Kekonen.indd 33Kekonen et al. 2005: Polar Research 24(1–2), 33–40 Volcanic ash particles are commonly detect- ed from ice cores because of their importance for dating (e.g. Grönvold et al. 1995; Zielinski et al. 1997). Volcanic eruptions usually produce large volumes of SO2 gas, dust, lava, ash and rock (Thordarson et al. 2001). Volcanic material can travel high into the atmosphere and mix with air masses, which can spread very widely. This mate- rial is eventually scavenged in precipitation, or deposited dry in very arid regions. Volcanic tephra includes all rock and lava par- ticles that are erupted into the air, regardless of particle size. In addition to volcanic ash particles, tephra contains other larger sand and rock par- ticles. Ash and other small particles can travel long distances, but bigger sand particles are much heavier than ash and are deposited much closer to the eruption site. Volcanic ash is the smallest tephra fragment (< 2 mm) composed of silicon, aluminium, iron, calcium, magnesium, sodium and other trace elements. Each volcanic eruption produces volcanic ash particles with a specifi c signature in these elements, thereby producing a chemical fi ngerprint by which it can be identifi ed The Icelandic Laki volcanic tephra layer in the Lomonosovfonna ice core, Svalbard Teija Kekonen, John Moore, Paavo Perämäki & Tõnu Martma The largest sulphuric acid event revealed in an ice core from the Lomono- sovfonna ice cap, Svalbard, is associated with the densest concentration of microparticles in the ice core at 66.99 m depth. Electron microscope analysis of a volcanic ash particle shows it has the same chemical compo- sition as reported for debris from the eruption of Iceland’s Laki fi ssure in 1783 and confi rms the identifi cation of the tephra. Most of the particles in the deposit are not ash, but are common sand particles carried aloft during the eruption event and deposited relatively nearby and downwind of the long-lasting eruption. The tephra layer was found 10 - 20 cm deeper than high sulphate concentrations, so it can be inferred that tephra arrived to Lomonosovfonna about 6 - 12 months earlier than gaseous sulphuric acid precipitation. The sulphuric acid spike has a signifi cant cooling impact recorded in the oxygen isotope profi le from the core, which corresponds to a sudden drop in temperature of about 2 °C which took several years to recover to previous levels. These data are the fi rst particle analyses of Laki tephra from Svalbard and confi rm the identifi cation of the large acidic signal seen in other ice cores from the region. They also confi rm the very large impact that this Icelandic eruption, specifi cally the sulphu- ric acid rather than ash, had on regional temperatures. T. Kekonen, University of Oulu, Box 3000, FI-90014 University of Oulu, Finland and Arctic Centre, Uni- versity of Lapland, Box 122, FI-96101 Rovaniemi, Finland, teija.kekonen@oulu.fi ; J. Moore, Arctic Centre, University of Lapland, Box 122, FI-96101 Rovaniemi, Finland; P. Perämäki, Dept. of Chemistry, University of Oulu, Box 3000, FI-90014 University of Oulu, Finland; T. Martma, Institute of Geology, Tallinn Univer- sity of Technology, Estonia pst 7, EE-10143 Tallinn, Estonia. 34 The Laki tephra layer in the Lomonosovfonna ice core (e.g. Palais et al. 1992; Grönvold et al. 1995; Zie- linski et al. 1997; Zielinski et al. 1998). The eruption of Iceland’s Laki fracture in 1783 was one of largest basaltic fi ssure eruptions in recorded history. The volume of aerosols inject- ed into the atmosphere by the eruption was one of the greatest atmospheric pollution events over Europe during historic times (Thordarson & Self 2003). The Laki volcanic eruption lasted for eight months (June 1783 to February 1784) and pro- duced one of the largest recorded basaltic lava fl ows in Iceland. The sulphuric and, especially, the hydrofl uoric acid produced by the eruption were responsible for the deaths of more than half the animals on Iceland (Thordarson & Hoskulds- son 2002). There were also widespread effects in the Northern Hemisphere, including cooling (Thordarson & Hoskuldsson 2002; Highwood & Stevenson 2003; Thordarson & Self 2003). A strong sulphate acid signal corresponding to an age of 1783–84 has