a holocene north atlantic sst record and regional climate variability abstract by combined use of 210 pb dates identification of icelandic tephras of known age and wiggle matching of 14 c radiocarbon dates exceptional accurate chronologies have been established for two cores p1003mc and sc raised from the same location on the norwegian continental margin and that span the last 8 ka they are located directly under the core of the eastern branch of atlantic water entering the nordic seas comparing oxygen isotope measurements on the planktonic foraminiferal species neogloboquadrina pachyderma dex with nearby instrumental time series suggest that this parameter at this site primarily reflects summer temperature conditions of near surface c 50 m waters we argue that this proxy to some degree reflects north atlantic sea surface temperature variability through the holocene a detailed correlations of the oxygen isotope record with solar proxies for the last 1 ka was not apparent for the whole 8 ka record however a statistically significant 95 spectral peak at c 83 yr may represent the so called gleissberg solar cycle a relative high correlation r 0 53 between 14 c productivity and the ocean near surface temperature proxy was obtained on 800 1500 year band filtered data the latter lagging 180 year after the solar proxy multi channel singular spectrum analyses carried out on the p1003 time series the oxygen isotope record from the renland ice core from eastern greenland and on the tornetrask tree ring record from central scandinavia reveals a significant common frequency at 280 year the expression of this frequency in the different records shows variability in phase relationship and strength over time and does not appear to have any similarity to any known modes of climate variability in the area in order to predict future climate change in the region it is of utmost importance to develop a better understanding of the mechanisms behind multi decadal and multi centennial scale climate variability

diatoms as hydrographic tracers example from bering sea sediments variations in the distribution of diatom species in surface sediments mirror distinct hydrographic regimes on the bering shelf spring salinity fronts divide the water column into four zones with different vertical structures and different productivity patterns four assemblages of diatoms can be distinguished in sediments underlying the zones

bristlecone pine tree rings and volcanic eruptions over the last 5000 yr many years of low growth identified in a western usa regional chronology of upper forest border bristlecone pine pinus longaeva and pinus aristata over the last 5000 yr coincide with known large explosive volcanic eruptions and or ice core signals of past eruptions over the last millennium the agreement between the tree ring data and volcano ice core data is high years of ring width minima can be matched with known volcanic eruptions or ice core volcanic signals in 86 of cases in previous millennia while there is substantial concurrence the agreement decreases with increasing antiquity many of the bristlecone pine ring width minima occurred at the same time as ring width minima in high latitude trees from northwestern siberia and or northern finland over the past 4000 5000 yr suggesting climatically effective events of at least hemispheric scale in contrast with the ice core records the agreement between widely separated tree ring records does not decrease with increasing antiquity these data suggest specific intervals when the climate system was or was not particularly sensitive enough to volcanic forcing to affect the trees and they augment the ice core record in a number of ways by providing confirmation from an alternative proxy record for volcanic signals by suggesting alternative dates for eruptions and by adding to the list of years when volcanic events of global significance were likely including the mid 2nd millennium bc eruption of thera

late quaternary sea levels and crustal movements coastal british columbia late quaternary sea level fluctuations on the british columbia coast have been established from studies of terrestrial and marine sediments and landforms these studies indicate that the sea level history of mainland british columbia and eastern vancouver island is very different from that of the queen charlotte islands and western vancouver island specifically in the former areas there was a rapid rise of submerged coastal lowlands between about 13 000 and 10 000 years ago emergence culminated about 6000 9000 years ago depending on the locality when the sea relative to the land was 12 m or more lower than at present in some areas during middle and late holocene time relative sea level rose on the mainland coast and at least locally on eastern vancouver island resulting in inundation of coastal archaeological sites and low lying terrestrial vegetation tidal records and precise levelling suggest ongoing submergence of at least part of this region in contrast shorelines on the queen charlotte i

