- Email: [email protected]
Green mosses date the Storegga tsunami to the chilliest decades of the 8.2 ka cold event
Quaternary Science Reviews 45 (2012) 1e6
Contents lists available at SciVerse ScienceDirect
Quaternary Science Reviews journal homepage: www.elsevier.com/locate/quascirev
Rapid communication
Green mosses date the Storegga tsunami to the chilliest decades of the 8.2 ka cold event Stein Bondevik a, b, *, Svein Kristian Stormo c, Gudrun Skjerdal d a
Sogn og Fjordane University College, Faculty of Science, P.O. Box 133, N-6851 Sogndal, Norway Department of Geology, University of Tromsø, N-9037 Tromsø, Norway c Nofima Marin, Muninbakken 9–13, P.O. Box 6122, N-9291 Tromsø, Norway d Sogndal Upper Secondary School, Trolladalen 28, N-6851 Sogndal, Norway b
a r t i c l e i n f o
a b s t r a c t
Article history: Received 16 December 2011 Received in revised form 1 March 2012 Accepted 24 April 2012 Available online 23 May 2012
Chlorophyll in dead plants ordinarily decomposes completely before permanent burial through exposure to light, water and oxygen. Here we describe 8000-year-old terrestrial mosses that retain several percent of its original chlorophyll. The mosses were ripped of the land surface, carried 50e100 m off the Norwegian coast of the time, and deposited in depressions on the sea floor by the Storegga tsunami. A little of the chlorophyll survived because, within hours after entraining it, the tsunami buried the mosses in shell-rich sediments. These sediments preserved the chlorophyll by keeping out light and oxygen, and by keeping the pH above 7dthree factors known to favour chlorophyll’s stability. Because the green mosses were buried alive, their radiocarbon clock started ticking within hours after the Storegga Slide had set off the tsunami. Radiocarbon measurement of the mosses therefore give slide ages of uncommon geological precision, and these, together with a sequence of ages above and below the boundary, date the Storegga Slide to the chilliest decades of the 8.2 ka cold event at 8120e8175 years before AD 1950. North Atlantic coastal- and fjord- climatic records claimed to show evidence of the 8.2 cold event should be carefully examined for possible contamination and disturbance from the Storegga tsunami. Ó 2012 Elsevier Ltd. All rights reserved.
Keywords: Storegga tsunami Isolation basins Chlorophyll Radiocarbon dating 8.2 ka cold event
1. Introduction and setting The largest Holocene slide on the surface of the Earth, Storegga, has been known for decades from its sea floor expression (Bugge et al., 1987) and from the deposits that the giant tsunami spawned in coastal areas bordering the Norwegian Sea (e.g. Bondevik et al., 2005) (Fig. 1). Because of its large extent, short duration and extensive deposits e recognizable in many different coastal settings e the Storegga tsunami deposit can be a useful stratigraphic marker. Earlier radiocarbon ages indicate that the event happened between 7250 and 7350 radiocarbon years BP, corresponding to 8000e8200 calendar years BP, the time of the 8.2 cold event (Dawson et al., 2011). Here we report the unexpected finding of green mosses that the tsunami buried alive, their radiocarbon ages and present a calendar year date of the event within the time of the 8.2 cold event.
* Corresponding author. Sogn og and Fjordane University College, Faculty of Science, P.O. Box 133, N-6851 Sogndal, Norway. Tel.: þ47 47 33 76 23. E-mail address: [email protected] (S. Bondevik). 0277-3791/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved. doi:10.1016/j.quascirev.2012.04.020
Backwash of the Storegga tsunami deposited terrestrial material into offshore basins along Norway’s rocky coast (Bondevik et al., 1997a) that is remarkably well preserved. Onshore the tsunami reached heights metres to a few tens of metres (Bondevik et al., 2005) above sea level of its time (Fig. 1). Because of subsequent isostatic uplift, submarine basins that were as much as 40 m below sea level and a few hundred metres offshore now hold onshore lakes and bogs (Fig. 2A). The lake mud and bog peat of these basins overlie marine mud that contains Storegga backwash deposits (Fig. 2B). These deposits include terrestrial fragments of plants, trees, roots and ripped-up clasts of soil and peat (Fig. 2CeE and Supplementary data Figs S1 and S2). The plant fragments include pieces of terrestrial mosses that were still green when we found them in cores (Fig. 3). We found such green mosses in backwash deposits in two emerged basins in northern Norway; Djupmyra (‘djupmyra’ ¼ deep bog) at Hommelstø and lake L2 at Stormyra, Lyngen (Fig. 1). Both basins were part of the sea floor about 8000 years agodL2 about 8e10 m (Corner and Haugane, 1993) and Djupmyra 15e20 m below sea level of that time (Fig. 2A) and both were situated within 100 m of the nearest shore. Run-up has been traced to 8e9 m above the 8000-year-old relative sea level at Lyngen (Rasmussen and
2
S. Bondevik et al. / Quaternary Science Reviews 45 (2012) 1e6
Fig. 1. The Storegga slide triggered a giant tsunami in the Norwegian Sea; red dots show location of tsunami deposits. Right: Reconstructed run-up heights from field evidence; black is minimum estimate, grey is maximum. Greenland (Wagner et al., 2007); northern Norway (Rasmussen and Bondevik, 2006; Romundset and Bondevik, 2011); western Norway (Bondevik et al., 1997b); Faroe Island (Grauert et al., 2001); Shetland Islands (Bondevik et al., 2003; Bondevik et al., 2005) and Scotland (Smith et al., 2004). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
