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

the geochemistry of rhenium and osmium in recent sediments from the black sea abstract the os isotopic composition of recent sediments from the black sea are reported with the concentrations of re os and major and minor elements osmium concentrations range from 0 23 to 0 69 ppb and re concentrations range from 21 to 85 ppb concentrations of both elements are large relative to average crustal material and are positively correlated with organic carbon 187 os 186 os ratios range from 5 7 to 7 1 all of these values are less radiogenic than the estimated 187 os 186 os ratio of seawater and average continental crust material variations in the os isotopic composition of these sediments are attributed to mixing of a hydrogenous component 187 os 186 os ratio between 7 and 9 and a less radiogenic detrital component 187 os 186 os ratio between 1 and 4 a mixing model is used to determine the fraction of os in the sediment associated with each component and the burial fluxes of re and os in the black sea are calculated in addition the data are used to estimate the magnitude of systematic error which such initial os isotopic heterogeneity may introduce into re os age determinations of ancient organic rich sediments

troposphere planetary boundary layer interactions and the evolution of ocean surface density lessons from red sea corals a time series of oxygen isotope d18o measurements of a coral from the northern red sea rs is presented and used as a direct proxy for water surface density rs with a relatively constant subsurface density the generated surface density time series closely tracks water mass formation variability two positive and two negative high amplitude rs anomalies are studied and associated atmospheric and oceanic data are analyzed to understand large scale ocean atmosphere processes the dominant process is lower tropospheric subsidence it dries the boundary layer bl increases surface evaporation and rs and ultimately drives water mass formation the main cause of the subsidence is a temperature increase along the principal axis of the rs from the eastern mediterranean to the convergence zone cz 188 228n the increase entails isentropes sloping down to the southeast crossing pressure surfaces due to their tilt with nearly adiabatic flow along the principal axis air parcels move roughly along the sloped isentropes toward ever increasing pressure that is they subside the subsidence supplies the northern rs bl with upstream air from higher altitudes where humidity is low thus drying the bl the resultant high evaporation north of 258n with low evaporation minus precipitation south of 228n depresses sea levels in the northern rs and thus drives the rs thermohaline circulation and controls water mass formation excluded from the presented picture but probably very important is mixing with the hot dry air of the surrounding deserts

ru ir ratios at the cretaceous tertiary boundary implications for pge source and fractionation within the ejecta cloud abstract ruthenium and ir are the least mobile platinum group elements pges within the cretaceous tertiary k t boundary clay the ru ir ratio is therefore the most useful pge interelement parameter for distinguishing terrestrial and extraterrestrial contributions to the boundary clay the ru ir ratio of european marine k t sections 1 67 0 38 is statistically different from that of the north american continental sections 0 76 0 26 it is unlikely that this difference is due to secondary pge remobilization pge input to the boundary clay during multiple impacts or volcanic emissions the global difference in ru ir ratios in the boundary clay may therefore be primary the positive correlation between distance from the chicxulub impact structure yucatan mexico and ru ir ratio and the more than 1000 c difference in the condensation temperatures of these elements lead us to propose that fractionation of ru from ir during condensation from the ejecta cloud may have occurred resulting in the global difference in ru ir ratios

the record of sea water 187os 186os variation through the cenozoic the variation of sea water 187os 186os during the cenozoic has been determined by analyzing the hydrogenous os released by acidic hydrogen peroxide leaching of layers in an abyssal north pacific pelagic clay core overall sea water 187os 186os has increased from 3 2 at 58 ma to the present day value of 8 6 this pattern is similar to the well known 87sr 86sr evolution of sea water the increase in the proportion of continental os 187os 186os 10 could be due to enhanced weathering rates of black shales associated with the uplift of the himalayas other elements associated with black shale weathering such as u and p should show effects in the sedimentary record

distinct modes of east asian winter monsoon documented by a southern red sea coral record the large scale boreal winter climatic patterns associated with interannual variability in a coral oxygen isotope 18o record from the southern red sea covering most of the last century are investigated from the early 1930s to the early 1960s the winter coral 18o record reflecting temperature and salinity variations in southern red sea surface waters is associated with global or large scale sea surface temperature sst and 850 mb geopotential height z850 anomalies which project on the corresponding patterns associated with the el nino southern oscillation enso in contrast since the early 1960s the winter coral 18o record is related to a z850 pattern that reflects the enso independent part of the east asian winter monsoon eawm which includes the siberian high the east asian through and the east asian upper tropospheric jet our results indicate a weakening of the enso control on interannual temperature salinity variations in southern red sea surface waters in the early 1960s due to the warming of the indian ocean and suggest that information about the nonstationarity in the relationship between enso and two distinct modes of eawm can be documented in southern red sea coral 18o records

