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Feature Bulletin of the Atomic 2015, Vol. 71(3) 46–57 ! The Author(s) 2015 Reprints and permissions: Can nuclear weapons fallout sagepub.co.uk/journalsPermissions.nav DOI: 10.1177/0096340215581357 mark the beginning of the http://thebulletin.sagepub.com Anthropocene Epoch?

Colin N. Waters, James P. M. Syvitski, Agnieszka Gałuszka, Gary J. Hancock, Jan Zalasiewicz, Alejandro Cearreta, Jacques Grinevald, Catherine Jeandel, J. R. McNeill, Colin Summerhayes, and Anthony Barnosky

Abstract Many scientists are making the case that humanity is living in a new geological epoch, the Anthropocene, but there is no agreement yet as to when this epoch began. The start might be defined by a historical event, such as the beginning of the fossil-fueled Industrial Revolution or the first nuclear in 1945. Standard strati- graphic practice, however, requires a more significant, globally widespread, and abrupt signature, and the fallout from appears most suitable. The appearance of 239 (used in post- 1945 above-ground nuclear weapons tests) makes a good marker: This isotope is rare in nature but a significant component of fallout. It has other features to recommend it as a stable marker in layers of sedimentary rock and soil, including: long half-life, low solubility, and high particle reactivity. It may be used in conjunction with other radioactive isotopes, such as 241 and carbon 14, to categorize distinct fallout signatures in sediments and ice caps. On a global scale, the first appearance of plutonium 239 in sedimentary sequences corresponds to the early 1950s. While plutonium is easily detectable over the entire Earth using modern meas- urement techniques, a site to define the Anthropocene (known as a Ògolden spikeÓ) would ideally be located between 30 and 60 degrees north of the equator, where fallout is maximal, within undisturbed marine or lake environments.

Keywords Anthropocene, golden spike, nuclear weapons fallout, radioactive isotope, radiogenic signature, test