Bondevik, 2006). At Hommelstø run-up probably exceeded 3 m elevation (Bondevik et al., 2005), based on the presence of terrestrial plant fragments, soil, and peat in the backwash deposits (Fig. 2C). The green mosses are Pleurozium schreberi, Hylocomium splendens, Rhytidiadelphus sp., Dicranum sp. and Racomitrium sp. e species of bryophytes that are common in boreal forests in the northern hemisphere (Hallingbäck and Holmåsen, 1985). 2. Chlorophyll detection in the 8000-year-old mosses The green mosses were picked out of the tsunami deposits in the field, identified to species, washed in water, placed in aluminium foil and brought to the laboratory for freeze storage as quickly as possible. The plants were freeze dried, crushed, dissolved in acetone, concentrated and centrifuged. The solutions were then injected into a High performance liquid chromatographer e HPLC (More details in Supplementary Data Methods S1). Coring was done with a Russian peat corer. Small amounts of preserved chlorophyll account for the green colour. The absorption spectrum shows a maximum at 432.1 nm and at 665.3 nm from chlorophyll a, and at 469.5 nm and 647 nm for chlorophyll b (Fig. 3C). These wave lengths are the same as standard values for the absorption spectra of chlorophyll, though the amount of chlorophyll is only a percent or two of what modern mosses of the same species contain (Supplementary Data Table S1). Nevertheless, the preserved chlorophyll is enough to make the moss look green to the eye. Though chlorophyll is often preserved in lacustrine and marine sediments (Leavitt, 1993), only very rarely do the plant remains themselves retain anything of their original colour (Dickson, 1973). Chlorophyll has been directly measured in lichen that had been buried beneath glacier ice for 1350 years in North Greenland (Fahselt et al., 2001). These lichens contain 0.038 mg/g of chlorophyll a and 0.020 mg/g of chlorophyll b; similar to the ones we measured (0.027 mg/g and 0.044 mg/g for chlorophyll a and 0.017 mg/g and 0.0057 mg/g for chlorophyll b; Table S1). Sudden burial must have protected the Storegga moss fragments from the light and oxygen that would have otherwise destroyed their chlorophyll. The tsunami deposits are covered by impermeable marine mud. We infer that the tsunami ripped the
moss from land it overran, delivered the fragments to the sea in backwash, and deposited them in submarine basins where subsequent deposition of marine mud shielded them from light and oxygen. The preservation of the chlorophyll was further aided by nearly neutral pH. Chlorophyll decomposes more quickly in acidic solutions. Laboratory experiments show chlorophyll degradation to be about 2e3 times faster at pH 5.5 than at pH 7.5 at 70 C (Koca et al., 2006). pH measured in the tsunami deposits is close to 7; we found acidic conditions solely in the overlying lacustrine deposits, where pH falls as low as 4.6 (Fig. 2D). The green moss fragments are typically clumped within sandy deposits rich in shell fragments (Figs S1, S2). We infer that shells have buffered the pore waters in contact with the moss fragments, such that the pH has stayed at 7 or above throughout their 8000 years of burial. 3. Radiocarbon ages of the green mosses The green mosses provide excellent material for radiocarbon dating of the Storegga tsunami and of the slide that triggered it. Because the radiocarbon clock starts when an organism dies, only the victims of a geologic catastrophe will return geologically accurate ages for that event. Ordinarily, most or all of the organic material entrained by a tsunami has been dead for years, decades, or even millennia before deposition, as illustrated by recycled leaves in tsunami deposits in Thailand (Jankaew et al., 2008). Although it has been possible to date the remains of plants or animals that an ancient tsunamigenic earthquake killed by raising or lowering a coast (Nelson et al., 1995; Sieh et al., 2008), it is usually difficult to identify victims of the ancient tsunami itself. By contrast, the preserved chlorophyll shows that the radiocarbon clock for the green mosses began running during the Storegga tsunami. The green mosses gave radiocarbon ages with a weighted mean of 7300 20 years before A.D. 1950 (14C yr BP). This mean combines seven ages, each on different pieces of green mosses, that range from 7231 64 to 7387 72 14C yr BP (Fig. 2C, Table 1). The mean corresponds to a 2s range of calendar ages, 8030e8180 cal yr before AD 1950 (cal yr BP), that spans the entire length of a 150-year-long plateau in the graph of radiocarbon age as a function of calendar age (Fig. 4A, B). We position the Storegga tsunami within this plateau on the basis of radiocarbon dating of terrestrial plant fragments that bracket the tsunami deposit (Fig. 4A). These also show ages around 7300 14C yr BP. A sample of plant fragments in undisturbed deposits 1e2 cm below the tsunami deposits in Gorrtjønna I (Bjugn) gave an age of 7325 85 14C yr BP (Fig. S3 and Table S2). Samples 5, 10 and 15 cm above the top of the tsunami deposits (Fig. 2C) in Djupmyra similarly gave ages of 7230 50, 7221 41 and 7338 42 14C yr BP (Table S2). All these ages plot on the 150-year-long plateau. This indicates that the Storegga tsunami happened sometime within the 7300-year-plateau. Through a Bayesian analysis of all the radiocarbon ages (Biasi and Weldon, 1994), the original 2s-range date of the green mosses could be reduced by 40 years. We modelled the bracketing ages with the Sequence function (Blockley et al., 2004; Ramsey, 2009) in the calibration program OxCal that allows stratigraphic order to shave off uncertainty of the calendar dates (Fig. S4 and Table S3). The only assumption that goes into the modelling is that calendar dates should increase with depth. The results narrow the calibrated age interval for the green mosses to 8120e8175 (68.2% level) and to 8070e8180 (95.4% level) cal yr BP. (Details about the age modelling in Supplementary Data Methods S1).
S. Bondevik et al. / Quaternary Science Reviews 45 (2012) 1e6
4. Discussion This dating assigns the Storegga Slide to the chilliest part of the greatest cold snap of the last 10,000 years, the 8.2 ka cold
3
event. We used the GRIP d18O dataset adjusted to the radiocarbon dated tree ring record (Fig. 4C) (Muscheler et al., 2004) to compare the Greenland ice core record with the shaved, calibrated radiocarbon age of the green mosses. The isotopic
Fig. 2. Storegga backwash deposits in Djupmyra, Hommelstø: A) Map showing the basin Djupmyra and surroundings 8000 years ago; the floor of the basin Djupmyra was then 15e20 m below sea level. Today the surface of the filled-in basin is 45 m above sea level (see Fig. S1). B) Cross section through the deepest part of the basin. Grey lines show core locations (Drange, 2003). C) Backwash deposits and radiocarbon ages (see photo of deposits in Fig. S1 and details about radiocarbon samples in Table 1 and Table S2). D) pH is close to 7 within the tsunami deposits and decrease up-core. Loss on ignition varies from 1 to 80% in the tsunami backwash deposits, but is stable in the marine mud above and below. E) The change from tsunami backwash deposits to marine mud is very distinct and abrupt at 659 cm depth. The tsunami deposit has thousands of particles larger than 1 mm, whereas in the marine mud above there are only a few particles larger than 1 mm pr. 100 g of sediments.
