Period of climatic warming that reached its peak approximately 90 million years ago
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
Ma,
Pangaea covered the Earth's surface, forming one super continent and one gargantuan ocean. During the breakup of
Pangaea from 150 to 130 Ma, the
Atlantic Ocean began to form the "Atlantic Gateway".[6] Geological records from both the
Deep Sea Drilling Project (DSDP) and the
Ocean Drilling Program (ODP) support the enhancement of the CTM by the rifting of the Atlantic Ocean. Rising atmospheric carbon dioxide is thought to have been enhanced by the changing geography of the oceans.[4] While rising carbon dioxide levels caused increased global warming, the climate models of the
Cretaceous period do not show such elevated global temperatures due to the Earth's carbon dioxide variations. Geologic records show evidence of dissociation of
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
Cenomaniansea 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.
^
abcdFoster, 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>
^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>.
^McInerney, Francesca A.; Wing, Scott L. (2011-05-30). "The Paleocene-Eocene Thermal Maximum: A Perturbation of Carbon Cycle, Climate, and Biosphere with Implications for the Future". Annual Review of Earth and Planetary Sciences. 39 (1): 489–516.
Bibcode:
2011AREPS..39..489M.
doi:
10.1146/annurev-earth-040610-133431.
ISSN0084-6597.