% (depending on the model) of the years in the 1979–2016 period. Although this PFA presence is confirmed by recent observations, its extent in the models appears underestimated. Other notable PFA locations are Wordie Ice Shelf, an ice shelf that has almost completely disappeared in recent decades, and the relatively warm north-western side of mountain ranges in Palmer Land, where accumulation rates can be extremely high, and PFAs are formed frequently. PFAs are not necessarily more frequent in areas with the largest melt and accumulation rates, but they do grow larger and retain more meltwater, which could increase the likelihood of ice shelf hydrofracturing. We find that not only the magnitude of melt and accumulation is important but also the timing of precipitation events relative to melt events. Large accumulation events that occur in the months following an above-average summer melt event favour PFA formation in that year. Most PFAs are predicted near the grounding lines of the (former) Prince Gustav, Wilkins, and Wordie ice shelves. This highlights the need to further investigate how PFAs may impact ice shelf disintegration events through the process of hydrofracturing in a similar way as supraglacial lakes do.