4
S. Bondevik et al. / Quaternary Science Reviews 45 (2012) 1e6
Fig. 3. Evidence for chlorophyll in 8000-year-old moss species: A) Offshore backwash deposits are rich in terrestrial plants and organic rip-up clasts. Photograph shows 18 cm of the middle part of the 70-cm-thick deposit at Lyngen (Fig. S2). The green moss species in B) where extracted from this core. B) Dried moss species from the core in A) Hylocomium splendencs and Rhytidiadelphus triquetrus are the same samples as pictured in A). C) HPLC separation of chlorophyll from samples of green coloured mosses extracted from the core in A). Chlorophyll b at spike at 10.8 min and chlorophyll a at 18.5 min. Above are absorption diagrams.
minimum in the ice cores at 8125e8175 cal yr BP (Thomas et al., 2007) coincides with the highest probability of the calibrated date of the green mosses (Fig 4B, C and Table S3). This means that the 8.2 cooling had already started when the Storegga tsunami happened. Sediments carried offshore in the tsunami backwash have been little studied, (Dawson and Stewart, 2007; Bourgeois, 2009) but could contain important information. A large amount of eroded sediments and terrestrial debris are carried and deposited offshore in the tsunami outflow. Satellite images and video footage of the
2004 Indian Ocean tsunami and the 2011 Tohoku-oki tsunami show the backwash as high density rivers in topographic lows filled with terrestrial debris and sediments moving offshore. The green moss species with small amounts of intact chlorophyll demonstrates the preservation capacity for organic material in these offshore backwash deposits. We found the green mosses in two different areas that indicate that this kind of storage is not unique, but can probably be found many places where the sea floor has depressions and bays that can act as sediment traps for the tsunami backwash. The tsunami event
S. Bondevik et al. / Quaternary Science Reviews 45 (2012) 1e6
5
Table 1 Radiocarbon measurements of green mosses in storegga tsunami backwash deposits. Lab. no
14 C age (yr BP)
d13C Weight Core: (& PDB) (mg) depth (cm)
Description of samples
Djupmyra, Hommelstø TUa-2892
7300 70 27.1
30.0
TUa-2893
7231 64 21.1
31.5
TUa-3054
7351 72 22.8
35.7
TUa-3055
7387 72 24.6
12.2
TUa-4732
7280 45 27.2
29.6
TUa-4733
7283 42 25.2
55.6
Loc. 5: 680e681 Loc. 5: 710e714 Loc. 5: 705e708 Loc. 5: 710e714 Tu6-0409: 675e678 Tj3-0409: 674e675
2 stems of Hylocomium splendens. 1 stem of Racomitrium sp. 2 stems of Racomitrium sp. 4 stems of Pleurozium schreberi. 6 stems of P. schreberi, 2e4 cm in length. 9 stems of H. splendens, 1.5e4 cm in length.
Stormyra-L2, Lyngen Beta 221622 7318 43 26.9
20.2
Beta 221624 7402 34a 26.6
20.3
BaL2-Cs2W: 7 stems of Pleurozium 645e665 schreberi, the longest stem is 6 cm, others from 1 cm to 4 cm in length. BaL2-Cs2W: 2 stems of Hylocomnium 645e680 splendens, 3e4 cm in length, 1 stem of Rhytidiadelphus triquetrus, 2 cm in length with branch 1.5 cm.
7300 20b Weighted mean See Methods S1 for treatment of samples and measurements. a Outlier, see test below. b We used the c2 test to check the internal variability of the green moss ages before calculating the weighted mean. The deviation of a single measurement (Ri) from the weighted mean (Rp) should on average be close to the measurement error (Ei). c2 is the sum of squared ratios between deviations and errors, given as P (Ri Rp)2/E2i and should therefore be close to the number of measurements (n), or more precisely the degrees of freedom, (n 1) (Ward and Wilson, 1978; Ascough et al., 2005). Thus, if the quantity c2/(n 1) is 1 it means that measurement uncertainties explain the variance, while values >1 indicates that the group has additional variance. For all eight radiocarbon ages of the green mosses, c2/ (n 1) ¼ 1.46. Omitting the outlier of 7402 34 yr BP (Beta 221624), c2/ (n 1) ¼ 0.61. Thus we discarded the 7402 34 date in the calculation of the weighted mean of 7300 20.
provides rapid burial of the terrestrial material together with marine sand and shell fragments, and the suspended mud settles quickly and seals of the deposits from oxygen and light. Such an anoxic environment with high pH could also be excellent for preserving delicate artifacts or provide samples for DNA-analysis of ancient organic material catastrophically buried in an offshore tsunami deposit. The coincidence of these two major events in the North Atlantic could be accidental (Dawson et al., 2011), but the strong bottom currents during the Storegga event may have had practical consequences in disturbing many near shore Early Holocene sedimentary archives. Deposits in coastal lakes, bays and fjord settings around the North Atlantic could lack the beginning of the 8.2 cold event due to erosion from the tsunami waves. Also the sedimentation at the later part of the cold event could be disturbed by changes and adjustments in the sediment supply caused by the tsunami inundation and backwash. Coastal- and fjord climatic records claimed to show evidence and details of the 8.2 cold event in the North Atlantic region should be carefully examined for possible contamination and disturbance from the Storegga tsunami.
Fig. 4. Calendar date of the Storegga green mosses compared to d18O and methane in the ice core record: A) Radiocarbon ages verses calibrated dates plotted at the weighted average of their modelled probability distribution (Fig. S4 and Table S3). Tree ring curve from IntCal09 (Reimer et al., 2009). B) Original and modelled probability distribution of the calendar date of 7300 20 yr BP e the weighted average of seven radiocarbon ages of the green mosses (Fig. S4 and Table 1). C) 5-point running average through the GRIP d18O data synchronised to the tree-ring curve; data from Muscheler et al. (2004). The 8.2 event lasts 160 years, from 8040 to 8200 (Thomas et al., 2007). D) Methane concentrations from the GISP ice core (Kobashi et al., 2007).
