erosional and climatic effects on long term chemical weathering rates in granitic landscapes spanning diverse climate regimes abstract we used cosmogenic nuclide and geochemical mass balance methods to measure long term rates of chemical weathering and total denudation in granitic landscapes in diverse climatic regimes our 42 study sites encompass widely varying climatic and erosional regimes with mean annual temperatures ranging from 2 to 25 c average precipitation ranging from 22 to 420 cm year 1 and denudation rates ranging from 23 to 755 t km 2 year 1 long term chemical weathering rates range from 0 to 173 t km 2 year 1 in several cases exceeding the highest granitic weathering rates on record from previous work chemical weathering rates are highest at the sites with rapid denudation rates consistent with strong coupling between rates of chemical weathering and mineral supply from breakdown of rock a simple empirical relationship based on temperature precipitation and long term denudation rates explains 89 95 of the variation in long term weathering rates across our network of sites our analysis shows that for a given precipitation and temperature chemical weathering rates increase proportionally with fresh material supply rates we refer to this as supply limited weathering in which fresh material is chemically depleted to roughly the same degree regardless of its rate of supply from breakdown of rock the temperature sensitivity of chemical weathering rates is two to four times smaller than what one would expect from laboratory measurements of activation energies for feldspar weathering and previous inter comparisons of catchment mass balance data from the field our results suggest that climate change feedbacks between temperature and silicate weathering rates may be weaker than previously thought at least in actively eroding unglaciated terrain similar to our study sites to the extent that chemical weathering rates are supply limited in mountainous landscapes factors that regulate rates of mineral supply from erosion such as tectonic uplift may lead to significant fluctuations in global climate over the long term

hydrothermal source of radiogenic sr to himalayan rivers 1 k 1 and cl 2 all of which are high in the hydrothermal waters cation concentrations decrease along the lesser himalayan reach of the river hot spring dissolved co2 has a d 13 c value to 15 9 indicating that metamorphic decarbonation reactions contribute co2 to the fluids hydrothermal co2 is partially neutralized in high temperature weathering reactions which generate alkalinity and yield abundant radiogenic sr radiogenic hydrothermal carbonate can form from these solutions and later weather releasing silicate sr but imparting carbonate characteristics to the overall water chemistry

back folds in the core of the himalayan orogen an alternative interpretation the hanging wall of the south tibetan detachment system in the central nepal himalaya is characterized by regional scale northeast verging folds classically interpreted as gravity induced structures developed during down to the north extensional shearing along the detachment system new structural observations and balanced cross sections of the tethyan sedimentary sequence in the kali gandaki area and new u pb geochronology support an alternative interpretation the northeast verging folds developed before ductile extensional shearing along the detachment system thereby recording some of the earliest contraction of this part of the orogen we propose a new model in which the northeast verging folds of the kali gandaki area represent the northern part of a late eocene to oligocene contractional fan structure

globorotalia truncatulinoides growth and chemistry as probes of the past thermocline 1 shell size this work identifies features of the life history of the deep living planktonic foraminifer globorotalia truncatulinoides that offer possibilities for reconstructing characteristics of the past ocean s main thermocline part 1 considers two aspects of variation in shell size the predictability of growth related size changes which we need to calculate changes in shell chemistry and a model for environmentally forced changes in shell size frequency which suggests how shell size may be a direct source of paleoceanographic information even though size variation among shells of g truncatulinoides at the same stage of growth same number of chambers exceeds the size difference between successive growth stages growth related size changes are predictable because shells tend to grow at the same rate variation in initial shell size is sufficient to account for the large size variation found among shells at the same stage of growth several lines of evidence suggest that g truncatulinoides reproduces at 600 m in the water column and it appears that vertical mixing to that depth is required to return juvenile shells to the surface anything that prevents this such as shallowing of the thermocline can interfere with g truncatulinoides life history in such a way that its shell size frequency distributions are altered among shells falling to the seafloor from a reproducing population are large numbers of both juvenile and adult sizes and if reproduction is inhibited the frequencies of those sizes are reduced and the relative frequency of intermediate sized shells increases a paleoceanographically useful result of this is that the topography of the main thermocline tends to be reflected in the size frequency distribution of g truncatulinoides shells from the underlying sediments in areas where the top of the main thermocline is shallower than 600 m production of juveniles 125 177 m and reproductive adults 425 m is reduced leaving predominantly intermediate sized 212 355 m shells

florida straits deglacial temperature and salinity change implications for tropical hydrologic cycle variability during the younger dryas temperature and d 18 osw a proxy for surface salinity records based on mg ca ratios and oxygen isotope measurements in the planktonic foraminifera globigerinoides ruber from a sediment core located on the western margin of the florida straits as a proxy for meltwater discharge influence on florida straits surface water salinity we also measured ba ca ratios in g ruber from the same core results show that riverine influence on florida straits surface water started by 17 2 ka bp and ended by 13 6 ka bp 600 years before the start of the younger dryas yd cold interval the initiation of the yd is marked by an abrupt increase in florida straits d 18 osw values indicating a shift to elevated sea surface salinity occurring in 130 years most likely resulting from increased regional aridity and or reduced precipitation in order to resolve the timing of tropical atmospheric circulation change relative to amoc variability across this transition we compare the timing of surface water changes to a recently published record of florida current variability in the same core reconstructed from benthic oxygen isotope measurements we find synchronous changes in atmospheric and ocean circulation on the transition into the yd consistent with an abrupt reduction in amoc as the driver of tropical atlantic atmospheric circulation change at this time

fast advective recovery of the atlantic meridional overturning circulation after a heinrich event ice core reconstructions and ocean sediment analysis have revealed that the climate of the last glacial period was highly variable with rapid stadial interstadial transitions and glacial meltwater pulses heinrich events modulating the climate evolution in the northern and southern hemispheres heinrich events had the potential to weaken the atlantic meridional overturning circulation amoc substantially mechanisms that led to the resumption of the amoc after such events have not been fully disentangled yet here a coupled atmosphere ocean sea ice model of intermediate complexity is employed to identify important negative climate feedbacks that contribute to a fast recovery of the glacial amoc shortly after the amoc collapse thermal processes weaken the stratification in the northern north atlantic making it more vulnerable to perturbations eventually 300 400 years after the main collapse of the amoc the mean advection of salinity anomalies within the horizontal gyres generates an unstable stratification that will be homogenized through the resumption of convective activity eventually isopycnal slopes in the north atlantic are readjusted thereby reinitiating the large scale meridional overturning flow

warming of surface waters in the mid latitude north atlantic during heinrich events 1 during the six heinrich events of the last 70 kyr episodic calving from the circum atlantic ice sheets released large numbers of icebergs into the north atlantic these icebergs and associated meltwater flux are hypothesized to have led to a shutdown of atlantic meridional overturning circulation and severe cooling in large parts of the northern hemisphere however due to the limited availability of high resolution records the magnitude of sea surface temperature sst changes related to the impact of heinrich events on the midlatitude north atlantic is poorly constrained here we present a record of u37k based ssts derived from sediments of integrated ocean drilling project site u1313 located at the southern end of the ice rafted debris ird belt in the midlatitude north atlantic 41 n we demonstrate that all six heinrich events are associated with a rapid warming of surface waters by 2 4 c in a few thousand years the presence of ird leaves no doubt about the simultaneous timing and correlation between rapid surface water warming and heinrich events we argue that this warming in the midlatitude north atlantic is related to a northward expansion of the subtropical gyre during heinrich events as a wide range of studies demonstrated that in the central ird belt heinrich events are associated with low ssts these results thus identify an antiphased seesaw pattern in ssts during heinrich events between the midlatitude warm and northern north atlantic cold this highlights the complex response of surface water characteristics in the north atlantic to heinrich events that is poorly reproduced by freshwater hosing experiments and challenges the widely accepted view that within the ird belt of the north atlantic heinrich events coincide with periods of low ssts

a simple evaluation of cleaning procedures on fossil benthic foraminiferal mg ca 1 recent studies suggest that benthic foraminiferal mg ca may be useful in reconstructing deep water temperature changes during the quaternary and on longer timescales rosenthal et al 1997 lear et al 2000 martin et al 2002 because changes in deep water temperature may be small sample preparation could play an important role in reconstructing accurate temperatures from shell mg ca a simple examination of changes in measured shell chemistry of benthic foraminifera from two intervals subjected to increasingly rigorous cleaning reveals that fossil benthic foraminiferal samples cleaned by oxidation yield lower mg ca values than samples only rinsed and weak acid leached reductive cleaning further lowered the shell mg ca of one of the two benthic species examined lower mg ca values following oxidation and reduction appear to reflect removal of contaminant mg associated with remnant organic matter and adsorbed phases

atlantic meridional overturning circulation slowdown cooled the subtropical ocean 1 observations show that the upper 2 km of the subtropical north atlantic ocean cooled throughout 2010 and remained cold until at least december 2011 we show that these cold anomalies are partly driven by anomalous air sea exchange during the cold winters of 2009 2010 and 2010 2011 and more surprisingly by extreme interannual variability in the ocean s northward heat transport at 26 5 n this cooling driven by the ocean s meridional heat transport affects deeper layers isolated from the atmosphere on annual timescales and water that is entrained into the winter mixed layer thus lowering winter sea surface temperatures here we connect for the first time variability in the northward heat transport carried by the atlantic meridional overturning circulation to widespread sustained cooling of the subtropical north atlantic challenging the prevailing view that the ocean plays a passive role in the coupled ocean atmosphere system on monthly to seasonal timescales

reevaluation of the oxygen isotopic composition of planktonic foraminifera experimental results and revised paleotemperature equations cultured planktonic foraminifera orbulina universa symbiotic and globigerina bulloides nonsymbiotic are used to reexamine temperature 18o relationships at 15 25 c relationships for both species can be described by linear equations equations for o universa grown under low light ll and high light hl share a slope of 4 80 0 21 c 1 with a hl ll offset of 0 33 due to symbiont photosynthetic activity the effect of co32 on o universa is 0 002 mol 1 kg 1 and is insensitive to temperature for g bulloides ontogenetic effects produce size related trends in temperature 18o whereby larger shells are enriched in 18o relative to smaller specimens the o universa temperature 18o relationships are more accurate than previously published equations for describing plankton tow data our equations do not explain planktonic core top data with the same precision but provide a good fit to benthic cibicidoides data below 10 c temperature 18o relationships for g bulloides provide good agreement with field data for this species from the northeast pacific

