Robert J. Delmas

Bio: Robert J. Delmas is an academic researcher from Centre national de la recherche scientifique. The author has contributed to research in topics: Snow & Ice core. The author has an hindex of 45, co-authored 93 publications receiving 5681 citations.

Carbon dioxide and methane emissions and the carbon budget of a 10-year old tropical reservoir (Petit Saut, French Guiana)

Abstract: emissions, 0.07 ± 0.01) the first 3 years after impounding (1994–1996) and then decreased to 0.12 ± 0.01 Mt yr 1 C( CO2, 0.10 ± 0.01; CH4, 0.016 ± 0.006) since 2000. On average over the 10 years, 61% of the CO2 emissions occurred by diffusion from the reservoir surface, 31% from the estuary, 7% by degassing at the outlet of the dam, and a negligible fraction by bubbling. CH4 diffusion and bubbling from the reservoir surface were predominant (40% and 44%, respectively) only the first year after impounding. Since 1995, degassing at an aerating weir downstream of the turbines has become the major pathway for CH4 emissions, reaching 70% of the total CH4 flux. In 2003, river carbon inputs were balanced by carbon outputs to the ocean and were about 3 times lower than the atmospheric flux, which suggests that 10 years after impounding, the flooded terrestrial carbon is still the predominant contributor to the gaseous emissions. In 10 years, about 22% of the 10 Mt C flooded was lost to the atmosphere. Our results confirm the significance of greenhouse gas emissions from tropical reservoir but stress the importance of: (1) considering all the gas pathways upstream and downstream of the dams and (2) taking into account the reservoir age when upscaling emissions rates at the global scale.

The ice record of greenhouse gases

Abstract: Gases trapped in polar ice proved our most direct record of the changes in greenhouse gas levels during the past 150,000 years. The best documented trace-gas records are for CO[sub 2] and CH[sub 4]. The measurements corresponding to the industrial period document the recent changes in growth rate. The variability observed over the last 1000 years constrains the possible feedbacks of a climate change on the trace gases under similar conditions as exist today. Changes in the levels of greenhouse gases during the glacial-interglacial cycle overall paralleled, at least at high southern latitudes, changes in temperature; this relation suggests that greenhouse gases play an important role as an amplifier of the initial orbital forcing of Earth's climated and also helps to assess the feedbacks on the biogeochemical cycles in a climate system in which the components are changing at different rates.

Polar ice evidence that atmospheric CO 2 20,000 yr BP was 50% of present

Abstract: Analysis of the air enclosed in polar ice (∼0.1 ml per g of ice1) provides one of the most promising ways of discovering atmospheric composition over the past 100,000 yr. Until now, because of an apparent but not well understood enrichment of CO2 in the trapped air, all attempts to reconstitute the ancient atmospheric CO2 content from polar ice have failed2–6. We have obtained CO2 contents that can reasonably be considered representative of present or past atmospheric contents using a new method of air extraction. The results reported here, based on the CO2 analysis of two deep Antarctic cores including the last climatic interchange, strongly suggest that during the coldest part of the last Ice Age (20,000–15,000 yr ago) the atmospheric CO2 content was half (0.016%) that of today's level (0.033%).

Decrease in anthropogenic lead, cadmium and zinc in Greenland snows since the late 1960s

Abstract: MORE than twenty years ago, Patterson and co-workers1 showed that evidence of lead concentrations in Greenland ice and snow had increased about 200-fold since ancient times. From their results, they concluded that more than 99% of this highly toxic metal in the global troposphere of the Northern Hemisphere originated from human activities in the mid 1960s—mainly from the use of alkyl-leaded petrol. At least in part because of this evidence, the United States and other countries limited the use of lead additives in petrol from about 1970. Here we report that, as a result of these policy initiatives, lead concentrations in Greenland snow have decreased by a factor of 7.5 over the past twenty years. We also show that over the same time period, cadmium and zinc concentrations have decreased by a factor of 2.5.