Author contribution S.B. discovered the green coloured mosses, led the field- and lab work, and wrote the paper. S.K.S. performed the HPLC analysis and detected the chlorophyll. G.S. participated in the field work, picked
6
S. Bondevik et al. / Quaternary Science Reviews 45 (2012) 1e6
and identified plant fragments for radiocarbon dating, counted particles, and identified the green mosses for HPLC analysis. Acknowledgements The work was supported by the University of Tromsø, the Norwegian Research Council and Norsk Hydro. I. Drange and H. Rasmussen participated in the field at an early stage. S. Gulliksen performed most of the radiocarbon measurements at the Trondheim Radiocarbon Laboratory. The manuscript greatly benefitted from comments by B. F. Atwater. H. Aarnes answered questions about chlorophyll. A. Dawson and M. Hald provided critical comments in addition to the two journal reviewers. Appendix A. Supplementary data Supplementary data related to this article can be found online at doi:10.1016/j.quascirev.2012.04.020. References Ascough, P.L., Cook, G.T., Dugmore, A.J., Scott, E.M., Freeman, S.P.H.T., 2005. Influence of mollusk species on marine delta R determinations. Radiocarbon 47, 433e440. Biasi, G.P., Weldon, R., 1994. Quantitative refinement of calibrated C-14 distributions. Quaternary Research 41, 1e18. Blockley, S.P.E., Lowe, J.J., Walker, M.J.C., Asioli, A., Trincardi, F., Coope, G.R., Donahue, R.E., Pollard, A.M., 2004. Bayesian analysis of radiocarbon chronologies: examples from the European Lateglacial. Journal of Quaternary Science 19, 159e175. Bondevik, S., Svendsen, J.I., Mangerud, J., 1997a. Tsunami sedimentary facies deposited by the Storegga tsunami in shallow marine basins and coastal lakes, western Norway. Sedimentology 44, 1115e1131. Bondevik, S., Svendsen, J.I., Johnsen, G., Mangerud, J., Kaland, P., 1997b. The Storegga tsunami along the Norwegian coast, its age and runup. Boreas 26, 29e53. Bondevik, S., Løvholt, F., Harbitz, C., Mangerud, J., Dawson, A., Svendsen, J.I., 2005. The Storegga Slide tsunamidcomparing field observations with numerical simulations. Marine & Petroleum Geology 22, 195e208. Bondevik, S., Mangerud, J., Dawson, S., Dawson, A., Lohne, Ø., 2003. Record-breaking height for 8000-year-old tsunami in the North Atlantic. Eos, Transactions American Geophysical Union 84, 289. Bourgeois, J., 2009. Geological effects and records of tsunamis. In: Robinson, A., Bernard, E.N. (Eds.), The Sea. Tsunamis, vol 15. Harvard University Press, pp. 53e91. Bugge, T., Befring, S., Belderson, R., Eidvin, T., Jansen, E., Kenyon, N., Holtedahl, H., Sejrup, H.P., 1987. A giant three-stage submarine slide off Norway. Geo-Marine Letters 7, 191e198. Corner, G., Haugane, E., 1993. Marine-lacustrine stratigraphy of raised coastal basins and postglacial sea-level changes at Lyngen and Vanna, Troms, northern Norway. Norsk Geologisk Tidsskrift 73, 175e197. Dawson, A., Bondevik, S., Teller, J.T., 2011. Relative timing of the Storegga submarine slide, methane release, and climate change during the 8.2 ka cold event. The Holocene 21, 1167e1171. Dawson, A.G., Stewart, I., 2007. Tsunami deposits in the geological record. Sedimentary Geology 200, 166e183.
Dickson, J., 1973. Bryophytes of the Pleistocene. Cambridge University Press, Cambridge. Drange, I., 2003. Strandforskyvningsundersøkelser og kartlegging av tsunamisedimenter i Nordland. Department of Geology. University of Bergen, Bergen, p. 114. Fahselt, D., Krol, M., Alstrup, V., Hüner, N., 2001. Detection of pigments in specimens of recent and subfossil umbilicaria from North Greenland. The Bryologist 104, 593e599. Grauert, M., Björck, S., Bondevik, S., 2001. Storegga tsunami deposits in a coastal lake on Suderøy, the Faroe Islands. Boreas 30, 263e271. Hallingbäck, T., Holmåsen, I., 1985. Mossor e en fälthandbok. Interpublishing AB, Stockholm. Jankaew, K., Atwater, B.F., Yuki, S., Choowong, M., Charoentitirat, T., Martin, M.E., Prendergast, A., 2008. Medieval forewarning of the 2004 Indian Ocean tsunami in Thailand. Nature 455, 1228e1231. Kobashi, T., Severinghaus, J.P., Brook, E.J., Barnola, J.-M., Grachev, A.M., 2007. Precise timing and characterization of abrupt climate change 8200 years ago from air trapped in polar ice. Quaternary Science Reviews 26, 1212e1222. Koca, N., Karadeniz, F., Burdurlu, H., 2006. Effect of pH on chlorophyll degradation and colour loss in blanched green peas. Food Chemistry 100, 609e615. Leavitt, P.R., 1993. A review of factors that regulate carotenoid and chlorophyll deposition and fossil pigment abundance. Journal of Paleolimnology 9, 109e127. Muscheler, R., Beer, J., Vonmoos, M., 2004. Causes and timing of the 8200 yr BP event inferred from the comparison of the GRIP 10Be and the tree ring D14C record. Quaternary Science Reviews 23, 2101e2111. Nelson, A.R., Atwater, B.F., Bobrowsky, P.T., Bradley, L.-A., Clague, J.J., Carver, G.A., Darienzo, M.E., Grant, W.C., Krueger, H.W., Sparks, R., Stafford, T.W., Stuiver, M., 1995. Radiocarbon evidence for extensive plate-boundary rupture about 300 years ago at the Cascadia subduction zone. Nature 378, 371e374. Ramsey, C.B., 2009. Bayesian analysis of radiocarbon dates. Radiocarbon 51, 337e360. Rasmussen, H., Bondevik, S., 2006. A tsunami in Lyngen, Northern Norway e a regional or local event? In: Peltonen, P., Pasanen, A. (Eds.), The 27th Nordic Geological Winter Meeting Bulletin of the Geological Society of Finland. Reimer, P.J., Baillie, M.G.L., Bard, E., Bayliss, A., Beck, J.W., Blackwell, P.G., Ramsey, C.B., Buck, C.E., Burr, G.S., Edwards, R.L., Friedrich, M., Grootes, P.M., Guilderson, T.P., Hajdas, I., Heaton, T.J., Hogg, A.G., Hughen, K.A., Kaiser, K.F., Kromer, B., McCormac, F.G., Manning, S.W., Reimer, R.W., Richards, D.A., Southon, J.R., Talamo, S., Turney, C.S.M., van der Plicht, J., Weyhenmeye, C.E., 2009. Intcal09 and Marine09 radiocarbon age calibration curves, 0e50,000 years cal bp. Radiocarbon 51, 1111e1150. Romundset, A., Bondevik, S., 2011. Propagation of the Storegga tsunami into ice-free lakes along the southern shores of the Barents Sea. Journal of Quaternary Science 26, 457e462. Sieh, K., Natawidjaja, D.H., Meltzner, A.J., Shen, C.-C., Cheng, H., Li, K.-S., Suwargadi, B.W., Galetzka, J., Philibosian, B., Edwards, R.L., 2008. Earthquake supercycles inferred from sea-level changes recorded in the corals of west Sumatra. Science 322, 1674e1678. Smith, D.E., Shi, S., Cullingford, R.A., Dawson, A.G., Dawson, S., Firth, C.R., Foster, I.D.L., Fretwell, P.T., Haggart, B.A., Holloway, L.K., Long, D., 2004. The holocene Storegga Slide tsunami in the United Kingdom. Quaternary Science Reviews 23, 2291e2321. Thomas, E.R., Wolff, E.W., Mulvaney, R., Steffensen, J.P., Johnsen, S.J., Arrowsmith, C., White, J.W., Vaughn, B., Popp, T., 2007. The 8.2 ka event from Greenland ice cores. Quaternary Science Reviews 26, 70e81. Wagner, B., Bennike, O., Klug, M., Cremer, H., 2007. First indication of Storegga tsunami deposits from East Greenland. Journal of Quaternary Science 22, 321e325. Ward, G.K., Wilson, S.R., 1978. Procedures for comparing and combining radiocarbon age determinations. A critique. Archaeometry 20, 19e31.