the 8 2 ka event abrupt transition of the subpolar gyre toward a modern north atlantic circulation 1 climate model simulations of the 8 2 ka event show an abrupt strengthening of the atlantic subpolar gyre that allows us to connect two major but apparently contradictory climate events of the early holocene the freshwater outburst from proglacial lakes and the onset of labrador sea water formation the 8 2 ka event is the largest climatic signal of our present interglacial with a widespread cooling in the north atlantic region about 8200 years before present it coincides with a meltwater outburst from north american proglacial lakes that is believed to have weakened the atlantic meridional overturning circulation and northward heat transport followed by a recovery of the deep ocean circulation and rising temperatures after a few centuries marine proxy data however date the onset of deep water formation in labrador sea to the same time the subsequent strengthening of the slope current system created a regional signal recorded as an abrupt and persistent surface temperature decrease although similarities in timing are compelling a mechanism to reconcile these apparently contradictory events was missing our simulations show that an abrupt and persistent strengthening of the atlantic subpolar gyre provides a plausible explanation the intense freshwater pulse triggered a transition of the gyre circulation into a different mode of operation stabilized by internal feedbacks and persistent after the cessation of the perturbation as a direct consequence deep water formation around its center intensifies this corresponds to the modern flow regime and stabilizes the meridional overturning circulation possibly contributing to the holocene s climatic stability

persistent solar influence on north atlantic climate during the holocene surface winds and surface ocean hydrography in the subpolar north atlantic appear to have been influenced by variations in solar output through the entire holocene the evidence comes from a close correlation between inferred changes in production rates of the cosmogenic nuclides carbon 14 and beryllium 10 and centennial to millennial time scale changes in proxies of drift ice measured in deep sea sediment cores a solar forcing mechanism therefore may underlie at least the holocene segment of the north atlantic9s 1500 year cycle the surface hydrographic changes may have affected production of north atlantic deep water potentially providing an additional mechanism for amplifying the solar signals and transmitting them globally

rapid subtropical north atlantic salinity oscillations across dansgaard oeschger cycles geochemical and sedimentological evidence suggest that the rapid climate warming oscillations of the last ice age the dansgaard oeschger cycles were coupled to fluctuations in north atlantic meridional overturning circulation through its regulation of poleward heat flux the balance between cold meltwater from the north and warm salty subtropical gyre waters from the south influenced the strength and location of north atlantic overturning circulation during this period of highly variable climate here we investigate how rapid reorganizations of the ocean atmosphere system across these cycles are linked to salinity changes in the subtropical north atlantic gyre we combine mg ca palaeothermometry and oxygen isotope ratio measurements on planktonic foraminifera across four dansgaard oeschger cycles spanning 45 9 59 2 kyr ago to generate a seawater salinity proxy record from a subtropical gyre deep sea sediment core we show that north atlantic gyre surface salinities oscillated rapidly between saltier stadial conditions and fresher interstadials covarying with inferred shifts in the tropical atlantic hydrologic cycle and north atlantic overturning circulation these salinity oscillations suggest a reduction in precipitation into the north atlantic and or reduced export of deep salty thermohaline waters during stadials we hypothesize that increased stadial salinities preconditioned the north atlantic ocean for a rapid return to deep overturning circulation and high latitude warming by contributing to increased north atlantic surface water density on interstadial transitions

the timing of deglacial circulation changes in the atlantic 1 well dated benthic foraminifer oxygen isotopic records 18o from different water depths and locations within the atlantic ocean exhibit distinct patterns and significant differences in timing over the last deglaciation this has two implications on the one hand it confirms that benthic 18o cannot be used as a global correlation tool with millennial scale precision but on the other hand the combination of benthic isotopic records with independent dating provides a wealth of information on past circulation changes comparing new south atlantic benthic isotopic data with published benthic isotopic records we show that 1 circulation changes first affected benthic 18o in the 1000 2200 m range with marked decreases in benthic 18o taking place at 17 5 cal kyr b p ka due to the southward propagation of brine waters generated in the nordic seas during heinrich stadial 1 hs1 cold period 2 the arrival of 18o depleted deglacial meltwater took place later at deeper north atlantic sites 3 hydrographic changes recorded in north atlantic cores below 3000 m during hs1 do not correspond to simple alternations between northern and southern sourced water but likely reflect instead the incursion of brine generated deep water of northern as well as southern origin and 4 south atlantic waters at 44 s and 3800 m depth remained isolated from better ventilated northern sourced water masses until after the resumption of north atlantic deep water nadw formation at the onset of the bolling allerod which led to the propagation of nadw into the south atlantic

the sensitivity of the climate response to the magnitude and location of freshwater forcing last glacial maximum experiments abstract proxy records indicate that the locations and magnitudes of freshwater forcing to the atlantic ocean basin as iceberg discharges into the high latitude north atlantic laurentide meltwater input to the gulf of mexico or meltwater diversion to the north atlantic via the st lawrence river and other eastern outlets may have influenced the north atlantic thermohaline circulation and global climate we have performed last glacial maximum lgm simulations with the ncar community climate system model ccsm3 in which the magnitude of the freshwater forcing has been varied from 0 1 to 1 sv and inserted either into the subpolar north atlantic ocean or the gulf of mexico in these glacial freshening experiments the less dense freshwater provides a lid on the ocean water below suppressing ocean convection and interaction with the atmosphere above and reducing the atlantic meridional overturning circulation amoc this is the case whether the freshwater is added directly to the area of convection south of greenland or transported there by the subtropical and subpolar gyres when added to the gulf of mexico the amoc reduction is less for the smaller freshwater forcings but is not linear with the size of the freshwater perturbation the recovery of the amoc from a slow state is 200 years for the 0 1 sv experiment and 500 years for the 1 sv experiment for glacial climates with large northern hemisphere ice sheets and reduced greenhouse gases the cold subpolar north atlantic is primed to respond rapidly and dramatically to freshwater that is either directly dumped into this region or after being advected from the gulf of mexico greenland temperatures cool by 6 8 c in all the experiments with little sensitivity to the magnitude location or duration of the freshwater forcing but exhibiting large seasonality sea ice is important for explaining the responses the northern hemisphere high latitudes are slow to recover antarctica and the southern ocean show a bipolar response with warming and reduced sea ice this warming continues after the cessation of the freshwater forcing and shows a dependence on the duration of the freshwater forcing equatorward of the expanded sea ice the simulated temperature and salinity anomalies are sensitive to the amount of colder and fresher waters that are advected out of the subpolar north atlantic in the tropical atlantic the recovery of the intertropical convergence zone itcz from its more southerly position during the freshwater forcing is much more rapid than the recovery of the amoc and is more related to the recovery of low latitude surface temperatures than greenland temperature or sea ice these results have implications for using proxy records as indirect measures of the amoc

circulation and deep water export at the western exit of the subpolar north atlantic the current system east of the grand banks was intensely observed by world ocean circulation experiment woce array acm 6 during 1993 95 with eight moorings reaching about 500 km out from the shelf edge and covering the water column from about 400 m depth to the bottom more recently a reduced array by the institut fur meerskunde ifm at kiel germany of four moorings was deployed during 1999 2001 focusing on the deep water flow near the western continental slope both sets of moored time series each about 22 months long are combined here for a mean current boundary section and both arrays are analyzed for the variability of currents and transports a mean hydrographic section is derived from seven ship surveys and is used for geostrophic upper layer extrapolation and isopycnal subdivision of the mean transports into deep water classes the offshore part of the combined section is dominated by the deep reaching north atlantic current nac with currents still at 10 cm s 1 near the bottom and a total northward transport of about 140 sv sv 106 m3 s 1 with the details depending on the method of surface extrapolation used the mean flow along the western boundary was southward with the section mean north atlantic deep water outflow determined to be 12 sv below the 27 74 kg m 3 isopycnal however east of the deep western boundary current dwbc the deep nac carries a transport of 51 sv northward below 27 74 kg m 3 resulting in a large net northward flow in the western part of the basin from watermass signatures it is concluded that the deep nac is not a direct recirculation of dwbc water masses transport time series for the dwbc variability are derived for both arrays the variance is concentrated in the period range from 2 weeks to 2 months but there are also variations at interannual and longer periods with much of the dwbc variability being related to fluctuations and meandering of the nac a significant annual cycle is not recognizable in the combined current and transport time series of both arrays the moored array results are compared with other evidence on deep outflow and recirculation including recent models of different types and complexity

position of the polar front along the western iberian margin during key cold episodes of the last 45 ka 1 this paper documents the migration of the polar front pf over the iberian margin during some of the cold climatic extremes of the last 45 ka it is based on a compilation of robust and coherent paleohydrological proxies obtained from eleven cores distributed between 36 and 42 n planktonic 18o globigerina bulloides ice rafted detritus concentrations and the relative abundance of the polar foraminifera neogloboquadrina pachyderma sinistral were used to track the pf position these three data sets compared from core to core show a consistent evolution of the sea surface paleohydrology along the iberian margin over the last 45 ka we focused on five time slices representative of cold periods under distinct paleoenvironmental forcings the 8 2 ka event and the younger dryas two recent cold events occurring within high values of summer insolation heinrich events 1 and 4 reflecting major episodes of massive iceberg discharges into the north atlantic and the last glacial maximum typifying the highest ice volume accumulated in the northern hemisphere for each event we generated schematic maps mirroring past sea surface hydrological conditions the maps revealed that the polar front presence along the iberian margin was restricted to heinrich events the sea surface conditions during the last glacial maximum were close to those at present day except for the northern sites which briefly experienced subarctic conditions

isotope evidence for secondary sulfide precipitation along the marsyandi river nepal himalayas abstract we present sulfur and oxygen isotope data from 41 samples of dissolved riverine sulfate from along 65 km of the marsyandi river in the northern himalayas coupled sulfur and oxygen isotopic composition of riverine sulfate 34 s so 4 and 18 o so 4 respectively yield unique constraints on the source of sulfur to the river system the headwaters of the marsyandi river have light 34 s so 4 and 18 o so 4 which requires that the source of sulfate to the river is through the anoxic weathering of pyrite likely via fe3 the 34 s so 4 and 18 o so 4 of sulfate in tributaries to the marsyandi increase downstream which could result either from inputs from evaporites or bacterial sulfate reduction with subsequent sulfide precipitation in warmer and wetter catchments either of these processes could result in heavy 34 s so 4 and 18 o so 4 of the residual river sulfate elemental ratios such as sr ca and ca so4 suggest as previous studies have also concluded that evaporite weathering is not important in the marsyandi river we conclude that the isotope data is most consistent with the onset of bacterial sulfate reduction and secondary sulfide precipitation in the soils in the warmer and wetter downstream catchments our results have implications for understanding the source of sulfate to the ocean as well as the redox and acidity budget within rapidly eroding catchments