been reported in many ice cores from Greenland and Svalbard (Fiacco et al. 1994; Zielinski et al. 1994; Thordarson et al. 1996; Watanabe et al. 2001; Thordarson & Self 2003). In this work we have analysed samples close to a major sulphate peak in the ice core and found a particle-rich layer at a depth of 66.99 m using SEM-EDS. This is the fi rst published result relat- ing to the tephra layer and volcanic ash particle from the Laki eruption located in Svalbard gla- ciers. Study site and methods The 121 m long ice core was recovered with an electromechanical drill from the summit of the Lomonosovfonna ice cap (1255 m a.s.l.), on the island of Spitsbergen, Svalbard, in 1997 (Fig. 1) (Isaksson et al. 2001). Total ice depth from radar sounding was 123 m, and the site is close to the highest point of the ice cap with roughly radial ice fl ow. The ice core represents an approximate- ly 800 year period. The time scale of the core was based on an ice layer thinning model (Nye 1963) tied with the known dates of prominent reference horizons (1963 radioactive layer and 1783 Laki volcanic sulphate layer and volcanic ash particle; see Kekonen et al. [2005] for details). The accu- mulation rate for the 1997–1963 period is 0.41 m water equivalent per year and a somewhat lower value of 0.31 m w.e. per year for the period 1963– 1783. The model age profi le can be independently checked by comparison with automated seasonal cycle counting in stable isotopes and ions down to 81 m (Pohjola et al. 2002). The model age at 81 m depth is 1705, while the cycle counting method gives a date of 1715. There is a thus a discrepan- cy of 10 years in about 75 years between the Laki horizon and the limit of cycle counting. Howev- er, the cycle counting method will always tend to miss a fraction of low accumulation rate years due to the resolution of the data and isotope dif- fusion effects, so a good model dating should be more reliable (on average) than cycle counting. The current annual temperature range is from 0 °C to about –40 °C. Any summer meltwater is refrozen mostly within the previous winter’s snow, and the remainder within the next two or three lower annual layers. Although percolation can be up to eight years in the warmest years in the 20th century, it was much reduced during the Little Ice Age (Kekonen et al. 2005). Vari- ous statistical analytical methods (see Kekonen Fig 1. Map showing Svalbard and Iceland and the inferred plume direction of the westerly jet stream on 10 June 1783. Transport paths are based on the data of Thordarson & Self (2003) and Fiacco et al. (1994). 35Kekonen et al. 2005: Polar Research 24(1–2), 33–40 et al. 2005; Moore et al. 2005) show that chemi- cal and isotopic stratigraphy are suffi ciently well preserved that signifi cant decadal-scale periodic- ities can be found, annual layers can be count- ed for about 300 years, and changes in chemical composition related to changes in climate are far more signifi cant than changes in chemical com- position in ice layers subject to various degrees of percolation. The core was transported and stored in a frozen state (–22 °C). The whole ice core was cut into 5 cm sections and the outer parts of the samples were removed in a cold room under a laminar fl ow hood. For particle analyses, selected sam- ples were melted and fi ltered under a laminar fl ow hood. The 10 - 20 ml of meltwater was fi ltered just after melting with Nuclepore polycarbonate membranes (25 mm diameter and 0.2 mm pore size) using a vacuum fi lter system. Each sample was fi ltered through separate fi lter membranes. Filter membranes were glued onto the stubs using carbon-coated double-sided tape and coated with a thin fi lm of carbon. Samples were analysed for major elements using a Jeol JMS-6400 scanning electron microscope combined with a Link ISIS and INCA energy dispersive spectrometer. An acceleration voltage of 15 kV and a beam current of 1.2 nA were used for the SEM-EDS (scanning electron microscope energy dispersive spectrom- eter) analysis with the sample distance of 15 mm. Acidity was measured using a Radiometer Copen- hagen PHM 205 pH meter and XC 161 combined pH electrode. For acidity measurements, samples were melted under nitrogen atmosphere to pre- vent carbon