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Timothy G. Fisher - One of the best experts on this subject based on the ideXlab platform.
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megaflooding associated with Glacial Lake Agassiz
2020Co-Authors: Timothy G. FisherAbstract:Abstract Significant baseline and episodic megaflooding from Glacial Lake Agassiz was routed to the south, east and north coasts of North America over the Lake’s nearly 6000 year history. The five phases of Lake-level change were controlled by which outlet was active, which in turn was controlled by ice margin position and glacioisostatic adjustment. The southern outlet is the oldest and best understood outlet, while successively younger outlets are progressively less understood. Eastern drainage synchronous with the Younger Dryas chronozone had been assumed by most studies, but a spillway to accommodate the ∼90 m drop in Lake level is yet to be described. With the south and east outlets unable to accommodate the necessary Lake level drawdown, the northwest outlet has become the default outlet with Arctic Ocean Core data supporting it. However, extant terrestrial data from the continent only provides data for a large flood from the Fort McMurray area closer to the end of the Younger Dryas, coinciding with the timing of the Preboreal Oscillation. The challenge remains to find agreement between the marine and terrestrial records. Uncontroversial is the geomorphic and sedimentologic evidence for flooding into and out of the Lake consisting of large spillways, large boulders, and in places giant current ripples composed of boulders. Flood discharge estimates into and out of the Lake range from 0.04 to ∼1 Sv, with final subGlacial drainage into the Tyrell Sea estimated at ∼5 Sv, sufficient to raise global sea level by 0.18 m and initiate the 8.2 ka stadial.
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determining the Lake Agassiz moorhead phase lowstand elevation from compaction ridges and newly identified strandlines in the red river valley usa
2018Co-Authors: John Dilworth, Timothy G. FisherAbstract:Abstract A variety of low-relief and subtle landforms mapped from high-resolution, hill-shaded DEMs are used to assign a lower limit to the poorly constrained lowstand elevation of the Moorhead Phase of Glacial Lake Agassiz. Downstream ends of compaction ridges (low-relief ridges that trace former stream channels) and weakly developed scarps on either side of the valley at ~247 m are used to provide a best estimate for a lowstand elevation based on geomorphology. Compaction ridges are often sinuous, oriented congruent with modern hydrology, cross-cut younger strandlines, sometimes end at deltas, and formed as a result of delayed greater subsidence of finer-grained sediment than coarser-grained sediment. Previously unmapped, abandoned stream channels of similar scale to compaction ridges are restricted to zones south of Fargo and in places transition downstream into compaction ridges. Many abandoned channels are linear and not occupied by modern streams. Further north, iceberg scours increase in density in lowland areas adjacent to the Red River of the North, where they cross-cut newly identified, low-relief scarps interpreted as erosional scarp strandlines. The 1–2 m relief scarps are currently the strongest geomorphic evidence for the lowest level of the Moorhead Phase of Lake Agassiz.
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10Be ages of flood deposits west of Lake Nipigon, Ontario: evidence for eastward meltwater drainage during the early Holocene Epoch
2016Co-Authors: Meredith A. Kelly, Thomas V. Lowell, Timothy G. Fisher, Peter J. Barnett, Roseanne SchwartzAbstract:The Nipigon channels, located to the west and northwest of Lake Nipigon, Ontario, are thought to have enabled the eastward drainage of meltwater from Glacial Lake Agassiz during the last deglaciation. Here we present the first direct ages of flood deposits in two of these channels using 10Be surface exposure dating. Five 10Be ages of a coarse-grained deposit near the Roaring River in the Kaiashk channel complex indicate deglaciation and cessation of water flow by ∼11 070 ± 430 years. To test for inherited nuclides in boulder samples, we also measured the 10Be concentrations of the undersides of two boulders at the Roaring River site. Five 10Be ages of boulders atop a large bedform near Mundell Lake in the Pillar channel complex indicate deglaciation and cessation of water flow by ∼10 770 ± 240 years. Two 10Be ages of nearby bedrock are slightly younger (10 340 ± 260 and 9860 ± 270 years). The 10Be ages from the two sites are statistically indistinguishable and indicate that Laurentide Ice Sheet recession ...
