Cretaceous Thermal Maximum

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The Cretaceous Thermal Maximum (CTM), also known as Cretaceous Thermal Optimum, was a period of climatic warming that reached its peak approximately 90 million years ago (90 Ma) during the Turonian age of the Late Cretaceous epoch. The CTM is notable for its dramatic increase in global temperatures characterized by high carbon dioxide levels.

A graph depicting data from the Phanerozoic Geological era, showing oxygen isotopes from present to 500 Ma. The isotope levels show an correlating increase in global temperatures due to glaciation and glacial retreat.

Characteristics

During the Cretaceous Thermal Maximum (CTM), atmospheric carbon dioxide levels rose to over 1,000 parts per million (ppm) compared to the pre-industrial average of 280 ppm. Rising carbon dioxide resulted in a significant increase in the greenhouse effect, leading to elevated global temperatures.[1] In the seas, crystalline or "glassy" foraminifera predominated, a key indicator of higher temperatures.[2] The CTM began during the Cenomanian/Turonian transition and was associated with a major disruption in global climate as well as global anoxia during Oceanic Anoxic Event 2 (OAE-2).[3] The CTM was one of the most extreme disruptions of the carbon cycle in the past 100 million years.[2][4] It represented one of the most prominent peaks in the global temperature record of the Phanerozoic eon.[5]

Geological causes

From 250 to 150

methane clathrates, which causes a rise in carbon dioxide, as the oxygen gas in the atmosphere will oxidize the released methane.[7]

Progression with time

Measurements of the ratio of stable oxygen isotopes in samples of calcite from foraminifera from sediment cores show gradual warming starting in the Albian period and leading to the interval of peak warmth in the Turonian[8] followed by a gradual cooling of surface temperatures to the end of the Maastrichitan age.[9] During the Turonian, several pronounced but relatively short-lived cooler intervals punctuate the otherwise remarkably stable interval of extreme warmth.

Impact

Late Cenomanian sea surface temperatures (SSTs) in the equatorial Atlantic Ocean were substantially warmer than today (~27-29 °C).[2] Turonian equatorial SSTs are conservatively estimated based on δ18O and high pCO2 estimates to have been ~32 °C, but may have been as high as 36 °C.[10] TEX86L values suggest minimum and maximum low-latitude SSTs of 33-34 ± 2.5 °C and 37-38 ± 2.5 °C, respectively.[11] Rapid tropical sea surface temperature changes occurred during the CTM.[2] High global temperatures contributed to diversification of terrestrial species during the Cretaceous Terrestrial Revolution and also led to warm stratified oceans during the Oceanic Anoxic Event 2 (OAE-2).[12]

Depiction of average planetary temperature of Earth over the past 500 million years. Note that the scale of 500-100 Ma is halved to fit on the graph, with the Cretaceous Thermal Maximum occurring at the peak just before 100 Ma.

See also

References

  1. PMID 11904360
    .
  2. ^ a b c d Foster, A., et al. "The Cretaceous Thermal Maximum and Oceanic Anoxic Event 2 in the Tropics: Sea- Surface Temperature and Stable Organic Carbon Isotopic Records from the Equatorial Atlantic." American Geophysical Union, Fall Meeting 2006. The Smithsonian/NASA Astrophysics Data System. Web. 20 Oct. 2009. <http://adsabs.harvard.edu/abs/2006AGUFMPP33C..04F>
  3. ^ Norris, Richard (2018). "Cretaceous Thermal Maximum ~85-90 Ma." Scripps Institution of Oceanography. Accessed 20 September 2018. http://scrippsscholars.ucsd.edu/rnorris/book/cretaceous-thermal-maximum-85-90-ma Archived 2018-09-20 at the Wayback Machine
  4. ^
    doi:10.1130/0091-7613(2003)031<0115:DTROTA>2.0.CO;2
    . Retrieved 17 March 2023.
  5. S2CID 233579194
    . Retrieved 17 March 2023.
  6. ISSN 0883-8305
    .
  7. ISSN 0091-7613
    .
  8. ISSN 0091-7613
    .
  9. ISSN 0016-7606
    .
  10. ^ Wilson, Paul A., Richard D. Norris, and Matthew J. Cooper. "Testing the Cretaceous greenhouse hypothesis using glassy foraminiferal calcite from the core of the Turonian tropics on Demerara Rise." Geology 30.7 (2002):607-610. Web. Oct.2009.<http://geology.geoscienceworld.org/cgi/content/abstract/30/7/607>.
  11. S2CID 55405082
    .
  12. ISSN 0084-6597
    .
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