Editing Diatom (section)

== Evolution and fossil record ==
=== Origin ===
Heterokont chloroplasts appear to derive from those of [[red algae]], rather than directly from [[prokaryote]]s as occurred in [[plant]]s. This suggests they had a more recent origin than many other algae. However, fossil evidence is scant, and only with the evolution of the diatoms themselves do the heterokonts make a serious impression on the fossil record.

=== Earliest fossils ===
The earliest known fossil diatoms date from the early [[Jurassic]] (~185 [[Mega-annum|Ma ago]]),<ref name="Kooistra 1996">{{cite journal |doi=10.1006/mpev.1996.0088 |pmid=8975694 |title=Evolution of the Diatoms (Bacillariophyta) |journal=Molecular Phylogenetics and Evolution |volume=6 |issue=3 |pages=391–407 |year=1996 |last1=Kooistra |first1=Wiebe H.C.F. |last2=Medlin |first2=Linda K. }}</ref> although the [[molecular clock]]<ref name="Kooistra 1996" /> and [[sedimentary rock|sedimentary]]<ref name="Schieber 2000">{{cite journal |doi=10.1038/35023143 |pmid=10984049 |year=2000 |last1=Schieber |first1=Jürgen |title=Diagenetic origin of quartz silt in mudstones and implications for silica cycling |journal=Nature |volume=406 |issue=6799 |pages=981–5 |last2=Krinsley |first2=Dave |last3=Riciputi |first3=Lee |bibcode=2000Natur.406..981S |s2cid=4417951 }}</ref> evidence suggests an earlier origin. It has been suggested that their origin may be related to the [[Permian–Triassic extinction event|end-Permian mass extinction]] (~250 Ma), after which many marine [[ecological niche|niches]] were opened.<ref name="Medlin 1997">{{cite journal |hdl=10013/epic.12689 | last1=Medlin | first1=L. K. | last2=Kooistra | first2=W. H. C. F. | last3=Gersonde | first3=R. | last4=Sims | first4=P. A. | last5=Wellbrock | first5=U. | year=1997 | title=Is the origin of the diatoms related to the end-Permian mass extinction? | journal=Nova Hedwigia | volume=65 | issue=1–4 | pages=1–11 | doi=10.1127/nova.hedwigia/65/1997/1 | bibcode=1997NovaH..65....1M }}</ref> The gap between this event and the time that fossil diatoms first appear may indicate a period when diatoms were unsilicified and their evolution was [[cryptic (zoology)|cryptic]].<ref name="Raven 2004">{{cite journal |doi=10.1111/j.1469-8137.2004.01022.x |jstor=1514475 |title=The evolution of silicification in diatoms: Inescapable sinking and sinking as escape? |journal=New Phytologist |volume=162 |issue=1 |pages=45–61 |year=2004 |last1=Raven |first1=J. A. |last2=Waite |first2=A. M. |doi-access=free |bibcode=2004NewPh.162...45R }}</ref> Since the advent of silicification, diatoms have made a significant impression on the fossil record, with major fossil deposits found as far back as the early [[Cretaceous]], and with some rocks such as [[diatomaceous earth]], being composed almost entirely of them.

