Geological Survey of Denmark and Greenland Bulletin 26 ... - Geus

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2006) that allows for a high proportion of easily degradable organic matter to enter the zone of methanogenesis (Henrichs & Reeburgh 1987). At site C in the area west of Aasiaat the much lower methane concentration than at sites A and B may be explained by the high sulphate concentration (Figs 1, 6), which generally excludes the presence of methane (Iversen & Jørgensen 1985). Still the concentration of methane is significantly above background values for other sulphate pore-water concentrations in the Disko Bugt region. This may suggest upward migration of methane from gas hydrates as indicated by seismic data from the area (Fig. 3). The slight decrease in pore-water chloride concentrations with depth (Fig. 6) may further sustain the assumption of an upward migration of fluids depleted in chloride from below. Pore-water sulphate in sediment cores from site D located in the southern end of the strait Vaigat is almost exhausted at approximately 5 m below the sea floor (Figs 1, 6). However, the low sulphate concentration is presumably not entirely due to in situ microbial sulphate reduction, as the decrease in pore-water chloride concentration with depth indicates a considerable contribution of freshwater from submarine groundwater discharge (Fig. 6). Additional field work was conducted during the cruise in an area off the mouth of Jakobshavn Isfjord (site E). Pockmarks observed during an earlier multibeam survey in that area (Weinrebe et al. 2008) were suspected to have formed due to upward gas migration (Hovland & Svendsen 2006). However, the absence of methane together with the sediment texture observed in sediment cores from the area indicate that the pockmarks form from upwelling water and not from gas seepage. Concluding remarks The geochemical data obtained as a result of the 2011 cruise to the Disko Bugt region indicate that gas hydrates may occur in the region. Further investigation of the possible gas hydrates will continue during a new cruise in the area in 2012. Acknowledgements The 2011 cruise was supported by a grant from Geocenter Denmark to the project Permagas. The success of the cruise depended very much on the operational skills of the captain and crew of the R/V Paamiut and the smooth co-operation during the cruise with a scientific team from the Greenland Institute of Natural Resources. References Christiansen, F. G., Bate, K.J., Dam, G., Marcussen, C. & Pulvertaft, T.C.R. 1996: Continued geophysical and petroleum geological activities in West Greenland in 1995 and the start of onshore exploration. Bulletin Grønlands Geologiske Undersøgelse 172, 15–21. Henrichs, S.M. & Reeburgh, W.S. 1987: Anaerobic mineralization of marine sediments organic matter: rates and role of anaerobic processes in the oceanic carbon economy. Geomicrobiology Journal 5, 191–237. Hovland, M. & Svendsen, H. 2006: Submarine pingoes: indicators of shallow gas hydrates in a pockmark at Nyegga, Norwegian Sea. Marine Geology 228, 15–23. Iversen, N. & Jørgensen, B.B. 1985: Anaerobic methane oxidation rates at the sulphate–methane transition in marine sediments from Kattegat and Skagerrak (Denmark). Limnology Oceanography 30, 944–955. Kvenvolden K.A. & Rogers B.W. 2005: Gaia’s breath – global methane exhalations. Marine and Petroleum Geology 22, 579–590. Kuijpers, A., Lloyd, J.M., Jensen, J.B., Endler, R., Moros, M., Park, L.A., Schulz, B., Jensen, K.G. & Laier, T. 2001: Late Quaternary circulation changes and sedimentation in Disko Bugt and adjacent fjords, central West Greenland. Geology of Greenland Survey Bulletin 189, 41–47. MacKay, M.E., Jarrard, R.D., Westbrook, G.K. & Hyndman, R.D. 1994: Origin of bottom-simulating reflectors: geophysical evidence from the Cascadia accretionary prism. Geology 22, 459–462, http://dx.doi. org/10.1130/0091-7613(1994)022%3C0459:OOBSRG%3E2.3.CO;2 Moros, M., Jensen, K.G. & Kuijpers, A. 2006: Mid- to late-Holocene hydrological and climatic variability in Disko Bugt, Central West Greenland. The Holocene 16, 357–367. Nielsen, T., Laier, T., Mikkelsen, N. & Kristensen, J.B. 2011: Permagas project: Sampling gas hydrates in the Disko Bay area. Cruise Report – R/V Paamiut 20 to 26 June 2011. Danmarks og Grønlands Geologiske Undersøgelser Rapport 2011/105, 40 pp. Weinrebe, W., Kuijpers, A., Klaucke, I., Fink, M., Jensen, J.B. & Mikkelsen, N. 2008: High-resolution bathymetry of Disko Bay and Ilulissat Icefjord, West Greenland. American Geophysical Union fall meeting, San Fransisco, California, 15–19 December 2008 (Abstract C31E- 0563). Yamamoto, S., Alcauskas, J.B. & Crozier, T.E. 1976: Solubility of methane in distilled water and seawater. Journal of Chemical and Engineering Data 21, 78–80. Authors’ address Geological Survey of Denmark and Greenland, Øster Voldgade 10, DK-1350 Copenhagen K, Denmark. E-mail: nm@geus.dk 72
