response of the uppermost mantle to indo eurasian collisional tectonics abstract the rheological law for the power law creep field of peridotite suggested by chopra and paterson 1981 1984 is combined with theoretically modelled thermal and stress perturbations for continent continent collisions bird et al 1975 bird 1978a to determine the effect of such collisions on the uppermost mantle below the zone of convergence the model predicts a change from continental to oceanic geotherms during the oceanic subduction phase followed by a rapid rise in differential stress during the collisional phase these perturbations when combined cause a cyclical change in the steady state flow of the uppermost mantle ending with a re equilibration of thermal and stress regimes the thermal re equilibration proceeds at a much slower rate with a suggested total re equilibration period of about 100 m y after collision has ceased the combination of the flow law with the model predicts that the perturbations in the mantle are limited in depth with no changes in mantle behavior below about 100 km

climate swings in the northern red sea over the last 150 000 years from end and mg ca of marine sediments abstract the end and mg ca compositions of terrigenous material from a meridional transect of seven marine sediment cores located between the northern red sea and the gulf of aqaba together with modern dust sample compositions reveal the temporal and spatial changes in precipitation and dust sources over the last 150 kyrs and are further used to discuss the late quaternary climate history of this region two recent glacial periods marine isotopes stages mis 6 and 2 are characterized by low end values associated with a saharan dust source 12 while mg ca ratios suggest increased transport of dust containing authigenic clays during the last deglacial which most likely originated from the arabian peninsula by contrast mis5e sediments are characterized by an abrupt basin wide shift of end values toward the local arabian nubian shield end member 2 that are exposed around the red sea this shift stems from intense fluvial events and is coeval with other regional paleo precipitation records that all point to an extensive northward shift of precipitation from the tropics during mis5e considering model simulations and regional precipitation dynamics we conclude that although the african summer monsoon probably intensified and extended somewhat northward during mis5e it was not the driver of significant precipitation and the main contribution of precipitation to the northern red sea was due to increased frequency and possible intensity of tropical plumes and red sea troughs that triggered massive fluvial floods within the red sea catchment considering mis5e as an analogue to a future warmer world this currently hyperarid region could be exposed over the coming decades to an increased impact of extreme rainfall events with critical implications for water availability and infrastructure sustainability

mesozoic tertiary weathering and soil formation on slates of the rhenish massif germany abstract weathering of paleozoic slates and sandstones of the rhenish massif in western germany which occurred during the upper mesozoic and tertiary under warm humid tropical to subtropical climatic conditions led to the formation of a regolith up to 150 metres thick in flat upland areas of the hunsru ck and eifel where the tectonic uplift was relatively weak remnants of this weathering mantle more or less truncated by upper tertiary and pleistocene erosion are still preserved on overlapping sections and drill cores of an autochthonous paleosoil and the saprolite underneath the morphological geochemical and mineralogical zonation of a complete profile of the weathering mantle has been reconstructed a fossil pre oligocene plinthitic acrisol covered by oligocene fluvial sediments displays characteristics formed under a high groundwater table on the other hand the underlying saprolite can be subdivided into a lower reduction horizon and an upper oxidation horizon each of them more than 40 meters thick this indicates a polygenesis of the weathering mantle during the tertiary due to descending groundwater tables caused by the beginning tectonic uplift of the rhenish massif and drier climatic periods during the middle tertiary during the upper oligocene the deposition of kaolinitic clays derived from removed horizons of the kaolinitic soils started in fault block depressions periglacial processes during the pleistocene led to a further removal of the weathering mantle and to the deposition of superficial layers on top of the autochthonous remnants of the saprolite presently the kaolinitic sediments as well as the saprolite are exploited as kaolin deposits

paleoclimate and location of the border between mediterranean climate region and the saharo arabian desert as revealed by speleothems from the northern negev desert israel speleothem bearing karstic caves of the northern negev desert southern israel provides an ideal site for reconstructing the paleoclimate and paleo location of the border between mediterranean climate region and the saharo arabian desert major periods of speleothem deposition representing humid periods were determined by high resolution 230 th u dating and corresponding studies of stableisotopecompositionwereusedtoidentifythesourceofrainfallduringhumidperiodsandthevegetationtype majorhumidintervals

effects of acidic and basic parent materials on formation of some soils in quebec canada abstract five profiles developed on basic or acidic parent materials were sampled in southern quebec canada physical chemical and mineralogical properties were determined among the three profiles developed on basic parent materials one formed in disaggregated metabasalt whereas the two others developed in preglacial saprolites derived from the metabasalt as indicated by till cover in a nearby area in the lower part of the latter profiles the saprolites had a loamy texture and the mineralogical plus chemical data indicated very slight changes with respect to the metabasalt in these profiles cbd extractable fe content was 1 in most horizons and the pyrophosphate extractable fe was generally higher in the ah than in the b horizons in the profiles developed on acidic till cbd extractable fe was 1 only in the b horizons which also contained the maximum of pyrophosphate extractable fe in the latter profiles free fe and al sesquioxides were associated with the clay fractions whereas in the former profiles one third of the fe came from the sand and silt fractions chlorite was the dominant phyllosilicate in the basic material and it was transformed into interstratified minerals and smectite several hypotheses about smectite formation and distribution were discussed in the profiles developed on acidic till illite and chlorite were the major phyllosilicates and through weathering transformed into interstratified minerals vermiculite and smectite major differences in the properties of the profiles developed on the two parent materials were not reflected by current soil classification

nannoplankton successions in the northern red sea during the last glaciation 60 to 14 5 ka bp reactions to climate change abstract due to its restricted connection with the indian ocean the desert enclosed red sea is extremely sensitive to global sea level changes and thus ideally suited for paleoceanographic studies of what occurred during the last glaciation the understanding of its glacial history is however still limited a serious obstacle to obtain satisfactory paleoecological information has been the rarity of microfossil proxy species caused by high salinities here we present a continuous and well dated calcareous nannoplankton record from the northern red sea covering the interval from 60 14 5 ka bp our investigation shows that the composition of the calcareous nannoplankton community varied between 32 ka bp and 14 5 ka bp in response to rapid environmental changes which are closely correlated to climatic fluctuations described from the north atlantic region heinrich events h3 h2 and h1 are dominated by emiliania huxleyi gephyrocapsa oceanica and especially gephyrocapsa ericsonii are abundant between h3 h2 and h2 h1 a less pronounced response of the calcareous nannoplankton to the high latitudinal climatic oscillations is documented prior to 32 ka bp suggesting that a strong atmospheric coupling between the northern red sea and the north atlantic realm was established in the late marine isotope stage 3 in contrast to the previously held view of a sea level related salinity increase as the major cause for changes of the plankton communities within the glacial red sea we interpret the documented variations as being caused by local hydrographic changes under the atmospheric control from the extratropics temperature changes and especially variations of the water stratification appear to be critical selective factors for the calcareous nannoplankton composition

insolation values for the climate of the last 10 million years new values for the astronomical parameters of the earth s orbit and rotation eccentricity obliquity and precession are proposed for paleoclimatic research related to the late miocene the pliocene and the quaternary they have been obtained from a numerical solution of the lagrangian system of the planetary point masses and from an analytical solution of the poisson equations of the earth moon system the analytical expansion allows the direct determination of the main frequencies with their phase and amplitude numerical and analytical comparisons with the former astronomical solution ber78 are performed so that the accuracy and the interval of time over which the new solution is valid can be estimated the corresponding insolation values have also been computed this analysis leads to the conclusion that the new values are expected to be reliable over the last 5 ma in the time domain and at least over the last 10 ma in the frequency domain

a paleoclimate interpretation derived from pedogenic clay minerals from the piedmont province virginia abstract oxygen isotope ratios of pedogenic kaolinites were measured to estimate the ambient climate conditions during the formation of a saprolite in the piedmont province woodbridge va kaolinite is the predominant pedogenic clay mineral in this saprolite it is formed mostly from weathering of muscovite and to a lesser extent from weathering of microcline a dioctahedral smectite vermiculite phase formed by weathering muscovite is present in minor amounts the 18o 16o ratios indicate that most if not all the kaolinite formed in a cooler climatic regime in which meteoric waters were more depleted in 18o than most present meteoric waters it is possible that the pedogenic kaolinite formed shortly after or during the pleistocene glacial stage in north america this interpretation is consistent with the age of this saprolite derived from 10be dating methods the oxygen isotopic signatures of these kaolinites are not consistent with an older middle or early miocene age for this saprolite

postglacial and pre last glacial weathering of till on the high plateaus of central gaspesie quebec canada geochemical data from mineral exploration surveys are used to assess postglacial and pre last glacial weathering on the high plateaus of central gaspesie by comparing the distribution of 30 elements in the b and c horizons of a thin soil developed on glacial deposits under postglacial weathering fe2o3 tio2 p2o5 cr li u and v are immobile relative to al2o3 whereas the other elements are mobile and have been depleted to various degrees from the b horizon loss on ignition value is the only parameter showing a significant enrichment from the c to the b horizons the apparently high degree of geochemical weathering of the glacial deposits in respect to their source bedrock lithologies suggests that the deposits also contain previously weathered material the spatial distribution of the geochemical weathering index values calculated for the c horizon shows no clear relation to the underlying bedrock formations the high values are located on topographic highs with maxima over deeply weathered bedrock

controls on carbonate mineral accumulation in bahamian basins and adjacent atlantic ocean sediments abstract carbonate mineralogical studies of surface bahamian periplatform ooze containing pelagic calcite as well as bank derived aragonite and magnesian calcite were coupled with studies of the carbonate chemistry of the waters overlying these sediments the presence of metastable aragonite and magnesian calcite in the periplatform ooze presents a unique opportunity to assess the relation between the extent of carbonate saturation in the water column and the disappearance of metastable carbonate minerals in an area of the north atlantic ocean where intermediate and deep waters are saturated with respect to calcite aragonite is present in the fine fraction of the surface sediment to a water depth of 4 800 m but decreases sharply below 4 000 m this is also the depth limit of the occurrence of pteropod tests and fragments in the coarse fraction of the sediment the aragonite compensation depth should be by extrapolation between 5 000 and 5 200 m the saturation depth with respect to aragonite was estimated to be located between 3 800 and 4 500 m this corresponds fairly well with the depth of a sharp decrease of the fine aragonite as well as the depth of pteropod disappearance magnesian calcite in the fine fraction of the sediment decreases irregularly with depth and disappears between 3 700 and 4 000 m the calculated saturation depth with respect to magnesian calcite 13 mole mgco3 is between 900 and 1 500 m at this depth a significant drop in the concentration of magnesian calcite occurs this decrease of magnesian calcite from 25 to 15 percent could be caused by both dissolution and the increasing distance of deeper waters from the banks however the higher values of specific alkalinity of the waters ranging between 750 and 2 000 m when compared with the alkalinity values of the sargasso sea at the same latitude are interpreted to be indicative that some dissolution of magnesian calcite occurs in the bahamian basins at these water dept s our results show depressed levels by 500 m or more of the aragonite saturation depth in the water column as well as of the depth of aragonite disappearance in the surface sediment when compared with open ocean studies in the northwest atlantic in addition our results indicate that fine magnesian calcite 12 to 13 mole mgco3 disappears 1 200 to 1 500 m above the extrapolated disappearance depth of aragonite this observation is consistent with results for experimental studies showing that aragonite is more stable in seawater than a magnesian calcite of 12 to 13 mole mgco3