===Relation to grasslands ===
The expansion of [[grassland]] [[biome]]s and the [[evolutionary radiation]] of [[grass]]es during the [[Miocene]] is believed to have increased the flux of soluble silicon to the oceans, and it has been argued that this promoted the diatoms during the Cenozoic era.<ref>{{cite journal |doi=10.1126/science.1095964 |pmid=15256663 |title=The Evolution of Modern Eukaryotic Phytoplankton |journal=Science |volume=305 |issue=5682 |pages=354–60 |year=2004 |last1=Falkowski |first1=P. G. |last2=Katz |first2=Miriam E. |last3=Knoll |first3=Andrew H. |last4=Quigg |first4=Antonietta |last5=Raven |first5=John A. |last6=Schofield |first6=Oscar |last7=Taylor |first7=F. J. R. |bibcode=2004Sci...305..354F |citeseerx=10.1.1.598.7930 |s2cid=451773 }}</ref><ref>{{cite journal |doi=10.2110/palo.2003.p03-108 |jstor=27670327 |title=Impact of Grassland Radiation on the Nonmarine Silica Cycle and Miocene Diatomite |journal=PALAIOS |volume=20 |issue=2 |pages=198–206 |year=2005 |last1=Kidder |first1=D. L. |last2=Gierlowski-Kordesch |first2=E. H. |bibcode=2005Palai..20..198K |s2cid=140584104 }}</ref> Recent work suggests that diatom success is decoupled from the evolution of grasses, although both diatom and grassland diversity increased strongly from the middle Miocene.<ref name="Lazarus2014">{{cite journal |doi=10.1371/journal.pone.0084857 |pmid=24465441 |pmc=3898954 |title=Cenozoic Planktonic Marine Diatom Diversity and Correlation to Climate Change |journal=PLOS ONE |volume=9 |issue=1 |pages=e84857 |year=2014 |last1=Lazarus |first1=David |last2=Barron |first2=John |last3=Renaudie |first3=Johan |last4=Diver |first4=Patrick |last5=Türke |first5=Andreas |bibcode=2014PLoSO...984857L |doi-access=free }}</ref>

===Relation to climate ===
Diatom diversity over the Cenozoic has been very sensitive to global temperature, particularly to the equator-pole temperature gradient. Warmer oceans, particularly warmer polar regions, have in the past been shown to have had substantially lower diatom diversity. Future warm oceans with enhanced polar warming, as projected in global-warming scenarios,<ref>IPCC Core Writing Team, 2007. "Climate Change 2007: Synthesis Report". 104.</ref> could thus in theory result in a significant loss of diatom diversity, although from current knowledge it is impossible to say if this would occur rapidly or only over many tens of thousands of years.<ref name="Lazarus2014" />

=== Method of investigation ===
The fossil record of diatoms has largely been established through the recovery of their siliceous [[frustule]]s in marine and non-marine sediments. Although diatoms have both a marine and non-marine stratigraphic record, diatom [[biostratigraphy]], which is based on time-constrained evolutionary originations and extinctions of unique taxa, is only well developed and widely applicable in marine systems. The duration of diatom species ranges have been documented through the study of ocean cores and rock sequences exposed on land.<ref name="Scherer 2007">{{cite journal |last1=Scherer |first1=R. P. |last2=Gladenkov |first2=A. Yu. |last3=Barron |first3=J. A. |year=2007 |title=Methods and applications of Cenozoic marine diatom biostratigraphy |journal=Paleontological Society Papers |volume=13 |pages=61–83 |doi=10.1017/S1089332600001467 }}</ref> Where diatom [[biozone]]s are well established and calibrated to the [[geomagnetic polarity time scale]] (e.g., [[Southern Ocean]], [[North Pacific]], eastern equatorial [[Pacific]]), diatom-based age estimates may be resolved to within <100,000 years, although typical age resolution for [[Cenozoic]] diatom assemblages is several hundred thousand years.

Diatoms preserved in lake sediments are widely used for [[Paleoecology|paleoenvironmental reconstructions]] of [[Quaternary]] climate, especially for closed-basin lakes which experience fluctuations in water depth and salinity.

===Isotope records===
[[File:Triceratium morlandii var. morlandii.jpg|thumb| {{center|Intricate silicate (glass) shell, 32-40 million years old, of a diatom [[microfossil]]}}]]
{{further|microfossils}}