a tex86 lake record suggests simultaneous shifts in temperature in central europe and greenland during the last deglaciation high resolution quantitative temperature records from continents covering glacial to interglacial transitions are scarce but important for understanding the climate system we present the first decadal resolution record of continental temperatures in central europe during the last deglaciation similar to 14 60010 600cal yrb p based on the organic geochemical palaeothermometer tex86 the tex86 inferred temperature record from lake lucerne vierwaldstattersee switzerland reveals typical oscillations during the late glacial interstadial followed by an abrupt cooling of 2 degrees c at the onset of younger dryas and a rapid warming of 4 degrees c at the onset of the holocene within less than 350years the remarkable resemblance with the greenland and regional stable oxygen isotope records suggests that temperature changes in continental europe were dominated by large scale reorganizations in the northern hemispheric climate system

structural evolution of the tethyan sedimentary sequence in the annapurna area central nepal himalaya the tethyan sedimentary sequence of central nepal has been affected by three phases of folding d1 d 2 and d4 with contrasting vergence interspersed by two major extensional events d3 and d5 the north verging second phase folds f2 are the dominant deformation features preserved in the studied area these d2 structures indicate a vertical structural zonation that is interpreted to mark a preserved d2 strain gradient increasing with depth to a presumed north verging decollement plane at an approximate depth of 10 km palinspastic bed length restoration of the sequence implies a minimum 43 shortening and a minimum 150 vertical thickening due to d2 deformation the d4 event overprints the d3 annapurna detachment and manifests itself as post peak metamorphic south verging kink folds and spaced crenulation cleavage in the structurally lowest level observed d4 is associated with thrust sense meter scale fault zones the youngest extensional event d5 marks the initiation and eventual southward propagation of the thakkhola graben a newly named northeast dipping normal fault the lupra fault is described in the early stages of extension the lupra fault may have acted as a southern termination of the graben system dropping down cretaceous rocks and high level structural features in its hanging wall it is suggested that as the extension progressed southward the lupra fault was itself down faulted in the graben and the extent of the thakkhola graben reached the present position of the annapurna detachment q 2003 elsevier ltd all rights reserved

iles clastic wedge development and sediment partitioning within a 300 km fluvial to marine campanian transect 3 m y western interior seaway southwestern wyoming and northern colorado a 300 km 186 mi transect was reconstructed across the 500 m 1640 ft thick 3 m y duration iles clastic wedge in southern wyoming and northern colorado using well logs and stratigraphic columns this wedge developed into the middlelate campanian aged western interior seaway by progradation from the active sevier fold and thrust belt and adjacent uplifted areas the wedge thickens basinward because late stage widespread uplift of the fold belt caused multiple unconformities across the proximal former foredeep reaches of the foreland basin transect analysis allows the wedge and its component sequences to be better understood and permits a two dimensional characterization of the sand and mud distribution the iles wedge exhibits 11 low gradient regressive transgressive high frequency sequences that were correlated across several hundred kilometers sediment partitioning analysis along the transect shows the following 1 within the regressive limb of the iles wedge the component higher order regressive compartments tend to thicken into the medial reaches of the wedge whereas transgressive compartments thicken landward this geometry is driven by preferential erosion in proximal areas during regression bypassing much sediment to the marine shorelines and transgressive backfilling into proximal areas previously eroded more deeply 2 the greatest concentration of sands tends to be located in the proximal fluvial and estuarine facies of the transgressive compartments and within the medial shoreline deltaic facies of the regressive compartments 3 as the high frequency sequences develop the effectiveness of basinward sand partitioning reaches a maximum value near the peak regression level of the wedge apparently reflecting stronger erosion and sediment bypass during these times

a subtropical fate awaited freshwater discharged from glacial lake agassiz 1 the 8 2 kyr event is the largest abrupt climatic change recorded in the last 10 000 years and is widely hypothesized to have been triggered by the release of thousands of kilometers cubed of freshwater into the north atlantic ocean using a high resolution 1 6 global ocean ice circulation model we present an alternative view that freshwater discharged from glacial lake agassiz would have remained on the continental shelf as a narrow buoyant coastal current and would have been transported south into the subtropical north atlantic the pathway we describe is in contrast to the conceptual idea that freshwater from this lake outburst spread over most of the sub polar north atlantic and covered the deep open ocean convection regions this coastally confined freshwater pathway is consistent with the present day routing of freshwater from hudson bay as well as paleoceanographic evidence of this event using a coarse resolution 2 6 version of the same model we demonstrate that the previously reported spreading of freshwater across the sub polar north atlantic results from the inability of numerical models of this resolution to accurately resolve narrow coastal flows producing instead a diffuse circulation that advects freshwater away from the boundaries to understand the climatic impact of freshwater released in the past or future e g greenland and antarctica the ocean needs to be modeled at a resolution sufficient to resolve the dynamics of narrow coastal buoyant flows

the thakkhola mustang graben in nepal and the late cenozoic extension in the higher himalayas abstract the thakkhola mustang graben is located at the northern side of the dhaulagiri and annapurna ranges in north central nepal the structural pattern is mainly characterised by the n020 040 thakkhola fault system responsible for the development of the half graben a detailed study of the substrate and the sedimentary fill in several outcrops indicates polyphased faulting pre sedimentation faulting miocene with a mainly nnw sse to n s compressional stress expressed in the substratum by n020 040 and n180 n010 sinistral and n130 140 dextral conjugate strike slip faults syn sedimentation faulting pliocene pleistocene characterised by a w e to wnw ese extensional stress and tectonic subsidence of the half graben during the tetang period pliocene probably followed by a doming of the tetang deposits and a short period of erosion cf pliocene planation surface and unconformity between the tetang and thakkhola formations the thakkhola period pleistocene is characterized by a w e to wnw ese extensional stress and a major subsidence of the half graben post sedimentation recurrent extensional faulting and n s and ne sw normal faults in the late quaternary terrace formations geodynamic interpretation of the faulting is discussed in relation to the following 1 the geographic situation of the thakkhola mustang half graben in the southern part of tibet and its setting in the tethyan series above the south tibetan detachment system stds 2 the geodynamic conditions of the convergence between india and eurasia and the dextral east west shearing between the high himalayas and south tibet 3 the possible relations between the sinistral thakkhola and the dextral karakorum strike slip faults in a n s compressional stress regime during the miocene

mg ca and sr ca ratios in planktonic foraminifera proxies for upper water column temperature reconstruction reliable temperature estimates from both surface and subsurface ocean waters are needed to reconstructpast upper water column temperature gradients and past oceanic heat content this work examines therelationships between trace element ratios in fossil shells and seawater temperature for surface dwellingforaminifera species globigerinoides ruber white and globigerina bulloides and deep dwelling species globorotalia inflata globorotalia truncatulinoides dextral and sinistral and pulleniatina obliquiloculata mg ca and sr ca ratios in shells picked in 29 modern core tops from the north atlantic ocean are calibratedusing calculated isotopic temperatures mg ca ratios on g ruber and g bulloides agree with published dataand relationships for deep dwelling species mg ca calibration follows the equation mg ca 0 78 0 04 exp 0 051 0 003 t with a significant correlation coefficient of r

a poisoned chalice deep sea sediments often carry information about past temperatures in the upper ocean directly above their location but as mccave cautions in this perspective interpretation of the sediments can be complicated by deep sea processes for example material transported laterally in the deep ocean may distort the upper ocean signal in the sediments a report by ohkouchi illustrates such processes at bermuda rise the study yields a detailed understanding of deep sea sediment transport processes aiding the interpretation of sediment records at this site and sounding a warning for others

circulation patterns and transport of the azores front current system in this paper different types of new data sets hydrography lagrangian and eulerian current measurements and quasi geostrophic model results obtained after altimetric data assimilation are used to study the structure and variability of the azores current and frontal system the azores current was observed to transport between 11 0 and 18 0 sv eastwards and the associated counter current some 2 0 10 0 sv to the west resulting in a net value of about 8 9 sv furthermore both data and model results revealed a meandering azores current where some freely rotating eddies were also identified these hydrographic and lagrangian results exhibit space and time scales that agree fairly well with the dynamics shaped by baroclinic instability current meters moored across the azores current system delineated a mean counter current flowing westwards with a maximum subsurface core of about 2 0 cm s at a mean depth of 800 dbar this is in excellent agreement with previous studies which explains this azores counter current as the rectification process of the geostrophic turbulence occurring north of the main azores current stream a new scheme is proposed for the formation mechanism of the freely rotating cyclonic eddies observed south of the azores it is shown that the north south contrast thickness of the 17 19 c water layer across the azores front decreases downstream this will create in turn a downstream increase of the most unstable wavelength in a non linear baroclinic instability context as a consequence both large cyclonic and anticyclonic features are able to form at the eastern side of the azores current around 19 w while at the western side around 35 w only large anticyclones will survive western generated cyclones will be small enough to be quickly dissipated this means that the eastern cyclones of the azores current may live longer than the shorter western ones however because longer lived cyclonic eddies propagate westwards with a mean speed of 2 5 km day they may be observed south of azores and of the main stream several months later although they were not formed there

ocean surface water response to short term climate changes revealed by coccolithophores from the gulf of cadiz ne atlantic and alboran sea w mediterranean the response of coccolithophore assemblages to short term millennial and centennial climatic changes over the last 50 kyr is studied in core m39029 7 from the gulf of cadiz atlantic ocean and core md95 2043 from the alboran sea western mediterranean sea the nannoplankton data are compared with oxygen isotopes u37k sst and other biogeochemical and sedimentological proxies to obtain a new perspective of the paleoceanography and paleoecology of the area during these short term climatic changes coccolithophores indicate that heinrich events he were characterised by the presence of cold low salinity and turbid water masses on both sides of the strait of gibraltar high abundances of the lower photic zone lpz species florisphaera profunda in the gulf of cadiz synchronous with he are interpreted as being an evidence of upper water column stratification on the atlantic side these episodes coincided with input of terrigenous material especially during h2 surface waters during dansgaard oeschger do stadials were also cold and turbid while most of do interstadials were characterised by warm water flora the increase in small placoliths small gephyrocapsa and emiliania huxleyi 4 m which is considered here as a cold water indicator the sharp decrease in large specimens of e huxleyi related to the warming trend in the last deglaciation can be used as a biostratigraphic reference level that marks at least approximately the deglaciation and the beginning of the holocene peaks of f profunda are observed during termination 1 t1 in the alboran sea they are isochronous with the organic rich layer 1 recognised in the western mediterranean in this interval the water column of the region was stratified as a consequence of the global increase in the sea level following the deglaciation quantitative analyses of the coccolithophore assemblage allow us to interpret that coccolithophore production has been higher in the alboran sea than in the gulf of cadiz during the holocene

