C31G-01
The Norwegian-US IPY Traverse 2007/2008: First Results From Dielectric Profiling of Four Shallow Firn Cores
Antarctica's mass balance is still quite uncertain today and vast parts of the East Antarctic ice sheet are not covered by ground-based measurements. Yet knowledge of the variability of accumulation rates in Antarctica is crucial for estimation of future sea-level change. The Norwegian-US IPY traverse through East Antarctica aims to close some of those data gaps and to help constraining the mass balance of the East Antarctic ice sheet and its impact on sea-level rise. Here, we present first results of firn-core records obtained from the first leg of the traverse in 2007/2008. We show data from dielectric profiling on four shallow (20-25 m deep) firn cores along the traverse route, going through Dronning Maud Land from Norwegian Troll Station to South Pole. Dielectric profiling (DEP) yields high-resolution information about dielectric permittivity and electrical conductivity along the firn core. We discuss the presence and depth of prominent events like the Tambora eruption within the conductivity records of the different firn cores. Furthermore dielectric permittivity is used to calculate density according to mixing models like the one established by Looyenga and compared to bulk density. Using the density data and the volcanic chronology, accumulation rates are calculated for the last ~200-250 years. Their spatial variability between the different drilling sites is discussed as well as the temporal accumulation pattern. Our firn cores show accumulation rates in the range of 20-32 mm a-1 w.e., based on the preliminary core chronology. Three firn cores show a decrease in accumulation for the time period 1884- 2007 in relation to 1762-1884. We compare the accumulation data with other data sets from Dronning Maud Land and discuss upcoming use of the dielectric permittivity for calibration of radar data and the subsequent calculation of the accumulation pattern along the entire traverse route. Together, the data from the Norwegian-US IPY traverse should provide valuable insight in the variation of accumulation rates and related physical parameters on the remote East Antarctic plateau and will serve as ground-truthing for satellite data.
C31G-02
Melt Pond Development on Arctic Land-Fast Sea Ice in Relation to Snow and Ice Properties During the Ice Growth Season
The dynamics of melt pond development on sea ice were studied on a well-defined patch of level land-fast sea ice off the coast of Barrow, Alaska in 2008. The pond development was correlated with both sea ice properties and the history of snow distribution during the ice growth season. In mid January, the ice was covered by an almost level snow layer of 4~cm thickness. We observed an increase in snow depth and development of snow dunes since February. At least some snow dunes stayed in place, and at the end of April ice thickness was negatively correlated with the thickness of compacted snow dunes. Snow salinity remained above 5~psu in the bottom 4 to 5~cm of the snow pack throughout the ice growth season. In comparison, snow more than 5~cm above the snow--ice interface was almost devoid of salt. The air temperature increased rapidly in early May and started to exceed 0°C on May 15. From this day on, thermistor string data show that the sea ice temperature profile deviated from linear with the lowest temperature inside the body of ice rather than at the surface. Superimposed ice was present with certainty after May 24. The superimposed ice investigated in early June exhibited a rough texture consistent with meltwater percolation columns in the snow pack. It was found only under snow dunes; no superimposed ice was observed under thin snow (2~cm) or melt ponds. Meltwater collected at topographic low points that surrounded distinct ice islands. Aerial photography and surface LiDAR measurements at various times during the early melt season showed that the location of these ice islands coincided with the locations of wind packed snow dunes that had been tracked since February. The lateral movement of surface waters was relatively slow during the very early stages of melt pond formation. However, we observed a significant lateral redistribution of meltwater under the ice surface; this redistribution happened through distinct veins. The sea ice salinity profiles showed evidence of meltwater flushing during the period of increasing melt pond coverage. At the same time, a significant amount of meltwater appeared to have drained through natural flaws (seal holes) rather than ice. Over the course of a few days, the area covered by melt ponds shrank as the meltwater table dropped toward the freeboard level. However, patches of near-impermeable ice persisted beyond this point. Laser-level transects showed that isolated puddles of elevated water level remained. The ice islands that developed during the early stages of melt persisted throughout the mature stages of ice melt. They were surrounded by ponds that typically contained dark ice patches that were apparent in the early stage of melt. Our observations on melt pond evolution may be useful in the context of interpreting and modeling regional differences in sea ice albedo and assessing the sensitivity of spring and early-summer ice albedo to changing Arctic snow and sea ice conditions.
C31G-03
Reassessment of the potential contribution to sea level from a collapse of the West Antarctic Ice Sheet
Theory has suggested that the West Antarctic Ice Sheet may be inherently unstable. Recent observations lend weight to this hypothesis. Earlier estimates of the potential contribution to sea level rise were based on incomplete data on bed and surface topography and, therefore, the volume and extent of marine-based ice. They also lacked a complete calculation for how this volume would be distributed over the World's oceans as a result of changes in the gravity field after collapse. We assess the potential contribution of a collapse of the ice sheet using the theoretical constraints imposed by the marine ice sheet instability hypothesis. We find that the global contribution has been overestimated by 65-120 percent (depending on the historical value chosen). We obtain a global mean sea level contribution of 3.1 m, with large and important regional variations. These variations, due to changes in the gravity field, the Earth's rotational vector and glacio-isostatic adjustment have been identified previously. Here, we combine our glaciologically-consistent collapse scenario with the appropriate sea-level theory to reconstruct the spatial pattern resulting from a collapse. Maxima lie along the Pacific and Atlantic seaboard of the US with a value of 3.9 m for a complete collapse.
