internal characteristics of ice marginal sediments deduced from georadar profiling and sediment properties brogger peninsula svalbard abstract georadar and sedimentological data were acquired in the ny alesund area on brogger peninsula in order to study diamicton in frontal areas of vestre broggerbreen and midre lovenbreen parallel common offset georadar lines were acquired for information on thickness and layering and multioffset measurements served to deduce the subground velocity short permafrost cores

massive sulfides of mount jourdanne along the super slow spreading southwest indian ridge and their genesis abstract modern massive sulfide deposits are known to occur in diverse tectonic settings and it is generally expected that hydrothermal deposits of similar geological settings shall have more or less similar mineralogical and geochemical signatures however the mount jourdanne sulfide deposits along the super slow spreading southwest indian ridge deviate from this common concept these sulfide precipitates are zn rich up to 35 wt and are characterized by high concentrations of pb 3 5 wt as 1 1 wt ag 0 12 wt au 11 ppm sb 967 ppm and cd 0 2 wt which are unusual for a modern sediment free mid oceanic ridge system therefore we have reinvestigated the sulfide samples collected during the indoyo cruise in 1998 in order to explain their unusual mineralogy and geochemical composition the sulfide samples are polymetallic and are classified as a chimneys b mounds and c hydrothermal breccias the chimneys are small tube like symmetrical bodies 30 40 cm high 10 cm diameter and consist mainly of sphalerite and less chalcopyrite set in a matrix of late amorphous silica the inner wall shows a late stage colloform sphalerite containing co precipitates of galena and or pb as sulfosalts in contrast the mound samples are dominated either by fe sulfides pyrite or by a mixture of pyrite and chalcopyrite with less sphalerite pyrrhotite amorphous silica and barite both the chimney and mound samples are characterized by layering and mineral zonation the hydrothermal breccias are highly altered and mineralogically heterogeneous they consist of silicified basaltic material that are impregnated with sulfides and contain cm sized chimney fragments within a matrix of low temperature minerals such as sphalerite and pyrite the latter fragments mainly consist of chalcopyrite with isocubanite lamellae in addition these breccias contain late stage realgar boulangerite galena pb as sulfosalts and barite that are mostly confined to vugs or fractures at least five mineralogical associations are distinguished that indicate different thermal episodes ranging from black smoker mineralization conditions to cessation of the hydrothermal activity based on the mineralogical associations and established literature in this regard it is inferred that the mineralization at mt jourdanne occurred mainly in three temperature domains above 300 c the chalcopyrite with isocubanite pyrrhotite association formed whereas the sphalerite dominated assemblage with much less chalcopyrite and pyrite formed around and below 300 c the late stage mineralization below 200 c contains colloform sphalerite galena pb as sulfosalts realgar and barite the unusual mineralogy and trace element chemistry for this modern vhms deposit could be explained assuming hydrothermal leaching of some felsic differentiates underneath the basaltic cover and subsequent zone refining processes

low temperature silica rich gold mineralization in mafic vms systems evidence from the troodos ophiolite cyprus the troodos ophiolite cyprus hosts the on land analogue for actively forming mafic cu rich or cyprus type vms deposits in addition to high temperature 350 c sulfide mound related mineralization other fossil seafloor mineralizing systems are known to operate including those characterized by an enrichment in au and abundant silicification in this study the mineralogy and geochemistry of four au and silica rich localities in troodos are considered and these include kokkinovounaros mathiatis south touronjia and alpen rose we present whole rock geochemical and mineralogical data characterizing the distribution of au in the hydrothermal systems of troodos samples from silica rich localities have two distinct sample mineralogies supergene samples that contain predominantly goethite hematite and jarosite and hypogene samples that contain quartz amorphous silica and minor hematite hypogene samples from mathiatis south and kokkinovounaros are enriched in au with a median concentration of 1 5 ppm relative to supergene samples that contain 0 1 ppm n 107 this indicates that au enrichment occurred on the seafloor and is not solely related to supergene weathering of silica rich mineralization we suggest that silica rich au mineralization in troodos formed during the migration of newly formed crust off axis or as white smokers proximal to known vms deposits in silica rich mineralization that is located distally from known massive sulfide deposits au was probably remobilized from shallow crustal reservoirs during the low temperature fluid flow 100 300 c in the lower extrusive sequence as the crust cooled and migrated off axis based on modern seafloor analogues we propose a revised model for the troodos hydrothermal system that explains the distribution of au in silica rich mineralization that formed off axis and postdates vms formation and in zones proximal to vms deposits that formed simultaneously as white smoker type vents we suggest that silica rich mineralized zones formed an intermediary between high temperature 350 c on axis vms deposits and the low temperature silicification of umbers 100 c

evolution of seawater 87sr86sr over the last 400 ka the absence of glacial interglacial cycles abstract fluctuations in the 87 sr 86 sr ratio of seawater accompanying glacial interglacial climate changes have been reported in recent studies but remain highly controversial to investigate these potential fluctuations we present very high precision 13 ppm 87 sr 86 sr measurements on planktonic foraminifera from indian ocean and pacific cores 87 sr 86 sr ratios from three different foraminiferal species are indistinguishable from one another in both core top and 50 ka samples demonstrating that changes due to diagenesis or contamination do not influence the measurements average 87 sr 86 sr ratios for pacific ocean and indian ocean samples are also indistinguishable at three intervals core top 50 ka and 300 370 ka demonstrating that the oceans have remained well mixed with respect to sr also 87 sr 86 sr ratios are not affected by changes in the precleaning of samples measurements from pacific core v28 238 that used in the study of dia et al 1 do not reproduce the cycles seen in the previous study and are statistically well explained by a linear increase in the seawater 87 sr 86 sr ratio it seems likely that an analytical artefact caused the cycles in the previous study measurements from two key sections of core from odp site 758 that used in the study of clemens et al 2 do not reproduce the largest shifts seen in the previous study despite the considerably better precision reported here the apparent cyclicity in the clemens et al 2 data is also suggested to be due to an unknown analytical artefact the 48 measurements presented here are a statistically good fit to a straight line defined by 87sr ppm 0 0613 age ka at the 13 ppm level of precision no evidence for a glacial interglacial variation in the seawater 87 sr 86 sr ratio is seen glacial interglacial variation may still exist but this data constraints its maximum amplitude to 6 9 ppm which would correspond to changes in the riverine sr flux of 30

gold speciation and transport in geological fluids insights from experiments and physical chemical modelling this contribution provides an overview of available experimental thermodynamic and molecular data on au aqueous speciation solubility and partitioning in major types of geological fluids in the earth s crust from low temperature aqueous solution to supercritical hydrothermal magmatic fluids vapours and silicate melts critical revisions of these data allow generation of a set of thermodynamic properties of the auoh aucl 2 auhs and au hs 2 complexes dominant in aqueous hydrothermal solutions however other complexes involving different sulphur forms chloride and alkali metals may operate in high temperature sulphur rich fluids vapours and melts the large affinity of au for reduced sulphur is responsible for au enrichment in s rich vapours and sulphide melts which are important gold sources for hydrothermal deposits thermo dynamic speciation and partitioning data and their comparison with au and s contents in natural fluid inclusions from magmatic hydrothermal gold deposits provide new constraints on the major physical chemical parameters temperature pressure salinity acidity redox and ubiquitous fluid components sulphur carbon dioxide arsenic affecting au concentration transport precipitation and fractionation from other metals in the crust the availability and speciation of sulphur and their changes with the fluid and melt evolution are the key factors controlling gold behaviour in most geological situations

europe s southernmost glaciers response and adaptation to climate change the southernmost glaciers in europe are located on the iberian apennine and balkan peninsulas in mid latitudes between 41 n and 44 n at altitudes ranging from 2000 to 3000 m a s l all these glaciers are a legacy of the little ice age lia they survive in a relatively warm environment mean annual temperature 0 ct o 1 c due to local topographic controls and high levels of accumulation as a result of avalanche and wind blown snow in the pirin mountains bulgaria snezhnika glacieret has been cored providing an archive of recent climate change small glaciers such as this respond quickly to climatic extremes since the lia maximum during the 19th century all southern european glaciers have retreated losing 30 100 of their volume however despite the trend towards warmer years since the late 1970s some glaciers still survive even after some of the hottest summers on record predicted future warming especially in summer and drier conditions in the mediterranean basin may result in the disappearance of all glacier features at these latitudes in europe within the next few decades

tracing dust sources and transport patterns using sr nd and pb isotopes continental dust transported through the atmosphere can be a tracer of atmospheric circulation and transport as well as being a source of information about climate in the dust s source area this information about the provenance of dust transported from desert areas and deposited elsewhere on the oceans and continents can be evaluated using several observational techniques satellite imagery has been used to this end in recent decades and air mass back trajectories have been calculated to trace dust deposits back to their source area another method consists of analysis of the concentration and composition of certain tracers in the dust itself and comparing them to soils and sediments from possible source areas this method has the advantage of being useable for paleo atmospheric circulation and paleo dust transport studies whereas satellite imagery and air mass back trajectories are restricted to relatively recent times we review here different kinds of isotopic tracers that have been used to trace dust provenance but special attention is focused on the use of sr nd and pb isotopes we evaluate their use in studies of both spatially as well as temporally varying continental dust source and transport

high resolution hydrothermal structure of hansbreen spitsbergen mapped by ground penetrating radar detailed ground penetrating radar gpr surveys at 50 and 200 mhz on hansbreen a polythermal glacier in southern svalbard are presented and interpreted comparison of the variations in character of the radar reflections with borehole thermometry and water levels in moulins suggests that gpr can be used to study the hydrothermal properties of the glacier the high resolution of the gpr data shows that the hydrothermal structure of the glacier is highly variable both along the centre line and on transverse profiles water contents for many places and depths within the glacier were calculated by estimating radar wave velocities to point reflectors we find typical water contents of 1 2 for the temperate ice but wetter ice associated with surface crevassing and moulins typically 4 water content there is evidence that wet ice sometimes overlays drier ice the hydrothermal structure is thus shown to be very complex temperature gradients in the cold ice indicate freezing rates of temperate ice below cold ice of 0 1 0 5 m a while isolated point reflectors within the cold ice indicate large water filled bodies that are probably related to the regular drainage structure of the glacier