deglacial abrupt climate change in the atlantic warm pool a gulf of mexico perspective 1 during the last deglaciation greenland ice core and north atlantic sediment records exhibit multiple abrupt climate events including the younger dryas cold episode 12 9 11 7 ka however evidence for the presence of the younger dryas in the gulf of mexico gom and the relationship between gom sea surface temperature sst and high latitude climate change is less clear we present new mg ca sst records from two varieties of the planktonic foraminifer globigerinoides ruber white and pink to assess northern gom sst history from approximately 18 4 10 8 ka thirty five accelerator mass spectrometry ams 14c dates from orca basin core md02 2550 provide excellent age control and document high sedimentation rates 40 cm kyr g ruber white and pink mg ca sst data exhibit increases 4 6 0 6 c and 2 2 0 5 c respectively from at least 17 8 16 6 ka with nearly decadal resolution that are early relative to the onset of the bolling allerod interstadial moreover g ruber white sst decreases at 16 0 14 7 ka 1 0 0 5 c and 12 8 11 6 ka 2 4 0 6 c correlate to the oldest and younger dryas in greenland and cariaco basin the g ruber pink sst record which reflects differences in seasonality and or depth habitat is often not in phase with g ruber white and closely resembles antarctic air temperature records overall it appears that orca basin sst records follow antarctic air temperature early in the deglacial sequence and exhibit enhanced seasonality during greenland stadials

phase relationships between millennial scale events 64 000 24 000 years ago a core recovered on the iberian margin off southern portugal can be correlated with greenland ice cores using oxygen isotope variability in planktonic foraminifera which closely matches the ice core records of temperature over greenland our age model identifies the base of every interstadial between 64 000 and 24 000 years ago and uses the greenland ice core project grip timescale the oxygen isotope signal in benthic foraminifera on this grip based timescale is quite different from the planktonic record and resembles the temperature record over antarctica when this is synchronized with greenland using the record of methane in the atmospheric air in the polar ice cores we interpret the benthic record as indicating significant fluctuations in ice volume during millennial events and we suggest that antarctic temperature changed as a function of ice volume

warm and saline events embedded in the meridional circulation of the northern north atlantic 1 ocean state estimates from 1958 to 2005 from the simple ocean assimilation system soda system are analyzed to understand circulation between subtropical and subpolar atlantic and their connection with atmospheric forcing this analysis shows three periods 1960s around 1980 and 2000s with enhanced warm saline waters reaching high latitudes alternating with freshwater events originating at high latitudes it complements surface drifter and altimetry data showing the subtropical subpolar exchange leading to a significant temperature and salinity increase in the northeast atlantic after 2001 the warm water limb of the atlantic meridional overturning cell represented by soda expanded in density salinity space during these warm events tracer simulations using soda velocities also show decadal variation of the gulf stream waters reaching the subpolar gyre and nordic seas the negative phase of the north atlantic oscillation index usually invoked in such variability fails to predict the warming and salinization in the early 2000s with salinities not seen since the 1960s wind stress curl variability provided a linkage to this subtropical subpolar gyre exchange as illustrated using an idealized two layer circulation model the ocean response to the modulation of the climatological wind stress curl pattern was found to be such that the northward penetration of subtropical tracers is enhanced when amplitude of the wind stress curl is weaker than normal in this case both the subtropical and subpolar gyres weaken and the subpolar density surfaces relax hence the polar front moves westward opening an enhanced northward access of the subtropical waters in the eastern boundary current

rapid oceanic and atmospheric changes during the younger dryas cold period the younger dryas event which began approximately 12 900 years ago was a period of rapid cooling in the northern hemisphere driven by large scale reorganizations of patterns of atmospheric and oceanic circulation 1 3 environmental changes during this period have been documented by both proxy based reconstructions 3 and model simulations 4 but there is currently no consensus on the exact mechanisms of onset stabilization or termination of the younger dryas 5 8 here we present high resolution records from two sediment cores obtained from lake krakenes in western norway and the nordic seas multiple proxies from lake krakenes are indicative of rapid alternations between glacial growth and melting during the later younger dryas meanwhile reconstructed sea surface temperature and salinity from the nordic seas show an alternation between sea ice cover and the influx of warm salty north atlantic waters we suggest that the influx of warm water enabled the westerly wind systems to drift northward closer to their present day positions the winds thus brought relatively warm maritime air to northern europe resulting in rising temperatures and the melting of glaciers subsequent input of this fresh meltwater into the ocean spurred the formation of sea ice which forced the westerly winds back to the south cooling northern europe we conclude that rapid alternations between these two states immediately preceded the termination of the younger dryas and the permanent transition to an interglacial state the impact of freshwater pulses released from northern hemisphere ice sheets on the north atlantic meridional overturning circulation has been suggested as a likely mechanism for the younger dryas cooling 7 11 in addition a responsive sea ice cover has been proposed as a mechanism that could rapidly alter the heat exchange between the ocean and atmosphere during the last glacial period 12 13 the roles of the ocean and the atmosphere in triggering the climate shifts around the younger dryas are much discussed 9 these hypotheses are difficult to resolve partly because the temporal resolution of most palaeoclimate archives is too coarse to enable the anatomy of the younger dryas stadial to be adequately described 14 to address these questions we here present a lake sediment record at sub annual resolution together with new data on the sea surface conditions of the norwegian atlantic current nwac throughouttheyoungerdryasstadial fig 1

calibration of the mg ca of globorotalia truncatulinoides r for the reconstruction of marine temperature gradients 1 recent work has provided useful mg ca to water temperature calibrations for shallow dwelling planktonic foraminifer species globorotalia truncatulinoides right coiling r is a deep dwelling species that can serve as a source of information about the temporal variability in the water characteristics of the thermocline we present a temperature calibration for the mg ca in the shell of g truncatulinoides r and examine some of the practical issues associated with evaluating the usefulness of the technique the mg ca in the primary and the secondary calcite of individual g truncatulinoides r correlates exponentially with water column temperatures showing a change of 10 in the mg ca per 1 c r2 0 92 a limited comparison with plankton tow samples demonstrates that the average mg ca temperature was offset 1 c from the average temperature calculated using the 18o calibration of o neil et al 1969 and the mg ca temperatures have a range similar to the 18o temperatures comparisons of the mg in the core top samples to water depth of deposition indicates that dissolution does not alter the measured value of mg in the primary calcite

lithologic and climatologic controls of river chemistry abstract the chemistries of rivers draining a variety of lithologic and climatic regions have been surveyed for the purpose of quantifying the fluxes of bicarbonate and silica from rivers with respect to bedrock lithology and runoff in all 101 different rivers each draining a primary lithology were examined across the united states puerto rico and iceland to minimize seasonal effects only rivers with at least two years of data were used basaltic catchments were examined in the greatest detail in a survey of hawaiian island watersheds the average river chemistries could be related to the distribution of soil associations within each catchment an analysis of cation activity relationships among rivers draining basaltic catchments shows that the river compositions define slopes which are consistent with an equilibrium ion exchange control on cation ratios among different lithologies unique weathering rate relationships were developed with yields at typical present day runoff rates 1 100 cm y increasing in the order sandstones granites basalts shales and carbonates the bicarbonate and silica fluxes for each of these lithologies have been quantified for use in global studies of chemical denudation our study confirms that the dissolved yield of a given drainage basin is determined by a balance between physical and chemical weathering thus a warm wet climate or the presence of abundant vegetation cannot guarantee high rates of chemical denudation unless accompanied by high rates of physical removal

millennial scale surface and subsurface paleothermometry from the northeast atlantic 55 8 ka bp we present high resolution records of upper ocean temperatures derived from mg ca ratios of surface dwelling globigerina bulloides and subsurface dwelling neogloboquadrina pachyderma sinistral and the relative abundance of n pachyderma sinistral for the period 55 8 ka bp from ne atlantic sediment core md01 2461 millennial scale temporal variability and longer term trends in these records enable us to develop a detailed picture of past ocean conditions such as a weakening of thermocline intensity from marine isotope stage 3 mis 3 to the last glacial maximum lgm the correspondence of all temperature proxies and convergence of paired oxygen isotope 18o records from both planktonic species implies a breakdown in the thermocline and year round mixing of the upper water column through the lgm perhaps related to decreasing insolation and additional cooling in association with the expansion of the circum north atlantic ice sheets millennial scale divergence in surface and subsurface temperatures and 18o across the last glacial correspond to meltwater release and the development of a strong halocline associated with both heinrich h events and instabilities of the nw european ice sheet during such episodes g bulloides mg ca appears to record ambient even warming summer sea surface temperatures across h events while the other proxies record maximum cooling

interhemispheric atlantic seesaw response during the last deglaciation the asynchronous relationship between millennial scale temperature changes over greenland and antarctica during the last glacial period has led to the notion of a bipolar seesaw which acts to redistribute heat depending on the state of meridional overturning circulation within the atlantic ocean here we present new records from the south atlantic that show rapid changes during the last deglaciation that were instantaneous within dating uncertainty and of opposite sign to those observed in the north atlantic our results demonstrate a direct link between the abrupt changes associated with variations in the atlantic meridional overturning circulation and the more gradual adjustments characteristic of the southern ocean these results emphasize the importance of the southern ocean for the development and transmission of millennial scale climate variability and highlight its role in deglacial climate change and the associated rise in atmospheric carbon dioxide

direct comparison of astronomical and 40ar 39ar ages of ash beds potential implications for the age of mineral dating standards we present first results of 40ar 39ar multiple single fusion datings on biotites and feldspars from two volcanic ash beds found on crete gavdos and koufonisi greece preferred 40ar 39ar ages calculated against tcr sanidine with an age of 27 92 ma intercalibrated to an age of 28 09 0 10 ma 1 for fct 3 biotite and an age of 24 99 0 07 ma for dra sanidine are slightly but consistently younger than astronomical ages obtained independently for the same ash beds the best fit to the astronomical ages is obtained when the age of tcr sanidine is increased slightly to 27 98 0 19 ma the age of fct 3 biotite to 28 15 0 19 ma and the age of dra sanidine to 25 05 0 17 ma the ages for the standards arrive slightly younger if the 40ar 39ar age of 6 936 0 006 ma 1 for a single pure sanidine separate of the lower ash dated astronomically at 6 941 ma is considered most reliable

