Jacob Charles Walker

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We develop a numerical simulation of the global biogeochemical cycles of carbon that works over time scales extending from years to millions of years. The ocean is represented by warm and cold shallow water reservoirs, a thermocline reservoir, and deep Atlantic, Indian, and Pacific reservoirs. The atmosphere is characterized by a single carbon reservoir(More)
Reconstructions of early Eocene climate depict a world in which the polar environments support mammals and reptiles, deciduous forests, warm oceans and rare frost conditions. At the same time, tropical sea surface temperatures are interpreted to have been the same as or slightly cooler than present values. The question of how to warm polar regions of(More)
Anomalous isotopic composition has been reported for the carbon in carbonate minerals of banded iron formations. Well studied examples show and enrichment in the light isotope of carbon, 12C. This enrichment presumably reflects unusual circumstances in the deposition of these sedimentary rocks. It is suggested here that the isotopically-light carbonate(More)
The pace of tidal evolution for the past approximately 450 Myr implies an Earth/Moon collision some 1,500-2,000 Myr BP, an event for which there is no corroborating evidence. Here we present the first direct determination of the lunar distance in the Precambrian. We interpret a 23.3 +/- 0.3-yr periodicity preserved in a 2,500 Myr BP Australian banded iron(More)
Time resolved data on the carbon isotopic composition of carbonate minerals and the sulfur isotopic composition or 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(More)
Photosynthesis produces reduced organic carbon and an oxidized partner in equivalent molar amounts. These compounds can react with one another, again in equivalent molar amounts, so that no net change occurs in the overall level of oxidation of the biosphere (here taken to mean the biota together with the part of the Earth with which living things(More)
As worldwide automotive ownership is set to exceed 2 billion vehicles by 2030 [1], environmental and economical pressures on the automotive industry mean there is a trend to reduce harmful greenhouse gas emissions whilst simultaneously improving fuel economy. The use of electrical hybrid, start-stop idling and materials light-weighting are some of the(More)
Climate is an important environmental parameter of the early Earth, likely to have affected the origin and evolution of life, the composition and mineralogy of sedimentary rocks, and stable isotope ratios in sedimentary minerals. There is little observational evidence constraining Precambrian climates. Most of our knowledge is at present theoretical. (More)
In the last two decades large radars have proved to be powerful instruments for the measurement of the properties of the upper atmosphere. These radars were used initially to measure properties of the ionosphere by the Thomson scattering technique at heights above 100 kilometers. Careful interpretation of the power and spectrum of radar echoes yielded data(More)
A boxmodel of the Great Lakes is used to estimate meltwater flow into the North Atlantic between 8000 and 14,000 calendar years B.P. Controls on the model include the oxygen isotopic composition of meltwaters and lake waters as measured in the shells of ostracodes. Outflow rates are highest when oxygen isotopic values of the lake waters are most negative,(More)