http://hol.sagepub.com

The Holocene

DOI: 10.1177/0959683609105296 2009; 19; 729 The Holocene

Zoltán Kern, Mihály Molnár, Éva Svingor, Aurel Persoiu and Balázs Nagy Romania

High-resolution, well-preserved tritium record in the ice of Bortig Ice Cave, Bihor Mountains,

http://hol.sagepub.com/cgi/content/abstract/19/5/729 The online version of this article can be found at:

Published by:

http://www.sagepublications.com

can be found at:The Holocene Additional services and information for

http://hol.sagepub.com/cgi/alerts Email Alerts:

http://hol.sagepub.com/subscriptions Subscriptions:

http://www.sagepub.com/journalsReprints.navReprints:

http://www.sagepub.co.uk/journalsPermissions.navPermissions:

http://hol.sagepub.com/cgi/content/refs/19/5/729 Citations

by Zoltan Kern on October 4, 2009 http://hol.sagepub.comDownloaded from

(Ravoire et al., 1970; Theodórsson, 1977; Merlivat et al., 1977;Jouzel et al., 1979; Pourchet et al., 1995; Stuart and Sharp, 2003;Weiler et al., 2005) and mid-latitude/high-altitude sites (Romanov,1977; Ambach et al., 1977; Schwikowski et al., 1999; Eichler et al.,2000; Olivier et al., 2003, 2004; Ginot et al., 2006).Among these radiochemical tracers, tritium (3H) is probably the

most frequently used. Natural tritium is produced in the upper tro-posphere and lower stratosphere by the influence of cosmic radia-tion, and after it is oxidized to water it enters the water cycle in theform of HTO. However, a much greater production accompaniedthe atmospheric testing of thermonuclear bombs during the secondhalf of the twentieth century. Although the earliest thermonuclearweapon detonation was carried out on 9 May 1951 (Goncharov,1996), the major deposition of anthropogenic-released tritiumstarted only in 1953/1954 in Europe (Eriksson, 1965). Since 1963,when nuclear powers agreed on a Limited Test Ban Treaty, whichprohibited nuclear tests in the atmosphere (Barth, 1998), 3H activity

Introduction

Geochemical composition of permanent surface ice bodies are com-monly studied to reveal past climatic conditions and environmentalpollution history. Ice sheets, ice caps and glaciers are, however,restricted exclusively to polar latitudes and mountain regions whereelevation exceeds the altitude of the regional climatic snowline. Icecaves (defined at the 1st International Workshop on Ice Caves,2004, as: rock hosted caves containing perennial ice and snow accu-mulation) potentially preserve similar palaeoclimatic archives fromnon-glaciated areas so they can provide a unique opportunity toexpand glaciochemical studies to broader regions of the Earth.The anthropogenic radiochemical tracers (eg, 3H, 137Cs, 36Cl, 239,240Pu)

are widely applied as a useful dating tool and represent an objectivecontrol in age-accumulation models in ice core studies both at polar

Abstract: Two 2 m long ice cores (BAand BB) were extracted from the floor ice of Bortig Ice Cave in December2005. Below a co-existing dust horizon (~13 cm underneath the 10 December 2005 ice surface) neither core pre-sented any sign of hiatus, so the ice deposition is considered to be continuous. Tritium concentration of 94 sam-ples from a 1.85 m long ice section were analysed by liquid scintillation counting technique. Samples from thelower 0.33 m of the sequence did not contain tritium above the critical level (7.2 TU). The highest value of tri-tium content (166.4±4.0 TU) was found at ~96 cm below the surface. This salient value is considered to be syn-chronous with the climax of tritium concentration in the Northern Hemisphere’s atmospheric precipitation(1963). Beside this characteristic global radiochemical marker event, minor events were also detected, and dated(ie, 1954, 1958 and 1975) by corresponding peaks in the tritium concentration record of BB ice core to peaks ofan estimation of tritium activity of past precipitation at Bortig Ice Cave location. The estimation was based on adata set from four nearby stations of the Global Network of Isotopes in Precipitation. The highest annual accu-mulation rate (6.74 cm/yr) was between 1958 and 1963 and gradually decreased to 0.54 cm/yr for the recentdecades. The mean ice accumulation rate was 4.34 cm/yr over the 1954–1986 period. The estimated age at thebottom of the 21 m thick ice block assuming constant accumulation is roughly 500 years.

Key words: 3H, central Europe, precipitation, cave ice, bomb-peak, liquid scintillation counting (LSC).