Ablation observations for 2008–2011 from the Programme for Monitoring of the Greenland Ice Sheet (PROMICE) Robert S. Fausto, Dirk van As and the PROMICE project team* Recent estimates from the glaciological community agree that the Greenland ice sheet is losing mass at an accelerated pace due to climate change (Velicogna 2009; Khan et al. 2010; Rignot et al. 2011). This has caught the attention of the public and policy makers due to the potential impact on sea-level rise (Dahl-Jensen et al. 2009). The mass loss can be attributed approximately equally to increases in meltwater runoff from surface melt and iceberg production (van den Broeke et al. 2009). The robustness of mass-balance predictions relies heavily on observational data from the Greenland ice sheet and in recent years the need for frequent, reliable surface mass-balance measurements has increased (IPCC 2007; Dahl-Jensen et al. 2009). In anticipation of this need, the Programme for Monitoring of the Greenland Ice Sheet (PROMICE) was initiated in 2007, delivering in situ data from a network of automatic weather stations (AWS) covering eight different regions of the ice sheet (Fig. 1; van As et al. 2011). Apart from the direct insight into the surface mass balance provided by these stations, the in situ data are also valuable for calibrating and validating melt estimates from remote sensors and surface mass-balance models (Dahl-Jensen et al. 2009). In this paper, we present the ablation records for the PROMICE AWSs for 2008–2011, and the impact of the extraordinary atmospheric conditions on ablation in 2010 (Tedesco et al. 2011) are compared to the other years. 80°N 75°N 70°N 65°N 60°N 80°W 60°W 40°W THU 1500 UPE 1250 1000 1500 1750 2000 2250 KAN 1750 2250 NUK 2750 2500 QAS 2000 2250 3000 20°W 0°W 50°W 40°W 20°W 2750 2500 Greenland TAS KPC SCO 500 km PROMICE automatic weather stations Fig. 1. Map of Greenland showing the locations of the PROMICE automatic weather stations. Each dot represents two or three stations. Station names are found in Table 1. Dashed lines: elevation contours. The PROMICE network in Greenland currently consists of eight sites with two (or three) AWSs placed at different elevations (Fig. 1; Table 1; Ahlstrøm et al. 2008) with a total of 18 stations. At each site, one station is typically located in the lower ablation zone close to the margin and the other in the upper ablation zone. Exceptions are station KAN_U, which is placed in the lower part of the accumulation zone, and station TAS_U, which is placed well below the equilibrium-line altitude for reasons of accessibility. Each station measures all relevant meteorological parameters and ice and snow ablation (Fig. 2). It measures and stores data every ten minutes * Andreas P. Ahlstrøm, Signe B. Andersen, Morten L. Andersen, Michele Citterio, Karen Edelvang, Signe H. Larsen, Horst Machguth, Søren Nielsen and Anker Weidick. © 2012 GEUS. Geological Survey of Denmark and Greenland Bulletin 26, 73–76. Open access: www.geus.dk/publications/bull 73
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GEOLOGICAL SURVEY OF DENMARK AND GR
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Greenland Denmark Mexico Nigeria Gh
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Review of Survey activities 2011 Fl
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Nano-quartz in North Sea Danian cha
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Dispersed in distilled water Disper
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Geology of the Femern Bælt area be
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Biostratigraphic marker fossils: Di
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Rock-cored drumlins on Bornholm, De
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N 50 km Pre-Quaternary geology Gran
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Geological Survey of Denmark and Greenland Bulletin 26 ... - Geus

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