sulfidation equilibria as guides to gold mineralization in volcanogenic massive sulfides evidence from sulfide mineralogy and the composition of sphalerite hydrothermal fluids responsible for the formation of volcanogenic massive sulfides may transport gold in solution as au hs 2 super at low temperatures or 350 degrees c low ph and elevated salinities or 1 m nacl the documented fluid chemistry of active hydrothermal vents on the modern seafloor confirms that gold transport is mainly due to au hs 2 super and the calculated solubility of gold as au hs 2 super is highest in low temperature 150 degrees 250 degrees c vent fluids at elevated oxygen and sulfur activities sulfides which coprecipitate with gold commonly have properties which can be related to the temperature and sulfidation state of the hydrothermal fluids and therefore reflect conditions which were favorable for the transport or deposition of gold as au hs 2 super a comparison of gold grades with sulfide mineral equilibria and the fes contents in sphalerite from a variety of deposits indicates that gold enrichment is closely related to the temperature a sub s 2 conditions in the ore forming fluids sea floor sulfides range from sulfur rich pyrite marcasite assemblages to relatively sulfur deficient pyrrhotite isocubanite assemblages with coexisting sphalerite containing 0 to 55 mole percent fes significant gold enrichment occurs exclusively in low temperature 300 degrees c contain ferich sphalerite 1 5 mole fes and gold grades 1 ppm au archean cu zn deposits at noranda quebec consist mainly ofpyrite pyrrhotite ores containing 0 5 to 1 ppm au together with fe rich sphalerite 10 12 mole fes however pyritic ores which occur stratigraphically up section commonly contain 1 to 3 ppm au and relatively fe poor sphalerite 5 mole fes different sulfide mineral equilibria and fes contents in sphalerite are interpreted to reflect the same physical and chemical conditions which influence gold grades and suggest that petrologic indicators of the sulfidation state may be useful guides to gold mineralization in volcanogenic massive sulfides

late quaternary changes in desert dust inputs to the red sea and gulf of aden from 87sr 86sr ratios in deep sea cores abstract strontium isotope ratios of the hcl insoluble residue isr and foraminifera of cores from the red sea and gulf of aden are used to monitor effects of hydrothermal fluvial and desert dust transport to these regions during the past 0 5 ma while the gulf of aden was open ocean during low glacial sea levels the red sea was a semi isolated basin allowing the possibility to study the effects regional versus global inputs during glacial interglacial cycles the isr from the gulf of aden and the red sea display different ranges of 87 sr 86 sr ratios of 0 7085 0 7107 and 0 7062 0 7085 respectively these reflect mixtures between three components granitic hydrothermal and loess strontium with representative 87 sr 86 sr of 0 711 0 706 and 0 7085 respectively gulf of aden isr represent mixtures of the loess and granitic sources while red sea isr are mixtures of the loess and sea floor hydrothermal sources in the gulf of aden loess sources dominate during glacials indicating intensification of the ne moonsonal wind regime and granitic sources dominate during interglacials reflecting wetter conditions related to an enhanced regional sw monsoon red sea isr show no clear glacial interglacial distinction but display a general temporal increase in 87 sr 86 sr ratios over the past 380 ka toward loess like values indicating increasing loess contributions toward the present day the ranges of isr 87 sr 86 sr ratios in the red sea and the gulf of aden were distinct prior to the last glacial period 87 sr 86 sr ratios following major climate transitions at 10 80 130 190 240 and 330 ka bp that coincide with sapropel episodes in the eastern mediterranean which originated from the african monsoonal system and indicate enhanced wetness in the desert belt 87 sr 86 sr ratios of foraminifera show a very narrow range from 0 70912 to 0 70917 over 530 ka and in most samples are consistent with the contemporaneous global ocean in the red sea foraminifera and pteropods show slightly more variability than the gulf of aden a few red sea samples fall slightly above the seawater trend in marine isotope stages 5 and 9 and below during the last deglaciation suggesting local effects that occurred when the flow of surface ocean water from the gulf of aden to the red sea was limited and the red sea behaved like an amplifier basin

the characterisation of saharan dusts and nile particulate matter in surface sediments from the levantine basin using sr isotopes abstract the provenance of sediments within the levantine basin of the eastern mediterranean was studied using 87 sr 86 sr isotopic ratios together with major elements measurements were made on the detrital fraction of surface sediments and the two most important sources of detrital matter to the region saharan dust was characterised by an 87 sr 86 sr isotopic ratio in the range 0 7160 0 7192 there was a small systematic decrease in 87 sr 86 sr from west to east which is interpreted as due to a change in the balance of aeolian source material the nile particulate matter had a 87 sr 86 sr isotopic ratio in the range 0 7057 0 7071 87 sr 86 sr isotopic signatures together with sr concentration were used to calculate the contributions made by saharan dust and nile particulate matter to the surface sediments of the levantine basin it was shown that nile derived sediment was dispersed widely across the levantine basin enabling the area affected by retention of sediment behind the aswan dam to be determined

carbonate preservation and climatic changes in the central red sea during the last 380 kyr as recorded by pteropods abstract numerical abundances of pteropods and planktic foraminifera and the mode of pteropod preservation were determined in core kl 11 taken from the central part of the red sea the abundance of pteropods shells g dry sediment was compared to that of planktic foraminifera pt pf pt a technique that permits detection of changes in carbonate preservation for the last 380 kyr the numerical abundance of pteropods is influenced by the properties of the water column and preservation is influenced by the bottom water during the last 200 kyr except during isotope stage 5 5 carbonates are in general well preserved during this period the abundance pattern of the pteropods and planktic foraminifera is very similar and follows the climatic signal of the red sea with high numbers during the interglacial stages changing to very low numbers during glacial maximum conditions the similar abundance trends of the two groups and between them and the 18o curve indicates abundance is strongly linked to salinity from isotope stage 6 to the bottom of the core the pteropods occur in low numbers unlike the planktic foraminifera which continue to display the high amplitude glacial interglacial cyclicity the deviations mainly during interglacial stages between the abundance pattern of the two groups and the low pt pf pt values indicate a significant change in carbonate preservation distinctive carbonate dissolution intervals are recognized in the red sea correlating to large scale deep water dissolution events of the mid brunhes dissolution cycle in the indian ocean the anti estuarine circulation pattern of the red sea prevents a direct connection between the deep water masses of the two oceans and rules out the likelihood that changes in the deep water circulation caused these carbonate dissolution events the numerical variations between nonmigratory epipelagic and migratory mesopelagic pteropods were used to evaluate changes in the structure of the water column abundance maxima of mesopelagic pteropods as in the recent red sea indicate an aerated water column with 0 5 ml o2 l oxygen concentrations at the minimum zone mesopelagic abundance maxima coincide commonly with negative monsoonal index values indicating a more aerated water column connected to increasing aridity in the red sea region abundance maxima of epipelagic pteropods indicate a strongly stratified water column at times causing severe depletion in oxygen at intermediate water depths epipelagic peak events coincide often with positive monsoon index values implying an overall milder and more humid climate in the red sea probably associated with enhanced precessional controlled southwest monsoon activity

links between topography wind deflation lakes and dust the case of the bodele depression chad the bodele depression chad is the planet s largest single source of dust deflation from the bodele could be seen as a simple coincidence of two key prerequisites strong surface winds and a large source of suitable sediment but here we hypothesise that long term links between topography winds deflation and dust ensure the maintenance of the dust source such that these two apparently coincidental key ingredients are connected by land atmosphere processes with topography acting as the overall controlling agent we use a variety of observational and numerical techniques including a regional climate model to show that 1 contemporary deflation from the bodele is delineated by topography and a surface wind stress maximum 2 the tibesti and ennedi mountains play a key role in the generation of the erosive winds in the form of the bodele low level jet llj 3 enhanced deflation from a stronger bodele llj during drier phases for example the last glacial maximum was probably sufficient to create the shallow lake in which diatoms lived during wetter phases such as the holocene pluvial winds may therefore have helped to create the depression in which erodible diatom material accumulated instead of a simple coincidence of nature dust from the world s largest source may result from the operation of long term processes on paleo timescales which have led to ideal conditions for dust generation in the world s largest dust source similar processes plausibly operate in other dust hotspots in topographic depressions

abrupt post glacial climate events in west asia and north africa monsoon domains regions beyond the present or past penetration of the indian and african monsoons have experienced several large and abrupt climatic fluctuations over the past 13 14c kyr pollen and lake records from west asia western tibet and rajasthan east africa ethiopia and west africa western sahara sahel and subequatorial africa were selected on the basis of chronological control sensitivity of both site and environmental indicators to climate change the continuity of the record and interdisciplinary control of the palaeoclimatic interpretation conditions wetter than those of today prevailed during the early mid holocene period but major dry spells are recorded at all sites during the intervals 11 0 9 5 kyr bp 8 7 kyr bp and 3 4 kyr bp several records also suggest dry events of minor amplitude around 6 kyr bp potential boundary forcings of insolation and sea surface and tropical land surface conditions are discussed the solar radiation accounts for the general envelop of the post glacial monsoon fluctuations but explains neither the timing nor the amplitude of the short term changes in spite of apparent covariation between fluctuations in sea surface conditions in the north atlantic and the monsoon record no direct mechanism could be found relating the intensity of the oceanic thermohaline conveyor belt to the monsoon strength changes in tropical land surface conditions soil moisture negative feedback and changes in ch4 production from wetlands provide a more satisfactory hypothesis for explaining abrupt reversal events