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

influence of late cenozoic mountain building on ocean geochemical cycles in a steady state ocean input fluxes of dissolved salts to the sea must be balanced in mass and isotopic value by output fluxes for the elements strontium calcium and carbon rivers provide the primary input whereas marine biogenic sedimentation dominates removal dissolved fluxes in rivers are related to rates of continental weathering which in turn are strongly dependent on rates of uplift the largest dissolved fluxes today arise in the himalayan and andean mountain ranges and the tibetan plateau during the past 5 m y uplift rates in these areas have increased significantly this suggests that weathering rates and river fluxes may have increased also the oceanic records of carbonate sedimentation level of the calcite compensation depth and delta sup 13 c and delta sup 87 sr in biogenic sediments are consistent with a global increase in river fluxes since the late miocene the cooling of global climate over the past few million years may be linked to a decrease in atmospheric co sub 2 driven by enhanced continental weathering in these tectonically active regions

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

the osmium isotopic composition of organic rich marine sediments abstract the osmium os concentration and 187 os 186 os ratio of several recent marine organic rich sediment samples from three widely separated sites have been measured os concentrations range from 0 095 to 0 212 ppb and 187 os 186 os ratios range from 8 2 to 8 9 the calculated fraction of hydrogenous os exceeds 78 in all samples thus the 187 os 186 os ratio of these samples reflects os isotopic composition of seawater the small range in measured 187 os 186 os ratio indicates that the os isotopic composition at these sites is fairly homogeneous the large magnitude of the os burial flux at these sites indicates the os burial in association with organic rich sediments is an important sink in the marine cycle of os these data also suggest that ancient organic rich sediments may provide a record of past variations in the os isotopic composition of seawater

a coral oxygen isotope record from the northern red sea documenting nao enso and north pacific teleconnections on middle east climate variability since the year 1750 a 245 year coral oxygen isotope record from the northern red sea ras umm sidd egypt 28 n in bimonthly resolution is presented the mean annual coral 18o signal apparently reflects varying proportions of both sea surface temperature and 18oseawater variability in conjunction with instrumental observations of climate the coral record suggests for interannual and longer timescales that colder periods are accompanied by more arid conditions in the northern red sea but increased rainfall in the southeastern mediterranean whereas warmer periods are accompanied by decreased rainfall in the latter and less arid conditions in the northern red sea a 70 year oscillation of probably north atlantic origin dominates the coral time series interannual to interdecadal variability is correlated with instrumental indices of the north atlantic oscillation nao the el nino southern oscillation enso and north pacific climate variability the results suggest that these modes contributed consistently to middle east climate variability since at least 1750 preferentially at a period of 5 7 years

multicentennial scale hydrological changes in the black sea and northern red sea during the holocene and the arctic north atlantic oscillation 1 paleoenvironmental proxy data for ocean properties eolian sediment input and continental rainfall based on high resolution analyses of sediment cores from the southwestern black sea and the northernmost gulf of aqaba were used to infer hydroclimatic changes in northern anatolia and the northern red sea region during the last 7500 years pronounced and coherent multicentennial variations in these records reveal patterns that strongly resemble modern temperature and rainfall anomalies related to the arctic oscillation north atlantic oscillation ao nao these patterns suggest a prominent role of ao nao like atmospheric variability during the holocene beyond interannual to interdecadal timescales most likely originating from solar output changes

