Diatom paleoceanography and paleoclimatology of the central and eastern equatorial Pacific between 18 and 6.2Ma.

Abstract

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 14.5-13.5Ma, presumably reflecting reorganization of equatorial surface-water masses in response to polar cooling. Increasing numbers of the cold-water diatom Denticulopsis hustedtii indicate cooling of equatorial Pacific surface waters during the middle Miocene, especially between 12-11.5Ma. The onset of severe carbonate dissolution at 12Ma 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 (NAFW) in the North Atlantic at 12Ma is believed to have been a possible triggering event for these middle/late Miocene changes. Increased polar cooling at 11.3Ma contributed to steepening of latitudinal thermal gradients by altering circulation 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 Pacific surface-water circulation were probably present by 11Ma.-Author