Ice core records reveal low (~350 - 550 parts per billion (ppb)) atmospheric methane concentratio... more Ice core records reveal low (~350 - 550 parts per billion (ppb)) atmospheric methane concentrations during cold climatic intervals. Further, Greenland ice core records show substantial increases in methane concentrations associated with many of the abrupt warming events during the last glacial period. The two largest rapid methane perturbations occurred at the ends of the Younger Dryas (~500 to 750
Ice core records reveal low (~350 - 550 parts per billion (ppb)) atmospheric methane concentratio... more Ice core records reveal low (~350 - 550 parts per billion (ppb)) atmospheric methane concentrations during cold climatic intervals. Further, Greenland ice core records show substantial increases in methane concentrations associated with many of the abrupt warming events during the last glacial period. The two largest rapid methane perturbations occurred at the ends of the Younger Dryas (~500 to 750
ABSTRACT We present the first measurements of 14C of methane (14CH4) in ancient glacial ice. 14CH... more ABSTRACT We present the first measurements of 14C of methane (14CH4) in ancient glacial ice. 14CH4 should distinguish unambiguously between wetland and fossil (clathrate or other geologic CH4) contributions to abrupt atmospheric CH4 increases observed at times of rapid warming in Greenland ice cores. 1000-kg-sized ice samples, dating to the Younger Dryas - Preboreal (around 11,600 yr BP) and Oldest Dryas - Bølling (around 14,700 yr BP) abrupt climatic transitions, were obtained from an ablation site in West Greenland. Measured 14CH4 values (28 - 35 pMC) were higher than predicted under any scenario based on sample age. Sample 14CH4 appears to be elevated by in- situ CH4 production in the ice for some samples as well as by a second process that is likely direct cosmogenic production of 14CH4 molecules in the ice. 14C of CO and CO2 was measured to better understand these processes and corrections were applied to sample 14CH4. Although the corrected results have substantial uncertainties, they suggest that wetland sources were responsible for the majority of the Younger Dryas - Preboreal CH4 rise. The uncertainties in the corrected results for the Oldest Dryas - Bølling transition are too large to draw conclusions about 14CH4 changes during that transition.
ABSTRACT We present the first measurements of 14C of methane (14CH4) in ancient glacial ice. 14CH... more ABSTRACT We present the first measurements of 14C of methane (14CH4) in ancient glacial ice. 14CH4 should distinguish unambiguously between wetland and fossil (clathrate or other geologic CH4) contributions to abrupt atmospheric CH4 increases observed at times of rapid warming in Greenland ice cores. 1000-kg-sized ice samples, dating to the Younger Dryas - Preboreal (around 11,600 yr BP) and Oldest Dryas - Bølling (around 14,700 yr BP) abrupt climatic transitions, were obtained from an ablation site in West Greenland. Measured 14CH4 values (28 - 35 pMC) were higher than predicted under any scenario based on sample age. Sample 14CH4 appears to be elevated by in- situ CH4 production in the ice for some samples as well as by a second process that is likely direct cosmogenic production of 14CH4 molecules in the ice. 14C of CO and CO2 was measured to better understand these processes and corrections were applied to sample 14CH4. Although the corrected results have substantial uncertainties, they suggest that wetland sources were responsible for the majority of the Younger Dryas - Preboreal CH4 rise. The uncertainties in the corrected results for the Oldest Dryas - Bølling transition are too large to draw conclusions about 14CH4 changes during that transition.
Ice core records reveal low (~350 - 550 parts per billion (ppb)) atmospheric methane concentratio... more Ice core records reveal low (~350 - 550 parts per billion (ppb)) atmospheric methane concentrations during cold climatic intervals. Further, Greenland ice core records show substantial increases in methane concentrations associated with many of the abrupt warming events during the last glacial period. The two largest rapid methane perturbations occurred at the ends of the Younger Dryas (~500 to 750
... Kendrick C. Taylor1, Richard B. Alley2, Howard Conway3, David Holland4, Paul A. Mayewski5, Je... more ... Kendrick C. Taylor1, Richard B. Alley2, Howard Conway3, David Holland4, Paul A. Mayewski5, Jeffrey P. Severinghaus6, Christopher A. Shuman7 ... We infer that climate conditions in the vicinity of the polar atmospheric vortex, high latitude dust source areas, and mid-latitude ...