paleogeographic reconstruction of the eocene idaho river north american cordillera eocene lake gosiute in southwestern wyo ming was progressively fi lled in by volcani clastic sediment between 49 6 and 47 0 ma the source of this material has long been thought to have been the absaroka volcanic province immediately north of the greater green river basin lead isotope compositions of sandstone from this interval however are consistent with derivation from the challis volcanic fi eld the 40 ar 39 ar ages of single de trital k feldspar crystals from greater green river basin sandstones are nearly identical to 40 ar 39 ar eruptive ages for volcanic rocks of the challis volcanic fi eld 49 8 45 5 ma but we also identify mesozoic and proterozoic crystals that are consistent with cooling ages for rocks that were likely exposed in the idaho segment of the north american cordillera during the eocene most of these rocks are traversed by or are up gradient of a major eocene paleovalley in central idaho the sud den appearance of challis derived sediment in the greater green river basin indicates that a major river here named the idaho river connected the interior of the north american cordillera to the greater green river basin this connection requires 500 km to reach from central idaho to the greater green river ba sin the idaho river probably carried detritus that was stripped from distant uplifted moun tains above the active challis volcanic fi eld as far south as the piceance creek basin suggest ing a total length of at least 1000 km middle eocene metamorphic core complexes in the northern cordillera likely produced a major highland in the headwaters of the idaho river which generated river systems that drained both eastward into the wyoming foreland and westward into the oregon coast ranges

late pleistocene holocene paleoceanographic changes on the eastern canadian margin stable isotopic evidence abstract earlier studies of this area show profound holocene pleistocene paleoceanographic changes along the eastern continental margin of canada based on benthic foraminiferal assemblages here we demonstrate that stable isotopic measurements from benthonic foraminifera substantiate and place numerical limits on physical parameters from some of the glacial postglacial environments in holocene intervals where modern analogues of present day benthonic foraminiferal faunas can be used to delimit the physical environment the isotopic results closely parallel the faunal results in the glacial marine intervals where we have no modern analogues the isotopic results provide us with the first independent evidence that the salinities were not lower than 30 in the bottom waters along this former ice margin at the time of peak glaciation salinities may actually have been above normal we see no indication of a large meltwater event in the 10 11 k y b p time period that has been suggested to occur with the younger dryas events these results demonstrate that stable isotopes can be useful outside the context of relatively stable deep sea environments

foraminiferal stratigraphy and environment of late weichselian deposits on the continental shelf off troms northern norway abstract based on the analysis of 8 selected gravity cores from the upper sediment layers of andfjorden and malangsdjupet off northern norway six late weichselian foraminiferal assemblage zones are defined the two oldest assemblage zones 8 and 7 are found in basal tills and contain mixed faunas reworked and deposited by glaciers which reached the shelf edge during the early late weichselian during the earliest phase of the deglaciation of the continental shelf a sparse fauna characterized by buccella frigida zone 6 was deposited zone 5 is dominated by cassidulina laevigata and a fairly high content of planktic foraminifera indicating periods of ice free normal marine surface waters during a glacial advance between 14 000 and 13 000 b p the fauna zone 4 was dominated by elphidium excavatum this fauna reflects near glacial conditions characterized by unstable bottom water conditions the last c 500 years of this period suffered from oxygen depleted bottom waters zone 3 formed between 13 000 and 10 000 b p comprises several species e g cassidulina reniforme nonion barleeanum n labradoricum and cibicides lobatulus during the first 2000 years of this period the fauna reflects a climatic amelioration e g an increase in temperature salinity and current activity probably due to intrusion of atlantic water during the younger dryas zone 3 reflects a climatic deterioration

