Late Miocene decoupling of oceanic warmth and atmospheric carbon dioxide forcing.
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.
Ocean Sciences Department, University of California, Santa Cruz, California 95064, USA. jlarivie@ucsc.edu
Jonathan P
JP
LaRiviere
A Christina
AC
Ravelo
Allison
A
Crimmins
Petra S
PS
Dekens
Heather L
HL
Ford
Mitch
M
Lyle
Michael W
MW
Wara
D001272:Atmosphere / Q000737:chemistry*; D002245:Carbon Dioxide / Q000032:analysis* / Q000737:chemistry; D056908:Foraminifera / Q000737:chemistry; D019015:Geologic Sediments / Q000737:chemistry; D057232:Global Warming / Q000266:history* / Q000706:statistics & numerical data; D049690:History, Ancient; D006358:Hot Temperature; D009792:Oceans and Seas; D010103:Oxygen Isotopes / Q000032:analysis; D012623:Seawater / Q000032:analysis / Q000737:chemistry; D014919:Wind
D010103:Oxygen Isotopes; D002245:Carbon Dioxide