climate evolution during the holocene a study with an earth system model of intermediate complexity an earth system model of intermediate complexity mobidic has been used to simulate the transient variations in continental temperature sea surface temperature sst thermohaline circulation thc and sea ice cover over the last 9000 years 9 kyr experiments were designed to determine a the deviation of the climatic system with respect to equilibrium over the last 9 kyr b the individual contributions of oceans and vegetation to climatic changes as well as the potential synergies between these components and c the relative importance of precession obliquity and co2 concentration changes during this period results show a monotonous cooling trend in the northern high latitudes between 9 kyr bp and the present day both over the oceans and the continents north of 60 n this cooling is noticed throughout the year but the largest variations appear in spring and summer up to 6 c over continents along with this cooling the model exhibits a southward shift of the northern treeline by about 600 km most of this shift takes place between 4 and 1 kyr bp during this period reorganisations of the boreal forest introduce a lag of about 200 years in the system with respect to a state in equilibrium with the external forcing sensitivity experiments illustrate the strong impact of this vegetation shift both on the oceans and the continents especially in spring and early summer however the model exhibits a weak synergy between vegetation and ocean throughout the holocene finally a sensitivity study to the forcing components shows the dominant role of the astronomical forcing with respect to co2 as well as the non linear behaviour of climate in response to obliquity and precession

the role of oceanic forcing in mid holocene northern hemisphere climatic change previous model investigations suggested that changes in orbital forcing and feedbacks associated with northward expansion of the boreal forest were both required to explain the full magnitude of enhanced high latitude northern hemisphere summer warming at 6 ka thus implying that biospheric feedbacks decreased planetary albedo associated with forest expansion may be large in the future foley et al 1994 tempo testing earth system models with paleo observations 1996 before the magnitude of past biospheric and other feedbacks can be estimated with confidence however the role of realistic high latitude oceanic forcing i e sea surface temperature sst increases and sea ice reductions should also be considered here we review existing paleoceanographic observations that suggest portions of the north atlantic were up to 4 c warmer than today at 6 ka we then combine our estimates of mid holocene north atlantic sst and sea ice conditions with new climate model simulations to suggest that a significant portion of high latitude summer warming at 6 ka in the northern hemisphere can be accounted for by altered orbital forcing ssts and sea ice relative to today our results underscore the importance of incorporating realistic boundary conditions when using paleoenvironmental data to evaluate the climate system s sensitivity to altered forcing and suggest that high latitude oceanic feedbacks were major contributors to enhanced high latitude summer warming in the northern hemisphere at 6 ka

multicentury scale records of carbonate hydrographic variability on the northern iceland margin over the last 5000 years the waters off northern iceland are subjected to extreme hydrographic variability on annual to decadal timescales in years when cold low salinity water moves coastward and sea ice is prevalent i e the late 1960s marine productivity of surface waters is low because the water column is well stratified in the opposite oceanographic mode warm salty atlantic water dominates the shelf and vertical mixing results in high productivity we track these two contrasting modes by measuring the carbonate content of marine sediments a proxy for productivity in three cores from northern iceland the fjord record b997 328pc is anchored by eleven 14c ams dates and has a resolution of one sample every 50 yr thirteen oscillations occurred over the last 4800 cal yr with an average length of 370 yr these are superimposed on a long term decrease in net carbonate accumulation the little ice age is marked by the largest decrease in carbonate content and in flux with smaller minima at 2300 and 3000 cal yr b p marked peaks in carbonate optima occurred at 2000 and 3800 cal yr b p the carbonate record from b997 328pc can be correlated with records on the inner shelf b997 330pc and midshelf b997 327pc indicating that significant regional changes in oceanography occurred at the southern margin of the norwegian greenland sea the marine carbonate fluctuations closely track temperature reconstructions from the greenland summit site for the last 2000 cal yr and show similar but slightly offset oscillations between 2000 and ca 4800 cal yr b p

nonuniform response of the major surface currents in the nordic seas to insolation forcing implications for the holocene climate variability 1 high resolution sediment cores from the voring plateau the north iceland shelf and the east greenland shelf have been studied to investigate the stability of major surface currents in the nordic seas during the holocene results from diatom assemblages and reconstructed sea surface temperatures ssts indicate a division of the holocene into three periods the holocene climate optimum 9500 6500 calendar cal years bp the holocene transition period 6500 3000 cal years bp and the cool late holocene period 3000 0 cal years bp the overall climate development is in step with the decreasing insolation on the northern hemisphere but regional differences occur regarding both timing and magnitude of sst changes sites under the direct influence of the norwegian atlantic current and the irminger current indicate sst cooling of 4 5 c from early holocene to present compared to 2 c recorded under the east greenland current superimposed on the general holocene cooling trend there is a high frequency sst variability which is in the order of 1 1 5 c for the voring plateau and the east greenland shelf and 2 5 3 c on the north iceland shelf

trace element characterization of usgs reference materials by hr icp ms and q icp ms abstract a trace element characterization of united states geological survey usgs reference materials has been carried out using three different inductively coupled plasma mass spectrometer instruments nu instruments attom thermo scientific element 2 and agilent 7700x the six usgs reference materials bhvo 2 bcr 2 agv 2 stm 2 rgm 2 and g 3 include both extrusive and intrusive rocks with compositions ranging from mafic to felsic that encompass a wide range of trace element concentrations and mineral phases the prevalence of these 2nd and 3rd generation reference materials among geochemical laboratories and the added care that was taken during sample preparation make this generation of reference materials more suitable for characterization and use by the geochemical community the mafic intermediate reference materials bhvo 2 bcr 2 and agv 2 had the most abundant published characterization prior to this study which allowed for thorough and direct comparison with previous studies and usgs certificates published data for these reference materials are relatively well constrained for most elements i e not highly variable and the results of this study generally correspond well with the literature this can at least partially be attributed to the relatively simple matrices of these reference materials together with their overall smaller range of trace element concentrations unlike the mafic intermediate reference materials stm 2 lacked any published trace element concentrations prior to this study and data for rgm 2 and g 3 were relatively sparse data for stm 2 and rgm 2 from this study are compared to preliminary usgs certificates while data for g 3 are compared to the g 2 certificate values for comparison with published data rgm 1 and g 2 are included overall the published data for rgm and g are variable across the entire suite of trace elements and display poorer agreement with the data from this study this can be explained by the fact that in addition to the comparison between generations that may add heterogeneity the felsic reference materials have relatively complex matrices and larger ranges in trace element concentration given the new data that this study provides the felsic reference materials can now be used by the geochemical community to produce more accurate trace element concentration analyses of felsic materials by using three instruments with different configurations this study also serves as a comparison of the performance of each instrument in response to an array of geologic matrices the data reveal that the tested instruments are all capable of producing accurate and precise trace element concentration data over a range of geologic matrices provided that each instrument is carefully operated within its dynamic range in many cases this could be accomplished simply by ensuring proper dilution of samples however when matrices are more complex the use of medium and high resolutions can be useful in reducing the amount of preparative chemistry that is required to manage highly variable trace element concentrations within a single sample as well as any potential isobaric interferences

variations in melt layer frequency in the gisp2 ice core implications for holocene summer temperatures in central greenland the rare melt features in the gisp2 central greenland deep ice core have decreased in frequency over the most recent 7000 years calibration of this change in melt frequency against modern spatial variation of melt frequency and temperature in central greenland and against modern temporal variability of temperatures in central greenland indicates that mean mid summer temperatures have cooled over the most recent 7000 years probably by slightly more than l c if variability of summer temperatures has not changed comparison to grip isotopic records from central greenland and to the melt record from the agassiz ice cap arctic canada suggests some seasonal and regional coherence for this cooling signal as well as for a cold event about 8000 8500 bp