The Holocene 19,5 (2009) pp. 729–736

© The Author(s), 2009. Reprints and permissions: http://www.sagepub.co.uk/journalsPermissions.nav

10.1177/0959683609105296

*Author for correspondence (e-mail: kern@geochem.hu)

High-resolution, well-preserved tritiumrecord in the ice of Bortig Ice Cave,Bihor Mountains, RomaniaZoltán Kern,1* Mihály Molnár,2 Éva Svingor,2 Aurel Persoiu3

and Balázs Nagy4

( 1Institute for Geochemical Research, Hungarian Academy of Sciences, Budaörsi út 45, H-1112

Budapest, Hungary; 2Institute of Nuclear Research of the Hungarian Academy of Sciences, Bem tér

18/c, H-4026 Debrecen, Hungary; 3Karst Research Group, University of South Florida, Tampa FL,

USA; 4Eötvös Loránd University, Department of Physical Geography, Pázmány Péter sétány 1/c,

H-1117 Budapest, Hungary)

Received 3 July 2008; revised manuscript accepted 19 January 2009

by Zoltan Kern on October 4, 2009 http://hol.sagepub.comDownloaded from

in atmospheric precipitation have rapidly decreased (Fourré et al.,2006). In 1963 the yearly average of the tritium content of precip-itation in the Northern Hemisphere exceeded the natural level bya factor of 1000, it is still high (100 TU) at the present time.A major advantage of tritium as a tracer of bomb tests in ice

compared with 137Cs, 36Cl etc., is that tritium is part of the icematrix and therefore much less susceptible to secondary effectssuch as melting or ablation in general.Tritium concentration, not only in surface ice bodies but also in

cave ice, seems a feasible objective to analyse. The history of 3Hconcentration of intensively monitored atmospheric precipitationpromises valuable marker horizons for twentieth-century depositedcave ice owing to the large emissions connected to abovemen-tioned atmospheric nuclear tests (Eriksson, 1965; Fourré et al.,2006). On the other hand, 3H provides a reliably detectable radio-chemical tracer for any potential geochemical migration processesin the subterranean ice bodies.Horvatincic (1996) has presumed the preservation of the 1963-sig-

nal by investigating 3H of nine isolated cave ice samples in theLedena jama (Croatia). In contrast, in another ice cave of the WestBalkan (Ledena Pecina, Montenegro) tritium data apparently indi-cated significant ablation period(s), hardly allowing the preservationof any cave ice from the 1950–1970 interval (Kern et al., 2007a).Luetscher et al. (2007) have differentiated a modern (tritiated) and arelict (non-tritiated) section of the ice deposit of Monlesi Ice Cave(Switzerland), but a more detailed interpretation was hindered by thelack of data over a 4.5 m thick section between the two units.In this paper we present a high-resolution tritium concentration

record of atmospheric precipitation over the past half century recov-ered from the uppermost 2 m section of Bortig Ice Cave’s under-ground ice body. Our aims are to validate the previously gained 3Hrecord from the Bortig Ice Cave (Kern et al., 2007b) and to developa detailed age-scale for the recent part of the cave ice deposit.

Materials and methods

Description of the caveBortig Ice Cave (46.56°N 22.69°E; 1236 m a.s.l.) is located in theBihor Mountains, in the western part of Romania (Figure 1). Themorphology of the cave is rather simple, with a 44 m deep shaft

leading down to a small room, with the floor fully occupied by anice block. At the contact between the rock and the ice, a few nar-row rimayes, narrow openings between the ice block and the rockwall, have formed, giving access to the lower, partly non-glaciatedsectors of the cave (Figure 2). According to the process-basedclassification of alpine and subalpine ice caves (Luetscher andJeannin, 2004), Bortig Ice Cave belongs to the group of staticcaves containing congelation ice and firn. The cave hosts25 000 m3 of stratified ice (Orghidan et al., 1984), with an esti-mated maximum thickness of 21 m. Regular observationsthroughout the past three years (2005–2008) revealed that themain water supply of floor ice is the atmospheric precipitation inthe Bortig Ice Cave and the role of dripping water is negligible.The most prominent period of ice formation is theNovember–May interval while the June–October period is charac-terized by ablation. Annual net balance depends on the differencebetween these seasonal balances.

