Editing Biogeochemical cycle (section)

====Hydrosphere====
{{main|Hydrosphere}}
{{see also|Marine biogeochemical cycles}}
[[File:Role of marine organisms in biogeochemical cycling.jpg|thumb|upright=1.6| Some roles of marine organisms in biogeochemical cycling in the Southern Ocean<ref name=Henley2020>{{cite journal |title = Changing Biogeochemistry of the Southern Ocean and Its Ecosystem Implications|year = 2020|doi = 10.3389/fmars.2020.00581|doi-access = free|last1 = Henley|first1 = Sian F.|last2 = Cavan|first2 = Emma L.|last3 = Fawcett|first3 = Sarah E.|last4 = Kerr|first4 = Rodrigo|last5 = Monteiro|first5 = Thiago|last6 = Sherrell|first6 = Robert M.|last7 = Bowie|first7 = Andrew R.|last8 = Boyd|first8 = Philip W.|last9 = Barnes|first9 = David K. A.|last10 = Schloss|first10 = Irene R.|last11 = Marshall|first11 = Tanya|last12 = Flynn|first12 = Raquel|last13 = Smith|first13 = Shantelle|journal = Frontiers in Marine Science|volume = 7| page=581 | bibcode=2020FrMaS...7..581H |hdl = 11336/128446|hdl-access = free}} [[File:CC-BY icon.svg|50px]] Material was copied from this source, which is available under a [https://creativecommons.org/licenses/by/4.0/ Creative Commons Attribution 4.0 International License] {{Webarchive|url=https://web.archive.org/web/20171016050101/https://creativecommons.org/licenses/by/4.0/ |date=2017-10-16 }}.</ref>]]

The global ocean covers more than 70% of the Earth's surface and is remarkably heterogeneous. Marine productive areas, and [[coastal ecosystem]]s comprise a minor fraction of the ocean in terms of surface area, yet have an enormous impact on global biogeochemical cycles carried out by [[microbial communities]], which represent 90% of the ocean's biomass.<ref>{{cite journal |doi = 10.1007/s12526-011-0084-1|title = The Census of Marine Life—evolution of worldwide marine biodiversity research|year = 2011|last1 = Alexander|first1 = Vera|last2 = Miloslavich|first2 = Patricia|last3 = Yarincik|first3 = Kristen|journal = Marine Biodiversity|volume = 41|issue = 4|pages = 545–554|s2cid = 25888475|doi-access = free| bibcode=2011MarBd..41..545A }}</ref> Work in recent years has largely focused on cycling of carbon and macronutrients such as nitrogen, phosphorus, and silicate: other important elements such as sulfur or trace elements have been less studied, reflecting associated technical and logistical issues.<ref name=Murillo2019 /> Increasingly, these marine areas, and the taxa that form their ecosystems, are subject to significant anthropogenic pressure, impacting marine life and recycling of energy and nutrients.<ref>Galton, D. (1884) [https://www.proquest.com/openview/792c496cb0a1bdf11778db87c126ff44/1?pq-origsite=gscholar&cbl=1816417 10th Meeting: report of the royal commission on metropolitan sewage] {{Webarchive|url=https://web.archive.org/web/20210924063154/https://www.proquest.com/openview/792c496cb0a1bdf11778db87c126ff44/1?pq-origsite=gscholar&cbl=1816417 |date=2021-09-24 }}. ''J. Soc. Arts'', '''33''': 290.</ref><ref>{{cite journal |doi = 10.2307/1294478|jstor = 1294478|last1 = Hasler|first1 = Arthur D.|title = Cultural Eutrophication is Reversible|journal = BioScience|year = 1969|volume = 19|issue = 5|pages = 425–431}}</ref><ref>{{cite journal |doi = 10.1002/2016GB005586|title = A reevaluation of the magnitude and impacts of anthropogenic atmospheric nitrogen inputs on the ocean|year = 2017|last1 = Jickells|first1 = T. D.|last2 = Buitenhuis|first2 = E.|last3 = Altieri|first3 = K.|last4 = Baker|first4 = A. R.|last5 = Capone|first5 = D.|last6 = Duce|first6 = R. A.|last7 = Dentener|first7 = F.|last8 = Fennel|first8 = K.|last9 = Kanakidou|first9 = M.|last10 = Laroche|first10 = J.|last11 = Lee|first11 = K.|last12 = Liss|first12 = P.|last13 = Middelburg|first13 = J. J.|last14 = Moore|first14 = J. K.|last15 = Okin|first15 = G.|last16 = Oschlies|first16 = A.|last17 = Sarin|first17 = M.|last18 = Seitzinger|first18 = S.|last19 = Sharples|first19 = J.|last20 = Singh|first20 = A.|last21 = Suntharalingam|first21 = P.|last22 = Uematsu|first22 = M.|last23 = Zamora|first23 = L. M.