Lacelle D, Radtke K, Clark ID, Fisher D, Lauriol B, Utting N, Whyte LG. 2011. Geomicrobiology and occluded O2-CO2-Ar gas analyses provide evidence of microbial respiration in ancient terrestrial ground ice. Earth and Planetary Science Letters 306: 46-54.
These authors compared the gas composition of ice from massive ground ice bodies (e.g. 30 000-year-old buried snowbanks) to atmospheric gas concentrations and gas contents from glacial ice. They also cultivated some microorganisms collected from within the ice, and used some non-culture-dependent methods to examine the diversity of those organisms.
Loss of O2, as determined by comparison of the ratio of O2 to Ar in samples, as well as changes to the 13C-CO2 contents indicate heterotrophic microbial activity in the ice, most likely by organisms living in high-salt brine channels in cracks in the ice, using dissolved organic carbon as both energy and C source.
This paper provides an overview of methods for extracting and measuring the gases trapped in microscopic bubbles in permafrost and ground ice, as well as interesting findings about microbial activities.
Showing posts with label Geology. Show all posts
Showing posts with label Geology. Show all posts
Thursday, August 25, 2011
Lacelle et al. 2008
Lacelle D, Juneau V, Pellerin A, Lauriol B, Clark ID. 2008. Weathering regime and geochemical conditions in a polar desert environment, Haughton impact structure region, Devon Island, Canada. Canadian Journal of Earth Science 45: 1139-1157.
These authors examined the soils and waters near the Haughton crater on Devon Island, to determine the importance of chemical and mechanical weathering in this polar desert environment. They examined dissolved material in streams, lakes, snow, and groundwaters, and the size distribution, shape, and chemical composition of particles from soils in several different local landforms and parent materials.
Despite low temperatures, low precipitation, and very low vegetation presence, significant chemical weathering was found. Signs of chemical weathering, rather than mechanical, include rounded surfaces and pits in sand particles and the concentrations of Ca2+, Mg2+, and HCO3- in waters. Signs of mechanical weathering were also found, including sharp fracture lines in particles.
A gradient of increasing chemical weathering and decreasing mechanical weathering was found from the surface to the permafrost table. Thermal buffering reduces the frequency of frost-driven forces and thermal expansion from daily at the surface to annually at the permafrost table. The permafrost acts as a barrier to water movement, creating relatively wet condtions at depth that allow aqueous chemistry including the dissolution of dolomite to proceed.
These authors examined the soils and waters near the Haughton crater on Devon Island, to determine the importance of chemical and mechanical weathering in this polar desert environment. They examined dissolved material in streams, lakes, snow, and groundwaters, and the size distribution, shape, and chemical composition of particles from soils in several different local landforms and parent materials.
Despite low temperatures, low precipitation, and very low vegetation presence, significant chemical weathering was found. Signs of chemical weathering, rather than mechanical, include rounded surfaces and pits in sand particles and the concentrations of Ca2+, Mg2+, and HCO3- in waters. Signs of mechanical weathering were also found, including sharp fracture lines in particles.
A gradient of increasing chemical weathering and decreasing mechanical weathering was found from the surface to the permafrost table. Thermal buffering reduces the frequency of frost-driven forces and thermal expansion from daily at the surface to annually at the permafrost table. The permafrost acts as a barrier to water movement, creating relatively wet condtions at depth that allow aqueous chemistry including the dissolution of dolomite to proceed.
Monday, August 23, 2010
Pennock et al. 1987
Pennock DJ, Zebarth BJ, De Jong E. 1987. Landform classification and soil distribution in hummocky terrain, Saskatchewan, Canada. Geoderma 40: 297-315.
These authors present a method of analysing irregular terrain for the purposes of examining important soil parameters such as soil depth and soil hydrology. Three variables (profile curvature, plan curvature, and gradient) can be calculated from a matrix of elevation data; taken together for a given point or area, these variables can be used to classify an area into one of seven landforms. These landforms are level (for summits or bottom lands), shoulders, backslopes, and footslopes; the three non-level forms come in “divergent” (convex plan) and “convergent” (concave plan) varieties. Shoulders have convex profiles, backslopes have flat profiles (i.e. constant gradient when looking up or down the slope), and footslopes are concave. Divergent landforms shed water laterally; convergent landforms tend to collect water. Where water collects and is moving slowly, rates of infiltration will be highest, and erosion will tend to deposit, rather than remove, material at these places.
The variables required to calculate profile and plan curvature and gradient are relatively easy to calculate from a matrix of elevation data, using an interpolating topographical software package and some differential calculus. The seven categories of slope elements can be estimated in the field by eye, making for a useful method for field studies.
This paper was on the recommended reading list for SLSC 834; in addition, the course instructor is Dr. Pennock, lead author of this study. The study site, near Hafford, Saskatchewan, is perhaps 1 to 1.5 hours drive away from Saskatoon, suggesting this area may be the destination of one of the day trips scheduled for the week of August 30, 2010.