the nature of the crust under cayman trough from gravity abstract considerable crustal thickness variations are inferred along cayman trough a slow spreading ocean basin in the caribbean sea from modeling of the gravity field the crust to a distance of 50 km from the spreading center is only 2 3 km thick in agreement with dredge and dive results crustal thickness increases to 5 5 km at distances between 100 and 430 km west of the spreading center and to 3 5 6 km at distances between 60 and 370 km east of the spreading center the increase in thickness is interpreted to represent serpentinization of the uppermost mantle lithosphere rather than a true increase in the volume of accreted ocean crust serpentinized peridotite rocks have indeed been dredged from the base of escarpments of oceanic crust rocks in cayman trough laboratory measured density and p wave speed of peridotite with 40 50 serpentine are similar to the observed speed in published refraction results and to the inferred density from the model crustal thickness gradually increases to 7 8 km at the far ends of the trough partially in areas where sea floor magnetic anomalies were identified basement depth becomes gradually shallower starting 250 km west of the rise and 340 km east of the rise in contrast to the predicted trend of increasing depth to basement from cooling models of the oceanic lithosphere the gradual increase in apparent crustal thickness and the shallowing trend of basement depth are interpreted to indicate that the deep distal parts of cayman trough are underlain by highly attenuated crust not by a continuously accreted oceanic crust

geology sulfide geochemistry and supercritical venting at the beebe hydrothermal vent field cayman trough the beebe vent field bvf is the world s deepest known hydrothermal system at 4960m below sea level located on the mid cayman spreading centre caribbean the bvf hosts high temperature 401 c black smoker vents that build cu zn and au rich sulphide mounds and chimneys the bvf is highly gold rich with au values up to 93 ppm and an average au ag ratio of 0 15 gold precipitation is directly associated with diffuse flow through beehive chimneys significant mass wasting of sulphide material at the bvf accompanied by changes in metal content results in metaliferous talus and sediment deposits situated on very thin 2 3km thick oceanic crust at an ultraslow spreading centre the hydrothermal system circulates fluids to a depth of 1 8km in a basement that is likely to include a mixture of both mafic and ultramafic lithologies we suggest hydrothermal interaction with chalcophile bearing sulphides in the mantle rocks together with precipitation of au in beehive chimney structures has resulted in the formation of a au rich volcanogenic massive sulphide vms deposit with its spatial distribution of deposit materials and metal contents the bvf represents a modern day analogue for basalt hosted au rich vms systems this article is protected by copyright all rights reserved

summer melt regulates winter glacier flow speeds throughout alaska 1 predicting how climate change will affect glacier and ice sheet flow speeds remains a large hurdle toward accurate sea level rise forecasting increases in surface melt rates are known to accelerate glacier flow in summer whereas in winter flow speeds are believed to be relatively invariant here we show that wintertime flow speeds on nearly all major glaciers throughout alaska are not only variable but are inversely related to melt from preceding summers for each additional meter of summertime melt we observe an 11 decrease in wintertime velocity on glaciers of all sizes geometries climates and bed types this dynamic occurs because interannual differences in summertime melt affect how much water is retained in the subglacial system during winter the ubiquity of the dynamic indicates it occurs globally on glaciers and ice sheets not frozen to their beds and thus constitutes a new mechanism affecting sea level rise projections

ground based remote sensing techniques for diagnosis of the current state and recent evolution of the monte perdido glacier spanish pyrenees this work combines very detailed measurements from terrestrial laser scanner tls ground based interferometry radar gb sar and ground penetrating radar gpr to diagnose current conditions and to analyse the recent evolution of the monte perdido glacier in the spanish pyrenees from 2011 to 2017 thus this is currently one of the best monitored small glacier 2 worldwide the evolution of the glacier surface was surveyed with a tls evidencing an important decline of 6 1 0 3 m on average with ice losses mainly concentrated over 3 years 2012 2015 and 2017 ice loss is unevenly distributed throughout the study period with 10 15 m thinning in some areas while unchanged areas in others gb sar revealed that areas with higher ice losses are those that are currently with no or very low ice motion in contrast sectors located beneath the areas with less ice loss are those that still exhibit noticeable ice movement average 2 4 5 cm d 1 in summer and annual movement of 9 98 ma 1 from ablation stakes data gpr informed that ice thickness was generally

sr nd and pb isotope constraints on the formation of the metalliferous sediments in the nereus deep red sea previous chemical analyses of sediments from nereus deep core 412 located in the northern part of the red sea at about 23 20 n have demonstrated the occurrence of v rich authigenic magnetites associated with fe zn and cu sulphides mostly located at the bottom of the core the evolutionary stage of nereus deep is intermediate between that of the immature shaban deep and the more evolved atlantis ii deep previous studies have proposed either morb basalts by analogy with east pacific rise sulphide deposits or sediments as possible sources of the metals in the red sea metalliferous sediments sr nd and pb isotope systematics observed at ten levels in nereus core 412 lead us to distinguish three types of sediments 1 with predominantly basaltic fragments associated with loose titanomagnetite crystals 0 70413 87sr86sr 0 70622 0 51271 143nd144nd 0 51300 18 618 206pb204pb 18 673 2 detrital or biogenic sediments with a continental isotopic imprint 0 70938 87sr86sr 0 71323 0 51242 143nd144nd 0 51262 18 848 206pb204pb 18 890 and 3 v rich metalliferous sediments 0 70872 87sr86sr 0 70895 0 51260 143nd144nd 0 51274 18 717 206pb204pb 18 851 on sr nd and pb pb isotope diagrams this last group of sediments defines a field located between the fields of the first two groups our data suggest that the sr nd and pb in the studied metalliferous sediments were derived from overlying sedimentary beds in which the two main constituent detrital components show very distinct origins red sea morb and continental arabo nubian shield these data clearly support a model of convective circulation within the nereus deep sedimentary pile this model involves leaching two main components from the upper sedimentary layers of the core and a downward circulation of a hot fluid promoting the growth of v rich magnetites and fe zn and cu sulphides when the fluid cooled by mixing with the pore water of sediments from the lower part of the core a driving force represented by magmatic activity located near the 412 core in the nereus deep is required to explain the presence of hot convective fluids these data also suggest that for sedimented ridges the isotopic imprint of a basaltic source in metalliferous sediments or a hydrothermal ore deposit may result by interaction of a hot fluid with detrital sediments that are enriched in basaltic clasts and loose magmatic crystals

rapid growth of some major segments of continental crust some major segments of continental crust display a narrow range of sm nd crustal formation ages the sizes of the canadian shield the svecokarelian province of northern europe the west central united states and the arabian nubian shield suggest rapid crustal growth island arc accretion models rank among the most favored tectonic models for the formation of these areas a quantitative comparison of the growth rates of these crustal segments to mesozoic cenozoic arc addition rates shows however that island arc accretion alone seems insufficient to account for the amount of crust that was produced in each of these terrains other additional mechanisms such as hot spot volcanism and underplating may have been active in addition to arc accretion alternatively large amounts of preexisting basement have gone so far undetected

relict hydrothermal events along the super slow southwest indian spreading ridge near 63 56 e mineralogy chemistry and chronology of sulfide samples abstract during the indoyo cruise in 1998 with shinkai 6500 a massive sulfide field was located in a water depth of about 2940 m near 27 51 s 63 56 e east of the melville fracture zone the newly discovered hydrothermal field is situated at the summit of an axial volcanic ridge informally called mount jourdanne within the field inactive chimneys as well as hydrothermal mounds were observed on the ocean floor but no indications such as shimmering water chemical anomalies in the water column or faunal relicts which might point to an active vent site were observed our discovery proves for the first time that high temperature massive sulfide chimneys can also develop at a super slow spreading ridge such as the southwest indian ridge this discovery of massive sulfides will possibly open new aspects in the understanding of hydrothermal processes along super slow spreading ridges since the sulfide samples from mt jourdanne show interesting differences in their mineralogical as well as chemical compositions when compared to sulfide samples from faster opening ridge environments to reconstruct the history of the evolution of this field age dating studies were carried out on the recovered sulfide samples these indicate activity between 70 000 and 13 000 years ago

chemical and isotopic 87sr 86sr δ18o δd constraints to the formation processes of red sea brines abstract about twenty deeps filled with hot brines and or metalliferous sediments are located along the red sea axis these brines present a well suited framework to study the hydrothermal activity in such a young ocean the present study outlines the results of a geochemical approach combining major trace element and isotopic oxygen hydrogen strontium analyses of brines in six of the deeps to evaluate different processes of brine formation and to compare the evolution of each deep important heterogeneities in temperature salinity hydrographic structure and chemistry are recorded each brine having its own characteristics the intensity of hydrothermal circulation varies among the deeps and ranges from being strong atlantis ii and nereus to weak port soudan and even to negligible valdivia and suakin and it varies along the entire red sea axis these observations do not favour a unique formational model for all of the brines for example the brines of the suakin deep appear to have been formed by an old sea water which dissolved evaporite beds without significant fluid circulation and hydrothermal input while others such as atlantis ii or nereus deeps appear to be dominated by hydrothermal influences a striking feature is the absence of a relationship between the position of the deeps along the axis and their evolutionary maturity

on the late pleistocene holocene sapropel record of climatic and oceanographic variability in the eastern mediterranean sapropels and intercalated marls in a piston core from the eastern mediterranean are chemically and mineralogical distinct kaolinite smectite and total s contents fe a1 ba a1 co a1 mo a1 and v a1 are higher whereas quartz mg calcite illite contents si a1 ti a1 k a1 rb a1 and zr a1 are lower in the sapropels missing and ghost sapropels are identified by mineralogical and chemical properties that are not prone to diagenesis primary production was higher ba a1 and bottom water and or interstitial oxygenation was lower co a1 mo a1 ni a1 and v a1 during sapropel formation wind speeds quartz clay si a1 and zr a1 and bottom water salinities mg calcite calcite were higher during periods of marl formation sapropels represent a fundamentally different sedimentary facies whose formation is linked to changes in the hydrological balance in the basin driven by precessionally modulated changes in monsoon strength and subtropical precipitation changes which altered circulation production and sediment source areas

wind influence on snow depth distribution and accumulation over glaciers 1 in mountain regions wind is known to cause snow redistribution while physically based models of snow redistribution have been developed for flat to gently rolling terrain extension of these findings to steep terrain has been limited by the complexity of wind fields in such areas in this study we applied a nonhydrostatic and compressible atmospheric prediction model to steep alpine topography and compared the results to a fully distributed data set of snow depth estimations the results show reduced horizontal wind velocity as well as an increasing downward vertical wind velocity over areas with the largest winter accumulation which are mostly glacierized we show that the wind velocity normal to the local surface which should be zero in a nondivergent flow field and is a direct measure of increased or decreased local deposition is a function of small scale features of local topography the correlation between wind fields snow accumulation and glacierization suggests that accurate modeling of wind fields over glacierized areas in complex terrain is a key factor for understanding the mass balance distribution of glaciers

