Basal ice accretion and debris entrainment within the coastal ice margin, Law Dome, Antarctica

Goodwin, Ian

doi:10.1017/s002214300001580x

Cited by 16 publications

(10 citation statements)

References 24 publications

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“…The estimate derived from Figure 4a (63%) is clearly higher than debris visible in Figure 6a (∼5%), which may represent a lower end‐member of the spectrum of debris concentrations for the stratified ice facies observed in Kamb Ice Stream. Values appear to range between 5 and 60%, which is comparable to debris concentrations for a banded ice facies (6–33%) observed at the coastal margin of Law Dome, East Antarctica [ Goodwin , 1993]. Dispersed debris‐poor and laminated facies also observed by Goodwin [1993] may correspond to the clear and debris‐sparse, stratified facies observed highest in the accreted ice layer of Kamb Ice Stream (Figures 4a, 6a, and 6b).…”

Section: Borehole Camera Imagerysupporting

confidence: 63%

“…Values appear to range between 5 and 60%, which is comparable to debris concentrations for a banded ice facies (6–33%) observed at the coastal margin of Law Dome, East Antarctica [ Goodwin , 1993]. Dispersed debris‐poor and laminated facies also observed by Goodwin [1993] may correspond to the clear and debris‐sparse, stratified facies observed highest in the accreted ice layer of Kamb Ice Stream (Figures 4a, 6a, and 6b). The predicted debris contents of massive dirty facies (∼51%) and solid dirty facies (∼63%) fit very well with values estimated from borehole camera images shown in Figure 4c (51%) and Figure 4d (66%).…”

Section: Borehole Camera Imagerysupporting

confidence: 63%

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A quantitative framework for interpretation of basal ice facies formed by ice accretion over subglacial sediment

Christoffersen¹,

Tulaczyk²,

Carsey³

et al. 2006

J. Geophys. Res.

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[1] We have constructed a numerical model of basal ice formation for glacier ice in contact with subglacial sediment. The model predicts four different ice facies whose formation is controlled by availability of subglacial water to satisfy the basal freeze-on rate. Clean (or clotted) facies may result from congelation (or frazil) ice growth occurring when (supercooled) meltwater separates ice base from substrate or if a groundwater source can supply water to the ice base at a velocity equal to the freezing rate. Laminated facies develops when the supply of subglacial water is sufficiently constrained for cryostatic suction to raise the subglacial effective stress above a threshold for intrusion of ice into sediment by regelation. Debris laminas ($1 mm) are entrained by short, periodic regelation events (of a few hours) separated by longer periods (days to months) of congelation. Further meltwater limitation produces a massive dirty ice facies due to stacking of debris laminas. The model predicts growth of solid dirty ice facies when the bed is meltwater-depleted with fast freezing (5 mm yr À1) causing enhanced erosion (30 mm yr À1 ). We find that basal ice facies and sediment entrainment are controlled mainly by the ratio of freezing rate to water supply rate. The predicted ice facies compare favorably with borehole camera imagery of the basal ice layer in Kamb Ice Stream, West Antarctica. Facies variability in this layer suggests complex hydrologic history for the West Antarctic Ice Sheet with significant changes occurring over a period of several thousand years.Citation: Christoffersen, P., S. Tulaczyk, F. D. Carsey, and A. E. Behar (2006), A quantitative framework for interpretation of basal ice facies formed by ice accretion over subglacial sediment,

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Section: Borehole Camera Imagerysupporting

confidence: 63%

Section: Borehole Camera Imagerysupporting

confidence: 63%

A quantitative framework for interpretation of basal ice facies formed by ice accretion over subglacial sediment

Christoffersen¹,

Tulaczyk²,

Carsey³

et al. 2006

J. Geophys. Res.

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“…7a and b). Previous studies interpreted the presence of a mixing slope, together with a larger isotopic range (of up to 18.00‰ δ 18 O; Table 1) than observed at SMIS of isotopically depleted samples, as the result of a mixed water source of sea water and varying proportions of melted meteoric ice (Goodwin, 1993; Souchez and others, 1995, 1998). The marine ice source water for all sample sites at SMIS, however, could consist of a mixture of all three water sources – melted meteoric ice, melted marine ice and sea water – whereby melted meteoric ice would contribute least to the mixture (in the order of 5%) due to its high isotopic depletion.…”