Methane and carbon dioxide emissions from tropical reservoirs: Significance of downstream rivers

Abstract: [1] Methane (CH4) andcarbon dioxide (CO2) concentrations and water-air fluxes were measured in three tropical reservoirs and their respective rivers downstream of the dams. From reservoirs, CH4 and CO2 flux were in the range of 3 ± 2 and 254± 392mmol.m � 2 .d � 1 ,respectively.Riversdownstreamof dams were significantly enriched in CH4 and CO2 originating from reservoir hypolimnions. From rivers, CH4 and CO2 flux were in the range of 60 ± 38 and 859 ± 400 mmol.m � 2 .d � 1 , respectively. Despite their relatively small surfaces, rivers downstream of dams accounted for a significant fraction (9– 33% for CH4 and 7–25% for CO2) of the emissions across the reservoir surfaces classically taken into account for reservoirs. A significant fraction of CH4 appeared to degas at the vicinity of the dam (turbines and spillways), although it could not be

Climate and atmospheric history of the past 420,000 years from the Vostok ice core, Antarctica

Abstract: The recent completion of drilling at Vostok station in East Antarctica has allowed the extension of the ice record of atmospheric composition and climate to the past four glacial–interglacial cycles. The succession of changes through each climate cycle and termination was similar, and atmospheric and climate properties oscillated between stable bounds. Interglacial periods differed in temporal evolution and duration. Atmospheric concentrations of carbon dioxide and methane correlate well with Antarctic air-temperature throughout the record. Present-day atmospheric burdens of these two important greenhouse gases seem to have been unprecedented during the past 420,000 years.

Climate and atmospheric history of the past 420,000 years from the Vostok ice core, Antarctica

Abstract: The recent completion of drilling at Vostok station in East Antarctica has allowed the extension of the ice record of atmospheric composition and climate to the past four glacial–interglacial cycles. The succession of changes through each climate cycle and termination was similar, and atmospheric and climate properties oscillated between stable bounds. Interglacial periods differed in temporal evolution and duration. Atmospheric concentrations of carbon dioxide and methane correlate well with Antarctic air-temperature throughout the record. Present-day atmospheric burdens of these two important greenhouse gases seem to have been unprecedented during the past 420,000 years.

Evidence for general instability of past climate from a 250-kyr ice-core record

Abstract: RECENT results1,2 from two ice cores drilled in central Greenland have revealed large, abrupt climate changes of at least regional extent during the late stages of the last glaciation, suggesting that climate in the North Atlantic region is able to reorganize itself rapidly, perhaps even within a few decades. Here we present a detailed stable-isotope record for the full length of the Greenland Ice-core Project Summit ice core, extending over the past 250 kyr according to a calculated timescale. We find that climate instability was not confined to the last glaciation, but appears also to have been marked during the last interglacial (as explored more fully in a companion paper3) and during the previous Saale–Holstein glacial cycle. This is in contrast with the extreme stability of the Holocene, suggesting that recent climate stability may be the exception rather than the rule. The last interglacial seems to have lasted longer than is implied by the deep-sea SPECMAP record4, in agreement with other land-based observations5,6. We suggest that climate instability in the early part of the last interglacial may have delayed the melting of the Saalean ice sheets in America and Eurasia, perhaps accounting for this discrepancy.

Emission of trace gases and aerosols from biomass burning

Abstract: A large body of information on emissions from the various types of biomass burning has been accumulated over the past decade, to a large extent as a result of International Geosphere-Biosphere Programme/International Global Atmospheric Chemistry research activities. Yet this information has not been readily accessible to the atmospheric chemistry community because it was scattered over a large number of publications and reported in numerous different units and reference systems. We have critically evaluated the presently available data and integrated these into a consistent format. On the basis of this analysis we present a set of emission factors for a large variety of species emitted from biomass fires. Where data were not available, we have proposed estimates based on appropriate extrapolation techniques. We have derived global estimates of pyrogenic emissions for important species emitted by the various types of biomass burning and compared our estimates with results from inverse modeling studies.

Agricultural Intensification and Ecosystem Properties

Abstract: Expansion and intensification of cultivation are among the predominant global changes of this century. Intensification of agriculture by use of high-yielding crop varieties, fertilization, irrigation, and pesticides has contributed substantially to the tremendous increases in food production over the past 50 years. Land conversion and intensification, however, also alter the biotic interactions and patterns of resource availability in ecosystems and can have serious local, regional, and global environmental consequences. The use of ecologically based management strategies can increase the sustainability of agricultural production while reducing off-site consequences.