730 The Holocene 19,5 (2009)

Figure 1 Location of Bortig Ice Cave and the surrounding stations from the Global Network of Isotopes in Precipitation (GNIP) database (IAEA, 2004)

Figure 2 Sketch of Bortig Ice Cave. Tip of arrows indicate thedrilling site of BA and BB ice cores

by Zoltan Kern on October 4, 2009 http://hol.sagepub.comDownloaded from

Ice drillingWe extracted two shallow ice cores (BA and BB), using manualdrilling equipment, from the ice body on 11 and 12 December2005. The drilling sites were positioned on the flat surface ofthe ice block situated in the entrance shaft of the Bort ig IceCave (Figure 2). Dust layers were scarce and faint in the icecores (Kern et al., 2007b). The 1.97 m long BB core (diame-ter=3 cm) was sectioned into 98 subsamples labelled BB1 toBB98, starting from the surface of the ice body, the length ofeach subsample being ~2 cm. Each subsample was sealed intoa 4.5 cm long, 3 cm diameter air-proof plastic container andtransported to the laboratory. Melted samples were stored in arefrigerator until analysis. Tritium concentration was measuredon the upper 1.85 m (94 subsamples). We have anchored thelevel of the ice before the coring procedure and all depth data isreferred, uniformly, as depth below the 10 December 2005 icesurface.

Tritium measurementsTritium activities were measured on water melted from 94 sam-ples of BB core, using liquid scintillation counting (LSC) tech-nique. Water samples were distilled before LSC measurements tominimize quenching (Svetlik and Budska, 2001). 10 ml of dis-tilled water sample was mixed with 10 ml of Ultima Gold LLTcocktail in a low-diffusion PE-vial and measured by aWallac 1220Quantulus (Perkin Elmer) ultra low-level liquid scintillation spec-trometer at the Institute of Nuclear Research (ATOMKI).Measuring time was 1000 minutes per sample, resulting in a crit-ical level (LC) of 7.2 TU (detection limit LD was 14.4 TU) (tritiumunit, 1 TU is 0.1183 Bq/l) (Curie, 1995). Critical level:level of sig-nificance, calculated for probability of the first kind of observationerror about 5% (Curie, 1995).Although results below the detection limit gave information

with only a small probability about the sample activity, it is stillrecommended to report them with their error if they exceed thecritical level to avoid information lost (Curie, 2004). Detectionlimit represents the limit for higher probability (>95%) of obser-vation (so-called ‘second kind of observation error’) but evensmaller activities can be reported down to critical level (LC). In ourparticular situation we had only 15–20 g of each sample for analy-ses, as a result of the applied sampling geometry and strategy. Theuse of longer parts of the core as a sampling step just for havingmore water in one sample would have strongly decreased the res-olution of the record. In addition, other methods such as the tri-tium enrichment method (normal sample size is >200 g water) orthe more sensitive T-3He in-growth method (normal sample size is>1000 g water) have lower detection limit parameters and higheraccuracy if the sample amount is not limited. But in our case theycould not have given much improved result quality and wouldhave significantly raised the costs.The results are presented in tritium units, calculated for 10

December 2005. For calculations we applied the half-life of tri-tium as 12.32 years (Lucas and Unterweger, 2000). Since tritiumconcentration of 16 samples below BB78 had not reached the LC,

and the lower part of the previously analysed BA core did notpresent a signal above LC (Kern et al., 2007b), we have neglectedthe measurement of the remaining four deepest samples becauseof the high probability that they also have tritium content belowthe LC of the applied method.

Estimation of past 3H concentrationsof precipitation based on surroundingstation dataAs no tritium measurements are available in the vicinity of thecave, we have used data from the three nearest meteorological sta-tions with multidecadal time series of monthly average tritiumconcentration in atmospheric precipitation (International AtomicEnergyAgency (IAEA), 2004): Belgrade (Serbia), Budapest (Hungary)and Odessa (Ukraine) (Figure 1; Table 1). In addition, the tritiumcontent of precipitation has been monitored, in the broader area of thecave, in Vienna since 1961. The Vienna record has already proved tobe a reliable indicator for the changes of 3H of precipitation in thecentral part of the Carpathian Basin (Deák, 2006).The procedure to estimate tritium content in precipitation at

Bortig Ice Cave for the 1961–2000 period using data from thesestations is described below.When monthly values were available for all the stations

(Belgrade, Budapest, Odessa) the weighted average was com-puted for the location of Bortig Ice Cave. Weights were calcu-lated from the stations’ geographical coordinates. By thisinterpolation, 102 monthly values were determined over theJanuary 1977–October 1990 period. Each interpolated data wasput into a linear regression against the corresponding measuredmonthly data of Vienna (Figure 3, inset). Applying the regres-sion equation another estimation of tritium content of precipita-tion was calculated for the location of Bortig Ice Cave from theseries measured in Vienna (Figure 3). Interpolated series werecompleted with the regressed record. Neither interpolated norregressed data were available for six separate months in theperiod between January 1961 and December 2000. For these sixmonths the gaps in the estimation were filled by the arithmeticmean of preceding and succeeding monthly values. Subannualvariability was filtered by a 13-month non-weighted movingaverage.

