3-104 2008-2012 UNAVCO PROPOSAL: GEODESY ADVANCING EARTH SCIENCE RESEARCH Polar at adistance100kmfrom thegrounding line.On the occurring duringslipsdecreased upstream tobelow50% ited stick-slipmotion,althoughthefractionofmotion Whillans Ice Stream wastheonlyicestream thatexhib in McMurdo toensure that thesystemsworked reliably. bothinthe continentalU.S.(CONUS)and ing expertise ments, butUNAVCO wasextremely helpfulinprovid required externalstoragetomeetourscientific require receivers includedanumberofolder Trimble 4000’s that along-stream strength ofthesensitivity. TheUNAVCO to determinethenature ofthemodulationand in totheRoss Ice Shelf. These receivers were deployed shire were deployed amongalltheicestreams draining owned by Penn State andtheUniversity ofNew Hamp field season,15UNAVCO receivers alongwithsome of suchreceivers from UNAVCO. During the2003-04 of GPSreceivers andtheavailability ofalargenumber tions oftheiceshelfwasbasedlargelyoncapabilities modulated strongly bywithtidaloscilla forces thatvary that themotionofmajor West Antarctic icestreams is Investigation oftherecently discovered phenomenon Richard Alley » Robert Bindschadler » Sridhar Anandakrishnan» Tidal Modulation ofIce Stream Motion Penn State University NASA Penn State University - - - - - interpretation isthatthetillbeneathmouthofice motion occurringduringslipwasincreasing. Thesimple result from thecollecteddatawasthatamountof study ofstick-slipon Whillans Ice Stream. Adramatic with Penn State receivers toconductamore focused some 5700’s andsomeNet RS’s) againwere combined In the2004-05season, UNAVCO receivers (some4000’s upstream. diminishing beyond detectionthreshold about400km in speedfrom themeanspeed,anddecreased upstream, lation wasmore gradual,butstilluptoa50%variation other fouricestreams occupied,thenature ofthemodu Matt » King Ian Joughin » Donald Voigt » Bindschadler, R.A.,M.King,R.A.Alley, S.AnandakrishnanandL.Padman, Anandakrishnan S,D.E. Voigt, R.R.Alley, M.A.King,2003.Ice stream D Publications: These dataare stillbeinganalyzed. tion ofBindschadler Ice Stream (formerlyicestream D). ous season,butfocusedonthemore graduallymodula Finally, the2005-06fieldseasonwassimilartoprevi this icestream iscontinuing. with anotherresult thatthelonger-termdecelerationof stream isbecomingmore sticky. Thisfindingisconsistent Stream, Science, Vol. 301,p. 1087-1089. 2003. Tidally Controlled Stick-Slip Discharge ofa West Antarctic Ice Geophysical Research Letters, Vol. 30,No. 7,art.no. 1361. flow speedisstrongly modulated by thetidebeneath Ross Ice Shelf, University ofNewcastle University of Washington Penn State University - - - 3-105 Polar Observations and Models of Tidally Pulsed Flow of the Ross Ice Shelf,

Kelly M. Brunt » Dept of Geological Sciences, University of Montana Luke Copeland » University of Ottawa, Canada Emily B. O’Donnell » Dept of Geophysical Sciences, University of Chicago Douglas R. MacAyeal » Dept of Geophysical Sciences, University of Chicago

We examine the temporal pulsation of ice-stream flow associ- 2008-2012 UNAVCO PROPOSAL: GEODESY ADVANCING EARTH SCIENCE RESEARCH ated with ocean tide along the Siple Coast of using observations of similar flow pulsations at three locations near the front of the Ross Ice Shelf (RIS). A 16-day campaign of geodetic GPS observations was conducted at the front of the RIS (and processed using the Canadian PPP processor) where time-average flow of the ice shelf has greatest magnitude. The data reveal a smooth, diurnal cycle of horizontal flow vary- ing both along and transverse to the direction of time-average flow (Figure 1). The amplitude of tidally pulsed velocity is approximately 70% of the time-average flow (about 3 m/day at all three locations), and maxima of velocity along the direc- Figure 1: Geodetic GPS data illustrating the horizontal (longitudi- tion of time-average flow appear to lag local high tide by only nal) variations at Nascent as a function of time. an hour or two. This tidally driven flow pulsation is consistent Figure 2: Predicted tidal height for GPS location data collected with magnitudes observed at the grounding line of ice stream at Nascent Iceberg based on Padman et al. [2002]; the z-axis, or color axis, is in units of meters. Periods of high tide (red regions) D [Anandakrishnan et al., 2003], and the degree to which flow are consistently associated with the most northward movement; pulsations vary in both along and across time-average flow periods of low tide are consistently associated with little northward direction is consistent with observations on the movement. [Doake et al., 2002]. To assess the possible causes of tidal pulsations of ice-shelf and ice-stream flow, we conduct a series of ice-shelf model experi- ments using ocean tidal fields provided by the Padman et al. [2002] tide model analysis (Figure 2). We evaluate four separate hypotheses: that tidal pulsations are caused by (1) sea-surface slope and sub-ice-shelf currents associated with tide alone act- ing on ice-shelf creep rates, (2) velocity pulsations at grounding lines (ice stream inflows) alone acting on ice-shelf boundary conditions, (3) accordion-like collapse and expansion of void space within and at the edges of the RIS, and (4) stick-slip like behavior of ice-shelf flow over pinning points and past stagnant coastal boundaries. Initial results suggest that hypothesis (1) is unable to explain the full magnitude of the flow pulsations.

References Doake, C. S. M., H. F. J. Corr, K. W. Nicholls, A. Gaffikin, A. Jenkins, W. I. Bertiger, and M. A. King (2002), Tide-induced lateral movement of Brunt Ice Shelf, Ant- Anandakrishnan, S., D. E. Voigt, R. B. Alley, and M. A. King arctica. Geophys. Res. Lett., 29(8), 67-1. (2003), Ice Stream D flow speed is strongly modulated by the tide beneath the Ross Ice Shelf. Geophys. Res. Lett., 30(7), Padman, L., H. A. Fricker, R. Coleman, S. Howard, and L. Erofeeva (2002), A new 13-1. tide model for the Antarctic ice shelves and seas. Ann. Glaciol., 34(1), 247-254.

