Drivers of change in East Antarctic ice shelves

Antarctica holds enough landlocked ice to raise the global sea level by nearly 60 m in the event of wholesale ice sheet collapse. In East Antarctica, the Aurora Subglacial Basin is drained by Totten Glacier and is one of the world’s largest and most rapidly-changing ice catchment systems. In recent decades, Totten Glacier has exhibited variability in its flow rate, mass balance, and ice thickness, each led by changes at the ice sheet margin. Totten Glacier dynamics are linked to processes in the Totten Ice Shelf, which buttresses the flow of grounded ice while being subjected to variable ocean forcing from below. Understanding the stability of the Aurora Subglacial Basin in a changing climate requires an understanding of how Totten Ice Shelf responds to changes in its environment. This dissertation investigates ice shelf processes on spatial scales of 1 km to 100 km, that act on sub-annual to decadal time scales. The independent roles of channelized basal melt and large-scale basal melt resulting from a variable supply of oceanic heat content are examined using surface elevation changes measured by airborne laser altimetry, satellite laser altimetry, and a new method of photometry applied to satellite images. A new method of satellite image template matching is also developed to understand ice shelf velocity response to several environmental forcing mechanisms. On the interannual time scale, Totten Ice Shelf is seen accelerating in response to nearby upwelling of warm circumpolar deep water that enhances basal melt rates. On the subannual time scale, Totten Ice Shelf exhibits winter slowdown as buttressing from seasonal landfast sea ice at the ice shelf front slows the flow of the glacier. These findings show that the Totten Glacier catchment is sensitive to changes in its environment, and may be susceptible to changes in the coastal wind stress projected for the 21st century.Geological Science

Seasonal dynamics of Totten Ice Shelf controlled by sea ice buttressing

Previous studies of Totten Ice Shelf have employed surface velocity measurements to estimate its mass balance and understand its sensitivities to interannual changes in climate forcing. However, displacement measurements acquired over timescales of days to weeks may not accurately characterize long-term flow rates wherein ice velocity fluctuates with the seasons. Quantifying annual mass budgets or analyzing interannual changes in ice velocity requires knowing when and where observations of glacier velocity could be aliased by subannual variability. Here, we analyze 16 years of velocity data for Totten Ice Shelf, which we generate at subannual resolution by applying feature-tracking algorithms to several hundred satellite image pairs. We identify a seasonal cycle characterized by a spring to autumn speedup of more than 100&thinsp;m&thinsp;yr−1 close to the ice front. The amplitude of the seasonal cycle diminishes with distance from the open ocean, suggesting the presence of a resistive back stress at the ice front that is strongest in winter. Springtime acceleration precedes summer surface melt and is not attributable to thinning from basal melt. We attribute the onset of ice shelf acceleration each spring to the loss of buttressing from the breakup of seasonal landfast sea ice.</p

Utilizing Science and Technology to Enhance a Future Planetary Mission: Applications to Europa

