Internal structure and recent dynamics of a moraine complex in an alpine glacier forefield revealed by geophysical surveying and Sentinel-1 InSAR time series

Abstract. Aside from many well-known sources, the greenhouse gas methane (CH4) was recently discovered entrapped in the sediments of Swiss Alpine glacier forefields derived from calcareous bedrock. A first study performed in one glacial catchment indicated that CH4 was ubiquitous in sediments and rocks and was largely of thermogenic origin. Here, we present the results of a follow-up study that aimed at (1) determining the occurrence and origin of sediment-entrapped CH4 in other calcareous glacier forefields across Switzerland and (2) providing an inventory of this sediment-entrapped CH4, i.e., determining the contents and total mass of CH4 present, and its spatial distribution within and between five different Swiss glacier forefields situated on calcareous formations of the Helvetic nappes in the Central Alps. Sediment and bedrock samples were collected at high spatial resolution from the forefields of Im Griess, Griessfirn, Griessen, Wildstrubel, and Tsanfleuron glaciers, representing different geographic and geologic regions of the Helvetic nappes. We performed geochemical analyses on gas extracted from sediments and rocks, including the determination of CH4 contents, stable carbon-isotope analyses (δ13CCH4), and the determination of gas-wetness ratios (ratio of CH4 to ethane and propane contents). To estimate the total mass of CH4 entrapped in glacier-forefield sediments, the total volume of sediment was determined based on the measured forefield area and either literature values of mean sediment thickness or direct depth measurements using electrical resistivity tomography. Methane was found in all sediments (0.08–73.81 µg CH4 g−1 dry weight) and most rocks (0.06–108.58 µg CH4 g−1) collected from the five glacier forefields, confirming that entrapped CH4 is ubiquitous in these calcareous formations. Geochemical analyses further confirmed a thermogenic origin of the entrapped CH4 (average δ13CCH4 of sediment of −28.23 (± 3.42) ‰; average gas-wetness ratio of 75.2 (± 48.4)). Whereas sediment-entrapped CH4 contents varied moderately within individual forefields, we noted a large, significant difference in the CH4 content and total CH4 mass (range of 200–3881 t CH4) between glacier forefields at the regional scale. The lithology and tectonic setting within the Helvetic nappes appeared to be dominant factors determining rock and sediment CH4 contents. Overall, a substantial quantity of CH4 was found to be entrapped in Swiss calcareous glacier forefields. Its potential release and subsequent fate in this environment is the subject of ongoing studies.

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ACCELERATING CLIMATE CHANGE IMPACTS ON ALPINE GLACIER FOREFIELD ECOSYSTEMS IN THE EUROPEAN ALPS

Ecological Applications ◽

10.1890/07-1188.1 ◽

2008 ◽

Vol 18 (3) ◽

pp. 637-648 ◽

Cited By ~ 92

Author(s):

Nicoletta Cannone ◽

Guglielmina Diolaiuti ◽

Mauro Guglielmin ◽

Claudio Smiraglia

Keyword(s):

Climate Change ◽

Climate Change Impacts ◽

European Alps ◽

Alpine Glacier ◽

Glacier Forefield

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Iron speciation and isotope fractionation during silicate weathering and soil formation in an alpine glacier forefield chronosequence

Geochimica et Cosmochimica Acta ◽

10.1016/j.gca.2011.07.008 ◽

2011 ◽

Vol 75 (19) ◽

pp. 5559-5573 ◽

Cited By ~ 44

Author(s):

Mirjam Kiczka ◽

Jan G. Wiederhold ◽

Jakob Frommer ◽

Andreas Voegelin ◽

Stephan M. Kraemer ◽

...

Keyword(s):

Isotope Fractionation ◽

Soil Formation ◽

Silicate Weathering ◽

Iron Speciation ◽

Alpine Glacier ◽

Glacier Forefield

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High Temporal and Spatial Variability of Atmospheric-Methane Oxidation in Alpine Glacier Forefield Soils

Applied and Environmental Microbiology ◽

10.1128/aem.01139-17 ◽

2017 ◽

Vol 83 (18) ◽

Cited By ~ 7

Author(s):

Eleonora Chiri ◽

Philipp A. Nauer ◽

Edda-Marie Rainer ◽

Josef Zeyer ◽

Martin H. Schroth

Keyword(s):