Results

Results of measured tritium activity of the BB ice profile are pre-sented in Figure 4, plotted against depth below surface (the depthvalues represent the mean of the range of depth for each sample).The 3H concentration data from the five times coarser sampled BAcore (Kern et al., 2007b) are also plotted.Samples below 153.9 cm (sample BB79 and following) did not

contain detectable tritium, while above this level all samples,except sample BB5 (7.5–9.4 cm), had measurable tritium content.The first sample with detectable tritium content was BB78(152.2–153.9 cm) with 8.9±2.4 TU. The 3H concentration starts to

Zoltán Kern et al.: Tritium in an ice core from a Romanian cave 731

Table 1 Surrounding GNIP stations with significant long series of 3H of atmospheric precipitation and their characteristics

GNIP measurements

Station Lat. (deg) Long. (deg) Alt. (m a.s.l.) Distance from Bortig (km) Begin End Missing monthly data

Belgrade 44.47 20.32 243 299 Jan. 1976 Aug. 2002 35 (11%)Budapest 47.43 19.22 139 280 Jan. 1977 Dec. 1992 11 (5.8%)Odessa 46.48 30.63 64 610 Jul. 1969 Nov. 1990 54 (21.1%)Vienna 48.25 16.37 203 515 Jan. 1961 Dec. 2002 16 (3.2%)

by Zoltan Kern on October 4, 2009 http://hol.sagepub.comDownloaded from

rise, reaching the first peak (19.2±2.5 TU) in sample BB75(147.1–148.8 cm). Steady increase with fluctuation within uncer-tainty intervals follows and a new peak occurs in sample BB64(126.6–128.7 cm) with 26.3±2.5 TU. Between BB52 and BB55(102.7–110.3 cm) a low-arched plateau appears, relaxing around69 TU. Sharp increase follows this plateau culminating in the mostprominent peak of the Bortig ice core record in sample BB48(95.1–97.0 cm) reaching the highest tritium content (166.4±4.0 TU)of the record. Above this level, the 3H concentration steeplydeclines, reaching the local minimum with 15.4±3.1 TU in sampleBB30 (58.2–60.4 cm). Following some fluctuations a peakappears again spiking in sample BB24 (45.5–47.6 cm) with a

value of 29.5±3.2 TU. The lowest detectable value was found inBB7 (5.1±2.5 TU, 11.3–13.2 cm). Above this level, an increasingtrend towards the top of the core was found.

Discussion

Impurity layers constituted from organic and non-organic materialare frequently described from cave ice profiles (Hanzlik and Ulrich,1938; Serban et al., 1967; Racovita, 1972; Rygielski et al., 1995;Kern et al., 2004, 2007b; Luetscher, 2005; Citterio et al., 2005;Holmlund et al., 2005). According to the researcher’s congruent

732 The Holocene 19,5 (2009)

Figure 3 Estimated past tritium concentration of the atmospheric precipitation at Bortig Ice Cave. Inset graph: linear regression between inter-polated values of tritium concentration of precipitation from the Belgrade–Odessa–Budapest triangle and Vienna

Figure 4 Tritium depth profiles of parallel ice cores (BA, Kern et al. (2007b); BB, this study) from Bortig Ice Cave

by Zoltan Kern on October 4, 2009 http://hol.sagepub.comDownloaded from

opinion, these impurity layers are stratigraphic documents of shorter(seasonal) and longer (multiannual) melting events.Both BA and BB ice cores of Bortig Ice Cave had a dust layer

situated at almost the same depth below the 10 December 2005 icesurface (BA: 12.99 cm, BB: 13.07 cm) suggesting that they docu-ment the same negative mass balance event (Kern et al., 2007b).The BA core presented also a faint dust veil at −6 cm, not foundin the BB core. Below the −13 cm dust horizon neither core haspresented further dust horizon or any other stratigraphical or tex-tural evidence of hiatus, so we can regard them as a record of con-tinuous ice deposition.Derived tritium concentration profiles of BA and BB ice cores

perfectly match (Figure 4) but, as was expected, the finer sampledBB record shows a larger variability. The long-term changes of tri-tium concentrations in the ice cores from Bortig Ice Cave haveranged over three orders of magnitude, very similarly to the esti-mation (Figure 5).The applied principle in interpretation of BB tritium record was

