In the deep ocean,
marine snow is a continuous shower of mostly organic
detritusDetritus is a biological term used to describe dead or waste organic material.Detritus may also refer to:* Detritus , a geological term used to describe the particles of rock produced by weathering...
falling from the upper layers of the water column. Its origin lies in activities within the productive
photic zoneThe photic zone or euphotic zone is the depth of the water in a lake or ocean, that is exposed to sufficient sunlight for photosynthesis to occur...
. Consequently, the prevalence of marine snow changes with seasonal fluctuations in
photosyntheticPhotosynthesis is a process that converts carbon dioxide into organic compounds, especially sugars, using the energy from sunlight. Photosynthesis occurs in plants, algae, and many species of Bacteria, but not in Archaea...
activity and ocean currents. Thus marine snow is heavier in spring, and the reproductive cycles of some deep-sea animals are synchronized to take advantage of this.
Marine snow has a composition which includes: dead or dying animals and plants (
planktonPlankton consist of any drifting organisms that inhabit the pelagic zone of oceans, seas, or bodies of fresh water. Plankton are defined by their ecological niche rather than their phylogenetic or taxonomic classification...
),
protistProtists , are a diverse group of eukaryotic microorganisms. Historically, protists were treated as the kingdom Protista but this group is no longer recognized in modern taxonomy...
s (
diatomDiatoms are a major group of eukaryotic algae, and are one of the most common types of phytoplankton. Most diatoms are unicellular, although they can exist as colonies in the shape of filaments or ribbons Diatoms (Greek: (dia) = "through" + (temnein) = "to cut", i.e., "cut in half") are a major...
s), fecal matter, sand, soot and other inorganic dust.
In the deep ocean,
marine snow is a continuous shower of mostly organic
detritusDetritus is a biological term used to describe dead or waste organic material.Detritus may also refer to:* Detritus , a geological term used to describe the particles of rock produced by weathering...
falling from the upper layers of the water column. Its origin lies in activities within the productive
photic zoneThe photic zone or euphotic zone is the depth of the water in a lake or ocean, that is exposed to sufficient sunlight for photosynthesis to occur...
. Consequently, the prevalence of marine snow changes with seasonal fluctuations in
photosyntheticPhotosynthesis is a process that converts carbon dioxide into organic compounds, especially sugars, using the energy from sunlight. Photosynthesis occurs in plants, algae, and many species of Bacteria, but not in Archaea...
activity and ocean currents. Thus marine snow is heavier in spring, and the reproductive cycles of some deep-sea animals are synchronized to take advantage of this.
Marine snow has a composition which includes: dead or dying animals and plants (
planktonPlankton consist of any drifting organisms that inhabit the pelagic zone of oceans, seas, or bodies of fresh water. Plankton are defined by their ecological niche rather than their phylogenetic or taxonomic classification...
),
protistProtists , are a diverse group of eukaryotic microorganisms. Historically, protists were treated as the kingdom Protista but this group is no longer recognized in modern taxonomy...
s (
diatomDiatoms are a major group of eukaryotic algae, and are one of the most common types of phytoplankton. Most diatoms are unicellular, although they can exist as colonies in the shape of filaments or ribbons Diatoms (Greek: (dia) = "through" + (temnein) = "to cut", i.e., "cut in half") are a major...
s), fecal matter, sand, soot and other inorganic dust. The "snowflakes" (which are more like clumps or strings) are aggregates of smaller particles held together by a sugary mucus, transparent
exopolymerAn exopolymer is a biopolymer that is secreted by an organism into the environment . These exopolymers include the biofilms produced by bacteria to anchor them and protect them from environmental conditions....
particles (TEPs); natural
polymerA polymer is a large molecule composed of repeating structural units typically connected by covalent chemical bonds. While polymer in popular usage suggests plastic, the term actually refers to a large class of natural and synthetic materials with a variety of properties.Due to the extraordinary...
s exuded as waste products by bacteria and
phytoplanktonPhytoplankton are the autotrophic component of the plankton community. The name comes from the Greek words φυτον , or "plant", and πλαγκτος , meaning "wanderer" or "drifter". Most phytoplankton are too small to be individually seen with the unaided eye...
. These aggregates grow over time and may reach several centimetres in diameter, travelling for weeks before reaching the ocean floor.
However, most organic components of marine snow are consumed by microbes,
zooplanktonZooplankton are the heterotrophic type of plankton. Plankton are organisms drifting in the water column of oceans, seas, and bodies of fresh water. The name of zooplankton is derived from the Greek zoon , meaning "animal", and , meaning "wanderer" or "drifter"...
and other filter-feeding animals within the first 1,000 metres of their journey. In this way marine snow may be considered the foundation of deep-sea
mesopelagicThe mesopelagic is a pelagic zone extending from 200 m down to around 1000 m below sea level. It is located between the photic epipelagic and the aphotic bathypelagic, where there is no light at all. Although some light penetrates this deep, it is insufficient for photosynthesis...
and benthic
ecosystemAn ecosystem is a system of interdependent organisms which share the same habitat, in an area functioning together with all of the physical factors of the environment. Ecosystems can be permanent or temporary. Ecosystems usually form a number of food webs...
s: As sunlight cannot reach them, deep-sea organisms rely heavily on marine snow as an energy source. The small percentage of material not consumed in shallower waters becomes incorporated into the muddy "ooze" blanketing the ocean floor, where it is further decomposed through biological activity.
Study
Export production is the amount of organic matter produced in the
oceanAn ocean is a large body of saline water, and a principal component of the hydrosphere. Approximately 75% 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...
by
primary production400px|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...
that is not recycled (
remineralisedIn biogeochemistry, remineralisation refers to the transformation of organic molecules to inorganic forms, typically mediated by biological activity....
