PEDOLOGICAL AND PALAEOECOLOGICAL ASPECTS REVIEWED IN

Posted by Dan H. Yaalon 10 Nov 2002 15:41:49

A critique of Phanerozoic climatic models involving changes in the CO2 content of the atmosphere. By A.J. Boucot and J. Gray, Earth Science Reviews 56, 159pp, 2001, Elsevier, The Netherlands.

The reason that this book-length (159 pp) discussion of climatic models for the geologic past is reviewed here is that about half of its content deals with chemical and microbiotic weathering processes and their effects in soils – from ancient rock surfaces to current rhizosphere characteristics. Judging from the title and the keywords, it would not normally attract soil scientists, though it is actually one of the more detailed reviews and discussion of the evolutionary history of the rhizosphere, of microbiotic weathering effects as controlled by environmental factors, of microbial desert crusts, temperature effects and more. Factors controlling soil organic and inorganic carbon sequestration and preservation are also treated but in less detail. It is a nice example of the function and impact of pedology in paleoecology. Hence it is valuable to soil biologists, soil ecologists, paleopedologists and weathering processes specialists, who will find here references to many useful publications. There are some 750 references.

The purpose of the authors Art Boucot and the late Jane Gray (both from Oregon) , is to present an alternative model of climatic change to the geochemically based model of Robert Berner from Yale, most widely cited in the literature. They point out that such models of ancient and past climates need to take into account and be validated by actual field evidence – paleoecological and paleopedological. The documentation which they have assembled and reviewed indicates shifting climatic temperate gradients from pole to equator, varying both in time and intensity, not in accord with those postulated by Berner’s model based on past pCO2 reconstructions. They consider the geological field data more reliable and a better proxy indicator than other reconstructions of past climates. Hence indirectly they also cast a suspicion on the current global climate change models which invariably rely mainly on the recent atmospheric pCO2 variations. Though it deals with a wide range of different topics, the discussion is suitably organized, but it is not easy reading. Vascular plants are here called tracheophytes and hence soil rock/microbiotic interactions become pre-tracheophyte effects. The role of the rhizosphere is well reviewed and that the rhizosphere in temperate forest soils occupies only a relatively small volume of the total soil is pointed out. The role of varying precipitation quantities is hardly touched upon.

In summary, the review is highly recommended to all pedologists and soil ecologists, whether interested in past or current processes cum effects. For me – a process oriented pedologist - it will become a valuable reference to the understanding of terrestrization and early soil forming processes, whether now or in the past.

Dan H. Yaalon
Institute of Earth Sciences, Hebrew University
Jerusalem 91904, Israel

May 2002