Degassing

Measurements of the concentration of rare gases and trace elements in oceanic basalts provided a new information concerning the structure if the Earth mantle and its evolution. The results set important constraints that need to be incorporated into any comprehensive understanding of the early history of the planets. Some of the highlights of these results are described and an indication is given how they are derived

How life affects the geochemical cycle of carbon

Developing a quantitative understanding of the biogeochemical cycles of carbon as they have worked throughout Earth history on various time scales, how they have been affected by biological evolution, and how changes in the carbon content of ocean and atmosphere may have affected climate and the evolution of life are the goals of the research. Theoretical simulations were developed that can be tuned to reproduce such data as exist and, once tuned, can be used to predict properties that have not yet been observed. This is an ongoing process, in which models and results are refined as new data and interpretations become available and as understanding of the global system improves. Results of the research are described in several papers which were published or submitted for publication. These papers are summarized. Future research plans are presented

Some Perspectives of the Major Biogeochemical Cycles

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/94582/1/eost3946.pd

Carbon Cycle Modelling

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/94608/1/eost3991.pd

Comments requested

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95017/1/eost3321.pd

The geochemical carbon cycle and the uptake of fossil fuel CO2

Atmospheric carbon dioxide levels are controlled over long time scales by the transfer of carbon between the atmosphere, oceans, and sedimentary rocks— a process referred to as the CO2 geochemical cycle. Carbon dioxide is injected into the atmosphere‐ocean system by volcanism; it is removed by the weathering of silicate rocks on the continents followed by the deposition of carbonate minerals on the sea floor. Humans are currently perturbing the natural carbon cycle by burning fossil fuels and deforesting the tropics, both of which add CO2 to the atmosphere. The effects of human activities on future atmospheric CO2 levels can be estimated by including anthropogenic emissions in a model of the long‐term carbon cycle. The model predicts that CO2 concentrtions could increase by a factor of six or more during the next few centuries if we consume all of the available fossil fuels. Preserving existing forests and/or reforesting parts of the planet could mitigate the CO2 increase to some extent, but cannot be depended on to make a significant difference. Because the removal processes for atomspheric CO2 are slow, the maximum CO2 level reached is relatively insensitive to the fossil fuel burning rate unless the burning rate is many times smaller than its present value. The model also predicts that hundreds of thousand of years could pass before atmospheric CO2 returns to its original preindustral level. Implications of these results for future energy and land use policies are discussed.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87506/2/175_1.pd

Why the oxygen isotopic composition of sea water changes with time

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/94773/1/grl4282.pd

Climate shocks: Natural and anthropogenic : by K. Ya. Kondratyev (translated from Russian by A. P. Kostrova), Wiley Series in Climate and the Biosphere, edited by Michael H. Glantz and Robert E. Dickinson. J. Wiley & Sons, 1988, 296p., $52.50 (ISBN 0-471-83019-4).

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/28080/1/0000526.pd

Impact erosion of planetary atmospheres

The impact of a large extraterrestrial body onto a planet deposits considerable energy in the atmosphere. If the radius of the impactor is much larger than an atmospheric scale height and its velocity much larger than the planetary escape velocity, some of the planetary atmosphere may be driven off into space. The process is analyzed theoretically in this paper. The amount of gas that escapes is equal to the amount of gas intercepted by the impacting body multiplied by a factor not very different from unity. Escape occurs only if the velocity of the impacting body exceeds the planetary escape velocity. At large impact velocities the enhancement factor, which is the factor multiplying the amount of atmosphere intercepted by the impacting body, approaches a constant value approximately equal to 1012/Ve2, where Ve is the escape velocity (in cm/sec). The enhancement factor is independent of atmospheric mass or surface pressure. Ablation of the impacting body and the planetary surface adds to the mass of gas that must be accelerated into space if escape is to occur. As a result, impact erosion of the atmosphere does not occur from a planet with an escape velocity in excess of 10 km/sec.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/26018/1/0000089.pd

Global geochemical cycles of carbon, sulfur and oxygen

Time-resolved data on the carbon isotopic composition of carbonate minerals and the sulfur isotopic composition of sulfate minerals show a strong negative correlation during the Cretaceous. Carbonate minerals are isotopically heavy during this period while sulfate minerals are isotopically light. The implication is that carbon is being transferred from the oxidized, carbonate reservoir to the reservoir of isotopically light reduced organic carbon in sedimentary rocks while sulfur is being transferred from the reservoir of isotopically light sedimentary sulfide to the oxidized, sulfate reservoir. These apparently oppositely directed changes in the oxidation state of average sedimentary carbon and sulfur are surprising because of a well-established and easy to understand correlation between the concentrations of reduced organic carbon and sulfide minerals in sedimentary rocks. Rocks rich in reduced carbon are also rich in reduced sulfur. The isotopic and concentration data can be reconciled by a model which invokes a significant flux of hydrothermal sulfide to the deep sea, at least during the Cretaceous.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/26276/1/0000361.pd