Contents lists available at SciVerse ScienceDirect
Quaternary Science Reviews journal homepage: www.elsevier.com/locate/quascirev
Rapid communication
Green mosses date the Storegga tsunami to the chilliest decades of the 8.2 ka cold event Stein Bondevik a, b, *, Svein Kristian Stormo c, Gudrun Skjerdal d a
Sogn og Fjordane University College, Faculty of Science, P.O. Box 133, N-6851 Sogndal, Norway Department of Geology, University of Tromsø, N-9037 Tromsø, Norway c Nofima Marin, Muninbakken 9–13, P.O. Box 6122, N-9291 Tromsø, Norway d Sogndal Upper Secondary School, Trolladalen 28, N-6851 Sogndal, Norway b
a r t i c l e i n f o
a b s t r a c t
Article history: Received 16 December 2011 Received in revised form 1 March 2012 Accepted 24 April 2012 Available online 23 May 2012
Chlorophyll in dead plants ordinarily decomposes completely before permanent burial through exposure to light, water and oxygen. Here we describe 8000-year-old terrestrial mosses that retain several percent of its original chlorophyll. The mosses were ripped of the land surface, carried 50e100 m off the Norwegian coast of the time, and deposited in depressions on the sea floor by the Storegga tsunami. A little of the chlorophyll survived because, within hours after entraining it, the tsunami buried the mosses in shell-rich sediments. These sediments preserved the chlorophyll by keeping out light and oxygen, and by keeping the pH above 7dthree factors known to favour chlorophyll’s stability. Because the green mosses were buried alive, their radiocarbon clock started ticking within hours after the Storegga Slide had set off the tsunami. Radiocarbon measurement of the mosses therefore give slide ages of uncommon geological precision, and these, together with a sequence of ages above and below the boundary, date the Storegga Slide to the chilliest decades of the 8.2 ka cold event at 8120e8175 years before AD 1950. North Atlantic coastal- and fjord- climatic records claimed to show evidence of the 8.2 cold event should be carefully examined for possible contamination and disturbance from the Storegga tsunami. Ó 2012 Elsevier Ltd. All rights reserved.
Keywords: Storegga tsunami Isolation basins Chlorophyll Radiocarbon dating 8.2 ka cold event
1. Introduction and setting The largest Holocene slide on the surface of the Earth, Storegga, has been known for decades from its sea floor expression (Bugge et al., 1987) and from the deposits that the giant tsunami spawned in coastal areas bordering the Norwegian Sea (e.g. Bondevik et al., 2005) (Fig. 1). Because of its large extent, short duration and extensive deposits e recognizable in many different coastal settings e the Storegga tsunami deposit can be a useful stratigraphic marker. Earlier radiocarbon ages indicate that the event happened between 7250 and 7350 radiocarbon years BP, corresponding to 8000e8200 calendar years BP, the time of the 8.2 cold event (Dawson et al., 2011). Here we report the unexpected finding of green mosses that the tsunami buried alive, their radiocarbon ages and present a calendar year date of the event within the time of the 8.2 cold event.
* Corresponding author. Sogn og and Fjordane University College, Faculty of Science, P.O. Box 133, N-6851 Sogndal, Norway. Tel.: þ47 47 33 76 23. E-mail address: [email protected] (S. Bondevik). 0277-3791/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved. doi:10.1016/j.quascirev.2012.04.020
Backwash of the Storegga tsunami deposited terrestrial material into offshore basins along Norway’s rocky coast (Bondevik et al., 1997a) that is remarkably well preserved. Onshore the tsunami reached heights metres to a few tens of metres (Bondevik et al., 2005) above sea level of its time (Fig. 1). Because of subsequent isostatic uplift, submarine basins that were as much as 40 m below sea level and a few hundred metres offshore now hold onshore lakes and bogs (Fig. 2A). The lake mud and bog peat of these basins overlie marine mud that contains Storegga backwash deposits (Fig. 2B). These deposits include terrestrial fragments of plants, trees, roots and ripped-up clasts of soil and peat (Fig. 2CeE and Supplementary data Figs S1 and S2). The plant fragments include pieces of terrestrial mosses that were still green when we found them in cores (Fig. 3). We found such green mosses in backwash deposits in two emerged basins in northern Norway; Djupmyra (‘djupmyra’ ¼ deep bog) at Hommelstø and lake L2 at Stormyra, Lyngen (Fig. 1). Both basins were part of the sea floor about 8000 years agodL2 about 8e10 m (Corner and Haugane, 1993) and Djupmyra 15e20 m below sea level of that time (Fig. 2A) and both were situated within 100 m of the nearest shore. Run-up has been traced to 8e9 m above the 8000-year-old relative sea level at Lyngen (Rasmussen and
2
S. Bondevik et al. / Quaternary Science Reviews 45 (2012) 1e6
Fig. 1. The Storegga slide triggered a giant tsunami in the Norwegian Sea; red dots show location of tsunami deposits. Right: Reconstructed run-up heights from field evidence; black is minimum estimate, grey is maximum. Greenland (Wagner et al., 2007); northern Norway (Rasmussen and Bondevik, 2006; Romundset and Bondevik, 2011); western Norway (Bondevik et al., 1997b); Faroe Island (Grauert et al., 2001); Shetland Islands (Bondevik et al., 2003; Bondevik et al., 2005) and Scotland (Smith et al., 2004). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
Bondevik, 2006). At Hommelstø run-up probably exceeded 3 m elevation (Bondevik et al., 2005), based on the presence of terrestrial plant fragments, soil, and peat in the backwash deposits (Fig. 2C). The green mosses are Pleurozium schreberi, Hylocomium splendens, Rhytidiadelphus sp., Dicranum sp. and Racomitrium sp. e species of bryophytes that are common in boreal forests in the northern hemisphere (Hallingbäck and Holmåsen, 1985). 