Olivier Magand - Academia.edu (original) (raw)

Papers by Olivier Magand

Quaternary Science Reviews, 2010

A 14-meter long piston core was retrieved from Lake Le Bourget, NW Alps (France), in order to pro... more A 14-meter long piston core was retrieved from Lake Le Bourget, NW Alps (France), in order to provide a continuous record of flooding events of the Rhone River during the Holocene. The selection of the coring site was based on high resolution seismic profiling, in an area with limited mass wasting deposits and accumulated proximal Rhone River inter-and under-flow deposits. The age-depth model of this core is based on (i) 14 AMS radiocarbon dates, (ii) radionuclide dating ( 137 Cs) and (iii) the identification of historical data (flood events, eutrophication of the lake). The sedimentary record dates back to 9 400 cal BP, and includes a thin mass wasting event deposited around 4500 cal BP. A multi-proxy approach was used to track the evolution and origin of clastic sedimentation during the Holocene, in order to identify periods of higher hydrological activity in the catchment area. Spectrophotometry was used to detect fluctuations in clastic supply and the study of clay minerals (especially the Illite cristallinity index) allowed locating the main source area of fine grained clastic particles settling at the lake after flood events. This dataset highlights up to 12 periods of more intense flooding events over the last 9 400 years in Lake Le Bourget and shows that the main source area of clastic particles during this period is the upper part of the Arve River drainage basin. This part of the catchment area drains several large glaciers from the Mont Blanc Massif, and fluctuations in Rhone River flood supply in Lake Le Bourget is interpreted as resulting essentially from Mont Blanc Glacier activity during the Holocene. The comparison of clastic sedimentation in Lake Le Bourget with periods of increasing land use and periods of Alpine glacier and mid-European lake level fluctuations, suggest that the core LDB04 clastic record in Lake Le Bourget is a continuous proxy of the Holocene hydrological history of the NW Alps. Aprahamian, J., 1974. La cristallinité de l'illite et les minéraux argileux en bordure des massifs cristallins externes de Belledonne et du Pelvoux. Géologie Alpine, t. 50, p 5-15. Arnaud F. Lignier V., Revel M., Desmet M., Beck C., Pourchet M., Charlet A., Trentesaux A., Tribovillard N. 2002. Flood and earthquake disturbance of 210Pb geochronology (Lake Anterne, North French Alps). Terra Nova, 14-4, pp. 225-232 Arnaud, F., 2005. Discriminating bio-induced and detrital sedimentary processes from particle size distribution of carbonates and non-carbonates in hard water lake sediments, Journal of Paleolimnology 34: 519-526 Arnaud F., Revel M., Chapron E., Desmet M., Tribovillard N., 2005. 7000 years of Rhône river flooding activity in Lake Le Bourget: A High-resolution sediment record of NW Alps hydrology. The Holocene. 15, No. 3, 420-428.

Quaternary Science Reviews, 2007

Two twin short gravity cores and a long piston core recovered from the deepest part of proglacial... more Two twin short gravity cores and a long piston core recovered from the deepest part of proglacial Lake Bramant (Grandes Rousses Massif, French Alps), under and overlying a large slump identified by high-resolution seismic profile, allow the investigation of Holocene natural hazards and interactions between human activity and climatic changes at high-altitude. Annual sedimentation throughout the cores (glacial varves) is identified on photographs, ITRAX (high-resolution continuous microfluorescence-X) and CAT-Scan (computerized axial tomography) analyses and is supported by (1) the number of dark and light laminations between dates obtained by radionuclide measurements ( 137 Cs, 241 Am), (2) the correlation of a slump triggered by the nearby AD 1881 Allemond earthquake (MSK intensity VII) and of a turbidite triggered by the AD 1822 Chautagne regional earthquake (MSK intensity VIII), (3) the number of laminations between two accelerator mass spectrometry (AMS) 14 C dates, and (4) archaeological data. In Lake Bramant, dark layers are coarser, contain less detrital elements, but more neoformed elements and organic matter content. These darker laminations result from calm background sedimentation, whereas the lighter layers are finer and rich in detrital elements and reflect the summer snowmelt. Traces of mining activity during the Roman civilization apogee (AD 115-330) and during the Early Bronze Age (3770-3870 cal BP) are recorded by lead and copper content in the sediments and probably result from regional and local mining activity in the NW Alps. Warmer climate during the Bronze Age in this part of the Alps is suggested by (1) two organic deposits (4160-3600 cal BP and 3300-2850 cal BP) likely reflecting a lower lake level and smaller glaciers and (2) evidence of a different vegetation cover around 2500 m a.s.l. The onset of clastic proglacial sedimentation between 3600-3300 cal BP and since 2850 cal BP is synchronous with periods of glacier advances documented in the Alps and high-lake levels in west-central Europe. This major change in proglacial sedimentation highlights the development of a larger St. Sorlin glacier in the catchment area of Lake Bramant. r

