Editing Tritium (section)

== Use as an oceanic transient tracer ==
Aside from [[chlorofluorocarbon]]s, tritium can act as a transient tracer and can "outline" the biological, chemical, and physical paths throughout the world's oceans because of its evolving distribution.<ref name="Oceanus">
{{cite report
 |last1=Jenkins |first1=William J. |display-authors=etal
 |year=1996
 |article=Transient Tracers Track Ocean Climate Signals
 |title=Oceanus
 |publisher=Woods Hole Oceanographic Institution
 |url=http://www.whoi.edu/oceanus/viewArticle.do?id=2330
}}
</ref> Tritium has thus been used as a tool to examine ocean circulation and ventilation and, for such purposes, is usually measured in tritium units, where 1&nbsp;TU is defined as 1 tritium atom per 10{{sup|18}} hydrogen atoms,<ref name="Oceanus" /> equal to about 0.118 Bq/liter.<ref>
{{cite journal
 |first1=David A. |last1=Stonestrom  |display-authors=etal
 |date=2013
 |title=On the conversion of tritium units to mass fractions for hydrologic applications
 |journal=Isotopes Environ Health Stud
 |volume=9 |number=2 |pages=250–256
 |doi=10.1080/10256016.2013.766610  |pmid=23464868 |pmc=3664909
|bibcode=2013IEHS...49..250S }}
</ref><ref name="Eawag_3H">{{cite web | last1=Swiss Federal Institute of Aquatic Science and Technology | first1=Department Water Resources and Drinking Water | title=Tritium (<sup>3</sup>H) | website=Eawag | url=https://www.eawag.ch/en/department/wut/main-focus/environmental-isotopes/tritium-h3/ | access-date=2024-11-09}}</ref><ref name="Phillips2014">{{cite book |last1=Phillips |first1=F. M. |last2=Castro |first2=M. C. |title=Treatise on Geochemistry |date=1 January 2014 |publisher=Elsevier |isbn=978-0-08-098300-4 |pages=361–400 |url=https://doi.org/10.1016/B978-0-08-095975-7.00513-1 |language=en |chapter=7.11 – Groundwater Dating and Residence-Time Measurements|edition=Second |doi=10.1016/B978-0-08-095975-7.00513-1 }}</ref> As noted earlier, nuclear tests, mainly in the Northern Hemisphere at high latitudes, throughout the late 1950s and early 1960s introduced lots of tritium into the atmosphere, especially the [[stratosphere]]. Before these nuclear tests, there were only about 3-4 kg of tritium on the Earth's surface; but these amounts rose by 2-3 orders of magnitude during the post-test period.<ref name="Oceanus"/> Some sources reported natural background levels were exceeded by about 1,000&nbsp;TU in 1963 and 1964 and the isotope is used in the northern hemisphere to estimate the age of groundwater and construct hydrogeologic simulation models.<ref>
{{cite book
 |editor-last=Maidment |editor-first=David R.
 |year=1993
 |title=Handbook of Hydrology   |pages=6–39
 |place=New York, NY
 |publisher=McGraw-Hill
 |isbn=0-07-039732-5
}}
</ref> Estimated atmospheric levels at the height of weapons testing to approach 1,000&nbsp;TU and pre-fallout levels of rainwater to be between 5 and 10&nbsp;TU.<ref>
{{cite report
 |last=Cossairt |first=J. Donald
 |date=September 2012
 |title=Background Levels of Tritium  |pages=2–3
 |series=Environmental Protection Note |id=No. 28
 |department=Fermilab Environmental Safety & Health Section
 |publisher=[[Fermi National Accelerator Laboratory]]
 |place=Batavia, Illinois
 |url=http://esh-docdb.fnal.gov/cgi-bin/RetrieveFile?docid=2167&filename=EP%20Note%2028%20September%202012.pdf&version=1
}}
</ref> In 1963 [[Valentia Island]] Ireland recorded 2,000&nbsp;TU in precipitation.<ref>Wunsch, Carl. (2015). Modern observational physical oceanography : understanding the global ocean. Princeton : Princeton University Press. p. 44 Figure 2.29. {{ISBN|978-0-691-15882-2}}.</ref>

=== North Atlantic Ocean ===
While in the stratosphere (post-test period), the tritium interacted with and oxidized to water molecules and was present in much of the rapidly produced rainfall, making tritium a prognostic tool for studying the evolution and structure of the [[water cycle]] as well as the ventilation and formation of water masses in the North Atlantic.<ref name="Oceanus"/>