When diatoms die their shells ([[frustule]]s) can settle on the [[seafloor]] and become [[microfossil]]s. Over time, these microfossils become buried as [[opal]] deposits in the [[marine sediment]]. [[Paleoclimatology]] is the study of past climates. [[Proxy data]] is used in order to relate elements collected in modern-day sedimentary samples to climatic and oceanic conditions in the past. [[Paleoclimate proxies]] refer to preserved or fossilized physical markers which serve as substitutes for direct meteorological or ocean measurements.<ref>{{Cite web|title=What Are "Proxy" Data? {{!}} National Centers for Environmental Information (NCEI) formerly known as National Climatic Data Center (NCDC)|url=https://www.ncdc.noaa.gov/news/what-are-proxy-data|access-date=2020-10-20|website=www.ncdc.noaa.gov|archive-date=8 March 2020|archive-url=https://web.archive.org/web/20200308170642/https://www.ncdc.noaa.gov/news/what-are-proxy-data|url-status=live}}</ref> An example of proxies is the use of diatom [[marine isotope stage|isotope records]] of [[δ13C]], [[δ18O]], [[Isotopes of silicon|δ30Si]] (δ13C<sub>diatom</sub>, δ18O<sub>diatom</sub>, and δ30Si<sub>diatom</sub>). In 2015, Swann and Snelling used these isotope records to document historic changes in the photic zone conditions of the north-west [[Pacific Ocean]], including nutrient supply and the efficiency of the soft-tissue [[biological pump]], from the modern day back to [[Marine Isotope Stage 5#Marine Isotope Stage (MIS) 5e|marine isotope stage 5e]], which coincides with the [[Eemian|last interglacial period]]. Peaks in opal productivity in the marine isotope stage are associated with the breakdown of the regional [[halocline]] stratification and increased nutrient supply to the [[photic zone]].<ref name="Swann Snelling 2015">{{cite journal | last1=Swann | first1=G. E. A. | last2=Snelling | first2=A. M. | title=Photic zone changes in the north-west Pacific Ocean from MIS 4–5e | journal=Climate of the Past | publisher=Copernicus GmbH | volume=11 | issue=1 | date=2015-01-06 | issn=1814-9332 | doi=10.5194/cp-11-15-2015 | pages=15–25| bibcode=2015CliPa..11...15S | doi-access=free }} [[File:CC-BY icon.svg|50px]] Material was copied from this source, which is available under a [https://creativecommons.org/licenses/by/3.0/ Creative Commons Attribution 3.0 International License] {{Webarchive|url=https://web.archive.org/web/20110223101209/http://creativecommons.org//licenses//by//3.0// |date=23 February 2011 }}.</ref>

<gallery mode="packed" style="float:left" heights="220px">
File:Ocean changes from the last interglacial to the modern day A.png
File:Ocean changes from the last interglacial to the modern day B.png
</gallery>
{{clear}}

