Jacob C. Yde

Basal ice microbiology at the margin of the Greenland ice sheet

Abstract Basal ice at the margin of the Greenland ice sheet was studied with respect to its physical characteristics and microbiological community. The basal ice contained high concentrations of dissolved ferrous Fe and must therefore be anoxic. Oxygen consumption experiments indicate that 50% of the oxidation was due to biological activity while the rest could be attributed to chemical processes, most likely weathering reactions with ferrous Fe. At least six different Fe-containing mineral sources were detected in basal ice together with potential bioavailable Fe nanoparticles. An active denitrifier population was identified due to formation of 30N-dinitrogen gas after amendment of anoxic sediment slurries with 15N-NO3 −. Sulfate reduction could not be detected. The solid ice facies contained an abundant (∼108 cells cm−3) and complex microbial community that harbored representatives of at least eight major phyla within the domain Bacteria. The clone library was dominated by members of the β-subdivision of proteobacteria of which the largest proportion was affiliated to the genus Rhodoferax that comprises facultative aerobic iron reducers. The second most abundant phylum was Bacteroidetes. The solid ice facies had many physical similarities with the overlying debris-rich banded ice facies, indicating that they formed by similar subglacial processes and harbor similar microbial communities. This study extends our knowledge of life in subglacial environments such as beneath ice sheets. GenBank accession numbers: HM439882-HM439950; HQ144215-HQ144221.

Methane flux and high-affinity methanotrophic diversity along the chronosequence of a receding glacier in Greenland.

Abstract Methane consumption in upland soils represents an important part of the biologically mediated sink of tropospheric methane. The present study focuses on the role of glacier forefields as a potential methane sink. The role of these environments, though increasing in size, has not yet been taken into account in the global methane budget. Net methane fluxes were analysed based on a static chamber method on a proglacial chronosequence from the Mittivakkat valley, southeast Greenland. Methane uptake could be measured in 7of the 12 study sites, with highest rates in the oldest materials from the chronosequence, suggesting that methane oxidation potential may increase during glacier recession (80–150 years). In the chamber located at the glacier front, net methane production was observed, indicating that the microbial community changes after glacial recession from being net methanogenic to becoming net methanotrophic. Diversity analyses based on denaturing gradient gel electrophoresis (DGGE) from the methanotrophic communities responsible for methane uptake at atmospheric levels demonstrate that methanotrophic microbial diversity changes along the chronosequence and show that there is a tendency to a larger diversity in the oldest part of the chronosequence. Sequencing of DNA retrieved from the DGGE revealed a restricted diversity of the methanotrophic community: GenBank accession numbers HM534684–HM534736.

A new cycle of jokulhlaups at Russell Glacier, Kangerlussuaq, West Greenland

Jokulhlaups in 2007 and 2008 from an ice-dammed lake at the northern margin of Russell Glacier, West Greenland, marked the onset of a renewed jokulhlaup cycle after 20 years of stability. We present a record of successive ice-dammed lake drainage events and associated ice-margin dynamics spanning 25 years. Robust calculations of lake volumes and peak discharges are made, based on intensive field surveys and utilizing high-spatial-resolution orthophotographs of the lake basin and ice margin. These data enable identification of controls on the behaviour of the ice-dammed lake and provide the first field-based examination of controls on jokulhlaup magnitude and frequency for this system. We find that Russell Glacier jokulhlaups have a much higher peak discharge than predicted by the Clague-Mathews relationship, which we attribute to an unusually short englacial/subglacial routeway and the presence of a thin ice dam that permits incomplete sealing of jokulhlaup conduits between lake drainage events. Additionally, we demonstrate that the passage of jokulhlaups through an interlinked system of proglacial bedrock basins produces significant attenuation of peak discharge downstream. We highlight that improved understanding of jokulhlaup dynamics requires accurate information about ice-dammed lake volume and ice-proximal jokulhlaup discharge.