reconstructing enso the influence of method proxy data climate forcing and teleconnections in this study we compare three newly developed independent nino3 4 sea surface temperature sst reconstructions using data from 1 the central pacific corals 2 the texmex region of the usa tree rings and 3 other regions in the tropics corals and an ice core which are teleconnected with central pacific ssts in the 20th century although these three reconstructions are strongly calibrated and well verified inter proxy comparison shows a significant weakening in inter proxycoherenceinthe 19thcentury thisbreakdownin commonsignalcouldberelatedtoinsufficient data dating errors in some of the proxy records or a breakdown in el nino southern oscillation s enso s influence on other regions however spectral analysis indicates that each reconstruction portraysenso likespectralproperties superposedepochanalysisalsoshowsthateachreconstruction shows a generally consistent el nino like response to major volcanic events in the following year while duringyearst 4tot 7 la nina like conditions prevail theseresults suggest thateachofthe series expresses enso like behaviour but this behaviour does not appear to be spatially or temporally consistent this result may reflect published observations that there appear to be distinct types of enso variability depending on location within the tropical pacific future work must address potential dating issues within some proxies i e sampling of multiple coral heads for one location as well as assessing the time stability of local climate relationships with central pacific ssts more emphasis is needed on sampling new and extending old coral proxy records from the crucial central and eastern tropical pacific region copyright 2009 john wiley sons ltd and crown copyright 2009

pattern and forcing of northern hemisphere glacier variations during the last millennium time series depicting mountain glacier fluctuations in the alps display generally similar patterns over the last two centuries as do chronologies of glacier variations for the same interval from elsewhere in the northern hemisphere episodes of glacier advance consistently are associated with intervals of high average volcanic aerosol production as inferred from acidity variations in a greenland ice core advances occur whenever acidity levels rise sharply from background values to reach concentrations 1 2 equiv h kg above background a phase lag of about 10 15 yr equivalent to reported response lags of alpine glacier termini separates the beginning of acidity increases from the beginning of subsequent ice advances a similar relationship but based on limited and less reliable historical data and on lichenometric ages is found for the preceding 2 centuries calibrated radiocarbon dates related to advances of non calving and non surging glaciers during the earlier part of the little ice age display a comparable consistent pattern an interval of reduced acidity values between about 1090 and 1230 a d correlates with a time of inferred glacier contraction during the medieval optimum the observed close relation between noothern hemisphere glacier fluctuations and variations in greenland ice core acidity suggests that sulfur rich aerosols generated by volcanic eruptions are a primary forcing mechanism of glacier fluctuations and therefore of climate on a decadal scale the amount of surface cooling attributable to individual large eruptions or to episodes of eruptions is simlar to the probable average temperature reduction during culminations of little ice age alacier advances ca 0 5 1 2 c as inferred from depression of equilibrium line altitudes

wisconsin holocene paleoenvironment of the bering sea evidence from diatoms pollen oxygen isotopes and clay minerals abstract a core from the southeastern bering sea contains a depositional record of the wisconsin glacial interval and the holocene four lithologic units show distinctive changes in diatom species palynomorphs oxygen isotopes in diatom silica and clay minerals unit 4 the oldest probably represents the glacial advance of the early wisconsin and records extensive sea ice cover and a soggy herbaceous tundra on the exposed continental shelf unit 3 represents the stades and interstades of the middle wisconsin including an early period of high seasonal variability and a later period with expansion of winter sea ice in the basin and of tundra onshore unit 2 represents the late wisconsin glacial maximum and subsequent deglaciation with a tundra covered shelf sea ice cover increased to a maximum during which the surface waters were probably covered by sea ice throughout the year subsequent to the sea ice maximum the isotope ratios record a major meltwater event unit 1 represents the holocene with expansion of shrub tundra or scrub forest in the coastal upland and waters of increased temperature and salinity in the bering sea