Here we present measurements of the gas content and isotopic composition of debris-rich basal lay... more Here we present measurements of the gas content and isotopic composition of debris-rich basal layers of a polar glacier, Meserve Glacier, Antarctica, which has a basal temperature of -17 °C. These measurements show that debris entrainment has occurred without alteration of the glacial ice, and provide the most direct evidence to date that active entrainment occurs at the beds of cold glaciers, without bulk freezing of water. Entrainment at subfreezing temperatures may have formed the U-shaped trough containing Meserve Glacier. In addition to possibly allowing some cold-based glaciers to be important geomorphic agents, entrainment at subfreezing temperatures provides a general mechanism for formation of the dirty basal layers of polar glaciers and ice sheets, which are rheologically distinct and can limit the time span of ice-core analyses. Furthermore, accumulating evidence suggests that geomorphologists should abandon the assumption that cold-based glaciers do not slide and abrade ...
Isotopic measurements in polar ice core have shown a succession of rapid warming periods during t... more Isotopic measurements in polar ice core have shown a succession of rapid warming periods during the last glacial period over Greenland. However, this method underestimates the surface temperature variations. A new method based on gas thermal diffusion in the firn manages to quantify surface temperature variations through associated isotopic fractionations. We developed a method to extract air from the ice
ABSTRACT The oxygen-18 content of atmospheric dioxygen (δ18Oatm) is known from ice core trapped a... more ABSTRACT The oxygen-18 content of atmospheric dioxygen (δ18Oatm) is known from ice core trapped air records to vary on orbital timescales, primarily the ~21,000 year periodicity. The cause is thought to be a combination of 1) ice sheet growth and consequent variation in O-18 of ocean water, the original source of all substrate H2O used for photosynthetic O2, and 2) changes in the biogeochemical fractionation of O2 relative to ocean water, known as the Dole Effect. Because the turnover time of O2 in the atmosphere is ~1000 years, variations on shorter timescales are not expected and previous studies have not searched for them. Here we present a new record of δ18Oatm at approximately 100-year resolution from the Siple Dome ice core, Antarctica, covering the past 95 kyr. The record shows evidence of artifactual fractionation during gas loss, in the form of an inverse correlation of O2/N2 and δ18Oatm in pair differences with slope of -0.01, probably due to poor core quality (low O2/N2 is associated with highly fractured pieces of ice). The light isotope O-16 appears to escape more readily from the bubbles during leakage of gas out of the ice, leaving the remaining gas enriched in O-18. An empirical correction for gas loss fractionation is made using the measured δO2/N2 and a slope of -0.01. Both raw and corrected records show distinct millennial-duration positive anomalies in δ18Oatm, suggesting that the anomalies are real features of the paleo-atmosphere. They occur at times of Antarctic warmth (designated A1, A2, etc.), which are also times of weak Asian monsoons and Heinrich events or `mystery intervals' in the northern hemisphere. The anomalies typically have an amplitude of +0.15‰, which compares with analytical error of ±0.02‰. We speculate that the anomalies are caused by the increase in O-18 of terrestrial precipitation associated with the weak monsoons, as seen in Asian and Brazilian speleothem records, in addition to evaporative enrichment of leaf water O-18 in the low relative humidity of the weak-monsoon regime. Regardless of origin, the anomalies may be useful as interpolar stratigraphic markers for synchronizing Antarctic and Greenland ice core records during times when methane variations are absent.
