last abundant appearance datum of hemidiscus karstenii driven by climate change abstract the last abundant appearance datum of the endemic southern ocean diatom hemisdiscus karstenii jouse is dated at around 190 000 years before present which provides a robust and convenient biostratigraphic marker to late pleistocene paleoceanographic studies however no prior studies have sought to understand what processes may have driven h karstenii to extinction we here present the first morphometric investigation of h karstenii over marine isotope stage mis 10 to 6 355 000 years to 150 000 years the combination of these data to records of h karstenii absolute abundances fragilariopsis kerguelensis biometry and absolute abundances and southern high latitude air and ocean temperatures over the past 355 000 years suggests that h karstenii populations reduced their mean size and productivity in response to the rapid drop in temperatures across the mis 7 to mis 6 glacial inception this prolonged cooling event may have pushed h karstenii to its adaptive limit until it could not sustain physiological viability the repetitive occurrence of very cold events during the early mis 6 may have additionally prevented surviving populations of h karstenii from re establishing abundant communities leading to extinction late in mis 6

silicic acid dynamics in the glacial sub antarctic implications for the silicic acid leakage hypothesis 1 the silicic acid leakage hypothesis salh purports that changes in silicon and nitrogen depletion ratios in the glacial antarctic created a large pool of unused silicic acid that was transported to lower latitudes in subantarctic mode water samw where it enhanced diatom productivity lowering atmospheric pco2 however increased opal accumulation beneath the sub antarctic during glacial times implies significant consumption of silicic acid in subantarctic surface waters that may have significantly diminished or eliminated si leakage to test how nutrient dynamics in the sub antarctic affected the si oh 4 content of samw during the last glacial period we produced 30si opal records for cores from the subantarctic and subtropical zones of the indian ocean spanning the last 50 000 years comparison with diatom bound 15n records shows that subantarctic surface waters were enriched in si relative to n during the last glaciation consistent with the salh the record from the subtropics does not show this enrichment in si during the last glacial period suggesting that subantarctic surface waters were mainly incorporated into samw rather than being transported across the subtropical front isotope mass balance calculations were used to test for si leakage from the sub antarctic the results show that silicic acid concentration in samw would more than double during the last glaciation if upwelling and northward ekman drift in the antarctic were similar to the present day circulation calculations that assume increased stratification in the glacial antarctic eliminate si leakage but they do not produce the known increase in opal burial in the glacial sub antarctic reconciling the isotope data and opal burial records with a highly stratified antarctic requires the addition of a large local source of silicic acid in the glacial sub antarctic that is inconsistent with present day circulation and nutrient distributions including such a source in our calculations results in significant opal burial in the sub antarctic but it does not enhance si leakage over that occurring in the holocene resolving past changes in the circulation of the southern ocean is clearly vital to future tests of the salh

glacial valve size variation of the southern ocean diatom fragilariopsis kerguelensis preserved in the benguela upwelling system southeastern atlantic abstract the valve size variations of the southern ocean so diatom fragilariopsis kerguelensis from the sediments of antarctic polar front and subantarctic front were shown to be strongly correlated with iron availability at the glacial interglacial timescale however recent evidence from the subtropical region of the so has suggested sea surface temperature to be a key controlling factor by mediating silica uptake other than the iron availability we present here the first record of f kerguelensis size variation in core geob3606 1 collected in the benguela upwelling system bus se atlantic 25 28 s 13 05 e where f kerguelensis valves were preserved during the glacial period 68 30 ka as a consequence of silicic acid leakage from polar to mid latitudes our study presents the first record of diatom morphology variations of f kerguelensis from a mid latitude core location to test the previous hypotheses proposed for so our results demonstrate that f kerguelensis valves at geob3606 1 were almost half of the mean size of specimens compared to the so downcore records further f kerguelensis valves were smaller and more abundant during early marine isotope stage mis 3 and conversely larger and less abundant during mis4 and late mis3 however such patterns are not supported by the linear regression analyses suggesting that iron availability could have mediated the size changes of f kerguelensis rather than the species productivity during 68 30 ka these findings agree with the recently gained knowledge on the life cycle patterns of f kerguelensis related to reproduction strategies cell size range and formation of initial cells

concentrations of reduced sulphur in inclusion fluids associated with black shale hosted quartz vein gold deposits implications for mechanisms of transport and deposition of gold and a possible exploration tool abstract analyses of reduced s and other inclusion volatiles in vein quartz from the black shale hosted clogau st davids au deposit n wales show that a relation exists between elevated inclusion s content and au grade this relation is better at discriminating between high and low grade vein material than criteria based on the other inclusion volatiles analyses of material from a similar but subeconomic vein system yields a small number of samples with an auriferous signature on the basis of either s 2 content or co 2 ch 4 ratio but application of both criteria would reject all samples the concentration of reduced s species in metamorphic fluids thought to have transported au suggests that au hs 2 was the dominant au complex thermodynamic calculations indicate that up to 8 mg au kg h 2 o may have been transported in this manner gold precipitation in the ore body resulted from destabilisation of the au hs 2 complex probably either through reduction by the black shales or as a result of flashing of h 2 s into the ch 4 rich phase which was generated during the mineralising event

origin of lode gold deposits of the juneau gold belt southeastern alaska mesothermal gold bearing quartz veins along the juneau gold belt formed in the early tertiary from h 2 o co 2 n 2 h 2 s ch 4 rich low salinity fluids at temperatures of 200 to 325 c and pressures in excess of 1 1 5 kbar isotopically heavy ore forming fluids with 18 o values between 8 and 12 and d values of 20 to 30 indicate a deep seated fluid source the data are compatible with a model of ore fluid generation via metamorphic devolatilization within material subducted below the southern alaska continental margin prograde metamorphic fluids infiltrated up zones of mechanically enhanced permeability associated with the coast range megalineament and formed the gold bearing veins within brittle units at higher retrograding crustal levels deposition of gold was accomplished by several mechanisms including boiling fluid wall rock reactions and decreases in pressure and temperature of the hydrothermal fluids

synthetic fluid inclusions vii re equilibration of fluid inclusions in quartz during laboratory simulated metamorphic burial and uplift p t conditions inferred from fluid inclusions in metamorphic rocks often disagree with the values predicted from mineral equilibria calculations these observations suggest that inclusions formed during early stages of regional metamorphism continue to re equilibrate during burial and subsequent uplift in response to differential pressure p t conditions accompanying burial and uplift were experimentally simulated by initially forming pure h2o inclusions in quartz at elevated temperatures and pressures and then re equilibrating the inclusions in the presence of a 20 wt nacl solution such that final confining pressures ranged from 5 kbar above to 4 kbar below the initial internal pressure of the inclusions at the temperature of re equilibration in all samples re equilibrated at confining pressures below the internal pressure some inclusions were formed that had compositions of 20 wt nacl and densities in accord with the final p t conditions additionally some inclusions were observed to contain fluids of intermediate salinities between 0 and 20 wt nacl densities of these inclusions were also consistent with formation at the re equilibration p t conditions the remainder of the fluid inclusions observed in these samples contained pure h2o and their homogenization temperatures corresponded to densities intermediate between the initial and final p t conditions in short term experiments 7 days where the initial internal overpressure exceeded 1 kbar no inclusions were found that contained the original density and none were found to have totally re equilibrated instead most h2o inclusions re equilibrated until their internal pressures were between 750 and 1500 bars above the confining pressure regardless of the initial pressure differential in a long term experiment 52 days inclusions re equilibrated at a lower confining pressure than the initial internal pressure displayed homogenization temperatures corresponding to a range in final internal pressures between 0 kbar i e total re equilibration and 1 2 kbar above the confining pressure in experiments where the confining pressure during re equilibration exceeded the initial internal pressure densities of pure h2o inclusions increased to values intermediate between the initial and final p t conditions additionally these inclusions were generally surrounded by a three dimensional halo of smaller inclusions also of intermediate density resulting in a texture similar to that previously ascribed to decrepitation from internal overpressure in extreme cases where confining pressures were 4 5 kbar above the initial pressure the parent inclusion almost completely closed leaving only the three dimensional array of small 5 m inclusions the outline of which may be several times the volume of the original inclusion groups of such inclusions closely resemble textures commonly observed in medium to high grade metamorphic rocks inclusions containing 10 and 42 wt nacl solutions trapped at 600 c and 3 kbar were re equilibrated at 600 c and 1 kbar for 5 days in dry argon to evaluate the importance of h2o diffusion as a mechanism of lowering the inclusion bulk density salinities of re equilibrated inclusions obtained from freezing point depressions and halite dissolution temperatures indicate that original compositions were preserved density changes similar to those previously described were noted in these experiments in inclusions showing no visible microfractures therefore density variations observed in inclusions in this study re equilibrated under rapid deformation conditions are considered to result from a change in the inclusion volume without significant loss of contents by diffusion or leakage

