G31A-0634
The Influence of Laterally Varying Mantle Viscosity on Glacially Induced Surface Motion and Mass Redistribution
Lateral heterogeneities in the Earth's crust and mantle are demanded from seismic tomographic models, surface data and constraints derived from mantle dynamics. Nevertheless, such structural features are often neglected in GIA and only a 1D structure is assumed for the prediction of the earth's response to glacial loading as for the inversion of mantle viscosity. 1D model assumption is valid when focussing on vertical motions which are less sensitive to lateral variations in mantle structure but it is questionable for the prediction of horizontal motions. In this presentation, we discuss the consequences which arise for the deformational behaviour of the Earth's interior if we consider lateral viscosity variations. In particular, we will focus on variations in plate motions and the global gravity field which are induced by glacial loading.
G31A-0635
Shallow-Earth Thermomechanical Models of NW-Europe From GIA Constrained by GOCE Gravity Data
Current constraints on the process of glacial-isostatic adjustment (GIA) in Northern Europe are mainly provided by relative sea level data and GPS measurements. Due to a lack of resolving power in the shallow earth (down to about 200 km), these data sets only provide weak constraints on the shallow viscosity structure and thickness of the lithosphere. High-resolution gravity data, as expected from ESA's Gravity and Ocean Circulation Explorer (GOCE) satellite - due for launch October 5 2008 at the time this abstract was submitted -, are predicted to provide additional information on the shallow earth, especially the viscosity structure. However, mass inhomogeneities due to chemical and thermal anomalies are expected to interfere with the gravity signals induced by shallow low- viscosity structures. We test therefore if heat flow data and laboratory-derived creep laws for the crust (plagioclase feldspars) and shallow upper mantle (olivine) can provide additional information on the shallow earth. For this, we use a thermal model constrained by surface heat flow data and a mechanical model based on the commercially available finite-element package Abaqus. We show estimates of lithospheric thickness and viscosities that can be expected in the shallow earth, and generate predictions for Northern Europe using heat flow data and representative creep laws.
G31A-0636
Assimilation of GPS, GRACE, and Tide-Gauge Measurements into a GIA Model for Fennoscandia
Our ability to estimate long-term rates of sea-level change using tide gauges has long been hampered by the difficulty in separating land and ocean processes observed in the relative sea-level measurements. For example, despite the fact that the tide-gauge network in Fennoscandia is dense and long-running, it has not generally been used for estimation of eustatic sea-level rise due to the difficulty in removing the Glacial Isostatic Adjustment (GIA) signal from the estimated tide-gauge rates. In the past, tide-gauge rates have been "corrected" for GIA using either model predictions of the GIA or direct measurements of the land uplift from geodetic surveys. Both methods have their drawbacks, with the former requiring an accurate knowledge of the ice history (both spatial and temporal) and earth structure (e.g., mantle viscosity and lithospheric thickness) and the latter facing problems with limited data availability, difficulty in colocating geodetic stations with tide gauges, etc. In this study, we use an alternative approach that assimilates geodetic data into an a priori GIA model. One goal is to provide an updated GIA field for "correction" of the geodetic measurements. Assimilation of estimated rates from the tide-gauge data also means that we can simultaneously estimate a uniform rate of sea-level change for the region. Additional to the tide-gauge rates, we utilize rate estimates from continuous GPS sites in the BIFROST network and gravity data from the GRACE mission. We thus combine three independent data sets into our model. In this study we investigate the various contributions of these different data types, as well as discuss the utility of this approach for estimation of regional rates of sea-level rise.
G31A-0637
Glacial Isostatic Adjustment in Laurentia and Fennoscandia Observed by TOPEX/POSEIDON Radar Altimetry Over Land
A novel method to estimate vertical crustal motion from satellite altimetry over land has been developed and applied to Laurentia and Fennoscandia, where the observed vertical motion is dominated by the incomplete Glacial Isostatic Adjustment (GIA) process resulting from viscoelastic rebound of the Earth surface following the deglaciation since the last glacial maximum. 10-Hz land altimetry stackfiles are built over the study regions with waveform-retracked decadal (1992-2002) TOPEX/POSEIDON radar altimetry. In order to correct for the surface gradient error, the 90-m resolution C-band SRTM DEM and a 25-m Finnish DEM are used for Laurentia and Fennoscandia, respectively. The estimated vertical motion is compared with available solutions from GPS, tide gauge and altimetry combined solutions, and GRACE. The observations are further compared to several GIA model predictions, including the 3-D laterally heterogeneous RF3S20 model, to study the potential of constraining Earth's rheology, ice history, and the GIA models by assimilating land altimetry derived vertical motion in areas where other observations are lacking.