3-104 3-105 3-106 2008-2012 UNAVCO PROPOSAL: GEODESY ADVANCING EARTH SCIENCE RESEARCH Polar Funding forthisproject wasprovided by NSFOPP#338224Stability ofLandscapesandIce Sheets inDry Valleys, Antarctica: aSystematic Study ofExposure fusivity are slightlylower thanotheraridclimatesaround theworld. be shown thatthemorainesofDry Valleys are slowly degradingandthemaximumvalues fortopographic dif and therelaxation ofthemoraineslopesover time.By visualinspectionandsimpleslopeanglemeasurements itcan erosion. Using thefielddatatoconstrainparameters,modeltrackedsoiltransport over the moraine surface withsharpcrestedassumption thatglacialmorainesstart profiles, which over timebecomesmeared and rounded by To erosion andmagnitudesoftopographic diffusivity, calculateratesofsurface acomputermodelwasusedwiththe GPS wasusedtocreate high-resolution topographic profiles ofpreviously datedmorainesinthelower Wright valley. the active degradationofglacialmorainescontradictthesuggested stabilityoftheDry Valley’s landscape.Differential ofancientlandscapes(~10millionyearsleys suggestnearlytotalpreservation old).Our on recent fieldobservations Erosion ofEarth’s isgenerally assumedtobeubiquitous,butpublishedfindingsfrom theAntarctic surface Dry Val Jaakko Putkonen » Jon Connolly» Soil Erosion inDry Valleys, Antarctica Ages ofSoils andSurface Deposits. Department of Earth andSpace ofEarth Department Sciences,University of Washington Department of Earth andSpace ofEarth Department Sciences,University of Washington - - 3-107 Polar Histories of Climate and Ice Sheet Dynamics

H. Conway » Dept of Earth and Space Sciences, University of Washington E.D Waddington » Dept of Earth and Space Sciences, University of Washington C.F. Raymond » Dept of Earth and Space Sciences, University of Washington

References Catania, G., H. Conway, C.F. Raymond and T.A. Scambos, 2005. Surface morphology and internal layer stratigraphy in the downstream end of Kamb Ice Stream, West Antarctica. J. Glaciology, 51(174), 423-431. 2008-2012 UNAVCO PROPOSAL: GEODESY ADVANCING EARTH SCIENCE RESEARCH Catania, G., H. Conway, C.F. Raymond and T.A. Scambos, 2006. Evidence for grounding-line fluctuations prior to the stagnation of Kamb Ice Stream, West Antarctica. J. Geophys. Res. 111 F01005, doi:10.1029/ 2005JF000355.. Conway, H., B.L. Hall, G.H. Denton, A.M. Gades, and E.D. Waddington. Polar ice sheets contain information about past climate 1999. Past and future grounding-line retreat of the . Science, 286(5438), 280-283. and past ice dynamics in their internal stratigraphy, Conway, H., G. Catania, C. F. Raymond, A. M. Gades, T. A. Scambos and which consists of isochronous layers of accumulated H. Engelhardt, 2002. Switch of flow direction in an Antarctic ice snow, subsequently deformed by ice flow. This stratigra- stream. Nature, 419, 465-467. phy has been widely imaged by ice-penetrating radars. Nereson, N.A. and C.F. Raymond,2001. The elevation history of ice streams When combined with continuous profiles of ice-sheet and the spatial accumulation pattern along the Siple Coast of West Antarctica inferred from ground-based radar data from three inter-ice- topography along flow lines as obtained with kinematic stream ridges. Journal of Glaciology, 47(157) 303-313. GPS, and measurements of ice motion and strain rate, Nereson, N.A., C.F. Raymond, R.W. Jacobel and E.D. Waddington. 2000. these layers reveal spatial and temporal patterns of snow The accumulation pattern across , West Antarctica, inferred from radar-detected internal layers. Journal of Glaciology, 46(152), accumulation (Nereson et al., 2000; Waddington et al., 75-87. in review) as well as histories of ice-sheet configuration Ng, F. and H. Conway, 2004. Fast-flow signature in the stagnated Kamb Ice and flow (Conway et al., 1999; Nereson and Raymond, Stream, West Antarctica. Geology, 32(6), 481-484. 2001; Conway et al., 2002; Ng and Conway, 2004; Raymond, C.F., G.A. Catania, N.A. nereson and C.J. van der Veen, 2006. Catania et al., 2005; 2006; Raymond et al., 2006). GPS Bed radar reflectivity across the north margin of Whillans Ice Stream, West Antarctica, and implications for margin processes. Journal of data is routinely used in glaciology studies, and is crucial Glaciology, 52(176), 3-10. to the advancement of our modern day understanding of Waddington, E.D., T.A. Neumann, M.R. Koutnik, H.P. Marshall, and D.L. ice dynamics. Morse. In review. Inference of accumulation-rate pattern from deep radar layers. Journal of Glaciology. Research supported by NSF OPP-9316807, OPP-9615347, OPP-9725882, OPP-9909518; OPP-0087144.