eventy years agoÑat 5:30 a.m. on flash of light and heat, and a roaring shock July 16, 1945Ñthe worldÕs first wave that took 40 seconds to reach the S nuclear device exploded at the closest observers, a fireball rose into the Trinity Test Site in what was then the sky, forming a mushroom 7.5 miles Alamogordo Bombing and Gunnery high. J. Robert Oppenheimer later wrote Range in . After an intense that he and other Waters et al. 47 scientists who had gathered to watch the Industrial Revolution, or some other test Òknew the world would not be the major shift that left its mark on the geo- same.Ó The Ònuclear ageÓ had begun logical record. One recent paper argues (Ackland and McGuire, 1986; Eby et al., for either 1610 (when atmospheric 2010; Groves, 1962). carbon dioxide levels dipped after the Arguably, Trinity was also the begin- arrival of Europeans brought death to ning of something even bigger: a new about 50 million native people in the geological epoch (Zalasiewicz et al., Americas) or 1964 (based on peak 2015). Human activities have had such a carbon 14 fallout signatures) as potential great impact upon the Earth that many kickoff dates (Lewis and Maslin, 2015). researchers suggest we are no longer But if geoscientists want to establish a living in the Holocene Epoch (a term starting point for the Anthropocene, Tri- describing the most recent slice of geo- nity and the nuclear bombings and tests logical time that literally means Òentirely that followed it from 1945 to the early newÓ), but instead within a brand-new 1960s created an extremely distinctive time unit: the Anthropocene, from the radiogenic signatureÑa unique pattern Greek words for ÒhumanÓ and Ònew.Ó of radioactive isotopes captured in the Since 2009, a small group of us, com- layers of the planetÕs marine and lake posed of geoscientists and other experts sediments, rock, and glacial ice that can from across the globe, have assembled to serve as a clear, easily detected book- develop a proposal for this new termin- mark for the start of a new chapter in ology and to make recommendations to our planetÕs history. the official bodyÑknown as the Interna- Does it really matter what epoch tional Commission on StratigraphyÑthat we are living in? ItÕs obviously important determines geological time units. To to geologists and other Earth scientists, accomplish this, our panel, the Anthropo- who use the geological timescale to meas- cene Working Group, has not only been ure, describe, and compare events and examining the evidence for the Anthro- changes that happened in our planetÕs poceneÕs existence but attempting to past. For many people outside these determine the duration of this potential fields, though, the potential designation new unit (Zalasiewicz et al., 2012). The of a new epoch has political overtones. group will also make recommendations As an editorial in a leading scientific jour- about where the Anthropocene, if it nal observed a few years ago, the Anthro- does exist, fits into the hierarchy of geo- pocene Òreflects a grim reality on the logical time: period, epoch, or age (per- ground, and it provides a powerful frame- haps even within the Holocene Epoch). work for considering global change and Many scientists agree that the Earth how to manage itÓ (Nature, 2011). has left the Holocene behind and is now Although the Anthropocene has, in in the Anthropocene, but there is less the public sphere, become closely agreement about when the Anthropo- associated with climate change and par- cene began. Some researchers make ticularly the burning of fossil fuels, it is good arguments for dating the beginning much bigger than that. We and other sci- of this new epoch to the advent of entists who are considering whether a agriculture, or to the increase in fossil new epoch has begunÑand if so, how fuel consumption that ushered in the best to mark its onsetÑare examining a 48 Bulletin of the Atomic Scientists 71(3) host of environmental changes wrought Anthropocene: the range of globally by humans, from the domestication of extensive and abrupt signatures during plants and animals to the nuclear arms the mid-20th century (Waters et al., race. Public discussion of these changes 2014) that coincide with the ÒGreat can only lead to a growing awareness AccelerationÓ of population growth, eco- that humans have left an enormous nomic development, industrialization, footprint on the EarthÑand not just a and hydrocarbon exploitation, carbon oneÑand may help increase the manufacturing of novel materials public understanding of how a warming such as plastics, the emergence of mega- climate relates to other momentous cities, and increased species extinctions global changes. and invasions (Steffen et al., 2007, 2015). Some researchers even suggest that the Origins of the Anthropocene onset of the Anthropocene is marked by a ÒdiachronousÓ boundary in sedi- In the geological timescale used by Earth mentsÑone in which a boundary between scientists, the Holocene Epoch began human-modified and ÒnaturalÓ ground about 11,700 years ago, after the planetÕs can be found that is of different ages at last glacial phase came to an end. When different locationsÑand thus is not a geo- the Anthropocene concept (Crutzen, logical time unit (Edgeworth et al., 2015). 