Stable-isotope pattern predicted in surge-type glaciers

1988 ◽  
Vol 25 (5) ◽  
pp. 657-668 ◽  
Author(s):  
E. D. Waddington ◽  
G. K. C. Clarke
Keyword(s):  
Stable Isotope ◽  
Background Noise ◽  
Ice Cores ◽  
Stable Isotope Ratio ◽  
Yukon Territory ◽  
Ice Streams ◽  
Ice Flow ◽  
Order Of Magnitude ◽  
Longitudinal Sampling ◽  
Isotopic Signal

The distribution pattern of stable-isotope ratio δ18O in cold glaciers, ice streams, and ice sheets has the potential to reveal past changes in flow rate, for example those associated with surges. In this study, we use a time-dependent numerical model of ice flow to establish that each surge creates a stratigraphic horizon across which δ18O is discontinuous. Two plausible relations between glacier geometry and δ18O in snowfall allow us to bracket the expected magnitude of this isotopic signal. These stratigraphic markers could be located by δ18O analysis of a longitudinal series of ice cores or by detailed longitudinal sampling of exposed ice.Calculations for a model with characteristics resembling those of Steele Glacier, Yukon Territory, showed that at most three stratigraphic markers could be detected at any one time. The discontinuities in δ18O were as large as 0.8‰. This is an order of magnitude larger than mass spectrometer precision but comparable to observed background noise at Steele Glacier.

scholarly journals Of isbræ and ice streams

2003 ◽  
Vol 36 ◽  
pp. 66-72 ◽  
Author(s):  
Martin Truffer ◽  
Keith A. Echelmeyer
Keyword(s):  
Ice Sheet ◽  
Shear Zones ◽  
West Antarctica ◽  
Ice Streams ◽  
Ice Flow ◽  
Bed Topography ◽  
Ice Stream ◽  
Fast Ice ◽  
Fast Flow ◽  
End Members

AbstractFast-flowing ice streams and outlet glaciers provide the major avenues for ice flow from past and present ice sheets. These ice streams move faster than the surrounding ice sheet by a factor of 100 or more. Several mechanisms for fast ice-stream flow have been identified, leading to a spectrum of different ice-stream types. In this paper we discuss the two end members of this spectrum, which we term the “ice-stream” type (represented by the Siple Coast ice streams in West Antarctica) and the “isbræ” type (represented by Jakobshavn Isbræ in Greenland). The typical ice stream is wide, relatively shallow (∼1000 m), has a low surface slope and driving stress (∼10 kPa), and ice-stream location is not strongly controlled by bed topography. Fast flow is possible because the ice stream has a slippery bed, possibly underlain by weak, actively deforming sediments. The marginal shear zones are narrow and support most of the driving stress, and the ice deforms almost exclusively by transverse shear. The margins seem to be inherently unstable; they migrate, and there are plausible mechanisms for such ice streams to shut down. The isbræ type of ice stream is characterized by very high driving stresses, often exceeding 200 kPa. They flow through deep bedrock channels that are significantly deeper than the surrounding ice, and have steep surface slopes. Ice deformation includes vertical as well as lateral shear, and basal motion need not contribute significantly to the overall motion. The marginal shear zone stend to be wide relative to the isbræ width, and the location of isbræ and its margins is strongly controlled by bedrock topography. They are stable features, and can only shut down if the high ice flux cannot be supplied from the adjacent ice sheet. Isbræs occur in Greenland and East Antarctica, and possibly parts of Pine Island and Thwaites Glaciers, West Antarctica. In this paper, we compare and contrast the two types of ice streams, addressing questions such as ice deformation, basal motion, subglacial hydrology, seasonality of ice flow, and stability of the ice streams.

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