assessment of the record of the 1982 el chichon eruption as preserved in greenland snow variability in the so42 and cl time series for the 1980s from 12 shallow snow pits across the greenland ice sheet is used to evaluate the record of the 1982 el chichon eruption and the potential for recording a moderate northern equatorial eruption in a single greenland ice core composition of volcanic glass found in spring 1983 snow in one of the pits in the summit region matches that from el chichon glass thereby verifying the deposition of material from the eruption high na and cl concentrations in this same layer probably represent deposition of the reaction products of halite and h2so4 as observed in the stratosphere following the eruption these findings and the presence of a cl signal in five of the other pits indicate that the cl aerosol component of some eruptions has the potential to remain aloft for at least 1 year after the eruption some of these aerosols may be adsorbed onto tephra particles distinct so42 peaks that can be confidently linked to el chichon were found in only 50 of the records developed through subseasonal sampling however in several other pits an elevated baseline thought to represent more lengthy periods of el chichon aerosol deposition as opposed to deposition from a single snowfall event were observed smoothing of the original data by the calculation of annual so42 flux resulted in the presence of high flux values between 1982 and 1984 years thought to be affected by el chichon aerosol deposition in 9 of the 12 pits these results suggest that a single ice core from anywhere in greenland may record a signal from a northern equatorial eruption of magnitude similar to that of el chichon about 75 of the time this is despite the overall high levels of so2 4 deposition from anthropogenic sources that now make identification and quantification of the volcanic so2 portion of the record more difficult than obtaining the same data for preindustrial volcanism nevertheless composite records from all the pits sampled yielded stratospheric loading 20 mt and optical depth 0 13 estimates similar to stratospheric and satellite based measurements following the eruption equally high so42 concentration and flux values in snow from 1980 to 1982 reflect deposition from the series of middle to high northern latitude volcanic eruptions 1979 1981

the foreslope hills large scale fine grained sediment waves in the strait of georgia british columbia abstract the foreslope hills are a set of 20 m high 5 km long ridges at 230 350 m water depth in the south central strait of georgia occupying a 60 km 2 area at the base of the fraser river delta foreslope they are composed of clay silt and fine sand previous authors have interpreted them as 1 a single mass slide deposit 2 mud diapirs 3 in situ rotational failures and 4 creep deformation features but collaborative evidence for these interpretations is lacking seafloor surface morphological renders derived from recent multibeam sonar bathymetry data show linear evenly spaced symmetrical ridges with ridge bifurcation resembling wave ripples but on a much larger scale detailed multichannel and single channel seismic reflection data show sinusoidal internal reflections suggesting upslope migration the ridges occur within the uppermost portion of the holocene section in a very high sedimentation rate environment consequently they are probably less than 3000 years old moored current meter records for the region show reversing currents largely oriented normal to the ridge crests averaging 10 cm s with a maximum of 50 cm s this evidence combined with increasing documentation of large scale sedimentary bedforms in slope and rise environments suggests that the foreslope hills should be re interpreted as sediment waves upslope migration is typical of many large scale fine grained sediment waves the preferred physical interpretation for the creation and maintenance of the foreslope hills as sediment waves is the lee wave model requiring a phase shift in density stratified flow as it passes over the wavy topography maximum measured bottom currents are easily strong enough to entrain silt and clay delivered to the site by turbidity currents or by sediment plume fallout from fraser river outflow either strong flood tides or severe biannual density intrusions due to their intense stratification may be susceptible to lee wave formation and the creation of sediment waves leading to the observed pattern of upslope migration

dust and sea salt variability in central east antarctica dome c over the last 45 kyrs and its implications for southern high latitude climate a detailed record of non sea salt calcium a proxy for dust and sea salt sodium a proxy for sea salt covering the last 45 kyr is presented it shows that in the first part of the transition from the last glacial period to the holocene 18 15 kyr bp the changes in dust flux mainly reflect changes at the dust source namely vegetation cover and local climate the changes in the later part of the transition 12 11 kyr bp are similar in extent to the changes seen in sea salt and most likely reflect a reorganization of the atmospheric circulation during the last glacial period considerable variation of dust but not of sea salt is observed pointing to climatic changes in patagonia the main dust source for dome c a comparison of the glacial records from dome c and taylor dome suggests that similar influences controlled aerosol input at both sites during this period

