Abstract
AbstractIn‐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.
Highlights
VAŇKOVÁ ET AL.Journal of Geophysical Research: OceansThe processes by which frazil ice grows into platelets that consolidate to form a marine-ice layer that is bubble-free, more saline, and crystallographically different to glacial ice of meteoric origin can be inferred from ice cores (Craven et al, 2009; Oerter et al, 1992)
The key observations from the ApRES time series are as follows: 1. At all three sites, the instances when the basal return amplitude is reduced coincide with instances when ice appears to be accreted at the ice-shelf base
We observed that, when ice accretes at the base, the basal reflection changes its phase and amplitude and that this change is different for different transmit frequencies. This led us to conclude that phase changes during apparent basal accretion cannot be directly interpreted as changes in thickness and that the lack of knowledge of the electromagnetic properties of the accreted ice limits precise measurements of changes in ice thickness for the time the accreted ice is present
Summary
The processes by which frazil ice grows into platelets that consolidate to form a marine-ice layer that is bubble-free, more saline, and crystallographically different to glacial ice of meteoric origin can be inferred from ice cores (Craven et al, 2009; Oerter et al, 1992). Direct in-situ observations of the process of freezing and basal accretion beneath ice shelves are challenging as the instrumentation disrupts the supercooled environment it attempts to observe and the icing-up of sensors corrupts the measurements At times transitions between basal melting and accretion regimes beneath an ice shelf have been observed indirectly in surprising ways. Craven et al (2014) inferred transient periods of frazil ice formation beneath Amery Ice Shelf from changing pressure readings of moored instruments that occasionally became sufficiently coated with platelets that the change in buoyancy caused them to rise. Evidence of relatively recently ceased basal accretion has been gathered from the central Ross Ice Shelf, where a camera descended to the ice-shelf base through a borehole recorded imagery featuring a 10cm layer of crystals, despite weakly melting conditions (Stevens et al, 2020)
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
