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Slawek Tulaczyk

Bio: Slawek Tulaczyk is an academic researcher from University of California, Santa Cruz. The author has contributed to research in topics: Ice stream & Ice sheet. The author has an hindex of 52, co-authored 139 publications receiving 8284 citations. Previous affiliations of Slawek Tulaczyk include University of Kentucky & California Institute of Technology.


Papers
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Journal ArticleDOI
TL;DR: In this paper, the Coulomb-plastic rheology was used to model the subglacial till deformation in the Upstream B camp of West Antarctica, and the results showed that failure strength of this till is strongly dependent on effective stress.
Abstract: Data from laboratory geotechnical tests on till recovered from beneath Ice Stream B, West Antarctica, at the Upstream B camp (hereinafter the UpB till) show that failure strength of this till is strongly dependent on effective stress but is practically independent of strain and strain rate. These data support use of a Coulomb-plastic rheology in modeling of ice stream behavior and subglacial till deformation. Our testing program combined triaxial, ring shear, and confined uniaxial tests to investigate till strength and compressibility. Results show that the UpB till follows closely Coulomb's equation in which shear strength is a linear function of normal effective stress (apparent cohesion near zero and internal friction angle ϕ equal to 24°). Till compressibility is best described by a logarithmic function that relates void ratio to normal effective stress. In general, the behavior of the UpB till is consistent with other experimental evidence regarding mechanical behavior of granular materials. Based on our laboratory results we formulate the Compressible-Coulomb-Plastic till model in which there are three interrelated, primary state variables: shear strength, void ratio, and normal effective stress. This model is used in the second part of our study to simulate response of subglacial till to realistic effective stress forcings. These simulations demonstrate that the model is capable of reproducing fundamental aspects of subglacial till kinematics: (1) occurrence of tilt rate oscillations and negative tilt rates in tiltmeter records, and (2) distributed till deformation to depths of 0.1–1.0 m beneath the ice base. Our laboratory and modeling results substantiate application of the Compressible-Coulomb-Plastic model in simulations of the motion of Ice Stream B over its weak till bed.

478 citations

Journal ArticleDOI
TL;DR: In this article, the undrained plastic bed model (henceforth the UPB model) was proposed to model the relationship among ice sliding velocity, till strength, water storage in till, and basal melt rate.
Abstract: Based on the results of our studies of the physical conditions beneath Ice Stream B, we formulate a new analytical ice stream model, the undrained plastic bed model (henceforth the UPB model). Mathematically, the UPB model is represented by a non-linear system of four coupled equations which express the relationships among ice sliding velocity, till strength, water storage in till, and basal melt rate. We examine this system of equations for conditions of ice stream stability over short timescales that permit holding ice stream geometry constant (less than hundreds of years). Temporal variability is introduced into the UPB model only by the direct dependence of till void ratio changes (ė = ∂e/∂t) on the basal melting rate m_r. Since till strength τ_b{e} and ice stream velocity U_b{τ_b} change as long as till void ratio varies, the first condition for ice stream stability is that of constant till water storage ė = 0. The second condition for ice stream stability arises from the feedback between ice stream velocity, till strength, and the basal melting rate which depends on shear heating m_r{ U_b τ_b}. This is the “weak till” condition which requires that in a steady state till strength is a small fraction of the gravitational driving stress τ_b < (n + 1)^(−1) τ_d. The salient feature of the UPB model is its ability to produce two thermo mechanically controlled equilibrium states, one with a strong bed and slow ice velocities (“ice sheet” mode) and one with a weak bed and fast ice velocities (“ice-stream” mode). This bimodality of basal conditions is consistent with the available observations of subglacial conditions beneath slow and fast moving ice in West Antarctica. Basal conditions that do not correspond to these two steady states may occur transiently during switches between the two stable modes. The UPB model demonstrates that ice streams may be prone to thermally triggered instabilities, during which small perturbations in the basal thermal energy balance grow, leading to generation or elimination of the basal conditions which cause ice streaming.

316 citations

Journal ArticleDOI
TL;DR: In this paper, the authors presented the first comprehensive study of active lakes for the Antarctic ice sheet north of 868 S, based on 4.5 years (2003-08) of NASA's ICESat laser altimeter data.
Abstract: Through the detection of surface deformation in response to water movement, recent satellite studies have demonstrated the existence of subglacial lakes in Antarctica that fill and drain on timescales of months to years. These studies, however, were confined to specific regions of the ice sheet. Here we present the first comprehensive study of these 'active' lakes for the Antarctic ice sheet north of 868 S, based on 4.5 years (2003-08) of NASA's Ice, Cloud and land Elevation Satellite (ICESat) laser altimeter data. Our analysis has detected 124 lakes that were active during this period, and we estimate volume changes for each lake. The ICESat-detected lakes are prevalent in coastal Antarctica, and are present under most of the largest ice-stream catchments. Lakes sometimes appear to transfer water from one to another, but also often exchange water with distributed sources undetectable by ICESat, suggesting that the lakes may provide water to or withdraw water from the hydrologic systems that lubricate glacier flow. Thus, these reservoirs may contribute pulses of water to produce rapid temporal changes in glacier speeds, but also may withdraw water at other times to slow flow.

316 citations

Journal ArticleDOI
03 Jul 1998-Science
TL;DR: The occurrence of young diatoms and high concentrations of beryllium-10 beneath grounded ice indicates that the Ross Embayment was an open marine environment after a late Pleistocene collapse of the marine ice sheet.
Abstract: Some glacial sediment samples recovered from beneath the West Antarctic ice sheet at ice stream B contain Quaternary diatoms and up to 108 atoms of beryllium-10 per gram. Other samples contain no Quaternary diatoms and only background levels of beryllium-10 (less than 10^6 atoms per gram). The occurrence of young diatoms and high concentrations of beryllium-10 beneath grounded ice indicates that the Ross Embayment was an open marine environment after a late Pleistocene collapse of the marine ice sheet.