Journal of Geophysical Research, 2008

Geochimica et Cosmochimica Acta, 2011

The cosmogenic nuclide beryllium-10 ( 10 Be), recovered from ice cores, is often used to study so... more The cosmogenic nuclide beryllium-10 ( 10 Be), recovered from ice cores, is often used to study solar activity on long timescales. However, the 10 Be signal is also influenced by factors other than the Sun. To identify and quantify various contributions to the 10 Be signal, two Antarctic snow records from the Vostok and Concordia sites spanning the last 60 years were studied at a sub-annual resolution. Three factors that contribute to the 10 Be signal were identified. First, a significant period of approximately 11 yr that can be associated with the modulation of 10 Be production by solar activity was detected in both records. The solar imprint constitutes 20-35% of the variance within the total signal. The 11-yr 10 Be snow component was attenuated by a factor of 0.5andwasdelayedby0.5 and was delayed by 0.5andwasdelayedby1.4 yr compared to the 10 Be production expected within the polar atmosphere. The result could be interpreted as the composite response of a stratospheric 10 Be reservoir with an 11-yr modulation that was attenuated and delayed (with respect to 10 Be polar production) and to a tropospheric 10 Be reservoir with an 11-yr modulation that was not attenuated or delayed. Then, peaks in 10 Be concentrations that were 6666% and 6635% higher than the average concentration were observed during the stratospheric volcanic eruptions of Agung (in 1963) and Pinatubo (in 1991), respectively. In light of these new results, published 10 Be ice core records could be reinterpreted because spikes in 10 Be concentration appear at the time of several stratospheric events. The data indicate that stratospheric volcanic eruptions can impact 10 Be transport and deposition as a result of the roles played by the sedimentation of sulfate aerosols and the formation and rapid settling of polar stratospheric clouds (PSC). Also, an interannual variability of 4yrwasdeterminedinboth10Berecords,correspondingto4 yr was determined in both 10 Be records, corresponding to 4yrwasdeterminedinboth10Berecords,correspondingto26% of the variance within the signal at Vostok. As with species of marine origin (sodium), this 4-yr variability is interpreted as a tropospheric modulation. The 4-yr variability could be associated with atmospheric circulation associated with the coupled Southern Ocean ocean-atmosphere system. The results presented here, from sites within the high Antarctic plateau, open new possibilities for ice core dating over the last few centuries and for the reconstruction of past solar activity in relation to climate.

Atmospheric Chemistry and Physics Discussions, 2016

Atmospheric Chemistry and Physics Discussions, 2016

Egs Agu Eug Joint Assembly, Apr 1, 2003

As a part of ITASE project (International TransAntarctic Scientific Expedition) France and Italy ... more As a part of ITASE project (International TransAntarctic Scientific Expedition) France and Italy carried out different traverses covering Dome C drainage area. Surface snow samples (1 m cores and pits), shallow firn cores (10-50 m) firn temperature were collected along the traverses. Oxygen-isotope and beta activity measurements were carried out on the samples to provide information on accumulation rate and climatic condition of snow precipitation. The results of these analyses are compared with the firn temperatures. The oxygen-isotope composition shows a linear correlation with firn temperature in the different sector. Indeed snow accumulation rate and firn temperature over Antarctica is recognised as important climate parameters. The study aims to better understand latitudinal and longitudinal climatic gradients along transepts, while documenting atmospheric and surface conditions in the eastern and north-eastern portions of the Dome C drainage area and in Northern Victoria Land.

