TY - JOUR
A1 - Heeschen, Katja U.
A1 - Janocha, Julian
A1 - Spangenberg, Erik
A1 - Schicks, Judith Maria
A1 - Giese, Ronny
T1 - The impact of ice on the tensile strength of unconsolidated sand
BT - a model for gas hydrate-bearing sands?
JF - Marine and petroleum geology
N2 - Tensile strength is an important parameter when it comes to predictions of potential fracturing of sediments by natural processes such as the emplacement of ice or gas hydrate lenses, as well as anthropogenic fracturing or else the stability of engineering constructions such as boreholes. Yet, tensile strength (sigma(tau)) measurements of unconsolidated ice-bearing or gas hydrate-bearing sands are scarce and affected by a large variability.
In the course of the SUGAR project we successfully used ice as a model for pore-filling and "load-bearing" gas hydrate in sand to determine compressional wave velocity. We were thus able to verify comparable formation characteristics and morphologies of ice and gas hydrate within the pore space. As these are important values for the tensile strength of ice/hydrate-bearing sands, ice was also used as a model for hydrate-bearing sands, despite differences in the mechanical behavior and strength of pure ice and gas hydrate. Water-saturated sand cores with ice saturations (S-ice) between 0 and 100% were tested at -6.8 degrees C. The varying S-ice were a result of the freezing point depression caused by saline solutions of different concentrations. The sigma(tau) was directly determined using a sleeve-fracturing test with an internal pressure that was created within the frozen samples. The setup was also adapted to fit a pressure vessel for tests using confining pressure.
The correlation of S-ice - sigma(tau) shows an exponential increase of sigma(tau) with S-ice. Whereas at S-ice < 60% the increase is small, it is large at S-ice > 80%. In conjunction with the change in strength, the viscoelastic behavior changes. A clear peak strength occurs at S-ice > 80%. We conclude that given 60% < S-ice < 80% the pore-filling morphology of the ice converts into a frame-building habitus and at S-ice > 80% the frame gains strength while the amount of residual water decreases. Tensile failure and cracking now exceed grain boundary sliding as the prevailing failure mode. The ice morphology in the sand is non-cementing and comparable to a gas hydrate-sand mixture.
KW - tensile strength
KW - ice-grain mixture
KW - gas hydrate
KW - saline permafrost
KW - ice
KW - frozen soil
Y1 - 2020
U6 - https://doi.org/10.1016/j.marpetgeo.2020.104607
SN - 0264-8172
SN - 1873-4073
VL - 122
PB - Elsevier
CY - Oxford
ER -
TY - GEN
A1 - Lara, Mark J.
A1 - Nitze, Ingmar
A1 - Große, Guido
A1 - McGuire, David
T1 - Tundra landform and vegetation productivity trend maps for the Arctic Coastal Plain of northern Alaska
T2 - Postprints der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe
N2 - Arctic tundra landscapes are composed of a complex mosaic of patterned ground features, varying in soil moisture, vegetation composition, and surface hydrology over small spatial scales (10-100 m). The importance of microtopography and associated geomorphic landforms in influencing ecosystem structure and function is well founded, however, spatial data products describing local to regional scale distribution of patterned ground or polygonal tundra geomorphology are largely unavailable. Thus, our understanding of local impacts on regional scale processes (e.g., carbon dynamics) may be limited. We produced two key spatiotemporal datasets spanning the Arctic Coastal Plain of northern Alaska (similar to 60,000 km(2)) to evaluate climate-geomorphological controls on arctic tundra productivity change, using (1) a novel 30m classification of polygonal tundra geomorphology and (2) decadal-trends in surface greenness using the Landsat archive (1999-2014). These datasets can be easily integrated and adapted in an array of local to regional applications such as (1) upscaling plot-level measurements (e.g., carbon/energy fluxes), (2) mapping of soils, vegetation, or permafrost, and/or (3) initializing ecosystem biogeochemistry, hydrology, and/or habitat modeling.
T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 1035
KW - spatial-distribution
KW - lake basins
KW - microtopography
KW - water
KW - ice
KW - accumulation
KW - degradation
KW - permafrost
KW - dynamics
KW - barrow
Y1 - 2020
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-459875
SN - 1866-8372
IS - 1035
ER -
TY - GEN
A1 - Lara, Mark J.
A1 - Nitze, Ingmar
A1 - Grosse, Guido
A1 - Martin, Philip
A1 - McGuire, A. David
T1 - Reduced arctic tundra productivity linked with landform and climate change interactions
T2 - Postprints der Universität Potsdam Mathematisch-Naturwissenschaftliche Reihe
N2 - Arctic tundra ecosystems have experienced unprecedented change associated with climate warming over recent decades. Across the Pan-Arctic, vegetation productivity and surface greenness have trended positively over the period of satellite observation. However, since 2011 these trends have slowed considerably, showing signs of browning in many regions. It is unclear what factors are driving this change and which regions/landforms will be most sensitive to future browning. Here we provide evidence linking decadal patterns in arctic greening and browning with regional climate change and local permafrost-driven landscape heterogeneity. We analyzed the spatial variability of decadal-scale trends in surface greenness across the Arctic Coastal Plain of northern Alaska (similar to 60,000 km(2)) using the Landsat archive (1999-2014), in combination with novel 30 m classifications of polygonal tundra and regional watersheds, finding landscape heterogeneity and regional climate change to be the most important factors controlling historical greenness trends. Browning was linked to increased temperature and precipitation, with the exception of young landforms (developed following lake drainage), which will likely continue to green. Spatiotemporal model forecasting suggests carbon uptake potential to be reduced in response to warmer and/or wetter climatic conditions, potentially increasing the net loss of carbon to the atmosphere, at a greater degree than previously expected.
T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 550
KW - winter warming events
KW - permafrost
KW - Alaska
KW - trends
KW - ice
KW - CO2
KW - degradation
KW - landscapes
KW - ecosystem
KW - exchange
Y1 - 2019
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-423132
SN - 1866-8372
IS - 550
ER -