Bomb-tritium data were used from the Transient Tracers in the Ocean (TTO) program in order to quantify the replenishment and overturning rates for deep water located in the North Atlantic.<ref name="Bomb Tritium">
{{cite journal
 |last=Doney |first=Scott C.
 |year=1992
 |title=Bomb tritium in the deep north Atlantic
 |journal=Oceanography
 |volume=5 |issue=3 |pages=169–170
 |doi=10.5670/oceanog.1992.11 |doi-access=free
}}
</ref>

Bomb-tritium also enters the deep ocean around the Antarctic.<ref name="Bomb Tritium Antarctic">
{{cite journal
 |last1=Michel    |first1=Robert
 |first2=Peter M. |last2=Williams
 |date=1973
 |title=Bomb-produced tritium in the Antarctic Ocean
 |journal=Earth and Planetary Science Letters
 |volume=20  |issue=3  |pages=381–384
 |doi=10.1016/0012-821X(73)90013-7  |bibcode=1973E&PSL..20..381M
}}
</ref> Most of the bomb tritiated water (H{{sup|3}}HO) throughout the atmosphere can enter the ocean through the following processes:
* precipitation
* vapor exchange
* river runoff
These processes make H{{sup|3}}HO a great tracer for time scales of up to a few decades.<ref name="Bomb Tritium"/>

Using the data from these processes for 1981, the 1-TU isosurface lies between 500 and 1,000&nbsp;meters deep in the [[subtropical]] regions and then extends to 1,500–2,000&nbsp;meters south of the [[Gulf Stream]] due to recirculation and ventilation in the upper portion of the Atlantic Ocean.<ref name="Oceanus"/> To the north, the isosurface deepens and reaches the floor of the [[abyssal plain]] which is directly related to the ventilation of the ocean floor over 10–20&nbsp;year time-scales.<ref name="Oceanus"/>

Also evident in the Atlantic Ocean is the tritium profile near [[Bermuda]] between the late 1960s and late 1980s. There is a downward propagation of the tritium maximum from the surface (1960s) to 400&nbsp;meters (1980s), which corresponds to a deepening rate of about 18&nbsp;meters per year.<ref name="Oceanus" /> There are also tritium increases at 1,500&nbsp;m depth in the late 1970s and 2,500&nbsp;m in the middle of the 1980s, both of which correspond to cooling events in the deep water and associated deep water ventilation.<ref name="Oceanus"/>

From a study in 1991, the tritium profile was used as a tool for studying the mixing and spreading of newly formed [[North Atlantic Deep Water]] (NADW), corresponding to tritium increases to 4&nbsp;TU.<ref name="Bomb Tritium" /> This NADW tends to spill over sills that divide the [[Norwegian Sea]] from the North Atlantic Ocean and then flows to the west and equatorward in deep boundary currents. This process was explained via the large-scale tritium distribution in the deep North Atlantic between 1981 and 1983.<ref name="Bomb Tritium" /> The sub-polar gyre tends to be freshened (ventilated) by the NADW and is directly related to the high tritium values (>1.5&nbsp;TU). Also evident was the decrease in tritium in the deep western boundary current by a factor of 10 from the [[Labrador Sea]] to the [[Tropics]], which is indicative of loss to ocean interior due to turbulent mixing and recirculation.<ref name="Bomb Tritium" />

=== Pacific and Indian oceans ===
In a 1998 study, tritium concentrations in surface seawater and atmospheric water vapor (10&nbsp;meters above the surface) were sampled at the following locations: the [[Sulu Sea]], [[Fremantle Bay]], the [[Bay of Bengal]], [[Penang Bay]], and the [[Strait of Malacca]].<ref name="Tritium">
{{cite journal
 |last1=Kakiuchi  |first1=H.
 |last2=Momoshima |first2=N.
 |last3=Okai      |first3=T.
 |last4=Maeda |first4=Y.
 |title=Tritium concentration in ocean
 |date=1999
 |journal=Journal of Radioanalytical and Nuclear Chemistry
 |volume=239  |issue=3  |page=523
 |doi=10.1007/BF02349062
 |bibcode=1999JRNC..239..523K
 |s2cid=94876087
}}
</ref> Results indicated that the tritium concentration in surface seawater was highest at the Fremantle Bay (about 0.40&nbsp;Bq/liter), which could be accredited to the mixing of runoff of freshwater from nearby lands due to large amounts found in coastal waters.<ref name="Tritium" /> Typically, lower concentrations were found between [[35th parallel south|35]] and [[45th parallel south|45]]° south, and near the [[equator]]. Results also indicated that (in general) tritium has decreased over the years (up to 1997) due to the physical decay of bomb tritium in the [[Indian Ocean]]. As for water vapor, the tritium concentration was about one order of magnitude greater than surface seawater concentrations (ranging from 0.46 to 1.15&nbsp;Bq/L).<ref name="Tritium"/> Therefore, the water vapor tritium is not affected by the surface seawater concentration; thus, the high tritium concentrations in the vapor were concluded to be a direct consequence of the downward movement of natural tritium from the stratosphere to the troposphere (therefore, the ocean air showed a dependence on latitudinal change).<ref name="Tritium" />

