Sunday, October 9, 2011

Hit-or-myth? Linking a 1259 AD acid spike with an Okataina eruption.

Hit-or-myth? Linking a 1259 AD acid spike with an Okataina eruption. Introduction: Bronze Age catastrophes and myth-makingIn their recent provocative paper, Buckland et al. (1997) examinedevidence for two Bronze Age 'catastrophes'. The first, thedestruction of Bronze Age Thera (Santorini) by a cataclysmic volcaniceruption, was described as 'real and in need of a calendardate' (p. 581). The second, the apparent collapse of Middle BronzeAge settlement in upland Britain, was considered as a speculative event'hypothesized on archaeological grounds and dated by a tenuous linkthrough tree rings to an Icelandic volcano' (p. 581). Thefundamental purpose of their critique was to demonstrate that greatcaution is required in the interpretation of interdisciplinary studiesthat attempt to link archaeological findings with those from otherdisciplines. This caution is essential because such age-based linkagesmay enter the literature as if proven fact because the limitations ofthe data are rarely communicated clearly, either unwittingly orotherwise. This is anathema to archaeology because the distinctionbetween 'fact' and 'interpretation' may not alwaysbe obvious to its practitioners.Whilst we agree in general with their conclusions, we think Bucklandet al. have unintentionally violated one of their own tenets byconstructing a linkage, based on the assumed correlation of radiometricand ice-core derived dates alone, between the 1259 AD acid spike in icecores and an Okataina-derived volcanic eruption in New Zealand. Althoughonly a minor part of their paper, the construction of this link byBuckland et al. nonetheless is viewed as the initial step in themythicizing process they rightly wish to avoid. We demonstrate that sucha link is untenable because the age data Buckland et al. applied to theOkataina eruption are flawed, and we suggest that the 'link'needs correcting before a new myth develops. This correction isparticularly relevant to archaeological studies in the South Pacificbecause the Okataina-derived eruptive provides a valuable regional datumin dating New Zealand's exceptionally brief prehistory (Higham& Hogg 1997; Newnham et al. 1998).The 1259 An acid spike and the Kaharoa eruption, OkatainaThe 1259[+ or -]2 AD acid signal is one of the largest recorded inice cores from Greenland and Antarctica for the past 2000 years (Hammeret el. 1980; Langway et al. 1988; Zielinski et al. 1994). Because thespike is common to ice-core records at both poles, Langway et al. (1988)suggested that the eruption must have been large and equatorial. ElChichon volcano (Mexico) is a possible source (Palais et al. 1992).Buckland et el, however, attributed the 1259 AD acid spike to amid-latitude eruption from Okataina volcano in North Island[ILLUSTRATION FOR FIGURE 1 OMITTED]. The 'Okataina' eruptionis clearly the Kaharoa episode, the largest and most recent rhyoliticevent in New Zealand, which resulted in extensive tephra teph��ra?n.Solid matter that is ejected into the air by an erupting volcano.[Greek tephr fallout[ILLUSTRATION FOR FIGURE 1 OMITTED] (Lowe et al. in press a). The basisof Buckland et al.'s correlation with the 1259 AD ice-core acidityrecord is evidently the derivation of a date of 1259[+ or -]11 AD forthe Kaharoa eruption via calibration of associated radiocarbon ages(Ramsey 1994). This calibrated date is based on the mean age of 770[+ or-]20 b.p. reported in Simkin & Siebert (1994) following Froggatt& Lowe (1990). We do not dispute the calibration process per seexcept to comment that the Southern Hemisphere offset correction (Vogelet al. 1993; McCormac et al. in press) does not seem to have beenapplied. based on Stuiver & Reimer (1993) and Stuiver & Becker(1993) and the intercepts method, 770[+ or -]20 b.p. corresponds to1258-1283 AD without the offset, but with a -40-year offset correctionthe calibrated 1[Sigma] range is 1280-1291 AD, clearly incompatable with1259[+ or -]11 AD at this level of significance. Of more importance toour discussion is the fact that the 770[+ or -]20 b.p. age has beenrevised since its original publication in 1990. Consequently it