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geochemical characteristics of Glacial Lake Agassiz sediments and new ages for the moorhead phase at fargo north dakota usa
2014Co-Authors: Xiuju Liu, Kenneth Lepper, Timothy G. Fisher, Thomas V. LowellAbstract:The cause and age of the Moorhead low-water Phase of Glacial Lake Agassiz remains uncertain. New geochemical (X-ray fluorescence (XRF) and elemental analysis) and chronological (optically stimulated luminescence (OSL)) data are used to test for evaporative enrichment within lacustrine sediment from Rabbit Lake, a small basin just above the highest Lake Agassiz strandline, and from two Lake Agassiz sediment cores at Fargo, North Dakota. Increases in quartz and gypsum interpreted to be of aeolian origin suggest increased aridity at Rabbit Lake sometime after 13 540–13 750 cal years BP. From the Fargo cores, lacustrine sediment of the Brenna and Sherack formations did not show convincing evidence for evaporative enrichment. However, this result is complicated by an erosional contact at the top of the Brenna Formation. A thin middle sand unit between the Brenna and Sherack formation clays is stratigraphically equivalent to the Poplar River Formation, West Fargo Member, but its properties differ from the fluvial sand of the West Fargo Member. Four OSL ages from the organic-poor, middle sand unit at Fargo range between 12.8 ± 0.2 and 13.5 ± 0.2 ka (with ±1.6 ka uncertainty) and suggest Lake level fell at Fargo at, or before, 13.1 ± 0.2 ka, the average of the OSL ages. With different sedimentological properties, and a difference of ∼1750 years between the new OSL ages and previously published ages on the West Fargo Member sand, additional work is required to determine whether the middle sand unit is a new member of the Poplar River Formation, recording an earlier and different depositional environment than the West Fargo Member. From a plot of available ages for the Moorhead Phase, the regression remains poorly constrained in time.
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what caused the low water phase of Glacial Lake Agassiz
2013Co-Authors: Thomas V. Lowell, Timothy G. Fisher, Patrick J Applegate, Kenneth LepperAbstract:First-order modeling suggests that a low-water phase in late-Glacial Lake Agassiz can be explained through changes in the balance between evaporation, precipitation, and runoff, rather than drainage. The low-water Moorhead Phase is often attributed to drainage through outlets opened by isostatic depression and retreat of the Laurentide ice margin. However, new data indicate that the proposed outlets were ice-covered during the Moorhead Phase. Instead, the Lake water levels dropped to the Moorhead Phase before the start of the Younger Dryas chronozone and remained there until 11.3 ka. Thus, drainage seems to be an implausible explanation for Younger Dryas-aged low water levels in Lake Agassiz. An alternative explanation is that evaporation equaled or exceeded water inputs from the adjacent ice margin and the deglaciated parts of the drainage basin. To evaluate whether this hypothesis is plausible, we constructed a simple model that considers the paleo-basin geometry, hydrology, and meltwater production from the adjacent ice margin. Modest hydrologic changes (within the range of present-day variability), coupled with low meltwater production, produce a closed basin. Shifts in the location of the polar jet, driven by increased Arctic albedo, may explain our inferred hydrologic changes.
Thomas V. Lowell - One of the best experts on this subject based on the ideXlab platform.
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10Be ages of flood deposits west of Lake Nipigon, Ontario: evidence for eastward meltwater drainage during the early Holocene Epoch
2016Co-Authors: Meredith A. Kelly, Thomas V. Lowell, Timothy G. Fisher, Peter J. Barnett, Roseanne SchwartzAbstract:The Nipigon channels, located to the west and northwest of Lake Nipigon, Ontario, are thought to have enabled the eastward drainage of meltwater from Glacial Lake Agassiz during the last deglaciation. Here we present the first direct ages of flood deposits in two of these channels using 10Be surface exposure dating. Five 10Be ages of a coarse-grained deposit near the Roaring River in the Kaiashk channel complex indicate deglaciation and cessation of water flow by ∼11 070 ± 430 years. To test for inherited nuclides in boulder samples, we also measured the 10Be concentrations of the undersides of two boulders at the Roaring River site. Five 10Be ages of boulders atop a large bedform near Mundell Lake in the Pillar channel complex indicate deglaciation and cessation of water flow by ∼10 770 ± 240 years. Two 10Be ages of nearby bedrock are slightly younger (10 340 ± 260 and 9860 ± 270 years). The 10Be ages from the two sites are statistically indistinguishable and indicate that Laurentide Ice Sheet recession ...
