Cretaceous Thermal Maximum

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.

Phanerozoic Climate Change
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 1000 parts per million 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 the most extreme disruption of the carbon cycle in the past 100 million years.[2][4]

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".[5] 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 readily combine with the dissociated carbon atom from methane.[6]

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[7] followed by a gradual cooling of surface temperatures to the end of the Maastrichitan age.[8] 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 in the equatorial Atlantic Ocean were substantially warmer than today (~27-29°C).[2] They are estimated to have been ~33°C, but may have been as high as 36°C.[9] 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).[10]

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

See also

References

  1. ^ Rothman, Daniel H. (2002-04-02). "Atmospheric carbon dioxide levels for the last 500 million years". Proceedings of the National Academy of Sciences. 99 (7): 4167–4171. Bibcode:2002PNAS...99.4167R. doi:10.1073/pnas.022055499. ISSN 0027-8424. PMC 123620. 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
  4. ^ a b 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. <http://geology.geoscienceworld.org/cgi/content/abstract/31/2/115>.
  5. ^ Pucéat, Emmanuelle; Lécuyer, Christophe; Sheppard, Simon M. F.; Dromart, Gilles; Reboulet, Stéphane; Grandjean, Patricia (2003-05-03). "Thermal evolution of Cretaceous Tethyan marine waters inferred from oxygen isotope composition of fish tooth enamels". Paleoceanography. 18 (2): 1029. Bibcode:2003PalOc..18.1029P. doi:10.1029/2002pa000823. ISSN 0883-8305.
  6. ^ Jahren, A. Hope; Arens, Nan Crystal; Sarmiento, Gustavo; Guerrero, Javier; Amundson, Ronald (2001). "Terrestrial record of methane hydrate dissociation in the Early Cretaceous". Geology. 29 (2): 159–162. Bibcode:2001Geo....29..159J. doi:10.1130/0091-7613(2001)029<0159:TROMHD>2.0.CO;2. ISSN 0091-7613.
  7. ^ Clarke, Leon J.; Jenkyns, Hugh C. (1999). "New oxygen isotope evidence for long-term Cretaceous climatic change in the Southern Hemisphere". Geology. 27 (8): 699–702. Bibcode:1999Geo....27..699C. doi:10.1130/0091-7613(1999)027<0699:NOIEFL>2.3.CO;2. ISSN 0091-7613.
  8. ^ Huber, Brian T.; Hodell, David A.; Hamilton, Christopher P. (October 1995). "Middle–Late Cretaceous climate of the southern high latitudes: Stable isotopic evidence for minimal equator-to-pole thermal gradients". Geological Society of America Bulletin. 107 (10): 1164–1191. Bibcode:1995GSAB..107.1164H. doi:10.1130/0016-7606(1995)107<1164:MLCCOT>2.3.CO;2. ISSN 0016-7606.
  9. ^ 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>.
  10. ^ 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. ISSN 0084-6597.
2019 in paleontology

Paleontology or palaeontology is the study of prehistoric life forms on Earth through the examination of plant and animal fossils. This includes the study of body fossils, tracks (ichnites), burrows, cast-off parts, fossilised feces (coprolites), palynomorphs and chemical residues. Because humans have encountered fossils for millennia, paleontology has a long history both before and after becoming formalized as a science. This article records significant discoveries and events related to paleontology that occurred or were published in the year 2019.

Antarctic Peninsula

The Antarctic Peninsula, known as O'Higgins Land in Chile, Tierra de San Martin in Argentina, and originally known as the Palmer Peninsula in the US and as Graham Land in Great Britain, is the northernmost part of the mainland of Antarctica, located at the base of the Southern Hemisphere.

