The North American monsoon is an important feature of the atmospheric circulation over the continent, with a research literature that dates back almost 100 years. The authors review the wide range of past and current research dealing with the meteorological and climatological aspects of the North American monsoon, highlighting historical development and major research themes. The domain of the North American monsoon is large, extending over much of the western United States from its region of greatest influence in northwestern Mexico. Regarding the debate over moisture source regions and water vapor advection into southwestern North America, there is general agreement that the bulk of monsoon moisture is advected at low levels from the eastern tropical Pacific Ocean and the Gulf of California, while the Gulf of Mexico may contribute some upper-level moisture (although mixing occurs over the Sierra Madre Occidental). Surges of low-level moisture from the Gulf of California are a significant part of intrase...

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The North American Monsoon

A sudden and sharp rise in the C-14 content of the atmosphere, which occurred between ca. 850 and 760 calendar yr BC (ca. 2750-2450 BP on the radiocarbon time-scale), was contemporaneous with an abrupt climate change. In northwest Europe (as indicated by palaeoecological and geological evidence) climate changed from relatively warm and continental to oceanic. As a consequence, the ground-water table rose considerably in certain low-lying areas in The Netherlands. Archaeological and palaeoecological evidence for the abandonment of such areas in the northern Netherlands is interpreted as the effect of a rise of the water table and the extension of fens and bogs. Contraction of population and finally migration from these low-lying areas, which had become marginal for occupation, and the earliest colonisation by farming communities of the newly emerged salt marshes in the northern Netherlands around 2550 BP, is interpreted as the consequence of loss of cultivated land. Thermic contraction of ocean water and/or decreased velocity and pressure on the coast by the Gulf Stream may have caused a fall in relative sea-level rise and the emergence of these salt marshes. Evidence for a synchronous climatic change elsewhere in Europe and on other continents around 2650 BP is presented. Temporary aridity in tropical regions and a reduced transport of warmth to the temperate climate regions by atmospheric and/or oceanic circulation systems could explain the observed changes. As yet there is no clear explanation for this climate change and the contemporaneous increase of C-14 in the atmosphere. The strategy of C-14 wiggle-match dating can play an important role in the precise dating of organic deposits, and can be used to establish possible relationships between changing C-14 production in the atmosphere, climate change, and the impact of such changes on hydrology, vegetation, and human communities.

Archaeological and palaeoecological indications of an abrupt climate change in The Netherlands, and evidence for climatological teleconnections around 2650 BP

Missing link

Environmental reconstruction of a Roman Period settlement site in Uitgeest (The Netherlands), with special reference to coprophilous fungi

Hunter-gatherer adaptations to long-term fluctuations in regional resource structure require mechanisms to cope with periodic subsistence stresses. Among documented groups, a common response to such stress is temporary movement into adjacent occupied areas-moving in with "relatives" when things go wrong. However, in the case of early (ca. 12,000-10,000 B.P.) Paleoindian groups in the Americas, the availability of neighboring groups with a detailed knowledge of local resource geography could not be relied upon. Post-Pleistocene environmental changes and the low initial population of the New World are important factors conditioning a lifeway characterized by a dependence on hunting (though not exclusively of megafauna), and by high residential, logistical, and range (territorial) mobility. Early Paleoindian groups had to adopt a subsistence technology that could be employed regardless of the specific resource microstructure. In some regards, Paleoindians seem to have behaved like tropical foragers while in others like arctic collectors. Use of high quality lithic raw materials from large quarry sources, reliance on a bifacial technology, limited use of caves and rockshelters, and a low level of processing of food products for storage all may be indicative of such a subsistence technology, which would have been unlike that of any modern hunter-gatherers.

Owen K. Davis

Papers

Sporormiella fungal spores, a palynological means of detecting herbivore density

Antioxidant activity of Sonoran Desert bee pollen

Spores of the Dung Fungus Sporormiella: Increased Abundance in Historic Sediments and Before Pleistocene Megafaunal Extinction

Rapid climatic change in coastal southern California inferred from pollen analysis of San Joaquin Marsh

Pollen frequencies reflect vegetation patterns in a great basin (U.S.A.) mountain range