depositional environment and mechanism of preservation of microfossils upper proterozoic bitter springs formation australia microfossils preserved in black chert nodules from the upper proterozoic bitter springs formation of australia represent the preserved remnants of cyanobacterial communities that inhabited a series of nonmarine saline lakes and ponds groundwaters of halite salinity pickled the microorganisms and thus inhibited their early bacterial degradation these same groundwaters were saturated in silica so that upon evaporation the silica and halite precipitated and formed a series of chert concretions nodules and bipyramidal quartz crystals where the chert nodules formed in areas of buried cyanobacterial mats further degradation of the buried sheaths and cells was arrested and the microorganisms were preserved

calcitic aragonitic and mixed calcitic aragonitic ooids from the mid proterozoic belt supergroup montana a great variety of ooid types occurs within the siyeh and snowslip formations of the mid proterozoic belt supergroup montana cortical layers are inferred to have been composed either of calcite in a radial concentric or radial with dark rays fabric or aragonite in a radial or concentric fabric the calcitic cortical layers record their original fabrics but the originally aragonitic cortical layers have been replaced by calcite in a range of textures and by quartz and dolomite some formerly aragonitic cortical layers are replaced by calcite spar which contains relics of the original cortical structure others consist of calcite spar without inclusions or columnar calcite which grew radially from the nucleus commonly a calcitic ooid some ooids were wholly composed of calcite others were of aragonite but two phase ooids were common mostly consisting of an inner calcitic part and an outer aragonitic part probable microdolomite inclusions suggest a high mg content of the calcitic cortical layers the depositional environment of these oolites was probably analogous to baffin bay texas where a similar range of ooid types is forming today

sea ice atmosphere and upper ocean variability in the weddell sea antarctica a frequency domain singular value decomposition is performed on 20 years 1979 1998 of monthly sea ice concentration sea ice drift and sea level pressure data in the weddell sea antarctica interannual oscillations with periods of around 3 4 years are found to dominate the variability in this region anomalous atmospheric patterns periodically reach the weddell sea from the west and perturb the sea ice circulation and distribution in the weddell gyre through changes in the intensity and direction of the climatological winds sea ice accumulates in the southeastern weddell sea every 3 4 years owing to two atmospherically driven processes 1 weak ice export to the north due to a weak northward branch of the gyre driven by weak southerly winds and 2 large ice import from the east due to a strong east wind drift driven by strong easterly winds along the coast the opposite situation gives rise to a depletion of sea ice in the same region half a cycle later sea ice anomalies are then advected north northeastward before turning eastward in the gyre circulation the eastward propagation of ice anomalies along the ice margin accounts for the passage of the antarctic circumpolar wave through the atlantic sector of the southern ocean a low frequency signal is also detected in the weddell sea variations albeit rather speculatively in this 20 year long record sea ice variability on this timescale appears to be associated with a change in the shape and characteristics of the weddell gyre circulation around 1990 this mode of variability implicates feedbacks between the gyre and weddell deep water temperature variations whose impact is observed near the maud rise topographic feature

secular change in the precambrian silica cycle insights from chert petrology chert deposits preserve a record of secular change in the oceanic silica cycle the evolutionary radiation of silica secreting organisms resulted in a transition from abiological silica deposition characteristic of the archean and proterozoic eons to the predominantly biologically controlled silica deposition of the phanerozoic comparative petrography of phanerozoic and precambrian cherts indicates that an earlier change in chert deposition occurred toward the end of the paleoproterozoic era ca 1 8 ga in neoproterozoic and mesoproterozoic strata early diagenetic chertification is largely restricted to peritidal environments these early diagenetic cherts typically occur as nodules or discontinuous beds within carbonate deposits that have similar depositional textures the cherts formed primarily by carbonate replacement with subsidiary direct silica precipitation some of the paleoproterozoic cherts associated with iron formations however are distinctly different from younger cherts and appear to have formed largely by direct silica precipitation at or just below the seabed these primary cherts lack ghosts or inclusions of carbonate precursors have fine scale grain fracturing possibly from syneresis exhibit low grain packing densities and are not associated with unsilicified carbonate deposits of similar depositional composition cherts in some paleoproterozoic iron formations e g the gunflint formation northwestern lake superior region are composed of silica types similar to those in phanerozoic sinters e g the devonian rhynie and windyfield cherts scotland such cherts may provide evidence that basinal and perhaps global oceanic silica concentrations were higher during the paleoproterozoic era than at later times

an ice core indicator of antarctic sea ice production 1 the sea ice surface not open water is the dominant source of sea salt to aerosol and ice cores in coastal antarctica here we show that it may also form the dominant source for central antarctica we can then explain higher concentrations in the winter and last glacial maximum lgm as being due to increased sea ice production this suggests that ice core sea salt can indicate at least the timing of changes in antarctic sea ice production the pattern of sea salt in ice cores is consistent with marine evidence about sea ice changes in the holocene and lgm sea salt shows no change at the initial co2 increase out of the last glacial making it unlikely this was primarily due to changing sea ice cover the sea salt record should not be treated as an indicator of meridional transport

environmental signals in a highly resolved ice core from james ross island antarctica 1 the accumulation isotopic and chemical signals of an ice core from james ross island antarctica are investigated for the interval from 1967 to 2008 over this interval comparison with station satellite and reanalysis data allows for a detailed assessment of the environmental information preserved in the ice accumulation at james ross island is enhanced during years when the circumpolar westerlies are weak allowing more precipitation events to reach the northeastern antarctic peninsula the stable water isotope composition of the ice core has an interannual temperature dependence consistent with the spatial isotope temperature gradient across antarctica and preserves information about both summer and winter temperature variability in the region sea salts in the ice core are derived from open water sources in the marginal sea ice zone to the north of james ross island and transported to the site by strengthened northerly and westerly winds in the winter a strong covariance with temperature means that the sea salt record may be able to be utilized in conjunction with the isotope signal as an indicator of winter temperature marine biogenic compounds in the ice core are derived from summer productivity within the sea ice zone to the south of james ross island this source region may have become significant only in recent decades when the collapse of nearby ice shelves established new sites of open water with high summer productivity these findings provide a foundation for interpreting the environmental signals in the james ross island ice core which extends though the whole holocene and represents the oldest ice core that has been recovered from the antarctic peninsula region

ice core reconstruction of sea ice change in the amundsen ross seas since 1702 a d antarctic sea ice has been increasing in recent decades but with strong regional differences in the expression of sea ice change declining sea ice in the bellingshausen sea since 1979 the satellite era has been linked to the observed warming on the antarctic peninsula while the ross sea sector has seen a marked increase in sea ice during this period here we present a 308 year record of methansulphonic acid from coastal west antarctica representing sea ice conditions in the amundsen ross sea we demonstrate that the recent increase in sea ice in this region is part of a longer trend with an estimated 1 northward expansion in winter sea ice extent sie during the twentieth century and a total expansion of 1 3 since 1702 the greatest reconstructed sie occurred during the mid 1990s with five of the past 30 years considered exceptional in the context of the past three centuries

corrigendum to hydrographic development of the aral sea during the last 2000 years based on a quantitative analysis of dinoflagellate cysts

temporal variations in marine chemical concentrations in coastal areas of eastern antarctica and associated climatic causes abstract snow pit and a firn core samples obtained from coastal areas in the eastern lambert basin of eastern antarctica enabled us to investigate the temporal variations in soluble marine ion concentrations and the possible mechanisms influencing their variations the concentrations of seasonal sea salt ions na cl and mg2 at the coastal site lh406 were maximal in the spring and minimal in the summer broad maximal values also occurred in the winter and minimal values occurred in the summer in the interior site zg050 the sea ice extent sie in the indian ocean sector of eastern antarctica followed similar temporal distribution patterns two sulfur compounds so42 and msa experienced seasonal variations similar to those observed for sea salt ions at the lh406 site however distinct variations were reported at the zg050 site the variations in nssso42 levels in the zg050 snow pit that occurred over a 14 year period were positively correlated with variations in sie however this relationship was different from that at the western lambert basin the change in direction of the supplementary prevailing wind during 1994 1995 produced a significant change in the concentrations of marine ions a change in the source region may be the primary cause of this difference

diagenesis of skeletal and nonskeletal components of mid cretaceous limestones abstract skeletal and nonskeletal components from mid cretaceous limestones have been investigated using coordinated textural isotopic and chemical methods to delineate the conditions under which they formed or were altered the degree of alteration was determined by means of cathodoluminescence light microscopy and scanning electron microscopy along with inferences from isotopic and chemical compositions oxygen isotopic values 2 9 to 0 5 pdb of non luminescent parts of most bivalves a pectenid chondrodontids and most oysters and of radiaxial fibrous calcite appear to reflect isotopic equilibrium with contemporaneous mid cretaceous surface seawater in contrast oxygen isotopic compositions of non luminescent texturally unaltered calcite outer layers of rudists and the calcitic shells of some oysters 4 0 to 2 5 are significantly lower than luminescent altered portions of the same specimens or equant calcite cements within skeletal molds this apparent isotopic reversal suggests that vital effects are involved in the secretion of skeletal calcite in rudists and some o sters all the radiaxial fibrous calcite rfc cements analyzed contain less than 1 mole mgco3 retention of a primary marine 18o signature and the absence of microdolomite inclusions within well preserved rfc suggest that this cement precipitated as primary low mg calcite cements also micritic envelopes algal coatings and internal sediments within the rfc strongly suggest that those cements were formed in shallow marine environments isotopic and chemical contents of calcitized skeletons together with coexisting equant calcite cements indicate that the sediments were mostly stabilized during meteoric phreatic diagenesis and that effects of deep burial diagenesis were negligible the similarity of isotopic and chemical trends in those calcitized skeletons and the equant cements suggests that the skeletons were altered by fluids in a diagenetic system which was open with respect to 18o sr and mg but closed with respect to 13c fe and mn