is nolonger appropriate for obtaining a calibrated date, irrespective ofapplication of the inter-hemispheric offset correction.Lowe & Hogg (1992) published four new radiocarbon ages forKaharoa eruptives that gave a significantly younger mean age of 665[+ or-]17 b.p. An identical mean age of 665[+ or -]15 b.p. was obtained morerecently using cluster analysis of 22 radiocarbon ages. This new age,derived from unscreened ages minus outliers, is supported bystatistically identical ages obtained from three sets of screened agesselected to minimize the effects of inbuilt in��built?adj.Built-in; inherent.inbuiltAdjective(of a quality or feeling) present from the beginning: an inbuilt prejudiceAdj. 1. age or contamination (Loweet al. in press a). The calibration curve in the vicinity of 665 b.p. isvery wiggly and so even high precision radiocarbon ages translate into arelatively wide range of calendar dates [ILLUSTRATION FOR FIGURE 2OMITTED]: 665[+ or -]15 b.p. corresponds to 1299-1327 AD and 1350-1391AD at the 1[Sigma] level, and to 1291-1331 AD and 1343-1399 AD at the2[Sigma] level (Lowe et al. in press a). These new calibrated dates showthat the Kaharoa eruption must have taken place well after the 1259 ADacid spike was emplaced, and thus there can be no link between the twoevents. In reaching this conclusion we assume the 1259 AD acid signaldate is accurate.Conclusion: avoiding myth-makingThat there is demonstrably no connection between the 1259 AD acidspike and the c. 1300-1400 AD Kaharoa eruption has little bearing on themain conclusions reached by Buckland et al., which are forcefully arguedand timely (though disputed: Baillie 1998). Our point is that Bucklandet al. have violated one of their own tenets - the need for caution inconsidering possible relationships between events connected bychronological matching alone - by implying that there is a link betweenthe 1259 AD spike and a New Zealand eruption. The risk is that the'link', unless corrected in the literature, will eventuallymove along the pathway from 'reasonable speculation' to'proven fact'. Establishing an accurate date for the Kaharoaeruption (and discrediting a 'wrong' one) is essential forarchaeology in New Zealand and potentially other parts of EastPolynesia. This is because no prehistoric cultural remains are known tooccur beneath the Kaharoa Tephra (Anderson 1991), and because of thecritical role the tephra has in dating the earliest human-inducedenvironmental impacts in New Zealand (Newnham et al. in press; Lowe etal. in press b).The age data in FIGURE 2 imply that a sulphate spike (or otherenvironmental effects) from the Kaharoa eruption may be represented inthe ice-core and/or tree-ring records from c. 1290 to 1330 AD or c. 1340to 1400 AD. The presence of volcanic glass in the same layer as asulphate signal in an ice core provides the best way of directlyidentifying the source eruption, as shown for Santorini by Zielinski& Germani (1998). It also provides a potential means of linking theice-core and tree-ring records (Baillie 1996). Thus, if glass from thecompositionally distinctive Kaharoa eruption (Stokes et al. 1992) wereidentifiable in the ice sheets (e.g. Antarctica), it would provide animportant late Holocene chronostratigraphic marker event for globalice-core and tree-ring studies and hence other disciplines includingarchaeology. In view of its importance, we are attempting to determine amore precise date for the Kaharoa eruption using dendrochronology dendrochronology:see dating. dendrochronologyMethod of scientific dating based on the analysis of tree rings. Because the width of annular rings varies with climatic conditions, laboratory analysis of timber core samples allows scientists to (Loweet al. in press a).Acknowledgements. We are grateful to Greg Zielinski for discussionsand a pre-print of Zielinski & Germani (1998}, and to anonymousreviewers for their comments.ReferencesANDERSON, A.J. 1991. The chronology of colonization in New Zealand,Antiquity 65: 767-95.BAILLIE, M.G.L. 1996. Extreme environmental events and the linking ofthe tree-ring and ice-core records, Radiocarbon 38: 703-11.1998. Bronze Age myths expose archaeological shortcomings? a reply toBuckland et al. 1997, Antiquity 72: 4257.BUCKLAND, P.C., A.J. DUGMORE & K.J. EDWARDS. 