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geochemical characteristics of Glacial Lake Agassiz sediments and new ages for the moorhead phase at fargo north dakota usa
2014Co-Authors: Xiuju Liu, Kenneth Lepper, Timothy G. Fisher, Thomas V. LowellAbstract:The cause and age of the Moorhead low-water Phase of Glacial Lake Agassiz remains uncertain. New geochemical (X-ray fluorescence (XRF) and elemental analysis) and chronological (optically stimulated luminescence (OSL)) data are used to test for evaporative enrichment within lacustrine sediment from Rabbit Lake, a small basin just above the highest Lake Agassiz strandline, and from two Lake Agassiz sediment cores at Fargo, North Dakota. Increases in quartz and gypsum interpreted to be of aeolian origin suggest increased aridity at Rabbit Lake sometime after 13 540–13 750 cal years BP. From the Fargo cores, lacustrine sediment of the Brenna and Sherack formations did not show convincing evidence for evaporative enrichment. However, this result is complicated by an erosional contact at the top of the Brenna Formation. A thin middle sand unit between the Brenna and Sherack formation clays is stratigraphically equivalent to the Poplar River Formation, West Fargo Member, but its properties differ from the fluvial sand of the West Fargo Member. Four OSL ages from the organic-poor, middle sand unit at Fargo range between 12.8 ± 0.2 and 13.5 ± 0.2 ka (with ±1.6 ka uncertainty) and suggest Lake level fell at Fargo at, or before, 13.1 ± 0.2 ka, the average of the OSL ages. With different sedimentological properties, and a difference of ∼1750 years between the new OSL ages and previously published ages on the West Fargo Member sand, additional work is required to determine whether the middle sand unit is a new member of the Poplar River Formation, recording an earlier and different depositional environment than the West Fargo Member. From a plot of available ages for the Moorhead Phase, the regression remains poorly constrained in time.
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what caused the low water phase of Glacial Lake Agassiz
2013Co-Authors: Thomas V. Lowell, Timothy G. Fisher, Patrick J Applegate, Kenneth LepperAbstract:First-order modeling suggests that a low-water phase in late-Glacial Lake Agassiz can be explained through changes in the balance between evaporation, precipitation, and runoff, rather than drainage. The low-water Moorhead Phase is often attributed to drainage through outlets opened by isostatic depression and retreat of the Laurentide ice margin. However, new data indicate that the proposed outlets were ice-covered during the Moorhead Phase. Instead, the Lake water levels dropped to the Moorhead Phase before the start of the Younger Dryas chronozone and remained there until 11.3 ka. Thus, drainage seems to be an implausible explanation for Younger Dryas-aged low water levels in Lake Agassiz. An alternative explanation is that evaporation equaled or exceeded water inputs from the adjacent ice margin and the deglaciated parts of the drainage basin. To evaluate whether this hypothesis is plausible, we constructed a simple model that considers the paleo-basin geometry, hydrology, and meltwater production from the adjacent ice margin. Modest hydrologic changes (within the range of present-day variability), coupled with low meltwater production, produce a closed basin. Shifts in the location of the polar jet, driven by increased Arctic albedo, may explain our inferred hydrologic changes.
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a chronology for Glacial Lake Agassiz shorelines along upham s namesake transect
2013Co-Authors: Kenneth Lepper, Alex W Buell, Timothy G. Fisher, Thomas V. LowellAbstract:Abstract Four traditionally recognized strandline complexes in the southern basin of Glacial Lake Agassiz are the Herman, Norcross, Tintah and Campbell, whose names correspond to towns in west-central Minnesota that lie on a linear transect defined by the Great Northern railroad grade; the active corridor for commerce at the time when Warren Upham was mapping and naming the shorelines of Lake Agassiz (ca.1880–1895). Because shorelines represent static water planes, their extension around the Lake margin establishes time-synchronous Lake levels. Transitions between shoreline positions represent significant water-level fluctuations. However, geologic ages have never been obtained from sites near the namesake towns in the vicinity of the southern outlet. Here we report the first geologic ages for Lake Agassiz shorelines obtained at field sites along the namesake transect, and evaluate the emerging chronology in light of other paleoclimate records. Our current work from 11 sampling sites has yielded 16 independent ages. These results combined with a growing OSL age data set for Lake Agassiz's southern basin provide robust age constraints for the Herman, Norcross and Campbell strandlines with averages and standard deviations of 14.1 ± 0.3 ka, 13.6 ± 0.2 ka, and 10.5 ± 0.3 ka, respectively.
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age determinations for Glacial Lake Agassiz shorelines west of fargo north dakota usa
2011Co-Authors: Kenneth Lepper, Timothy G. Fisher, Kelly L Gorz, Thomas V. LowellAbstract:Understanding the evolution of Lake Agassiz is vital to developing a comprehensive late Quaternary history of central North America. Although many of the geomorphic features of the Lake are well kn...
Paul H Glaser - One of the best experts on this subject based on the ideXlab platform.
