DOCSLIB.ORG

PDF (Chapter 1-Introduction)

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
PDF (Chapter 1-Introduction) Introduction 1 Chapter 1 Thesis Introduction Sea level rise. Tipping points. Global warming. Today, the field of glaciology is irrevocably linked to the study of climate change, from the ivory tower to the network news. However, beyond attempts to quantify ice melting rates and predictions of the lifespans of dwindling glaciers, many aspects of the fundamental physics underlying the deformation of glaciers are poorly understood. Computational modeling of the response of glaciers in Greenland and Antarctica to hydrologic forcing over a timescale shorter than one month is the focus of this thesis. The results presented here are almost completely based on computational modeling but the goal is to explain several field observations of outlet glaciers and ice streams in the published literature. The interaction between ocean tides and ice stream motion (chapters 2, 3, and 4) and the rapid drainage of supraglacial meltwater lakes are the two glacial processes on which this thesis focuses. The introductory section describes the Earth’s cryosphere, focusing on the current scientific interest in glacier dynamics. The next section outlines the classical treatment of ice dynamics—both for general ice masses and the specific case of ice streams. The introduction then summarizes the current understanding of the interaction between the ocean tides and outlet glaciers, specifically over timescales shorter than a month. The next section discusses observations of the tidal influence on outlet glaciers from Antarctica and Greenland. The penultimate introductory section is a brief synopsis of the Introduction 2 finite element modeling methods used throughout this thesis. Last is a short outline of the remainder of this thesis. 1.1 The Cryosphere The term cryosphere refers to all frozen water on planet Earth. While sea ice, river and lake ice, snow, and permafrost all belong to the cryosphere, glacial ice dominates the system. A glacier refers to any mass of crystalline ice that both persists over the course of an entire year and is large enough to flow under its own weight. The largest glaciers on the planet are the Antarctic and Greenland Ice Sheets, which together contain nearly 85% of all the freshwater on the planet (e.g., SMIC Report, 1971; L’vovich, 1979; IPCC, 1990; 1996; Van der Veen, 1999). In the past few decades, the specter of global climate change has driven a renewed interest in the cryosphere, focusing on the fact that water in the cryosphere, primarily in the Greenland and Antarctic Ice Sheets, is equivalent to about 65 meters of sea level equivalent height (e.g., Cuffey and Paterson, 2010; Lythe et al., 2001; Bamber et al., 2001; Meier et al., 2007; Dyurgerov and Meier, 2005). As highlighted by the International Panel on Climate Change’s (IPCC’s) Fourth Assessment Report (2007), the lack of understanding of the interaction between the cryosphere and hydrosphere (i.e., ice sheets and the ocean) is a key piece of missing information that limits the believability of forward, predictive climate modeling. Upwards of 60% of the ice leaving the Greenland Ice Sheet and upwards of 90% of the ice leaving the Antarctic Ice Sheet is carried through a limited number of fast moving outlet glaciers, thus understanding the dynamics of these outlet glaciers is critical to predicting future ice levels (e.g., Cuffey and Paterson, 2010; Morgan et al., 1982; Bauer, 1961; Rignot and Kanagaratnam, 2006). The focus of Introduction 3 the first two research chapters is the interaction of these outlet glaciers and the short-term ocean tides. We use Cuffey and Paterson (2010) as the reference for defining the characteristics of outlet glaciers. The technical definition of an outlet glacier is a fast- moving region of ice bounded by visible rock; an ice stream is a fast-moving region of ice bounded only by slower-moving ice. However following the convention of Cuffey and Paterson (2010), these terms are used interchangeably. The distinction between outlet glaciers and ice streams is generally too strict for practical use as many glaciers transition between ice-ice and ice-rock boundaries over their lengths. Note that while ice streams and outlet glaciers almost always flow into the ocean, the presence of a floating ice shelf or ice tongue is not a defining characteristic. Figure 1.1 shows the locations of all the ice streams discussed in this thesis. As mentioned earlier, the majority of ice leaving the Greenland and Antarctic Ice Sheets travels through outlet glaciers. Direct calving of icebergs and basal melt are two of the primary mechanisms for removal of ice mass (e.g., Jacobs et al, 1992; Vaughan and Doake, 1996; Reeh et al., 1999; Mote, 2003; Wild et al., 2003; Hanna et al., 2005; Box et al., 2006; Krinner et al., 