subpolar mode water in the northeastern atlantic 1 averaged properties and mean circulation 1 subpolar mode waters spmw in the eastern north atlantic subpolar gyre are investigated with hydrographic and lagrangian data surface drifters and isopycnal floats historical hydrographic data show that spmws are surface water masses with nearly uniform properties confined between the ocean surface and the permanent pycnocline spmws represented by densities 27 3 27 4 and 27 5 are present in the eastern subpolar gyre and are influenced by the topography and the regional circulation construction of an absolute surface stream function from surface drifters shows that spmws are found along the mean path of each of the several branches of the north atlantic current nac and their density increases gradually downstream the rockall trough branch of the nac carries 27 3 27 4 and 27 5 spmw toward the iceland faroe front in the iceland basin the subarctic front along the western flank of the rockall plateau carries a similar sequence of spmw the western side of the central iceland basin branch of the nac on the other hand veers westward and joins the east reykjanes ridge current feeding the 27 5 spmw on the reykjanes ridge the separation among the various nac branches most likely explains the different properties that characterize the 27 5 spmw found on the reykjanes ridge and on the iceland faroe ridge since the branches of the nac have a dominant northeastward direction the newly observed distribution of spmw combined with the new stream function calculation modify the original hypothesis of mccartney and talley 1982 of a smooth cyclonic pathway for spmw advection and density increase around the subpolar gyre

pre miocene deformation of the himalayan superstructure hidden valley central nepal abstract throughout the himalaya the tethyan sedimentary sequence forms the detached carapace or superstructure to exhumed mid crustal rocks in central nepal low metamorphic grade cambrian to jurassic rocks of this carapace preserve five phases of deformation structurally dominated by second phase d 2 north verging back folds that oppose the vergence of the orogen the folds are overprinted and cross cut by the c 22 ma south tibetan detachment system and the manaslu leucogranite new structural mapping in hidden valley provides further constraints on the character of d 2 megascopically large asymmetric north verging folds define d 2 microscopically it is characterized by an axial planar cleavage balanced cross sections and bed length restoration of f 2 folds indicate a minimum of 32 38 shortening and 180 thickening during d 2 these data indicate that north verging folds played a significant role in pre miocene crustal thickening of the himalayan superstructure the formation of these folds is compatible with wedge extrusion or channel flow of the underlying mid crustal rocks whereby their geometry reflects early coupling between the upper and middle crust

transient simulation of last deglaciation with a new mechanism for bolling allerod warming we conducted the first synchronously coupled atmosphere ocean general circulation model simulation from the last glacial maximum to the bolling allerod ba warming our model reproduces several major features of the deglacial climate evolution suggesting a good agreement in climate sensitivity between the model and observations in particular our model simulates the abrupt ba warming as a transient response of the atlantic meridional overturning circulation amoc to a sudden termination of freshwater discharge to the north atlantic before the ba in contrast to previous mechanisms that invoke amoc multiple equilibrium and southern hemisphere climate forcing we propose that the ba transition is caused by the superposition of climatic responses to the transient co 2 forcing the amoc recovery from heinrich event 1 and an amoc overshoot

multimethod radiometric age for a bentonite near the top of the baculites reesidei zone of southwestern saskatchewan campanian maastrichtian stage boundary a 15 cm thick bentonite at the top of the baculites reesidei zone in cruikshank coulee north of herbert in southwestern saskatchewan yielded biotite sanidine plagioclase and zircon rb sr analyses give a mineral isochron with an age of 72 5 0 2 ma 2 u pb analyses of zircon produced concordant 206pb 238u and 207pb 235u ages of 72 4 0 4 ma 2 and 72 6 0 4 ma 2 respectively laser 40ar 39ar dating of sanidine and biotite revealed ages of 72 5 0 2 ma se and 72 6 0 2 ma se respectively if the campanian maastrichtian stage boundary is near the top of the baculites reesidei zone then the overall average age of 72 5 0 4 ma dates the stage boundary

natural hazards versus climate change and their potential impacts in the dry northern himalayas focus on the upper kali gandaki mustang district nepal in the himalayas the consequences of climate change are a fairly debated issue mainly questioning the availability of water resources to the lowland population north of the monsoon himalayas a semi arid continental climate prevails and settlements rely economically mostly on irrigated crops high altitude rangelands trade and tourism the upper kali gandaki mustang is situated in this area with sharp contrasts between valley bottoms 3 000 m and high glaciated peaks up to 8 000 m the impacts of climate change may appear in different ways gullying is common and might increase with greater climate variability increased ground instabilities earthflows and occasional debris flows affecting extensive shale marly substrates are also expected linked to changes in snow cover and seasonality similarly the combination of higher snowfall and rapid melting may favour the occurrence of flash floods the possibility of glacial outburst floods is less probable because of the present limited glaciation eventually permafrost melting may induce rock avalanches down the steepest cliffs and might impact the adjacent valley floors collectively these hazards will affect irrigation canals and fields new infrastructures and the associated growing settlements water availability in the near future is more difficult to predict however any change in the amount and nature of precipitation may affect groundwater reserves hence spring discharge and runoff with consequences for agricultural products eventually the overall potential increase in natural hazards may jeopardize the development of small markets and the good connection of these upper valleys to the main urban centres of nepal a country with a very low economic and social capacity to adjust

evidence of time mean cyclonic cell southwest of iberian peninsula the mediterranean outflow driven β plume 1 first observational evidence of time mean cyclonic recirculation southwest of iberia is presented data sets of hydrography satellite altimetry and surface drifters velocities are analyzed jointly in order to obtain an accurate time averaged circulation in the mid latitude northeast atlantic off the gulf of cadiz a cyclonic recirculation cell with characteristics similar to those predicted by theoretical and modeling studies is detected in all computed velocity fields the cell in the upper 1000 m layer exhibits transports of 3 to 4 sv that are only slightly smaller than the model transports the cell is centered at approximately 36 n 10 w is elongated zonally and extends to 15 w westwards wind driven sverdrup transport and plume dynamics are both suggested to play a role in the generation of the cyclonic cell but the relative contribution of these effects is yet to be clarified the core of the recirculation appears compact and the magnitude of the cell fades westwards much faster than predicted by the theoretical and modeling studies considered

hydrographic conditions along the western iberian margin during marine isotope stage 2 the surface water hydrography along the western iberian margin as part of the north atlantic s eastern boundary upwelling system consists of a complex seasonally variable system of equatorward and poleward surface and subsurface currents and seasonal upwelling not much information exists to ascertain if the modern current and productivity patterns subsisted under glacial climate conditions such as during marine isotope stage mis 2 and how north atlantic meltwater events especially heinrich events affected them to help answer these questions we are combining stable isotope records of surface to subsurface dwelling planktonic foraminifer species with sea surface temperature and export productivity data for four cores distributed along the western and southwestern iberian margin md95 2040 md95 2041 md99 2336 and md99 2339 the records reveals that with the exception of the heinrich events and greenland stadial gs 4 hydrographic conditions along the western iberian margin were not much different from the present during the last glacial maximum lgm subtropical surface and subsurface waters penetrated poleward to at least 40 6 n site md95 2040 export productivity was in general high on the western margin during the lgm and low in the central gulf of cadiz in agreement with the modern situation during the heinrich events and gs 4 on the other hand productivity was high in the gulf of cadiz and suppressed in the upwelling regions along the western margin where a strong halocline inhibited upwelling heinrich event 1 had the strongest impact on the hydrography and productivity off iberia and was the only period when subarctic surface waters were recorded in the central gulf of cadiz south of lisbon 39 n the impact of the other heinrich events was diminished and not all of them led to a significant cooling in the surface waters thus climatic impacts of heinrich events highly varied with latitude and the prevailing hydrographic conditions in this region

modern erosion rates in the high himalayas of nepal abstract current theories regarding the connections and feedbacks between surface and tectonic processes are predicated on the assumption that higher rainfall causes more rapid erosion to test this assumption in a tectonically active landscape a network of 10 river monitoring stations was established in the high himalayas of central nepal across a steep rainfall gradient suspended sediment flux was calculated from sampled suspended sediment concentrations and discharge rating curves accounting for solute and bedload contributions the suspended sediment fluxes were used to calculate watershed scale erosion rates that were then compared to monsoon precipitation and specific discharge we find that in individual watersheds annual erosion rates increase with runoff in addition our data suggest average erosion rate increases with discharge and precipitation across the entire field site such that the wetter southern watersheds are eroding faster than the drier northern watersheds the spatially non uniform contemporary erosion rates documented here are at odds with other studies that have found spatially uniform long term rates 10 5 10 6 yr across the pronounced rainfall gradient observed in the region the discrepancy between the modern rates measured here and the long term rates may be reconciled by considering the high erosional efficiency of glaciers the northern catchments were much more extensively glacierized during the pleistocene and therefore they likely experienced erosion rates that were significantly higher than the modern rates we propose that in the northern watersheds the high rates of erosion during periods of glaciation compensate for the low rates during interglacials to produce a time averaged rate comparable to the landslide dominated southern catchments

rb sr and u pb dating of bentonites a 6 in 15 cm bentonite in the z coal cretaceous tertiary boundary in eastern montana was sampled at four different places and biotite sanidine and zircon were separated from the clay u pb analyses of purified zircons yielded small systematic variations from concordant u pb dates plotting the data on a concordia diagram a short linear discordia line intersects the concordia at with an mswd of 1 16 the systematic variation of the four sets of zircon u pb data on the concordia plot may be an artifact of the sampling and purification procedure or could result from natural sample variation from minor contamination biotite fractions of varying specific gravity were obtained for each of the four z coal bentonite samples and together with the matching purified sanidine fraction were analysed for rb sr dating excluding those lighter biotite fractions found to have lost 30 or more of their original rb an isochron was obtained giving an age of 63 7 0 3 ma with an initial 87sr 86sr ratio of 0 706

