Editing Diatom (section)

===Turnover===
Although no mass extinctions of marine diatoms have been observed during the [[Cenozoic]], times of relatively rapid evolutionary turnover in marine diatom species assemblages occurred near the [[Paleocene]]–[[Eocene]] boundary,<ref name="Strelnikova 1990">{{cite book |last=Strelnikova |first=N. I. |year=1990 |chapter=Evolution of diatoms during the Cretaceous and Paleogene periods |editor-last=Simola |editor-first=H. |title=Proceedings of the Tenth International Diatom Symposium |publisher=Koeltz Scientific Books |location=Koenigstein |pages=195–204 |isbn=3-87429-307-6 }}</ref> and at the [[Eocene]]–[[Oligocene]] boundary.<ref name="Baldauf 1993">{{cite book |last=Baldauf |first=J. G. |year=1993 |contribution=Middle Eocene through early Miocene diatom floral turnover |editor-last=Prothero |editor-first=D. |editor2-last=Berggren |editor2-first=W. H. |title=Eocene-Oligocene climatic and biotic evolution |publisher=Princeton University Press |location=Princeton |pages=310–326 |isbn=0-691-02542-8 }}</ref> Further turnover of assemblages took place at various times between the middle [[Miocene]] and late [[Pliocene]],<ref name="Barron 2003">{{cite journal |last=Barron |first=J. A. |year=2003 |title=Appearance and extinction of planktonic diatoms during the past 18&nbsp;m.y. in the Pacific and Southern oceans |journal=Diatom Research |volume=18 |pages=203–224 |doi=10.1080/0269249x.2003.9705588 |s2cid=84781882 }}</ref> in response to progressive cooling of polar regions and the development of more endemic diatom assemblages.

A global trend toward more delicate diatom frustules has been noted from the [[Oligocene]] to the [[Quaternary]].<ref name="Scherer 2007" /> This coincides with an increasingly more vigorous circulation of the ocean's surface and deep waters brought about by increasing latitudinal thermal gradients at the onset of major [[ice sheet]] expansion on [[Antarctica]] and progressive cooling through the [[Neogene]] and [[Quaternary]] towards a bipolar glaciated world. This caused diatoms to take in less silica for the formation of their frustules. Increased mixing of the oceans renews silica and other nutrients necessary for diatom growth in surface waters, especially in regions of coastal and oceanic [[upwelling]].