ライフサイエンスコーパス: radiocarbon

1 mporary levels and highly depleted levels of radiocarbon.

2 re work on in-situ monitoring of atmospheric radiocarbon.

3 We used the radiocarbon ((14) C) 'bomb spike' as a tracer of substra

4 ch and sugars in a subset of trees using the radiocarbon ((14) C) bomb spike.

5 ws the determination of the full spectrum of radiocarbon ((14)C) ages present in a soil or sediment s

6 m natural samples are often insufficient for radiocarbon ((14)C) analyses (<50 mug C).

7 (AMS), has been investigated for the online radiocarbon ((14)C) analysis of carbonate records.

8 Radiocarbon ((14)C) analysis revealed that B. chinensis

9 Here, via an extensive radiocarbon ((14)C) characterisation of CO(2) and DOC in

10 origin of two large peaks in the atmospheric radiocarbon ((14)C) concentration at AD 774/5 and 993/4

11 Many applications are sensitive to the radiocarbon ((14)C) content of atmospheric CO2, which ha

12 sition, and stable isotopic (delta(13)C) and radiocarbon ((14)C) contents of DOM.

13 We support our arguments with radiocarbon ((14)C) data of higher plant leaf-wax n-alka

14 mporal frequency distributions of aggregated radiocarbon ((14)C) dates are used as a proxy of populat

15 Existing radiocarbon ((14)C) dates on American mastodon (Mammut a

16 Radiocarbon ((14)C) dating is an attractive alternative,

17 ugh 1962 nearly doubled the concentration of radiocarbon ((14)C) in the atmosphere.

18 Radiocarbon ((14)C) is potentially significant in terms

19 Stable carbon ((13)C) and radiocarbon ((14)C) isotopic data demonstrate a predomin

20 sil contributions to carbonaceous particles, radiocarbon ((14)C) measurements were performed on organ

21 versity experiment (The Jena Experiment) and radiocarbon ((14)C) modelling.

22 curely dated, decadally-resolved atmospheric radiocarbon ((14)C) record spanning GS-1.

23 Here, we used the radiocarbon ((14)C) signature of microbial DNA isolated

24 the opposing patterns of atmospheric CO2 and radiocarbon activities (Delta(14)C) suggest the release

25 Radiocarbon activities were measured in annual tree ring

26 Based on stable isotope signatures and radiocarbon activity of organic matter in soil profiles,

27 Radiocarbon activity tracks changes in ocean ventilation

28 Using radiocarbon age also implicitly models the preferential

29 The PDMS CH3 groups are of "infinite" radiocarbon age due to the fossil carbon origin of the f

30 origin, which explains the observed middepth radiocarbon age maximum and may play an important role i

31 m the Southern Ocean, producing a widespread radiocarbon age maximum at mid-depths and depriving the

32 Here we present unique simultaneous radiocarbon age measurements of inland water CO(2), CH(4

33 AMEs, which would lead to a maximum shift in radiocarbon age of <3 years toward older values.

34 ided in the basin for millennia, with a mean radiocarbon age of 5,800 +/- 800 years, much older than

35 ecific fluorescence intensity of DOM and its radiocarbon age were identified, indicating that optical

36 ir with two distinct components of differing radiocarbon age.

37 however, discrepancies between the measured radiocarbon ages and expected ages were observed.

38 Radiocarbon ages further reveal that high-energy, minera

39 Offsets towards older radiocarbon ages in Mediterranean-Anatolian wood can be

40 c carbon activation energy and corresponding radiocarbon ages in soils, sediments and dissolved organ

41 Comparison of radiocarbon ages of bulk organic carbon and terrestrial

42 ciently high concentrations, would shift the radiocarbon ages of trapped compounds to older ages.

