Editing Oceanography (section)

====Ocean acidification====
{{Main|Ocean acidification}}
Ocean acidification describes the decrease in ocean [[PH#Seawater|pH]] that is caused by [[human impact on the environment|anthropogenic]] [[carbon dioxide]] ({{CO2}}) emissions into the [[Earth's atmosphere|atmosphere]].<ref name="cald03">{{Cite journal|last=Caldeira|first=K.|author2=Wickett, M. E.|date=2003|title=Anthropogenic carbon and ocean pH|url=http://pangea.stanford.edu/research/Oceans/GES205/Caldeira_Science_Anthropogenic%20Carbon%20and%20ocean%20pH.pdf |archive-url=https://web.archive.org/web/20070604185633/http://pangea.stanford.edu/research/Oceans/GES205/Caldeira_Science_Anthropogenic%20Carbon%20and%20ocean%20pH.pdf |archive-date=2007-06-04 |url-status=live|journal=[[Nature (journal)|Nature]]|volume=425|issue=6956|pages=OS11C–0385|doi=10.1038/425365a|pmid=14508477|bibcode=2001AGUFMOS11C0385C|s2cid=4417880}}</ref> Seawater is slightly [[alkalinity|alkaline]] and had a preindustrial [[pH]] of about 8.2. More recently, anthropogenic activities have steadily increased the [[carbon dioxide]] content of the atmosphere; about 30–40% of the added CO<sub>2</sub> is absorbed by the oceans, forming [[carbonic acid]] and lowering the pH (now below 8.1<ref name="EPA_Ocean_Acidity">{{cite web|title=Ocean Acidity|publisher=[[EPA]]|date=13 September 2013|url=http://www.epa.gov/climatechange/science/indicators/oceans/acidity.html|access-date=1 November 2013}}</ref>) through ocean acidification.<ref name="Feely04">{{cite journal|last=Feely|first=R. A.|display-authors=etal|title=Impact of Anthropogenic CO<sub>2</sub> on the CaCO<sub>3</sub> System in the Oceans|journal=Science|volume=305|date=July 2004|pages=362–366|bibcode=2004Sci...305..362F|doi=10.1126/science.1097329 |pmid=15256664|issue=5682|s2cid=31054160}}</ref><ref name="Zeebe2008">{{cite journal|last1=Zeebe|first1=R. E.|last2=Zachos|first2=J. C.|last3=Caldeira|first3=K.|last4=Tyrrell|first4=T.|title=OCEANS: Carbon Emissions and Acidification|journal=Science|volume=321|issue=5885|date=4 July 2008|pages=51–52|doi=10.1126/science.1159124|pmid=18599765|s2cid=206513402}}</ref><ref name="GattusoHansson2011">{{cite book|author1=Gattuso, J.-P.|author2=Hansson, L.|title=Ocean Acidification|url=https://books.google.com/books?id=8yjNFxkALjIC|date=15 September 2011|publisher=[[Oxford University Press]]|isbn=978-0-19-959109-1|oclc=730413873}}</ref> The pH is expected to reach 7.7 by the year 2100.<ref name="AboutAntarctica"/>

