P-wave velocities and applied bed thickness and velocity changes for synthetic seismograms, ODP Leg 188 and Leg 119 sites

Synthetic seismograms provide a crucial link between lithologic variations within a drill hole and reflectors on seismic profiles crossing the site. In essence, they provide a ground-truth for the interpretation of seismic data. Using a combination of core and logging data, we created synthetic seismograms for Ocean Drilling Program Sites 1165 and 1166, drilled during Leg 188, and Site 742, drilled during Leg 119, all in Prydz Bay, Antarctica. Results from Site 1165 suggest that coring penetrated a target reflector initially thought to represent the onset of drift sedimentation, but the lithologic change across the boundary does not show a change from predrift to drift sediments. The origin of a shallow reflector packet in the seismic line across Site 1166 and a line connecting Sites 1166 and 742 was resolved into its constituent sources, as this reflector occurs in a region of large-scale, narrowly spaced impedance changes. Furthermore, Site 1166 was situated in a fluvio-deltaic system with widely variable geology, and bed thickness changes were estimated between the site and both seismic lines.

Corrected ICESat altimetry data, surface mass balance, and firn elevation change on Antarctic ice shelves

Accurate prediction of global sea-level rise requires that we understand the cause of recent, widespread and intensifying glacier acceleration along Antarctic ice-sheet coastal margins. Floating ice shelves buttress the flow of grounded tributary glaciers and their thickness and extent are particularly susceptible to changes in both climate and ocean forcing. Recent ice-shelf collapse led to retreat and acceleration of several glaciers on the Antarctic Peninsula. However, the extent and magnitude of ice-shelf thickness change, its causes and its link to glacier flow rate are so poorly understood that its influence on the future of the ice sheets cannot yet be predicted. Here we use satellite laser altimetry and modelling of the surface firn layer to reveal for the first time the circum-Antarctic pattern of ice-shelf thinning through increased basal melt. We deduce that this increased melt is the primary driver of Antarctic ice-sheet loss, through a reduction in buttressing of the adjacent ice sheet that has led to accelerated glacier flow. The highest thinning rates (~7 m/a) occur where warm water at depth can access thick ice shelves via submarine troughs crossing the continental shelf. Wind forcing could explain the dominant patterns of both basal melting and the surface melting and collapse of Antarctic ice shelves, through ocean upwelling in the Amundsen and Bellingshausen Seas and atmospheric warming on the Antarctic Peninsula. This implies that climate forcing through changing winds influences Antarctic Ice Sheet mass balance, and hence global sea-level, on annual to decadal timescales.

The glacier inventory of Salzburg, Austria, 2007/2009

A third glacier inventory (GI3) is presented for the province of Salzburg where 173 glaciers are located in the seven mountain ranges: Ankogel (47°4'N, 13°14'E), Glockner, Granatspitz, Sonnblick (Goldberg), Hochkönig, Venediger and Zillertal (47°8'N, 12°7'E). The basis for the new GI3 are orthophotos of 2007 and 2009 and the digital elevation model (DEM) of the southern part of Salzburg. On the basis of former inventories, area- and volume changes have been calculated. The biggest relative loss of glacier area per mountain range was found in the Ankogel range and on Hochkönig as a result of the disrupted structure of their small and thin glaciers. In terms of absolute values, the largest changes took place in the Glockner- and Venediger range with an area loss of -10.1 km**2 and -9.7 km**2 during the period between GI1 (1969) and GI3 (2007/2009), respectively. Volume changes have been calculated for nearly half of the glacier area in Salzburg, where DEMs were available. The Glockner, Granatspitz and Sonnblick mountain ranges showed a volume loss of -0.481 km**3 which corresponds to a mean thickness change of -10.5 m. An extrapolation of these changes to all of the 173 glaciers in Salzburg results in a loss of about 1.04 km**3 between GI1 and GI3 and 0.44 km**3 between GI2 and GI3. Overall annual changes in the province of Salzburg between GI2 and GI3 were higher than between GI1 and GI2 and show likewise changes such as those of Tyrol.

