Diurnal and semidiurnal tide‐induced lateral movement of Ronne Ice Shelf, Antarctica

Makinson, Keith; King, Matt; Nicholls, Keith W.; Gudmundsson, G. Hilmar

doi:10.1029/2012gl051636

Cited by 67 publications

(70 citation statements)

References 25 publications

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“…Variations in basal friction from sub-ice ocean currents driven by the tides were proposed as a mechanism to induce lateral movement of the ice shelf at tidal frequencies, and it was inferred that these motions would pull or push against the adjacent ice streams, thereby causing variations in horizontal velocities at the same frequency. Although this explanation for the motion of ice shelves has since been discounted (Brunt, 2008;Makinson et al, 2012;Brunt and MacAyeal, 2014), the back stress arising from these motions will still affect the ice streams, but this cannot explain longer-period frequencies which are not large in the ice shelf.…”

Section: Overview Of Previous Studiesmentioning

confidence: 99%

“…Ocean tides play an important role in ice dynamics of the continent: inducing currents that alter basal melting beneath the floating ice shelves , affecting the motion of the ice shelves (Doake et al, 2002;Brunt et al, 2010;Makinson et al, 2012) and causing changes in short-term and mean flow of ice streams, often far upstream of the grounding line (Anandakrishnan et al, 2003;Bindschadler et al, 2003a, b;Gudmundsson, 2006;Murray et al, 2007;Marsh et al, 2013).…”

Section: Introductionmentioning

confidence: 99%

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Insights into ice stream dynamics through modelling their response to tidal forcing

2014

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Abstract. The tidal forcing of ice streams at their ocean boundary can serve as a natural experiment to gain an insight into their dynamics and constrain the basal sliding law. A nonlinear 3-D viscoelastic full Stokes model of coupled ice stream ice shelf flow is used to investigate the response of ice streams to ocean tides. In agreement with previous results based on flow-line modelling and with a fixed grounding line position, we find that a nonlinear basal sliding law can qualitatively reproduce long-period modulation of tidal forcing found in field observations. In addition, we show that the inclusion of lateral drag, or allowing the grounding line to migrate over the tidal cycle, does not affect these conclusions. Further analysis of modelled ice stream flow shows a varying stress-coupling length scale of boundary effects upstream of the grounding line. We derive a viscoelastic stresscoupling length scale from ice stream equations that depends on the forcing period and closely agrees with model output.

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Section: Overview Of Previous Studiesmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Insights into ice stream dynamics through modelling their response to tidal forcing

2014

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“…On the other hand, ocean currents are the dominant physical driver of the turbulence responsible for the heat and salt transfers at the ice shelf base. Tides in particular are though to be a major source of turbulent kinetic energy in ice shelf cavities (MacAyeal, 1984a(MacAyeal, ,b,c, 1985Holland, 2008;Jenkins et al, 2010b;Mueller et al, 2012;Makinson et al, 2012). In the constant turbulent transfer velocities parameterization of melt rates, ocean currents have no direct control on distribution of phase changes.…”

Section: 42mentioning

confidence: 99%

Ice shelf-ocean interactions in a general circulation model : melt-rate modulation due to mean flow and tidal currents

Dansereau¹

2012

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Interactions between the ocean circulation in sub-ice shelf cavities and the overlying ice shelf have received considerable attention in the context of observed changes in flow speeds of marine ice sheets around Antarctica.Modeling these interactions requires parameterizing the turbulent boundary layer processes to infer melt rates from the oceanic state at the ice-ocean interface. Here we explore two such parameterizations in the context of the MIT ocean general circulation model coupled to the z-coordinates ice shelf cavity model of Losch (2008).We investigate both idealized ice shelf cavity geometries as well as a realistic cavity under Pine Island Ice Shelf (PIIS), West Antarctica. Our starting point is a three-equation melt rate parameterization implemented by Losch (2008), which is based on the work of Hellmer and Olbers (1989). In this form, the transfer coefficients for calculating heat and freshwater fluxes are independent of frictional turbulence induced by the proximity of the moving ocean to the fixed ice interface. More recently, Holland and Jenkins (1999) have proposed a parameterization in which the transfer coefficients do depend on the ocean-induced turbulence and are directly coupled to the speed of currents in the ocean mixed layer underneath the ice shelf through a quadratic drag formulation and a bulk drag coefficient. The melt rate parameterization in the MITgcm is augmented to account for this velocity dependence.First, the effect of the augmented formulation is investigated in terms of its impact on melt rates as well as on its feedback on the wider sub-ice shelf circulation. We find that, over a wide range of drag coefficients, velocity-dependent melt rates are more strongly constrained by the distribution of mixed layer currents than by the temperature gradient between the shelf base and underlying ocean, as opposed to velocity-independent melt rates. This leads to large differences in melt rate patterns under PIIS when including versus not including the velocity dependence. In a second time, the modulating effects of tidal currents on melting at the base of PIIS are examined. We find that the temporal variability of velocity-dependent melt rates under tidal forcing is greater than that of velocity-independent melt rates. Our experiments suggest that because tidal currents under PIIS are weak and buoyancy fluxes are strong, tidal mixing is negligible and tidal rectification is restricted to very steep bathymetric features, such as the ice shelf front. Nonetheless, strong tidally-rectified currents at the ice shelf front significantly increase ablation rates there when the formulation of the transfer coefficients includes the velocity dependence. The enhanced melting then feedbacks positively on the rectified currents, which are susceptible to insulate the cavity interior from changes in open ocean conditions.

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“…Ocean tides are known to greatly affect the horizontal flow of both ice shelves and adjoining ice streams, even far upstream of grounding lines (Doake et al, 2002;Brunt et al, 2010;Makinson et al, 2012;Legresy et al, 2004;King et al, 2011;Bindschadler et al, 2003b, a;Anandakrishnan et al, 2003;Alley, 1997;Gudmundsson, 2006;Marsh et al, 2013;Minchew et al, 2016;Rosier 15 et al, 2017). In some cases the ice flow responds at a different frequency to the tidal forcing, for example on the Rutford Ice Stream (RIS) the largest response is at a fortnightly (M sf ) frequency (Gudmundsson, 2006).…”

Section: Introductionmentioning

confidence: 99%

Tidal bending of ice shelves as a mechanism for large-scale temporal variations in ice flow

Rosier¹,

Gudmundsson²

2017

Preprint

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Abstract. GPS measurements reveal strong modulation of horizontal ice-shelf and ice-stream flow at a variety of tidal frequencies, most notably a fortnightly (M sf ) frequency not present in the vertical tides themselves. Current theories largely fail to explain the strength and prevalence of this signal over floating ice shelves. We propose that tidal bending stresses, through the nonlinear rheology of glacier ice, can have a sufficiently large impact on the effective viscosity of ice along its floating 5 margins to give rise to significant and widespread temporal variations in the horizontal velocity of ice shelves. Using full-Stokes viscoelastic modelling, we show that inclusion of tidal bending within the model accounts for much of the observed tidal modulation of ice-shelf flow. Furthermore, our model shows that, in the absence of vertical tidal forcing, the mean flow of the ice shelf is reduced by almost 30 % for the geometry that we consider.

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Diurnal and semidiurnal tide‐induced lateral movement of Ronne Ice Shelf, Antarctica

Cited by 67 publications

References 25 publications

Insights into ice stream dynamics through modelling their response to tidal forcing

Insights into ice stream dynamics through modelling their response to tidal forcing

Ice shelf-ocean interactions in a general circulation model : melt-rate modulation due to mean flow and tidal currents

Tidal bending of ice shelves as a mechanism for large-scale temporal variations in ice flow

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