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Lionel Siame - One of the best experts on this subject based on the ideXlab platform.
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Deglaciation pattern during the Lateglacial/Holocene transition in the southern French Alps. Chronological data and geographical reconstruction from the Clarée Valley (upper Durance catchment, southeastern France)
Palaeogeography Palaeoclimatology Palaeoecology, 2012Co-Authors: Etienne Cossart, Monique Fort, Romain Perrier, Didier Bourlès, Régis Braucher, Lionel SiameAbstract:Abstract In this paper, we make an inventory of geomorphic remnants of past glaciations, especially glacial stages that occurred just after the Last Glacial Maximum (LGM). More than 35 terrestrial cosmogenic radionuclide (TCR) ages were obtained, providing new chronological benchmarks for defining the transition between the LGM and the Holocene, thus answering some remaining questions in the southern French Alps (upper Durance catchment). TCR ages fit very well with the scenario defined in other parts of the European Alps: two main generations of post-LGM moraines were identified, highlighting a synchronicity of glacial responses during the Younger Dryas and the Preboreal. Indeed, the first generation we identified corresponds to the Younger Dryas period, while the second generation was shaped during the Preboreal period. They suggest that a relatively thick glacier tongue (300 m thick) occupied the upper catchment until the end of the Lateglacial period. The glacier tongue disappeared at the very beginning of the Holocene, before a short glacial re-advance during the Preboreal period. This scenario is linked to a very low equilibrium line altitude (ELA) during the Younger Dryas and the Preboreal: located respectively 340 and 150 m below the Little Ice Age (LIA) ELA. Collectively, the results highlight a significant west–east gradient in ELA, probably in relation to westerly and northwesterly winds. Finally, the deglaciation pattern in this area is similar to that of the western and northern Alps, and appears significantly different from the patterns found in the inner and eastern Alps (such as the Ubaye and Maritime Alps patterns).
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Deglaciation pattern during the Lateglacial/Holocene transition in the southern French Alps. Chronological data and geographical reconstruction from the Clarée Valley (upper Durance catchment, southeastern France)
Palaeogeography Palaeoclimatology Palaeoecology, 2012Co-Authors: Etienne Cossart, Monique Fort, Romain Perrier, Didier Bourlès, Régis Braucher, Lionel SiameAbstract:In this paper, we make an inventory of geomorphic remnants of past glaciations, especially glacial stages that occurred just after the Last Glacial Maximum (LGM). More than 35 terrestrial cosmogenic radionuclide (TCR) ages were obtained, providing new chronological benchmarks for defining the transition between the LGM and the Holocene, thus answering some remaining questions in the southern French Alps (upper Durance catchment).TCR ages fit very well with the scenario defined in other parts of the European Alps: two main generations of post-LGM moraines were identified, highlighting a synchronicity of glacial responses during the Younger Dryas and the Preboreal. Indeed, the first generation we identified corresponds to the Younger Dryas period, while the second generation was shaped during the Preboreal period. They suggest that a relatively thick glacier tongue (300. m thick) occupied the upper catchment until the end of the Lateglacial period. The glacier tongue disappeared at the very beginning of the Holocene, before a short glacial re-advance during the Preboreal period. This scenario is linked to a very low equilibrium line altitude (ELA) during the Younger Dryas and the Preboreal: located respectively 340 and 150. m below the Little Ice Age (LIA) ELA. Collectively, the results highlight a significant west-east gradient in ELA, probably in relation to westerly and northwesterly winds. Finally, the deglaciation pattern in this area is similar to that of the western and northern Alps, and appears significantly different from the patterns found in the inner and eastern Alps (such as the Ubaye and Maritime Alps patterns). © 2011 Elsevier B.V.
Geoffrey D Corner - One of the best experts on this subject based on the ideXlab platform.