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climatic drivers for multidecadal shifts in solute transport and methane production zones within a large peat basin
2016Co-Authors: Paul H Glaser, A S Reeve, Donald I Siegel, Donald O Rosenberry, Jeffrey P Chanton, Elizabeth J Corbett, Soumitri S Dasgupta, Zeno F LevyAbstract:Northern peatlands are an important source for greenhouse gases but their capacity to produce methane remains uncertain under changing climatic conditions. We therefore analyzed a 43-year time series of pore-water chemistry to determine if long-term shifts in precipitation altered the vertical transport of solutes within a large peat basin in northern Minnesota. These data suggest that rates of methane production can be finely tuned to multi-decadal shifts in precipitation that drive the vertical penetration of labile carbon substrates within the Glacial Lake Agassiz Peatlands. Tritium and cation profiles demonstrate that only the upper meter of these peat deposits was flushed by downwardly moving recharge from 1965 through 1983 during a Transitional Dry-to-Moist Period. However, a shift to a moister climate after 1984 drove surface waters much deeper, largely flushing the pore waters of all bogs and fens to depths of 2 m. Labile carbon compounds were transported downward from the rhizosphere to the basal peat at this time producing a substantial enrichment of methane in ∆14C with respect to the solid-phase peat from 1991 to 2008. These data indicate that labile carbon substrates can fuel deep production zones of methanogenesis that more than doubled in thickness across this large peat basin after 1984. Moreover, the entire peat profile apparently has the capacity to produce methane from labile carbon substrates depending on climate-driven modes of solute transport. Future changes in precipitation may therefore play a central role in determining the source strength of peatlands in the global methane cycle.
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HYDROLOGICAL PROCESSES Hydrol. Process. (in press) Published online in Wiley InterScience (www.interscience.wiley.com) DOI: 10.1002/hyp.6239 Heat transport in the Red Lake Bog, Glacial Lake Agassiz
2015Co-Authors: Jeffrey M Mckenzie, Paul H Glaser, Donald I Siegel, Donald O Rosenberry, Clifford I VossAbstract:We report the results of an investigation on the processes controlling heat transport in peat under a large bog in the Glacial Lake Agassiz Peatlands. For 2 years, starting in July 1998, we recorded temperature at 12 depth intervals from 0 to 400 cm within a vertical peat profile at the crest of the bog at sub-daily intervals. We also recorded air temperature 1 m above the peat surface. We calculate a peat thermal conductivity of 0Ð5 W m1 °C1 and model vertical heat transport through the peat using the SUTRA model. The model was calibrated to the first year of data, and then evaluated against the second year of collected heat data. The model results suggest that advective pore-water flow is not necessary to transport heat within the peat profile and most of the heat is transferred by thermal conduction alone in these waterlogged soils. In the spring season, a zero-curtain effect controls the transport of heat through shallow depths of the peat. Changes in local climate and the resulting changes in thermal transport still may cause non-linear feedbacks in methane emissions related to the generation of methane deeper within the peat profile as regional temperatures increase. Copyright 2006 John Wiley & Sons, Ltd. KEY WORDS Glacial Lake Agassiz Peatlands; heat transfer; thermal conductivity; SUTR
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investigating dissolved organic matter decomposition in northern peatlands using complimentary analytical techniques
2013Co-Authors: Malak M Tfaily, Paul H Glaser, J Corbett, Jeffrey P Chanton, Rasha Hamdan, William T CooperAbstract:Abstract The chemical transformations that govern storage, degradation, and loss of organic matter in northern peatlands are poorly characterized, despite the significance of these peat deposits as pivotal reservoirs in the global carbon cycle. One of the most challenging problems concerns the character of dissolved organic matter (DOM) in peat porewaters, particularly higher-molecular weight compounds that may function either as non-reactive sinks or reactive intermediates for organic byproducts of microbial decay. The complexity of these large molecules has defied attempts to characterize their molecular structure in bulk samples with a high degree of precision. We therefore determined the composition and reactivity of DOM from representative bog and fen sites in the Glacial Lake Agassiz Peatlands (GLAP) in northern Minnesota, USA. We applied four complementary techniques: electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI-FT-ICR MS), proton nuclear magnetic resonance spectroscopy (1H NMR), specific UV absorbance (SUVA) and excitation–emission matrix (EEM) fluorescence spectroscopy. We observed that the vast majority (>80%) of molecular formulas that appear in the surface bog DOM are also present at 2.9 m depth, indicating that much of DOM in the bog is resistant to microbial degradation. In contrast to bog samples, a considerable number of new compounds with low O/C and high H/C elemental ratios were observed in the 3 m fen horizon relative to surface samples. These results indicate a more pronounced difference in the composition of surface and deep DOM in the fen. SUVA, determined at 254 nm, indicated significantly lower aromaticity in deep fen samples relative to deep bog samples. This trend was verified by 1H NMR. Aromatic and carbohydrate components represented up to 70% of deep bog DOM but comprised a much smaller proportion of deep fen DOM, which was dominated by functionalized and non-functionalized aliphatics. Molecular formula data determined by FT-ICR mass spectrometry were consistent with results from optical and NMR spectroscopy measurements and showed that compounds with low O/C and high H/C were generated with depth in the fen. Such compounds were absent in both surface fen and in surface and deep bog samples respectively, providing further evidence of qualitative and quantitative differences in the evolution of DOM in fens and bogs. These differences, attributed to either variations in source vegetation or environmental factors that render DOM more reactive in fen sites or less reactive in bog sites, have important implications for the response of peatlands to climate change, since climatic change leading to moister conditions may enhance the abundance of sedge-dominated fens and increase the pool of more labile soil carbon.