2006; Rignot et al., 2008; Cuffey and Paterson, 2010). Calving occurs when fractures propagate through the ice thickness at the edge of a glacier, resulting in blocks of ice shearing off the main ice body. Usually these new icebergs are carried out to sea, where they eventually melt. Basal melting occurs due to frictional heating along the base of grounded ice, melting due to geothermal heat along the base (e.g., subglacial volcanism, such as in Iceland), and the melting of floating ice shelves due to warmer ocean water reaching the ice’s base. Introduction 4 Over long timescales, changes in the climate system can dramatically impact the response of ice streams to the conditions of the ocean. Increased melting, both on-land and at the grounding line due to higher ocean temperatures, reduces ice in the ice stream system and lubricates the ice stream’s base, further increasing flow speeds. The combination of increased flow speeds and increased basal melt can thin ice streams to the point that any attached ice shelf breaks up. Ice shelf breakup in turn causes increased ice stream speeds due to the removal of the buttressing stress of the ice shelf, as was observed in the 1995 breakup of the Larsen A Ice Shelf and the 2002 breakup of the Larsen B Ice Shelf in Antarctica (Rott et al., 2002; De Angelis and Skvarca, 2003; Rignot et al., 2004, Scambos et al., 2004). Thus, the long-term behavior (and future) of ice shelves is linked to the interaction, and potential feedback, between the cryosphere and the earth’s oceans. However, the loss of ice through outlet glaciers is not the only mechanism for removing mass from the Greenland and Antarctic Ice Sheets on yearly timescales. Surface melt accounts for about 40% of the ice lost from Greenland and about 10% of the ice lost from Antarctica each year (e.g., Box et al., 2006; Krinner et al., 2006; Cuffey and Paterson, 2010). While this mass loss alone is significant, there is evidence from Greenland that supraglacial meltwater, should it reach the glacier’s bed, can increase ice flow rates (e.g., Zwally et al., 2002; Joughin et al., 2008). The potential for such a feedback to cause a dramatic increase in the loss of ice mass with increasing temperatures (and thus melt rates) is not fully established, but modeling suggests that the effect can increase the mass-loss by upwards of a factor of two (Parizek and Alley, 2004). Introduction 5 Ultimately, while this thesis is not a direct study of the interaction of the cryosphere and the global climate system, that connection is the background motivation of this work. The hope is that the research presented here helps to elucidate some of the fundamentals of the response of ice to short timescale forcing. Understanding the hourly and daily dynamics of outlet glaciers requires more study. Through the investigation of tidal forcing of ice streams (chapters 2 to 4) and rapid drainage of supraglacial lakes (chapter 5), this thesis demonstrates some of the modeling concerns of processes that span the gap between very rapid (elastic) response on the order of days and more measured (viscous) response of ice streams on the order of years. The remainder of this introduction focuses on background information related to tidal forcing of ice streams, while the introductory material for the lake drainage problem is deferred to chapter 5 as that background material is unrelated to the remainder of this thesis. 1.2 Ice Stream Dynamics This section provides a brief summary of ice stream dynamics. Information is presented from the introductory textbooks on glaciology by Van der Veen (1999) and Cuffey and Paterson (2010). A discussion of the general deformation of ice sheets and other non- streaming glaciers illustrates the unique nature of ice stream behavior. A description of the general physics in the extreme cases of ice stream geometry follows. Consider a cross-sectional view of an ice sheet, as is shown in figure 1.2. The surface deformation at the location of a longitudinal cross section can be approximated by: = + (1.1) 푢�⃗ 푢�⃗푑 푢�⃗푏 Introduction 6 where the total velocity vector is the additive sum of the internal deformation and 푑 the basal sliding . 푢�⃗ 푢�⃗ 푏 In terms of푢�⃗ internal deformation, we assume that glacier flow is driven by the weight of the ice itself, where the basal driving stress for a vertical profile of the ice is: 푏 = sin( )휏 (1.2) 푏 푖 where is the ice density, is gravitational휏 휌 푔퐻 acceleration,훼 is the ice thickness, and is 푖 the surface휌 slope. Assuming푔 that ice deforms viscously over퐻 most timescales, that 훼 viscous deformation can be expressed using a canonical Glen-style flow law (Glen, 1955; 1958), and that glacier flow is laminar, we find that: 2 = ( ) (1.3) + 1 퐴퐷 푛 푢�⃗푑 휏푏 퐻 The value for the stress exponent n is traditionally푛 chosen to be equal to three based on laboratory stress-strain curves (e.g., Glen, 1955; 1958).