the gold content of volcanogenic massive sulfide deposits volcanogenic massive sulfide deposits contain variable amounts of gold both in terms of average grade and total gold content with some vms deposits hosting world class gold mines with more than 100 t au previous studies have identified gold rich vms as having an average gold grade expressed in g t exceeding the total abundance of base metals expressed in wt however statistically meaningful criteria for the identification of truly anomalous deposits have not been established this paper presents a more extensive analysis of gold grades and tonnages of 513 vms deposits worldwide revealing a number of important features in the distribution of the data a large proportion of deposits are characterized by a relatively low gold grade 2 g t with a gradual decrease in frequency towards maximum gold grades defining a log normal distribution in the analysis presented in this paper the geometric mean and geometric standard deviation appear to be the simplest metric for identifying subclasses of vms deposits based on gold grade especially when comparing deposits within individual belts and districts the geometric mean gold grade of 513 vms deposits worldwide is 0 76 g t the geometric standard deviation is 2 70 g t au in this analysis deposits with more than 3 46 g t au geometric mean plus one geometric standard deviation are considered auriferous the geometric mean gold content is 4 7 t au with a geometric standard deviation of 26 3 t au deposits containing 31 t au or more geometric mean plus one geometric standard deviation are also considered to be anomalous in terms of gold content irrespective of the gold grade deposits with more than 3 46 g t au and 31 t au are considered gold rich vms a large proportion of the total gold hosted in vms worldwide is found in a relatively small number of such deposits the identification of these truly anomalous systems helps shed light on the geological parameters that control unusual enrichment of gold in vms at the district scale the gold rich deposits occupy a stratigraphic position and volcanic setting that commonly differs from other deposits of the district possibly due to a step change in the geodynamic and magmatic evolution of local volcanic complexes the gold rich vms are commonly associated with transitional to calc alkaline intermediate to felsic volcanic rocks which may reflect a particularly fertile geodynamic setting and or timing e g early arc rifting or rifting front at the deposit scale uncommon alteration assemblages e g advanced argillic aluminous strongly siliceous or potassium feldspar alteration and trace element signatures may be recognized e g au ag as sb bi hg te suggesting a direct magmatic input in some systems

high resolution stratigraphy with strontium isotopes the isotopic ratio of strontium 87 to strontium 86 shows no detectable variation in present day ocean water but changes slowly over millions of years the strontium contained in carbonate shells of marine organisms records the ratio of strontium 87 to strontium 86 of the oceans at the time that the shells form sedimentary rocks composed of accumulated fossil carbonate shells can be dated and correlated with the use of high precision measurements of the ratio of strontium 87 to strontium 86 with a resolution that is similar to that of other techniques used in age correlation this method may prove valuable for many geological paleontological paleooceanographic and geochemical problems

short term surface ice motion variations measured with a ground based portable real aperture radar interferometer we report measurements using a portable real aperture radar gamma portable radar interferometer gpri for interferometric imaging of the surface ice motion on gornergletscher switzerland during the drainage of the adjacent ice marginal lake gornersee the gpri tracked the surface ice motion in line of sight over an area of 3k m 2 down glacier of gornersee almost continuously during the drainage event the displacement maps derived from the acquired interferograms capture the spatial distribution of the surface ice motion due to fast acquisition times of the microwave images the gpri was able to record sub daily variations of the ice displacements most likely caused by the impact of the gornersee drainage on the ice motion of gornergletscher in situ point measurements of the ice displacement agree reasonably well with the results obtained by the gpri and highlight the use of the gpri for high resolution measurements of glacier surface ice motion motion of gornergletscher these variations in surface ice motion were triggered by the subglacial drainage of the adjacent marginal ice dammed lake gornersee we present ice displacement maps derived from the gpri interfero grams and analyze the performance of the radar device for remote sensing of surface ice motions of a glacier on spatial and temporal scales lower than in conventional d insar applications we compare the radar displacements against local in situ ice displacement measurements to complete the study a brief discussion of the observed displacements in relation to the drainage phenomena is given

mediterranean quaternary sapropels an immediate response of the african monsoon to variation of insolation abstract in the subsurface of the east mediterranean sea eleven discrete basin wide organic rich black sapropels were deposited during the last 465 000 years they are dated by oxygen isotopic chronostratigraphy the most recent sapropel has been shown to be the consequence of heavy nile river summer floods due to increased monsoonal summer precipitation over ethiopia and not of scandinavian ice sheet meltwater influx into the east mediterranean sea as was previously believed while most sapropels were deposited during interglacials two thick sapropels formed during glacial periods as shown by their position in the oxygen isotopic stratigraphy and by their pollen record in core rc9 181 the new evidence presented here is that the sapropel sequence in this core including the two glacial sapropels correlates on a one to one basis with the highest values of an index of insolation on top of the atmosphere the concept of this index derives from an analysis of the african monsoon process the index variation is computed for the last 465 000 years from the caloric northern summer insolation in the tropical latitudes controlled by variations of the earth s orbital parameters it is conjectured that this index might be linked through the climate system to the monsoonal precipitation which in africa produces the nile river summer flood

geologic investigations in the cayman trough evidence for thin oceanic crust along the mid cayman rise the mid cayman rise is a 110 km long accreting plate boundary 2cm yr full rate characterized by a deep rift valley eighteen transponder navigated dives were made by the submersible alvin along the rift valley walls in two areas on opposite sides of the rift valley the relief of the walls is produced by a large number of inward facing small throw fault escarpments with vertical displacements ranging from a few tens of meters to perhaps as much as 400 m from these escarpments 142 samples were collected and gabbroic rocks 116 samples characterized by a wide range of compositions and a complex metamorphic history predominate in number over other rock types basalt serpentinized ultramafic we interpret the assemblage of rocks exposed on the escarpments to indicate that a shallow level magma reservoir exists beneath the axis of accretion at the mid cayman rise and creates anomalously thin oceanic crust with a carapace of only several hundreds of meters of diabase and basalt this carapace is und

lidar measurement of snow depth a review laser altimetry lidar is a remote sensing technology that holds tremendous promise for mapping snow depth in snow hydrology and avalanche applications recently lidar has seen a dramatic widening of applications in the natural sciences resulting in technological improvements and an increase in the availability of both airborne and ground based sensors modern sensors allow mapping of vegetation heights and snow or ground surface elevations below forest canopies typical vertical accuracies for airborne datasets are decimeter scale with order 1 m point spacings ground based systems typically provide millimeter scale range accuracy and sub meter point spacing over 1 m to several kilometers many system parameters such as scan angle pulse rate and shot geometry relative to terrain gradients require specification to achieve specific point coverage densities in forested and or complex terrain additionally snow has a significant volumetric scattering component requiring different considerations for error estimation than for other earth surface materials we use published estimates of light penetration depth by wavelength to estimate radiative transfer error contributions this paper presents a review of lidar mapping procedures and error sources potential errors unique to snow surface remote sensing in the near infrared and visible wavelengths and recommendations for projects using lidar for snow depth mapping

volcanism and metallogenesis of axial and off axial structures on the east pacific rise near 13 degrees n a fast spreading segment 12 cm yr super 1 of the east pacific rise near 12 degrees 50 n explored in detail by surface ship and manned submersible displays intense hydrothermal activity the rise crest about 1 500 m in width with a regional depth of 2 600 m is occupied at its center by an axial graben 1 3 titania alkali enriched olivine ti k basalts with high tio 2 1 4 and high alkali content na 2 o 3 0 k 2 o 0 3 occur on the southeastern seamount the fractionated tholeiites are believed to have been derived from primitive melts during differentiation which took place within a magma reservoir asymmetrical with respect to the axis of the graben which supplied both axial and off axial lava flows the ti k enriched basalts are believed to have been produced from an alkali enriched magmatic source

moytirra discovery of the first known deep sea hydrothermal vent field on the slow spreading mid atlantic ridge north of the azores geological biological morphological and hydrochemical data are presented for the newly discovered moytirra vent field at 45on this is the only high temperature hydrothermal vent known between the azores and iceland in the north atlantic and is located on a slow to ultraslow spreading mid ocean ridge uniquely situated on the 300 m high fault scarp of the eastern axial wall 3 5 km from the axial volcanic ridge crest furthermore the moytirra vent field is unusually for tectonically controlled hydrothermal vents systems basalt hosted and perched midway up on the median valley wall and presumably heated by an off axis magma chamber the moytirra vent field consists of an alignment of four sites of venting three actively emitting black smoke producing a complex of chimneys and beehive diffusers the largest chimney is 18 m tall and vigorously venting the vent fauna described here are the only ones documented for the north atlantic azores to reykjanes ridge and significantly expands our knowledge of north atlantic biodiversity the surfaces of the vent chimneys are occupied by aggregations of gastropods peltospira sp and populations of alvinocaridid shrimp mirocaris sp with rimicaris sp also present other fauna present include bythograeid crabs segonzacia sp and zoarcid fish pachycara sp but bathymodiolin mussels and actinostolid anemones were not observed in the vent field the discovery of the moytirra vent field therefore expands the known latitudinal distributions of several vent endemic genera in the north atlantic and reveals faunal affinities with vents south of the azores rather than north of iceland

continuous profiles of electromagnetic wave velocity and water content in glaciers an example from bench glacier alaska usa we conducted two dimensional continuous multi offset georadar surveys on bench glacier south central alaska usa to measure the distribution of englacial water we acquired data with a multichannel 25 mhz radar system using transmitter receiver offsets ranging from 5 to 150 m we towed the radar system at 5 10 km h 1 with a snow machine with transmitter receiver positions established by geodetic grade kinematic differentially corrected gps nominal 0 5 m trace spacing for radar velocity analyses we employed reflection tomography in the pre stack depth migrated domain to attain an estimated 2 velocity uncertainty when averaged over three to five wavelengths we estimated water content from the velocity structure using the complex refractive index method equation and use a three phase model ice water air that accounts for compression of air bubbles as a function of depth our analysis produced laterally continuous profiles of glacier water content over several kilometers these profiles show a laterally variable stratified velocity structure with a low water content 0 0 5 shallow layer 20 30 m underlain by high water content 1 2 5 ice

