Chemocline

A chemocline is a type of cline, a layer of fluid with different properties, characterized by a strong, vertical chemistry gradient within a body of water. In bodies of water where chemoclines occur, the cline separates the upper and lower layers, resulting in different properties for those layers.^[1] The lower layer shows a change in the concentration of dissolved gases and solids compared to the upper layer.^[2]

Chemoclines most commonly occur where local conditions favor the formation of anoxic bottom water — deep water deficient in oxygen, where only anaerobic forms of life can exist. Common anaerobic organisms that live in these conditions include phototrophic purple sulfur bacteria and green sulfur bacteria.^[3] The Black Sea is an example of a body of water with a prominent chemocline, though similar bodies (classified as meromictic lakes) exist across the globe.^[4]^[5] Meromictic lakes are the result of meromixis, which is a circumstance where a body of water does not fully mix and circulate, causing stratification.^[1]^[6]

In any body of water in which oxygen-rich surface waters are well-mixed (holomictic), no chemocline will exist, as there is no stratification of layers.^[7] Chemoclines can become unstable when dissolved gases become supersaturated, such as H₂S, due to mixing associated with bubbling or boiling (ebullition).^[8]

^ ^a ^b Stewart KM, Walker KF, Likens GE (2009). "Meromictic Lakes". Encyclopedia of Inland Waters. Elsevier. pp. 589–602. doi:10.1016/b978-012370626-3.00027-2. ISBN 9780123706263.
^ Uveges BT, Junium CK, Scholz CA, Fulton JM (2020-10-15). "Chemocline collapse in Lake Kivu as an analogue for nitrogen cycling during Oceanic Anoxic Events". Earth and Planetary Science Letters. 548: 116459. Bibcode:2020E&PSL.54816459U. doi:10.1016/j.epsl.2020.116459. ISSN 0012-821X. S2CID 224981010.
^ Danza F, Storelli N, Roman S, Lüdin S, Tonolla M (2017-12-15). "Dynamic cellular complexity of anoxygenic phototrophic sulfur bacteria in the chemocline of meromictic Lake Cadagno". PLOS ONE. 12 (12): e0189510. Bibcode:2017PLoSO..1289510D. doi:10.1371/journal.pone.0189510. PMC 5731995. PMID 29245157.
^ Sinninghe Damsté JS, de Leeuw JW, Wakeham SG, Hayes JM, Kohnen ME (1993-12-02). "Chemocline of the Black Sea". Nature. 366 (6454): 416. Bibcode:1993Natur.366..416S. doi:10.1038/366416a0. ISSN 1476-4687. S2CID 11974369.
^ Oikonomou A, Filker S, Breiner HW, Stoeck T (June 2015). "Protistan diversity in a permanently stratified meromictic lake (Lake Alatsee, SW Germany)". Environmental Microbiology. 17 (6): 2144–2157. Bibcode:2015EnvMi..17.2144O. doi:10.1111/1462-2920.12666. PMID 25330396.
^ Blees J, Niemann H, Wenk CB, Zopfi J, Schubert CJ, Kirf MK, et al. (2014-01-27). "Micro-aerobic bacterial methane oxidation in the chemocline and anoxic water column of deep south-Alpine Lake Lugano (Switzerland)". Limnology and Oceanography. 59 (2): 311–324. Bibcode:2014LimOc..59..311B. doi:10.4319/lo.2014.59.2.0311. ISSN 0024-3590. S2CID 56401767.
^ Čanković, M; Žućko, J; Petrić, I; Marguš, M; Ciglenecćki, I (2020-05-14). "Impact of euxinic holomictic conditions on prokaryotic assemblages in a marine meromictic lake". Aquatic Microbial Ecology. 84: 141–154. doi:10.3354/ame01931. ISSN 0948-3055. S2CID 216313230.
^ Riccardi, Anthony L.; Arthur, Michael A.; Kump, Lee R. (2006-12-01). "Sulfur isotopic evidence for chemocline upward excursions during the end-Permian mass extinction". Geochimica et Cosmochimica Acta. A Special Issue Dedicated to Robert A. Berner. 70 (23): 5740–5752. Bibcode:2006GeCoA..70.5740R. doi:10.1016/j.gca.2006.08.005. ISSN 0016-7037.

[:0-1] Stewart KM, Walker KF, Likens GE (2009). "Meromictic Lakes". Encyclopedia of Inland Waters. Elsevier. pp. 589–602. doi:10.1016/b978-012370626-3.00027-2. ISBN 9780123706263.

[2] Uveges BT, Junium CK, Scholz CA, Fulton JM (2020-10-15). "Chemocline collapse in Lake Kivu as an analogue for nitrogen cycling during Oceanic Anoxic Events". Earth and Planetary Science Letters. 548: 116459. Bibcode:2020E&PSL.54816459U. doi:10.1016/j.epsl.2020.116459. ISSN 0012-821X. S2CID 224981010.

[3] Danza F, Storelli N, Roman S, Lüdin S, Tonolla M (2017-12-15). "Dynamic cellular complexity of anoxygenic phototrophic sulfur bacteria in the chemocline of meromictic Lake Cadagno". PLOS ONE. 12 (12): e0189510. Bibcode:2017PLoSO..1289510D. doi:10.1371/journal.pone.0189510. PMC 5731995. PMID 29245157.

[4] Sinninghe Damsté JS, de Leeuw JW, Wakeham SG, Hayes JM, Kohnen ME (1993-12-02). "Chemocline of the Black Sea". Nature. 366 (6454): 416. Bibcode:1993Natur.366..416S. doi:10.1038/366416a0. ISSN 1476-4687. S2CID 11974369.

[5] Oikonomou A, Filker S, Breiner HW, Stoeck T (June 2015). "Protistan diversity in a permanently stratified meromictic lake (Lake Alatsee, SW Germany)". Environmental Microbiology. 17 (6): 2144–2157. Bibcode:2015EnvMi..17.2144O. doi:10.1111/1462-2920.12666. PMID 25330396.

[:4-6] Blees J, Niemann H, Wenk CB, Zopfi J, Schubert CJ, Kirf MK, et al. (2014-01-27). "Micro-aerobic bacterial methane oxidation in the chemocline and anoxic water column of deep south-Alpine Lake Lugano (Switzerland)". Limnology and Oceanography. 59 (2): 311–324. Bibcode:2014LimOc..59..311B. doi:10.4319/lo.2014.59.2.0311. ISSN 0024-3590. S2CID 56401767.

[:2-7] Čanković, M; Žućko, J; Petrić, I; Marguš, M; Ciglenecćki, I (2020-05-14). "Impact of euxinic holomictic conditions on prokaryotic assemblages in a marine meromictic lake". Aquatic Microbial Ecology. 84: 141–154. doi:10.3354/ame01931. ISSN 0948-3055. S2CID 216313230.

[:3-8] Riccardi, Anthony L.; Arthur, Michael A.; Kump, Lee R. (2006-12-01). "Sulfur isotopic evidence for chemocline upward excursions during the end-Permian mass extinction". Geochimica et Cosmochimica Acta. A Special Issue Dedicated to Robert A. Berner. 70 (23): 5740–5752. Bibcode:2006GeCoA..70.5740R. doi:10.1016/j.gca.2006.08.005. ISSN 0016-7037.

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