that tritium maxima in the BB record can be linked to tritium max-ima of past precipitation. This principle relies on the theory thateven if some process (eg, repeated partial melting and refreezing)blurs the interannual differences, the original position of any peak

in the ice deposit remains, although its absolute amplitude mightbe depressed.This conjunction procedure is illustrated in Figure 5. We believe

the salient tritium concentration in the BB48 sample archives thewell-known maximum of 3H from 1963. It agrees reasonably wellwith our previous results when we estimated the location of the1963 bomb peak to ~95 cm depth from the BA core (Kern et al.,2007b).The double spike that characterizes the early 1970s is identified

in the BB record between BB30 and BB26 (60.4–49.7 cm), whereasthe next peak (BB24) corresponds to 1975. Kozák et al. (1993) havereported elevated tritium fallout in the Eastern Alps for the sametime, but they suggested that this phenomenon is a local anomaly.Our new data from the Bortig record confirms the existence of thispeak and as the distance between the Eastern Alps and Bihor Mts is~1000 km, a regional tritium signal at that time can be suspected.BB15 displays a small peak in the record dated to 1981, just

before the onset of a decreasing trend towards values below10 TU. Finally, sample BB6, situated between the lowestdetectable (BB7) and the unmeasurable (BB5) samples, wasassigned to 1986 when interpolated data present a small peakbetween the mid-1980s and late-1980s minima.

Zoltán Kern et al.: Tritium in an ice core from a Romanian cave 733

Figure 5 Links between (a) the curve of measured tritium content of BB cave ice core and (b) of estimated atmospheric precipitation. Peaks ofBB record served as anchor points owing to the remarkably similar pattern of the curves (BB75: 1954, BB64: 1958, BB48: 1963, BB27: 1972,BB24: 1975, BB15: 1981, BB6: 1986)

by Zoltan Kern on October 4, 2009 http://hol.sagepub.comDownloaded from

Above this level minor fluctuations hardly exceed the measure-ment error, so their interpretation might be ambiguous.Apart from these points, two additional reference points were

designated in the older part of the record.According to mosaics of fragmented data during early records

the first peak in the concentration of anthropogenic-induced tri-tium in the atmospheric precipitation was experienced in 1954,with a second one in 1958 over Europe (Eriksson, 1965). The exis-tence of this latter peak in the region was additionally confirmedby analysis of tritium concentration of cellulose from tree rings ofspruce samples taken from the Mátra Mts, Hungary (Kozák et al.,1989). These two peaks (1954 and 1958) were attributed to sam-ples BB75 and BB64, respectively, in our record.

Having these peaks and the attributed ages, a linear regressionwas fitted to them, perfectly matching to the points (Figure 6). Theslope of the regression line indicates that mean ice accumulationrate was 4.34 cm/yr between 1954 and 1986. Age–depth modeldates BB78, the first sample with measurable tritium, to 1953,which is in line with the first European observations (Eriksson,1965). Close agreement between the position of the most signifi-cant dust horizon and the tritium maximum in BA and BB coresargues that the same age model is valid for both ice cores. Usingthe equation of the abovementioned regression line as a linearage–depth model, the deepest layer from BA (−205 cm) and BB(−197 cm) core is estimated to originate in 1942 and 1944, respec-tively. Finally, the model yields AD 1521 for the deepest part (−21 m)of the ice deposit.However it is clearly visible in Figure 6 that despite the almost

perfect fit (R2=0.99) minor deviations appear from the averagerate; and moreover, this linear growth model tends to overestimatethe ice growth at 20 cm depth and strongly overestimates for theuppermost/youngest 10 cm.Annual average growth rate was calculated for the dated periods

over the past five decades (Figure 7). Highest annual growth (6.74cm/yr) is derived for 1958–1963. The cave ice growth ratedegraded down to (3.14 cm/yr) until 1981. Slightly higher growthrate (3.47 cm/yr) is noticed for the first half of the 1980s. The pasttwo decades were characterized by the lowest growth rate (0.54cm/yr) among the seven periods. This moderate mean growth rateis not simply the result of decreasing ice accumulation but melt-back has also taken place in this period as evidenced by dust hori-zons. It means that the mass balance regime of Bortig Ice Cave hasreached a threshold in the recent past when annual fluctuation inthe mass balance tends to be negative. This is anomalous behaviour

734 The Holocene 19,5 (2009)

Figure 6 Linear age–depth model of BB ice core constructed fromseven dated points