C31G-04
Arctic Ocean Sea Ice Drift Studied Through Radionuclides
Sea ice in the Arctic Ocean incorporates radionuclides during its formation and drifting, frequently associated with sediments entrained in the ice from resuspension of continental shelf bottom sediments. A large fraction of sea ice formed on the shelves is exported to the central Arctic, and it drifts until reaching melting areas such as the Fram Strait. Thus, sea ice becomes an important mechanism for transport and redistribution of radionuclides. We have analysed natural [7Be, 210Pb] and artificial [137Cs and Pu isotopes] radionuclides in sea ice-sediment (SIS) samples collected from the Makarov [1998] and Nansen [2002] basins and the Fram Strait [2001, 2003]. The combination of our results with other available data showed that the specific activities of 137Cs and 239,240Pu present analogous distributions and are in agreement with the concentration patterns of Pu and Cs in surface sediment of the sea ice source areas. Moreover, they mirror the average sea ice drift patterns in the Beaufort Gyre, the Polar and Siberian Branches of the TransPolar Drift (TPD) and the Fram Strait. Relatively low activities of 137Cs and 239,240Pu in SIS were found in the Polar Branch of the TPD and the Beaufort Gyre, while the highest concentrations were determined in the Siberian Branch of the TPD. In the Fram Strait, a high degree of variability in 137Cs and 239,240Pu activities was observed, as a consequence of the mixture of sea ice floes transported via different pathways. The 240Pu/239Pu atom ratio is an useful indicator that allows local source of Pu to be separated from global fallout [0.18]. In general, the 240Pu/239Pu atom ratios in SIS are characteristic of global fallout. However, relatively low 240Pu/239Pu atom ratios were found between north of Svalbard and the Franz Josep Land and in the Fram Strait, implying that the corresponding ice floes would have been originated in specific continental shelf areas affected by local fallout, such as Novaya Zemlya archipelago and the Kara Sea. In contrast, specific activities of 7Be and excess 210Pb in SIS are not consistent with those in the continental shelves and do not allow us to establish a geographical distribution. Also, their activities suggest an enrichment process during the sea ice drifting, namely atmospheric input and, to a lesser extent, uptake from surface sea water. The data provide evidence that radionuclides help to determine the importance of sea ice drift in redistributing the particles and associated particle-reactive chemical species to melting areas and also identify sea ice source areas.
C31G-05
Global Cryosphere Watch: A New WMO Initiative
Legacy of the IPY 2007-2008 will take many forms, and one key legacy for the cryosphere is the
development of a WMO Global Cryosphere Watch (GCW), a proposal welcomed by the 15th WMO Congress
(May 2007). GCW involves research, monitoring, assessment, product development and prediction. It will
cover all aspects of the cryosphere. GCW would contribute to WMO's integrated observing and
information systems and the GCOS (Global Climate Observing System), like the Global Atmosphere Watch
does. It will be an intergovernmental mechanism for supporting key cryospheric in situ and remote sensing
observations implementing the recommendations of the IGOS Cryosphere Theme. GCW will provide reliable,
comprehensive observations of the elements of the cryosphere through an integrated observing approach
on global and regional scales, in collaboration with other international programmes and agencies. It will work
with, and build on existing programs, such as the GTN-G and GTN-P (Global Terrestrial Networks for Glaciers
/ for Permafrost) and work with external partners such as space agencies and World Data Centers for
Glaciology. GCW can provide an integrating mechanism required to ensure better quality data and
metadata, comparison of algorithms, the means to provide the scientific community to predict the future state
of the cryosphere, facilitate assessment of changes in the cryosphere and their impact, and use this
information to aid the detection of climate change, and organize assessments of changes in regional and
global components of the cryosphere to support decision making and policy development.
GCW is envisioned to include "cold GAW-like stations" - key stations/sites working on a coherently
agreed program on monitoring of changes in all components of the cryosphere, producing valuable long-
term records, covering key areas of the globe with cryospheric observations. It will help existing elements
function better and contribute to a global system, and will help IPY cryospheric projects to develop elements
of a sustained cryospheric observing system. A goal is to provide a one-stop portal for authoritative
cryosphere data and products/information on the current state and projected fate of the cryosphere for use
by the media, public, decision and policy makers.