2002; Crutzen and Stoermer, 2000) was The standard accepted practice for initially proposed, the Industrial Revolu- defining geological time units during tion was suggested as its starting point. the current eon (which began about 541 The reasoning was that industrializa- million years ago) is to identify a single tionÕs accelerated population expansion, reference point (or Ògolden spikeÓ), at a technological changes, and economic specific location, that marks the lower growth caused increased urbanization, boundary of a succession of rock layers mineral exploitation, and crop cultiva- as the beginning of the time unit. This tion; these factors in turn elevated atmos- internationally agreed-upon physical pheric carbon dioxide and methane reference point is representative of the concentrations enormously (Waters sum of environmental changes that jus- et al., 2014; Williams et al., 2011). tify recognition of the time unitÑthe Alternatively, the proponents of an appearance or extinction of a fossil spe- Òearly AnthropoceneÓ or ÒPalaeoan- cies, say, or a geochemical signature left thropoceneÓ interval that preceded the by a massive volcanic eruption (Smith, Industrial Revolution (Foley et al., 2013) 2014). For example, the boundary emphasize that this interval had a diffuse between the Cretaceous and Paleogene beginning, with signatures associated Periods has as its golden spike the base with the onset of deforestation, agricul- of an iridium-enriched layer of rock in El ture, and animal domestication; some Kef, TunisiaÑa marker for the debris scientists propose that these changes spewed into the atmosphere when a broadly coincide with the beginning huge meteorite struck the Earth and for of the existing Holocene Epoch (Smith the mass extinctions of dinosaurs and and Zeder, 2013). other creatures that followed that event. But there is growing evidence for The mid-20th century saw substantial another, later starting point for the changes to living things and their Waters et al. 49 ecological relationsÑalso known as burning of coal and other fossil biotic changes (Barnosky, 2014)Ñbut fuels, initially beginning during the those changes have not yet been well Industrial Revolution and then rapidly enough documented from the strati- increasing after 1945. Such increases, graphic perspective to be the primary however, do not provide a clear marker for the Anthropocene. The 1945 marker because the radioactive sub- detonation of the Trinity device would stances are not uniquely anthropogenic make a well-defined, historically import- in origin and may be locally abundant ant reference point, but a single deton- for other, natural reasons. ation lacks a clear signature in the global In addition to these sources, the geological record, even though nuclear medical use of represents testing converted sand into a -like the earliest anthropogenic source of substance known in the as radiation exposure (see Figure 1). Diag- ÒtrinititeÓ (Eby et al., 2010) and in Kaz- nostic medical examinations currently akhstan as Òkharitonchik.Ó This may well contribute the largest dosage after be considered a durable signature in the natural exposure (UNSCEAR, 2000) stratigraphic record, but one that is very but they target individuals, not the envir- localized in extent. onment, so their impact in the geologic In contrast, the fallout from the record would be small. Medical waste numerous thermonuclear weapons tests incinerators and uncontrolled disposal that began in 1952 deposited large of equipment can produce local contam- amounts of radionuclides in the environ- ination, but they are not useful as wide- ment and left a well-defined radiogenic spread stratigraphic signatures. signature. That level would provide an Besides these sources, there are effective global signal that marks the the contributions of . beginning of the Anthropocene, in com- The first commercial nuclear power parison to using the Trinity Test as a plant, at Calder Hall in northern England, marker. The difference between the two opened in 1956. Nuclear power grew rap- suggested levels is just seven years, and idly from 1970 to 1985, but the growth represents only fine-tuning of a generally stopped after the 1986 Chernobyl mid-20th-century boundary; ultimately, accident. The 2011 Fukushima the choice between them will depend produced similar hemispheric fallout, on analysis and debate of the whole though with less discharge. Radioactive ensemble of stratigraphic evidence cur- releases from reprocessing plants, which rently being assembled. recover and plutonium from spent fuels, are typically greater than Sources of human-made for nuclear power plants (Jeandel et al., radiation 1980). Such controlled releases, mainly uranium series isotopes from sites such Admittedly, the fallout from nuclear as the Sellafield () and testing is not the only source of La Hague () reprocessing plants, radiation that would show up in the peaked in the mid-1970s (Aarkrog, 2003). geological record. Naturally radioactive dumping caused substances have increased worldwide, localized contamination mainly in the due to the mining of ore and the Northeast Atlantic until 1982 and the 50 Figure 1. Timeline of anthropogenic radiogenic signatures: Frequency of atmospheric and underground nuclear weapons testing

