intra oceanic subduction related hydrothermal venting kermadec volcanic arc new zealand intra oceanic volcanic arcs mark the boundaries between converging lithospheric plates where subduction produces volcanic and tectonic activity that ensures a steady supply of magmatic heat and hydrothermal fluids to the seafloor here we report on the first broad and systematic survey of hydrothermal emissions generated along a submarine arc front more than half seven of 13 of the volcanoes surveyed along 260 km of the southern kermadec arc ne of new zealand are hydrothermally active our results indicate that volcanic arcs represent a previously unheeded but potentially extensive source of shallow 2 km water depth vent fields expelling fluids of a unique and heterogeneous composition into the oceans

new constraints on the 138la β decay constant based on a geochronological study of granites from the yilgarn block western australia abstract the decay constant of 138 la has been geochronologically determined using archean granites from the yilgarn block western australia rb sr and sm nd mineral isochron ages were obtained for the two granite samples which are nearly identical with the ion microprobe u pb zircon ages this agreement indicates that the closure date for these samples is the same within analytical error making them suitable for geochronological estimation of the decay constant for 138 la applying a new method of ce isotope analysis with analytical reproducibility of 0 008 la ce isotope data for the studied samples resulted in precise mineral isochrons based on these internal mineral isochrons and ages determined by other geological clocks the decay constant for 138 la was estimated to be 2 33 0 24 10 12 a 1 2

multi scale morphologic variability of the north fiji basin ridge southwest pacific abstract two cruises of the french japanese starmer joint project carried out with the submersibles nautile 1989 and shinkai 6500 1991 have been devoted to the in situ exploration of the north fiji basin ridge four areas located near 16 20 17 18 50 and 19 s have been explored during 42 dives at 16 20 s the axial zone trending n160 corresponds to a prominent graben with walls 1000 m high tectonic features and recent screes are present and the hydrothermal activity is characterized by sporadic fluid discharge at 17 s present accretion is confined to a high dome less than 1900 m deep and cut in its axial part by a wide graben trending n15 at this site hydrothermal features of two types are observed fossil chimneys of sulfides and active vents made of anhydrite and expelling water at 285 c the site at 18 50 s is located on top of an axial dome very similar to those of the east pacific rise small fissures and very fresh volcanic flows argue for a present day activity with weak evidence of tectonics hydrothermal emanations with animal colonies are found scattered over the whole area the fourth site at 19 s shows old and viscous lavas and a very mature tectonic activity compared to the preceding station which is located only 20 km northward large scale variations have been detected between three segments different thermal regimes can explain the distinct morphologies observed decakilometric scale variations do occur between stations 14 with volcanic predominance and 19 s where tectonic activity is dominating finally small scale variations are observed on sites 4 and 14 where volcanic features gradually give way to tectonic structures the north fiji basin ridge with an intermediate average spreading rate shows tectonic volcanic and hydrothermal variability ranging from 1 km to tens of kilometres and related to a temporary fine scale organisation of the accretionary processes

fluctuation of chemical compositions of the phase separated hydrothermal fluid from the north fiji basin ridge ishibashi j grimaud d nojiri y auzende j m and urabe t 1994 fluctuation of chemical compositions of the phase separated hydrothermal fluid from the north fiji basin ridge in j m auzende and t urabe editors north fiji basin starmer french japanese program mar geol 116 215 226 on the central ridge of the north fiji basin southwest pacific hydrothermal activities were located in 1989 it was the second discovery of the hydrothermal fluid undergo phase separation during a dive mission of slrinkai 6500 in 1991 we revisited the hydrothermal area and collected fluid samples from the same anhydrite chimney fluid composition of the end member shows no significant changes during this two years other fluid ventings 150 m apart show similar chemistry suggesting that the phase separation and segregation processes occur throughout the hydrothermal area small fluctuation in chemical composition of the fluids from two sites is attributed to subseafloor fluid rock interaction after the phase segregation

the north fiji basin basalts and their magma sources part ii sr nd isotopic and trace element constraints abstract sr nd isotope and trace element data are reported for basalts from the north fiji basin nfb nfb basalts are characterized by extreme variations in isotopic ratios and trace element abundances which are related to mantle heterogeneities values of 87 sr 86 sr for basalts from the northern segments n160 and triple junction range from 0 7029 to 0 7041 whereas 143 nd 144 nd values vary from 0 51281 to 0 51313 most of the basalts from these segments are characterized by strong relative enrichments in rb ba sr k nb ta la ce and ti that are comparable to oib components the central segments n15 and n s have 143 nd 144 nd ratios between 0 51298 and 0 51363 and 87 sr 86 sr ratios between 0 7029 and 0 7033 and are depleted in large ion lithophile light rare earth and high field strength elements similar to n morb covariation between trace element and isotopic ratios among nfb basalts supports a model in which melts from the nfb rift system are derived by mixing of oib type and depleted n morb mantle components the sr nd isotopic and trace element variability indicates that the nfb basalt source is heterogeneous on the scale of individual melt batches

multi stage growth and fluid evolution of a hydrothermal sulphide chimney in the east pacific ridge 1 2 s hydrothermal field constraints from in situ sulphur isotopesx meng and othersin situ sulphur isotopes of hydrothermal sulphides sulphur isotopes can be used as a powerful tool to trace fluid evolution and explore the formation of chimneys to clarify the in situ s isotopic variations of sulphides at the micro scale we analyzed a sulphide chimney collected from the hydrothermal field in the east pacific rise 1 2 s using a sensitive high mass resolution ion micro probe for stable isotopes shrimp si three mineral zones can be identified in the chimney an external outer wall of porous anhydrite and colloform pyrite an internal middle zone of sub euhedral pyrite and massive chalcopyrite and an inner zone of massive pyrite the 34 s v cdt values of the sulphides fall within the range 1 83 7 51 avg 4 05 n 16 and s isotopic values increase from the core 3 09 n 3 to the middle 3 78 n 11 to the edge 6 99 n 2 these results illustrate mineral crystallization processes and the mixing between seawater derived s and magmatic hydrothermal fluids during the growth of the chimney the zones from the edge to the core are characterized by crystal morphologies of colloform anhedral pyrite to massive pyrite with decreasing 34 s values revealing multi stage mineral deposition and sulphur isotopic fractionation in contrast to the increase in 34 s values from the core to the edge in one profile profile a anomalously low 34 s values in fine grained pyrite relative to chalcopyrite in another profile profile b in the middle zone result from s isotopic exchange between seawater so 4 2 and fluid h 2 s due to different fluid seawater mixing possibly caused by variations in permeability and porosity across the chimney

formation of hydrothermal deposits at kings triple junction northern lau back arc basin sw pacific the geochemical perspectives an inactive hydrothermal field was discovered near kings triple junction ktj in northern lau back arc basin during 19th cruise of r v akademik mstislav keldysh in 1990 the field consisted of a large elongated basal platform the pedestal with several small chimneys on its periphery and one main mound superposed over it the surrounding region is carpeted with lava pillows having ferromanganese precipitate as infillings the adjoining second field consisted of small chimney like growths termed as christmas tree field the basal pedestal the peripheral chimneys and small christmas tree like growths samples collected by mir submersibles though parts of the same hydrothermal field differ significantly in their mineralogy and elemental composition indicating different history of formation the pedestal slab consisting of chalcopyrite and pyrite as major minerals and rich in cu is likely to have formed at higher temperatures than sphalerite dominated peripheral chimney extremely low concentration of high field strength elements e g zr hf nb and ta and enrichment of light ree in these sulfides indicate prominent influence of aqueous arc magma rich in subduction components the oxide growths in the christmas tree field have two distinct layers fe rich orange red basal part which seems to have formed at very low temperature as precipitates from diffused hydrothermal flows from the seafloor whereas mn rich black surface coating is formed from hydrothermal fluids emanated from the seafloor during another episode of hydrothermal activity perhaps this is for the first time such unique hydrothermal oxide growths are being reported in association with hydrothermal system here we discuss the possible processes responsible for the formation of these different hydrothermal deposits based on their mineralogy and geochemistry

factors affecting the rare earth element compositions in massive sulfides from deep sea hydrothermal systems to reconstruct the evolution of ore forming fluids and determine the physicochemical conditions of deposition associated with seafloor massive sulfides we must better understand the sources of rare earth elements rees the factors that affect the ree abundance in the sulfides and the ree flux from hydrothermal fluids to the sulfides here we examine the ree profiles of 46 massive sulfide samples collected from seven seafloor hydrothermal systems these profiles feature variable total ree concentrations 37 2 4092 ppb and ree distribution patterns la cn lu cn ratios 2 00 73 8 eu eu cn ratios 0 34 7 60 the majority of the ree distribution patterns in the sulfides are similar to those of vent fluids with the sulfides also exhibiting light ree enrichment we demonstrate that the variable ree concentrations eu anomalies and fractionation between light rees and heavy rees in the sulfides exhibit a relationship with the ree properties of the sulfide forming fluids and the massive sulfide chemistry based on the sulfide ree data we estimate that modern seafloor sulfide deposits contain approximately 280 t of rees according to the flux of hydrothermal fluids at mid ocean ridges mors and an average ree concentration of 3 ng g in these fluids hydrothermal vents at mors alone transport more rees 360 t to the oceans over the course of just 2 years than the total quantity of rees in seafloor sulfides the excess rees i e the quantity not captured by massive sulfides may be transported away from the systems and become bound in sulfate deposits and metalliferous sediments

