V. Lipenkov - Academia.edu (original) (raw)

Papers by V. Lipenkov

T he tra nsform ation of dry snow to firn is described by th e tra nsiti on b etween d en sificat... more T he tra nsform ation of dry snow to firn is described by th e tra nsiti on b etween d en sification by d eformationless res tacking a nd d ensificati on by p ower-l aw creep. The obse rved decrease with temperature of the dens it y at the snow-firn transiti on seem s to res ult from th e competition betwee n g rain-bo und a r y sliding a nd power-l aw creep. Th ese two densification processess occ ur concurrenLl y in snow, a lthoug h there a re probably micro-regions in which sliding a lone occ urs. Validation of a geometrical densification model developed for ce ra mics has been obta i ned from d ensificatio n d a ta from several Anta rctic a nd Greenl a nd sites a nd from the cha racterization of the structure of pola r firn .

Journal of Raman Spectroscopy, 1997

ABSTRACT N2 and O2 hydrates (clathrates) from a polar ice core (Vostok) were analysed by high-sen... more ABSTRACT N2 and O2 hydrates (clathrates) from a polar ice core (Vostok) were analysed by high-sensitivity Raman microspectrometry. Three new lines in the region of the stretching modes of N2 and O2 guest molecules were observed and were interpreted by considering both small (512) and large (51264) cages in type II clathrates, isotopic effects and the possibility of double occupancy of the large cages. The isotopic effect for N2 and O2 guest molecules in clathrates is demonstrated. © 1997 John Wiley & Sons, Ltd.

Earth and Planetary Science Letters, 2007

An accurate chronology of ice cores is still needed for interpreting the paleoclimatic record and... more An accurate chronology of ice cores is still needed for interpreting the paleoclimatic record and to understand the relation between insolation and climate. A new domain of research in this area has been stimulated by the work of M. Bender linking the record of N 2 /O 2 ratio in the air trapped in the ice with the local insolation. Here we investigate the potential of the air content of polar ice, V, as another and complementary ice proxy of local insolation. We propose that the long-term changes in air content recorded in ice from the high Antarctic plateau is dominantly imprinted by the local summer insolation. The V measurements covering the last 440,000 yr and obtained along the EPICA DC (EDC) ice core are presented. 86% of the variance observed in the V record can be explained neither by air pressure nor by temperature changes, and then should reflect properties influencing the porosity at close-off other than temperature. A wavelet analysis indicates a dominant obliquity period (around 41 ka) over the last 440 ka. We propose a mechanism, which can account for the observed anti-correlation between local insolation and V and explain how the local insolation, via the integrated summer insolation, can affect the near-surface snow structure and consequently the porosity at close-off. The V and the integrated summer insolation changes show high coherency over all the record and a variable phase relationship with a maximum phase difference of about 4000 yr around 200 ka ago. The phase difference may reflect the difference between the EDC2 chronology based on an inverse dating method and an accurately dated insolation curve. Our work, by proposing a new and complementary ice proxy for local insolation should eventually contribute to the establishment of an absolute dating of the ice paleo-record.

We present here the first deltaO2/N2 record of trapped air from the EPICA Dome C (EDC) ice core, ... more We present here the first deltaO2/N2 record of trapped air from the EPICA Dome C (EDC) ice core, covering the period between 300 and 800 ka, which includes two periods of low orbital eccentricity. This record is a composite of several measurement series performed on ice samples stored at -25°C or -50°C. The samples stored at -25°C show clear gas loss on the order of 6.50/00. Two different gas loss corrections are proposed to account for this effect, with both corrections preserving the strong spectral powers at orbital frequencies of deltaO2/N2, in particular the antiphase relationship with local summer insolation. Although the exact mechanism underlying this relationship remains unclear, previous studies have proposed a link between surface insolation and ice grain properties at close-off and have used deltaO2/N2 to orbitally date the Vostok and Dome Fuji ice core records over the last 400 ka. Unlike previous studies, we find the strongest correlation between deltaO2/N2 and an integrated summer insolation (21st of December to 21st of March). Choice of tuning target and data filtering are shown to add at least 2 ka of uncertainty to the orbital tuning method. Moreover, we show that over periods of low eccentricity, the correlation between deltaO2/N2 and the different insolation curves is ambiguous because some peaks in the insolation curves cannot be identified in the deltaO2/N2 record (or vice versa). Recognizing these limitations of this dating method for the period 300-800 ka on the EDC ice core, we use the deltaO2/N2 signal to test the accuracy of the recommended EDC age scale (EDC3). From the comparison between the summer insolation curves, we reveal that the EDC3 age scale is generally correct within its published uncertainty (6 ky) over the 300-800 ka period except over the following periods corresponding to minima in eccentricity: 360-450 ka and 720-760 ka (and possibly 520-560 ka). The link between delta18Oatm and precession confirms that these periods are problematic periods in the EDC3 chronology. Finally, we use the deltaO2/N2 signal to propose the minimal and maximal durations of MIS 11: 21.5 ka and 37.9 ka.

