ALBERT

Description: Intensification of the North and South Equatorial Current systems and trade winds occurred during glacial periods, according to a comparison of late Holocene (interglacial), 18,000 B.P. (glacial), and late Quaternary (0 to 180,000 B.P.) faunal assemblages and sea-surface temperature estimates from the equatorial Atlantic and Caribbean regions. Faster circulation of the North Equatorial Current system in glacial Northern Hemisphere winters (February) is indicated by increased upwelling of cool (15°C) water off northwest Africa and slightly cooler conditions across the northern tropical Atlantic and Caribbean. Intensification of the South Equatorial Current occurred along the Equator during the Southern Hemisphere winter (August). This interpretation is based on the dominance of a cool-equatorial assemblage, which indicated that waters of 16° to 18°C replaced the tropical assemblage that lives today in 24° to 26°C water in this region. The cool influence of the glacial (August) Benguela-South Equatorial Current decreased rapidly westward along the equatorial belt so that the fauna was dominated by the tropical assemblage in the Caribbean. Sea-surface temperatures increased rapidly from east to west in the equatorial belt, so that at long 35°W, the 16°C water had reached ambient temperatures of 24° to 26°C. Both faunal assemblages and temperature estimates of eight late Quaternary Atlantic and Caribbean sediment cores show that the equatorial region experienced three maximum incursions of cool Benguela Current water during the past 150,000 yr—at approximately 135,000 B.P., 73,000 B.P., and 18,000 B.P. Differences of glacial to interglacial sea-surface temperatures range from 5° to 10°C in the eastern equatorial Atlantic to 2° to 3°C in the western Atlantic and the Caribbean. During this time, only two periods with similar faunas and surface temperatures occurred—today and 125,000 B.P. Seasonal temperature contrast (August to February) is three to four times greater in all cores for glacial conditions than for interglacial conditions. The winter temperatures (February to the north of the thermal equator and August south of it) show the greatest changes, and they control the overall temperature pattern. Identical temperature patterns for cores affected by the North and the South Equatorial Currents suggest that the Northern and Southern Hemispheres are generally in phase and that more severe winters control the glacial temperature pattern.