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Yellowstone (USA), then re-colonisation of pioneer species will take even longer as recovery of flora must do so from the edges of the affected area. There is new evidence to suggest that the large Toba (Sumatra, Indonesia) eruption around 73,000 years ago caused major deforestation in and around India, where forested areas were replaced by wooded to open grassland (Williams et al., 2009). A large ash blanket can affect surface temperatures by raising the surface albedo. Tephra can have a dry albedo as high as 0.7 (comparable to snow) so the local radiative effect of ash deposition leads to less heat retention by vegetation and the reflection of a greater proportion of incoming radiation (Jones et al., 2007). This instigates localised relative surface cooling. This climatic disruption from an ash blanket will last for longer than that induced by stratospheric aerosols as a slowing of the hydrological cycle, the scale of the ash blanket, and the cohesive nature of fine tephra will prolong the residence time of the ash blanket (Collins & Dunne, 1986). A key factor to the subsequent climate forcing is the geomorphology and location of the area affected by ash deposition. Coverage of an archipelago will differ considerably from a continent, as an ash blanket covering the latter would affect a greater surface area and would have a longer residence time. Deposition of ash into ocean surface waters has its own capacity to alter the climate, so the ratio between continental and oceanic effects is dictated by what proportion of the fallout area they cover. The residence time of an ash blanket is dependent on local precipitation patterns, as deposition in a tropical environment would lead to quicker erosion than deposition in a more arid environment. Oceanic impact As with terrestrial ecosystems, the aerosol induced Volcanic Winter will affect marine primary productivity. A net decrease in direct solar radiation thins the euphotic zone, limiting the depth to which photosynthesis can occur. This would be a transient effect limited to the lifetime of the stratospheric aerosols, but may affect the health of stationary organisms such as corals. While the temperature changes in the oceans are much less than terrestrial ecosystems, the previously described effects in the atmosphere and on land alter global heat and freshwater fluxes and therefore the temperature and salinity of the surface oceans. This is particularly important in the North Atlantic, where the increase in winds speeds that causes the Winter Warming lead to an increase in the thermo-haline circulation. Again, this effect is predicted to be transient (Jones et al., 2005), but an important consideration nonetheless. Another key factor is the deposition of tephra directly into ocean surface waters, which can lead to rapid biogeochemical changes. The solid particles in an eruption cloud act as nuclei for condensing gases, aerosols and metal salts (Rose, 1977; Oskarsson, 1980). These surface accumulations are highly soluble, dissolving rapidly on contact with water (Frogner et al., 2001; Duggen et al., 2007). Both nutrients and toxins are released into the water column, which have the potential to both fertilize and poison surface water environments (Frogner-Kockum et al., 2006; Duggen et al., 2007). This has important ramifications for the ocean-atmosphere system, as it has been suggested that an enhancement in primary productivity from increased nutrient supply could increase the biological pump for atmospheric CO 2 (Sarmiento, 1993; Watson, 1997). Mechanical mixing experiments using volcanic ash with seawater suggests that deposition of just 4mm of ash coverage can significantly increase micronutrient levels (Jones & Gislason, 2008). These are new and exciting developments but the science is still in its infancy. Any increase in marine primary productivity would be offset by the decrease in incoming radiation during the Volcanic Winter. Moreover, the potential for fertilisation is dependent on the pre-existing chemistry of surface waters (Duggen et al., 2009). Areas that have high nutrient levels but low chlorophyll levels, such as the eastern-equatorial Pacific Ocean, can have large phytoplankton bloom when enriched in key limiting nutrients such as Fe (e.g. Morel et al., 1991). Deposition in areas with regular replenishment of nutrients, such as areas of upwelling, may have a more limited impact. Importantly, nutrient release is accompanied by the release of elements that can inhibit biological growth, including many that are fertilisers at lower concentrations (Sunda, 1988-1989; Bruland et al., 1991). Ecosystem stress is further increased by a