Environmental Context. Lake Vostok is a large subglacial lake trapped below the East Antarctic ic... more Environmental Context. Lake Vostok is a large subglacial lake trapped below the East Antarctic ice sheet. The meteoric ice from deep Vostok ice cores has been used to document the climatic history of the Earth over hundreds of millennia, while the deeper part of the core preserves some basal rock fragments. These rock fragments represent unique geological samples of the inhospitable, ice-covered East Antarctic Plateau.

Air content of polar ice, V, depends primarily on air pressure, temperature and pore volume at cl... more Air content of polar ice, V, depends primarily on air pressure, temperature and pore volume at close-off prevailing at the site of ice formation. Here we present the recently measured V record of the EPICA DC (EDC) Antarctic ice core covering the last 650,000 years. The first 440,000 years remarkably displays the fundamental Milankovitch orbital frequencies. The 100 kyr period, corresponding to the eccentricity of the Earth's orbit and found in the V record, likely reflects essentially the pressure/elevation signature of V. But most of the variations observed in the V record cannot be explained neither by air pressure nor by temperature changes, and then should reflect properties influencing the porosity at close-off other than temperature. A wavelet analysis indicates a dominant period around 41 kyr, the period characteristic of the obliquity variations of the Earth's axis. We propose that the local insolation, via the solar radiation absorbed by the snow, leaves its imprint on the snow structure, then affects the snow-firn transition, and therefore is one of the controlling factors for the porosity at close-off. Such mechanism could account for the observed anti-correlation between local insolation and V. We estimate the variations of the absorbed solar flux in the near-surface snow layers on the basis of a simple albedo model (Lemieux-Dudon et al., this session). We compare the dating of the ice obtained using the local insolation signal deduced from the V record with a chronology based on ice flow modelling. We discuss the glaciological implications of the comparison between the two chronologies, as well as the potential of local insolation markers for approaching an absolute dating of ice core. The latest results covering the period 440-650 kyr BP will also be presented.

Climate Dynamics, 1992

In the interpretation of the Antarctic deep ice-core data, little attention has been given to the... more In the interpretation of the Antarctic deep ice-core data, little attention has been given to the Holocene part of the records. As far as translation of the stable isotope content in terms of temperature is concerned, this can be understood because expected temperature changes may be obscured by isotopic noise of various origins and because no 14C dating has yet

Nature, 2009

On entering an era of global warming, the stability of the Greenland ice sheet (GIS) is an import... more On entering an era of global warming, the stability of the Greenland ice sheet (GIS) is an important concern 1 , especially in the light of new evidence of rapidly changing flow and melt conditions at the GIS margins 2 . Studying the response of the GIS to past climatic change may help to advance our understanding of GIS dynamics. The previous interpretation of evidence from stable isotopes (d 18 O) in water from GIS ice cores was that Holocene climate variability on the GIS differed spatially 3 and that a consistent Holocene climate optimum-the unusually warm period from about 9,000 to 6,000 years ago found in many northernlatitude palaeoclimate records 4 -did not exist. Here we extract both the Greenland Holocene temperature history and the evolution of GIS surface elevation at four GIS locations. We achieve this by comparing d 18 O from GIS ice cores 3,5 with d 18 O from ice cores from small marginal icecaps. Contrary to the earlier interpretation of d 18 O evidence from ice cores 3,6 , our new temperature history reveals a pronounced Holocene climatic optimum in Greenland coinciding with maximum thinning near the GIS margins. Our d 18 O-based results are corroborated by the air content of ice cores, a proxy for surface elevation 7 . State-of-the-art ice sheet models are generally found to be underestimating the extent and changes in GIS elevation and area; our findings may help to improve the ability of models to reproduce the GIS response to Holocene climate.