Load more

Recommended publications
  • A Significant Acceleration of Ice Volume Discharge Preceded a Major Retreat of a West Antarctic Paleo–Ice Stream
    https://doi.org/10.1130/G46916.1 Manuscript received 26 August 2019 Revised manuscript received 23 November 2019 Manuscript accepted 26 November 2019 © 2019 Geological Society of America. For permission to copy, contact [email protected]. A signifcant acceleration of ice volume discharge preceded a major retreat of a West Antarctic paleo–ice stream Philip J. Bart1 and Slawek Tulaczyk2 1 Department of Geology and Geophysics, Louisiana State University, Baton Rouge, Louisiana 70803, USA 2 Department of Earth and Planetary Sciences, University of California Santa Cruz, Santa Cruz, California 95064, USA ABSTRACT SEDIMENT AND ICE DISCHARGE For the period between 14.7 and 11.5 cal. (calibrated) kyr B.P, the sediment fux of Bind- FROM THE PALEO–BINDSCHADLER schadler Ice Stream (BIS; West Antarctica) averaged 1.7 × 108 m3 a−1. This implies that BIS ICE STREAM velocity averaged 500 ± 120 m a−1. At a fner resolution, the data suggest two stages of ice Radiocarbon ages from benthic foramin- stream fow. During the frst 2400 ± 400 years of a grounding-zone stillstand, ice stream fow ifera (Bart et al., 2018) (Table 1) indicate that averaged 200 ± 90 m a−1. Following ice-shelf breakup at 12.3 ± 0.2 cal. kyr B.P., fow acceler- the paleo-BIS grounding line had retreated ated to 1350 ± 580 m a−1. The estimated ice volume discharge after breakup exceeds the bal- 70 km from its maximum (LGM) position by ance velocity by a factor of two and implies ice mass imbalance of −40 Gt a−1 just before the 14.7 ± 0.4 cal.
    [Show full text]
  • Education Personal Research Interests Employment
    Douglas Reed MacAyeal Department of the Geophysical Sciences The University of Chicago 5734 S. Ellis Ave. HGS 424 Chicago, IL Phone: (773) 702-8027 (o) (773) 752-6078 (h) (773) 702-9505 (f) (224) 500-7775 (c) [email protected] [email protected] last updated: March, 2020 Education 1983 Ph.D. Princeton University, Princeton, NJ Geophysical Fluid Dynamics advisor: Kirk Bryan 1979 M.S. University of Maine, Orono, ME Physics/Glaciology advisor: Robert Thomas 1976 Sc.B. Brown University, Providence, RI Physics Magna cum laude, honors in physics Personal Birth Date: 8 December, 1954; Age: 65 Birth Place: Boston, MA, USA Marital Status: Married, Linda A. MacAyeal (Sparks) Children: Leigh C. (MacAyeal) Kasten (Brown U., Sc.B.; Cornell U., DVM), Hannah R. MacAyeal (U. Penn, B.S., U. Penn Veterinary Medicine, DVM), Evan C. MacAyeal (Carleton College, B.A., Columbia University, Financial Engineering, M.S.) Research Interests The physical processes that determine the evolution of ice and climate on Earth over the past, present and future. Employment Department of the Geophysical Sciences, University of Chicago 1983-Present Professor (Asst. until 1987, Assoc. until 1992 and Full until present) Prior to 1983: I was a graduate student at Princeton University and University of Maine. Awards and Honors • 2019 Seligman Crystal, International Glaciological Society (IGS) • 2013 Nye Lecture, American Geophysical Union (AGU), Fall Meeting • 2010 Goldthwait Award (Polar Medal) of the Byrd Polar Research Center, Ohio State University • 2005 Provost’s Teaching Award of the University of Chicago • 2002 Quantrell Teaching Award of the University of Chicago • 1997 Richardson Medal of the IGS • 1988 James Macelwane Medal of the AGU • 1988 Fellow of the AGU • Antarctic geographic names: MacAyeal Ice Stream, MacAyeal Peak Teaching Experience • GeoSci 242: Geophysical Fluid Dynamics, I.