G31A-0638
Predicting present-day rates of glacial isostatic adjustment using a smoothed GPS velocity field for the reconciliation of NAD83 reference frames in Canada
Glacial isostatic adjustment following the last glacial period is the dominant source of crustal deformation in
Canada east of the Rocky Mountains. The present-day vertical component of motion associated with this
process may exceed 1 cm/y and is being directly measured with the Global Positioning System (GPS). A
consequence of this steady deformation is that high accuracy coordinates at one epoch may not be
compatible with those at another epoch. For example, modern precise point positioning (PPP) methods
provide coordinates at the epoch of observation while NAD83, the officially adopted reference frame in
Canada and the U.S., is expressed at some past reference epoch. The PPP positions are therefore
incompatible with coordinates in such a realization of the reference frame and need to be propagated back to
the frame's reference epoch. Moreover, the realizations of NAD83 adopted by the provincial geodetic
agencies in Canada are referenced to different coordinate epochs; either 1997.0 or 2002.0. Proper
comparison of coordinates between provinces therefore requires propagating them from one reference
epoch to another. In an effort to reconcile PPP results and different realizations of NAD83, we empirically
represent crustal deformation throughout Canada using a velocity field based solely on high accuracy
continuous and episodic GPS observations. The continuous observations from 2001 to 2007 were obtained
from nearly 100 permanent GPS stations, predominately operated by Natural Resources Canada (NRCan)
and provincial geodetic agencies. Many of these sites are part of the International GNSS Service (IGS) global
network. Episodic observations from 1994 to 2006 were obtained from repeated occupations of the
Canadian Base Network (CBN), which consists of approximately 160 stable pillar-type monuments across the
entire country. The CBN enables a much denser spatial sampling of crustal motions although coverage in the
far north is still rather sparse. NRCan solutions of the continuous GPS data were combined with those from
other agencies as part of the North American Reference Frame (NAREF) effort to improve the reliability of
the results. This NAREF solution has then been combined with our CBN results to obtain a denser velocity
sampling for fitting different types of surfaces in a first attempt to determine a continuous GPS velocity field
for the entire country. Expressing this velocity field as a grid enables users to interpolate to any location in
Canada, allowing for the propagation of coordinates to any desired reference epoch. We examine the
accuracy and limitations of this GPS velocity field by comparing it to other published GPS velocity solutions
(which are all based on less data) as well as to GIA models, including versions of ICE-3G, ICE-5G and the
recent Stable North America Reference Frame (SNARF) model. Of course, the accuracy of the GPS velocity
field depends directly on the density of the GPS coverage. Consequently, the GPS velocity field is unable to
fully represent the actual GIA motion in the far north and tends to smooth out the signal due to the spatially
sparse coverage. On the other hand, the model performs quite well in the southern parts of the country
where there is a much greater spatial density of GPS measurements.
http://www.naref.org/
G31A-0639
Glacio-isostatic Adjustment Modeling of new Relative Sea-level Observations From the Northern Cascadia Subduction Zone, British Columbia, Canada
Late-glacial sea-level curves located above the Cascadia Subduction Zone (CSZ) in southwestern British Columbia show that glacio-isostatic adjustment (GIA) was rapid when the Cordilleran ice sheet collapsed in the late Pleistocene. GIA models developed to explain the sea-level observations employ an ice sheet model modified from previous studies. The Earth models vary radially and feature an elastic lithosphere and a linear Maxwell viscoelastic mantle with the VM2 viscosity structure in the deeper parts of the mantle. The thickness and viscosity of a laterally homogeneous asthenosphere are systematically varied to find the combinations that best explain the sea-level observations. The observations can be equally well fit across a wide range of asthenospheric thicknesses, provided that the asthenospheric viscosity is varied from 3 x 1018 Pa s for a thin (140 km) asthenosphere to 1019 Pa s at 220 km thickness to 4 x 1019 Pa s for a thick (380 km) asthenosphere. The sea-level observations are located in the CSZ forearc above the stagnant mantle wedge. Thus, the model viscosity values probably pertain largely to the viscosity of the oceanic mantle beneath the subducting Juan de Fuca plate, although a contribution from the hot, low- viscosity arc and backarc continental mantle is also likely. Effective viscosities for the upper mantle due to tectonics (subduction) were computed using the strain-rates and temperatures of a geodynamic model of the CSZ and a wet-olivine power-law rheology. The effective viscosities agree well with GIA model viscosities of 1019 Pa s or less, corresponding to an asthenosphere of one or two hundred kilometers thickness. Models of the megathrust earthquake cycle at young subduction zones that feature oceanic mantle asthenosphere viscosities larger than about 1019 Pa s need to be modified to incorporate the new constraints provided by the GIA modeling. An implication for megathrust earthquake models of a reduction in oceanic asthenospheric viscosities is that it may require significant deep afterslip on the subduction interface to explain observations of rapid postseismic uplift following great earthquakes. Present-day vertical crustal motion predicted by the GIA models shows rates of a few tenths of a millimeter per year, consistent with previous analyses.