a study of zn and mo attenuation by waste rock mixing in neutral mine drainage using mixed material field barrels and humidity cells abstract we studied the attenuation of mo and zn in neutral ph drainage from waste rock at the antamina mine in peru we hypothesized that mo or zn contained in leachate produced in one waste rock type can be attenuated when the mo or zn containing leachate is allowed to contact a different waste rock type we tested the hypothesis using mixed material stacked field barrels and humidity cells connected in series where leachate from a mo or zn releasing waste rock type flows through a second waste rock material type results from both the humidity cells laboratory conditions and field barrels field conditions showed the same general attenuation patterns when drainage from mo releasing waste rock flowed through pb rich black marble waste rock mo was removed from solution molybdenum attenuation was not observed when the order of the waste rock materials was reversed such that drainage from pb rich waste rock flowed through mo releasing intrusive rock geochemical modeling mla and sem analyses supported the hypothesis that wulfenite precipitation was responsible for the observed attenuation of mo zinc is shown to be removed from leachate both by contact with mo releasing intrusive rock and by contact with calcite rich grey hornfels material results from geochemical modeling in phreeqc suggested that precipitation of zn carbonate or zn hydroxide minerals could not account for the degree of zn attenuation observed in this study scanning electron microscopy suggested that zn may have been incorporated into the crystal structure of phyllosilicate clay minerals

scandinavian glacial and climatic fluctuations during the holocene abstract historical documents and lichenometric studies give a detailed picture of the little ice age in scandinavia there was a large advance in norway which has been dated at a few places to 1750 small readvances during the retreat occurred around a d 1780 1810 1840 1850 1850 1870 1890 1910 and 1930 in sweden most of these advances have been recognized and in addition extensive advances are dated by lichenometry to around a d 1600 1650 and 1700 1720 soils buried beneath moraines often yield radiocarbon dates that are much too old methods dependent on these must therefore be used with care evidence for pre little ice age advances are often considered equivocal the most reliable information is probably provided by studies of lacustrine sediments combining information from all sources the most significant pre little ice age glacier advances most likely occurred in 7 5 5 1 4 5 3 2 2 8 2 2 1 9 and 1 5 1 1 radiocarbon ka bp advances that were less extensive or for which there is less evidence occurred around 6300 5600 2500 940 600 560 and 380 bp

multi proxy records showing significant holocene environmental variability the inner n iceland shelf hunafloi abstract over the last 50 yr the n iceland margin has seen dramatic changes in temperature and salinity associated with the relative dominance of warm atlantic water versus cold arctic or polar waters we report a study of holocene environmental changes to assess the sensitivity of this area on a longer timescale we present sedimentologic isotopic and biotic coccolith proxies from a 5 5 m piston core b997 330pc that was retrieved from a small basin on the inner n iceland shelf seven ams dates indicate a relatively constant rate of sediment accumulation which averaged 55 cm kyr sampling resolution of our proxies varied between 16 and 90 yr sample our data indicate substantial variability in environmental conditions over the last 10 000 cal yr total carbonate content and coccolith concentrations track each other and indicate that the early holocene was a time of low net carbonate accumulation net accumulation of carbonate reached maximum values in the mid to late holocene 4 2 cal ka but there has since been a substantial decrease with a minima during the little ice age north atlantic drift coccolith species show peaks in accumulation rates at 2 and 8 cal ka and low influx between 3 5 and 6 cal ka reworked neogene coccoliths occur also 8 ka and coincide with light 18 o values in the epifaunal foraminifera cibicides lobatulus principal component analysis indicates considerable covariance between biotic isotopic and sedimentological parameters three axes explain 84 of the variance in the data set and define three groups of interrelated variables a major change occurs ca 5 cal ka after which conditions become more variable with a 1 5 kyr cyclicity

early preboreal cooling in the nordic seas region triggered by meltwater at the younger dryas preboreal transition a high resolution core from the northeastern norwegian sea reveals a two step warming of sea surface temperatures dated at respectively 10 200 10 000 and 9700 9500 14 c yr b p 11 450 11 350 and 11 150 11 000 cal yr b p warming was interrupted by a period having stable temperatures and a reduction in sea surface salinity and we suggest that this pause in warming was triggered by an increase in freshwater supply that may have hampered the north atlantic heat conveyor the freshwater influx correlates to an atmospheric cooling over both the greenland ice sheet and northwest europe and to cooling of surface temperatures in the nordic seas freshwater may have been supplied from the waning fennoscandian ice sheet

what is the thermohaline circulation the term thermohaline circulation is widely used in the context of past and future climate change in his perspective wunsch argues that there are many different and inconsistent definitions for this term he defines ocean circulation in terms of mass fluxes which are largely driven by surface forces such as wind and tides and argues that thermohaline circulation should only refer to the separate transport of heat and salinity in the ocean

spatial and temporal patterns of iceberg rafting ird along the east greenland margin ca 68 n over the last 14 cal ka twelve 1 2 m 10 cm diameter gravity cores collected in 1988 and 1991 from the continental shelf and fjords of east greenland near kangerlussuaq fjord trough ca 68 n 32 w have distinct changes in lithofacies and in the quantity of iceberg rafted ird sediments these changes are readily observed in x radiographs of the split cores we quantify the ird contribution through grain size analyses and counting the number of clasts 2 mm from the x radiographs chronological control is provided by acclerated mass spectroscopy 14c dates on foraminifera during deglaciation after 14 cal ka there was one interval of ird accumulation ca 12 13 cal ka followed by a brief return to ird conditions centred at 9 cal ka thereafter a prominent feature of most cores on the shelf is an increase in ird accumulation that started ca 5 6 cal ka and which has increased toward the present indicators of iceberg rafting such as the net sand flux and numbers of clasts 2 mm ka 1 follow a power law distribution when graphed against distance from the present east greenland coast a measure of the position of the glacier margins the form of the relationship indicates that there is a dramatic decrease in the supply of sediment from the fjords to the shelf these relationships are used to estimate changes in the location of the ice margin during the late quaternary based on a site on the east greenland slope denmark strait and to discuss factors that can negate such a simple transfer function 1997 by john wiley sons ltd

late holocene summer sea surface temperatures based on a diatom record from the north icelandic shelf diatom assemblages from a high resolution core on the north icelandic shelf reveal a general late holocene cooling trend which is interrupted by three relatively warm periods diatom data from sur

on the structure and origin of major glaciation cycles 1 linear responses to milankovitch forcing time series of ocean properties provide a measure of global ice volume and monitor key features of the wind driven and density driven circulations over the past 400 000 years cycles with periods near 23 000 41 000 and 100 000 years dominate this climatic narrative when the narrative is examined in a geographic array of time series the phase of each climatic oscillation is seen to progress through the system in essentially the same geographic sequence in all three cycles we argue that the 23 000 and 41 000 year cycles of glaciation are continuous linear responses to orbitally driven changes in the arctic radiation budget and we use the phase progression in each climatic cycle to identify the main pathways along which the initial local responses to radiation are propagated by the atmosphere and ocean early in this progression deep waters of the southern ocean appear to act as a carbon trap to stimulate new observations and modeling efforts we offer a process model that gives a synoptic view of climate at the four end member states needed to describe the system s evolution and we propose a dynamic system model that explains the phase progression along causal pathways by specifying inertial constants in a chain of four subsystems solutions to problems involving systems of such complexity are not born full grown like athena from the head of zeus rather they evolve slowly in stages each of which requires a pause to examine data at great lengths in order to guarantee a sure footing and to properly choose the next step victor p starr