abstract: A thorough understanding of Europa's geology through the synergy of science and technology, by combining geologic mapping with autonomous onboard processing methods, enhances the science potential of future outer solar system missions. Mapping outlines the current state of knowledge of Europa's surface and near sub-surface, indicates the prevalence of distinctive geologic features, and enables a uniform perspective of formation mechanisms responsible for generating those features. I have produced a global geologic map of Europa at 1:15 million scale and appraised formation scenarios with respect to conditions necessary to produce observed morphologies and variability of those conditions over Europa's visible geologic history. Mapping identifies areas of interest relevant for autonomous study; it serves as an index for change detection and classification and aids pre-encounter targeting. Therefore, determining the detectability of geophysical activity is essential. Activity is evident by the presence of volcanic plumes or outgassing, disrupted surface morphologies, or changes in morphology, color, temperature, or composition; these characteristics reflect important constraints on the interior dynamics and evolutions of planetary bodies. By adapting machine learning and data mining techniques to signatures of plumes, morphology, and spectra, I have successfully demonstrated autonomous rule-based response and detection, identification, and classification of known events and features on outer planetary bodies using the following methods: 1. Edge-detection, which identifies the planetary horizon and highlights features extending beyond the limb; 2. Spectral matching using a superpixel endmember detection algorithm that identifies mean spectral signatures; and 3. Scale invariant feature transforms combined with supervised classification, which examines brightness gradients throughout an image, highlights extreme gradient regions, and classifies those regions based on a manually selected library of features. I have demonstrated autonomous: detection of volcanic plumes or jets at Io, Enceladus, and several comets, correlation between spectral signatures and morphological appearances of Europa's individual tectonic features, detection of &le;94% of known transient events on multiple planetary bodies, and classification of similar geologic features. Applying these results to conditions expected for Europa enables a prediction of the potential for detection and recommendations for mission concepts to increase the science return and efficiency of future missions to observe Europa.Dissertation/ThesisPh.D. Geological Sciences 201

Program and abstracts

Lunar and Planetary Institute, NASA's Mars Exploration Programconvener, Timothy Titus ; scientific organizing committee Timothy Titus ... [and others].PARTIAL CONTENTS: Modeling Aeolian Erosion Potential on Mars with the MRAMS LES -- Huygens Boundary Layer Data Explain the ~3 km Spacing of Titan's Dunes -- Active Dune Fields of the Navajo Nation, Southwestern United States -- Characteristic Time Scales of Dune-related Processes in Polar Regions of Mars -- Sand Composition of the Gran Desierto: A Terrestrial Analogue for Thermal Infrared Imaging and Spectroscopy Techniques

Geology and Physical Properties Investigations by the InSight Lander

Although not the prime focus of the InSight mission, the near-surface geology and physical properties investigations provide critical information for both placing the instruments (seismometer and heat flow probe with mole) on the surface and for understanding the nature of the shallow subsurface and its effect on recorded seismic waves. Two color cameras on the lander will obtain multiple stereo images of the surface and its interaction with the spacecraft. Images will be used to identify the geologic materials and features present, quantify their areal coverage, help determine the basic geologic evolution of the area, and provide ground truth for orbital remote sensing data. A radiometer will measure the hourly temperature of the surface in two spots, which will determine the thermal inertia of the surface materials present and their particle size and/or cohesion. Continuous measurements of wind speed and direction offer a unique opportunity to correlate dust devils and high winds with eolian changes imaged at the surface and to determine the threshold friction wind stress for grain motion on Mars. During the first two weeks after landing, these investigations will support the selection of instrument placement locations that are relatively smooth, flat, free of small rocks and load bearing. Soil mechanics parameters and elastic properties of near surface materials will be determined from mole penetration and thermal conductivity measurements from the surface to 3–5 m depth, the measurement of seismic waves during mole hammering, passive monitoring of seismic waves, and experiments with the arm and scoop of the lander (indentations, scraping and trenching). These investigations will determine and test the presence and mechanical properties of the expected 3–17 m thick fragmented regolith (and underlying fractured material) built up by impact and eolian processes on top of Hesperian lava flows and determine its seismic properties for the seismic investigation of Mars’ interior

Scientific results of the NASA-sponsored study project on Mars : evolution of volcanism, tectonics, and volatiles

The objectives of the project are to outline the volcanic and tectonic history of Mars; to determine the influence of volatiles on Martian volcanic and tectonic processes; and to attempt to determine the compositional, thermal, and volatile history of Mars from its volcanic and tectonic evolution. Available data sets were used to test general models of the volcanic and tectonic history of Mars.Sean C. Solomon, Virgil L. Sharpton, James R. Zimbelman.Martian Magmas and Mantle Source Regions: Current Experimental and Petrochemical Constraints / Holloway, J.R. -- Geophysics at Mars: Issues and Answers / Phillips, R.J. -- Martian Geologic "Revolutions": A Tale of Two Processes / Tanaka, K.L. -- Martian impact craters: Continuing analysis of lobate ejecta sinuosity / Barlow, Nadine G. -- Obliquity histories of Earth and Mars: Influence of inertial and dissipative core-mantle coupling / Bills, Bruce

