warming of global abyssal and deep southern ocean waters between the 1990s and 2000s contributions to global heat and sea level rise budgets abyssalglobalanddeepsouthern oceantemperature trendsarequantifiedbetweenthe1990sand2000sto assesstheroleofrecentwarmingoftheseregionsin globalheatandsealevelbudgets theauthors1 compute warming rates with uncertainties along 28 full depth high quality hydrographic sections that have been occupied two or more times between 1980 and 2010 2 divide the global ocean into 32 basins defined by the topography and climatological ocean bottom temperatures and then 3 estimate temperature trends in the 24 sampled basins the three southernmost basins show a strong statistically significant abyssal warming trend with that warming signal weakening to the north in the central pacific western atlantic and eastern indian oceans eastern atlantic and western indian ocean basins show statistically insignificant abyssal cooling trends excepting the arctic ocean and nordic seas the rate of abyssal below 4000 m global ocean heat content change in the 1990s and 2000s is equivalent to a heat flux of 0 027 60 009 w m 22 applied over the entire surface of the earth deep 1000 4000 m warming south of the subantarctic front of the antarctic circumpolar current adds 0 068 60 062 w m 22 the abyssal warming produces a 0 053 60 017 mm yr 21 increase in global average sea level and the deep warming south of the subantarctic front adds another 0 093 60 081 mm yr 21 thus warmingin theseregions ventilatedprimarilyby antarcticbottomwater accounts for a statistically significant fraction of the present global energy and sea level budgets

detection and attribution of atlantic salinity changes 1 an analysis of observed and modeled oceanic salinity changes shows that significant changes of salinity which are predicted in the world s oceans as a result of human influence are beginning to emerge a significant increase in salinity has been observed in recent decades in the 20n 50n latitude band of the atlantic ocean although changes at sub polar latitudes of the atlantic and in other ocean basins are not found to be significant compared to modeled internal variability an optimal detection analysis of spatial patterns of salinity trends detects a human influence on the observed salinity increases in the atlantic ocean these results indicate the growing potential for using observations to constrain important properties of the climate system s response to anthropogenic forcing

pacific ocean heat content during the past 10 000 years observed increases in ocean heat content ohc and temperature are robust indicators of global warming during the past several decades we used high resolution proxy records from sediment cores to extend these observations in the pacific 10 000 years beyond the instrumental record we show that water masses linked to north pacific and antarctic intermediate waters were warmer by 2 1 0 4 c and 1 5 0 4 c respectively during the middle holocene thermal maximum than over the past century both water masses were 0 9 c warmer during the medieval warm period than during the little ice age and 0 65 warmer than in recent decades although documented changes in global surface temperatures during the holocene and common era are relatively small the concomitant changes in ohc are large

diagenesis and geochemistry of porites corals from papua new guinea implications for paleoclimate reconstruction coral proxy records of sea surface temperature sst and hydrological balance have become important tools in the field of tropical paleoclimatology however coral aragonite is subject to post depositional diagenetic alteration in both the marine and vadose environments to understand the impact of diagenesis on coral climate proxies two mid holocene porites corals from raised reefs on muschu island papua new guinea were analysed for sr ca 18 o and 13 c along transects from 100 aragonite to 100 calcite thin section analysis showed a characteristic vadose zone diagenetic sequence beginning with leaching of primary aragonite and fine calcite overgrowths transitional to calcite void filling and neomorphic fabric selective replacement of the coral skeleton average calcite sr ca and 18 o values were lower than those for coral aragonite decreasing from 0 0088 to 0 0021 and 5 2 to 8 1 respectively the relatively low sr ca of the secondary calcite reflects the sr ca of dissolving phases and the large difference between aragonite and calcite sr ca partition coefficients the decrease in 18 o of calcite relative to coral aragonite is a function of the 18 o of precipitation carbon isotope ratios in secondary calcite are variable though generally lower relative to aragonite ranging from 2 5 to 10 4 the variability of 13 c in secondary calcite reflects the amount of soil co 2 contributing 13 c depleted carbon to the precipitating fluids diagenesis has a greater impact on sr ca than on 18 o the calcite compositions reported here convert to sst anomalies of 115 c and 14 c respectively based on calcite sr ca compositions in this study and in the literature the sensitivity of coral sr ca sst to vadose zone calcite diagenesis is 1 1 to 1 5 c per percent calcite in contrast the rate of change in coral 18 o sst is relatively small 0 2 to 0 2 c per percent calcite we show that large shifts in 18 o reported for mid holocene and last interglacial corals with warmer than present sr ca ssts cannot be caused by calcite diagenesis low level calcite diagenesis can be detected through x ray diffraction techniques thin section analysis and high spatial resolution sampling of the coral skeleton and thus should not impede the production of accurate coral paleoclimate reconstructions copyright 2003 elsevier science ltd

