| The timing, frequencies, and rates of change of tropical Atlantic climates are studied on a glacial/interglacial scale, using foraminferal faunal abundance and stable isotopic data to estimate temperatures, ice volumes, and water mass properties of the surface and deep ocean. Oxygen-isotope and radiocarbon data constrain the timing of the last deglacial transition (Termination 1) to between 14,000 and 6000 yr BP. Deglaciation was not a continuous process, but may have occurred in steps from 14,000 to 12,000 yr BP, 10,000 to 8,000 yr BP, and 7000 to 6000 yr BP. Changes in the (delta)('18)O of glacier ice may induce a lag of the marine (delta)('18)O record behind ice volume of 1000 to 3000 years. Temperature changes estimated by foraminiferal transfer functions were not detected in down-core planktonic foraminferal (delta)('18)O data.; Hemispheric symmetry of glacial (20,000 - 14,000 yr BP) cooling (based on foraminiferal temperature estimates) may reflect linkage to high-latitude climate changes via trade wind intensities and/or directions. During deglaciation (14,000 - 6000 yr BP) the North Atlantic was relatively cold, the South Atlantic was relatively warm, and equatorial seasonal contrast was low. This may reflect reduction of northward cross-equatorial heat transport in the ocean, and possible monsoonal effects.; Climate changes also extend to the deep ocean. At mid-depths of the tropical Atlantic, minimum Atlantic-Pacific (delta)('13)C difference occurring on average during deglaciation (with a strong 23,000-yr "precession" cycle) suggests reduced formation of a warm component of NADW during deglaciation. At deeper sites in the North Atlantic, reduced ventilation of deep basins during glacial maxima is linked to surface-water variability of the subpolar North Atlantic. This may reflect the coupled effects of reduced NADW formation, and increased preformed nutrients (and thus decreased preformed (delta)('13)C) of a cold northern-source water mass that formed in the North Atlantic during glacial time. |