3-106 3-107 3-108 2008-2012 UNAVCO PROPOSAL: GEODESY ADVANCING EARTH SCIENCE RESEARCH Polar at all three sites, including at half-hourly intervals atthe at allthree sites,includingathalf-hourlyintervals monitored. Ablation wasmeasured atregular intervals where temperature, humidityandstream stagewere also logger andwasnotfarfrom theproglacial stream site panied by aminiature temperature andrelative humidity The five-minute intervals. lowermost stationwasaccom temperature, andrelative humiditywere monitored at where netradiation,windspeedanddirection, air stations were accompaniedby meteorological stations accumulation zone intheupperglacier. Thetwoupper was placedmid-glacier, andthethird wasplacedinthe be relatively stagnanticefrom thelastsurge,another was placedneartheterminusinwhatthoughtto order tomeasure thelocalicevelocities. One receiver installed alongalongitudinalprofile oftheglacier, in Yukon Territory, Canada.Three DGPS receivers were Kaskawulsh Glacier intheSt Elias Mountains, southwest tothe and climatesensitivityofasurge-typetributary gram wasestablishedin2006tostudythedynamics high temporalresolutions. field Anew research pro allows fortheiruse in measuringglaciericevelocity at The highaccuracyofdifferential GPS(DGPS)systems Gwenn Flowers » Chris Doughty » DGPS Measurement ofIce Motion onaPost-Surge AlpineGlacier Department of Earth Sciences,Simon ofEarth Department Fraser University, Canada Department of Earth Sciences,Simon ofEarth Department Fraser University, Canada - - points inarelatively periodoftimecompared short nique allowing forthecollectionofover 16,000data mapoftheglacier,a surface withtheeaseofthistech Real-time wasusedtocreate kinematic DGPSsurveying that area. the dominanceofmoulin-basedsupraglacialdrainagein between slow-flowing iceneartheglacierterminusand we are investigating whetherthere isacorrespondence ogy varies dramaticallyover thelengthofglacierand Thesupraglacialhydrolconditions attheglaciersurface. lution fluctuationsinflow ratethatmaybe relatedto examining themforsignsofdiurnalorotherhigh-reso midstation. We are currently processing thedataand This work was supported This workby grantsfrom wassupported theCanada Foundation for Innova future numericalmodelingstudies. and create digitalelevation modelsthatwillbeusedfor oftheglacier ice thicknesstocharacterize thegeometry combined withice-penetratingradarmeasurements of methods.Thesedatawillbe to traditionalsurveying Canada. tion andtheNatural SciencesandEngineering Research Councilof - - - - 3-109 Polar Tidal Modulation of Ross-Ice-Shelf Flow and its Relationship with Similar Modulation of Siple Coast Ice-Stream Flow

Doug MacAyeal » University of Chicago Kelly Brunt » University of Chicago

In June 2007, we will propose to the National Science Founda- tion a project that involves deploying 10 UNAVCO geodetic GPS receivers on the Ross Ice Shelf during the 2008-2009 field season. This project is designed to collect GPS data simultaneously along 2008-2012 UNAVCO PROPOSAL: GEODESY ADVANCING EARTH SCIENCE RESEARCH a transect between the front of the Ross Ice Shelf and regions up- stream of the grounding line of (formerly Ice Stream D) for a minimum of two months. Several GPS instru- ments will be configured for 12-month deployment to investigate seasonal effects and the “inverse barometer effect.” The latter effect produces sea-surface displacements comparable to tides, but over different time scales, and should have a modulating effect on ice- shelf flow. Our goal is to better understand the connection between the front of the Ross Ice Shelf and the ice streams, paying close attention to the grounding line region. More GPS data are needed to resolve this relationship. During the 2005-2006 Antarctic field season, geodetic quality GPS receivers were deployed at Nascent Iceberg for two weeks in an Figure 1. The spatial response of our preliminary model to a tidal forcing; purple circles represent McMurdo Station and effort to examine a diurnal, horizontal motion measured during a Nascent Iceberg; dark pink circles represent sites occupied three days period of the previous season. A similar diurnal, hori- by Anandakrishnan et al. (2003); gray triangles represent proposed GPS sites for this study. zontal motion has been observed at Bindschadler (D) Ice Stream (Anandakrishnan et al., 2003). The signal observed in the GPS data at the front of the ice shelf and in the ice stream prompted the generation of an ice shelf model aimed at describing its pos- sible causes. Preliminary model results indicate that the source of the signal is more complex than previously believed; results from two different types of forcing have generated two spatially different responses. Figure 1 is the response of our preliminary model to a tidal forcing. The purple circles represent McMurdo Station and Nascent Iceberg and the dark pink circles, labeled 0, 40, and 80, represent sites on Bindschadler (D) Ice Stream occupied by Anandakrishnan et al. (2003). Figure 2 is similar to Figure 1, however, in this case, the forcing mechanism is a pulse of the ice streams. The gray triangles on both figures represent the 10 proposed GPS sites for this study.

References Anandakrishnan, S., D. E. Voigt, R. B. Alley, and M. A. King (2003), Ice Stream D flow speed is strongly modulated by the tide beneath the Ross Ice Shelf. Geophys. Res. Figure 2. The spatial response of our preliminary model Lett., 30(7), 13-1. to ice stream pulsing; purple circles represent McMurdo Station and Nascent Iceberg; dark pink circles represent sites King, M. A., R. Coleman, and L. Nguyen (2003), Spurious periodic horizontal signals in occupied by Anandakrishnan et al. (2003); gray triangles sub-daily GPS position estimates. J. Geod., 77(1-2), 15-21. represent proposed GPS sites for this study. This work was supported formerly by I-190; NSF OPP-0229546.