2. Chlorophyll detection in the 8000-year-old mosses The green mosses were picked out of the tsunami deposits in the field, identified to species, washed in water, placed in aluminium foil and brought to the laboratory for freeze storage as quickly as possible. The plants were freeze dried, crushed, dissolved in acetone, concentrated and centrifuged. The solutions were then injected into a High performance liquid chromatographer e HPLC (More details in Supplementary Data Methods S1). Coring was done with a Russian peat corer. Small amounts of preserved chlorophyll account for the green colour. The absorption spectrum shows a maximum at 432.1 nm and at 665.3 nm from chlorophyll a, and at 469.5 nm and 647 nm for chlorophyll b (Fig. 3C). These wave lengths are the same as standard values for the absorption spectra of chlorophyll, though the amount of chlorophyll is only a percent or two of what modern mosses of the same species contain (Supplementary Data Table S1). Nevertheless, the preserved chlorophyll is enough to make the moss look green to the eye. Though chlorophyll is often preserved in lacustrine and marine sediments (Leavitt, 1993), only very rarely do the plant remains themselves retain anything of their original colour (Dickson, 1973). Chlorophyll has been directly measured in lichen that had been buried beneath glacier ice for 1350 years in North Greenland (Fahselt et al., 2001). These lichens contain 0.038 mg/g of chlorophyll a and 0.020 mg/g of chlorophyll b; similar to the ones we measured (0.027 mg/g and 0.044 mg/g for chlorophyll a and 0.017 mg/g and 0.0057 mg/g for chlorophyll b; Table S1). Sudden burial must have protected the Storegga moss fragments from the light and oxygen that would have otherwise destroyed their chlorophyll. The tsunami deposits are covered by impermeable marine mud. We infer that the tsunami ripped the
moss from land it overran, delivered the fragments to the sea in backwash, and deposited them in submarine basins where subsequent deposition of marine mud shielded them from light and oxygen. The preservation of the chlorophyll was further aided by nearly neutral pH. Chlorophyll decomposes more quickly in acidic solutions. Laboratory experiments show chlorophyll degradation to be about 2e3 times faster at pH 5.5 than at pH 7.5 at 70 C (Koca et al., 2006). pH measured in the tsunami deposits is close to 7; we found acidic conditions solely in the overlying lacustrine deposits, where pH falls as low as 4.6 (Fig. 2D). The green moss fragments are typically clumped within sandy deposits rich in shell fragments (Figs S1, S2). We infer that shells have buffered the pore waters in contact with the moss fragments, such that the pH has stayed at 7 or above throughout their 8000 years of burial. 3. Radiocarbon ages of the green mosses The green mosses provide excellent material for radiocarbon dating of the Storegga tsunami and of the slide that triggered it. Because the radiocarbon clock starts when an organism dies, only the victims of a geologic catastrophe will return geologically accurate ages for that event. Ordinarily, most or all of the organic material entrained by a tsunami has been dead for years, decades, or even millennia before deposition, as illustrated by recycled leaves in tsunami deposits in Thailand (Jankaew et al., 2008). Although it has been possible to date the remains of plants or animals that an ancient tsunamigenic earthquake killed by raising or lowering a coast (Nelson et al., 1995; Sieh et al., 2008), it is usually difficult to identify victims of the ancient tsunami itself. By contrast, the preserved chlorophyll shows that the radiocarbon clock for the green mosses began running during the Storegga tsunami. The green mosses gave radiocarbon ages with a weighted mean of 7300 20 years before A.D. 1950 (14C yr BP). This mean combines seven ages, each on different pieces of green mosses, that range from 7231 64 to 7387 72 14C yr BP (Fig. 2C, Table 1). The mean corresponds to a 2s range of calendar ages, 8030e8180 cal yr before AD 1950 (cal yr BP), that spans the entire length of a 150-year-long plateau in the graph of radiocarbon age as a function of calendar age (Fig. 4A, B). We position the Storegga tsunami within this plateau on the basis of radiocarbon dating of terrestrial plant fragments that bracket the tsunami deposit (Fig. 4A). These also show ages around 7300 14C yr BP. A sample of plant fragments in undisturbed deposits 1e2 cm below the tsunami deposits in Gorrtjønna I (Bjugn) gave an age of 7325 85 14C yr BP (Fig. S3 and Table S2). Samples 5, 10 and 15 cm above the top of the tsunami deposits (Fig. 2C) in Djupmyra similarly gave ages of 7230 50, 7221 41 and 7338 42 14C yr BP (Table S2). All these ages plot on the 150-year-long plateau. This indicates that the Storegga tsunami happened sometime within the 7300-year-plateau. Through a Bayesian analysis of all the radiocarbon ages (Biasi and Weldon, 1994), the original 2s-range date of the green mosses could be reduced by 40 years. We modelled the bracketing ages with the Sequence function (Blockley et al., 2004; Ramsey, 2009) in the calibration program OxCal that allows stratigraphic order to shave off uncertainty of the calendar dates (Fig. S4 and Table S3). The only assumption that goes into the modelling is that calendar dates should increase with depth. The results narrow the calibrated age interval for the green mosses to 8120e8175 (68.2% level) and to 8070e8180 (95.4% level) cal yr BP. (Details about the age modelling in Supplementary Data Methods S1).
S. Bondevik et al. / Quaternary Science Reviews 45 (2012) 1e6
4. Discussion This dating assigns the Storegga Slide to the chilliest part of the greatest cold snap of the last 10,000 years, the 8.2 ka cold
3
event. We used the GRIP d18O dataset adjusted to the radiocarbon dated tree ring record (Fig. 4C) (Muscheler et al., 2004) to compare the Greenland ice core record with the shaved, calibrated radiocarbon age of the green mosses. The isotopic
Fig. 2. Storegga backwash deposits in Djupmyra, Hommelstø: A) Map showing the basin Djupmyra and surroundings 8000 years ago; the floor of the basin Djupmyra was then 15e20 m below sea level. Today the surface of the filled-in basin is 45 m above sea level (see Fig. S1). B) Cross section through the deepest part of the basin. Grey lines show core locations (Drange, 2003). C) Backwash deposits and radiocarbon ages (see photo of deposits in Fig. S1 and details about radiocarbon samples in Table 1 and Table S2). D) pH is close to 7 within the tsunami deposits and decrease up-core. Loss on ignition varies from 1 to 80% in the tsunami backwash deposits, but is stable in the marine mud above and below. E) The change from tsunami backwash deposits to marine mud is very distinct and abrupt at 659 cm depth. The tsunami deposit has thousands of particles larger than 1 mm, whereas in the marine mud above there are only a few particles larger than 1 mm pr. 100 g of sediments.
