Estuaries beneath ice sheets

Horgan, Huw; Alley, Richard B.; Christianson, Knut; Jacobel, R. W.; Anandakrishnan, S.; Muto, Atsuhiro; Beem, L.; Siegfried, Matthew R.

doi:10.1130/g34654.1

Cited by 73 publications

(110 citation statements)

References 21 publications

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“…The KIS trunk estuary shows some similarities to the WIS trunk estuary reported by Horgan et al (2013) and Christianson et al (2013), i.e., similarities in the shapes of the estuaries, potential saddles dividing the estuaries from upstream potential lows and upstream subglacial lakes which probably supply subglacial water into the estuaries. However, the KIS trunk estuary is located on the upstream side of the current grounding line and has higher hydraulic potentials (300-500 kPa), indicating that it is entirely grounded at present; whereas the estuary downstream of the WIS, with almost 0 kPa potential, is probably exchanging water and sediment across the grounding zone through viscoelastic flexure induced by tidal forcing.…”

Section: Discussionsupporting

confidence: 56%

“…If the current thinning of the ice sheet over the KIS trunk estuary (∼ 0.1 m yr −1 ) are maintained in the future, the ice would begin to partially float after a few centuries. Horgan et al (2013) have also imaged a subglacial outlet channel incised into the underlying sediment, which probably drains melt water flow or episodic floodwater from subglacial lakes. Similarly, there might be a subglacial outlet channel crossing the sediment bed of the KIS trunk estuary towards the narrow trough shown in Fig.…”

Section: Discussionmentioning

confidence: 99%

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Active subglacial lakes and channelized water flow beneath the Kamb Ice Stream

et al. 2016

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Abstract. We identify two previously unknown subglacial lakes beneath the stagnated trunk of the Kamb Ice Stream (KIS). Rapid fill-drain hydrologic events over several months are inferred from surface height changes measured by CryoSat-2 altimetry and indicate that the lakes are probably connected by a subglacial drainage network, whose structure is inferred from the regional hydraulic potential and probably links the lakes. The sequential fill-drain behavior of the subglacial lakes and concurrent rapid thinning in a channel-like topographic feature near the grounding line implies that the subglacial water repeatedly flows from the region above the trunk to the KIS grounding line and out beneath the Ross Ice Shelf. Ice shelf elevation near the hypothesized outlet is observed to decrease slowly during the study period. Our finding supports a previously published conceptual model of the KIS shutdown stemming from a transition from distributed flow to well-drained channelized flow of subglacial water. However, a water-piracy hypothesis in which the KIS subglacial water system is being starved by drainage in adjacent ice streams is also supported by the fact that the degree of KIS trunk subglacial lake activity is relatively weaker than those of the upstream lakes.

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Section: Discussionsupporting

confidence: 56%

Section: Discussionmentioning

confidence: 99%

Active subglacial lakes and channelized water flow beneath the Kamb Ice Stream

et al. 2016

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“…This mechanism tends to accelerate grounding-line retreat, leading to rapid mass loss in the initial centuries of the experiments, and greater long-term (near-equilibrium) sea-levelequivalent mass loss from the simulated ice sheets (Table 2). It is conceptually supported by geophysical studies of modern-day grounding lines that infer an "estuarine"-type environment at ice-stream grounding zones (Horgan et al, 2013), and although less catastrophic than the cliff-collapse mechanism used in other models DeConto and Pollard, 2016) the approach is consistent with recent grounding-line process analyses (Gladstone et al, 2016). Basal melt beneath ice shelves (and at the grounding line) is calculated from a three-equation model that uses temperature, salinity, and pressure to determine the freezing point in the boundary layer (Hellmer et al, 1998;Holland and Jenkins, 1999).…”

