Frank Carsey

Subglacial conditions during and after stoppage of an Antarctic Ice Stream: Is reactivation imminent?

Borehole observations from the base of the West-Antarctic Ice Sheet (WAIS) reveal the presence of a 10 to 15 m thick accretionary basal ice layer in the upstream area of Kamb Ice Stream (KIS). This ice layer has formed over a time of several thousand years by freeze-on of subglacial water to the ice base and has recorded during this time basal conditions upstream of its current location. Analysis of samples and videos sequences from boreholes drilled to the bottom of KIS confirms that KIS-stoppage was due to basal freeze-on and that relubrication of the ice stream is well underway. These results further suggest that ice stream cyclicity may be shorter than expected (1000s of years) and that a restart of KIS may be imminent within decades to centuries.

NASA/JPL Tumbleweed polar rover

The Tumbleweed rover, currently under development at the Jet Propulsion Laboratory (JPL) in Pasadena, California, is a large, windblown, inflated ball, which carries an instrument payload in its interior. Such rovers offer an effective and simple means of gathering data over large spatial extents of Earth, Mars, and other solar system bodies. Tumbleweeds could prove to be a safe and economical way of deploying instruments such as a ground penetrating radar or a magnetometer in numerous hostile environments. The latest version of the rover was recently deployed in Greenland, where it completed a more than 130km autonomous traverse across an ice sheet. Communicating via the Iridium satellite network, the rover in question successfully and reliably relayed live GPS, temperature, and pressure data to a ground station at JPL for nearly ten days. The follow-on rover is currently being readied for a traverse from the South Pole to the coast of Antarctica some 2000km away. The Antarctic test is set to take place in February of 2004 and will serve to verify Tumbleweed as an effective means of harvesting data in extreme and remote settings.

A borehole camera system for imaging the deep interior of ice sheets

The design and first deployment is described for the Jet Propulsion Laboratory-California Institute ofTechnology ice borehole camera system for acquisition of down-looking and side-looking images in a borehole made by a hot-water drill. The objective of the system is to acquire images in support of studies of the basal dynamics and thermodynamics of West Antarctic ice streams. A few sample images, obtained during the 2000/01 Antarctic field season, are shown from the basal layers of Ice Stream C.

Review and status of remote sensing of sea ice

The status of obtaining geophysical observations through the interpretation of satellite data over sea ice is discussed. It is pointed out that the community working in this area has grown in size and sophistication over the last decade, that the connection between microscopic properties of ice and its microwave behavior is now being understood, and that a good deal of accurate satellite-derived information on sea ice can now be obtained. Areas of ongoing, as well as needed, work are outlined, especially in the understanding of first-year and old-ice microwave properties, and it is pointed out that the efficient advance of remote sensing will require more active participation of scientists focused on in situ studies. >

Borehole imagery of meteoric and marine ice layers in the Amery Ice Shelf, East Antarctica

A real-time video camera probe was deployed in a hot-water drilled borehole through the Amery Ice Shelf, East Antarctica, where a total ice thickness of 480 m included at least 200 m of basal marine ice. Down-looking and side-looking digital video footage showed a striking transition from white bubbly meteoric ice above to dark marine ice below, but the transition was neither microscopically sharp nor flat, indicating the uneven nature (at centimetre scale) of the ice-shelf base upstream where the marine ice first started to accrete. Marine ice features were imaged including platelet structures, cell inclusions, entrained particles, and the interface with sea water at the base. The cells are assumed to be entrained sea water, and were present throughout the lower 100-150m of the marine ice column, becoming larger and more prevalent as the lower surface was approached until, near the base, they became channels large enough that the camera field of view could not contain them. Platelets in the marine ice at depth appeared to be as large as 1-2 cm in diameter. Particles were visible in the borehole meltwater; probably marine and mineral particles liberated by the drill, but their distribution varied with depth.