Figure 7 Mean cave ice growth from Bortig Ice Cave for seven discrete periods of the past five decades. Horizontal dotted line indicates the calcu-lated long-term mean growth rate based on 3H data. Both increasing temperature and decreased snow are candidate triggers for recent depression of icegrowth. Inset graph: mean annual air temperature (a) and November–March (snow season) total precipitation at the nearest high-elevation meteorologi-cal station (Vladeasa, 46.75°N, 22.80°E, 1800 m a.s.l.). Dashed horizontal grey lines indicate of the long-term mean of the respected climatic variable

by Zoltan Kern on October 4, 2009 http://hol.sagepub.comDownloaded from

compared with the preceding periods. Both temperature and precip-itation are plausible candidates to trigger this phenomenon becauseinstrumental data of a nearby climate station show a steady increasein annual mean temperature since the mid-1980s and a more abruptdrop in November–March precipitation (ie, snow) in the early 1980s(Figure 7 inset). Similar changes in cave ice mass balance and mete-orological factors were reported from the Swiss Jura Mts(Luetscher, 2005; Luetscher et al., 2005). Future research mustfocus on investigation and interpretation of the controlling role ofexternal climatic factors on the subterranean ice mass balance.

Conclusion

Two ice cores (BA, BB) were extracted from the floor ice ofBortig Ice Cave in December 2005. Beneath a co-existing dusthorizon (~13 cm below the 10 December 2005 ice surface) neithercore has presented any sign of hiatus.The salient value of tritium content BB48 of the Bortig ice core

record is connected to the 1963 climax of tritium concentration inthe Northern Hemisphere’s atmospheric precipitation. Beside thischaracteristic global radiochemical marker event, minor eventswere also detected (1954, 1958 and 1975). Trusting in the patternof 3H BB record, finally, seven peaks were attributed to calendardates. The 1975 peak is suggested to apply as a time marker inother ongoing cave ice dating studies from the Carpathians(Holmlund et al., 2005; Clausen et al., 2007; Turri et al., 2008).The mean ice accumulation rate is estimated as 4.34 cm/yr dur-

ing the 1954–1986 period. The mean annual growth rate hasdegraded to one-twelfth of its semi-centennial maximum for therecent decades. The explanation of this significant decrease mustbe climate related (surface temperature increase combined withdecrease in the amount of snow) and further research is needed toinvestigate its detailed interpretation.However, the results highlighted that if a subsurface ice body is

accumulated dominantly from unaltered atmospheric precipita-tion, and long-term melting has not erased a significant part of thetwentieth-century ice deposition, then tritium concentration datagained from cave ice can be applied in a retrospective evaluationof local tritium fallout history. In addition, the above results prom-ise that if radioactive isotopic features of water molecules of pre-cipitation have been preserved in the cave ice then stable isotopiccomposition is also preserved by the same resolution and fidelityand they can be applied as a palaeothermometer in future climatereconstruction studies.

Acknowledgements

We say special thanks to Dániel Balogh, Balázs Kohán, DénesKovács and Péter László who helped transport drilling equipmentand ice samples in harsh winter weather. The research was par-tially funded by the Hungarian Science Foundation (OTKA)K67583. Travel cost was financed by RO-37/2005. MarcLuetscher and an anonymous reviewer provided comments thatgreatly improved the scientific quality of the paper.

References

Ambach, W., Eisner, H., Elsässer, M., Löschhorn, U., Moser, H.,Rauert, W. and Stichler, W. 1977: Deuterium, tritium and grossβ-activity investigations on alpine glaciers (Oetztal Alps). Proceedingsof 16th IUGG General Assembly. IAHS Publication 118, 285–88.Barth, K.H. 1998: Science and politics in the early Nuclear Test Bannegotiations. Physics Today 51, 34–39.