a field based study on variation in mg ca and sr ca in larger benthic foraminifera 1 the mg ca and sr ca ratios of foraminifera are used as proxies of paleotemperature although the mg ca is found to be related with temperature in planktonic foraminifera the reliability of this proxy in benthic foraminifera has yet to be established it is essential therefore to understand the minor elements composition and their relation to ambient water parameters in different benthic foraminiferal species in this study a systematic field based study was carried out on larger benthic foraminifera lbf of okinawa japan to assess if mg ca and sr ca in their tests could be used as proxies of seawater temperature five seasonal samples were collected from the reef flat to pick live specimens of amphistegina lessonii neorotalia calcar calcarina hispida calcarina gaudichaudii baculogypsina sphaerulata and marginopora kudakajimaensis the mg ca in a lessonii was 60 mmol mol while in the remaining five species the values were 200 mmol mol substantially higher than that recorded in planktonic and smaller benthic foraminifera interspecies and intraspecies mg ca variations were fairly large even in samples of the same season the sr ca were quite uniform 2 mmol mol across the species and seasons the correlations between test mg ca and sr ca and ambient water temperature and salinity were found to be poor the possible reasons are 1 the influence of biological activities particularly the photosynthesis respiration cycle of algal symbionts and 2 masking of the true relationship due to an averaging effect in whole test analysis of species having longer a life span in view of this it is suggested that the whole shell mg ca and sr ca of lbf is not an apt proxy of paleotemperature

a review of the nature and origin of limestone microporosity abstract limestone microporosity is ubiquitous and extensively developed in most phanerozoic limestones from an economic perspective microporosity is important because it contributes substantially to the carbonate pore system which can host significant volumes of water and hydrocarbons therefore determining the presence and distribution of limestone micropores is necessary for accurate hydrocarbon estimations reservoir characterization and fluid flow simulations from an academic standpoint microporosity is important because its genesis is intimately linked with the mineralogical stabilization of metastable sediments a fundamental process in carbonate diagenesis many types of micropores contribute to what has been referred to as microporosity but the vast majority is hosted among low magnesium calcite lmc microcrystals that are present in limestone matrix and allochems geochemical textural and mineralogical data from natural settings and laboratory experiments indicate that lmc microcrystals are diagenetic in origin more specifically these data support a diagenetic model of mineralogical stabilization that involves dissolution of precursor sediments dominated by aragonite and high magnesium calcite hmc minerals and precipitation of lmc microcrystal cements the stabilization process is inferred to take place in the meteoric marine and burial diagenetic realms although it has not been directly observed carbon and oxygen isotopes as well as trace element data suggest that lmc microcrystals form during burial diagenesis in marine like fluids evidence suggests that porosity is not generated during this dissolution precipitation process but rather inherited from the precursor sediments the final arrangement of the micropores in a limestone however depends on the precise diagenetic pathway lmc microcrystals exhibit a range of microcrystalline textures that are classified on the basis of crystal morphology and size the three main textural classes granular framework fitted mosaic and clustered have been recognized across a wide range of ages depositional settings burial depths and precursor types and are characterized by distinct petrophysical properties such as porosity permeability and pore throat size observations from modern sediments also support the hypothesis that lmc microcrystals develop from aragonite and hmc dominated lime mud the origin of lime mud has been extensively studied but still highly debated of particular interest to the discussion of microporosity are proposed secular variations in the dominant mineralogy of carbonate sediments through the phanerozoic microporous limestones comprised of lmc microcrystals are equally abundant during times of aragonite seas and calcite seas which suggests that no special mineral precursor is required microporous textures are also observed in deep marine chalks where micropores are hosted between chalk constituents unlike shallow marine limestones deep marine sediments start out as mostly lmc therefore mineralogical stabilization is not a significant process in chalk diagenesis

global ocean meridional overturning abstract a decade mean global ocean circulation is estimated using inverse techniques incorporating air sea fluxes of heat and freshwater recent hydrographic sections and direct current measurements this information is used to determine mass heat freshwater and other chemical transports and to constrain boundary currents and dense overflows the 18 boxes defined by these sections are divided into 45 isopycnal neutral density layers diapycnal transfers within the boxes are allowed representing advective fluxes and mixing processes air sea fluxes at the surface produce transfers between outcropping layers the model obtains a global overturning circulation consistent with the various observations revealing two global scale meridional circulation cells an upper cell with sinking in the arctic and subarctic regions and upwelling in the southern ocean and a lower cell with sinking around the antarctic continent and abyssal upwelling mainly below the crests of the major bathymetric ridges