The Antarctic Peninsula is part of the larger peninsula of West Antarctica, protruding 1,300 km (810 miles) from a line between Cape Adams (Weddell Sea) and a point on the mainland south of Eklund Islands. Beneath the ice sheet which covers it, the Antarctic Peninsula consists of a string of bedrock islands; these are separated by deep channels whose bottoms lie at depths considerably below current sea level. They are joined together by a grounded ice sheet. Tierra del Fuego, the southernmost tip of South America, lies only about 1,000 km (620 miles) away across the Drake Passage.The Antarctic Peninsula is currently dotted with numerous research stations and nations have made multiple claims of sovereignty. The peninsula is part of disputed and overlapping claims by Argentina, Chile and the United Kingdom. None of these claims have international recognition and, under the Antarctic Treaty System, the respective countries do not attempt to enforce their claims. The British claim is recognised though by Australia, France, New Zealand and Norway. Argentina has the most bases and personnel stationed on the peninsula.

Belemnitida

Belemnitida (or belemnites) is an extinct order of squid-like cephalopods that existed from the Late Triassic to Late Cretaceous. Unlike squid, belemnites had an internal skeleton that made up the cone. The parts are, from the arms-most to the tip: the tongue-shaped pro-ostracum, the conical phragmocone, and the pointy guard. The calcitic guard is the most common belemnite remain. Belemnites, in life, are thought to have had 10 hooked arms and a pair of fins on the guard. The chitinous hooks were usually no bigger than 5 mm (0.20 in), though a belemnite could have had between 100 and 800 hooks in total, using them to stab and hold onto prey.

Belemnites were an important food source for many Mesozoic marine creatures, both the adults and the planktonic juveniles, and likely played an important role in restructuring marine ecosystems after the Triassic–Jurassic extinction event. They may have laid between 100 and 1,000 eggs. Some species may have been adapted to speed and swam in the turbulent open ocean, whereas others resided in the calmer littoral zone (nearshore) and fed off the seafloor. The largest belemnite known, Megateuthis elliptica, had guards of 60 to 70 cm (24 to 28 in).

Belemnites are coleoids, a group that includes squid and octopuses, and are often grouped into the superorder Belemnoidea, though the higher classification of cephalopods is volatile and there is no clear consensus how belemnites are related to modern coleoids. Guards can give information on the climate, habitat, and the carbon cycle of the ancient waters they inhabited. Guards have been found since antiquity and have become part of folklore.

Cretaceous

The Cretaceous ( , krih-TAY-shəs) is a geologic period and system that spans from the end of the Jurassic Period 145 million years ago (mya) to the beginning of the Paleogene Period 66 mya. It is the last period of the Mesozoic Era, and the longest period of the Phanerozoic Eon. The Cretaceous Period is usually abbreviated K, for its German translation Kreide (chalk, creta in Latin).

The Cretaceous was a period with a relatively warm climate, resulting in high eustatic sea levels that created numerous shallow inland seas. These oceans and seas were populated with now-extinct marine reptiles, ammonites and rudists, while dinosaurs continued to dominate on land. During this time, new groups of mammals and birds, as well as flowering plants, appeared.

The Cretaceous (along with the Mesozoic) ended with the Cretaceous–Paleogene extinction event, a large mass extinction in which many groups, including non-avian dinosaurs, pterosaurs and large marine reptiles died out. The end of the Cretaceous is defined by the abrupt Cretaceous–Paleogene boundary (K–Pg boundary), a geologic signature associated with the mass extinction which lies between the Mesozoic and Cenozoic eras.

Medieval Warm Period

The Medieval Warm Period (MWP) also known as the Medieval Climate Optimum, or Medieval Climatic Anomaly was a time of warm climate in the North Atlantic region lasting from c. 950 to c. 1250. It was likely related to warming elsewhere while some other regions were colder, such as the tropical Pacific. Average global mean temperatures have been calculated to be similar to early-mid 20th century warming. Possible causes of the Medieval Warm Period include increased solar activity, decreased volcanic activity, and changes to ocean circulation.The period was followed by a cooler period in the North Atlantic and elsewhere termed the Little Ice Age. Some refer to the event as the Medieval Climatic Anomaly as this term emphasizes that climatic effects other than temperature were important.It is thought that between c. 950 and c. 1100 was the Northern Hemisphere's warmest period since the Roman Warm Period. It was only in the 20th and 21st centuries that the Northern Hemisphere experienced higher temperatures. Climate proxy records show peak warmth occurred at different times for different regions, indicating that the Medieval Warm Period was not a globally uniform event.

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