THE PLATE TECTONIC IMPACT ON CLIMATIC-CHANGE WITH PARTICULAR RELEVANCE TO MESOAMERICA

The oceanic circulation and associated climatic zonations some 120 Ma can be taken as more geologically 'normal' than the last few million y ears. It was dominated by a strong circum-Equatorial current accompani ed by warm water circulation well into Polar areas. This resulted in a marked increase in salinity between 10 and 25 degrees N/S, with conse quential strong ocean stratification and circulation mostly in the upp er one kilometre. This pattern was likely to be associated with a simp le Two Hadley-Cell atmospheric circulation. Orbitally forced periodica l variations in solar insolation gave eustatic sea-level changes of le ss than 10 m amplitude. During the last 50 Ma, the relative positions of the MesoAmerican continental plates have not changed greatly and he nce plate motions have had little or no effect on the Atlantic deep-oc ean haline circulation. Secondary plate tectonic processes - topograph ic change, volcanism and seismic activity - were more important and ha d marked local effects on the climate which could be mistaken for glob al changes. The Chihuahua area of Mexico provides the optimum site for identifying Recent global climatic changes. (C) 1997 INQUA/Elsevier S cience Ltd.