reversal of the 1960s to 1990s freshening trend in the northeast north atlantic and nordic seas hydrographic time series in the northeast north atlantic and nordic seas show that the freshening trend of the 1960s 1990s has completely reversed in the upper ocean since the 1990s temperature and salinity have rapidly increased in the atlantic inflow from the eastern subpolar gyre to the fram strait in 2003 2006 salinity values reached the previous maximum last observed around 1960 and temperature values exceeded records the mean properties of the atlantic inflow decrease northwards but variations seen in the eastern subpolar gyre at 57 n persist with the same amplitude and pattern along the pathways to fram strait time series correlations and extreme events suggest a time lag of 3 4 years over that distance this estimate allows predictions to be made the temperature of atlantic water in the fram strait may start to decline in 2007 or 2008 salinity a year later but both will remain high at least until 2010

transformation of the labrador sea water in the subpolar north atlantic development spreading and decay of the thermohaline properties of two labrador sea water lsw classes are described during the development phase a specific lsw class repeatedly mixed by winter convection in the labrador sea becomes colder denser thicker and deeper once convection weakens the lsw class becomes isolated from the upper layer and starts to decay rapidly losing its volume while retaining the same density due to isopycnal mixing with the neighbouring warm saline intermediate waters a similar pattern in temperature salinity and density is seen in the other basins with different time lags from about two years in the irminger sea to ten years in the northern iceland basin and rockall trough regions the influence of lsw on the thermohaline properties of other north atlantic water masses is also discussed

decline of subpolar north atlantic circulation during the 1990s observations of sea surface height reveal that substantial changes have occurred over the past decade in the mid to high latitude north atlantic ocean topex poseidon altimeter data show that subpolar sea surface height increased during the 1990s and the geostrophic velocity derived from altimeter data exhibits declining subpolar gyre circulation combining the data from earlier satellites we find that subpolar circulation may have been weaker in the late 1990s than in the late 1970s and 1980s direct current meter observations in the boundary current of the labrador sea support the weakening circulation trend of the 1990s and together with hydrographic data show that the mid to late 1990s decline extends deep in the water column analysis of the local surface forcing suggests that the 1990s buoyancy forcing has a dynamic effect consistent with altimetric and hydrographic observations a weak thermohaline forcing allows the decay of the domed structure of subpolar isopycnals and weakening of circulation

geochemistry based coral palaeoclimate studies and the potential of non traditional non massive porites corals recent developments and future progression understanding the natural variability of the earth s climate system and accurately identifying potential anthropogenic influences requires long term geographically distributed records of key climate indicators such as temperature and precipitation that extend prior to the last 400 years of the holocene reef corals provide an excellent source of high resolution climate records and importantly represent the tropical marine environment where palaeoclimate data are urgently required recent decades have seen significant improvement in our understanding of coral biomineralisation the associated uptake of geochemical proxies and methods of identifying and understanding the effects of both early and late post depositional diagenetic alteration these processes all have significant implications for interpreting geochemical proxies relevant to palaeoclimatic reconstructions this paper reviews the current state of the art in terms of coral based palaeoclimate reconstructions and highlights a key remaining problem the majority of coral based palaeoclimate research has been derived from massive colonies of porites however massive porites are not globally abundant and may not provide material of a particular age of interest in those regions where they are present therefore there is great potential for alternate coral genera to act as complimentary climate archives while it remains critical to consider five key factors vital effects differential growth morphologies geochemical heterogeneity in the skeletal ultrastructure transfer equation selection and diagenetic screening of skeletal material in order to allow the highest level of accuracy in coral palaeoclimate reconstructions it is also important to develop alternate taxa for palaeoclimate studies in regions where porites colonies are absent or rare currently as many as nine genera other than porites have proven at least limited utility in palaeothermometry most of which are found in the atlantic caribbean region where massive porites do not exist even branching taxa such as acropora have significant potential to preserve environmental archives increasing this capability will greatly expand the number of potential geochemical archives available for longer term temporal records of palaeoclimate