little ice age glaciation of trollaskagi peninsula northern iceland climatic implications for reconstructed equilibrium line altitudes elas comparison of the equilibrium line altitudes elas for the present 1980s and the maximum little ice age depression determined for glaciers in the skioadalur svarfaoardalur area of the trollaskagi peninsula northern iceland shows a rise of c 50 m over the last 100 150 years meteoro logical data suggest that over the same period the mean summer temperature at the equilibrium line changed by at least 2 0 c application of a model of the relationship between mean summer temperature and winter accumulation at the ela for glaciers in southern norway suggests that such a temperature change should have led to a movement of up to 300 m in the ela the discrepancy between the observed and expected results is accounted for by an almost two fold increase in winter accumulation the application of this model highlights the potential importance of interpreting changes in ela in terms of both temperature and precipitation and the results from northern iceland demonstrate that in some areas accumulation changes

late quaternary glaciation in southern africa moraine ridges and glacial deposits at mount enterprise in the drakensberg of the eastern cape province south africa late quaternary moraines and diamictons containing striated clasts are described from near elliot in the drakensberg of south africa an equilibrium line altitude ela of 2109 m is suggested for the palaeoglacier associated with the innermost moraine this glacier was fed by a very extensive snowblow area and the ela may reflect the temperature precipitation wind ela rather than the temperature precipitation ela and be considerably below the regional ela mean annual air temperatures when glaciation occurred were probably at least 10 0 c below those of the present copyright 2001 john wiley sons ltd

s sr and pb isotopic systematics of hydrothermal chimney precipitates from the eastern manus basin western pacific evaluation of magmatic contribution to hydrothermal system 1 sulfur strontium and lead isotopic analyses were performed on chimneys from the hydrothermal vent fields the pacmanus and susu knolls in the eastern manus back arc basin lead isotope composition varies in a narrow range 206pb 204pb 18 75 18 78 207pb 204pb 15 51 15 54 and 208pb 204pb 38 31 38 40 strontium isotopic ratios 87sr 86sr of sulfate minerals vary from 0 7051 to 0 7077 falling between those of seawater 0 7090 and the hydrothermal fluid end member 0 7050 the 34s values of the chimneys are 8 0 to 3 9 for the susu knolls sulfide 1 0 to 4 3 for the pacmanus sulfides and 7 4 to 20 6 for sulfate the susu knolls sulfides have the lowest values so far reported for volcanic hosted massive sulfides from modern seafloor the low 34s values of sulfates and sulfides cannot be explained by a simple seawater circulation model without an additional source of light sulfur this is also supported by the presence of sulfate in hydrothermal end member fluid indicated by sulfur and strontium isotopic ratios in chimney sulfates biogenic sulfur and or oxidation of h2s after boiling are excluded from the possible sources of light sulfur because of the lack of sediment cover and nonequilibrium in isotopic fractionation by boiling at seafloor disproportionation of magmatic so2 introduced into hydrothermal system through preeruptive degassing is the most plausible mechanism for the observed low 34s values the lighter 34s values and more radiogenic lead isotope compositions of the susu knolls samples indicate that magmatic degassing was more vigorous at the susu knolls than pacmanus

late holocene climate in central west greenland meteorological data and rock glacier isotope evidence the central west greenland climate during the instrumental period since ad 1873 is analysed con cerning interannual and seasonal variations a marked temperature rise was experienced from ad 1920 to 1930 especially affecting the winter season after which the mean annual air temperature for ten years was about 3 5 c higher than during the previous period effectively changing coastal central west greenland from having the climatological character of a continuous permafrost region to a discontinuous permafrost region since then temperatures have gradually decreased and are now approaching the little ice age level experienced in the late nineteenth century and early twentieth century interannual twentieth century temperature variations since ad 1923 have been substantial 5 15 c for the winter season intermediate 2 7 c for the spring season and smaller 1 2 c regarding summer and autumn seasons during the instrumental period the overall atmospheric circulation rather than air temperature appear

the quaternary glacial history of the zanskar range north west indian himalaya abstract three glacial stages and a minor advance are recognised from the zanskar range of the north western indian himalaya a glaciated palaeosurface 280 m above river level a r l with associated erratics represents the oldest and most extensive glaciation the chandra stage this ice covered a landscape of broad gentle valleys probably as an ice cap with an erratic distribution indicating that the ice shed lay to the south over the high himalaya a change in valley form from broad glacial troughs to narrow v shaped gorges along with large subdued moraine ridges delimits a separate later extensive valley glaciation the batal stage with its maximum at 78 0 12 3 ka bp distinct sets of moraine ridges represent a less extensive younger glaciation the kulti stage which dates close to the global last glacial maximum a minor advance the sonapani is represented by sharp crested moraine ridges within 2 km of current ice bodies possibly belonging to the little ice age glacier elevation indexes geis calculated for this and adjacent areas show a rise in elevation from the south west to the north east but dip again to the indus valley for both the batal and kulti stages reflecting attenuation of the south westerly monsoon and possible channelling of westerly depressions along the broad upper indus valley gei depression are 500 and 300 m for the batal and kulti stages respectively the change in extent and style from the chandra stage to the later glaciations may be related to uplift of more southerly ranges blocking monsoon precipitation and incision of the landscape such that ice reached lower altitudes over shorter horizontal distances why ice extent was greater during oxygen isotope stage ois 4 than 2 is not clear although recent high resolution plaeomonsoon records show complex peaks in monsoon intensity and it is possible that there was a more favourable combination of precipitation and temperature earlier rather than later during the last glaciation

glaciation style and the geomorphological record evidence for younger dryas glaciers in the eastern lake district northwest england the younger dryas c 12 900 11 700 years ago in britain witnessed renewed glaciation with the readvance of ice masses that had survived the preceding lateglacial interstadial as well as the formation of new glaciers the extents of these former glaciers have been mapped by many workers over the past fifty years usually as a basis for palaeoclimatic investigations it has frequently been asserted that the landform record is sufficiently clear to allow accurate ice mass reconstructions at or near maximum extents detailed geomorphological mapping in the eastern lake district in nw england however demonstrates that this confidence may not always be warranted whereas previous workers have interpreted the well developed moraines that exist in some locations as evidence for an alpine style of glaciation with ice restricted to a small number of valleys this study shows that the most recent glaciation to affect the area was characterised by i extensive summit icefields which supplied ice to the surrounding valleys and ii a much greater volume of ice in the valleys than previously thought the discovery that summit icefields were relatively common at this time is consistent with recent studies elsewhere in the lake district and beyond more significant however is the recognition that changing glacier topographic interactions over both space and time appears to have had a profound impact on valley floor glacial landform development with the absence of clear moraines not necessarily indicating ice free conditions at this time this complicates glacier reconstructions based solely on the geomorphological record similar geomorphological complexity may be present in other areas that previously supported summit icefields and this needs to be taken into account in glacier reconstructions

metal sources in the middle valley massive sulphide deposit northern juan de fuca ridge pb isotope constraints abstract massive sulphides drilled from the bent hill deposit during ocean drilling program leg 139 at middle valley northern juan de fuca ridge have 206 pb 204 pb 18 43 18 86 207 pb 204 pb 15 43 15 63 208 pb 204 pb 38 08 38 60 these span 35 of the total pb isotope range measured in hydrothermal sulphides from the east pacific ocean 206 pb 204 pb ratios overlap the range of local basalts but 208 pb 204 pb and 207 pb 204 pb require a contribution from a more radiogenic source that is similar to the overlying sedimentary sequence three samples have lower 207 pb 204 pb ratios than the mean basalt value which may reflect the preservation of heterogeneities in the local basalts the pb isotopic compositions of primary pyrrhotites are indistinguishable from the secondary pyrite dominated assemblage which recrystallised from low temperature hydrothermal fluids this may be explained by the importance of the sulphosalts as a host for pb in the deposit clastic sulphides from sediments at bent hill are at the radiogenic end of the massive sulphide range suggesting that surficial sulphides may not provide an unbiased sample of the past hydrothermal circulation responsible for massive sulphide deposition if the pb content of sediment is 100 times greater than the basalts the sulphide pb isotopes imply that the hydrothermal fluids have extracted pb from 60 to 900 times more basalt than sediment lead in the massive sulphide deposit has been extracted from 2 10 8 3 10 8 m 3 of oceanic crust demonstrating the local nature of hydrothermal circulation at mid ocean ridges the 3 he 4 he of hydrothermal fluids in the sulphides 6 2 10 6 7 8 10 6 show only half the variation between the sediment and basalt end members displayed by pb isotopes this is consistent with volatile acquisition from magma degassing while the pb is leached during hydrothermal fluid interaction with crystallised oceanic crust