evidence for initial calcite aragonite composition of lower algal chert member ooids and stromatolites paleoproterozoic gunflint formation ontario canada the chert members of the paleoproterozoic gunflint formation ontario canada are commonly regarded as examples of primary silica chemical sediments this interpretation is founded upon the ubiquitous nature of silica high fidelity of preservation of microfossils found within and lack of observed primary carbonate previous arguments for silica replacement of carbonate are based on indirect evidence and are largely dismissed thus gunflint microfossils are regarded as having lived in a silica rich environment which makes them unusual compared to most other pre phanerozoic microfossils that are known from silicified carbonates we present evidence that carbonate was a primary mineral species of the lower algal chert member where most of the microbiota are found most compelling are iron stained low mg calcite ooids containing 1 well preserved growth laminae 2 textures indicating a disrupted tan gential fabric of growth laminae and 3 quartz crosscutting the growth laminae these indicate the initial mineral was a carbonate possibly aragonite less compelling evidence is found in stromatolite columns specularite crystals in low mg calcite display crosscutting relationships with calcite and quartz indicating that calcite was primary specularite sec ondary and quartz tertiary the crosscutting relations show that silicification took place in at least two stages one of the silicification events took place very early in diagenesis thus the gunflint microbiota may not have existed in a radically different environment silica precipitating than those of most other known proterozoic microbiota high fidel ity of preservation of microfossils does not always indicate that the mineral entombing them was the primary mineral precipitated from aqueous solution

petrological and stable isotope studies of carbonate and sulfide minerals from the gunflint formation ontario evidence for the origin of early proterozoic iron formation abstract the 1 9 ga gunflint formation in the thunder bay district of ontario principally comprises iron formation overlain by an iron poor limestone dolostone member the upper limestone member rocks are virtually unmetamorphosed retaining primary textures except locally around diabase sills the gunflint presents an opportunity to study both unmetamorphosed and metamorphosed iron formation and to study the changes from iron rich to iron poor sedimentation of the carbonate minerals in iron rich units siderite formed at or near the sediment water interface with ankerite and calcite forming later during diagenesis and during metamorphism around sills heaviest 13c values of siderite and of dolomite in the upper limestone member are consistently near 0 throughout the stratigraphic section indicating that marine bicarbonate was the source of carbon a spread of values between 0 and 7 for unmetamorphosed rocks is the result of the incorporation of oxidized organic matter during diagenesis whereas 13c values more negative than 7 are the result of metamorphism the heaviest 18o values from unmetamorphosed rocks 5 3 pdb for siderite 6 1 for ankerite and 6 7 for calcite are considered to represent the original marine composition lighter values to 17 represent isotopic exchange reactions with pore fluids at higher temperatures and or isotopic exchange with 18o depleted meteoric water low s c ratios and a relatively narrow range of positive 34s values in pyrite throughout most of the formation are consistent with bacterial sulphate reduction of seawater containing sulphate at a significantly lower concentration than the modern ocean locally higher sulfide contents and a wider range of 34s values were the product of the introduction of sulfur after deposition it is proposed that the gunflint formation was deposited in a stratified water column with anoxic bottom water the depositional basin had restricted communication with the open ocean and was affected by distal volcanism hydrothermal activity associated with the volcanism provided a large source of dissolved iron and possibly silica which helped buffer o2 and sulphate in water to low levels low concentrations of sulphate limited the generation of h2s that would otherwise have restricted the solubility of iron during periods of increased hydrothermal activity the anoxic oxic water boundary moved upwards permitting transport of iron to the shallow shelf where it was precipitated as siderite iron hydroxides iron silicates or pyrite depending on physico chemical conditions the transition to the overlying limestone marks a decrease in hydrothermal activity with a contraction of the redox boundary

chemical and textural overprinting of ancient stromatolites timing processes and implications for their use as paleoenvironmental proxies abstract shale normalized rare earth element ree sn patterns and transition metal abundances in banded iron formations bif and shales have long been used as paleoenvironmental proxies to investigate the evolving geochemistry of precambrian oceans apparent similarities between the ree sn of modern stromatolites and contemporary seawater values also mean that some ancient stromatolites could record paleo ocean chemistry to test this hypothesis we present comparative mineralogical textural and spectral analyses of multifurcate silicified and iron oxide carbonate rich stromatolites from the ca 1 88 ga gunflint formation ontario canada previous studies show that these organo sedimentary structures represent the initiation of shallow marine sedimentation in the animikie basin on the southern tip of the superior province we present evidence that these structures were originally stabilized by aragonite and mg bearing carbonates fabrics indicative of stromatolite accretion under local hypersaline conditions are also present with la anomalies suggestive of laterally variable freshwater runoff the admixture of partially evaporated seawater and silica oversaturated deep seawater led to pervasive silicification of metastable carbonates and preservation of less soluble early diagenetic carbonate cements bulk rock transition metal contents point to lateral variability and dissimilar partitioning and fractionation during mineral formation yet ce anomalies amongst samples are similar considering the pronounced differences between the ree partitioning between fe oxyhydroxide precipitates and carbonates our results point to hematite and siderite as secondary minerals that postdate the stabilization of these structures by carbonates and silica stratabound relations of the fe rich stromatolites with diabase sills and dikes indicate that the pore water fluids evolved towards a localized state of hematite and siderite oversaturation towards the mesoproterozoic if hematite and siderite are both early diagenetic phases then the ce anomalies of these stromatolites may be a poor measure of the redox conditions of the shallow areas of the animikie basin at the time of accretion

the antarctic dipole and its predictability this study investigates the nature of interan nualvariability ofantarcticseaiceanditsrelationshipwith the tropical climate we nd that the dominant interan nual variance structure in the sea ice edge and surface air temperature elds is organized as a quasi stationary wave which we call the antarctic dipole adp it is charac terized by an out of phase relationship between the ice and temperature anomalies in the central eastern pacic and atlantic sectors of the antarctic the dipole consists of a strong standing mode and a weaker propagating motion within each basin s ice eld it has the same wavelength as the antarctic circumpolar wave acw and dominates the acw variance the dipole is clearly associated with tropical enso events it can be predicted with moderate skill using linear regression involving surface temperature two to four months ahead the prediction performs better in extreme warm cold years and best in la ni na years

organic walled microfossils from earliest cambrian or latest proterozoic tindir group rocks northwest canada abstract uppermost tindir group limestones exposed in the headwaters of tindir creek yukon territory canada contain a diverse and abundant microbiota of mineralized and organic walled microfossils preserved primarily in chert modules and chert beds the organic walled forms include mat building cyanobacterial filaments and coccoids accompanied by less common bacteria fungi and forms of uncertain affinity as well as planktonic coccoidal cyanobacteria and acritarchs several lines of evidence support interpretation of an early cambrian age whereas others suggest a late proterozoic age of the 54 organic walled taxa recognized 12 are newly described yukonosphaeridion interior awramik n gen n sp microagglomeratus borealis awramik n gen n sp phacelogeminus lineatus awramik n gen n sp palaeoanacystis magna awramik n sp cephalophytarion majesticum allison n sp heliconema bulbosa allison n sp trachyhystrichosphaera magna allison n sp fusilabellum brevistriatum awramik n gen n sp sphaeranasillos irregularis allison n gen n sp hyalocyrillium clardyi allison n gen n sp eophycomyces herkoides allison n gen n sp and archeomyces dimakeloides allison n gen n sp

prevalence of the antarctic circumpolar wave over the last two millenia recorded in dronning maud land ice 1 the influence of atmospheric circulation patterns on sea salt aerosol deposition in the study area of the new epica european project for ice coring in antarctica deep drilling in dronning maud land dml antarctica has been investigated comparison of ice core records with reanalysis data showed that recent sea salt concentrations are strongly influenced by the occurrence of a blocking high pressure ridge over the eastern and enhanced storm activity over the western atlantic sector of the southern ocean so leading to marine intrusions thus enhanced sea salt export into dml these variations occur with periods of 4 5 and 12 14 yr the prior being associated with the antarctic circumpolar wave acw the prevalence of these periodicities in a 2000 year ice core record from dml shows for the first time that the acw is a prevalent feature of so atmosphere dynamics over the last two millennia

firn accumulation records for the past 1000 years on the basis of dielectric profiling of six cores from dronning maud land antarctica this paper presents an overview of firn accumulation in dronning maud land dml antarctica over the past 1000 years it is based on a chronology established with dated volcanogenic horizons detected by dielectric profiling of six medium length firn cores in 1998 the british antarctic survey retrieved a medium length firn core from western dml during the nordic epica european project for ice coring in antarctica traverse of 2000 01 a 160 m long firn core was drilled in eastern dml together with previously published data from four other medium length ice cores from the area these cores yield 50 possible volcanic horizons all six firn cores cover a mutual time record until the 29th eruption this overlapping period represents a period of approximately 1000 years with mean values ranging between 43 and 71 mm w e the cores revealed no significant trend in snow accumulation running averages over 50 years averaged over the six cores indicate temporal variation in the order of 5 all cores display evidence of a minimum in the mean annual firn accumulation rate around ad 1500 and maxima around ad 1400 and 1800 the mean increase over the early 20th century was the strongest increase but the absolute accumulation rate was not much higher than around ad 1400 in eastern dml a 13 increase is observed for the second half of the 20th century

the presence of polynyas in the weddell sea during the last glacial period with implications for the reconstruction of sea ice limits and ice sheet history cores from a contourite drift on the continental slope in the nw weddell sea antarctica contain up to four sandy foraminifer rich layers wa1 4 with dispersed ice rafted debris ird interbedded with silty clayey sands and sandy muds accelerator mass spectrometry ams 14c dating on neogloboquadrina pachyderma from the foraminifer rich layers wa2 and wa3 yielded ages spanning the last glacial maximum lgm and marine isotope stage mis 2 20 319 28 543 cal yr bp and the middle part of mis 3 41 349 43 242 cal yr bp respectively we attribute the high abundances of planktonic and benthic foraminifera to deposition in a seasonally open marine environment given that the nw weddell sea shelf was covered by grounded ice at the lgm and probably during mis 2 and mis 3 and that diatom based reconstructions place the northern limit of winter and summer sea ice coverage to the north of the core sites during the last glacial period our results document the presence of a seasonal or perennial polynya in the nw weddell sea the polynya may have been formed by katabatic winds blowing off the antarctic peninsula ice sheet apis when it was grounded at the continental shelf break although polynya formation through upwelling of deep water cannot be ruled out in addition we argue that previously published data from the southern southeastern and southwestern weddell sea as well as the ross sea may indicate the widespread occurrence of polynyas along the antarctic continental margin during the last glacial period the widespread occurrence of polynyas could help explain how i aabw formation through brine rejection continued throughout the lgm and ii antarctic shelf benthos survived glacial periods the presence of polynyas through glacial periods also has implications for sea ice reconstructions from ice core records possibly biasing the signal towards a reduced sea ice cover finally we propose that the fringes of the apis which probably influence the presence or absence of polynyas in the nw weddell sea are sensitive to changes in antarctic temperature that may be related to a reduction in oceanic heat transport from the north atlantic