transient drop in pH due to acids such as H 2 SO 4 (Frogner et al., 2001; Jones & Gislason, 2008). Decreases in pH levels affect organisms dependent on CaCO 3 for shell or skeleton formation (Riebesell et al., 2000; Feely et al., 2004). Biogenic carbonate precipitation is dominated by micro-organisms (Milliman, 1993), suggesting that declines in these species has serious implications for food web structure and health. Decreases in pH would lead to reduced calcification rates, malformation, and enhanced dissolution of susceptible organisms. This is the same problem receiving attention in the world’s media at present with the rising CO 2 levels from human activity causing an “ocean acidification” (e.g. Riebesell et al., 2000), except this is a natural transient effect. Whether this effect occurs at all is dependent on the magnitude of tephra deposition, the chemistry of the dissolving acids (which vary considerably in quantity and speciation between volcanoes), and the extent of diffusion and mixing in the water column. In summary, there are many unknowns associated with the fate of volcanic 28 Teaching Earth Sciences Vol 35 No 1 2010 www.esta-uk.net
emissions in ocean surface waters, but initial studies suggest that in some cases the effects may be considerable. Conclusion I hope this summary has conveyed to you the difficulties associated with assessing the impact of a future eruption, as there are many variables to be taken into consideration and there are still big gaps in our understanding. Large eruptions have been suggested as possible catalysts for longer term changes to the ocean-earth system (Rampino & Self, 1992), though this relationship remains contentious (e.g. Oppenheimer, 2002). Predictions of a 100x Pinatubo sulphate aerosol forcing suggest that the depressed temperatures during Volcanic Winter are insufficient to initiate a glaciation at current climatic conditions (Jones et al., 2005) (Figure 3). Deforestation and an increase in surface albedo from tephra deposition encourage more persistent snow cover (Jones et al., 2007). While these effects last longer than the Volcanic Winter and would act as an amplifier to the cooling signal, the scale of the disturbance appears inadequate to instigate prolonged changes to the climate at current conditions. While the aerosol induced Volcanic Winter is the dominant forcing for historic eruptions, there are other factors that may only become significant for larger eruptions. Terrestrial surface effects can have a large effect on the carbon cycle, such as changes to soil respiration, deforestation, and changes to primary productivity. In marine environments, variations in marine primary productivity can have a large impact on atmospheric CO 2 levels. However, predicting these changes is extremely difficult, and could feasibly be unique for each eruption as much depends on the time, location, chemistry, and magnitude of the eruption. Timescales of ecosystem stresses, fertilization events, and recovery of flora and fauna are poorly constrained, although it is plausible that these disruptions could combine to significantly enhance decadal, centurial, or even millennial climatic variability. Super-eruptions that have occurred in the Upper Pleistocene have been implicated as bottlenecks for human and animal populations, based on evidence of overall low human genetic diversity (Rampino & Ambrose, 2000). Major historic eruptions have caused famines, plagues, and crop failures, so the impact of an event the scale of a super-eruption will have serious implications for food web structure and health. If a super-eruption were to occur in the near future (a very big “if”) the impact would be catastrophic. Agriculture and water supply would be initially devastated in many communities, with supplies unable to sustain the current human population. The Northern Hemisphere would be particularly threatened as this is where most food production occurs and where population densities are highest (Self, 2006). Such large events are extremely uncommon, so the chances of one occurring in our lifetime are very slim. However, there will be future super-eruptions, so it is imperative that we learn all we can about such phenomena. References Andronova, N.G., Rozanov, E.V., Yang, F., Schlesinger, M.E. & Stenchikov, G.L. (1999) Radiative forcing by volcanic aerosols from 1850 to 1994. Journal of Geophysical Research, 104, pp.16807-16826. Bluth, G.J., Doiron, S.D., Schnetzler, C.C., Krueger, A.J. & Waleter, L.S. (1992) Global tracking of the SO2 clouds fro the June 1991 Mount Pinatubo eruptions. Geophysical Research Letters, 19(2), pp.151-154. Bruland, K.W., Donat, J.R. & Hutchins, D.A. (1991) Interactive influences of bioactive