In the [[North Pacific Ocean]], the tritium (introduced as bomb tritium in the Northern Hemisphere) spread in three dimensions. There were subsurface maxima in the middle and low latitude regions, which is indicative of lateral mixing (advection) and [[diffusion]] processes along lines of constant [[potential density]] ([[isopycnal]]s) in the upper ocean.<ref name="Circulation">
{{cite journal
 |last1=Fine    |first1=Rana A.
 |last2=Reid    |first2=Joseph L.
 |last3=Östlund |first3=H. Göte
 |year=1981
 |title=Circulation of Tritium in the Pacific Ocean
 |journal=Journal of Physical Oceanography
 |volume=11|issue=1|pages=3–14
 |doi=10.1175/1520-0485(1981)011<0003:COTITP>2.0.CO;2
 |bibcode = 1981JPO....11....3F
 |doi-access=free
}}
</ref> Some of these maxima even correlate well with [[salinity]] extrema.<ref name="Circulation" /> In order to obtain the structure for ocean circulation, the tritium concentrations were mapped on 3 surfaces of constant potential density (23.90, 26.02, and 26.81).<ref name="Circulation" /> Results indicated that the tritium was well-mixed (at 6 to 7&nbsp;TU) on the 26.81 isopycnal in the subarctic cyclonic gyre and there appeared to be a slow exchange of tritium (relative to shallower isopycnals) between this gyre and the anticyclonic gyre to the south; also, the tritium on the 23.90 and 26.02 surfaces appeared to be exchanged at a slower rate between the central gyre of the North Pacific and the equatorial regions.<ref name="Circulation" />

The depth penetration of bomb tritium can be separated into three distinct layers:
; Layer 1 : ''Layer 1'' is the shallowest layer and includes the deepest, ventilated layer in winter; it has received tritium via radioactive fallout and lost some due to advection and/or vertical diffusion and contains about 28% of the total amount of tritium.<ref name="Circulation" />
; Layer 2 : ''Layer 2'' is below the first layer but above the 26.81 [[isopycnal]] and is no longer part of the mixed layer. Its two sources are diffusion downward from the mixed layer and lateral expansions outcropping strata (poleward); it contains about 58% of the total tritium.<ref name="Circulation" />
; Layer 3 : ''Layer 3'' is representative of waters that are deeper than the outcrop isopycnal and can only receive tritium via vertical diffusion; it contains the remaining 14% of the total tritium.<ref name="Circulation" />

=== Mississippi River system ===
Trace amounts of radioactive materials from atomic weapons testing settled throughout the [[Mississippi River System]]. Tritium concentrations have been used to understand the [[residence time]]s of continental hydrologic systems such as lakes, streams, and rivers.<ref name="Mississippi">
{{cite journal
 |last1=Michel  |first1=Robert L.
 |year=2004
 |title=Tritium hydrology of the Mississippi River basin
 |journal=Hydrological Processes
 |volume=18  |issue=7  |page=1255
 |doi=10.1002/hyp.1403  |bibcode = 2004HyPr...18.1255M
 |s2cid=130033605
 |url=https://zenodo.org/record/1229196
}}
</ref> 
In a 2004 study, several rivers were taken into account during the examination of tritium concentrations (starting in the 1960s) throughout the Mississippi River Basin: [[Ohio River]] (largest input to the Mississippi River flow), [[Missouri River]], and [[Arkansas River]].<ref name="Mississippi" /> The highest tritium concentrations were found in 1963 across locations throughout these rivers.  The peak correlates with implementation of the US & Soviet atmospheric test ban treaty in 1962. The overall highest concentrations occurred in the Missouri River (1963) and were greater than 1,200&nbsp;TU while the lowest concentrations were found in the Arkansas River (never greater than 850&nbsp;TU and less than 10&nbsp;TU in the mid-1980s).<ref name="Mississippi" />

As for the mass flux of tritium through the main stem of the Mississippi River into the [[Gulf of Mexico]], data indicated that approximately 780&nbsp;grams of tritium has flowed out of the River and into the Gulf between 1961 and 1997,<ref name="Mississippi"/> an average of 21.7&nbsp;grams/yr and 7.7&nbsp;PBq/yr. Current fluxes through the Mississippi River are 1 to 2 grams, per year as opposed to the pre-bomb period fluxes of roughly 0.4&nbsp;grams per year.<ref name="Mississippi" />