43 Twenty-seven new radiocarbon ages on the bones of these animals revise th

44 Thirty-four radiocarbon ages show that beaver cuttings have accumula

45 X-ray diffraction analysis (XRD) and six AMS radiocarbon ages show that between ~ 2185 and 965 cal yr

46 Radiocarbon analyses are commonly used in a broad range

47 Radiocarbon analyses demonstrate that CH4 and CO2 are pr

48 from bulk carbon to compound class specific radiocarbon analysis (CCSRA) to determine Delta(14)C and

49 Compound-specific radiocarbon analysis (CSRA) of amino acids (AAs) is of g

50 Radiocarbon analysis allowed us to elucidate cryptic die

51 In this study, we advanced the radiocarbon analysis from bulk carbon to compound class

52 Radiocarbon analysis of perylene indicated that 70-85% o

53 Using radiocarbon analysis of phospholipid fatty acids (PLFAs)

54 Radiocarbon analysis of pyrogenic PAHs showed a 50% decr

55 Radiocarbon analysis of the skulls shows that the indivi

56 Radiocarbon analysis showed overall no significant diffe

57 latile or semivolatile organic compounds for radiocarbon analysis using accelerator mass spectrometry

58 croplands, the remaining SIC had more modern radiocarbon and a delta(13) C composition that was close

59 More than 50 radiocarbon and luminescence dates provide chronological

60 Radiocarbon and luminescence dating of the surrounding s

61 by characterizing community RNA through its radiocarbon and ribosomal RNA (rRNA) signatures.

62 New radiocarbon and sedimentological results from the Gulf o

63 its impact on respired carbon storage using radiocarbon and stable carbon isotope data from the Braz

64 Our results are based on coupled radiocarbon and uranium-series dates, along with clumped

65 pyrolysis (delta(13)Cpyr), natural abundance radiocarbon, and high resolution Orbitrap mass spectrome

66 Here we use the lipid profiles, radiocarbon, and stable carbon isotopic signatures of li

67 Radiocarbon apportionment of EC indicates that fossil so

68 Using the bomb-spike radiocarbon approach we were able to estimate the averag

69 Analyzing radiocarbon at different treatment points within municip

70 Radiocarbon-based estimates indicated that the mean age

71 We address this knowledge gap by coupling a radiocarbon-based model to 7 years (2008-2014) of contin

72 explain the ~190 per mil drop in atmospheric radiocarbon between ~17 and 14.5 ka.

73 sharks (220 cm or less) showed signs of the radiocarbon bomb pulse, a time marker of the early 1960s

74 The new radiocarbon calibration curve (IntCal20) allows us to ca

75 and (40)Ar/(39)Ar ages for refining both the radiocarbon calibration curve and the Late Pleistocene t

76 w that sampling biases, atmospheric effects, radiocarbon calibration error, and taphonomic processes

77 proach to remove the age artifacts caused by radiocarbon calibration from a large series of dated meg

78 we used the continuous label offered by the radiocarbon (carbon-14, (14) C) bomb spike to estimate t

79 n addition, both gradual and rapid deglacial radiocarbon changes in these Pacific records are coeval

80 an bones to produce a robust, high-precision radiocarbon chronology for the site.

81 Its application yields a consistent radiocarbon chronology of all soil horizons formed betwe

82 mum between 48 and 40 ka BP during which the radiocarbon clock runs almost twice as fast as it should

83 ifferentiating the two CO2 samples, with the radiocarbon concentration 3 orders of magnitude apart, C

84 can be made of past increases in atmospheric radiocarbon concentration or so-called Miyake events.

85 uld affect the seasonal cycle of atmospheric radiocarbon concentrations recorded in different geograp

86 Radiocarbon-constrained chronologies from marine sedimen

87 surements to quantify the absolute amount of radiocarbon-containing methane ((14)CH4) in the past atm

88 , we present a full year characterization of radiocarbon content ((14) C) of dissolved organic carbon

89 than expected from the observed increase in radiocarbon content from those at the greatest depths.

90 This work links DOM composition with its radiocarbon content in permafrost peatlands.

91 e we use time-integrated observations of the radiocarbon content of CO2 ((14)CO2) to quantify the rec

92 The radiocarbon content of DOC in the surface water of the A

93 We measured the radiocarbon content of DOC in the water column on the we

94 Trends in concentrations and radiocarbon content of pyrogenic PAHs and perylene were

95 The depleted radiocarbon content of the warm and salty water mass imp

96 struct changes in deep water and thermocline radiocarbon content over the last deglaciation in the ea

97 e achieve this by integrating archaeological radiocarbon data and palaeoclimatic time series to show

98 We compared ancient DNA and radiocarbon data from 31 detailed time series of regiona

99 Here we combine new radiocarbon data from the Eastern Equatorial Pacific (EE

100 Here, we report radiocarbon data from uranium-thorium-dated deep-sea cor

101 eoretical underpinning for this expectation, radiocarbon data on watermass ventilation ages conflict,

