Tidal pacing, skipped slips and the slowdown of Whillans Ice Stream, Antarctica

Winberry, J. Paul; Anandakrishnan, S.; Alley, Richard B.; Wiens, Douglas A.; Pratt, Martin

doi:10.3189/2014jog14j038

Cited by 91 publications

(93 citation statements)

References 58 publications

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“…7, we propose two distinct mechanisms to account for the observed anomalous seismic amplitudes: stiffening of the bed and reduction of aseismic slip. Skipped events have become more frequent in the last decade (Winberry et al, 2014c). The physical conditions that result in elevated seismic amplitudes during tremor may therefore be related to the conditions that will prevail in the near-future if stagnation continues.…”

Section: ∼2×10mentioning

confidence: 99%

“…Direct borehole access to the bed has measured effective pressure in the range of −30 to 200 kPa (Kamb, 2001). Numerous ice flow model-based inversions of geodetic data have found localized regions of high basal shear stress in the vicinity of the seismometers that record the WIP tremor episodes (Joughin et al, 2004;Winberry et al, 2014c;Sergienko et al, 2014). These areas of high resistance to flow are juxtaposed against an active subglacial lake system (Siegfried et al, 2014) where basal resistance to flow is presumably negligible.…”

Section: B P Lipovsky and E M Dunham: Ice Stream Tremormentioning

confidence: 99%

“…Clearly observed tremor is most common at the stations BB09 and GS17, although stations BB02 and GS07 near BB09 also have multiple tremor bands. These three stations are located in regions of the WIP, where more than 90 % of sliding occurs during large-scale slip events (Winberry et al, 2014c, their Fig. 3a), although not all stations located in such regions exhibit equally clear tremor.…”

Section: Observationsmentioning

confidence: 99%

“…During the time between large-scale sliding events, several ∼100 km 2 regions exhibit a high degree of locking (Winberry et al, 2014c). Slip motion observed by on-ice GPS instruments ( Fig.…”

Section: ∼2×10mentioning

confidence: 99%

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Tremor during ice-stream stick slip

Lipovsky¹,

Dunham²

2016

The Cryosphere

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Abstract. During the 200 km-scale stick slip of the Whillans Ice Plain (WIP), West Antarctica, seismic tremor episodes occur at the ice-bed interface. We interpret these tremor episodes as swarms of small repeating earthquakes. The earthquakes are evenly spaced in time, and this even spacing gives rise to spectral peaks at integer multiples of the recurrence frequency ∼10-20 Hz. We conduct numerical simulations of the tremor episodes that include the balance of forces acting on the fault, the evolution of rate-and statedependent fault friction, and wave propagation from the fault patch to a seismometer located on the ice. The ice slides as an elastic block loaded by the push of the upstream ice, and so the simulated basal fault patch experiences a loading velocity equal to the velocity observed by GPS receivers on the surface of the WIP. By matching synthetic seismograms to observed seismograms, we infer fault patch area ∼10 m 2 , bed shear modulus ∼20 MPa, effective pressure ∼10 kPa, and frictional state evolution distance ∼1 µm. Large-scale slip events often occur twice daily, although skipped events have been increasing in frequency over the last decade. The amplitude of tremor (recorded by seismometers on the ice surface) is greater during the double wait time events that follow skipped events. The physical mechanism responsible for these elevated amplitudes may provide a window into nearfuture subglacial conditions and the processes that occur during ice-stream stagnation.

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Section: ∼2×10mentioning

confidence: 99%

Section: B P Lipovsky and E M Dunham: Ice Stream Tremormentioning

confidence: 99%

Section: Observationsmentioning

confidence: 99%

Section: ∼2×10mentioning

confidence: 99%

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Tremor during ice-stream stick slip

Lipovsky¹,

Dunham²

2016

The Cryosphere

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“…Water piracy within the catchment supplying SLW is not limited to KIS, but also occurs further downstream and plays an essential role in supplying water to SLW. In 2005, a region just upstream of the point where WIS widens and flattens substantially began slowly rising in response to uneven slowdown of the ice stream [39], which manifested as a small, localized ice-surface elevation change. This event caused water from the upper KIS and WIS, which was flowing into a larger subglacial lake to the south, to be diverted towards SLW, and increased the filling rate of SLW by a factor of 20 [38].…”

Section: Ecological Setting Of Subglacial Lake Whillansmentioning

confidence: 99%

Subglacial Lake Whillans microbial biogeochemistry: a synthesis of current knowledge

Mikucki

Lee

Ghosh

et al. 2016

Phil. Trans. R. Soc. A.

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Liquid water occurs below glaciers and ice sheets globally, enabling the existence of an array of aquatic microbial ecosystems. In Antarctica, large subglacial lakes are present beneath hundreds to thousands of metres of ice, and scientific interest in exploring these environments has escalated over the past decade. After years of planning, the first team of scientists and engineers cleanly accessed and retrieved pristine samples from a West Antarctic subglacial lake ecosystem in January 2013. This paper reviews the findings to date on Subglacial Lake Whillans and presents new supporting data on the carbon and energy metabolism of resident microbes. The analysis of water and sediments from the lake revealed a diverse microbial community composed of bacteria and archaea that are close relatives of species known to use reduced N, S or Fe and CH4 as energy sources. The water chemistry of Subglacial Lake Whillans was dominated by weathering products from silicate minerals with a minor influence from seawater. Contributions to water chemistry from microbial sulfide oxidation and carbonation reactions were supported by genomic data. Collectively, these results provide unequivocal evidence that subglacial environments in this region of West Antarctica host active microbial ecosystems that participate in subglacial biogeochemical cyclingauthorsversionPeer reviewe

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Seismic and geodetic evidence for grounding‐line control of Whillans Ice Stream stick‐slip events

et al. 2014

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The tidally modulated, stick-slip events of Whillans Ice Stream in West Antarctica produce seismic energy from three locations near the grounding line. Using ice velocity records obtained by combining time series from colocated broadband seismometers and GPS receivers installed on the ice stream during the 2010-2011 and 2011-2012 austral summers, along with far-field seismic recordings of elastic waves, we locate regions of high rupture velocity and stress drop. These regions, which are analogous to "asperities" in traditional seismic fault studies, are areas of elevated friction at the base of the ice stream. Slip events consistently initiate at one of two locations: near the center of the ice stream, where events associated with the Ross Sea high tide originate, or a grounding-line spot, where events associated with the Ross Sea low tide initiate, as well as occasional high-tide events following a skipped low-tide event. The grounding-line site, but not the central site, produces Rayleigh waves observable up to 1000 km away, through fast expansion of the slip area. Grounding-line initiation events also show strong directivity in the downstream direction, indicating initial rupture propagation at 1.5 km/s, compared to an average of 0.150 km/s for the entire slip event. Following slip initiation, additional seismic energy is produced from two sources located near the grounding line: first at the downstream end of Subglacial Lake Engelhardt and second toward the farthest downstream extent of the ice stream. This evidence suggests that the stronger, higher-friction material along the grounding line controls motion throughout the stick-slip region.

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Tidal pacing, skipped slips and the slowdown of Whillans Ice Stream, Antarctica

Cited by 91 publications

References 58 publications

Tremor during ice-stream stick slip

Tremor during ice-stream stick slip

Subglacial Lake Whillans microbial biogeochemistry: a synthesis of current knowledge

Seismic and geodetic evidence for grounding‐line control of Whillans Ice Stream stick‐slip events

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