variations in neoarchean microbialite morphologies clues to controls on microbialite morphologies through time the neoarchean carawine formation hamersley group western australia is a carbonate ramp that preserves diverse microbial structures which are characteristic of specific depositional environments these distinctive structures are distributed in five shallow subtidal and two deeper water facies in the oakover area of the carawine formation the shallow subtidal facies are composed of biohermal and bedded stromatolites centimetre scale ridge shaped microbialites and wavy laminated microbialites the deeper water facies are composed of fenestrate microbialites planar laminated dolostone and dolostone with rolled up microbial laminae microbialites in the carawine formation lie within a continuum of archean to proterozoic microbial facies some shallow water microbial facies in the carawine formation are similar to proterozoic facies such as large bioherms internally composed of a variety of stromatolite morphologies in contrast fenestrate microbialites grew in quiet subtidal environments and are common in archean rocks but have not been documented in similar proterozoic environments the similarity of shallow water facies across the archean proterozoic transition before and after the oxidation of the atmosphere and surface oceans indicates that stromatolite growth in shallow subtidal environments was not strongly affected by the chemical changes associated with oxidation of the oceans or by biological responses to those chemical changes rather stromatolite morphology was controlled mostly by the physical environment and the corresponding biological responses to that environment in contrast the absence of fenestrate microbialites from proterozoic deep subtidal environments suggests that the morphology of deep subtidal microbial structures was influenced by chemical or biological changes that occurred in association with oxidation of the surface oceans

variability of sea ice in the northern weddell sea during the 20th century the record of winter fast ice in the south orkney islands northern weddell sea antarctica is over a century long and provides the longest observational record of sea ice variability in the southern hemisphere here we present analyses of the series of fast ice formation and breakout dates from 1903 to 2008 we show that over the satellite era post 1979 the timing of both final autumn formation and complete spring breakout of fast ice is representative of the regional sea ice concentrations sic in the northern weddell sea and associated with atmospheric conditions in the amundsen sea region to the west of the antarctic peninsula variation in the fast ice breakout date is influenced by the intensity of the westerly north westerly winds associated with the southern annular mode sam in contrast the date of ice formation displays correlations with regional oceanic and sea ice conditions over the previous 18 months which indicate a preconditioning during the previous summer and winter and exhibits variability associated with variation in tropical pacific sea surface temperature i e the el nino sothern oscillation enso a reduction in fast ice duration at the south orkney islands around the 1950s was associated with both later formation and earlier breakout however there were marked changes in variability with periodicities of 3 5 year 7 9 year and 20 year in each of the series and in their relationships with enso and sam indicating the need for caution in interpreting changes in ice conditions based on shorter term satellite series

geochemical and nd pb isotopic evidence for the provenance of the early proterozoic virginia formation minnesota implications for the tectonic setting of the animikie basin the early proterozoic animikie basin is located at a major crustal boundary between archean crust of the superior craton and penecontemporaneous early proterozoic crust of the wisconsin magmatic terranes the provenance of sedimentary rocks within the animikie basin constrains the tectonic evolution of the early proterozoic margin of the superior craton published geological petrographic and nd pb isotopic data indicate that the pokegama quartzite lower passive margin unit of the animikie group has a late archean provenance in contrast the virginia formation upper deep water turbidite shale unit of the animikie group was derived from dominantly early proterozoic sources with isotopic compositions similar to igneous rocks of the wisconsin magmatic terranes shales of the virginia formation have nd depleted mantle model ages 2 14 to 2 35 ga and mu 1 of 7 81 to 8 09 ashes within the virginia are more evolved geochemically than shales and have younger model ages of 1 86 and 1 99 ga and simila

post depositional movement of methanesulphonic acid at law dome antarctica and the influence of accumulation rate a series of ice cores from sites with different snow accumulation rates across law dome east antarctica was investigated for methanesulphonic acid msa movement the precipitation at these sites up to 35 km apart is influenced by the same air masses the principal difference being the accumulation rate at the low accumulation rate w20k site 0 17 m ice equivalent msa was completely relocated from the summer to winter layer moderate movement was observed at the intermediate accumulation rate site 0 7 m ice equivalent dome summit south dss while there was no evidence of movement at the high accumulation rate de08 site 1 4 m ice equivalent the main dss record of msa covered the epoch ad 1727 2000 and was used to investigate temporal post depositional changes co deposition of msa and sea salt ions was observed in the surface layers outside of the main summer msa peak which complicates interpretation of these peaks as evidence of movement in deeper layers a seasonal study of the 273 year dss record revealed msa migration predominantly from summer into autumn in the up core direction but this migration was suppressed during the tambora 1815 and unknown 1809 volcanic eruption period and enhanced during an epoch 1770 1800 with high summer nitrate levels a complex interaction between the gradients in nss sulphate nitrate and sea salts which are influenced by accumulation rate is believed to control the rate and extent of movement of msa

potential and limitations of marine and ice core sea ice proxies an example from the indian ocean sector diatom assemblages in marine cores and sea salt deposition fluxes in ice cores have been used as sea ice proxies in the southern hemisphere here a marine and an ice core proxy record for the indian ocean covering the last two glacial cycles are compared in order to illustrate their potential and limitations the marine core was extracted in a location completely ice free under present day conditions and therefore was unable to record changes to the recent sea ice extent similarly no sea ice was recorded at that location during the previous interglacial period during the last glacial period however the site was seasonally covered by sea ice and the diatom assemblages allowed an estimation of average seasonal sea ice presence the ice core data originated from the east antarctic plateau the marine sodium present in the ice core was used as a proxy of the sea ice coverage and on average a larger sea ice surface led to an increased sea salt aerosol flux seen e g at the last glacial inception however the response of the sea salt flux to increasing sea ice extent diminished during peak glacial conditions when only minimal variability was recorded in the ice core record a first order approximation is used to take this non linear response of the ice core sea ice proxy into account based on the ice core proxy record sea ice extent was reduced considerably during the warm episodes of the previous two interglacial periods compared to modern sea ice extent in particular during the peak warmth of the last interglacial the ice core proxy also showed a very strong precessional variability pronounced spectral peak at 23 ka period over the past 240 ka the advantage of combining the two proxy records lies in the complementary nature of their response while the ice core proxy showed limited sensitivity during full glacial conditions the marine proxy recorded the seasonal sea ice coverage once the sea ice retreated south of the location of the marine core the ice core proxy responded to changes in sea ice extent a composite of marine and ice core records may thus provide a data basis for a more detailed reconstruction of sea ice around antarctica over the last few glacial interglacial cycles

stable isotope geochemistry of cherts and carbonates from the 2 0 ga gunflint iron formation implications for the depositional setting and the effects of diagenesis and metamorphism abstract 18 o values for all but three of 97 samples of chert along a 220 km transect through the 2 0 ga gunflint iron formation of the animikie basin north america range from 21 3 to 24 7 o there is no correlation between 18 o and the type of chert i e deeper water lutitic chert shallower water arenitic chert and peritidal algal chert the fact that the gunflint iron formation has been exposed to thermal conditions only slightly above burial diagenesis suggests that the values of the chert have not been significantly affected by metamorphism field and petrographic observations and the small 18 o range of all the chert types suggests that silicification lithification and any conversion to quartz chert from a hydrous silica precursor occurred close to the sediment water interface the uniform 18 o values of all the different chert types suggest that all cherts precipitated over a relatively common temperature interval 20 c from a common parent water having a relatively uniform 18 o the isotopic data suggest silica saturation and precipitation was not the result of the mixing of seawater and meteoric water or the result of evaporative processes siderite in the deep water banded facies of the gunflint displays a 18 o range of 6 0 to 2 6 o whereas siderite in the more shoreward organic rich shale facies is significantly enriched in 13 c 13 c 2 5 to 0 5 o 18 c of siderite does not appear to have been altered as a result of neomorphic recrystallization and authigenic microsparitic siderite along stylolites displays the same 13 c range as primary and neomorphosed siderite however neomorphic and authigenic siderite are depleted in 18 o by up to 7 o relative to primary unaltered microspheroidal siderite the lower 13 c of banded facies siderite relative to the shale facies siderite does not seem to be the result of thermal decarboxylation or anaerobic oxidation abiotic or bacterial of organic matter but rather is better explained by primary precipitation in an ocean system that was layered with respect to carbon isotopes the more basinward banded facies siderite precipitated from a 13 c depleted fe 2 rich hydrothermal water mass that was moved by advective upwelling from submarine regions of magmatic volcanic hydrothermal activity onto the continental shelf the siderite of the shale facies precipitated from a more near shore shallow seawater mass that was comparatively enriched in 13 c 13 c 0 2 o ankerite in the gunflint iron formation occurs as a replacement of primary siderite in the banded facies and as a replacement of greenalite and chert in the arenite facies many ankerite samples have 13 c values that are similar to those of the shale facies siderite which suggests that shallow seawater was a major component of the diagenetic fluid later neomorphism of the replacement ankerite at higher burial temperatures and probably in the presence of 18 o depleted waters resulted in a wide range of 18 o values 13 8 22 5 o the unique mineralogy of the upper most gunflint iron formation calcite serpentine and magnetite compared to the majority of the formation the very low values and overlying diabase sills suggest that the non ferroan nature of the carbonate in the upper gunflint is the result of contact metamorphism

southern ocean sea ice extent productivity and iron flux over the past eight glacial cycles sea ice and dust flux increased greatly in the southern ocean during the last glacial period palaeorecords provide contradictory evidence about marine productivity in this region but beyond one glacial cycle data were sparse here we present continuous chemical proxy data spanning the last eight glacial cycles 740 000 years from the dome c antarctic ice core these data constrain winter sea ice extent in the indian ocean southern ocean biogenic productivity and patagonian climatic conditions we found that maximum sea ice extent is closely tied to antarctic temperature on multi millennial timescales but less so on shorter timescales biological dimethylsulphide emissions south of the polar front seem to have changed little with climate suggesting that sulphur compounds were not active in climate regulation we observe large glacial interglacial contrasts in iron deposition which we infer reflects strongly changing patagonian conditions during glacial terminations changes in patagonia apparently preceded sea ice reduction indicating that multiple mechanisms may be responsible for different phases of co2 increase during glacial terminations we observe no changes in internal climatic feedbacks that could have caused the change in amplitude of antarctic temperature variations observed 440 000 years ago