|journal = Global Biogeochemical Cycles|volume = 31|issue = 2|page = 289|bibcode = 2017GBioC..31..289J|hdl = 1874/348077| s2cid=5158406 |hdl-access = free}}</ref> A key example is that of [[cultural eutrophication]], where [[agricultural runoff]] leads to nitrogen and phosphorus enrichment of coastal ecosystems, greatly increasing productivity resulting in [[algal bloom]]s, [[Ocean deoxygenation|deoxygenation]] of the water column and seabed, and increased greenhouse gas emissions,<ref name=Bouwman2005>{{cite journal |doi = 10.1029/2004GB002314|title = Exploring changes in river nitrogen export to the world's oceans|year = 2005|last1 = Bouwman|first1 = A. F.|last2 = Van Drecht|first2 = G.|last3 = Knoop|first3 = J. M.|last4 = Beusen|first4 = A. H. W.|last5 = Meinardi|first5 = C. R.|journal = Global Biogeochemical Cycles|volume = 19|issue = 1|bibcode = 2005GBioC..19.1002B| s2cid=131163837 |doi-access = free}}</ref> with direct local and global impacts on [[nitrogen cycle|nitrogen]] and [[carbon cycle]]s. However, the runoff of [[organic matter]] from the mainland to [[coastal ecosystem]]s is just one of a series of pressing threats stressing microbial communities due to global change. Climate change has also resulted in changes in the [[cryosphere]], as glaciers and permafrost melt, resulting in intensified [[Ocean stratification|marine stratification]], while shifts of the [[redox|redox-state]] in different biomes are rapidly reshaping [[microbial assemblage]]s at an unprecedented rate.<ref>{{cite journal |doi = 10.1111/gcb.12754|title = Climate change and dead zones|year = 2015|last1 = Altieri|first1 = Andrew H.|last2 = Gedan|first2 = Keryn B.|journal = Global Change Biology|volume = 21|issue = 4|pages = 1395–1406|pmid = 25385668|bibcode = 2015GCBio..21.1395A| s2cid=24002134 }}</ref><ref name=Breitburg2018>{{cite journal |doi = 10.1126/science.aam7240|title = Declining oxygen in the global ocean and coastal waters|year = 2018|last1 = Breitburg|first1 = Denise|last2 = Levin|first2 = Lisa A.|last3 = Oschlies|first3 = Andreas|last4 = Grégoire|first4 = Marilaure|last5 = Chavez|first5 = Francisco P.|last6 = Conley|first6 = Daniel J.|last7 = Garçon|first7 = Véronique|last8 = Gilbert|first8 = Denis|last9 = Gutiérrez|first9 = Dimitri|last10 = Isensee|first10 = Kirsten|last11 = Jacinto|first11 = Gil S.|last12 = Limburg|first12 = Karin E.|last13 = Montes|first13 = Ivonne|last14 = Naqvi|first14 = S. W. A.|last15 = Pitcher|first15 = Grant C.|last16 = Rabalais|first16 = Nancy N.|last17 = Roman|first17 = Michael R.|last18 = Rose|first18 = Kenneth A.|last19 = Seibel|first19 = Brad A.|last20 = Telszewski|first20 = Maciej|last21 = Yasuhara|first21 = Moriaki|last22 = Zhang|first22 = Jing|journal = Science|volume = 359|issue = 6371|pages = eaam7240|pmid = 29301986|bibcode = 2018Sci...359M7240B|s2cid = 206657115|doi-access = free}}</ref><ref name=Cavicchioli2019>{{cite journal |doi = 10.1038/s41579-019-0222-5|title = Scientists' warning to humanity: Microorganisms and climate change|year = 2019|last1 = Cavicchioli|first1 = Ricardo|last2 = Ripple|first2 = William J.|last3 = Timmis|first3 = Kenneth N.|last4 = Azam|first4 = Farooq|last5 = Bakken|first5 = Lars R.|last6 = Baylis|first6 = Matthew|last7 = Behrenfeld|first7 = Michael J.|last8 = Boetius|first8 = Antje|last9 = Boyd|first9 = Philip W.|last10 = Classen|first10 = Aimée T.|last11 = Crowther|first11 = Thomas W.|last12 = Danovaro|first12 = Roberto|last13 = Foreman|first13 = Christine M.|last14 = Huisman|first14 = Jef|last15 = Hutchins|first15 = David A.|last16 = Jansson|first16 = Janet K.|last17 = Karl|first17 = David M.|last18 = Koskella|first18 = Britt|last19 = Mark Welch|first19 = David B.|last20 = Martiny|first20 = Jennifer B. H.|last21 = Moran|first21 = Mary Ann|last22 = Orphan|first22 = Victoria J.|last23 = Reay|first23 = David S.|last24 = Remais|first24 = Justin V.|last25 = Rich|first25 = Virginia I.|last26 = Singh|first26 = Brajesh K.|last27 = Stein|first27 = Lisa Y.|last28 = Stewart|first28 = Frank J.|last29 = Sullivan|first29 = Matthew B.|last30 = Van Oppen|first30 = Madeleine J. H.