    [Show full text]
  • Studies of Antarctic Ice Shelf Stability: Surface Melting, Basal Melting, and Ice Flow Dynamics
    Studies of Antarctic ice shelf stability: surface melting, basal melting, and ice flow dynamics by Karen E. Alley B.A., Colgate University, 2012 A thesis submitted to the Faculty of the Graduate School of the University of Colorado in partial fulfillment of the requirement for the degree of Doctor of Philosophy Department of Geological Sciences 2017 This thesis entitled: Studies of Antarctic ice shelf stability: Surface melting, basal melting, and ice flow dynamics written by Karen E. Alley has been approved for the Department of Geological Sciences James White Ted Scambos Date The final copy of this thesis has been examined by the signatories, and we find that both the content and the form meet acceptable presentation standards of scholarly work in the above-mentioned discipline. ii Alley, Karen Elizabeth (Ph.D., Department of Geological Sciences) Studies of Antarctic ice shelf stability: Surface melting, basal melting, and ice flow dynamics Thesis directed by Senior Research Scientist T.A. Scambos and Professor J.W.C. White Abstract: Floating extensions of ice sheets, known as ice shelves, play a vital role in regulating the rate of ice flow into the Southern Ocean from the Antarctic Ice Sheet. Shear stresses imparted by contact with islands, embayment walls, and other obstructions transmit “backstress” to grounded ice. Ice shelf collapse reduces or eliminates this backstress, increasing mass flux to the ocean and therefore rates of sea level rise. This dissertation presents studies that address three main factors that regulate ice shelf stability: surface melt, basal melt, and ice flow dynamics. The first factor, surface melt, is assessed using active microwave backscatter.
    [Show full text]
  • Did Holocene Climate Changes Drive West Antarctic Grounding Line Retreat and Re-Advance?
    https://doi.org/10.5194/tc-2020-308 Preprint. Discussion started: 19 November 2020 c Author(s) 2020. CC BY 4.0 License. Did Holocene climate changes drive West Antarctic grounding line retreat and re-advance? Sarah U. Neuhaus1, Slawek M. Tulaczyk1, Nathan D. Stansell2, Jason J. Coenen2, Reed P. Scherer2, Jill 5 A. Mikucki3, Ross D. Powell2 1Earth and Planetary Sciences, University oF CaliFornia Santa Cruz, Santa Cruz, CA, 95064, USA 2Department oF Geology and Environmental Geosciences, Northern Illinois University, DeKalb, IL, 60115, USA 3Department oF Microbiology, University oF Tennessee Knoxville, Knoxville, TN, 37996, USA 10 Correspondence to: Sarah U. Neuhaus ([email protected]) Abstract. Knowledge oF past ice sheet conFigurations is useFul For informing projections of Future ice sheet dynamics and For calibrating ice sheet models. The topology oF grounding line retreat in the Ross Sea Sector oF Antarctica has been much debated, but it has generally been assumed that the modern ice sheet is as small as it has been for more than 100,000 years 15 (Conway et al., 1999; Lee et al., 2017; Lowry et al., 2019; McKay et al., 2016; Scherer et al., 1998). Recent findings suggest that the West Antarctic Ice Sheet (WAIS) grounding line retreated beyond its current location earlier in the Holocene and subsequently re-advanced to reach its modern position (Bradley et al., 2015; Kingslake et al., 2018). Here, we further constrain the post-LGM grounding line retreat and re-advance in the Ross Sea Sector using a two-phase model of radiocarbon input and decay in subglacial sediments From six sub-ice sampling locations.