A large topographic high commonly occurs near the intersection of a rifted spreading center and a... more A large topographic high commonly occurs near the intersection of a rifted spreading center and a transform fault. The high occurs at the inside of the 90° bend in the plate boundary, and is called the ‘high inside corner’, while the area across the spreading center, the ‘outside corner’, is often anomalously low. To better understand the origin of this
Ice core records reveal low (~350 - 550 parts per billion (ppb)) atmospheric methane concentratio... more Ice core records reveal low (~350 - 550 parts per billion (ppb)) atmospheric methane concentrations during cold climatic intervals. Further, Greenland ice core records show substantial increases in methane concentrations associated with many of the abrupt warming events during the last glacial period. The two largest rapid methane perturbations occurred at the ends of the Younger Dryas (~500 to 750
Ice core records reveal low (~350 - 550 parts per billion (ppb)) atmospheric methane concentratio... more Ice core records reveal low (~350 - 550 parts per billion (ppb)) atmospheric methane concentrations during cold climatic intervals. Further, Greenland ice core records show substantial increases in methane concentrations associated with many of the abrupt warming events during the last glacial period. The two largest rapid methane perturbations occurred at the ends of the Younger Dryas (~500 to 750
ABSTRACT We present the first measurements of 14C of methane (14CH4) in ancient glacial ice. 14CH... more ABSTRACT We present the first measurements of 14C of methane (14CH4) in ancient glacial ice. 14CH4 should distinguish unambiguously between wetland and fossil (clathrate or other geologic CH4) contributions to abrupt atmospheric CH4 increases observed at times of rapid warming in Greenland ice cores. 1000-kg-sized ice samples, dating to the Younger Dryas - Preboreal (around 11,600 yr BP) and Oldest Dryas - Bølling (around 14,700 yr BP) abrupt climatic transitions, were obtained from an ablation site in West Greenland. Measured 14CH4 values (28 - 35 pMC) were higher than predicted under any scenario based on sample age. Sample 14CH4 appears to be elevated by in- situ CH4 production in the ice for some samples as well as by a second process that is likely direct cosmogenic production of 14CH4 molecules in the ice. 14C of CO and CO2 was measured to better understand these processes and corrections were applied to sample 14CH4. Although the corrected results have substantial uncertainties, they suggest that wetland sources were responsible for the majority of the Younger Dryas - Preboreal CH4 rise. The uncertainties in the corrected results for the Oldest Dryas - Bølling transition are too large to draw conclusions about 14CH4 changes during that transition.
ABSTRACT We present the first measurements of 14C of methane (14CH4) in ancient glacial ice. 14CH... more ABSTRACT We present the first measurements of 14C of methane (14CH4) in ancient glacial ice. 14CH4 should distinguish unambiguously between wetland and fossil (clathrate or other geologic CH4) contributions to abrupt atmospheric CH4 increases observed at times of rapid warming in Greenland ice cores. 1000-kg-sized ice samples, dating to the Younger Dryas - Preboreal (around 11,600 yr BP) and Oldest Dryas - Bølling (around 14,700 yr BP) abrupt climatic transitions, were obtained from an ablation site in West Greenland. Measured 14CH4 values (28 - 35 pMC) were higher than predicted under any scenario based on sample age. Sample 14CH4 appears to be elevated by in- situ CH4 production in the ice for some samples as well as by a second process that is likely direct cosmogenic production of 14CH4 molecules in the ice. 14C of CO and CO2 was measured to better understand these processes and corrections were applied to sample 14CH4. Although the corrected results have substantial uncertainties, they suggest that wetland sources were responsible for the majority of the Younger Dryas - Preboreal CH4 rise. The uncertainties in the corrected results for the Oldest Dryas - Bølling transition are too large to draw conclusions about 14CH4 changes during that transition.
Ice core records reveal low (~350 - 550 parts per billion (ppb)) atmospheric methane concentratio... more Ice core records reveal low (~350 - 550 parts per billion (ppb)) atmospheric methane concentrations during cold climatic intervals. Further, Greenland ice core records show substantial increases in methane concentrations associated with many of the abrupt warming events during the last glacial period. The two largest rapid methane perturbations occurred at the ends of the Younger Dryas (~500 to 750
... Kendrick C. Taylor1, Richard B. Alley2, Howard Conway3, David Holland4, Paul A. Mayewski5, Je... more ... Kendrick C. Taylor1, Richard B. Alley2, Howard Conway3, David Holland4, Paul A. Mayewski5, Jeffrey P. Severinghaus6, Christopher A. Shuman7 ... We infer that climate conditions in the vicinity of the polar atmospheric vortex, high latitude dust source areas, and mid-latitude ...