millennial scale variability of deep water temperature and δ18odw indicating deep water source variations in the northeast atlantic 0 34 cal ka bp 1 paired measurements of mg ca and 18occ calcite 18o in benthic foraminifera from a deep sea core recovered on the iberian margin md99 2334k 37 48 n 10 10 w 3 146 m have been performed in parallel with planktonic 18occ analyses and counts of ice rafted debris ird the synchrony of temperature changes recorded in the greenland ice cores and in north atlantic planktonic 18occ allows the proxy records from md99 2334k to be placed confidently on the gisp2 time scale this correlation is further corroborated by ams 14c dates benthic mg ca measurements in md99 2334k permit the reconstruction of past deep water temperature tdw changes since 34 cal ka bp calendar kiloyears before present using these tdw estimates and parallel benthic 18occ measurements a record of deep water 18o 18odw has been calculated results indicate greatly reduced tdw in the deep northeast atlantic during the last glaciation until 15 cal ka bp when tdw warmed abruptly to near modern values in parallel with the onset of the bolling allerod interstadial subsequently tdw reverted to cold glacial values between 13 4 and 11 4 cal ka bp in parallel with the younger dryas cold reversal and the h0 ice rafting event similar millennial scale tdw changes also occurred during the last glaciation indeed throughout the last 34 cal ka millennial 18odw and tdw changes have remained well coupled and are linked with ird pulses coincident with heinrich events 3 2 1 and the younger dryas when transitions to lower tdw and 18odw conditions occurred in general millennial tdw and 18odw variations recorded in md99 2334k describe an alternation between colder low 18odw and warmer high 18odw conditions which suggests the changing local dominance of northern sourced north atlantic deep water nadw versus southern sourced antarctic bottom water aabw the observed similarity of the tdw and gisp2 18oice records would therefore suggest a common component of variability resulting from the coupling of nadw formation and greenland climate a link between greenland stadials and the incursion of cold low 18odw aabw in the deep northeast atlantic is thus implied which contributes to the relationship between greenland climate and the millennial benthic 18occ signal since 34 cal ka bp

tectonometamorphic discontinuities within the greater himalayan sequence in western nepal central himalaya insights on the exhumation of crystalline rocks abstract the core of the greater himalayan sequence in the mugu karnali area western nepal is affected by a thick shear zone with development of nearly 4 km of mylonites mangri shear zone it is a contractional shear zone showing a top to the sw and wsw sense of shear the shear zone developed during the decompression in the sillimanite stability field of rocks that previously underwent relatively high pressure metamorphism deformed under the kyanite stability field p t conditions indicate that the footwall experienced higher pressure 1 0 0 9 gpa than the hanging wall 0 7 gpa and similar temperatures 675 700 c u pb in situ dating of monazites indicate a continuous activity of the shear zone between 25 and 18 ma samples from the lower part of the greater himalayan sequence underwent similar ductile shearing at 17 13 ma these ages and the associated p t t paths revealed that peak metamorphic conditions were reached 5 7 ma later in the footwall of the shear zone with respect to the hanging wall pointing to a diachroneity in the metamorphism triggered by the shear zone itself mangri shear zone with the other recently documented tectonic and metamorphic discontinuities within the greater himalayan sequence point to the occurrence of a regional tectonic feature the high himalayan discontinuity running for more than 500 km along the strike of the central himalayas it was responsible of the exhumation of the upper part of the greater himalayan sequence starting from 28 ma well before the activation of the main central thrust and the south tibetan detachment our data point out that exhumation of the greater himalayan sequence was partitioned in space and time and different slices were exhumed in different times starting from the older in the upper part to the younger in the lower one

tephrostratigraphy study for the last 18 000 14 c years in a deep sea sediment sequence for the south adriatic abstract a detailed tephrostratigraphy supported by accelerator mass spectrometry ams 14c dating and isotopic and geochemical analyses has been carried out for a deep sea core collected from the southern adriatic sea which spans the last 18 14c kyr fourteen ash layers have been recognized in the marine core and the origin was determined by comparing their age and geochemistry with tephra detected in terrestrial deposits the geochemical signatures of marine ash layers indicate a prevailing campanian and subordinate etnean and eolian provenances collectively they are attributed to sources in the phlegraean fields lam lagno amendolare ln1 ln2 gm1 c 2 nyt neapolitan yellow tuff c 1 agnano pomici principali ams pf agnano monte spina ast astroni somma vesuvius l9 pomici di base l8 greenish mount etna et1 y1 biancavilla ignimbrite lipari e 1 gabellotto fiumebianco and palinuro seamount pal 1 some of these eruptions have been detected for the first time in marine cores astroni lam l9 l8 and three were detected and dated by marine tephra ln1 ln2 and pal 1 providing new more precise stratigraphic markers for the last 18 kyr in the south adriatic marine record

bentonite chemical features as proxy of late cretaceous provenance changes a case study from the western interior basin of canada abstract bentonite beds are fairly common in both marine and terrestrial upper cretaceous campanian maastrichtian deposits of the western interior basin of western canada and northwestern united states a detailed stratigraphic sedimentologic geochemical x ray fluorescence and mineralogical x ray diffraction study of twenty one bentonites from the puskwaskau and wapiti formations in the grande prairie area west central alberta canada is here presented major and trace element concentrations from altered volcanic ashes document the presence in the study area of predominantly trachyandesitic and rhyolitic volcanogenic products resulted from intense volcanic arc to within plate pyroclastic activity concentration values of high field strength elements hfse and selected large ion lithophile elements lile e g nb zr th and y obtained by x ray fluorescence spectroscopy strongly support the presence of multiple volcanic sources integrated paleoenvironmental and geochemical criteria for provenance determination indicate a bimodal occurrence of basic and acid volcanic products interpreted as reflection of source areas characterized by different tectonic setting and magmatic composition a comparative analysis of geochemical compositions between grande prairie bentonites and 30 known volcanic beds from central and southern alberta manitoba and montana 1 documents a trend toward more acidic and alkali depleted volcanic products during the late campanian early maastrichtian interval and 2 suggests a well constrained stratigraphic and geographic subdivision of the non marine successions of the foreland basin on the basis of geochemical characteristic of volcanic ash beds furthermore geochemical fingerprints of several decimeter to meter thick bentonite beds have been coupled with volcanic ash subsurface signature in order to investigate their role as marker beds this multiple approach provides a reliable tool for basin scale identification and correlation of non marine sedimentary successions

hydrographic changes in the eastern subpolar north atlantic during the last deglaciation abstract millennial scale climate fluctuations of the last deglaciation have been tied to abrupt changes in the atlantic meridional overturning circulation moc a key to understanding mechanisms of moc collapse and recovery is the documentation of upper ocean hydrographic changes in the vicinity of north atlantic deep convection sites here we present new high resolution ocean temperature and 18osw records spanning the last deglaciation from an eastern subpolar north atlantic site that lies along the flow path of the north atlantic current approaching deep convection sites in the labrador and greenland iceland norwegian gin seas high resolution temperature and 18osw records from subpolar site 980 help track the movement of the subpolar subtropical front associated with temperature and atlantic moc changes throughout the last deglaciation distinct 18osw minima during heinrich 1 h1 and the younger dryas yd correspond with peaks in ice rafted debris and periods of reduced atlantic moc indicating the presence of melt water in this region that could have contributed to moc reductions during these intervals increased tropical and subtropical 18osw during these periods of apparent freshening in the subpolar north atlantic suggest a buildup of salt at low latitudes that served as a negative feedback on reduced atlantic moc

vivaldi 1991 a study of the formation circulation and ventilation of eastern north atlantic central water abstract a synoptic hydrographic data set comprising 32 full depth ctd casts and 2500 ctd seasoar profiles to 500 m is used to describe the s properties and circulation of central water east of the mid atlantic ridge and between 39 n and 54 n eastward transport of 20 10 6 m 3 s 1 in the north atlantic current turns entirely northwards to the west of 54 n 20 w this transport consists in the upper layers of western north atlantic water freshened at temperatures below 10 c by mixing with subarctic intermediate water northern and southern branches of the north atlantic current are well defined and both turn northwards west of 20 w a further 10 10 6 m 3 s 1 of eastern north atlantic water forms and recirculates anticyclonically to the west of spain south of the north atlantic current and north of 40 n eastern north atlantic water is most weakly stratified east of 20 w and there is clear correlation between weakly stratified pycnostads and positive salinity anomalies relative to western north atlantic water thus eastern north atlantic water is a winter mode water in which strong winter cooling has increased the density and hence also the salinity anomaly at a given temperature near the southern entrance to the rockall trough there is evidence that salinities are also increased by mediterranean water influence circulation south of the north atlantic current is complex there is no evidence for direct ventilation southwards across 40 n where water properties s potential vorticity and cfc 113 and historical data all indicate westward ventilation east of 24 w with weak southward ventilation occurring further west in the vicinity of the azores the circulation pattern suggested is remarkably similar to that proposed by helland hansen and nansen in 1926 the eastern north atlantic geophysiske publicajoner 4 1 76 with anticyclonic circulation of colder eastern north atlantic water north of 40 n meeting warmer water from south of 40 n circulating cyclonically north of the azores current the distribution of pycnostads and s properties between 20 w and 35 w north of the azores indicates alternate bands of western and eastern north atlantic water moving eastward and westward respectively including evidence for westward motion immediately south of the southern branch of the north atlantic current possibly by westward propagation of anticyclonic eddies containing deep pycnostads

ammonite correlation of the uppermost campanian of western europe the u s gulf coast atlantic seaboard and western interior and the numerical age of the base of the maastrichtian

findings on water quality in upper mustang nepal from a preliminary geochemical and geological survey the major ion and trace element chemistry of water samples including springs rivers and irrigation ditches collected during a survey on august 2016 in the upper mustang region of the mustang district of dhawalagiri zone nepal has been investigated the upper mustang region a cold desert represents a hot spot for climate change indeed violent hailstorms and rainstorms have been recently observed consequently exposing land to erosion results of this study indicate that waters in the region belong to the ca hco3 ca mg cl so4 and na k cl types reflecting different hydrochemical regimes uranium is widespread in waters with concentrations up to 19 g l recorded in a potable water supply locally anoxic conditions affect uranium mobility due to the low solubility of u iv minerals highly toxic thallium was detected in a thermal spring at an elevated concentration 45 g l tl the association of thallium with high concentrations of iron suggests that these elements are derived from pyrite oxidation detectable levels of thallium were also measured in the water of an irrigation ditch lithium concentrations ranged from 7 g l to 12 mg l in the thermal water and showed a strong association with chloride ions arsenic concentrations up to 4 7 g l were measured in tributaries of the kali gandaki river the data provide evidence that solutes in water have originated from an array of input sources including carbonate dissolution the dissolution of soluble salts silicate weathering and localized sulfide oxidation in particular chemical weathering of granitic rocks is likely the primary source for metals and metalloids in waters since the erosion rate is a factor affecting lithological weathering high intensity rainfalls due to climate change are expected to influence the release and fate of potentially harmful elements in the in the upper mustang valley