200

150 ATMOSPHERIC TESTS UNDERGROUND TESTS

100 NUCLEAR WEAPONS TESTING CESSATION (NOV. 1958–FEB. 1960)

50 AGGREGATE NUMBER OF TESTS

0 1970 1975 1955 2000 2010 2005 ultno h tmcSinit 71(3) Scientists Atomic the of Bulletin 1945 1950 1895 1900 1965 1985 1995 1960 1980 1990 ) 2011 ( TREATY (1963) REENTRY (1964) PARTIAL TEST BAN SNAP-9A SATELLITE (WILHELM ROENTGEN) OCEANIC DUMPING OF CALDER HALL NUCLEAR PLANT ACCIDENT PLANT ACCIDENT (1986) TEST BAN TREATY (1996) & DETONATIONS RADIOACTIVE WASTE (1972) ALAMOGORDO, COMPREHENSIVE OPENS (1956) MEDICAL RADIOLOGY STARTS FUKUSHIMA NUCLEAR POWER CHERNOBYL NUCLEAR POWER LONDON CONVENTION BANNING

Source: UNSCEAR (2000) Waters et al. 51

Kara Sea near and the The signature of nuclear weapons Sea of until 1993, despite the testing London Convention of 1972 banning this practice (Livingston and Povinec, The case for using the fallout from 2000). The accidental discharges at nuclear weapons testing as a marker for Chernobyl and Fukushima and con- the onset of the Anthropocene is strong. trolled releases at Sellafield from 1952 There were 2,053 nuclear weapons tests to the mid-1980s contributed only small from 1945 to 1998 (Figure 1), mainly in amounts (UNSCEAR, 2000). central Asia, the , and the The disintegration of the navigational western United States (see Figure 2); 543 satellite SNAP-9A in 1964 off Mozam- were atmospheric tests. Test frequency bique produced significant additional peaked in 1951”1958 and especially atmospheric input of plutonium 238 1961”1962, interrupted by a moratorium (shown in Figure 1) and provided import- (UNSCEAR, 2000). Underground tests ant dating information in the southern occurred at the rate of 50 or more per hemisphere (for example, see Hancock year from 1962 to 1990. From 1945 to et al., 2014; Koide et al., 1979). But the 1951, the tests involved fission (ÒatomicÓ) future usefulness of plutonium 238 as a weapons producing fallout along test signature will be limited by its half-life of site latitudes in the lowest layer of the 88 years. atmosphere (Aarkrog, 2003). Larger All told, such discharges compose fusion (ÒthermonuclearÓ or ÒhydrogenÓ) only a small, regional component of weapons tests, starting in 1952, produced the total anthropogenic radionuclide higher-altitude fallout dispersed over budget, so they are poor candidates the entire Earth surface, with a marked for defining the beginning of the Anthro- peak in fallout yields in 19611962. pocene. In contrast, atmospheric nuclear Radionuclide fallout rapidly declined weapons testing, or wartime usage in the during the late 1960s, when tests were case of Hiroshima and Nagasaki, mainly underground, and effectively resulted in regional to global distribution ceased in 1980. of fallout. Most anthropogenic radio- The geographical distribution of nuclides in the environment today, radionuclides associated with fallout locked in soils and sediments, originated has been measured for the commoner from atmospheric testing that took components, such as strontium 90 place over a 35-year period from 1945 to (Figure 2) and cesium 137; comparable 1980. This fallout started abruptly and measurements for plutonium 239 and shows distinct, globally recognizable 240 are not available. Strontium 90 fall- phases, such as a rapid decline after the out is concentrated in the mid-latitudes Partial Nuclear Test Ban Treaty of 1963. (30”60 degrees) of each hemisphere (Underground tests, on the other hand, (Figure 2), and is smallest at the had much lower yields and releases to and equator (Aarkrog, 2003; Livingston the atmosphere.) The fallout signature and Povinec, 2000). Approximately is locally augmented by accidental 76 percent of all radionuclide fallout discharges from power stations, repro- was in the northern hemisphere, where cessing plants, and satellite burn-up on most testing occurred (Livingston and atmospheric reentry. Povinec, 2000). 52 Figure 2. Distribution and total fission and fusion yields, in megatons, of atmospheric nuclear weapons tests (red); and location of significant nuclear accidents/discharges (blue); with superimposed latitudinal variation of global strontium 90 fallout, in becquerels per square meter. Note that two sites, Novaya Zemlya in and the French Pacific atolls, contributed significantly to the total fallout