    [Show full text]
  • Variability in the Mass Flux of the Ross Sea Ice Streams, Antarctica, Over the Last Millennium
    Portland State University PDXScholar Geology Faculty Publications and Presentations Geology 1-1-2012 Variability in the Mass Flux of the Ross Sea Ice Streams, Antarctica, over the last Millennium Ginny Catania University of Texas at Austin Christina L. Hulbe Portland State University Howard Conway University of Washington - Seattle Campus Ted A. Scambos University of Colorado at Boulder C. F. Raymond University of Washington - Seattle Campus Follow this and additional works at: https://pdxscholar.library.pdx.edu/geology_fac Part of the Geology Commons Let us know how access to this document benefits ou.y Citation Details Catania. G. A., C.L. Hulbe, H.B. Conway, T.A. Scambos, C.F. Raymond, 2012, Variability in the mass flux of the Ross Sea ice streams, Antarctica, over the last millennium. Journal of Glaciology, 58 (210), 741-752. This Article is brought to you for free and open access. It has been accepted for inclusion in Geology Faculty Publications and Presentations by an authorized administrator of PDXScholar. Please contact us if we can make this document more accessible: [email protected]. Journal of Glaciology, Vol. 58, No. 210, 2012 doi: 10.3189/2012JoG11J219 741 Variability in the mass flux of the Ross ice streams, West Antarctica, over the last millennium Ginny CATANIA,1,2 Christina HULBE,3 Howard CONWAY,4 T.A. SCAMBOS,5 C.F. RAYMOND4 1Institute for Geophysics, University of Texas, Austin, TX, USA E-mail: [email protected] 2Department of Geology, University of Texas, Austin, TX, USA 3Department of Geology, Portland State University, Portland, OR, USA 4Department of Earth and Space Sciences, University of Washington, Seattle, WA, USA 5National Snow and Ice Data Center, University of Colorado, Boulder, CO, USA ABSTRACT.
    [Show full text]
  • Information to Users
    Variations In Ice Flow And Glaciers Over Time And Space Item Type Thesis Authors Elsberg, Daniel Harry Download date 24/09/2021 03:40:40 Link to Item http://hdl.handle.net/11122/8657 INFORMATION TO USERS This manuscript has been reproduced from the microfilm master. UMI films the text directly from the original or copy submitted. Thus, some thesis and dissertation copies are in typewriter face, while others may be from any type of computer printer. The quality of this reproduction is dependent upon the quality of the copy submitted. Broken or indistinct print, colored or poor quality illustrations and photographs, print bleedthrough, substandard margins, and improper alignment can adversely affect reproduction. In the unlikely event that the author did not send UMI a complete manuscript and there are missing pages, these will be noted. Also, if unauthorized copyright material had to be removed, a note will indicate the deletion. Oversize materials (e.g., maps, drawings, charts) are reproduced by sectioning the original, beginning at the upper left-hand comer and continuing from left to right in equal sections with small overlaps. ProQuest Information and Learning 300 North Zeeb Road, Ann Arbor, Ml 48106-1346 USA 800-521-0600 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. VARIATIONS IN ICE FLOW AND GLACIERS OVER TIME AND SPACE A THESIS Presented to the Faculty of the University of Alaska Fairbanks in Partial Fulfillment of the Requirements for the Degree of DOCTOR OF PHILOSOPHY By Daniel Harry Elsberg, B.S.
    [Show full text]
  • Spatiotemporal Variations in the Surface Velocities of Antarctic Peninsula Glaciers
    Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | The Cryosphere Discuss., 8, 5875–5910, 2014 www.the-cryosphere-discuss.net/8/5875/2014/ doi:10.5194/tcd-8-5875-2014 TCD © Author(s) 2014. CC Attribution 3.0 License. 8, 5875–5910, 2014 This discussion paper is/has been under review for the journal The Cryosphere (TC). Spatiotemporal Please refer to the corresponding final paper in TC if available. variations in the surface velocities of Spatiotemporal variations in the surface Antarctic Peninsula glaciers velocities of Antarctic Peninsula glaciers J. Chen et al. J. Chen1,2, C. Q. Ke1,2, and Z. D. Shao1,2 1Jiangsu Provincial Key Laboratory of Geographic Information Science and Technology, Title Page Nanjing University, Nanjing, 210023, China Abstract Introduction 2Key Laboratory for Satellite Mapping Technology and Applications of State Administration of Surveying, Mapping and Geoinformation of China, Nanjing University, Nanjing, 210023, China Conclusions References Received: 25 October 2014 – Accepted: 2 November 2014 – Published: 25 November 2014 Tables Figures Correspondence to: C. Q. Ke ([email protected]) J I Published by Copernicus Publications on behalf of the European Geosciences Union. J I Back Close Full Screen / Esc Printer-friendly Version Interactive Discussion 5875 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Abstract TCD Velocity is an important parameter for the estimation of glacier mass balance, which directly signals the response of glaciers to climate change. Antarctic ice sheet move- 8, 5875–5910, 2014 ment and the associated spatiotemporal velocity variations are of great significance to 5 global sea level rise. In this study, we estimate Antarctic Peninsula glacier velocities Spatiotemporal using the co-registration of optically sensed images and correlation (hereafter referred variations in the to as COSI-Corr) based on moderate-resolution imaging spectroradiometer Level 1B surface velocities of data (hereafter referred to as MODIS L1B).