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characterization of dissolved organic matter in northern peatland soil porewaters by ultra high resolution mass spectrometry
2010Co-Authors: Juliana Dandrilli, Paul H Glaser, Jeffrey P Chanton, William T CooperAbstract:Abstract Electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI-FT-ICR-MS) was used to identify the qualitative differences between dissolved organic matter (DOM) in fen and bog porewaters from the Red Lake II system in the Glacial Lake Agassiz Peatlands (GLAP) of northern Minnesota. Approximately 80% of the molecular composition in surface porewater was maintained throughout the upper portion of the bog profile (0.17–2.50 m). The qualitative stability of the composition of the DOM was accompanied by a quantitative increase in dissolved organic carbon (DOC) with depth. The composition of DOM in the fen was significantly different at depth, with slightly varying DOC levels. Aromaticity index (AI) values were used to identify condensed aromatic and phenol-type compounds in the porewater of both peatlands. Surface bog and deep fen DOM had surprisingly similar molecular composition. Differences in enzymatic degradation rates via phenol oxidase in the bog and surface fen horizons, slower transport down the bog vertical profile and the presence of a stratum of Sphagnum-woody peat at depth in the fen are suggested as being responsible for the observed variations in DOM composition.
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heat transport in the red Lake bog Glacial Lake Agassiz peatlands
2007Co-Authors: Jeffrey M Mckenzie, Paul H Glaser, Donald I Siegel, Donald O Rosenberry, Clifford I VossAbstract:We report the results of an investigation on the processes controlling heat transport in peat under a large bog in the Glacial Lake Agassiz Peatlands. For 2 years, starting in July 1998, we recorded temperature at 12 depth intervals from 0 to 400 cm within a vertical peat profile at the crest of the bog at sub-daily intervals. We also recorded air temperature 1 m above the peat surface. We calculate a peat thermal conductivity of 0·5 W m−1 °C−1 and model vertical heat transport through the peat using the SUTRA model. The model was calibrated to the first year of data, and then evaluated against the second year of collected heat data. The model results suggest that advective pore-water flow is not necessary to transport heat within the peat profile and most of the heat is transferred by thermal conduction alone in these waterlogged soils. In the spring season, a zero-curtain effect controls the transport of heat through shallow depths of the peat. Changes in local climate and the resulting changes in thermal transport still may cause non-linear feedbacks in methane emissions related to the generation of methane deeper within the peat profile as regional temperatures increase. Copyright © 2006 John Wiley & Sons, Ltd.
Donald I Siegel - One of the best experts on this subject based on the ideXlab platform.
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climatic drivers for multidecadal shifts in solute transport and methane production zones within a large peat basin
2016Co-Authors: Paul H Glaser, A S Reeve, Donald I Siegel, Donald O Rosenberry, Jeffrey P Chanton, Elizabeth J Corbett, Soumitri S Dasgupta, Zeno F LevyAbstract:Northern peatlands are an important source for greenhouse gases but their capacity to produce methane remains uncertain under changing climatic conditions. We therefore analyzed a 43-year time series of pore-water chemistry to determine if long-term shifts in precipitation altered the vertical transport of solutes within a large peat basin in northern Minnesota. These data suggest that rates of methane production can be finely tuned to multi-decadal shifts in precipitation that drive the vertical penetration of labile carbon substrates within the Glacial Lake Agassiz Peatlands. Tritium and cation profiles demonstrate that only the upper meter of these peat deposits was flushed by downwardly moving recharge from 1965 through 1983 during a Transitional Dry-to-Moist Period. However, a shift to a moister climate after 1984 drove surface waters much deeper, largely flushing the pore waters of all bogs and fens to depths of 2 m. Labile carbon compounds were transported downward from the rhizosphere to the basal peat at this time producing a substantial enrichment of methane in ∆14C with respect to the solid-phase peat from 1991 to 2008. These data indicate that labile carbon substrates can fuel deep production zones of methanogenesis that more than doubled in thickness across this large peat basin after 1984. Moreover, the entire peat profile apparently has the capacity to produce methane from labile carbon substrates depending on climate-driven modes of solute transport. Future changes in precipitation may therefore play a central role in determining the source strength of peatlands in the global methane cycle.