Elevation change and mass balance of Svalbard glaciers from geodetic data

This thesis uses ground-based, airborne and spaceborne elevation measurements to estimate elevation change and mass balance of glaciers and ice caps on the Svalbard archipelago in the Norwegian Arctic. Remote sensing data are validated against field measurements from annual campaigns at the Austfonna ice cap. A new and more accurate DEM of the ice cap is constucted by combining SAR interferometry with ICESat laser altimetry. The precision of the DEM is sufficient to correct ICESat near repeat-tracks for the cross-track topography such that multitemporal elevation profiles can be compared along each reference track. The calculated elevation changes agree well with more accurate elevation change data from airborne laser scanning and GNSS surface profiling. The average mass balance of Austfonna between 2002 and 2008 is estimated to -1.3 ± 0.5 Gt y-1, corresponding to an area-averaged water equivalent elevation change of -0.16 ± 0.06 m w.e. y-1. The entire net loss is due to a retreat of the tidewater fronts. Earlier time periods are difficult to assess due to limitations in the amount and quality of previous elevation data sets. Other Svalbard regions have been precisely mapped by aerial photogrammetry, so the ICESat profiles from 2003-2008 can be compared with existing topographic maps and DEMs from 1965-1990. The mass balance for this period is estimated to -9.7 ± 0.6 Gt y-1 (or -0.36 ± 0.02 m w.e. y-1), excluding Austfonna. Repeat-track ICESat data are also analysed for the entire Svalbard yielding an average 2003-2008 mass balance of -4.3 ± 1.4 Gt y-1 (or -0.12 ± 0.04 m w.e. y-1) when tidewater front retreat is not accounted for. The most accurate elevation change estimates are obtained using all available ICESat data in a joint regression where surface slope and elevation change are estimated for rectangular planes that are fitted to the data along each track. The good performance of the plane method implies that it can also be used in other Arctic regions where accurate DEMs typically are not available

Workshop on Martian Gullies : theories and tests, February 4-5, 2008, Houston, Texas

Considering the potential significance of gullies to NASA's Mars program and spacecraft missions, it is important that hypotheses of gully origin be refined, constrained, and tested. The purposes of this workshop are: To provide a venue for scientific interchange on the ideas of gully origins; To formulate tests of these various ideas.Lunar and Planetary Institute, National Aeronautics and Space Administration, NASA Mars Exploration Programconvener, Allan Treiman ; scientific organizing committee Allan Treiman ... [and others]PARTIAL CONTENTS: Theories Without Fluids: Dry and Gases--Slope Steepness of Channels and Aprons: Implications for Origin of Martian Gullies -- Martian Gullies: Variety of Settings and Implications for Formation Processes -- Modeling Bright Gully Deposits' Formation in Hale Crater -- Drag Forces from Concentrated Salt Solutions in Martian Gullies -- Atacama Desert Mudflow as an Analog for Recent Gully Activity on Mars -- The Water Cycling and Secondary Ice-Salt Structures in the Gullies and Crater on Mars

The Twenty-Fifth Lunar and Planetary Science Conference. Part 1: A-G

Papers from the conference are presented, and the topics covered include the following: planetary geology, meteorites, planetary composition, meteoritic composition, planetary craters, lunar craters, meteorite craters, petrology, petrography, volcanology, planetary crusts, geochronology, geomorphism, mineralogy, lithology, planetary atmospheres, impact melts, volcanoes, planetary evolution, tectonics, planetary mapping, asteroids, comets, lunar soil, lunar rocks, lunar geology, metamorphism, chemical composition, meteorite craters, and planetary mantles