GLOBAL STRONTIUM 90 FALLOUT (BECQUERELS PER SQUARE METER ) 0 1000 2000 3000

NOVAYA ZEMLYA (239.6 MT) 60 TOTSK (0.04 MT) SEMIPALATINSK (6.6 MT) CALDER HALL/ CHERNOBYL SELLAFIELD ALAMOGORDO LOP NOR FUKUSHIMA (1.0 MT) (0.02 MT) (20.7 MT) (1.0 MT) 30 HIROSHIMA & REGGANE NAGASAKI (0.04 MT) (0.07 MT) (20.8 MT) (76.8 MT) MALDEN (1.2 MT) & ENEWETAK (31.7 MT) CHRISTMAS (29.8 MT) ISLANDS 0 ultno h tmcSinit 71(3) Scientists Atomic the of Bulletin MONTE BELLO MURUROA (6.4 MT) & (0.1 MT) MARALINGA & (3.7 MT) EMU (0.08 MT) 30 < 1 MT

OPERATION ARGUS, 1–5 MT SOUTH ATLANTIC (0.004 MT) 5–10 MT

60 > 10 MT

> 100 MT

0100020003000

Source: UNSCEAR (2000) Waters et al. 53

The best radioactive markers for from normal stratigraphic practice in the Anthropocene placing their suggested beginning Anthropocene level at the peak of the sig- To define the Anthropocene boundary, nature, rather than at its onset. radioactive isotopes should ideally be In contrast, the use of plutonium as a absent or rare in nature; have long half- marker offers several advantages. lives that provide a long-lasting signa- Plutonium isotopes have low solubility ture; have low solubilities and high and high particle reactivity, rapidly asso- reactivities so that they are less mobile ciating with clay or organic particles. and form a fixed marker in geological The long half-life of plutonium 239 deposits; and be present in sufficient (24,110 years) makes it the most persist- quantity to be easily detectable. The ent artificial radionuclide, detectable by short half-lives of cesium 137, strontium modern mass spectrographic techniques 90, and (a short-lived radio- for about 100,000 years (Hancock et al., nuclide of hydrogen associated with 2014). Plutonium 240, also a product fusion ) limit their potential to of nuclear weapons testing, is less serve as geologically ÒpermanentÓ mar- abundant and has a shorter half-life kers. Americium 241 has a deeper-water (6,563 years), and hence will decay distribution than plutonium 239 and 240, below easily detectable levels sooner. being more readily transported to the Few direct plutonium fallout measure- bottom of deep oceans on sinking ments were made during the 1950s and organic particles (Cochran et al., 1987; 1960s, but the historical pattern of pluto- Lee et al., 2005), and so may be a more nium isotope distribution is believed to suitable signature in the comparatively be similar to that of the widely studied undisturbed deep-water environments. isotope cesium 137, especially after 1960 However, the lower abundance of ameri- (Hancock et al., 2014). cium 241 and its 432-year half-life would WhatÕs more, plutonium in the air make it useful for only one or two millen- is now dominated by atmospheric nia. Radiocarbon (carbon 14) shows a discharge from nuclear power plants Òbomb peakÓ at 19631964 in most and the re-suspension of plutonium- carbon reservoirs, including peat depos- bearing soil particles, whereas during its, soil, wood, and coral (Hua et al., 2013; 1945”1960 the major source of plutonium Reimer et al., 2004), and this has been was nuclear weapons testing. Since 1960, proposed by Lewis and Maslin (2015) as plutonium concentrations in the atmos- a potential marker for the base of the phere have been decreasing almost Anthropocene. This spike will be detect- exponentially following international able for about 50,000 years into the test-ban treaties (Choppin and Morgen- future, so it represents a long-lasting stern, 2001). and important signature on land. Another benefit to using plutonium is However, the high solubility and low that this element mostly binds with reactivity of carbon 14 in marine sedi- decayed plant material and ments (Jeandel et al., 1981; Livingston on the surface of soil particles (Chawla and Povinec, 2000) limit its suitability et al., 2010), thus locking it in place; as a marker in the worldÕs oceans. plants mobilize only a little plutonium Lewis and Maslin (2015), too, depart through uptake by roots. But a drawback 54 Bulletin of the Atomic Scientists 71(3) may be that plutonium can migrate food chain (Livingston and Povinec, in peat profiles and can probably move 2000)Ñcan modify the radiogenic signa- downward in organic-rich soils and ture to the point where it no longer sediments (Quinto et al., 2013), adding represents a time series of discrete fall- anthropogenic plutonium to layers that out events that can be precisely corre- were deposited before nuclear weapons lated from one location to the next. testing. This may limit the application of Another consideration is the delay plutonium as an Anthropocene signature between detonation and eventual fallout, in acidic, organic-rich environments. with radioactive debris residence times Within the oceans, plutonium sticks in the troposphere of about 70 days for to the surface of suspended matter that small-yield detonations (Norris and falls through the water column, and Arkin, 1998) and 15 to 18 months in consequently its distribution in the the for large thermonuclear ocean is affected by currents and by tests (Zandler and Araskog, 1973). Such movement of sediment (Zheng and delays account for why radionuclides Yamada, 2006). Plutonium in particular such as cesium 137 reach peak abundance accumulates in coastal sediments, several years after the maximum intro- especially in low-, organic-rich duction of fallout in the atmosphere. environments (Livingston and Povinec, This delay is exacerbated in ocean 2000) where few bottom-dwelling ani- environments as fallout is transferred mals can survive, and so their move- through the water column to bottom ments do not disrupt the radioactive sediment. From 1973 to 1997, the sediment layers. Plutonium is taken up maximum plutonium signature in the by organic material in shallow sunlit Northwest Pacific descended from 500 levels of the sea and then released back meters to 800 meters below the oceanÕs into solution when reaching a depth of surface through gradual settling of the several kilometers (Livingston and Povi- early-1960s fallout peak at an average nec, 2000). Coral skeletons thus become rate of 12.5 meters per year (Livingston archives of plutonium contamination et al., 2001), and in the mid-latitudes history, with plutonium concentrations more than 70 percent of plutonium 239 in their growth bands reflecting the and 240 still remains in the water plutonium levels in the oceans (Lindahl column (Lee et al., 2005). This suggests et al., 2012). at least decadal residence times in Most Ògolden spikesÓ lie within oceanic waters, and a resultant smearing marine sedimentary successions be- of potential plutonium signatures in cause they tend to be more continuous marine sediments, such that annual than terrestrial strata and contain resolution of sediment layers in the traces of plant and animal life that oceans is unlikely. can be easily matched with sediments There are alternative environments at other sites. These criteria hold true in which a Ògolden spikeÓ section could for the potential use of a radiogenic be located: for example, undisturbed signature. However, dynamic transport lake deposits where fallout material has of radionuclides in the water col- accumulated, or where sediment accu- umnÑthrough erosion, suspension, and mulation is too rapid for the layering to re-sedimentation and via the biological be disrupted by burrowing animals Waters et al. 55

