Late Miocene decoupling of oceanic warmth and atmospheric carbon dioxide forcing

Abstract

Deep-time palaeoclimate studies are vitally important for developing a complete understanding of climate responses to changes in the atmospheric carbon dioxide concentration (that is, the atmospheric partial pressure of CO(2), p(co(2))). Although past studies have explored these responses during portions of the Cenozoic era (the most recent 65.5 million years (Myr) of Earth history), comparatively little is known about the climate of the late Miocene (∼12-5 Myr ago), an interval with p(co(2)) values of only 200-350 parts per million by volume but nearly ice-free conditions in the Northern Hemisphere and warmer-than-modern temperatures on the continents. Here we present quantitative geochemical sea surface temperature estimates from the Miocene mid-latitude North Pacific Ocean, and show that oceanic warmth persisted throughout the interval of low p(co(2)) ∼12-5 Myr ago. We also present new stable isotope measurements from the western equatorial Pacific that, in conjunction with previously published data, reveal a long-term trend of thermocline shoaling in the equatorial Pacific since ∼13 Myr ago. We propose that a relatively deep global thermocline, reductions in low-latitude gradients in sea surface temperature, and cloud and water vapour feedbacks may help to explain the warmth of the late Miocene. Additional shoaling of the thermocline after 5 Myr ago probably explains the stronger coupling between p(co(2)), sea surface temperatures and climate that is characteristic of the more recent Pliocene and Pleistocene epochs.

Roles of dental development and adaptation in rodent evolution

“…Filled ellipses correspond to pictures of dental microwear (scale bar, 100 mm). The d 18 0 record characterizes the trend of high-latitude temperatures 48,49 , whereas the green and yellow box represent the gradient from closed and humid to open and arid environments is southwestern Europe derived from hypsodonty-based estimates of paleoprecipitations 31 .…”

Effect of Vegetation on the Late Miocene Ocean Circulation

“…Sensitivity experiments indicate that the direct wind effect turns out to be of secondary importance in our simulations (not shown). [78]). A detailed model-data comparison is however not our intension here.…”

Response of marine palynomorphs to Neogene climate cooling in the Iceland Sea (ODP Hole 907A)

“…Villanueva et al, 2002;McClymont et al, 2005). SST records for the Pliocene (Dekens et al, 2007;Lawrence et al, 2009Lawrence et al, , 2010Naafs et al, 2010;Seki et al, 2012), Miocene (Herbert and Schuffert, 1998;Mercer and Zhao, 2004;Huang et al, 2007;Rommerskirchen et al, 2011;LaRiviere et al, 2012;Rousselle et al, 2013), and lowermost Miocene and Eocene (Weller and Stein, 2008) demonstrate the capability to obtain reliable temperature estimates on pre-Quaternary time scales.…”