Accumulation, velocities, fluxes and mass balance of glacial tributaries to the Lambert Glacier-Amery Ice Shelf system, Antarctica

By incorporating recently available remote sensing data, we investigated the mass balance for all individual tributary glacial basins of the Lambert Glacier-Amery Ice Shelf system, East Antarctica. On the basis of the ice flow information derived from SAR interferometry and ICESat laser altimetry, we have determined the spatial configuration of eight tributary drainage basins of the Lambert-Amery glacial system. By combining the coherence information from SAR interferometry and the texture information from SAR and MODIS images, we have interpreted and refined the grounding line position. We calculated ice volume flux of each tributary glacial basin based on the ice velocity field derived from Radarsat three-pass interferometry together with ice thickness data interpolated from Australian and Russian airborne radio echo sounding (RES) surveys and inferred from ICESat laser altimetry data. Our analysis reveals that three tributary basins have a significant net positive imbalance, while five other subbasins are slightly positive or close to zero balance. Overall, in contrast to previous studies, we find that the grounded ice in Lambert Glacier-Amery Ice Shelf system has a positive mass imbalance of 22.9 ± 4.4 Gt/a. The net basal melting for the entire Amery Ice Shelf is estimated to be 27.0 ± 7.0 Gt/a. The melting rate decreases rapidly from the grounding zone to the ice shelf front. Significant basal refreezing is detected in the downstream section of the ice shelf. The mass balance estimates for both the grounded ice sheet and the ice shelf mass differ substantially from other recent estimates.

Annual-layer thickness, d18O and sodium values on Akademii Nauk ice core (AD 900-1998) based on core chronology AN 2012

Understanding recent Arctic climate change requires detailed information on past changes, in particular on a regional scale. The extension of the depth-age relation of the Akademii Nauk (AN) ice core from Severnaya Zemlya (SZ) to the last 1100 yr provides new perspectives on past climate fluctuations in the Barents and Kara seas region. Here, we present the easternmost high-resolution ice-core climate proxy records (d18O and sodium) from the Arctic. Multi-annual AN d18O data as near-surface air-temperature proxies reveal major temperature changes over the last millennium, including the absolute minimum around 1800 and the unprecedented warming to a double-peak maximum in the early 20th century. The long-term cooling trend in d18O is related to a decline in summer insolation but also to the growth of the AN ice cap as indicated by decreasing sodium concentrations. Neither a pronounced Medieval Climate Anomaly nor a Little Ice Age are detectable in the AN d18O record. In contrast, there is evidence of several abrupt warming and cooling events, such as in the 15th and 16th centuries, partly accompanied by corresponding changes in sodium concentrations. These abrupt changes are assumed to be related to sea-ice cover variability in the Barents and Kara seas region, which might be caused by shifts in atmospheric circulation patterns. Our results indicate a significant impact of internal climate variability on Arctic climate change in the last millennium.

(Table 1) Ice thickness at lake Nam Co, Tibet, during 2008-2009

Lake ice change is one of the sensitive indicators of regional and global climate change. Different sources of data are used in monitoring lake ice phenology nowadays. Visible and Near Infrared bands of imagery (VNIR) are well suited for the observation of freshwater ice change, for example data from AVHRR and MODIS. Active and passive microwave data are also used for the observation of lake ice, e.g., from satellite altimetry and radiometry, backscattering coefficient from QuickSCAT, brightness temperature (Tb) from SSM/I, SMMR, and AMSR-E. Most of the studies are about lake ice cover phenology, while few studies focus on lake ice thickness. For example, Hall et al. using 5 GHz (6 cm) radiometer data showed a good relationship between Tb and ice thickness. Kang et al. found the seasonal evolution of Tb at 10.65 GHz and 18.7 GHz from AMSR-E to be strongly influenced by ice thickness. Many studies on lake ice phenology have been carried out since the 1970s in cold regions, especially in Canada, the USA, Europe, the Arctic, and Antarctica. However, on the Tibetan Plateau, very little research has focused on lake ice-cover change; only a small number of published papers on Qinghai Lake ice observations. The main goal of this study is to investigate the change in lake ice phenology at Nam Co on the Tibetan Plateau using MODIS and AMSR-E data (monitoring the date of freeze onset, the formation of stable ice cover, first appearance of water, and the complete disappearance of ice) during the period 2000-2009.

