Editing Photic zone (section)

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

[[Phytoplankton]] are [[unicellular]] [[Marine microorganisms|microorganisms]] which form the base of the [[ocean food chain]]s. They are dominated by [[diatom]]s, which grow silicate shells called [[frustule]]s. When diatoms die their shells 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}}</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|halocline stratification]] and increased nutrient supply to the photic zone.<ref name=Swann2015>{{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].</ref>

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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
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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 }}</ref><ref name=Haug2005>{{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 | 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 }}</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 | doi-access=free }}</ref><ref name=Nie2008>{{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=Haug2005 /> 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 |archive-url=https://ghostarchive.org/archive/20221009/http://nora.nerc.ac.uk/id/eprint/11147/1/swann_et_al_2010.pdf |archive-date=2022-10-09 |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/ | doi-access=free }}</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=Swann2015 />