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 The Turonian is, in the ICS' geologic timescale, the second age in the Late Cretaceous Epoch, or a stage in the Upper Cretaceous Series. It spans the time between 93.9 ± 0.8 Ma and 89.8 ± 1 Ma (million years ago). The Turonian is preceded b ...

age of the

Late Cretaceous The Late Cretaceous (100.5–66 Ma) is the younger of two epochs into which the Cretaceous Period is divided in the geologic time scale. Rock strata from this epoch form the Upper Cretaceous Series. The Cretaceous is named after ''creta'', ...

epoch. The CTM is notable for its dramatic increase in global temperatures characterized by high

carbon dioxide Carbon dioxide ( chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is trans ...

levels.

Characteristics

During the Cretaceous Thermal Maximum (CTM), atmospheric carbon dioxide levels rose to over 1,000

parts per million In science and engineering, the parts-per notation is a set of pseudo-units to describe small values of miscellaneous dimensionless quantities, e.g. mole fraction or mass fraction. Since these fractions are quantity-per-quantity measures, th ...

(ppm) compared to the pre-industrial average of 280 ppm. Rising carbon dioxide resulted in a significant increase in the

greenhouse effect The greenhouse effect is a process that occurs when energy from a planet's host star goes through the planet's atmosphere and heats the planet's surface, but greenhouse gases in the atmosphere prevent some of the heat from returning directly ...

, leading to elevated global temperatures. In the seas, crystalline or "glassy"

foraminifera Foraminifera (; Latin for "hole bearers"; informally called "forams") are single-celled organisms, members of a phylum or class of amoeboid protists characterized by streaming granular ectoplasm for catching food and other uses; and commonly ...

predominated, a key indicator of higher temperatures. The CTM began during the Cenomanian/

transition and was associated with a major disruption in global climate as well as global anoxia during Oceanic Anoxic Event 2 (OAE-2). The CTM was the most extreme disruption of the

carbon cycle The carbon cycle is the biogeochemical cycle by which carbon is exchanged among the biosphere, pedosphere, geosphere, hydrosphere, and atmosphere of the Earth. Carbon is the main component of biological compounds as well as a major componen ...

in the past 100 million years.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. Poulsen, Christopher J., Andrew S. Gendaszek, and Robert L. Jacob. "Did the rifting of the Atlantic Ocean cause the Cretaceous thermal maximum?" Geology 31.2 (2003): 115-118. Web. 20 Oct. 2009. .

Geological causes

From 250 to 150 Ma,

Pangaea Pangaea or Pangea () was a supercontinent that existed during the late Paleozoic and early Mesozoic eras. It assembled from the earlier continental units of Gondwana, Euramerica and Siberia during the Carboniferous approximately 335 million y ...

covered the Earth's surface, forming one super continent and one gargantuan ocean. During the breakup of

from 150 to 130 Ma, the

Atlantic Ocean The Atlantic Ocean is the second-largest of the world's five oceans, with an area of about . It covers approximately 20% of Earth's surface and about 29% of its water surface area. It is known to separate the " Old World" of Africa, Europe ...

began to form the "Atlantic Gateway". Geological records from both the Deep Sea Drilling Project (DSDP) and the

Ocean Drilling Program The Ocean Drilling Program (ODP) was a multinational effort to explore and study the composition and structure of the Earth's oceanic basins. ODP, which began in 1985, was the successor to the Deep Sea Drilling Project initiated in 1968 by th ...

(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. While rising carbon dioxide levels caused increased global warming, the climate models of the

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of ...

period do not show such elevated global temperatures due to the Earth's carbon dioxide variations. Geologic records show evidence of dissociation of methane clathratess, which causes a rise in carbon dioxide, as the oxygen gas in the atmosphere will oxidize the released

methane Methane ( , ) is a chemical compound with the chemical formula (one carbon atom bonded to four hydrogen atoms). It is a group-14 hydride, the simplest alkane, and the main constituent of natural gas. The relative abundance of methane on Ea ...

Progression with time

Measurements of the ratio of stable oxygen isotopes in samples of calcite from

from sediment cores show gradual warming starting in the Albian period and leading to the interval of peak warmth in the

followed by a gradual cooling of surface temperatures to the end of the Maastrichitan age. During the

, 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

were substantially warmer than today (~27-29°C). Turonian equatorial SSTs are conservatively estimated based on

δ18O In geochemistry, paleoclimatology and paleoceanography ''δ''18O or delta-O-18 is a measure of the ratio of stable isotopes oxygen-18 (18O) and oxygen-16 (16O). It is commonly used as a measure of the temperature of precipitation, as a measur ...

and high ''p''CO₂ estimates to have been ~32°C, but may have been as high as 36°C.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.. TEX₈₆^L values suggest minimum and maximum low-latitude SSTs of 33-34 ± 2.5°C and 37-38 ± 2.5°C, respectively. Rapid tropical sea surface temperature changes occurred during the CTM. High global temperatures contributed to diversification of terrestrial species during the

Cretaceous Terrestrial Revolution The Cretaceous Terrestrial Revolution (abbreviated KTR), also known as the Angiosperm Terrestrial Revolution (ATR) by authors who consider it to have lasted into the Palaeogene, describes the intense diversification of angiosperms, insects, reptile ...

and also led to warm stratified oceans during the Oceanic Anoxic Event 2 (OAE-2).{{Cite journal, last1=McInerney, first1=Francesca A., last2=Wing, first2=Scott L., date=2011-05-30, title=The Paleocene-Eocene Thermal Maximum: A Perturbation of Carbon Cycle, Climate, and Biosphere with Implications for the Future, journal=Annual Review of Earth and Planetary Sciences, language=en, volume=39, issue=1, pages=489–516, doi=10.1146/annurev-earth-040610-133431, issn=0084-6597, bibcode=2011AREPS..39..489M All palaeotemps

References

History of climate variability and change Historical geology Late Cretaceous

Characteristics

Geological causes

Progression with time

Impact

See also

References