(Hancock et al., 2014). There is some itself is a poor geological indicator for a precedent for this; the base of the new epoch, at least when viewed over a Holocene Epoch is defined in a Green- recent timescale of decades. There is a land ice core (Walker et al., 2009), and significant time lag between the recent this type of deposit might also be used striking increase in atmospheric carbon to define the base of the Anthropocene. dioxide levels and significant climate Such cores can provide annual records and sea level changes, with the latter through layer-counting known Saharan effects not yet clearly expressed in geo- dust events, volcanic eruptions, and the logical deposits. 1963 tritium horizon when abundances of The advent of the nuclear age in itself this radionuclide peaked. Plutonium does not merit the identification of a new appears to be immobile in ice (Gabrieli geological epoch. The signature of weap- et al., 2011; Koide et al., 1979), and high- ons testing coincides with a range of resolution records of plutonium fallout human-driven changes that have pro- have been measured in polar ice cores duced stratigraphic signals that indicate (Koide et al., 1977, 1979). With greater a dramatic shift in the Earth system fallout of radionuclides in the mid-lati- around the mid-20th century, which in tudes, alpine glaciers may be more suit- total may be considered the distinctive able. Ice cores from Swiss and Italian feature of the Anthropocene. The fact alpine glaciers display the earliest rise that the plutonium 239 signature is coin- of plutonium 239 fallout from 1954 to cident with other changes makes it a 1955, with subsequent peaks in 1958 and useful tool for defining the Anthro- 1963 and a sharp decrease following the poceneÕs base. Partial Nuclear Test Ban Treaty in 1963 A summary of the evidence and rec- (Gabrieli et al., 2011). The worldÕs ice ommendations for defining an Anthro- caps, however, are undergoing increased pocene Epoch will be presented at the wastage through global warming, and so next International Geological Congress their potential to provide a long-term in 2016. The Anthropocene Working record may be limited. Group is still collecting evidence; nuclear are likely to be critical A time of global changes to the definition of the Anthropocene, and contributions to this discussion If we want to use the fallout from nuclear would be welcomed. weapons to mark the beginning of the Anthropocene Epoch, the 1945 Ala- Acknowledgements mogordo nuclear weapons test marks The authors thank Irka Hajdas for her comments on the start of the nuclear age but lacks a radiocarbon signatures. clear radiogenic signature in the global geological record. By comparison, the Funding most pronounced rise in plutonium Colin Waters publishes with the permission of the dispersal commences in 1952 and can Executive Director, British Geological Survey provide a practical radiogenic signature (BGS), Natural Environment Research Council, funded with the support of the BGSÕs Engineering for the beginning of the Anthropocene. Geology program. This research received no Although the Anthropocene may be a other specific grant from any funding agency in the time of global warming, climate change public, commercial, or not-for-profit sectors. 56 Bulletin of the Atomic Scientists 71(3)

