Reginald R. Muskett

Alaskan Permafrost Groundwater Storage Changes Derived from GRACE and Ground Measurements

Abstract: The Arctic is in transition from climate-driven thawing of permafrost. We investigate satellite-derived water equivalent mass changes, snow water equivalent with in situ measurements of runoff and ground-survey derived geoid models from 1999 through 2009. The Alaskan Arctic coastal plain groundwater storage (including wetland bog, thaw pond and lake) is increasing by 1.15 ± 0.65 km 3 /a (area-average 1.10 ± 0.62 cm/a), and Yukon River watershed groundwater storage is decreasing by 7.44 ± 3.76 km 3 /a (area-average 0.79 ± 0.40 cm/a). Geoid changes show increases within the Arctic coastal region and decreases within the Yukon River watershed. We hypothesize these changes are linked to the development of new predominately closed- and possibly open-talik in the continuous permafrost zone under large thaw lakes with increases of lakes and new predominately open-talik and reduction of permafrost extent in the discontinuous and sporadic zones with decreases of thaw lakes.

Airborne and spaceborne DEM- and laser altimetry-derived surface elevation and volume changes of the Bering Glacier system, Alaska, USA, and Yukon, Canada, 1972-2006

Using airborne and spaceborne high-resolution digital elevation models and laser altimetry, we present estimates of interannual and multi-decadal surface elevation changes on the Bering Glacier system, Alaska, USA, and Yukon, Canada, from 1972 to 2006. We find: (1) the rate of lowering during 1972-95 was 0.9 � 0.1 m a -1 ; (2) this rate accelerated to 3.0 � 0.7 m a -1 during 1995-2000; and (3) during 2000-03 the lowering rate was 1.5 � 0.4 m a -1 . From 1972 to 2003, 70% of the area of the system experienced a volume loss of 191 � 17 km 3 , which was an area-average surface elevation lowering of 1.7 � 0.2 m a -1 . From November 2004 to November 2006, surface elevations across Bering Glacier, from McIntosh Peak on the south to Waxell Ridge on the north, rose as much as 53 m. Up-glacier on Bagley Ice Valley about 10 km east of Juniper Island nunatak, surface elevations lowered as much as 28 m from October 2003 to October 2006. NASA Terra/MODIS observations from May to September 2006 indicated muddy outburst floods from the Bering terminus into Vitus Lake. This suggests basal-englacial hydrologic storage changes were a contributing factor in the surface elevation changes in the fall of 2006.

Surging, accelerating surface lowering and volume reduction of the Malaspina Glacier system, Alaska, USA, and Yukon, Canada, from 1972 to 2006

Near-concurrent surges and multi-decadal surface-elevation changes on the Malaspina Glacier system Alaska, USA, and Yukon, Canada, were investigated using digital elevation models and laser altimetry from airborne and space-borne sensors. Surface-elevation changes on Seward Lobe in two time periods support a hypothesis of moraine folding by a mechanism of sequential surges alternating from southeast to south-southwest. The near-concurrent surges of Agassiz, Lower Seward and Marvine glaciers support a hypothesis of englacial water storage being a critical factor of surging. Acceleration of area-average surface lowering on the piedmont glaciers occurred, from 1.5 � 0.1 m a -1 between 1972 and 1999 to 2.3 � 0.3 m a -1 between 1999 and 2002. On the western half of Upper Seward Glacier, above 1600 m, acceleration of surface lowering occurred from 2000 to 2003 relative to that from 1976 to 2000, indicating an effect from the surge of Lower Seward Glacier. From 2003 to 2006, the rate of surface lowering on Upper Seward Glacier has moderated back to the pre-2000 rate, indicating a recovery of surface elevation following the surge. From 1972 to 2002, the Malaspina Glacier system lost 156 � 19 km 3 (ice equivalent) on an area of 3661 km 2 .

DEM Control in Arctic Alaska With ICESat Laser Altimetry

Use of Ice, Cloud, and land Elevation Satellite (ICESat) laser altimetry is demonstrated for control of a digital elevation model (DEM) that is synthesized from repeat-pass ERS-1 and 2 synthetic aperture radar (SAR) imagery using interferomet-ric SAR (InSAR). Our study area is 15 650 km2 of the Barrow, AK coastal plain adjacent to the Arctic Ocean; a vast expanse of tundra, lakes, and arctic wetlands of such low relief as to be nearly devoid of terrain features. The accuracy of the ICESat-derived elevation measurements is assessed by comparison with differential global positioning system (DGPS) data acquired along ICESat ground tracks. The ICESat-derived elevations have a mean accuracy, relative to the DGPS elevations, of -0.01 plusmn 0.18 m. ICESat-derived elevations on the Arctic coastal plain provide an excellent source for DEM control. We employ the ICESat-derived ground control points (GCPs) in two distinct InSAR processing steps: 1) selected points are used to perform baseline refinements, which improves the ERS-1 and 2 interfero-grams and 2) the ICESat-derived GCP position data (latitude, longitude, elevation) are then used as control in mosaicking multiple InSAR-derived DEMs. The resulting ICESat-controlled DEM has a mean accuracy of -1.11plusmn 6.3 m relative to an independent standard, which is a commercial airborne InSAR-derived DEM having 0.5 m rms accuracy. This easily meets DTED-2 standards and suggests that DEMs derived using only ICESat altimetry for ground control would meet similar standards in other regions of low relief.

To Measure the Changing Relief of Arctic Rivers: A Synthetic Aperture RADAR Experiment in Alaska

This river crossing the lowland tundra-permafrost of the continuous permafrost zone of the Alaska North Slope can have extensive floodplain relief not simply created by channel migration during spring floods alone. Many of the rivers have channel-beds inherited from glacial landscapes and Holocene to present-day paraglacial and periglacial processes and mountain gradient sources [1][2][3][4]. Interest is turning to understand effects from permafrost and ice wedge networks (ground ice) thaw, degradation and erosion and how such effects impact carbon and water equivalent mass balance. The 2015 flooding of the Sagavanirktok River crossing the Alaska North Slope brings this and additional impacts to-and-by human infrastructure into focus. Geodetic methods to measure centimeter to millimeter-scale changes using aircraft- and satellite-deployed Synthetic Aperture (SA) RAdio Detection And Ranging (RADAR) cannot ignore volume scattering. Backscatter and coherence at L-frequency and others possess both surface and volumetric scattering. On lowland tundra underlain by permafrost volume scattering dominants the RADAR backscatter coherence (the results of this work and [16]). Measurement of the L-frequency penetration depth for evaluation of mass change (carbon and water equivalent loss and transport) through permafrost and ground ice thaw-degradation with erosion is necessary. The Jet Propulsion Laboratory-National Aeronautical and Space Administration airborne Uninhabited Aerial Vehicle SAR (UAVSAR) L-frequency full quad-polarimetry cross-pole HHVV (polarization rotation, Horizontal to Vertical) confirms the dominance of volume scattering on lowland tundra (RADAR-soft targets) whereas surface scattering (HHHH or VVVV, no rotation) dominates on river channel deposits, rock outcrops and metal objects (RADAR-hard targets). Quantifying polarization rotation and the L-frequency penetration depth on lowland tundra are challenges for a new field validation and verification experiment.