Here are four noteworthy Jakobshavn talks to be presented at AGU 2016 in December, including 3 of 17 (!) from the E Rignot group. None provided supplemental material, draft documents on researchgate, or title matches at google scholar. (However gs does not index articles under open review.)
Progress seems to have been made near the calving front for ocean bathymetry, thickness of ice and bed topography; if so, earlier numbers we've used here are wrong
if the depth right at the calving front is only 900 m. However 500 m resolution is less than thrilling as it amounts to 10-12 pixels at the width of Jakobshavn's calving front.
It does not appear that radar altimetry will have captured the height of the October ice stream waves above mean ice stream surface. They don't seem to have cast shadows in oblique S2A's, being too gradual but possibly nukefix can get at that from the S1AB perspective.
Bed Topography of Jakobshavn Isbræ and Helheim Glacier
Lu An, E Rignot, M Morlighem, JD Paden,D Holland, D Hollandhttps://agu.confex.com/agu/fm16/meetingapp.cgi/Paper/136824
It is essential to know their ice thickness and bed topography as well as the bathymetry in the fjords. Here we infer the glacier bed topography, ice thickness and sea floor bathymetry near the grounding line using high-resolution airborne gravity data from AIRGrav collected in August 2012 with a helicopter at 500 m spacing grid, 50 knots ground speed, 80 m ground clearance and sub-milligal accuracy, which improves on OIB's 5.2 km resolution, 290 knots, and 450 m clearance.
We use a 3D inversion of the gravity data combining our observations and a forward modeling of the surrounding gravity field with point measurements of the bathymetry at the ice-ocean boundary and a reconstruction of the glacier bed topography upstream using a mass conservation method combining re-analyzed airborne radar-derived ice thickness data from CReSIS with ice flow motion vectors from satellite radar interferometry.
The results provide a more accurate view of the bed topography of these glaciers and resolve major uncertainties from past attempts to probe the deepest part of the bed near the ice front from radio echo sounding data alone. The results reveal that Jakobshavn is now retreating into an even deeper bed, from 600 m in 1996 to 900 m at present
and 1,400 m in the next 25 km. The glacier will continue to retreat at an increasing rate (0.6 km/yr at present) along its retrograde bed into thicker ice.
On the impact of ice-ocean interaction on Greenland glaciers versus calving speed
E Rignot et alhttps://agu.confex.com/agu/fm16/meetingapp.cgi/Paper/199909
Glacier retreat from frontal ablation is a delicate balance between subaqueous melt, calving processes and bed geometry. Here, we model subaqueous melt from a large number of Greenland tidewater glaciers using generalized 3D, high resolution simulations of ice melt from the MITgcm ocean model constrained by subglacial melt from RACMO2.3 and ISSM, ocean temperature from ECCO2-4km Arctic, and bed topography from OMG and MC for 1992–2015. The results are analyzed in combination with ice-front retreat and glacier speed from Landsat and imaging radar data since the 1990s.
We find that subaqueous melt is 2–3 times greater in summer than in winter and doubled in magnitude since the 1990s because of enhanced ice sheet runoff and warmer ocean temperature. Glaciers that retreated rapidly are characterized by subaqueous melt rates comparable to their calving speed and favorable bed geometry. Glaciers dominated by calving processes are in contrast more resilient to thermal forcing from the ocean, especially in the presence of stabilizing geometry.
Surveying Greenland’s marine terminating glaciers with an airborne radar altimeter
A Khazendar IG Fente EJ Rignot JK Willishttps://agu.confex.com/agu/fm16/meetingapp.cgi/Paper/163483
Oceans Melting Greenland is a NASA suborbital mission to investigate the role of the oceans in ice loss around the margins of the Greenland Ice Sheet. A five-year airborne and ship-based campaign, the project will directly measure ocean temperatures and glacier changes around most of Greenland.
A main component of the airborne campaign is a once-per-year survey of glacier surface elevations of most of the marine terminating glaciers with GLISTIN-A. This radar is a topographic mapper that measures ice surface elevations with 50 cm vertical accuracy at 25 m horizontal resolution over a 10-12 km swath, independent of weather.
The first survey took place in March 2016 over 10 days and nearly 65 flight hours. We present here a first look at the measurements made during this campaign, how they compare with existing laser and radar altimetry data and a preliminary evaluation of their contribution in estimating ice thinning rates.
HF/VHF Dual-Frequency Sounding of Temperate and Fast-flowing Glaciers
E Arnold PS Gogineni S Yan F Rodriguez-Moraleshttps://agu.confex.com/agu/fm16/meetingapp.cgi/Paper/186981
One of the greatest challenges in airborne remote sensing of ice sheets is the sounding of temperate and fast-flowing glaciers. Temperate ice has a much higher liquid water content than “dry” ice which results in significantly greater attenuation and scattering of the radar signal. In addition, the surface of fast-flowing glaciers is highly crevassed and rough which also scatters the signal.
Radars designed to sound these glaciers must overcome the volumetric and surface scattering to detect the ice bed echo. While progress has been made in mapping fast-flowing glaciers with high-sensitivity Very High Frequency (VHF) radars, the significant signal attenuation at these frequencies results in a weak bed echo that is difficult to detect in the presence of strong clutter returns.
CReSIS has developed a dual-frequency High Frequency (HF)/VHF sounder for the purpose of sounding temperate and fast-flowing glaciers, particularly near their calving front, where surface clutter is the greatest and the effectiveness of existing microwave VHF radars is more limited. The longer wavelength of this system, which operates at 14 and 35 MHz, makes it much less sensitive to the temperate ice attenuation and scattering and crevassing.
In October of 2016, the HF/VHF sounder will be integrated onto a Twin Otter aircraft and flown over Jakobshavn Glacier. These flights will target the first 10 km from the calving front in an effort to sound and image the most challenging and significant part of this outlet glacier. We plan to present the results from this field campaign.