variability within a saprolite deposit near quebec city canada samples were collected in two trenches opened in a saprolite developed in a mylonite derived from biotite garnet gneiss near quebec city in order to investigate the spatial variability from the points of view of morphological physical mineralogical and chemical properties phyllosilicate assemblages were a kaolinite b mica c kaolinite mica and d mica interstratified minerals smectite grouping of the samples according to prominent colour in the matrix showed a relation between chroma and kaolinite content total chemical analyses were in good agreement with mineral assemblages the spatial distribution of these assemblages corresponded to the degree of transformation of the gneiss into mylonite

distribution of crenarchaeota tetraether membrane lipids in surface sediments from the red sea abstract the red sea represents an extreme marine environment with high salinity high temperature and low level of nutrients complicating the application of standard geochemical palaeotemperature proxies in order to investigate the applicability of the tex 86 tetraether index of gdgts with 86 carbons proxy for sea surface temperature sst in the red sea the distribution of glycerol dialkyl glycerol tetraether membrane lipids gdgts in sediments from the red sea and the gulf of aden were examined against expectations tex 86 values for the red sea do not show a simple linear relationship with sst and deviate from the global core top calibration in the northern red sea at temperatures between 25 and 28 c the values increase linearly with sst whereas in the southern red sea at temperatures above 28 c tex 86 decreases with increasing temperature factors like seasonality and depth of production salinity and nutrient availability as well as diagenetic overprint or influence of allochtonous terrestrial lipids cannot explain this pattern however the observed tex 86 relationship with sst could be explained by the presence of a hypothetical endemic crenarchaeota population in the red sea with a specific tex 86 vs sst relationship in the southern red sea a two component mixing model implies an exponential decrease in the endemic population towards the gulf of aden thus the application of the tex 86 as a palaeotemperature proxy in the red sea is likely only possible for the northern red sea area with the specific sst vs tex 86 relationship determined in this study and potentially for the whole red sea basin during glacials when water exchange with the indian ocean was more restricted than today and the endemic archaeal lipid distribution was not affected by transport from the indian ocean our results suggest that distinct populations of crenarchaeota in extreme environments such as evaporitic basins may have different membrane composition necessitating application of another calibration than the global core top calibration for tex 86 palaeothermometry

paleoceanographic record of the last glacial interglacial cycle in the red sea and gulf of aden abstract hydrographic conditions in the red sea are strongly controlled by regional climatic conditions and the restricted water exchange with the gulf of aden indian ocean in turn intermediate and deep water masses in the gulf of aden reflect the nature of red sea outflow planktonic and benthic foraminiferal faunas and the lithology and mineralogy of red sea and gulf of aden sediments were studied in order to evaluate changes in water mass conditions in the two basins during the last 18 000 years the results indicate that changes in the local climate and circulation regime during this period resulted in significant hydrographic changes in surface and bottom waters in the red sea and intermediate waters in the gulf of aden during the last glacial maximum high aridity and glacio eustatic sea level lowering resulted in surface and bottom water salinities in the red sea which were considerably higher than at present in the gulf of aden glacial surface salinities and temperatures remained similar to holocene values while surface water productivity may have been lower surface salinities in the red sea decreased after 18 000 years b p as the connection between the red sea and gulf of aden was reestablished however bottom water salinities remained high until at least 11 000 years b p pluvial conditions during deglaciation enhanced the density difference between surface and bottom waters in the red sea and resulted in a decrease in the oxygen content of the bottom waters hydrographic conditions in the western gulf of aden reflect a change in the properties of outflowing red sea water during deglaciation

halokinetics and other features of gloria long range sidescan sonar data from the red sea abstract the red sea is an unusual example of a rift basin that transitioned from its evaporitic stage to fully open ocean conditions at the end of the miocene 5 3 ma much more recently than older mesozoic margins around the atlantic and gulf of mexico the patterns of halokinetic deformation occurring in the red sea are potentially of interest for understanding more generally how evaporite deposits deform during this early stage relevant to this issue a line of reconnaissance sidescan sonar data gloria collected along the red sea in 1979 is re evaluated here we first interpret the data with the aid of newly compiled bathymetry from multibeam sonars in the central and southern red sea features in the acoustic backscatter data are associated with ridges valleys and rounded flow fronts produced by halokinetic deformation some areas of higher acoustic backscattering from the evaporites are suggested to relate to roughness produced by deformation of the evaporite surface within the volcanic oceanic axial valleys areas of differing high and low backscattering suggest varied sediment cover and or carbonate encrustations with the benefit of the above experience we then interpreted data from the northern red sea where there are fewer multibeam data available rounded fronts of halokinetic deformation are present in the zabargad fracture zone a broad shallow valley crossing the red sea obliquely the presence of halokinetic deformation here is evidence that subsidence has occurred along the fracture zone elsewhere in the northern red sea the gloria data reveal folds in the evaporite surface suggesting local areas of convergence like those implied by multibeam data from inter trough zones further south some linear features are observed many of which are likely to be ridges overlying salt walls interestingly several such features are oriented along an accommodation zone that is oriented parallel to the plate spreading direction several rounded corrugated features are interpreted as possible evaporite flow fronts overall the impression from the data is of a strongly mobile seabed in the red sea because of halokinetic deformation involving both vertical and horizontal movements however salt walls appear more common than in the central and southern axial red sea where horizontal movements instead tend to dominate

the arid humid transition in the sahara and the sahel during the last deglaciation at the time of the last glacial maximum the sahara and sahel regions of north africa were extremely dry new records of rainfall show that during the subsequent deglaciation the transition from arid to humid conditions in these regions occurred synchronously in two main steps comparison with other records of palaeoclimate in europe and the north atlantic ocean shows that certain common factors controlled changes in ocean and atmosphere dynamics during the deglaciation

renewal of deep water in the red sea during 1982 1987 between october 1982 and may 1983 the deep water in the northern red sea was ventilated through slope convection the deep water became cooler fresher and more oxygenated dense bottom water formed in the gulf of suez during winter cooling sank down the continental slope thereby entraining near surface and intermediate depth waters from the application of a one dimensional plume model a vertical transport of 0 58 106 m3 s 1 over a period of 7 months was estimated long term time series of atmospheric heat fluxes show that such a major convection event can occur every 4 7 years the corresponding renewal time of the red sea deep water is thus of the order of 40 90 years in agreement with previous estimates

millennial scale variability in red sea circulation in response to holocene insolation forcing in order to assess how insolation driven climate change superimposed on sea level rise and millennial events influenced the red sea during the holocene we present new paleoceanographic records from two sediment cores to develop a comprehensive reconstruction of holocene circulation dynamics in the basin we show that the recovery of the planktonic foraminiferal fauna after the younger dryas was completed earlier in the northern than in the central red sea implying significant changes in the hydrological balance of the northern red sea region during the deglaciation in the early part of the holocene the environment of the red sea closely followed the development of the indian summer monsoon and was dominated by a circulation mode similar to the current summer circulation with low productivity throughout the central and northern red sea the climatic signal during the late holocene is dominated by a faunal transient event centered around 2 4 ka bp its timing corresponds to that of north atlantic bond event 2 and to a widespread regionally recorded dry period this faunal transient is characterized by a more productive foraminiferal fauna and can be explained by an intensification of the winter circulation mode and high evaporation the modern distribution pattern of planktonic foraminifera reflecting the prevailing circulation system was established after 1 7 ka bp

abrupt climate induced changes in carbonate burial in the arabian sea causes and consequences we present high resolution records of aragonite contents and pteropods abundance in two sediment cores sk 17 and md 76 131 within the oxygen minimum zone omz of the eastern arabian sea we show large increases in aragonite contents during glacial and particularly during stadials heinrich events using aragonite content pteropods abundance organic carbon percentage and abundance of fertile species of planktonic foraminifer we demonstrate that aragonite contents in the eastern arabian sea primarily reflects preservation linked to the deepening of aragonite compensation depth acd in the arabian sea we show that these aragonite preservation events correspond with time equivalents of henrich events when arabian sea experienced large declines in monsoon driven productivity and greater penetration of antarctica intermediate water aaiw into the arabian sea thus pteropod preservation in the arabian sea appears to be the result of rapid climate change through atmospheric and oceanic teleconnections we suggest that the role of aragonite carbonate production and burial in margins and the resultant co2 climate feedback to rapid climate changes remains poorly constrained

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

climatic change and caco3 preservation an 800 000 year bathymetric reconstruction from the central equatorial pacific ocean sixteen deep sea cores from the central equatorial pacific are used to reconstruct a continuous 800 000 year 800 kyr record of bathymetric variations in carbonate preservation as measured by calcium carbonate caco3 content the depth of the sedimentary lysocline has fluctuated markedly in conjunction with late pleistocene climate cycles while the carbonate critical depth ccrd which is the water depth where the sediments contain 10 caco3 has remained relatively constant as a result the depth of the lysocline controls the bathymetric position and thickness of the caco3 transition zone defined as the depth from the lysocline to the ccrd modern and interglacial aged sediments show poor caco3 preservation and thick caco3 transition zones glacial aged sediments show good preservation and deep thin zones due to the deepening of the lysocline detailed comparison of the caco3 preservation and oxygen isotope records from the central equatorial pacific confirms the observation that preservation maxima and minima tend to occur during the latter half of glacial and interglacial stages and on climate transitions rather than during the middle of climatic stages during the nine major glacial stages of the last 800 kyr the lysocline deepened by at least 400 to 800 m this deepening indicates an increase in the abyssal carbonate ion concentration co3 and a depression of the calcite saturation horizon best explained by the deeper presence of a more carbonate saturated water mass the bottom of the transition zone has remained at a relatively constant depth during the brunhes chron indicating a balance between caco3 sedimentation and dissolution in the deepest waters of the central equatorial pacific