trace metals on biological production in oceanic waters. Limnology and oceanography, 36(8), pp.1555-1577. Coles, S.G. & Sparks, R.S.J. (2006) Extreme Value Methods for Modelling Historical Series of Large Volcanic Magnitudes. In: Mader, H.M. et al. (Eds.) Statistics in Volcanology. London. Collins, B.D. & Dunne, T. (1986) Erosion of tephra from the 1980 eruption of Mount St. Helens. Geological Society of America Bulletin, 97(7), pp.896-905. Duggen, S., Croot, P., Schacht, U. & Hoffmann, L. (2007) Subduction zone volcanic ash can fertilize the surface ocean and stimulate phytoplankton growth: Evidence from biogeochemical experiments and satellite data. Geophysical Research Letters, 34, L01612. Duggen, S., Olgun, N., Croot, P., Hoffmann, L., Dietze, H. & Teschner, C. (2009) The role of airborne volcanic ash for the surface ocean biogeochemical iron-cycle: a review. Biogeosciences Discussions, 6, pp.6441-6489. Fagan, W. & Bishop, J. (2000) Trophic interactions during primary succession: herbivores slow a plant reinvasion at Mount St. Helens. American Naturalist, 155, pp.238-251. Feely, R., Sabine, C., Lee, K., Berelson, W., Kleypas, J., Fabry, V. & Millero, F. (2004) Impact of Anthropogenic CO2 on the CaCO3 system in the oceans. Science, 305(5682), pp.362-366. Frogner-Kockum, P.C., Herbert, R.B. & Gislason, S.R. (2006) A diverse ecosystem response to volcanic aerosols. Chemical Geology, 231, pp.57-66. Frogner, P., Gislason, S.R. & Oskarsson, N. (2001) Fertilizing potential of volcanic ash in ocean surface water. Geology, 29(6), pp.487-490. Gu, L., Baldocchi, D.D., Wofsy, S.C., Munger, J.W., Michalsky, J.J., Urbanski, S.P. & Boden, T.A. (2003) Response of a deciduous forest to the Mount Pinatubo eruption: enhanced photosynthesis. Science 299, pp.2035-2038. Harshvardhan, (1979) Perturbation of the zonal radiation balance by a stratospheric aerosol layer. Journal of the Atmospheric Sciences, 36(7), pp.1274-1285. Jones, G.S., Gregory, J.M., Stott, P.A., Tett, S.F.B. & Thorpe, R.B. (2005) An AOGCM simulation of the climatic response to a volcanic super-eruption. Climate Dynamics, 25(7-8), pp.725-738. Jones, M.T. & Gislason, S.R. (2008) Rapid releases of metal salts and nutrients following the deposition of volcanic ash into aqueous environments. Geochimica et cosmochimica acta, 72, pp.3661-3680. Jones, M.T., Sparks, R.S.J. & Valdes, P.J. (2007) The climatic impact of supervolcanic ash blankets. Climate Dynamics, 29(6), pp.553-564. Knight, T. & Chase, J., 2005. Ecological succession: out of the ash. Current Biology, 15(22), R926-R927. Krakauer, N.Y. & Randerson, J.T. (2003) Do volcanic eruptions enhance or diminish net primary production? Evidence from tree rings. Global Biogeochemical Cycles, 17(4), p.1118. Long, C.S. & Stowe, L.L. (1994) Using the NOAA/AVHHR to study stratospheric aerosol optical thicknesses following the Mt. Pinatubo eruption. Geophysical Research Letters, 21(20) pp.2215-2218. www.esta-uk.net Vol 35 No 1 2010 Teaching Earth Sciences 29
Page 1 and 2: Teaching ISSN 0957-8005 Earth Scien
Page 3 and 4: Contents From the Editor Hazel Clar
Page 5 and 6: From the Chair Niki Whitburn Welcom
Page 7 and 8: Fred Broadhurst remembered 5 Februa
Page 9 and 10: Geology and Society - ESTA Annual C
Page 11 and 12: ESTA Conference, Southampton 2009 P
Page 13 and 14: Teaching Ideas from the ‘Bring an
Page 15 and 16: Idea Title: Presenter: Brief descri
Page 21 and 22: Sub-surf Rocks! ESTA at Southampton
Page 23 and 24: Potential exists to use Google Eart
Page 25 and 26: Conclusion Since the development of
Page 27 and 28: Figure 1 A simple diagram showing t
Page 29: Figure 3 Predicted annual surface t
Page 33 and 34: Greenhouse to icehouse: Arctic clim
Page 35 and 36: the results are extremely striking.
Page 37 and 38: experienced by this region have bee
Page 39 and 40: Climate Change . . . Save the Plane
Page 41 and 42: 14-18) from King Edward VI Five Way
Page 43 and 44: Figure 2 The living roof planted wi
Page 45 and 46: Peneplains and plate tectonics Mark
Page 47 and 48: Figure 2 Planation surfaces (penepl
Page 49 and 50: Lidmar-Bergström, K. (1999) Uplift
Page 51 and 52: The formation of Gondwana (and Laur
Page 53 and 54: The fracturing of Gondwana was a pr
Page 55 and 56: Figure 5 Plunge refers to the dip o
Page 57 and 58: The foregoing is a summary of terms
Page 59 and 60: Reviews The Control of Nature John
Page 61 and 62: The starting point of the Deep Time
Page 63 and 64: With an introductory textbook of th
Page 65 and 66: Earth’s Climate provides a multid
Page 67 and 68: Excursion Guide to the Geology of E
Page 69 and 70: Diary March 2010 1st March until 11
Page 71: 9th June Lecture: The Chemistry of

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