the si cycle in the pacific sector of the southern ocean seasonal diatom production in the surface layer and export to the deep sea abstract dissolved silicic acid si oh 4 and biogenic silica bsio 2 concentrations were measured on four different cruises in the southern ocean along 170 w from late october 1997 to mid march 1998 these data were used to construct a vertically integrated si budget in the surface layer from 58 to 68 s throughout that period there was a distinct southward moving meridional si oh 4 gradient with concentrations increasing to the south in october the gradient was centered on the antarctic polar front apf at 61 s surface layer si oh 4 increased from 10 to 40 mmol m 3 between 58 and 62 s while bsio 2 concentrations were 3 and 2 throughout the study area as the surface mixed layer stratified and shoaled in december diatoms bloomed in response to the more favorable light conditions consuming si oh 4 in the process by late december bsio 2 concentrations were exceptionally high for the open ocean with maximum integrated values of 700 mmol si m 2 around 62 s while vertically integrated si oh 4 in the upper 50 m had dropped from 2500 to 870 mmol m 2 an average decrease of 30 mmol si m 3 the diatom bloom persisted into january with maximum integrated bsio 2 of 600 mmol m 2 between 64 and 65 s while si oh 4 was depleted to 3 in surface waters as far south as 64 5 s the center of the si oh 4 gradient had moved southward to 65 s by late january coincident with maximal diatom biomass at that time the bloom ended by march with the disappearance of most of the diatom biomass from the surface layer deeper mixed layers and increased si oh 4 by late january diatom production had removed 70 of the of si oh 4 initially present in the upper 50 m everywhere north of 65 s and had displaced the si oh 4 gradient 400 km southward while the apf remained stationary between november and late january 80 days an average of 2200 mmol si m 2 had been removed from the upper 50 m between 61 and 65 s based on changes in vertically integrated si oh 4 and bsio 2 concentrations between november and march an average of 2 mol si m 2 was exported from the upper 50 m between 61 and 65 s with 59 of that export occurring between late december and late january the observed seasonal export is very high in comparison with other oceans and the high export coincides spatially with a well documented zone of high opal flux to 1000 m and high opal content in modern sediments north of 61 s bsio 2 export was limited by the low initial standing stock of si oh 4 in surface waters and south of 65 s export was likely limited by the shorter growing season thus the combined effect of a large initial supply of si oh 4 in surface waters and conditions that permit efficient use of that si by diatoms appears to be the primary cause of opal rich sediment accumulation in the pacific sector of the southern ocean

a record of pleistocene diatom preservation from the amundsen sea west antarctica with possible implications on silica leakage article i nfo accumulation of fossil diatoms in marine sediments is variably affected by the production and dissolution of diatom frustules across space and time no quantitative proxy exists for estimating the amount of silica lost to dissolution in southern ocean sediment cores to address this gap cultured valves of fragilariopsis kerguelensis the dominant planktonic diatom in the pleistocene to recent southern ocean were dissolved progressively under controlled laboratory conditions expansion and eventual conjoining of the areolae of f kerguelensis advances through several phases which are presented herein as a measure of diatom dissolution in order to evaluate the validity of laboratory methods this proxy is applied to sediments from piston core ps58 254 from the amundsen sea dissolution induced degradation morphologies from laboratory experiments are seen to be identical to those preserved naturally in sediments thus suggesting the laboratory conditions accurately reflect the natural process of dissolution these resultsrepresentthe firstapplication of afullyquantitativeproxyfordiatomdissolution tosouthernocean sediments revealing that meaningful paleoceanographic data can be generated via taphonomic analysis of diatom valves intensity of diatom dissolution in core ps58 254 does not correspond to the relative abundance of any diatom species clay mineralogy or linear sedimentation rates however a correlation does exist between glacial cyclicity and diatom dissolution indicating that variation in average wall thickness and susceptibility to dissolution reflects primary conditions during formation of the silica wall transit through the water column and eventual deposition higher overall silica dissolution is observed during each glacial period and enhanced silica preservation during interglacials this result is consistent with the predictions of the silicic acid leakage hypothesis salh whereby reduced rates of si usage in the southern ocean lead to shifts in marine primary productivity in the tropics from coccolithophoriddominance duringinterglacialstodiatomdominanceduringglacials thiswouldfuela decrease in atmospheric pco2duringglacials silica acidleakage isdrivenbya decreaseinthe si nratioofdiatoms caused by increased iron input to glacial aged southern ocean waters this resulted in more lightly silicified diatom valves in the southern ocean which dissolved more quickly in the upper water column thereby maintaining the high silica content of glacial aged so waters and allowing for export of si to upwelling zones in the lower latitudes

nutrient cycling in the indian sector of the southern ocean over the last 50 000 years most high southern latitude records of carbon and nitrogen isotopic ratios and elemental ratios are from the antarctic and polar front zones thus hindering a comprehensive view of nutrient cycling in the southern ocean we present for the first time two records from the subantarctic zone and the southern subtropical zone of the indian ocean these records provide a latitudinal transect covering the main oceanographic systems of the southern ocean carbon and nitrogen content of the diatom bound organic matter increases during the last glacial in the antarctic and subantarctic zones but does not show a clear climate related signal in the subtropical zone comparison of these records with sea surface temperatures reconstructed at the core locations and record of dust deposition over antarctica suggests that eolian iron input possibly switched diatom physiology toward higher carbon to silica and nitrogen to silica uptake and storage south of the subantarctic front due to the dependency of photosynthesis on iron concentration levels conversely the northernmost core was too remote from any iron source over the last 50 000 years antarctic diatoms therefore have the sole potential to change the nutrient content of the waters escaping from the southern ocean hence providing partial support to the silicic leakage hypothesis as a potential cause of lower glacial atmospheric co 2

tank study of physico chemical controls on gas content and composition during growth of young sea ice during an ice tank experiment samples were taken to study the processes of acquisition and alteration of the gas properties in young first year sea ice during a complete growth warming cooling cycle the goal was to obtain reference levels for total gas content and concentrations of atmospheric gases o2 n2 co2 in the absence of significant biological activity the range of total gas content values obtained 3 5 to 18 ml of gas per kilo of ice was similar to previous measurements or estimates however major differences occurred between the current and quiet basins showing the role of water dynamics at the ice water interface in controlling bubble nucleation processes extremely high co2 concentrations were observed in all the experiments up to 57 in volume parts it is argued that these could have resulted from two unexpected biases in the experimental settings concentrations of bubbles nucleated at the interface are controlled by diffusion both from the ice water interface towards the well mixed reservoir and between the interface water and the bubble itself this double kinetic effect results in a transition of the gas composition in the bubbles from values close to solubility in sea water towards values close to atmospheric as the ice cover builds up

evolution of metamorphic fluids at the variscan fold and thrust belt in eastern belgium abstract quartz veins in the southern greenschist facies metamorphic border of the stavelot venn massif belgium have been examined a detailed petrographical study of these quartz veins indicates the presence of eleven quartz stages a microthermometric analysis shows the expulsion of three main fluid types during the palaeozoic in the first quartz stage i of caledonian age mixed aqueous gaseous h 2 o co 2 nacl fluid inclusions are present the post caledonian and pre variscan second stage ii is characterised by gaseous co 2 n 2 inclusions occurring along inter crystal grain boundaries and by aqueous h 2 o nacl intra crystal inclusions the quartz stages iii vi which formed during the variscan period contain primary mixed aqueous gaseous h 2 o co 2 nacl inclusions all with an equal bulk chemical composition post variscan quartz stages vii xi could not be investigated microthermometrically the combination of microthermometry chlorite geothermometry and geothermal gradients reveals minimum trapping conditions of 200 mpa and 200 c for stage i quartz and 175 275 mpa and 385 435 c for quartz stages iii vi the trapping conditions of stage ii quartz could not be determined due to the strong recrystallisation of the quartz veins at the lower metamorphic variscan thrust front distinct temperature anomalies are associated with thrust faults as indicated by conodont colour alteration index cai vitrinite reflectance data chlorite geothermometry and fluid inclusion microthermometry the expulsion of metamorphic fluids generated at the southern part of the stavelot venn massif could have caused the distinct temperature anomalies along variscan thrust faults alternatively some of these anomalies could have been induced by deeply circulating meteoric fluids