E3S Web of Conferences, 2013

The role of oceans in the global cycle of mercury is still poorly characterized, mainly because o... more The role of oceans in the global cycle of mercury is still poorly characterized, mainly because of a lack a long-term data on atmospheric mercury concentrations in the remote Southern Ocean. In the frame of GMOS (Global Mercury Observation System), we present here the first results from a new monitoring station at Amsterdam Island in the Southern Indian Ocean. For the period January to April 2012, we recorded mean concentration of gaseous elemental mercury (GEM), reactive gaseous mercury (RGM) and particulate-bounded mercury (PHg) of 1.03 ng m -3 , 0.37 and 0.34 pg m -3 respectively. While GEM concentrations showed little variations, RGM and PHg exhibited fast variations with alternation of value below the instrumental detection limit and maximum values up to 4 pg m -3 .

The study of mercury (Hg) cycle in Arctic regions is a major subject of concern due to the dramat... more The study of mercury (Hg) cycle in Arctic regions is a major subject of concern due to the dramatic increases of Hg concentrations in ecosystem in the last few decades. The causes of such increases are still in debate, and an important way to improve our knowledge on the subject is to study the exchanges of Hg between atmosphere and snow during springtime. We organized an international study from 10 April to 10 May 2003 in Ny-Å lesund, Svalbard, in order to assess these fluxes through measurements and derived calculations.

Laguna Chichój (Lake Chichój) is the only deep permanent lake in the central highlands of Guatema... more Laguna Chichój (Lake Chichój) is the only deep permanent lake in the central highlands of Guatemala. The lake is located in the boundary zone between the North American and Caribbean plates. The lake has been struck by devastating earthquakes and tropical cyclones in historical times. We investigated the imprint of 20 th century extreme events on the sedimentary record of this tropical lake using a bathymetric survey of the lake, coring the lake floor, and providing a chronology of sediment accumulation. The lake occupies a series of circular depressions likely formed by the rapid dissolution of a buried body of gypsum. 210 Pb and 137 Cs inventories and varve counting indicate high rates of sedimentation (1-2 cm/y). The annually layered sediment is interrupted by turbidites of two types: a darker-colored turbidite, enriched in lake-derived biogenic constituents, and interpreted as a seismite, and a lighter-colored type, enriched in catchment-derived constituents, interpreted as a flood layer. Comparison of our 137 Cs -determined layer ages with a catalog of 20 th century earthquakes shows that an earthquake on the Motagua fault in 1976 generated a conspicuous darker-colored turbidite and slumped deposits in separate parts of the lake. The entire earthquake inventory further reveals that mass movements in the lake are triggered at Modified Mercalli Intensities (MMI) higher than V. Tropical cyclonic depressions known to have affected the lake area had limited effect on the lake, including Hurricane Mitch in 1998. One storm however produced a significantly thicker flood layer in the 1940s. This storm is reportedly the only event to have generated widespread slope failures in the lake catchment. It is thus inferred that abundant landsliding provided large amounts of concentrated sediment to the lake, through hyperpycnal flows.

The Cryosphere, 2008

Satellite records of microwave surface emission have been used to interpolate in-situ observation... more Satellite records of microwave surface emission have been used to interpolate in-situ observations of Antarctic surface mass balance (SMB) and build continental-scale maps of accumulation. Using a carefully screened subset of SMB measurements in the 90 • -180 • E sector, we show a reasonable agreement with microwave-based accumulation map in the dry-snow regions, but large discrepancies in the coastal regions where melt occurs during summer. Using an emission microwave model, we explain the failure of microwave sensors to retrieve SMB by the presence of layers created by melt/refreeze cycles. We conclude that regions potentially affected by melting should be masked-out in microwave-based interpolation schemes.

Sedimentary Geology, 2007

... meso-or hyperpycnal flows cf. [Bates, 1953], [Sturm and Matter, 1978], [Ashley et al., 1985] ... more ... meso-or hyperpycnal flows cf. [Bates, 1953], [Sturm and Matter, 1978], [Ashley et al., 1985] and [Hsü, 1989]) and to what extent they control the geometry of clastic sedimentary environments. The influence of interflows (mesopycnal ...