Section: Discussionmentioning

confidence: 89%

“…The exact percentage contribution of recycled marine ice, however, is difficult to determine, especially since marine ice can be repeat-recycled. Goodwin (1993) considered the possibility that δ 18 O marine ice samples, which are not as enriched as in Souchez and others’ (1991) study (i.e. only up to 1.56‰ δ 18 O; Table 1), could have formed from repeat recycling of previously formed marine ice.…”

Section: Discussionmentioning

confidence: 95%

Marine ice recycling at the southern McMurdo Ice Shelf, Antarctica

Koch¹,

Fitzsimons²,

Samyn

et al. 2015

J. Glaciol.

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Marine ice accretes at the base of ice shelves, often infilling open structural weaknesses and increasing ice-shelf stability. However, the timing and location of marine ice formation remain poorly understood. This study determines marine ice source water composition and origin by examining marine ice crystal morphology, water isotope and solute chemistry in ice samples collected from the southern McMurdo Ice Shelf (SMIS), Antarctica. The measured co-isotopic record together with the output of a freezing model for frazil crystals indicate a spatio-temporally varying water source of sea water and relatively fresher water, such as melted meteoric or marine ice. This is in agreement with the occurrence of primarily banded and granular ice crystal facies typical for frazil ice crystals that nucleate in a supercooled mixture of water masses. We propose that marine ice exposed at the surface of SMIS, which experiences summer melt, is routed to the ice-shelf base via the tide crack. Here frazil crystals nucleate in a double diffusion mechanism of heat and salt between two water masses at their salinity-dependent freezing point. Recycling of previously formed marine ice facilitates ice-shelf self-sustenance in a warming climate.

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“…Unlike basal melting, freeze‐on leaves behind a physical record of its action in the form of basal ice layers. Such layers have been found in many of the deep boreholes drilled in modern polar ice sheets [ Goodwin , 1993; Gow et al , 1979; Herron and Langway , 1979; Hooker et al , 1999; Koerner and Fisher , 1979; Siegert et al , 2000]. Recent borehole investigation with digital video camera at the base of Ice Stream C has shown up to 25‐m‐thick layers of debris‐bearing and clear basal ice, which has been interpreted as a product of basal freeze‐on [ Carsey et al , 2003; Kamb , 2001b].…”

Section: Introductionmentioning

confidence: 99%

Response of subglacial sediments to basal freeze‐on 1. Theory and comparison to observations from beneath the West Antarctic Ice Sheet

2003

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[1] We have constructed a high-resolution numerical model of heat, water, and solute flows in sub-ice stream till subjected to basal freeze-on. The model builds on quantitative treatments of frost heave in permafrost soils. The full version of the Clapeyron equation is used. Hence, ice-water phase transition depends on water pressure, osmotic pressure, and surface tension. The two latter effects can lead to supercooling of the ice base. This supercooling, in turn, induces hydraulic gradients that drive upward flow of pore water, which feeds the growth of segregation ice onto the freezing interface. This interface may progress into the till and form ice lenses if supercooling is sufficiently strong. Hence, the ice segregation process develops a stratified basal ice layer. In our model, a high basal temperature gradient ($0.054°C m À1 ) triggers ice stream stoppage, and the loss of basal shear heating leads to relatively high basal freeze-on rates ($3-5 mm a À1 ). In response, the subglacial till experiences comparatively rapid consolidation. Till porosity can decrease from 40% to <25%, and till strength can increase from $3 kPa to >120 kPa, approximately within one century. Basal supercooling arising from redistribution of solutes and ice-water interfacial effects amounts to ca. À0.35°C below the pressuremelting point. Fine-grained till is in our model associated with widely spaced, thick ice lenses. Coarse-grained till yields thinner ice lenses that are more closely spaced. Our model results compare favorably, although not in all details, with available observational evidence from borehole studies of West Antarctic ice streams.

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Basal ice accretion and debris entrainment within the coastal ice margin, Law Dome, Antarctica

Cited by 16 publications

References 24 publications

A quantitative framework for interpretation of basal ice facies formed by ice accretion over subglacial sediment

A quantitative framework for interpretation of basal ice facies formed by ice accretion over subglacial sediment

Marine ice recycling at the southern McMurdo Ice Shelf, Antarctica

Response of subglacial sediments to basal freeze‐on 1. Theory and comparison to observations from beneath the West Antarctic Ice Sheet

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