The nature of ice intermittently accreted at the base of Ronne Ice Shelf, Antarctica, assessed using phase‐sensitive radar

In-situ phase-sensitive radar measurements from the Ronne Ice Shelf (RIS) reveal evidence of intermittent basal accretion periods at several sites that are melting in the long-term mean. Periods when ice is accreted at the ice-shelf base coincide with a decrease in the amplitude of the basal return of up to 4 dB. To quantify basal accretion we constrain simultaneously the dielectric constant, electrical conductivity, and thickness of the accreted ice. We do this by exploring the sensitivity of the received basal echo strength and phase to different transmit frequencies using the radar data in combination with a simple model. Along the western RIS we detect episodic basal accretion events leading to ice accumulation at a rate equivalent to 1-3 mm of meteoric ice per day. The inferred accumulation rates and electromagnetic properties of the accreted ice imply that these events are caused primarily by the deposition of frazil ice crystals. Our findings offer the possibility of monitoring and studying the evolution of boundaries between ice-shelf basal melting and accretion regimes using remote observations, collected from the ice-shelf surface.