Glaciology Commons^™

Sensitivity Of The Relationship Between Antarctic Ice Shelves And Iron Supply To Projected Changes In The Atmospheric Forcing, Michael S. Dinniman, Pierre St-Laurent, Kevin R. Arrigo, Eileen E. Hofmann, Gert L. Van Dijken

CCPO Publications

Upward advection or mixing of iron-rich deep waters due to circulation changes driven by the rate of basal ice shelf melt was shown to be a primary control on chlorophyll a production in coastal polynyas over the Antarctic continental shelf. Here, the effects of atmospheric changes projected in 2100 on this relationship were examined with a 5-km resolution ocean/sea ice/ice shelf model of the Southern Ocean with different simulated dissolved iron sources and idealized biological uptake. The atmospheric changes are added as idealized increments to the forcing. Inclusion of a poleward shift and strengthening of the winds, increased precipitation, and …

On The Relative Importance Of Offshelf/Onshelf Drivers Of Variability In Mcdw Inventory On The Amundsen Shelf, Antarctica, Pierre St-Laurent, S. E. Stammerjohn, T. Maksym, R. M. Sherrell

Presentations

Ice shelves in the Amundsen Sea (west Antarctica) are melting rapidly and may raise global sea levels substantially over the coming century through reduced buttressing. The high basal melt rates are associated with the presence of warm modified Circumpolar Deep Water (mCDW) that intrudes across the continental shelf and melts the floating portion of the ice sheet from its base near the grounding zone. How much mCDW is present on the continental shelf (its volume inventory) is thus thought to be a key proxy for the year-to-year variability in ice shelf melt rates. Over the past decade, the literature has …

Sustained High Basal Motion Of The Greenland Ice Sheet Revealed By Borehole Deformation, Claudia Ryser, Martin P. Lüthi, Lauren C. Andrews, Matthew J. Hoffman, Ginny A. Catania, Robert L. Hawley

Dartmouth Scholarship

Ice deformation and basal motion characterize the dynamical behavior of the Greenland ice sheet (GrIS). We evaluate the contribution of basal motion from ice deformation measurements in boreholes drilled to the bed at two sites in the western marginal zone of the GrIS. We find a sustained high amount of basal motion contribution to surface velocity of 44–73% in winter, and up to 90% in summer. Measured ice deformation rates show an unexpected variation with depth that can be explained with the help of an ice-flow model as a consequence of stress transfer from slippery to sticky areas. This effect …

Ice Dynamics And Surface Glaciology Along Us Itase Traverse Routes In East Antarctica, Gordon Hamilton

University of Maine Office of Research Administration: Grant Reports

This award supports a series of field measurements that will improve our understanding of the East Antarctic ice sheet. The objectives of this project are to take advantage of the overland traverse logistics framework provided by US ITASE and to collaborate with other US ITASE investigators to calculate rates of ice sheet thickness change (mass balance) on domes, along elevation contours and along flow lines in East Antarctica using precise global positioning system methods. In addition, the variability (both spatial and temporal) in snow accumulation rates will be assessed using shallow ice cores and ground-penetrating radar profiling, and will provide …

Microstructural Evolution Of Fine-Grained Layers Through The Firn Column At Summit, Greenland, R. Lomonaco, M. Albert, I. Baker

Dartmouth Scholarship

We present a microstructural characterization of fine-grained layers from the top 90 m of firn from Summit, Greenland, performed using a combination of scanning electron microscopy techniques including secondary electron imaging, energy-dispersive spectroscopy and electron backscattered patterns, and X-ray microcomputed tomography. The impurities in the firn, both soluble impurities and dust particles, were found largely in the grain interiors. Both c- and a-axis pole figures do not show strong evidence of a preferred orientation of the grains even at the bottom of the firn column. The firn structure became increasingly anisotropic with vertical alignment in the top 3 m, probably …

Permafrost, Ice Sheets, And Sea Level, Beth Caissie, Julie Brigham-Grette

IPY STEM Polar Connections

Sea level rise and inhabited coastlines. Ice shelves and sea ice do not contribute to sea level but they can buttress the land ice sheets from rapid retreat. Causes of Sea Level Rise:

•Melting of glaciers, ice caps, ice sheets •Thermal expansion of sea water ••Small scale changes due to anthropogenic land water storage (damming rivers, over-pumping of water and fuels, wetland and forest destruction) •Relative changes in sea level due to tectonic movements (land subsidence or rebound)

A New Technique For Firn Grain-Size Measurement Using Sem Image Analysis, N.E. Spaulding, D.A. Meese, I. Baker, P.A. Mayewski

Dartmouth Scholarship

Firn microstructure is accurately characterized using images obtained from scanning electron microscopy (SEM). Visibly etched grain boundaries within images are used to create a skeleton outline of the microstructure. A pixel-counting utility is applied to the outline to determine grain area. Firn grain sizes calculated using the technique described here are compared to those calculated using the techniques of Gow (1969) and Gay and Weiss (1999) on samples of the same material, and are found to be substantially smaller. The differences in grain size between the techniques are attributed to sampling deficiencies (e.g. the inclusion of pore filler in the …

Climate Investigations Using Ice Sheet And Mass Balance Models With Emphasis On North American Glaciation, Sean David Birkel

Electronic Theses and Dissertations

This dissertation describes the application of the University of Maine Ice Sheet Model (UM-ISM) and Environmental Change Model (UM-ECM) to understanding mechanisms of ice-sheet/climate integration during ice ages. The UM-ECM, written by the author for this research, calculates equilibrium biome and snow/ice mass balance solutions for the globe based on modern input climatology and user-defined parameter values. The program was produced in conjunction with a National Science Foundation ITEST grant meant to seed inquiry-based classroom study of Earth systems using computer models. To that end, the UM-ECM serves as both a research and teaching tool. The model has a web-based …

Using Electron Backscatter Diffraction Patterns To Examine Recrystallization In Polar Ice Sheets, Rachel Obbard, Ian Baker, Katherine Sieg

Dartmouth Scholarship

The fabric of polycrystalline ice is typically described using the c-axis orientation alone, but this is insufficient for a full description of grain orientations in this hexagonal material. Electron backscatter diffraction (EBSD) provides full c- and a-axis orientation of individual grains, and is used here to study Greenland Ice Sheet Project 2 (GISP2) ice specimens from depths of 1551, 1642 and 1745 m. Complete orientation data are used to compare nearest-neighbor relationships to overall fabric and to differentiate between recrystallization mechanisms. Changes in orientation between grains and subgrains in GISP2 specimens were correlated with the appearance of grain boundaries on …

Is Mwp 1a Real And Could It Have Originated In The Northern Hemisphere In Response To Bolling Warming, Sean D. Birkel

Electronic Theses and Dissertations

Meltwater Pulse 1A (MWP 1A) is thought to have encompassed an abrupt rise in sea-level of 19 - 24 m ca. 14,000 calendar years B.P. The postulated rate of sea-level rise during the event was 24 - 50 mrnJyr. In contrast, the average rate of change during the overall glacial termination was 13 mrn/yr. Although MWP 1A is commonly accepted at face value, a compilation of all basic data points casts doubts on its validity. The Laurentide Ice Sheet (LIS) is commonly cited as the source of MWP 1A. Accelerated discharge of freshwater from the ice sheet could have weakened …