Tidal modulation of ice shelf buttressing stresses

Robel, Alexander; Tsai, Victor C.; Minchew, Brent; Simons, M.

doi:10.1017/aog.2017.22

Cited by 33 publications

(75 citation statements)

References 43 publications

(87 reference statements)

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“…Brunt and MacAyeal (2014), however, used a viscous ice shelf model to demonstrate that neither direct forcing through sea surface slope changes nor indirect forcing through inflow velocity changes was sufficient to explain the relationship between ice velocity and tidal height at the front of Ross Ice Shelf; this model did not investigate the impacts of these forcings on an elastic or viscoelastic ice rheology. Robel et al (2017) developed a viscoelastic ice shelf model and demonstrated that tidal modulation of contact stresses near the grounding line (similar to Tsai & Gudmundsson, 2015) and at bathymetric pinning points is sufficient to explain the phase and amplitude of tidally modulated ice shelf velocities on both Filchner-Ronne Ice Shelf (near Rutford Ice Stream) and Ross Ice Shelf (near Bindschadler Ice Stream). They suggested that monitoring ice shelves for changes in how ice velocity responds to ocean tides may help diagnose changes in buttressing due to ice shelf thinning.…”

Section: Modelingmentioning

confidence: 99%

Ocean Tide Influences on the Antarctic and Greenland Ice Sheets

Padman

Siegfried

Fricker

2018

Reviews of Geophysics

146

160

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Ocean tides are the main source of high‐frequency variability in the vertical and horizontal motion of ice sheets near their marine margins. Floating ice shelves, which occupy about three quarters of the perimeter of Antarctica and the termini of four outlet glaciers in northern Greenland, rise and fall in synchrony with the ocean tide. Lateral motion of floating and grounded portions of ice sheets near their marine margins can also include a tidal component. These tide‐induced signals provide insight into the processes by which the oceans can affect ice sheet mass balance and dynamics. In this review, we summarize in situ and satellite‐based measurements of the tidal response of ice shelves and grounded ice, and spatial variability of ocean tide heights and currents around the ice sheets. We review sensitivity of tide heights and currents as ocean geometry responds to variations in sea level, ice shelf thickness, and ice sheet mass and extent. We then describe coupled ice‐ocean models and analytical glacier models that quantify the effect of ocean tides on lower‐frequency ice sheet mass loss and motion. We suggest new observations and model developments to improve the representation of tides in coupled models that are used to predict future ice sheet mass loss and the associated contribution to sea level change. The most critical need is for new data to improve maps of bathymetry, ice shelf draft, spatial variability of the drag coefficient at the ice‐ocean interface, and higher‐resolution models with improved representation of tidal energy sinks.

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Section: Modelingmentioning

confidence: 99%

Ocean Tide Influences on the Antarctic and Greenland Ice Sheets

Padman

Siegfried

Fricker

2018

Reviews of Geophysics

146

160

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“…Initially, Doake et al (2002) suggested that currents beneath the Brunt Ice Shelf could be responsible for the tidal signals found there and this idea was explored further by Legresy et al (2004) and Brunt and MacAyeal (2014). More recently, the discovery of an M sf signal far upstream of the RuIS (Rutford Ice Stream) grounding line (Gudmundsson, 2006) 10 has lead to a focus on replicating these observations (Gudmundsson, 2007(Gudmundsson, , 2011Rosier et al, 2014Rosier et al, , 2015Minchew et al, 2016;Robel et al, 2017) and much less has been done to understand the origin of horizontal tidal signals on ice shelves. Makinson et al (2012) suggested that the large high frequency tidal modulation of the Ronne Ice Shelf could be explained by an elastic response to tilting of the ice shelf as tides rotate around the amphidromic point.…”

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confidence: 99%

“…In addition, the grounding line migration may be assymetric (Tsai and Gudmundsson, 2015) resulting in a greater migration upstream during high tide than downstream during low tide (Rosier et al, 2014). This idea of grounding line migration was explored in more detail by Robel et al (2017) who suggested that changes in buttressing arising from grounding line migration could explain 30 observations on RuIS.…”

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confidence: 99%

Exploring mechanisms responsible for tidal modulation in flow of the Filchner-Ronne Ice Shelf