pattern and forcing of northern hemisphere glacier variations during the last millennium time series depicting mountain glacier fluctuations in the alps display generally similar patterns over the last two centuries as do chronologies of glacier variations for the same interval from elsewhere in the northern hemisphere episodes of glacier advance consistently are associated with intervals of high average volcanic aerosol production as inferred from acidity variations in a greenland ice core advances occur whenever acidity levels rise sharply from background values to reach concentrations 1 2 equiv h kg above background a phase lag of about 10 15 yr equivalent to reported response lags of alpine glacier termini separates the beginning of acidity increases from the beginning of subsequent ice advances a similar relationship but based on limited and less reliable historical data and on lichenometric ages is found for the preceding 2 centuries calibrated radiocarbon dates related to advances of non calving and non surging glaciers during the earlier part of the little ice age display a comparable consistent pattern an interval of reduced acidity values between about 1090 and 1230 a d correlates with a time of inferred glacier contraction during the medieval optimum the observed close relation between noothern hemisphere glacier fluctuations and variations in greenland ice core acidity suggests that sulfur rich aerosols generated by volcanic eruptions are a primary forcing mechanism of glacier fluctuations and therefore of climate on a decadal scale the amount of surface cooling attributable to individual large eruptions or to episodes of eruptions is simlar to the probable average temperature reduction during culminations of little ice age alacier advances ca 0 5 1 2 c as inferred from depression of equilibrium line altitudes

the behavior of molybdenum and its isotopes across the chemocline and in the sediments of sulfidic lake cadagno switzerland abstract molybdenum mo isotope studies in black shales can provide information about the redox evolution of the earth s oceans provided the isotopic consequences of mo burial into its major sinks are well understood previous applications of the mo isotope paleo ocean redox proxy assumed quantitative scavenging of mo when buried into sulfidic sediments this paper contains the first complete suite of mo isotope fractionation observations in a sulfidic water column and sediment system the meromictic lake cadagno switzerland a small alpine lake with a pronounced oxygen sulfide transition reaching up to h 2 s 200 m in the bottom waters or about 300 m total sulfide s 2 h 2 s hs s 2 we find that mo behaves conservatively in the oxic zone and non conservatively in the sulfidic zone where dissolved mo concentrations decrease from 14 nm to 2 8 nm across this transition dissolved mo in the upper oxic waters has a 98 mo oxic 0 9 0 1 which matches that of the riverine input 98 mo river 0 9 0 1 in the deeper sulfidic waters a subaquatic source delivers mo at 1 55 0 1 but the dissolved mo is even heavier at 98 mo sulfidic 1 8 sediment traps in the sulfidic zone of the lake collect particles increasingly enriched in mo with depth with 98 mo values significantly fractionated at 0 8 to 1 2 both near the chemocline and in the deepest trap suspended particulates in the sulfidic waters carry lighter mo than the ambient dissolved mo pool by 0 3 1 5 sedimentary mo concentrations correlate with total organic carbon and yield mo levels which are two orders of magnitude higher than typical crustal values found in rocks from the catchment area solid phase mo in the sediment shows a slightly positive 98 mo trend with depth from 98 mo 1 2 to 1 4 while the pore waters show dramatic enrichments of mo 2000 nm with a relatively light isotope signature of 98 mo 0 9 1 0 these data are explained if mo is converted to particle reactive oxythiomolybdates in the sulfidic waters and is fractionated during removal from solution onto particles isotope fractionation is expressed in the water column despite the high sulfide concentrations because the rate of mo removal is fast compared to the slow reaction kinetics of thiomolybdate formation however elemental and isotopic mass balances show that mo is indeed quantitatively removed to the lake sediments and thus the isotopic composition of the sediments reflects sources to the sulfidic water this efficient mo drawdown is expected to occur in settings where h 2 s is very much in excess over mo or in a restricted setting where the water renewal rate is slow compared to the mo burial rate we present a model for the mo isotope fractionation in sulfidic systems associated with the slow reaction kinetics and conclude that quantitative removal will occur in highly sulfidic and restricted marine systems

molybdenum isotope fractionation in pelagic euxinia evidence from the modern black and baltic seas here we present stable isotope data for vertical profiles of dissolved molybdenum of the modern euxinic water columns of the black sea and two deeps of the baltic sea dissolved molybdenum in all water samples is depleted in salinity normalized concentration and enriched in the heavy isotope 98mo values up to 2 9 compared to previously published isotope data of sedimentary molybdenum from the same range of water depths furthermore 98mo values of all water samples from the black sea and anoxic deeps of the baltic sea are heavier than open ocean water the observed isotope fractionation between sediments and the anoxic water column of the black sea are in line with the model of thiomolybdates that scavenge to particles under reducing conditions an extrapolation to a theoretical pure mos42 solution indicates a fractionation constant between mos42 and authigenic solid mo of 0 5 0 3 measured waters with all thiomolybdates coexisting in various proportions show larger but non linear fractionation the best explanation for our field observations is mo scavenging by the thiomolybdates dominantly but not exclusively present in the form of mos42 the mo isotopic compositions of samples from the sediments and anoxic water column of the baltic sea are in overall agreement with those of the black sea at intermediate depth and corresponding sulphide concentrations the more dynamic changes of redox conditions in the baltic deeps complicate the black sea derived relationship between thiomolybdates and mo isotopic composition in particular the occasional flushing mixing of the deep waters affects the corresponding water column and sedimentary data 98mo values of the upper oxic waters of both basins are higher than predicted by mixing models based on salinity variations the results can be explained by non conservative behaviour of mo under suboxic to anoxic conditions in the shallow bottom parts of the basin most pronounced on the nw shelf of the black sea

oceanic evidence for coherent fluctuations in fennoscandian and laurentide ice sheets on millennium timescales proxy temperature records from greenland ice cores1 2 and north atlantic sediment cores3 have provided evidence for a high degree of climate instability during the last glacial period much of this variability seems to be linked with the dynamics of the laurentide ice sheet that covered north america at this time3 which dis charged iceberg flotillas into the north atlantic that are now recorded in sediment cores as heinrich events4 how if at all this variability was manifested on the other side of the atlantic in the nordic seas and the ice sheets of northwest europe and scandinavia has been unclear here we present sediment micro fossil and oxygen isotope data from a sediment core in the norweg ian sea which reveal cooling events and iceberg discharges analogous to heinrich events we show that these climate fluctua tions in the norwegian sea were in phase or were phase locked with air temperatures over greenland suggesting that the rapid changes in heat fluxes in the north atlantic recorded in previous records3 were felt in this high latitude region the iceberg dis charges in our record seem to have come from the fennoscandian ice sheet implying that this and the laurentide ice sheets fluctu ated coherently on timescales shorter than those of milankovitch orbital cycles