This presentation will update the status of GCW, consultations with scientists and agencies and at specialty
workshops and the next steps in scoping the initiative
http://clic.npolar.no/
C31G-06
Four important features in the Ward Hunt Ice Shelf revealed from the high-temporal- and high-spatial-resolution images taken by Formosat-2 in Summer 2008
Massive ice shelf collapsing in Polar Regions is indisputably a clear warning of global warming. To investigate such a rapid change of a breaking up event at a remote site requires an innovative approach that is able to make both high-temporal- and high-spatial-resolution observations. Deploying a high-spatial-resolution sensor in a daily revisit orbit, Formosat-2 successfully captured the details of Wilkins Ice Shelf disintegration event in March 2008, using its 2-m multi-spectral remote sensing imagery. Right after a few extensive fractures were found in the largest ice shelf in the Arctic (Ward Hunt Ice Shelf, WHIS) and reported in May 2008, Formosat-2 was employed to make an intensive observation in this region. A total of eleven scenes of WHIS were acquired from 5 June to 30 August 2008, and ten of them were taken in a preferable low-cloud- cover condition. After the basic processing of level-2 georeferencing, band-to-band coregistration, spectral summation intensity modulation pan-sharpening, and multi-temporal images coregistration, we are able to summarize four important features in WHIS from the time series of Formosat-2 images. First, the sea ice velocity field in the vicinity of WHIS can be inferred by using ice floes as tracers and manually identifying identical floes in consecutive images. There is an eastward flow along the coast of Ellesmere Island. This flow is one of the main forces that gradually tears apart the outermost WHIS in summer. Second, a considerable number of melt ponds with scales of a few to tens of meters is found across the lower part of WHIS. As the temperature rises in summer, the total area of melt ponds increases as a result. In some cases, the melting water soon drains away and a large scale of disintegration occurs afterwards. Third, the extent of organic sedimentary material, namely microbial mat, can be clearly identified from these multispectral images. Fourth, the recent break-up event poses a threat to Disraeli Fiord, the largest remaining epishelf lake in the Northern Hemisphere. A new channel has formed recently, which may accelerate the drainage of the epishelf lake. This research demonstrates that high-spatial- and high- temporal-resolution optical imagery taken from Formosat-2 is a useful data source for studying the collapse of ice shelf in Polar Regions.
C31G-07
SPIRIT. SPOT 5 stereoscopic survey of Polar Ice: Reference Images and Topographies during the fourth International Polar Year (2007-2009)
Monitoring the evolution of polar glaciers, ice caps and ice streams is of utmost importance because they
constitute a good indicator of global climate change and contribute significantly to ongoing sea level rise.
Accurate topographic surveys are particularly relevant as they reflect the geometric evolution of ice masses.
Improving our knowledge of the topography of Polar Regions is the goal of the SPIRIT (SPOT 5 stereoscopic
survey of Polar Ice: Reference Images and Topographies) IPY project. SPIRIT allows (1) the acquisition of a
large archive of SPOT 5 stereoscopic images covering most polar ice masses and, (2) the free delivery of
digital terrain models (DTM) to the scientific community.
Here, we present the architecture of this project and the coverage achieved over northern and southern
polar areas during the first year of IPY (July 2007 to November 2008). We also provide the first accuracy
assessments of the SPIRIT DTMs. Over Jakobshavn Isbrae (West Greenland), SPIRIT elevations are within
± 5 m (RMSE) of ICESat elevations. Some comparisons with ICESat profiles over Devon ice cap
(Canada), St Elias Mountains (Alaska) and west Svalbard confirm the good overall quality of the SPIRIT
DTMs although large errors are observed in the flat accumulation area of Devon ice cap.
We also demonstrate the potential of SPIRIT DTMs for mapping glacier elevation changes. The comparison
of summer-2007 SPIRIT DTMs with October-2003 ICESat profiles shows that the thinning of Jakobshavn
Isbrae (by 30 to 40 m in 4 years) is restricted to the fast glacier trunk. The thinning of the coastal part of the
ice stream (by over 100 m) and the retreat of its calving front (by up to 10 km) are clearly depicted by
comparing the SPIRIT DTM to an ASTER April-2003 DTM.
http://www.spotimage.fr/IPY/
C31G-08
International Polar Year – Back to the Future (IPY-BTF): Re-Sampling Sites More Than 25 Years Old to Assess Change in Arctic Ecosystem Structure and Function
In the absence of long-term monitoring, revisiting, re-sampling and analyzing environmental change that has occurred at Arctic research sites established several decades ago represents a largely untapped change detection capacity. The primary objective of this three-year International Polar Year (IPY) project (214) coordinated through the Circumarctic Environmental Observatories Network (CEON) is to determine how key structural and functional characteristics of high latitude arctic terrestrial ecosystems have changed over the past 25 or more years and assess if such trajectories of change are likely to continue in the future. Key activities include: 1. Establishing a focused international BTF coordination and information portal, including an interactive web-based information system. 2. Rescuing data and re-establishing and re-sampling BTF sites across the Arctic. 3. Coordination of two international BTF syntheses. One synthesis will focus on the production of a special issue with site-based papers and the second will develop a cross-site synthesis. 4.Archiving data for open access at the National Snow and Ice Data Center (NSIDC). 5. Educating the next generation of scientist by providing an opportunity for students to resample historical research sites and gain hands on research experience under the mentorship of senior researchers. We welcome additional partnerships with arctic researchers actively resampling old research sites – this poster outlines how such participation can be initiated.