The initial development of the halocline and [[Stratification (water)|stratified water column]] has been attributed to the onset of major [[Würm glaciation|Northern Hemisphere glaciation]] at 2.73 Ma, which increased the flux of freshwater to the region, via increased monsoonal rainfall and/or glacial meltwater, and [[sea surface temperature]]s.<ref>{{cite journal | last1=Sigman | first1=Daniel M. | last2=Jaccard | first2=Samuel L. | last3=Haug | first3=Gerald H. | title=Polar ocean stratification in a cold climate | journal=Nature | publisher=Springer Science and Business Media LLC | volume=428 | issue=6978 | year=2004 | issn=0028-0836 | doi=10.1038/nature02357 | pages=59–63 | pmid=14999278 | bibcode=2004Natur.428...59S | s2cid=4329978 | url=https://gfzpublic.gfz-potsdam.de/pubman/item/item_230448 | access-date=15 December 2021 | archive-date=19 February 2022 | archive-url=https://web.archive.org/web/20220219150343/https://gfzpublic.gfz-potsdam.de/pubman/faces/ViewItemOverviewPage.jsp?itemId=item_230448 | url-status=live }}</ref><ref name="Haug etal 2005">{{cite journal | last1=Haug | first1=Gerald H. | last2=Ganopolski | first2=Andrey | last3=Sigman | first3=Daniel M. | last4=Rosell-Mele | first4=Antoni | last5=Swann | first5=George E. A. | last6=Tiedemann | first6=Ralf | last7=Jaccard | first7=Samuel L. | last8=Bollmann | first8=Jörg | last9=Maslin | first9=Mark A. | last10=Leng | first10=Melanie J. | last11=Eglinton | first11=Geoffrey | display-authors = 6 | title=North Pacific seasonality and the glaciation of North America 2.7 million years ago | journal=Nature | publisher=Springer Science and Business Media LLC | volume=433 | issue=7028 | year=2005 | issn=0028-0836 | doi=10.1038/nature03332 | pages=821–825 | pmid=15729332 | bibcode=2005Natur.433..821H | s2cid=24116155 | url=https://gfzpublic.gfz-potsdam.de/pubman/item/item_231798 | access-date=15 December 2021 | archive-date=19 February 2022 | archive-url=https://web.archive.org/web/20220219150343/https://gfzpublic.gfz-potsdam.de/pubman/faces/ViewItemOverviewPage.jsp?itemId=item_231798 | url-status=live }}</ref><ref>{{cite journal | last1=Swann | first1=George E. A. | last2=Maslin | first2=Mark A. | last3=Leng | first3=Melanie J. | last4=Sloane | first4=Hilary J. | last5=Haug | first5=Gerald H. | title=Diatom δ18O evidence for the development of the modern halocline system in the subarctic northwest Pacific at the onset of major Northern Hemisphere glaciation | journal=Paleoceanography | publisher=American Geophysical Union (AGU) | volume=21 | issue=1 | date=2006-02-24 | issn=0883-8305 | doi=10.1029/2005pa001147 | pages=n/a| bibcode=2006PalOc..21.1009S | url=http://eprints.nottingham.ac.uk/id/eprint/2009 | doi-access=free }}</ref><ref name="Nie etal 2008">{{cite journal | last1=Nie | first1=Junsheng | last2=King | first2=John | last3=Liu | first3=Zhengyu | last4=Clemens | first4=Steve | last5=Prell | first5=Warren | last6=Fang | first6=Xiaomin | title=Surface-water freshening: A cause for the onset of North Pacific stratification from 2.75 Ma onward? | journal=Global and Planetary Change | publisher=Elsevier BV | volume=64 | issue=1–2 | year=2008 | issn=0921-8181 | doi=10.1016/j.gloplacha.2008.08.003 | pages=49–52| bibcode=2008GPC....64...49N }}</ref> The decrease of [[abyssal]] water upwelling associated with this may have contributed to the establishment of globally cooler conditions and the expansion of glaciers across the Northern Hemisphere from 2.73 Ma.<ref name="Haug etal 2005" /> While the halocline appears to have prevailed through the [[late Pliocene]] and [[Gelasian|early Quaternary]] [[glacial cycle|glacial–interglacial cycles]],<ref>{{cite journal | last=Swann | first=George E.A. | title=Salinity changes in the North West Pacific Ocean during the late Pliocene/early Quaternary from 2.73Ma to 2.52Ma | journal=Earth and Planetary Science Letters | publisher=Elsevier BV | volume=297 | issue=1–2 | year=2010 | issn=0012-821X | doi=10.1016/j.epsl.2010.06.035 | pages=332–338 | bibcode=2010E&PSL.297..332S | url=http://nora.nerc.ac.uk/id/eprint/11147/1/swann_et_al_2010.pdf | access-date=15 December 2021 | archive-date=19 July 2018 | archive-url=https://web.archive.org/web/20180719072730/http://nora.nerc.ac.uk/id/eprint/11147/1/swann_et_al_2010.pdf | url-status=live }}</ref> other studies have shown that the stratification boundary may have broken down in the [[late Quaternary]] at glacial terminations and during the early part of interglacials.