4
S. Bondevik et al. / Quaternary Science Reviews 45 (2012) 1e6
Fig. 3. Evidence for chlorophyll in 8000-year-old moss species: A) Offshore backwash deposits are rich in terrestrial plants and organic rip-up clasts. Photograph shows 18 cm of the middle part of the 70-cm-thick deposit at Lyngen (Fig. S2). The green moss species in B) where extracted from this core. B) Dried moss species from the core in A) Hylocomium splendencs and Rhytidiadelphus triquetrus are the same samples as pictured in A). C) HPLC separation of chlorophyll from samples of green coloured mosses extracted from the core in A). Chlorophyll b at spike at 10.8 min and chlorophyll a at 18.5 min. Above are absorption diagrams.
minimum in the ice cores at 8125e8175 cal yr BP (Thomas et al., 2007) coincides with the highest probability of the calibrated date of the green mosses (Fig 4B, C and Table S3). This means that the 8.2 cooling had already started when the Storegga tsunami happened. Sediments carried offshore in the tsunami backwash have been little studied, (Dawson and Stewart, 2007; Bourgeois, 2009) but could contain important information. A large amount of eroded sediments and terrestrial debris are carried and deposited offshore in the tsunami outflow. Satellite images and video footage of the
2004 Indian Ocean tsunami and the 2011 Tohoku-oki tsunami show the backwash as high density rivers in topographic lows filled with terrestrial debris and sediments moving offshore. The green moss species with small amounts of intact chlorophyll demonstrates the preservation capacity for organic material in these offshore backwash deposits. We found the green mosses in two different areas that indicate that this kind of storage is not unique, but can probably be found many places where the sea floor has depressions and bays that can act as sediment traps for the tsunami backwash. The tsunami event
S. Bondevik et al. / Quaternary Science Reviews 45 (2012) 1e6
5
Table 1 Radiocarbon measurements of green mosses in storegga tsunami backwash deposits. Lab. no
14 C age (yr BP)
d13C Weight Core: (& PDB) (mg) depth (cm)
Description of samples
Djupmyra, Hommelstø TUa-2892
7300 70 27.1
30.0
TUa-2893
7231 64 21.1
31.5
TUa-3054
7351 72 22.8
35.7
TUa-3055
7387 72 24.6
12.2
TUa-4732
7280 45 27.2
29.6
TUa-4733
7283 42 25.2
55.6
Loc. 5: 680e681 Loc. 5: 710e714 Loc. 5: 705e708 Loc. 5: 710e714 Tu6-0409: 675e678 Tj3-0409: 674e675
2 stems of Hylocomium splendens. 1 stem of Racomitrium sp. 2 stems of Racomitrium sp. 4 stems of Pleurozium schreberi. 6 stems of P. schreberi, 2e4 cm in length. 9 stems of H. splendens, 1.5e4 cm in length.
Stormyra-L2, Lyngen Beta 221622 7318 43 26.9
20.2
Beta 221624 7402 34a 26.6
20.3
BaL2-Cs2W: 7 stems of Pleurozium 645e665 schreberi, the longest stem is 6 cm, others from 1 cm to 4 cm in length. BaL2-Cs2W: 2 stems of Hylocomnium 645e680 splendens, 3e4 cm in length, 1 stem of Rhytidiadelphus triquetrus, 2 cm in length with branch 1.5 cm.
7300 20b Weighted mean See Methods S1 for treatment of samples and measurements. a Outlier, see test below. b We used the c2 test to check the internal variability of the green moss ages before calculating the weighted mean. The deviation of a single measurement (Ri) from the weighted mean (Rp) should on average be close to the measurement error (Ei). c2 is the sum of squared ratios between deviations and errors, given as P (Ri Rp)2/E2i and should therefore be close to the number of measurements (n), or more precisely the degrees of freedom, (n 1) (Ward and Wilson, 1978; Ascough et al., 2005). Thus, if the quantity c2/(n 1) is 1 it means that measurement uncertainties explain the variance, while values >1 indicates that the group has additional variance. For all eight radiocarbon ages of the green mosses, c2/ (n 1) ¼ 1.46. Omitting the outlier of 7402 34 yr BP (Beta 221624), c2/ (n 1) ¼ 0.61. Thus we discarded the 7402 34 date in the calculation of the weighted mean of 7300 20.
provides rapid burial of the terrestrial material together with marine sand and shell fragments, and the suspended mud settles quickly and seals of the deposits from oxygen and light. Such an anoxic environment with high pH could also be excellent for preserving delicate artifacts or provide samples for DNA-analysis of ancient organic material catastrophically buried in an offshore tsunami deposit. The coincidence of these two major events in the North Atlantic could be accidental (Dawson et al., 2011), but the strong bottom currents during the Storegga event may have had practical consequences in disturbing many near shore Early Holocene sedimentary archives. Deposits in coastal lakes, bays and fjord settings around the North Atlantic could lack the beginning of the 8.2 cold event due to erosion from the tsunami waves. Also the sedimentation at the later part of the cold event could be disturbed by changes and adjustments in the sediment supply caused by the tsunami inundation and backwash. Coastal- and fjord climatic records claimed to show evidence and details of the 8.2 cold event in the North Atlantic region should be carefully examined for possible contamination and disturbance from the Storegga tsunami.
Fig. 4. Calendar date of the Storegga green mosses compared to d18O and methane in the ice core record: A) Radiocarbon ages verses calibrated dates plotted at the weighted average of their modelled probability distribution (Fig. S4 and Table S3). Tree ring curve from IntCal09 (Reimer et al., 2009). B) Original and modelled probability distribution of the calendar date of 7300 20 yr BP e the weighted average of seven radiocarbon ages of the green mosses (Fig. S4 and Table 1). C) 5-point running average through the GRIP d18O data synchronised to the tree-ring curve; data from Muscheler et al. (2004). The 8.2 event lasts 160 years, from 8040 to 8200 (Thomas et al., 2007). D) Methane concentrations from the GISP ice core (Kobashi et al., 2007).