southern ocean sea ice and frontal changes during the late quaternary and their linkages to asian summer monsoon abstract the present study documents the interactions between southern hemisphere high latitude antarctica southern ocean southern indian ocean subtropics agulhas leakage and asian summer monsoon the study uses sst and sea ice reconstructions along with diatom absolute abundances and diatom biometry from two sediment cores located at the subantarctic front saf and antarctic polar front apf in the southwest indian sector of the southern ocean sea ice records suggest the presence of the mean winter sea ice limit at around the modern apf location during mis 2 and mis 4 and episodic and unconsolidated winter sea ice far north as 43 s during lgm when the ssts were lowest higher diatom productivity and larger mean sizes of f kerguelensis and t lentiginosa recorded at the northern core site during the glacial stages suggest a northward shift of the apf a decrease in diatom productivity and sizes at the southern core site highlights stratified permanent open ocean zone pooz surface waters in response to longer sea ice presence during the glacial stages the comparative study between the records of southern hemisphere high latitude and asian summer monsoon climate variability revealed that the asian summer monsoon variability could have been more likely forced by low latitude insolation gradient changes and supported by antarctic climate changes via meridional shifts of the fronts and sea ice the past changes in the intensity of asian summer monsoon along with the southern ocean frontal variation might have influenced the southern indian ocean surface circulation by changing the agulhas leakage intensity

fluid immiscibility in late alpine gold bearing veins eastern and northwestern european alps gold bearing quartz veins fill late alpine brittle structures in pennine nappes of austria in the tauern window and in northern italy the veins formed in the latter stages of uplift of the alps fluid inclusions in veins sampled from bockstein austria and valle anzasca italy have a wide variety of compositions ranging from aqueous brine about 5 wt nacl equiv to about 50 mol co2 at room temperature the inclusions range with increasing co2 content from two phase aqueous through three phase in which the co2 homogenizes to vapour to three phase with co2 homogenizing to liquid this wide range of inclusion compositions is interpreted as evidence for fluid immiscibility with most inclusions being accidental mixtures of the two end member immiscible fluids the homogenization temperatures of the aqueous inclusions 200 280 c gives the best estimate of temperature of formation of the veins vein formation fluid pressure at bockstein and valle anzasca was about 1 kbar and bockstein veins formed at lower pressure than valle anzasca veins fluid immiscibility may have contributed to deposition of gold at both valle anzasca and bockstein and possibly many other uplift related alpine gold localities

abrupt cooling of antarctic surface waters and sea ice expansion in the south atlantic sector of the southern ocean at 5000 cal yr b p antarctic surface waters were warm and ice free between 10 000 and 5000 cal yr b p as judged from ice rafted debris and microfossils in a piston core at 53 s in the south atlantic this evidence shows that about 5000 cal yr b p sea surface temperatures cooled sea ice advanced and the delivery of ice rafted detritus ird to the subantarctic south atlantic increased abruptly these changes mark the end of the hypsithermal and onset of neoglacial conditions they coincide with an early neoglacial advance of mountain glaciers in south america and new zealand between 5400 and 4900 cal yr b p rapid middle holocene climate changes inferred from the taylor dome ice core antarctica cooling and increased ird in the north atlantic and the end of the african humid period the near synchrony and abruptness of all these climate changes suggest links among the tropics and both poles that involved nonlinear response to gradual changes in northern hemisphere insolation sea ice expansion in the southern ocean may have provided positive feedback that hastened the end of the hypsithermal and african humid periods in the middle holocene

diatom distribution and paleoceanographic reconstruction in the southern ocean present and last glacial maximum abstract diatom assemblage and preservational data are used to reconstruct paleoceanographic conditions at the last glacial maximum 18 000 yrs bp in the southern ocean from these data the following points can be made about the last glacial maximum in this region 1 contraction and slight northern shift of the belt of well preserved diatoms appears to be related to the northward shift of late spring early summer sea ice cover 2 presence of open ocean though poorly preserved diatom assemblages to the south of this belt strongly suggest that during many summers large areas of the southern ocean were ice free 3 the distribution of thenitzschia kerguelensis factor both in surface sediments and at the last glacial maximum indicates that the gyre systems particularly the weddell gyre were intensified during glacial times 4 although data are sparse in the higher latitude south atlantic there is an indication that the weddell polynya also existed during glacial times although it was shifted a few degrees northward

the fall dump a new perspective on the role of a shade flora in the annual cycle of diatom production and export flux investigations of diatom fluxes recorded in laminated sediments using scanning electron microscope techniques together with evidence from sediment trap studies have contributed to a reappraisal of the annual cycle of diatom production and export flux we propose that where there is a strong seasonal thermocline and nutricline a number of diatoms hitherto regarded as typical sparse summer flora characteristic of oligotrophic waters are able to generate substantial production at depth these species including rhizosolenia spp stephanopyxis palmeriana thalassiothrix spp and some coscinodiscus spp may represent a shade flora that have adapted to grow in low light conditions and or to regulate their buoyancy to move between a deep nutrient source and the euphotic zone although rates of growth and primary production are substantially lower than species characteristic of spring bloom or upwelling conditions the total primary production integrated over the several month period of summer stratification may be as significant as the spring bloom or greater the term fall or autumn bloom as a counterpart of the spring bloom is therefore a misnomer whereas the spring bloom involves a rapid burst of reproduction and sedimentation the fall dump is the sedimentation of a long lived episode of production lasting the duration of the seasonal thermocline and triggered by the fall winter mixing that breaks down stratification the fall dump may produce as much or in some cases more export production than the spring bloom the results of this study suggest that a reorientation of thinking on diatom ecology and palaeoecology may be required

timing of mineralization and source of fluids in a slate belt auriferous vein system hill end goldfield nsw australia evidence from 40ar39ar dating and o and h isotopes abstract 40 ar 39 ar dating of metamorphic biotite and alteration muscovite from the auriferous veins and host rocks at the hill end goldfield n s w australia has distinguished four major geological events including the timing of gold mineralization the earliest hydrothermal event occurred during the middle devonian tabberabberan orogeny 370 380 ma and resulted in the formation of quartz veins barren of au a second and major episode of vein emplacement occurred in the early carboniferous during the principal phase of metamorphism and deformation at 359 363 ma this was followed by au accumulation in two stages 1 after the major phases of quartz deposition and 2 during and after the development of conspicuous internal vein laminations 357 ma and 343 ma respectively two sources of fluid are proposed for vein and ore formation the first is a local metamorphic fluid characterized by 18 o h 2 o values of 8 9 to 12 5 per mil and d h 2 o values of 87 to 90 per mil the second is a mixed ore fluid with 18 o and d values in the range of 18 o h 2 o 8 4 to 11 per mil and d h 2 o of 49 to 36 per mil progressive entry of this second fluid sourced from trough fill or deeper crustal rocks is linked closely to cycles of gold precipitation at hill end

morphometric variability in the diatom fragilariopsis kerguelensis implications for southern ocean paleoceanography abstract diatoms play a central role in the ecosystem of the southern ocean where they represent the main producers and carriers of organic carbon and dissolved silicon towards the deep ocean variability in space and time of the size of the most abundant species fragilariopsis kerguelensis may directly impact the way this ecosystem functions and also affect the nutrient balance of the global ocean as important water masses e g the antarctic intermediate water get their nutrient signature in this area we used a biometric approach and analyzed the size variability of f kerguelensis valves in sixty four surface sediment samples from the southern ocean in sediment trap samples from a mooring site pf3 at the antarctic polar front apf and along a nearby piston core ps1654 2 the average length and valve area of f kerguelensis displayed a distinct increase in the proximity of the apf and lower values to the north and south of it and also changed markedly over seasonal cycles as diatom blooms and nutrient availability waxe and wane the last glacial to interglacial transition also witnesses important changes in the general shape and valve size of f kerguelensis with specimens from glacial intervals being ca 30 larger than their interglacial counterparts 195 versus 150 m 2 valve area a sharp peak in average area and a very specific valve morphology correspond to the first signs of deglaciation and concurring sst sea surface temperature increase and sea ice retreat the latter together with melting icebergs may have contributed dissolved iron to surface waters the highest average sizes during glacial intervals are higher than what found anywhere in the southern ocean today the newly proposed proxy valve area and shape of f kerguelensis may thus prove useful for the reconstruction of the past position and nutrient characteristics of the apf and opal belt a region characterized by high production and export of biogenic silica in a particularly sensitive and dynamic area such as the southern ocean