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Preboreal deglaciation chronology and marine limits of the lyngen storfjord area troms north norway
Boreas, 2008Co-Authors: Geoffrey D CornerAbstract:Scattered marginal moraines in the Lyngen-Storfjord area proximally to the Tromso-Lyngen moraine were formed by the Scandinavian ice-sheet during its retreat in the Preboreal. They correspond to ice-front positions in the main fjords and fjord-valleys where between three and four major and, in places, some minor ice-front accumulations occur. These have been correlated using the marine limits related to synchronous shorelines. Dates for the shorelines and moraines have been derived from a shoreline emergence curve based on 14C dated shore levels from North Norway. Two major, and probably at least one minor, climatically induced, glacial events are indicated: the Ornes event c. 9800–9900±150 B.P., the Skibotn event 95–9600±150 B. P., and a younger event c. 9400±250 B. P. The inner fjord-valleys were probably deglaciated by c. 9100 B. P. Final deglaciation of the innerplateau during late Preboreal or early Boreal was characterized by downwasting.
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Preboreal deglaciation chronology and marine limits of the Lyngen‐Storfjord area, Troms, North Norway
Boreas, 2008Co-Authors: Geoffrey D CornerAbstract:Scattered marginal moraines in the Lyngen-Storfjord area proximally to the Tromso-Lyngen moraine were formed by the Scandinavian ice-sheet during its retreat in the Preboreal. They correspond to ice-front positions in the main fjords and fjord-valleys where between three and four major and, in places, some minor ice-front accumulations occur. These have been correlated using the marine limits related to synchronous shorelines. Dates for the shorelines and moraines have been derived from a shoreline emergence curve based on 14C dated shore levels from North Norway. Two major, and probably at least one minor, climatically induced, glacial events are indicated: the Ornes event c. 9800–9900±150 B.P., the Skibotn event 95–9600±150 B. P., and a younger event c. 9400±250 B. P. The inner fjord-valleys were probably deglaciated by c. 9100 B. P. Final deglaciation of the innerplateau during late Preboreal or early Boreal was characterized by downwasting.
Etienne Cossart - One of the best experts on this subject based on the ideXlab platform.
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Deglaciation pattern during the Lateglacial/Holocene transition in the southern French Alps. Chronological data and geographical reconstruction from the Clarée Valley (upper Durance catchment, southeastern France)
Palaeogeography Palaeoclimatology Palaeoecology, 2012Co-Authors: Etienne Cossart, Monique Fort, Romain Perrier, Didier Bourlès, Régis Braucher, Lionel SiameAbstract:Abstract In this paper, we make an inventory of geomorphic remnants of past glaciations, especially glacial stages that occurred just after the Last Glacial Maximum (LGM). More than 35 terrestrial cosmogenic radionuclide (TCR) ages were obtained, providing new chronological benchmarks for defining the transition between the LGM and the Holocene, thus answering some remaining questions in the southern French Alps (upper Durance catchment). TCR ages fit very well with the scenario defined in other parts of the European Alps: two main generations of post-LGM moraines were identified, highlighting a synchronicity of glacial responses during the Younger Dryas and the Preboreal. Indeed, the first generation we identified corresponds to the Younger Dryas period, while the second generation was shaped during the Preboreal period. They suggest that a relatively thick glacier tongue (300 m thick) occupied the upper catchment until the end of the Lateglacial period. The glacier tongue disappeared at the very beginning of the Holocene, before a short glacial re-advance during the Preboreal period. This scenario is linked to a very low equilibrium line altitude (ELA) during the Younger Dryas and the Preboreal: located respectively 340 and 150 m below the Little Ice Age (LIA) ELA. Collectively, the results highlight a significant west–east gradient in ELA, probably in relation to westerly and northwesterly winds. Finally, the deglaciation pattern in this area is similar to that of the western and northern Alps, and appears significantly different from the patterns found in the inner and eastern Alps (such as the Ubaye and Maritime Alps patterns).