Citterio, M., Turri, S., Persoiu, A., Bini, A. and Maggi, V. 2005:Radiocarbon ages from two ice caves in the Italian Alps and theRomanian Carpathians and their significance. In Mavlyudov, B.R., edi-tor,Glacier caves and glacial karst in high mountains and polar regions.Institute of Geography of the Russian Academy of Sciences, 87–92.Clausen, H. B., Vrana, K., Hansen, S.B., Larsen, L.B., Baker, J.,Siggaard-Andersen, M-L., Sjolte, J. and Lundholm, S.C. 2007:Continental ice body in Dobšiná Ice Cave (Slovakia) – part II. Resultsof chemical and isotopic study. In Zelinka, J., editor, Proceedings ofthe 2nd international workshop on ice caves. Liptovsky Mikulás,29–37.Curie, L.A. 1995: Nomenclature in evaluation of analytical methodsincluding detection and quantification capabilities. (IUPACRecommendation 1995) Pure & Applied Chemistry 67, 1699–723.—— 2004: Uncertainty in measurements close to detection limits:detection and quantification capabilities. Quantifying uncertainty innuclear analytical measurements. IAEA, IAEA-TECDOC-1401,9–34.Deák, J. 2006: A Duna-Tisza köze rétegvíz áramlási rendszerénekizotóp-hidrológiai vizsgálata. PhD thesis, Eötvös LorándUniversity.Eichler, A., Schwikowski, M., Gäggeler, H.W., Furrer, V., Synal,H., Beer, J., Saurer, M. and Funk, M. 2000: Glaciochemical datingof an ice core from upper Grenzgletscher (4200 m a.s.l.). Journal ofGlaciology 154, 507–15.Eriksson, E. 1965: An account of the major pulses of tritium and theireffects in the atmosphere. Tellus 17, 118–30.Fourré, E., Jean-Baptiste, P., Dapoigny, A., Baumier, D., Petit, J.and Jouzel, J. 2006: Past and recent tritium levels in Arctic andAntarctic polar caps. Earth and Planetary Science Letters 245, 56–64.doi: 10.1016/j.epsl.2006.03.003Ginot, P., Kull, C., Schotterer, U., Schwikowski, M. and Gäggeler,H.W. 2006: Glacier mass balance reconstruction by sublimationinduced enrichment of chemical species on Cerro Tapado. Climate ofthe Past 2, 21–30.Goncharov, G.A. 1996: The American effort. Physics Today 49,45–48.Hanzlik, S. and Ulrich, F. 1938: The ice cave of Dobsina inCzechoslovakia. IAHS publication 23, 695–98.Holmlund, P., Onac, B.P., Hansson, M., Holmgren, K., Mörth, M.,Nyman, M. and Persoiu, A. 2005: Assessing the palaeoclimate poten-tial of cave glaciers: the example of Scarisoara Ice Cave (Romania),Geografiska Annaler 87 A, 193–201.Horvatincic, N. 1996: Izotopina mjerenja u ledu, Jama Ledenica,Velebit. (Isotopic measurement in ice, Ledenica Cave, Velebit,Croatia.) In Kubelka, D. and Kovac, J., editors, Proceedings of thethird symposium of the Croatian Radiation Protection Association.297–302 (in Croatian).International Atomic Energy Agency 2004: Isotope hydrologyinformation system. The ISOHIS database. Accessible athttp://isohis.iaea.orgJouzel, J., Merlivat, L., Pourchet, M. and Lorius, C. 1979: A con-tinuous record of artificial tritiumfallout at the South Pole (1954–78).Earth and Planetary Science Letters 45, 188–200.Kern, Z., Fórizs, I., Kázmér, M., Nagy, B., Szántó, Zs., Gál, A.,Palcsu, L. and Molnár, M. 2004: Late Holocene environmentalchanges recorded at Ghetarul de la Focul Viu, Bihor Mts, Romania.Theoretical and Applied Karstology 17, 51–60.Kern, Z., Surányi, G., Molnár, M., Nagy, B. and Balogh, D. 2007a:Investigation of natural perennial ice deposits of Durmitor Mts,Montenegro. In Zelinka, J., editor, Proceedings of the 2nd interna-tional workshop on ice caves. Liptovsky Mikulás, Slovakia, 70–73.Kern, Z., Molnár, M., Persoiu, A. and Nagy, B. 2007b:Radiochemical and stratigraphic analysis of two ice cores from BortigIce Cave, Apuseni Mts, Romania. In Zelinka, J., editor, Proceedingsof the 2nd international workshop on ice caves. Liptovsky Mikulás,Slovakia, 65–69.Kozák, K., Obelic, B. and Horvatincic, N. 1989: Tritium and 14C intree rings of the last three decades. Radiocarbon 31, 766–70.Kozák, K., Rank, D., Biró, T., Rajner, V., Golder, F. and Staudner,F. 1993: Retrospective evaluation of tritium fallout by tree-ring analy-sis. Journal of Environmental Radioactivity 19, 67–77.