References anthropogenic environmental change. Anthropo- cene 3: 83”88. Available at: http://www.science Aarkrog A (2003) Input of anthropogenic radio- direct.com/science/article/pii/S2213305413000404. nuclides into the World Ocean. Deep-Sea Research Gabrieli J, Cozzi G, Vallelonga P, et al. (2011) Contam- II 50(17”21): 2597”2606. Available at: http:// ination of Alpine snow and ice at Colle Gnifetti, www.sciencedirect.com/science/article/pii/S09 Swiss/Italian Alps, from nuclear weapons tests. 67064503001371. Atmospheric Environment 45(3): 587”593. Avail- Ackland L and McGuire S (eds) (1986) Assessing the able at: http://www.sciencedirect.com/science/ Nuclear Age: Selections from the Bulletin of the article/pii/S1352231010009258. Atomic Scientists. Chicago, IL: Educational Foun- Groves LR (1962) Alamogordo. In: Now It Can Be dation for Nuclear Science/University of Chicago Told: The Story of the Manhattan Project. New Press. York: Harper, pp. 288”304. Barnosky AD (2014) Palaeontological evidence for defin- Hancock GJ, Tims SG, Fifield LK, et al. (2014) ing the Anthropocene. In: Waters CN, et al. (eds) A The release and persistence of radioactive Stratigraphical Basis for the Anthropocene. Special anthropogenic nuclides. In: Waters CN, et al. Publications 395. London: Geological Society, (eds) A Stratigraphical Basis for the Anthropocene. pp. 149”165. Available at: http://sp.lyellcollectio- Special Publications 395. London: Geological n.org/content/395/1/149. Society, pp. 265”281. Available at: http://sp.lyell- Chawla F, Steinmann P, Loizeau J-L, et al. (2010) Bind- 239 90 collection.org/content/395/1/265. ing of Pu and Sr to organic colloids in soil Hua Q, Barbetti M and Rakowski AZ (2013) Atmo- solutions: Evidence from a field experiment. spheric radiocarbon for the period 1950”2010. Environmental Science & 44(22): Radiocarbon 55(4): 2059”2072. Available at: 8509”8514. Available at: http://pubs.acs.org/doi/ https://journals.uair.arizona.edu/index.php/radio abs/10.1021/es101766g. carbon/article/view/16177. Choppin GR and Morgenstern A (2001) Distribution Jeandel C, Martin J-M and Thomas AJ (1980) Origine and movement of environmental plutonium. et comportement du plutonium et du cesium 137 In: Kudo A (ed.) Radioactivity in the Environment. dans lÕEstuaire de la Seine. Comptes rendus de Volume 1, Plutonium in the Environment. Ams- lÕAcadmie des Sciences, Paris 291: 125”128. terdam: Elsevier, pp. 91”105. Available at: http:// Jeandel C, Martin J-M and Thomas AJ (1981) Les radio- www.sciencedirect.com/science/article/pii/S156 nucleides artificiels dans les estuaires franais. In: 9486001800097. Radionuclide releases into the marine environ- Cochran JK, Livingston HD, Hirschberg DJ, et al. ment, IAEA-SM-248/123. Vienna: International (1987) Natural and anthropogenic radionuclide Atomic Energy Agency, pp. 15”32. distributions in the northwest Atlantic Ocean. Koide M, Goldberg ED, Herron MM, et al. (1977) Earth and Planetary Science Letters 84(2”3): Transuranic depositional history in South Green- 135”152. Available at: http://www.sciencedirect. land firn layers. Nature 269: 137”139. Available at: com/science/article/pii/0012821X87900811. http://www.nature.com/nature/journal/v269/n5 Crutzen PJ (2002) Geology of mankind. Nature 415: 23. 624/abs/269137a0.html. Available at: http://www.nature.com/nature/ Koide M, Michel R, Goldberg ED, et al. (1979) Deposi- journal/v415/n6867/full/415023a.html. tional history of artificial radionuclides in the Ross Crutzen PJ and Stoermer EF (2000) The Ice Shelf, Antarctica. Earth and Planetary Science Let- ÒAnthropoceneÓ. Global Change Newsletter 41: ters 44(2): 205”223. Available at: http://www.science- 17”18. Available at: http://www.igbp.net/down direct.com/science/article/pii/0012 821X79901699. load/18.316f18321323470177580001401/13763830884 Lee S-H, Povinec PP, Wyse E, et al. (2005) Distribution 52/NL41.pdf. and inventories of 90Sr, 137Cs, 241Am and Pu iso- Eby N, Hermes R, Charnley N, et al. (2010) Triniti- topes in sediments of the Northwest Pacific teÑthe atomic rock. Geology Today 26(5): Ocean. Marine Geology 216(4): 249”263. Available 180”185. Available at: http://onlinelibrary.wiley. at: http://www.sciencedirect.com/science/art- com/doi/10.1111/j.1365-2451.2010.00767.x/full. icle/pii/S0025322705000721. Edgeworth M, Richter D, deB, Waters C, et al. (2015) Lewis SL and Maslin MA (2015) Defining the Anthro- Diachronous beginnings of the Anthropocene: pocene. Nature 519: 171”180. Available at: http:// The lower bounding surface of anthropogenic www.nature.com/nature/journal/v519/n7542/full/ deposits. Anthropocene Review 2(1): 33”58. Avail- nature14258.html. able at: http://anr.sagepub.com/content/2/1/33. Lindahl P, Andersen MB, Keith-Roach M, et al. (2012) Foley SF, Gronenborn D, Andreae MO, et al. (2013) Spatial and temporal distribution of Pu in the The PalaeoanthropoceneÑThe beginnings of Northwest Pacific Ocean using modern coral Waters et al. 57