Reviews of Geophysics, 2008

Quaternary Science Reviews, 2007

Two twin short gravity cores and a long piston core recovered from the deepest part of proglacial... more Two twin short gravity cores and a long piston core recovered from the deepest part of proglacial Lake Bramant (Grandes Rousses Massif, French Alps), under and overlying a large slump identified by high-resolution seismic profile, allow the investigation of Holocene natural hazards and interactions between human activity and climatic changes at high-altitude. Annual sedimentation throughout the cores (glacial varves) is identified on photographs, ITRAX (high-resolution continuous microfluorescence-X) and CAT-Scan (computerized axial tomography) analyses and is supported by (1) the number of dark and light laminations between dates obtained by radionuclide measurements ( 137 Cs, 241 Am), (2) the correlation of a slump triggered by the nearby AD 1881 Allemond earthquake (MSK intensity VII) and of a turbidite triggered by the AD 1822 Chautagne regional earthquake (MSK intensity VIII), (3) the number of laminations between two accelerator mass spectrometry (AMS) 14 C dates, and (4) archaeological data. In Lake Bramant, dark layers are coarser, contain less detrital elements, but more neoformed elements and organic matter content. These darker laminations result from calm background sedimentation, whereas the lighter layers are finer and rich in detrital elements and reflect the summer snowmelt. Traces of mining activity during the Roman civilization apogee (AD 115-330) and during the Early Bronze Age (3770-3870 cal BP) are recorded by lead and copper content in the sediments and probably result from regional and local mining activity in the NW Alps. Warmer climate during the Bronze Age in this part of the Alps is suggested by (1) two organic deposits (4160-3600 cal BP and 3300-2850 cal BP) likely reflecting a lower lake level and smaller glaciers and (2) evidence of a different vegetation cover around 2500 m a.s.l. The onset of clastic proglacial sedimentation between 3600-3300 cal BP and since 2850 cal BP is synchronous with periods of glacier advances documented in the Alps and high-lake levels in west-central Europe. This major change in proglacial sedimentation highlights the development of a larger St. Sorlin glacier in the catchment area of Lake Bramant. r

Journal of Paleolimnology, 2014

Journal of Geophysical Research, 2007

1] On the basis of thousands of surface mass balance (SMB) field measurements over the entire Ant... more 1] On the basis of thousands of surface mass balance (SMB) field measurements over the entire Antarctic ice sheet it is currently estimated that more than 2 Gt of ice accumulate each year at the surface of Antarctica. However, these estimates suffer from large uncertainties. Various problems affect Antarctic SMB measurements, in particular, limited or unwarranted spatial and temporal representativeness, measurement inaccuracy, and lack of quality control. We define quality criteria on the basis of (1) an up-to-date review and quality rating of the various SMB measurement methods and (2) essential information (location, dates of measurements, time period covered by the SMB values, and primary data sources) related to each SMB data. We apply these criteria to available SMB values from Queen Mary to Victoria lands (90°-180°E Antarctic sector) from the early 1950s to present. This results in a new set of observed SMB values for the 1950-2005 time period with strong reduction in density and coverage but also expectedly reduced inaccuracies and uncertainties compared to other compilations. The quality-controlled SMB data set also contains new results from recent field campaigns (International Trans-Antarctic Scientific Expedition (ITASE), Russian Antarctic Expedition (RAE), and Australian National Antarctic Research Expeditions (ANARE) projects) which comply with the defined quality criteria. A comparative evaluation of climate model results against the quality-controlled updated SMB data set and other widely used ones illustrates that such Antarctic SMB studies are significantly affected by the quality of field SMB values used as reference. Citation: Magand, O., C. Genthon, M. Fily, G. Krinner, G. Picard, M. Frezzotti, and A. A. Ekaykin (2007), An up-to-date qualitycontrolled surface mass balance data set for the 90°

Journal of Climate, 2008

This work reports on high-resolution (60 km) atmospheric general circulation model simulations of... more This work reports on high-resolution (60 km) atmospheric general circulation model simulations of the Antarctic climate for the periods 1981-2000 and 2081-2100. Our analysis focuses on the surface mass balance change, one of the components of the total ice sheet mass balance, and its impact on global eustatic sea level. Contrary to previous simulations, in which we directly used sea