This study aims at refining the synchronisation between the EPICA Dome C (EDC) and Vostok ice cor... more This study aims at refining the synchronisation between the EPICA Dome C (EDC) and Vostok ice cores in the time interval 0-145 kyr BP by using the volcanic signatures. 111 common volcanic events were identified by using continuous electrical conductivity (ECM), di-electrical profiling (DEP) and sulfate measurements while trying to minimize the distortion of the glaciological chronologies. This is an update and a continuation of previous works performed over the 0-45 kyr interval which provided 56 tie points to the ice core chronologies [Udisti et al, 2004]. This synchronisation will serve for the establishment of the next synchronised Antarctic dating. A change of slope in the EDC-depth/Vostok-depth diagram is probably related to a change of accumulation regime as well as to a change of ice thickness upstream of the Vostok lake, but we did not invoke any significant temporal change of surface accumulation at EDC relative to Vostok. A significant phase difference is detected between the EDC and Vostok isotopic records during the 95-120 kyr interval, but not during Termination II. Three possible candidates for the Toba volcanic supereruption ~73 kyr ago are suggested in the Vostok and EDC volcanic records. However the ECM, DEP and sulfate fingerprints for these three events are not significantly larger than many others in the records.

by Karin Lochte, Daniela Liggett, Don Cowan, C. Elfring, Heinz Miller, Martin Siegert, Michael Sparrow, Polina Morozova, V. Lipenkov, Sanghoon Lee, Azizan Samah, José Retamales, Peter Convey, Xichen Li, Jane Francis, Redruello B, Sergio Marenssi, Irene R Schloss, Marcelo Leppe, Robert Dunbar, Erli Costa, and Jeff Ayton

Nature

T he tra nsform ation of dry snow to firn is described by th e tra nsiti on b etween d en sificat... more T he tra nsform ation of dry snow to firn is described by th e tra nsiti on b etween d en sification by d eformationless res tacking a nd d ensificati on by p ower-l aw creep. The obse rved decrease with temperature of the dens it y at the snow-firn transiti on seem s to res ult from th e competition betwee n g rain-bo und a r y sliding a nd power-l aw creep. Th ese two densification processess occ ur concurrenLl y in snow, a lthoug h there a re probably micro-regions in which sliding a lone occ urs. Validation of a geometrical densification model developed for ce ra mics has been obta i ned from d ensificatio n d a ta from several Anta rctic a nd Greenl a nd sites a nd from the cha racterization of the structure of pola r firn .

Journal of Raman Spectroscopy, 1997

ABSTRACT N2 and O2 hydrates (clathrates) from a polar ice core (Vostok) were analysed by high-sen... more ABSTRACT N2 and O2 hydrates (clathrates) from a polar ice core (Vostok) were analysed by high-sensitivity Raman microspectrometry. Three new lines in the region of the stretching modes of N2 and O2 guest molecules were observed and were interpreted by considering both small (512) and large (51264) cages in type II clathrates, isotopic effects and the possibility of double occupancy of the large cages. The isotopic effect for N2 and O2 guest molecules in clathrates is demonstrated. © 1997 John Wiley & Sons, Ltd.

