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  • 1
    Publication Date: 2018-07-09
    Type: Conference or Workshop Item , NonPeerReviewed
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  • 2
    Publication Date: 2017-09-13
    Description: A multi-year mooring record (2007-2014) and satellite imagery highlight the strong temperature variability and unique hydrographic nature of the Laptev Sea. This Arctic shelf is a key region for river discharge and sea ice formation and export, and includes submarine permafrost and methane deposits, which emphasizes the need to understand the thermal variability near the seafloor. Recent years were characterized by early ice retreat and a warming near-shore environment. However, warming was not observed on the deeper shelf until year-round under-ice measurements recorded unprecedented warm near-bottom waters of +0.6°C in winter 2012/2013, just after the Arctic sea ice extent featured a record minimum. In the Laptev Sea, early ice retreat in 2012 combined with Lena River heat and solar radiation produced anomalously warm summer surface waters, which were vertically mixed, trapped in the pycnocline, and subsequently transferred toward the bottom until the water column cooled when brine rejection eroded stratification.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed
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  • 3
    Publication Date: 2018-08-24
    Description: Ice-rich permafrost coasts in the Arctic are susceptible to a variety of changing environmental factors, all of which currently point to increasing coastal erosion rates and mass fluxes of sediment and carbon to the shallow arctic shelf seas. Coastal erosion and flooding inundate terrestrial permafrost with seawater and create submarine permafrost. Permafrost begins to warm under marine conditions, which can destabilize the sea floor and may release greenhouse gases. The rate and spatial distribution of subsea permafrost degradation in the Laptev, East Siberian and Chukchi seas, which together comprise more than half of the Arctic Ocean continental shelf, remain poorly explored. We report on the transition of terrestrial to subsea permafrost at four coastal sites in the Laptev Sea: Cape Mamontov Klyk in the western Laptev Sea, and Buor Khaya Peninsula, Muostakh Island and the Bykovsky Peninsula in the central Laptev Sea. We use coastal erosion rates from about the last 70 years to estimate the period of inundation at these sites. Combined with direct (drilling and temperature) and indirect (geophysical) observations of thaw depths of ice-bonded permafrost, we estimate recent degradation rates of permafrost over the past centuries. Based on these observations, the unfrozen sediment layer overlying ice-bonded permafrost increased from less than a meter at the shoreline to over 30 m below seabed with increasing distance from the shoreline at our study sites, with high spatial variability between and within sites. Observed temperatures of the sediment ranged from -5 °C to positive temperatures. In coastal sediments, it is difficult to establish an age-depth model, making corroboration of estimated degradation rates a challenge. Nonetheless, as the thickness of the unfrozen sediment layer increases over time, the vertical thermal and salt concentration gradients decrease, slowing the downward heat and mass fluxes responsible for degradation. High sedimentation rates and ice contents probably stabilize subsea permafrost. We suggest that permafrost degradation relevant to gas flow is likely to have occurred where permafrost warmed prior to inundation.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , NonPeerReviewed
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  • 4
    Publication Date: 2018-08-08
    Description: Abstract Waterbodies in the arctic permafrost zone are considered a major source of the greenhouse gas methane (CH4) in addition to CH4 emissions from arctic wetlands. However, the spatio-temporal variability of CH4 fluxes from waterbodies compli- cates spatial extrapolation of CH4 measurements from single waterbodies. There- fore, their contribution to the CH4 budget of the arctic permafrost zone is not yet well understood. Using the example of two study areas of 1,000 km2 each in the Mackenzie Delta, Canada, we approach this issue (i) by analyzing correlations on the landscape scale between numerous waterbodies and CH4 fluxes and (ii) by analyzing the influence of the spatial resolution of CH4 flux data on the detected relation- ships. A CH4 flux map with a resolution of 100 m was derived from two aircraft eddy-covariance campaigns in the summers of 2012 and 2013. We combined the CH4 flux map with high spatial resolution (2.5 m) waterbody maps from the Per- mafrost Region Pond and Lake Database and classified the waterbody depth based on Sentinel-1 SAR backscatter data. Subsequently, we reduced the resolution of the CH4 flux map to analyze if different spatial resolutions of CH4 flux data affected the detectability of relationships between waterbody coverage, number, depth, or size and the CH4 flux. We did not find consistent correlations between waterbody characteristics and the CH4 flux in the two study areas across the different resolu- tions. Our results indicate that waterbodies in permafrost landscapes, even if they seem to be emission hot spots on an individual basis or contain zones of above average emissions, do currently not necessarily translate into significant CH4 emis- sion hot spots on a regional scale, but their role might change in a warmer climate. KEYWORDS airborne eddy-covariance, Arctic, CH4, lakes, ponds, remote sensing, Sentinel-1, TerraSAR-X
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed
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  • 5
    Publication Date: 2019-05-03