redox zonation of elements at an oxic post oxic boundary in deep sea sediments abstract deep sea sediments generally provide limited evidence of redox control on the post depositional redistributions of elements this is because only a fraction of any element is reactive and observed elemental distributions are the result of a number of competing processes which are simultaneously active so that redox effects are not dominant a detailed investigation is reported of a core which is unusual in showing unequivocal evidence of direct redox control operating in a homogeneous environment that is relatively free from competing processes a progressive oxidation front has migrated slowly downwards into a uniform turbidite over a long period ca 250 ky the reactive fractions of several redox sensitive elements now show a remarkable degree of organisation around the redox boundary of this front with the different elements exhibiting individual responses solid phase enrichments are not coincident but are arranged in a clear succession of concentration peaks along the redox gradient from oxic to postoxic conditions the succession is mn i fe se and pt cu and pb v zn and sb and u the movement directions of most elements can be inferred from the peak shapes against the homogeneous turbidite background composition the system seems to have been essentially isolated within the sediment for most elements so that no loss or gain can be ascribed to redox processes exceptions are u and v which have been augmented by uptake from ocean bottom waters into the sediments by an efficient redox trap mechanism

the role of skeletal porosity in aragonite neomorphism strombus and montastrea from the pleistocene key largo limestone florida abstract the neomorphism of aragonite to calcite involves complex textural and chemical alterations that are in part controlled by the degree of communication between diagenetic and ambient formation fluids two taxa montastrea annularis and strombus gigas from the vadose zone of the pleistocene key largo formation in southern florida were examined in order to evaluate the effect of initial skeletal porosity on system closure during neomorphism fabrics of replacement calcite in both taxa are similar consisting of blocky crystals largely restricted to areas of former skeletal aragonite oriented aragonite and organic inclusions result in the preservation of relic fabrics in both taxa the chemical signatures of coralline and molluscan aragonite and calcite are strongly dependent on initial skeletal porosity compared to original aragonite montastrea calcite is enriched in magnesium 1 151 64 ppm versus 2 114 619 ppm and depleted in strontium 7 397 376 ppm versus 2 510 43 ppm these data in conjunction with large calcite oxygen depletions 3 8 0 2 versus 5 7 0 3 and variable calcite carbon depletions 0 6 0 6 versus 1 3 to 7 3 demonstrate significant exchange between neomorphic front and formational fluids in contrast strombus calcite composition is largely inherited from original aragonite and is only slightly enriched in strontium and magnesium 2 299 316 ppm versus 2 519 759 ppm and 96 23 ppm versus 173 79 ppm while carbon exhibits a small depletion 5 3 0 5 versus 4 4 0 8 similarity of str mbus aragonite and calcite compositions reflects high rock water ratios in relatively closed diagenetic systems calcite oxygen depletion 0 5 0 5 versus 3 6 0 4 observed in strombus however requires some exchange between formation and neomorphic front fluids differences in the thickness of replacement calcite rims between taxa reflect variable skeletal porosities and rates of migration of neomorphic fronts neomorphism was six times faster by volume in porous montastrea than in dense strombus skeletal structures thus skeletal porosity influences degrees of system openness during aragonite neomorphism

geochemical indicators of depositional and early diagenetic facies in holocene carbonate muds and their preservation potential during stabilisation holocene carbonate muds 63 m fraction and macro organic matter were collected from marine subtidal mudbanks and supralittoral mud islands of florida bay and freshwater marshes of the florida everglades u s a geochemistry sedimentology and mineralogy were used to determine whether carbonate mud formation in specific marine and freshwater environments was geochemically distinct and to assess the importance of early diagenetic reactions on mud chemistry and mineralogy significant variations were found in the relative amounts of carbonate minerals not just between the marine and freshwater environments but also within florida bay in particular mg calcite is enriched in crane key muds by 10 relative to nearby cross bank the mg calcite appears to precipitate in the surface living cyanobacterial mats of the key and seems to be linked to mg chelation by the cyanobacterial organic matter this mg calcite has a distinct 13c around 4 6 lighter than mg calcite derived from thalassia epibionts in the cross bank muds dolomite was found just below the cyanobacterial mats forming in the only part of the core where reactive organic carbon has been completely removed by sulphate reducing bacteria the 13c values of this dolomite at least 4 are consistent with previously published 13c values of dissolved inorganic carbon in pore waters at this horizon which support dolomite formation in situ mg supply for dolomite formation may be from dissolution of the overlying cyanobacterial mat mg calcite the various types of organic matter have distinctive 13c values ranging from 25 mangrove and sawgrass to 10 cyanobacterial mats and 8 thalassia seagrass values intermediate between these end members record mixing of the organic matter types which shows particularly the time when the bank muds became dominated by thalassia organic matter i e were relatively removed from mangrove vegetation five holocene mud suites bank key cyanobacterial mats mangrove swamp and freshwater everglades swamp show distinct chemical signatures in their mean 13c 18o mgco3 and sr values na distinguishes between seawater and non seawater influenced environments but fe mn and p are mainly controlled by non carbonate materials comparison with published stable isotope and elemental data for pleistocene limestones in the south florida area suggests that only the facies diagnostic signatures of 13c and mg will be resolvable once the muds have been stabilised to micrite alteration of the 18o and sr values during stabilisation will probably be more severe to the extent that original facies variations are destroyed