<ref>{{cite journal | last1=Sarnthein | first1=M. | last2=Gebhardt | first2=H. | last3=Kiefer | first3=T. | last4=Kucera | first4=M. | last5=Cook | first5=M. | last6=Erlenkeuser | first6=H. | title=Mid Holocene origin of the sea-surface salinity low in the subarctic North Pacific | journal=Quaternary Science Reviews | publisher=Elsevier BV | volume=23 | issue=20–22 | year=2004 | issn=0277-3791 | doi=10.1016/j.quascirev.2004.08.008 | pages=2089–2099| bibcode=2004QSRv...23.2089S }}</ref><ref>{{cite journal | last1=Jaccard | first1=S.L. | last2=Galbraith | first2=E.D. | last3=Sigman | first3=D.M. | last4=Haug | first4=G.H. | title=A pervasive link between Antarctic ice core and subarctic Pacific sediment records over the past 800kyrs | journal=Quaternary Science Reviews | publisher=Elsevier BV | volume=29 | issue=1–2 | year=2010 | issn=0277-3791 | doi=10.1016/j.quascirev.2009.10.007 | pages=206–212| bibcode=2010QSRv...29..206J }}</ref><ref>{{cite journal | last1=Galbraith | first1=Eric D. | last2=Kienast | first2=Markus | last3=Jaccard | first3=Samuel L. | last4=Pedersen | first4=Thomas F. | last5=Brunelle | first5=Brigitte G. | last6=Sigman | first6=Daniel M. | last7=Kiefer | first7=Thorsten | title=Consistent relationship between global climate and surface nitrate utilization in the western subarctic Pacific throughout the last 500 ka | journal=Paleoceanography | publisher=American Geophysical Union (AGU) | volume=23 | issue=2 | date=2008-05-23 | issn=0883-8305 | doi=10.1029/2007pa001518 | pages=n/a | bibcode=2008PalOc..23.2212G | s2cid=4082469 | url=https://archimer.ifremer.fr/doc/00237/34840/33281.pdf | access-date=15 December 2021 | archive-date=15 July 2021 | archive-url=https://web.archive.org/web/20210715195452/https://archimer.ifremer.fr/doc/00237/34840/33281.pdf | url-status=live }}</ref><ref>{{cite journal | last1=Brunelle | first1=Brigitte G. | last2=Sigman | first2=Daniel M. | last3=Jaccard | first3=Samuel L. | last4=Keigwin | first4=Lloyd D. | last5=Plessen | first5=Birgit | last6=Schettler | first6=Georg | last7=Cook | first7=Mea S. | last8=Haug | first8=Gerald H. | title=Glacial/interglacial changes in nutrient supply and stratification in the western subarctic North Pacific since the penultimate glacial maximum | journal=Quaternary Science Reviews | publisher=Elsevier BV | volume=29 | issue=19–20 | year=2010 | issn=0277-3791 | doi=10.1016/j.quascirev.2010.03.010 | pages=2579–2590| bibcode=2010QSRv...29.2579B }}</ref><ref>{{cite journal | last1=Kohfeld | first1=Karen E. | last2=Chase | first2=Zanna | title=Controls on deglacial changes in biogenic fluxes in the North Pacific Ocean | journal=Quaternary Science Reviews | publisher=Elsevier BV | volume=30 | issue=23–24 | year=2011 | issn=0277-3791 | doi=10.1016/j.quascirev.2011.08.007 | pages=3350–3363| bibcode=2011QSRv...30.3350K }}</ref><ref name="Swann Snelling 2015" />

===Diversification===
The [[Cretaceous]] record of diatoms is limited, but recent studies reveal a progressive diversification of diatom types. The [[Cretaceous–Paleogene extinction event]], which in the oceans dramatically affected organisms with calcareous skeletons, appears to have had relatively little impact on diatom evolution.<ref name="Harwood etal 2007">{{cite journal |last1=Harwood |first1=D. M. |last2=Nikolaev |first2=V. A. |last3=Winter |first3=D. M. |year=2007 |title=Cretaceous record of diatom evolution, radiation, and expansion |journal=Paleontological Society Papers |volume=13 |pages=33–59 |doi=10.1017/S1089332600001455 }}</ref>

===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]].