    [Show full text]
  • Fast-Flow Signature in the Stagnated Kamb Ice Stream, West Antarctica
    This is a repository copy of Fast-flow signature in the stagnated Kamb Ice Stream, West Antarctica. White Rose Research Online URL for this paper: http://eprints.whiterose.ac.uk/92154/ Version: Accepted Version Article: Ng, F. and Conway, H. (2004) Fast-flow signature in the stagnated Kamb Ice Stream, West Antarctica. Geology, 32 (6). 481 - 484. ISSN 0091-7613 https://doi.org/10.1130/G20317.1 Reuse Unless indicated otherwise, fulltext items are protected by copyright with all rights reserved. The copyright exception in section 29 of the Copyright, Designs and Patents Act 1988 allows the making of a single copy solely for the purpose of non-commercial research or private study within the limits of fair dealing. The publisher or other rights-holder may allow further reproduction and re-use of this version - refer to the White Rose Research Online record for this item. Where records identify the publisher as the copyright holder, users can verify any specific terms of use on the publisher’s website. Takedown If you consider content in White Rose Research Online to be in breach of UK law, please notify us by emailing [email protected] including the URL of the record and the reason for the withdrawal request. [email protected] https://eprints.whiterose.ac.uk/ Ng & Conway (G20317), p. 1 1 2 3 Fast-flow signature in the stagnated Kamb Ice 4 Stream, West Antarctica 5 Felix Ng 6 Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of 7 Technology, Cambridge, Massachusetts 02139, USA 8 Howard Conway 9 Department of Earth and Space Sciences, University of Washington, Seattle, Washington 98195, 10 USA 11 12 ABSTRACT 13 Among the major ice streams that drain West Antarctica, Kamb Ice Stream 14 (formerly called Ice Stream C) is unique in that it stagnated ~150 yr ago, but its former 15 fast-flow conditions are virtually unknown.
    [Show full text]
  • Scaling of Instability Time-Scales of Antarctic Outlet Glaciers Based On
    The Cryosphere Discuss., https://doi.org/10.5194/tc-2018-252 Manuscript under review for journal The Cryosphere Discussion started: 15 January 2019 c Author(s) 2019. CC BY 4.0 License. Scaling of instability time-scales of Antarctic outlet glaciers based on one-dimensional similitude analysis Anders Levermann1,2,3 and Johannes Feldmann1 1Potsdam Institute for Climate Impact Research (PIK), Potsdam, Germany 2LDEO, Columbia University, New York, USA 3Institute of Physics, University of Potsdam, Potsdam, Germany Correspondence: Anders Levermann ([email protected]) Abstract. Recent observations and ice-dynamic modeling suggest that a marine ice sheet instability (MISI) might have been triggered in West Antarctica. The corresponding outlet glaciers, Pine Island Glacier (PIG) and Thwaites Glacier (TG), showed significant retreat during at least the last two decades. While other regions in Antarctica have the topographic predisposition for the same kind of instability it is so far unclear how fast these instabilities would unfold if they were initiated. Here we 5 employ the concept of similitude to estimate the characteristic time scales of several potentially MISI-prone outlet glaciers around the Antarctic coast. The proposed one-dimensional scaling approach combines observational and model data with a scaling analysis of the governing equations for fast ice flow. Evaluating outlet-characteristic ice and bed geometry, surface mass balance and basal friction in the relevant region near the grounding line, we assume that the inferred time scales correspond to the outlet-specific initial responses time to potential destabilization. Our results suggest that TG and PIG have the fastest 10 responses time of all investigated outlets, with TG responding about 1.25 to 2 times as fast as PIG, while other outlets around Antarctica would be up to ten times slower if destabilized.