early silica cementation and subsequent diagenesis in arenites from four early proterozoic iron formations of north america abstract in four unmetamorphosed north american iron formations that display arenitic granular textures much of the chert and megaquartz occupies former intergranular pore space and exhibits textures typical of cements iron bearing phases are very rare in these cements excluding replacive crystals cracks and more irregular cavities that formed in these arenites soon after deposition probably via the shrinkage of gelatinous silica are filled with similar chert and megaquartz cements silica cemented intraclastic pebbles of arenite local occurrences of cross stratified cherty internal sediments resting on the cements and numerous zones where the abundance of cement equals the porosity of comparable modern sands indicate the cementation commenced near the sediment water interface opa ine silica fibrous silica polymorphs and megaquartz druses are inferred to have been the most voluminous initial precipitates and they are very inhomogeneously distributed silica concentrations in the pore waters of newly deposited iron formation sands must therefore have been high but variable the lack of evidence for subaerial desiccation or normal saline deposits renders an evaporative origin for either the cements or iron formations as a whole highly unlikely steeper geothermal gradients are suggested as a more likely cause of rapid silica cementation and silica cements from geothermal areas show very similar textures most of the cements in iron formation arenites were affected by neomorphism replacement mechanical compaction and or pressure solution regardless of their origin the cements are noteworthy for the following reasons they indicate that modern iron formations are enriched in silica relative to their precursor sediments they provide new evidence that iron formations are not replaced limestones or dolomites and the iron minerals they are associated with are probably the closest approaches to primary ferruginous phases in iron formation arenites early silica cements also appear to be widespread in lutitic or banded iron formations in the form of chert pods

the paleoproterozoic fossil record implications for the evolution of the biosphere during earth s middle age abstract the paleoproterozoic 2 5 1 6 ga era is a decisive time in earth and life history the paleobiological record microfossils stromatolites biomarkers and isotopes illustrates the biosphere evolution during a time of transitional oceanic and atmosphere chemistries benthic microfossil assemblages are recorded in a variety of oxygenated sulfidic and ferruginous environments representative of the spatial heterogeneities and temporal variations characteristic of this era the microfossil assemblages include iron metabolizing and or iron tolerant prokaryotes sulfur metabolizing prokaryotes cyanobacteria other undetermined prokaryotes and eukaryotes the undetermined microfossils represent a majority of the assemblages and thus raise a challenge to determine the nature and role of microorganisms in these changing environments despite the early evolution of the eukaryotic cellular toolkit early eukaryotic crown group diversification may have been restrained in the paleoproterozoic by ocean chemistry conditions but it increased during the late mesoproterozoic early neoproterozoic despite the continuation of similar conditions through the miscalled boring billion then amplified significantly but perhaps within lower taxonomic levels with the demise of euxinic conditions and increase in ecological complexity the emerging picture is one of a changing and more complex biosphere in which the three domains of life archaea bacteria and eukarya were diversifying in various ecological niches marked by the diversification of identified microfossils stromatolites increasing abundance of preserved biomarkers and appearance of macroscopic problematic fossils or trace fossils

ammonium and non sea salt sulfate in the epica ice cores as indicator of biological activity in the southern ocean sulfate so42 and ammonium nh4 flux records over the last 150 000 years from both antarctic epica ice cores european project for ice coring in antarctica are presented the ice core record from dome c is influenced by the indian sector of the southern ocean so whereas dronning maud land is facing the atlantic sector generally they reflect the past atmospheric aerosol load and thus potentially reveal the fingerprint of marine biogenic sources from the so the most important feature of both the nssso 4 2 as well as nh4 flux records is the absence of any significant glacial cycles in contrary to the distinct transitions for mineral dust and sea salt aerosol over the last 150 000 years this finding challenges the iron fertilization hypothesis on long time scales as the significant changes in dust e g from the last glacial maximum toward the holocene have neither an impact on nssso 4 2 nor on nh4 fluxes found in interior antarctica the inter site correlation of both species is weak r 2 0 42 for the nssso 4 2 flux and r 2 0 12 for the nh4 flux respectively emphasizing the local source characteristics of biogenic aerosol from the so millennial variability in nh4 and nssso 4 2 is within the uncertainty of our flux estimates correlation with mineral dust and sea ice derived sodium shows only a very weak influence of dust deposition on those insignificant changes in nssso 4 2 flux for the atlantic sector of the southern ocean but also small transport changes or terrigeneous sulfate contributions may contribute to those variations at edml c 2009 elsevier ltd all rights reserved

sea ice variability and primary productivity in the ross sea antarctica from methylsulphonate snow record 1 the ross sea contains the most biologically productive continental shelf in antarctica and is a region where the annual formation of sea ice drives substantial amounts of bottom water formation we present snow pit chemistry data from mt erebus saddle that provide a quantitative proxy to reconstruct summer sea ice conditions and rates of marine primary production the methylsulphonate ms record is strongly correlated with changes in the area of open water r2 0 903 p 0 05 caused by differences in atmospheric circulation and the sea ice damming effect of large icebergs b 15 and c 19 which calved from the ross ice shelf in 2000 and 2002 respectively furthermore ms and phytoplankton net primary production correlate significantly r2 0 927 p 0 01 our results demonstrate the potential of the mt erebus saddle ice core to reconstruct sea ice and primary productivity variability in the ross sea beyond the observational record

valence state fossils in proterozoic stromatolites by l edge x ray absorption spectroscopy 1 paleoproterozioc ca 1 9 ga stromatolites from the biwabik iron formation minnesota united states contain fossil forms which in the literature have been attributed to ancient microbes including iron oxidising bacteria and cyanobacteria to search for valence state fossils we measured fe3 fe fe fe2 fe3 transverse to the laminae of a biwabik probably biogenic stromatolite and compared the results with a scan across the enclosing likely abiotic sedimentary rock or interstromatolite fill to obtain fe3 fe and information about the site symmetry and crystal field strength we used l3 2p3 2 3d soft x ray absorption spectroscopy and interpreted the measurements using our calculated spectra we found that fe3 fe is approximately constant at 0 3 within the stromatolite increases steeply to around 0 6 in the region of the stromatolite fill boundary and then reduces significantly in the interstromatolite fill the crystal field strength for octahedral fe3 increased and became more irregular as the scan moved from the stromatolite into the fill our results tentatively suggest that a combination of ancient biological and later diagenetic processes can produce steep gradients in fe3 fe and alterations in the crystal field strength across a probable abiotic biotic boundary to describe the l3 absorption spectra in the stromatolite fill region it was necessary to include a significant fe3 tetrahedral component which suggests the presence of magnetite at other positions fits using only octahedral fe2 and fe3 theoretical curves satisfactorily reproduce the spectra the search for a possible new type of spatial biosignature in the valence state record for ancient stromatolites might help differentiate between the biogenic stromatolites and abiogenic stromatolite like structures and could even be relevant to the search for fossil evidence of life in extraterrestrial rocks

was the deposition of large precambrian iron formations linked to major marine transgressions geochemical evidence suggests the iron and silica rich precipitates that compose large neoarchean and paleoproterozoic iron formations formed along a chemocline between iron rich deep water and iron poor surface water sedimento logical evidence indicates many large iron formations accumulated in marine shelf environments during major transgressions we suggest this occurred because the chemocline could only impinge on continental shelves during times of sea level rise or highstand on the other hand the stratigraphic record indicates that deposition of iron formations ceased during regressions in some basins and transgressions in others to explain this we propose that iron concentrations in the precambrian ocean were greatest at mid water depths in a zone on the order of 100 m thick radiometric age dates from the hamersley basin of western australia suggest major iron formation deposition had a periodicity of ca 20 to 125 m y close to second order cycles in phanerozoic sea level driven by long te

migration of methane sulphonate in antarctic firn and ice we investigate the seasonal relationship of the sulphur bearing anions methane sulphonate msa and non sea salt sulphate nssso42 in sections of firn and ice cores from the antarctic peninsula and weddell sea region of antarctica in cores from dolleman island and berkner island msa has clearly migrated from the summer snow layer where it is initially deposited to become concentrated in the winter layer a similar behavior is evident in a core from the dyer plateau though in deeper layers cores from gomez nunatak and beethoven peninsula show little evidence of relocation of msa though migration at greater depth in the ice sheet cannot be ruled out in contrast in all these cores non sea salt sulphate remains in the summer layer from comparisons between the ice core characteristics and the migration behavior at these sites we conclude that the movement of msa does not occur via percolation and refreezing of meltwater simple concentration driven diffusion is also not a factor as the msa peaks are sharp in the winter layer the data presented indicate that the movement of msa in firn is likely to be linked to the concentration of other ionic species in the snowpack and to the snow accumulation rate a possible mechanism for the migration of msa in the snowpack is via an initial diffusion in the liquid or vapor phase which is halted by trapping in the winter layer when the msa forms a salt with a cation

spatial and seasonal variations of the snow chemistry at the central filchner ronne ice shelf antarctica the chemical stratigraphy of the surface firn of the central filchner ronne ice shelf was determined in conjunction with stable isotopes from shallow firn cores and snow pit samples collected at 1 1 widely distributed sites and covering a time period of at least 20 years the chemical analysis included ecm profiling and the determination of chloride non sea salt nss sulphate methanesulphonate msa nitrate and partly sodium and bromide throughout the investigated area winter time nss sulphate levels are found to be substantially negative indicating that the sulphate to sodium ratio in airborne sea salt particles is depleted by a factor of 5 approximately in relation to the bulk sea water ratio while winter firn layers appear to be marked by episodic events of large sea salt inputs pronounced annual cycles with maxima in summer firn layers are commonly observed for the ecm signal and for nss sulphate nitrate and msa at all sites for msa however this phase relation is almost reversed for depths greater than 3 4m the mean impurity levels consistently are strongly depleted with increasing distance from the ice edge by about 30 100 km for sea salt 25 100 km for msa and only 10 100 km for nss sulphate however no substantial trend is observed for nitrate it is concluded therefore that the sea salt and the biogenic sulphur compounds deposited on the filchner ronne ice shelf mainly originate from the adjacent weddell sea further important implications of the continental effects are a an atmospheric residence time of nss sulphate apparently exceeding that of msa probably due to the supplementary sulphate production on the ice shelf from biogenic so 2 and b a substantial limitation of the potential of deep ice cores already drilled on the filchner ronne ice shelf in extracting reliable net temporal changes of sea salt and biogenic sulphur species