dioxide dissolution. All the ions (Na+, K+, NH4+, Mg2+, Ca2+, Cl–, NO3–, SO42–, CH3SO3–) were analysed over the whole core in 5 - 10 cm resolution using a Dionex ion chromatograph with conductivity detector and suppressor housed in a clean laboratory. Details for ion chromatography analyses are described by Kekonen et al. (2002) and Kekonen et al. (2004). δ18O was determined using a Finnigan-MAT Delta-E mass spectrometer (Isaksson et al. 2001). Results are measured against laboratory inter- nal standard water, which has been calibrated on the V-SMOW/SLAP scale using the international reference materials V-SMOW (Vienna Standard Mean Oceanic Water) and SLAP (Standard Light Antarctic Precipitation) from the International Atomic Energy Agency. Reproducibility of repli- cate analyses is generally better than ± 0.1 ‰. We used an automated particle analyser to measure the chemical composition of all the par- ticles present on a 271 × 191 mm subsections of the 490 mm2 fi lter membrane. In total we ana- lysed 2063 particles in 44 different subsections of the same fi lter membrane. Results and discussion There are no visible dust or tephra bands in the ice core, but particles were sought at many depths using the method described above. Enormous amounts of tephra (approximately half a mil- lion particles) were detected on the 66.99 - 67.04 m depth fi lter membrane. The subsection typical- ly contained 30 - 100 particles, most commonly 50. (For comparison, at other depths a subsection usually contained less than 10 particles.) This is the only depth where tephra were found close to a high sulphate and acidity peak (66.69 - 66.89 m) (Fig. 2). Most of the tephra were small sand par- ticles of basaltic composition (Fig. 3). The SiO2 composition is approximately same as in parti- cles originating from Laki eruption as reported in the literature (see references in Table 1). While the automated analyses in Fig. 3 do not give very exact chemical compositions due to the nature of the particle morphology, the large numbers of analyses give a statistical view of tephra com- position relative to the composition of the Laki tephra. A volcanic ash particle (that is, an amorphous glassy shard indicative of volcanic eruption activ- ity) was found amongst the many sand particles (Fig. 4) and was analysed in detail using a spot analyser at 40 points on the particle. Comparison of the chemical composition of the particle with the composition of tephra from known eruptions indicates that particles found in the Lomonosov- fonna ice core originate from the volcanic erup- tion of Laki in 1783 (Table 1). The tephra (includ- ing sand and ash) was ejected into the atmosphere by the fi ssure eruption mechanism that is typifi ed by the Laki eruption (Fiacco et al. 1994). Atmos- pheric transport directed the Laki aerosol plume fi rst to the east and the north-east (Thordarson & Self 2003) (Fig. 1). Since Svalbard is rather near to Iceland—less than 2000 km—and general- ly downwind of it, many heavy sand particles in addition to ash particles are observed in the core. The volcanic tephra layer is about 10 - 20 cm deeper than the high sulphate concentration and acidity peaks (seen between 66.69 and 66.89 m) 36 The Laki tephra layer in the Lomonosovfonna ice core (Fig. 2). At this depth (66 - 67 m), the 5 cm sample resolution roughly corresponds to few months of time. This indicates that the volcanic tephra was carried to Lomonosovfonna ice cap about 3 - 9 months before the sulphuric acid started to pre- cipitate on the glacier, and 6 - 12 months before the main sulphuric acid precipitation occurred. Sulphuric acid precipitation on the Lomonosv- fonna ice cap lasted for 9 - 15 months. ECM anal- yses of Greenland ice cores (Clausen et al. 1997) indicate that the fallout from the Laki eruption lasted 1.0 and 1.6 years there. After the main sulphate concentration and acid- ity peaks, a smaller peak can also be observed (Figs. 2, 5). Thordarson et al. (1996) reported that high discharge basaltic eruptions, such as Fig. 2. Sulphate (thick line) concentrations and acidity (thin line) near the Laki peak. The tephra layer is marked by the thick black vertical line. Table 1. Mean value and standard deviation for the 40 spot analysis of