31. DIATOM PALEOCEANOGRAPHY AND PALEOCLIMATOLOGY OF THE CENTRAL AND EASTERN EQUATORIAL PACIFIC BETWEEN 18 AND 6.2 Ma1

• Main Authors: John A. Barron, U. S. Geological Survey, Menlo Park
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Subjects: Pacific; NADW; North Atlantic Deep Water; North Atlantic
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.560.1075; http://www.deepseadrilling.org/85/volume/dsdp85_31.pdf

Diatom assemblages in the central and eastern equatorial Pacific record the effects of polar cooling in the middle Miocene and across the middle/late Miocene boundary. Diatom evolutionary events (appearances and extinctions) were numerous between 14.5 and 13.5 Ma, presumably reflecting reorganization of equatorial surface-water masses in re-sponse to polar cooling. Increasing numbers of the cold-water diatom Denticulopsis hustedtii indicate cooling of equa-torial Pacific surface waters during the middle Miocene, especially between 12 and 11.5 Ma. The onset of severe carbon-ate dissolution at 12 Ma marked the beginning of the late Neogene period of high-amplitude fluctuations of carbonate in the equatorial Pacific. Initiation or a substantial increase in the production of North Atlantic Deep Water (NADW) in the North Atlantic at 12 Ma is believed to have been a possible triggering event for these middle/late Miocene changes. Increased polar cooling at 11.3 Ma contributed to steepening of latitudinal thermal gradients by altering circu-lation patterns. Tropical surface waters became warmer, cold-water diatoms were excluded from the equatorial Pacific, and latitudinal provincialism was enhanced in all planktonic groups. Most of the modern-day features of equatorial Pa-cific surface-water circulation were probably present by 11 Ma.