Hydrochemical characteristics of bulk meltwater from an entire ablation season, Longyearbreen, Svalbard

The ionic and isotopic characteristics of bulk waters emanating from the cold-based Longyearbreen, central Svalbard, in 2004 are examined to determine lithological, hydrological and glaciological controls on water composition, solute provenance and chemical denudation. The geology consisted of reactive coal seams and associated sedimentary rocks. Acidity caused by microbial-mediated oxidation of sulfides and, to a lesser extent, nitrogen-bearing minerals was neutralized by congruent dissolution of dolomite and incongruent weathering of silicates in open-system subglacial drainage channels. The ablation season was divided into an early melt season, a peak-flow period and a late melt season. The runoff distribution during these periods was 1.7%, 89.7% and 8.6%, respectively, whereas the solute flux distribution was 1.9%, 82.1% and 16.0%, respectively. Comparisons between different annual solute flux estimation methods indicated that extrapolation of peak-flow period data significantly underestimated both the early- and late-melt-season solute fluxes. About 3.8% of the solutes derived from sea-salt spray, 0.7% from acid aerosol deposition and 95.5% from crustal/organic sources. The physical and chemical conditions resulted in diffusion of CO 2 rather than atmospheric drawdown. The cation-equivalent weathering rate and the crustal solute yield were 322 ΣmEq + m -2 a -1 and 22 tkm -2 a -1 , respectively, which are within the regional range of Svalbard. However, the chemical weathering intensity was as high as 940 ΣmEq + m -3 owing to the relatively low specific discharge of 0.34 ma -1 .

20th-century glacier fluctuations on Disko Island (Qeqertarsuaq), Greenland

Abstract This study assesses glacier fluctuations on Disko Island (Qeqertarsuaq), central West Greenland, during the 20th century. A total of 247 glaciers, of which 75 are classified as surge-type glaciers, are included, representing about 95% of the glacierized area. Based on expedition accounts and early maps, it is concluded that recession rates were highest during the first half of the century. Between 1953 and 2005, 70% of the glaciers showed recession, 28% remained stationary and 2% experienced overall advance due to glacier surging. The mean recession rate of quiescent surge-type glaciers was 20 ma–1 compared to 8ma–1 for normal glaciers. Identification of changes in glacier length controlled by climate changes is achieved by excluding surge-type glaciers from the dataset. The result indicates that glaciers with ablation areas facing in the arc south to northwest, covering an area above 5 km2 and having a terminus elevation below 800 m are the most climate-sensitive.

Reconstructing Climate Change: Not All Glaciers Suitable

Glaciers are among the most trusted indicators of climate change, not just because they retreat due to the current rise in global temperatures but also because of their central role in reconstructing past climates. Glaciers come in many forms, and their sensitivity to climate change depends partly on the physics governing the individual glacier, implying that a response can be fast or slow, straightforward or complex, which in sum suggests that not all glaciers are equally suitable for reconstructing past and present climate conditions. In particular, surging and debris-covered glaciers may especially yield misleading results (Figure 1).

Spatial Patterns of Soil Development, Methane Oxidation, and Methanotrophic Diversity along a Receding Glacier Forefield, Southeast Greenland

Abstract Increasing global annual temperature leads to massive loss of ice cover worldwide. Consequently, glaciers retreat and ice-covered areas become exposed. We report on a study from the Mittivakkat Gletscher forefield in Southeast Greenland with special focus on methanotrophy in relation to exposure time to the atmosphere. The Mittivakkat Gletscher has receded since the end of the Little Ice Age (LIA; about AD 1850) and has left behind a series of deposits of decreasing age concurrently with its recession. Soil samples from this chronosequence were examined in order to elucidate main soil variables, as well as the activity and community structure of methanotrophs, a group of microorganisms involved in regulation of atmospheric methane. Soil variables revealed poor soil development, and incubation experiments showed methane consumption rates of 2.14 nmol CH4 day−1 gsoil−1 at 22 °C and 1.24 nmol CH4 day−1 gsoil−1 at 10 °C in the LIA terminal moraine. Methane consumption was not detected in younger samples, despite the presence of high-affinity methanotrophs in all samples. This was indicated by successful amplification of partial pmoA genes, which code for a subunit of a key enzyme involved in methane oxidation. In addition, the results of the diversity study show that the diversity of the methanotrophic community at the younger, recently deglaciated site P5 is poorer than the diversity of the community retrieved from the LIA moraine. We put forward the hypothesis that aerobic methanotrophs were at very low abundance and diversity during glaciation probably due to anoxia at the ice-sediment interface and that colonization after deglaciation is not completed yet. More detailed studies are required to explain the causes of discrepancy between activity and presence of high-affinity methanotrophs and its relation to the transit from ice-covered probably anoxic to ice-free oxic conditions.