Identification of modeled ocean plumes in Greenland Gyre ERS‐1 SAR data

Oceanic convective plumes modeled with a thermobaric large-eddy simulation and driven by conditions similar to those of the Greenland Sea are compared to observations from ERS-1 Synthetic Aperture Radar (SAR) data from the Greenland Sea for the winter of 1992. In both form and size the two representations are seen to compare favorably. The plume-filled area of the SAR image occupies a region about 20 km by 90 km at the ice edge of the open water in “Nordbukta”, the large seasonal ice retreat, in the “Odden” ice protuberance in the southern Greenland gyre. In the SAR data the plumes appear to be ice covered while the convective-return areas are open.

Observations of the Late-Summer to Fall Sea Ice Transition with the 14.6 Ghz Seasat Scatterometer

Seasat 14.6-GHz scatterometer data are used to investigate variations in the large area-averaged backscatter signature during the late summer to fall transition. The temporal evolution in the backscatter coefficient indicates general changes in the surface properties of the sea ice which are attributed to the seasonal cycle. Notable events in this typical cycle are the meltpond maximum, rapid drainage or disappearance of the meltponds, fall cooling and freeze-up, and ultimately snowfall. All are manifested in the signature record, and a simple empirical scattering model is used to infer the mean snow and ice properties and their temporal variation.

Remote sensing of ice and snow: review and status

The status of obtaining geophysically useful observations of ice and snow through the interpretation of satellite data is discussed. Over the last decade, the examination of satellite data for information on ice and snow has developed rapidly; datasets of results have been generated; the connections between ice and snow microscopic properties and their electromagnetic behaviour are now better understood; and a good deal of accurate satellite-derived information on ice and snow can now be obtained.

Fusion of satellite active and passive microwave data for sea ice type concentration estimates

Young first-year sea ice is nearly as important as open water in modulating heat flux between the ocean and atmosphere in the Arctic. Just after the onset of freeze-up, first-year ice is in the early stages of growth and will consist of young first-year and thin ice. The distribution of sea ice in this thickness range impacts heat transfer in the Arctic. Therefore, improving the estimates of ice concentrations in this thickness range is significant. The NASA Team Algorithm (NTA) for passive microwave data inaccurately classifies sea ice during the melt and freeze-up seasons because it misclassifies multiyear ice as first-year ice. We developed a hybrid fusion technique for incorporating multiyear ice information derived from synthetic aperture radar (SAR) images into a passive microwave algorithm to improve ice type concentration estimates. First, we classified SAR images using a dynamic thresholding technique and estimated the multiyear ice concentration. Then we used the SAR-derived multiyear ice concentration to constrain the NTA and obtained an improved first-year ice concentration estimate. We computed multiyear and first-year ice concentration estimates over a region in the eastern-central Arctic in which field observations of ice and in situ radar backscatter measurements were performed. The fused estimates of first-year and multiyear ice concentration appear to be more accurate than NTA, based on ice observations that were logged aboard the US Coast Guard Icebreaker Polar Star in the study area during 1991.

MEMS enablement and analysis of the miniature autonomous submersible explorer

The miniature autonomous submersible explorer (MASE) was designed as a vehicle for astrobiology science by Behar et al. . This paper focuses on the MASE concept and extrapolates a future design based on microelectromechanical systems (MEMS), multifunctional microsystems (MMS), and three-dimensional multichip modules (3-D-MCM). Miniaturization of the electronics increases the payload volumes and power capabilities significantly and this is the main rationale for pursuing extreme miniaturization. The original MASE vehicle accommodated 1-2 instruments while the MEMS enhanced miniature autonomous submersible explorer (MEMSEMASE) accommodates up to six instruments. It is shown that the occupied area of the electronics components is reduced eight times, and the volume 25 times. The vehicle is shaped as a tube with 5 cm in diameter and 20 cm in length and can support 8 W continuously over 5 h. The maximum range is 25 km while the typical onboard instrumentation is conductivity, temperature, depth (CTD), and a high resolution camera. An optical fiber is used for bidirectional communication with the vessel. The goal of this enriched concept is to present an extremely miniaturized submersible design. The vehicle volume is defined to fit inside host vehicles with the goal of future deployment on Europa, oceans on Earth, and bore holes. The paper will focus on showing how electronics can be densely packed into micromachined silicon modules and how these can be designed and interconnected theoretically.