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HYDROLOGICAL PROCESSES Hydrol. Process. (in press) Published online in Wiley InterScience (www.interscience.wiley.com) DOI: 10.1002/hyp.6239 Heat transport in the Red Lake Bog, Glacial Lake Agassiz
2015Co-Authors: Jeffrey M Mckenzie, Paul H Glaser, Donald I Siegel, Donald O Rosenberry, Clifford I VossAbstract:We report the results of an investigation on the processes controlling heat transport in peat under a large bog in the Glacial Lake Agassiz Peatlands. For 2 years, starting in July 1998, we recorded temperature at 12 depth intervals from 0 to 400 cm within a vertical peat profile at the crest of the bog at sub-daily intervals. We also recorded air temperature 1 m above the peat surface. We calculate a peat thermal conductivity of 0Ð5 W m1 °C1 and model vertical heat transport through the peat using the SUTRA model. The model was calibrated to the first year of data, and then evaluated against the second year of collected heat data. The model results suggest that advective pore-water flow is not necessary to transport heat within the peat profile and most of the heat is transferred by thermal conduction alone in these waterlogged soils. In the spring season, a zero-curtain effect controls the transport of heat through shallow depths of the peat. Changes in local climate and the resulting changes in thermal transport still may cause non-linear feedbacks in methane emissions related to the generation of methane deeper within the peat profile as regional temperatures increase. Copyright 2006 John Wiley & Sons, Ltd. KEY WORDS Glacial Lake Agassiz Peatlands; heat transfer; thermal conductivity; SUTR
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heat transport in the red Lake bog Glacial Lake Agassiz peatlands
2007Co-Authors: Jeffrey M Mckenzie, Paul H Glaser, Donald I Siegel, Donald O Rosenberry, Clifford I VossAbstract:We report the results of an investigation on the processes controlling heat transport in peat under a large bog in the Glacial Lake Agassiz Peatlands. For 2 years, starting in July 1998, we recorded temperature at 12 depth intervals from 0 to 400 cm within a vertical peat profile at the crest of the bog at sub-daily intervals. We also recorded air temperature 1 m above the peat surface. We calculate a peat thermal conductivity of 0·5 W m−1 °C−1 and model vertical heat transport through the peat using the SUTRA model. The model was calibrated to the first year of data, and then evaluated against the second year of collected heat data. The model results suggest that advective pore-water flow is not necessary to transport heat within the peat profile and most of the heat is transferred by thermal conduction alone in these waterlogged soils. In the spring season, a zero-curtain effect controls the transport of heat through shallow depths of the peat. Changes in local climate and the resulting changes in thermal transport still may cause non-linear feedbacks in methane emissions related to the generation of methane deeper within the peat profile as regional temperatures increase. Copyright © 2006 John Wiley & Sons, Ltd.
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use of hydraulic head to estimate volumetric gas content and ebullition flux in northern peatlands
2003Co-Authors: Donald O Rosenberry, Paul H Glaser, Donald I Siegel, Edwin P WeeksAbstract:[1] Hydraulic head was overpressured at middepth in a 4.2-m thick raised bog in the Glacial Lake Agassiz peatlands of northern Minnesota, and fluctuated in response to atmospheric pressure. Barometric efficiency (BE), determined by calculating ratios of change in hydraulic head to change in atmospheric pressure, ranged from 0.05 to 0.15 during July through November of both 1997 and 1998. The overpressuring and a BE response were caused by free-phase gas contained primarily in the center of the peat column between two or more semielastic, semiconfining layers of more competent peat. Two methods were used to determine the volume of gas bubbles contained in the peat, one using the degree of overpressuring in the middepth of the peat, and the other relating BE to specific yield of the shallow peat. The volume of gas calculated from the overpressuring method averaged 9%, assuming that the gas was distributed over a 2-m thick overpressured interval. The volume of gas using the BE method averaged 13%. Temporal changes in overpressuring and in BE indicate that the volume of gaseous-phase gas also changed with time, most likely because of rapid degassing (ebullition) that allowed sudden loss of gas to the atmosphere. Estimates of gas released during the largest ebullition events ranged from 0.3 to 0.7 mol m−2 d−1. These ebullition events may contribute a significant source of methane and carbon dioxide to the atmosphere that has so far largely gone unmeasured by gas-flux chambers or tower-mounted sensors.