303 citations

Journal ArticleDOI
06 Jun 2013-Nature
TL;DR: The past six years of progress are discussed and key problems that remain are examined, including whether East Antarctica has been gaining or losing ice mass over the past 20 years, and uncertainties in ice-mass change for West Antarctica and the Antarctic Peninsula remain large.
Abstract: Since the 2007 Intergovernmental Panel on Climate Change Fourth Assessment Report, new observations of ice-sheet mass balance and improved computer simulations of ice-sheet response to continuing climate change have been published. Whereas Greenland is losing ice mass at an increasing pace, current Antarctic ice loss is likely to be less than some recently published estimates. It remains unclear whether East Antarctica has been gaining or losing ice mass over the past 20 years, and uncertainties in ice-mass change for West Antarctica and the Antarctic Peninsula remain large. We discuss the past six years of progress and examine the key problems that remain.

268 citations


Cited by
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Journal Article
TL;DR: In this article, the authors present a document, redatto, voted and pubblicato by the Ipcc -Comitato intergovernativo sui cambiamenti climatici - illustra la sintesi delle ricerche svolte su questo tema rilevante.
Abstract: Cause, conseguenze e strategie di mitigazione Proponiamo il primo di una serie di articoli in cui affronteremo l’attuale problema dei mutamenti climatici. Presentiamo il documento redatto, votato e pubblicato dall’Ipcc - Comitato intergovernativo sui cambiamenti climatici - che illustra la sintesi delle ricerche svolte su questo tema rilevante.

4,187 citations

Journal ArticleDOI
01 Mar 2000
TL;DR: In this paper, the authors present a review of the techniques of interferometry, systems and limitations, and applications in a rapidly growing area of science and engineering, including cartography, geodesy, land cover characterization, and natural hazards.
Abstract: Synthetic aperture radar interferometry is an imaging technique for measuring the topography of a surface, its changes over time, and other changes in the detailed characteristic of the surface. By exploiting the phase of the coherent radar signal, interferometry has transformed radar remote sensing from a largely interpretive science to a quantitative tool, with applications in cartography, geodesy, land cover characterization, and natural hazards. This paper reviews the techniques of interferometry, systems and limitations, and applications in a rapidly growing area of science and engineering.

3,042 citations

Journal ArticleDOI
TL;DR: It is explained how, in principle, early warning systems could be established to detect the proximity of some tipping points, and critically evaluate potential policy-relevant tipping elements in the climate system under anthropogenic forcing.
Abstract: The term "tipping point" commonly refers to a critical threshold at which a tiny perturbation can qualitatively alter the state or development of a system. Here we introduce the term "tipping element" to describe large-scale components of the Earth system that may pass a tipping point. We critically evaluate potential policy-relevant tipping elements in the climate system under anthropogenic forcing, drawing on the pertinent literature and a recent international workshop to compile a short list, and we assess where their tipping points lie. An expert elicitation is used to help rank their sensitivity to global warming and the uncertainty about the underlying physical mechanisms. Then we explain how, in principle, early warning systems could be established to detect the proximity of some tipping points.

2,660 citations

Journal ArticleDOI
TL;DR: In this paper, a review of the use of radar interferometry to measure changes in the Earth's surface has exploded in the early 1990s, and a practical summary explains the techniques for calculating and manipulating interferograms from various radar instruments, including the four satellites currently in orbit: ERS-1, ERS2, JERS-1 and RADARSAT.
Abstract: Geophysical applications of radar interferometry to measure changes in the Earth's surface have exploded in the early 1990s. This new geodetic technique calculates the interference pattern caused by the difference in phase between two images acquired by a spaceborne synthetic aperture radar at two distinct times. The resulting interferogram is a contour map of the change in distance between the ground and the radar instrument. These maps provide an unsurpassed spatial sampling density (∼100 pixels km−2), a competitive precision (∼1 cm), and a useful observation cadence (1 pass month−1). They record movements in the crust, perturbations in the atmosphere, dielectric modifications in the soil, and relief in the topography. They are also sensitive to technical effects, such as relative variations in the radar's trajectory or variations in its frequency standard. We describe how all these phenomena contribute to an interferogram. Then a practical summary explains the techniques for calculating and manipulating interferograms from various radar instruments, including the four satellites currently in orbit: ERS-1, ERS-2, JERS-1, and RADARSAT. The next chapter suggests some guidelines for interpreting an interferogram as a geophysical measurement: respecting the limits of the technique, assessing its uncertainty, recognizing artifacts, and discriminating different types of signal. We then review the geophysical applications published to date, most of which study deformation related to earthquakes, volcanoes, and glaciers using ERS-1 data. We also show examples of monitoring natural hazards and environmental alterations related to landslides, subsidence, and agriculture. In addition, we consider subtler geophysical signals such as postseismic relaxation, tidal loading of coastal areas, and interseismic strain accumulation. We conclude with our perspectives on the future of radar interferometry. The objective of the review is for the reader to develop the physical understanding necessary to calculate an interferogram and the geophysical intuition necessary to interpret it.

2,319 citations

Journal ArticleDOI
TL;DR: Landsat 8, a NASA and USGS collaboration, acquires global moderate-resolution measurements of the Earth's terrestrial and polar regions in the visible, near-infrared, short wave, and thermal infrared as mentioned in this paper.

1,697 citations