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

variations of the187os 186os ratio of seawater over the past 28 million years as inferred from metalliferous carbonates abstract the os concentration and isotopic composition of metalliferous carbonates deposited on the east pacific rise over the past 28 ma are reported with complimentary sr isotope data variations in the os isotopic composition of these samples are interpreted as a record of past changes in the os isotopic composition of seawater these results are consistent with isotopic analyses of leachable os in pelagic clays which have also been interpreted as a record of the187os 186os ratio of seawater through time 1 the metalliferous carbonate record clearly shows that seawater os and sr isotope systems are partially decoupled from one another over the past 28 ma accelerated weathering of ancient organic rich sediments is suggested as a possible mechanism to account for this decoupling and the rapid increase in the187os 186os ratio of seawater over the past 15 ma this rapid increase suggests that the seawater os record can potentially be used as a stratigraphic tool in some neogene marine deposits

monsoons and the dynamics of deserts the existence of subtropical deserts such as the sahara has often been attributed to the annual mean zonal mean hadley circulation which shows strong descent in the subtropics however the zonal mean hadley circulation shows considerable evolution over the course of the year with very strong subtropical descent during winter but practically no zonal mean subtropical descent during summer when rainfall over the eastern sahara and the mediterranean is least charney 1975 proposed a biosphere albedo feedback mechanism whereby local anthropogenic effects related to over grazing could affect the radiative balance enhancing summertime diabatic descent and leading to desertification of the subtropics in general the present study which uses an idealized model suggests a monsoon desert mechanism for desertification whereby remote diabatic heating in the asian monsoon region can induce a rossby wave pattern to the west integral with the rossby wave solution is a warm thermal structure that interacts with air on the southern flank of the mid latitude westerlies causing it to descend this adiabatic descent is localized over the eastern sahara and mediterranean and over the kyzylkum desert to the south east of the aral sea by the mountains of north africa and south west asia trajectories indicate that the monsoon desert mechanism does not represent a simple walker type overturning cell instead the descending air is seen to be mainly of mid latitude origin it is speculated that the monsoon forced adiabatic descent may result in clear air and therefore a local diabatic enhancement which effectively doubles the strength of descent with this mechanism desertification can be forced by remote changes in monsoon strength rather than by local effects this conclusion is supported by the observed dramatic strengthening of descent over the mediterranean and east sahara during the onset of the asian monsoon and on the longer timescale by relating prehistoric lake levels to milankovitch monsoon forcing the latter may help to explain the perceived discrepancies between the palaeoclimate of the eastern sahara and the strength of a tropic wide monsoon the monsoon desert mechanism may not be confined to the asian monsoon alone and the existence of other monsoon climate regions over the globe may in a similar way explain the observed summertime strengthening of the oceanic sub tropical anticyclones and the existence of western continental deserts and mediterranean type climate regions

strontium isotopes and rubidium in the ganga brahmaputra river system weathering in the himalaya fluxes to the bay of bengal and contributions to the evolution of oceanic87sr 86sr the concentrations of rb and sr and87sr 86sr isotopic ratios have been measured in the dissolved load of the ganga brahmaputra g b river system the ganga was sampled extensively from its source at gangotri in the higher himalaya to patna on the alluvial plains the brahmaputra was sampled in its stretch in assam in india the average sr concentration in the ganga at patna is 1 2 mol l and that in the brahmaputra at goalpara is 0 73 mol l the mean87sr 86sr ratios are 0 7239 and 0 7192 respectively the87sr 86sr in the ganga source waters the alaknanda the bhagirathi and their tributaries range between 0 7300 and 0 7986 considerably higher than the global average runoff value of 0 7119 the high87sr 86sr in the ganga source waters result from the intense weathering of precambrian granites and gneisses enriched in radiogenic sr the sr isotope systematics of the ganga waters is dominated by silicate weathering whereas carbonate weathering plays a significant role in their major ion chemistry the g b system transports about 910 million moles of dissolved sr annually to the bay of bengal with an average87sr 86sr of 0 7213 the sr transported by the g b system is about 2 7 of the global dissolved sr flux to the oceans via rivers model calculations reveal that the g b system has contributed significantly to the sr isotope evolution of seawater during the past 20 ma the flux of rb through the g b system is 24 million moles per year this is about 5 of the global river supply of rb to the oceans nearly twice the contribution of water via the g b system to the oceans our study suggests that the marine geochemistries of sr and rb and possibly u may have been influenced considerably by the himalayan orogeny

cretaceous tertiary boundary of dsdp site 596 south pacific sediments from the cretaceous tertiary k t boundary at deep sea drilling project site 596 record accumulation of pelagic clays at about lat 45 s in the center of the ancestral south pacific the k t boundary in this region is characterized by oxidized thoroughly bioturbated sediments containing large amounts of ir and relict high pressure and high temperature mineral phases the net ir fluence 320 ng cm 2 is among the largest on earth and the number of shocked quartz grains 30 m in size 1800 cm 2 exceeds that in all localities outside of north america