Earth and Planetary Science Letters, 2007

An accurate chronology of ice cores is still needed for interpreting the paleoclimatic record and... more An accurate chronology of ice cores is still needed for interpreting the paleoclimatic record and to understand the relation between insolation and climate. A new domain of research in this area has been stimulated by the work of M. Bender linking the record of N 2 /O 2 ratio in the air trapped in the ice with the local insolation. Here we investigate the potential of the air content of polar ice, V, as another and complementary ice proxy of local insolation. We propose that the long-term changes in air content recorded in ice from the high Antarctic plateau is dominantly imprinted by the local summer insolation. The V measurements covering the last 440,000 yr and obtained along the EPICA DC (EDC) ice core are presented. 86% of the variance observed in the V record can be explained neither by air pressure nor by temperature changes, and then should reflect properties influencing the porosity at close-off other than temperature. A wavelet analysis indicates a dominant obliquity period (around 41 ka) over the last 440 ka. We propose a mechanism, which can account for the observed anti-correlation between local insolation and V and explain how the local insolation, via the integrated summer insolation, can affect the near-surface snow structure and consequently the porosity at close-off. The V and the integrated summer insolation changes show high coherency over all the record and a variable phase relationship with a maximum phase difference of about 4000 yr around 200 ka ago. The phase difference may reflect the difference between the EDC2 chronology based on an inverse dating method and an accurately dated insolation curve. Our work, by proposing a new and complementary ice proxy for local insolation should eventually contribute to the establishment of an absolute dating of the ice paleo-record.

We present here the first deltaO2/N2 record of trapped air from the EPICA Dome C (EDC) ice core, ... more We present here the first deltaO2/N2 record of trapped air from the EPICA Dome C (EDC) ice core, covering the period between 300 and 800 ka, which includes two periods of low orbital eccentricity. This record is a composite of several measurement series performed on ice samples stored at -25°C or -50°C. The samples stored at -25°C show clear gas loss on the order of 6.50/00. Two different gas loss corrections are proposed to account for this effect, with both corrections preserving the strong spectral powers at orbital frequencies of deltaO2/N2, in particular the antiphase relationship with local summer insolation. Although the exact mechanism underlying this relationship remains unclear, previous studies have proposed a link between surface insolation and ice grain properties at close-off and have used deltaO2/N2 to orbitally date the Vostok and Dome Fuji ice core records over the last 400 ka. Unlike previous studies, we find the strongest correlation between deltaO2/N2 and an integrated summer insolation (21st of December to 21st of March). Choice of tuning target and data filtering are shown to add at least 2 ka of uncertainty to the orbital tuning method. Moreover, we show that over periods of low eccentricity, the correlation between deltaO2/N2 and the different insolation curves is ambiguous because some peaks in the insolation curves cannot be identified in the deltaO2/N2 record (or vice versa). Recognizing these limitations of this dating method for the period 300-800 ka on the EDC ice core, we use the deltaO2/N2 signal to test the accuracy of the recommended EDC age scale (EDC3). From the comparison between the summer insolation curves, we reveal that the EDC3 age scale is generally correct within its published uncertainty (6 ky) over the 300-800 ka period except over the following periods corresponding to minima in eccentricity: 360-450 ka and 720-760 ka (and possibly 520-560 ka). The link between delta18Oatm and precession confirms that these periods are problematic periods in the EDC3 chronology. Finally, we use the deltaO2/N2 signal to propose the minimal and maximal durations of MIS 11: 21.5 ka and 37.9 ka.

Environmental Context. Lake Vostok is a large subglacial lake trapped below the East Antarctic ic... more Environmental Context. Lake Vostok is a large subglacial lake trapped below the East Antarctic ice sheet. The meteoric ice from deep Vostok ice cores has been used to document the climatic history of the Earth over hundreds of millennia, while the deeper part of the core preserves some basal rock fragments. These rock fragments represent unique geological samples of the inhospitable, ice-covered East Antarctic Plateau.

Air content of polar ice, V, depends primarily on air pressure, temperature and pore volume at cl... more Air content of polar ice, V, depends primarily on air pressure, temperature and pore volume at close-off prevailing at the site of ice formation. Here we present the recently measured V record of the EPICA DC (EDC) Antarctic ice core covering the last 650,000 years. The first 440,000 years remarkably displays the fundamental Milankovitch orbital frequencies. The 100 kyr period, corresponding to the eccentricity of the Earth's orbit and found in the V record, likely reflects essentially the pressure/elevation signature of V. But most of the variations observed in the V record cannot be explained neither by air pressure nor by temperature changes, and then should reflect properties influencing the porosity at close-off other than temperature. A wavelet analysis indicates a dominant period around 41 kyr, the period characteristic of the obliquity variations of the Earth's axis. We propose that the local insolation, via the solar radiation absorbed by the snow, leaves its imprint on the snow structure, then affects the snow-firn transition, and therefore is one of the controlling factors for the porosity at close-off. Such mechanism could account for the observed anti-correlation between local insolation and V. We estimate the variations of the absorbed solar flux in the near-surface snow layers on the basis of a simple albedo model (Lemieux-Dudon et al., this session). We compare the dating of the ice obtained using the local insolation signal deduced from the V record with a chronology based on ice flow modelling. We discuss the glaciological implications of the comparison between the two chronologies, as well as the potential of local insolation markers for approaching an absolute dating of ice core. The latest results covering the period 440-650 kyr BP will also be presented.