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

carbonate dissolution in recent sediments of the eastern equatorial indian ocean preservation patterns and carbonate loss above the lysocline abstract multiple dissolution indices from 45 sediment samples show that the foraminiferal lysocline is near 3800 m in the eastern equatorial indian ocean close to the saturation horizon with respect to calcite in the water column below the lysocline the increase in foraminiferal fragmentation decrease in absolute abundance and progressive modification of planktic foraminiferal assemblages with depth is accompanied by an increasing rate of loss of carbonate from the sediments above the lysocline some dissolution must occur in order to produce the dramatic reduction in foraminiferal numbers up to 60 and the pattern of increased fragmentation with depth however the amount of carbonate actually lost from supralysoclinal sediments reaches at most 20 30 of the total at the depth of the lysocline the principal driving force behind supralysoclinal dissolution is most likely the oxidation of organic matter incorporated into the sediments dissolution above the lysocline has a greater apparent impact on relative preservation in the coarse 150 m fraction than it does on total carbonate loss because of redistribution of carbonate to the finer size fractions as fragments though the effects of dissolution on foraminiferal preservation are clearly visible at all depths the lysocline itself does appear to mark the local onset of large scale loss of dissolved carbonate from the sediments such an interpretation is broadly consistent with models regarding the saturation state of the overlying waters as the principal driving force behind the preservation or dissolution of recent carbonate sediments on the sea floor

modes of subsurface intermediate and deep water renewal in the red sea a linear box model of the red sea is presented the model which inverts hydrographic and 3he data for the main features of the width integrated circulation is able to describe a large part of the seasonal and annual mean circulation by combining and reconciling major elements of current theories of the red sea circulation available flow measurements and tracer data the model provides a unified conceptual framework for the understanding of the circulation of the red sea the model forms deep water in the extreme north in two modes as first suggested by cember 1988 the convective mode renews the bottom water at an annual mean rate of 0 04 sv in the winter the isopycnal mode water renews the uppermost part of the deep water mass it flows to the south along the bottom of the pycnocline at an annual mean rate of 0 02 0 04 sv a new feature in the model s near surface circulation scheme is the ventilation of the thermocline in the winter at a mean rate of 0 04 sv also from the extreme north there is also a middepth return flow to the north at an annual mean rate of 0 07 sv this flow has been suggested but never rigorously quantified before

quaternary interglacial and associated deposits in southwest newfoundland a coastal cliff section near codroy newfoundland exposes five distinctive lithologic units which are defined lithologically and structurally as colluvial lacustrine or glacial in origin they have been preserved in a gypsum karst depression but continuing karst evolution has disturbed their original attitudes the two oldest units 5 and 4 were formed by sidewall slumping of local bedrock and earlier glacial material from the failing rim of a newly formed sinkhole unit 3 represents tranquil sedimentation of thin sand and silt clay laminae first in a freshwater sinkhole pond then in brackish marine waters that entered after breaching of its seaward wall and finally again in fresh water as sea level fell below the sill of the small embayment units 2 and 1 are glacial deposits laid down over older units after a second major sinkhole collapse collapse has continued to the present day pollen and spores from unit 3 indicate that during its deposition regional vegetation changed from tundra zone a t

dust transport and synoptic conditions over the sahara arabia deserts during the mis6 5 and 2 1 transitions from grain size chemical and isotopic properties of red sea cores abstract the red sea situated between the sahara and arabia deserts is a natural trap for fine grained particles transported by winds and floods from weathered materials in these deserts derived from the proterozoic crustal granitic and basaltic terrains and phanerozoic carbonates the accumulated fine particles provide valuable information on the climate conditions in the source regions and modes of atmospheric circulation over the red sea region here we report on the grain size mineralogy chemical composition and nd and sr isotope ratios of fine grained insoluble residues ir from acid leaching that were recovered from two deep sea cores kl23 and kl11 drilled in the northern and central red sea respectively we focus on the mis6 5 and mis2 1 transitions kl23 samples are closer to the sahara granitoids field and display significant variations during the mis6 5 transition between end of 7 to 2 and 87sr 86sr of 0 7096 to 0 7114 smaller variations occurred during the mis2 1 transition between end of 5 to 6 and 87sr 86sr of 0 7104 to 0 7118 the kl11 values are closer to the blue nile field which comprises mixtures of granitoid and basalt derived particles during the mis6 5 transition their end varies from 4 to 1 and in 87sr 86sr from 0 7059 to 0 7091 during periods equivalent to sapropels s5 and s1 both cores appear to converge to similar isotope ratios of e nd 2 and 87sr 86sr 0 7095 indicating derivation from the granitoid terrains of the arabian nubian shield occurring adjacent to the red sea and possibly distributed by runoff in terms of synoptic conditions the data indicate that during glacials dust was blown to the northern red sea from the northern sahara desert in association with the mediterranean winter cyclones and to the central red sea from the ethiopian plateau by southern winds that are associated with monsoonal circulation during interglacials especially sapropel intervals monsoonal rains caused erosion and flooding at the arabian nubian shield margins of the red sea during the heinrich events associated with the studied intervals h11 and h1 dust from mixed basaltic granitic terrains was blown from all of the regional sources in the red sea region reflecting severe regional aridity and transport of dust by regional winds when monsoonal activity and mediterranean cyclone activity were weak

three hundred eighty thousand year long stable isotope and faunal records from the red sea influence of global sea level change on hydrography stable isotope and faunal records from the central red sea show high amplitude oscillations for the past 380 000 years positive 18o anomalies indicate periods of significant salt buildup during periods of lowered sea level when water mass exchange with the arabian sea was reduced due to a reduced geometry of the bab el mandeb strait salinities as high as 53 and 55 are inferred from pteropod and benthic foraminifera 18o respectively for the last glacial maximum during this period all planktonic foraminifera vanished from this part of the red sea environmental conditions improved rapidly after 13 ka as salinities decreased due to rising sea level the foraminiferal fauna started to reappear and was fully reestablished between 9 ka and 8 ka spectral analysis of the planktonic 18o record documents highest variance in the orbital eccentricity obliquity and precession bands indicating a dominant influence of climatically driven sea level change on environmental conditions in the red sea variance in the precession band is enhanced compared to the global mean marine climate record specmap suggesting an additional influence of the indian monsoon system on red sea climates

synoptic conditions of fine particle transport to the last interglacial red sea dead sea from nd sr compositions of sediment cores abstract the sediments deposited at the depocenter of the dead sea comprise high resolution archive of hydrological changes in the lake s watershed and record the desert dust transport to the region this paper reconstructs the dust transport to the region during the termination of glacial marine isotope stage 6 mis 6 135 129 ka and the last interglacial peak period mis5e 129 116 ka we use chemical and nd and sr isotope compositions of fine detritus material recovered from sediment core drilled at the deepest floor of the dead sea the data is integrated with data achieved from cores drilled at the floor of the red sea thus forming a red sea dead sea transect extending from the desert belt to the mediterranean climate zone the dead sea accumulated flood sediments derived from three regional surface cover types settled desert dust mountain loess soils and loess soils filling valleys in the dead sea watershed termed here valley loess the valley loess shows a distinct 87sr 86sr ratio of 0 7081 1 inherited from dissolved detrital calcites that originate from dried waterbodies in the sahara and are transported with the dust to the entire transect our hydro climate and synoptic conditions reconstruction illustrates the following history during glacial period mis6 mediterranean cyclones governed the transport of saharan dust and rains to the dead sea watershed driving the development of both mountain soils and valley loess then at heinrich event 11 dry western winds blew saharan dust over the entire red sea dead sea transect marking latitudinal expansion of the desert belt later when global sea level rose the dead sea watershed went through extreme aridity the lake retreated depositing salt and accumulating fine detritus of the valley loess during peak interglacial mis 5e enhanced flooding activity flushed the mountain soils and fine detritus from all around the dead sea and red sea marking a significant contraction of the desert belt at the end of mis 5e the effect of the regional precipitation diminished and the dead sea and red sea areas re entered sever arid conditions with extensive salt deposition at the dead sea

influences stationnelles sur l alteration chimique des sols derives de till sherbrooke que canada abstract in a small watershed of the canadian appalachians five trenches were studied in two catenas facing each other one forested the other under recent prairie vegetation 100 years of age to investigate the character of chemical weathering in these sites on the top of the forested catena there was a humo ferric fragic podzol and further down and orthic gleysol the other catena had a humo ferric fragic podzol then downwards a grey gleyified luvisol and a luvic fragic gleysol percolating waters near these trenches were sampled regularly at various depth the distribution of the ions on the meadow side indicated on one hand that h 4 sio 4 na and mg 2 in percolating waters are related to the total volume of soil through wich waters percolate that the dissolution of aluminium is accelerated in acid sites upslope and that the solubility of iron reaches a maximum in the zone influenced by the water table on the other hand calcium which is easily liberated in the high sections is in part fixed when the solutions get concentrated iron and aluminium are soon traped silicium is less mobile than the basic cations the constituants of primary minerals organize as follows concentration of al 2 o 3 and fe 2 o 3 upslope when the contrary is for the basic oxydes and sio 2 this trend stands out more clearly in the top 30 cm thus on top of the forested catena chemical weathering is intense the aluminium and iron oxydes are highly evacuated in this podzol at the same altitude in the prairie podzol which probaly had 100 years ago a less acidifying vegetation hardwoods than in the first case feldspars and micas are degraded and we find mostly transformed minerals montmorillonite al minerals are very much less degraded downslope because of their confined position and the high ionic content of the percolating waters

dissolution and water mass patterns in the southeast indian ocean part ii the pleistocene record from brunhes to matuyama age sediments calcium carbonate dissolution patterns were determined for portions of the past 2 5 m y in 9 eltanin piston cores distributed along the southeast indian ridge in the southeast indian ocean oxygen isotope and foraminiferal faunal records were used to determine the relationship between paleoclimate water mass changes and the dissolution intervals caco 3 dissolution was generally more intense during glacial periods but dissolution pulses of short duration also occur during several interglacial periods particularly on the shallower portions of the southeast indian ridge the glacially related increases in dissolution are in phase with northern migrations of the polar front during the past 250 000 yr the polar front has migrated to 45 s latitude in the region south of australia and as far north as 40 s in the mid southern indian ocean during the same time period from the mid brunhes chron to the present an over all increase in caco 3 content indicates a gradual deepening of the carbonate lysocline unlike the brunhes chron the carbonate fluctuations in the matuyama age cores are due mainly to productivity variations as a function of water mass migrations and are of lower magnitude than are the brunhes fluctuations the magnitude of the oxygen isotopic fluctuations in the matuyama chron is also smaller than it was during the brunhes chron suggesting less climatic variability