using an ultra long range terrestrial laser scanner to monitor the net mass balance of urumqi glacier no 1 eastern tien shan china at the monthly scale we describe the use of a terrestrial laser scanner tls to monitor the net mass balance of urumqi glacier no 1 eastern tien shan we used an ultra long range riegl vz 6000 tls which is specially designed for surveying snow and ice covered terrain to create repeated high spatiotemporal resolution dems focusing on the monthly scale 25 april 28 may 2015 net mass balance according to the tls derived dems the area of urumqi glacier no 1 was 1 558 km 2 on 25 april 2015 and the average surface elevation change was 0 225 m by comparing the results from the use of tls with the conventional glaciological mass balance method the correlation coefficient r 2 between glaciological elevation changes of individual stakes and the tls derived geodetic elevation change of corresponding points was 0 85 considering the uncertainty of both methods this is a promising result using the in situ measured snow densities snow pits of the glacier surface the geodetic net mass balance was 0 074 m w e which is slightly positive the mean uncertainty in the tls derived monthly net mass balance was 0 018 m w e showing that the tls surveying system presented accurate and relevant results and is therefore suitable to monitor mass balance evolution of mountain glaciers

glacio eustatic sea level control on red sea salinity previous studies of the red sea demonstrated that glacial surface and bottom water salinities in the basin were significantly higher than at present the very low abundance of planktonic foraminifera the so called aplanktonic zone during the last glacial indicates that surface water conditions approached or exceeded the tolerance limits of this plankton group1 2 glacial sediments are also characterized by high concentrations of magnesian calcite3 4 dolomite3 inorganically precipitated aragonite4 5 and benthic foraminifera typical of hypersaline environments3 6 additional evidence from oxygen isotope records of planktonic2 7 and benthic foraminifera8 9 as well as pteropods2 demonstrate that glacial interglacial contrasts in the red sea have an amplitude much larger than typically observed in open ocean records here we use both oxygen isotope data and a fractional overmixing model to estimate the impact of the most recent 18 000 yr bp pleistocene glacio eustatic sea level lowering on red sea salinity we estimate that during the last glacial maximum surface salinities in the central red sea were more than 10 0 higher than at present deep water salinities were also higher during the last glaciation and remained unusually high through deglaciation the combination of very high bottom salinities and the onset of pluvial conditions during deglaciation in the red sea region prevented ventilation of red sea bottom waters and resulted in the accumulation of organic rich sediments

divining gold in seafloor polymetallic massive sulfide systems hydrothermal fluids on the modern seafloor are important carriers of base and precious metals in a wide range of volcanic and tectonic settings the concentrations and distribution especially of gold and silver in associated seafloor massive sulfide sms deposits are strongly influenced by variable source rocks fluid chemistry and precipitation mechanisms compositional data of 130 sms deposits around the world show a large range of gold and silver grades in part reflecting strong buffering of the hydrothermal fluids by their host rocks geochemical reaction path modeling shows that in most cases the investigated hydrothermal fluids are undersaturated with gold and silver and solubilities can be orders of magnitude higher than the au and ag concentrations measured in the corresponding fluids precipitation of gold during conductive cooling of mid ocean ridge black smoker mor fluids occurs at low temperatures but can be very rapid with 90 of the gold deposited in the first 25 c of cooling below 150 c the result is a zn au polymetallic assemblage with au and ag deposited at the same time together with pb and sulfosalts in ultramafic dominated um systems the strongly reduced hydrothermal fluids promote the deposition of gold at higher temperatures and explain the correlation between gold and copper in these deposits in this case the lower stability of the auhs complex at low o2 buffered by fayalite magnetite and quartz results in gold deposition at 250 c with early bornite and chalcopyrite and before sphalerite and silver producing a high temperature cu au assemblage in sediment hosted sed systems the much higher ph stabilizes au hs 2 and keeps gold in solution to very low temperatures after the precipitation of chalcopyrite sphalerite and galena resulting in au poor polymetallic sulfides and very late stage deposition of gold commonly with amorphous silica in arc related arc systems gold deposition occurs at somewhat higher temperatures than in the mor case in part because the fluids start with higher gold concentrations this can be explained by probable direct magmatic contributions and the high o2 of the fluids which promotes the solubility of gold at the source during cooling gold precipitates at about 160 c with sphalerite tennantite silver and galena resulting in an au rich polymetallic sulfide assemblage the mixing of hydrothermal fluids with seawater generally causes oxidation and eventually a decrease in the ph at a mixing ratio of 1 1 causing an initial increase in the solubility of gold and silver this can delay gold deposition from aqueous species to very low temperatures these complex systematics make prediction of au and ag grades difficult however important new data are coming to light on the actual concentrations of the precious metals in hydrothermal fluids in particular the input of magmatic volatiles and leaching of pre existing gold can lead to significant increases in the au and ag concentrations of the venting fluids and earlier deposition in several cases it appears that at least part of the gold load is present as nanoparticles in suspension allowing bulk gold concentrations that may be far in excess of liquid saturation boiling at the seafloor is now widely observed even at great water depths close to the critical point of seawater model calculations of phase separation during boiling show the competing effects on gold solubility of h2 h2s and co2 partitioning into the vapor which can result in highly variable gold to base metal ratios in the deposits flashing of the vent fluids into steam at high temperatures is also commonly observed and can lead to spectacular au grades with a strong cu au association in the deepest and hottest vents

the influence of spreading rate basement composition fluid chemistry and chimney morphology on the formation of gold rich sms deposits at slow and ultraslow mid ocean ridges seafloor massive sulphide sms deposits are variably enriched in precious metals including gold however the processes invoked to explain the formation of auriferous deposits do not typically apply to mid ocean ridge settings here we show a statistically significant negative correlation between the average gold concentration of sms deposits with spreading rate at non sedimented mid ocean ridges deposits located at slow spreading ridges 20 40 mm a have average gold concentrations of between 850 and 1600 ppb however with increasing spreading rate up to 140 mm a gold concentrations gradually decrease to between 50 and 150 ppb this correlation of gold content with spreading rate may be controlled by the degree and duration of fluid rock interaction which is a function of the heat flux crustal structure faulting and the permeability of the source rocks deposits at ultraslow ridges including ultramafic hosted deposits are particularly enriched in gold this is attributed to the higher permeability of the ultramafic source rocks achieved by serpentinisation and the inherent porosity of serpentine minerals combined with relatively high gold concentrations in peridotite compared with mid ocean ridge basalt variations in fluid chemistry such as reducing conditions and the potential for increased sulphur availability at ultramafic hosted sites may also contribute to the high concentrations observed beehive chimneys which offer more favourable conditions for gold precipitation may be more prevalent at ultramafic hosted sites due to diffuse low velocity venting compared with more focussed venting at basalt hosted sites

the sahara east mediterranean dust and climate connection revealed by strontium and uranium isotopes in a jerusalem speleothem this paper explores the potential of sr and u isotope systems in speleothems as tracers of eolian dust transport and hydrological conditions the study focuses on a speleothem from jerusalem spanning the past 220 kyr this speleothem provides a precisely dated record of dust flux from the sahara to the east mediterranean enhanced dust flux and terra rossa soil development are reflected by elevated 87sr 86sr ratios in the speleothem 0 7082 0 7086 while lower 87sr 86sr ratios 0 7078 indicate higher contribution of the local bedrock due to low dust flux and low soil accumulation the strontium isotope system in the speleothem is a robust monitor of the sahara monsoon modulated climate since dust uptake is related to development or reduction in vegetation cover of sahara soil the 234u 238u activity ratios in the speleothem range between 1 12 and 1 0 the high activity values may indicate selective removal of 234u from the soil while the low values converge to the bedrock the migration of 234u to the cave reflects mainly the regional hydrological conditions that are modulated by the north atlantic mediterranean climate system thus the speleothem provides a combined record of the monsoon north atlantic climatic systems long term stability in glacial 87sr 86sr ratios 0 7083 0 0001 over the past 220 kyr suggests an overall similarity in eolian dust sources and uniformity in the synoptic conditions that dominate the dust storm tracks during glacial periods

after the deluge mediterranean stagnation and sapropel formation in an east mediterranean marine core the upper sapropel begins soon after the start of a global event a very heavy precipitation which occurred in the equatorial latitudes during the late glacial early holocene this heavy precipitation in africa channelled by the nile river across 35 of latitude produced a low salinity surface layer in the east mediterranean in this confined basin with high bottom salinity the steep salinity gradient stratified the water column the stagnant bottom waters triggered the sapropel formation cretaceous sapropels in the tropical oceans may result from the same chain of events in warm humid climates with contrasting wet and dry seasonal rhythm

a chemical model for the concentration of gold in volcanogenic massive sulphide deposits abstract study and review of the gold distribution in selected volcanogenic massive sulphide deposits rosebery and hellyer in tasmania mt chalmers in queensland and millenbach in quebec indicates that gold has two distinct occurrences in these deposits 1 a gold zinc lead silver association which is commonly found in the upper part of zinc rich massive sulphide lenses e g rosebery and hellyer and 2 a gold copper association which is commonly present in the stringers and lower portions of copper rich deposits e g mt chalmers and millenbach in each deposit one of these occurrence dominates almost to the exclusion of the other thermodynamic modelling of the volcanogenic fluid which is based on previous work by large 1977 eldridge et al 1983 and pisutha arnond and ohmoto 1983 indicates that gold in the upper part of the zinc rich massive sulphide lenses was transported as au hs 2 while gold in the stringers and bases of copper rich massive sulphide deposits was transported as aucl 2 the ph and o 2 of the ore forming fluid have an important control on gold deposition and therefore gold grades high gold grades in zinc rich massive sulphide are promoted by near neutral oxidised and low temperature 150 c to 275 c fluids as indicated by the presence of barite carbonate feldspar gangue high gold grades in the copper rich stringers and base of the massive sulphide are promoted by higher temperatures 275 c to 350 c relatively oxidised fluids as indicated by bornite or by barite or hematite gangue and relatively acid fluids as indicated by kaolinite gangue in o 2 t space significant gold transport by au hs 2 occurs only in the pyrite stability field at relatively low temperatures 2 is not restricted by iron mineral equilibria but is greatest in the hematite magnetite and pyrite fields at high temperatures 300 c and high o 2 10 30 under conditions of au hs 2 transport bonanza type gold deposition may be found in areas where the hydrothermal fluids passed from the field of pyrite stability to that of hematite stability oxidation of hydrothermal fluids by seawater mixing and the rapid precipitation of sulphide minerals at the top of the massive sulphide lens may cause the precipitation of gold via the mechanisms of either h 2 s oxidation or sulphide gold coprecipitation other types of gold deposits may be classified into either the gold zinc or gold copper association the gold copper bismuth association is developed in higher temperature systems of moderate to high salinity where aucl 2 is the dominant complex e g porphyry cu au deposits and au rich skarns whereas the gold zinc lead silver association is developed in systems of low salinity and high h 2 s where au hs 2 is the dominant complex e g epithermal au ag and archean greenstone hosted au quartz