1997. Bronze Agemyths? Volcanic activity and human responses in the Mediterranean andNorth Atlantic regions, Antiquity 71: 581-93.FROGGATT, P.C. & D.J. LOWE.1990. A review of late Quaternary quaternary/qua��ter��nary/ (kwah��ter-nar?e)1. fourth in order.2. containing four elements or groups.qua��ter��nar��yadj.1. Consisting of four; in fours. silicic si��lic��ic?adj.Relating to, resembling, containing, or derived from silica or silicon. and some other tephra formations from New Zealand: theirstratigraphy, nomenclature, distribution, volume, and age, New ZealandJournal of Geology and Geophysics 33: 89-109.HAMMER, C.U., H.B. CLAUSEN & W. DANSGAARD.1980. Greenland icesheet Greenland Ice SheetSingle ice cap, Greenland. Covering about 80% of the island of Greenland, it is the largest ice mass in the Northern Hemisphere, second only to the Antarctic. evidence of post-glacial volcanism volcanismor vulcanismAny of various processes and phenomena associated with the surface discharge of molten rock or hot water and steam, including volcanoes, geysers, and fumaroles. and its climatic impact, Nature288: 230-35.HIGHAM, T.F.G. & A.G. HOGG.1997. Evidence for late Polynesiancolonisation of New Zealand: University of Waikato In 2002 over 14,000 students were enrolled at the university. More than a quarter of students were aged over 25, and over half were women. It has the highest proportion of Māori students on any campus in New Zealand. radiocarbonmeasurements, Radiocarbon 39: 149-92.LANGWAY, C.C., JR, H.B. CLAUSEN & C.U. HAMMER. 1988. Aninter-hemispheric volcanic time-marker in ice cores from Greenland andAntarctica, Annals of Glaciology glaciologyScientific discipline concerned with all aspects of ice on landmasses. It deals with the structure and properties of glacier ice, its formation and distribution, the dynamics of ice flow, and the interactions of ice accumulations with climate. 10: 1028.LOWE, D.J. & A.G. HOGG. 1992. Application of new technologyliquid scintillation scintillation/scin��til��la��tion/ (sin?ti-la��shun)1. an emission of sparks.2. a subjective visual sensation, as of seeing sparks.3. spectrometry to radiocarbon dating of tephradeposits, New Zealand, Quaternary International 13114: 135-42.LOWE, D.J., B.G. MCFADGEN, T.F.G. HIGHAM, A.G. HOGG, P.C. FROGGATT& I.A. NAIRN Nairn, town, ScotlandNairn(nârn), town (1991 pop. 7,721), Highland, N Scotland, at the mouth of the Nairn River on Moray Firth. It is a tourist resort and fishing harbor. . IN PRESS A. Radiocarbon age of the Kaharoa Tephra, akey marker for late Holocene stratigraphy and archaeology in NewZealand, The Holocene 8.LOWE, D.J. R.M. NEWNHAM, T.F.G. HIGHAM, J.M. WILMSHURST, M.S. MCGLONE& A.G. HOGG. In press b. Dating earliest human impact and settlementin New Zealand, in D.G. Sutton (ed.), Origins of the first NewZealanders, 2nd edition. Auckland: Auckland University Press.MCCORMAC, F.G., A.G. HOGG, T.F.G. HIGHAM, J. LYNCH-STIEGLITZ, W.BROECKER, M.G.L. BAILLIE, J.G. PALMER, L. XIONG, D. BROWN & S.T.HOPER. In press. Interhemispheric difference in 14C: an anthropogenic an��thro��po��gen��ic?adj.1. Of or relating to anthropogenesis.2. Caused by humans: anthropogenic degradation of the environment. C[O.sub.2] effect, Geophysical Research Letters Geophysical Research Letters is a publication of the American Geophysical Union. GRL is the organization's only letters journal. Since its introduction in 1974, GRL has published only short research letters, typically 3-5 pages long, which focus on a specific discipline or .NEWNHAM, R.M., D.J. LOWE, M.S. MCGLONE, J.M. WILMSHURST & T.F.G.HIGHAM. 1998. The Kaharoa Tephra as a critical datum for earliest humanimpact in northern New Zealand, Journal of Archaeological Science 25.PALAIS, J.M., M.S. GERMANI & G.A. ZIELINSKL 1992,Inter-hemispheric transport of volcanic ash from a 1259 AD volcaniceruption to the Greenland and Antarctic ice sheets, Geophysical ResearchLetters 19: 801-4.PULLAR, W.A., B.P. KOHN & J.E. COX. 1977. Air-fall Kaharoa Ashand Taupo Pumice pumice(pŭm`ĭs), volcanic glass formed by the solidification of lava that is permeated with gas bubbles. Usually found at the surface of a lava flow, it is colorless or light gray and has the general appearance of a rock froth. , and sea-rafted Loisels Pumice, Taupe taupe?n.A brownish gray.