Phase‐sensitive FMCW radar system for high‐precision Antarctic ice shelf profile monitoring

Brennan, Paul V.; Lok, Lai Bun; Nicholls, Keith W.; Corr, Hugh

doi:10.1049/iet-rsn.2013.0053

Cited by 100 publications

(162 citation statements)

References 6 publications

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“…A reconnaissance of potential drill sites was made in early May 2014, and a site located close to the central flowline, 30 km from the terminus was selected, hereafter named S30 (N70°31

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, W49°55

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, 982 m above sea level (asl); Figure ). Global positioning system (GPS) receivers and an automated weather station (AWS) were deployed and an ice thickness survey was conducted using phase‐sensitive radar (e.g., Brennan et al, ; Young et al, ). Ice thickness at S30 was determined to be ∼600 m, and between 12 May and 14 July 2014 the surface velocity averaged 608 m yr −1 in the WSW direction 253°.…”

Section: Field Sitementioning

confidence: 99%

Physical Conditions of Fast Glacier Flow: 1. Measurements From Boreholes Drilled to the Bed of Store Glacier, West Greenland

et al. 2018

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Marine‐terminating outlet glaciers of the Greenland Ice Sheet make significant contributions to global sea level rise, yet the conditions that facilitate their fast flow remain poorly constrained owing to a paucity of data. We drilled and instrumented seven boreholes on Store Glacier, Greenland, to monitor subglacial water pressure, temperature, electrical conductivity, and turbidity along with englacial ice temperature and deformation. These observations were supplemented by surface velocity and meteorological measurements to gain insight into the conditions and mechanisms of fast glacier flow. Located 30 km from the calving front, each borehole drained rapidly on attaining ∼600 m depth indicating a direct connection with an active subglacial hydrological system. Persistently high subglacial water pressures indicate low effective pressure (180–280 kPa), with small‐amplitude variations correlated with notable peaks in surface velocity driven by the diurnal melt cycle and longer periods of melt and rainfall. The englacial deformation profile determined from borehole tilt measurements indicates that 63–71% of total ice motion occurred at the bed, with the remaining 29–37% predominantly attributed to enhanced deformation in the lowermost 50–100 m of the ice column. We interpret this lowermost 100 m to be formed of warmer, pre‐Holocene ice overlying a thin (0–8 m) layer of temperate basal ice. Our observations are consistent with a spatially extensive and persistently inefficient subglacial drainage system that we hypothesize comprises drainage both at the ice‐sediment interface and through subglacial sediments. This configuration has similarities to that interpreted beneath dynamically analogous Antarctic ice streams, Alaskan tidewater glaciers, and glaciers in surge.

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“…A reconnaissance of potential drill sites was made in early May 2014, and a site located close to the central flowline, 30 km from the terminus was selected, hereafter named S30 (N70°31

^{'}

, W49°55

^{'}

Section: Field Sitementioning

confidence: 99%

Physical Conditions of Fast Glacier Flow: 1. Measurements From Boreholes Drilled to the Bed of Store Glacier, West Greenland

et al. 2018

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“…The ApRES (Brennan et al, ; Nicholls et al, ) was deployed from January to December in 2016 on the RBIS (Figure ) about 90 km from the ice shelf front and 5 km seaward from the grounded ice on the fast‐flowing portion of the West Ragnhild glacier, which is the third largest outlet glacier along the Dronning Maud Land Coast (Callens et al, ). The ice thickness at the site was ∼300 m in the trough of a channel (Drews, ) but increases up to 600 m in the grounding zone upstream, and ice flow velocities in this region range between 250 and 300 m/a (Rignot et al, ).…”

Section: Data Collection and Processingmentioning

confidence: 99%

“…Differences between the predicted and observed motion of the basal reflector arise because of subshelf melting or accretion (Figure ). All reflector displacements were processed using the method described by Brennan et al (). Details of the assumptions and derivations are given by Jenkins et al ().…”

Section: Data Collection and Processingmentioning

confidence: 99%

Topographic Shelf Waves Control Seasonal Melting Near Antarctic Ice Shelf Grounding Lines

Sun

Hattermann

Pattyn

et al. 2019

Geophysical Research Letters

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The buttressing potential of ice shelves is modulated by changes in subshelf melting, in response to changing ocean conditions. We analyze the temporal variability in subshelf melting using an autonomous phase‐sensitive radio‐echo sounder near the grounding line of the Roi Baudouin Ice Shelf in East Antarctica. When combined with additional oceanographic evidence of seasonal variations in the stratification and the amplification of diurnal tides around the shelf break topography (Gunnerus Bank), the results suggest an intricate mechanism in which topographic waves control the seasonal melt rate variability near the grounding line. This mechanism has not been considered before and has the potential to enhance local melt rates without advecting different water masses. As topographic waves seem to strengthen in a stratified ocean, the freshening of Antarctic surface water, predicted by observations and models, is likely to increase future basal melting in this area.

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“…Phase-sensitive radar allows precise measurements of ice thickness and vertical strain between internal layers in the ice column, and repeat measurements can be differenced to derive ice thinning rates [Corr et al, 2002;Brennan et al, 2014]. We estimated thinning of between 15 and 22 m a À1 at five sites (CH01-CH05) at the upstream end of the channel ( Figure 1).…”

Section: Local Melt Rate Measurementsmentioning

confidence: 99%

High basal melting forming a channel at the grounding line of Ross Ice Shelf, Antarctica

Marsh

Fricker

Siegfried

et al. 2016

Geophysical Research Letters

102

113

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Antarctica's ice shelves are thinning at an increasing rate, affecting their buttressing ability. Channels in the ice shelf base unevenly distribute melting, and their evolution provides insight into changing subglacial and oceanic conditions. Here we used phase‐sensitive radar measurements to estimate basal melt rates in a channel beneath the currently stable Ross Ice Shelf. Melt rates of 22.2 ± 0.2 m a−1 (>2500% the overall background rate) were observed 1.7 km seaward of Mercer/Whillans Ice Stream grounding line, close to where subglacial water discharge is expected. Laser altimetry shows a corresponding, steadily deepening surface channel. Two relict channels to the north suggest recent subglacial drainage reorganization beneath Whillans Ice Stream approximately coincident with the shutdown of Kamb Ice Stream. This rapid channel formation implies that shifts in subglacial hydrology may impact ice shelf stability.

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Phase‐sensitive FMCW radar system for high‐precision Antarctic ice shelf profile monitoring

Cited by 100 publications

References 6 publications

Physical Conditions of Fast Glacier Flow: 1. Measurements From Boreholes Drilled to the Bed of Store Glacier, West Greenland

Physical Conditions of Fast Glacier Flow: 1. Measurements From Boreholes Drilled to the Bed of Store Glacier, West Greenland

Topographic Shelf Waves Control Seasonal Melting Near Antarctic Ice Shelf Grounding Lines

High basal melting forming a channel at the grounding line of Ross Ice Shelf, Antarctica

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