Author contribution S.B. discovered the green coloured mosses, led the field- and lab work, and wrote the paper. S.K.S. performed the HPLC analysis and detected the chlorophyll. G.S. participated in the field work, picked
6
S. Bondevik et al. / Quaternary Science Reviews 45 (2012) 1e6
and identified plant fragments for radiocarbon dating, counted particles, and identified the green mosses for HPLC analysis. Acknowledgements The work was supported by the University of Tromsø, the Norwegian Research Council and Norsk Hydro. I. Drange and H. Rasmussen participated in the field at an early stage. S. Gulliksen performed most of the radiocarbon measurements at the Trondheim Radiocarbon Laboratory. The manuscript greatly benefitted from comments by B. F. Atwater. H. Aarnes answered questions about chlorophyll. A. Dawson and M. Hald provided critical comments in addition to the two journal reviewers. Appendix A. Supplementary data Supplementary data related to this article can be found online at doi:10.1016/j.quascirev.2012.04.020. References Ascough, P.L., Cook, G.T., Dugmore, A.J., Scott, E.M., Freeman, S.P.H.T., 2005. Influence of mollusk species on marine delta R determinations. Radiocarbon 47, 433e440. Biasi, G.P., Weldon, R., 1994. Quantitative refinement of calibrated C-14 distributions. Quaternary Research 41, 1e18. Blockley, S.P.E., Lowe, J.J., Walker, M.J.C., Asioli, A., Trincardi, F., Coope, G.R., Donahue, R.E., Pollard, A.M., 2004. Bayesian analysis of radiocarbon chronologies: examples from the European Lateglacial. Journal of Quaternary Science 19, 159e175. Bondevik, S., Svendsen, J.I., Mangerud, J., 1997a. Tsunami sedimentary facies deposited by the Storegga tsunami in shallow marine basins and coastal lakes, western Norway. Sedimentology 44, 1115e1131. Bondevik, S., Svendsen, J.I., Johnsen, G., Mangerud, J., Kaland, P., 1997b. The Storegga tsunami along the Norwegian coast, its age and runup. Boreas 26, 29e53. Bondevik, S., Løvholt, F., Harbitz, C., Mangerud, J., Dawson, A., Svendsen, J.I., 2005. The Storegga Slide tsunamidcomparing field observations with numerical simulations. Marine & Petroleum Geology 22, 195e208. Bondevik, S., Mangerud, J., Dawson, S., Dawson, A., Lohne, Ø., 2003. Record-breaking height for 8000-year-old tsunami in the North Atlantic. Eos, Transactions American Geophysical Union 84, 289. Bourgeois, J., 2009. Geological effects and records of tsunamis. In: Robinson, A., Bernard, E.N. (Eds.), The Sea. Tsunamis, vol 15. Harvard University Press, pp. 53e91. Bugge, T., Befring, S., Belderson, R., Eidvin, T., Jansen, E., Kenyon, N., Holtedahl, H., Sejrup, H.P., 1987. A giant three-stage submarine slide off Norway. Geo-Marine Letters 7, 191e198. Corner, G., Haugane, E., 1993. Marine-lacustrine stratigraphy of raised coastal basins and postglacial sea-level changes at Lyngen and Vanna, Troms, northern Norway. Norsk Geologisk Tidsskrift 73, 175e197. Dawson, A., Bondevik, S., Teller, J.T., 2011. Relative timing of the Storegga submarine slide, methane release, and climate change during the 8.2 ka cold event. The Holocene 21, 1167e1171. Dawson, A.G., Stewart, I., 2007. Tsunami deposits in the geological record. Sedimentary Geology 200, 166e183.
Dickson, J., 1973. Bryophytes of the Pleistocene. Cambridge University Press, Cambridge. Drange, I., 2003. Strandforskyvningsundersøkelser og kartlegging av tsunamisedimenter i Nordland. Department of Geology. University of Bergen, Bergen, p. 114. Fahselt, D., Krol, M., Alstrup, V., Hüner, N., 2001. Detection of pigments in specimens of recent and subfossil umbilicaria from North Greenland. The Bryologist 104, 593e599. Grauert, M., Björck, S., Bondevik, S., 2001. Storegga tsunami deposits in a coastal lake on Suderøy, the Faroe Islands. Boreas 30, 263e271. Hallingbäck, T., Holmåsen, I., 1985. Mossor e en fälthandbok. Interpublishing AB, Stockholm. Jankaew, K., Atwater, B.F., Yuki, S., Choowong, M., Charoentitirat, T., Martin, M.E., Prendergast, A., 2008. Medieval forewarning of the 2004 Indian Ocean tsunami in Thailand. Nature 455, 1228e1231. Kobashi, T., Severinghaus, J.P., Brook, E.J., Barnola, J.-M., Grachev, A.M., 2007. Precise timing and characterization of abrupt climate change 8200 years ago from air trapped in polar ice. Quaternary Science Reviews 26, 1212e1222. Koca, N., Karadeniz, F., Burdurlu, H., 2006. Effect of pH on chlorophyll degradation and colour loss in blanched green peas. Food Chemistry 100, 609e615. Leavitt, P.R., 1993. A review of factors that regulate carotenoid and chlorophyll deposition and fossil pigment abundance. Journal of Paleolimnology 9, 109e127. Muscheler, R., Beer, J., Vonmoos, M., 2004. Causes and timing of the 8200 yr BP event inferred from the comparison of the GRIP 10Be and the tree ring D14C record. Quaternary Science Reviews 23, 2101e2111. Nelson, A.R., Atwater, B.F., Bobrowsky, P.T., Bradley, L.-A., Clague, J.J., Carver, G.A., Darienzo, M.E., Grant, W.C., Krueger, H.W., Sparks, R., Stafford, T.W., Stuiver, M., 1995. Radiocarbon evidence for extensive plate-boundary rupture about 300 years ago at the Cascadia subduction zone. Nature 378, 371e374. Ramsey, C.B., 2009. Bayesian analysis of radiocarbon dates. Radiocarbon 51, 337e360. Rasmussen, H., Bondevik, S., 2006. A tsunami in Lyngen, Northern Norway e a regional or local event? In: Peltonen, P., Pasanen, A. (Eds.), The 27th Nordic Geological Winter Meeting Bulletin of the Geological Society of Finland. Reimer, P.J., Baillie, M.G.L., Bard, E., Bayliss, A., Beck, J.W., Blackwell, P.G., Ramsey, C.B., Buck, C.E., Burr, G.S., Edwards, R.L., Friedrich, M., Grootes, P.M., Guilderson, T.P., Hajdas, I., Heaton, T.J., Hogg, A.G., Hughen, K.A., Kaiser, K.F., Kromer, B., McCormac, F.G., Manning, S.W., Reimer, R.W., Richards, D.A., Southon, J.R., Talamo, S., Turney, C.S.M., van der Plicht, J., Weyhenmeye, C.E., 2009. Intcal09 and Marine09 radiocarbon age calibration curves, 0e50,000 years cal bp. Radiocarbon 51, 1111e1150. Romundset, A., Bondevik, S., 2011. Propagation of the Storegga tsunami into ice-free lakes along the southern shores of the Barents Sea. Journal of Quaternary Science 26, 457e462. Sieh, K., Natawidjaja, D.H., Meltzner, A.J., Shen, C.-C., Cheng, H., Li, K.-S., Suwargadi, B.W., Galetzka, J., Philibosian, B., Edwards, R.L., 2008. Earthquake supercycles inferred from sea-level changes recorded in the corals of west Sumatra. Science 322, 1674e1678. Smith, D.E., Shi, S., Cullingford, R.A., Dawson, A.G., Dawson, S., Firth, C.R., Foster, I.D.L., Fretwell, P.T., Haggart, B.A., Holloway, L.K., Long, D., 2004. The holocene Storegga Slide tsunami in the United Kingdom. Quaternary Science Reviews 23, 2291e2321. Thomas, E.R., Wolff, E.W., Mulvaney, R., Steffensen, J.P., Johnsen, S.J., Arrowsmith, C., White, J.W., Vaughn, B., Popp, T., 2007. The 8.2 ka event from Greenland ice cores. Quaternary Science Reviews 26, 70e81. Wagner, B., Bennike, O., Klug, M., Cremer, H., 2007. First indication of Storegga tsunami deposits from East Greenland. Journal of Quaternary Science 22, 321e325. Ward, G.K., Wilson, S.R., 1978. Procedures for comparing and combining radiocarbon age determinations. A critique. Archaeometry 20, 19e31.