[French, from Old French, mole, from Latin talpa.]taupe adj.Noun 1. Pumice, and LeighPumice in northern and eastern parts of the North Island, New Zealand,New Zealand Journal of Geology and Geophysics 20: 697-717.RAMSEY, C.B.1994. OxCal.v. 2.14: radiocarbon calibration andstatistical analysis program. Oxford: Research Laboratory forArchaeology.SIMKIN, T. & L. SIEBERT.1994. Volcanoes of the world. 2ndedition. Tucson [AZ): Geoscience ge��o��sci��ence?n.Any one of the sciences, such as geology or geochemistry, that deals with the Press.STOKES, S., D.J. LOWE & P.C. FROGGATT.1992. Discriminant functionanalysis Discriminant function analysis involves the predicting of a categorical dependent variable by one or more continuous or binary independent variables. It is statistically the opposite of MANOVA. and correlation of late Quaternary rhyolitic tephra depositsfrom Taupe and Okataina volcanoes, New Zealand, using glass shard majorelement composition, Quaternary International 13/14: 102-17.STUIVER, M. & B. BECKER. 1993. High-precision decadal calibrationof the radiocarbon time scale. AD 1950-6000 BC, Radiocarbon 35: 35-65.STUIVER, M. & P.J. REIMER. 1993. Extended 14C data base andrevised CALIB 3.0 14C age calibration programme, Radiocarbon 35: 215-31.VOGEL, J.C., A. FULS FULS Federation for Ulster Local Studies (UK), E: VISSER & B. BECKER. 1993. Pretoriacalibration curve for short-lived samples, 1930-3350 BC, Radiocarbon 35:73-85.ZIELINSKI, G.A. & M.S. GERMANI. 1998. New ice core evidencechallenges the 1620s BC age for the Santorini (Minoan) eruption, Journalof Archaeological Science 25: 279-89.ZIELINSKI, G.A., P.A. MAYEWSKI, L.D. MEEKER, S. WHITLOW whitlow/whit��low/ (hwit��lo) felon.herpetic whitlow? primary herpes simplex infection of the terminal segment of a finger, with extensive tissue destruction, sometimes accompanied by systemic , M.S.TWICKLER, M. MORRISON, D. MEESE, R.B. ALLEY & A.J. GOW GOW God of War (video game)GOW Gears of War (video game)GoW Gods of War (Jedi Academy gaming clan)GOW Grapes of WrathGOW Garden of War (War2 map). 1994. Recordof volcanism since 7000 BC from the GISP GISP Global Invasive Species ProgrammeGISP Gonococcal Isolate Surveillance ProjectGISP Greenland Ice Sheet ProjectGISP Geographic Information Systems ProfessionalGISP Group Independent Study ProjectGISP Global Information Society Project 2 Greenland ice core andimplications for the volcano-climate system, Science 264: 946-52.Paul C. Buckland, Andy J. Dugmore & Kevin J. Edwards comment:We have to admit that the suggestion of the link between the AD 1259tephra in both Greenland and Antarctic ice cores and an eruption ofOkataina, New Zealand, in table I of Buckland et al. (1997), reflected avery deliberate piece of coat-trailing to elicit response. Indeed,between the correction of final proofs and publication of the paper,Greg Zielinski (pers. comm.), on geochemical grounds, had alreadyrendered the connection most unlikely. The eruption in 1259, however,provides one of the few isochrones which is potentially of globalsignificance, and there is an urgent need to track it down to source andto refine tephrochronological techniques to the level of locating it,and many other eruptions, in sediments other than ice. We areparticularly pleased to see Lowe & Higham's carefully reasonedresponse, updating the research and clarifying the situation for theSouthern Hemisphere.To a great extent, Baillie's response is understandable forseeking to bolster the dendrochronological dates for Santorini and Hekla3, but we, trained as environmental scientists, refute any accusation ofprotecting archaeologists from environmental determinism. Yet havingspent many years researching the relationships been human populationsand environments in the North Atlantic region and beyond (cf. Dugmore& Buckland 1991), it is evident that rigid socio-economicconstraints can push systems into collapse in the face of relativelyminor environmental changes - the case of Norse Greenland, lost withoutany intercession by volcanoes in the late medieval period [Buckland etal. 1996), is particularly apposite ap��po��site?adj.Strikingly appropriate and relevant. See Synonyms at relevant.