G31A-0640
Effects of Present-Day Ice Melting on the Geodetic Measurements in Southeast Alaska
It is known that the southeast Alaska (SE-AK) is undergoing a rapid land uplift, which is considered to be mainly due to the effect of melting of past ice, especially in the last two hundred years after the little ice age (LIA). The crustal deformation caused by the post-glacial rebound (PGR) has been clearly detected by GPS and tidal gauge measurements and modeled (Larsen et al., 2004 and 2005). On the other hand, it is considered also that the observed uplift rate is affected by the present-day ice melting (PDIM), which is considered to be the effect of recent global warming (Larsen et al., 2005; Sato et al., 2006). The displacement measurements provide us useful information to evaluate the ice-melting rate and to discuss the viscosity of the earth. However, usually, it is difficult to separate the uplift rate due to the long- term viscous response of the earth by only using displacement observations, because the two effects (i.e. the elastic and viscous deformations) are mixed in the observed data. Related to this problem, Wahr et al. (1995) demonstrated a method to separate the viscous contribution from the observed data by collocating position and gravity measurements. Considered this, since 2006, we, a joint team of Japanese and U.S. researchers are carrying out the absolute gravity (AG) measurements once a year adding to the temporal and continuous GPS observations in SE-AK. Combining the AG measurements and GPS measurements is useful because the attraction part of gravity measurement is sensitive to a mass change of the present-day ice melting, while the past-ices should have no effect to the attraction part of the observed gravity change. In this context of the discussion, precise numerical estimation of the PDIM effect is important (Sato et al., 2007). Based on the two kinds of DEM (Digital Elevation Model), i.e. one is from the 2000 Shuttle Radar Topography Mission (SRTM) and other is that from air photo dating data which were obtained in the period of 1948-1987, Larsen et al. (2007) estimate the volume changes in SE-AK and adjoining area of Canada. Their results show that the glacier surface elevations lowered by a rate of about -1.1 m/yr as an average over the area of 14,580 square km glacier-covered area. According to the Farrell’s method (1972) and using this thinning data, we have evaluated the effects of PDIM on our AG and GPS measurements in SE-AK. The gravity effect consists of two parts (i.e. the attraction and the effect of elastic deformation). Different from the elastic part, the computation results for the attraction part are sensitive to the assumed mean thickness of the glaciers and the elevation of glacier mass. Therefore, although the computation is still preliminary one, our results indicate that, the maximum gravity effect for our 6 AG sites is -1.4 micro Gal/yr as sum of the two parts mentioned above. Compared with the observed gravity rate of -5 micro Gal/yr, we may say that the PDIM effect is not negligible. On the other hand, for the vertical displacement, it is estimated at the order of +2.4 mm/yr at the most. Therefore, compared the observed maximum uplift rate of +30 mm/yr, the magnitude of the PDIM effect is not so large.