102 n cycle impacts remains to be confirmed, the radiocarbon data suggest an increase in the efficiency o

103 conic site and a Bayesian analysis of legacy radiocarbon data, which nuance previous conclusions and

104 The Canadian Archaeological Radiocarbon Database contains more than 35,000 (14)C dat

105 Large radiocarbon datasets have been analysed statistically to

106 of 55 individuals, each with an independent radiocarbon date between 2,440 and 100 cal BP, from two

107 d busts in the context of uncertainty in the radiocarbon date calibration curve and archaeological sa

108 We demonstrate that summed calibrated radiocarbon date distributions and simulation can be use

109 cause of the lack either of a direct hominin radiocarbon date or of molecular confirmation of the Nea

110 ulation proxy based on summed archaeological radiocarbon date probability densities.

111 ley in Iberia at ca. 36 ka calBP (calibrated radiocarbon date ranges).

112 , and Holocene climate via an archaeological radiocarbon date series of unprecedented sampling densit

113 We describe the find and identify and radiocarbon date the construction materials.

114 om northern Greenland to the Laptev Sea were radiocarbon dated and analyzed for their micropaleontolo

115 Radiocarbon dated fossils indicate that hutias were pres

116 Washington state (USA) in 1996 and initially radiocarbon dated to 8,340-9,200 calibrated years before

117 Five of the individuals (directly radiocarbon dated to a time transect spanning the 7(th)-

118 alyze organic residues from a ritual bundle, radiocarbon dated to approximately 1,000 C.E., recovered

119 04 AD, around the nuclear bombs period, were radiocarbon dated.

120 A 3800 year-long radiocarbon-dated and highly-resolved palaeoecological r

121 dings on the cultural spread of farming from radiocarbon-dated archaeological sites.

122 Our isotope records from modern and ancient, radiocarbon-dated bones provide evidence of over 3,000 y

123 We measured Hg stable isotope signatures of radiocarbon-dated boreal forest soils and modeled atmosp

124 Here, we show that radiocarbon-dated charcoal recovered from an ice deposit

125 Radiocarbon-dated fossils show that late Quaternary loss

126 assemblage overlaps with the latest directly radiocarbon-dated Neanderthal remains, suggesting that N

127 Here we present a radiocarbon-dated record from Integrated Ocean Drilling

128 sibericum, was isolated from a >30,000-y-old radiocarbon-dated sample when we initiated a survey of t

129 l time-series analysis of a high-resolution, radiocarbon-dated sequence of 22 faunas spanning the Hol

130 adiogenic isotope ratios of strontium for 84 radiocarbon-dated skeletons from seven archaeological si

131 al formed during or after this period may be radiocarbon-dated using the abrupt rise and steady fall

132 sediments retained within seven out of nine, radiocarbon-dated, Late Pleistocene mammoth (Mammuthus p

133 The new radiocarbon dates align Iberian chronologies with AMH di

134 Here, we use radiocarbon dates and ancient mitochondrial DNA from lat

135 Direct radiocarbon dates and cob morphological data from the ro

136 tie-points allows direct comparison between radiocarbon dates and Greenland climate records.

137 t statistical analyses of large ensembles of radiocarbon dates are robust and valuable for quantitati

138 t is exposing intact plant communities whose radiocarbon dates demonstrate entombment during the Litt

139 s of spacings and frequency distributions of radiocarbon dates for each region support the idea that

140 Radiocarbon dates for the ancient drawings in the Chauve

141 y them to a new, extensive dataset of 14,535 radiocarbon dates for the Mesolithic and Neolithic perio

142 All bat radiocarbon dates from Abaco (Bahamas) that represent ex

143 son with summed probability distributions of radiocarbon dates from archaeological sites indicate tha

144 climate, together with a compilation of 627 radiocarbon dates from archeological sites in Northeast

145 /- 3300 to 29,400 +/- 2300 BP, and three AMS radiocarbon dates from charcoal samples belonging to the

146 ined by a divergence between high-resolution radiocarbon dates from the recent generation of accelera

147 Six new radiocarbon dates help establish the chronology of the n

148 Radiocarbon dates indicate that peat began accumulating

149 A series of radiocarbon dates indicate that the precinct's different

150 Our accelerator mass spectrometry radiocarbon dates of 14 individual charcoal particles ar

151 We combined novel radiocarbon dates of bat fossils with time-scaled ecolog

152 latest chronology for the site, based on AMS radiocarbon dates of shell ornaments, suggests that the

153 Though radiocarbon dates on archaeological remains such as char

154 Radiocarbon dates on charcoal are consistent with a mid-

155 gy based on 26 accelerator mass spectrometry radiocarbon dates on ostrich eggshells indicates an age

156 ologies that contained previously determined radiocarbon dates on other materials(11-15).