alteration profonde preglaciaire d un gneiss a charlesbourg quebec canada abstract a saprolite derived from a gneiss has been sampled in a fault zone at charlesbourg near quebec city the weathering largely exceeding 6 m in depth and a till overburden suggest preglacial alteration under warmer climatic conditions this is further supported by the presence of high up to 15 percentages of crystalline iron oxides goethite and lepidocrocite four different facies were defined in the saprolite mineralogical analyses were performed on the clay fractions and the following associations were found swelling minerals kaolinite kaolinite kaolinite gibbsite swelling minerals kaolinite the degree of weathering of 2 1 minerals into kaolinite seemed to be related to internal drainage conditions cation exchange capacity of the saprolite was adequately explained by the clay and silt fraction contributions

on the sources formation and circulation of red sea deep water red sea deep water is renewed from sources in the far north of the red sea upwelling of deep water throughout the basin maintains the sharp pycnocline with its base near the depth of the sill at bab el mandeb before now deep water renewal was thought to occur mainly by means of convective deep water formation in the north which renews the bottom water and gives rise to a southward flowing bottom current carbon 14 and 3he data from the geosecs indian ocean expedition lead to the identification of an additional volumetrically larger mode of northern deep water formation in which new deep water is injected immediately beneath the pycnocline this mode of deep water formation to be called the isopycnal mode also gives rise to a southward flowing current in this case at the top of the deep water mass geosecs data also demonstrate the existence at intermediate depths in the deep water of a return flow to the north the surface history in the nuclear era of the 14c in the deep water source region was reconstructed by direct radiocarbon measurements on annual growth bands of corals calculation then shows that new deep water forms in the convective mode at a rate of 0 05 0 01 sverdrup sv expressed as if the flow were continuous and is due principally to processes occurring in the mouth of the gulf of suez the injection beneath the pycnocline of new deep water formed in the isopycnal mode is 0 11 0 02 sv this new deep water appears to originate mainly in the extreme open northern red sea the gulf of aqaba makes a modest but significant contribution to both modes the total deep water renewal rate is about 0 16 sv yielding a bulk deep water residence time of about 36 years oxygen consumption in the deep water shows approximately exponential decrease of consumption rate with depth as expected on geological and geophysical grounds hydrographically significant fluxes of heat and salt from the sea floor into the red sea deep water are discernible in the hydrography helium 3 flux from the sea floor into the deep water is about 69 1 stp year

glacier hydrology in svalbard norwegian high arctic abstract progress in glacier hydrology has focused on temperate glaciers although partly or wholly non temperate glaciers are found in many parts of the world and significant areas of former ice sheets were probably non temperate it has usually been assumed that drainage from non temperate glaciers consists of relatively dilute and invariable supraglacial runoff in this paper the hydrology of glaciers in the high arctic archipelago of svalbard is examined variations in the thermal regimes of glaciers and their implications for drainage are first addressed results from svalbard concerning meltwater discharge and storage and solute and suspended sediment dynamics are then reviewed in general meltwater penetration of non temperate ice is limited and drainage from non temperate glaciers in svalbard has many of the characteristics of sub aerial drainage however it would be erroneous to view this drainage simply as dilute supraglacial runoff as significant material transport occurs in suspension and solution furthermore twentieth century climate change has probably led to changes in the thermal regimes of some svalbard glaciers such that relict drainage structures are sometimes observed while meltwater yields are augmented by runoff which can be attributed to the loss of mass from glaciers at large spatial scales turbid plumes observed at the marine margins of polythermal ice caps indicate that meltwater can be routed subglacially through non temperate ice

stratigraphic and paleoceanographic significance of late quaternary pteropods from deep sea cores in the gulf of aqaba elat and northernmost red sea abstract the quantitative distribution of 16 thecosomatous pteropod species from four deep sea cores recovered from the gulf of aqaba elat and northernmost red sea is summarized the distribution facilitates a relatively high resolution stratigraphic subdivision of the 6 8 m long core sequences and their correlation the sequences of pteropod assemblages can be related to oxygen isotope curves and thus dated beyond the radiocarbon range the oldest strata penetrated are dated at about 150 000 yr b p considering the present day distribution of the species recognized the core assemblages are of a tropical subtropical character throughout the late quaternary on the basis of the composition of the living pteropod populations in the hypersaline 41 moderately oligotrophic and desert enclosed gulf of aqaba the pteropod core assemblages associated foraminiferal assemblages and the oxygen isotope values determined on both groups a sequence of paleoceanographic changes during the late quaternary is derived these changes are primarily influenced by productivity of the waters and pertain less to temperature and salinity the glacial periods isotope stages 2 3 4 and upper 6 were characterized by lower temperature than at present higher salinity and greater fertility of the waters during the glacial maxima monospecific creseis acicula assemblages characterize periods of metahaline more than 50 salinity conditions in highly productive waters although not identical in detail the last interglacial stage 5 assemblages are similar to the holocene warm water oligotrophic ones between 8000 and 3000 yr b p a short period of slightly higher productivity is indicated

the effect of paleo oceanographic changes on the sedimentary recording of hydrothermal activity in the red sea during the last 30 000 years abstract the restricted exchange of water with the indian ocean makes the red sea extremely sensitive to global oceanographic changes such as sea level variations linked with quaternary climate change the 120 m global sea level lowering during the last glacial maximum caused great reduction in water exchange with the open ocean at that time salinities reached 50 and were beyond the tolerance of planktonic foraminifera some topographic depressions located on the red sea axial zone are the centre of hydrothermal activity they are filled with hot brines and contain metalliferous sediments we studied three sediment cores in the axial part of the red sea one from the metal rich suakin deep depression and two cores sampled outside any deep at two different depths the sediment of the core located in the anoxic brine filled suakin deep contained no benthic foraminifera indicating the deep was filled by a brine pool during the recovered period of marine isotopic stages 1 2 and 3 the distribution of benthic foraminifera in the two other cores indicates that red sea waters were saltier during stage 2 and 3 than today and that at 2000 m depth red sea waters were anoxic during stage 2 and dysoxic during stage 3 profiles of fe mn and zn indicate that the sedimentary flux of metals was higher during stage 1 than during stage 2 in hydrothermal brine filled deeps in contrast the sedimentary flux of metal in cores outside the anoxic depressions was higher during stage 2 the shape of the metal profiles can be attributed to hydrological changes that induced variations of redox conditions in water column during isotopic stage 1 2 and 3 during interglacial periods metals dissolved in anoxic brines precipitated at the redox boundary that corresponded to the brine seawater interface so that metals precipitated only in the deeps during glacial period the deep water was anoxic and the redox boundary was located above the brine seawater interface therefore the hydrothermal metals could diffuse into the anoxic deep red sea water and be precipitated over a large area this interpretation suggests that the observed variations of metal concentrations are not only related to fluctuations of the hydrothermal fluid discharge but also to the varying redox conditions in the deep red sea water

coarse fraction fluctuations in pelagic carbonate sediments from the tropical indian ocean a 1500 kyr record of carbonate dissolution appendix table al is available with entire article onmicrofiche order from the american geophysical union 2000florida avenue n w washington d c 20009 documentp94 001 2 50 payment must accompany order we examined coarse fraction contents of pelagic carbonates deposited between 2000 and 3700 m water depth in the tropical indian ocean using ocean drilling program odp sites 722 owen ridge arabian sea and 758 ninetyeast ridge eastern equatorial indian ocean and four giant piston cores collected by the french r v marion dufresne during the seymama expedition over the last 1500 kyr coarse fraction records display high amplitude oscillations with an irregular wavelength on the order of 500 kyr these oscillations can be correlated throughout the entire equatorial indian ocean from the seychelles area eastward to the ninetyeast ridge and into the arabian sea changes in grain size mainly result from changes in carbonate dissolution as evidenced by the positive relationship between coarse fraction content and a foraminiferal preservation index based on test fragmentation the well known mid bruhes dissolution cycle represents the last part of this irregular long term dissolution oscillation the origin of this long term oscillation is still poorly understood our observations suggest that it is not a true cycle it has an irregular wavelength and we propose that it may result from long term changes in ca flux to the ocean sites 722 and 758 18o records provide a high resolution stratigraphy that allows a detailed intersite comparison of the two coarse fraction records over the last 1500 kyr site 722 2030 m lies above the present and late pleistocene lysocline the lysocline shoaled to the position of site 758 2925 m only during the interglacial intervals that occurred between about 300 and 500 ka peterson and prell 1985a despite these supralysoclinal positions of the two sites short term changes in coarse fraction contents are correctable from one site to another and probably result from regional or global dissolution pulses by stacking the normalized coarse fraction records from sites 722 and 758 we constructed a composite coarse fraction index ccfi curve in which most of the local signals cancelled out the last 800 kyr of this curve appear to compare extremely well with the composite dissolution index curve from core v34 53 ninetyeast ridge which unambiguously records past variations of carbonate dissolution in the equatorial indian ocean peterson and prell 1985a in the late pleistocene the ccfi variations are mainly associated with glacial interglacial changes they show strong 100 and 41 kyr periodicities but no clear precession related periodicities as proposed earlier by peterson and prell 1985a the lack of precession frequencies may suggest that the regional carbonate dissolution signal is driven by changes in deepwater circulation we cannot totally reject the possibility however that low temporal resolution and or bioturbation degrade somehow the precessional signal at odp sites 722 and 758 in contrast spectral density of dissolution cycles in the giant 53 m long piston core md900963 maldives area displays clear maxima centered on the precession frequencies 23 and 19 kyr 1 as well as on the kyr 1 frequency but shows little power at the 100 kyr 1 frequency these high frequency changes most probably result from changes in surface productivity associated with monsoon variability dissolution at this site may be ultimately controlled by the oxidation of organic matter which appears to be incorporated into the sediments in greater quantity during periods of weak sw monsoon and or increased dry ne monsoon