distribution and sources of pre anthropogenic lead isotopes in deep ocean water from fe mn crusts abstract the lead isotope composition of ocean water is not well constrained due to contamination by anthropogenic lead here the global distribution of lead isotopes in deep ocean water is presented as derived from dated ca 100 ka surface layers of hydrogenetic fe mn crusts the results indicate that the radiogenic lead in north atlantic deep water is probably supplied from the continents by river particulates and that lead in pacific deep water is similar to that characteristic of island and continental volcanic arcs despite a short residence time in deep water 80 100 a the isotopes of lead appear to be exceedingly well mixed in the pacific basin there is no evidence for the import of north atlantic deep water derived lead into the pacific ocean nor into the north indian ocean this implies that the short residence time of lead in deep water prohibits advection over such long distances consequently any climate induced changes in deep water flow are not expected to result in major changes in the seawater pb isotope record of the pacific ocean

glacier fluctuations equilibrium line altitudes and palaeoclimate in lyngen northern norway during the lateglacial and holocene based on lacustrine and morpho stratigraphical evidence from lyngen in troms northern norway 13 marginal moraines have been mapped in front of lenangsbreene in strupskardet moraines m1 m13 are inferred to represent glacier halts or advance readvance taking place during the lateglacial and holocene the presence of collapse depressions suggests that some of them were ice cored m1 m3 a chronological framework taking into account a combination of former shorelines and related glacier meltwater channels lichenometry and ams radiocarbon dated lacustrine sediments spanning the last 20 000 cal yr bp has been established the distal glacier fed lake aspvatnet was isolated from the sea c 10 300 cal yr bp and the lacustrine sediments have been investigated by use of loss on ignition loi magnetic susceptibility water content wet and dry bulk density dbd and the magnetic parameters anhysteretic remanent magnetization arm and saturation remanent magnetization sirm there is in general good agr

a latest pleistocene and holocene glacial history and paleoclimate reconstruction at three sisters and broken top volcanoes oregon u s a abstract at least three sets of moraines mark distinct glacial stands since the last glacial maximum lgm in the three sisters region of the oregon cascade range the oldest stand predates 8 1 ka defined here as post lgm followed by a second between 2 and 8 ka neoglacial and a third from the little ice age lia advance of the last 300 years the post lgm equilibrium line altitudes were 260 100 m lower than that of modern glaciers requiring 23 9 increased winter snowfall and 1 4 0 5 c cooler summer temperatures than at present the lia advance had equilibrium line altitudes 110 40 m lower than at present implying 10 4 greater winter snowfall and 0 6 0 2 c cooler summer temperatures

chironomid inferred late glacial air temperatures at whitrig bog southeast scotland this paper presents the first chironomid inferred mean july air temperature reconstruction for the late glacial in britain the reconstruction suggests that the thermal maximum occurred early in the interstadial with temperatures reaching about 12 degreesc there was then a gradual downward trend to about 11 degreesc punctuated by four distinct cold oscillations of varying intensity at the beginning of the younger dryas mean july temperatures fell to about 7 5 degreesc but gradually increased to about 9 degreesc before a rapid rise at the onset of the holocene the chironomid inferred temperature curve agrees closely both in general trends and in detail with the grip ice core oxygen isotope curve the reconstructed temperatures are 2 4 degreesc lower than coleopteran inferred temperatures but are closer to those inferred from plant macrofossils and glacial equilibrium line altitudes during the younger dryas copyright c 2000 john wiley sons ltd

surface temperature in nw europe during the younger dryas agcm simulation compared with temperature reconstructions during the younger dryas yd the climate in nw europe returned to near glacial conditions to improve our understanding of climate variability during this cold interval we compare an agcm simulation of this climate performed with the echam model with temperature reconstructions for nw europe based on geological and paleoecological records maps for the mean winter summer and annual temperature are presented the simulated winters are consistent with reconstructions in the northern part of the study area a strong deviation is noted in ireland and england where the simulation is too warm by at least 10 c it appears that the n atlantic was cooler than prescribed in the yd simulation including a southward expansion of the sea ice margin the comparison for the summer shows a too warm continental europe in the simulation supposedly these anomalously warm conditions are caused by the agcm s response to the prescribed increased summer insolation the region of maximum summer cooling is similar in both the simulation and reconstruction i e s sweden we suggest that this is due to the local cooling effect of the scandinavian ice sheet compared to the present climate a considerable increase of the annual temperature range is inferred especially for regions close to the atlantic ocean

sulfur and strontium isotopic study of epithermal mineralization a case study from the se afar rift djibouti epithermal mineralization was recently described in synrift volcanic rocks from the se afar rift in djibouti to infer fluid sources in this system coupled sulfur and strontium isotopic analyses were performed on mineralized samples from hydrothermal veins and stockwork zones mineralization includes gypsum and chalcedony and or quartz carbonate containing gold and sulfides sulfur isotopic compositions of sulfides and sulfates were determined using multicollector inductively coupled plasma mass spectrometer mc icpms laser ablation mc icpms and continuous flow elemental analyzer isotope ratio mass spectrometry while strontium isotopes were determined by thermal ionisation mass spectrometry tims methods sulfur isotopic composition of sulfides mainly pyrite varies from 9 2 to 6 6 these values are classically reported for hydrothermal sulfides resulting from the mixing of variable s sources such as seawater sulfate and magmatic source in addition individual pyrite grains within the same sample show both positive and negative 34s values suggesting multi phase mineralization processes coupled sulfur and strontium isotopic compositions of seven sulfate samples hosted in i gypsum mound ii evaporites iii stockwork veins in sediments or in volcanic rocks were also investigated to characterize the sources of sr and s the 34s values of the sulfate ranged from 0 8 to 14 3 while the 87sr 86sr ranged from 0 70389 to 0 70639 consistent with variable mixing ratios of sr and s derived from volcanic sources and seawater derived sulfate this study shows that although precious metal deposition is related to low sulfidation epithermal environment both acidic fluid of magmatic and saline origins contributed to the hydrothermal system in the se afar rift

cosmogenic 10be insights into the extent and chronology of the last deglaciation in wester ross northwest scotland cosmogenic 10be surface exposure ages for bedrock sites around torridon and the applecross peninsula in wester ross northwest scotland provide new insights into the lateglacial transition accounting for postglacial weathering six statistically comparable exposure ages give a late younger dryas g 1 exposure age of 11 8 1 1 ka two further outliers are tentative pre younger dryas exposure ages of 13 4 0 5 ka in torridon and 17 5 1 2 ka in applecross the younger dryas exposure ages have compelling implications for the deglaciation of marginal loch lomond stadial ice fields in torridon and applecross firstly they conflict with predictions of restricted ice cover and rapid retreat based on modelling experiments and climate proxies instead fitting a model of vertically extensive and prolonged ice coverage in wester ross secondly they indicate that 2 m of erosion took place in the upper valleys of torridon and applecross during the younger dryas implying a dominantly warm based glacial regime finally the exposure ages have clarified that corrie cirque glaciers did not readvance in wester ross following final deglaciation copyright 2011 john wiley sons ltd

the loch lomond readvance on the isle of mull scotland glacier reconstruction and palaeoclimatic implications geomorphological mapping of mull provides evidence for an icefield 143 km2 in area flanked by six corrie glaciers with a total area of ca 13 km2 the absence of lateglacial periglacial features shorelines and pollen sites from the area occupied by this readvance together with radiocarbon dating of shell fragments confirm that it occurred during the loch lomond younger dryas stade the thickness of glacigenic deposits within the area of the readvance is attributed to reworking of paraglacial sediments up valley continuity of recessional moraines indicates that the ice remained active and near to equilibrium during retreat consistent with slow warming following the coldest part of the stade reconstructed equilibrium line altitudes elas imply vigorous snow blowing by westerly winds and are consistent with a general southwestwards decline in elas across the scottish highlands an ela of 250 m was calculated for the mull icefield using an ablation accumulation balance ratio abr approach palaeotemperature and palaeoprecipitation estimates were derived by calculating a theoretical regional ela from meteorological data and assuming that the combination of temperature and precipitation implied by the theoretical ela approximates conditions at 250 m on mull during the loch lomond stade the result indicates a mean july sea level temperature of 5 7 0 5 c and a mean annual precipitation at 250 m of ca 2700 3800 mm best estimate 3200 mm indicating higher precipitation totals than at present owing to more vigorous atmospheric circulation copyright 2002 john wiley sons ltd

