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Humans first acquired knowledge of the waves and currents of the [[sea]]s and [[ocean]]s in pre-historic times. Observations on [[tide]]s were recorded by [[Aristotle]] and [[Strabo]]. Early exploration of the oceans was primarily for [[cartography]] and mainly limited to its surfaces and of the animals that fishermen brought up in nets, though depth soundings by lead line were taken.
Although [[Juan Ponce de León]] in 1513 first identified the [[Gulf Stream]], and the current was well-known to mariners, [[Benjamin Franklin]] made the first scientific study of it and gave it its name. Franklin measured water temperatures during several Atlantic crossings and correctly explained the Gulf Stream's cause. Franklin and Timothy Folger printed the first map of the Gulf Stream in 1769-1770.<ref name="NOAA_Franklin">[http://oceanexplorer.noaa.gov/library/readings/gulf/gulf.html 1785: Benjamin Franklin's 'Sundry Maritime Observations'] {{webarchive|url=https://web.archive.org/web/20051218185445/http://oceanexplorer.noaa.gov/library/readings/gulf/gulf.html |date=2005-12-18 }}</ref><ref>Wilkinson, Jerry. [http://www.keyshistory.org/gulfstream.html History of the Gulf Stream] 1 January 2008</ref>
[[File:Rennel map 1799.png|left|thumb|280px|1799 map of the currents in the [[Atlantic Ocean|Atlantic]] and [[Indian Ocean]]s, by [[James Rennell]]]]
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[[File:Challenger.jpg|right|thumb|[[HMS Challenger (1858)|HMS ''Challenger'']] undertook the first global marine research expedition in 1872.]]
The seminal event in the founding of the modern science of oceanography was the 1872-76 [[Challenger expedition]]. As the first true oceanographic cruise, this expedition laid the groundwork for an entire academic and research discipline.<ref name="NOAAA">[http://oceanexplorer.noaa.gov/explorations/03mountains/background/challenger/challenger.html Then and Now: The HMS Challenger Expedition and the 'Mountains in the Sea' Expedition], Ocean Explorer website (NOAA), accessed 2 January 2012</ref> In response to a recommendation from the [[Royal Society]], [[The British Government]] announced in 1871 an expedition to explore world's oceans and conduct appropriate scientific investigation. [[Charles Wyville Thompson]] and [[John Murray (oceanographer)|Sir John Murray]] launched the Challenger expedition. The Challenger, leased from the [[Royal Navy]], was modified for scientific work and equipped with separate laboratories for [[natural history]] and [[chemistry]].<ref name="Rice">{{cite book|last=Rice|first=A. L.|title=Understanding the Oceans: Marine Science in the Wake of HMS Challenger|publisher=[[Routledge]]|date=1999|pages=27–48|chapter=The Challenger Expedition|isbn=978-1-85728-705-9|url=https://books.google.com/books?id=F5agn3NSzEoC&pg=PA27}}</ref> Under the scientific supervision of Thomson, Challenger travelled nearly {{convert|70000|nmi|km}} surveying and exploring. On her journey circumnavigating the globe,<ref name="Rice"/> 492 deep sea soundings, 133 bottom dredges, 151 open water trawls and 263 serial water temperature observations were taken.<ref>''Oceanography: an introduction to the marine environment'' (Peter K. Weyl, 1970), p. 49</ref> Around 4,700 new species of marine life were discovered. The result was the ''Report Of The Scientific Results of the Exploring Voyage of H.M.S. Challenger during the years 1873-76''. Murray, who supervised the publication, described the report as "the greatest advance in the knowledge of our planet since the celebrated discoveries of the fifteenth and sixteenth centuries". He went on to found the academic discipline of oceanography at the [[University of Edinburgh]], which remained the centre for oceanographic research well into the 20th century.<ref>{{cite web|url=http://www.geos.ed.ac.uk/public/JohnMurray.html|title=Sir John Murray (1841-1914) - Founder Of Modern Oceanography|publisher=Science and Engineering at The University of Edinburgh|accessdate=7 November 2013|deadurl=yes|archiveurl=https://web.archive.org/web/20130528123837/http://www.geos.ed.ac.uk/public/JohnMurray.html|archivedate=28 May 2013|df=}}</ref> Murray was the first to study marine trenches and in particular the [[Mid-Atlantic Ridge]], and map the sedimentary deposits in the oceans. He tried to map out the world's ocean currents based on salinity and temperature observations, and was the first to correctly understand the nature of [[coral reef]] development.