G31A-0641
Geodetic measurements for monitoring rapid crustal uplift in southeastern Alaska caused by the recent deglaciation
Glaciers at high latitudes are considered to be extremely sensitive to climate change and thus monitoring of glaciers is a clue to evaluate the future effect of global warming and the related phenomena. Ice mass changes also produce a time-variable surface load and give us useful data to investigate subsurface structure of the earth, especially to constrain the flow characteristics of the mantle. Larsen et al. [EPSL05] have extensively studied on vertical crustal movement in SE Alaska to reveal the world's fastest glacial isostatic uplifting, which can be attributed to the response associated with deglaciation. Displacement data, however, can only be used to constrain the sum of the elastic response to present-day ice melting (PDIM) and the viscoelastic one to past changes in ice. A Japan-US joint research project, ISEA (International geodetic research project in SouthEast Alaska), was initiated in 2005 to add new geodetic data and to refine the viscoelastic model derived by the previous studies. Absolute gravity data have been acquired at the five sites in the stdudy area using a Micro-g LaCoste absolute gravimeter, FG5#111. At each site data were collected over a 48~62 hour period. The long-term variation in absolute gravity at 2 stations, HNSG and BRM, where the measurements were performed in 1987 by Sasagawa et al. [JGR89] demonstrates rapid gravity decrease with rates of -4.4 micro-gal/yr, and -3.0 micro-gal/yr, respectively, and can be attributed to uplifting and mass-redstribution. ISEA supplements pre-existing continuous GPS (CGPS) stations operated by the U.S. Coast Guard (USCG) and the UNAVCO (Plate Boundary Observatory, PBO) and improves the spatial coverage in and around Glacier Bay. The time series of the site coordinates obtained for Queen Inlet (QUIC), which locates close to a zone of maximum uplift, shows obvious uplifting, even though there are long- term gaps because of an antenna cable trouble in 2006 and power outage in 2008 causing rather obscure temporal variation. Taking the differences between the vertical coordinates in July-October in 2006 and those in 2008, the uplifting rate for this period ranges about 10-20 mm/yr, which is much smaller than the previous study [Larsen et al., EPSL05]. It may be related to heavy snow accumulation in the winter of 2006-2007 around the study area and left for the further investigation.
G31A-0642
GPS-Constrained Glacial Isostatic Adjustment Models for West Antarctica: Implications for Ice Sheet Mass Balance Measurements
Data from the Gravity Recovery and Climate Experiment (GRACE) have recently been used to infer mass change rates of the Antarctic ice sheet. A leading source of uncertainty in interpretation of the GRACE measurements is the poorly constrained Glacial Isostatic Adjustment (GIA) correction. We use the recent IJ05 ice sheet history to load a suite of over 1000 different two-layered, laterally-homogeneous spherical Earth models and compare the uplift rate predictions to a small number of in-situ Global Positioning System (GPS) measurements from West Antarctica. Once the best-fit models are found, the gravity contribution is determined. The best-fit model features a 40-km thick elastic lithosphere with a mantle viscosity of 2 x 1020 Pa s above the 640 km seismic discontinuity and a viscosity of 1022 Pa s in the lower mantle. The second best fit to the GPS shows an even weaker mantle profile with an upper mantle of 1019 Pa s and a lower mantle of 3 x 1021 Pa s. These weak, thin lithosphere models are realistic for West Antarctica. It is underlain by the West Antarctic rift system and is considered analogous to the Basin and Range province of the western USA. Active volcanoes along the flank of the West Antarctic rift system, and possibly beneath the West Antarctic ice sheet, suggest a weak, warm upper mantle. This view also is supported by global seismic tomography models. Our GIA predictions, produced using low viscosities and thin lithosphere, suggest crustal uplift rates of between 4 and 24 mm/yr for much of the coastal regions of West Antarctica. These uplift rates are slightly larger in magnitude than those predicted in previous studies. The apparent gravity signal caused by GIA is doubled when using the best-fit rheology and quadrupled when using the second-best-fit rheology compared to Chen et al. (2006). When the GIA 'correction' is removed from the GRACE data the results become correspondingly more negative, indicating that ice mass loss from West Antarctica is occurring at a more rapid rate than previously estimated
G31A-0643
Antarctic Ice Sheet Mass Variation Using GRACE Satellite Gravity Data- Removal of Atmospheric Correction Error and Recalculation of the Interannual Mass Trend-
An accurate knowledge of Antarctic ice sheet mass trend is one of the important issues for the study of global scale sea level change. GRACE has provided information on the temporal mass variations on the Earth in the form of monthly gravity field solutions, and has enabled us to monitor the ice sheet mass changes directly. However, GRACE cannot distinguish between the various sources of the mass variations. It is well known that Post Glacial Rebound (PGR) also causes large mass trends in Antarctica. To estimate Antarctic ice sheet mass change, PGR mass trend should be estimated and subtracted from the GRACE’s mass trend. One of the methods to estimate PGR mass trend is to compare elevation change data from ICESat satellite altimetry with mass variation data from GRACE satellite gravimetry. Using GRACE and ICESat data, we previously estimated PGR mass trend in Antarctica and obtained agreeable value for some large mass trend areas. However, because of large errors and limited time span of both GRACE and ICESat