last glacial interglacial sea ice cover in the sw atlantic and its potential role in global deglaciation sea ice growth and decay in antarctica is one of the biggest seasonal changes on earth expanding ice cover from 4 106 km2 to a maximum of 19 106 km2 during the austral winter analyses of six marine sediment cores from the scotia sea sw atlantic yield records of sea ice migration across the basin since the lateglacial the cores span nearly ten degrees of latitude from the modern seasonal sea ice zone to the modern polar front surface sediments in the cores comprise predominantly diatomaceous oozes and muddy diatom oozes that reflect holocene conditions the cores exhibit similar down core stratigraphies with decreasing diatom concentrations and increasing magnetic susceptibility from modern through to the last glacial maximum lgm sediments in all cores contain sea ice diatoms that preserve a signal of changing sea ice cover and permit reconstruction of past sea ice dynamics the sea ice records presented here are the first to document the position of both the summer and winter sea ice cover at the last glacial maximum lgm in the scotia sea comparison of the lgm and holocene sea ice conditions shows that the average winter sea ice extent was at least 5 further north at the lgm average summer sea ice extent was south of the most southerly core site at the lgm and suggests that sea ice expanded from approximatelyw61s tow52s each season our data also suggest that the average summer sea ice position at the lgm was not the maximum extent of summer sea ice during the last glacial instead the sediments contain evidence of a pre lgm maximum extent of summer sea ice between w30 ka and 22 ka that extended to w59s close to the modern average winter sea ice limit based on our reconstruction we propose that the timing of the maximum extent of summer sea ice and subsequent retreat by 22 ka could be insolation controlled and that the strong links between sea ice and bottom water formation provide a potential mechanism by which southern hemisphere regional sea ice dynamics at the lgm could have a global impact and promote deglaciation

retreating glacier fronts on the antarctic peninsula over the past half century the continued retreat of ice shelves on the antarctic peninsula has been widely attributed to recent atmospheric warming but there is little published work describing changes in glacier margin positions we present trends in 244 marine glacier fronts on the peninsula and associated islands over the past 61 years of these glaciers 87 have retreated and a clear boundary between mean advance and retreat has migrated progressively southward the pattern is broadly compatible with retreat driven by atmospheric warming but the rapidity of the migration suggests that this may not be the sole driver of glacier retreat in this region

the preservation of methanesulphonic acid in frozen ice core samples ice core records of methanesulphonic acid msa provide a potentially powerful tool for producing proxy records of sea ice a critical but poorly understood component of the earth s climate system however msa is able to diffuse through solid ice and here we examine the effect of two different methods of frozen storage on the preservation of msa in archived ice core samples re analysis of archived ice sticks confirms that msa diffuses out of ice cores archived in this manner despite msa losses of up to 39 after 7 years storage the ice sticks studied here preserve much of the variability of the original msa record suggesting that useful proxy records can be obtained from archived ice sticks furthermore re analysis of ice core samples that had been refrozen into discrete bottled samples for storage demonstrates that it is possible to archive ice samples in a way that prevents msa loss in this case accurate records of msa variability and concentration were preserved even over storage periods of 15 years this has important implications for the storage of ice cores and subsequent determination of msa and demonstrates that ice storage history needs to be considered when interpreting msa records

bellingshausen sea ice extent recorded in an antarctic peninsula ice core annual net accumulation an from the bruce plateau bp ice core retrieved from the antarctic peninsula exhibits a notable relationship with sea ice extent sie in the bellingshausen sea over the satellite era both bp an and bellingshausen sie are influenced by large scale climatic factors such as the amundsen sea low southern annular mode and southern oscillation in addition to the direct response of bp an to bellingshausen sie e g more open water as a moisture source these large scale climate phenomena also link the bp and the bellingshausen sea indirectly such that they exhibit similar responses e g northerly wind anomalies advect warm moist air to the antarctic peninsula and neighboring bellingshausen sea which reduces sie and increases an comparison with a time series of fast ice at south orkney islands reveals a relationship between bp an and sea ice in the northern weddell sea that is relatively consistent over the twentieth century except when it is modulated by atmospheric wave patterns described by the trans polar index the trend of increasing accumulation on the bruce plateau since 1970 agrees with other climate records and reconstructions in the region and suggests that the current rate of sea ice loss in the bellingshausen sea is unrivaled in the twentieth century

the silica cycle in the precambrian abstract whereas the modem silica cycle is heavily dependent on the biology of silica secreting organisms such as the diatoms the precambrian silica cycle was dominated by inorganic reactions among dissolved silica clay and zeolite minerals and organic matter there is no evidence for deposition of a layered amorphous silica but abundant evidence for diagenetic silicification in the neoproterozoic the time period chosen for this analysis the influx of silica to the neoproterozoic ocean would have been governed as today by the balance among tectonism weathering and hydrothermal input the evidence of neoproterozoic rocks favors tectonic and weathering regimes not very dissimilar to those of the early phanerozoic and hydrothermal inputs significantly altered at certain periods one flux would have been very different the present diffusional influx of silica from interstitial waters into the oceans would have been altered to an efflux from the oceans to interstitial waters reactions of dissolved silica with inorganic phases would have controlled silica concentrations at a level of about 60 ppm this figure is based on experimental determinations of solubility and silica sorption on clay minerals and zeolites as silica in interstitial waters was lowered by opal ct precipitation a diffusional efflux from the ocean into the sediment was set up silicification would have started in early diagenesis as opal ct precipitated from interstitial waters diffusion of silica from overlying seawater declined as the sediment was buried a few hundred meters and the diffusion path lengthened during this still relatively shallow burial silicification continued but this time powered by hydrologie transport of dissolved silica from coastal plain sediments during transgressions and regressions thus the major removal of silica from the neoproterozoic ocean took place by diagenetic reactions

ice core evidence for antarctic sea ice decline since the 1950s the instrumental record of antarctic sea ice in recent decades does not reveal a clear signature of warming despite observational evidence from coastal antarctica here we report a significant correlation p

the mechanism of skeletal aragonite neomorphism evidence from neomorphosed mollusks from the upper purbeck formation late jurassic early cretaceous southern england abstract the trace element geochemistry and microtextures of neomorphosed mollusks from the upper purbeck formation late jurassic early cretaceous of southern england suggest that calcite replacement of aragonite occurs by a force of crystallization driven mechanism similar to that of non polymorphic skeletal carbonate replacement reactions such as silicification the purbeck neomorphic calcites are substantially enriched in mg mn and fe and depleted in sr compared to skeletal aragonite indicating that the neomorphic reaction zones were not chemically isolated from the bulk pore waters to a significant degree neomorphic calcite microtextures are fundamentally similar to the replacement microtextures of silicified and celestite replaced fossils in terms of the degree and style of preservation of traces of skeletal microtextures in authigenic crystals and the relationships of authigenic crystal morphology and crystallographic orientation to shell microtexture the neomorphic replacement of aragonite by calcite differs from most non polymorphic replacement reactions in that the calcite cannibalizes aragonite decreases in the intraskeletal pore water calcium carbonate ion activity product caused by calcite precipitation results in aragonite dissolution adjacent to aragonite calcite contacts i e chalkification in some fossils chalkification does not occur in non polymorphic replacements of skeletal carbonate

chemically oscillating reactions during the diagenetic oxidation of organic matter and in the formation of granules in late palaeoproterozoic chert from lake superior abstract filamentous and coccoidal microfossils have been reported since the 1950 s from a range of granular cherts from the late palaeoproterozoic southwestern superior craton canada united states however the chemical and mineral compositions of granules the presence of microfossils in granules and the common presence of granules in intercolumnar space of stromatolitic chert are poorly documented and explained furthermore the depositional model for the origin of granules in wave agitated waters does not entirely explain their mineral diversity nor their characteristic morphologies and patterns we report on the crystallinity of organic matter mineral diversity and compositions of microfossils in granules from three different kinds of late palaeoproterozoic cherts namely phosphatic organic and haematitic stromatolitic organic rich chert from the gunflint fm contains granules with euhedral carbonate and equidistant concentric laminations of organic matter akin to fractal patterns from the belousov zhabotinsky b z chemically oscillating reaction these granules also contain authigenic anatase ferric ferrous silicates and fe oxides filamentous and coccoidal microfossils similar to those of the gunflint occur in chert from the biwabik formation and share morphology and co occur with mn siderite and apatite granules in phosphatic chert in the michigamme formation often contain filamentous and coccoidal microfossils composed of organic matter sericite and apatite bulk carbonate associated with these michigamme granular phosphatic chert beds has systematically negative 13ccarb values around 3 1 0 9 1 and 18ocarb smow between 20 8 and 30 7 which suggest some contribution from the diagenetic oxidation of organic matter notably residual carboxylic acid is detectable in c xanes spectra of organic matter from granular phosphatic chert which is a residual reactant of b z type reactions along with previously reported observations of pyritised microfossils from the gunflint formation these distinct mineralogies indicate variable modes of preservation for the products of chemically oscillating reactions that likely relate to the availability of different oxidants in the diagenetic environment we conclude that the late palaeoproterozoic shallow marine environments of the lake superior area were populated by morphologically similar micro organisms and that the diagenetic oxidation of organic matter through chemically oscillating reactions contributed to the formation of spheroidal rosettes granules and concretions during a late palaeoproterozoic great putrefaction event granules in chert that contain organic matter or microfossils thus provide a reliable petrographic context to search for a record of putrefaction of microbial life on the early earth and on other ancient planetary surfaces

an antarctic circumpolar wave in surface pressure wind temperature and sea ice extent the southern ocean is the only oceanic domain encircling the globe it contains the strong eastward flow of the antarctic circumpolar current and is the unifying link for exchanges of water masses at all depths between the world s major ocean basins1 as these exchanges are an important control on mean global climate the southern ocean is expected to play an important role in transmitting climate anomalies around the globe interannual variability has been often observed at high southern latitudes and observations of sea ice extent suggest that such features propagate eastwards around the southern ocean2 3 here we use data from a variety of observational techniques to identify significant interannual variations in the atmospheric pressure at sea level wind stress sea surface temperature and sea ice extent over the southern ocean these anomalies propagate eastward with the circumpolar flow with a period of 4 5 years and taking 8 10 years to encircle the pole this system of coupled anomalies which we call the antarctic circumpolar wave is likely to play an important role in climate regulation and dynamics both within and beyond the southern ocean