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Deglaciation pattern during the Lateglacial/Holocene transition in the southern French Alps. Chronological data and geographical reconstruction from the Clarée Valley (upper Durance catchment, southeastern France)
Palaeogeography Palaeoclimatology Palaeoecology, 2012Co-Authors: Etienne Cossart, Monique Fort, Romain Perrier, Didier Bourlès, Régis Braucher, Lionel SiameAbstract:In this paper, we make an inventory of geomorphic remnants of past glaciations, especially glacial stages that occurred just after the Last Glacial Maximum (LGM). More than 35 terrestrial cosmogenic radionuclide (TCR) ages were obtained, providing new chronological benchmarks for defining the transition between the LGM and the Holocene, thus answering some remaining questions in the southern French Alps (upper Durance catchment).TCR ages fit very well with the scenario defined in other parts of the European Alps: two main generations of post-LGM moraines were identified, highlighting a synchronicity of glacial responses during the Younger Dryas and the Preboreal. Indeed, the first generation we identified corresponds to the Younger Dryas period, while the second generation was shaped during the Preboreal period. They suggest that a relatively thick glacier tongue (300. m thick) occupied the upper catchment until the end of the Lateglacial period. The glacier tongue disappeared at the very beginning of the Holocene, before a short glacial re-advance during the Preboreal period. This scenario is linked to a very low equilibrium line altitude (ELA) during the Younger Dryas and the Preboreal: located respectively 340 and 150. m below the Little Ice Age (LIA) ELA. Collectively, the results highlight a significant west-east gradient in ELA, probably in relation to westerly and northwesterly winds. Finally, the deglaciation pattern in this area is similar to that of the western and northern Alps, and appears significantly different from the patterns found in the inner and eastern Alps (such as the Ubaye and Maritime Alps patterns). © 2011 Elsevier B.V.
Adrian Schilt - One of the best experts on this subject based on the ideXlab platform.
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Minimal geological methane emissions during the Younger Dryas–Preboreal abrupt warming event
Nature, 2017Co-Authors: Vasilii V. Petrenko, Andrew M. Smith, Edward J. Brook, Katja Riedel, Hinrich Schaefer, Daniel Baggenstos, Christina Harth, Christo Buizert, Adrian SchiltAbstract:Measurements from Antarctic ice suggest that geological methane emissions are much lower than previously thought, and that methane emissions from hydrates and permafrost in response to climate warming are minimal. Natural geological sources of methane such as marine seepage and volcanic areas are estimated to contribute around 52 million tonnes per year to global methane emissions, but the true figure remains uncertain. Data retrieved from ancient ice in Antarctica now suggest that natural geological methane emissions were on average no higher than 15.4 million tonnes per year over the Younger Dryas–Preboreal warming event of about 11,600 years ago. Assuming that past geological methane emissions were not lower than today, the finding indicates that current estimates of geological methane emissions might be too high and, in consequence, anthropogenic fossil-fuel-related methane emission estimates might be too low. The study also provides further support for the idea that the rapid increase in atmospheric methane during this past warming event was probably the result of methane emissions from wetlands rather than from old carbon reservoirs such as marine gas hydrates or permafrost regions. Methane (CH4) is a powerful greenhouse gas and plays a key part in global atmospheric chemistry. Natural geological emissions (fossil methane vented naturally from marine and terrestrial seeps and mud volcanoes) are thought to contribute around 52 teragrams of methane per year to the global methane source, about 10 per cent of the total, but both bottom-up methods (measuring emissions)1 and top-down approaches (measuring atmospheric mole fractions and isotopes)2 for constraining these geological emissions have been associated with large uncertainties. Here we use ice core measurements to quantify the absolute amount of radiocarbon-containing methane (14CH4) in the past atmosphere and show that geological methane emissions were no higher than 15.4 teragrams per year (95 per cent confidence), averaged over the abrupt warming event that occurred between the Younger Dryas and Preboreal intervals, approximately 11,600 years ago. Assuming that past geological methane emissions were no lower than today3,4, our results indicate that current estimates of today’s natural geological methane emissions (about 52 teragrams per year)1,2 are too high and, by extension, that current estimates of anthropogenic fossil methane emissions2 are too low. Our results also improve on and confirm earlier findings5,6,7 that the rapid increase of about 50 per cent in mole fraction of atmospheric methane at the Younger Dryas–Preboreal event was driven by contemporaneous methane from sources such as wetlands; our findings constrain the contribution from old carbon reservoirs (marine methane hydrates8, permafrost9 and methane trapped under ice10) to 19 per cent or less (95 per cent confidence). To the extent that the characteristics of the most recent deglaciation and the Younger Dryas–Preboreal warming are comparable to those of the current anthropogenic warming, our measurements suggest that large future atmospheric releases of methane from old carbon sources are unlikely to occur.
