Hypolith
Encyclopedia
In Arctic
and Antarctic
ecology
, a hypolith is a photosynthetic organism
that lives
underneath rocks
in climatically
extreme desert
s such as Cornwallis Island
and Devon Island
in the Canadian high Arctic. The community itself is the hypolithon.
Hypolithons are protected from harsh ultraviolet
radiation and wind
scouring by their rock, which can also trap moisture. The rocks are generally translucent to allow for the penetration of light
. Writing in Nature
, ecologist Charles S. Cockell
of the British Antarctic Survey
and Dale Stokes describe how hypoliths reported to date (until 2004) had been found under quartz
, which is one of the most common translucent rocks.
However, Cockell reported that on Cornwallis Island and Devon Island, 94-95% of a random sample
of 850 opaque
dolomitic
rocks were colonized by hypoliths, and found that the communities were dominated by cyanobacteria. The rocks chosen were visually indistinguishable from those nearby, and were about 10 cm across; the hypolithon was visible as a greenish coloured band. Cockell proposed that rock sorting by periglacial
action, including that during freeze–thaw cycles, improves light penetration around the edges of rocks (see granular material
and Brazil nut effect
).
Cockell and Stokes went on to estimate the productivity
of the Arctic communities by monitoring the uptake of sodium bicarbonate
labelled with Carbon-14
and found that (for Devon Island) productivity of the hypolithon was comparable to that of plant
s, lichen
s, and bryophyte
s combined (0.8 ± 0.3 g m−2 y−1 and 1 ± 0.4 g m−2 y−1 respectively) and concluded that the polar hypolithon may double previous estimates of the productivity of that region of the rocky polar desert.
Arctic
The Arctic is a region located at the northern-most part of the Earth. The Arctic consists of the Arctic Ocean and parts of Canada, Russia, Greenland, the United States, Norway, Sweden, Finland, and Iceland. The Arctic region consists of a vast, ice-covered ocean, surrounded by treeless permafrost...
and Antarctic
Antarctic
The Antarctic is the region around the Earth's South Pole, opposite the Arctic region around the North Pole. The Antarctic comprises the continent of Antarctica and the ice shelves, waters and island territories in the Southern Ocean situated south of the Antarctic Convergence...
ecology
Ecology
Ecology is the scientific study of the relations that living organisms have with respect to each other and their natural environment. Variables of interest to ecologists include the composition, distribution, amount , number, and changing states of organisms within and among ecosystems...
, a hypolith is a photosynthetic 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...
that lives
underneath rocks
Rock (geology)
In geology, rock or stone is a naturally occurring solid aggregate of minerals and/or mineraloids.The Earth's outer solid layer, the lithosphere, is made of rock. In general rocks are of three types, namely, igneous, sedimentary, and metamorphic...
in climatically
Climate
Climate encompasses the statistics of temperature, humidity, atmospheric pressure, wind, rainfall, atmospheric particle count and other meteorological elemental measurements in a given region over long periods...
extreme desert
Desert
A desert is a landscape or region that receives an extremely low amount of precipitation, less than enough to support growth of most plants. Most deserts have an average annual precipitation of less than...
s such as Cornwallis Island
Cornwallis Island
Cornwallis Island may refer to:* Cornwallis Island , Canada* Cornwallis Island , Australia* Cornwallis Island , South Shetland Islands...
and Devon Island
Devon Island
Devon Island , claimed to be the largest uninhabited island on Earth, is located in Baffin Bay, Qikiqtaaluk Region, Nunavut, Canada. It is one of the larger members of the Canadian Arctic Archipelago, the second-largest of the Queen Elizabeth Islands, Canada's sixth largest island, and the 27th...
in the Canadian high Arctic. The community itself is the hypolithon.
Hypolithons are protected from harsh ultraviolet
Ultraviolet
Ultraviolet light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than X-rays, in the range 10 nm to 400 nm, and energies from 3 eV to 124 eV...
radiation and wind
Wind
Wind is the flow of gases on a large scale. On Earth, wind consists of the bulk movement of air. In outer space, solar wind is the movement of gases or charged particles from the sun through space, while planetary wind is the outgassing of light chemical elements from a planet's atmosphere into space...
scouring by their rock, which can also trap moisture. The rocks are generally translucent to allow for the penetration of light
Light
Light or visible light is electromagnetic radiation that is visible to the human eye, and is responsible for the sense of sight. Visible light has wavelength in a range from about 380 nanometres to about 740 nm, with a frequency range of about 405 THz to 790 THz...