late glacial and holocene palaeoceanography of the north icelandic shelf high resolution gravity cores and box cores from the north icelandic shelf have been studied for palaeoceanographic history based on lithological and biostratigraphical foramin iferal data results from two outer shelf cores covering the last 13 6 k 14 c yr bp are presented in this paper the sediments accumulated in north south trending basins on each side of the kolbeinsey ridge at water depths of ca 400 m sedimentation rates up to 1 5 m kyr 1 are observed during the late glacial and holocene the vedde and saksunarvatn tephras are present in the cores as well as the hekla 1104 a new tephra kol gs 2 has been identified and dated to 13 4 k 14 c yr bp and another tephra geochemically identical to the borrobol tephra has been found at the same level at present the oceanographic polar front is located on the north icelandic shelf which experiences sharp oceanographic surface boundaries between the cold east icelandic current and the warmer irminger current past changes in sedimentological and biological processes in the study area are assumed to be related to fluctuations of the polar front the area was deglaciated before ca 14 kyr bp but there is evidence of ice rafting up to the end of the gs 1 greenland stadial 1 younger dryas period increasing again towards the end of the holocene foraminiferal studies show a relatively strong gs 2 pre 13 kyr bp palaeo irminger current followed by severe cooling and then by unstable conditions during the remainder of the gi 1 greenland interstadial 1 bolling allerod and gs 1 younger dryas another cooling event occurred during the preboreal before the holocene current system was established at about 9 kyr bp after a climatic optimum between 9 and 6 kyr bp the climate began to deteriorate and fluctuate copyright 2000 john wiley sons ltd

molybdenum isotope behaviour accompanying weathering and riverine transport in a basaltic terrain the application of the molybdenum mo isotope system as a proxy for determining changes in the redox state of the oceans is predicated on the assumption that the composition of continental input can be characterised from crustal rock types and remains constant however it has recently been shown that the 98 95mo composition of global rivers varies between 0 15 and 2 4 and is therefore systematically heavier than the average composition of the continental crust 0 in order to understand the processes that control mo isotope fractionation during weathering this study presents 98 95mo and mo abundance data for rivers and estuarine samples from iceland that drain predominantly basaltic terrains resolvable differences are observed in the isotopic composition of the riverine mo sources ice 98 95moice 1 8 basaltic bedrock 98 95mobedrock 0 0 and hydrothermal waters 98 95mohydrothermal 3 4 systematic changes in the dissolved mo isotope composition are also observed within river catchments with 98 95mo values increasing from 0 in glacial rivers close to the source to 1 downstream consistent with mo isotopes being fractionated during weathering analysis of other riverine phases bedload colloids and iron precipitates demonstrates that these phases preferentially incorporate light mo isotopes and remain coupled to the dissolved load during riverine transportation a 98 95mo profile through the borgarfjor eth ur estuary exhibits a predominantly conservative mixing behaviour but suggests that the release of isotopically light mo from the particulate and or colloidal phases may occur in the low salinity part of the estuarine mixing zone 2010 elsevier b v

the last 18 kyr fluctuations in norwegian sea surface conditions and implications for the magnitude of climatic change evidence from the north sea a combined record of three cores spanning the last 18 kyr from the northern north sea is investigated for content of benthic and planktonic foraminifera and stable oxygen isotopes the paleoenvironmental development through this time period shows an early deglaciation 18 14 4 ka and the younger dryas 12 7 11 5 ka characterized by arctic polar conditions and increased ice rafting in the norwegian channel during the bolling allerod period warm sea surface temperature 9 c conditions similar to present conditions are inferred while bottom waters stayed cold 0 1 c with normal salinity the bolling allerod period is interrupted twice at 13 9 13 6 ka older dryas and at 13 0 12 8 ka inter allerod cooling period by reductions in sea surface temperatures and increased sea ice cover the beginning of the holocene period is marked by increases in surface and bottom water temperature superimposed on the broad climatic changes through the holocene a series of short lived oscillations in the ocean circulation are recorded the amplitude of these holocene events appears larger in the early holocene prior to 8 ka than compared with the remaining part of the holocene this amplification can possibly be attributed to a general increased freshwater budget in the north atlantic at this time during the final stages of the deglaciation of the laurentide and scandinavian ice sheets

the gin sea a synthesis of its physical oceanography and literature review 1972 1985 abstract a synthesis and review of the physical oceanography of the gin sea greenland iceland and norwegian seas is presented an accompanying bibliography is included from 1972 through 1985 some 1986 works are also noted emphasis is placed on describing the gin sea as a major semi enclosed basin that plays a role unique among the world s oceans by providing a strong two way advective exchange between the ice covered polar sea and the north atlantic ocean and at the same time acting as the primary site for northern hemisphere bottom water formation the water masses for the gin sea are defined in a manner as consistent as possible with the literature the large scale oceanographic and meteorological factors influencing the water mass formation and circulation are described a sample calculation of the various horizontal and vertical thermohaline driven exchanges is given

distribution and mobility of geogenic molybdenum and arsenic in a limestone aquifer matrix abstract to investigate the potential of mo and as as possible geogenic contaminants three sediment cores were examined to evaluate their mineralogical association distribution and mobility the cores were described and analyzed for total organic carbon toc ca mg si al p sr as mo fe and s content except in the uppermost segment limestone was the main lithology with the occasional presence of dolomite and clay that change in lithology was also observed in the bulk chemical composition where ca mg and sr concentrations increased with depth while si al and p concentrations decreased with depth minor minerals included pyrite fes 2 powellite camoo 4 and ferrihydrite the minimum maximum median and standard deviations for all analyzed elements including as and mo were comparable for all three cores molybdenum and as however varied significantly with depth and median as and mo values were above their respective crustal averages of approximately 1 1 mg kg and 1 5 mg kg the median values for as were 1 9 mg kg in core dep 1 3 3 mg kg in dep 2 and 1 mg kg in dep 5 the median values for mo were 2 3 mg kg in core dep 1 2 5 mg kg in dep 2 and 2 5 mg kg in dep 5 maximum concentrations for as were 101 9 mg kg 47 5 mg kg and 56 2 mg kg in cores dep 1 dep 2 and dep 5 respectively maximum concentrations for mo were 880 mg kg 123 mg kg and 225 mg kg in cores dep 1 dep 2 and dep 5 respectively electron microprobe analyses of individual minerals revealed variable concentrations of as ranging from approximately 300 to 9000 mg kg in pyrite and up to 17 600 mg kg in powellite camoo 4 the mo concentration in pyrite was consistently below the detection limit of approximately 100 mg kg in powellite the mo concentration was up to 42 wt a subset of 10 samples from different stratigraphic sections and with different as and mo concentrations was further investigated to assess as and mo mobility under changing physicochemical conditions leaching the aquifer matrix with a 1 m naoac solution at a ph of 8 1 removed more than 70 mo in 8 of the 10 samples the maximum value was 97 in contrast to mo as was mobilized to a lesser degree in 8 of the samples less than 30 were removed and the maximum was only 50 molybdenum which seemed to be loosely bound to mineral and organic matter surfaces thus could easily be removed from the aquifer matrix while as on the other hand should be much less mobile because it occurred either tightly adsorbed by hydrous ferric oxide or as an impurity in pyrite thus it is advisable to include mo in the analytical program whenever elevated as concentrations are encountered in groundwater

