Developing an early to middle Miocene benthic foraminiferal isotope chronostratigraphy across the Pacific "paleoequator transect" (IODP PEAT Expedition 320/321)
Final Report Abstract
The Miocene climatic optimum (MCO, ~17-14.7 Ma) represents an intriguing phase of global warming, which interrupted the long-term Cenozoic cooling trend for more than 2 Myr. At the end of the MCO, Earth’s climate transitioned back into a colder mode with re-establishment of permanent ice sheets on Antarctica after 14 Ma, thus marking a fundamental step in Cenozoic cooling. We present high-resolution (~1-5 kyr time resolution) benthic foraminiferal isotopes in three exceptional, continuous, carbonate-rich sedimentary archives in the eastern equatorial Pacific Ocean (IODP Sites U1335, U1337 and U1338), which offer a new view of climate evolution over the onset and development of the MCO and the transition into the "Icehouse" climate. Our astronomically-tuned isotope time series (20-13 Ma) reveal that the onset of the MCO coincided with a sharp decline in delta 18 O and delta 13 C at ~16.9 Ma, contemporaneous with a massive increase in carbonate dissolution, demonstrating that abrupt climate warming was coupled to an intense perturbation of the carbon cycle. During the MCO, episodes of peak warmth at (southern hemisphere) insolation maxima coincided with transient shoaling of the carbonate compensation depth and enhanced carbonate dissolution in the deep ocean. Our results lend support to the notion that atmospheric pCO2 variations drove profound changes in the global carbon reservoir through the MCO, implying a delicate balance between changing CO2 fluxes, rates of silicate weathering and global carbon sequestration. A switch to obliquity-paced climate variability after 14.7 Ma concurred with a general improvement in carbonate preservation and the onset of stepwise global cooling, culminating with extensive ice growth over Antarctica at ~13.8 Ma. We find that two major increases in opal accumulation between ~14.0 and ~13.8 Ma support the notion that enhanced siliceous productivity and organic carbon burial in the eastern equatorial Pacific played a role in fostering CO2 drawdown and climate cooling.
Publications
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The Pacific Equatorial Age Transect, IODP Expeditions 320 and 321: Building a 50-Million-Year-Long Environmental Record of the Equatorial Pacific. Scientific Drilling, Vol.9. 2010, pp.4-15.
Lyle, M., Pälike, H., Nishi, H., Raffi, I., Gamage, K., Klaus A., and the IODP Expeditions 320/321 Scientific Party, 2010,
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2012. A Cenozoic record of the equatorial Pacific carbonate compensation depth. Nature, Vol. 488. 2012, Number 7413, pp. 609-614.
Pälike, H., Lyle, M.W., Nishi, H., Raffi, I., Ridgwell, A., Gamage, K., Klaus A. et al.
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2012. Data report. In: Pälike, H., Lyle, M., Nishi, H., Raffi, I., Gamage, K., Klaus A., and the Expedition 320/321 Scientists. Proceedings of the Integrated Ocean Drilling Program, Vol. 320/321.2012: Tokyo (Integrated Ocean Drilling Program Management International, Inc.).
Lyle, M., Olivarez Lyle, A., Gorgas, T., Holbourn, A.E., Westerhold, T., Hathorne, E., Kimoto K., and Yamamoto S.
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2013. Middle Miocene climate cooling linked to intensification of eastern equatorial Pacific upwelling. Geology, Vol. 42. 2013, Issue 1, pp. 19-22.
Holbourn, A.E., Kuhnt, W., Lyle, M., Schneider, L., Romero, O., Andersen. N.
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Global perturbation of the carbon cycle at the onset of the Miocene climatic optimum. Geology, Vol. 43. 2015, Issue, 2, pp. 123-126.
Holbourn, A.E., Kuhnt, W., Kochhann, K.G.D., Andersen, N., and Meier, K.J.S.