Here we present measurements of the gas content and isotopic composition of debris-rich basal lay... more Here we present measurements of the gas content and isotopic composition of debris-rich basal layers of a polar glacier, Meserve Glacier, Antarctica, which has a basal temperature of -17 °C. These measurements show that debris entrainment has occurred without alteration of the glacial ice, and provide the most direct evidence to date that active entrainment occurs at the beds of cold glaciers, without bulk freezing of water. Entrainment at subfreezing temperatures may have formed the U-shaped trough containing Meserve Glacier. In addition to possibly allowing some cold-based glaciers to be important geomorphic agents, entrainment at subfreezing temperatures provides a general mechanism for formation of the dirty basal layers of polar glaciers and ice sheets, which are rheologically distinct and can limit the time span of ice-core analyses. Furthermore, accumulating evidence suggests that geomorphologists should abandon the assumption that cold-based glaciers do not slide and abrade ...
Isotopic measurements in polar ice core have shown a succession of rapid warming periods during t... more Isotopic measurements in polar ice core have shown a succession of rapid warming periods during the last glacial period over Greenland. However, this method underestimates the surface temperature variations. A new method based on gas thermal diffusion in the firn manages to quantify surface temperature variations through associated isotopic fractionations. We developed a method to extract air from the ice
ABSTRACT The oxygen-18 content of atmospheric dioxygen (δ18Oatm) is known from ice core trapped a... more ABSTRACT The oxygen-18 content of atmospheric dioxygen (δ18Oatm) is known from ice core trapped air records to vary on orbital timescales, primarily the ~21,000 year periodicity. The cause is thought to be a combination of 1) ice sheet growth and consequent variation in O-18 of ocean water, the original source of all substrate H2O used for photosynthetic O2, and 2) changes in the biogeochemical fractionation of O2 relative to ocean water, known as the Dole Effect. Because the turnover time of O2 in the atmosphere is ~1000 years, variations on shorter timescales are not expected and previous studies have not searched for them. Here we present a new record of δ18Oatm at approximately 100-year resolution from the Siple Dome ice core, Antarctica, covering the past 95 kyr. The record shows evidence of artifactual fractionation during gas loss, in the form of an inverse correlation of O2/N2 and δ18Oatm in pair differences with slope of -0.01, probably due to poor core quality (low O2/N2 is associated with highly fractured pieces of ice). The light isotope O-16 appears to escape more readily from the bubbles during leakage of gas out of the ice, leaving the remaining gas enriched in O-18. An empirical correction for gas loss fractionation is made using the measured δO2/N2 and a slope of -0.01. Both raw and corrected records show distinct millennial-duration positive anomalies in δ18Oatm, suggesting that the anomalies are real features of the paleo-atmosphere. They occur at times of Antarctic warmth (designated A1, A2, etc.), which are also times of weak Asian monsoons and Heinrich events or `mystery intervals' in the northern hemisphere. The anomalies typically have an amplitude of +0.15‰, which compares with analytical error of ±0.02‰. We speculate that the anomalies are caused by the increase in O-18 of terrestrial precipitation associated with the weak monsoons, as seen in Asian and Brazilian speleothem records, in addition to evaporative enrichment of leaf water O-18 in the low relative humidity of the weak-monsoon regime. Regardless of origin, the anomalies may be useful as interpolar stratigraphic markers for synchronizing Antarctic and Greenland ice core records during times when methane variations are absent.
A large topographic high commonly occurs near the intersection of a rifted spreading center and a... more A large topographic high commonly occurs near the intersection of a rifted spreading center and a transform fault. The high occurs at the inside of the 90° bend in the plate boundary, and is called the ‘high inside corner’, while the area across the spreading center, the ‘outside corner’, is often anomalously low. To better understand the origin of this
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