a mid holocene shift in arctic sea ice variability on the east greenland shelf records of iceberg rafting and palaeohydrography from two east greenland shelf cores jm96 1206 1 gc and jm96 1207 1 gc are reported benthic foraminifera stable isotopes and ird e uxes indicate a shift toward colder lower salinity polar conditions c 5 cal ka a new proxy of iceberg rafting on the east greenland shelf is the e ux of calcium carbonate tic thought to be derived from glacial erosion of cretaceous calcareous mudstones a change in the regularity and spacing of carbonate e ux peaks at c 4 7 cal ka in jm96 1207 coincides with the onset of neoglacial cooling in the renland ice core d 18 o record we propose that the carbonate e ux peaks between 4 7 and 0 4 cal ka are related to sea surface coolings associated with increased e ux of polar water and sea ice in the east greenland current these peaks are synchronous with sea surface coolings interpreted from north atlantic deep sea cores but additional peaks centred around 2 4 and 3 8 cal ka in jm96 1207 suggest that the shelf site captures higher frequency events the data indicate that severe arctic sea ice events began in the neoglacial interval and that earlier holocene cool events in deep sea records are associated with other processes such as release of meltwater from residual glacier ice and glacial lakes

the impact of igneous bedrock weathering on the mo isotopic composition of stream waters natural samples and laboratory experiments abstract river waters have been shown to be systematically enriched in the heavy molybdenum mo isotopes when compared to typical granites and basalts which generally possess mo isotopic compositions 98 95 mo of around 0 this inconsistency has been used to argue against weathering of crustal rocks as the cause for heavy riverine 98 95 mo signatures incongruent dissolution of primary bedrock however may be an important process by which the anomalous mo signatures of the river dissolved load are produced this study therefore investigates the effect of igneous crustal rock weathering on the aquatic 98 95 mo signal by comparing stream water and bedrock mo isotope data to results of bulk rock leach experiments for this purpose stream water and bedrock orthogneiss granite basalt as well as soil and vegetation samples were collected in a small catchment in the french massif central in accordance with the results of earlier studies on riverine mo both streams are isotopically heavier 98 95 mo 0 5 1 1 than the typical granites and basalts the excellent agreement of these data with those of mo released during experimental leaching of the basalt bedrock 0 6 1 0 identifies a predominance of basalt weathering over the stream water mo geochemistry while other processes i e soil formation secondary mineral precipitation and adsorption are subordinate in this catchment given that the basalt bulk rock 98 95 mo reflects a value typical for crustal magmatic rocks ca 0 1 mo isotope fractionation during the incongruent dissolution of basalt can explain the observed isotopically heavy aquatic mo signatures laser ablation analyses demonstrate that the volumetrically minor magmatic sulfides can be highly enriched in mo and mass balance calculations identify the sulfide melt inclusions as the principal mo source for the leach solutions these data suggest that the magmatic sulfides possess a distinctly heavier 98 95 mo signature than the coexisting silicate melt in this case mo would behave like fe by showing a detectable isotope fractionation at magmatic temperatures incongruent crustal bedrock weathering may thus cause a preferential release of heavy mo isotopes this effect however is highly dependent on the primary bedrock mineralogy consequently the average continental runoff may have been significantly affected by incongruent weathering during periods when the earth system was exceptionally far from steady state e g large glaciations with enhanced physical weathering or large subaerial basalt eruptions such as the deccan and the siberian plateau

holocene periodicity in north atlantic climate and deep ocean flow south of iceland climate fluctuations during the past millennium are relatively well documented1 on a longer timescale there is growing evidence of millennial scale variability of holocene climate at periodicities of 2 500 and 950 years possibly caused by changes in solar flux 2 3 and 1 500 years maybe related to an internal oscillation of the climate system 4 5 6 but the involvement of deep water masses in these holocene climate changes has yet to be established here we use sediment grain size data from the iceland basin to reconstruct past changes in the speed of deep water flow the study site is under the influence of iceland scotland overflow water isow the flow of which is an important component of the thermohaline circulation that modulates european climate flow changes coincide with some known climate events the little ice age and the mediaeval warm period and extend over the entire holocene epoch with aquasi periodicity of 1 500 years the grain size data indicate afaster isow flow when the climate of northern europe is warmer however a second mode of operation is observed in the early holocene when warm climate intervals are associated with slower isow flow at that time the melting remnant of land based glacial age ice may have provided a sufficient source of fresh water to the ocean to reduce isow flow south of iceland

molybdenum sources and isotopic composition during early stages of pedogenesis along a basaltic climate transect abstract molybdenum mo is an essential micronutrient and redox sensitive trace metal that has the potential to be a tracer of pedogenic processes globally riverine 98mo values based on 98mo 95mo relative to nist srm 3134 are heavier relative to bedrock suggesting weathering processes preferentially retain light mo isotopes however the mechanisms governing this process in soils are poorly understood we investigated soil mo abundance and isotopic composition as a function of climate along a well constrained climosequence on a 10 kyr lava flow in hawaii receiving 660 to 2100 mm year 1 mean annual precipitation map we assessed mo abundance and isotopic composition as a function of soil organic matter om content short ranged ordered sro iron fe oxyhydr oxide abundance and mo loss gain we find net accumulation of mo across all soils up to 139 gain that is positively correlated with increasing map the highest mo gains are in surface soil horizons and are correlated with high om content the isotopic composition of soil mo deviates from underlying basaltic bedrock which ranges from 98mo values of 0 11 to 0 26 soil mo isotopic values are lightest at the dry sites 98mo 0 63 and become heavier with increasing precipitation up to 98mo 0 03 samples with the heaviest 98mo values are from horizons with the largest net gains of mo relative to bedrock and have higher om content in order to further constrain mo fluxes into and out of the soil system we measured mo isotope ratios in local rainwater average 98mo 1 11 groundwater average 98mo 0 14 and vegetation 98mo values between 0 18 and 0 64 based on these data we propose that mo in these soils is substantially augmented by additions from precipitation volcanic fog and potentially anthropogenic inputs of mo and that retention of these inputs within soils is likely related to mo om interactions the large atmospheric inputs of mo strongly modulate the 98mo values of dissolved mo fluxes from soil to values only slightly heavier than bedrock these patterns illustrate the potential for mo as a tracer of atmospheric inputs and pedogenic processes in soils and help elucidate the mechanisms that drive heavy 98mo values in the global riverine mo flux

unusually heavy stable mo isotope signatures of the ottawa river causes and implications for global riverine mo fluxes abstract the accurate use of mo isotope mass balance modelling of ancient oceans relies on the assumption that the 98mo of modern riverine inputs represents a reasonable estimate of the past a growing number of studies of global rivers have demonstrated significant variation in 98mo from the bedrock sources of mo the ottawa river canada was previously identified as having an anomalously heavy mo isotope composition with a 98mo signature close to seawater 2 3 for a seemingly pristine natural river to further explore this unusual signature we collected and filtered 29 water samples from the ottawa river tributaries and small lakes and analysed them for mo isotopes as well as major and trace elements here we fully document heavy 98mo signatures throughout the ottawa river and its absence in surrounding areas of the wider ottawa river basin orb our results reveal a progressive upstream increase in both mo concentration and 98mo signatures in the ottawa river towards values even heavier than seawater up to 3 13 the heaviest mo isotopic signature of river water measured to date in contrast the tributaries and lakes display far lighter and more consistent 98mo signatures within the range previously found in other rivers weathering of an isotopically heavy bedrock source fractionation during weathering and retention of light isotopes in soils have all been proposed as sources of heavy 98mo in rivers however none of these mechanisms can satisfactorily explain our new observations colloidal and particulate processes that remove elements downstream as inferred from some trace element proxies also cannot explain the decreasing 98mo since the preferential removal of light mo isotopes is predicted from these processes similarly the downstream trends show no apparent relationships with constructed dams or known potential industrial sources therefore our findings from the ottawa river are best explained as the dilution of a yet unidentified point source of heavy mo upstream of sampling or a significant permanent sink for light isotopes existing only in the upper reaches of the catchment in both cases anthropogenic contribution from a large mining district in the headwaters of the river must be considered and should be explored further fractionation of mo in waste rock storage facilities have been previously identified and may provide an unnatural sink for isotopically light mo through the rayleigh type fractionation of dissolved mo on oxyhydr oxide mineral surfaces the implied anthropogenic alteration of the natural mo cycle highlights the significant and wide reaching effects of unnatural point sources of mo on the cumulative 98mo signatures of the catchment and emphasises the necessity for detailed geochemical screening of anomalous river water isotope signatures before natural isotope compositions are inferred