stratigraphy and sedimentary history of the nepal tethys himalaya passive margin abstract the sedimentary history of the nepal tethys himalaya began with deposition of thick carbonates in the cambro ordovician followed by a mixed siliciclastic carbonate epicontinental succession recording two major deepening events in the early silurian and late devonian fossiliferous carbonate ramp deposits in the tournaisian were disconformably followed by white quartzose sandstones and black mudrocks with locally intercalated diamictites derived from sedimentary rocks and deposited in asymmetric tectonic basins rift stage break up in the mid early permian locally associated with effusion of tholeiitic lava flows was followed by a transgressive sandy to shaly locally coal bearing or bioclastic unit capped by condensed pelagic carbonates in the middle to late permian juvenile ocean stage subsidence of the cooling stretched crust led close to bathyal water depths in the olenekian but then slowed down in the middle triassic to increase again sharply in the late triassic owing to renewed extensional tectonic activity and sediment loading during up and out building of the indian continental terrace deposition of tropical platform carbonates finally became widespread in the middle liassic mature passive margin stage the initial fragmentation of gondwana in the middle jurassic led to rejuvenation of the indian craton and deposition of quartzo feldspathic hybrid arenites capped by condensed oolitic ironstones deposited at warm subtropical latitudes in the late bathonian middle callovian next a discontinuous pelagic grey marly limestone unit was followed by the ammonoid rich offshore spiti shale in the late jurassic the final disintegration of gondwana began in the berriasian when quartzose siliciclastics derived again from the rejuvenated indian craton and partly from recycling of older clastic successions were followed by thick deltaic to shelf volcaniclastics documenting eruption of alkali basalts in the valanginian followed in the hauterivian to albian by more felsic differentiates such as the trachyandesites exposed in the lesser himalaya 120 km to the south a widespread drowning episode fostered by waning volcaniclastic supply during a global eustatic rise is documented by a major glauconitic horizon deposited at middle southern latitudes in the late albian overlain by scaglia like pelagic limestones in the latest albian the final part of sedimentary history during the rapid northward flight of india and its collision with eurasia is not documented anywhere in nepal due to later erosion of upper cretaceous to lower tertiary strata

coccolithophore paleoproductivity and ecology response to deglacial and holocene changes in the azores current system 1 in order to test the sensitivity of marine primary productivity in the midlatitude open ocean north atlantic to changes in the atlantic meridional overturning circulation amoc we investigated two spliced sediment cores from a site south of the azores islands at the northern rim of the north atlantic subtropical gyre for this purpose we analyzed coccolithophore assemblages diatom abundances alkenones and conducted x ray fluorescence xrf core scanning during times of reduced amoc especially during heinrich event 1 h1 and the younger dryas we observe a strong increase in productivity as evidenced by high coccolith accumulation rates high alkenone concentrations accumulation rates high ba ti ratios high abundances of diatoms and low abundances off profunda the increased productivity is partly caused by a more southern position of the azores front azf and hence by a less northward extension of the subtropical gyre as deduced from high abundances of the temperate coccolithophore species g muellerae and low abundances of subtropical species oolithotus spp umbellosphaera spp umbilicosphaeraspp however to explain the full range of the observed productivity increase other factors like increased westerly winds and advection of nutrient rich surface waters have also to be considered because this pattern can also be observed in other sediment cores from the midlatitude north atlantic we propose that during times of reduced amoc there has been a band of strongly increased productivity across the north atlantic at the northern rim of the contracted subtropical gyre which partly counteracts the decreased organic carbon pump in the high northern latitudes

deglacial sea surface temperature and salinity increase in the western tropical atlantic in synchrony with high latitude climate instabilities a sediment core from the western tropical atlantic covering the last 21 000 yr has been analysed for centennial scale reconstruction of sea surface temperature sst and ice volume corrected oxygen isotopic composition of sea water delta 18 o ivc sw using mg ca and delta 18 o of the shallow dwelling planktonic foraminifer globigerinoides ruber white at a period between 15 5 and 17 5 kyrbp the mg ca sstand delta 18 o ivc sw a proxy for sea surface salinity sss reveals a warming of around 2 5 degrees c along with all increase in salinity a second period of pronounced warming and sss increase occurred between 11 6 and 13 5 kyr bp within age model uncertainties both warming intervals were synchronous with air temperature increase over antarctica and ice retreat in the southern south atlantic and terminated with abrupt centennial scale sss decrease and slight sst cooling in conjunction with interglacial reactivation of the meridional overturning circulation moc we suggest that during these warm intervals production of saline and warm water of the north brazil current resulted in pronounced heat and salt accumulation and was associated with warming in the southern atlantic southward displacement of the intertropical convergence zone and weakened moc at the termination of the younger dryas and heinrich event 1 intensification of cross equatorial heat and salt transport caused centennial scale cooling and freshening of the western tropical atlantic surface water this study shows that the western tropical atlantic served as a heat and salt reservoir during deglaciation the sudden release of accumulated heat and salt at the end of younger drays and heinrich event 1 may have contributed to the rapid reinvigoration of the atlantic moc c 2005 elsevier b v all rights reserved

spatial variations in chemical weathering and co2 consumption in nepalese high himalayan catchments during the monsoon season the major ion chemistry of the marsyandi basin and six of its tributaries in the nepalese himalaya have been investigated during the monsoon months of 2002 weekly water samples taken at 10 river monitoring stations in the annapurna watershed over the course of 4 months provide chemical weathering data for the region at an unprecedented temporal and spatial resolution the river chemistry of all but one basin is heavily dominated by carbonate weathering which compared to silicate weathering contributes 80 to 97 of the total solute load this prevalence is due to a combination of a intrinsically faster dissolution kinetics of carbonates b relatively high runoff and c glacial meltwater and low temperatures at high altitudes resulting in enhanced carbonate solubilities monitoring stations with headwaters in the tethyan sedimentary series tss are particularly carbonate rich and slightly supersaturated with respect to calcite through half of the monsoon season silicate weathering in the tss is driven largely by sulfuric acid and therefore does not contribute significantly to the drawdown of atmospheric co2 with respect to the tributaries in the greater himalayan sequence ghs carbonate weathering is practically as predominant as for the tss in spite of the largely felsic lithology of the ghs relative to the tss the primary proton source in the ghs has shifted with at least 80 of the protons derived from carbonic acid averaged over the whole field area the co2 fluxes based on silicate derived ca and mg are considerably lower than the global average assuming that this study area is representative of the entire range we conclude that in situ weathering of the high himalayas does not represent a significant sink of atmospheric carbon dioxide despite the presence of a watershed south of the ghs that is characterized by a four times higher co2 consumption rate than the global average silicate weathering rates of all basins appear to be climate controlled displaying a tight correlation with runoff and temperature given the extremely low chemical weathering under transport limited conditions in high altitude crystalline terrains outside of the monsoon season this would result in virtually no chemical exhumation for 2 3 of the year in such a cold and arid climate north of the rain shadow cast by the high himalayas 2009 elsevier ltd all rights reserved

new insights into the glacial latitudinal temperature gradients in the north atlantic results from uk 37 sea surface temperatures and terrigenous inputs abstract sea surface temperatures sst and input of continental materials have been reconstructed from the study of the long chain alkenones and n alkanes respectively in a core located in the western side of the mid atlantic ridge md952037 37 05 n 32 02 w 2630 m depth both the long and short term variability recorded by the temperatures and the planktonic 18o are basically the same over the last 280 kyr showing a clear glacial interglacial evolution comparison with core su90 08 located only 6 north and directly influenced by the cold polar waters associated with the polar front during glacial times revealed different climatic conditions during glacial periods at both locations whereas core md952037 recorded similar sst values during the last two glacial periods ca 14 15 c the northern core displayed colder conditions during isotopic stage 2 8 10 c than in stage 6 13 15 c these results indicate the existence of a well developed steep north south gradient between 37 and 43 n during the last glacial period but not during stage 6 which suggests a southern expansion of the polar front during the last glacial maximum

response of the subtropical north atlantic surface hydrography on deglacial and holocene amoc changes the north atlantic subtropical gyre stg circulates warm waters between 10 and 40 degrees n and is a potential area of heat storage during periods of reduced north atlantic meridional overturning circulation amoc when warm salt rich waters are retained in the subtropics in this study we investigated multicentennial to millennial scale changes in subtropical north atlantic hydrography in response to amoc changes during the last deglaciation and early holocene using sediment cores md08 3180 and geofar kf16 the coring site 38 degrees n is situated near the boundary between transitional eastern north atlantic waters and stg waters that is formed by the azores front hydrographic changes are reconstructed using new stable isotope data of benthic and subsurface dwelling planktonic foraminifera mg ca measurements on planktonic foraminifera and planktonic foraminifera abundances that are supplemented with published sea surface temperature and stable isotope data these multiproxy data indicate a close coupling between the latitudinal position of the northern stg boundary and deglacial amoc modes during weak amoc phases heinrich event 1 younger dryas yd 8 2ka event northern hemisphere subpolar water reached down to the northern stg boundary displacing the boundary southward during the bolling allerod warm period a strong warming trend of the subtropical region to 19 degrees c is observed a cooling of the sea surface temperature by 6 degrees c during the yd is accompanied by ongoing northward transport of warm subsurface water that might have contributed to the restart of amoc

chemical and pb isotope composition of phenocrysts from bentonites constrains the chronostratigraphy around the cretaceous paleogene boundary in the hell creek region montana an excellent record of environmental and paleobiological change around the cretaceous paleogene boundary is preserved in the hell creek and fort union formations in the western williston basin of northeastern montana these records are present in fluvial deposits whose lateral discontinuity hampers long distance correlation geochronology has been focused on bentonite beds that are often present in lignites to better identify unique bentonites for correlation across the region the chemical and pb isotopic composition of feldspar and titanite has been measured on 46 samples many of these samples have been dated by 40ar 39ar the combination of chemical and isotopic compositions of phenocrysts has enabled the identification of several unique bentonite beds in particular three horizons located at and above the cretaceous paleogene boundary can now be traced based on their unique compositions across the region clarifying previously ambiguous stratigraphic relationships other bentonites show unusual features such as pb isotope variations consistent with magma mixing or assimilation that will make them easy to recognize in future studies this technique is limited in some cases by more than one bentonite having compositions that cannot be distinguished or bentonites with abundant xenocrysts the pb isotopes are consistent with a derivation from the bitterroot batholith whose age range overlaps that of the tephra these data provide an improved stratigraphic framework for the hell creek region and provide a basis for more focused tephrostratigraphic work and more generally demonstrate that the combination of mineral chemistry and pb isotope compositions is an effective technique for tephra correlation