    Description: The Laptev and Eastern Siberian shelves are the world’s broadest shallow shelf systems. Large Siberian rivers and coastal erosion of up to meters per summer deliver large volumes of terrestrial matter into the Arctic shelf seas. In this chapter we investigate the applicability of Ocean Colour Remote Sensing during the ice-free summer season in the Siberian Laptev Sea region. We show that the early summer river peak discharge may be traced using remote sensing in years characterized by early sea-ice retreat. In the summer time after the peak discharge, the spreading of the main Lena River plume east and north-east of the Lena River Delta into the shelf system becomes hardly traceable using optical remote sensing methods. Measurements of suspended particulate matter (SPM) and coloured dissolved organic matter (cDOM) are of the same magnitude in the coastal waters of Buor Khaya Bay as in the Lena River. Match-up analyses of in situ chlorophyll-a (Chl-a) show that standard Medium Resolution Imaging Spectrometer (MERIS) and Moderate Resolution Imaging Spectroradiometer (MODIS) satellite-derived Chl-a is not a valid remote sensing product for the coastal waters and the inner shelf region of the Laptev Sea. All MERIS and MODIS-derived Chl-a products are overestimated by at least a factor of ten, probably due to absorption by the extraordinarily high amount of non-algal particles and cDOM in these coastal and inner-shelf waters. Instead, Ocean Colour remote sensing provides information on wide-spread resuspension over shallows and lateral advection visible in satellite-derived turbidity. Satellite Sea Surface Temperature (SST) data clearly show hydrodynamics and delineate the outflow of the Lena River for hundreds of kilometres out into the shelf seas.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Book , NonPeerReviewed
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  • 6
  • 7
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    Publisher Laboratoire EDYTEM - UMR5204 Université Savoie Mont Blanc Bâtiment « Pôle Montagne » 5 bd de la mer Caspienne F-73376 Le Bourget du Lac cedex
    Publication Date: 2018-08-08
    Description: Waterbodies in the arctic permafrost zone are considered a major source of the greenhouse gas methane (CH4). Spatial extrapolation of these CH4 fluxes to a region or the circum-Arctic, however, are still associated with large uncertainties. Here, we address this issue by using a combination of airborne CH 4 flux measurements and waterbody mapping based on TerraSAR-X and Sentinel-1 data across two study areas (1000 km2) in the Mackenzie Delta, Canada. Our results indicate that permafrost waterbodies, even if they seem to be strong emitters on an individual basis, do not necessarily translate into significant CH 4 emission hot spots on a regional scale. Our results show inconsistent patterns in the correlations between waterbody types and the CH 4 flux in the two study areas and across different spatial resolutions. Technical advances enabling the determination of the CH4 flux of individual waterbodies across a region provide a prospective direction to improve our understanding.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , NonPeerReviewed
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  • 8
    Publication Date: 2019-08-25
    Description: River water is the main source of dissolved organic carbon (DOC) in the Arctic Ocean. DOC plays an important role in the Arctic carbon cycle, and its export from land to sea is expected to increase as ongoing climate change accelerates permafrost thaw. However, transport pathways and transformation of DOC in the land-to-ocean transition are mostly unknown. We collected DOC and aCDOM(λ) samples from 11 expeditions to river, coastal and offshore waters and present a new DOC–aCDOM(λ) model for the fluvial–marine transition zone in the Laptev Sea. The aCDOM(λ) characteristics revealed that the dissolved organic matter (DOM) in samples of this dataset are primarily of terrigenous origin. Observed changes in aCDOM(443) and its spectral slopes indicate that DOM is modified by microbial and photo-degradation. Ocean colour remote sensing (OCRS) provides the absorption coefficient of coloured dissolved organic matter (aCDOM(λ)sat) at λ=440 or 443 nm, which can be used to estimate DOC concentration at high temporal and spatial resolution over large regions. We tested the statistical performance of five OCRS algorithms and evaluated the plausibility of the spatial distribution of derived aCDOM(λ)sat. The OLCI (Sentinel-3 Ocean and Land Colour Instrument) neural network swarm (ONNS) algorithm showed the best performance compared to in situ aCDOM(440) (r2=0.72). Additionally, we found ONNS-derived aCDOM(440), in contrast to other algorithms, to be partly independent of sediment concentration, making ONNS the most suitable aCDOM(λ)sat algorithm for the Laptev Sea region. The DOC–aCDOM(λ) model was applied to ONNS-derived aCDOM(440), and retrieved DOC concentration maps showed moderate agreement to in situ data (r2=0.53). The in situ and satellite-retrieved data were offset by up to several days, which may partly explain the weak correlation for this dynamic region. Satellite-derived surface water DOC concentration maps from Medium Resolution Imaging Spectrometer (MERIS) satellite data demonstrate rapid removal of DOC within short time periods in coastal waters of the Laptev Sea, which is likely caused by physical mixing and different types of degradation processes. Using samples from all occurring water types leads to a more robust DOC–aCDOM(λ) model for the retrievals of DOC in Arctic shelf and river waters.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed
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  • 9
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    In:  [Talk] In: Russian-German Cooperation in the Scientific Exploration of Northern Eurasia and the Adjacent Arctic Ocean, 10.09.-12.09.2012, St. Petersburg, Russia .
    Publication Date: 2019-09-23
    Type: Conference or Workshop Item , NonPeerReviewed
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  • 10
    Publication Date: 2019-09-23
    Type: Conference or Workshop Item , NonPeerReviewed
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