molybdenum isotope variations in molybdenite vapor transport and rayleigh fractionation of mo molybdenum isotopes in 20 molybdenite samples dated by the re os method and representing a range of geologic settings show mass dependent fractionation spanning 0 63 per atomic mass unit amu previous mo isotope data for molybdenite reveal variations in fractionation of 0 5 amu interpretation of these data is hampered however by limited sample numbers in each study lack of a common standard for interlaboratory comparison and limited range of geologic settings here we show that mo isotope compositions of molybdenites do not correlate with crystallization temperature age geographic distribution or geologic conditions rather rayleigh distillation may explain variations of as much as 0 34 amu in a single molybdenite occurrence exceeding the proposed variability in average continental crust vapor transport and rapid precipitation of mo in propagating fractures may account for isotope fractionation of mo and perhaps other metals at very small scales if so the average isotopic composition of mo at each molybdenite occurrence may be representative of bulk crust our results suggest that the isotopic composition of mo delivered to the oceans is uniform geographically and through geologic time

sorption of trace metals to an aluminum precipitate in a stream receiving acid rock drainage snake river summit county colorado the quality of water in streams that are contaminated by acid drainage from mines and from the weathering of mineralized rocks improves as the water flows downstream the purpose of this study was to investigate the geochemical processes that occur in one such stream and to determine the fate of the trace metals that are removed from the water the stream chosen for this purpose was the snake river summit county colorado which is affected by natural acid rock drainage ard containing so4 al fe and various trace elements such as zn cu pb ni and others most of the fe in the snake river is removed from solution by the oxidation of fe2 to fe3 and the subsequent precipitation of fe oxyhydroxides that form a massive ferricrete deposit near the springs that feed the river further downstream the snake river ph 3 0 mixes with water from deer creek ph 7 0 thereby increasing its ph to 6 3 and causing so4 rich precipitates of al oxyhydroxide to form the precipitates and associated organic c complexes sorb trace metals from the water and thus have high concentrations of certain elements including zn 540 11 400 ppm cu 34 221 ppm pb 90 340 ppm and ni 11 197 ppm the concentrations of these elements in the precipitates that coat the streambed rise steeply in the zone of mixing and then decline downstream the trace element concentrations of the water in the mixing zone at the confluence with deer creek decrease by 75 or more and are up to 3 orders of magnitude lower than those of the precipitates sorption curves for zn cu pb ni and so4 were derived by stepwise neutralization of a sample of snake river water collected above the confluence with deer creek and indicate that the trace metals are sorbed preferentially with increasing ph in the general order pb cu zn and ni sulfate is removed between ph 4 and 5 to form an al hydroxysulfate and or by sorption to microcrystalline gibbsite the sorption data determined from the neutralization experiment were used to account for the downstream decrease of trace metal concentrations in the precipitates the results of this study demonstrate that the partitioning of trace metals in the snake river is not only a function of ph but also depends on the progressive removal of trace metals as the water of the snake river flows through its confluence with deer creek the chemical composition of the water also determines what compounds precipitate with increasing ph

early miocene continental subduction and rapid exhumation in the western mediterranean new lu hf garnet growth ages from high pressure rocks from the structurally lowest terrane nevado filabride complex in the betic cordillera of southern spain indicate early miocene subduction of continental crust requiring significant revision of the timing and processes of orogeny in the western part of the alpine orogenic system mafic eclogite and pelitic schist give lu hf ages in the range 18 14 ma and fission track data show that the terrane was exhumed by 12 8 ma the overlying terrane alpujarride complex shows early tertiary high pressure temperature metamorphism this was followed by a thermal event that accompanied rapid crustal extension at 22 18 ma leading to the formation of the alboran sea backarc basin the evidence therefore suggests two phases of continental subduction separated by a phase of large scale intraorogenic extension the two terranes are now separated by a mid late miocene low angle extensional fault the timing and paleogeographic setting suggest that the nevado filabride terrane originally was close to the rifted south iberian margin and was subducted during westward motion of the extending upper terrane between the converging african and iberian plates

molybdenum mo stable isotopic variations as indicators of mo attenuation in mine waste rock drainage abstract measurements of molybdenum mo stable isotopes 98mo were applied along with conventional geochemical analyses of water and rock samples at a mo mine in the usa to assess controls on mo mobility in two unsaturated waste rock storage facilities wrsfs that are differentiated by acidic and alkaline drainages unweathered waste rock mo ore and mine tailings from the site were also analyzed to constrain the isotopic composition of the source of mo entering mine drainage via weathering processes the surfaces of weathered waste rock samples were sequentially leached using a two step chemical extraction to determine the distribution and isotopic composition of mo among primary and secondary mineral assemblages the observed variation in 98mo among all samples exceeded 5 the 98mo of mo rich 340 g l mine process water and pit wall runoff ranged from 0 6 to 0 7 which was equal within error to the average 98mo of waste rock tailings and ore samples and indicated negligible isotopic fractionation during molybdenite oxidative dissolution in contrast drainage from the base of both waste rock storage facilities was isotopically heavier ranging from 1 6 to 1 9 coupled 98mo and mo so42 ratios in mine drainage and sequential chemical extractions of weathered waste rock surfaces indicated that mo adsorption onto mineral surfaces was most likely driving the increase in 98mo in drainage from both wrsfs molybdenum stable isotope data provided a powerful tracer of processes controlling mo mobility when used in conjunction with conventional geochemical analyses

influence of insolation and glaciation on atmospheric circulation in the north atlantic sector implications of general circulation model experiments for the late quaternary climatology of europe abstract atmospheric general circulation models have been used to simulate the sensitivity of regional climates to late quaternary changes in insolation ice sheets and atmospheric co 2 model results for full glacial conditions 18 ka show the atlantic westerly jet strengthened and shifted south a corresponding southward shift of the icelandic low and a strengthening and northward shift of the subtropical anticyclone sta a glacial anticyclone developed over the european ice sheet and cold dry conditions prevailed over much of europe the full glacial climate anomaly for the north atlantic sector is explained by a combination of low atmospheric co 2 reducing global surface temperatures and circulation changes caused by the ice sheets by the early holocene 9 ka the ice sheets were much reduced while the orbital anomaly was near its maximum producing mid continental summer warming and winter cooling and a reduced latitudinal temperature gradient in the northern hemisphere in both seasons the jet and the icelandic low were displaced to north of their present position producing strong onshore flow and mild wet winters in northern europe while the sta was also shifted northwards producing offshore flow and dry summers in the same region during the late glacial transition the effects of insolation and glaciation were antagonistic for some features of the circulation and synergistic for others the model results suggest palaeoclimatic hypotheses that could be directly tested by comparison with palaeoclimatic data mapped at a synoptic scale