3-108 3-109 3-110 2008-2012 UNAVCO PROPOSAL: GEODESY ADVANCING EARTH SCIENCE RESEARCH Polar few hundredfew years insouthern Alaska. processes actingontimescalesofonly a ofglacialisostaticrebound observation Icefield beganits retreat. Thisisadirect same timethemassive Glacier Bay shows thattheybeganupliftingatthe while thedatingoftheseshorelines peak GPSupliftratesinGlacier Bay, higher upliftsurrounding theregion of The raisedshorelines show apatternof the ongoinguplifttolessthan250yrs. to 5.5m,andconstrainedtheageof continuous totalsealevel changesofup These studiesdocumentedrapidand raised shorelines throughout theregion. ogy wasemployed toidentify anddate dendrochronology andgeomorphol measurements. Acombinationof found inanearlierstudyoftidegauge Glacier Bay area are similartothose of tidegaugemeasurements inthe 25 mm/yr)basedondecadalaverages tion ofregional sealevel rates(upto The recent magnitudeanddistribu Yakutat withpeakratesof32mm/yr. second centerofrapiduplifteast in Glacier Bay, andalsodelineateda show peakupliftratesof30mm/yr uplift (1 raised shoreline measurements oftotal changes (1 tide gaugemeasurements ofsea-level mm/yr, =±2.1mm/yr);2)18 vertical 1- tion arrayconsistingof74sites(average mented by 1)aregional GPSdeforma in southeastAlaskahave beendocu Extreme upliftandsealevel changes Keith A.Echelmeyer » Jeffrey T. Freymueller » Christopher F. Larsen» Roman JMotyka » PostObserving LittleIce AgeGlacier Rebound inSoutheast Alaska σ uncertainties: horizontal =±0.8 uncertainties: σ =±0.3m).TheGPSdata σ =±5mm/yr);and3)27 Geophysical Institute, University ofAlaskaFairbanks Geophysical Institute, University ofAlaskaFairbanks Geophysical Institute, University ofAlaskaFairbanks Geophysical Institute, University ofAlaskaFairbanks - - - - This work was supported This workby NSF wassupported Grants EAR-9870144,EAR-0229934,andEAR-040881. Larsen, CF, Motyka, RJ,Freymueller, JT, Echelmeyer, KA,Ivins, ER,2005.Rapidviscoelastic Larsen, CF, RJMotyka, JTFreymueller, KAEchelmeyer, andERIvins, 2004.Rapidupliftof Larsen, C.F., Freymueller, J. T., Echelmeyer, K.A.,andMotyka, R.J.,2003. Tide gaugerecords of References peak). (northern is 2mm/yr. Peak upliftratesare foundinGlacier Bay (southernpeak)andthe Yakutat Icefield Figure 1. Science Letters237,548–560. uplift insoutheastAlaskacausedby post-LittleIce Ageglacialretreat. andPlanetary Earth 1133. southern Alaskacausedby recent iceloss.Geophysical Journal International, 158, 1118– Geophysical Research, 108(B4),2216-2231. uplift alongtheNorthern Pacific-North American Plate Boundary, 1937to2001. Journal of GPS upliftrates(mm/yr).stationsare shown withred diamonds.Contourinterval 3-111 Polar Terminus Dynamics and Active Deformation of Proglacial Sediments at an Advancing Glacier: Taku Glacier, Alaska

Roman J Motyka » Geophysical Institute, University of Alaska Fairbanks Martin Truffer »Geophysical Institute, University of Alaska Fairbanks Keith A. Echelmeyer » Geophysical Institute, University of Alaska Fairbanks

Taku Glacier, an advancing former tidewater glacier in Alaska, has been actively pushing its 2008-2012 UNAVCO PROPOSAL: GEODESY ADVANCING EARTH SCIENCE RESEARCH proglacial sediments along part of its terminus over the last 50 years, producing so-called push moraines. The mobilization of these sediments, which were locally lifted more than 20 m above sea level by 2004, has happened episodically rather than steadily. The last major event of proglacial sediment deformation occurred in 2001, presumably caused by sliding along a basal detachment layer. Since then, most deformation has been localized within a few meters of the terminus, including impressive deformational features of the terminal ice, where slabs of ice, tens of centimeters in thickness, have undercut proglacial sediments and vegetation and lifted them up. Between 2002 and 2004, surface veloci- ties and horizontal displacements were measured across the terminus and in the proglacial push moraine area using GPS. Sediment displacement was highest between the end of March and mid- June. A decrease in displacement with distance from the terminus revealed that the sediments were deforming internally rather than along a basal de´collement. An observed wet clay-rich layer presumably acted as a major fault plane dur- ing the 2001 event.

Figure 1. Push moraine area in front of Taku Glacier. (a) Ortho- photo 2002 with terminus positions from 2001 to 2004. The contour lines represent the topography of the glacier surface near the terminus (m HAE). The toes of the bulges are shown with solid lines where based on measurements and with a dashed line where inferred. Points A–E refers to sites where different deformational features at the glacier-sediment interface were observed (note that A is 400 m west of figure boundary). (b) Map view with the contour lines of the glacier bed (m HAE). GPS2003 and GPS2004 are the References locations of continuously running GPS. The arrow labeled ‘‘trench’’ Kuriger, M Truffer, EM, RJ Motyka, and AK Bucki. 2006. Episodic reactivation of shows the location where a trench was dug, and T-T’’ and P-P’-P’’ large scale push moraines in front of the advancing Taku Glacier, Alaska. J. indicate the profiles discussed in the text. (c) Cross profile along Geoph. Res., 111(F1), doi:10.1029/2005JF000385. profile P-P’’. The thrust layer at bulge 1 and at the toes of the other bulges was observed. The basal de´collement is inferred from seismic Motyka, RJ and KA Echelmeyer, 2003. Taku Glacier on the move again: Active defor- refraction measurements (not shown here). mation of proglacial sediments. Journal of Glaciology, 10(164), 50-59. This work was supported by NSF Grant OPP-0221307.