. Writing in Nature
Nature (journal)
Nature, first published on 4 November 1869, is ranked the world's most cited interdisciplinary scientific journal by the Science Edition of the 2010 Journal Citation Reports...
, ecologist Charles S. Cockell
Charles S. Cockell
Charles S. Cockell is Professor of Geomicrobiology with the Open University. Prior to this, he was a microbiologist with the British Antarctic Survey, Cambridge, UK...
of the British Antarctic Survey
British Antarctic Survey
The British Antarctic Survey is the United Kingdom's national Antarctic operation and has an active role in Antarctic affairs. BAS is part of the Natural Environment Research Council and has over 400 staff. It operates five research stations, two ships and five aircraft in and around Antarctica....
and Dale Stokes describe how hypoliths reported to date (until 2004) had been found under quartz
Quartz
Quartz is the second-most-abundant mineral in the Earth's continental crust, after feldspar. It is made up of a continuous framework of SiO4 silicon–oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall formula SiO2. There are many different varieties of quartz,...
, which is one of the most common translucent rocks.
However, Cockell reported that on Cornwallis Island and Devon Island, 94-95% of a random sample
Random sample
In statistics, a sample is a subject chosen from a population for investigation; a random sample is one chosen by a method involving an unpredictable component...
of 850 opaque
Opacity (optics)
Opacity is the measure of impenetrability to electromagnetic or other kinds of radiation, especially visible light. In radiative transfer, it describes the absorption and scattering of radiation in a medium, such as a plasma, dielectric, shielding material, glass, etc...
dolomitic
Dolomite
Dolomite is a carbonate mineral composed of calcium magnesium carbonate CaMg2. The term is also used to describe the sedimentary carbonate rock dolostone....
rocks were colonized by hypoliths, and found that the communities were dominated by cyanobacteria. The rocks chosen were visually indistinguishable from those nearby, and were about 10 cm across; the hypolithon was visible as a greenish coloured band. Cockell proposed that rock sorting by periglacial
Periglacial
Periglacial is an adjective originally referring to places in the edges of glacial areas, but it has later been widely used in geomorphology to describe any place where geomorphic processes related to freezing of water occur...
action, including that during freeze–thaw cycles, improves light penetration around the edges of rocks (see granular material
Granular material
A granular material is a conglomeration of discrete solid, macroscopic particles characterized by a loss of energy whenever the particles interact . The constituents that compose granular material must be large enough such that they are not subject to thermal motion fluctuations...
and Brazil nut effect
Brazil nut effect
Granular convection is a phenomenon where granular material subjected to shaking or vibration will exhibit circulation patterns similar to types of fluid convection...
).
Cockell and Stokes went on to estimate the productivity
Primary production
400px|thumb|Global oceanic and terrestrial photoautotroph abundance, from September [[1997]] to August 2000. As an estimate of autotroph biomass, it is only a rough indicator of primary production potential, and not an actual estimate of it...
of the Arctic communities by monitoring the uptake of sodium bicarbonate
Sodium bicarbonate
Sodium bicarbonate or sodium hydrogen carbonate is the chemical compound with the formula Na HCO3. Sodium bicarbonate is a white solid that is crystalline but often appears as a fine powder. It has a slightly salty, alkaline taste resembling that of washing soda . The natural mineral form is...
labelled with Carbon-14
Carbon-14
Carbon-14, 14C, or radiocarbon, is a radioactive isotope of carbon with a nucleus containing 6 protons and 8 neutrons. Its presence in organic materials is the basis of the radiocarbon dating method pioneered by Willard Libby and colleagues , to date archaeological, geological, and hydrogeological...
and found that (for Devon Island) productivity of the hypolithon was comparable to that of plant
Plant
Plants are living organisms belonging to the kingdom Plantae. Precise definitions of the kingdom vary, but as the term is used here, plants include familiar organisms such as trees, flowers, herbs, bushes, grasses, vines, ferns, mosses, and green algae. The group is also called green plants or...
s, lichen
Lichen
Lichens are composite organisms consisting of a symbiotic organism composed of a fungus with a photosynthetic partner , usually either a green alga or cyanobacterium...
s, and bryophyte
Bryophyte
Bryophyte is a traditional name used to refer to all embryophytes that do not have true vascular tissue and are therefore called 'non-vascular plants'. Some bryophytes do have specialized tissues for the transport of water; however since these do not contain lignin, they are not considered to be...
s combined (0.8 ± 0.3 g m−2 y−1 and 1 ± 0.4 g m−2 y−1 respectively) and concluded that the polar hypolithon may double previous estimates of the productivity of that region of the rocky polar desert.