Community Structure ◽

Temporal Variability ◽

Physical Parameters ◽

Spatial And Temporal Variability ◽

Alpine Glacier ◽

Glacier Forefield ◽

Methane Oxidizing Bacteria ◽

Uptake Rates ◽

Soil Age ◽

Upland Soils

ABSTRACT Glacier forefield soils can provide a substantial sink for atmospheric CH4, facilitated by aerobic methane-oxidizing bacteria (MOB). However, MOB activity, abundance, and community structure may be affected by soil age, MOB location in different forefield landforms, and temporal fluctuations in soil physical parameters. We assessed the spatial and temporal variability of atmospheric-CH4 oxidation in an Alpine glacier forefield during the snow-free season of 2013. We quantified CH4 flux in soils of increasing age and in different landforms (sandhill, terrace, and floodplain forms) by using soil gas profile and static flux chamber methods. To determine MOB abundance and community structure, we employed pmoA gene-based quantitative PCR and targeted amplicon sequencing. Uptake of CH4 increased in magnitude and decreased in variability with increasing soil age. Sandhill soils exhibited CH4 uptake rates ranging from −3.7 to −0.03 mg CH4 m−2 day−1. Floodplain and terrace soils exhibited lower uptake rates and even intermittent CH4 emissions. Linear mixed-effects models indicated that soil age and landform were the dominating factors shaping CH4 flux, followed by cumulative rainfall (weighted sum ≤4 days prior to sampling). Of 31 MOB operational taxonomic units retrieved, ∼30% were potentially novel, and ∼50% were affiliated with upland soil clusters gamma and alpha. The MOB community structures in floodplain and terrace soils were nearly identical but differed significantly from the highly variable sandhill soil communities. We concluded that soil age and landform modulate the soil CH4 sink strength in glacier forefields and that recent rainfall affects its short-term variability. This should be taken into account when including this environment in future CH4 inventories. IMPORTANCE Oxidation of methane (CH4) in well-drained, “upland” soils is an important mechanism for the removal of this potent greenhouse gas from the atmosphere. It is largely mediated by aerobic, methane-oxidizing bacteria (MOB). Whereas there is abundant information on atmospheric-CH4 oxidation in mature upland soils, little is known about this important function in young, developing soils, such as those found in glacier forefields, where new sediments are continuously exposed to the atmosphere as a result of glacial retreat. In this field-based study, we investigated the spatial and temporal variability of atmospheric-CH4 oxidation and associated MOB communities in Alpine glacier forefield soils, aiming at better understanding the factors that shape the sink for atmospheric CH4 in this young soil ecosystem. This study contributes to the knowledge on the dynamics of atmospheric-CH4 oxidation in developing upland soils and represents a further step toward the inclusion of Alpine glacier forefield soils in global CH4 inventories.

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Unlocking annual firn layer water equivalents from ground-penetrating radar data on an Alpine glacier

The Cryosphere ◽

10.5194/tc-9-1075-2015 ◽

2015 ◽

Vol 9 (3) ◽

pp. 1075-1087 ◽

Cited By ~ 15

Author(s):

L. Sold ◽

M. Huss ◽

A. Eichler ◽

M. Schwikowski ◽

M. Hoelzle

Keyword(s):

Time Series ◽

Mass Balance ◽

Ground Penetrating Radar ◽

Spatial Representation ◽

Radar Data ◽

Glacier Mass Balance ◽

Accumulation Rates ◽

Alpine Glacier ◽

Ground Penetrating ◽

Over Time

Abstract. The spatial representation of accumulation measurements is a major limitation for current glacier mass balance monitoring approaches. Here, we present a method for estimating annual accumulation rates on a temperate Alpine glacier based on the interpretation of internal reflection horizons (IRHs) in helicopter-borne ground-penetrating radar (GPR) data. For each individual GPR measurement, the signal travel time is combined with a simple model for firn densification and refreezing of meltwater. The model is calibrated at locations where GPR repeat measurements are available in two subsequent years and the densification can be tracked over time. Two 10.5 m long firn cores provide a reference for the density and chronology of firn layers. Thereby, IRHs correspond to density maxima, but not exclusively to former summer glacier surfaces. Along GPR profile sections from across the accumulation area we obtain the water equivalent (w.e.) of several annual firn layers. Because deeper IRHs could be tracked over shorter distances, the total length of analysed profile sections varies from 7.3 km for the uppermost accumulation layer (2011) to 0.1 km for the deepest (i.e. oldest) layer (2006). According to model results, refreezing accounts for 10% of the density increase over time and depth, and for 2% of the water equivalent. The strongest limitation to our method is the dependence on layer chronology assumptions. We show that GPR can be used not only to complement existing mass balance monitoring programmes on temperate glaciers but also to retrospectively extend newly initiated time series.