3-110 3-111 3-112 2008-2012 UNAVCO PROPOSAL: GEODESY ADVANCING EARTH SCIENCE RESEARCH Polar front, resulting inatotallinearstrainduringthedeployment ofmore than3%.Thehorizontal flow speeds are tidally variation in flow speedfrom about25m/daynearthecalvingfront toabout4m/dayatalocation35kmbehindthe stage usingapressure sensorneartheendofHelheim Fjord for~3weeks duringtheexperiment.Initial results show a ing fieldvisitsinlate June, late July, andlate August, and we recorded thetidal operated several receivers dayseachjustbehindthecalving front forafew dur the GPSreceivers recorded atarateofleast1sample/5sec.In addition,we tions were deployed inlateJune 2006,and retrieved inlateAugust 2006.Allof receivers atnearby rock sitestohelpdefineastable reference frame.Thesta from apoint ~10kmbehindthecalvingfront. We alsoinstalledthree GPS largest outletglaciers,inanetwork spanninganupglacierdistanceof~25km occur. We installed16GPSreceivers onHelheim glacier, oneofGreenland’s bed, butlittleisunderstoodaboutthemechanismby whichtheearthquakes mayresultearthquakes from therapidslidingofglacialiceover theglacier land (Ekström etal.,2003). Teleseismic analysisindicatesthattheseglacial occurringatglaciersinAlaska,Antarctica, andGreen classofearthquakes new field asafunctionoftime.Theexperimentwasmotivated bythediscovery ofa onand around theglaciertomeasureof GPSinstruments theicedeformation periment atHelheim Glacier, EastGreenland, inwhichwe deployed anetwork During apilotgeophysicalex thesummer2006fieldseason, we undertook R. Forsberg » L. Stenseng » » S. A.Khan A. P. Ahlstrom » T. B.Larsen» P. Elósegui » G. S.Hamilton » L. A.Stearns » J. L.Davis » G. Ekström » M. Langer» M. Nettles » Helheim 2006:Geodetic Of Observations Glacier Flow Lamont-Doherty Earth Observatory ofColumbiaUniversity Observatory Lamont-Doherty Earth Lamont-Doherty Earth Observatory ofColumbiaUniversity Observatory Lamont-Doherty Earth Harvard-Smithsonian CenterforAstrophysics Institute forSpace Sciences,CSIC/IEEC, Danish National Space Center, Denmark Danish National Space Center, Denmark Lamont-Doherty Earth Observatory ofColumbiaUniversity Observatory Lamont-Doherty Earth Geological Survey ofDenmark andGreenland (GEUS),Denmark Danish National Space Center, Denmark Climate ChangeInstitute, University ofMaine Geological Survey ofDenmark andGreenland (GEUS),Denmark ClimateChangeInstitute, University ofMaine Figure 1. Project fundingwas provided by NSF-ARC 06-12609,NASANNG04GL69G, Zwally, H.J., W. Abdalati, T. Herring, K.Larson,J.Saba, andK.Steffen, melt-in Surface Joughin, I., Greenland louderasglaciersaccelerate,Science,311,1719-1720, 2006. rumbles Ekström, G.,M.Nettles, and V. C. Tsai, Seasonality andincreasing frequency ofGreenland Ekström, G.,M.Nettles, andG.A.Abers, Science, 302,622-624,2003. Glacial earthquakes, References areglacial earthquakes generatedandonthedynamicsofglacierflow. toplaceconstraints on theconditionsunderwhich cal observations will combineourgeodeticresults withseismologicalandglaciologi grounding line. We are currently processing thefullGPS dataset,and due tothewatertideindicatesprobable locationoftheglacier displacements spatialchangeinvertical modulated, andanabrupt NNG04-GK39G andothers. duced accelerationofGreenland ice-sheetflow, Science, 297, 218-222,2002. Science,311,1756-1758,2006. glacial earthquakes, Helheim 2006network geometry, overlain ona2001LANDSAT image. - - - - Figure 2. Replacing asolarpanelinJuly 2006. - - 3-113 Polar

Aircraft Based CO2 and Energy Fluxes on the Alaska North Slope

Dr. Walt Oechel » Global Change Research Group, San Diego State University Rommel Zulueta » Global Change Research Group, San Diego State University Joe Verfaillie » Global Change Research Group, San Diego State University

San Diego State University (SDSU) and the Global Change Research Group the ground speed from the airspeed. (GCRG) have been carrying out various aspects of ecological research on Long flight lines of 100 km or more Arctic ecosystems since the early 1970s. The GCRG is currently heading close to the ground (10 m AGL) and

a comprehensive study involving an integrated framework of multi-scale the need for high frequency data (up 2008-2012 UNAVCO PROPOSAL: GEODESY ADVANCING EARTH SCIENCE RESEARCH

aircraft and satellite remote sensing, micrometeorological and CO2 and to 50 Hz) make it necessary to do

CH4 flux measurements, and hydro-ecological process model simulations differential GPS corrections in post over a 350-km North-South transect spanning the dominant Arctic topo- processing. The availability of reli- graphic and land cover units of northern Alaska. An extensive soil moisture able, high speed (10 Hz) GPS data manipulation involving a 60-hectare flooding/draining experiment from the UNAVCO base stations in near Barrow, Alaska, is also underway. This research examines how biological Barrow and Atqasuk have greatly im- and physical processes interact to control carbon uptake, storage and release proved the precision and robustness in Arctic tundra ecosystems and how the self-organizing nature of these of the ground speed calculations. interactions varies across multiple spatial and temporal scales. Approximately 25% of the world’s soil organic carbon reservoir is stored at high northern latitudes in permafrost and seasonally-thawed soils, a region that is currently undergoing unprecedented warming and drying, as well as dramatic changes in human land use. Understanding how changes in annual and inter-an- nual ecosystem productivity interact and potentially offset the balance and stability of the Arctic soil carbon reservoir is of utmost importance to global climate change science. Since 1999, a light aircraft, the Sky Arrow, has been employed to extend the ground-based measurements over a larger area. The Sky Arrow 650TCN is an FAA certified aircraft from the Italian aircraft manufacturer, Iniziative Industriali Italiane (3I). One of the key components needed to measure

CO2 and energy fluxes from the Sky Arrow is wind speed. To calculate wind Figure 1. The current Alaska study area is indi- speed, the motion of the aircraft relative to both the air and the ground must cated by a rectangular overlay of AVHRR satellite be known as precisely as possible. Airspeed is calculated from a gust probe data. Permanent, ground-based measurements are located at Barrow, Atqasuk, and Ivotuk. The red with pressure sensors and a fluid dynamics model. Ground speed is calcu- dots indicate UNAVCO GPS base stations used lated with GPS attitude, accelerometers and post-processed differential GPS by SDSU aircraft operations. position and velocity measurements. Wind speed is calculated by subtracting

