Abstract
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.
Highlights
The basal hydrology of the Siple Coast Ice Streams plays a critical role in the ice dynamics of this region and its ongoing evolution (Bell, 2008; van der Wel et al, 2013).The Kamb Ice Stream (KIS), located on the eastern boundary of the Ross Ice Shelf, ceased streaming ice flow approximately 160 years ago (Retzlaff and Bentley, 1993)
We infer the presence of previously undiscovered subglacial lakes in the KIS trunk on the basis of localized elevation changes at sites of low hydraulic potential
The subglacial lakes appear to be relatively tightly connected by channelized flow, following paths predicted by the hydraulic potential field, and respond in sequence to the apparent input of water from a known lake system upstream of the KIS trunk
Summary
The basal hydrology of the Siple Coast Ice Streams (i.e., the Kamb, Whillans, Bindschadler and MacAyeal Ice Streams) plays a critical role in the ice dynamics of this region and its ongoing evolution (Bell, 2008; van der Wel et al, 2013).The Kamb Ice Stream (KIS), located on the eastern boundary of the Ross Ice Shelf, ceased streaming ice flow approximately 160 years ago (Retzlaff and Bentley, 1993). Van der Wel et al (2013) showed numerically that the period of the long-term velocity cycles in the KIS is strongly associated with its subglacial hydrology, ice thermodynamics, and till regime All these factors are related to the basal melt rate and upstream subglacial water supplies. One hypothesis for the KIS stagnation is that it resulted from a change in the configuration of the subglacial drainage system from sheet flow to channelized water flow (Retzlaff and Bentley, 1993), no previous direct evidence of channelized flow beneath the KIS has been observed Another hypothesis suggests that reduced lubrication of the KIS basal interface, caused by a change in the subglacial water pathway in an upstream region, provoked the stagnation of the downstream region. This is known as the water-piracy hypothesis (Anandakrishnan and Alley, 1997)
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