157 To that end, we compiled lists of direct radiocarbon dates on paleontological specimens of extinc

158 Here we show that pre-Holocene radiocarbon dates on plants collected at the margins of

159 Here, we report 88 radiocarbon dates on the botanical remains from El Gigan

160 Here we report a series of AMS radiocarbon dates on the marine gastropod Phorcus turbin

161 rt a series of accelerator mass spectrometry radiocarbon dates on ultrafiltered bone collagen extract

162 Radiocarbon dates on wetland plants exposed along its re

163 orous pretreatment protocols have been used, radiocarbon dates should be assumed to be inaccurate unt

164 47 archaeological sites and 5,464 calibrated radiocarbon dates spanning fourteen thousand to two thou

165 dar survey coupled with multiple proxies and radiocarbon dates that reveal ancient field uses and chr

166 The radiocarbon dates were calibrated using a Bayesian stati

167 Through the analysis of radiocarbon dates with Monte Carlo methods, we find mult

168 ever, two-thirds of dates from the south are radiocarbon dates, a technique that is particularly sens

169 a proxy evidence from tree rings, ice cores, radiocarbon dates, and documentary sources is integrated

170 In the absence of radiocarbon dates, bat extinctions had been presumed to

171 , and stone tool residues, combined with 126 radiocarbon dates, demonstrate that maize was widely gro

172 sequences, sampling dates, phenotypic data, radiocarbon dates, fossil occurrences, and biogeographic

173 he basis of Bayesian analyses, a total of 26 radiocarbon dates, including 17 new ones, show that repl

174 They include 259 radiocarbon dates, mainly related to the rock art and hu

175 We obtained radiocarbon dates, pollen, macrofossils and metagenomic

176 Using a regional database of n = 523 radiocarbon dates, we find a significant drop in relativ

177 Sample age was estimated by interpolating 40 radiocarbon dates.

178 1000 and 800 BC using a Bayesian analysis of radiocarbon dates.

179 various timescales and corroborate or refine radiocarbon dates.

180 ive suite of both bulk and compound-specific radiocarbon dates.

181 Measurements included radiocarbon dating (to determine peat accumulation rates

182 ntial alternative to the use of charcoal for radiocarbon dating analyses.

183 This result, combined with radiocarbon dating and archaeological evidence, reveals

184 oring possible applications in the fields of radiocarbon dating and atmospheric monitoring.

185 Direct accelerator mass spectometry radiocarbon dating and Bayesian modeling confirm that th

186 e damage of collagen, and screen samples for radiocarbon dating and DNA analysis.

187 s morphometrics, taphonomy, stable isotopes, radiocarbon dating and genetic analyses.

188 servations of Siberian permafrost exposures, radiocarbon dating and spatial analyses to quantify Holo

189 sites the existing age information based on radiocarbon dating and visual stratigraphy corroborates

190 n dioxide is fixed in the carbonate, and its radiocarbon dating can be used as a proxy for the age of

191 Archaeological, osteological and radiocarbon dating data were consistent with these being

192 locene epoch and previous attempts at direct radiocarbon dating have failed.

193 Following early radiocarbon dating in the 1970s, an alternative hypothes

194 Radiocarbon dating indicates that the three burial event

195 Radiocarbon dating indicates that these remains were not

196 arbon in various fields, and it implies that radiocarbon dating may no longer provide definitive ages

197 ion(1), accurate dating of pottery using the radiocarbon dating method has proven extremely challengi

198 e, we show, by accelerator mass spectrometry radiocarbon dating of 23 individuals, including cross-va

199 he accuracy of accelerator mass spectrometry radiocarbon dating of 29 herbivore and plant tissues col

200 ithic contexts formed by 6000 BC, but recent radiocarbon dating of a dozen 'early' grains cast doubt

