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Cibicidoides; Temporal range: Pg - Present
	Cibocidoides sp.
Scientific classification
Domain:	Eukaryota
Clade:	Diaphoretickes
Clade:	SAR
Phylum:	Retaria
Subphylum:	Foraminifera
Class:	Globothalamea
Order:	Rotaliida
Family:	Cibicididae
Subfamily:	Cibicidinae
Genus:	Cibicidoides; Thalmann, H. E., 1939.
Species
	Many, including: C. basilanensis[page needed]; C. borealis; C cicatricosus (Schwager, 1866); C clarionensis[page needed];

Cibicidoides are an extant genus of benthic foraminifera, with the oldest known remains dating back to the Paleogene Period.^[5] (66 mya - 23 mya)^[6]

Like other benthic foraminifera, Cibicidoides are singled celled eucaryotic protists. They secrete a shell, or test, formed out of calcium carbonate (CaCO₃), which provides a durable source of protection compared to other protists.^[5]

Cibicidoides are structurally distinguished from other foraminifera by their segmented, spiral shaped tests. While Cibicidoides life span ranges from days to months depending on the species, all construct their segments in a clockwise order from the umbilical side (or counterclockwise order from the spinal side). This allows the age of an individual Cibicidoides to be determined based on the number segments present.^[5]

Cibicidoides tests are generally transparent/translucent in color, allowing the color of the single celled organic matter to partially show from inside the test. The color of a test is also a primary indicator as to whether or not a Cibicidoides is considered dead or alive, as the organic matter will decay rapidly after death, leaving only the empty translucent test behind.^[5]

Use in paleoceanography

Due to the benthic nature of Cibicidoides (ie., since they live in ocean sediment), it is very common for the tests of deceased Cibicidoides to be pushed deep into the sediment as sedimentary accumulation occurs. This makes them excellent for use in Palaeoceanographic studies, as fossilized remains of Cibicidoides tests dating back millions of years can found in extracted sediment cores^[5]

A primary use for fossilized Cibicidoides tests comes in the determination of the stable-isotopes present, such as δ¹³C.^[7] δ¹³C can be used to track changes in the deep-water circulation, as collisions in different water masses can produce distinct changes in known percentages of δ¹³C. Two water masses that exemplify this are the North Atlantic Deep Water and the Antarctic bottom water.^[8]^[9]^[10]^[7]

One problem that can affect the isotopic data of fossilized Cibicidoides is through their modification via a process known as diagenesis. Diagenesis encompasses a diverse range of alterations that can affect a material as it transitions from its original chemical composition to its fossilized state.^[11] With Cibicidoides, the alterations caused by diagenesis can bias the isotopic data of their tests.^[9] For example, calcite (a stable polymorph/crystalline structure of CaCO₃) can precipitate (i.e., come out of solution in a solid state) from the sediment fluid filling the pores of a foraminiferal test. This "new" calcite will show up in isotopic analysis of the test, but it may come from sediment that is geographically and temporarily unrelated to the original sample, thus meaning that it heavily biases the isotopic data of the Cibicidoides in question.^[12]^[13]^[9]^[11]