an improved technique for the reconstruction of former glacier mass balance and dynamics abstract the recognition of past glacier extent and dynamics is a fundamental aspect of investigations of the climatic sensitivity of glaciers especially when examining short lived climate events such as the younger dryas or little ice age existing approaches to the reconstruction of glacier form and dynamics depend on speculative reasoning of key glacier dynamic parameters including the role of basal slip and subglacial deformation in glacier mass transfer this study reviews approaches to glacier reconstruction derivation of former glacier equilibrium line altitudes ela s and estimation of mass balance and dynamics concluding that most reconstructions of glacier mass balance are compromised by a lack of glaciological considerations an alternative approach to glacier reconstruction is presented demonstrated and discussed by which an empirical relationship between ablation gradient and mass loss at the ela is used to derive mass balance mass flux through the ela and average balance velocity at the ela this glaciological approach is applied to four reconstructed glaciers to test previous interpretations that each reflects younger dryas glaciation in the uk the study concludes that this approach provides a more robust technique for reconstructing former glacier dynamics and may be applied to test geomorphological interpretations of former mountain glaciation

formation of hydrothermal vents in the north fiji basin sulfur and lead isotope constraints abstract hydrothermal sulfides were recovered from the 16 50 s triple junction area in the north fiji basin at a water depth of ca 1900 m the chimney samples can be divided into three groups based on their major metal contents 1 type 1 fe cu rich 2 type 2 fe cu rich with minor zn and 3 type 3 zn rich chimneys type 1 chimneys are mainly composed of chalcopyrite and pyrite and are enriched in elements commonly precipitated under high temperature conditions 300 c such as cu co mo and se type 3 chimneys consist dominantly of sphalerite and marcasite with traces of pyrite and chalcopyrite and are enriched in elements commonly associated with relatively low temperatures 150 to 250 c such as zn cd pb as and ga type 2 chimneys have a mineralogy similar to that of type 1 chimneys although their trace metal contents range between those of type 1 and type 3 samples type 2 chimneys appear to be the products of low temperature replacement which might be related to formation of type 3 chimneys of type 1 chimneys the trace element composition of basaltic rocks indicates that magma generation in the triple junction area was influenced by two different sources n morb and e morb sulfur and lead isotope patterns of the hydrothermal chimneys show distinct differences between the type 1 and type 3 chimneys the type 1 sulfides 34 s 2 8 1 2 206 pb 204 pb 18 082 to 18 132 207 pb 204 pb 15 440 to 15 481 208 pb 204 pb 37 764 to 37 916 are depleted in 34 s and have lower pb isotope ratios compared to types 2 and 3 chimneys 34 s 4 1 0 9 206 pb 204 pb 18 122 to 18 193 207 pb 204 pb 15 475 to 15 554 208 pb 204 pb 37 882 to 38 150 the higher 34 s values for types 2 and 3 sulfides than type 1 sulfides can be explained by mixing of hydrothermal fluids with ambient seawater the more radiogenic pb isotope composition of types 2 and 3 chimneys compared to type 1 chimneys suggest that the formation of types 2 and 3 chimneys were possibly related to e morb volcanism that shows higher pb isotope composition than n morb rocks however ferromanganese crust samples have radiogenic pb isotope compositions that are identical to those of e morb therefore input of hydrogenous pb is also a possible source for radiogenic pb isotopes in the types 2 and 3 chimneys

a complete record of holocene glacier variability at austre okstindbreen northern norway an integrated approach arctic glaciers are currently undergoing major changes but accurate knowledge about how they varied during the entire holocene is still scarce here we present a new complete glacier record from austre okstindbreen in nordland northern norway this reconstruction is based on a number of short and long cores retrieved from several downstream basins which have been analyzed by a suite of methods including geochemical elements xrf rock magnetic properties dry bulk density dbd and loss on ignition loi lake sediment distribution was surveyed and mapped prior to coring by the use of ground penetrating radar gpr independently lichen dated marginal moraines and historical information about the glacier frontal positions from old photographs and maps have made it possible to link the moraine sequence to the 210pb dated lake sediment chronology this integrated approach reveals that austre okstindbreen is the first known glacier in scandinavia to possibly have survived the holocene thermal optimum it also brackets the four largest glacier advances to c 7400 7000 1400 1200 900 700 and 300 150 years before ad 2000 b2k in contrast to most reconstructed glaciers in scandinavia the largest glacier advance was not associated with the little ice age but rather to an earlier period centred at 1300 b2k both the moraine chronology and the lacustrine records document this neoglacial advance compared to other glacier reconstructions from the northern hemisphere we identify near synchronous glacier advances occurring roughly at 4000 b2k 2700 b2k 1300 b2k and during the little ice age these correlative advances across the northern hemisphere suggest that these observed centennial scale events are a shared feature regardless of the large geographical distances separating them some minor discrepancies between different geographical areas may be caused by lack of precise dating but local climatic conditions may play a role as well

reconstruction of a lateglacial younger dryas mountain ice field in sutherland northwestern scotland and its palaeoclimatic implications quaternary geomorphological and geological mapping of a large area 1800 km2 in the northwestern scottish highlands has led to the reconstruction of a coherent mountain ice field approximately 45 km long and 30 km wide at its maximum extent this west sutherland ice field covered an area of 350 km2 and had a mean equilibrium line altitude of 334 m assuming that the outlet glaciers all reached their maxima simultaneously numerical dating strongly suggests a younger dryas 12 9 11 7 ka age of the mapped limits of this mountain ice field this study also shows that the area of northwestern scotland covered by younger dryas glaciers was five times larger than previously thought palaeo temperature estimates obtained from chironomid and beetle assemblages elsewhere have been used to reconstruct palaeo precipitation during the younger dryas for west sutherland using a previously published global empirical dataset annual precipitation of 2344 248 mm a 1 at sea level is inferred from our new palaeo glacier reconstruction suggesting slightly wetter conditions compared to the present day these figures are in good agreement with those reconstructed for other parts of the scottish highlands and islands and this may indicate a marked w e palaeo precipitation gradient during the younger dryas this paper goes on to discuss the wider validity of palaeo climatic reconstructions from inferred palaeo glacier geometries and presents a number of possible scottish lateglacial climate scenarios which warrant further testing copyright 2010 john wiley sons ltd

constraints on water depth of massive sulfide formation evidence from modern seafloor hydrothermal systems in arc related settings the results of three decades of seafloor research provide the most reliable information on the importance of water depth in massive sulfide formation available data from over 130 occurrences show that water depths of seafloor vent sites vary with plate tectonic setting and the regional magmatic and volcanic environment the shallowest hydrothermal systems in subduction related settings are hosted by arc volcanoes these shallow vent sites have a number of features in common with subaerial epithermal systems massive sulfide occurrences in arc related rifts the most likely setting for many ancient analogs are generally restricted to water depths from 700 to 2 000 m with rifts developing within old arc crust at the deeper end of this range back arc spreading centers proximal to arcs host massive sulfide deposits at depths of 1 500 to 2 000 m the deepest hydrothermal systems occur along mature back arc spreading centers distal to volcanic arcs where water depths range from 2 000 to 3 700 m these deeper vent sites probably represent the best modern analogues of ophiolite hosted massive sulfide deposits boiling of the hydrothermal fluids is common at volcanic arcs and in arc related rifts in these environments elevated magmatic gas contents of the hydrothermal fluids can contribute to the widespread occurrence of phase separation and associated gas loss by contrast the high ambient pressures in deep marine hydrothermal systems along mature back arc spreading centers prevent fluids from boiling during their ascent to the seafloor boiling controls the maximum temperature at which hydrothermal fluids discharge at the seafloor and therefore influences the metal content of seafloor sulfide deposits copper rich massive sulfides typically occur at water depths exceeding 1 000 m whereas zn and pb rich occurrences may form at any water depth boiling can be an important control on ag and au grades but is not the only factor controlling precious metal enrichment in massive sulfides shallow marine hot spring deposits can be highly enriched in trace metals such as as hg and sb submarine volcanic arc and back arc settings are geologically complex and significant variations in water depth can occur over short distances paleoenvironmental reconstruction of these environments in ancient volcanic terranes is hampered by the lack of unequivocal volcanological or sedimentological criteria that indicate water depth the relationships established here using modern seafloor observations provide important constraints on the paleoenvironmental setting of ancient volcanic hosted massive sulfide deposits

application of a degree day model to reconstruct pleistocene glacial climates there is empirical evidence of a nonlinear relation between annual precipitation or accumulation and summer mean temperature at the equilibrium line altitude ela on glaciers around the world the degree day model gives a similar relation between accumulation and summer temperature although instead of a single universal curve there is a family of curves depending upon the annual temperature range furthermore the degree day model also gives nonlinear relations between accumulation and annual mean temperature thus estimations of accumulation can be made from both summer and annual temperatures at the ela of former reconstructed glaciers such as those in greece this is particularly useful since these climatic variables have major implications for biological proxies such as vegetation history indicated in the pollen record and for periglacial proxies such as permafrost distributions indicated in the geomorphological record the close relationship between glaciers and climate provides one of the most precise methods for reconstructing former climates and offers considerable potential for resolving our understanding of pleistocene cold stage climates