volcanic ash particle (Fig. 4) compared to other Laki particles. “Ref. 1” is the composition of the glass phase of the Laki eruption. An average of six samples and ten glass grains were analysed in each sample (. Grönvold, pers. comm. 2002). Refs. 2 and 3 are the composition of Laki tephra (T. Thordarson, unpubl. data; Fiacco et al. 1994). Ref. 4 is the composition of particles from fi lter paper collected from the GIPS2 ice core (Fiacco et al. 1994). Ref. 5 is the major element composition of Laki glass (Thordarson et al. 1996). The number of analyses is shown in the last column (n). wt. % Na2O MgO Al2O3 SiO2 SO3 K2O CaO TiO2 MnO FeO n Mean 2.81 6.59 13.16 50.64 0.45 0.18 10.20 2.07 0.03 13.85 40 SD 0.50 0.65 0.56 1.09 0.22 0.12 1.17 0.23 0.09 1.50 Ref. 1 2.61 5.32 12.70 49.10 0.47 10.10 2.96 0.24 13.70 Ref. 2 2.78 5.40 13.26 49.97 0.44 9.90 3.02 0.21 14.08 18 SD 0.11 0.02 0.02 0.07 0.01 0.03 0.01 0.00 0.05 Ref. 3 1.83 5.48 12.96 54.47 0.50 9.23 2.84 12.69 3 SD 0.18 0.47 1.56 1.05 0.01 0.59 0.35 1.01 Ref. 4 1.26 4.81 13.05 52.26 0.69 10.41 2.88 14.64 5 SD 0.52 0.65 0.95 2.45 0.25 0.90 0.34 2.59 Ref. 5 2.84 5.78 13.05 49.68 0.42 10.45 2.96 0.22 13.78 21 SD 0.12 0.30 0.48 0.36 0.05 0.28 0.17 0.03 0.61 37Kekonen et al. 2005: Polar Research 24(1–2), 33–40 Laki, are able to loft huge quantities of gas to alti- tudes (including the troposphere and lower strat- osphere) where the resulting aerosol can reside for 1 - 2 years (Stevenson et al. 2003). In Green- land ice cores high sulphate peaks are observed in spring, summer and autumn 1784, indicating that the increased atmospheric loading of SO2 lasted for about a year (Fiacco et al. 1994; Thordarson et al. 1996). The highest sulphate concentration observed in the Greenland ice cores is about 1300 µg L–1 (Fiacco et al. 1994), which is slightly lower than we observe in the Lomonosvfonna ice core (Fig. 2). The mean acidity of the Laki signal is 18 ± 8 µg L–1. Thordarson & Self (2003) estimat- ed the excess optical depth caused by the eruption relative to that due to the absolutely calibrated Krakatau aerosol cloud with a correction for the different geographic extent of the volcanic clouds. The method requires only the mean amplitude of the acidity of the Laki peak in Greenland ice cores, and produces an excess optical depth of 0.8 ± 0.4. Applying the same procedure to the Lomonosov- fonna acidity record results in an excess optical depth of 0.9 ± 0.4, which is in excellent agreement with Thordarson & Self (2003). Clausen et al. (1997) report acidic fallout in central and south- ern Greenland ice cores (147 and 177 kg km–2, respectively). This compares with a fallout pre- served in the Lomonosovfonna ice core of 390 kg km–2. This much larger fallout is a consequence of Svalbard being virtually downwind of Iceland during the eruption, while southern and, especial- ly, central Greenland were essentially upwind. The impact of the large acidity pulse on Europe- an temperatures has been well documented using various historical and proxy archives (Thordar- son & Self 2003). The impact on the Lomonos- ovfonna δ18O isotopic temperature proxy (Isaks- son et al. 2003) can be seen in Fig. 5. It is clear that there is an immediate drop in δ18O follow- ing the acid deposition rather than the ash fall- out recorded by the tephra layer deposit. There is a 0.8 ‰ dip in 3-year running means relative to 30-year running means in δ18O for the 3 years following the acidic fallout, and this represents the lowest value of δ18O between 1400 and the Fig. 3. Chemical compositions of 2063 particles by automated analysis in 44 different subsections of the membrane fi lter from a depth of 66.99 m. The box shows the chemical composition of Laki volcanic ash particles from the literature cited in Table 1. Fig. 4. A volcanic ash particle from a depth of 66.99 m. 38 The Laki tephra layer in the Lomonosovfonna ice core 1820s, and may therefore be regarded as highly signifi cant. This is in contrast with the signal in the Greenland ice cores, where either a modest rise in δ18O or no change is seen immediately fol- lowing the eruption (Vinther et al. 2003). How- ever, this apparent discrepancy may be explained by the larger acidic fallout to the west of Iceland over Europe and