Climate Dynamics, 1992

In the interpretation of the Antarctic deep ice-core data, little attention has been given to the... more In the interpretation of the Antarctic deep ice-core data, little attention has been given to the Holocene part of the records. As far as translation of the stable isotope content in terms of temperature is concerned, this can be understood because expected temperature changes may be obscured by isotopic noise of various origins and because no 14C dating has yet

Nature, 2009

On entering an era of global warming, the stability of the Greenland ice sheet (GIS) is an import... more On entering an era of global warming, the stability of the Greenland ice sheet (GIS) is an important concern 1 , especially in the light of new evidence of rapidly changing flow and melt conditions at the GIS margins 2 . Studying the response of the GIS to past climatic change may help to advance our understanding of GIS dynamics. The previous interpretation of evidence from stable isotopes (d 18 O) in water from GIS ice cores was that Holocene climate variability on the GIS differed spatially 3 and that a consistent Holocene climate optimum-the unusually warm period from about 9,000 to 6,000 years ago found in many northernlatitude palaeoclimate records 4 -did not exist. Here we extract both the Greenland Holocene temperature history and the evolution of GIS surface elevation at four GIS locations. We achieve this by comparing d 18 O from GIS ice cores 3,5 with d 18 O from ice cores from small marginal icecaps. Contrary to the earlier interpretation of d 18 O evidence from ice cores 3,6 , our new temperature history reveals a pronounced Holocene climatic optimum in Greenland coinciding with maximum thinning near the GIS margins. Our d 18 O-based results are corroborated by the air content of ice cores, a proxy for surface elevation 7 . State-of-the-art ice sheet models are generally found to be underestimating the extent and changes in GIS elevation and area; our findings may help to improve the ability of models to reproduce the GIS response to Holocene climate.

This study aims at refining the synchronisation between the EPICA Dome C (EDC) and Vostok ice cor... more This study aims at refining the synchronisation between the EPICA Dome C (EDC) and Vostok ice cores in the time interval 0-145 kyr BP by using the volcanic signatures. 111 common volcanic events were identified by using continuous electrical conductivity (ECM), di-electrical profiling (DEP) and sulfate measurements while trying to minimize the distortion of the glaciological chronologies. This is an update and a continuation of previous works performed over the 0-45 kyr interval which provided 56 tie points to the ice core chronologies [Udisti et al, 2004]. This synchronisation will serve for the establishment of the next synchronised Antarctic dating. A change of slope in the EDC-depth/Vostok-depth diagram is probably related to a change of accumulation regime as well as to a change of ice thickness upstream of the Vostok lake, but we did not invoke any significant temporal change of surface accumulation at EDC relative to Vostok. A significant phase difference is detected between the EDC and Vostok isotopic records during the 95-120 kyr interval, but not during Termination II. Three possible candidates for the Toba volcanic supereruption ~73 kyr ago are suggested in the Vostok and EDC volcanic records. However the ECM, DEP and sulfate fingerprints for these three events are not significantly larger than many others in the records.

by Karin Lochte, Daniela Liggett, Don Cowan, C. Elfring, Heinz Miller, Martin Siegert, Michael Sparrow, Polina Morozova, V. Lipenkov, Sanghoon Lee, Azizan Samah, José Retamales, Peter Convey, Xichen Li, Jane Francis, Redruello B, Sergio Marenssi, Irene R Schloss, Marcelo Leppe, Robert Dunbar, Erli Costa, and Jeff Ayton

Nature