|journal = Nature Reviews Microbiology|volume = 17|issue = 9|pages = 569–586|pmid = 31213707|pmc = 7136171|display-authors = 1}}</ref><ref name=Hutchins2019>{{cite journal |doi = 10.1038/s41579-019-0178-5|title = Climate change microbiology — problems and perspectives|year = 2019|last1 = Hutchins|first1 = David A.|last2 = Jansson|first2 = Janet K.|last3 = Remais|first3 = Justin V.|last4 = Rich|first4 = Virginia I.|last5 = Singh|first5 = Brajesh K.|last6 = Trivedi|first6 = Pankaj|journal = Nature Reviews Microbiology|volume = 17|issue = 6|pages = 391–396|pmid = 31092905|s2cid = 155102440}}</ref><ref name=Murillo2019>{{cite journal |doi = 10.3389/fmars.2019.00657|doi-access = free|title = Editorial: Marine Microbiome and Biogeochemical Cycles in Marine Productive Areas|year = 2019|last1 = Murillo|first1 = Alejandro A.|last2 = Molina|first2 = Verónica|last3 = Salcedo-Castro|first3 = Julio|last4 = Harrod|first4 = Chris|journal = Frontiers in Marine Science|volume = 6| page=657 | bibcode=2019FrMaS...6..657M }} [[File:CC-BY icon.svg|50px]] Material was copied from this source, which is available under a [https://creativecommons.org/licenses/by/4.0/ Creative Commons Attribution 4.0 International License] {{Webarchive|url=https://web.archive.org/web/20171016050101/https://creativecommons.org/licenses/by/4.0/ |date=2017-10-16 }}.</ref>

Global change is, therefore, affecting key processes including [[Marine primary production|primary productivity]], CO<sub>2</sub> and N<sub>2</sub> fixation, organic matter respiration/[[remineralization]], and the sinking and burial deposition of fixed CO<sub>2</sub>.<ref name=Hutchins2019 /> In addition to this, oceans are experiencing an [[Ocean acidification|acidification process]], with a change of ~0.1 [[pH]] units between the pre-industrial period and today, affecting [[carbonate]]/[[bicarbonate]] [[Buffering agent|buffer]] chemistry. In turn, acidification has been reported to impact [[planktonic]] communities, principally through effects on calcifying taxa.<ref>{{cite journal |doi = 10.1242/jeb.115584|title = Biochemical adaptation to ocean acidification|year = 2015|last1 = Stillman|first1 = Jonathon H.|last2 = Paganini|first2 = Adam W.|journal = Journal of Experimental Biology|volume = 218|issue = 12|pages = 1946–1955|pmid = 26085671|s2cid = 13071345|doi-access = free| bibcode=2015JExpB.218.1946S }}</ref> There is also evidence for shifts in the production of key intermediary volatile products, some of which have marked greenhouse effects (e.g., N<sub>2</sub>O and CH<sub>4</sub>, reviewed by Breitburg in 2018,<ref name=Breitburg2018 /> due to the increase in global temperature, ocean stratification and deoxygenation, driving as much as 25 to 50% of nitrogen loss from the ocean to the atmosphere in the so-called [[oxygen minimum zone]]s<ref>{{cite journal |doi = 10.1038/s41579-018-0087-z|title = Microbial niches in marine oxygen minimum zones|year = 2018|last1 = Bertagnolli|first1 = Anthony D.|last2 = Stewart|first2 = Frank J.|journal = Nature Reviews Microbiology|volume = 16|issue = 12|pages = 723–729|pmid = 30250271|s2cid = 52811177}}</ref> or [[Anoxic waters|anoxic]] marine zones,<ref>{{cite journal |doi = 10.1073/pnas.1205009109|title = Microbial oceanography of anoxic oxygen minimum zones|year = 2012|last1 = Ulloa|first1 = O.|last2 = Canfield|first2 = D. E.|last3 = Delong|first3 = E. F.|last4 = Letelier|first4 = R. M.|last5 = Stewart|first5 = F. J.|journal = Proceedings of the National Academy of Sciences|volume = 109|issue = 40|pages = 15996–16003|pmid = 22967509|pmc = 3479542|bibcode = 2012PNAS..10915996U|s2cid = 6630698|doi-access = free}}</ref> driven by microbial processes. Other products, that are typically toxic for the marine [[nekton]], including reduced sulfur species such as H<sub>2</sub>S, have a negative impact for marine resources like fisheries and coastal aquaculture. While global change has accelerated, there has been a parallel increase in awareness of the complexity of marine ecosystems, and especially the fundamental role of microbes as drivers of ecosystem functioning.<ref name=Cavicchioli2019 /><ref name=Murillo2019 />