pele s tears and spheres examples from kilauea iki abstract pele s tears are a well known curiosity commonly associated with low viscosity basaltic explosive eruptions however detailed studies of these pyroclasts are rare and thus there is no full explanation for their formation these intriguing pyroclasts have smooth glassy surfaces vesiculated interiors 30 and fluidal morphologies trending towards teardrops and then spheres as they decrease in size to

modern glacier characteristics as a basis for inferring former climates with particular reference to the loch lomond stadial abstract studies of the mass balance of modern glaciers have indicated that the equilibrium line altitude ela is the most critical parameter in the link between glaciers and climate average accumulation on a glacier includes components derived from direct precipitation on the glacier surface as well as wind drifting and avalanching of snow and approximates closely to accumulation at the equilibrium line ablation is most usefully predicted by mean summer temperature and there is a close non linear relationship between accumulation and mean summer temperature at the equilibrium line following discussion of methods of reconstructing former glaciers and calculating their equilibrium line altitudes the application of the above relationships to the loch lomond readvance glaciers of highland britain is considered and an outline of the precipitation pattern and the mean summer temperature of the loch lomond stadial is given

late pleistocene glacial equilibrium line altitudes in the colorado front range a comparison of methods abstract six methods for approximating late pleistocene pinedale equilibrium line altitudes elas are compared for rapidity of data collection and error rmse from first order trend surfaces using the colorado front range trend surfaces computed from rapidly applied techniques such as glaciation threshold median altitude of small reconstructed glaciers and altitude of lowest cirque floors have relatively high rmses 97 186 m because they are subjectively derived and are based on small glaciers sensitive to microclimatic variability surfaces computed for accumulation area ratios aars and toe to headwall altitude ratios thars of large reconstructed glaciers show that an aar of 0 65 and a thar of 0 40 have the lowest rmses about 80 m and provide the same mean ela estimate about 3160 m as that of the more subjectively derived maximum altitudes of pinedale lateral moraines rmse 149 m second order trend surfaces demonstrate low elas in the latitudinal center of the front range perhaps due to higher winter accumulation there the mountains do not presently reach the ela for large glaciers and small front range cirque glaciers are not comparable to small glaciers existing during pinedale time therefore pleistocene ela depression and consequent temperature depression cannot reliably be ascertained from the calculated ela surfaces

influence of seasonality on glacier mass balance and implications for palaeoclimate reconstructions climates inferred from former glacier geometries in some areas exhibit discrepancies with regional palaeoclimates predicted by general circulation models gcms and modelling of palaeoecological data possibly as a consequence of their differing treatments of climatic seasonality since glacier based climate reconstructions potentially offer an important tool in the calibration of gcms which themselves need validation if used to predict future climate scenarios we attempt to resolve mismatches between these techniques by 1 investigating the influence of seasonality on glacier mass balance and 2 refining the methodology used for the derivation of glacier based palaeoclimates focussing on the younger dryas stadial glaciation of scotland northeast atlantic we show that sea ice amplified seasonality led to a significantly drier climate than has been suggested by glacier based interpretations this was characterised by a relatively short ablation season and the survival of a more substantial winter snowpack we suggest that if palaeoglaciological studies were to account for changes in seasonal temperature and precipitation variability their results would agree more closely with the cold arid northeast atlantic palaeoenvironment predicted by atmospheric modelling and northwest european pollen studies and would therefore provide more accurate constraints for gcm calibration

sulfur cycle in the valles caldera volcanic complex new mexico letter 1 sulfate sources in aqueous system and implications for s isotope record in gale crater on mars abstract initial in situ sulfur s isotope measurements of the martian bedrock in gale crater have revealed an unexpectedly wide range of 34 s values 47 to 28 generally it is unclear what processes could have contributed to these large isotope fractionations therefore we studied s sources and aqueous so 4 2 cycling in the valles caldera volcanic complex new mexico to better understand s isotope fractionations related to s degassing hydrothermal activity and low temperature processes in aqueous environment overall our study demonstrates that volcanic systems show large spatial heterogeneity in 34 s magmatic s sources are obvious in steam dominated h2s degassing and precipitation of secondary minerals from hydrothermal fluids with low 34 s values of 0 9 3 locally however hydrothermal processes have resulted in more negative 34 s values in sulfide minerals 18 to 4 and more positive 34 s values in sulfate minerals 1 to 3 major aqueous so 4 2 sources are oxidation of h2s from modern hydrothermal gas emission and oxidation and dissolution of sulfide and sulfate minerals present in the hydrothermally altered bedrock and crater lake sediments the 34 s of aqueous so 4 2 in surface water and groundwater varies widely 8 to 5 and is similar to major s endmembers that undergo oxidation and or dissolution by active hydrological system minor so 4 2 contributions with more positive 34 s values 9 to 14 come from deeply circulating geothermal fluids and negligible amounts from atmospheric deposition 5 to 7 in snow elevated so 4 2 contents are mainly associated with modern and past h2s emissions and oxidations near the surface on regional scale however most of the intracaldera bedrock is s depleted thus the so 4 2 contents are usually low in the surface aquatic system and younger sedimentary lake deposits formed at times of negligible near surface hydrothermal activity in general magmatic hydrothermal processes apparently cause the largest 34 s variation in s bearing minerals on volcanic terrains therefore we infer that the measured wide range of 34 s values in the gale sediments by the curiosity rover on mars can be explained by s isotope composition of magmatic hydrothermal sulfide and sulfate minerals that were present in the initial igneous volcanic rocks prior to crater formation later aqueous processes involved oxidation and dissolution of s minerals initially present in these rocks and led to subsequent formation of diagenetic fluids and alteration products enriched in so 4 2 with relatively large 34 s variation additionally physical erosion transport and deposition of detrital hydrothermal s minerals from igneous volcanic rocks might be in part responsible for the measured wide range of 34 s in gale crater these unique s isotope results measured in situ on another planet for the first time imply the importance of magmatic hydrothermal fluids in s transport on early mars and their subsequent alteration in low temperature aqueous environments

modeled patterns of late pleistocene glacier inception and growth in the southern and central rocky mountains usa sensitivity to climate change and paleoclimatic implications abstract high resolution modern climate data for the southern and central rocky mountains provide a starting point for analysis of climate changes necessary to produce regional late pleistocene glaciation a gis based model was used to assess the sensitivity of glaciation in different ranges to climatic change and the combinations of temperature and precipitation change necessary to sustain the last glacial maximum lgm extent of glaciation in each range extensive glaciation initiates first in the wind river range of wyoming under every climate change scenario tested in absence of precipitation change a summer temperature depression of 6 8 c would be necessary to maintain lgm ice extents in colorado and wyoming if precipitation was halved necessary summer temperature depression would be 8 10 c if precipitation was doubled a depression of 3 5 5 5 c would suffice given model uncertainties these values may underestimate necessary temperature depression by as much as 2 c under all scenarios tested lgm glaciation in utah particularly the wasatch range requires either more temperature depression for given precipitation change or more precipitation for a given temperature depression than is required in the colorado wyoming rockies a summer temperature depression of 7 c which would suffice to sustain lgm ice extent with little change from modern precipitation in the colorado wyoming rockies would need to be coupled with a near doubling of precipitation to maintain lgm ice extent in the wasatch range this difference appears to reflect lgm precipitation enhancement in the wasatch range and to a lesser degree the uinta mountains resulting from the presence of lake bonneville immediately upwind of these ranges

sulfur species and biosignatures in sulphur springs valles caldera new mexico implications for mars astrobiology abstract a biogeochemical so 4 2 cycle was investigated in the acid hot springs of valles caldera new mexico using s isotopes and distribution of amino acids in 2007 a major contribution of so 4 2 in this modern volcanic setting came from oxidation of h 2 s from hydrothermal sources which largely increased so 4 2 concentrations up to 2550 mg l 1 and decreased ph down to 2 27 in surface water a relatively small variation of 34 s among the analyzed s bearing minerals 2 1 to 4 0 fumarole h 2 s 1 7 to 4 6 and dissolved so 4 2 in modern surface and groundwater 2 5 to 7 9 indicates poor evidence of s isotope biosignatures related to microbial disproportionation of elemental s to h 2 s and so 4 2 which in turn are not effectively captured in the hydrothermal minerals of the studied volcanic setting this is mainly due to prevailing contribution of reduced s forms from magmatic hydrothermal sources and considerably smaller microbial activity in acid hot spring areas although hydrothermal gypsum and elemental s effectively trap amino acids their preservation lifetimes in s bearing hydrothermal minerals appear to be small the minimal lifetimes are inferred to be the result of increased temperatures and rapid recycling time of s materials in hydrothermal settings landed missions to the martian surface at sites inferred to have experienced active hydrothermal activity similar to the one studied in valles caldera e g elevated volcanic s flux may provide valuable insight into geological and geochemical processes that have influenced the martian surface but may provide minimal potential for recording either amino acid or s isotopic biosignatures of an extinct martian ecosystem