Geophysical Research Letters, 2006

Geophysical Research Letters, 2006

Quaternary Science Reviews, 2010

A 14-meter long piston core was retrieved from Lake Le Bourget, NW Alps (France), in order to pro... more A 14-meter long piston core was retrieved from Lake Le Bourget, NW Alps (France), in order to provide a continuous record of flooding events of the Rhone River during the Holocene. The selection of the coring site was based on high resolution seismic profiling, in an area with limited mass wasting deposits and accumulated proximal Rhone River inter-and under-flow deposits. The age-depth model of this core is based on (i) 14 AMS radiocarbon dates, (ii) radionuclide dating ( 137 Cs) and (iii) the identification of historical data (flood events, eutrophication of the lake). The sedimentary record dates back to 9 400 cal BP, and includes a thin mass wasting event deposited around 4500 cal BP. A multi-proxy approach was used to track the evolution and origin of clastic sedimentation during the Holocene, in order to identify periods of higher hydrological activity in the catchment area. Spectrophotometry was used to detect fluctuations in clastic supply and the study of clay minerals (especially the Illite cristallinity index) allowed locating the main source area of fine grained clastic particles settling at the lake after flood events. This dataset highlights up to 12 periods of more intense flooding events over the last 9 400 years in Lake Le Bourget and shows that the main source area of clastic particles during this period is the upper part of the Arve River drainage basin. This part of the catchment area drains several large glaciers from the Mont Blanc Massif, and fluctuations in Rhone River flood supply in Lake Le Bourget is interpreted as resulting essentially from Mont Blanc Glacier activity during the Holocene. The comparison of clastic sedimentation in Lake Le Bourget with periods of increasing land use and periods of Alpine glacier and mid-European lake level fluctuations, suggest that the core LDB04 clastic record in Lake Le Bourget is a continuous proxy of the Holocene hydrological history of the NW Alps. Aprahamian, J., 1974. La cristallinité de l'illite et les minéraux argileux en bordure des massifs cristallins externes de Belledonne et du Pelvoux. Géologie Alpine, t. 50, p 5-15. Arnaud F. Lignier V., Revel M., Desmet M., Beck C., Pourchet M., Charlet A., Trentesaux A., Tribovillard N. 2002. Flood and earthquake disturbance of 210Pb geochronology (Lake Anterne, North French Alps). Terra Nova, 14-4, pp. 225-232 Arnaud, F., 2005. Discriminating bio-induced and detrital sedimentary processes from particle size distribution of carbonates and non-carbonates in hard water lake sediments, Journal of Paleolimnology 34: 519-526 Arnaud F., Revel M., Chapron E., Desmet M., Tribovillard N., 2005. 7000 years of Rhône river flooding activity in Lake Le Bourget: A High-resolution sediment record of NW Alps hydrology. The Holocene. 15, No. 3, 420-428.

Quaternary Science Reviews, 2007

Two twin short gravity cores and a long piston core recovered from the deepest part of proglacial... more Two twin short gravity cores and a long piston core recovered from the deepest part of proglacial Lake Bramant (Grandes Rousses Massif, French Alps), under and overlying a large slump identified by high-resolution seismic profile, allow the investigation of Holocene natural hazards and interactions between human activity and climatic changes at high-altitude. Annual sedimentation throughout the cores (glacial varves) is identified on photographs, ITRAX (high-resolution continuous microfluorescence-X) and CAT-Scan (computerized axial tomography) analyses and is supported by (1) the number of dark and light laminations between dates obtained by radionuclide measurements ( 137 Cs, 241 Am), (2) the correlation of a slump triggered by the nearby AD 1881 Allemond earthquake (MSK intensity VII) and of a turbidite triggered by the AD 1822 Chautagne regional earthquake (MSK intensity VIII), (3) the number of laminations between two accelerator mass spectrometry (AMS) 14 C dates, and (4) archaeological data. In Lake Bramant, dark layers are coarser, contain less detrital elements, but more neoformed elements and organic matter content. These darker laminations result from calm background sedimentation, whereas the lighter layers are finer and rich in detrital elements and reflect the summer snowmelt. Traces of mining activity during the Roman civilization apogee (AD 115-330) and during the Early Bronze Age (3770-3870 cal BP) are recorded by lead and copper content in the sediments and probably result from regional and local mining activity in the NW Alps. Warmer climate during the Bronze Age in this part of the Alps is suggested by (1) two organic deposits (4160-3600 cal BP and 3300-2850 cal BP) likely reflecting a lower lake level and smaller glaciers and (2) evidence of a different vegetation cover around 2500 m a.s.l. The onset of clastic proglacial sedimentation between 3600-3300 cal BP and since 2850 cal BP is synchronous with periods of glacier advances documented in the Alps and high-lake levels in west-central Europe. This major change in proglacial sedimentation highlights the development of a larger St. Sorlin glacier in the catchment area of Lake Bramant. r