Section: The Ice-sheet Modelsupporting

confidence: 54%

Antarctic climate and ice-sheet configuration during the early Pliocene interglacial at 4.23 Ma

et al. 2017

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Abstract. The geometry of Antarctic ice sheets during warm periods of the geological past is difficult to determine from geological evidence, but is important to know because such reconstructions enable a more complete understanding of how the ice-sheet system responds to changes in climate. Here we investigate how Antarctica evolved under orbital and greenhouse gas conditions representative of an interglacial in the early Pliocene at 4.23 Ma, when Southern Hemisphere insolation reached a maximum. Using offlinecoupled climate and ice-sheet models, together with a new synthesis of high-latitude palaeoenvironmental proxy data to define a likely climate envelope, we simulate a range of icesheet geometries and calculate their likely contribution to sea level. In addition, we use these simulations to investigate the processes by which the West and East Antarctic ice sheets respond to environmental forcings and the timescales over which these behaviours manifest. We conclude that the Antarctic ice sheet contributed 8.6 ± 2.8 m to global sea level at this time, under an atmospheric CO 2 concentration identical to present (400 ppm). Warmer-than-present ocean temperatures led to the collapse of West Antarctica over centuries, whereas higher air temperatures initiated surface melting in parts of East Antarctica that over one to two millennia led to lowering of the ice-sheet surface, flotation of grounded margins in some areas, and retreat of the ice sheet into the Wilkes Subglacial Basin. The results show that regional variations in climate, ice-sheet geometry, and topography produce long-term sea-level contributions that are non-linear with respect to the applied forcings, and which under certain conditions exhibit threshold behaviour associated with behavioural tipping points.

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“…Detailed descriptions on active‐source seismic and RES surveys can be found in Horgan et al . [; ] and Christianson et al . [; submitted to Geophysical Research Letters , 2013], respectively.…”

Section: Supporting Datamentioning

confidence: 99%

Bathymetry and geological structures beneath the Ross Ice Shelf at the mouth of Whillans Ice Stream, West Antarctica, modeled from ground‐based gravity measurements

et al. 2013

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[1] New gravity data reveal important geologic controls on the location and behavior of the grounding zone of Whillans Ice Stream (WIS), West Antarctica. Grounding zones of ice sheets and contiguous ice shelves are important for understanding ice sheet dynamics, as key processes that influence the grounded ice and its discharge into the ocean occur in these regions. Here, we model the bathymetry and shallow geological structures beneath the Ross Ice Shelf in an embayment of the WIS grounding zone using gravity data collected on the ground, in conjunction with seismic and radar data. We find that the region of shallow ocean water (<~50 m) is extensive; oceanographic models suggest that grounding zones exhibiting thin ocean cavities with gently sloping ice-ocean interfaces are likely to be tidally well mixed, leading to slower basal melting than would occur in a thicker, stratified water column. Beneath the ocean water column, we model a fault and a sedimentary basin in a half-graben, filled with two layers of sediments. The total thickness of the sediment layer is 900 to 1250 m in the half-graben, and 600 to 800 m on the upthrown block, and the basement depth is no more than 2000 m. We observe that the upper, softer sediment is thinnest near the modern grounding line and may possibly pinch out near our grid, and that the modeled fault is roughly parallel to part the grounding. We therefore hypothesize that the WIS grounding line stabilized in its current location in part due to the subglacial geology.

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Estuaries beneath ice sheets

Cited by 73 publications

References 21 publications

Active subglacial lakes and channelized water flow beneath the Kamb Ice Stream

Active subglacial lakes and channelized water flow beneath the Kamb Ice Stream

Antarctic climate and ice-sheet configuration during the early Pliocene interglacial at 4.23 Ma

Bathymetry and geological structures beneath the Ross Ice Shelf at the mouth of Whillans Ice Stream, West Antarctica, modeled from ground‐based gravity measurements

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Estuaries beneath ice sheets

Cited by 73 publications

References 21 publications

Active subglacial lakes and channelized water flow beneath the Kamb Ice Stream

Active subglacial lakes and channelized water flow beneath the Kamb Ice Stream

Antarctic climate and ice-sheet configuration during the early Pliocene interglacial at 4.23 Ma

Bathymetry and geological structures beneath the Ross Ice Shelf at the mouth of Whillans Ice Stream, West Antarctica, modeled from ground‐based gravity measurements

Contact Info

Product

Resources

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Antarctic climate and ice-sheet configuration during the early Pliocene interglacial at 4.23 Ma