impact of late quaternary environmental changes on deep sea benthic foraminiferal faunas of the red sea abstract fluctuations in abundance diversity and species composition of benthic foraminifera from two sites of the northern and southern red sea indicate strong variability of deep sea ecosystems during the last four glacial to interglacial cycles in total five and four different benthic foraminiferal assemblages have been identified in the northern core and southern core respectively comparison with recent faunas from the red sea and adjacent oceans allowed the reconstruction of temporal changes in deep water ventilation salinity and food availability at the seafloor generally the abundance of infaunal and miliolid taxa increase during glacial intervals indicating increased organic matter fluxes oxygen decrease and salinity increase in deep waters during these times these fluctuations are attributed to enhanced oxygen consumption rates and temporarily reduced deep water formation in the northern red sea during glacial intervals the recorded environmental changes are a reflection of both high and low latitude climate changes the northern red sea is mainly influenced by glacio eustatic sea level fluctuations that control deep water formation rates and by mid latitude climate changes of the mediterranean region that control surface productivity in contrast deep sea ecosystem variability of the southern red sea is additionally influenced by low latitude climate changes attributed to the ne monsoon intensity that drives the inflow of nutrient rich surface waters from the gulf of aden these results demonstrate the high sensitivity of deep sea ecosystems of the red sea to both global and regional climate changes

red sea circulation during marine isotope stage 5e we have employed a regional massachusetts institute of technology oceanic general circulation model of the red sea to investigate its circulation during marine isotope stage mis 5e the peak of the last interglacial approximately 125 ka before present compared to present day conditions mis 5e was characterized by higher northern hemisphere summer insolation accompanied by increases in air temperature of more than 2 c and global sea level approximately 8 m higher than today as a consequence of the increased seasonality intensified monsoonal conditions with increased winds rainfall and humidity in the red sea region are evident in speleothem records and supported by model simulations to assess the dominant factors responsible for the observed changes we conducted several sensitivity experiments in which the mis 5 boundary conditions or forcing parameters were used individually overall our model simulation for the last interglacial maximum reconstructs a red sea that is colder less ventilated and probably more oligotrophic than at present day the largest alteration in red sea circulation and properties was found for the simulation of the northward displacement and intensification of the african tropical rain belt during mis 5e leading to a notable increase in the fresh water flux into the red sea such an increase significantly reduced the red sea salinity and exchange volume of the red sea with the gulf of aden the red sea reacted to the mis 5e insolation forcing by the expected increase in seasonal sea surface temperature amplitude and overall cooling caused by lower temperatures during deep water formation in winter

paleoenvironment of jawa basalt plateau jordan inferred from calcite speleothems from a lava tube this paper explores the environmental conditions that faced the people of ancient jawa during the holocene as well as previous prehistoric periods of the mid late pleistocene calcite speleothems in a lava tube are dated using the u th method to marine oxygen isotope stage 7 from 250 to 240 ka and from 230 to 220 ka and the stage 5 4 transition between 80 and 70 ka the available evidence indicates general aridity of the black desert during most of the mid late quaternary punctuated by short wetter periods when the mediterranean cyclonic systems intensified and penetrated the north arabian desert these mediterranean systems had a longer and more intense effect on the desert fringe closer to the mediterranean and only rarely penetrated the black desert of jawa the results do not exclude some increase of rainfall which did not change water availability dramatically during the warm holocene the ancient jawa city appears to have depended on technological ability to build elaborate runoff collection systems which became the prime condition for success 2008 university of washington all rights reserved

climatic changes in the northern red sea during the last 22 000 years as recorded by calcareous nannofossils 1 we present a high resolution record of calcareous nannofossils from the northern red sea for the last 22 kyr extreme conditions with enhanced salinities during the last glacial maximum are characterized by high values of gephyrocapsa ericsonii the dominance of emiliania huxleyi in heinrich event 1 indicates a climatic cooling favoring the bloom of opportunistic species the calcareous nannofossils record a two step onset of the postglacial humid climate punctuated by the younger dryas both steps show an early oligotrophic phase dominated by florisphaera profunda and gladiolithus flabellatus and a subsequent fertile phase characterized by e huxleyi the younger dryas is described by high values of gephyrocapsa oceanica indicating an increased mixing of the water column in the late holocene repetitive increases in abundance of f profunda and g flabellatus reflect restricted oligotrophic conditions caused by the high aridity following the holocene humid period

bedrock jointing and geomorphology in southwestern ontario canada an example of tectonic predesign in southwestern ontario canada palaeozoic sedimentary strata are covered by pleistocene glacial sediments the topography of the buried bedrock surface has been mapped over an area of some 45 000 km2 using new computerised depth to bedrock data from more than 200 000 waterwells this information shows that arching of the underlying proterozoic basement canadian shield and differential erosion of carbonate and shale strata are first order regional controls on bedrock geomorphology these data also define a network of buried bedrock channels quantitative analysis of the trends of these channels reveals a statistical correspondence between channel orientation and regional bedrock joint sets formed in response to the mid continent stress field the orientations of bedrock channels and joints correspond regionally with mean trends at 153 and 164 respectively in addition two dominant orientations of postglacial river valleys and bedrock joints correspond with mean trends at 104 vs 104 and 54 vs 52 respectively our findings show that the erosional channelled topography cut on bedrock together with the postglacial drainage pattern cut into younger glacial sediments are related to the trend of bedrock joints and consequently can be described as tectonically predesigned in addition this study yields new insights into the form of the preglacial tertiary drainage system in southern ontario prior to pleistocene glaciation regardless of the precise age of this preglacial system and degree of subsequent glacial modification an important factor in its geomorphic development has been the mid continent stress field

the experimental deformation of dunite deformation experiments have been carried out on two dunites anita bay of 100 m grain size and aheim of 900 m grain size at strain rates from 10 3 to 10 6 s 1 and temperatures from 1000 c to 1300 c in a gas medium deformation apparatus at 300 mpa confining pressure most of the tests were under wet conditions defined by the presence of small amounts of water from hydrous minerals initially present constant strain rate and relaxation experiments covering ranges of flow stress down to about 70 mpa and 7 mpa respectively show that there is a change in flow law in going below about 100 mpa differential stress and that the coarser grained rock is stronger than the finer grained one power law parameters above the transition are n 4 48 0 31 and q 498 38 kj mol 1 for aheim dunite and n 3 35 0 17 and q 444 24 kj mol 1 for anita bay dunite while below the transition relaxation tests on anita bay dunite give n 2 44 0 18 and q 386 27 kj mol 1 it is concluded that there is a weakening effect of water that this effect is mainly in the grain boundaries and that grain boundary sliding is probably a significant deformation mechanism at the lower stresses under wet conditions

properties and genesis of a soil and the underlying gibbsite bearing saprolite cape breton island canada brownish yellow saprolite derived from granite gneiss is exposed beneath 1 2 m of reddish brown till along a roadcut in the cape breton highlands the strongly acid soil is similar to other podzolic soils of the region except for the presence of gibbsite in the silt and clay fractions in the saprolite feldspar and biotite have weathered to poorly crystalline kaolinite gibbsite and a minor component of iron oxide the poorly crystalline kaolinite does not occur in the overlying till the evidence presented is consistent with the view that the area was covered either by cold based or by stagnant warm based glaciers that eroded the pre quaternary surface only slightly and deposited a thin discontinuous veneer of till derived mainly from local bedrock and saprolite weathering products from the saprolite are probably incorporated commonly in tills of the area during the formation of soils in these tills the poorly crystalline kaolinite and most of the gibbsite are either transformed to other minerals

paleosols and holocene soils occurring over the north mountain basalt in nova scotia and grand manan island canada abstract on the northwest coast of nova scotia the north mountain basalt makes a major contribution to local lithology on this formation there are occurrences of pre wisconsinan saprolite which has survived one or more periods of glaciation holocene weathering has produced brunisolic soils inceptisols on the saprolite and a variety of soil types on the till covering this formation the clay sized fraction of the pre wisconsinan saprolite is almost wholly smectitic and weathering has only slightly changed its composition although the till formed over the basalt contains only basaltic fragments the clay sized fractions have a variety of mica type clay minerals which are not significantly dissimilar to those developed in a soil profile occurring in till over neighbouring granite

globally increased pelagic carbonate production during the mid brunhes dissolution interval and the co2 paradox of mis 11 the mid brunhes dissolution interval mbdi represents a period of global carbonate dissolution lasting several hundred thousand years centred around marine isotope stage mis 11 here we report the effects of dissolution in odp core 982 taken from 1134 m in the north atlantic paradoxically records of atmospheric co2 from antarctic ice cores reveal no long term trend over the last 400 kyr and suggest that co2 during mis 11 was no higher than during the present interglacial we suggest that a global increase in pelagic carbonate production during this period possibly related to the proliferation of the gephyrocapsa coccolithophore could have altered marine carbonate chemistry in such a way as to drive increased dissolution under the constraints of steady state an increase in the production of carbonate in surface waters would cause a drawdown of global carbonate saturation and increase dissolution at the seafloor in order to reconcile the record of atmospheric co2 variability we suggest that an increase in the flux of organic matter from the surface to deep ocean associated with either a net increase in primary production or the enhanced ballasting effect provided by an increased flux of caco3 could have countered the effect of increased calcification on co2

biodiversity of foraminifera from late pleistocene to holocene coral reefs south sinai egypt tropical coral reefs are among the most diverse marine ecosystems in order to better understand temporal and spatial variation in late quaternary biodiversity foraminiferal faunas of two fossil raised reef terraces at the southern sinai peninsula were studied and compared to modern coral reef faunas eleven u series dates of shell fragments of the giant clam tridacna sp indicates deposition largely during marine isotope stage 5 mis 5 77 129 kyr bp for the two raised terraces in these terraces amphistegina a lessonii and a lobifera dominates the five fossil foraminiferal associations the fossil reef flat association 1 has common gypsina plana homotrema rubra and acervulina spp and fossil reef flat association 2 consists of amphistegina spp of the three fossil fore reef associations one has abundant porcelaneous taxa including sorites amphisorus peneroplis and borelis one has a mix of porcelaneous taxa and attached arborescent taxa homotrema and placopsilina and one has abundant attached and arborescent taxa miniacina gypsina acervulina and planogypsina the modern fringing reef is dominated by porcelaneous foraminifera and three modern associations are identified these include a lagoonal association with abundant peneroplis pertusus a reef flat association dominated by sorites orbiculus and a fore reef association with porcelaneous taxa plus common h rubra amphistegina lessonii and a lobifera based on our data and including additional published information on regional biodiversity it appears that during mis 5 foraminiferal biodiversity was higher and community structure was different than within the modern reefs these data and regional paleo climate patterns indicate that oceanographic conditions in the red sea were probably closer to normal marine conditions during the last interglacial than they are today