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regional ground water flow modeling of the Glacial Lake Agassiz peatlands minnesota
2001Co-Authors: A S Reeve, J Warzocha, Paul H Glaser, Donald I SiegelAbstract:Abstract Three-dimensional ground-water modeling experiments were done to test the hypothesis that regional ground-water flow is an important component of the water budget in the Glacial Lake Agassiz Peatlands of northern Minnesota. Previous data collected from the Glacial Lake Agassiz Peatlands suggest that regional ground-water flow discharges to these peatlands, maintaining saturation, controlling the peat pore-water chemistry, and driving ecological change. To test this hypothesis, steady-state MODFLOW models were constructed that encompassed an area of 10,160 km 2 . Data used in this modeling project included surface-water and water-table elevations measured across the study area, digital elevation data, and well logs from scientific test wells and domestic water wells drilled in the study area. Numerical simulations indicate that the Itasca Moraine, located to the south of the peatland, acts as a recharge area for regional ground-water flow. Ground water recharged at the Itasca Moraine did not discharge to the Red Lake Peatlands, but rather was intercepted by the Red Lakes or adjacent rivers. Simulations suggest that ground-water flow within the peatlands consists of local-flow systems with streamlines that are less than 10 km long and that ground water from distant recharge areas does not play a prominent role in the hydrology of these peatlands. Ground-water flow reversals previously observed in the Red Lake Peatlands are either the result of interactions between local and intermediate-scale flow systems or the transient release of water stored in Glacial sediments when the water-table is lowered.
James T Teller - One of the best experts on this subject based on the ideXlab platform.
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comments on assessing the ages of the moorhead and emerson phases of Glacial Lake Agassiz and their temporal connection to the younger dryas cold reversal by joseph m young alberto v reyes and duane g froese
2021Co-Authors: James T TellerAbstract:Abstract The paucity of radiocarbon ages in Lake Agassiz sediments between 12.9 and 12.4 ka probably reflects conditions in the Lake that were unsuitable for the growth and accumulation of datable vegetation, not a delay in the time when the level of the Lake declined. Thus, it does not seem appropriate to reject an apparent coincidence of the time of a major drop of the Lake to the Moorhead low-water phase with the start of the Younger Dryas at 12.9 ka. Furthermore, the so-called Emerson phase of Lake Agassiz that followed the Moorhead phase was not a prolonged period of Lake stability, only a brief time when the Lake reached its maximum transgressive limit, stranding the Campbell beach before receding; dates older than ∼10.6 ka reflect sediments deposited during, or reworked from, the Moorhead low-water phase.
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identification of younger dryas outburst flood path from Lake Agassiz to the arctic ocean
2010Co-Authors: Julian B Murton, James T Teller, Mark D Bateman, S R Dallimore, Zhirong YangAbstract:The melting Laurentide Ice Sheet discharged thousands of cubic kilometres of fresh water each year into surrounding oceans, at times suppressing the Atlantic meridional overturning circulation and triggering abrupt climate change1, 2, 3, 4. Understanding the physical mechanisms leading to events such as the Younger Dryas cold interval requires identification of the paths and timing of the freshwater discharges. Although Broecker et al. hypothesized in 1989 that an outburst from Glacial Lake Agassiz triggered the Younger Dryas1, specific evidence has so far proved elusive, leading Broecker to conclude in 2006 that our inability to identify the path taken by the flood is disconcerting2. Here we identify the missing flood pathevident from gravels and a regional erosion surfacerunning through the Mackenzie River system in the Canadian Arctic Coastal Plain. Our modelling of the isostatically adjusted surface in the upstream Fort McMurray region, and a slight revision of the ice margin at this time, allows Lake Agassiz to spill into the Mackenzie drainage basin. From optically stimulated luminescence dating we have determined the approximate age of this Mackenzie River flood into the Arctic Ocean to be shortly after 13,000years ago, near the start of the Younger Dryas. We attribute to this flood a boulder terrace near Fort McMurray with calibrated radiocarbon dates of over 11,500years ago. A large flood into the Arctic Ocean at the start of the Younger Dryas leads us to reject the widespread view that Agassiz overflow at this time was solely eastward into the North Atlantic Ocean.
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alternative routing of Lake Agassiz overflow during the younger dryas new dates paleotopography and a re evaluation
2005Co-Authors: James T Teller, Matthew Boyd, Zhirong Yang, Phillip S G Kor, Amir Mokhtari FardAbstract:Abstract Overflow from Glacial Lake Agassiz has been implicated in affecting late-Glacial ocean circulation and climate. The timing of the diversion of Lake Agassiz overflow away from its southern routing (to the Gulf of Mexico) correlates closely with the Younger Dryas ca 11–10 14 C ka. New models of paleotopography in the eastern outlet region of Lake Agassiz, adjusted for differential isostatic rebound, show that overflow to the Superior basin would have occurred when the Lake formed its Herman, Norcross, and Tintah beaches, just after ∼10.9 14 C ka, if the Laurentide Ice Sheet (LIS) had retreated from the Thunder Bay, Ontario, region by that time. However, the absence of coarse flood deposits normally associated with large overflows, plus the morphology of possible overflow channels in the Thunder Bay region, suggest that Agassiz overflow may not have been routed into the Great Lakes during the Younger Dryas, as previously believed. In addition, non-carbonate radiocarbon dates in the Thunder Bay area are all younger than 10 14 C ka, suggesting that this area may not have been deglaciated until after the Younger Dryas, thus preventing Lake Agassiz overflow through this area. An alternative route of overflow from Lake Agassiz during the Younger Dryas could have been through the northwestern (Clearwater) outlet to the Arctic Ocean, although all research to date shows that this region was covered by ice until ∼10 14 C ka. On the other hand, it is possible that older and coarser overflow sediment may now lie buried beneath finer deposits associated with the 10 14 C ka Marquette readvance of the LIS, which ponded waters in valleys between Lake Agassiz and Lake Superior, or that eastward overflow in this area was not catastrophic.
