Lysocline
Encyclopedia
The lysocline is a term used in geology
, geochemistry
and marine biology
to denote the depth in the ocean
below which the rate of dissolution of calcite
increases dramatically.
Shallow marine waters are generally supersaturated in calcite, CaCO3, so as marine organism
s (which often have shells made of calcite or its polymorph
, aragonite
) die, they will tend to fall downwards without dissolving. As depth (i.e. pressure) increases within the water column, the corresponding calcite saturation of seawater
decreases and the shells start to dissolve. The reaction involved, though more complex, can be thought as: CaCO3(s) + H2O + CO2 → Ca2+(aq) + 2HCO3-(aq). At the lysocline, the rate of dissolution increases dramatically. Below this, there exists a depth known as the carbonate compensation depth
(CCD) below which the rate of supply of calcite equals the rate of dissolution, such that no calcite is deposited. This depth is the equivalent of a marine snow-line, and averages about 4,500 meters below sea level
. Hence, the two are not equivalent. The lysocline and compensation depth occur at greater depths in the Atlantic (5000-6000 m) than in the Pacific (4000 - 5000 m), and at greater depths in equatorial regions than in polar regions.
The depth of the CCD varies as a function of the chemical composition of the seawater and its temperature. 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. Furthermore, it is not constant over time, having been globally much shallower in the Cretaceous
through to Eocene
. If the atmospheric concentration of carbon dioxide
continues to increase, the CCD can be expected to rise, along with the ocean's acidity.
Geology
Geology is the science comprising the study of solid Earth, the rocks of which it is composed, and the processes by which it evolves. Geology gives insight into the history of the Earth, as it provides the primary evidence for plate tectonics, the evolutionary history of life, and past climates...
, geochemistry
Geochemistry
The field of geochemistry involves study of the chemical composition of the Earth and other planets, chemical processes and reactions that govern the composition of rocks, water, and soils, and the cycles of matter and energy that transport the Earth's chemical components in time and space, and...
and marine biology
Marine biology
Marine biology is the scientific study of organisms in the ocean or other marine or brackish bodies of water. Given that in biology many phyla, families and genera have some species that live in the sea and others that live on land, marine biology classifies species based on the environment rather...
to denote the depth in the ocean
Ocean
An ocean is a major body of saline water, and a principal component of the hydrosphere. Approximately 71% of the Earth's surface is covered by ocean, a continuous body of water that is customarily divided into several principal oceans and smaller seas.More than half of this area is over 3,000...
below which the rate of dissolution of calcite
Calcite
Calcite is a carbonate mineral and the most stable polymorph of calcium carbonate . The other polymorphs are the minerals aragonite and vaterite. Aragonite will change to calcite at 380-470°C, and vaterite is even less stable.-Properties:...
increases dramatically.
Shallow marine waters are generally supersaturated in calcite, CaCO3, so as marine organism
Organism
In biology, an organism is any contiguous living system . In at least some form, all organisms are capable of response to stimuli, reproduction, growth and development, and maintenance of homoeostasis as a stable whole.An organism may either be unicellular or, as in the case of humans, comprise...
s (which often have shells made of calcite or its polymorph
Polymorphism (materials science)
Polymorphism in materials science is the ability of a solid material to exist in more than one form or crystal structure. Polymorphism can potentially be found in any crystalline material including polymers, minerals, and metals, and is related to allotropy, which refers to chemical elements...
, aragonite
Aragonite
Aragonite is a carbonate mineral, one of the two common, naturally occurring, crystal forms of calcium carbonate, CaCO3...
) die, they will tend to fall downwards without dissolving. As depth (i.e. pressure) increases within the water column, the corresponding calcite saturation of seawater
Seawater
Seawater is water from a sea or ocean. On average, seawater in the world's oceans has a salinity of about 3.5% . This means that every kilogram of seawater has approximately of dissolved salts . The average density of seawater at the ocean surface is 1.025 g/ml...
decreases and the shells start to dissolve. The reaction involved, though more complex, can be thought as: CaCO3(s) + H2O + CO2 → Ca2+(aq) + 2HCO3-(aq). At the lysocline, the rate of dissolution increases dramatically. Below this, there exists a depth known as the carbonate compensation depth
Carbonate Compensation Depth
Calcite compensation depth is the depth in the oceans below which the rate of supply of calcite lags behind the rate of solvation, such that no calcite is preserved. Aragonite compensation depth describes the same behaviour in reference to aragonitic carbonates.Calcium carbonate is essentially...
(CCD) below which the rate of supply of calcite equals the rate of dissolution, such that no calcite is deposited. This depth is the equivalent of a marine snow-line, and averages about 4,500 meters below sea level
Sea level
Mean sea level is a measure of the average height of the ocean's surface ; used as a standard in reckoning land elevation...
. Hence, the two are not equivalent. The lysocline and compensation depth occur at greater depths in the Atlantic (5000-6000 m) than in the Pacific (4000 - 5000 m), and at greater depths in equatorial regions than in polar regions.
The depth of the CCD varies as a function of the chemical composition of the seawater and its temperature. 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. Furthermore, it is not constant over time, having been globally much shallower in the Cretaceous
Cretaceous
The Cretaceous , derived from the Latin "creta" , usually abbreviated K for its German translation Kreide , is a geologic period and system from circa to million years ago. In the geologic timescale, the Cretaceous follows the Jurassic period and is followed by the Paleogene period of the...
through to Eocene
Eocene
The Eocene Epoch, lasting from about 56 to 34 million years ago , is a major division of the geologic timescale and the second epoch of the Paleogene Period in the Cenozoic Era. The Eocene spans the time from the end of the Palaeocene Epoch to the beginning of the Oligocene Epoch. The start of the...
. If the atmospheric concentration of carbon dioxide
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...
continues to increase, the CCD can be expected to rise, along with the ocean's acidity.