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

origin of the middle pleistocene transition by ice sheet erosion of regolith the transition in the middle pleistocene 0 9 ma seen in 18o deep sea core records from relatively low amplitude high frequency 41 kyr to high amplitude low frequency 100 kyr ice volume variations under essentially the same orbital forcing can be attributed to a change from an all soft bedded to a mixed hard soft bedded laurentide ice sheet through glacial erosion of a thick regolith and resulting exposure of unweathered crystalline bedrock a one dimensional ice sheet and bedrock model which includes transport of sediment and ice by subglacial sediment deformation demonstrates that a widespread deforming sediment layer maintains thin ice sheets before the transition which respond linearly to the dominant 23 and 41 kyr orbital forcing progressive removal of the sediment layer eventually causes a transition to thicker ice sheets whose dominant timescale of change 100 kyr reflects nonlinear deglaciation processes in model simulations over the last 3 ma initialized with no ice and a uniform 50 m sediment layer the time series of ice volume and extent agree in several important aspects with the observed records

large floods during late oxygen isotope stage 3 southern negev desert israel abstract slackwater deposits were found in a cave in the nahal netafim catchment 35 km 2 near the head of the gulf of aqaba in the southern negev israel the sedimentological record includes 27 large paleofloods dated by infrared stimulated luminescence to 33 000 29 000 years ago the scatter of the ages and their large uncertainties prevented an assessment of the exact duration of the record and the specific timing of each flood bayesian analysis was used to adjust the dense dating results so that the time interval between the first and last flood deposit preserved in the cave could be estimated minimum peak discharges were reconstructed based on the estimated elevation of the late pleistocene channel bed as indicated by fluvio pedogenic layers found near the cave the average frequency of these large floods 200 600 m 3 s 1 for the period between 33 000 and 29 000 years ago is about 1 flood per 150 years while for the mid late holocene it is only 1 large flood per 1000 years eight floods out of the 27 recorded deviate from the envelope curves of mid late holocene paleofloods and measured floods in the hyperarid negev desert indicating a different hydroloclimatological regime the anomalous large floods are hypothesized to have resulted from an increase in regional rainfall intensity and or duration attributed to increased frequency of the red sea trough low pressure system that affects the region available records indicate that the northern negev and areas farther north in israel controlled by mediterranean pressure systems were wetter 40 20 ka bp at the same time the southern negev probably in response to the red sea trough system also experienced short episodes of more and or larger rainstorms the timing of these episodes in both the northern and the southern negev towards the last glacial maximum points to a potential synchronous strengthening of both the mediterranean and red sea systems currently acting at different seasons these episodes of increased storminess in the area were brief and were not able to alter the general hyperarid conditions in this area

transition from marine to hypersaline conditions in the messinian tripoli formation from the marginal areas of the central sicilian basin abstract three sections of the early messinian tripoli formation from the northern and southern margins of the central sicilian basin serra pirciata torrente vaccarizzo and marianopoli have been studied with the aim to reconstruct the sedimentary and environmental changes which occurred during the transition between marine conditions and the evaporitic events of the salinity crisis recorded in the overlying calcare di base formation a detailed biostratigraphic and cyclostratigraphic study provided the opportunity of cycle by cycle correlations between the marginal sections and the reference section of falconara the main paleoenvironmental changes are recorded by 1 the evolution of calcareous microfossils towards low diversity and their complete disappearance 2 the composition of the carbonate fraction which commonly changes from calcite mostly related to calcareous microfossils to authigenic carbonate phases consisting of either calcite dolomite and or aragonite 3 the appearance of shallow water deposits and evaporite pseudomorphs 4 the variation of the stable isotope composition of the carbonate fraction indicative of large fluctuations of the freshwater dilution evaporation balance with a general trend towards hypersaline conditions both mineralogical and isotope data indicate that the dolomite precipitated generally from concentrated pore waters while other carbonates formed in the water column submitted to large fluctuations of salinity except locally the increase in salinity did not reach concentrations high enough to precipitate significant volumes of evaporites as during the deposition of the overlying calcare di base the transition from normal marine to hypersaline conditions is recorded diachroneously in the three sections respectively in cycle 34 6 32 ma at serra pirciata cycle 42 6 15 ma at torrente vaccarrizzo and cycle 44 6 12 ma at marianopoli these changes represent the hydrological and sedimentary response to the fragmentation of a large marine basin into different subbasins which ended in the more or less complete closure recorded by the deposition of the overlying evaporite rich calcare di base fm true onset of the evaporitic event two hypotheses not exclusive may explain this change either the regional consequence of the compressive tectonics or the incipient drop of the global sea level which led to the salinity crisis our results confirm that the salinity crisis was preceded by evaporative episodes in the evolution towards hypersaline conditions which occurred diachroneously as a response to the diversity of paleogeographical settings even if the paroxysmal phase seems to have affected the basin at the same time

paleoenvironmental events during the last 13 000 years in the central red sea as recorded by pteropoda a high resolution record was obtained by investigating a sedimentary sequence from two cores taken in the central red sea r v meteor cruise 5 leg 2 the numerical variations between nonmigratory and migratory pteropods and their stable isotopic record were studied together with variations in the carbonate and total organic carbon content in order to estimate changes in the structure of the water column during the last 13 kyr the results indicate the existence of a highly stratified water column during deglaciation and early holocene 13 8 5 ka during this period the depth of the mixed layer varied between less than 50 100 m at most and productivity was markedly reduced in comparison to the recent situation the intermediate and deep water were constantly highly depleted in oxygen a pronounced younger dryas event was recognized at 10 4 ka which coincides with an arid phase on the border land the oxygenation of the intermediate water improved remarkably after 7 5 ka and peaked during the period between 4 6 and 2 0 ka during this period the mixed layer reached its present depth and the productivity which was maximal during middle holocene attained present level during the last 4 6 kyr

red sea isolation history suggested by plio pleistocene seismic reflection sequences abstract high evaporation rates in the desert climate of the red sea ensure that during glacial sea level lowstands when water exchange with the indian ocean was more restricted water salinity and 18 o became unusually extreme modeling of the effect on red sea sedimentary 18 o has been used previously to reconstruct relative sea level to 500 ka and now poses the question of whether that sea level model could be extended if continuous core material of older sediment became available we attempt to address this question here by examining seismic reflection data the upper pleistocene hemipelagic sediments in the red sea contain intervals of inorganic aragonite precipitated during supersaturated conditions of sea level lowstands seismic impedance changes associated with boundaries to those aragonite rich layers appear to explain seismic reflection sequences a segment of chirp sediment profiler data from the central red sea reveals prominent reflections at 1 5 23 26 and 36 ms two way travel time twt from the seabed based on depths to the glacial marine isotope stages mis in cores we relate the upper three reflections to the tops of aragonite rich layers and hence the sea level rises immediately following mis 2 6 and 12 the reflection at 26 ms is related to an unusually rapid fall into mis 12 predicted by one sea level reconstruction which may have created an abrupt lower boundary to the mis 12 aragonite rich layer with the aid of seismogram modeling we tentatively associate the 36 ms reflection with the top of an aragonite rich layer formed during mis 16 furthermore some segments of lower frequency airgun and sparker seismic data from the central and southern red sea show a lower earlier plio pleistocene pp interval that is less reflective than the upper late pp interval this implies less variability in sediment impedance and that extreme variability in water salinity did not develop water exchange with the indian ocean likely continued throughout this interval these results suggest that viable relative sea level reconstructions may be recovered from red sea sediment 18 o data to at least mis 16 and perhaps even as far back as the early pliocene

quaternary paleo oceanography pteropod preservation and stable isotope record of the red sea abstract an abundance of pteropod species their mode of preservation and stable isotope ratios of carbon and oxygen in benthic and planktic foraminifera have been determined in core md76 140 from the northern red sea isotopic data and benthic foraminiferal species indicate changes in o2 concentration in the bottom sediments the glacial stages are characterized by an almost anoxic bottom while the interglacial bottom was generally well ventilated in general very well preserved pteropod shells occur in glacial oxygen depleted intervals and also on recent well ventilated bottoms in the interglacial stages the preservation deteriorates and in the most extreme cases there is a complete dissolution of the aragonitic shells in these cases most of the assemblage is lost and the only traces of the original shells are their internal molds these are cemented with high magnesium calcite hmc which is a more stable carbonate phase in bottom sediments of the interglacial dissolution of aragonite discriminates between large and small shells the latter tend to be removed completely while the larger ones may be preserved as internal hmc molds limacina inflata is more readily molded than l trochiformis and thus its relative abundance increases in poorly preserved assemblages the state of aragonitic shell preservation depends on the degree of organic matter combustion in the sediments well preserved shells occur in sediments where the supply of organic matter is limited and o2 levels are high preservation deteriorates with increasing supply of organic carbon o2 consumption and increasing production of co2 in this case the dissolved carbonate is reprecipitated as hmc cement with further increase in organic matter supply and reduced ventilation nearly all oxygen is consumed and no3 and subsequently so42 become the oxidizing agents this is followed by an increasing carbonate alkalinity and excellent aragonitic shell preservation

late quaternary record of pteropod preservation from the andaman sea abstract in order to understand the glacial to interglacial fluctuations in pteropod preservation and productivity during the late quaternary 54 ka bp to present we investigated pteropod organic carbon corg and globigerina bulloides abundance in a deep sea core from the western andaman sea pteropod abundance and preservation is similar to the indo pacific carbonate preservation type showing better preservation during glacial and poor preservation during interglacial periods the core site appears to have remained below the aragonite compensation depth acd throughout the holocene indicated by the total absence of pteropods maximum abundance and good preservation of pteropods was observed during stadials such as younger dryas yd heinrich events hes and last glacial maxima lgm indicating weaker oxygen minimum zone omz and deeper acd furthermore the high relative abundance of mesopelagic pteropods over epipelagic forms suggests a well ventilated water column with weak omz particularly during lgm apparently driven by intense winter monsoon increased monsoon driven productivity was observed during 45 40 ka of early marine isotope stage 2 mis 2 24 22 ka bolling allerod b a 15 13 5 ka yd and late holocene as evidenced by corg content and g bulloides enhanced pteropod preservation of h1 associated with low corg content and g bulloides suggests that reduced monsoonal driven productivity might have influenced pteropod preservation deglacial preservation spike in the andaman sea is consistent with other northern indian ocean records and elsewhere outside the indian ocean implying the event is global in nature marked by deepening of acd probably driven by enhancement of winter monsoon on local and changes in intermediate water circulation on regional scale