sulfidity controls molybdenum isotope fractionation into euxinic sediments evidence from the modern black sea molybdenum mo isotope fractionation has recently been introduced as a new proxy in oceanography and biogeochemistry it is therefore fundamental to understand the processes controlling mo partitioning into modern marine environments this study identifies the availability of dissolved sulfide as the dominant control on overall mo removal from the water column in euxinic systems mo isotopic composition of surface sediments from different localities of the black sea demonstrates complete fixation of mo only below 400 m water depth above a critical concentration of 11 mol l 1 aqueous hydrogen sulfide in the bottom water the mo isotopic composition of these sediments reflects the homogeneous seawater isotopic composition of 2 3 in contrast significant mo isotope fractionation into less euxinic sediments is evident at shallower depths in the black sea as well as in temporarily euxinic deeps of the baltic sea consistent with the observed lower maximum sulfide concentrations in the respective water columns therefore mo isotope signatures in the modern black sea constrain the processes responsible for global mo removal from the ocean by euxinic sediments furthermore models of past ocean anoxia reconstruction have to consider that the seawater mo isotopic composition is not per se archived in euxinic sediments

the isotopic signature of the global riverine molybdenum flux and anoxia in the ancient oceans despite important biological and biogeochemical consequences of extensive ocean anoxic events their identification is controversial the marine isotope geochemistry of molybdenum can help quantify the past oxygenation state of the ocean if the riverine input of mo isotopes is known analysis of a set of rivers that account for 28 of global river runoff suggests more variable mo isotopic ratios in rivers that are also isotopically enriched in the heavy isotopes suggesting near total anoxia in the proterozoic ocean and during mesozoic ocean anoxic events despite its important biological and biogeochemical consequences1 2 3 the identification of extensive oceanic anoxia in the geological record is controversial in particular global anoxia is difficult to distinguish from spatially restricted anoxia in the deep ocean or in tectonically isolated basins such as the modern black sea the marine isotope geochemistry of molybdenum mo can help quantify the past oxygenation state of the ocean4 5 6 7 8 9 10 11 12 13 14 because to first approximation under oxic conditions lighter isotopes of mo are preferentially removed to sediments whereas in euxinic conditions quantitative removal leads to no fractionation however the isotopic composition of the mo input from rivers the main contributor of mo to the oceans is poorly constrained and had been assumed to be isotopically comparable to the narrow range found in a small dataset of continental rocks4 5 6 7 8 9 10 11 12 13 14 here we present an isotopic analysis of mo in a set of rivers that together account for 22 of the global riverine water discharge we find a broad range of variability in the mo isotopic composition of these rivers with almost all samples enriched in the heavy isotopes compared with continental rocks our data remove key uncertainties associated with the marine mo isotope budget14 and strongly suggest near total anoxia in the mid proterozoic ocean8 as well as during mesozoic ocean anoxic events13

chemical weathering controls on variations in the molybdenum isotopic composition of river water evidence from large rivers in china abstract mo isotopic composition in large rivers is very important for understanding global mo cycle at present temporal variation signatures in the 98 95 mo in large rivers have not been investigated which hinder a comprehensive understanding on the mechanism for the variations of mo isotopic compositions in river water in this study we report a one year long time series march 2010 to march 2011 of the 98 95 mo of both the water and suspended particulates collected at guiping from the middle reaches of the xijiang river xjr and of the water 98 95 mo from the lower reaches of the huanghe river hhr or yellow river collected at lijin china the results indicate that the temporal variations in the concentration and 98 95 mo of dissolved mo in the xjr range from 4 32 to 10 5 nmol l mean 7 31 nmol l and 1 04 to 1 31 relative to nist 3134 mean 1 20 respectively but that the particulates have a lower 98 95 mo 0 18 to 0 58 analysis of the suspended particulates and other chemical parameters of the river water suggests that the weathering of silicates and sulfides is the main contributor to the dissolved mo content in the xjr subsequently the highly efficient preferential trapping of lighter 98 95 mo by weathering products such as clay minerals fe mn oxides and organic materials in soils and saprolites which are abundant in the tropical catchment is the key to the heavy mo isotope signatures in the xjr furthermore it seems that neither mo scavenging by suspended particulates during riverine transportation nor the weathering of sulfates significantly influences the 98 95 mo of the xjr water cross comparison among the 98 95 mo in the waters of the three largest rivers in china the changjiang cjr hhr and xjr indicates that the hhr has the highest mo concentrations but the lightest 98 95 mo the xjr has the lowest mo concentrations but the heaviest 98 95 mo and the values for the cjr are intermediate between those for the other two rivers this supports the conclusion that the efficiency of the selective trapping of mo by soils and saprolites is the main factor controlling 98 95 mo in these large rivers the tropical subtropical xjr catchment experiences intense chemical weathering the semi arid temperate hhr catchment experiences very little and the cjr catchment falls somewhere between the two such a relationship between water mo concentrations and 98 95 mo agrees with previous observations from many large rivers worldwide it is therefore suggested that chemical weathering on continents is the key to variations in the isotopic composition of mo in the waters of large rivers

magmatic hydrothermal molybdenum isotope fractionation and its relevance to the igneous crustal signature abstract we analysed the mo isotope composition of a comprehensive series of molybdenite samples from the porphyry type questa deposit nm usa as well as one rhyolite and one granite sample directly associated with the mo mineralization the 98mo of the molybdenites ranges between 0 48 and 0 40 with a median at 0 05 the median mo isotope composition increases from early magmatic 0 29 to hydrothermal 0 05 breccia mineralization median bulk breccia 0 17 to late stockwork veining 0 22 moreover variations of up to 0 34 are found between different molybdenite crystals within an individual hand specimen the rhyolite sample with 0 12 g g 1 mo has 98mo 0 57 and is lighter than all molybdenites from the questa deposit interpreted to represent the igneous leftover after aqueous ore fluid exsolution we recognize three mo isotope fractionation processes that occur between about 700 and 350 c affecting the mo isotope composition of magmatic hydrothermal molybdenites 1mo minerals preferentially incorporate light mo isotopes during progressive fractional crystallization in subvolcanic magma reservoirs leaving behind a melt enriched in heavy mo isotopes 2mo magmatic hydrothermal fluids preferentially incorporate heavy mo isotopes upon fluid exsolution 3mo light mo isotopes get preferentially incorporated in molybdenite during crystallization from an aqueous fluid leaving behind a hydrothermal fluid that gets heavier with progressive molybdenite crystallization the sum of all three fractionation processes produces molybdenites that record heavier 98mo compositions than their source magmas this implies that the mean 98mo of molybdenites published so far 0 4 likely represents a maximum value for the mo isotope composition of phanerozoic igneous upper crust

molybdenum isotope fractionation during adsorption by manganese oxides the isotopic composition of mo 97 95mo in seawater is 2 heavier than mo in marine ferromanganese crusts and nodules barling et al earth planet sci lett 193 2001 447 457 siebert et al earth planet sci lett 211 2003 159 171 to explore this phenomenon we have conducted an experimental investigation into the mass dependent fractionation of mo isotopes during adsorption onto mn oxyhydroxide two series of experiments were carried out a time series in which adsorption proceeded for 2 96 h and a ph series in which ph varied from 6 5 to 8 5 the extent of mo adsorption by mn oxyhydroxides decreases with increasing ph a trend typical of anion adsorption and takes 48 h to reach steady state lighter mo isotopes are preferentially adsorbed experimentally determined fractionation factors soln mnox exhibit no systematic variation with either time or experimental ph the mean soln mnox for all experiments is 1 0018 0 0005 2 s d comparison of the mo isotopic data for experimental solutions and mo adsorbed to mn oxyhydroxide with predictions for closed system equilibrium and rayleigh fractionation models indicates that isotope fractionation occurs as a result of closed system equilibrium exchange between dissolved and adsorbed mo the isotopic offset between dissolved and adsorbed mo is comparable to that observed between mo in seawater and mo in ferromanganese nodules and crusts it is therefore likely that adsorption of mo to mn oxyhydroxides is a significant factor in the fractionation of mo isotopes in the oceans