An important element for the [[skeleton]]s of marine animals is [[calcium]], but [[calcium carbonate]] becomes more soluble with pressure, so carbonate shells and skeletons dissolve below the [[carbonate compensation depth]].<ref name="Pinet">{{cite book|last=Pinet|first=Paul R.|date=1996|title=Invitation to Oceanography|pages=126, 134–135|publisher=[[West Publishing Company]]|url=https://books.google.com/books?id=eAqQvGYap24C|isbn=978-0-314-06339-7}}</ref> Calcium carbonate becomes more soluble at lower pH, so ocean acidification is likely to affect marine organisms with calcareous shells, such as oysters, clams, sea urchins and corals,<ref name="PMEL">{{cite web|url=http://www.pmel.noaa.gov/co2/story/What+is+Ocean+Acidification%3F|title=What is Ocean Acidification?|publisher=NOAA PMEL Carbon Program|access-date=15 September 2013|archive-date=2 September 2013|archive-url=https://web.archive.org/web/20130902071022/http://www.pmel.noaa.gov/co2/story/What+is+Ocean+Acidification%3F|url-status=dead}}</ref><ref name="orr05">{{Cite journal|last=Orr|first=James C.|display-authors=etal|date=2005|title=Anthropogenic ocean acidification over the twenty-first century and its impact on calcifying organisms|url=http://www.ipsl.jussieu.fr/~jomce/acidification/paper/Orr_OnlineNature04095.pdf|archive-url=https://web.archive.org/web/20080625100559/http://www.ipsl.jussieu.fr/~jomce/acidification/paper/Orr_OnlineNature04095.pdf|archive-date=25 June 2008|journal=Nature|volume=437|issue=7059|pages=681–686|doi=10.1038/nature04095|pmid=16193043|bibcode=2005Natur.437..681O|s2cid=4306199}}</ref> and the carbonate compensation depth will rise closer to the sea surface. Affected [[plankton]]ic organisms will include [[pteropod]]s, [[coccolithophorid]]s and [[foraminifera]], all important in the [[food chain]]. In tropical regions, [[coral]]s are likely to be severely affected as they become less able to build their calcium carbonate skeletons,<ref name="Cohen2009">{{cite journal|last1=Cohen|first1=A.|last2=Holcomb|first2=M.|date=2009|title=Why Corals Care About Ocean Acidification: Uncovering the Mechanism|journal=Oceanography|volume=24|pages=118–127|doi=10.5670/oceanog.2009.102|issue=4|hdl=1912/3179|doi-access=free|bibcode=2009Ocgpy..22d.118C |hdl-access=free}}</ref> in turn adversely impacting other [[Coral reef|reef]] dwellers.<ref name="AboutAntarctica">{{cite web|url=http://www.antarctica.gov.au/about-antarctica/environment/climate-change/ocean-acidification-and-the-southern-ocean|title=Ocean acidification|date=28 September 2007|publisher=Department of Sustainability, Environment, Water, Population & Communities: Australian Antarctic Division |access-date=17 April 2013}}</ref>

The current rate of ocean chemistry change seems to be unprecedented in Earth's geological history, making it unclear how well marine ecosystems will adapt to the shifting conditions of the near future.<ref name="Hönisch2012">{{cite journal |last1=Hönisch |first1=Bärbel |author-link=Bärbel Hönisch |last2=Ridgwell |first2=Andy |last3=Schmidt |first3=Daniela N. |last4=Thomas |first4=E. |last5=Gibbs |first5=S. J. |last6=Sluijs |first6=A. |last7=Zeebe |first7=R. |last8=Kump |first8=L. |last9=Martindale |first9=R. C. |last10=Greene |first10=S. E. |last11=Kiessling |first11=W. |display-authors=4 |date=2012 |title=The Geological Record of Ocean Acidification |journal=[[Science (journal)|Science]] |volume=335 |issue=6072 |pages=1058–1063 |bibcode=2012Sci...335.1058H |doi=10.1126/science.1208277 |pmid=22383840 |last12=Ries |first12=J. |last13=Zachos |first13=J. C. |last14=Royer |first14=D. L. |last15=Barker |first15=S. |last16=Marchitto |first16=T. M. |last17=Moyer |first17=R. |last18=Pelejero |first18=C. |last19=Ziveri |first19=P. |last20=Foster |first20=G. L. |last21=Williams |first21=B. |hdl=1983/24fe327a-c509-4b6a-aa9a-a22616c42d49 |s2cid=6361097|url=https://dspace.library.uu.nl/bitstream/1874/385704/1/Geological_Record.pdf }}</ref> Of particular concern is the manner in which the combination of acidification with the expected additional stressors of higher [[ocean temperature]]s and [[hypoxia (environmental)|lower oxygen levels]] will impact the seas.<ref name="Gruber2011">{{cite journal|last=Gruber|first=N.|title=Warming up, turning sour, losing breath: ocean biogeochemistry under global change|journal=Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences|volume=369|issue=1943|date=18 April 2011|pages=1980–96|doi=10.1098/rsta.2011.0003|pmid=21502171|bibcode = 2011RSPTA.369.1980G |doi-access=free}}</ref>