fluid evolution in a slate belt gold deposit a fluid inclusion study of the hill end goldfield nsw australia auriferous quartz veins in the hill end goldfield nsw australia comprise bedding parallel vein sets and minor extension and fault controlled veins which are hosted by a multiply deformed late silurian slate metagreywacke turbidite sequence fluid inclusions in quartz either from bedding parallel veins or from narrow steeply n dipping veins leader veins indicate a similar range in homogenisation temperatures th from 350 c to 110 c within this range th data demonstrate five groupings in the temperature intervals 350 280 c 280 250 c 250 190 c 190 150 c and 150 110 c corresponding to a variety of primary and secondary inclusions developed during five periods of vein growth under a generally declining temperature regime inclusion fluids are characterised by a low salinity of around 0 1 to 3 6 wt nacl equivalent laser raman microprobe inclusion analysis indicates that gas phase compositions relate to the paragenetic stage of the host quartz h2o g and n2 dominate in the primary inclusions from barren stage i quartz ch4 and ch4 h2o g are important in inclusions related to the early gold forming events equivalent to stages ii and iii quartz but inclusions developed during the last episode of gold deposition are characterised by h2o g co2 rich and liquid co2 bearing fluids precipitation of gold was aided by sulphidation reactions or phase separation in response to periods of vein opening late in the paragenesis gold deposition may have been promoted by oxidation of the ore fluid

late quaternary sea ice history in the indian sector of the southern ocean as recorded by diatom assemblages abstract a modern analog technique mat5201 31 has been applied to fossil diatom assemblages to provide down core estimates of february sea surface temperatures ssts and of sea ice duration over the past 220 000 years at 56 40 s 160 14 e at the core location sea ice progression lagged the sst drop by 1 ka at interglacial glacial transitions and sea ice retreat was almost synchronous to the sst increase at glacial interglacial terminations sea ice increased continuously during glacial periods to reach its maximum extent at the end of glacial times although ssts were almost constant during glacials this indicates that ssts are the major parameter determining the advance and retreat of sea ice at transitions but that the sea ice advance during glacial conditions may be related to positive feedbacks of the ice on albedo air temperature and meridional wind stress the strong correlation r 0 75 between sea ice duration at the core location and the vostok co2 record argues for a control of antarctic sea ice extent on atmospheric co2 concentration via the modification of the ocean to atmosphere gas balance

natural iron fertilization of the atlantic sector of the southern ocean by continental shelf sources of the antarctic peninsula in large parts of the southern ocean primary production is limited due to shortage of iron fe we measured vertical fe profiles in the western weddell sea weddell scotia confluence and antarctic circumpolar current acc showing that fe is derived from benthic fe diffusion and sediment resuspension in areas characterized by high turbulence due to rugged bottom topography our data together with literature data reveal an exponential decrease of dissolved fe dfe concentrations with increasing distance from the continental shelves of the antarctic peninsula and the western weddell sea this decrease can be observed 3500 km eastward of the antarctic peninsula area downstream the acc we estimated dfe summer fluxes into the upper mixed layer of the atlantic sector of the southern ocean and found that horizontal advection dominates dfe supply representing 54 15 of the total flux with significant vertical advection second most important at 29 13 horizontal and vertical diffusion are weak with 1 2 and 1 1 respectively the atmospheric contribution is insignificant close to the antarctic continent but increases to 15 10 in the remotest waters 1500 km offshore of the acc translating southern ocean carbon fixation by primary producers into biogenic fe fixation shows a twofold excess of new dfe input close to the antarctic continent and a one third shortage in the open ocean fe recycling with an estimated fe ratio of 0 59 is the likely pathway to balance new dfe supply and fe fixation

climate evolution at the last deglaciation the role of the southern ocean abstract two sediment sequences recovered close to and south of the present polar front 50 53 s in the atlantic sector of the southern ocean were analysed in order to evaluate the environmental evolution of the southern ocean surface over the last deglaciation and the holocene our reconstruction is based on radiocarbon dated records of diatom based sea surface temperature and sea ice proxies and planktic foraminiferal stable isotopes the onset of the deglacial warming and gradual southward retreat of the winter sea ice field between 18 and 17 cal kyr bp occurrence of a thermal reversal centered at ca 13 cal kyr bp antarctic cold reversal or acr and early holocene occurrence of the climatic optimum well correlate with climatic reconstructions available from the indian southern ocean and from antarctic ice cores time correspondence of southern ocean warming and heinrich event 1 in the north atlantic is compatible with the transmission of the climate signal from the northern to the southern hemisphere through the bipolar seesaw our data support modeling results suggesting that the northern hemisphere bolling warming and turn on of the north atlantic deep water formation are triggered by gradual warming and sea ice retreat in the southern ocean meltwater shedding into the southern ocean associated with the acr may maintain northern hemisphere warming during the allerod the development of sea surface warming and sea ice retreat is compatible with a southern ocean control on the atmospheric co2 increase during the deglaciation during the early holocene 9 7 cal kyr bp our southern core records renewed surface ocean cooling and northward readvance of the winter sea ice field such early holocene cooling is common to cores from the high latitude atlantic sector and might be brought about by expansion of the weddell gyre circulation at that time

holocene productivity changes off adelie land east antarctica 1 this study presents the first high resolution multiproxy investigation of primary productivity pp during the holocene from the antarctic continental margins micropaleontological and geochemical data from the sediment core md03 2601 associated to sea ice model outputs give unprecedented insights into the biological pump of the antarctic coastal area off adelie land in response to climatic changes plurimillennial and millennial changes of pp are observed in the study area in response to changes in nutrient availability stratification and growing season duration which are linked to sea ice upwelling wind and glacier dynamics the precessional cycle seems to be responsible in the pp long term variations while forcing factors involved at the millennial timescale remain more enigmatic our results emphasize enhanced biological pump during warmer and windier holocene phases because of a longer growing season and greater nutrient input antarctic coastal and continental shelf zones may therefore represent a more intense carbon sink in the future

diatom distribution in southern ocean surface sediments atlantic sector implications for paleoenvironmental reconstructions abstract a study of 230 surface sediment samples collected in the atlantic sector of the southern ocean between the southernmost weddell sea and the subtropical zone documents the modern distribution of diatoms revealing patterns of paleoenvironmental significance estimations of diatom valves per gram dry sediment display numbers of 50 200 106 in the zone of high opal burial located between the mean position of the winter sea ice edge and the polar front and maximum values of greater than 200 106 in the near shore sedimentary basins off the antarctic peninsula lowest diatom concentrations and assemblages strongly affected by dissolution were encountered in the weddell basin despite alteration of the diatom assemblages prior to their incorporation into the sediment record the biogeographic distribution and the abundance pattern of most of the 35 studied diatom species shows a close relationship with the surface hydrography water temperature these relationships can be used to estimate past surface water temperatures based on statistical treatments of the assemblages or on simple relations of species occurrences in the geological record another close link occurs between the distribution of sea ice and sea ice related diatoms

fluid evolution during burial and variscan deformation in the lower devonian rocks of the high ardenne slate belt belgium sources and causes of high salinity and c o h n fluids fluid inclusions in quartz veins of the high ardenne slate belt have preserved remnants of prograde and retrograde metamorphic fluids these fluids were examined by petrography microthermometry and raman analysis to define the chemical and spatial evolution of the fluids that circulated through the metamorphic area of the high ardenne slate belt the earliest fluid type was a mixed aqueous gaseous fluid h2o nacl co2 ch4 n2 occurring in growth zones and as isolated fluid inclusions in both the epizonal and anchizonal part of the metamorphic area in the central part of the metamorphic area epizone in addition to this mixed aqueous gaseous fluid primary and isolated fluid inclusions are also filled with a purely gaseous fluid co2 n2 ch4 during the variscan orogeny the chemical composition of gaseous fluids circulating through the lower devonian rocks in the epizonal part of the slate belt evolved from an earlier co2 ch4 n2 composition to a later composition enriched in n2 finally a late variscan aqueous fluid system with a h2o nacl composition migrated through the lower devonian rocks this latest type of fluid can be observed in and outside the epizonal metamorphic part of the high ardenne slate belt the chemical composition of the fluids throughout the metamorphic area shows a direct correlation with the metamorphic grade of the host rock in general the proportion of non polar species i e co2 ch4 n2 with respect to water and the proportion of non polar species other than co2 increase with increasing metamorphic grade within the slate belt in addition to this spatial evolution of the fluids the temporal evolution of the gaseous fluids is indicative for a gradual maturation due to metamorphism in the central part of the basin in addition to the maturity of the metamorphic fluids the salinity of the aqueous fluids also shows a link with the metamorphic grade of the host rock for the earliest and latest fluid inclusions in the anchizonal part of the high ardenne slate belt the salinity varies respectively between 0 and 3 5 eq wt nacl and between 0 and 2 7 eq wt nacl while in the epizonal part the salinity varies between 0 6 and 17 eq wt nacl and between 3 and 10 6 eq wt for the earliest and latest aqueous fluid inclusions respectively although high salinity fluids are often attributed to the original sedimentary setting the increasing salinity of the fluids that circulated through the lower devonian rocks in the high ardenne slate belt can be directly attributed to regional metamorphism more specifically the salinity of the primary fluid inclusions is related to hydrolysis reactions of cl bearing minerals during prograde metamorphism while the salinity of the secondary fluid inclusions is rather related to hydration reactions during retrograde metamorphism the temporal and spatial distribution of the fluids in the high ardenne slate belt are indicative for a closed fluid flow system present in the lower devonian rocks during burial and variscan deformation where fluids were in thermal and chemical equilibrium with the host rock such a closed fluid flow system is confirmed by stable isotope study of the veins and their adjacent host rock for which uniform 180 values of both the veins and their host rock demonstrate a rock buffered fluid flow system