the influence of the ne winter monsoon on productivity changes in the gulf of aden nw arabian sea during the last 530ka as recorded by foraminifera abstract benthic and selected planktic foraminifera and stable isotope records were determined in a piston core from the gulf of aden nw arabian sea that spans the last 530 ka the benthic foraminifera were grouped into four principal assemblages using q mode principal component analyses comparison of each of these assemblages with the fauna of the nearby regions enabled us to identify their specific environmental requirements as a function of variability in food supply and strength of the oxygen minimum zone and by that to use them as indicators of surface water productivity the benthic foraminiferal productivity indicators coupled with the record of globigerina bulloides a planktic foraminifer known to be sensitive to productivity changes in the region all indicate higher productivity during glacial intervals and productivity similar to present or even reduced during interglacial stages this trend is opposite to the productivity pattern related to the sw summer monsoon of the arabian sea and indicates the role of the ne winter monsoon on the productivity of the gulf of aden a period of exceptionally enhanced productivity is recognized in the gulf of aden region between 60 and 13 kyr indicating the intensification of the ne winter monsoon to its maximal activity contemporaneous indication of increased productivity in other parts of the arabian sea unexplained so far by the sw summer monsoon variability might be related to the intensification of the ne winter monsoon another prominent event of high productivity second in its extent to the last glacial productivity event is recognized between 430 and 460 kyr these two events seem to correspond to periods of similar orbital positioning of rather low precession and eccentricity amplitude for a relatively long period glacial boundary conditions seem to control to a large extent the ne winter monsoon variability as also indicated by the dominance of the 100 ka cycle in the investigated time series secondary in their importance are the 23 and 41 ka cycles which seem also to contribute to the ne monsoonal variability following the identification of productivity events related to the ne winter monsoon in the gulf of aden it is possible now to extend this observation to other parts of the arabian sea and consider the contribution of this monsoonal system to the productivity fluctuations preserved in the sedimentary records

atmospheric transport of iron and its deposition in the ocean the atmospheric transport of continental weathering products is responsible for much of the mineral material and fe entering the open ocean and is probably the dominant source of nutrient fe in the photic zone in regions where other nutrients are present in high concentrations the flux of fe from the atmosphere may be a limiting factor in primary productivity due to the larger source regions for dust north of the equator 8 times more atmospheric fe is deposited in the northern hemisphere than in the southern hemisphere the mineral aerosol and fe transport and deposition are highly variable due to the episodic nature of dust generation and its transport and deposition processes between 10 and 50 of the total atmospheric fe entering the world ocean appears to dissolve i e it will pass through a 0 4 m pore size filter rapidly when the mineral matter enters the ocean much of the atmospheric fe is present as fe ii apparently produced as a result of photochemical reduction reactions taking place during atmospheric transport this readily soluble fe ii should be available immediately for use as a nutrient by phytoplankton atmospheric transport from the continents is estimated to supply 3 times as much dissolved fe to the oceans as that delivered via rivers

mobility of au and related elements during the hydrothermal alteration of the oceanic crust implications for the sources of metals in vms deposits volcanogenic massive sulphide vms deposits are commonly enriched in cu zn and pb and can also be variably enriched in au as sb se and te the behaviour of these elements during hydrothermal alteration of the oceanic crust is not well known ocean drilling program odp hole 1256d penetrates a complete in situ section of the upper oceanic crust providing a unique sample suite to investigate the behaviour of metals during hydrothermal alteration a representative suite of samples was analysed for au as sb se and te using low detection limit methods and a mass balance of metal mobility has been carried out through comparison with a fresh mid oceanic ridge basalt morb glass database the mass balance shows that au as se sb s cu zn and pb are depleted in the sheeted dyke and plutonic complexes by 46 12 27 5 2 5 0 5 27 6 8 4 0 7 9 6 1 6 7 9 0 5 and 44 6 respectively arsenic and sb are enriched in the volcanic section due to seawater derived fluid circulation calculations suggest that large quantities of metal are mobilised from the oceanic crust but only a small proportion is eventually trapped as vms mineralisation the quantity of au mobilised and the ratio of au to base metals are similar to those of mafic vms and ten times enrichment of au would be needed to form a au rich vms the cu rich affinity of mafic vms deposits could be explained by base metal fractionation both in the upper sheeted dykes and during vms deposit formation

a silicate weathering mechanism linking increases in marine 87sr 86sr with global glaciation the 87sr 86sr ratio of sea water is generally regarded as a proxy for the rate of chemical weathering of the continents interpretation of the 87sr 86sr record in marine limestones requires an understanding of how changes in this quantity are linked to climate and tectonic events a connection between the strontium isotope record and the extent of global glaciation has been proposed1 8 but without a well established mechanism glaciation may influence marine 87sr 86sr by changing global riverine sr fluxes that is rock weathering rates and or 87sr 86sr ratios that is relative mineral weathering rates here we investigate how the 87sr 86sr release from silicate weathering is affected by glaciation using the sr isotope systematics of granitoid soils on alpine glacial moraines in the wind river range wyoming we observe a negative correlation between the 87sr 86sr ratio of exchangeable sr in soils and the soil age indicating that the 87sr 86sr ratio of sr released in the early stages of weathering is significantly higher than in later stages we estimate that this mechanism can increase global riverine 87sr 86sr by an average of 0 0002 during periods of glacial interglacial cycling when superimposed on long term trends controlled by tectonic processes2 7 9 10 this shift can account for the correlation between the rate of change of marine 87sr 86sr and the intensity of glaciation over at least the past 10 myr

strontium isotopic chemical and sedimentological evidence for the evolution of lake lisan and the dead sea precise strontium isotope ratios combined with chemical analyses and sedimentological information are used to monitor the water sources and the evolution of the dead sea and its late pleistocene precursor lake lisan 70 18 kyr b p the materials analyzed include bulk aragonite water leached soluble salts and residual aragonite and gypsum from the lisan formation in the perazim valley near the sw shore of the dead sea the residual aragonite and the associated soluble salts display systematic fluctuations in 17sr86sr ratios between 0 70803 and 0 70806 and from 0 70805 to 0 70807 respectively in individual soluble salt residual aragonite pairs the soluble salt displays a higher 87sr86sr ratio gypsum samples yield 17sr86sr ratios similar to the soluble salts from adjacent layers in the section this shows that in individual samples the source of sr in aragonite was distinct from that in soluble salts and the gypsum the sterility of the lisan sediments their strictly nonbioturbated fine lamination and their high content of chloride salts indicate that lake lisan was a saline or even hypersaline water body in the absence of alternative sources of hco3 and s042 the abundance of primary aragonite and gypsum in the lisan column reflects an import of very large volumes of freshwater into the otherwise saline lake resulting in a density stratification of this water body the history of the upper water layer and that of the lower brine is reflected in the chemical and strontium isotope composition of the aragonite and in that of the associated soluble salts and in the gypsum samples respectively whereas the bicarbonate and much of the ca2 required for aragonite crystallization were supplied by the freshwater the complementary ca2 and sr 2 were added by the lower brine the upper water layer of lake lisan acted as a so42 capacitor during the lake s rise periods it was removed therefrom as prominent gypsum beds upon climatic induced drier period mixing or even complete overturn of the lake the evolution of lake lisan took place between two distinct modes the first was characterized by an extensive supply of freshwater and resulted in a rise of the lake s level a density layered structure and precipitation of aragonite the second mode was marked by a diminishing freshwater input resulting in mixing or complete overturn of its water and precipitation of gypsum these two modes reflect the climatic evolution of the region in the late pleistocene which fluctuated between drier and wetter periods the transition to the holocene is accompanied by the dry up of lake lisan and its contraction to the present dead sea

the formation of gold rich seafloor sulfide deposits evidence from the beebe hydrothermal vent field cayman trough the beebe vent field bvf in the cayman trough has built an auriferous massive sulfide deposit on the ultra slow spreading mid cayman spreading centre the genesis of auriferous sulfide deposits at mid ocean ridges is not fully understood although there is a growing recognition that slow and ultra slow spreading centres are conducive to gold mineralization analysis of hydrothermal precipitates from the bvf indicates that the highest gold contents are present within beehive diffusers which have developed a highly porous pyrrhotite framework the beehive structure allows vent fluids to effuse slowly while allowing ingress of seawater to cool the fluid the prevalence of pyrrhotite in the beehive samples lack of sulfates association between pyrrhotite and gold grains and results of thermodynamic modelling suggests gold precipitation occurred under highly reduced conditions even during mixing with seawater in contrast high temperature chimneys with a single orifice maintain high temperatures to the primary vent orifice and much of the gold is lost to seawater despite this both chimney types are relatively gold enriched which points to a further underlying cause for high gold at the bvf such as interaction of hydrothermal fluids with ultramafic lithologies in the basement the final gold composition of the deposit is partially controlled by loss of gold during mass wasting of the material with gold depletion most prevalent in blocks formed at beehive type chimneys the bvf demonstrates that the overall gold content of a massive sulfide deposit is the sum of basement precipitation and surface processes

