Bore-Hole Survey at Dye 3, South Greenland

Gundestrup, N.; Hansen, B. Lyle

doi:10.3189/s0022143000006109

Cited by 48 publications

(71 citation statements)

References 20 publications

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“…Modeled temperatures are compared with measurements from three deep ice cores: Dye 3 (Gundestrup and Hansen, 1984;Dahl-Jensen and others, 1998); GRIP (Johnsen and others, 1995;Dahl-Jensen and others, 1998) and Greenland Ice Sheet Project 2 (GISP2) (Cuffey and others, 1995;Clow and others, 1996).…”

Section: Datamentioning

confidence: 99%

A fast Newton–Krylov solver for seasonally varying global ocean biogeochemistry models

Primeau

2008

Ocean Modelling

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A fast Newton-Krylov solver for seasonally varying global ocean biogeochemistry models ABSTRACT. Observations show that the Greenland ice sheet has been losing mass at an increasing rate over the past few decades, which makes it a major contributor to sea-level rise. Here we use a threedimensional higher-order ice-flow model, adaptive mesh refinement and inverse methods to accurately reproduce the present-day ice flow of the Greenland ice sheet. We investigate the effect of the ice thermal regime on (1) basal sliding inversion and (2) projections over the next 100 years. We show that steady-state temperatures based on present-day conditions allow a reasonable representation of the thermal regime and that both basal conditions and century-scale projections are weakly sensitive to small changes in the initial temperature field, compared with changes in atmospheric conditions or basal sliding. We conclude that although more englacial temperature measurements should be acquired to validate the models, and a better estimation of geothermal heat flux is needed, it is reasonable to use steady-state temperature profiles for short-term projections, as external forcings remain the main drivers of the changes occurring in Greenland.

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Section: Datamentioning

confidence: 99%

A fast Newton–Krylov solver for seasonally varying global ocean biogeochemistry models

Primeau

2008

Ocean Modelling

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“…The temperature profile (Gundestrup and Hansen, 1984) shows that most o[the change in temperature happens in the lowermost 400 m. This results in an enhancement (through the temperature dependence o[ the flow laws) of a factor of 2 between 400 m and the bed. The data used for strain rate, stress and temperature are shown in Figure 3.…”

Section: Journal Of Glaciologymentioning

confidence: 99%

“…The liquid-filled borehole was surveyed in 1981 after the drilling, and twice each year in 1983, 1985 and 1986. Temperature, diameter and liquid pressure were measured in addition to inclination and azimuth (Gundestrup and Hansen, 1984;DahlJcnsen and Gundestrup, 1987). The surface temperature at Dye 3 is about -20 u C, and the near-bedrock temperature is -]30e.…”

Section: Introductionmentioning

confidence: 99%

Strain-rate enhancement at Dye 3, Greenland

et al. 1999

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Ice at depth in ice sheets can be softer in bed-parallel shear than Glen's flow law predicts. For example, at Dye 3, Greenland, enhancement factors of3 4 are needed in order to explain the rate of borehole tilting. Previous authors have identified crystal fabric as the dominant contributor, but the role of impurities and crystal size is still incompletely resolved. Here we use two formulations of anisotropic flow laws for ice (Azuma's and Sachs' models) to account for the effects of anisotropy, and show that the measured anisotropy of the ice at Dye 3 cannot explain all the detailed variations in the measured strain rates. The jump in enhancement across the Holocene-\Visconsin boundary is larger than expected from the measured fabrics alone. Dust and soluble-ion concentration divided by crystal size correlates well with the residual enhancement, indicating that most of the "excess deformation" may be due to impurities or crystal size. \Vhile the major features orthe def(Jrrnation at Dye 3 are eXplained by anisotropy and temperature, results also suggest that further research into the role of impurities and crystal size is warranted.. Dahl:lensen and Gundestmp (1987). Fig I Enhancementthan is isotropic ice under the saIlle stress condition. From thin-section measurements and sonic logging ('laylor, 1982: Herron and others, 1985) at Dye 3, we know that the ice there develops an increasingly anisotropic fabric with depth.

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“…In their study, a surface-temperature history was derived using sound physical intuition as the primary guide for minimizing the mismatch b etween the observations and a computed temp erature-dep th profile. Differences between the results derived here and those Gundestrup and Hansen (1984). Also shown is the calculated temperature-depth profile associated with the inferred sch edule of surf ace-temperature flu ctuations derived from the control method.…”

Section: The Greenland Temperature Recordmentioning

confidence: 66%

Paleothermometry by control methods

1991

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ABSTRACT. The recovery of past climatic conditions from ice-sheet borehole temperatures can best be accomplished using the calculus of variations (control methods) to minimize mismatch between the observed profile and a solution of the heat equation which depends on the unknown climate history. Here, we use control methods and a simple one-dimensional heat equation and the temperature-depth profile observed at Dye-3 to infer the surface temperature of south Greenland over the last 30000 years. This history illustrates the virtues that recommend control methods for future use in borehole-temperature analysis, namely: (i) it meets objective performance criteria, and (ii) its uncertainty can be established quantitatively. Our inferred climate history displays what may be the Younger Dryas cold event at about 9000 years BP. Borehole paleothermometry by control methods may thus resolve the controversy concerning the interpretation of Greenland ice-core isotope records. INTRO DUCT I ONRecent revisions of carbon-14 dating chronology and eustatic sea-level records suggest that oxygen-isotope profiles in Greenland ice cores may not provide reliable records of past surface temperature (Fairbanks, 1989). In particular, the isotopic signal previously attributed to the Younger Dryas cold period 10 000 years BP alternatively may indicate isotopic modification of the oceanic reservoir from which Greenland precipitation is derived. Fairbanks (1989) identified glacial meltwater run-off as the likely cause of this modification. This interpretation has generated a controversy concerning the areal extent, timing and cause of the Younger Dryas event (Broecker and Denton, 1989). In an effort to resolve this controversy and to verify the interpretation of ice-core isotope stratigraphy, we explore the use of ice-sheet temperature profiles as paleothermometers.The interpretation of temperature-depth profiles to infer past climate is the subject of a large body of literature (see, for example, Paterson and Clarke, 1978;Budd and Young, 1983;Dahl-Jensen and Johnsen, 1986; Ritz, 1989). Sophisticated numerical models of ice-sheet heat transfer are common and few improvements in their accuracy or fidelity to physical processes remain to be developed. Our paper does not concern these models but rather the way in which they are used to estimate past climate.In this paper we introduce control methods as a means of recovering paleoclimatic information from ice-sheet temperature profiles. Control methods grew out of the 326 calculus of variations during the last 30 years. The typical problem that these methods address consists of optimizing the terminal state of a system which is constrained to evolve according to a prescribed set of differential equations. Control methods might be used, for example, to determine the best time to launch a spacecraft in order to achieve a desired planetary rendezvous. As this example suggests, the control variable is often an initial or boundary condition.We wish to exploit the fact that control methods deal with ...

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Bore-Hole Survey at Dye 3, South Greenland

Cited by 48 publications

References 20 publications

A fast Newton–Krylov solver for seasonally varying global ocean biogeochemistry models

A fast Newton–Krylov solver for seasonally varying global ocean biogeochemistry models

Strain-rate enhancement at Dye 3, Greenland

Paleothermometry by control methods

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