Chemocline
| Aquatic layers |
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| Stratification |
| See also |
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 an increase in the concentration of dissolved gases and solids compared to the upper layer.[2]
Chemoclines most commonly occur where local conditions favor the formations 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. The Black Sea is the classic example of such a body, though similar bodies of water (classified as meromictic lakes) exist across the globe. 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][3]
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.
Chemocline structure
Containing the largest chemical gradient, the chemocline is a layer that separates a meromictic lake into two parts: the upper mixolimnion and the lower monolimnion. The mixolimnion is a region that is mixed by the wind where the water can be fully mixed and circulated. However, the monolimnion cannot interact with the wind in the same manner and does not experience the same conditions. Furthermore, the chemocline's variability in density determines the degree to which the body of water will experiences mixing and circulation.[1]
Life and chemoclines
As a result of the differences between the upper and lower layers, aerobic life is restricted to the region above the chemocline, while anaerobic species reside below the cline. Additionally, above the chemocline, photosynthetic processes can occur due to the presence of light, but below, sufficient light is not present for photosynthetic bacteria to thrive.[4] At the chemocline itself, photosynthetic forms of anaerobic bacteria, like green phototrophic and purple sulfur bacteria, cluster and take advantage of both the sunlight from above and the hydrogen sulfide (H2S) produced by the anaerobic bacteria below. A study conducted in Ace Lake, located in Antarctica, investigated the process of anoxygenic photosynthesis done by green sulfur bacteria in the lake and found that they were located exclusively in the chemocline of the lake due to the presence of light and sulfide.[4]
Furthermore, microbial processes can be responsible for the presence of chemical differences in a chemocline. Processes like carbon dioxide fixation, sulfur cycling, and exoenzyme activities occur at heightened rates in the cline compared to the surrounding body of water. Because of the various chemical properties of a chemocline, it can often support a diverse array of lifeforms in a small layer.[5]
Sources
- ^ a b c Stewart, K.M.; Walker, K.F.; Likens, G.E. (2009), "Meromictic Lakes", Encyclopedia of Inland Waters, Elsevier, pp. 589–602, doi:10.1016/b978-012370626-3.00027-2, retrieved 2021-10-29
- ^ Uveges, Benjamin T.; Junium, Christopher K.; Scholz, Christopher A.; Fulton, James M. (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. doi:10.1016/j.epsl.2020.116459. ISSN 0012-821X.
- ^ Blees, Jan; Niemann, Helge; Wenk, Christine B.; Zopfi, Jakob; Schubert, Carsten J.; Kirf, Mathias K.; Veronesi, Mauro L.; Hitz, Carmen; Lehmann, Moritz F. (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. doi:10.4319/lo.2014.59.2.0311. ISSN 0024-3590.
- ^ a b Neretin, L.E. (2006). Past and present water column anoxia. Dordrecht: Springer. ISBN 978-1-4020-4297-3. OCLC 209932741.
- ^ Sass, Andrea M.; Sass, Henrik; Coolen, Marco J. L.; Cypionka, Heribert; Overmann, Jörg (2001-12-01). "Microbial Communities in the Chemocline of a Hypersaline Deep-Sea Basin (Urania Basin, Mediterranean Sea)". Applied and Environmental Microbiology. 67 (12): 5392–5402. doi:10.1128/AEM.67.12.5392-5402.2001. PMC 93321. PMID 11722884.
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