Journal of Geophysical Research, 2008

Geochimica et Cosmochimica Acta, 2011

The cosmogenic nuclide beryllium-10 ( 10 Be), recovered from ice cores, is often used to study so... more The cosmogenic nuclide beryllium-10 ( 10 Be), recovered from ice cores, is often used to study solar activity on long timescales. However, the 10 Be signal is also influenced by factors other than the Sun. To identify and quantify various contributions to the 10 Be signal, two Antarctic snow records from the Vostok and Concordia sites spanning the last 60 years were studied at a sub-annual resolution. Three factors that contribute to the 10 Be signal were identified. First, a significant period of approximately 11 yr that can be associated with the modulation of 10 Be production by solar activity was detected in both records. The solar imprint constitutes 20-35% of the variance within the total signal. The 11-yr 10 Be snow component was attenuated by a factor of 0.5andwasdelayedby0.5 and was delayed by 0.5andwasdelayedby1.4 yr compared to the 10 Be production expected within the polar atmosphere. The result could be interpreted as the composite response of a stratospheric 10 Be reservoir with an 11-yr modulation that was attenuated and delayed (with respect to 10 Be polar production) and to a tropospheric 10 Be reservoir with an 11-yr modulation that was not attenuated or delayed. Then, peaks in 10 Be concentrations that were 6666% and 6635% higher than the average concentration were observed during the stratospheric volcanic eruptions of Agung (in 1963) and Pinatubo (in 1991), respectively. In light of these new results, published 10 Be ice core records could be reinterpreted because spikes in 10 Be concentration appear at the time of several stratospheric events. The data indicate that stratospheric volcanic eruptions can impact 10 Be transport and deposition as a result of the roles played by the sedimentation of sulfate aerosols and the formation and rapid settling of polar stratospheric clouds (PSC). Also, an interannual variability of 4yrwasdeterminedinboth10Berecords,correspondingto4 yr was determined in both 10 Be records, corresponding to 4yrwasdeterminedinboth10Berecords,correspondingto26% of the variance within the signal at Vostok. As with species of marine origin (sodium), this 4-yr variability is interpreted as a tropospheric modulation. The 4-yr variability could be associated with atmospheric circulation associated with the coupled Southern Ocean ocean-atmosphere system. The results presented here, from sites within the high Antarctic plateau, open new possibilities for ice core dating over the last few centuries and for the reconstruction of past solar activity in relation to climate.

Atmospheric Chemistry and Physics Discussions, 2016

Atmospheric Chemistry and Physics Discussions, 2016

Egs Agu Eug Joint Assembly, Apr 1, 2003

As a part of ITASE project (International TransAntarctic Scientific Expedition) France and Italy ... more As a part of ITASE project (International TransAntarctic Scientific Expedition) France and Italy carried out different traverses covering Dome C drainage area. Surface snow samples (1 m cores and pits), shallow firn cores (10-50 m) firn temperature were collected along the traverses. Oxygen-isotope and beta activity measurements were carried out on the samples to provide information on accumulation rate and climatic condition of snow precipitation. The results of these analyses are compared with the firn temperatures. The oxygen-isotope composition shows a linear correlation with firn temperature in the different sector. Indeed snow accumulation rate and firn temperature over Antarctica is recognised as important climate parameters. The study aims to better understand latitudinal and longitudinal climatic gradients along transepts, while documenting atmospheric and surface conditions in the eastern and north-eastern portions of the Dome C drainage area and in Northern Victoria Land.

