Woods Hole Oceanographic Institution, United States

Major element and color reflectance data from Ocean Drilling Program (ODP) Site 1002 in the anoxic Cariaco Basin off Venezuela record with subcentennial to subdecadal resolution unexpected large and abrupt shifts in the hydrologic cycle of the tropical Atlantic during the last 90 ka. Marine productivity maxima and increased precipitation and riverine discharge from northern South America are closely linked to interstadial (warm) climate events of marine isotope stage 3 and to atmospheric methane maxima as recorded in Greenland ice cores. Increased precipitation at this latitude during interstadials suggests the potential for a net rise in moisture export from the Atlantic to Pacific, which would affect the salinity balance of the Atlantic and increase thermohaline heat transport to high northern latitudes. This supports the notion that the tropics played a pivotal role in modulating global climate during the last glacial. During the Holocene, significant variations in regional climate have been recognized, some of which have had clear societal relevance. Following a dry Younger Dryas, a period of increased precipitation and riverine discharge occurred during the Holocene 'thermal maximum'. Since approximately 5.4 kyr, a trend towards drier conditions is evident from the data, with high amplitude fluctuations and precipitation minima during the time interval 3.8 to 2.8 kyr and during the 'Little Ice Age'. These observations can be explained by changes in the position of the Atlantic Intertropical Convergence Zone (ITCZ), possibly driven by Pacific-based climate variability.