behavior of carbonate associated sulfate during meteoric diagenesis and implications for the sulfur isotope paleoproxy abstract although carbonate associated sulfate cas is used widely as a proxy for the sulfur isotope composition of ancient seawater little is known about the effects of diagenesis on retention of primary 34 s signals our case study of the key largo limestone pleistocene florida is the first systematic assessment of the impact of meteoric diagenesis on cas properties geochemical and petrographic data show that meteoric diagenesis has affected the exposed coralline facies to varying degrees yielding differences now expressed as sharp reaction fronts between primary and secondary carbonate minerals within individual coral heads specifically analyses across high resolution transects in the key largo limestone show that concentrations of strontium and sodium decrease across the recrystallization front from original aragonite to meteoric low magnesium calcite by factors of roughly 5 and 10 respectively predictably 18 o values decrease across these same fronts the 13 c relationships are more complex with the most depleted values observed in the latest formed calcite such trends likely reflect carbon isotope buffering capacity that decreased as reaction progressed as well as protracted development of soil profiles and the associated terrestrial biomass and thus depleted 13 c during sea level lowstand conversely 34 s values of cas vary within a narrow buffered range from 20 6 to 22 6 compared to 20 8 22 0 of coeval pleistocene seawater across the same mineralogical transition despite sulfate concentrations that drop in the diagenetic calcite by an average factor of 12 collectively these data point to robust preservation of primary 34 s for carbonates that have experienced intense meteoric diagenesis which is encouraging news for those using the isotopic composition of cas as a paleoceanographic proxy at the same time the vulnerability of cas concentrations to diagenetic resetting is clear

distribution and circulation of labrador sea water abstract labrador sea water is the final product of the cyclonic circulation of subpolar mode water in the open northern north atlantic mccartney and talley 1982 the temperature and salinity of the convectively formed subpolar mode water decrease from 14 7 c 36 08 to 3 4 c 34 88 on account of the cumulative effects of excess precipitation and cooling the coldest mode water is labrador sea water which spreads at mid depths and is found throughout the north atlantic ocean north of 40 n and along its western boundary to 18 n a vertical minimum in potential vorticity is used as the primary tracer for labrador sea water labrador sea water is advected in three main directions out of the labrador sea 1 northeastward into the irminger sea 2 southeastward across the atlantic beneath the north atlantic current and 3 southward past newfoundland with the labrador current and thence westward into the slope water region crossing under the gulf stream off cape hatteras the labrador sea water core is

global and full depth ocean temperature trends during the early twenty first century from argo and repeat hydrography the early 21st century s warming trend of the full depth global ocean is calculated by combining the analysis of argo top 2000m and repeat hydrography into a blended full depth observing system the surface to bottom temperature change over the last decade of sustained observation is equivalent to a heat uptake of 0 72 0 09 w m 2 applied over the surface of the earth 90 of it being found above 2000m depth we decompose the temperature trend point wise into changes in isopycnal depth heave and temperature changes along an isopycnal spiciness to describe the mechanisms controlling the variability the heave component dominates the global heat content increase with the largest trends found in the southern hemisphere s extratropics 0 2000m highlighting a volumetric increase of subtropical mode waters significant heave related warming is also found in the deep north atlantic and southern ocean 2000m 4000m reflecting a potential decrease in deep water mass renewal rates the spiciness component shows its strongest contribution at intermediate levels 700m 2000m with striking localised warming signals in regions of intense vertical mixing north atlantic and southern oceans finally the agreement between the independent argo and repeat hydrography temperature changes at 2000m provides an overall good confidence in the blended heat content evaluation on global and ocean scales but also highlights basin scale discrepancies between the two independent estimates those mismatches are largest in those basins with the largest heave signature southern ocean and reflect both the temporal and spatial sparseness of the hydrography sampling