Zoltán Kern et al.: Tritium in an ice core from a Romanian cave 735

by Zoltan Kern on October 4, 2009 http://hol.sagepub.comDownloaded from

Lucas, L.L. and Unterweger, M.P. 2000: Comprehensive review andcritical evaluation of the half-life of tritium. Journal of Research of theNational Institute of Standards, Technology 105, 541–49.Luetscher, M. 2005: Processes in ice caves and their significance forpaleoenvironmental reconstructions. SISKA.Luetscher, M. and Jeannin, P. 2004: A process-based classificationof alpine ice caves. Theoretical and Applied Karstology 17, 5–10.Luetscher, M., Jeannin, P. and Haeberli, W. 2005: Ice caves as anindicator of winter climate evolution: a case study from the JuraMountains. The Holocene 15, 982–93.Luetscher, M., Bolius, D., Schwikowski, M., Schotterer, U. andSmart, P.L. 2007: Comparison of techniques for dating of subsurfaceice from Monlesi ice cave, Switzerland. Journal of Glaciology 53,374–84.Merlivat, L., Jouzel, J., Robert, J. and Lorius, C. 1977: Distributionof artificial tritium in firn samples from East Antarctica. Proceedingsof 16th IUGG General Assembly. IAHS Publication 118, 138–45.Olivier, S., Schwikowski, M., Brütsch, S., Eyrikh, S., Gäggeler,H.W., Lüthi, M., Papina, T., Saurer, M., Schotterer, U., Tobler, L.and Vogel, E. 2003: Glaciochemical investigation of an ice core fromBelukha glacier, Siberian Altai. Geophysical Research Letters 30,2019, doi:10.1029/2003GL018290Olivier, S., Bajo, S., Fifield, L.K., Gäggeler, H.W., Papina, T.,Santichi, P.H., Schotterer, U., Schwikowski, M. and Wacker, L.2004: Plutonium from global fallout recorded in an ice core fromBelukha glacier, Siberian Altai. Environmental Science and Technology38, 6507–12. doi:10.1021/es0492900Orghidan, T., Neagra, S., Racovita, G. and Lascu, C. 1984: Pesteridin Romania. ghid turistic, Sport-Turism, 85–87.Pourchet, M., Lefauconnier, B., Pinglot, J.F. andHagen, J.O. 1995:Mean net accumulation of ten glacier basins in Svalbard estimatedfrom detection of radioactive layers in shallow ice cores. Zeitschriftfür Gletscherkunde und Glazialgeologie 31, 73–84.

Racovita, G. 1972: Sur la correlation entre l’évolution du climat et ladynamique des dépôts souterrains de glace de la Grotte de Scarisoara.Travaux de l’Institut de Spéologie ‘Emil Racovitza’ 11, 373–92.Ravoire, J., Lorius, C., Robert, J. and Roth, E. 1970: Tritium con-tent in a firn core from Antarctica. Journal of Geophysical Research75, 2331–35.Romanov, V.V. 1977: Tritium in Pamir glaciers. Proceedings of 16thIUGG General Assembly. IAHS Publication 118, 417.Rygielski, W., Siarzewski, W. andWieliczko, P. 1995: Variability ofthe ice deposit in ice cave on Mount Ciemniak in the West TatraMountains. Quaestiones Geographicae 17, 55–64.Schwikowski, M., Brütsch, S., Gäggeler, H.W. and Schotterer, U.1999: A high-resolution air chemistry record from an Alpine ice core:Fiescherhorn glacier, Swiss Alps. Journal of Geophysical Research104 D11, 13 709–19.Serban, M., Blaga, L., Blaga, L., Chifu, A. and Ciobotaru, T. 1967:Contributii la stratigrafia depozitelor de gheat a din Ghetarul de laScarisoara. Lucrarile Institutului de Speologie ‘Emil Racovita’ 6, 107–40.Stuart, C.T. and Sharp, M.J. 2003: Deriving glacier mass balanceand recent climate conditions from shallow ice cores. 60th easternsnow conference. Sherbrooke, 197–204.Svetlik, I. and Budska, E. 2001: Monitoring of tritium in atmosphericprecipitation. Bezpecnost jaderné energie (The safety of nuclearenergy) 9, 251–54.Theodórsson, P. 1977: 40-year tritium profiles in a polar and a tem-perate glacier. Proceedings of 16th IUGG General Assembly. IAHSPublication 118, 393–98.Turri, S., Maggi, V. and Bini, A. 2008: 2000 years history in theFocul Viu Ice Cave, Romania. In Turri, S., editor, 3rd internationalworkshop on ice caves. Volume of Abstracts, 15.Weiler, K., Fischer, H., Fritzsche, D., Ruth, U., Wilhelms, F. andMiller, H. 2005: Glaciochemical reconnaissance of a new ice core fromSevernaya Zemlya, Eurasian Arctic. Journal of Glaciology 172, 64–74.

736 The Holocene 19,5 (2009)

by Zoltan Kern on October 4, 2009 http://hol.sagepub.comDownloaded from