The isotopic composition of foraminiferal shells (oxygen, carbon) holds the key to a number of central problems in paleoceanography, such as paleotemperature determination, discovery of the nature of the age cycles, and the evolution of climate and circulation during the last 100 million years. The Pleistocene cyclicity appears tied to the Milankovitchmechanism; however, the peculiar shape of the 100,000 year “saw-tooth” cycle calls for certain feedback mechanisms. In particular, the deglaciation events suggest strong positive feedback, which may derive from salinity stratification of the ocean. There is evidence for such stratification during the last deglaciation. The Tertiary oxygen isotope stratigraphy indicates an overall cooling trend for high latitudes, while the tropics tend to stay warm. During the Eocene high latitudes were characterized by (isotopically light) low salinity surface waters. During the Neogene, a strong thermocline developed, and confined the vertical mixing of upper waters to privileged regions including upwelling areas. The steplike transitions in isotope stratigraphy (Eocene- Oligocene, Cretaceous-Tertiary) are of fundamental importance in the avolution of climate and of life.
Figures & Tables
Foraminiferal Ecology and Paleoecology
Perhaps no fossil group is used as much as foraminifera for paleoecologic inference, both in academia and industry. Since the late 1960s, new concepts and much additional data have appeared that make it difficult for the casual worker not immediately concerned with foraminiferal ecology and paleoecology to stay abreast of the latest developments. In these notes, the authors summarize much of that information, or provide reference to more detailed sources. They also attempt to point out problems and other methods of dealing with them. Most paleoecologic work with foraminifera in the past has relied on direct comparison of fossil assemblages with the most similar modern assemblages, and inferring then that the environments were similar also. The method is used widely in scientific studies and in industrial applications. The result is based on the single hypothesis that the fossils are environmentally analogous to their modern counterparts. These notes present a number of alternative working hypotheses, and in some cases, examine the data to attempt of disprove them.