Editing Lysocline

{{short description|Depth in the ocean below which the rate of dissolution of calcite increases dramatically}}
[[File:Surface ocean present-day omega calcite, GLODAPv2.png|thumb|The graphic presents the present-day annual mean surface omega calcite: the normalised saturation state of calcite. Areas with a value less an 1 indicate a likeliness for dissolution (undersaturated) while a value over 1 indicates areas less likely for dissolution (oversaturation).]]
The '''lysocline''' is the depth in the [[ocean]] dependent upon the [[carbonate compensation depth]] (CCD), usually around 5 km, below which the rate of [[Solvation|dissolution]] of [[calcite]] increases dramatically because of a pressure effect. While the lysocline is the upper bound of this transition zone of calcite saturation, the CCD is the lower bound of this zone.<ref name=":02">{{Citation|last=Broecker|first=W. S.|title=6.19 – The Oceanic CaCO3 Cycle|date=2003|url=http://www.sciencedirect.com/science/article/pii/B0080437516061193|work=Treatise on Geochemistry|pages=529–549|editor-last=Holland|editor-first=Heinrich D.|publisher=Pergamon|doi=10.1016/b0-08-043751-6/06119-3|isbn=9780080437514|access-date=2019-10-17|editor2-last=Turekian|editor2-first=Karl K.|url-access=subscription}}</ref>

CaCO<sub>3</sub> content in sediment varies with different depths of the ocean, spanned by levels of separation known as the transition zone. In the mid-depth area of the ocean, sediments are rich in CaCO<sub>3</sub>, content values reaching 85–95%.<ref name=":02" /> This area is then spanned hundreds of meters by the transition zone, ending in the abyssal depths with 0% concentration. The lysocline is the upper bound of the transition zone, where amounts of CaCO<sub>3</sub> content begins to noticeably drop from the mid-depth 85–95% sediment. The CaCO<sub>3</sub> content drops to 0% [[concentration]] at the lower bound, known as the calcite compensation depth.<ref name=":02" />

Shallow marine waters are generally [[Supersaturation|supersaturated]] in calcite, CaCO<sub>3</sub>, because as [[Marine life|marine organisms]] (which often have shells made of calcite or its polymorph, [[aragonite]]) die, they tend to fall downwards without dissolving.<ref>{{Cite journal|last=Shiraiwa|first=Y.|date=2003|title=Physiological regulation of carbon fixation in the photosynthesis and calcification of coccolithophorids|journal=Comparative Biochemistry and Physiology Part B: Biochemistry and Molecular Biology|volume=136|issue=4|pages=775–783|doi=10.1016/S1096-4959(03)00221-5|pmid=14662302|issn=1096-4959}}</ref> As depth and pressure increases within the [[water column]], calcite solubility increases, causing supersaturated water above the saturation depth, allowing for preservation and burial of CaCO<sub>3</sub> on the seafloor.<ref name=":1">{{Cite journal|last1=Sigman|first1=D. M.|last2=Boyle|first2=E. A.|date=2000|title=Glacial/interglacial variations in atmospheric carbon dioxide|journal=Nature|language=en|volume=407|issue=6806|pages=859–869|doi=10.1038/35038000|pmid=11057657|bibcode=2000Natur.407..859S|s2cid=7136822|issn=1476-4687}}</ref> However, this creates undersaturated seawater below the saturation depth, preventing CaCO<sub>3</sub> burial on the [[Seabed|sea floor]] as the shells start to dissolve.

The equation Ω = [Ca<sup>2+</sup>] X [CO<sub>3</sub><sup>2-</sup>]/K'<sub>sp</sub> expresses the CaCO<sub>3</sub> saturation state of seawater.<ref name=":2">{{Cite journal|last=Zeebe|first=R. E.|date=2012|title=History of Seawater Carbonate Chemistry, Atmospheric CO2, and Ocean Acidification|journal=Annual Review of Earth and Planetary Sciences|volume=40|issue=1|pages=141–165|doi=10.1146/annurev-earth-042711-105521|bibcode=2012AREPS..40..141Z|s2cid=18682623|issn=0084-6597}}</ref> The calcite saturation horizon is where Ω =1; dissolution proceeds slowly below this depth. The lysocline is the depth that this dissolution impacts is again notable, also known as the inflection point with sedimentary CaCO<sub>3</sub> versus various water depths.<ref name=":2" />

== Calcite compensation depth ==
The [[Carbonate compensation depth|calcite compensation depth]] (CCD) occurs at the depth that the rate of calcite to the sediments is balanced with the dissolution flux, the depth at which the CaCO<sub>3</sub> content are values 2–10%.<ref name=":2" />  Hence, the lysocline and CCD are not equivalent. The lysocline and compensation depth occur at greater depths in the [[Atlantic Ocean|Atlantic]] (5000–6000 m) than in the [[Pacific Ocean|Pacific]] (4000–5000 m), and at greater depths in [[Tropics|equatorial regions]] than in [[Polar regions of Earth|polar regions]].<ref>{{Cite journal|last1=Volat|first1=J. L.|last2=Pastouret|first2=L.|last3=V. G.|first3=Colette|date=1980|title=Dissolution and carbonate fluctuations in Pleistocene deep-sea cores: A review|journal=Marine Geology|volume=34|issue=1|pages=1–28|doi=10.1016/0025-3227(80)90138-3|bibcode=1980MGeol..34....1V|issn=0025-3227}}</ref>

The depth of the CCD varies as a function of the chemical composition of the seawater and its temperature.<ref>{{Cite journal|last=Broecker|first=W. S.|date=2009|title=Wally's Quest to Understand the Ocean's CaCO3 Cycle|journal=Annual Review of Marine Science|volume=1|issue=1|pages=1–18|doi=10.1146/annurev.marine.010908.163936|pmid=21141027|bibcode=2009ARMS....1....1B|s2cid=45348785|issn=1941-1405}}</ref> Specifically, it is the deep waters that are undersaturated with [[calcium carbonate]] primarily because its solubility increases strongly with increasing pressure and [[salinity]] and decreasing temperature. As the atmospheric concentration of [[carbon dioxide]] continues to increase, the CCD can be expected to decrease in depth, as the ocean's acidity rises.<ref name=":1" />

==See also==
* [[Biological pump]]
* [[Carbonate compensation depth]]
* [[Ocean acidification]]

==References==
{{Reflist}}

[[Category:Geochemistry]]
[[Category:Oceanography]]