late quaternary millennial scale variability in pelagic aragonite preservation off somalia abstract in order to better understand late quaternary pelagic aragonite preservation in the western arabian sea we have investigated a high resolution sediment core 905 off somalia pteropod preservation is enhanced in times of reduced monsoon driven productivity indicated by low amounts of corg and low barium to aluminium ba al ratios all periods corresponding to heinrich events in the north atlantic are represented by maxima in shell preservation of the common pteropod limacina inflata ldx values 2 66 good shell preservation is also found during stadials at 52 1 53 2 36 33 2 and 31 9 ka relative abundance of pteropods and their fragments in the coarse fraction reaches maxima during marine isotope stage mis 5 2 during time equivalents of heinrich events 4 6 and in stadials at 53 42 5 and 41 4 ka on longer time scales the pteropod abundance corresponds to the indo pacific carbonate preservation type with poor preservation during interglacials and better preservation during glacials late mis 5 to early mis 4 sections 84 1 64 8 ka and the late holocene interval 6 5 0 ka of core 905 contain only traces of pteropods the early holocene 9 2 6 5 ka part is characterized by low pteropod amounts between 64 8 and 43 4 ka strong fluctuations occur and an intermediate average relative pteropod abundance is revealed between 43 4 and 9 2 ka the highest amounts in relative pteropod abundance in core 905 are observed besides the regional monsoonal influence on deepwater chemistry changes in deepwater circulation occurring on glacial interglacial and stadial interstadial time scales might have affected pteropod preservation however it remains elusive whether 1 deep water formation in the arabian sea 2 inflow of glacial north atlantic intermediate water or 3 change in water mass properties of the circumpolar deep water which is the water mass currently bathing this site contributed to the observed pteropod preservation pattern

aragonite preservation in late quaternary sediment cores on the brazilian continental slope implications for intermediate water circulation we present late quaternary records of aragonite preservation determined for sediment cores recovered on the brazilian continental slope 1790 2585 m water depth where north atlantic deep water nadw dominates at present we have used various indirect dissolution proxies carbonate content aragonite calcite contents and sand percentages as well as gastropodal abundances and fragmentation of limacina inflata to determine the state of aragonite preservation in addition microscopic investigations of the dissolution susceptibility of three limacina species yielded the limacina dissolution index which correlates well with most of the other proxies excellent preservation of aragonite was found in the holocene section whereas aragonite dissolution gradually increases downcore this general pattern is attributed to an overall increase in aragonite corrosiveness of pore waters overprinted on this early diagenetic trend are high frequency fluctuations of aragonite preservation which may be related to climatically induced variations of intermediate water masses

red sea during the last glacial maximum implications for sea level reconstruction the red sea is connected to the indian ocean via a narrow and shallow strait and exhibits a high sensitivity to atmospheric changes and a reduced sea level we used an ocean general circulation model to investigate the hydrography and circulation in the red sea in response to reduced sea level and modified atmospheric conditions occurring during the last glacial maximum lgm the model salinity shows high sensitivity to sea level reduction together with a mild atmospheric impact sea level reduction affects the stratification and alters the circulation pattern at the strait of bab el mandab which experiences a transition from a submaximal flow to a maximal flow the best correlation to reconstructed conditions during lgm exists when the water depth of the hanish sill the shallowest part in the strait of bab el mandab is 33 10 75 m which would be affected by a sea level lowering of approximately 105 m our results support the reconstructed maximum salinity of around 57 practical salinity units because of a simple model that takes into account mixing processes along the strait and comparison of the surface salinity gradient to reconstructions based on isotopic records from sedimentary cores the salinity and 18o are sensitive to the mixing process at the strait and the sensitivity increases as the sea level is further reduced a local relative sea level reduction of approximately 105 m is also in close agreement with the inference of the lgm low stand of the sea at the location of the sill based on the ice 5g vm2 model

palaeoceanographic evolution of the central red sea during the late holocene three multicores were studied in the central red sea off port sudan at a w e transect in order to reconstruct palaeoceanographic conditions of the past 6000 years downcore fluctuations in the rel

aplanktonic zones in the red sea abstract we use micropalaeontological and stable isotope results for a series of cores from north to south through the red sea to assess temporal and spatial patterns of change in planktonic foraminiferal faunas leading up to the remarkable full glacial red sea aplanktonic zones aplanktonic zones reflect salinities in the red sea in excess of the lethal 49 p s u limit caused by reduced exchange transport through the strait of bab el mandab due to glacial sea level lowering concerning the last glacial cycle aplanktonic conditions began at 39 ka bp in the north where salinities eventually reached 55 57 p s u paradoxically planktonic faunas are reported to have survived the last glacial maximum in the northern gulf of aqaba suggesting a poorly understood freshwater dilution at that time aplanktonic conditions s 49 p s u reached the south central red sea by 22 ka bp while planktonic foraminiferal faunas continued albeit in very low abundances and limited diversity s 45 p s u in the southernmost red sea during marine isotope stage mis 6 the 49 p s u isohaline appears to have resided in the central red sea between cores kl11 and md921017 we observe a systematic sequence of species disappearances before all glacial maxima of the last 500 kyr absence of a logical relationship with sea levels suggests that the disappearance sequences are not related to a general salinity increase instead we argue that the sequences were driven by complex reorganisations in hydrography stratification productivity food availability and subsurface oxygenation reproduction habitats the onset is marked by dramatic basin wide expansion of conditions that today are restricted to only the southern red sea suggesting an expansion of the dominance of ne monsoonal circulation over the entire red sea this expansion occurred 15 or more kyr before the aplanktonic zones of mis 12 6 and 2 and also before mis 10 and 8 which never reach the aplanktonic stage regarding the last glacial cycle this event occurred as early as 75 ka bp mis 4 5 boundary after this major climatic reorganisation we reconstruct progressive intensification of the new conditions especially marked by northward expansion and intensification of the subsurface oxygen minimum zone omz during the last glacial cycle a shallow and very distinct omz affected the central red sea as early as 68 ka bp and the north as late as 55 ka bp the omz expansion intensification appears to have been interrupted by episodes of increased ventilation

evolution geochimique superficielle des pyroxenites ignees du mont saint bruno quebec samples were collected in a saprolite and soil profiles derived from the weathering of igneous pyroxenites at mount saint bruno quebec alternation of the disaggregated rock produces small amounts of 2 m material the various minerals present in the pyroxenite augite plagioclases olivine and biotite and their weathering products were separated and analyzed with a microprobe all primary minerals are transformed into smectites identified as beidellites montmorillonites saponites fe mg smectites and transition smectites the microenvironment determines the nature of the secondary minerals

a pronounced dry event recorded around 4 2 ka in brine sediments from the northern red sea partly laminated sediments were sampled from the brine filled anoxic shaban deep basin in the northern red sea at about 4200 cal yr bp more than two millennia of anoxic sedimentation is replaced by a sub oxic facies strongly suggesting the episodic absence of the brine at the same time stable oxygen isotopes from surface dwelling foraminifera show a sharp increase within less than 100 yr pointing to a strong positive salinity anomaly at the sea surface this major evaporation event significantly enhanced the renewal of deep water and the subsequent ventilation of the small shaban deep basin the timing and strength of the reconstructed environmental changes around 4200 cal yr bp suggest that this event is the regional expression of a major drought event which is widely observed in the neighboring regions and which strongly affected middle east agricultural civilizations

stratigraphy palaeoenvironments and model for the deposition of the abdur reef limestone context for an important archaeological site from the last interglacial on the red sea coast of eritrea stone tools discovered within uplifted marine terraces along the red sea coast of eritrea at the abdur archaeological site dated to 125 7 ka the last interglacial marine isotope stage 5e show that early humans occupied coastal areas by this time walter et al 2000 nature 405 65 69 in the present paper the stratigraphy facies types and faunal composition from 25 measured sections of the tool bearing abdur reef limestone arl are documented in detail and interpreted to provide a palaeoenvironmental context for the stone artefacts and a model for the deposition of the arl the arl represents a complex marine terrace sequence erosional surfaces indicative of interrupted sedimentation are locally observed at two levels within the arl they subdivide the complex into three subunits named 5e1 5e2 and 5e3 representing different stages of the marine isotope stage 5e sea level highstand comprising six depositional phases i vi of the arl subunit 5e1 begins with the initial transgression of the 5e sea level highstand leading to the deposition of widespread lag gravels on which rich oyster beds developed in shallow water phase i it further records rapid deepening accompanied by the deposition of low energy carbonates with scarce corals phase ii and later shoaling characterised by local development of a fringing reef tract in a sedimented environment phase iii subunit 5e1 is capped locally by a burrowed hardground that is laterally equivalent to depositional discontinuities interpreted as caused by a globally recognised mid 5e sea level low stand phase iv extensive reef build up in response to sea level rise and improved conditions for coral growth characterises subunit 5e2 phase v a possible second sea level drop during the 5e highstand is inferred from the oyster encrusted upper surface of subunit 5e2 subunit 5e3 encompasses restricted coral patches that developed on the upper surface of the underlying subunit during the last stage of the 5e marine high stand phase vi two different toolkits are found in the arl one consists of bifacial hand axes and cores of the acheulian industry typically associated with the oyster beds encrusted on the transgressive lag deposits the other consists of middle stone age msa type obsidian flakes and blades mainly found in the nearshore and beach environments alongside debris from marine invertebrates and large land mammals the distribution of these tools suggests that foraging activities of early humans varied with environmental setting the abdur archaeological site represents a late example of the acheulian msa transition seen as a benchmark for early modern human behaviour and is to date the earliest well dated example of early human adaptation to marine food resources

