A model of tidally dominated ocean processes near ice shelf grounding lines

Holland, Paul R.

doi:10.1029/2007jc004576

Cited by 37 publications

(81 citation statements)

References 70 publications

(107 reference statements)

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“…The thermal exchange velocity (γ T ) represents the molecular and turbulent mixing of heat in the oceanic boundary layers adjacent to the ice. It is sometimes modeled with a constant value, but is more commonly (e.g., Holland, 2008;Timmermann et al, 2012) parameterized as a function of the friction velocity (Jenkins et al, 2010). The friction velocity relies on some estimate of the under ice drag, which is usually set to a value similar to the drag between the ocean and the seabed; however, little is actually known about the roughness characteristics of an ice shelf base, other than they can be highly variable depending on ice type (Nicholls et al, 2006;Craven et al, 2009).…”

Section: Thermodynamicsmentioning

confidence: 99%

Modeling Ice Shelf/Ocean Interaction in Antarctica: A Review

Dinniman¹,

Asay‐Davis²,

et al. 2016

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Section: Thermodynamicsmentioning

confidence: 99%

Modeling Ice Shelf/Ocean Interaction in Antarctica: A Review

Dinniman¹,

Asay‐Davis²,

et al. 2016

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“…Reduced melt rates near the grounding line -parameterized with β by Walker and others (2008) and Gagliardini and others (2010) -may be relevant to these results. However, in upstream regions, ocean dynamics may depart from those governing slope dependence (Holland, 2008). A tail-off in melt rates near the grounding line may also reflect a coupled process driven by reduced thickness gradients near the grounding line.…”

Section: Capturing Rapid Changes: the Melting Parameterizationmentioning

confidence: 99%

On the coupled response to ice-shelf basal melting

Little

Goldberg²,

Gnanadesikan

et al. 2012

J. Glaciol.

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ABSTRACT. Ice-shelf basal melting is tightly coupled to ice-shelf morphology. Ice shelves, in turn, are coupled to grounded ice via their influence on compressive stress at the grounding line ('ice-shelf buttressing'). Here, we examine this interaction using a local parameterization that relates the basal melt rate to the ice-shelf thickness gradient. This formulation permits a closed-form solution for a steady-state ice tongue. Time-dependent numerical simulations reveal the spatial and temporal evolution of ice-shelf/ice-stream systems in response to changes in ocean temperature, and the influence of morphology-dependent melting on grounding-line retreat. We find that a rapid (<1 year) re-equilibration in upstream regions of ice shelves establishes a spatial pattern of basal melt rates (relative to the grounding line) that persists over centuries. Coupling melting to ice-shelf shape generally, but not always, increases grounding-line retreat rates relative to a uniform distribution with the same areaaverage melt rate. Because upstream ice-shelf thickness gradients and retreat rates increase nonlinearly with thermal forcing, morphology-dependent melting is more important to the response of weakly buttressed, strongly forced ice streams grounded on beds that slope upwards towards the ocean (e.g. those in the Amundsen Sea).

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“…Lastly, the modulating effects of tides on the melt rates and cavity circulation are investigated. In the case of 'cold' ice shelves that enter in contact with High Salinity Shelf Waters (HSSW) of about −1 • C in temperature such as Filchner-Ronne Ice Shelf (FRIS) (King et al, 2011;Makinson et al, 2011Makinson et al, , 2012, Ross Ice Shelf (MacAyeal, 1984a(MacAyeal, ,b,c, 1985Holland, 2008), Larsen C Ice Shelf (King et al, 2011;Mueller et al, 2012), such modulating impacts are relatively well documented. However, much less is known about the impacts of tides on 'warm' ice shelves forced with strong buoyancy fluxes such as that of the Amundsen and Bellingshausen Seas.…”

Section: 42mentioning

confidence: 99%

“…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%

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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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A model of tidally dominated ocean processes near ice shelf grounding lines

Cited by 37 publications

References 70 publications

Modeling Ice Shelf/Ocean Interaction in Antarctica: A Review

Modeling Ice Shelf/Ocean Interaction in Antarctica: A Review

On the coupled response to ice-shelf basal melting

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

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