201 Radiocarbon dating of both individuals (A120 to 533 AD [

202 AMS radiocarbon dating of cut-marked reindeer (Rangifer tara

203 Field surveys and radiocarbon dating of detrital materials provide evidenc

204 Radiocarbon dating of eye lens nuclei from 28 female Gre

205 ge of the Salkhit skull by compound-specific radiocarbon dating of hydroxyproline to 34,950-33,900 Ca

206 face waters in a boreal peat catchment using radiocarbon dating of particulate and dissolved organic

207 Accurate radiocarbon dating of pottery vessels can reveal: (1) th

208 nt (kyr B.P.) has limited the application of radiocarbon dating of samples from the Last Glacial peri

209 ogging, loss-on-ignition, ITRAX scanning and radiocarbon dating of the cores show that Kloverbladvatn

210 Radiocarbon dating of the earliest occupational phases a

211 Direct radiocarbon dating of Upper Palaeolithic tooth pendants

212 To overcome this problem, a radiocarbon dating protocol has been developed to date e

213 Subsequent radiocarbon dating revealed the bone to be >50,000 years

214 Accelerator mass spectrometry (AMS) radiocarbon dating showed fruits to be 31,800 +/- 300 y

215 ninvasive procedure presented here relies on radiocarbon dating the so-called angel's share: the trac

216 Here we use soil radiocarbon dating to quantitatively assess legacy carbo

217 Here, by radiocarbon dating various terrestrial OC components in

218 through changes in DOC concentration alone: Radiocarbon dating was essential to show that leaching o

219 We sampled 281 moa individuals and combined radiocarbon dating with ancient DNA analyses to help res

220 everal cranial fragments from the site using radiocarbon dating, ancient DNA, ZooMS and isotope analy

221 bining multiple lines of evidence, including radiocarbon dating, body size reconstructions, stable is

222 c and geomorphic data, physical volcanology, radiocarbon dating, tephra geochemistry, and chronicles,

223 ration to purify faunal bone collagen before radiocarbon dating, we obtain ages at least 10 ka (14)C

224 ving patterns, dyes/mordant, style, and even radiocarbon dating.

225 te resolution is the principal limitation of radiocarbon dating.

226 xonomy, ancient mitochondrial DNA and direct radiocarbon dating.

227 tubai Alps, Austria) allows for conventional radiocarbon dating.

228 pools in tailings sediment were essentially "radiocarbon dead" (i.e., Delta(14)C ~ -1000 per thousand

229 UCM to these environments, natural abundance radiocarbon (Delta(14)C) and stable carbon (delta(13)C)

230 Compound-specific stable (delta(13)C) and radiocarbon (Delta(14)C) isotopes of phospholipid fatty

231 e report spatially resolved DBC quantity and radiocarbon (Delta(14)C) measurements, paired with molec

232 he atmosphere, and respiration of relatively radiocarbon-depleted (i.e., older) substrate contributes

233 p Pacific Ocean that could have released its radiocarbon-depleted carbon stock to the atmosphere duri

234 ean is most likely the primary source of the radiocarbon-depleted CO2 released to the atmosphere duri

235 onstructed from deep-sea corals, which shows radiocarbon-depleted waters during the glacial period an

236 IntraCavity OptoGalvanic Spectroscopy as a radiocarbon detection technique was first reported by th

237 By combining radiocarbon detection using mid-infrared cavity ring-dow

238 This technique for radiocarbon detection was presented with tremendous pote

239 Galvanic Spectroscopy setup at Groningen for radiocarbon detection.

240 rbon-containing components that would affect radiocarbon determinations at the precisions achievable

241 Here we present 50 radiocarbon determinations from the late Middle and Uppe

242 We present accurate compound-specific radiocarbon determinations of lipids extracted from pott

243 re we use a global array of ocean-atmosphere radiocarbon disequilibrium estimates to demonstrate a ap

244 he chronological improvements enabled by the radiocarbon "earthworm clock" thus strongly enhance our

245 In-situ monitoring of radiocarbon emissions is challenging due to the lack of

246 We interpret these radiocarbon-enriched signals to represent two short-live

247 However, radiocarbon fingerprinting here clearly indicates that l

248 automatized continuous on-site monitoring of radiocarbon gaseous emissions from nuclear facilities.