E3S Web of Conferences, 2013

The role of oceans in the global cycle of mercury is still poorly characterized, mainly because o... more The role of oceans in the global cycle of mercury is still poorly characterized, mainly because of a lack a long-term data on atmospheric mercury concentrations in the remote Southern Ocean. In the frame of GMOS (Global Mercury Observation System), we present here the first results from a new monitoring station at Amsterdam Island in the Southern Indian Ocean. For the period January to April 2012, we recorded mean concentration of gaseous elemental mercury (GEM), reactive gaseous mercury (RGM) and particulate-bounded mercury (PHg) of 1.03 ng m -3 , 0.37 and 0.34 pg m -3 respectively. While GEM concentrations showed little variations, RGM and PHg exhibited fast variations with alternation of value below the instrumental detection limit and maximum values up to 4 pg m -3 .

The study of mercury (Hg) cycle in Arctic regions is a major subject of concern due to the dramat... more The study of mercury (Hg) cycle in Arctic regions is a major subject of concern due to the dramatic increases of Hg concentrations in ecosystem in the last few decades. The causes of such increases are still in debate, and an important way to improve our knowledge on the subject is to study the exchanges of Hg between atmosphere and snow during springtime. We organized an international study from 10 April to 10 May 2003 in Ny-Å lesund, Svalbard, in order to assess these fluxes through measurements and derived calculations.

Laguna Chichój (Lake Chichój) is the only deep permanent lake in the central highlands of Guatema... more Laguna Chichój (Lake Chichój) is the only deep permanent lake in the central highlands of Guatemala. The lake is located in the boundary zone between the North American and Caribbean plates. The lake has been struck by devastating earthquakes and tropical cyclones in historical times. We investigated the imprint of 20 th century extreme events on the sedimentary record of this tropical lake using a bathymetric survey of the lake, coring the lake floor, and providing a chronology of sediment accumulation. The lake occupies a series of circular depressions likely formed by the rapid dissolution of a buried body of gypsum. 210 Pb and 137 Cs inventories and varve counting indicate high rates of sedimentation (1-2 cm/y). The annually layered sediment is interrupted by turbidites of two types: a darker-colored turbidite, enriched in lake-derived biogenic constituents, and interpreted as a seismite, and a lighter-colored type, enriched in catchment-derived constituents, interpreted as a flood layer. Comparison of our 137 Cs -determined layer ages with a catalog of 20 th century earthquakes shows that an earthquake on the Motagua fault in 1976 generated a conspicuous darker-colored turbidite and slumped deposits in separate parts of the lake. The entire earthquake inventory further reveals that mass movements in the lake are triggered at Modified Mercalli Intensities (MMI) higher than V. Tropical cyclonic depressions known to have affected the lake area had limited effect on the lake, including Hurricane Mitch in 1998. One storm however produced a significantly thicker flood layer in the 1940s. This storm is reportedly the only event to have generated widespread slope failures in the lake catchment. It is thus inferred that abundant landsliding provided large amounts of concentrated sediment to the lake, through hyperpycnal flows.

The Cryosphere, 2008

Satellite records of microwave surface emission have been used to interpolate in-situ observation... more Satellite records of microwave surface emission have been used to interpolate in-situ observations of Antarctic surface mass balance (SMB) and build continental-scale maps of accumulation. Using a carefully screened subset of SMB measurements in the 90 • -180 • E sector, we show a reasonable agreement with microwave-based accumulation map in the dry-snow regions, but large discrepancies in the coastal regions where melt occurs during summer. Using an emission microwave model, we explain the failure of microwave sensors to retrieve SMB by the presence of layers created by melt/refreeze cycles. We conclude that regions potentially affected by melting should be masked-out in microwave-based interpolation schemes.

Sedimentary Geology, 2007

... meso-or hyperpycnal flows cf. [Bates, 1953], [Sturm and Matter, 1978], [Ashley et al., 1985] ... more ... meso-or hyperpycnal flows cf. [Bates, 1953], [Sturm and Matter, 1978], [Ashley et al., 1985] and [Hsü, 1989]) and to what extent they control the geometry of clastic sedimentary environments. The influence of interflows (mesopycnal ...