In the late 19th century, other [[Western culture|Western]] nations also sent out scientific expeditions (as did private individuals and institutions). The first purpose built oceanographic ship, the Albatros, was built in 1882. In 1893, [[Fridtjof Nansen]] allowed his ship, Fram, to be frozen in the Arctic ice. This enabled him to obtain oceanographic, meteorological and astronomical data at a stationary spot over an extended period.
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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|journal=[[Nature (journal)|Nature]]|volume=425|issue=6956|pages=365–365|doi=10.1038/425365a|pmid=14508477|bibcode=2001AGUFMOS11C0385C}}</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|work=[http://www.epa.gov/climatechange/ U.S. EPA climate change web site]|publisher=[[EPA]]|date=13 September 2013|url=http://www.epa.gov/climatechange/science/indicators/oceans/acidity.html|accessdate=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|url=http://www.sciencemag.org/content/305/5682/362.abstract|bibcode=2004Sci...305..362F|doi=10.1126/science.1097329 |pmid=15256664|issue=5682}}</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}}</ref><ref name="GattusoHansson2011">{{cite book|author1=Gattuso, J.-P.|author2=Hansson, L.|title=Ocean Acidification|url=https://books.google.com/books?id=8yjNFxkALjIC&printsec=frontcover|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&printsec=frontcover|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|accessdate=15 September 2013}}</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|archiveurl=https://web.archive.org/web/20080625100559/http://www.ipsl.jussieu.fr/~jomce/acidification/paper/Orr_OnlineNature04095.pdf|archivedate=25 June 2008|journal=Nature|volume=437|issue=7059|pages=681–686|doi=10.1038/nature04095|pmid=16193043|bibcode=2005Natur.437..681O}}</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|last=Cohen|first=A.|last2=Holcomb|first2=M.|date=2009|title=Why Corals Care About Ocean Acidification: Uncovering the Mechanism|journal=Oceanography|volume=24|pages=118–127|url=http://coralreef.noaa.gov/education/oa/resources/22-4_cohen.pdf|doi=10.5670/oceanog.2009.102|issue=4|deadurl=yes|archiveurl=https://web.archive.org/web/20131106020339/http://coralreef.noaa.gov/education/oa/resources/22-4_cohen.pdf|archivedate=2013-11-06|df=}}</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 |accessdate=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|display-authors=4|last2=Ridgwell|first2=Andy|last3=Schmidt|first3=Daniela N.|date=2012|title=The Geological Record of Ocean Acidification|journal=[[Science (journal)|Science]]|volume=335|issue=6072|pages=1058–1063|doi=10.1126/science.1208277|bibcode=2012Sci...335.1058H|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.|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.|pmid=22383840}}</ref> Of particular concern is the manner in which the combination of acidification with the expected additional stressors of higher temperatures 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|bibcode = 2011RSPTA.369.1980G }}</ref>
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* [http://www.whoi.edu Woods Hole Oceanographic Institution (WHOI)]. One of the world's largest private, non-profit ocean research, engineering and education organizations.
* [http://www.bodc.ac.uk/ British Oceanographic Data Centre]. A source of oceanographic data and information.
* [https://web.archive.org/web/20060211015453/http://dapper.pmel.noaa.gov/dchart/ NOAA Ocean and Weather Data Navigator]. Plot and download ocean data.
* [http://www.vega.org.uk/video/programme/10 Freeview Video 'Voyage to the Bottom of the Deep Deep Sea' Oceanography Programme] by the [[Vega Science Trust]] and the [[BBC]]/[[Open University]].
* [http://atlas.investigadhoc.com/ Atlas of Spanish Oceanography] by [http://www.investigadhoc.com InvestigAdHoc].
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