Sea ice thickness from airborne electromagnetic (EM) induction sounding acquired from fixed-wing aircraft POLAR 5 surveys from several airports in Spitsbergen, Greenland, Canada and Alaska

While summer Arctic sea-ice extent has decreased over the past three decades, it is subject to large interannual and regional variations. Methodological challenges in measuring ice thickness continue to hamper our understanding of the response of the ice-thickness distribution to recent change, limiting the ability to forecast sea-ice change over the next decade. We present results from a 2400 km long pan-Arctic airborne electromagnetic (EM) ice thickness survey in April 2009, the first-ever large-scale EM thickness dataset obtained by fixed-wing aircraft over key regions of old ice in the Arctic Ocean between Svalbard and Alaska. The data provide detailed insight into ice thickness distributions characteristic for the different regions. Comparison with previous EM surveys shows that modal thicknesses of old ice had changed little since 2007, and remained within the expected range of natural variability.

Abb. 3 Change of altitude in the EGIG-West-East-profile

The members of the two International Glaciological Greenland Expeditions (EGIG) in 1959 and 1968 determined the altitudes in the West-East-profile by levelling. The comparison of these two measurements gives evidence of the change of altitudes and of the surface-waves. The ways of measurement and of analysis are described here. The graphic representation of the result is discussed here in connexion with the possible causes.

Ice thickness distribution and glacier bed of Hallstätter Gletscher

Hallstätter Glacier is the northernmost glacier of Austria. Appendant to the northern Limestone Alps, the glacier is located at 47°28'50'' N, 13°36'50'' E in the Dachstein-region. At the same time with its advance linked to the Little Ice Age (LIA), research on changes in size and mass of Hallstätter glacier was started in 1842 by Friedrich Simony. He observed and documented the glacier retreat related to its last maximum extension in 1856. In addition, Hallstätter Glacier is a subject to scientific research to date. In this thesis methods and results of ongoing mass balance measurements are presented and compared to long term volume changes and meteorological observations. The current mass balance monitoring programm using the direct glaciological method was started 2006. In this context, 2009 the ice thickness was measured with ground penetrating radar. The result are used with digital elevation models reconstucted from historical maps and recent digital elevation models to calculate changes in shape and volume of Hallstätter Glacier. Based on current meteorological measurements near the glacier and longtime homogenized climate data provided by HISTALP, time series of precipitation and temperature beginning at the LIA are produced. These monthly precipitation and monthly mean temperature data are used to compare results of a simple degree day model with the volume change calculated from the difference of the digital elevation models. The two years of direct mass balance measurements are used to calibrate the degree day model. A number of possible future scenarios are produced to indicate prospective changes. Within the 150-year-period between 1856 and 2007 the Hallstätter Glacier lost 1940 meters of its length and 2.23 km**2 in area. 37% of the initial volume of 1856 remained. This retreat came along with a change in climate. The application of a running avarage of 30 years shows an increase in precipitation of 18.5% and a warming of 1.3°C near the glacier between 1866 and 1993. The mass loss was continued in the hydrological years 2006/2007 and 2007/2008 showing mean specific mass balance of -376 mm and -700 mm, respectively. Applying a temperature correction for the different minimum elevations of the glacier, the degree day approach based on the two measured mass balances can reproduce sign and order of magnitude of the volume change of Hallstätter Glacier since 1856. Nevertheless, the relative deviation is significant. Future scenarios show, that 30% of the entire glacier volume remains after subtracting the elevation changes between the digital elevation models of 2002 and 2007 ten times from the surface of 2007. The past and present mass changes of Hallstätter Glacier are showing a retreating glacier as a consequence of rising temperatures. Due to high precepitation, increased with previous warming, the Hallstätter Glacier can and will exist in lower elevation compared to inner alpine glaciers.