High export of dissolved silica from the Greenland Ice Sheet

Silica is an essential element for marine life and plays a key role in the biogeochemistry of the ocean. Glacial activity stimulates rock weathering, generating dissolved silica that is exported to coastal areas along with meltwater. The magnitude of the dissolved silica export from large glacial areas such as the Greenland Ice Sheet is presently poorly quantified and not accounted for in global budgets. Here we present data from two fjord systems adjacent to the Greenland Ice Sheet which reveal a large export of dissolved silica by glacial meltwater relative to other macronutrients. Upscaled to the entire Greenland Ice Sheet, the export of dissolved silica equals 22 ± 10 Gmol Si yr−1. When the silicate-rich meltwater mixes with upwelled deep water, either inside or outside Greenlands fjords, primary production takes place at increased silicate to nitrate ratios. This likely stimulates the growth of diatoms relative to other phytoplankton groups.

Recent marginal changes of the Mittivakkat Glacier, Southeast Greenland and the discovery of remains of reindeer (Rangifer tarandus), polar bear (Ursus maritimus) and peaty material

Abstract Geografisk Tidsskrift, Danish Journal of Geography 108(1):137–142, 2008 During field observations in August 2005 antler remains of a reindeer were found at a recently deglaciated site at about 500 m asl., and bones from a polar bear were found at about 300 m asl. along the margin of Mittivakkat Glacier, Southeast Greenland. Radio carbon dating determined the age of the samples to 720 14C years and 350 14C years, respectively. In August 2006 old surface vegetation covering peaty material became exposed due to ice recession close to the site where the antler was found. The radio carbon age of small roots from the material was determined to 1530 14C years, and is in agreement with dating of woody remains of Salix glauca found close by, at the top of a nearby nunatak in 1999. The antler indicates that reindeer lived in the area when the glacier began to advance from a position where it was close to or smaller than today. The vegetation surface and peaty material indicate that the climate was warmer before the onset of the Little Ice Age in Southeast Greenland than today.

Suspended sediment transport in glacial meltwater during the initial quiescent phase after a major surge event at Kuannersuit Glacier, Greenland

Abstract This paper describes a rough estimate of the suspended sediment transport in the bulk meltwater evacuated from Kuannersuit Glacier during the summers of 2000 and 2001. In 1995–98, an 11 km terrestrial surge of Kuannersuit Glacier, an outlet glacier of the largest ice cap on Disko Island, West Greenland, affected the catchment dramatically. The results show that in 2000, the daily sediment discharge was about 32,500 t day−1, corresponding to a specific sediment load of 19,000 t km-2 year−1. In 2001 the diurnal suspended sediment load was about 26,000 t day−1, corresponding to a specific sediment load of 15,000 t km−2 year−1. There was only a poor relation between meltwater discharge and suspended sediment transport, indicating that the drainage system was highly unstable. In 2001 the discharge and the sediment transport on several occasions was affected by collapse within the glacial drainage system and at the glacier margin. Assuming that suspended sediment transport and bedload is equal, the effective mechanical erosion is about 15 mm year−1. Compared to the sediment transport from other parts of Greenland and High Arctic regions the transport during the surge event and in the early quiescent phase is significantly higher. This indicates the importance of glacier surge in initiating sediment transport pulses in cold regions.