A flow tracer is any fluid property used to track flow, magnitude, direction, and circulation patterns. Tracers can be chemical properties, such as

radioactive material A radionuclide (radioactive nuclide, radioisotope or radioactive isotope) is a nuclide that has excess nuclear energy, making it unstable. This excess energy can be used in one of three ways: emitted from the nucleus as gamma radiation; transfer ...

, or chemical compounds, physical properties, such as density, temperature, salinity, or dyes, and can be natural or artificially induced. Flow tracers are used in many fields, such as physics,

hydrology Hydrology () is the scientific study of the movement, distribution, and management of water on Earth and other planets, including the water cycle, water resources, and environmental watershed sustainability. A practitioner of hydrology is calle ...

limnology Limnology ( ; from Greek λίμνη, ''limne'', "lake" and λόγος, ''logos'', "knowledge") is the study of inland aquatic ecosystems. The study of limnology includes aspects of the biological, chemical, physical, and geological characteristi ...

oceanography Oceanography (), also known as oceanology and ocean science, is the scientific study of the oceans. It is an Earth science, which covers a wide range of topics, including ecosystem dynamics; ocean currents, waves, and geophysical fluid dynamic ...

, environmental studies and atmospheric studies.

Conservative Conservatism is a cultural, social, and political philosophy that seeks to promote and to preserve traditional institutions, practices, and values. The central tenets of conservatism may vary in relation to the culture and civilization i ...

tracers remain constant following fluid parcels, whereas

reactive Reactive may refer to: *Generally, capable of having a reaction (disambiguation) *An adjective abbreviation denoting a bowling ball coverstock made of reactive resin *Reactivity (chemistry) *Reactive mind *Reactive programming See also *Reactanc ...

tracers (such as compounds undergoing a mutual chemical reaction) grow or decay with time. ''Active tracers'' dynamically alter the flow of the fluid by changing fluid properties which appear in the

equation of motion In physics, equations of motion are equations that describe the behavior of a physical system in terms of its motion as a function of time.''Encyclopaedia of Physics'' (second Edition), R.G. Lerner, G.L. Trigg, VHC Publishers, 1991, ISBN (Ver ...

such as

density Density (volumetric mass density or specific mass) is the substance's mass per unit of volume. The symbol most often used for density is ''ρ'' (the lower case Greek letter rho), although the Latin letter ''D'' can also be used. Mathematical ...

viscosity The viscosity of a fluid is a measure of its resistance to deformation at a given rate. For liquids, it corresponds to the informal concept of "thickness": for example, syrup has a higher viscosity than water. Viscosity quantifies the inte ...

, while ''passive tracers'' have no influence on flow.

Uses in oceanography

Ocean tracers are used to deduce small scale flow patterns, large-scale ocean circulation, water mass formation and changes, "dating" of water masses, and carbon dioxide storage and uptake. Temperature, salinity, density, and other conservative tracers are often used to track currents, circulation and water mass mixing. An interesting example was when 28,000 plastic ducks fell over board from a container ship in the middle of the Pacific Ocean. The following twelve years oceanographers recorded where the ducks washed ashore, some thousands of miles from the spill site, and this data was used to calibrate and verify the circulation patters of the

North Pacific Gyre The North Pacific Gyre (NPG) or North Pacific Subtropical Gyre (NPSG), located in the northern Pacific Ocean, is one of the five major oceanic gyres. This gyre covers most of the northern Pacific Ocean. It is the largest ecosystem on Earth, locate ...

. Transient tracers change over time, such as radioactive material (

Tritium Tritium ( or , ) or hydrogen-3 (symbol T or H) is a rare and radioactive isotope of hydrogen with half-life about 12 years. The nucleus of tritium (t, sometimes called a ''triton'') contains one proton and two neutrons, whereas the nucleus o ...

and

Cesium-137 Caesium-137 (), cesium-137 (US), or radiocaesium, is a radioactive isotope of caesium that is formed as one of the more common fission products by the nuclear fission of uranium-235 and other fissionable isotopes in nuclear reactors and nuclea ...

) and chemical concentrations (

CFCs Chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs) are fully or partly halogenated hydrocarbons that contain carbon (C), hydrogen (H), chlorine (Cl), and fluorine (F), produced as volatile derivatives of methane, ethane, and propan ...

and

SF6 Sulfur hexafluoride or sulphur hexafluoride (British spelling) is an inorganic compound with the formula SF6. It is a colorless, odorless, non-flammable, and non-toxic gas. has an octahedral geometry, consisting of six fluorine atoms attached ...

), which are used to date water masses and can also track mixing. In the mid-1900s,

Nuclear weapons testing Nuclear weapons tests are experiments carried out to determine nuclear weapons' effectiveness, Nuclear weapon yield, yield, and explosive capability. Testing nuclear weapons offers practical information about how the weapons function, how detona ...

and chemical production released tons of compounds that are not naturally found in the environment. While extremely unfortunate, scientists were able to use the concentrations of anthropogenic compounds and

half-lives Half-life (symbol ) is the time required for a quantity (of substance) to reduce to half of its initial value. The term is commonly used in nuclear physics to describe how quickly unstable atoms undergo radioactive decay or how long stable at ...

of radioactive material to determine how old a water body is. The

Fukushima nuclear disaster The was a nuclear accident in 2011 at the Fukushima Daiichi Nuclear Power Plant in Ōkuma, Fukushima, Japan. The proximate cause of the disaster was the 2011 Tōhoku earthquake and tsunami, which occurred on the afternoon of 11 March 2011 and ...

was really well studied by oceanographers, who tracked the radioactive material spread throughout the Pacific Ocean, and used that to better understand ocean currents and mixing patterns. Biological tracers can also be used to track water masses in the ocean.

Phytoplankton Phytoplankton () are the autotrophic (self-feeding) components of the plankton community and a key part of ocean and freshwater ecosystems. The name comes from the Greek words (), meaning 'plant', and (), meaning 'wanderer' or 'drifter'. Ph ...

blooms can be seen by satellites and move with the changing currents. They can be used as a "check point" to see how well water masses are mixing. Subtropical water is often warm, which is ideal for phytoplankton, but

nutrient A nutrient is a substance used by an organism to survive, grow, and reproduce. The requirement for dietary nutrient intake applies to animals, plants, fungi, and protists. Nutrients can be incorporated into cells for metabolic purposes or excret ...

poor, which inhibits their growth, while subpolar water is cold and nutrient rich. When these two types of water masses mix, such as the

Kuroshio Current The , also known as the Black or or the is a north-flowing, warm ocean current on the west side of the North Pacific Ocean basin. It was named for the deep blue appearance of its waters. Similar to the Gulf Stream in the North Atlantic, the Ku ...

in the north Pacific, it often causes huge phytoplankton blooms, because they now how conditions they need to grow—warm temperatures and high nutrients. Vertical mixing and eddy formation can also cause phytoplankton blooms, and these blooms are tracked by satellites to observe current patterns and mixing.

References

*{{cite journal , journal= Annual Review of Fluid Mechanics , volume= 23 , pages= 43–64 , year= 1991 , doi= 10.1146/annurev.fl.23.010191.000355 , title=Lagrangian Ocean Studies , author= R. E. Davis , bibcode = 1991AnRFM..23...43D

External links

ctraj
Library of advection codes, including passive tracer modelling.
Fluid dynamics Data collection Oceanography