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[MIS17-33] Changes in the Oligocene planktic foraminiferal depth habitat related to thermocline deepening in the eastern equatorial Pacific
Keywords:eastern equatorial Pacific, Oligocene, depth habitat, planktic foraminifera, oxygen-carbon isotope ratio
Here we reveal successive isotopic record of D. venezuelana along with Paragloborotalia siakensis group (mixed-layer dweller) by using sediments at IODP Site U1334 in the eastern equatorial Pacific throughout the Oligocene. Two-step depth habitat changes of D. venezuelana are recognized: 1) from upper to lower mixed-layer (~27.4 Ma), and 2) lower mixed-layer to thermocline depth (~26.3 Ma). In addition, planktic foraminiferal faunal assemblage also experienced significant change from dominant thermocline (deeper) species to abundant mixed-layer (shallower) species, suggesting depth habitat shifts of D. venezuelana was closely related with thermocline deepening in the eastern equatorial Pacific.
Multiple sites (Sites U1334, U1333, and 1218) comparison of first isotopic shift (~27.4 Ma) revealed southward depth habitat change of D. venezuelana within ~200 kyr, implying thermocline deepening occurred with reduced steepness in the eastern equatorial Pacific. Consequently, we advocate global warming condition during the late Oligocene likely caused thermocline deepening with upwelling decrease in the eastern equatorial Pacific, guiding D. venezuelana to adapt deeper depth in the water column.