Svalbard, and the typical see- saw behaviour of the North Atlantic Oscillation, resulting in temperature anomalies of opposite sign over Europe and Greenland, (e.g. Vinther et al. 2003). We can calibrate the δ18O–temperature relation- ship with borehole thermometry. Van de Wal et al. (2002) analysed the borehole temperature pro- fi le, fi nding that temperatures in the 19th centu- ry were 2.4 °C colder than the 20th century. This compares with a 0.8 ‰ difference in δ18O (Isaks- son et al. 2003) between the 19th and 20th centu- ries—virtually the same depression as caused by the Laki eruption. Thus we can estimate that the 3 year dip in δ18O corresponds to about a 2.4 °C temperature fall. We could also use a calibra- tion of isotopes against instrumental temperature records. However, extrapolating the calibrations to the colder pre-20th century period is unrelia- ble (e.g. von Storch et al. 2004), so we prefer to use the estimate based on the borehole tempera- ture profi le. Highwood & Stevenson (2003) and Thordarson & Self (2003) observed in their cal- culations that temperature decreased 0.21 °C and 1.3 °C, respectively, in the wider Northern Hemi- sphere after the Laki eruption. There are several reasons why the tempera- ture drop in Svalbard may have been higher than in mainland Europe. It is clear that recovery to more normal temperatures takes at least two to three years (Thordarson & Self 2003). Although the Laki eruption probably did not eject aero- sol into the upper stratosphere (Stevenson et al. 2003), where long residence times are possible, the long-lasting nature of the eruption helped to produce a persistent temperature depression, at least over much of Europe. The North Atlan- tic sea surface temperatures during the period 1780–1820 were monitored by the British Admi- ralty and are discussed by Bjerknes (1964): the ocean south of 40° N was up to 3 °C warmer than the present climate, while the northerly parts were 2 - 3 °C cooler. This condition would read- ily lead to increased sea ice cover in the Green- land, Iceland and Barents seas, providing a ready positive feedback mechanism for a year or two. Feedbacks with the large-scale atmospheric cir- culation patterns similar to those found for more recent eruptions (Kirchner et al. 1999) may also have enhanced the impact of the eruption. Fig. 5. Sulphate (thick line) concentrations and isotope δ18O value (thin line) as a proxy for temperature near the Laki sulphate peak. The tephra layer is marked by the thick black vertical line. 39Kekonen et al. 2005: Polar Research 24(1–2), 33–40 Conclusions The insoluble fractions of ice core samples show that during the 1783 Laki volcanic eruption mas- sive amounts of tephra arrived to the Lomonos- ovfonna ice cap in Svalbard. The volcanic tephra layer includes large amounts of sand particles which suggests that not only light ash particles were well transported downwind from the erup- tion site. The heavy particles would also have been resistant to removal on the ice cap by wind. The tephra layer was found 10 - 20 cm deeper than high sulphate concentrations and acidity and shows that tephra arrived to the ice cap 6 - 12 months earlier than gaseous sulphur dioxide was rained out as sulphuric acid. The sulphuric acid precipitation lasted 9 - 15 months. Analyses indi- cate that the geochemical compositions of the volcanic tephra are basaltic, and the geochemical signatures of an ash particle show derivation from the Icelandic Laki volcanic eruption in 1783. Acknowledgements.—The authors thank the Finnish Forest Research Institute Research Station in Rovaniemi for cold and clean room facilities and Aslak Grinsted for helpful anal- yses. The drilling of the Lomonosovfonna 1997 ice core was fi nanced by the Norwegian Polar Institute and the Institute for Marine and Atmospheric Research, Utrecht. The labora- tory work presented here was funded by the Finnish Academy Figare project. Elisabeth Isaksson, Veijo Pohjola, Roderik van de Wal and all the fi eld participants are also thanked. References Bjerknes, J. 1964: Atlantic air–sea interaction. Adv. Geophys. 10, 1–82. Clausen, H. B., Hammer, C. U., Hvidberg, C. S., Dahl-Jensen, D. & Steffensen, J. 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