late quaternary geology and geochronology of the central continental shelf of western canada piston cores and high resolution seismic profiles from queen charlotte sound have yielded new information on the late quaternary history of this part of the western canada continental shelf cores in three major troughs goose island mitchell s and moresby up to 130 km apart sample a similar sedimentary sequence this sequence comprises five units the lowest unit a which is up to 40 m thick is a laminated to massive mud containing coarse ice rafted debris deposited between pre 13 6 ka and 12 9 ka during deglaciation of queen charlotte sound this unit is overlain by a sequence of stratified sediments units b1 b3 up to 20 m thick deposited during the transition from the pleistocene to the holocene unit b1 directly overlies and is similar to unit a but lacks ice rafted detritus unit b2 is sandy mud locally gravelly deposited during a period of lagging and winnowing from about 12 9 to 10 2 ka when sea level in queen charlotte sound was lower relative to the land than it is today unit b3 is a laminated to massive mud similar to unit b1 deposited when water depths in queen charlotte sound rapidly increased at the end of the pleistocene due to the combined effect of eustatic sea level rise and forebulge collapse the sedimentary sequence is capped by up to 10 m of mud unit c which is more organic rich and contains more clay than any of the other units it was accumulating under present day conditions as early as 9 7 k y ago

skillful prediction of multidecadal variations in volcanic forcing stratospheric sulfate injections from explosive volcanic eruptions are a primary natural climate forcing improved statistical models can now capture and simulate dynamical relationships in temporal variations of binary data leveraging these new techniques the presented analysis clearly indicates that the number of large eruptions in the most recent records of explosive volcanism cannot be considered to be fully random including dynamical dependence in our models improves their ability to reproduce the historical record and thus forms a strong basis for skill in statistical prediction possible geophysical mechanisms behind the identified multi decadal variations are discussed including variations in the observed length of day

record of volcanism since 7000 b c from the gisp2 greenland ice core and implications for the volcano climate system sulfate concentrations from continuous biyearly sampling of the gisp2 greenland ice core provide a record of potential climate forcing volcanism since 7000 b c although 85 percent of the events recorded over the last 2000 years were matched to documented volcanic eruptions only about 30 percent of the events from 1 to 7000 b c were matched to such events several historic eruptions may have been greater sulfur producers than previously thought there are three times as many events from 5000 to 7000 b c as over the last two millennia with sulfate deposition equal to or up to five times that of the largest known historical eruptions this increased volcanism in the early holocene may have contributed to climatic cooling

historic eruptions of tambora 1815 krakatau 1883 and agung 1963 their stratospheric aerosols and climatic impact abstract decreases in surface temperatures after the eruptions of tambora 1815 krakatau 1883 and agung 1963 were of similar magnitude even though the amount of material dust and volatiles injected into the stratosphere by these three events differed greatly large amounts of fine ash and volatiles were dispersed into the upper atmosphere by krakatau and tambora the agung eruption in 1963 was a much smaller vulcanian type eruption which injected dust and volatiles into the stratospheric aerosol layer more directly analyses of magmatic volatiles indicate that the agung eruption was proportionately richer in so 2 and cl than either tambora or krakatau relative amounts of fine ash produced by the tambora krakatau and agung eruptions are estimated at about 150 20 1 whereas the masses of atmospheric sulfate aerosols produced were on the order of 7 5 3 1 decreases in surface temperature of a few tenths of a degree c for several years following volcanic eruptions are primarily a result of the sulfate aerosols rather than of the silicate dust the similarity in the atmospheric response after these three eruptions supports the idea of limiting mechanisms on volcanic stratospheric aerosol loading which is suggested by microphysical processes of aerosol particles fluctuations in stratospheric aerosol optical depth seem to be controlled to a large degree by high intensity sulfur rich eruptions e g agung 1963 which may however be relatively small in total ejecta volume such eruptions leave little geologic record but appear as acidity peaks in polar ice cores