) before it sinks into the
aphotic zoneThe aphotic zone is the portion of a lake or ocean where there is little or no sunlight. It is formally defined as the depths beyond which less than 1% of sunlight penetrates. Consequently, bioluminescence is essentially the only light found in this zone...
. Because of the role of export production in the ocean's
biological pumpIn oceanic biogeochemistry, the biological pump is the sum of a suite of biologically-mediated processes that transport carbon from the surface euphotic zone to the ocean's interior.-Overview:...
, it is typically measured in units of
carbonCarbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...
(e.g. mg C
m-2The square metre is the SI derived unit of area, with symbol m2. It is defined as the area of a square whose sides measure exactly one metre...
d-1A day is a unit of time equivalent to approximately 24 hours. It is not an SI unit but it is accepted for use with SI. The SI unit of time is the second....
).
The fraction of primary production that is exported to the aphotic zone is generally higher when primary production occurs in short (seasonal) bursts, than when it occurs more evenly spread out across a year.
Because of the relatively long residence time of the ocean's
thermohaline circulationThe term thermohaline circulation refers to the part of the large-scale ocean circulation that is driven by global density gradients created by surface heat and freshwater fluxes....
, carbon transported as marine snow into the deep ocean by the
biological pumpIn oceanic biogeochemistry, the biological pump is the sum of a suite of biologically-mediated processes that transport carbon from the surface euphotic zone to the ocean's interior.-Overview:...
can remain out of contact with the atmosphere for more than 1000 years. That is, when the marine snow is finally decomposed to inorganic nutrients and dissolved
carbon dioxideCarbon dioxide is a chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom. It is a gas at standard temperature and pressure and exists in Earth's atmosphere in this state...
, these are effectively isolated from the surface ocean for relatively long time-scales related to ocean circulation. Consequently, enhancing the quantity of marine snow that reaches the deep ocean is the basis of several
geoengineeringThe modern concept of geoengineering is usually taken to mean proposals to deliberately manipulate the Earth's climate to counteract the effects of global warming from greenhouse gas emissions...
schemes to enhance carbon sequestration by the ocean.
Ocean nourishmentOcean Nourishment is a type of geoengineering based on the purposeful introduction of nutrients to the upper ocean to increase the marine food chain and to sequester carbon dioxide from the atmosphere. Fertilization also creates stratospheric sulfur aerosols and can therefore be used for Solar...
and iron fertilisation seek to boost the production of organic material in the surface ocean, with a concomitant rise in marine snow reaching the deep ocean.
Projected increases in ocean temperatures caused by
global warmingGlobal warming is the increase in the average temperature of the Earth's near-surface air and oceans since the mid-20th century and its projected continuation. Global surface temperature increased 0.74 ± 0.18 °C during the last century...
may result in a decrease in the production of marine snow via the enhanced stratification of the water column. Increasing stratification decreases the availability of phytoplankton nutrients such as
nitrateIn inorganic chemistry, a nitrate is a salt of nitric acid with an ion composed of one nitrogen and three oxygen atoms . In organic chemistry the esters of nitric acid and various alcohols are called nitrates.-Chemical properties:...
,
phosphateA phosphate, an inorganic chemical, is a salt of phosphoric acid. In organic chemistry, a phosphate, or organophosphate, is an ester of phosphoric acid. Organic phosphates are important in biochemistry and biogeochemistry or ecology. Inorganic phosphates are mined to obtain phosphorus for use in...
and
silicic acidSilicic acid is a general name for a family of chemical compounds of the element silicon, hydrogen, and oxygen, with the general formula [SiOx4-2x]n...
, and could lead to a decrease in primary production and, thus, marine snow.
Marine snow has also begun to garner interest from
microbiologistsMicrobiology is the study of microorganisms, which are unicellular or cell-cluster microscopic organisms. This includes eukaryotes such as fungi and protists, and prokaryotes. Viruses, though not strictly classed as living organisms, are also studied...
, owing to the microbial communities associated with it. Recent research indicates transported bacteria may exchange
geneA gene is the basic unit of heredity in a living organism. All living things depend on genes. Genes hold the information to build and maintain their cells and pass genetic traits to offspring...
s with previously thought to be isolated populations of bacteria inhabiting the breadth of the ocean floor. In such an immense area there may be as yet undiscovered species tolerant of high pressures and extreme cold, perhaps finding use in bioengineering and
pharmacyPharmacy is the health profession that links the health sciences with the chemical sciences, and it is charged with ensuring the safe and effective use of medication....
.
See also
- Biological pump
In oceanic biogeochemistry, the biological pump is the sum of a suite of biologically-mediated processes that transport carbon from the surface euphotic zone to the ocean's interior.-Overview:...
- Detritivore
Detritivores, also known as detritus feeders or saprophages, are heterotrophs that obtain nutrients by consuming detritus . By doing so, they contribute to decomposition and the nutrient cycles....
- f-ratio
In oceanic biogeochemistry, the f-ratio is the fraction of total primary production fuelled by nitrate . This fraction is significant because it is assumed to be directly related to the sinking flux of organic marine snow from the surface ocean by the biological pump...
- Marine mucilage
Marine mucilage is a collection of mucus-like organic matter found in the sea. It is formed from the aggregation of "marine snow". The mucilage has many components, including a wide range of microorganisms including viruses and prokaryotes, and exopolymeric compounds with colloidal properties....
- Sediment trap
Sediment traps are instruments used in oceanography to measure the quantity of sinking particulate organic material in aquatic systems, usually oceans...
- Whale fall
Whale fall is the term used for a whale carcass that has fallen to the ocean floor. Whale falls were first observed in the 1980s, with the advent of deep-sea robotic exploration....
External links