archives. Environment International 40: 196”201. Walker M, Johnsen S, Olander Rasmussen S, et al. Available at: http://www.sciencedirect.com/sci (2009) Formal definition and dating of the GSSP ence/article/pii/S0160412011002194. (Global Stratotype Section and Point) for the Livingston HD and Povinec PP (2000) Anthropogenic base of the Holocene using the Greenland NGRIP marine radioactivity. Ocean & Coastal Management ice core, and selected auxiliary records. Journal of 43(8”9): 689”712. Available at: http://www.science- Quaternary Science 24(1): 3”17. Available at: http:// direct.com/science/article/pii/S09 64569100000545. onlinelibrary.wiley.com/doi/10.1002/jqs.12 27/pdf. Livingston HD, Povinec PP, Ito T, et al. (2001) The Waters CN, Zalasiewicz JA, Williams M, et al. (2014) A behaviour of plutonium in the Pacific Ocean. Stratigraphical Basis for the Anthropocene. Special In: Kudo A (ed.) Radioactivity in the Environment. Publications 395. London: Geological Society. Avail- Volume 1, Plutonium in the Environment. Amster- able at: http://sp.lyellcollection.org/content/395/1. dam: Elsevier, pp. 267”292. Available at: http:// Williams M, Zalasiewicz J, Haywood A, et al. (2011) www.sciencedirect.com/science/article/pii/S156 The Anthropocene: A new epoch of geological 948600180019X. time? Philosophical Transactions of the Royal Nature (2011) The human epoch. Editorial. Nature 473: Society 369A(1938): 833”1112. Available at: http:// 254. Available at: http://www.nature.com/nature/ rsta.royalsocietypublishing.org/content/369/1938. journal/v473/n7347/full/473254a.html. Zalasiewicz J, Crutzen PJ and Steffen W (2012) The Norris RS and Arkin WM (1998) Known nuclear tests Anthropocene. In: Gradstein FM, Ogg JG, Schmitz worldwide 1945”98. Bulletin of the Atomic Scien- MD, et al. (eds) The Geologic Time Scale. Amster- tists 54(6): 65”67. Available at: http://books.goo dam: Elsevier, pp. 1033”1040. Available at: http:// gle.ca/booksid¼sgsAAAAAMBAJ&pg¼PA65. www.sciencedirect.com/science/article/pii/B97 Quinto F, Hrnecek E, Krachler M, et al. (2013) Determi- 80444594259000329. nation of 239Pu, 240Pu, 241Pu and 242Pu at femtogram Zalasiewicz J, Waters CN, Williams M et al. (2015) and attogram levelsÑevidence for the migration of When did the Anthropocene begin? A mid-twenti- fallout plutonium in an ombrotrophic peat bog pro- eth century boundary level is stratigraphically opti- file. Environmental Science: Processes & Impacts mal. Quaternary International. Epub ahead of print, 15(4): 839”847. Available at: http://pubs.rsc.org/ January 12. Available at: http://www.sciencedir- en/content/articlelanding/2013/em/c3e m30910j. ect.com/science/article/pii/S1040618214009 136. Reimer PJ, Brown TA and Reimer RW (2004) Discus- Zandler I and Araskog WM (1973) Nuclear sion: Reporting and calibration of post- 14C 1945”1972, Basic Data. Research Institute of data. Radiocarbon 46: 1299”1304. Available at: National Defense, Stockholm. Available, in Swed- http://e-reports-ext.llnl.gov/pdf/312713.pdf. ish, at: http://www.iaea.org/inis/collection/ Smith BD and Zeder MA (2013) The onset of the NCLCollectionStore/_Public/05/137/5137568.pdf. Anthropocene. Anthropocene 4: 8”13. Available Zheng J and Yamada M (2006) Plutonium isotopes in at: http://www.sciencedirect.com/science/art- settling particles: Transport and scavenging of Pu icle/pii/S2213305413000052. in the western Northwest Pacific. Environmental Smith VC (2014) Volcanic markers for dating the Science & Technology 40(13): 4103”4108. Available onset of the Anthropocene. In: Waters CN, et al. at: http://pubs.acs.org/doi/abs/10.1021/es0601179. (eds) A Stratigraphical Basis for the Anthropocene. Special Publications 395. London: Geological Author biographies Society, pp. 283”299. Available at: http://sp.lyell- col lection.org/content/395/1/283. TenofthisarticleÕs11authorsaremembersofthe Steffen W, Crutzen PJ and McNeill JR (2007) The 38-person Anthropocene Working Group, Anthropocene: Are humans now overwhelming the established to examine the evidence for the great forces of nature? Ambio: A Journal of the Human Anthropocene Epoch of geological time. The Environment 36(8): 614”621. Available at: http:// group includes members from a broad range of www.bioone.org/doi/abs/10.1579/0044-7447%282 geosciences and social sciences. In addition, 007%2936%5B614%3ATAAHNO%5D2.0. CO%3B2. Gary Hancock, a senior research at Steffen W, Broadgate W, Deutsch L, et al. (2015) The the Commonwealth Scientific and Industrial trajectory of the Anthropocene: The Great Accel- Research Organisation (or CSIRO, AustraliaÕs eration. Anthropocene Review 2(1): 81”98. Avail- able at: http://anr.sagepub.com/content/2/1/81. nationalscienceagency)andanexpertonpluto- UNSCEAR (2000) Sources and effects of ionizing radi- nium radioisotopes in the environment, contrib- ation, 2000 report, Volume 1. New York: United uted to the article. The lead author can be Nations. Available at: http://www.unscear.org/ contacted at [email protected]. unscear/en/publications/2000_1.html. Copyright of Bulletin of the Atomic Scientists is the property of Bulletin of the Atomic Scientists and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use.