decadal changes in the thermohaline circulation of the north atlantic abstract a set of repeated full depth and mostly ocean wide hydrographic sections is used to describe the temporal and spatial changes of temperature and salinity at the intermediate layers of the north atlantic over the past 40 years they cover three distinct periods namely the late 1950s the early 1980s and the early 1990s but do not constitute a time series most parts of the recently observed changes in the subpolar and subtropical gyres are attributed to the changes of the labrador sea water lsw properties the latter is formed in the labrador sea and spreads into the north atlantic the spreading time of the lsw from the source region is evaluated it takes less than two years for the lsw to arrive in the newfoundland basin and 18 20 yr to reach the deep western basin interior at 24 5 n changing characteristics of the lsw are related to the varying intensity of the meridional overturning circulation moc and the meridional heat transport mht the intensification of the moc and mht around 1981 coincides with the rapid decrease of the lsw production the increase of the lsw production that began just after 1987 and resulted in a dramatic cooling and densification of this water mass was accompanied by a reduction of both moc and mht two scenarios of the moc interaction with the full depth circulation of the north atlantic are suggested these scenarios indicate that the development of the moc is governed by the changing transports of the deep waters of arctic origin the direct contribution of the lsw to the intensity of the moc is negligible the lsw is seen as an important part of the feedback loop in the north atlantic moc system

sst artifacts in coral proxy records produced by early marine diagenesis in a modern coral from rabaul papua new guinea 1 we investigated the effects of early marine diagenesis on the skeletal geochemistry of a porites coral collected live offshore of rabaul papua new guinea the lowermost 14 cm of the 1 9 m coral core contains physical evidence of alteration which is clearly visible in x radiograph sem and petrography images abrupt and significant increases in coral 18o and sr ca and decreases in coral mg ca occur at the transition from unaltered to altered skeleton all of which imply significant sst cooling if the altered nature of the coral skeleton went unrecognized screening for the effects of early marine diagenesis should become a standard procedure in coral climate studies

reduced antarctic meridional overturning circulation reaches the north atlantic ocean 1 we analyze abyssal temperature data in the western north atlantic ocean from the 1980s 2000s showing that reductions in antarctic bottom water aabw signatures have reached even that basin trans basin oceanographic sections occupied along 52 w from 1983 2003 and 66 w from 1985 2003 quantify abyssal warming resulting from deepening of the strong thermal boundary between aabw and north atlantic deep water nadw hence a local aabw volume reduction repeat section data taken from 1981 2004 along 24 n also show a reduced zonal gradient in abyssal temperatures consistent with decreased northward transport of aabw the reduction in the antarctic limb of the moc within the north atlantic highlights the global reach of climate variability originating around antarctica

deposition and diagenesis of marine oncoids implications for development of carbonate porosity abstract microbially mediated carbonates form in numerous environments and produce a range of lithologic fabrics and textures while the environmental and biological factors controlling microbial carbonate precipitation are becoming more established the influence of precursor microbial textures on diagenetic processes is less understood here we describe microbial oncolites from mare new caledonia to assess their formation textures and subsequent diagenetic alteration calcified filaments and sheets are interpreted as microbial mat constituents bacterial sheaths and eps sheets within a constructive micritic cortex of uniform crystal size 5 10 m and shape formed around a nucleus grain thin section analyses show trapped and bound grain inclusions and irregular laminations within the cortex also consistent with a microbial origin the combination of a dense micrite cortex subrounded shape and irregular laminations are consistent with oncoid formation under periodic wave agitation in a back reef setting the mare oncolites also display an unexpected pseudomorphic stabilization of the nucleus grains and cortex likely due to the original mineralogy and low permeability of the cortex micrite to our knowledge this is the first example of microbial coatings leading to pseudomorphic stabilization of aragonite and high mg calcite skeletal grains this textural preservation lies in stark contrast to the extensive dissolution and moldic porosity found outside the oncolite beds and common to many tropical shallow water carbonates these findings have implications for development of meteoric porosity the interpretation of 13c values in marine carbonates and potential controls on fluid flow

the formation of labrador sea water part iii the evolution of oxygen and nutrient concentration abstract oxygen nutrient and tritium concentrations observed in the western labrador sea in march 1976 during deep convective renewal of labrador sea water are analyzed to show how a newly formed water mass obtains its characteristics common to other winter observations of deep mixed layers the oxygen concentrations are some 6 undersaturated even in the upper 20 m a gas transfer model coupled to a simple mixed layer model illustrates the difficulty of transferring sufficient oxygen across the air sea boundary to fully oxygenate the mixed layer when the mixed layer depth exceeds a few hundred meters the nutrient concentrations of the mixed layers are fairly well mixed as is consistent with the fairly narrow range of nutrient concentrations of the source waters only the tritium concentrations exhibit any structure within the mixed layer and it is argued that this is due to the much larger range of tritium concentrations in the source waters that make up the mixed layer