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Minimal geological methane emissions during the Younger Dryas–Preboreal abrupt warming event
Nature, 2017Co-Authors: Vasilii Petrenko, Katja Riedel, Hinrich Schaefer, Andrew Smith, Edward Brook, Daniel Baggenstos, Christina Harth, Quan Hua, Christo Buizert, Adrian SchiltAbstract:Methane (CH$_4$) is a powerful greenhouse gas and plays a key part in global atmospheric chemistry. Natural geological emissions (fossil methane vented naturally from marine and terrestrial seeps and mud volcanoes) are thought to contribute around 52 teragrams of methane per year to the global methane source, about 10 per cent of the total, but both bottom-up methods (measuring emissions)1 and top-down approaches (measuring atmospheric mole fractions and isotopes)2 for constraining these geological emissions have been associated with large uncertainties. Here we use ice core measurements to quantify the absolute amount of radiocarbon-containing methane ($^{14}$CH$_4$) in the past atmosphere and show that geological methane emissions were no higher than 15.4 teragrams per year (95 per cent confidence), averaged over the abrupt warming event that occurred between the Younger Dryas and Preboreal intervals, approximately 11,600 years ago. Assuming that past geological methane emissions were no lower than today 3,4, our results indicate that current estimates of today’s natural geological methane emissions (about 52 teragrams per year)1,2 are too high and, by extension, that current estimates of anthropogenic fossil methane emissions 2 are too low. Our results also improve on and confirm earlier findings5,6,7 that the rapid increase of about 50 per cent in mole fraction of atmospheric methane at the Younger Dryas–Preboreal event was driven by contemporaneous methane from sources such as wetlands; our findings constrain the contribution from old carbon reservoirs (marine methane hydrates8, permafrost9 and methane trapped under ice10) to 19 per cent or less (95 per cent confidence). To the extent that the characteristics of the most recent deglaciation and the Younger Dryas–Preboreal warming are comparable to those of the current anthropogenic warming, our measurements suggest that large future atmospheric releases of methane from old carbon sources are unlikely to occur.
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minimal geological methane emissions during the younger dryas Preboreal abrupt warming event
Nature, 2017Co-Authors: Vasilii V. Petrenko, Edward J. Brook, Katja Riedel, Hinrich Schaefer, Daniel Baggenstos, Christina Harth, Christo Buizert, Adrian Schilt, A M Smith, Xavier FainAbstract:Measurements from Antarctic ice suggest that geological methane emissions are much lower than previously thought, and that methane emissions from hydrates and permafrost in response to climate warming are minimal. Natural geological sources of methane such as marine seepage and volcanic areas are estimated to contribute around 52 million tonnes per year to global methane emissions, but the true figure remains uncertain. Data retrieved from ancient ice in Antarctica now suggest that natural geological methane emissions were on average no higher than 15.4 million tonnes per year over the Younger Dryas–Preboreal warming event of about 11,600 years ago. Assuming that past geological methane emissions were not lower than today, the finding indicates that current estimates of geological methane emissions might be too high and, in consequence, anthropogenic fossil-fuel-related methane emission estimates might be too low. The study also provides further support for the idea that the rapid increase in atmospheric methane during this past warming event was probably the result of methane emissions from wetlands rather than from old carbon reservoirs such as marine gas hydrates or permafrost regions. Methane (CH4) is a powerful greenhouse gas and plays a key part in global atmospheric chemistry. Natural geological emissions (fossil methane vented naturally from marine and terrestrial seeps and mud volcanoes) are thought to contribute around 52 teragrams of methane per year to the global methane source, about 10 per cent of the total, but both bottom-up methods (measuring emissions)1 and top-down approaches (measuring atmospheric mole fractions and isotopes)2 for constraining these geological emissions have been associated with large uncertainties. Here we use ice core measurements to quantify the absolute amount of radiocarbon-containing methane (14CH4) in the past atmosphere and show that geological methane emissions were no higher than 15.4 teragrams per year (95 per cent confidence), averaged over the abrupt warming event that occurred between