Cibocidoides sp. (Spinal side) with minimal fossilization

Cibocidoides sp. (umbilical side) with minimal fossilization

Cibocidoides sp. (spinal side) with total fossilization

Cibocidoides sp. (umbilical side) with total fossilization

Cibocidoides sp. (spinal side) with partial fossilization

Cibocidoides sp. (umbilical side) with partial fossilization

References

^ Thalmann, Hans E. (1939). "Bibliography and Index to New Genera, Species, and Varieties of Foraminifera for the Year 1936". Journal of Paleontology. 13 (4): 425–465. JSTOR 1298535.
^ ^a ^b McCulloch, Irene Agnes (1977). Qualitative Observations on Recent Foraminiferal Tests with Emphasis on the Eastern Pacific. University of Southern California. OCLC 3311654.
^ Saidova, K. M. (1975). Бентосине фораминиферий Тихого океана-Bentosniye foraminifery Tikhogo Okeana-Benthonic Foraminifera of the Pacific Ocean. Институт океанологии им. П. П. Шершова Академии наук СССР-P.P. Shirshov Institute of Oceanology, Academy of Sciences of the USSR, Moscow. 3: parts.
^ Schwager, C. (1866). "Fossile Foraminiferen von Kar Nikobar". Reise der Österreichischen Fregatte Novara um die Erde in den Jahren 1857, 1858, 1859 unter den Befehlen des Commodore B. Von Wüllerstorf-Urbair. Geologischer Theil (Zweite Abtheilung, Paläontologische Mittheilungen). 2 (2): 187–268.
^ ^a ^b ^c ^d ^e "Foraminifera". British Geological Survey. 9 September 2021.
^ Cavin, Lionel (2017). "Assemblages of Freshwater Fishes in the Cenozoic". Freshwater Fishes: 250 Million Years of Evolutionary History. pp. 41–51. doi:10.1016/B978-1-78548-138-3.50003-0. ISBN 978-1-78548-138-3.
^ ^a ^b Katz, M. E.; Cramer, B. S.; Franzese, A.; Honisch, B.; Miller, K. G.; Rosenthal, Y.; Wright, J. D. (April 2010). "Traditional and Emerging Geochemical Proxies in Foraminifera". The Journal of Foraminiferal Research. 40 (2): 165–192. Bibcode:2010JForR..40..165K. doi:10.2113/gsjfr.40.2.165.
^ Sentman, Lori T.; Dunne, John P.; Stouffer, Ronald J.; Krasting, John P.; Toggweiler, J. R.; Broccoli, Anthony J. (July 2018). "The Mechanistic Role of the Central American Seaway in a GFDL Earth System Model. Part 1: Impacts on Global Ocean Mean State and Circulation". Paleoceanography and Paleoclimatology. 33 (7): 840–859. Bibcode:2018PaPa...33..840S. doi:10.1029/2018PA003364.
^ ^a ^b ^c Poirier, Robert K.; Gaetano, Madison Q.; Acevedo, Kimberly; Schaller, Morgan F.; Raymo, Maureen E.; Kozdon, Reinhard (May 2021). "Quantifying Diagenesis, Contributing Factors, and Resulting Isotopic Bias in Benthic Foraminifera Using the Foraminiferal Preservation Index: Implications for Geochemical Proxy Records". Paleoceanography and Paleoclimatology. 36 (5). Bibcode:2021PaPa...36.4110P. doi:10.1029/2020PA004110.
^ Saraswati, Pratul Kumar (2021). "Geochemical proxies of climate and environment". Foraminiferal Micropaleontology for Understanding Earth's History. pp. 181–236. doi:10.1016/B978-0-12-823957-5.00008-1. ISBN 978-0-12-823957-5.
^ ^a ^b Tarbuck, Edward J.; Lutgens, Frederick K.; Tasa, Dennis G. (2016). Earth: An Introduction to Physical Geology, Global Edition. Pearson Education. ISBN 978-1-292-16193-8.^{[page needed]}
^ Regenberg, M.; Nürnberg, D.; Schönfeld, J.; Reichart, G.-J. (12 November 2007). "Early diagenetic overprint in Caribbean sediment cores and its effect on the geochemical composition of planktonic foraminifera". Biogeosciences. 4 (6): 957–973. Bibcode:2007BGeo....4..957R. doi:10.5194/bg-4-957-2007.
^ Cisneros-Lazaro, Deyanira; Adams, Arthur; Guo, Jinming; Bernard, Sylvain; Baumgartner, Lukas P.; Daval, Damien; Baronnet, Alain; Grauby, Olivier; Vennemann, Torsten; Stolarski, Jarosław; Escrig, Stéphane; Meibom, Anders (10 January 2022). "Fast and pervasive diagenetic isotope exchange in foraminifera tests is species-dependent". Nature Communications. 13 (1): 113. Bibcode:2022NatCo..13..113C. doi:10.1038/s41467-021-27782-8. PMC 8748890. PMID 35013292.