a review of the source behaviour and distribution of arsenic in natural waters the range of as concentrations found in natural waters is large ranging from less than 0 5 g l 1 to more than 5000 g l 1 typical concentrations in freshwater are less than 10 g l 1 and frequently less than 1 g l 1 rarely much higher concentrations are found particularly in groundwater in such areas more than 10 of wells may be affected defined as those exceeding 50 g l 1 and in the worst cases this figure may exceed 90 well known high as groundwater areas have been found in argentina chile mexico china and hungary and more recently in west bengal india bangladesh and vietnam the scale of the problem in terms of population exposed to high as concentrations is greatest in the bengal basin with more than 40 million people drinking water containing excessive as these large scale natural as groundwater problem areas tend to be found in two types of environment firstly inland or closed basins in arid or semi arid areas and secondly strongly reducing aquifers often derived from alluvium both environments tend to contain geologically young sediments and to be in flat low lying areas where groundwater flow is sluggish historically these are poorly flushed aquifers and any as released from the sediments following burial has been able to accumulate in the groundwater arsenic rich groundwaters are also found in geothermal areas and on a more localised scale in areas of mining activity and where oxidation of sulphide minerals has occurred the as content of the aquifer materials in major problem aquifers does not appear to be exceptionally high being normally in the range 1 20 mg kg 1 there appear to be two distinct triggers that can lead to the release of as on a large scale the first is the development of high ph 8 5 conditions in semi arid or arid environments usually as a result of the combined effects of mineral weathering and high evaporation rates this ph change leads either to the desorption of adsorbed as especially as v species and a range of other anion forming elements v b f mo se and u from mineral oxides especially fe oxides or it prevents them from being adsorbed the second trigger is the development of strongly reducing conditions at near neutral ph values leading to the desorption of as from mineral oxides and to the reductive dissolution of fe and mn oxides also leading to as release iron ii and as iii are relatively abundant in these groundwaters and so4 concentrations are small typically 1 mg l 1 or less large concentrations of phosphate bicarbonate silicate and possibly organic matter can enhance the desorption of as because of competition for adsorption sites a characteristic feature of high groundwater as areas is the large degree of spatial variability in as concentrations in the groundwaters this means that it may be difficult or impossible to predict reliably the likely concentration of as in a particular well from the results of neighbouring wells and means that there is little alternative but to analyse each well arsenic affected aquifers are restricted to certain environments and appear to be the exception rather than the rule in most aquifers the majority of wells are likely to be unaffected even when for example they contain high concentrations of dissolved fe

the formation of labrador sea water part i large scale processes abstract data obtained in the western labrador sea during march 1976 by hudson are analysed to show that new labrador sea water was being formed at this time on the basis of hydrographic and moored current meter data it is hypothesized that a 200 km scale cyclonic gyre forms in winter in the western labrador sea and that this gyre retains the developing deep mixed layers in this general area long enough for the transformation to labrador sea water to take place using a model it is demonstrated that water columns found along the western boundary of the labrador sea can be modified by cooling evaporation and mixing to form deep mixed layers with the properties of labrador sea water approximately 105 km3 of new labrador sea water was formed in 1976 an estimate that is consistent with earlier estimates of mean annual production rates this water 2 9 c 34 84 is some 0 6 c cooler and 0 06 fresher than that defined by lazier 1973 from his data collected in 1966 the variation of labrador sea water

application of arsenic in barite as a redox indicator for suboxic anoxic redox condition abstract redox condition is an important factor that controls the behavior of various elements in an aquatic environment incorporation of redox sensitive trace elements in minerals describes redox conditions in water and provides information about past environmental changes unless it is dissolved or recrystallized during sediment burial in the present study we explore the application of arsenate arsenite ratios as v as iii in barite as a new geochemical proxy for paleo environmental reconstruction laboratory experiments showed that both as iii and as v could be incorporated into barite as as iii and as v coprecipitated barite respectively which could more or less retain the information of the as v as iii ratio in coexistent water if under equilibrium in terms of the redox reactions furthermore the as v as iii ratios in natural barite collected in i tamagawa hot spring and ii okinawa hydrothermal vent were determined by micro x ray fluorescence and micro x ray absorption fine structure analysis to a evaluate the reliability of the as v as iii ratio in barite as a redox indicator in natural system and b estimate the depositional redox condition in water whether barite precipitated below or above the redox boundary of as v as iii or the suboxic anoxic boundary our previous study showed that barite selenium oxyanion system could also be used as a proxy for the oxic suboxic boundary because the selenate selenite se vi se iv ratio in barite is primarily correlated with the ratio in water given that the redox boundary of the se vi se iv ratio has higher redox potential than the as v as iii boundary the combination of these two systems can extend the redox condition which can be specified by the analysis of one single barite grain to a wide region thus one barite particle can provide information on the as v as iii and se vi se iv ratios in water and whether barite precipitated under oxic suboxic or anoxic redox environments