the Younger Dryas and Preboreal intervals, approximately 11,600 years ago. Assuming that past geological methane emissions were no lower than today3,4, our results indicate that current estimates of today’s natural geological methane emissions (about 52 teragrams per year)1,2 are too high and, by extension, that current estimates of anthropogenic fossil methane emissions2 are too low. Our results also improve on and confirm earlier findings5,6,7 that the rapid increase of about 50 per cent in mole fraction of atmospheric methane at the Younger Dryas–Preboreal event was driven by contemporaneous methane from sources such as wetlands; our findings constrain the contribution from old carbon reservoirs (marine methane hydrates8, permafrost9 and methane trapped under ice10) to 19 per cent or less (95 per cent confidence). To the extent that the characteristics of the most recent deglaciation and the Younger Dryas–Preboreal warming are comparable to those of the current anthropogenic warming, our measurements suggest that large future atmospheric releases of methane from old carbon sources are unlikely to occur.
Hinrich Schaefer - One of the best experts on this subject based on the ideXlab platform.
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Minimal geological methane emissions during the Younger Dryas–Preboreal abrupt warming event
Nature, 2017Co-Authors: Vasilii V. Petrenko, Andrew M. Smith, Edward J. Brook, Katja Riedel, Hinrich Schaefer, Daniel Baggenstos, Christina Harth, Christo Buizert, Adrian SchiltAbstract:Measurements from Antarctic ice suggest that geological methane emissions are much lower than previously thought, and that methane emissions from hydrates and permafrost in response to climate warming are minimal. Natural geological sources of methane such as marine seepage and volcanic areas are estimated to contribute around 52 million tonnes per year to global methane emissions, but the true figure remains uncertain. Data retrieved from ancient ice in Antarctica now suggest that natural geological methane emissions were on average no higher than 15.4 million tonnes per year over the Younger Dryas–Preboreal warming event of about 11,600 years ago. Assuming that past geological methane emissions were not lower than today, the finding indicates that current estimates of geological methane emissions might be too high and, in consequence, anthropogenic fossil-fuel-related methane emission estimates might be too low. The study also provides further support for the idea that the rapid increase in atmospheric methane during this past warming event was probably the result of methane emissions from wetlands rather than from old carbon reservoirs such as marine gas hydrates or permafrost regions. Methane (CH4) is a powerful greenhouse gas and plays a key part in global atmospheric chemistry. Natural geological emissions (fossil methane vented naturally from marine and terrestrial seeps and mud volcanoes) are thought to contribute around 52 teragrams of methane per year to the global methane source, about 10 per cent of the total, but both bottom-up methods (measuring emissions)1 and top-down approaches (measuring atmospheric mole fractions and isotopes)2 for constraining these geological emissions have been associated with large uncertainties. Here we use ice core measurements to quantify the absolute amount of radiocarbon-containing methane (14CH4) in the past atmosphere and show that geological methane emissions were no higher than 15.4 teragrams per year (95 per cent confidence), averaged over the abrupt warming event that occurred between the Younger Dryas and Preboreal intervals, approximately 11,600 years ago. Assuming that past geological methane emissions were no lower than today3,4, our results indicate that current estimates of today’s natural geological methane emissions (about 52 teragrams per year)1,2 are too high and, by extension, that current estimates of anthropogenic fossil methane emissions2 are too low. Our results also improve on and confirm earlier findings5,6,7 that the rapid increase of about 50 per cent in mole fraction of atmospheric methane at the Younger Dryas–Preboreal event was driven by contemporaneous methane from sources such as wetlands; our findings constrain the contribution from old carbon reservoirs (marine methane hydrates8, permafrost9 and methane trapped under ice10) to 19 per cent or less (95 per cent confidence). To the extent that the characteristics of the most recent deglaciation and the Younger Dryas–Preboreal warming are comparable to those of the current anthropogenic warming, our measurements suggest that large future atmospheric releases of methane from old carbon sources are unlikely to occur.