Reviews of Geophysics, 2008

Quaternary Science Reviews, 2007

Two twin short gravity cores and a long piston core recovered from the deepest part of proglacial... more Two twin short gravity cores and a long piston core recovered from the deepest part of proglacial Lake Bramant (Grandes Rousses Massif, French Alps), under and overlying a large slump identified by high-resolution seismic profile, allow the investigation of Holocene natural hazards and interactions between human activity and climatic changes at high-altitude. Annual sedimentation throughout the cores (glacial varves) is identified on photographs, ITRAX (high-resolution continuous microfluorescence-X) and CAT-Scan (computerized axial tomography) analyses and is supported by (1) the number of dark and light laminations between dates obtained by radionuclide measurements ( 137 Cs, 241 Am), (2) the correlation of a slump triggered by the nearby AD 1881 Allemond earthquake (MSK intensity VII) and of a turbidite triggered by the AD 1822 Chautagne regional earthquake (MSK intensity VIII), (3) the number of laminations between two accelerator mass spectrometry (AMS) 14 C dates, and (4) archaeological data. In Lake Bramant, dark layers are coarser, contain less detrital elements, but more neoformed elements and organic matter content. These darker laminations result from calm background sedimentation, whereas the lighter layers are finer and rich in detrital elements and reflect the summer snowmelt. Traces of mining activity during the Roman civilization apogee (AD 115-330) and during the Early Bronze Age (3770-3870 cal BP) are recorded by lead and copper content in the sediments and probably result from regional and local mining activity in the NW Alps. Warmer climate during the Bronze Age in this part of the Alps is suggested by (1) two organic deposits (4160-3600 cal BP and 3300-2850 cal BP) likely reflecting a lower lake level and smaller glaciers and (2) evidence of a different vegetation cover around 2500 m a.s.l. The onset of clastic proglacial sedimentation between 3600-3300 cal BP and since 2850 cal BP is synchronous with periods of glacier advances documented in the Alps and high-lake levels in west-central Europe. This major change in proglacial sedimentation highlights the development of a larger St. Sorlin glacier in the catchment area of Lake Bramant. r

Journal of Paleolimnology, 2014

Journal of Geophysical Research, 2007

1] On the basis of thousands of surface mass balance (SMB) field measurements over the entire Ant... more 1] On the basis of thousands of surface mass balance (SMB) field measurements over the entire Antarctic ice sheet it is currently estimated that more than 2 Gt of ice accumulate each year at the surface of Antarctica. However, these estimates suffer from large uncertainties. Various problems affect Antarctic SMB measurements, in particular, limited or unwarranted spatial and temporal representativeness, measurement inaccuracy, and lack of quality control. We define quality criteria on the basis of (1) an up-to-date review and quality rating of the various SMB measurement methods and (2) essential information (location, dates of measurements, time period covered by the SMB values, and primary data sources) related to each SMB data. We apply these criteria to available SMB values from Queen Mary to Victoria lands (90°-180°E Antarctic sector) from the early 1950s to present. This results in a new set of observed SMB values for the 1950-2005 time period with strong reduction in density and coverage but also expectedly reduced inaccuracies and uncertainties compared to other compilations. The quality-controlled SMB data set also contains new results from recent field campaigns (International Trans-Antarctic Scientific Expedition (ITASE), Russian Antarctic Expedition (RAE), and Australian National Antarctic Research Expeditions (ANARE) projects) which comply with the defined quality criteria. A comparative evaluation of climate model results against the quality-controlled updated SMB data set and other widely used ones illustrates that such Antarctic SMB studies are significantly affected by the quality of field SMB values used as reference. Citation: Magand, O., C. Genthon, M. Fily, G. Krinner, G. Picard, M. Frezzotti, and A. A. Ekaykin (2007), An up-to-date qualitycontrolled surface mass balance data set for the 90°

Journal of Climate, 2008

This work reports on high-resolution (60 km) atmospheric general circulation model simulations of... more This work reports on high-resolution (60 km) atmospheric general circulation model simulations of the Antarctic climate for the periods 1981-2000 and 2081-2100. Our analysis focuses on the surface mass balance change, one of the components of the total ice sheet mass balance, and its impact on global eustatic sea level. Contrary to previous simulations, in which we directly used sea

Geophysical Research Letters, 2006

Geophysical Research Letters, 2006