late holocene glacier fluctuations in bevringsdalen jostedalsbreen region western norway ca 3200 1400 bp lithostratigraphy and radiocarbon dates from a 1 3 m deep gully section in bevringsdalen sw of jostedalsbreen in western norway with alternating minerogenic glacial and peat non glacial layers demonstrate that glaciers upvalley from the site were present during the following intervals 2595 85 bp 840 700 cal bc to 2360 80 bp 525 385 cal bc between 2250 65 bp 395 225 cal bc and 2150 80 bp 360 105 cal bc between 1740 75 bp cal ad 205 385 and 1730 75 bp cal ad 210 395 and subsequent to 1430 45 bp cal ad 595 645 detailed altitudinal fluctuations of the glaciation threshold equilibrium line relative to the present have been reconstructed for the time interval between 1430 45 bp cal ad 595 645 and 3180 90 bp 1540 1395 cal bc

a theoretical approach to glacier equilibrium line altitudes using meteorological data and glacier mass balance records from southern norway based on a close exponential relationship between mean ablation season temperature and winter precipitation at the equilibrium line altitude ela of 10 norwegian glaciers three equations are derived the e rst equation enables calculation of the minimum altitude of areas climatically suited for glacier formation and is termed the altitude of instantaneous glacierization aig equation 2 is derived based on the principle of terrain adaptation enabling quantie cation of the glacial buildup sensitivity gbs in presently non glaciated areas the theoretical climatic temperature precipitation ela c tp ela in presently non glaciated areas is calculated in equation three by combining gbs with terrain altitude mass balance records from four modern glaciers a lfotbreen nigardsbreen storbreen and gra subreen situated in maritime to continental climate regimes in southern norway are used to test these equations correlation between aig and net balance measure ments bn yielded correlation coefe cients of r 0 80 to r 0 84 calculated aigs correspond well with observed elas on a lfotbreen nigardsbreen and gra subreen while it deviates from the observed ela on storbreen the latter is probably due to leeward accumulation of wind blown snow on this cirque glacier based on this approach regional representative climatic elas can be calculated for non glaciated areas with instrumental records of ablation season temperature and winter precipitation

geochemistry of diffuse low temperature hydrothermal fluids in the north fiji basin low temperature 13 c diffuse hydrothermal fluids were sampled directly at the seafloor with a specially designed hydro bottom station in the north fiji basin and analyzed for gases major and minor elements and a large number of trace metals the fluids were significantly enriched in co2 si li rb cs ba mn and several trace metals compared to ambient seawater had high ch4 and h2s concentrations and had a slightly decreased salinity calculated end member concentrations of the low temperature fluids show a strong similarity to the neighboring hot vents implying that the diffuse fluids are hot vent waters diluted by seawater according to the chemical composition the sampled fluids derive from vapor phase fluids produced by subseafloor boiling and phase separation compared to hot vents from other regions mn fe and other trace metal concentrations are low subsurface metal sulfide precipitation during cooling and dilution with seawater has further decreased the dissolved metal contents of the diffuse fluids thus creating a very favorable environment for the hydrothermal fauna as indicated by a very low fe h2s ratio therefore the fluids support high bioproductivity but no hydrothermal mineral precipitation the emanation of the condensed vapor phase appears to have been stable during the past 10 years however the occurrence of metal sulfide particles in some fluid and sediment samples and small areas of dead fauna indicate that the hydrothermal system may be evolving toward the emanation of the stored brine phase

the geomorphological impact of loch lomond younger dryas stadial plateau icefields in the central lake district northwest england detailed geomorphological mapping has revealed evidence for the development of plateau icefields in the central fells of the english lake district during the loch lomond younger dryas stadial ca 12 9 11 5 ka the largest plateau icefield system which covered an area of approximately 55 km2 including outlet glaciers was centred on high raise to the west smaller plateau icefields developed on grey knotts brandreth and dale head covering areas of 7 km2 and 3 km2 respectively the geomorphological impact of these plateau icefields appears to have been minimal on the summits where the survival of blockfields and other frost weathered debris mostly peat covered implies the existence of at least patches of protective cold based ice ice moulded bedrock at some plateau edges however documents a transition to wet based erosive conditions prominent moraine systems were produced by outlet glaciers which descended into the surrounding valleys where their margins became sediment traps for supraglacial debris and inwash in some valleys ice marginal moraines record successive positions of outlet glaciers which actively back wasted towards their plateau source this interpretation differs from that of previous workers who assumed an alpine style of glaciation with reconstructed glaciers emanating from corries and valley heads it is likely that plateau icefields were more common at this time in upland britain than hitherto has been appreciated

cirque glacier activity in arctic norway during the last deglaciation abstract numerous cirques of the lofoten vesteralen archipelago in northern norway have distinct moraine sequences that previously have been assigned to the allerod younger dryas 13 400 to 11 700 yr bp interval constraining the regional distribution of the equilibrium line altitude ela of cirque and valley glaciers here we present evidence from a once glacier fed lake on southern andoya that contests this view analyses of radiocarbon dated lacustrine sediments including rock magnetic parameters grain size organic matter dry bulk density and visual interpretation suggest that no glacier was present in the low lying cirque during the younger dryas allerod the initiation of the glacial retreat commenced with the onset of the bolling warming 14 700 yr bp and was completed by the onset of allerod interstade 13 400 yr bp the reconstructed glacier stages of the investigated cirque coincide with a cool and dry period from 17 500 to 14 700 yr bp and a somewhat larger last glacial maximum lgm advance possibly occurring between 21 050 and 19 100 yr bp

volcanic eruption of the mid ocean ridge along the east pacific rise crest at 9 45 52 n direct submersible observations of seafloor phenomena associated with an eruption event in april 1991 in april 1991 we witnessed from the submersible alvin a suite of previously undocumented seafloor phenomena accompanying an in progress eruption of the mid ocean ridge on the east pacific rise crest at 9 45 n 52 n the volume of the eruption could not be precisely determined although comparison of pre and post eruption seabeam bathymetry indicate that any changes in ridge crest morphology resulting from the eruption were 10 m high effects of the eruption included 1 increased abundance and redistribution of hydrothermal vents disappearance of numerous vent communities and changes in characteristics of vent fauna and mineral deposits within the eruption area since december 1989 2 murkiness of bottom waters up to tens of meters above the seafloor due to high densities of suspended mineral and biogenic particulates 3 destruction of a vent community by lava flows mass wasting and possible hydrovolcanic explosion at a site known as tubeworm barbecue in the axial summit caldera asc at 9 50 6 n 4 near critical temperatures of hydrothermal vent fluids ranging up to 403 c 5 temporal variations over a 2 week interval in both temperatures and chemical isotopic compositions of hydrothermal fluids 6 unusual compositions of end member vent fluids with ph values ranging to a record low of 2 5 salinities ranging as low as 0 3 wt nacl one twelfth that of seawater and dissolved gases reaching high concentrations 65 mmol l for both co2 and h2s 7 venting at temperatures above 380 c of visually detectable white vapor that transformed to plumes of gray smoke a few centimeters above vent orifices 8 disorganized venting of both high temperature fluids black and gray smoke and large volumes of cooler diffuse hydrothermal fluids directly from the basaltic seafloor rather than from hydrothermal mineral constructions 9 rapid and extensive growth of flocculent white bacterial mats species unknown on and under the seafloor in areas experiencing widespread venting of diffuse hydrothermal fluid and 10 subseafloor downslope migration of magma normal to the ridge axis in a network of small scale 1 5 m diameter lava tubes and channels to distances at least 100 200 m outside the asc we suggest that in april 1991 intrusion of dikes in the eruption area to 200 m beneath the asc floor resulted in phase separation of fluids near the tops of the dikes and a large flux of vapor rich hydrothermal fluids through the overlying rubbly cavernous lavas low salinities and gas rich compositions of hydrothermal fluids sampled in the eruption area are appropriate for a vapor phase in a seawater system undergoing subcritical liquid vapor phase separation boiling and phase segregation hydrothermal fluids streamed directly from fissures and pits that may have been loci of lava drainback and or hydrovolcanic explosions these fissures and pits were lined with white mats of a unique fast growing bacteria that was the only life associated with the brand new vents the prolific bacteria which covered thousands of square meters on the ridge crest and were also abundant in subseafloor voids may thrive on high levels of gases in the vapor rich hydrothermal fluids initially escaping the hydrothermal system white bacterial particulates swept from the seafloor by hydrothermal vents swirled in an unprecedented biogenic blizzard up to 50 m above the bottom the bacterial proliferation of april 1991 is likely to be a transient bloom that will be checked quickly either by decline of dissolved gas concentrations in the fluids as rapid heat loss brings about cessation of boiling and or by grazing as other organisms are re established in the biologically devastated area