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Minimal geological methane emissions during the Younger Dryas–Preboreal abrupt warming event
Nature, 2017Co-Authors: Vasilii Petrenko, Katja Riedel, Hinrich Schaefer, Andrew Smith, Edward Brook, Daniel Baggenstos, Christina Harth, Quan Hua, Christo Buizert, Adrian SchiltAbstract:Methane (CH$_4$) is a powerful greenhouse gas and plays a key part in global atmospheric chemistry. Natural geological emissions (fossil methane vented naturally from marine and terrestrial seeps and mud volcanoes) are thought to contribute around 52 teragrams of methane per year to the global methane source, about 10 per cent of the total, but both bottom-up methods (measuring emissions)1 and top-down approaches (measuring atmospheric mole fractions and isotopes)2 for constraining these geological emissions have been associated with large uncertainties. Here we use ice core measurements to quantify the absolute amount of radiocarbon-containing methane ($^{14}$CH$_4$) in the past atmosphere and show that geological methane emissions were no higher than 15.4 teragrams per year (95 per cent confidence), averaged over the abrupt warming event that occurred between the Younger Dryas and Preboreal intervals, approximately 11,600 years ago. Assuming that past geological methane emissions were no lower than today 3,4, our results indicate that current estimates of today’s natural geological methane emissions (about 52 teragrams per year)1,2 are too high and, by extension, that current estimates of anthropogenic fossil methane emissions 2 are too low. Our results also improve on and confirm earlier findings5,6,7 that the rapid increase of about 50 per cent in mole fraction of atmospheric methane at the Younger Dryas–Preboreal event was driven by contemporaneous methane from sources such as wetlands; our findings constrain the contribution from old carbon reservoirs (marine methane hydrates8, permafrost9 and methane trapped under ice10) to 19 per cent or less (95 per cent confidence). To the extent that the characteristics of the most recent deglaciation and the Younger Dryas–Preboreal warming are comparable to those of the current anthropogenic warming, our measurements suggest that large future atmospheric releases of methane from old carbon sources are unlikely to occur.