data sets, it is difficult to obtain reliable value for small mass trend areas. One of the errors which give serious effect on the small mass trend area in Antarctica is modeling error of short time period atmospheric variation. In the GRACE monthly data processing, ECMWF operational objective analysis data is routinely used to remove atmospheric pressure effect for the purpose of the de- aliasing of the monthly solutions. However, the atmospheric model error is relatively large in Antarctica compared to other areas mainly because of small number of the reliable ground and satellite data. In this study, to improve the ice sheet mass estimation of small mass trend area in Antarctica and to obtain more reliable continental scale Antarctic ice sheet mass variation, we estimated and corrected the atmospheric modeling error in the GRACE monthly solutions. We firstly investigated correlation between GRACE monthly gravity field solutions in Antarctica and monthly average of atmospheric pressure, and removed the error of the atmospheric monthly components from the GRACE monthly solutions. We assumed that the obtained GRACE’s residual data can be mainly explained by the 3 following components: i.e. ice sheet mass variation, PGR mass trend and aliasing error from insufficient removal of short period atmospheric components. Spatial and Temporal correlation between the residual GRACE data and these 3 components are investigated and estimated atmospheric aliasing error by the least squares method. We used ICESat ice sheet elevation data obtained for the calculation. Using the corrected monthly solutions, we calculated Antarctic ice sheet mass trend and PGR mass trend, and assessed how much the uncertainty of the Antarctic ice sheet mass trend is improved by the correction.
G31A-0644
Ocean Loading Effects on Predictions of Uplift and Gravity Changes due to Glacial Isostatic Adjustment in Antarctica
The effect of relatively high fidelity regional ocean loading in Antarctica on predicted rates of glacial isostatic adjustment (GIA) is quantified for the IJ05 surface loading history. The recently developed IJ05 model was designed to incorporate the growing compilation of geological and glaciological constraints on the evolution of the Antarctic ice sheet that has emerged in the last decade. IJ05 defines its surface load history relative to the present-day surface load, rather than specifying an absolute, or total, loading history. Thus, IJ05 implicitly includes the 'water dumping' effect described by Milne, and the addition of explicit ocean loading only introduces a perturbative change to the calculated response. As a consequence, the changes in predicted GIA rates when regional ocean loading is included are greatly muted compared to the widely used ICE-3G model, which specifies an absolute load history. For example, the IJ05 uplift and gravity rates change at most by +1 mm/yr and +0.25 cm/yr water equivalent for Ivins and James' [2005] "average" viscosity structure (1021, 1022, and 8×1022 Pa s for the upper, middle and lower mantle, respectively). The changes for ICE-3G have much larger magnitude at -8 mm/yr and -3 cm/yr w.e., respectively. Thus, the conclusions of previous studies that used IJ05 predictions with implicit ocean loading are relatively robust. Future calculations, however, will include the full regional ocean loading effect in order to provide the best possible GIA correction for analysis of GRACE observations to determine present-day Antarctic mass balance and for interpretation of the growing body of GPS crustal motion observations.
G31A-0645
Mass transfer and global sea-level change during the last 100 years: GIA and cryospheric sources incorporating GRACE
Nominal theory of GIA-induced long-term polar motion now explain ~ 1/5 2/5th's of the polar wander signal observed during the 20th Century (e.g. Mitrovica et al. EPSL, 243, 390-399, 2006). On continents with glaciers and ice sheets, InSAR, feature tracking, on-ice GPS motion surveys, altimetry, elastic rebound all may now be used to complement more traditional glaciological methods for assessing mass balance of the cryosphere, including ice caps and mountain glaciers. Space gravimetry data generated by the Gravity Recovery and Climate Experiment (GRACE) now provide a relatively short time-window (5+ years) for studying intra-decadal ice mass gain and/or loss, with low-resolution, but spatially comprehensive coverage above 45° in latitude. The GRACE estimates for trend are in currently at -280 ± 90 Gt/yr (or mass contribution to sea-level of 0.79 ± 0.25 mm/yr). Both glacier and ice sheet loss may be gaining in pace, though on a century-long time scale this remains in debate. Polar motion observations show a mean linear drift of the pole of 3.51 ± 0.01 mas/yr towards W° 79.2 ± 0.2 longitude with respect to the mean pole fixed in geodetic latitude and longitude (Gross and Vondrak, 1999). We resurvey 20th and 21st century glacier balance, integrate ice sheet balances from data during 1995-2008, couple these observations to semi-empirical relations between known long-term atmospheric temperature changes and glacier lengths, and use the spatially comprehensive and GIA-corrected GRACE observations of the mass change of polar and sub-polar cryosphere. Self-consistent models are derived for GIA and cryospheric- induced polar wander and low-degree zonal gravity coefficient trends. A self-consistent model has an IJ05- modified ICE-5G load history, incorporates recently reassessed anthropogenic sea-level related water impoundment (Chao et al. Science, 320 212-214, 2008), has mantle viscosity increasing with a linearly-to- quadratically depth-dependence and has an average ice sheet imbalance of -140 ± 80 Gt/yr and a time- averaged mass loss of temperate glaciers and their proximal hydrological systems of about -125 ± 50 Gt/yr during the 20th Century.