the glaciation of dartmoor the southernmost independent pleistocene ice cap in the british isles the granite uplands of dartmoor have traditionally been considered to be relict permafrost and periglacial landscapes that lay beyond the limits of quaternary glaciations but a variety of landform evidence indicates that a plateau icefield existed on the northern part of the moor constituting the southernmost independent ice cap in the british isles overdeepened or weakly u shaped valley segments fringing north dartmoor document an early extensive phase of glaciation but the most convincing landform evidence relates to more recent valley based glacier occupancy a moraine ridge on the slipper stones represents the most unequivocal palaeo glacier on north dartmoor with a palaeo ela of c 460 m above sea level asl although this relates to the youngest and most restricted phase of glaciation a longer term ela is likely to be represented by the corn ridge proto cirque at 370 410 m asl more extensive valley glaciers are recorded in each of the major drainage basins of north dartmoor by arcuate and linear bouldery ridges and hummocky valley floor drift which are interpreted as latero frontal moraines deposited by outlet lobes of a plateau icefield recession of these lobes is marked by inset sequences of such ridges and occasional meltwater channels plateau ice was predominantly thin and protective and snowblow and preferential accumulation in valley heads facilitated the modest glacial erosion and debris transport recorded in the landforms and sediments it is proposed that the highest plateaux have been occupied by ice for the longest cumulative period of time throughout the quaternary average glacial conditions explaining the distribution of different tor types on northern dartmoor this also explains the lack of tors on the most expansive of the highest plateau terrain ice dispersal centres as the product of a average glacial conditions preferentially removing tors or dampening their production rates b the survival of high relief type 1 tors during glaciation if they occupy summits too narrow to develop significant plateau icefields and or ridges that are bypassed by faster moving ice in adjacent deep valleys and c the survival of subdued type 2 tors in areas glaciated less regularly during the quaternary simple ice flow modelling indicates that a plateau icefield type glaciation is required for significant ice flow to occur and confirms thin ice cover in particular on narrow summits thereby supporting the explanation of tor class distribution the modelling allows us to spatially correlate the geomorphological evidence of margin positions into two major stages and further indicates a strong altitude mass balance feedback leading to an ice cap that is not in balance with its climate and with an extent that is limited by the length of the cold phases rather than their severity

chemical and mineralogical influences on concentrations of trace metals in hydrothermal fluids abstract concentrations of trace metals in hydrothermal solutions from the southern juan de fuca ridge sjfr and the tag hydrothermal field on the mid atlantic ridge are influenced by the combined effects of source rock composition brine seawater mixing and complex interplay among various metals and minerals deposited and remineralized in vent mounds and chimneys copper mo and co show predicted sharp decreases in concentration for vent fluids as temperatures decrease below 350 c however concentrations of cu in 363 c fluids at the tag site are well above values determined from seawater basalt interactions due to subseafloor refining processes and remineralization of chalcopyrite concentrations of zn cd pb as and ga do not show any temperature dependence between 214 to 363 c however zn values do correlate well with cl on an area by area basis due to subseafloor mixing of brine with altered seawater zinc levels also correlate well with concentrations of cd pb and as for all vent fluid samples as well as with basalt and zn rich sulfides implying some continuity in behavior from source rock to vent fluid to sulfide minerals gallium values correlate with zn and cl levels for the sjfr but are high relative to zn at the tag site due to subseafloor refining processes concentrations of tl follow cl k and rb consistent with the behavior predicted for tl overall the cl and zn rich fluids from the sjfr are characteristic of a brine dominated system formed during recent volcanism in contrast high temperature fluids from the tag area are representative of a system that has evolved over the past 100 000 yr with high concentrations of cu co and ga that result from higher temperatures and complex refining processes within a large vent mound

the connection between iron ore formations and mud shrimp colonizations around sunken wood debris and hydrothermal sediments in a lower cretaceous continental rift basin mecsek mts hungary in the early cretaceous the continental rift basin of the mecsek mts hungary was situated on the southern edge of the european plate the opening of the north atlantic ocean created a dilatational regime that expanded to the southern edge of the european plate where several extensional basins and submarine volcanoes were formed during the early cretaceous epoch permanent seaquake activity caused high swell events during which a large amount of terrestrial wood fragments entered into submarine canyons from rivers or suspended woods which had sunk into the deep seafloor these fragments created extended wood fall deposits which contributed large scale flourishing of numerous burrowing thalassinid crustaceans twelve different thalassinid coprolite ichnospecies can be found in the berriasian hauterivian volcano sedimentary formations

quaternary glacial history of nw garhwal central himalayas a first account of the quaternary glacial history is presented for northwest garhwal central himalaya on the basis of sediments and landforms one glacial stage has been recognised this is called the bhagirathi glacial stage when extensive valley glaciers advanced down the bhagirathi valley to jhala 40 5 km from the snout of gangotri glacier the ela depression during this stage was ca 640 m the bhagirathi glacial stage is constrained by optically stimulated luminescence dates of ca 63 ka and 5 ka bp and this glaciation is considered equivalent to the last glaciation elsewhere in the world the maximum extent of ice occurred ca 63 ka bp this however does not correlate with the last glacial maximum for the northern hemisphere ice sheets 20 18 ka bp a series of sharp crested moraines are present between 1 to 3 km beyond the snouts of most of the present glaciers these moraines formed during the mid holocene 5 ka bp termed here the shivling glacial advance small moraines are inset into these and are dated at about 200 to 300 bp the bhujbas glacial advance ca 300 to 200 bp and considered equivalent to the little ice age in other parts of the world ela depressions of between 40 100 m and 20 60 m occurred during the shivling and bhujbas glacial advances respectively since the bhujbas glacial advance there has been progressive retreat of glaciers initially by downwasting and retreat and then by simple retreat this retreat has accelerated during the last few decades impressive paraglacial fans are associated with deglaciation representing very rapid resedimentation during and soon after ice retreat

a reinterpretation of scottish hummocky moraine and its significance for the deglaciation of the scottish highlands during the younger dryas or loch lomond stadial the aim of this paper is to demonstrate that much of the hummocky moraine present within the northern part of the lochlomond readvance ice cap formerly situated in the north west scottish highlands may be interpreted as suites of ice front moraines deposited during active decay these landforms can be used to reconstruct ice cap decay whichleads to important insights into the shrinking form of the ice cap and associated environmental conditions evidence has been collected from 10803 airphotographs and from detailed field survey it is presented at three spatial scales

trace metals in hydrothermal solutions from cleft segment on the southern juan de fuca ridge concentrations of trace metals in fe and cl rich hydrothermal solutions from the southern juan de fuca ridge sjfr have been determined and corrected for residual precipitates formed in the sampler precipitate corrections for ag cd cu mo pb sb and zn were variable contributing an average of 20 to total solution concentrations whereas corrections for co averaged less than 5 and essentially no corrections were required for fe and mn values for cu co and mo in these solutions showed a strong dependence on temperature with sharp decreases in concentrations as temperatures decreased to less than 320 c in addition and unlike most other metals studied all vent fluids from the sjfr were almost completely depleted in mo relative to seawater values of about 110 nmol kg 1 in contrast to the cu co mo group concentrations of ag cd sb and pb correlated well with those for zn and are presumed to follow a distribution that is influenced less by temperature over the 246 to 332 c range encountered in this study and more by the combined chemical processes that control zn levels along the transport pathway from the deep reaction zone to the vent orifice