the biogeography of major diatom taxa in southern ocean sediments 2 open ocean related species diatoms from 228 southern ocean core top sediment samples were examined to determine the geographic distributions of 32 major diatom species taxa preserved in the sediments of three zonally distinct regions sea ice open ocean and the tropical subtropical in the first of three papers 14 species taxa occurring in the region where sea ice covers the ocean surface on an annual basis are geographically documented comparisons are drawn between the diatom abundances on the sea floor sea ice parameters annual duration and concentration in february and september and february sea surface temperature such parameters are commonly used in reconstructing past oceanographic conditions in the sea ice and open ocean zones analysis of the geographic patterns and sea surface parameter correlations reveals species specific distributions regulated primarily by sea ice coverage and sea surface temperature which support the use of diatom remains for the estimation of these past seasurface environmental parameters comparison with reliable accounts of the 14 species from the sediments or plankton also provides the first glimpses into species specific ecology and habitat linkages d 2005 elsevier b v all rights reserved

production of giant marine diatoms and their export at oceanic frontal zones implications for si and c flux from stratified oceans from a synthesis of recent oceanic observations and paleo data it is evident that certain species of giant diatoms including rhizosolenia spp thalassiothrix spp and ethmodiscus rex may become concentrated at oceanic frontal zones and subsequently form episodes of mass flux to the sediment within the nutrient bearing waters advecting towards frontal boundaries these species are generally not dominant but they appear selectively segregated at fronts and thus may dominate the export flux ancient thalassiothrix diatom mat deposits in the eastern equatorial pacific and beneath the polar front in the southern ocean record the highest open ocean sedimentation rates ever documented and represent vast sinks of silica and carbon several of the species involved are adapted to a stratified water column and may thrive in deep chlorophyll maxima thus in oceanic regions and or at times prone to enhanced surface water stratification e g during meltwater pulses they provide a mechanism for generating substantial biomass at depth and its subsequent export with concomitant implications for si export and c drawdown this ecology has important implications for ocean biogeochemical models suggesting that more than one diatom functional type should be used in spite of the importance of these giant diatoms for biogeochemical cycling their large size coupled with the constraints of conventional oceanographic survey schemes and techniques means that they are undersampled an improved insight into these key species will be an important prerequisite for enhancing our understanding of marine biogeochemical cycling and for assessing the impacts of climate change on ocean export production

shrimp s isotope evidence for fluid mixing during gold mineralization in a slate belt gold deposit hill end new south wales australia abstract sensitive high resolution ion microprobe shrimp sulfur isotope data show that pyrrhotite pyrite galena and chalcopyrite in syntectonic auriferous quartz veins at the hill end goldfield are characterized by two populations with 34sfluid values of 7 and 0 these two populations are accounted for by fluid mixing involving two sources of sulfur during evolution of the vein systems a local sulfur source and reduced fluids derived from trough fill siluro devonian sedimentary and volcano sedimentary sequences are responsible for the first two gold bearing events whereas a more oxidized fluid and a sulfur source from turbidites and volcanics in deeper parts of the crustal sequences appear responsible for gold deposition late in the second gold forming event and are the dominant influences in the final gold forming stage for fine grained mixtures where mineral separation is difficult the shrimp analyses are particularly useful for tracing detailed 34s variations of sulfides precipitated in different paragenetic stages

southern ocean laminated diatom ooze mat deposits and potential for palaeo flux studies odp leg 177 site 1093 laminated diatom ooze samples collected during odp leg 177 were analysed using scanning electron microscope sem and optical microscopy to test their potential as high resolution records of polar front hydrography surface production and export sem analysis from two intervals marine isotope stage mis 29 and 12 11 respectively recovered from 50 s in the atlantic ocean odp site 1093 hole a sections 13h 4 0 18 cm and 23h 4 0 22 cm show abundant and well preserved thalassiothrix antarctica mats thought to be indicative of rapid export from the surface and deposition in the sediment a preliminary analysis of laminae succession points to a possible annual couplet triplet succession of laminae and suggests exceptionally high local sedimentation rates of 57 and 80 cm kyr 1 for mis 12 11 and 29 respectively such high accumulation rates imply that local export from the surface layer and sequestration of biogenic silica and organic matter to the sediments may have been much higher than previously suggested resume des depot sedimentaires lamines de diatomites recueillis pendant le leg 177 de l ocean drilling program odp ont ete analyses en microscopie electronique a balayage sem et en microscopie optique ces enregistrements sedimentaires presentent un fort potentiel pour reconstituer avec une haute resolution la production de matiere exportee depuis la couche de surface de l ocean au niveau du front polaire l analyse en sem des stades isotopiques 29 et 12 11 sur du materiel collecte a 50 s dans le secteur atlantique de l ocean austral site odp 1093 forage a sections 13h 4 0 18 cm et 23h 0 22 cm revele des depots abondants et bien preserves de tapis de thalassiothrix antarctica suggerant une exportation rapide jusqu au sediment de materiel biogene genere a la surface de l ocean une analyse preliminaire des successions laminees par couple ou triplet indique des vitesses d accumulation sedimentaire exceptionnellement elevees 57 et 80 cm kan 1 respectivement pour les stades 12 11 et 29 de telles vitesses d accumulation suggerent que l exportation de matiere depuis la couche de surface de l ocean et ou la preservation de silice biogene dans le sediment peuvent etre bien plus elevees qu on ne le pensait jusqu a present

melting history of antarctica during the past 60 000 years marked changes in the surface water hydrology of the southern ocean during the past 60 kyr are revealed by a detailed comparison of the oxygen isotopic composition of planktonic and benthic foraminifera from sediment cores and the surface water temperature estimated by a transfer function derived from the distribution of diatoms in the same sediments from 35 to 17 kyr bp the southern ocean polar front was covered by a melt water lid containing a significant contribution from melting icebergs calved from antarctic ice shelves these icebergs may have originated from a succession of surges of the ice shelves

changes in micronutrient supply to the surface southern ocean atlantic sector across the glacial termination major deepwater masses upwell and reach the surface in the southern ocean forming an important conduit supplying nutrients and micronutrients to the surface and playing a key role in the regulation of global climate through ocean atmosphere gas exchange here we reconstruct changes in micronutrient distribution in this region in response to past changes in upwelling oceanic mixing and sea ice seasonality we present two downcore zn si opal records from the scotia sea and drake passage region which we interpret in the context of micronutrient distribution in the atlantic sector of the southern ocean over the last glacial termination previous work shows that micronutrient availability in the surface waters in the south atlantic appear to be controlled dominantly by upwelling and mixing of micronutrient rich deepwaters which are additionally fuelled by the terrestrial sediment sources of the scotia arc and south georgia this is supported by our reconstructions which show micronutrient availability to the west of the scotia arc and south georgia are consistently lower than to the east over the last glacial termination due to downstream transport and mixing into surface waters of continentally derived material in the antarctic circumpolar current micronutrient availability in this region was at a minimum from 20 to 25 ky bp coinciding with maximum sea ice coverage and increased due to an expansion of the seasonal sea ice zone and increased mixing of subsurface waters our findings are consistent with largely diminished upwelling of micronutrients during the maximum glacial extent and reduced mixing due to the presence of persistent sea ice during the deglacial there was an increase in micronutrient availability as well as other nutrients and inorganic carbon within the antarctic circumpolar current as a result of an increase in deep oceanic upwelling mixing and strengthened zonal transport