References Brooks, S., Dumas, E., and Verfaillie, J. (2001) Development of the SkyArrow Surface/Atmosphere Flux Aircraft for Global Ecosystem Research. American Institute of Aeronautics and Astronautics 39th Aerospace Sciences Meeting and Exhibit Proceedings, January 8-11, 2001. Oechel, W.C., Vourlitis, G.L., Verfaillie, J., Crawford, T., Brooks, S., Dumas, E., Hope, A., Stow, D., Boynton, B., Nosov, V. and Zulueta, R. (2000) A scaling approach for quantifying the net CO2 flux of the Kuparuk River Basin, Alaska. Global Change Biology, 6, 160-173. Brooks, S.B., Oechel, W.C., and Hastings, S.J., The New FAA Certified SDSU/NSF Sky Arrow ERA (Environmental Research Aircraft) for the Barrow Region 1999 Growing Season Fluxes and Remote Sensing. Arctic System Science Land-Atmosphere-Ice Interactions (ARCSS LAII) 1999 Science Workshop Record of the Meeting, Seattle, WA. March 11-13, 1999. Figure 2. Rommel Zulueta, a private pilot and Oechel WC, Hastings SJ, Jenkins M, Riechers G, Grulke N, and Vourlitis GL. 1993. Recent change of Ph.D. student, flies the SDSU Sky Arrow past arctic tundra ecosystems from a net carbon sink to a source. Nature. 361: 520-526. an eddy covariance tower on the tundra south of This work is supported by NSF grants OPP-0421588, OPP-0436177, and OPP-0119060. Barrow, Alaska.

3-112 3-113 3-114 2008-2012 UNAVCO PROPOSAL: GEODESY ADVANCING EARTH SCIENCE RESEARCH Polar structure. Figure 1. Fahnestock, M., T. Scambos,C.Shuman, D. R.Arthern, Winebrenner, and References This researchby NSF-OPPgrant0125570. wassupported approximately 2.5kmbefore becomingundetectable. amplitude decreased, dunespacingalsodecreased, to showedphology tonormalplateausurface thatasdune A nearby region showing atransitionfrom dunemor from 5to 9 meters,andmeanamplitudewas3.9km. of 090.Amplitudethedunesinstudysitevaried the icemotiontobe3.85+/-0.2m/year, atabearing near thecenterofdunefieldstudy region showed andhorizontalboth vertical dimension.Aseriesofpoles direction andtopositionGPRprofile tracesproperly in measure duneamplitudeinthewinddirection profile katabatic windinversion layer. GPSunitswere usedto that likelyformby astanding-wave interactionwiththe meters tall,2to10kmwavelength anti-dunestructures in centralEastAntarctica. Snow megadunesare 2to10 interseasonal icemotioninaregion oflargesnow dunes etrating radar(GPR)iceprofiles as well astomeasure We usedprecision GPSunitstoaccompanyground pen R. Bauer » T. A.Scambos» Topography andIce Motion ofAntarctic Snow Megadunes 27(22), 3719-3722. extreme atmosphere-ice interaction.Geophysical Research Letters R. Kwok, 2000.Snow megadunefieldsontheEastAntarctic Plateau: Aerial ofmegadunes,somecolor enhancementtohighlight view National Snow andIce Data Center, CIRES,University ofColorado National Snow andIce Data Center, CIRES,University ofColorado - - core (core isoff-profile, toback ofpage, by~300m). Thesegenerallycoincidewiththelow-densityinto thesubsurface. zones inthe Blue bandsindicateextensionofduneleefaces(glaze or‘freezer-burn’ faces) locations, core locations,andindicatinglow-density regions intheicecore. Figure 3. magenta lineindicatestheGPR/GPSprofile of Figure 3. Figure 2. GPR/GPS profile ofcentralmegadunefieldsite,showing AWS Landsat 7sub-sceneoftheMegadunes Field camparea. The solid 3-115 Polar The Effect of Permafrost Thawing and Thermokarst on Vegetation and Ecosystem Carbon Cycling in Alaskan Tundra

Edward A.G. Schuur » Department of Botany, University of Florida Hanna Lee » Department of Botany, University of Florida Jason G. Vogel » Department of Botany, University of Florida

Up to 450 billion tons of soil carbon (C) are estimated to be stored in high processes in these ecosystems and

latitude ecosystems (Gorham, 1991). This quantity represents almost a third cause feedbacks to climate change. 2008-2012 UNAVCO PROPOSAL: GEODESY ADVANCING EARTH SCIENCE RESEARCH of the soil C stored in terrestrial ecosystems globally, and is several orders of We are testing how microelevation

magnitude greater than current annual anthropogenic CO2 emissions. Lati- as caused by ground subsidence can tudinal gradients of soil C, field experiments, and laboratory incubations all be used as a predictive variable for show that soil C cycling in these northern ecosystems is likely to be strongly ecosystem carbon fluxes and patterns influenced by the effect of cold temperatures on rates of decomposition of of vegetation following permafrost soil organic matter (Kirschbaum, 2000). This ‘old’ soil C, climatically pro- thawing. We used high-precision tected from microbial decomposition in frozen or waterlogged soil, has been GPS to quantify centimeter scale accumulating in these ecosystems throughout the Holocene since retreat of differences in surface topography the last major ice sheets. and related these to measurements Climate change scenarios predict that the greatest magnitude of warming of ecosystem net carbon exchange will occur at high latitudes. This predicted warming is supported by observa- (Figure 1). Developing regression tional evidence over the last 25 years and is associated with warmer ground relationships allows us to scale mea- temperatures, permafrost (permanently frozen soil) thawing, and thermo- surements of carbon exchange across karst (ground subsidence as a result of ground ice thawing) (ACIA, 2004). larger spatial scales based on micro- Thermokarst has the potential to alter ecosystem C cycling by changing the topography. vegetation structure and growth rates, and by altering soil microbial decom- References position rates. Together, these changes can alter the balance of C cycling ACIA. 2004. Impacts of a warming climate: Arctic climate impact assessment. Cambridge University Press, pp. 146. Gorham, E. 1991. Northern peatlands: role in the carbon cycle and probable responses to climatic warming. Ecological Applications 1:182-195. Kirschbaum, M. U. F. 2000. Will changes in soil organic carbon act as a positive or negative feedback on global warming. Biogeochemis- try 48: 21-51. This work was supported by NSF Grants DEB- 0516326 and EAR-0223193.