osmium isotopic variations in metalliferous sediments from the east pacific rise and the bauer basin the osmium concentration and isotopic composition of metalliferous sediments from the east pacific rise epr and bauer basin have been determined 187os186os ratios range from 7 9 to 8 6 with epr samples between 8 4 and 8 6 and bauer basin samples between 7 9 and 8 2 the osmium isotopic composition of epr samples is indistinguishable from the inferred osmium isotopic composition of seawater requiring that nearly all the osmium in these sediments is hydrogenous in origin this result is used to place broad constraints on the behavior of osmium in ridge crest hydrothermal systems while bauer basin samples also contain predominantly hydrogenous osmium an additional source of osmium with low 187os186os is required to account for the lower measured ratios calculation of total osmium burial fluxes in the bauer basin show that the background flux of cosmic osmium is adequate to produce the observed depression in bauer basin 187os186os ratios burial flux calculations also suggest that metalliferous sediment deposition is a significant sink in the marine osmium cycle

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

surface ocean density gradients during the last glacial maximum we have compiled published planktonic foraminiferal oxygen isotope values from the tropical to subtropical atlantic and pacific for the late holocene and last glacial maximum lgm we interpret the spatial distribution of 18o values in terms of meridional density gradients in the lgm surface ocean and discuss implications on tropical ocean thermocline structure in both oceans glacial 18o values display a pattern of interhemispheric asymmetry evidenced by increasingly higher glacial 18o values toward northern latitudes the 18o derived density estimates suggest that the northern subtropical surface ocean density was higher during the lgm than today which has significant implications on lgm thermocline ventilation in the atlantic steeper density gradients in the northern subtropics during the lgm are consistent with a more compressed subtropical gyre and thermocline water formation farther south than today in the pacific the steeper density gradients suggest a significant reduction in freshwater fluxes to the northern tropical and subtropical regions which raises the possibility of a more significant component of northern hemisphere source waters to the tropical pacific thermocline these predictions could be tested with numerical ocean models that assess the structure of the tropical thermocline in the glacial ocean

shift in enso teleconnections recorded by a northern red sea coral abstract el nino southern oscillation enso teleconnections over europe and the middle east are evaluated using an oxygen isotope coral time series from the northern red sea and various instrumental datasets a shift in the correlation between the nino 3 index and the red sea coral record in the 1970s is detected and it is shown that this shift can be attributed to nonstationary circulation regimes and related enso teleconnections it is found that positive anomalies of oxygen isotope in the red sea coral record from the middle 1930s to the late 1960s are associated with a strong pacific north atlantic teleconnection accompanied by a weak aleutian low a more zonal flow at midlatitudes and la nina conditions in tropical pacific in contrast positive anomalies of oxygen isotopes in the red sea coral after the 1970s are related to el nino conditions and weaker pan pacific atlantic circulation regimes using the window correlation of the northern red sea coral record with two coral records from the tropi

the isotopic composition of leachable osmium from river sediments the 187os186os ratios of acidic hydrogen peroxide leaches of river sediments are inferred to be representative of the isotopic composition of os delivered to sea water from the continents the 187os186os values for river sediment leaches from the eastern and central u s the ganges river and the rio maipo range from 10 1 to 21 5 these results suggest that the 187os186os of the soluble river load delivered from the major continental areas to the oceans is on average more radiogenic than average currently eroding continental crust 10 5 sediment leaches from three rivers from the western u s that drain ophiolitic peridotites have distinctly lower 187os186os values 1 4 7 1 such rivers may be significant contributors to sea water of the relatively unradiogenic osmium required to yield the contemporary oceanic 187os186os of 8 6

seawater sr isotope variations through time a procedure for constructing a reference curve to date and correlate marine sedimentary rocks a new curve of seawater 87 sr 86 sr variation through the past 450 m y enables dating and correlation of marine sedimentary rocks with quantifiable uncertainties we discuss the method by which this curve was constructed strictly standardized 87 sr 86 sr ratios and biostrat igraphic data for 1300 87 sr 86 sr analyses of marine minerals were input into a data base objective criteria were used to assign each data point a reliability score these scores were used as initial weights in a robust nonparametric regression lowess to obtain a curve of seawater 87 sr 86 sr variation with rigorous 95 confidence intervals for prediction of age uncertainty precise dating and stratigraphic correlation are feasible for much of the phanerozoic the main problem with future sr isotope stratigraphy is likely to be sample quality we discuss guidelines for sample selection