Total sediment thickness grid of the Southern Pacific Ocean off West Antarctica, links to NetCDF files

Paleotopographic models of the West Antarctic margin, which are essential for robust simulations of paleoclimate scenarios, lack information on sediment thickness and geodynamic conditions, resulting in large uncertainties. A new total sediment thickness grid spanning the Ross Sea-Amundsen Sea-Bellingshausen Sea basins is presented and is based on all the available seismic reflection, borehole, and gravity modeling data offshore West Antarctica. This grid was combined with NGDC's global 5 arc minute grid of ocean sediment thickness (Whittaker et al., 2013, doi:10.1002/ggge.20181) and extends the NGDC grid further to the south. Sediment thickness along the West Antarctic margin tends to be 3-4 km larger than previously assumed. The sediment volume in the Bellingshausen, Amundsen, and Ross Sea basins amounts to 3.61, 3.58, and 2.78 million km³, respectively. The residual basement topography of the South Pacific has been revised and the new data show an asymmetric trend over the Pacific-Antarctic Ridge. Values are anomalously high south of the spreading ridge and in the Ross Sea area, where the topography seems to be affected by persistent mantle processes. In contrast, the basement topography offshore Marie Byrd Land cannot be attributed to dynamic topography, but rather to crustal thickening due to intraplate volcanism. Present-day dynamic topography models disagree with the presented revised basement topography of the South Pacific, rendering paleotopographic reconstructions with such a limited dataset still fairly uncertain.

Pre-glacial to glacial sediment thickness grids for the Southern Pacific Margin of West Antarctica, NetCDF files

Circum-Antarctic sediment thickness grids provide constraints for basin evolution and paleotopographic reconstructions, which are important for paleo-ice sheet formation histories. By compiling old and new seismic data, we identify sequences representing pre-glacial, transitional and full glacial deposition processes along the Pacific margin of West Antarctica. The pre-glacial sediment grid depicts 1.3 to 4.0 km thick depocenters, relatively evenly distributed along the margin. The depocenters change markedly in the transitional phase at, or after, the Eocene/Oligocene boundary, when the first major ice sheets reached the shelf. Full glacial sequences, starting in the middle Miocene, indicate new depocenter formation North of the Amundsen Sea Embayment and localized eastward shifts in the Bellingshausen Sea and Antarctic Peninsula basins. Using present-day drainage paths and source areas on the continent, our calculations indicate an estimated observed total sedimentary volume of ~10 x 10**6 km**3 was eroded from West Antarctica since the separation of New Zealand in the Late Cretaceous. Of this 4.9 x 10**6 km**3 predates the onset of glaciation and need to be considered for a paleotopography reconstruction of 34 Ma. Whereas 5.1 x 10**6 km**3 postdate the onset of glaciation, of which 2.5 x 10**6 km**3 were deposited in post mid-Miocene full glacial conditions.

Under-ice fauna, sea-ice concentration, sea-ice thickness and under-ice water parameters from the Eurasian central Arctic Ocean during POLARSTERN cruise ARK-XXVII/3 (PS80) in August-September 2012

Arctic sea-ice decline is expected to have a significant impact on Arctic marine ecosystems. Ice-associated fauna play a key role in this context because they constitute a unique part of Arctic biodiversity and transmit carbon from sea-ice algae into pelagic and benthic food webs. Our study presents the first regional-scale record of under-ice faunal distribution and the environmental characteristics of under-ice habitats throughout the Eurasian Basin. Sampling was conducted with a Surface and Under-Ice Trawl, equipped with a sensor array recording ice thickness and other physical parameters during trawling. We identified 2 environmental regimes, broadly coherent with the Nansen and Amundsen Basins. The Nansen Basin regime was distinguished from the Amundsen Basin regime by heavier sea-ice conditions, higher surface salinities and higher nitrate + nitrite concentrations. We found a diverse (28 species) under-ice community throughout the Eurasian Basin. Change in community structure reflected differences in the relative contribution of abundant species. Copepods (Calanus hyperboreus and C. glacialis) dominated in the Nansen Basin regime. In the Amundsen Basin regime, amphipods (Apherusa glacialis, Themisto libellula) dominated. Polar cod Boreogadus saida was present throughout the sampling area. Abrupt changes from a dominance of ice-associated amphipods at ice-covered stations to a dominance of pelagic amphipods (T. libellula) at nearby ice-free stations emphasised the decisive influence of sea ice on small-scale patterns in the surface-layer community. The observed response in community composition to different environmental regimes indicates potential long-term alterations in Arctic marine ecosystems as the Arctic Ocean continues to change.