wall rock alteration and metamorphism of a volcanogenic massive sulfide deposit at que river tasmania petrology and mineralogy the rocks in the alteration halo surrounding the polymetallic massive sulfide deposit at que river preserve primary hydrothermal mineral textures and assemblages despite the imprint of later prehnite pumpellyite facies regional metamorphism their textural preservation is attributed to the mechanical strength of many of the hydrothermal minerals such as pyrite carbonates except calcite and quartz the competency of some of the host rocks and the low strain that has affected many rocks at the margin of the halo assemblages include quartz white mica carbonates albitized plagioclase pyrite and chlorite closer to the ore as intensity of alteration increases albite disappears pyrite apatite rutile and anatase become more common white mica quartz carbonates and chlorite vary in abundance and are distributed irregularly these minerals also occur in hydrothermal veins throughout the stockwork zone several generations of veins are commonly developed with each generation having its own distinctive hydrothermal assemblage both hydrothermal and metamorphic phases are compositionally variable despite some overlap there appear to be systematic differences in composition x ray diffraction and microprobe analyses show that the hydrothermal white micas are variable in composition ranging from illites or muscovites to fuchsites their metamorphic counterparts contain less pyrophyllite and more celadonite the hydrothermal carbonates are most commonly ferroan dolomite magnesian siderite and ferroan magnesite the latter two are more abundant than dolomite where alteration is intense calcite and ferroan dolomite formed during metamorphism and the composition of the hydrothermal and metamorphic carbonates may be different in individual specimens both hydrothermal and metamorphic chlorites are ferro clinochlores and magnesio chamosites metamorphic chlorites outside the halo are more fe rich and more al vi deficient than those within the hydrothermal chlorites exhibit fe mg and al iv al vi si iv mg fe vi tschermakite substitutions and contain al iv contents suggesting temperatures of crystallization of 290 degrees to 320 degrees c similar to the temperature of 280 degrees c inferred from fluid inclusions the chemistry of the hydrothermal phases varies throughout the halo overall fe and mg do not show a systematic trend toward mineralization however fe enrichment of hydrothermal phases in the ore is apparent as is mg enrichment of locally developed chlorite carbonate rocks na and celadonite in white micas and ca in carbonates on the other hand decrease with increasing alteration mg only became an important component in the fluid when seawater infiltrated into the hydrothermal system the heterogeneous distribution of the hydrothermal phases is attributed to successive influxes of hydrothermal fluids of varying composition into the alteration pipe variable water rock ratios and seawater entrainment

millennial scale instability of the antarctic ice sheet during the last glaciation records of ice rafted detritus ird concentration in deep sea cores from the southeast atlantic ocean reveal millennial scale pulses of ird delivery between 20 000 and 74 000 years ago prominent ird layers correlate across the polar frontal zone suggesting episodes of antarctic ice sheet instability carbon isotopes 13 c of benthic foraminifers a proxy of deepwater circulation reveal that south atlantic ird events coincided with strong increases in north atlantic deep water nadw production and inferred warming interstadials in the high latitude north atlantic sea level rise or increased nadw production associated with strong interstadials may have resulted in destabilization of grounded ice shelves and possible surging in the weddell sea region of west antarctica

climate mediated size variability of diatom fragilariopsis kerguelensis in the southern ocean abstract fragilariopsis kerguelensis o meara hustedt is the most abundant open ocean diatom species in southern ocean sediments and its average valve area has recently been used to infer glacial interglacial paleoceanographic conditions studies from the atlantic sector of the southern ocean demonstrated how larger average valve area of f kerguelensis during the last glacial compared to the interglacial possibly relate to greater availability of iron through wider sea ice coverage and higher eolian dust input we present here data on average valve area of f kerguelensis from three sediment cores covering the last 42 cal ka bp from different zones of the southern ocean our records confirm previous results from the atlantic sector but highlight a different pattern from the indian sector where the largest valves of f kerguelensis are encountered during the holocene fragilariopsis kerguelensis average valve area variations in the antarctic polar front apf of the atlantic sector and subantarctic front of the indian sector are in phase with records of opal burial while this correlation does not hold for the apf of the indian sector variations in circum polar upwelling were suggested as the main controlling factor of opal production during the last 20 000 years we here hypothesize that high nutrient input from the antarctic peninsula during the last deglaciation may have exerted a stronger control on f kerguelensis average valve area and opal export in the atlantic sector of the southern ocean than inferred changes in circum polar upwelling

origin and significance of ice rafted detritus in the atlantic sector of the southern ocean piston core tn057 14 from the eastern atlantic sector of the southern ocean contains several layers rich in volcanic tephra that were deposited during the last glacial period comparison with nearby cores tn057 13pc4 odp site 1094 indicates that these tephra layers are correlative with the south atlantic sa ice rafted detritus ird layers identified by kanfoush et al 2000 2002 we analyzed the tephra for major and trace elements as well as isotopic ratios of strontium neodymium and lead the elemental and isotopic composition of all tephra layers examined indicates the south sandwich island volcanic arc ssi as their dominant source with minor input from bouvet island similar analyses of clear mineral grains mainly feldspars quartz and olivine also point to the ssi as the main source we conclude that tephra erupted from the ssi was first deposited as air fall on sea ice and multiyear ice and then secondarily rafted to the studied sites deposition of the tephra rich ird layers was controlled by changes in sea surface temperature and sea ice conditions in the polar frontal zone of the south atlantic rather than antarctic ice sheet dynamics

dust sources and deposition during the last glacial maximum and current climate a comparison of model results with paleodata from ice cores and marine sediments mineral dust aerosols in the atmosphere have the potential to affect the global climate by influencing the radiative balance of the atmosphere and the supply of micronutrients to the ocean ice and marine sediment cores indicate that dust deposition from the atmosphere was at some locations 2 20 times greater during glacial periods raising the possibility that mineral aerosols might have contributed to climate change on glacial interglacial time scales to address this question we have used linked terrestrial biosphere dust source and atmospheric transport models to simulate the dust cycle in the atmosphere for current and last glacial maximum lgm climates we obtain a 2 5 fold higher dust loading in the entire atmosphere and a twenty fold higher loading in high latitudes in lgm relative to present comparisons to a compilation of atmospheric dust deposition flux estimates for lgm and present in marine sediment and ice cores show that the simulated flux ratios are broadly in agreement with observations differences suggest where further improvements in the simple dust model could be made the simulated increase in high latitude dustiness depends on the expansion of unvegetated areas especially in the high latitudes and in central asia caused by a combination of increased aridity and low atmospheric co2 the existence of these dust source areas at the lgm is supported by pollen data and loess distribution in the northern continents these results point to a role for vegetation feedbacks including climate effects and physiological effects of low co2 in modulating the atmospheric distribution of dust

sea ice seasonality during the holocene adelie land east antarctica abstract thin sections of laminated cores from different antarctic coastal areas have demonstrated the potential of diatom species to document climate change at the seasonal scale here we present the relative abundances of four diatom species and species groups fragilariopsis curta group as a proxy for yearly sea ice cover f kerguelensis as a proxy for summer sea surface temperature chaetoceros hyalochaete resting spores as a proxy for spring sea ice melting and the thalassiosira antarctica group as a proxy for autumn sea ice formation in core md03 2601 retrieved off adelie land on the antarctic continental shelf these abundances were compared to surface temperatures and sea ice cover modelled over the last 9000 years both the marine records and the simulated climate demonstrated a cooler early holocene 9000 7700 years bp a warmer mid holocene 7700 4000 years bp and a colder late holocene 4000 1000 years bp yearly sea ice cover followed an inverse pattern to temperatures with less sea ice during the mid holocene hypsithermal than during the late holocene neoglacial however diatom census counts and model output indicate that sea ice spring melting happened earlier in the season as expected but that autumn sea ice formation also occurred earlier in the season during the hypsithermal than during the colder neoglacial thereby following seasonal changes in local insolation

late quaternary changes in biogenic opal fluxes in the southern indian ocean abstract late quaternary sedimentary and paleoenvironmental conditions in the southern indian ocean have been reconstructed from radioisotope and proxy element profiles biogenic opal and organic carbon measured on five sediment cores taken along a transect across the indian sector of the antarctic circumpolar current dissolution corrected opal rain rates were used to reconstruct past changes of opal productivity for this region records from these five cores indicate that opal productivity during glacial periods was lower than presently recorded south of the antarctic polar front apf probably due to increased ice cover north of apf opal productivity was slightly greater during glacial periods than during the holocene probably in response to 1 the northward migration of the apf by approximately 5 latitude 2 a northward transport of si from the antarctic zone and 3 an increase of fe necessary for opal producing organisms via upwelling and the erosion of the kerguelen plateau we also invoke a decoupling between opal burial and organic carbon flux to the seabed to explain the variation in buried si c ratio between glacial and interglacial sediment this decoupling is principally explained by better organic carbon preservation in the glacial sediments due to strong sediment focussing an increase in glacial export paleoproductivity is not supported by the data implying that bioproductivity variations in the southern indian ocean are unlikely to have contributed to the glacial drawdown of atmospheric co 2 inferred from ice core data