G31A-0646
Constraining Models of Postglacial Rebound Using Space Geodesy
We are using observations from five space techniques (VLBI, SLR, GPS, DORIS, and GRACE) to (1) determine the character of Earth's viscous response to unloading of the ice sheets 5 to 20 thousand years ago, and (2) constrain models of postglacial rebound determined primarily from Holocene estimates of relative sea level and geophysical observations of Earth's spin and shape. The horizontal estimates of site velocity are constraining the postglacial rebound model. Places along the margins of the former Laurentide and Fennoscandia ice sheets are moving horizontally away from the centers at about 1 millimeter per year, at the speed predicted by the model of Peltier [1994], but significantly slower than the speeds predicted by the models of Peltier [1996] and Peltier [2004]. The parts of Antarctic, Eurasian, and North American plate interiors neither beneath nor along the margins of the former ice sheets are hardly deforming at all, allowing the angular velocity of the plates to be estimated meaningfully. The vertical estimates of site velocity are also constraining the postglacial rebound model. Algonquin Park (Ontario) is rising at 2.5 millimeters per year and Yellowknife (Northwest Territories) at 6 millimeters per year, constraining the thickness of the Laurentia ice sheet 20 thousand years ago. The eastern and central United States is subsiding at 1 to 2 millimeter per year, at about the speeds predicted by the models of Peltier [1994], Peltier [1996], and Peltier [2004]. We are attempting to modify the ice sheet thickness, mantle viscosity, and elastic lithospheric thickness in the model to fit all geodetic and geologic observations. We are furthermore quantifying the uncertainty in estimates of vertical velocity due to uncertainty in the velocity of Earth's center.
G31A-0647
Geodetic Observation-level Modelling for the Measurement of GIA
Modern space geodetic techniques, e.g., the Global Navigation Satellite Systems (GNSS), enable us to observe vertical velocities of station positions globally. Thus, they are important tools for separating the Glacial Isostatic Adjustment (GIA) from the ice sheet mass balance from missions like the Gravity Recovery and Climate Experiment (GRACE). However, special care has to be taken to perform optimal observation- level modelling and to apply methods for mitigating systematic errors. In this presentation we provide an overview of models needed for the analysis of space geodetic techniques and their impact on the determination of station coordinates and velocities in areas where GIA takes place. For example, we show the peculiarities of troposphere delay models and atmosphere loading corrections in Antarctica, because in that region tropospheric activity is very localised (and perturbing signatures are similar in estimated vertical path delay and vertical displacement). Other areas of interest are ocean loading corrections, thermal expansion of VLBI (or GNSS) monuments, technical aspects such as solution sensitivity to different GNSS receivers and antenna phase centre models (as well as site specific phase centre perturbations), or satellite orbit modelling.
G31A-0648
Advances in Remote Autonomous Geodetic GPS Data Acquisition in the International Polar Year
Continuous GPS data are required in order to provide major advances in the understanding of ongoing polar
ice mass change. Glacial Isostatic Adjustment (GIA) is the largest source of uncertainty for the Gravity
Recovery and Climate Experiment (GRACE). GIA is currently observed with 50 bedrock continuous GPS sites
in Antarctica and around Greenland. Non-linear ice dynamics of the ice sheet margins also have major
ramifications for both ice mass loading and sea level change. Data recorded at GPS stations on glaciers and
ice streams are providing new insight into the processes responsible for rapid ice mass changes. These data
are acquired in remote and extreme environments where logistical constraints require that the equipment
can operate unattended for several years. Science initiatives during the International Polar Year are
providing an unprecedented scale of continuous data collection from high latitude autonomous GPS stations.
We discuss the methodologies, hardware, and performance of new systems and networks.
http://www.unavco.org/polartechnology