Observations of turbulent heat exchange, surface melt and refreezing on the Larsen C ice shelf, Antarctica (2022-2025)

Ice shelves currently stabilize the Antarctic ice sheet but are vulnerable to hydrofracturing in the future. A faster increase in surface melt compared to accumulation will cause a reduction in available firn pore space and will thus eventually lead to meltwater ponding at the surface.  However, current climate models disagree on the total volume of meltwater production and accumulation, and thus on the evolution of firn density over ice shelves. A lack of direct melt and refreezing observations on ice shelves, especially in areas of high melt, prevents a detailed benchmarking of climate and firn models.

Since 2022, a dedicated experiment takes place at two contrasting locations with existing long-term automatic weather observations on the Larsen C ice shelf, which is at risk of collapsing in the future. Here we present results from 3 years of data from an eddy covariance system, which measured the sensible and latent heat fluxes, a GNSS antenna that measured snow height change by interferometry (GNSSir), and a snow cosmic ray counter that measured the change in snow mass and thus bulk snow density.

We discuss the main challenges and recommendations in acquiring such data, the derived surface energy balance (SEB) fluxes, and the variation of bulk snow density due to accumulation and meltwater refreezing. We demonstrate that the turbulent fluxes can be correctly simulated with a bulk turbulence model, that the variation of surface roughness in time can also be extracted from GNSSir, and that the hourly melt fluxes and refreezing can be simulated within 10% accuracy using a skin energy balance model forced by standard single level observations.