century scale perspectives on observed and simulated southern ocean sea ice trends from proxy reconstructions since 1979 when continuous satellite observations began southern ocean sea ice cover has increased whilst global coupled climate models simulate a decrease over the same period it is uncertain whether the observed trends are anthropogenically forced or due to internal variability or whether the apparent discrepancy between models and observations can be explained by internal variability the shortness of the satellite record is one source of this uncertainty and a possible solution is to use proxy reconstructions which extend the analysis period but at the expense of higher observational uncertainty in this work we evaluate the utility for change detection of 20th century southern ocean sea ice proxies we find that there are reliable proxies for the east antarctic amundsen bellingshausen and weddell sectors in late winter and for the weddell sea in late autumn models and reconstructions agree that sea ice extent in the east antarctic amundsen and bellingshausen seas has decreased since the early 1970s consistent with an anthropogenic response however the decrease is small compared to internal variability and the change is not robustly detectable we also find that optimal fingerprinting filters out much of the uncertainty in proxy reconstructions the ross sea is a confounding factor with a significant increase in sea ice since 1979 that is not captured by climate models however existing proxy reconstructions of this region are not yet sufficiently reliable for formal change detection

an emerging technique multi ice core multi parameter correlations with antarctic sea ice extent using results stemming from the international trans antarctic scientific expedition itase ice core array plus data from ice cores from the south pole and siple dome we investigate the use of sodium na non sea salt sulfate nssso4 2 and methylsulfonate ms as proxies for antarctic sea ice extent sie maximum and mean annual chemistry concentrations for these three species correlate significantly with maximum mean and minimum annual sie offering more information and clarification than single ice core and single species approaches significant correlations greater than 90 exist between na and maximum sie nssso4 2 with minimum and mean sie and ms with mean sie correlations with sie within large geographic regions are in the same direction for all ice core sites for na and nssso4 2 but not ms all ice cores display an sie correlation with nssso4 2 and ms but not all correlate with na this multi core multi parameter study provides the initial step in determining which chemical species can be used reliably and in which regions as a building block for embedding other ice core records once established the resulting temporal and spatial matrix can be used to relate ice extents atmospheric patterns biological productivity and site conditions

ice core records as sea ice proxies an evaluation from the weddell sea region of antarctica 1 ice core records of methanesulfonic acid msa from three sites around the weddell sea are investigated for their potential as sea ice proxies it is found that the amount of msa reaching the ice core sites decreases following years of increased winter sea ice in the weddell sea opposite to the expected relationship if msa is to be used as a sea ice proxy it is also shown that this negative msa sea ice relationship cannot be explained by the influence that the extensive summer ice pack in the weddell sea has on msa production area and transport distance a historical record of sea ice from the northern weddell sea shows that the negative relationship between msa and winter sea ice exists over interannual 7 year period and multidecadal 20 year period timescales national centers for environmental prediction national center for atmospheric research ncep ncar reanalysis data suggest that this negative relationship is most likely due to variations in the strength of cold offshore wind anomalies traveling across the weddell sea which act to synergistically increase sea ice extent sie while decreasing msa delivery to the ice core sites hence our findings show that in some locations atmospheric transport strength rather than sea ice conditions is the dominant factor that determines the msa signal preserved in near coastal ice cores a cautious approach is thus required in using ice core msa for reconstructing past sea ice conditions including the need for networks of ice core records and multiproxy studies to assess the significance of past msa changes at different locations around antarctica

ice sheet record of recent sea ice behavior and polynya variability in the amundsen sea west antarctica investigation of how regional sic is recorded in the ice sheet stratigraphy over the period 2002 2010 we find that the ice sheet chemistry is significantly correlated with sic variability within the as and pine island bay polynyas based on this result we evaluate the use of icecore chemistry as a proxy for interannual polynya variability in this region one of the largest and most persistent polynya areas in antarctica msa concentrations correlate strongly with summer sic within the polynya regions consistent with msa at this site being derived from marine biological productivity during the spring and summer cl concentrations correlate strongly with winter sic within the polynyas as well as some regions outside the polynyas consistent with cl at this site originating primarily from winter sea ice formation spatial correlations were generally insignificant outside of the polynya areas with some notable exceptions ice core glaciochemical records from this dynamic region thus may provide a proxy for reconstructing as and pine island bay polynya variability prior to the satellite era

improving ice core interpretation using in situ and reanalysis data 1 back trajectory analysis provided by the british atmospheric data centre using meteorological parameters from the european centre for medium range weather forecasts ecmwf reanalysis era 40 1980 2001 and operational analysis 2002 2006 is used to investigate transport pathways and source regions of climate proxies preserved in a new ice core gomez from the southwestern antarctic peninsula the ecmwf data are compared with automatic weather station data and ice core annual accumulation records to demonstrate that the ecmwf data capture a large proportion of the annual and subseasonal precipitation variability at the site the back trajectories reveal that precipitation preserved in the ice core accumulation record and hence climate proxies contained therein originate from the low pressure systems from the bellingshausen sea transported via circumpolar westerly winds hence precipitation dependent ice core proxies such as isotopic composition will be influenced by both localized sea ice extent and large scale circulation changes such as the southern annular mode sea ice proxies from the ice core are expected to be dominated by sea ice extent in the bellingshausen sea but also influenced by sea ice in the weddell sea with a small proportion of air mass trajectories originating from this region during the summer comparison with other ice core sites reveals a stronger influence of easterly transport at more northerly locations thus explaining the observed differences in snow accumulation records between ice cores and the poor correlation with instrumental records at these sites

a review of sea ice proxy information from polar ice cores sea ice plays an important role in earth s climate system the lack of direct indications of past sea ice coverage however means that there is limited knowledge of the sensitivity and rate at which sea ice dynamics are involved in amplifying climate changes as such there is a need to develop new proxy records for reconstructing past sea ice conditions here we review the advances that have been made in using chemical tracers preserved in ice cores to determine past changes in sea ice cover around antarctica ice core records of sea salt concentration show promise for revealing patterns of sea ice extent particularly over glacial interglacial time scales in the coldest climates however the sea salt signal appears to lose sensitivity and further work is required to determine how this proxy can be developed into a quantitative sea ice indicator methane sulphonic acid msa in near coastal ice cores has been used to reconstruct quantified changes and interannual variability in sea ice extent over shorter time scales spanning the last 160 years and has potential to be extended to produce records of antarctic sea ice changes throughout the holocene however the msa ice core proxy also requires careful site assessment and interpretation alongside other palaeoclimate indicators to ensure reconstructions are not biased by non sea ice factors and we summarise some recommended strategies for the further development of sea ice histories from ice core msa for both proxies the limited information about the production and transfer of chemical markers from the sea ice zone to the antarctic ice sheets remains an issue that requires further multidisciplinary study despite some exploratory and statistical work the application of either proxy as an indicator of sea ice change in the arctic also remains largely unknown as information about these new ice core proxies builds so too does the potential to develop a more comprehensive understanding of past changes in sea ice and its role in both long and short term climate changes

origin of precambrian iron formations in the lake superior region the precambrian banded cherty iron formations in the lake superior region were deposited on broad continental shelves and deposits of the supratidal intertidal and subtidal zones can be recognized in the well known facies of the iron formations the supratidal deposits were primarily calcitic aragonitic and sideritic muds other minerals in order of decreasing abundance may have been gypsum anhydrite ankerite dolomite quartz apatite and halite intraclasts were produced by desiccation granulation and some of this material was redeposited in the intertidal and subtidal zones the intertidal zone was characterized by the development of extensive algal reefs and digital sized and larger stromatolitic mounds desiccation granulation and tidal rip of mineralized stromatolites further added to the accumulation of intraclasts the intertidal zone was the domain of granules that were derived by abrasion and rounding of intraclasts the original mineralogy of the intertidal deposits was similar to that of the supratidal zone however because of photosynthesis the sea water was oxygenated lozenge shaped grains are considered to be secondary silicified and iron oxide replicates of original gypsum crystals and by comparison with recent evaporites some anhydrite and halite may also have been present the deposits of the intertidal and subtidal zones are considered to be comparable to the present day abu dhabi complex in the persian gulf spherical microstructures are abundant and well preserved in the chert of the subtidal deposits pyrite which characterizes these deposits probably was formed largely by the bacterial reduction of sulfate derived from the intertidal zone the laminations in the iron formations resulted from several causes that were controlled by chemical and mechanical processes such as the rates and localization of the precipitation of calcitic aragonitic and sideritic muds and the mechanical breakup and redistribution of these sediments as sand silt and mud these processes resulted in compositional and textural laminations the diversity of the banded cherty iron formations recognized in the different facies then can be explained largely in the diagenetic changes the large scale pervasive diagenetic changes were the replacement of calcite and aragonite by chert and the formation of iron silicates by the reactions between ionic silica and siderite and iron bearing dolomite vein like structures and the development of magnetite along stylolites indicate mobility of iron in late diagenetic stages and iron organic chelates are suggested to account for the mobility depending on the composition of the laminae and the chemical environment silicification during diagenesis produced the hematite magnetite siderite pyrite and mixed mineral facies

tropical pacific high latitude south atlantic teleconnections as seen in δ18o variability in antarctic coastal ice cores 1 we use a network of eight ice cores from coastal dronning maud land dml antarctica to examine the role of the tropical enso el nino southern oscillation in the temporal variability of 18o in annual accumulation the longest record from the s100 ice core covering the period 1737 1999 is used to analyze the teleconnections between the tropical pacific and coastal dml on decadal scales and longer a shorter stacked coastal dml 18o series spanning 1955 1999 is constructed to assess the variability of enso teleconnection on interannual scales results suggest that on typical enso timescales of 2 6 years the strength of the teleconnection varies in time being stronger for years with generally negative phase of the southern annular mode sam on the timescales of approximately two decades bidecadal positive isotope anomalies are associated with oceanic warming and a westward sea surface temperature sst gradient in the equatorial pacific bidecadal variability in sam forced by the tropical pacific is proposed as a critical element in the teleconnection our analysis suggests that a multidecadal positive trend in the annual mean 18o values from the analyzed cores can be indicative of the atmospheric warming that begun in this part of the dml already in the 1910s the trend in 18o quantified in terms of long term surface air temperature sat changes is consistent with the instrumental data yet we speculate that the accurate estimation of sat trends requires an assessment of the potential role of secular sam and sea ice extent changes in shaping the isotopic signal

a low level explanation for the recent large warming trend over the western antarctic peninsula involving blocked winds and changes in zonal circulation 1 we demonstrate a mechanism whereby the impact of stronger circumpolar westerly winds on the mountains of the antarctic peninsula contributes significantly to the enhanced warming trend observed over its western side in the last 50 years numerical and laboratory meteorological modelling demonstrate how when westerly winds impinge on this side warm air below the height 1 5 2 0 km of the peninsula is advected in a southerly direction the strength of the annual mean westerly winds has increased by about 15 20 since the 1960s while the modelling results indicate that contemporaneously the air advected to its western side originates from an increasingly northerly and warmer location this gives rise to increased northerlies and a greater transport of warm air into this region consequently there is a reduction in the sea ice extent further amplifying the local warming this low level orographic mechanism for the local climate trend is supported by observational evidence