climatological coastal jet collision intermediate water formation and the general circulation of the red sea the authors present climatologies of a numerical model of the red sea focusing on the dynamics of winter intermediate water formation northward flowing boundary currents are identified as the major dynamical elements at the northern boundary the eastern current follows the geometry eventually turning back to the south at 268n and the western wall the two boundary currents collide at the collision site the denser eastern current subducts under the western boundary current the subduction forces the western boundary current eastward into the interior convection communicates the surface fluxes to the downwelled plume and intermediate water forms the estimated rate 0 11 sv sv 106 m3 s21 agrees with previous estimates the authors identify basin scale sea surface tilt to the north due to variable thermohaline forcings as the key dynamical variable the resultant geostrophic eastward cross channel flow interacts with the boundaries and creates upwelling and surface topography spatial patterns that drive the coastal jets upwelling induced vortex stretching dominates the vorticity balance and governs the separation of the western boundary current from the western wall the process ceases in the summer

the osmium isotopic composition of the continental crust osmium isotopic compositions and concentrations have been determined for deltaic and continental shelf sediments from three major rivers the amazon changjiang and mississippi and for two loesses from the upper mississippi river valley the loesses have heavy mineral and clay compositions characteristic of mississippi river and delta sediment concentrations range from 15 to 120 pg os g and 187os 186os ratios range from 8 2 to 10 9 sediments which are polluted surface sediment from the changjiang estuary or which have scavenged metals from seawater gulf of mexico slope surface sediment and distal amazon shelf sediment have high osmium concentrations and less radiogenic isotopic compositions purely terrigenous sediments have 15 90 pg os g and 187os 186os 10 0 10 9 north american loess and mississippi delta sediment osmium isotopic compositions are indistinguishable we believe that 187os 186os 10 11 is a good average for currently eroding upper continental crust these sediments have neodymium isotopic compositions close to the global mean for river sediment terrigenous 187os 186os is significantly more radiogenic than seawater 187os 186os 8 6 requiring a nonriverine source of osmium to seawater terrigenous osmium is also significantly more radiogenic than bulk pelagic clay osmium we use the improved estimate of terrigenous 187os 186os to recalculate the flux of extraterrestrial osmium to pacific marine sediment if the residence age of osmium in an upper crustal region is similar to the neodymium model age of a sediment derived from that region a model dependent upper crustal 187re 186os ratio can be calculated for the model ages of the sediments analyzed in this study tdm 1 5 1 7 ga model 187re 186os ratios are 340 360 and can be used to correct for bias resulting from the preferential erosion of young crust the 187os 186os ratio of 2 2 ga crust with 187re 186os 400 is 14 2 we have also used the data from this study to estimate upper crustal osmium and rhenium concentrations of 50 pg g and 390 pg g respectively

increased seasonality in middle east temperatures during the last interglacial period the last interglacial period about 125 000 years ago is thought to have been at least as warm as the present climate owing to changes in the earth s orbit around the sun it is thought that insolation in the northern hemisphere varied more strongly than today on seasonal timescales which would have led to corresponding changes in the seasonal temperature cycle here we present seasonally resolved proxy records using corals from the northernmost red sea which record climate during the last interglacial period the late holocene epoch and the present we find an increased seasonality in the temperature recorded in the last interglacial coral today climate in the northern red sea is sensitive to the north atlantic oscillation a climate oscillation that strongly influences winter temperatures and precipitation in the north atlantic region from our coral records and simulations with a coupled atmosphere ocean circulation model we conclude that a tendency towards the high index state of the north atlantic oscillation during the last interglacial period which is consistent with european proxy records contributed to the larger amplitude of the seasonal cycle in the middle east

mild and arid climate in the eastern sahara arabian desert during the late little ice age the climate of the sahara and arabian deserts during the little ice age is not well known due to a lack of annually resolved natural and documentary archives we present an annual reconstruction of temperature and aridity derived from sr ca and oxygen isotopes in a coral of the desert surrounded northern red sea our data indicate that the eastern sahara and arabian deserts did not experience pronounced cooling during the late little ice age 1750 1850 but suggest an even more arid mean climate than in the following 150 years the mild temperatures are broadly in line with predominantly negative phases of the north atlantic oscillation during the little ice age the more arid climate is best explained by meridional advection of dry continental air from eurasia we find evidence for an abrupt termination of the more arid climate after 1850 coincident with a reorganization of the atmospheric circulation over europe

