Late Pleistocene history of ocean-atmosphere interaction in the eastern equatorial Pacific.

摘要

A high resolution study of late Pleistocene climatic and oceanic change was accomplished using eight sediment cores recovered from the eastern equatorial Pacific. Core locations form a north-south across-current transect at 110{dollar}spcirc{dollar}W, between 5.3{dollar}spcirc{dollar}N and 3{dollar}spcirc{dollar}S and an east-west transect from 110{dollar}spcirc{dollar} to 90{dollar}spcirc{dollar}W, at approximately 3{dollar}spcirc{dollar}S, underneath the South Equatorial Current.; The eolian flux record along the north-south transect reveals a history of the latitudinal movements of the Intertropical Convergence Zone (ITCZ) and of continental aridity in the southern hemisphere. During glacial stages the main position of the ITCZ is further south than presently, at approximately 3{dollar}spcirc{dollar}N. Humid-arid cycles in the northern Andes, based on lake levels, show synchroneity with latitudinal migrations of the paleo-ITCZ. The eolian records at the three southern sites in the transect reflect the aridity of the southern hemisphere source areas. Around 240 ky ago, aridity in South America increased as a result of intensification of the southern tropical anticyclone.; The history of biological productivity reflects the changes in the equatorial and coastal upwelling system in response to atmospheric circulation. The equatorial high-productivity belt is centered on the equator during interglacial periods and expands northward during glacial periods. Productivity maxima mainly occur at the glacial to interglacial transitions but may also occur at the interglacial to glacial transitions, especially during the last 220 ka. A shift in the locus of highest organic carbon accumulation from the equator prior to 220 ka to 1{dollar}spcirc{dollar}N since indicates that nutrient rich water associated with coastal upwelling and the South Equatorial Current traveled farther north since 220 ka.; Paleoproductivity along the 3{dollar}spcirc{dollar}S transect shows decreased CaCO{dollar}sb3{dollar} and C{dollar}rmsb{lcub}org{rcub}{dollar} fluxes between 240 ka and 30 ka. Superimposed on this long term cycle are productivity pulses which emanate from the east at the beginning and end of glacial cycles. This pattern suggests that the sites along the flowpath of the South Equatorial Current record variations in the eastern equatorial coastal upwelling.