These authors present a method of analysing irregular terrain for the purposes of examining important soil parameters such as soil depth and soil hydrology. Three variables (profile curvature, plan curvature, and gradient) can be calculated from a matrix of elevation data; taken together for a given point or area, these variables can be used to classify an area into one of seven landforms. These landforms are level (for summits or bottom lands), shoulders, backslopes, and footslopes; the three non-level forms come in “divergent” (convex plan) and “convergent” (concave plan) varieties. Shoulders have convex profiles, backslopes have flat profiles (i.e. constant gradient when looking up or down the slope), and footslopes are concave. Divergent landforms shed water laterally; convergent landforms tend to collect water. Where water collects and is moving slowly, rates of infiltration will be highest, and erosion will tend to deposit, rather than remove, material at these places.
The variables required to calculate profile and plan curvature and gradient are relatively easy to calculate from a matrix of elevation data, using an interpolating topographical software package and some differential calculus. The seven categories of slope elements can be estimated in the field by eye, making for a useful method for field studies.
This paper was on the recommended reading list for SLSC 834; in addition, the course instructor is Dr. Pennock, lead author of this study. The study site, near Hafford, Saskatchewan, is perhaps 1 to 1.5 hours drive away from Saskatoon, suggesting this area may be the destination of one of the day trips scheduled for the week of August 30, 2010.
Thursday, August 19, 2010
Christiansen 1979
Christiansen EA. 1979. The Wisconsinan deglaciation of southern Saskatchewan and adjacent areas. Canadian Journal of Earth Science 16: 913-938.
This author describes in considerable detail the process of deglaciation that occurred at the end of the last glacial maximum from about 17 000 years ago, as it occurs to Saskatchewan. Major geological features and patterns of melt-water drainage led to the inclusion of nearby parts of Alberta, Manitoba, Montana, and North Dakota in the analysis. Patterns during the deglaciation were identified by glacial landforms, many of which are apparent only from aerial photographs, with sample analysis in the lab including radio-carbon dating.
The period from 17 000 years to 10 000 years ago is divided into 9 phases corresponding to periods of rapid glacial retreat or temporary stasis or glacial advance. By 10 000 years ago the ice sheet that had covered nearly the entire province had retreated towards Hudson Bay and covered only a small part of the north of Saskatchewan. Glacial lakes formed from meltwater and from water flowing from the west (presumably sourced from glaciers in the Rocky mountains), sometimes reaching enormous sizes; these lakes were bordered by the glacier’s edge, and connected to each other via spillways that often carved large channels from the plains; the east-west valleys of southern Saskatchewan such as the Qu’Appelle valley are the remains of such spillways. Modern river systems such as the Saskatchewan River and the Churchill River formed during the glacial retreat, occupying low areas and spillway remnants.
The rate of deglaciation varied considerably over the studied 7 000 years, generally accelerating from about 150 m / yr to around 275 m / yr, though with frequent pauses, occasional re-advances, and variation across the glacial edge. The evidence from glacial lake-edge movements and depth patterns suggests the ice sheet melted fastest initially, but with the slowest retreat at that time indicating the sheet first thinned, and then retreated, especially around newly-uncovered Nunataks where the underlying land formed highlands.
This paper was on the suggested reading list for the course SLSC 834 in August 2010, but it is also personally interesting in describing Pleistocene events in areas I visit during Sunday drives across the center of the province.
This author describes in considerable detail the process of deglaciation that occurred at the end of the last glacial maximum from about 17 000 years ago, as it occurs to Saskatchewan. Major geological features and patterns of melt-water drainage led to the inclusion of nearby parts of Alberta, Manitoba, Montana, and North Dakota in the analysis. Patterns during the deglaciation were identified by glacial landforms, many of which are apparent only from aerial photographs, with sample analysis in the lab including radio-carbon dating.
The period from 17 000 years to 10 000 years ago is divided into 9 phases corresponding to periods of rapid glacial retreat or temporary stasis or glacial advance. By 10 000 years ago the ice sheet that had covered nearly the entire province had retreated towards Hudson Bay and covered only a small part of the north of Saskatchewan. Glacial lakes formed from meltwater and from water flowing from the west (presumably sourced from glaciers in the Rocky mountains), sometimes reaching enormous sizes; these lakes were bordered by the glacier’s edge, and connected to each other via spillways that often carved large channels from the plains; the east-west valleys of southern Saskatchewan such as the Qu’Appelle valley are the remains of such spillways. Modern river systems such as the Saskatchewan River and the Churchill River formed during the glacial retreat, occupying low areas and spillway remnants.
The rate of deglaciation varied considerably over the studied 7 000 years, generally accelerating from about 150 m / yr to around 275 m / yr, though with frequent pauses, occasional re-advances, and variation across the glacial edge. The evidence from glacial lake-edge movements and depth patterns suggests the ice sheet melted fastest initially, but with the slowest retreat at that time indicating the sheet first thinned, and then retreated, especially around newly-uncovered Nunataks where the underlying land formed highlands.
This paper was on the suggested reading list for the course SLSC 834 in August 2010, but it is also personally interesting in describing Pleistocene events in areas I visit during Sunday drives across the center of the province.
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