holocene long and short term climate changes off adelie land east antarctica diatom data from a marine sediment core give insight on holocene changes in sea surface conditions and climate at high southern latitudes off adelie land east antarctica the early to mid holocene was warmer than the late holocene with a transition at 4000 calendar years b p sea ice was less present and spring summer growing season was greater during the warm period relative to the cold one thus limiting sea ice diatom production and favoring more open ocean diatom to develop the long term holocene climatic evolution in east antarctica is explained by a combination of a delayed response to local seasonal insolation changes coupled to the long memory of the southern ocean abrupt variations of the diatom relative abundances indicating rapid climate changes are superimposed to the holocene long term trends spectral analyses calculate robust frequencies at 1600 a where a is years 1250 a 1050 a 570 a 310 a 230 a 150 125 a 110 a 90 a and 66 a such periods are very close to solar activity cyclicities except for the periods at 310 a and 1250 a which are close to internal climate variability cyclicities wavelet analyses estimate the same periods but indicate nonstationary cyclicities rapid climate changes at high southern latitudes may therefore be explained by a combination of external solar and internal thermohaline circulation forcings

a switch from si oh 4 to no 3 depletion in the glacial southern ocean 1 phytoplankton in the antarctic deplete silicic acid si oh 4 to a far greater extent than they do nitrate no3 this pattern can be reversed by the addition of iron which dramatically lowers diatom si oh 4 no3 uptake ratios higher iron supply during glacial times would thus drive the antarctic towards no3 depletion with excess si oh 4 remaining in surface waters new 30si and 15n records from antarctic sediments confirm diminished si oh 4 use and enhanced no3 depletion during the last three glaciations the present low si oh 4 water is transported northward to at least the subtropics we postulate that the glacial high si oh 4 water similarly may have been transported to the subtropics and beyond this input of si oh 4 may have caused diatoms to displace coccolithophores at low latitudes weakening the carbonate pump and increasing the depth of organic matter remineralization these effects may have lowered glacial atmospheric pco2 by as much as 60 ppm

an empirical phase diagram for a part of the n2co2 system at low temperature abstract microthermometric and chemical raman analysis data for 23 inclusions from triassic dolomites and evaporites northern tunisia are used to generate a t x section of the n2 co2 binary system most observed features including some metastable homogenizations are consistent with a simple topology well known in many binary and notably in the co2 ch4 system

summer plankton production and nutrient consumption patterns in the mertz glacier region of east antarctica abstract we report on a biological and nutrient survey conducted off the eastern adelie and george v coasts of east antarctica in late december 2000 and january 2001 the region was dominated by the mertz glacier tongue mgt and its associated polynya that controlled the amount of open water through the season and influenced stratification near forming and melting ice as in other regions of the southern ocean large concentrations of nitrate phosphate and silicic acid were found chlorophyll levels varied from 0 3 mg m 3 in pack ice and slope regions to greater than 10 mg m 3 in a phaeocystis bloom encountered among grounded ice northeast of the mgt net utilization rates of nutrients were derived from the deficit between measured concentrations and estimated winter values nitrate n n and silicic acid utilization rates ranged from 2 to 12 and 14 to 30 mmol m 2 d 1 respectively and were greatest in commonwealth bay the ratio of nitrate to phosphate utilization was low 10 lower silicic acid to n n ratios were found in regions with substantial populations of phaeocystis sp in the eastern grounded ice region however there was significant variation in the silicic acid to n n utilization that may be induced by mixed layer iron levels that varied from

sequence of events during the last deglaciation in southern ocean sediments and antarctic ice cores variation depends on the age model as 14 c determinations cannot be obtained for the time interval of 29 5 14 5 ka assuming a constant sedimentation rate for this interval our data suggest that sea ice and nutrient changes at about 19 ka b p lead the increase in atmospheric pco2 by approximately 2000 years our diatom based sea ice record is in phase with the sodium record of the vostok ice core which is related to sea ice cover and similarly leads the increase in atmospheric co2 if gas exchange played a major role in determining glacial to interglacial co2 variations then a delay mechanism of a few thousand years is needed to explain the observed sequence of events otherwise the main cause of atmospheric pco2 change must be sought elsewhere rather than in the southern ocean index terms 3344 meteorology and atmospheric dynamics paleoclimatology 4267 oceanography general paleoceanography 4845 oceanography biological and chemical nutrients and nutrient cycling 4870 oceanography biological and chemical stable isotopes 9325 information related to geographic region atlantic ocean keywords biogenic opal stable isotopes diatoms ird last glacial southern ocean

geochemistry of fluid inclusions from the mcintyre hollinger gold deposit timmins ontario canada type 1 h 2 o co 2 type 2 h 2 o co 2 type 3 ch 4 co 2 h 2 o and type 4 ch 4 fluid inclusions type 1 type 3 and some type 2 inclusions are primary or pseudosecondary in origin whereas type 4 and most type 2 inclusions are secondary the primary or pseudosecondary type 1 and 2 inclusions homogenized at temperatures of 220 degrees to 385 degrees c secondary type 2 inclusions homogenized at 160 degrees to 215 degrees c crushing tests confirm the presence of co 2 in samples with type 1 and 2 inclusions visually estimated x co2 values in type 1 inclusions range from 3 to 24 mole percent with bulk molar volumes of 19 to 28 cm 3 mole mineralizing fluids were at equilibrium with graphite at temperatures of 380 degrees to 480 degrees c and pressures of 1 to 3 kb calculated oxygen fugacities lie near the quartz fayalite magnetite buffer the mineralizing fluids differ compositionally from fluids in other types of ore deposits but resemble fluids derived from metamorphic rocks and deep level felsic intrusions modified journal abstract

ore forming fluids in archean gold bearing quartz veins at the sigma mine abitibi greenstone belt quebec canada archean gold bearing quartz veins at the sigma mine occur in deformed metavolcanics intruded by two generations of preore porphyries the veins were emplaced during a late compressional tectonic event and they consist primarily of quartz tourmaline carbonates pyrite and scheelite vein minerals have been deformed and are also cut by abundant healed fractures outlined by fluid inclusions in the veins gold typically occurs in late fractures and in recrystallized quartz microthermometric sem eda leachate analysis and gas chromatographic techniques were used to study fluid inclusions in quartz most fluid inclusions at sigma occur in late fractures and are secondary the fluid inclusions are commonly found in fractures parallel to or less commonly within gold bearing fractures and are genetically related to the gold three types of fluid inclusions are identified 1 high salinity na ca cl aqueous inclusions 25 34 wt salt with small amounts of co 2 some containing halite calcite and nahcolite as daughter minerals 2 co 2 rich inclusions containing small amounts of h 2 o and ch 4 and 3 low salinity h 2 o co 2 inclusions 10 equiv wt nacl with co 2 contents which are variable but commonly in the range of 15 to 30 mole percent co 2 leachate analyses show that in addition to na and ca the aqueous fluids contain minor amounts of k fe mg and li homogenization temperatures of h 2 o co 2 inclusions with constant phase ratios range from 285 degrees to 395 degrees c those of aqueous inclusions range from 60 degrees to 295 degrees c the aqueous and co 2 rich inclusions are interpreted to have trapped two coexisting fluids resulting from the unmixing of a homogeneous h 2 o co 2 parent fluid itself occasionally trapped in late fractures the ore bearing fluid is interpreted to be a low salinity 10 equiv wt nacl fluid containing 15 to 30 mole percent co 2 at minimum temperatures in the range of 285 degrees to 395 degrees c the relatively low homogenization temperatures of aqueous inclusions are interpreted to be the result of co 2 effervescence from a co 2 saturated aqueous fluid due to pressure fluctuations at the time of entrapment it is also proposed that the onset of gold deposition is related to the onset of fluid unmixing

extensive phytoplankton blooms in the atlantic sector of the glacial southern ocean 1 the sources and sinks of atmospheric carbon dioxide over glacial interglacial cycles are under debate variation in productivity of the antarctic circumpolar current acc could potentially play a significant role but current interpretations of sedimentary geochemical proxies suggest that glacial productivity was not higher than today we present areal and down core distribution patterns of previously overlooked diatom resting spores that indicate the occurrence of extensive phytoplankton blooms across the entire atlantic sector of the acc particularly in the seasonal ice zone siz linked to higher iron input during the last glacial sea ice acts as an effective transporter of iron and enhances its bioavailability the dominance of the deep living radiolarian cyladophora davisiana in glacial siz sediments indicates that organic carbon export to mesopelagic depths was at least tenfold higher than today