1000 year ice core records from berkner island antarctica two medium depth ice cores were retrieved from berkner island by a joint project between the alfred wegener institut and the british antarctic survey in the 1994 95 field season a151mdeep core from the northern dome reinwarthho he of berkner island spans 700 years while a 181m deep core from the southern dome thyssenho he spans approximately 1200 years both cores display clear seasonal cycles in electrical conductivity measurements allowing dating by annual layer counting and the calculation of accumulation profiles stable isotope measurements both d18o and dd together with the accumulation data allow us to estimate changes in climate for most of the past millennium the data show multi decadal variability around a generally stable long term mean in addition a full suite of major chemistry measurements is available to define the history of aerosol deposition at these sites again there is little evidence that the chemistry of the sites has changed over the past six centuries finally we suggest that the southern dome with an ice thickness of 950m is an ideal site from which to gain a climate history of the late stages of the last glacial and the deglaciation for comparison with the records from the deep antarctic ice cores and with other intermediate depth cores such as taylor dome and siple dome

late pleistocene and early holocene change in the weddell sea a new climate record from the patriot hills ellsworth mountains west antarctica the transition from the late pleistocene to the holocene 30 000 5000 years ago was a period of considerable climate variability which has been associated with changes in deep water formation and the intensity of the meridional overturning circulation although numerous records exist across the north atlantic region few antarctic ice core records have been obtained from the south here we exploit the potential of upwelling ancient ice so called blue ice areas bias from the patriot hills in the ellsworth mountains to derive the first deuterium isotope record d from continental antarctica south of the weddell sea gas analysis and glaciological considerations provide a first relative chronology inferred temperature trends from the patriot hills bia and snow pit suggest changing climate influences during the transition between the last glacial period and holocene under modern conditions the interplay between the antarctic high pressure system and the southern annular mode appears to play a significant role in controlling katabatic wind flow over the site while the bia record suggests that greater sea ice extent during the last glacial period was a major control our results demonstrate the considerable potential of the patriot hills site for reconstructing past climate change in the south atlantic region

sm nd isochron age and provenance of the argillites of the gunflint iron formation in ontario canada abstract sm nd rb sr and k ar isotope analyses were made on argillaceous sediments from the gunflint iron formation in the lake superior region in order to provide new information on their sedimentation age and evolutionary history the investigations indicate that it might be possible to date the time of sedimentation by the sm nd method by studying specific material such as argillaceous whole rocks enriched in organic matter and clay fractions the spread in the sm nd ratios seems here to have been favoured by the incorporation of organic material in the argillites the sm nd isotope data yield an isochron age of 2 08 0 25 ga which seems to be a fair estimation of deposition age model calculations indicate that the main source supplying the animikie seawater with ree was located at the northern border of the basin the argillites and their clay minerals did not behave as closed systems with regard to the rb sr and k ar systems during further diagenetic evolution

a 340 year record of biogenic sulphur from the weddell sea area antarctica detailed records of methanesulphonic acid msa and non sea salt sulpha te nss so have been obtained from ice cores drilled on dolleman island on the east coast of the antarctic peninsula i0 35 2 s 60 55 5 w annual average concentrations of msa arc presented for the period i 652 1992 over this lime span the mean ann ual concen tration of msa is 0 69 eq 1 1 cr 0 33 n 340 the range is 0 13 2 35 eq 1 1 a nd the msa nss s04 2 ratio is 0 22 the high msa concentration reflects the proximity of the weddell sea believed to be a region of high marine phyt0plankton production t he overa ll mean nss so concentration is about 66 of the total sulphate d eposited in the snowfall low frequency variations of msa and oxygen isolope signals correla te closely indicat ing that they may be modulated by similar atmospheric processes positive correlations are observed between the oxygenisotope signature and both l 1sa r 0 4 1 and nss s04 2 r 0 50 signilicant at the 99 level a small negative correlation can be seen between both species and the annual duration or sea ice a t scoria bay laurie island in the south orkneys since 1902 msa r 0 23 and nss so r 0 29 significant at 95 confidence no significant link between high msa concentrations and el nino even ts is observed at this location

high resolution dimethyl sulfide and dimethylsulfoniopropionate time series profiles in decaying summer first year sea ice at ice station polarstern western weddell sea antarctica high resolution profiles of ice dimethyl sulfide dms and dimethylsulfoniopropionate dmsp concentrations were measured together with a suite of ancillary physical and biological properties during a time series of decaying summer level first year sea ice throughout december 2004 during the ice station polarstern drift experiment western weddell sea antarctica ice dmsp and dms concentrations were always maximum at the bottom of the ice sheet 636 2627 and 292 1430 nm respectively where the highest chlorophyll a levels were also found 15 30 g l 1 throughout the observation period the autotrophic surface community 32 205 g c l 1 was dominated by phaeocystis sp while the bottom community 1622 3830 g c l 1 mainly consisted of pennate diatoms this illustrates that although being known for lower dmsp to chlorophyll a ratios than phaeocystis sp diatoms dominated the overall dmsp production because of their much larger biomass decreasing dmsp concentrations and increasing dms to dmsp ratios in the bottom layers with time suggested active dmsp to dms conversion in a slowly degrading environment drastic temporal brine volume and brine salinity changes associated with the decaying sea ice cover are shown to directly impact 1 the migration of dmsp and dms through the brine network 2 the dmsp to dms conversion processes within the ice interior and 3 the physiological response of the ice algae first order flux estimates show that decaying summer level first year sea ice alone can significantly contribute to the regional sulfur budget of the weddell sea with an estimated average loss rate of 5 7 mol dms p m 2 d 1 toward the atmosphere and the ocean copyright 2010 by the american geophysical union

the influence of the antarctic peninsula on the wind field over the western weddell sea the antarctic peninsula is a formidable barrier to the easterly flow of stable air over the weddell sea the damming up of cold stable air against the peninsula mountains creates a pressure field which provides the necessary dynamic support for strong mountain parallel winds often observed along the east side numerical experiments using a two dimensional x z primitive equation model incorporating a cross section of the terrain of the antarctic peninsula are carried out in attempt to simulate the principle features of these barrier winds implications of the wind field are discussed

twentieth century sea ice variability in the weddell sea and its effect on moisture transport evidence from a coastal east antarctic ice core record high resolution study of deuterium excess d excess sea salt sodium ss na and methane sulfonic acid msa in an ice core from coastal dronning maud land cdml east antarctica revealed the

consistent past half century trends in the atmosphere the sea ice and the ocean at high southern latitudes simulations performed with the climate model loveclim aided with a simple data assimilation technique that forces a close matching of simulated and observed surface temperature variations are able to reasonably reproduce the observed changes in the lower atmosphere sea ice and ocean during the second half of the twentieth century although the simulated ice area slightly increases over the period 1980 2000 in agreement with observations it decreases by 0 5 106 km2 between early 1960s and early 1980s no direct and reliable sea ice observations are available to firmly confirm this simulated decrease but it is consistent with the data used to constrain model evolution as well as with additional independent data in both the atmosphere and the ocean the simulated reduction of the ice area between the early 1960s and early 1980s is similar to the one simulated over that period as a response to the increase in greenhouse gas concentrations in the atmosphere while the increase in ice area over the last decades of the twentieth century is likely due to changes in atmospheric circulation however the exact contribution of external forcing and internal variability in the recent changes cannot be precisely estimated from our results our simulations also reproduce the observed oceanic subsurface warming north of the continental shelf of the ross sea and the salinity decrease on the ross sea continental shelf parts of those changes are likely related to the response of the system to the external forcing modifications in the wind pattern influencing the ice production melting rates also play a role in the simulated surface salinity decrease

tropical pacific influence on the source and transport of marine aerosols to west antarctica abstractthe climate of west antarctica is strongly influenced by remote forcing from the tropical pacific for example recent surface warming over west antarctica reflects atmospheric circulation changes over the amundsen sea driven by an atmospheric rossby wave response to tropical sea surface temperature sst anomalies here it is demonstrated that tropical pacific sst anomalies also influence the source and transport of marine derived aerosols to the west antarctic ice sheet using records from four firn cores collected along the amundsen coast of west antarctica the relationship between sea ice modulated chemical species and large scale atmospheric variability in the tropical pacific from 1979 to 2010 is investigated significant correlations are found between marine biogenic aerosols and sea salts and sst and sea level pressure in the tropical pacific in particular la nina like conditions generate an atmospheric rossby wave response that influences atmospheric circulation over pine island bay

modeled methanesulfonic acid msa deposition in antarctica and its relationship to sea ice 1 methanesulfonic acid msa has previously been measured in ice cores in antarctica as a proxy for sea ice extent and southern hemisphere circulation in a series of chemical transport model geos chem sensitivity experiments we identify mechanisms that control the msa concentrations recorded in ice cores sea ice is linked to msa via dimethylsulfide dms which is produced biologically in the surface ocean and known to be particularly concentrated in the sea ice zone given existing ocean surface dms concentration data sets the model does not demonstrate a strong relationship between sea ice and msa deposition in antarctica the variability of dms emissions associated with sea ice extent is small 11 30 due to the small interannual variability of sea ice extent wind plays a role in the variability in dms emissions but its contribution relative to that of sea ice is strongly dependent on the assumed dms concentrations in the sea ice zone atmospheric sulfur emitted as dms from the sea ice undergoes net transport northward our model runs suggest that dms emissions from the sea ice zone may account for 26 62 of msa deposition at the antarctic coast and 36 95 in inland antarctica though our results are sensitive to model assumptions it is clear that an improved understanding of both dms concentrations and emissions from the sea ice zone are required to better assess the impact of sea ice variability on msa deposition to antarctica