Figure 1. Map showing microelevation of a permafrost study plot where ground is locally subsided. Scale is in units of meters to an arbitrary baseline.

3-114 3-115 3-116 2008-2012 UNAVCO PROPOSAL: GEODESY ADVANCING EARTH SCIENCE RESEARCH Polar This researchby NSFOPP-9819056,OPP-0136112,INT-9802764, wassupported NASA1215388. blue.html). geophys.washington.edu/Surface/Glaciology/PROJECTS/BLUE_GLAC/ Glacier intheOlympic Mountains of Western Washington (http://www. topographytoestimateannualmassbalancechangesofBlueof surface Kinematic GPSmethodshave alsobeenusedtomakerepeat measurements (Raymondetal.,2005). of theglaciersurface by acombinationofclimateandfeedbacksassociatedmainlywith lowering cier inPatagonia over decades.Acceleration thelastfew appearstobedriven measurements oficethickness,show acceleratingshrinkageof Tyndall Gla GPS measurements elevation andicemotion,combinedwith ofsurface steinsson etal.,2005;Howat etal,submitted). ing” systemunderglaciersevolves seasonally(Andersonetal.,2005;Thor then slow down againduringthepeakofsummermelting,as“plumb the transientnature offlow, asglaciersspeedupintheearlymeltseason,and Continuously recording GPSstationsonactive valley glaciershave revealed C.F. » Raymond H. Conway» E.D Waddington » GPS Measurements ofMotion andMass Balance ofAlpineGlaciers Dept of Earth andSpaceDept ofEarth Sciences,University of Washington Dept of Earth andSpace Dept ofEarth Sciences,University of Washington Dept of Earth andSpaceDept ofEarth Sciences,University of Washington - - - Thorsteinsson, T., E.D. Waddington, K. Matsuo Raymond, C.F., T.A. Neumann, E.Rignot,K. Howat, I.M.,S. Tulaczyk, E.D. Waddington, I. Anderson, R.L.,S.P. Anderson,K.R.Mac References sjokull, S-Iceland. Jokull 55,155-162. of flow, topographyandablation on Myrdal ka, I.Howat, andS. Tulaczyk. 2005.Survey Journal ofGlaciology, 51(173),239-247. Echelmeyer, A.Rivera andG.Casassa,2005. Geophysical Research. basal slidinglawforglaciers.Journal of Joughin, H.Bjornsson.submitted.Asimple 10.1029/2004JF000120. Geophysical Research,109(F3), F03005doi: sliding ofasmallalpineglacier. Journal of Strong feedbacksbetween hydrology and C.A. RiihimakiandM.G.Loso. 2004. Gregor, E.D. Waddington, S.O‘Neel, - - - 3-117 Polar Ice-Core Site Selection: Detection of Slow Motion and Low Strain Rates on Polar Ice Sheets

E.D Waddington » Dept of Earth and Space Sciences, University of Washington H. Conway » Dept of Earth and Space Sciences, University of Washington C.F. Raymond » Dept of Earth and Space Sciences, University of Washington

Greenland, Antarctica, and other ice caps retain

a memory of past climate in ice-core geochemi- 2008-2012 UNAVCO PROPOSAL: GEODESY ADVANCING EARTH SCIENCE RESEARCH cal time series. Preferred ice-core sites are at ice divides, where the annual motion is slow, but displacements are significant over the age of the climate record. Because these sites are far from fixed benchmark references, GPS measurements are essential. Because the ice is always moving, the ice-core paleoclimate records must also be correct- ed for displacements from deposition site to core site. To extract precipitation rates from annual-lay- er thicknesses in a core, cumulative vertical strain since deposition as snow must also be determined with ice-flow models constrained by modern ice- motion measurements. With UNAVCO assis- tance, we have conducted ice-motion surveys for all U.S. Antarctic Program deep ice-core projects since 1993, including Taylor Dome (Morse et al., in review; Waddington et al., in review), Siple Dome (Nereson et al., 1998a; 1998b), and the upcoming Western Divide core in central West Antarctica (Conway et al., 2005).

This research is supported by NSF OPP-9221261, OPP-9421644, OPP-9316807, and OPP-008714. References Conway, H., T.A. Neumann, S. Price, E.D. Waddington, D. Morse, K. Taylor, P.A. Mayewski, D. Dixon, E. Pettit, and E.J. Steig. Candidate drill site near the Ross-Amundsen ice divide, West Antarctica. Report presented to the Working Group Meeting, Madison, WI. March 2005. Morse, D.L., E.D. Waddington, and L.A. Rasmussen. In review. Ice Figure 1. Horizontal surface velocity field across the Western Divide in Central deformation in the vicinity of an ice-core site at Taylor Dome, West Antarctica. The velocity field was derived from repeat measurements of loca- Antarctica, and a derived accumulation-rate history, Journal of tions of 104 survey poles placed in the ice. Drilling of a new deep ice core at site Glaciology. WDC (S79.4676, W112.0859) will start in 2006-07. Nereson, N.A., C.F. Raymond, E.D. Waddington and R.W. Jacobel. 1998a. Migration of the Siple Dome ice divide, West Antarc- tica. Journal of Glaciology, 44(148) 632-652. Nereson, N.A., R.C.A. Hindmarsh and C.F. Raymond. 1998b. Sensi- tivity of the divide position at Siple Dome, West Antarctica, to boundary forcing. Annals of Glaciology, 27, 207-214. Waddington, E.D., T.A. Neumann, M.R. Koutnik, H.P. Marshall, and D.L. Morse. In review. Inference of accumulation-rate pat- tern from deep radar layers. Journal of Glaciology.