a review of topographic controls on moraine distribution ice marginal moraines are often used to reconstruct the dimensions of former ice masses which are then used as proxies for palaeoclimate this approach relies on the assumption that the distribution of moraines in the modern landscape is an accurate reflection of former ice margin positions during climatically controlled periods of ice margin stability however the validity of this assumption is open to question as a number of additional nonclimatic factors are known to influence moraine distribution this review considers the role played by topography in this process with specific focus on moraine formation preservation and ease of identification topoclimatic controls are not considered published literature indicates that the importance of topography in regulating moraine distribution varies spatially temporally and as a function of the ice mass type responsible for moraine deposition in particular in the case of ice sheets and ice caps 1000 km2 one potentially important topographic control on where in a landscape moraines are deposited is erosional feedback whereby subglacial erosion causes ice masses to become less extensive over successive glacial cycles for the marine terminating outlets of such ice masses fjord geometry also exerts a strong control on where moraines are deposited promoting their deposition in proximity to valley narrowings bends bifurcations where basins are shallow and or in the vicinity of topographic bumps moraines formed at the margins of ice sheets and ice caps are likely to be large and readily identifiable in the modern landscape in the case of icefields and valley glaciers 10 1000 km2 erosional feedback may well play some role in regulating where moraines are deposited but other factors including variations in accumulation area topography and the propensity for moraines to form at topographic pinning points are also likely to be important this is particularly relevant where land terminating glaciers extend into piedmont zones unconfined plains adjacent to mountain ranges where large and readily identifiable moraines can be deposited in the case of cirque glaciers 10 km2 erosional feedback is less important but factors such as topographic controls on the accumulation of redistributed snow and ice and the availability of surface debris regulate glacier dimensions and thereby determine where moraines are deposited in such cases moraines are likely to be small and particularly susceptible to post depositional modification sometimes making them difficult to identify in the modern landscape based on this review we suggest that despite often being difficult to identify quantify and mitigate topographic controls on moraine distribution should be explicitly considered when reconstructing the dimensions of palaeoglaciers and that moraines should be judiciously chosen before being used as indirect proxies for palaeoclimate i e palaeoclimatic inferences should only be drawn from moraines when topographic controls on moraine distribution are considered insignificant

rhenium osmium abundance and isotopic compositions of massive sulfides from modern deep sea hydrothermal systems implications for vent associated ore forming processes studies of rhenium re and osmium os concentrations and isotopic compositions in seafloor hydrothermal sulfides are an important tool for understanding the evolution of hydrothermal systems allowing the determination of both metal sources and reconstructing the physicochemical conditions of their deposition the re os concentrations and isotopic compositions of 38 massive sulfide samples have been studied in different hydrothermal fields from the east pacific rise epr mid atlantic ridge mar central indian ridge cir southwest indian ridge swir and back arc basin bab the majority of the sulfides possess os 187 os 188 that span a narrow range 1 004 to 1 209 which is most easily explained as a seawater derived component this may suggest that those initial os 187 os 188 isotope compositions of ancient seafloor hydrothermal sulfide deposits which were formed by the mixing process between seawater and hydrothermal fluid are possible for analysing ancient seawater os components only two of samples mar05 tvg1 10 2 and mar05 tvg1 21 from the logatchev hydrothermal field lhf mar possess moderately less radiogenic os 187 os 188 0 645 to 0 730 which may reflect the lesser extent of hydrothermal fluid seawater mixing during hydrothermal ore forming process

holocene mean july temperature and winter precipitation in western norway inferred from palynological and glaciological lake sediment proxies reconstructions of mean july temperature tjul and winter precipitation pw for the last 11 500 years on the folgefonna peninsula are presented tjul was reconstructed using pollen climate transfer functions and pw was reconstructed based on the exponential relationship between mean solid winter precipitation and ablation season temperature at the equilibrium line altitude ela with a reconstructed former ela using tjul as the proxy for ablation season temperature the reconstructions from the folgefonna peninsula suggest that the early holocene was relatively cool and dry until c 8000 cal yr bp followed by a warm and humid mid holocene until c 4000 cal yr bp with inferred tjul above 128c and pw reaching as high as 225 of the present day subsequent to c 4000 cal yr bp a reduction is seen in both inferred tjul and pw with large fluctuations during the last 500 years in addition new calculations of pw from two glaciers hardangerjokulen and jostedalsbreen in southern norway are presented the results show that pw varied in phase at all glaciers probably as a response to the same climate forcing factor during the early holocene a major shift is suggested between winds from the west and the east

the role of seasonality in abrupt climate change abstract a case is made that seasonality switches dominated by wintertime were instrumental in abrupt climate changes in the north atlantic region during the last glaciation and into the holocene the primary evidence comes from mismatches between mean annual temperatures from greenland ice cores in comparison with snowline changes in east greenland northern europe and north america the most likely explanation is a shutdown or reduction in strength of the conveyor this allows the spread of winter sea ice across the north atlantic thus causing the northern region to experience much colder winters because they mimic the greenland temperature rather than the snowline signal changes in the atlantic intertropical convergence zone and the asian monsoon may also share a winter linkage with greenland thus the paleoclimate record is consistent with the notion that a huge continental sector of the northern hemisphere stretching from greenland to asia was close to an extreme winter threshold during much of the last glaciation winter climate crossed this threshold repeatedly with marked changes in seasonality that may well have amplified and propagated a signal of abrupt change throughout the hemisphere and into the tropics

topographic control of equilibrium line altitude depression on reconstructed little ice age glaciers grovabreen western norway little ice age marginal moraines in the grovabreen area inner sunnfjord are mapped and described the modem and little ice age mid eighteenth century equilibrium line altitude ela of the plateau glacier grovabreen is calculated by the use of an accumulation area ratio aar of 0 6 giving a little ice age ela depression of 125 m aar ela depression of the little ice age glaciers is also calculated for northern and southern outlet glaciers different estimates are considered to be the result of topographic differences other methods such as the mean elevation of glaciers meg and the toe to headwall altitude ratio thar gave ela depressions of 260 m and 315 m respectively these differences due to topographic conditions indicate that only glaciers with a uniform slope should be used to calculate the regional ela of former glaciers

recognition and palaeoclimatic implications of late quaternary niche glaciation in eastern lesotho geomorphic evidence of former glaciation in the high drakensberg of southern africa has proven controversial with conflicting glacial and non glacial interpretations suggested for many landforms this paper presents new geomorphological sedimentological and micromorphological data and glacier mass balance modelling for a site in the leqooa valley eastern lesotho preserving what are considered to be moraines of a former niche glacier that existed during the last glacial maximum lgm the geomorphology and macro sedimentology of the deposits display characteristics of both active and passive transport by glacial processes however micromorphological analyses indicate a more complex history of glacial deposition and subsequent reworking by mass movement processes the application of a glacier reconstruction technique to determine whether this site could have supported a glacier indicates a reconstructed glacier equilibrium line altitude ela of 3136 m a s l and palaeoglacier mass balance characteristics comparable with modern analogues reflecting viable if marginal glaciation radiocarbon dates obtained from organic sediment within the moraines indicate that these are of lgm age the reconstructed palaeoclimatic conditions during the lgm suggest that snow accumulation in the drakensberg was significantly higher than considered by other studies and has substantial relevance for tuning regional climate models for southern africa during the last glacial cycle copyright 2009 john wiley sons ltd

utilizing physical sediment variability in glacier fed lakes for continuous glacier reconstructions during the holocene northern folgefonna western norway the maritime plateau glacier of northern folgefonna in western norway has a short subdecadal response time to climatic shifts and is therefore well suited for reconstructing high resolution glac

reaction of the accumulation zone portions of glaciers to climatic change the response of the accumulation regions of glaciers to changes in accumulation rate and in surface temperature is calculated by considering perturbations to the ice flow the analysis is limited to glaciers in which flow is dominated by internal shear and not by bottom sliding and for which flowlines are geographically parallel in general glaciers begin to alter thickness immediately after a change in accumulation rate but the effect of a change in surface temperature is delayed by the time for this temperature change to penetrate to depth in the glacier a warming leads to glacial thinning the amount and timing of the response is very different for different glaciers characteristic times are on the order of tens of years for mountain glaciers and tens of thousands of years for the east antarctic ice sheet as an example the theory is applied to the ice sheet near byrd station antarctica for hypothetical changes in surface accumulation rate and temperature rates and amounts of thickness change are calculated and it is found that the measured thinning is probably too fast to have been caused by climatic variation alone the effects of hypothetical climatic variations on the depth age and depth temperature relationships through the ice sheet are also calculated it is hoped that the theory will prove valuable in the interpretation of future drill hole results

glaciation of scotland during the younger dryas stadial a review considerable research effort in recent years has refined our knowledge of the landforms and sedimentary sequences generated by glaciers of the last cold episode in scotland the younger dryas and the chronology of their formation these recent advances have benefited from new technologies such as high resolution digital terrain models numerical ice sheet simulations and cosmic ray surface exposure dating this review presents a summary of recent younger dryas research in scotland particularly focusing on studies from the last two decades the findings of these investigations are compared with those of earlier workers and critically are appraised in terms of their relevance to five key aspects of younger dryas glaciation growth of the ice cap its geometry dynamics mode of decay and likely stadial climate minor differences aside the consensus view appears to favour a relatively thick but areally restricted central ice cap surrounded by satellite ice fields at its centre the ice cap was probably thickest during the first 500 years of the stadial after which it most likely thinned as the climate became increasingly arid outlet glaciers were dynamic only in marginal areas where they produced abundant moraine sequences during deglaciation but throughout much of the stadial central areas of the ice cap effected only minimal landscape modification deglaciation took place by active retreat under a rapidly warming climate overall the stadial was dominated by much colder and drier conditions than present and probably experi enced greater intra annual temperature ranges copyright 2009 john wiley sons ltd