    [Show full text]
  • Author's Tracked Changes
    Mechanics and dynamics of pinning points on the Shirase Coast, West Antarctica Holly Still1 and Christina Hulbe1 1National School of Surveying, University of Otago, Dunedin, New Zealand Correspondence: Holly Still ([email protected]) Abstract. Ice rises and rumples, sites of localised ice-shelf grounding, modify ice-shelf flow by generating lateral and basal shear stresses, upstream compression and downstream tension. Studies of pinning points typically quantify this role indirectly, through related metrics such as a buttressing number. Here, we quantify the dynamic effects of pinning points directly, by comparing model-simulated stress states in the Ross Ice Shelf (RIS) with and without a specific set of pinning points located 5 downstream of the MacAyeal and Bindschadler Ice Streams (MacIS and BIS, respectively). Because ice properties are only known indirectly, the experiment is repeated with different realisations of the ice softness. While longitudinal stretching, and thus ice velocity, is smaller with the pinning points, flow resistance generated by other grounded features is also smaller. Conversely, flow resistance generated by other grounded features increases when the pinning points are absent, providing a non-local control on the net effect of the pinning points on ice-shelf flow. We find that an ice stream located directly upstream 10 of the pinning points, MacIS, is less responsive to their removal than the obliquely oriented BIS. This response is due to zones of locally higher basal drag acting on MacIS, which may itself be a consequence of the coupled ice-shelf and ice- stream response to the pinning points. We also find that inversion of present-day flow and thickness for basal friction and ice softness, without feature-specific, a posteriori adjustment, leads to the incorrect representation of ice rumple morphology and an incorrect boundary condition at the ice base.
    [Show full text]
  • 1 the NSF/OPP Contribution to Antarctic Glaciology: a Personal Perspective Terence J. Hughes Professor Emeritus of Earth Science
    The NSF/OPP Contribution To Antarctic Glaciology: A Personal Perspective Terence J. Hughes Professor Emeritus of Earth Sciences and Climate Change University of Maine Orono, Maine 04469-5790 30 October 2010 I retired from the University of Maine on 15 January 2010 from a joint appointment in the Department of Earth Sciences and the Climate Change Institute, both located in the Bryand Global Sciences Center. This provided the opportunity to produce a personal account of the contribution to Antarctic glaciology made by the Office of Polar Programs (OPP) in the United States National Science Foundation (NSF) over the last half century. For convenience, my account will be made decade-by-decade, beginning in the mid Twentieth Century. The old hands, affectionately called Old Antarctic Explorers (OAEs), are a vanishing breed, so it is important for an account to be made before the Dying of the Light. 1950—1960 The Cold War began at the end of World War II when the victors, primarily the USA and the USSR, battled diplomatically to dominate a new world hegemony. It was an ideological struggle that pitted Capitalism against Communism. The Communist hegemony spread first in Eastern Europe as the Red Army occupied these countries up to what Winston Churchill called an Iron Curtain. I like to have some fun with this in an age without teleprompters. Winston is at his podium in Missouri, looking out over the crowd: “From Trieste in the Baltic to Stettin in the Adriatic, an Iron Curtain has descended across the continent.” [pause] “I mean from Stettin in the Baltic to Trieste in the Adriatic!” [grumbles to himself] Then, in 1949, Mao Tse Tung overthrew the Nationalist Chinese government and China entered the Communist orbit.
    [Show full text]
  • Ice Stream Shear Margin Basal Melting, West Antarctica
    ICE STREAM SHEAR MARGIN BASAL MELTING, WEST ANTARCTICA A Thesis Presented in Partial Fulfillment for the Degree Masters of Science in the Graduate School of The Ohio State University By Lucas H. Beem, B.S. * * * * * * * The Ohio State University 2008 Master’s Examination Committee: Dr. Kenneth C. Jezek, Advisor Approved by Dr. William B. Lyons _____________________________ Dr. Douglas Alsdorf Advisor Geological Science Graduate Program ABSTRACT Basal water lubricates and enables the anomalous flow feature of ice streams in the West Antarctic Ice Sheet. As surface melt is insufficient to supply the base with the volume of water known to be there, basal melting must be the source of this water. How basal melt patterns vary spatial can be an insight into the dynamics of ice streams, which remain incompletely described by glaciological theory. Through a heuristic model extended from the work of Whillans and Van der Veen (2001) and Van der Veen et al. (2007) a spatial pattern of basal melt for the Whillans Ice Stream emerged that offer hypotheses for the onset of streaming flow, shear crevasse development and observed morphological changes of a slowing and widening ice stream. The limitations and the uncertainties of this model make the determination of exact basal melt rates difficult, but the patterns of melt rate distribution are robust. This allows for a perspective to better understand current dynamics and how basal melt may play a role in the ice stream’s future development. ii dedicated to my parents for their continued support iii ACKNOWLEDGMENTS I wish to express my gratitude to Dr.
    [Show full text]