249 anced sampling system, an elevated amount of radiocarbon in an atmospheric-like gas matrix was detect

250 evealed by anomalies in the concentration of radiocarbon in known-age tree-rings.

251 system is also able to discriminate between radiocarbon in organic or inorganic molecular form by co

252 gnized implications for many applications of radiocarbon in various fields, and it implies that radio

253 he coke plant fenceline samples had very low radiocarbon levels.

254 A radiocarbon mass balance quantified a predominantly natu

255 Based on a radiocarbon mass balance, we show that deep-DOC is consu

256 This setup allows direct radiocarbon measurements for over 70 samples daily by AM

257 The radiocarbon measurements of DOC, taken two years apart i

258 we utilize molecular-level natural-abundance radiocarbon measurements on an amalgamated sediment reco

259 Natural abundance radiocarbon measurements on surface sediment organic mat

260 hat the method is unsuited for ambient level radiocarbon measurements, and even highly enriched CO2 s

261 s older, close to or beyond the limit of the radiocarbon method for the Mousterian at Jarama VI and N

262 ndered reliable dating of the period, as the radiocarbon method reaches its limit at approximately 50

263 Bone collagen is an important material for radiocarbon, paleodietary, and paleoproteomic analyses,

264 ments, appear to delineate the modulation of radiocarbon production due to the Schwabe (11-year) sola

265 In this work we present specific radiocarbon radioactivity determinations and based on th

266 The new IntCal20 radiocarbon record continues decades of successful pract

267 Here we analyze the radiocarbon record of Iberia to reconstruct long-term ch

268 We present a 25,000-year-long Southern Ocean radiocarbon record reconstructed from deep-sea corals, w

269 Statistical analysis of the radiocarbon record shows that transitioning farming soci

270 ulation based on statistical analysis of the radiocarbon record.

271 hern Ocean, we show that existing deep-ocean radiocarbon records from the glacial period are sufficie

272 tarted developing this technique for various radiocarbon related applications.

273 chip (<200 ug), each delivering a different radiocarbon response.

274 cultural change in the region that multiple radiocarbon results extend back to 3,500 years ago.

275 stical approach to 2,410 currently available radiocarbon results from megalithic, partly premegalithi

276 The radiocarbon results suggest that megalithic graves emerg

277 ains of a palace complex dated by associated radiocarbon samples and ceramics to the Late Formative p

278 The outstanding radiocarbon sensitivity of accelerator mass spectrometry

279 Two major deglacial radiocarbon shifts occurred in phase with centennial atm

280 We locate the distinctive radiocarbon signal of the year 775 common era (CE) in wo

281 The RNA had a radiocarbon signature (Delta(14)C) of -193.4 +/- 5.6 per

282 Comparison of the RNA radiocarbon signature to those of potential carbon pools

283 even though it did not generate an anomalous radiocarbon signature.

284 technical refinement extends the utility of radiocarbon simulation methods and can provide a rigorou

285 We combine measurements of radiocarbon, stable carbon isotopes and element ratios t

286 This radiocarbon time dilation is due to the increase in the

287 Here we investigate three radiocarbon time-series of archaeological and historical

288 By combining our radiocarbon tip-dates with a split time prior that takes

289 aleolithic contexts were previously dated by radiocarbon to less than 42 ka calBP.

290 We used natural abundance radiocarbon to partition ecosystem respiration into auto

291 strath terraces, using dendrochronology and radiocarbon, to between 1893 CE and 1937 CE in the Middl

292 delling approach that combines chronometric (radiocarbon, uranium series and optical ages), stratigra

293 r, and use an average background or prespill radiocarbon value for sedimentary organic carbon that pr

294 in deep DOC concentration and the anomalous radiocarbon values of DOC in the Southern Ocean.

295 changes in AM circulation by reconstructing radiocarbon ventilation ages of the deep Nordic Seas ove

296 resent a record of North Atlantic deep-water radiocarbon ventilation, which we compare with similar d

297 Radiocarbon was detected in the form of (14)CO(2) after

298 t, CO2 samples containing elevated levels of radiocarbon were prepared in-house and experimented with

299 By around 15 to 14 thousand calibrated radiocarbon years before present (cal. kyr bp), glacial

300 nsis holotype (LB1), ~18 thousand calibrated radiocarbon years before present (kyr cal. BP), or the t