the great salinity anomaly in the northern north atlantic 1968 1982 the widespread freshening of the upper 500 800m layer of the northern north atlantic which this paper describes represents one of the most persistent and extreme variations in global ocean climate yet observed in this century though a range of explanations have been advanced to explain this event including in situ changes in the surface moisture flux this paper describes the great salinity anomaly as largely though not entirely an advective event traceable around the atlantic subpolar gyre for over 14 years from its origins north of iceland in the mid to late 1960s until its return to the greenland sea in 1981 1982 the overall propagation speed around this subpolar gyre is estimated at about 3cm s 1 of the total salt deficit associated with the anomaly as it passed south along the labrador coast in 1971 1973 about 72 109 tonnes a deficit equivalent to about two thirds of this figure 47 109 tonnes ultimately passed through the faroe shetland channel to the barents sea arctic ocean and greenland sea during the mid 1970s possible effects on deep water formation and on the representativeness of historical section data are discussed

a multiproxy reconstruction of the evolution of deep and surface waters in the subarctic nordic seas over the last 30 000yr on the basis of various lithological mircopaleontological and isotopic proxy records covering the last 30 000 calendar years cal kyr the paleoenvironmental evolution of the deep and surface water circulation in the subarctic nordic seas was reconstructed for a climate interval characterized by intensive ice sheet growth and subsequent decay on the surrounding land masses the data reveal considerable temporal changes in the type of thermohaline circulation open water convection prevailed in the early record providing moisture for the fennoscandian barents ice sheets to grow until they reached the shelf break at 26 cal kyr and started to deliver high amounts of ice rafted debris ird into the ocean via melting icebergs low epibenthic 18o values and small sized subpolar foraminifera observed after 26 cal kyr may implicate that advection of atlantic water into the nordic seas occurred at the subsurface until 15 cal kyr although modern like surface and deep water conditions first developed at 13 5 cal kyr thermohaline circulation remained unstable switching between a subsurface and surface advection of atlantic water until 10 cal kyr when ird deposition and major input of meltwater ceased during this time two depletions in epibenthic 13c are recognized just before and after the younger dryas indicating a notable reduction in convectional processes despite an intermittent cooling at 8 cal kyr warmest surface conditions existed in the central nordic seas between 10 and 6 cal kyr however already after 7 cal kyr the present day situation gradually evolved verified by a strong water mass exchange with the arctic ocean and an intensifying deep convection as well as surface temperature decrease in the central nordic seas this process led to the development of the modern distribution of water masses and associated oceanographic fronts after 5 cal kyr and eventually to today s steep east west surface temperature gradient the time discrepancy between intensive vertical convection after 5 cal kyr but warmest surface temperatures already between 10 and 6 cal kyr strongly implicates that widespread postglacial surface warming in the nordic seas was not directly linked to the rates in deep water formation

sudden changes in north atlantic circulation during the last deglaciation sudden changes in the flow of warm atlantic surface waters into the norwegian sea occurred frequently during the last deglaciation typically involving shifts in sea surface temperature of 5 c in fewer than 40 years these led to equally large and rapid changes in atmospheric temperatures and to shifts in atlantic deep thermo haline circulation and ice sheet melting rates

variation of mo isotopes from molybdenite in high temperature hydrothermal ore deposits measurable molybdenum isotope fractionation in molybdenites from different ore deposits through time provides insights into ore genesis and a new technique to identify open system behavior of re os in molybdenites molybdenite samples from six porphyry copper deposits one epithermal polymetallic vein deposit four skarns and three fe oxide cu au deposits were analyzed the 97mo where open image in new window for all samples varied from 1 34 0 09 to 0 26 0 04 this is the largest molybdenum isotopic variation in molybdenite from high temperature ore deposits recorded to date 97mo of molybdenite varies as a function of the deposit type and the rhenium and osmium concentrations of the samples isotope values for mo also vary within the individual deposits in general molybdenites from porphyry copper deposits have the lightest values averaging 0 07 0 23 1 molybdenites from the other deposit types average 0 49 0 26 1 the variations could be related to the fractionation of mo into different mineral phases during the ore forming processes a comparison of the mo isotope ratios and the re os ages obtained from the same aliquot may possess a geochronological evaluation tool samples that yielded robust ages have different mo isotopic compositions in comparison to samples that yielded geologically unreasonable ages another observed relationship between the re os and mo isotope data reveals a weak correspondence between re concentration and mo isotope composition molybdenites with higher concentrations of re correspond to lighter mo isotope values

ice sheet and ocean interactions margin of the east greenland ice sheet 14 ka to present diatom evidence seven marine sediment cores were collected from the kangerdlugssuaq trough off the southeast coast of greenland the trough cuts across the continental shelf from the fjord mouth to the upper slope in denmark strait and provides a sedimentary environment sheltered from the east greenland current flowing along the shelf the cores have been 14c dated accelerator mass spectroscopy dates and analyzed for diatom accumulation rates and changes in floral composition it was found that the shelf probably was not glaciated by grounded ice but occupied by an ice shelf and or permanent sea ice between 14 000 years b p and the present average retreat rates of glacial permanent sea ice were circa 60 m yr between circa 13 500 and 11 000 years b p the retreat rates increased to about 150 m yr between 11 000 to 10 000 years b p the increase is unexpected because this correlates with fairbanks 1989 projected low glacial meltwater discharge for the same time which is coeval with the younger dryas several events of sea surface warming cooling took place on the outer shelf from 12 000 to 9000 years b p followed by cooling to the present with a possible warming between 3000 4000 years bp on the inner shelf pulses of warm cool surface water occurred from 9000 to 6000 years b p which was succeeded by surface water cooling until present

paleoceanographic reconstructions of surface ocean conditions in the greenland iceland and norwegian seas through the last 14 ka based on diatoms prior reconstructions of the last glacial maximum and the holocene did not include detailed paleoclimate data from the greenland iceland and norwegian gin seas which cover sensitive areas for oceanographic boundaries sea ice distribution and deep water formation in order to fill this gap we studied nine well dated sediment cores from this area and reconstructed the paleoceanographic conditions of the surface gin seas at 2000 year intervals since 13 400 bp based on the diatom record results show that a n s extending sea ice free corridor had opened along norway already at 13 400 bp indicating a northward flow of a branch of the north atlantic drift possibly caused by a change in the jet stream flow due to the decreased height of the north american ice sheet a major change of climatic conditions occurred over the gin seas as the insolation anomaly reached its maximum around 9000 bp when the sea ice cover and the oceanic fronts retreated to a northwesterly position along greenland and the ocean temperatures rose the first half of the holocene is recorded as the warmest period during the last 13 400 bp in the gin seas the duration of this climatic optimum decreased both toward the north and toward the margins of the area the second half of the holocene is characterized by a cooling trend in step with the decreasing insolation these results support the proposal of imbrie et al 1992 that the gin seas region acts as an initial responder to insolation changes