Rosier¹,

Gudmundsson²

2019

Preprint

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An extensive network of GPS sites on the Filchner-Ronne Ice Shelf and adjoining ice streams show strong tidal modulation of horizontal ice flow at a range of frequencies. A particularly strong (horizontal) response is found at the fortnightly (M sf ) frequency. Since this tidal constituent is absent in the (vertical) tidal forcing, this observation implies the action of some nonlinear mechanism. Another striking aspect is the strong amplitude of the flow perturbation, causing a periodic reversal in the direction of ice shelf flow in some areas, and a 10-20% change in speed at grounding lines. No model has yet been able 5 to reproduce the quantitative aspects of the observed tidal modulation on the Filchner-Ronne Ice Shelf. The cause of the tidal response has therefore remained an enigma, indicating a serious limitation in our current understanding of the mechanics of large-scale ice flow. A further limitation of previous studies is that they have all focused on isolated regions and interactions between different areas have, therefore, not been fully accounted for. Here, we conduct the first large-scale ice-flow modelling study to explore these processes using a viscoelastic rheology and realistic geometry of the entire Filchner-Ronne ice shelf, 10 where the best observations of tidal response are available. We evaluate all the relevant mechanisms that have hitherto been put forward to explain how tides might affect ice-shelf flow and compare our results with observational data. We conclude that, while some are able to generate the correct general qualitative aspects of the tidally-induced perturbations in ice flow, most of these mechanisms must be ruled out as being the primary cause of the large observed nonlinear response. We find that only tidally-induced lateral migration of grounding lines can generate a sufficiently strong long-periodic M sf response on the ice 15 shelf to match observations. Furthermore, we show that the observed short-periodic diurnal tidal motion, causing twice-daily flow reversals at the ice front, can be generated through a purely elastic response to basin-wide tidal perturbations in the ice shelf slope. This model also allows us to quantify the effect of tides on mean ice flow and we find that the Filchner-Ronne Ice Shelf flows on average ∼21% faster than it would in the absence of large ocean tides.

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“…The observed suite of temporal, magnitude and migration features provides strong 267 constraints for modelling. Our model is based on an assumption that the observed cryogenic 268 events result from basal stick-slip motion of the ice shelf on a localized grounding feature 269 (ice shelf pinning point in e.g., Robel et al, 2017), as shown in the schematic plot of Fig. 5a.…”

Section: Model Setup 266mentioning

confidence: 99%

“…(e.g.,Padman et al, 2018). Although GPS measurements at a distance of ~ 30 km(Kohler 473 and Langley, 2016), closer to the Kupol Moskovskij ice rise, show a good fit to the tidal 474 model (~ 10 -15 min phase deviations), discrepancies from actual bathymetry might be 475 more pronounced at the source region Robel et al (2017). consider phase lags between 476 measured horizontal ice-displacement variations and tidal heights as indicators of stress 477 variations, in settings where ice shelf/sheet grounding occurs.…”

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confidence: 99%

Localised thickening and grounding of an Antarctic ice shelf from tidal triggering and sizing of cryoseismicity

Pirli¹,

Hainzl

Schweitzer

et al. 2018

Earth and Planetary Science Letters

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20We observe remarkably periodic patterns of seismicity rates and magnitudes at the Fimbul 21 Ice Shelf, East Antarctica, correlating with the cycles of the ocean tide. Our analysis covers 22 19 years of continuous seismic recordings from Antarctic broadband stations. Seismicity 23 commences abruptly during austral summer 2011 at a location near the ocean front in a 24 shallow water region. Dozens of highly repetitive events occur in semi-diurnal cycles, with 25 magnitudes and rates fluctuating steadily with the tide. In contrast to the common 26 unpredictability of earthquake magnitudes, the event magnitudes show deterministic trends 27 within single cycles and strong correlations with spring tides and tide height. The events 28 occur quasi-periodically and the highly constrained event sources migrate landwards during 29 rising tide. We show that a simple, mechanical model can explain most of the observations. 30Our model assumes stick-slip motion on a patch of grounded ice shelf, which is forced by 31 the variations of the ocean-tide height and ice flow. The well fitted observations give new 32 insights into the general process of frictional triggering of earthquakes, while providing 33 independent evidence of variations in ice shelf thickness and grounding. 34 35

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Tidal modulation of ice shelf buttressing stresses

Cited by 33 publications

References 43 publications

Ocean Tide Influences on the Antarctic and Greenland Ice Sheets

Ocean Tide Influences on the Antarctic and Greenland Ice Sheets

Exploring mechanisms responsible for tidal modulation in flow of the Filchner-Ronne Ice Shelf

Localised thickening and grounding of an Antarctic ice shelf from tidal triggering and sizing of cryoseismicity

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