paleoenvironments of the strait of georgia british columbia during the last deglaciation microfaunal and microfloral evidence the strait of georgia is situated between vancouver island and the western canadian mainland it was deglaciated quickly around 12 500 14c yr bp by in situ downwasting the subsequent marine invasion has left glacimarine sediments with foraminifers diatoms and dinocysts characterizing successive paleoenvironments recognizable basinwide the first paleoenvironment represents near ice conditions under the influence of the turbid meltwater plume marked by low algal productivity and few foraminifers mostly elphidium excavatum just off the plume the second environment shows a peak of nonionellina labradorica possibly resulting from an observed sudden increase in diatom numbers mostly ice dwelling forms implying a long annual sea ice cover further away cassidulina reniforme increases n labradorica decreases while other calcareous foraminifer species colonize the area there are fewer ice diatoms more marine planktonic diatoms and dinocysts become more abundant finally after 12 000 14c yr bp calcareous foraminifers are gradually replaced because of dissolution of calcium carbonate by a low diversity arenaceous assemblage at the same time abundant planktonic diatoms and dinocysts indicate warmer surface temperature the succession of fossils and environments compares well with modern horizontal off glacier successions observed in fjords of the european arctic

mid to late holocene climate change an overview the last 6000 years are of particular interest to the understanding of the earth system because the boundary conditions of the climate system did not change dramatically in comparison to larger glacial interglacial changes and because abundant detailed regional palaeoclimatic proxy records cover this period we use selected proxy based reconstructions of different climate variables together with state of the art time series of natural forcings orbital variations solar activity variations large tropical volcanic eruptions land cover and greenhouse gases underpinned by results from general circulation models gcms and earth system models of intermediate complexity emics to establish a comprehensive explanatory framework for climate changes from the mid holocene mh to pre industrial time the redistribution of solar energy due to orbital forcing on a millennial timescale was the cause of a progressive southward shift of the northern hemisphere nh summer position of the intertropical convergence zone itcz this was accompanied by a pronounced weakening of the monsoon systems in africa and asia and increasing dryness and desertification on both continents the associated summertime cooling of the nh combined with changing temperature gradients in the world oceans likely led to an increasing amplitude of the el nin o southern oscillation enso and possibly increasingly negative north atlantic oscillation nao indices up to the beginning of the last millennium on decadal to multi century timescales a worldwide coincidence between solar irradiance minima tropical volcanic eruptions and decadal to multi century scale cooling events was not found however reconstructions show that widespread decadal to multi century scale cooling events accompanied by advances of mountain glaciers occurred in the nh e g in scandinavia and the european alps this occurred namely during the little ice age lia between ad w1350 and 1850 when the lower summer insolation in the nh due to orbital forcing coincided with solar activity minima and several strong tropical volcanic eruptions the role of orbital forcing in the nh cooling the southward itcz shift and the desertifi cation of the sahara are supported by numerous model simulations other simulations have suggested that the fingerprint of solar activity variations should be strongest in the tropics but there is also evidence that changes in the ocean heat transport took place during the lia at high northern latitudes with possible additional implications for climates of the southern hemisphere sh

a record of past ocean atmosphere radiocarbon differences from the northeast pacific a record of the 14c age differences between atmosphere and the mixed layer of the northeast pacific ocean was obtained from 58 radiocarbon measurements on shells and associated wood from coastal sediments in british columbia this series of mixed layer reservoir ages spans the holocene and extends into the period of the younger dryas cold event in the north atlantic and surrounding regions the data reflect the extent of upwelling in the northeast pacific and thus constrain models of carbon cycling and ocean circulation most of the reservoir ages are only slightly less than than the present preindustrial value of about 800 years and may be identical when probable sampling errors are taken into account either the north pacific reached a state close to its present mode of circulation at or before the end of the younger dryas or a different circulation fortuitously produced a similar reservoir age our results support the hypothesis that slow changes in atmospheric radiocarbon concentrations over the holocene arose from 14c production rate changes data corresponding to a radiocarbon age of around 6400 years b p give a reservoir age of 1200 years if this result is confirmed it indicates a much greater variability for the holocene ocean circulation than was previously believed possible