holocene and little ice age glacial activity in the marbore cirque monte perdido massif central spanish pyrenees the marbore cirque which is located in the southern central pyrenees on the north face of the monte perdido peak 42 40 0 n 0 5 0 w 3355 m contains a wide variety of holocene glacial and perig

changing moisture sources over the last 330 000 years in northern oman from fluid inclusion evidence in speleothems speleothems from hoti cave in northern oman provide a record of continental pluvial periods over the last 330 000 yr periods of rapid speleothem deposition occurred from 6000 to 10 500 78 000 to 82 000 120 000 to 135 000 180 000 to 200 000 and 300 000 to 330 000 yr ago with little or no growth during the intervening periods during each of these five pluvial periods d values of water extracted from speleothem fluid inclusions dfi are between 60 and 20 vsmow and 18o values of speleothem calcite 18oc are between 12 and 4 to vpdb these values are much more negative than modern rainfall for d or modern stalagmites for 18o previous work on the isotopic composition of rainfall in oman has shown that northern and southern moisture sources are isotopically distinct combined measurements of the d values of fluid inclusion water with calculated 18o values from peak interglacial speleothems indicate that groundwater was predominantly recharged by the southern indian ocean moisture source when the monsoon rainfall belt moved northward and reached northern oman during each of these periods

gold in sea floor polymetallic sulfide deposits bulk chemical analyses of 48 samples of hydrothermal precipitates from seven polymstallic sulfide deposits at sea floor spreading centers in the eastern pacific reveal distinct patterns of gold enrichment high gold contents are found in samples from two sulfide deposits the axial seamount 45057 n 130002 w and the southern explorer ridge 49045 6 n 130016 2 w a large 160 kg sample composed of silica barite and sphalerite from the top of the axial seamount deposit gives analyses up to 6 700 ppb au averaging 4 900 ppb au similar material from the southern explorer ridge gives analyses up to 1 500 ppb au averaging 660 ppb au detailed mineralogical studies together with bulk chemical analyses of a wide range of samples from these two sites reveal strong elemental associations and paragenetic controls on gold deposition gold at concentrations of about 200 ppb is associated with high cu 1 wt and mo up to 470 ppm at concentrations 800 ppb with high zn 10 wt ba 3 wt and sio 20 wt and at concentrations 1 200 ppb with high pb 0 1 wt ag 100 ppm as 300 ppm and sb 50 100 ppm samples with the highest gold values from both locations contain late sinterlike low temperature sulfosalts of pb as sb ag and s in a matrix of amorphous silica these sulfosalts are the probable repositories of the gold published analyses of au poor 300oc cu fe rich sulfides and subsequently remobilized by late sustained low temperature 250oc fluids and concentrated in sio ba zn rich precipitates near the surface suitable fluid chemistry is required to mobilize the gold and a favorable precipitation mechanism is needed to concentrate it these observations could explain the occurrence of high gold concentrations in selected ore types of some ancient massive sulfide deposits on land

a review of terrestrial radar interferometry for measuring surface change in the geosciences this paper presents a review of the current state of the art in the use of terrestrial radar interferometry for the detection of surface changes related to mass movement different hardware types and acquisition concepts are described which use either real or synthetic aperture for radar image formation we present approaches for data processing procedures paying special attention to the separation of high resolution displacement information from atmospheric phase variations recent case studies are used to illustrate applications in terrestrial radar interferometry for change detection applications range from detection and quantification of very slow moving millimeters to centimeters per year displacements in rock walls from repeat monitoring to rapid processes resulting in fast displacements 50 m yr acquired during single measurement campaigns with durations of only a few hours fast and episodic acting processes such as rockfall and snow avalanches can be assessed qualitatively in the spatial domain by mapping decorrelation caused by those processes a concluding guide to best practice outlines the necessary preconditions that have to be fulfilled for successful application of the technique as well as in areas characterized by rapid decorrelation empirical data from a ku band sensor show the range of temporal decorrelation of different surfaces after more than two years for rock surfaces and after a few seconds to minutes in vegetated areas during windy conditions the examples show that the displacement field can be measured for landslides in dense grassland ice surfaces on flowing glaciers and snowpack creep copyright 2014 john wiley sons ltd

glacier fluctuations during the past 2000 years abstract a global compilation of glacier advances and retreats for the past two millennia grouped by 17 regions excluding antarctica highlights the nature of glacier fluctuations during the late holocene the dataset includes 275 time series of glacier fluctuations based on historical tree ring lake sediment radiocarbon and terrestrial cosmogenic nuclide data the most detailed and reliable series for individual glaciers and regional compilations are compared with summer temperature and when available winter precipitation reconstructions the most important parameters for glacier mass balance in many cases major glacier advances correlate with multi decadal periods of decreased summer temperature in a few cases such as in arctic alaska and western canada some glacier advances occurred during relatively warm wet times the timing and scale of glacier fluctuations over the past two millennia varies greatly from region to region however the number of glacier advances shows a clear pattern for the high mid and low latitudes and hence points to common forcing factors acting at the global scale globally during the first millennium ce glaciers were smaller than between the advances in 13th to early 20th centuries ce the precise extent of glacier retreat in the first millennium is not well defined however the most conservative estimates indicate that during the 1st and 2nd centuries in some regions glaciers were smaller than at the end of 20th early 21st centuries other periods of glacier retreat are identified regionally during the 5th and 8th centuries in the european alps in the 3rd 6th and 9th centuries in norway during the 10th 13th centuries in southern alaska and in the 18th century in spitsbergen however no single period of common global glacier retreat of centennial duration except for the past century has yet been identified in contrast the view that the little ice age was a period of global glacier expansion beginning in the 13th century or earlier and reaching a maximum in 17th 19th centuries is supported by our data the pattern of glacier variations in the past two millennia corresponds with cooling in reconstructed temperature records at the continental and hemispheric scales the number of glacier advances also broadly matches periods showing high volcanic activity and low solar irradiance over the past two millennia although the resolution of most glacier chronologies is not enough for robust statistical correlations glacier retreat in the past 100 150 years corresponds to the anthropogenic global temperature increase many questions concerning the relative strength of forcing factors that drove glacier variations in the past 2 ka still remain

petrography strontium barium and uranium concentrations and strontium and uranium isotope ratios in speleothems as palaeoclimatic proxies soreq cave israel the reconstruction of the palaeoclimate of the eastern mediterranean region for the last 60 ka bp is based on the 18o and 13c variations of speleothems from soreq cave israel climatic conditions during most of the time interval between 60 and 17 ka bp the period equivalent to the last glacial were relatively cold and dry while they were warmer and wetter from 17 ka bp to the present at 17 ka bp there was a major climatic change with a sharp increase in annual rainfall and temperature and a very wet period occurring between 8 5 and 7 0 ka bp during the colder and drier period large detritus free preferentially oriented calcite crystals were deposited from slow moving water as a result of a sharp change in the hydrological regime at 17 ka bp fast moving water started entrainment of the soil and carrying detrital material into the cave and the calcite crystals deposited became small and anhedral coinciding with the petrographic and isotopic changes a sharp drop occurred in the concentration

gold and native copper in supergene sulphides from the mid atlantic ridge in 1985 black smokers and massive sulphide deposits were discovered in the tag hydrothermal field in the rift valley of the mid atlantic ridge near latitude 26 08 n ref 1 sulphide samples from chimneys and mounds were recovered by dredging at depths between 3 620 and 3 670 m mineralogical and chemical analyses of the samples reveal 1 primary unaltered zn fe cu sulphides containing 0 8 4 0 p p m au 0 02 0 12 oz per ton and 2 secondary cu rich sulphides with native copper formed by supergene alteration of primary cu fe sulphides containing up to 16 4 p p m au 0 48 oz per ton as free native gold this is the first reported occurrence of secondary enrichment of gold and copper in recent submarine sulphides the high gold grades and native copper associated with secondary cu sulphides resemble occurrences in some supergene gossans overlying ancient massive sulphide deposits on land2

sea level events in the south pacific linked with the messinian salinity crisis cores drilled through the carbonate cap of niue a mid oceanic carbonate platform in the south pacific contain an unusually well resolved stratigraphic section of the latest miocene at 35 to 140 m depth below sea level intensely leached and chalky intervals associated with pronounced 18 o and 13 c depletions mark the position of dissolution unconformities representing eight episodes of eustatic falls that outstripped the local rate of subsidence we demonstrate on the basis of sr isotope chronostratigraphy that these eustatic changes are correlative with the messinian salinity crisis events in the mediterranean sea level changes of about 10 m amplitude commenced at 6 14 ma and culminated in a large sea level fall that reached at least 30 m at 5 26 ma corresponding to the miocene pliocene boundary evaluation of the sea level history reported here and the contemporaneous mediterranean events supports the model of coupling between tectonic and eustatic factors that caused the onset and demise of the salinity crisis the available evidence suggests that during messinian time glacio eustatic falls and rises are likely to have modulated the connection between the atlantic and the mediterranean and influenced the evaporite deposition and may have contributed significantly to the final phase of isolation and desiccation of the mediterranean and its subsequent refilling during the zan clean deluge