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Accuracy of mutual predictions of plant and microbe communities varies along a successional gradient in an alpine glacier forefield

10.1101/2021.08.27.457913 ◽

2021 ◽

Author(s):

Xie He ◽

Maximilian Hanusch ◽

Victoria Ruiz-Hernández ◽

Robert R. Junker

Keyword(s):

Environmental Factors ◽

Community Composition ◽

Diversity Indices ◽

List Type ◽

Alpine Glacier ◽

Glacier Forefield ◽

Successional Gradient ◽

Direct Indication ◽

Bacteria And Fungi ◽

Taxonomic Groups

SummaryDue to climate warming, recently deglaciated glacier forefields create virtually uninhabited substrates waiting for initial colonization of bacteria, fungi and plants and serve as an ideal ecosystem for studying transformations in community composition and diversity over time and the interactions between taxonomic groups.In this study, we investigated the composition and diversity of bacteria, and fungi, plants and environmental factors (pH, temperature, plot age and soil nutrients) along a 1.5km glacier forefield. We used random forest analysis to detect how well the composition and diversity of taxonomic groups and environmental factors can be mutually predicted.Community composition and diversity of taxonomic groups predicted each other more accurately than environmental factors predicted the taxonomic groups; within the taxonomic groups bacteria and fungi predicted each other best and the taxa’s composition was better predicted than diversity indices. Additionally, accuracy of prediction among taxonomic groups and environmental factors considerably varied along the successional gradient.Although our results are no direct indication of interactions between the taxa investigated and the environmental conditions, the accurate predictions among bacteria, fungi, and plants do provide insights into the concerted community assembly of different taxa in response to changing environments along a successional gradient.

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Quantity and distribution of methane entrapped in sediments of calcareous, Alpine glacier forefields

10.5194/bg-2019-490 ◽

2020 ◽

Author(s):

Biqing Zhu ◽

Manuel Kübler ◽

Melanie Ridoli ◽

Daniel Breitenstein ◽

Martin H. Schroth

Keyword(s):

Total Mass ◽

Tectonic Setting ◽

Regional Scale ◽

Stable Carbon Isotope ◽

Alpine Glacier ◽

Helvetic Nappes ◽

Glacier Forefield ◽

Significant Difference ◽

Geochemical Analyses

Abstract. Aside from many well-known sources, the greenhouse gas methane (CH4) was recently discovered entrapped in sediments of Swiss Alpine glacier forefields derived from calcareous bedrock. A first study performed in one glacial catchment indicated that CH4 was ubiquitous in sediments and rocks, and was largely of thermogenic origin. Here we present results of a follow-up study, which aimed at (1) determining occurrence and origin of sediment-entrapped CH4 in other calcareous glacier forefields across Switzerland, and (2) providing an inventory for this sediment-entrapped CH4, i.e., determining contents and total mass of CH4 present, and its spatial distribution within and between five different Swiss glacier forefields situated on calcareous formations of the Helvetic Nappes of the Central Alps. Sediment and bedrock samples were collected at high spatial resolution from the forefields of Im Griess, Griessfirn, Griessen, Wildstrubel, and Tsanfleuron glaciers, representing different geographic and geologic regions of the Helvetic Nappes. We performed geochemical analyses on gas extracted from sediments and rocks, including determination of CH4 contents, stable carbon-isotope analyses (δ13CCH4), and determination of gas-wetness ratios (ratio of CH4 to ethane and propane contents). To estimate the total mass of CH4 entrapped in glacier-forefield sediments, the total volume of sediment was determined based on measured forefield area and either literature values of mean sediment depth or direct depth measurements using electrical-resistivity tomography. Methane was found in all sediments (0.08–73.81 μg CH4 g−1 dry weight) and most rocks (0.06–108.58 µg CH4 g−1) collected from the five glacier forefields, confirming that entrapped CH4 is ubiquitous in these calcareous formations. Geochemical analyses further confirmed a thermogenic origin of the entrapped CH4 (average δ13C-CH4 of sediment: −28.23 (± 3.42) ‰; average gas-wetness ratio: 75.2 (± 48.4)). Whereas sediment-entrapped CH4 contents varied moderately within individual forefields, we noted a large, significant difference in CH4 content and total CH4 mass (range: 200–3881 t CH4) between glacier forefields at the regional scale. Lithology and tectonic setting within the Helvetic Nappes appeared to be dominant factors determining rock and sediment CH4 contents. Overall, a substantial quantity of CH4 was found to be entrapped in Swiss calcareous glacier forefields. Its potential release and subsequent fate in this environment is the subject of ongoing studies.

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