arctic oscillation signature in a red sea coral we show that the winter time series of the ras umm sidd coral oxygen isotope record from the northern red sea approximately 28 n is linked to the arctic oscillation phenomenon the northern hemisphere s dominant mode of atmospheric variability until now the detection of this mode which is most prominent in winter in proxy climate records was difficult due to the lack of a clear seasonality in most paleoclimatic archives the results suggest that northern red sea corals can provide information about the low frequency variability of the northern hemisphere winter circulation during the pre instrumental period

late cretaceous and paroxysmal cretaceous tertiary extinctions the various geological signatures at cretaceous tertiary time including iridium and other associated elements microspherules and shock deformation features are compatible with the suggestion that the transition is marked by a period of intense volcanism the volatile emissions from this volcanism would lead to acid rain reduction in the alkalinity and ph of the surface ocean global atmospheric temperature changes and ozone layer depletion these environmental effects coupled with those related to the major sea level regression of the late cretaceous provide the framework for an explanation of the selective nature of the observed extinction record

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

response to wilson p 2008 comment on carr s and coleman c 2007 an improved technique for the reconstruction of former glacier mass balance and dynamics geomorphology 92 76 90 geomorphology 99 443 444

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

climatological evaporation seasonality in the northern red sea 1 the dynamic and thermodynamic processes that underlie the exceptionally high evaporation over the northern red sea are examined through a combination of data analysis and a simple numerical model we show that the key boundary layer dehumidifier is ageostrophic cross channel sea breezes this circulation develops semidiurnally in response to thermal gradients across the red sea s coasts because of disparate land ocean heat capacities during the summer day the thermally induced high pressure center over the red sea axis results in near surface flows from the red sea toward the neighboring deserts the strong divergence associated with these flows is maximized along the red sea axis and is accompanied by strong subsidence that suppresses boundary layer relative humidity by both reducing specific humidity and increasing temperatures because the summer nighttime reversed thermal gradients are smaller in magnitude the daytime circulation dominates over the nighttime in summer and thus dominates over the daily and seasonal means following similar reasoning we also devise a winter dehumidifier we conclude by advancing a simple means of estimating red sea evaporation under diverse paleoinsolation regimes and we show small but clear evaporation changes during the course of the holocene our estimates represent lower bounds and we plan to refine them in follow up work

application of the 187re 187os system to black shale geochronometry the decay of 187re to 187os provides a tool for determining depositional ages of black shales re and os concentrations and os isotopic compositions of whole rock samples of the bakken shale a mississippian devonian boundary black shale yield a whole rock isochron with an age of 354 49 ma this age is in agreement with the accepted age of the bakken shale 360 ma the initial 187os186os ratio of the isochron is 6 2 3 3 this value is indistinguishable from the 187os186os ratios observed in modern black sea sediments the concentration of common os in bakken shale samples is strongly correlated with total nitrogen indicating that a large fraction of the os in these samples is associated with a hydrogenous component which overwhelms any os supplied to the sediment in association with detrital material or cosmic dust the dominance of the hydrogenous component imparts a relatively homogeneous initial 187os186os ratio to the sediment at the time of deposition the degree of scatter about the isochron exceeds the degree of scatter expected from either analytical error or from the estimated degree of initial isotopic heterogeneity the pattern of scatter is consistent with postdepositional mobilization of re and or os on a small spatial scale we suggest that this mobilization may be a consequence of petroleum formation and migration in the bakken shale