[Latin appositus, past participle of app .We were also aware of the supposed Exodus connection [Bruins &van der Plicht 1996), yet to mix Hebraic with Greek myth only servesfurther to bolster the modern myth. The most telling comment upon thedating of Santorini still comes from Bietak's (1996) work at Avarisand the Egyptian chronology; a 130-year revision in this wellestablished chronology in order to fit in with a speculative correlationbetween tree rings, ice cores and eruptions is unlikely, although thisdoes not mean that we should seek to reject this if proven on soundarchaeological evidence. Kuniholm et al. (1996) have identifiedanomalous growth in the drought-stressed trees of Anatolia in the 17thcentury BC, but the correlation to the Santorini eruption is not direct,and still requires a connecting climatic impact; the mechanism by whichthis could be achieved is still not clear.A central point of our argument is that coincidence between tree-ringanomalies and vulcanism does not necessarily prove causal relationships,especially when major eruptions significantly outnumber frost-ringdates. 75% of frost-ring dates shown in Baillie's (1998) table 1may indeed be associated with large historical eruptions, but, as shownin our table 1 (Buckland et al. 1997), in the period since AD 550 therehave been at least 83 eruptions [greater than or equal to] VEI VEI Volcanic Explosivity IndexVEI Vehicle Electronics InterfaceVEI Vector Engineering Incorporated (Olympia, Washington)VEI Valrik Enterprises Inc. (Ontario, Canada)4, whereonly 31 frost ring events have been identified (a 37% presumedassociation). This estimate of the number of large eruptions isconservative, and is likely to increase as more tephrochronological workis undertaken in poorly studied volcanic regions. A key point is thatthe mechanisms that might link eruptions and impacts upon the tree-ringrecord are not well understood. The type of eruption, the scale,location relative to global circulation systems, the timing andcoincidence with other eruptions may all be critical variables affectingthe impact of an eruption on climate, even before the ecologicalresponse of trees to environmental change is considered.We certainly have no intent to 'rubbish' the provision ofhypotheses, but we are only too aware, as Lowe & Higham have rightlypointed out, that hypotheses rapidly become 'fact' inarchaeology. There maybe connections between particular volcaniceruptions, tree rings and acidity spikes in ice cores in prehistory, butwe would still hold that, as in Scottish law, most remain 'notproven'.ReferencesBAILLIE, M. 1998. Bronze Age myths expose archaeologicalshortcomings? a reply to Buckland et al. 1997, Antiquity 72: 425-7.BIETAK, M. 1996. Avaris. Capital of the Hyksos. London: BritishMuseum Press.BRUINS, H.J. & J. VAN DER PLICHT. 1996. The Exodus enigma, Nature382: 213-14.BUCKLAND, P.C., A.J. DUGMORE & K.J. EDWARDS. 1997. Bronze Agemyths? Volcanic activity and human response in the Mediterranean andNorth Atlantic region, Antiquity 71: 581-93.BUCKLAND, P.C., T. AMOROSI Amorosi is a comune (municipality) in the Province of Benevento in the Italian region Campania, located about 45 km northeast of Naples and about 30 km northwest of Benevento. As of 31 December 2004, it had a population of 2,931 and an area of 11.0 km2. , L. BARLOW, A.J. DUGMORE, P. MAYEWSKI,T.H. MCGOVERN, A. OGILVIE, J.P. SADLER & P. SKIDMORE. 1996.Bioarchaeological and climatological cli��ma��tol��o��gy?n.The meteorological study of climates and their phenomena.clima��to��log evidence for the fate of Norsefarmers in medieval Greenland, Antiquity 70: 88-96.DUGMORE, A.J. & P.C. BUCKLAND. 1991. Tephrochronology and LateHolocene soil erosion in south Iceland, in J.K. Maizels & C.Caseldine (ed.), Environmental change in Iceland:past and present.147-60. Dordtrecht: Kluwer Academic Press.LOWE, D.J. & T.F.G. HIGHAM. 1998. Hit-or-myth? Linking a 1259 ADacid spike with an Okataina eruption, Antiquity: 427-31.

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