3-116 3-117 3-118 2008-2012 UNAVCO PROPOSAL: GEODESY ADVANCING EARTH SCIENCE RESEARCH Polar ated successfullyandiscurrently since late2000.Thesitehasoper collaborative siteatCapeRoberts at anOSU/USGS/LINZ/UNAVCO Continuous datahave beencollected for uptothree monthsperyear. been recorded inacampaignmode needs. In more recent years, datahas of thereceivers andtheirlargepower were limited capacity by the memory years ofthe project, dataquantities each australsummer. In thefirstfew Campaign datahave beencollected remote locationsaround theregion. tion ofseveral continuousstationsat The third phase involved the installa installed sitessouthward to82°S. of79°S,thesecond phase sites north three phases.Thefirstphaseinstalled project network was installedin of thewestern region. The models andexplore thetectonics used totestvarious isostaticrebound Land, Antarctica. Theratesare being reboundcrustal insouthern Victoria initiated in1996tomeasure ratesof Formation project (TAMDEF) was The TransAntarctic Mountains DE Stephanie Konfal » Terry Wilson » Mike Willis » TAMDEF: Measuring Neotectonic Motions intheAntarctic Interior Ohio State University Ohio State University Ohio State University - - - pole thatisessentiallythesameas Antarctic craton we derive an Euler the motionofsitesonstableEast GPS measurements. By inverting to belessnoisythanistypicalfor excellent andthedataare observed The agreement between packagesis package andtheBERNESEpackage. pleted usingboththePAGES Processing thedatahasbeencom related toourreference frame. region andtostrengthen thedata deflections ofEarth’s inthe crust to investigate theseasonalelastic tions in2003.Allsixsitesallow us were installedwithoutcommunica Three additionalcontinuoussites each dayusingasatellitemodem. UNAVCO, tosenddatatheU.S. has beenupgraded,withthehelpof way asCapeRoberts. Fishtail Point with aradiomodeminthesame 2001. Mount Fleming isequipped were by theUSGSin constructed in Boulder. Two additionalsites daily basistotheUNAVCO archive modem thatallows data uploadona equipped witha900MHzradio Tom James » Graeme Blick » HothemLarry » - Geological Survey ofCanada - LandInformation New Zealand U.S.Geological Survey Willis, Wilson andJames: Neotectonic Crustal References models. being compared tovarious rebound the entire region are positive andare Murdo Sound. Vertical motionsover tectonic strainoccurringover Mc motions reveals asmallamountof Spatial averaging oftheresidual that foundby Dietrich etal.,2004. southern Victoria Land,Antarctica. Figure 1. This workby NSFgrantnumber issupported Willis: The Crustal Response toChanging Tidal Willis, Wilson andJames: Acomparisonof Willis, Wilson andJames: Horizontal Mo Crustal Geophysical Union, Abstract. 2004 by the TAMDEF GPSNetwork American Motions intheAntarctic Interior Measured OPP 0230285 University. 2002. kanen Symposium inGeodesy. Ohio State Loads Imposed by aPinned Ice Shelf. Heis Géodynamique etdeSéismologie. 23.2003. Geodesy. CahiersduCentre Européen de sion: Separation Processes ofEarth by Space The State ofGPS Vertical Positioning Preci for Southern Victoria Land,Antarctica in Measured andModeled Bedrock Motions Joint Assembly, Abstract. 2003. bound Model Predictions. EGS/AGU/EUG of GPSMeasurements andPost-Glacial Re tions intheAntarctic interior:Comparison Example datasetfrom CapeRoberts, - - - - - 3-119 Polar Polar Earth Observatory Network (POLENET): Investigating Links between Geodynamics and Ice Sheets in Antarctica

Terry Wilson » Ohio State University and Byrd Polar A. Huerta » Penn State University Research Center A. Nyblade » Penn State University S. Anandakrishnan » Penn State University C. Raymond » Jet Propulsion Laboratory R. Aster » New Mexico Tech R. Smalley » University of Memphis M. Bevis » Ohio State University and Byrd Polar Re- D. Wiens » Washington University search Center R. Dietrich » Technical University of Dresden 2008-2012 UNAVCO PROPOSAL: GEODESY ADVANCING EARTH SCIENCE RESEARCH I. Dalziel » University of Texas Institute for Geophysics POLENET International Consortium L. Hothem » United States Geological Survey

The Polar Earth Observatory Net- work, or POLENET, is a recently proposed GPS/Seismic network, aimed at observing the Antarctic glaciologic and geologic system using a multidisci- plinary and internationally-coordinated approach. An observatory-style back- bone network of 18 co-located, contin- uously-recording GPS and broadband seismic sites across West Antarctica, as well as a two- to three- year GPS and seismic “International Polar Year (IPY)- only” deployment has been proposed (Figure 1). The co-location of GPS and seismic sensors provides important sci- ence synergies and significant logistical advantages. Cooperation of the GPS and seismic Principal Investigators,

UNAVCO, and the Incorporated Re- Figure 1. POLENET GPS and seismic site location map. Blue dots are backbone GPS sites, yellow search Institutes for Seismology (IRIS) dots are backbone seismic sites, red dots are both GPS and seismic backbone sites, green dots are will allow development and deploy- “IPY only” GPS sites, orange dots are “IPY only” seismic sites, and purple dots are GPS and/or seismic sites proposed or operated by international collaborators in the POLENET consortium. For ment of the next-generation power and more information regarding the POLENET proposal, please visit the following link: http://www. communication systems optimized for ipy.org/development/eoi/proposal-details.php?id=185 remote operations in extreme environ- ments. To refine estimates of recent ice mass from mass change can be modeled from continuous GPS measurements, change of the West Antarctic Ice Sheet, allowing for better estimates of Antarctica’s contribution to global sea we will measure isostatic rebound level change. Seismological investigations, integrated with results from with GPS, constrain mantle rheology the geodetic studies, will provide first-order constraints on geological/ through seismic studies, and dramati- tectonic parameters important for understanding ice sheet dynamics in cally improve continental-scale rebound West Antarctica. New seismic data will be used to develop high-resolu- model predictions used to correct ice tion seismic tomographic images, seismic receiver functions will be used mass trends derived from satellite al- to map the sediment thickness distribution beneath the ice sheet, and timetry and time-varying gravity. Both recordings of glacial earthquakes will help to constrain short-term slip the viscoelastic and elastic response events that are important for understanding ice sheet dynamics.

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