the marine187os 186os record of the past 80 million years we report new187os 186os data and re and os concentrations in metalliferous sediments from the pacific to construct a composite os isotope seawater evolution curve over the past 80 m y analyses of four samples of upper cretaceous age yield187os 186os values of between 3 and 6 5 and187re 186os values below 55 mass balance calculations indicate that the pronounced minimum of about 2 in the os isotope ratio of seawater at the k t boundary probably reflects the enormous input of cosmogenic material into the oceans by the k t impactor s following a rapid recovery to187os 186os of 3 5 at 63 ma data for the early and middle part of the cenozoic show an increase in187os 186os to about 6 at 15 ma variations in the isotopic composition of leachable os from slowly accumulating metalliferous sediments show large fluctuations over short time spans in contrast analyses of rapidly accumulating metalliferous carbonates do not exhibit the large oscillations observed in the pelagic clay leach data these results together with sediment leaching experiments indicate that dissolution of non hydrogenous os can occur during the hydrogen peroxide leach and demonstrate that os data from pelagic clay leachates do not always reflect the os isotopic composition of seawater new data for the late cenozoic further substantiate the rapid increase in the187os 186os of seawater during the past 15 ma we interpret the correlation between the marine sr and os isotope records during this time period as evidence that weathering within the drainage basin of the ganges brahmaputra river system is responsible for driving seawater sr and os toward more radiogenic isotopic compositions the positive correlation between87sr 86sr and u concentration the covariation of u and re concentrations and the high dissolved re u and sr concentrations found in the ganges brahmaputra river waters supports this interpretation accelerating uplift of many orogens worldwide over the past 15 ma especially during the last 5 ma could have contributed to the rapid increase in187os 186os from 6 to 8 5 over the past 15 ma prior to 15 ma the marine sr and os record are not tightly coupled the heterogeneous distribution of different lithologies within eroding terrains may play an important role in decoupling the supplies of radiogenic os and sr to the oceans and account for the periods of decoupling of the marine sr and os isotope records

187os 186os in marine manganese nodules and the constraints on the crustal geochemistries of rhenium and osmium during their formation marine manganese or more properly ferromanganese oxide nodules include and commonly concentrate elements dissolved in seawater this attribute makes them especially valuable recorders of the isotopic composition of elements supplied to the oceans having radiogenic isotopes for these can be used in exploring crustal composition and evolution1 5 from measurements of 187os 186os ratios in marine manganese nodules and comparison with the 143nd 144nd ratios of the same nodules we have calculated the os isotopic composition and the osmium and rhenium concentrations of the weatherable portion of the continental crust together with the proportions of ultra mafic and granitic rock that constitute this crustal mass

the geochemical cycle of rhenium a reconnaissance rhenium re is one of a suite of elements including uranium and molybdenum that display conservative behavior in seawater and are enriched in anoxic sediments the decay of187re to187os provides a geochronometer in ancient sedimentary rocks and gives rise to os isotopic variations in nature in order to better characterize its sources to seawater re was measured in three major rivers amazon orinoco ganges brahmaputra and some of their tributaries re concentrations span four orders of magnitude from 0 02 to 400 pmol kg with the highest concentrations found in rivers draining black shales in the venezuelan andes mainstream re levels in the three rivers are between 1 and 10 pmol kg with a flux weighted average of 2 3 pmol kg the residence time for re in the oceans is estimated to be 750 000 yr with respect to river inputs re profiles from the atlantic and pacific oceans confirm that re behaves conservatively in seawater with no significant uptake onto particles and or recycling within the water column this is also true in the anoxic water column of the black sea re removal into anoxic sediments occurs at or below the sediment water interface as demonstrated in sediment pore waters from chesapeake bay in oxic sediments re is not cycled with manganese oxides and it is not enriched in very slowly accumulating pelagic sediments with a large hydrogenous iron and manganese component or in manganese nodules burial of re in anoxic sediments which accumulate on 0 3 of the ocean floor removes approximately 50 of the riverine re flux to the oceans hence oceanic re concentrations may be very sensitive to changes in the area of anoxic sedimentation

a possible link between the seawater osmium isotope record and weathering of ancient sedimentary organic matter the os isotopic composition of leachable os from a north pacific pelagic clay sequence pegram et al 1992 and bulk sediment samples of metalliferous carbonates deposited near the east pacific rise ravizza 1993 display similar patterns of temporal variation fig 1 this similarity indicates that the composite record of t87os 186os ratio variations reflects changes in the os isotopic composition of seawater temporal changes in the sr isotopic composition of seawater record changes in the relative rates of continental weathering and oceanic crustal alteration the os isotopic composition of seawater should be influenced by similar processes in both the rb sr and re os systems the continental crust is characterized by large time integrated parent daughter ratios compared to the deep earth imparting relatively radiogenic sr and os signatures to continental material however the seawater sr and os records are decoupled from one another over the past 27 ma from 27 to 15 ma 87sr 86sr increased rapidly while the 18vos 186os ratio of seawater remained nearly constant at 15 ma the 87os ts6os ratio of seawater began to increase rapidly but the rate