synchronisation of palaeoenvironmental events in the north atlantic region during the last termination a revised protocol recommended by the intimate group abstract the north atlantic intimate group of the inqua palaeoclimate commission has previously recommended an event stratigraphy approach for the synchronisation of records of the last termination using the greenland grip isotopic record as the regional stratotype and intcal98 for the calibration of radiocarbon dates lowe j j hoek w intimate group 2001 inter regional correlation of palaeoclimatic records for the last glacial interglacial transition a protocol for improved precision recommended by the intimate project group quaternary science reviews 20 1175 1187 here we present a revised protocol for time stratigraphic correlation in the north atlantic region over a more extended time period 30 8 ka this employs the new ngrip isotopic record and associated greenland ice core chronology 2005 gicc05 as the regional stratotype intcal04 for the calibration of radiocarbon dates bayesian based statistical procedures for the construction of age models and tephrochronology to validate correlations between regional site records

the origin of himalayan anatexis and inverted metamorphism models and constraints abstract the key to comprehending the tectonic evolution of the himalaya is to understand the relationships between large scale faulting anatexis and inverted metamorphism the great number and variety of mechanisms that have been proposed to explain some or all of these features reflects the fact that fundamental constraints on such models have been slow in coming recent developments most notably in geophysical imaging and geochronology have been key to coalescing the results of varied himalayan investigations into constraints with which to test proposed evolutionary models these models fall into four general types 1 the inverted metamorphic sequences within the footwall of the himalayan thrust and adjacent hanging wall anatexis are spatially and temporally related by thrusting 2 thrusting results from anatexis 3 anatexis results from normal faulting and 4 apparent inverted metamorphism in the footwall of the himalayan thrust is produced by underplating of right way up metamorphic sequences we review a number of models and find that many are inconsistent with available constraints most notably the recognition that the exposed crustal melts and inverted metamorphic sequences not temporally related the generalization that appears to best explain the observed distribution of crustal melts and inverted metamorphic sequences is that due to specific petrological and tectonic controls episodic magmatism and out of sequence thrusting developed during continuous convergence juxtaposing allochthonous igneous and metamorphic rocks this coincidental juxtaposition has proven to be something of a red herring unduly influencing attention toward finding a causal relationship between anatexis and inverted metamorphism

a global perspective on last glacial maximum to holocene climate change while the abrupt climate events of the last deglaciation are well defined in ice core records from the polar regions of both hemispheres their manifestation elsewhere is less well constrained here we compile 104 high resolution paleoclimate records to characterize the timing and spatial pattern of climate change during the last deglaciation this compilation indicates relatively concurrent timing of the last glacial maximum lgm peak glacial conditions and the altithermal peak interglacial conditions in the northern 22 1 4 3 ka and 8 0 3 2 ka and southern 22 3 3 6 ka and 7 4 3 7 ka hemispheres suggesting the hemispheres were synchronized by greenhouse gases local insolation and or northern hemisphere induced ocean circulation changes the magnitude of the glacialeinterglacial temperature change increases with latitude reflecting the polar amplification of climate change with a likely minimum global mean cooling of ww4 9 c during the lgm relative to the altithermal empirical orthogonal function eof analysis of 71 records spanning 19e11 ka indicates that two modes explain 72 of deglacial climate variability eof1 61 of variance shows a globally near uniform pattern with its principal component pc1 strongly correlated with changes in atmospheric co2 e of2 11 of variance exhibits a bipolar seesaw pattern between the hemispheres with its principal component pc2 resembling changes in atlantic meridional overturning circulation strength eof analysis of 90 records from 15 to 11 ka indicates that northern and southern modes of climate variability characterize the younger dryas bolling allerod interval these modes dominate at the higher latitudes of each hemisphere and exhibit a complex interaction in the tropics the magnitude of the younger dryas climate anomaly cooler drier increases with latitude in the northern hemisphere with an opposite pattern warmer wetter in the southern hemisphere reflecting a general bipolar seesaw climate response global mean temperature decreased by w0 6 c during the younger dryas therefore our analysis supports the paradigm that while the younger dryas was a period of global climate change it was not a major global cooling event but rather a manifestation of the bipolar seesaw driven by a reduction in atlantic meridional overturning circulation strength

long term changes in the thermocline of the subtropical northeast atlantic 33 n 22 w highlights unique data set of daily temperature and current measurements over almost 30 years cooling of the thermocline in the 1980s and extensive warming in the 2000s currents indicate northward displacement of n atlantic subtropical gyre in 1990s influence of nao and enso on current regime even in 500 m water depth data from almost thirty years of time series observations from a deep sea mooring kiel276 33 n 22 w which was operated in the northeast atlantic ocean between 1980 and 2009 are studied to reveal information on the long term changes in the upper thermocline this includes daily records of temperature and currents at two depths 240 m and 500 m until 1988 our analysis shows decreasing temperature in the entire thermocline followed by a slight increase at both depths from 2000 on extensive warming began at the shallower depth 240 m and eight years later at the deeper 500 m level a northward displacement of the north atlantic subtropical gyre is indicated by both current measurements and calculated kinetic energy between 1991 and 1998 resulting in an altered current regime in terms of absolute velocity and current directions in the last ten years compared to the first twenty years coherences of the currents with large scale climatic patterns such as north atlantic oscillation and el nino southern oscillation evidence the atmospheric impact even at 500 m water depth

mixed layer deepening during heinrich events a multi planktonic foraminiferal δ18o approach proxies from greenland ice cores and north atlantic marine sediment cores document repeated extreme climate swings of a few decades to millennia during the last glacial cycle including periods of intense ice rafting called heinrich events hes we have found similar oxygen isotope variations recorded in mixed layer and thermocline dwelling planktonic foraminifera during hes 0 1 and 4 suggesting that three foraminiferal taxa calcified their shells at similar temperatures in a homogenized upperwater column this implies that the surface mixed layer was deeper during hes similar deepening occurred on the northern margin of the ice rafted debris belt implying that these deep mixed layers during hes were widespread in the region we suggest that an increase in storminess during hes intensified the vertical mixing of meltwater from ice rafting in the upper ocean

hydrological impact of heinrich events in the subtropical northeast atlantic reconstructing the impact of heinrich events outside the main belt of ice rafting is crucial to understanding the underlying causes of these abrupt climatic events a high resolution study of a marine sediment core from the iberian margin demonstrates that this midlatitude area was strongly affected both by cooling and advection of low salinity arctic water masses during the last three heinrich events these paleoclimatic time series reveal the internal complexity of each of the last three heinrich events and illustrate the value of parallel studies of the organic and inorganic fractions of the sediments

intermediate depth warming in the tropical atlantic related to weakened thermohaline circulation combining paleoclimate data and modeling results for the last deglaciation 1 benthic foraminiferal oxygen isotope ratios from two sediment cores recovered at 426 and 1299 m water depth in the eastern and western tropical atlantic show that a slowdown of the thermohaline circulation thc during heinrich event h1 and the younger dryas was accompanied by rapid and intense warming of intermediate depth waters millennial scale covariations of low paleosalinities in the subpolar north atlantic with decreased benthic oxygen isotope ratios in the eastern tropical atlantic throughout the past 10 000 years suggest that thc weakening might be related to middepth warming during the holocene period as well climate model experiments simulating a strong reduction of the thc in the atlantic ocean under present day and glacial conditions reveal that the increase of temperature in the middepth tropical and south atlantic is a common feature for both climatic states caused by a reduced ventilation of cold intermediate and deep waters in conjunction with downward mixing of heat from the thermocline from the similarity of the paleoclimatic records with the model simulations we infer that the characteristic pattern of temperature change in the atlantic ocean related to weakened thermohaline circulation can serve as an indicator of present day and future thc slowdown

geomorphic and climatic controls on chemical weathering in the high himalayas of nepal article i nfo the hypothesis that co2 consumption by chemical weathering is enhanced by the exposure of fresh minerals provides a mechanism linking tectonic geomorphic and atmospheric processes we present data from the high himalayas of nepal indicating a positive linear relationship between cation weathering rate and suspended sediment yield because of a steep precipitation gradient across the field area the weathering rates are normalized according to runoff to isolate erosion as the controlling factor adjusted for runoff increases in weathering rates do not keep pace with increasing erosion rates where suspended sediment yieldsn2000 t km 2 y this result supports studies that predict a nonlinear relationship between denudation and weathering in rapidly eroding landscapes in addition we document a decoupling of the weathering of si and silicate cations from a glacierized watershed the proportions of silicate derived na and k are high relative to si during the warm summer months and then drop when subfreezing temperatures arrive in the fall we propose that during the summer glacial abrasion creates fresh mineral surfaces that favor the release of cations and abundant meltwater flushes these weathering products from the subglacial bed as temperatures fall below freezing and the production of meltwater slows dramatically river discharge becomes dominated by groundwater bearing the chemical signature of more congruent weathering reactions

a radiometric age for the cretaceous tertiary boundary based upon k ar rb sr and u pb ages of bentonites from alberta saskatchewan and montana bentonites associated with coal seams at the north american cretaceous tertiary k t boundary in the red deer valley of alberta in the frenchman valley of saskatchewan and near hell creek montana were dated by the k ar rb sr and u pb methods based upon palynological stratigraphic correlation and the presence of a sharp iridium anomaly the three sampled bentonite horizons all occur less than 1 m above the established k t boundary there is evidence of possible systematic errors giving dating results outside nominal statistical error values despite possible constant errors the weighted mean of nine average dates is calculated as 64 3 1 2 ma 2 standard deviation an unweighted averaging produces a grand mean age of 64 4 1 2 ma

meandering of the subtropical front south east of the azores a subtropical front was observed in the area south and southeast of the azores during cruises of fs meteor and fs poseidon in early 1982 the front has a basically west east extension with considerable meandering observed meso scale eddies are found on both sides the overall flow pattern corresponds to earlier results on geopotential differences in the upper northeast atlantic but the baroclinic transport of the order of 107 m3 s 1 is found to be concentrated in a 60 km wide jet we suggest here that the current band is part of the gyre circulation resulting from a branching of the north atlantic current