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A POSSIBLE TSUNAMI IN THE LABRADOR SEA RELATED TO THE DRAINAGE OF Glacial Lake Agassiz ~8400 YEARS B.P.
2005Co-Authors: N. Nirupama, James T Teller, Tad Murty, P. ChittibabuAbstract:For thousands of years, the thick Laurentide Ice Sheet covered a large part of northern North America, damming northward-draining rivers. As this ice retreated, large Lakes formed along its margin. Glacial Lake Agassiz was the largest of these ice-marginal Lakes, covering an area of >800,000 km2 (more than twice the size of the largest Lake in the modern world, the Caspian Sea) before it drained catastrophically into the Labrador Sea. Even before that, Lake Agassiz had periodically released large volumes of water into the ocean via the Great Lakes-St. Lawrence and the Athabasca-Mackenzie River systems. The last and largest of these outbursts released >150,000 km3 through Hudson Bay and Hudson Strait in 6-12 months; the average flux over that period was ~5 Sv (1 Sv = 1×106 m3s-1).When a volume of water this large is discharged into a coastal sea like the Labrador Sea, it may generate a surface flood wave or a tsunami if the water mass is large enough and introduced in a short time. To our knowledge no previous calculations have been made to estimate the potential impact of a flood burst on the generation of solitary waves. Using analogies of tsunamis generated by submarine landslides and ocean earthquakes, the amplitude of a Lake Agassiz generated tsunami is estimated to have been at least 2 m. Directionality considerations, as well as the effect of the Coriolis Force in the Northern Hemisphere, suggest that the resulting tsunami probably traveled 50-100 km along the west coast of the Labrador Sea, south of Hudson Strait where the outburst entered the ocean, before being dissipated. The erosional and depositional affects of historic and prehistoric tsunamis are present in the geological record, and provide guidance in seeking evidence for the Lake Agassiz flood burst and subsequent tsunami. This record may be found along the western coast of the Labrador Sea as well as along the shores of Hudson Strait
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a possible tsunami in the labrador sea related to the drainage of Glacial Lake Agassiz 8400 years b p
2005Co-Authors: James T Teller, N. Nirupama, P. Chittibabu, T S Murty, W F BairdAbstract:For thousands of years, the thick Laurentide Ice Sheet covered a large part of northern North America, damming northward-draining rivers. As this ice retreated, large Lakes formed along its margin. Glacial Lake Agassiz was the largest of these ice-marginal Lakes, covering an area of >800,000 km 2 (more than twice the size of the largest Lake in the modern world, the Caspian Sea) before it drained catastrophically into the Labrador Sea. Even before that, Lake Agassiz had periodically released large volumes of water into the ocean via the Great Lakes-St. Lawrence and the Athabasca-Mackenzie River systems. The last and largest of these outbursts released >150,000 km 3 through Hudson Bay and Hudson Strait in 6-12 months; the average flux over that period was ~5 Sv (1 Sv = 1×10 6 m 3 s -1 ). When a volume of water this large is discharged into a coastal sea like the Labrador Sea, it may generate a surface flood wave or a tsunami if the water mass is large enough and introduced in a short time. To our knowledge no previous calculations have been made to estimate the potential impact of a flood burst on the generation of solitary waves. Using analogies of tsunamis generated by submarine landslides and ocean earthquakes, the amplitude of a Lake Agassiz generated tsunami is estimated to have been at least 2 m. Directionality considerations, as well as the effect of the Coriolis Force in the Northern Hemisphere, suggest that the resulting tsunami probably traveled 50-100 km along the west coast of the Labrador Sea, south of Hudson Strait where the outburst entered the ocean, before being dissipated. The erosional and depositional affects of historic and prehistoric tsunamis are present in the geological record, and provide guidance in seeking evidence for the Lake Agassiz flood burst and subsequent tsunami. This record may be found along the western coast of the Labrador Sea as well as along the shores of Hudson Strait.