influence of volcanic eruptions on the climate of the asian monsoon region 1 several state of the art general circulation models gcms predict that large volcanic eruptions should result in anomalous dry conditions throughout much of monsoon asia here we use long and well validated proxy reconstructions of asian droughts and pluvials to detect the influence of volcanic radiative forcing on the hydroclimate of the region since the late medieval period superposed epoch analysis reveals significantly wetter conditions over mainland southeast asia in the year of an eruption with drier conditions in central asia our proxy and model comparison suggests that gcms may not yet capture all of the important ocean atmosphere dynamics responsible for the influence of explosive volcanism on the climate of asia

foraminiferal zonations on the fraser river delta and their application to paleoenvironmental interpretations abstract well defined elevational zonations of foraminiferal species were found over the intertidal surface of the sand rich fraser river delta a zonation of foraminiferal species according to depth is also apparent on the delta foreslope although data here are more limited application of these findings to the interpretation of depositional environments within drill cores from the delta provided independent evidence of a 4 to 5 m lower sea level during the mid holocene this finding is in good agreement with a sea level curve developed for the fraser lowland region

statistical analysis of tropical explosive volcanism occurrences over the last 6 centuries 1 explosive volcanic eruptions are very violent events each with clearly individual characteristics instead of looking at specific eruptions we focus here on the long term record of tropical explosive volcanism to assess the distribution of volcanic occurrences over several centuries we employ sulfate measurements from polar ice cores from these measurements we compile a binary time series of sulfate deposition events that left a signature at both poles because of the binary nature of this problem a series of logistic statistical models are compared to best represent the data these models demonstrate the existence of a strong multi decadal variation in the occurrence of sulfur rich tropical eruptions more precisely a combination of a trend and a cycle explains best the evolution of eruption history to corroborate this result with a record independent of the ice cores we confirm these long term variations with the most recent volcanic explosivity index vei

reassessment of crete greenland ice core acidity volcanism link to climate change previous comparisons of the crete greenland ice core acidity record with climate variations of the last 1 400 years suggested that changes in volcanism may have significantly influenced climate on this time scale however the ice core acidity record consists of volcanically induced spikes superimposed on a background acidity of nonvolcanic origin that varied significantly in amplitude herein the authors produce a record of crete volcanism based solely on an objective definition of individual volcanic events in the ice core record there are 92 acidity peaks in the 1 420 year record since at least 26 of the post 1 600 eruptions are of local icelandic origin they estimate a mean recurrence interval of 20 8 years for hemispheric scale eruptions rich in sulphate on decadal time scales volcanism has varied by a factor of three four over the last 1 400 years however the climate volcanism correlation is considerably less impressive r minus 0 23 than previously concluded r minus 0 52 the good correspondence between volcanism and climate previously reported are due to background acidity levels that show a significant little ice age increase the background increase may reflect changes in ocean productivity 24 refs 5 figs 1 tab

volcanic eruptions and solar activity the historical record of large volcanic eruptions from 1500 to 1980 as contained in two recent eruption catalogs is subjected to detailed time series analysis two weak but probably statistically significant periodicities of 11 and 80 years are detected both cycles appear to correlate with well known cycles of solar activity the phasing is such that the frequency of volcanic eruptions increases decreases slightly around the times of solar minimum maximum the weak quasi biennial solar cycle is not obviously seen in the eruption data nor are the two slow lunar tidal cycles of 8 85 and 18 6 years time series analysis of the volcanogenic acidities in a deep ice core from greenland covering the years 553 1972 reveals several very long periods that range from 80 to 350 years and are similar to the very slow solar cycles previously detected in auroral and carbon 14 records mechanisms to explain the sun volcano link probably involve induced changes in the basic state of the atmosphere solar flares are believed to cause changes in atmospheric circulation patterns that abruptly alter the earth s spin the resulting jolt probably triggers small earthquakes which may temporarily relieve some of the stress in volcanic magma chambers thereby weakening postponing or even aborting imminent large eruptions in addition decreased atmospheric precipitation around the years of solar maximum may cause a relative deficit of phreatomagmatic eruptions at those times