water flow through temperate glaciers understanding water movement through a glacier is fundamental to several critical issues in glaci ology including glacier dynamics glacier induced floods and the prediction of runoff from glacierized drainage basins to this end we have synthesized a conceptual model of water movement through a temper ate glacier from the surface to the outlet stream pro cesses that regulate the rate and distribution of water input at the glacier surface and that regulate water movement from the surface to the bed play important but commonly neglected roles in glacier hydrology where a glacier is covered by a layer of porous perme able firn the accumulation zone the flux of water to the glacier interior varies slowly because the firn tempo rarily stores water and thereby smooths out variations in the supply rate in the firn free ablation zone in con trast the flux of water into the glacier depends directly on the rate of surface melt or rainfall and therefore varies greatly in time water moves from the surface to the bed through an upward branching arborescent net work consisting of both steeply inclined conduits formed by the enlargement of intergranular veins and gently inclined conduits spawned by water flow along the bottoms of near surface fractures crevasses engla cial drainage conduits deliver water to the glacier bed at a limited number of points probably a long distance downglacier of where water enters the glacier englacial conduits supplied from the accumulation zone are quasi steady state features that convey the slowly varying water flux delivered via the firn their size adjusts so that they are usually full of water and flow is pressurized in contrast water flow in englacial conduits supplied from the ablation area is pressurized only near times of peak daily flow or during rainstorms flow is otherwise in an open channel configuration the subglacial drainage system typically consists of several elements that are distinct both morphologically and hydrologically an up glacier branching arborescent network of channels in cised into the basal ice conveys water rapidly much of the water flux to the bed probably enters directly into the arborescent channel network which covers only a small fraction of the glacier bed more extensive spatially is a nonarborescent network which commonly includes cav ities gaps between the glacier sole and bed channels incised into the bed and a layer of permeable sediment the nonarborescent network conveys water slowly and is usually poorly connected to the arborescent system the arborescent channel network largely collapses during winter but reforms in the spring as the first flush of meltwater to the bed destabilizes the cavities within the nonarborescent network the volume of water stored by a glacier varies diurnally and seasonally small temper ate alpine glaciers seem to attain a maximum seasonal water storage of 200 mm of water averaged over the area of the glacier bed with daily fluctuations of as much as 20 30 mm the likely storage capacity of subglacial cavities is insufficient to account for estimated stored water volumes so most water storage may actually occur englacially stored water may also be released abruptly and catastrophically in the form of outburst floods

spatiotemporal variations in surface velocity of the gangotri glacier garhwal himalaya india study using synthetic aperture radar data the gangotri glacier is the largest in the garhwal himalaya india and its melt water forms the main source stream of the ganga river yet its dynamics are poorly understood its long record of terminus retreat measurements 1800 present shows multi decadal oscillations and more recently a slowing down of the retreat its complex dynamics are also indicated by studies of proglacial melt water at the terminus however there have been no systematic measurements of its surface velocity or how it changes seasonally or over longer term time scales here i have characterized the spatiotemporal variations of surface velocity of the gangotri glacier using synthetic aperture radar sar data spanning nearly two decades 1991 2011 the main findings are as follows 1 the glacier undergoes seasonal fluctuations in surface velocities there was a clear summer speedup of similar to 57 126 compared to winter velocities between 0 and 12 6 km from the terminus with peak summer speeds of 63 1 5 4 m yr in 1992 66 6 6 0 m yr in 1999 58 2 4 5 m yr in 2004 and 42 8 4 2 m yr in 2007 whereas winter speeds were relatively stable 25 30 m yr during the same period this summer speedup is indicative of increased basal sliding known to occur when melt waters penetrate to the glacier bed resulting in reduced friction 2 these summer velocities exhibited an inter annual reduction which was manifest as a reduction in summer speed up from 120 in 2004 to 60 in 2007 this pattern continued into 2011 despite the availability of abundant melt water during those years this inter annual reduction indicates the formation of increasingly efficient melt water channels year on year resulting in lesser lubrication at the glacier bed interface my results show that the gangotri glacier is dynamic throughout its length with systematic spatiotemporal variations in surface velocity that elucidate its subglacial processes based on my results and other evidence in the literature i propose that the subglacial drainage system of the gangotri glacier is subject to seasonal and inter annual hydrodynamic coupling between winters and melt seasons akin to other glaciers c 2016 elsevier inc all rights reserved

topographic influences on recent changes of very small glaciers in the monashee mountains british columbia canada an analysis of the local topographic setting of very small 0 4 km 2 glaciers within a small region of the monashee mountains british columbia was conducted to investigate its influence on recent changes in the extent of these glaciers net changes in glacier extent were determined from a detailed manual comparison of remotely sensed imagery acquired in 1951 2001 and 2004 most of the 86 glaciers included in the study showed no observable net change in area over the study period while six glaciers retreated four disappeared entirely and only one advanced indices derived to characterize elements of the local topographic setting that might affect the local mass balance suggest that most of the glaciers are situated in locations that favor ice preservation by enhancing mass input and or reducing ablation rates glaciers situated in less favorable settings generally either decreased in area or disappeared the results suggest that most of the glaciers studied have retreated as far as they are likely to under the climatic conditions of the late 20th century

influence of northern hemisphere climate and global sea level rise on the restricted red sea marine environment during termination i 1 we present high resolution paleoceanographic records of surface and deep water conditions within the northern red sea covering the last glacial maximum and termination i using alkenone paleothermometry stable oxygen isotopes and sediment compositional data paleoceanographic records in the restricted desert surrounded northern red sea are strongly affected by the stepwise sea level rise and appear to record and amplify well known millennial scale climate events from the north atlantic realm during the last glacial maximum lgm sea surface temperatures were about 4 c cooler than the late holocene pronounced coolings associated with heinrich event 1 2 c below the lgm level and the younger dryas imply strong atmospheric teleconnections to the north atlantic owing to the restricted exchange with the indian ocean red sea salinity is particularly sensitive to changes in global sea level paleosalinities exceeded 50 psu during the lgm a pronounced freshening of the surface waters is associated with the meltwater peaks mwp1a and mwp1b owing to an increased surface near inflow of normal saline water from the indian ocean vertical 18o gradients are also increased during these phases indicating stronger surface water stratification the combined effect of deglacial changes in sea surface temperature and salinity on water column stratification initiated the formation of two sapropel layers which were deposited under almost anoxic condition in a stagnant water body

climate change and the collapse of the akkadian empire evidence from the deep sea the akkadian empire ruled mesopotamia from the headwaters of the tigris euphrates rivers to the persian gulf during the late third millennium b c archeological evidence has shown that this highly developed civilization collapsed abruptly near 4170 150 calendar yr b p perhaps related to a shift to more arid conditions detailed paleoclimate records to test this assertion from mesopotamia are rare but changes in regional aridity are preserved in adjacent ocean basins we document holocene changes in regional aridity using mineralogic and geochemical analyses of a marine sediment core from the gulf of oman which is directly downwind of mesopotamian dust source areas and archeological sites our results document a very abrupt increase in eolian dust and mesopotamian aridity accelerator mass spectrometer radiocarbon dated to 4025 125 calendar yr b p which persisted for 300 yr radiogenic nd and sr isotope analyses confirm that the observed increase in mineral dust was derived from mesopotamian source areas geochemical correlation of volcanic ash shards between the archeological site and marine sediment record establishes a direct temporal link between mesopotamian aridification and social collapse implicating a sudden shift to more arid conditions as a key factor contributing to the collapse of the akkadian empire

mineralogy and geochemistry of hydrothermal precipitates from kairei hydrothermal field central indian ridge the kairei hydrothermal field was the first confirmed active submarine hydrothermal system on the central indian ridge it has been suggested to be related to mafic as well as ultramafic host rocks based on vent fluid composition and the presence of ultramafic rocks in its vicinity in this study detailed geochemical and mineralogical analyses have been carried out on the hydrothermal precipitates from the kairei vent field in order to investigate the possible presence of indications for an ultramafic substrate at this vent site the studied samples included fragments of sulfide chimneys massive sulfides and talc bearing and silicified breccias three mineralization stages were identified 1 a high temperature stage consisting largely of chalcopyrite isocubanite and pyrite 2 a medium to low temperature stage characterized by the mineral assemblages of sphalerite and pyrite and 3 a weathering stage characterized by secondary cu sulfides bornite digenite covellite and idaite fe oxihydroxides opal a and cu chloride paratacamite and atacamite the sulfide geochemistry is characterized by high concentrations of cu and zn cu zn up to 29 3 wt n 17 and au mean 5 28 ppm n 17 which is comparable to results from seafloor massive sulfides collected from ultramafic hosted sites in the atlantic ocean but differs from those of typical mafic hosted deposits the high concentrations of cu and au at the kairei hydrothermal field could be an indication for the involvement of ultramafic rocks in the subseafloor ultramafic hosted au rich sulfide deposits may not be restricted to the atlantic ocean and may be common along all slow and intermediate spreading ridges

gpr reflection profiles of clark and commonwealth glaciers dry valleys antarctica englacial horizons deeper than 100 m are absent within 100 mhz ground penetrating radar gpr surface profiles we recorded on clark and commonwealth glaciers in the antarctic dry valleys region both glaciers show continuous bottom horizons to 280 m with bottom signal to noise ratios near 30 db density horizons should fade below 50 m depth because impermeable ice occurred by 36 m folding within commonwealth glacier could preclude radar strata beneath about 80 m depth but there is no significant folding within clark glacier strong sulfate concentrations and contrasts exist in our shallow ice core however it appears that high background concentration levels and possible decreased concentration contrasts with depth placed their corresponding reflection coefficients at the limit of or below our system sensitivity by about 77 m depth further verification of this conclusion awaits processing of our deep core chemistry profiles

nile river sediment fluctuations over the past 7000 yr and their key role in sapropel development the provenance pattern of nile river sediments can be used as a proxy for paleoclimatic changes in east africa the 87sr 86sr ratios are particularly appropriate for such provenance investigations because the white nile drains predominantly crystalline basement rocks whereas the blue nile and atbara flow off the ethiopian highlands which consist of tertiary volcanic rocks a high resolution profile of 87sr 86sr and ti al ratios from a well dated core in the nile delta shows a close correspondence with known changes in nile flow over the past 7000 yr at times of higher river flow there was markedly decreased input of blue nile derived and total sediment this change was caused by northward movement of the inter tropical convergence zone resulting in increased vegetative cover in the ethiopian highlands due to higher rainfall and a longer wet season this inverse relationship between nile river flow and sediment flux may have had important implications in the development of agricultural technology in ancient egypt the marked minimum in 87sr 86sr at 4200 4500 yr b p is coincident with the end of the old kingdom in egypt and provides independent evidence that demise of the old kingdom might have been associated with an extended period of catastrophic low floods during the quaternary and late neogene there was periodic deposition of organic rich sediments sapropels in the eastern mediterranean that represent important indicators of major environmental change evidence from the ti al ratio suggests that the pattern of erosion and sediment supply from the nile catchment observed in this study also occurred throughout much of the neogene and quaternary the reduced inputs of blue nile sediment during times of sapropel formation contributed to the increased primary productivity by reducing the amount of phosphate removed on particles and to the observed change to n limitation in the eastern mediterranean which are important characteristics of sapropel deposition