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Article Evaluation

The article soil erosion, rated as C class - top importance by Wikipedia Project Soil, was very informative and did not have any extra information that was distracting from the main topic of soil erosion. The overview was a clear summary that hit all the main points discussed throughout the article. There were clear headings, sub headings, equal sections and nice visuals that accompanied the content; however, it would have been nice if there were images showing the actual process of soil erosion. This article was not written to enforce an opinion on anyone, but rather to inform people about what erosion is and how some factors in nature and human activities can increase soil erosion. The author of this article uses a variety of non-biased and reliable sources that support the claims made with most of them being online articles from reputable sources and publishing companies like Elsevier. The information is also not outdated as majority of the references are relatively recent with the citation links working. This article was last updated in February 2018 which means that there is still work being done on this article to perfect it which is crucial as the page recieves approximately 1500 visits daily. The talk page of this article only consists of fixing a copyright violation and modifying some external links. The way Wikipedia discusses this topic is very similar to how it was discussed in lectures.

Goal

I aim to contribute to the existing Wikipedia page on Paleoclimatology by adding a section about how measuring δ¹⁸O values in benthic foraminifera can reveal information about deep sea bottom temperature.

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Article Draft

What are forminiferas
Oxygen fractionation process --> δ¹⁸O signal
How foraminiferas specifically benthic forminiferas can reveal information about past climate
Limitations to using benthic forminiferas - size of the shell of the foraminifera

Article

Oxygen Fractionation Process

Oxygen undergoes a process called fractionation where water evaporates the lighter oxygen isotope (¹⁶O), and later condenses to precipitate as snow and forms ice sheets in higher latitudes^[1]. The heavier oxygen isotope, ¹⁸O gets left behind in the oceans. This ¹⁸O value that is prominent in oceans can then be measured and analyzed in benthic foraminifera to reveal information about deep-sea bottom temperature. This is because the two factors that affect the isotopic composition of foraminifera are the oxygen isotopic composition of water itself and the temperature of ocean water as the oxygen fractionation process is temperature dependent^[1].

The difference in the ratio of the sample compared with the standard can be calculated using the following equation:

δ¹⁸O = [((¹⁸O/¹⁶O _sample) – (¹⁸O/¹⁶O _standard))/ (¹⁸O/¹⁶O) _standard)] x 1000^[2]

A positive δ¹⁸O value means that the sample which in this case is the ocean is enriched in ¹⁸O (or depleted in ¹⁶O) relative to the standard^[3]. A negative δ¹⁸O value means that is the ocean is depleted in ¹⁸O (or enriched in ¹⁶O) relative to the standard^[3].

δ¹⁸O in Benthic Foraminifera

Foraminifera (formas) are shelled, unicellular organisms that can be found in all parts of the ocean. There are many different types of forams, however, scientists prefer to study benthic foraminiferas as they are one of the longest and most continuous paleoclimate records^[3]. These are a group of protists that lie on the sea floor where disturbance is minimal^[3]. Benthic forams use bicarbonate (HCO₃^-) to form their calcium carbonate (CaCO₃) shells which comes directly from the ocean water, thus, it gives climate scientists information on past variations of the δ¹⁸O signal^[3]. When the foraminiferas die, their shells shed off and accumulate on the seafloor which eventually becomes a part of the sedimentary record.

From the record of benthic forminifera δ¹⁸O over the last 65 million years (Myr), it can be seen that this δ¹⁸O signal begins to drift erratically toward more positive values near 50 Myr ago enriching the ocean in ¹⁸O, indicating that the deep-sea ocean water is cooling. Changes in δ¹⁸O values measured in the foraminiferal shells increase by 1% for each 4.2°C decrease in the temperature of ocean water where δ¹⁸O becomes more abundant than ¹⁶O (). The increase in δ¹⁸O values tells us that the ocean temperature has been dropping and getting colder over time. The temperature of today’s deep ocean averages about 2°C and has cooled by at least 14°C over the last 50 Myr, which means that the deep-ocean temperature must have been near 16°C before 50 Myr ago^[5].

Limitations

Notes

Ruddiman, W. (2008). Earth’s Climate: Past and Future. (2nd Ed.). New York: W.H. Freeman and Company.

https://pdfs.semanticscholar.org/4edf/ee5ecd2975de584b116a73def1ba29e88899.pdf

http://www.highstand.org/erohling/Rohling-papers/2013-Rohling-encyclopaedia-of-Quat-Sci.pdf

http://www.ldeo.columbia.edu/~peter/Resources/Seminar/readings/Ravelo%20&%20Hillaire-Marcel.2007.pdf

References

^ ^a ^b Rohling, E.J. (2013). "Oxygen Isotope Composition of Seawater" (PDF). The Encyclopedia of Quaternary Science. 2: 915–922 – via Elsevier.
^ Ravelo, Ana; Marcel, Claude (2007). "The Use of Oxygen and Carbon Isotopes of Foraminifera in Paleoceanography" (PDF). Developments in Marine Geology. 1: 735–764. doi:10.1016/S1572-5480(07)01023-8 – via Elsevier. {{cite journal}}: line feed character in |title= at position 41 (help)
^ ^a ^b ^c ^d ^e Pearson, Paul (2012). "OXYGEN ISOTOPES IN FORAMINIFERA: OVERVIEW AND HISTORICAL REVIEW" (PDF). The Paleontological Society Papers. 18: 1–38 – via Cambridge Core.
^ Ruddiman, William (2008). Earth's Climate - Past and Future. New York: Clancy Marshall. p. 101. ISBN 978-0-7167-8490-6.
^ Ruddiman, William (2008). Earth's Climate - Past and Future. New York: Clancy Marshall. p. 100. ISBN 978-0-7167-8490-6.

[:1-1] Rohling, E.J. (2013). "Oxygen Isotope Composition of Seawater" (PDF). The Encyclopedia of Quaternary Science. 2: 915–922 – via Elsevier.

[2] Ravelo, Ana; Marcel, Claude (2007). "The Use of Oxygen and Carbon Isotopes of Foraminifera in Paleoceanography" (PDF). Developments in Marine Geology. 1: 735–764. doi:10.1016/S1572-5480(07)01023-8 – via Elsevier. {{cite journal}}: line feed character in |title= at position 41 (help)

[:0-3] Pearson, Paul (2012). "OXYGEN ISOTOPES IN FORAMINIFERA: OVERVIEW AND HISTORICAL REVIEW" (PDF). The Paleontological Society Papers. 18: 1–38 – via Cambridge Core.

[4] Ruddiman, William (2008). Earth's Climate - Past and Future. New York: Clancy Marshall. p. 101. ISBN 978-0-7167-8490-6.

[5] Ruddiman, William (2008). Earth's Climate - Past and Future. New York: Clancy Marshall. p. 100. ISBN 978-0-7167-8490-6.

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