fluid infiltration into fault zones chemical isotopic and mechanical effects fluid infiltration into fault zones and their deeper level counterparts brittle ductile shear zones is examined in diverse tectonic environments in the 2 7 ga abitibi greenstone belt major tectonic discontinuities with lateral extents of hundreds of kilometres initiated as listric normal faults accommodating rift extension and acted as sites for komatiite extrusion and locally intense metasomatism during reverse motion on the structures accommodating shortening of the belt these transcrustal faults were utilised as a conduit for the ascent of trondhjemitic magmas from the base of the crust and of alkaline magmas from the asthenosphere and for the discharge of thousands of cubic kilometres of hydrothermal fluids such fluids were characterised by 18o 6 2 d 50 20 13c 4 4 and temperatures of 270 to 450 c probably derived from devolatilisation of crustal rocks undergoing prograde metamorphism hydrothermal fluids were more radiogenic 87sr 86sr 0 7010 to 0 7040 and possessed higher than did contemporaneous mantle komatiites or tholeiites and thus carried a contribution from older sialic basement a provinciality of87sr 86sr and 13c is evident signifying that fault plumbing sampled lower crust which was heterogeneous at the scale of tens of kilometres mineralised faults possess enrichments of large ion lithophile lil lil elements including k rb ba cs b and co2 and rare elements such as au ag as sb se te bi and w fluids were characterised by xco2 0 1 neutral to slightly acidic ph low salinity 3 wt k na 0 1 they carried minor ch4 co and n2 and they underwent transient effervescence of co2 during decompression clastic sediments occupy graben developed at fault flexures the40ar 39ar release spectra indicate that fault rocks experienced episodic disturbance on time scales of hundreds of millions of years

phytoplankton biomass and photosynthetic competency in the summertime mertz glacier region of east antarctica abstract vertical profiles of water temperature salinity beam transmission density pressure wind speed wind direction phytoplankton biomass chlorophyll a chl a plus phaeophytin a and photosynthetic competency by fast repetition rate fluorometry are presented for the mertz glacier region east antarctica for a 3 week period during the austral summer 2000 2001 injection of low salinity water from the melting of the ice pack formed a shallow ca 25 m mixed layer offshore two distinct deep mixing features were observed associated to varying degrees with high chlorophyll levels and high photosynthetic competency along the adelie land coast a deep mixing layer 1400 m with chl a concentrations of 386 mg m 2 and elevated fv fm 0 5 was observed at the eastern end of the study area along a seaward extension of fast ice a bloom of phaeocystis antarctica bloom formed within a shallow 24 m mixed layer with surface chl a concentrations of ca 8 mg m 3 and elevated fv fm 0 5 this feature also had high surface salinity 34 and was contiguous with a deep mixing feature 236 m frrf parameters fv fm and psii were strongly suppressed in surface waters

glacial interglacial size variability in the diatom fragilariopsis kerguelensis possible iron dust controls 1 the valve area of fragilariopsis kerguelensis the most abundant diatom species in the southern ocean strongly changes in size in response to varying conditions in the surface ocean we examined the link both in two iron fertilization experiments and in sediment samples covering several glacial terminations between size variability in this species and environmental conditions across the antarctic polar front including sea ice extent sea surface temperature and the input of eolian dust the iron fertilization experiments show valve area to be positively correlated with iron concentrations in ambient waters which suggests the possibility of a causal relation between valve size of fragilariopsis kerguelensis and ambient surface water iron concentration larger valves are usually found during glacial times and thus seem to be related to lower sea surface temperature and wider sea ice coverage moreover our results indicate that there usually is a strong correlation between larger valve size and increased input of eolian dust to the southern ocean however this correlation obvious for the fertilization experiments and for glacial terminations i ii iii and v does not seem to be valid for termination vi where size appears to be inversely correlated to dust input citation cortese g r gersonde k maschner and p medley 2012 glacial interglacial size variability in the diatom fragilariopsis kerguelensis possible iron dust controls paleoceanography 27 pa1208 doi 10 1029 2011pa002187

fluid inclusion evidence for p v t x evolution of hydrothermal solutions in late alpine gold quartz veins at brusson val d ayas northwest italian alps

microfossil and stable isotope evidence for changes in late holocene palaeoproductivity and palaeoceanographic conditions in the prydz bay region of antarctica microfaunal and microfloral data from two gravity cores and stable isotope results from one of these cores taken on fram bank near prydz bay antarctica indicate changes in sea ice patterns and oceanographic conditions which may have been linked to regional and global climate changes that occurred over the past 8000 yr modern diatom assemblages indicative of ice free conditions 1 2 months of the year and dominated by nitzschia species became prevalent some time around 2000 2700 yr b p the occurrence of chaetoceros spp diatom spore dominated assemblages and increased abundances of benthic and planktonic foraminifera ostracods and diatoms coupled with carbon and oxygen isotope changes around 2700 3400 yr b p strongly suggests that this area of the shelf experienced conditions conducive to increased productivity during this time period based on diatom assemblage associations recognized in modern environments the upper water column of fram bank shelf waters was probably stratified during that time due to the presence of low salinity melt water and a very shallow mixed layer protected from storms with sea ice cover for less than 10 months per year the close correspondence of 13c and 18o values from n pachyderma r2 0 74 throughout one core suggests that whatever oceanographic conditions influenced 18o also influenced 13c changes in prydz bay microfossil abundances and isotopes may result from alterations in circulation patterns upwelling conditions or sea ice patterns which significantly affected benthic and planktonic productivity in the area the environmental conditions indicated by older sediments in the cores are less clear but an ice tongue may have been in place 3200 3800 yr b p and minor fluctuations in productivity are indicated around 6000 and 7000 7500 yr b p the lower 100 cm of both cores may not represent in situ deposition but if the corrected ams dates reflect the actual age of the sediments analyzed microfossil and isotope data indicate that productivity and oceanographic conditions were very variable around 8500 8600 yr b p the chronology adopted herein must be regarded as tentative until further study of the area has been undertaken

rb sr k ar and stable isotope evidence for the ages and sources of fluid components of gold bearing quartz veins in the northern sierra nevada foothills metamorphic belt california gold bearing quartz veins occur in and near major fault zones in deformed oceanic and island arc rocks west of the main outcrop of the sierra nevada composite batholith veins typically occupy minor reverse faults that crosscut blueschist to amphibolite grade metamorphic rocks whose metamorphic ages range from early paleozoic to jurassic vein micas and carbonate quartz mica assemblages that formed by hydrothermal metasomatism of ultramafic wall rocks in the alleghany grass valley washington and mother lode districts yield concordant k ar and rb sr ages the dated veins are significantly younger than prograde metamorphism penetrative deformation and accretion of their host rocks to the continental margin new and previously published mineralization ages from 13 localities in the sierra foothills range from about 140 to 110 m y ago with mean and median between 120 and 115 m y the age relations suggest that mineralizing fluids were set in motion by deep magmatic activity related to the resumption of east dipping subduction along the western margin of north america following the late jurassic nevadan collision event co 2 bearing fluids responsible for metasomatism and much of the vein mica carbonate albite and quartz deposition in several northern mines were isotopically heavy delta 18 o asymp 8 14ppm delta d between about 10 and 50ppm and do not resemble seawater magmatic or meteoric waters metasomatic and vein filling mica dolomite magnesite and quartz in altered ultramafic rocks generally formed from fluids with similar sr and o isotope ratios at a given locality consistent quartz mica delta 18 o fractionations delta 18 o sub q m 4 5 4 9ppm from various localities imply uniform equilibration temperatures probably between 300 degrees and 350 degrees c on a local mine scale fluids responsible for both carbonate alteration of mafic and ultramafic wall rocks and albitic alteration of felsic and pelitic rocks had similar sr isotope ratios samples from three veins in the central alleghany district fit a 115 7 or 3 m y rb sr isochron with a 87 sr 86 sr i value of approximately 0 7119 inferred 87 sr 86 sr ratios of metasomatic fluids from mines in different parts of the foothills region vary considerably 0 704 0 718 suggesting that sr was derived from sources ranging from western assemblage mesozoic ophiolitic or arc volcanic rocks to early paleozoic continent derived clastic rocks of the shoo fly complex systematic geographic variations in both sr and o isotopes can be rationalized by assuming extensive fluid interaction with rocks similar to the ones that are exposed within a few kilometers of the veins but the ultimate sources of the fluids and of au and other constituents may be independent of these isotopically lighter meteoric fluids deposited some late quartz overgrowths and occupied secondary fluid inclusions in earlier vein quartz