coupled oscillations in antarctic sea ice and atmosphere in the south pacific sector interannual oscillations with period of about 3 6 years have dominated the winter atmospheric and ice variability in the ross amundsen and bellingshausen seas antarctica during 1979 1998 anomalies in sea ice concentration and drift propagate eastward in the winter ice pack coupled to sea level pressure anomalies this signal accounts for the ice and atmospheric components of the antarctic circumpolar wave during its eastward passage through the pacific sector of antarctica sea ice concentration anomalies at the ice margin seem to result from air ice sea interactions which involve both the dynamic effect of the anomalous wind driven ice motion and the thermodynamic ice growth and melting due to surface air and ocean temperature anomalies

antarctic sea ice extent during the holocene reconstructed from inland ice core evidence 1 interannual fluctuations in the antarctic sea ice extent sie affect the global albedo and heat balance and they may affect global co2 levels we found that the annual trend of sodium ion fluxes in the snowpack in the dome fuji region of east antarctica can serve as a proxy for the present day sie in the southern indian ocean and weddell sea sectors we then used sodium ion profiles obtained from the dome fuji ice core to reconstruct the sie during the holocene we observed that 1 the beginnings of both the climatic optimum 12 0 ka bp and neoglaciation 5 4 ka bp in the southern ocean indicated by siliceous microfossil records are consistent with decreases 11 8 ka bp and increases 5 4 ka bp in the sodium ion fluxes in the dome fuji ice core and 2 the interannual fluctuation in the sie during some periods of the neoglaciation was greater than the interannual fluctuation during the climatic optimum

shelf facies microbiotas from the odjick and rocknest formations epworth group 1 89 ga northwestern canada moderately well preserved microfossils are reported from two formations of the epworth group in the wopmay orogen an assemblage in a stromatolitic unit in the uppermost part of the odjick formation contains the microfossils huroniospora spp gunflintia sp and frutexites sp this assemblage which is remarkable for its preservation in a carbonate matrix is similar to one found in a stromatolitic chert facies in the gunflint iron formation of ontario taxa in four members of the overlying rocknest formation are preserved in cherty dolomites of inner shelf shallowing upward cycles capped by small digitate stromatolites these assemblages comprise the spheroidal taxa huroniospora spp melasmatosphaera magna sphaerophycus sp and palaeoanacystis sp the filamentous taxa archaeotrichion sp eomycetopsis sp siphonophycus sp brevitrichoides sp biocatenoides incrustata gunflintia sp and archaeonema sp the acritarch eomicrhystridium sp and rare specimens of two unidentified and problematic taxa

influence of large scale teleconnection patterns on methane sulfonate ice core records in dronning maud land records of methane sulfonate ms in ice cores from the high plateau of dronningmaud land dml antarctica drilled in the framework of the european project for icecoring in antarctica are investigated for their potential as an environmental andclimate archive for the atlantic sector of the southern ocean despite postdepositionalchanges years of extraordinary ms concentrations can be clearly detected in the icecore records we use composite anomaly maps of atmospheric parameters from thenational centers for environmental prediction national center for atmospheric researchreanalysis fields for years of extreme ms concentration to detect atmospheric patternscausing ms variability changing atmospheric transport is shown to be an important but not exclusive parameter being conserved in the ms record in dml the oftenhypothesized direct link between high ms concentrations and el nino events is notsupported for the observed region whereas the antarctic dipole adp which ismodulated by el nino southern oscillation conditions exerts significant influence aclear 13 9 year cycle can be found throughout a 2000 year ms record that can be relatedto variations in the adp over the last 300 years a 4 6 year cycle is revealed in thems and sea salt record which vanishes in the deeper part of the ice core as aconsequence of diffusion processes from the long term perspective periods of high msconcentrations are connected to on average higher sea salt aerosol as well reflecting aseasonally independent influence of transport on both species a distinctive period ofefficient atmospheric transport probably due to a pronounced adp could be foundfrom 1200 to 1600 a d

amplitude variations of 1470 year climate oscillations during the last 100 000 years linked to fluctuations of continental ice mass we describe amplitude variations of a 1470 year y signal in the oxygen isotope record from the gisp2 ice core as a function of continental ice mass as recorded in sea level variations the 1470 y signal is closely tied to dansgaard oeschger interstadial events which perturbed the climate system on a global scale large amplitude 1470 y oscillations occur only if continental ice mass exceeds a threshold level equivalent to sea level at approximately 45 m and are tied to times of change in ice mass minima of the 1470 y signal in the greenland ice are associated with short time intervals of relatively stable phases of sea level and with reduced climate variability in the entire periodicity range between approximately 550 5000 y

sea level pressure variability in the amundsen sea region inferred from a west antarctic glaciochemical record using european center for medium range weather forecasts ecmwf numerical operational analyses sea ice extent records and station pressure data we investigate the influence of sea level pressure variability in the amundsen sea region on a west antarctic siple dome glaciochemical record empirical orthogonal function analysis of the high resolution siple dome multivariate ice core chemical time series record sdeof1 documents lower tropospheric transport of sea salt aerosols to the site during 1985 1994 the sdeof1 record of high low aerosol transport corresponds to anomalously low high sea level pressure slp in the amundsen sea region spatial correlation patterns between ecmwf monthly slp fields and the annual sdeof1 record suggest that a majority of sea salt aerosol is transported to siple dome during spring september october and november analysis of zonal and meridional wind fields supports the slp sdeof1 correlation and suggests the sdeof1 record is sensitive to changes in regional circulation strength no relationship is found between sea ice extent and the sdeof1 record for the period 1973 1994 to investigate the sdeof1 record prior to ecmwf coverage a spring transpolar index stpi is created using normalized slp records from the new zealand and south america antarctic peninsula sectors and is significantly correlated at least 95 c l with the sdeof1 record on an annual r 5 0 32 p 0 001 and interannual 3 years r 5 0 51 p 0 001 basis dominant periodicities 3 3 and 7 1 years in the annual sdeof1 record 1890 1994 a d suggest that a portion of the recorded interannual variability may be related tropical extratropical enso teleconnections changes in the periodic structure of the full 850 1994 a d siple dome record suggests a shift in slp forcing during the little ice age 1400 1900 a d interval

the role of diffusion during carbonate diagenesis abstract the dissolution reprecipitation process which characterizes the early mineralogical stabilization of carbonate sediments takes place in a somewhat open chemical system studies of the trace element chemistries and isotopic compositions of carbonate grains before and after stabilization have documented the exchange of ions between the diagenetic site and the aquifer solution if the pores at reaction zone and in the immediate neighborhood of the diagenetic site are of insufficient diameter to allow effective solution flow the exchange of ions between the diagenetic site and the aquifer solution the large volume of water which flows through the macropores of the carbonate sediment takes place by aqueous diffusion this paper examines diffusion applied specifically to the conditions of carbonate diagenesis the diffusion equation modified to these circumstances serves as a guide to understanding the diffusion process at a given temperature three variables determine the efficacy of diffusion the diffusion coefficient the pore path and geometry and the concentration gradient the diffusion coefficient may be considered a measure of the inherent velocity at which a given ion travels under standard conditions the double positive cations common in carbonates ca2 sr2 ba2 zn2 mg2 etc and the carbonate anion all have similar diffusion coefficients thus this term of the equation exerts little influence during normal carbo ate diagenesis the pore path and geometry refer to the distance from aquifer to reaction zone and the diameter shape and directness of the pore passage this term is difficult to quantify in diagenetic systems but is constant for different ions at a single diagenetic site the longer and the more complex the path the less effective diffusion is there is a general facies dependence to this term grainstones have short paths from reaction zone to aquifer due to their permeability whereas mudstones and wackestones are characterized by long and torturous paths through the mud grains to the aquifer solution exchange of ions in the fast situation is more effective than in the second the concentration gradient the difference between the concentration of an ion in th reaction zone and in the proximal aquifer solution is the most variable parameter in diffusion the sign of the gradient which may be positive or negative indicates the direction of diffusion transport of the ions toward the region of lower concentration one cation may diffuse from the reaction zone while simultaneously a second cation diffuses toward the reaction zone this two way traffic has been documented in diagenetic calcite corals sr2 diffuses away from and mg2 diffuses toward the diagenetic site additionally one cation may diffuse effectively whereas a second diffuses ineffectively the latter species being characterized by a weaker concentration gradient thus a given diagenetic site may be chemically open for one cation and simultaneously somewhat closed for another application of diffusion principles to the aragonite calcite transformation during early diagenesis indicates the compositions of solutions and diagenetic calcites undergo temporal changes early on with few active diagenetic sites sr2 diffuses effectively from the reaction zone to the aquifer since there is a steep concentration gradient diagenetic calcites are relatively low in sr2 because of its effective removal from the diagenetic site as the number of active diagenetic sites increases so much sr2 may be delivered to the aquifer that sr2 builds up in the aquifer solution and the concentration gradient shallows diffusion from individual sites becomes less effective sr2 concentrates in the reaction zone and diagene ic calcites enriched in sr2 are produced as more and more aragonite is consumed a final phase is reached in which less total sr2 is delivered to the aquifer and the system returns to the conditions characteristic of the early phase

an ice core record of antarctic sea ice extent in the southern indian ocean for the past 300 years the differing response of ice extent in the arctic and antarctic to global average temperature change over approximately the last three decades highlights the importance of reconstructing long term sea ice history here using high resolution ice core records of methanesulfonate ms from the east antarctic ice sheet in princess elizabeth land we reconstruct southern indian ocean sea ice extent sie for the sector 62 92 e for the period ad 1708 2000 annual ms concentration positively correlates in this sector with satellite derived sie for the period 1979 2000 r 2 0 25 p 0 02 the 293 year ms record of proxy sie shows multi decadal variations with large decreases occurring in two warm intervals during the little ice age and during the 1940s it is very likely that the global temperature is the controlling factor of antarctic sea ice variation at the centennial scale although there has been a change in phase between them in recent decades