Thermal maximums

The Cenozoic Era: Climate in the last 65 Million Years

May 7, 2012, 6:55 pm
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Conditions during the Cenozoic Era. Oxygen and carbon isotope ratios (?18O and ?13C, respectively) (Zachos et al. 2001) and estimates of atmospheric CO2 concentrations (from boron isotope ratios, ?11B) (Pearson and Palmer 2000) through the Cenozoic Era (6

The most extreme climate event of the modern era (the Cenozoic—65 Ma to the present) was the Late Paleocene Thermal Maximum, which occurred at around 55 Ma. [1]

Apparently, deep-sea temperatures were warming gradually when methane hydrates (ice containing CH4) in seafloor sediments melted and belched massive amounts of CH4 into the atmosphere. [2] Addition of this greenhouse gas to the already high levels of CO2 (approximately 0.2%) triggered a global warming of 5°C to 7°C over about 10,000 years. [3] Recovery was slow, taking over 100,000 years from the onset of the event.

Support for this interpretation derives from the gradual decline in ?18O and ?13C values during the Paleocene (evident in drill core samples from deep-sea bed sediments), interrupted by a precipitous drop in both measures; the drop in ?18O values reflects a temperature spike, whereas that in ?13C values reflects that the CH4 released from the seafloor was enriched in the lighter isotope, 12C.

The two other major climatic deviations that occurred during the modern era were global cooling events, indicated by positive shifts in ?18O values. [4] The first of these (the Oi-1 Glaciation) involved the sudden growth of ice sheets on Antarctica at about 34.0 Ma (the Eocene–Oligocene boundary). This event inaugurated 400,000 years of glaciation and caused worldwide shifts in the distribution of marine biogenic sediments and an overall increase in ocean photosynthetic productivity (thereby increasing ?13C). The second climatic deviation (the Mi-1 Glaciation) was a brief but intense glacial maximum that occurred at about 23 Ma (the Oligocene–Miocene boundary). By the end of Mi-1, ocean productivity (and ?13C values) had again increased, and atmospheric CO2 concentrations had diminished to less than 0.03%.

The Late Paleocene Thermal Maximum, Oi-1, and Mi-1 events precipitated the loss of certain organisms and accelerated speciation of others. Of particular note are the extinction of benthic protozoans (single-celled animals who lived in sea or lake bottoms) at the Thermal Maximum, the appearance of baleen whales and decline of broadleaf forests at the Oi-1 Glaciation, and the extinction of Caribbean corals at the Mi-1 Glaciation. Although the isotope records and other geological evidence indicate climatic variation throughout the modern era, including numerous glacial and interglacial periods, no other events approach in magnitude the Thermal Maximum, Oi-1 Glaciation, or Mi-1 Glaciation.

[1] Zachos, J., M. Pagani, L. Sloan, E. Thomas, and K. Billups (2001) Trends, rhythms, and aberrations in global climate 65 Ma to present. Science 292:686-693.

[2] Katz, M. E., D. K. Pak, G. R. Dickens, and K. G. Miller (1999) The source and fate of massive carbon input during the latest Paleocene thermal maximum. Science 286:1531-1533.

[3] Panchuk, K., A. Ridgwell, and L. R. Kump (2008) Sedimentary response to Paleocene-Eocene Thermal Maximum carbon release: A model-data comparison. Geology 36:315-318 doi:10.1130/g24474a.1.

[4] Zachos, J., M. Pagani, L. Sloan, E. Thomas, and K. Billups (2001) Trends, rhythms, and aberrations in global climate 65 Ma to present. Science 292:686-693.

This is an excerpt from the book Global Climate Change: Convergence of Disciplines by Dr. Arnold J. Bloom and taken from UCVerse of the University of California.

©2010 Sinauer Associates and UC Regents

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Citation

Bloom, A. (2012). The Cenozoic Era: Climate in the last 65 Million Years. Retrieved from http://www.eoearth.org/view/article/51cbf03f7896bb431f6a0e2b

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