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

response of the pelagic environment to palaeoclimatic changes in the central mediterranean sea during the late quaternary abstract three central mediterranean deep sea cores have been studied to reconstruct the palaeoclimatic history of the basin over the time interval 34 0 kyr bp the intensity and duration of the climatic events that occurred in the mediterranean sea during the last glacial postglacial transition were estimated by observing compositional changes in the planktonic foraminifera and calcareous nannoplankton coccolithophores assemblages together with a reconstruction of sea surface temperatures using the modern analogue technique and u 37 k index the 18 o signal and pteropod fluxes the application of two independent and well established techniques for the determination of the past sst led to a number of considerations about the accuracy and efficacy of the use of such methodologies in the mediterranean sea notoriously dominated by local factors and characterised by a number of independent environments the recognition of millennial to centennial climatic instabilities in both the sst and microfossil records was possible because of the high resolution of the study a succession of nine main biozones and six sub zones based on the major changes in the planktonic foraminifera records has been recognised and compared with grip and gisp2 ice cores 18 o values and with records from four other studies from the central mediterranean sea during the early phase of the holocene a period characterised by relatively higher temperatures and lighter 18 o values has been recognised as being coeval with the climatic optimum between 10 5 and 6 1 kyr bp calendar age this interval was characterised by an abrupt drop in the pteropods relative abundances and fluxes the pteropodal fossil assemblage may have been affected by a possible event of selective dissolution of the aragonite driven by the shoaling of the acd a coeval change in the position of the pycnocline may have been responsible for a strong relative increase in abundance of neogloboquadrina pachyderma r c and a decrease in the abundance of globorotalia inflata in the western sector of the mediterranean sea

aragonite pteropod abundance and preservation records from the maldives equatorial indian ocean inferences on past oceanic carbonate saturation and dissolution events abstract during the international ocean discovery program iodp expedition 359 a long continuous carbonate rich sequence was recovered from the inner sea of maldives we investigated pteropod proxies absolute abundance of pteropods species total pteropods epipelagic to mesopelagic ratio fragmentation ratio limacina dissolution index ldx mean shell size variations of l inflata from sites u1467 water depth 487 m and u1468 water depth 521 m to understand both surface and sub surface paleoceanographic changes in the equatorial indian ocean and to improve our understanding of the factors responsible for pteropod preservation on longer timescales a total of 15 species of pteropods were identified and their downcore variations were documented from the core top to 707 49 mbsf in u1467 and from 447 4 to 846 92 mbsf in u1468 at the site u1467 pteropod shells show high abundances preservation up to a depth of 45 mbsf 1 2 ma which is consistent with the presence of aragonite content in sediments with the top 50 m bearing high aragonite content beyond 45 mbsf only fragmented pteropod shells were seen down to 50 mbsf corresponding to 1 5 ma followed by a total absence of pteropod shells and fragments from 50 mbsf 1 5 ma to the end of the core at 846 92 mbsf 24 ma a decrease in the so42 concentration and alkalinity in the interstitial fluid geochemistry is seen at these depths the presence of dolomite content below 50 mbsf also indicates the alteration of aragonite into dolomite analyses of the carbonate preservation proxies reveal that the pteropods exhibit considerable fluctuation in abundance preservation during the last 1 2 myr a good to moderate preservation ldx 2 to 3 is seen which correlates well with the fragmentation ratio but with an inverse relation with calcification rate the proxies for in life pteropod shell dissolution average size of l inflata and ldx indicate that glacial periods mis 16 14 6 4 and 2 have shown no signs of dissolution pointing better calcification under aragonite saturated water column which is in good correlation with reduced atmospheric co concentration epipelagic mesopelagic ratio indicates that the water column exhibited enhanced ventilation and mixing during glacial to interglacial periods but intervals of intense stratification a sign of poor ventilation or weakened circulation was prevalent beyond mis 14 the longest interval of poorest preservation was marked during mis 11 and 13 which corresponds to the mid brunhes dissolution interval mbdi on a longer time scale the abundances preservation of pteropods in the maldives seems to be controlled by changes in the seawater chemistry associated with monsoon productivity water column ventilation and atmospheric co2 concentration

late quaternary biostratigraphy and paleotemperatures of the red sea and the gulf of aden based on planktonic foraminifera and pteropods abstract the quantitative distributions of planktonic foraminifera and pteropods were analyzed in seven red sea cores and two deep sea cores from the gulf of aden and off sokotra island biostratigraphic intervals were distin guished corresponding to oxygen isotope stages 1 5 in the red sea and stages 1 3 in the gulf of aden the faunal assemblages demonstrate that in the red sea hydrological conditions changed significantly during the late quaternary especially at the last glacial maximum when water exchange at the bab el mandeb straits was at a minimum and at the pleistocene holocene boundary at the end of deglaciation water exchange renewal and pluvial conditions resulted in surface salinity decrease and stable stratification which was followed by a rise in planktonic fauna abundance and stagnation of bottom waters the more constant composition of rather cold water subtropical faunal assemblages in the gulf of aden during the last 40 000 50 000 yrs points to more stable hydrological parameters and to local upwelling or influx of arabian upwelling waters during the last stadial mean annual sea surface temperatures fell by at least 5 c compared to the present in the central part of the red sea and by 3 5 c in the western gulf of aden

the role of water in the deformation of dunite specimens of two natural dunites anita bay of 100 m grain size and aheirn of 900 m grain size have been deformed in experiments at temperatures between 1200 and 1400 c and constant strain rates between 10 4 and 10 6 s 1 in a gas medium deformation apparatus at 300 mpa confining pressure prior to these experiments the specimens were given a heat treatment in a controlled oxygen fugacity furnace at 1200 c for 60 hours to dehydrate the trace layer silicate minerals present and drive off adsorbed water the predried specimens are much stronger than specimens tested under wet conditions in an earlier study the predried specimens also do not show the apparent grain size dependence seen under wet conditions infrared absorption measurements on the present specimens and those of the earlier study indicate that for a given rock flow stress can be correlated with the intensity of a residual water related broad absorption the addition of water to a predried specimen results in both a mechanical reweakening and an intensifying of the broadband infrared component the weakening of the dunites under wet conditions is probably strongly influenced by the presence of small amounts of a water related species in the grain boundaries but intragranular weakening may also be contributing it is suggested that the concentration of the water related species in the grain boundaries is governed by its concentration in the small melt fraction present the amounts of water that have been found to be of importance for the strength of these dunites are of the order of 0 01 wt amounts much less than most estimates of the water content of the earth s undepleted upper mantle such water may have an important role in determining upper mantle flow behavior stress strain curves for all experiments are available with entire manuscript on microfiche order from american geophysical union 2000 florida avenue n w washington dc 20009 document b84 008 2 50 payment must accompany order

chemical weathering studies in relation to geomorphological research in southeastern canada abstract although chemical weathering provides fundamental information relevant to geomorphology the subject has been overlooked during the 20th century in canada this paper provides an overview of the current state of canadian research on chemical weathering in southeastern canada and takes into account three spatial and temporal contexts 1 the formation of bedrock morphology by chemical weathering 2 occurrences characteristics and age of saprolites and 3 contemporary chemical denudation rates long term geomorphological evolution of southeastern canadian landscapes shows that chemical weathering has played an important role an example is taken from the laurentide region of the canadian shield north of montreal quebec the present topography resulted from the stripping of the former weathering mantle and from the probable subsequent modification of the weathering front first by the action of hillslope processes and rivers and then by glaciers before and during plio pleistocene times the present landscape reflects the timing of the formation of erosion surfaces and of the stripping of the paleozoic cover rocks and exposure of the shield since the late seventies several isolated occurrences of saprolite soil profiles have been discovered in eastern canada and prompted a renewal of the study of these materials about the cenozoic evolution of these regions one of the problems in this field of research is the dating of saprolites and their inclusion in a chronostratigraphic framework along with the other cenozoic surficial deposits and landforms because of the multiple factors involved in the development of secondary minerals in saprolites during the course of weathering it is preferable to distinguish the dating of saprolites from the study of their mineralogical and geochemical evolution fortunately several new techniques are becoming available for the absolute dating of surficial deposits and saprolites including the use of cosmogenic radionuclides saprolites provide a strong potential field of research for our understanding of the geological evolution of eastern canada during the cenozoic contemporary weathering and erosion rates are fields of research that have gained increasing interest recently since modeling landscape geochemical response can be applied to various environmental stress situations such as acidification by rain and forest harvesting rock type may be the main factor explaining the large differences between watersheds in fact variability of cation removal in the temperate zone is probably most closely related to flow paths of water investigations at different scales from entire watersheds to slopes to individual pedons highlight the problem in the catamaran brook watershed new brunswick water chemistry is explained by a mix of groundwater and soil solution from the horizons at the base of the floodplain soils geochemical mass balances based on net outputs give little information on the weathering reactions of primary minerals the weathering products or on the nature of the weathering processes that provide the dissolved load of streams mineralogic and petrographic analysis of selected soil pedons are necessary to determine weathering reactions and their role as sources or sinks for bases silica aluminum and iron in the various compartments through which water percolates before it reaches the stream

limited modification of mid latitude landscapes by ice sheets the case of northeast scotland the paper uses a case study in scotland to examine the amount and processes of landscape modification by quaternary ice sheets there is an inverse correlation between the distribution of landforms of glacial erosion and pre glacial landscape remnants in northeast scotland the implication is that in places ice sheets can preserve a pre glacial landscape unscathed while elsewhere they remove the pre glacial weathered rock the location of glacial protection or erosion is strongly influenced by the topography and its influence on former ice sheet flow and basal thermal regime the classic glacially eroded landscape of areal scouring can be produced by the removal of only 10 50 m of weathered rock furthermore rock basins often regarded as the hallmark of glacial erosion may be directly inherited from the pre glacial pattern of deep weathering

glacigenic rafting of weathered granite charlie lake new brunswick glaciation in the area of charlie lake new brunswick has produced a granitic till very similar in appearance to weathered bedrock portions of weathered granite were moved intact and redeposited as imbricated rafts under basal till the rafts vary from 0 3 to 2 m in thickness over a 10 m wide exposure and show deep weathering zones and brittle deformation despite the fact that they are highly friable the rafts are separated by glacigenic fault planes defined by lenses of diamict and rare clasts of distant origin they are recognizable only in excavations where fault planes can be seen to delineate slabs of rock imbricated mainly upglacier surface weathering features including core stones were preserved during movement over short distances

cosmogenic chlorine 36 chronology for glacial deposits at bloody canyon eastern sierra nevada deposits from mountain glaciers provide an important record of quaternary climatic fluctuations but have proved difficult to date directly a chronology has been obtained for glacial deposits at bloody canyon california by measurement ofthe accumulation of chlorine 36 produced by cosmic rays in boulders exposed on moraine crests the accumulation ofchlorine 36 indicates that episodes of glaciation occurred at about 21 24 65 115 145 and 200 ka thousand years ago although the timing of the glaciations correlates well with peaks of global ice volume inferred from the marine oxygen isotope record the relative magnitudes differ markedly the lengths of the moraines dating from 115 ka and 65 ka show that the early glacial episodes were more extensive than those during the later wisconsin and indicate that the transition from interglacial to full glacial conditions was rapid