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minimal geological methane emissions during the younger dryas Preboreal abrupt warming event
Nature, 2017Co-Authors: Vasilii V. Petrenko, Edward J. Brook, Katja Riedel, Hinrich Schaefer, Daniel Baggenstos, Christina Harth, Christo Buizert, Adrian Schilt, A M Smith, Xavier FainAbstract:Measurements from Antarctic ice suggest that geological methane emissions are much lower than previously thought, and that methane emissions from hydrates and permafrost in response to climate warming are minimal. Natural geological sources of methane such as marine seepage and volcanic areas are estimated to contribute around 52 million tonnes per year to global methane emissions, but the true figure remains uncertain. Data retrieved from ancient ice in Antarctica now suggest that natural geological methane emissions were on average no higher than 15.4 million tonnes per year over the Younger Dryas–Preboreal warming event of about 11,600 years ago. Assuming that past geological methane emissions were not lower than today, the finding indicates that current estimates of geological methane emissions might be too high and, in consequence, anthropogenic fossil-fuel-related methane emission estimates might be too low. The study also provides further support for the idea that the rapid increase in atmospheric methane during this past warming event was probably the result of methane emissions from wetlands rather than from old carbon reservoirs such as marine gas hydrates or permafrost regions. Methane (CH4) is a powerful greenhouse gas and plays a key part in global atmospheric chemistry. Natural geological emissions (fossil methane vented naturally from marine and terrestrial seeps and mud volcanoes) are thought to contribute around 52 teragrams of methane per year to the global methane source, about 10 per cent of the total, but both bottom-up methods (measuring emissions)1 and top-down approaches (measuring atmospheric mole fractions and isotopes)2 for constraining these geological emissions have been associated with large uncertainties. Here we use ice core measurements to quantify the absolute amount of radiocarbon-containing methane (14CH4) in the past atmosphere and show that geological methane emissions were no higher than 15.4 teragrams per year (95 per cent confidence), averaged over the abrupt warming event that occurred between the Younger Dryas and Preboreal intervals, approximately 11,600 years ago. Assuming that past geological methane emissions were no lower than today3,4, our results indicate that current estimates of today’s natural geological methane emissions (about 52 teragrams per year)1,2 are too high and, by extension, that current estimates of anthropogenic fossil methane emissions2 are too low. Our results also improve on and confirm earlier findings5,6,7 that the rapid increase of about 50 per cent in mole fraction of atmospheric methane at the Younger Dryas–Preboreal event was driven by contemporaneous methane from sources such as wetlands; our findings constrain the contribution from old carbon reservoirs (marine methane hydrates8, permafrost9 and methane trapped under ice10) to 19 per cent or less (95 per cent confidence). To the extent that the characteristics of the most recent deglaciation and the Younger Dryas–Preboreal warming are comparable to those of the current anthropogenic warming, our measurements suggest that large future atmospheric releases of methane from old carbon sources are unlikely to occur.
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14CH4 Measurements in Greenland Ice: Investigating Last Glacial Termination CH4 Sources
Science, 2009Co-Authors: Vasilii V. Petrenko, Andrew M. Smith, Edward J. Brook, D. C. Lowe, Katja Riedel, Gordon Brailsford, Hinrich Schaefer, Niels Reeh, Ray F. WeissAbstract:The cause of a large increase of atmospheric methane concentration during the Younger Dryas–Preboreal abrupt climatic transition (~11,600 years ago) has been the subject of much debate. The carbon-14 ( 14 C) content of methane ( 14 CH 4 ) should distinguish between wetland and clathrate contributions to this increase. We present measurements of 14 CH 4 in glacial ice, targeting this transition, performed by using ice samples obtained from an ablation site in west Greenland. Measured 14 CH 4 values were higher than predicted under any scenario. Sample 14 CH 4 appears to be elevated by direct cosmogenic 14 C production in ice. 14 C of CO was measured to better understand this process and correct the sample 14 CH 4 . Corrected results suggest that wetland sources were likely responsible for the majority of the Younger Dryas–Preboreal CH 4 rise.
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ice record of δ13c for atmospheric ch4 across the younger dryas Preboreal transition
Science, 2006Co-Authors: Vasilii V. Petrenko, Edward J. Brook, Hinrich Schaefer, Michael J Whiticar, Dominic F Ferretti, J. P. SeveringhausAbstract:We report atmospheric methane carbon isotope ratios (δ13CH4) from the Western Greenland ice margin spanning the Younger Dryas–to–Preboreal (YD-PB) transition. Over the recorded ∼800 years, δ13CH4 was around –46 per mil (‰); that is, ∼1‰ higher than in the modern atmosphere and ∼5.5‰ higher than would be expected from budgets without 13C-rich anthropogenic emissions. This requires higher natural 13C-rich emissions or stronger sink fractionation than conventionally assumed. Constant δ13CH4 during the rise in methane concentration at the YD-PB transition is consistent with additional emissions from tropical wetlands, or aerobic plant CH4 production, or with a multisource scenario. A marine clathrate source is unlikely.