the climatology of the north atlantic abstract data from approximately 144 000 hydrographic stations in the north atlantic have been retrieved from the national oceanic data centre and analysed to produce maps of mean pressure temperature salinity and oxygen on selected potential density surfaces for the domain bounded by 0 85 w and 0 65 n the data span the period from 1904 to 1990 with the majority of the data from the last four decades the data set for this region is 60 larger than that used in the production of levitus climatological world atlas this increase in stations coupled with smoothing scales specific to the north atlantic rather than the global ocean considerably improves the resolution of the basin s features the mean property fields and their associated standard deviations are resolved on a one degree grid with little smoothing contrasting with the levitus atlas where properties although presented on a one degree grid have been smoothed on the order of 1000km another important feature of this database is the process by which irregularly spaced data are averaged onto a regular grid in a significant departure from the levitus analysis which averaged on depth surfaces these data were averaged on potential density surfaces thus eliminating an artificial mixing of water mass properties the database is used to describe the baroclinicity of well known features such as the gulf stream the north atlantic current and the deep western boundary current and to elucidate the recirculations associated with these currents it additionally resolves several new features in the intermediate and deep north atlantic these features include the signature of a large scale deep recirculation that extends southwestward from the eastward extension of the north atlantic current to the separation point of the gulf stream near cape hatteras this recirculation which spans approximately 2000m of the water column encompasses more local recirculations and potentially mixes subpolar and subtropical waters furthermore in the upper thermocline this database reveals a coherent azores current that stretches from the gulf stream system south of the tail of the grand banks to madeira this flow is marked by divergences to the south and convergences from the north such that its downstream transport is not much changed

mg isotopic systematics during early diagenetic aragonite calcite transition insights from the key largo limestone abstract the seawater magnesium mg isotopic composition 26mgsw can be applied to quantify marine mg cycle in earth s history however reconstruction of 26mgsw by using marine carbonate has been challenged by the large range of variation in mg isotopic composition of carbonate 26mgcarb such variation on the one hand reflects e g the mineralogy temperature and precipitation rate dependent isotopic fractionation during ca carbonate precipitation on the other hand the pristine seawater record could be modified in carbonate diagenesis during which less stable carbonate minerals would spontaneously convert to more stable mineral phases in the modern ocean with high mg ca molar ratio 5 aragonite precipitation is favored however aragonite is thermodynamically less stable than low mg calcite at ambient surface environment resulting in the spontaneous transition from aragonite to low mg calcite in the earliest stage of diagenesis i e the aragonite calcite transition as a common process in the modern ocean mg isotopic fractionation in aragonite calcite transition may provide valuable constraints on the variation of 26mgcarb in this study we measured mg isotopic compositions of pleistocene key largo limestone florida which has been experiencing the aragonite calcite transition during early diagenesis the key largo limestone samples consist of a mixture of calcite and aragonite 26mg of aragonite 26mgarag shows higher and more stable values while calcite has lower yet more variable mg isotopes 26mgcal we suggest a model conceptualizing a water film attached to the mineral surface in which the aragonite calcite transition initiates with aragonite dissolution and the mg exchange with external fluid can be variable followed by mg isotopes fractionate during low mg calcite precipitation in this model 26mgcal is controlled by 1 the chemical composition of water film which is dependent on the mineralogical composition of aragonite i e mg content and 26mgarag the composition of external fluid i e fresh water seawater or mixed fresh water and seawater and the mixing ratio between dissolved aragonite and external fluid and 2 the isotopic fractionation during calcite precipitation because the isotopic fractionation in calcite is sensitive to the rate of calcite precipitation that is dependent on the calcite saturation state of solution therefore 26mgcal could be highly heterogeneous depending on the aragonite dissolution and calcite precipitation processes further complicating the interpretation of carbonate data thus the process controlled mg isotopic fractionation should be taken into consideration when reconstructing 26mgsw by using carbonate sediments rocks

arsenic in marine sediments how robust a redox proxy abstract arsenic as is reputed to be a redox sensitive element but has not been fully explored yet as a proxy in marine sediments and sedimentary rocks compared to extensively examined elements such as molybdenum mo and uranium u here the behavior of as is compared to that of mo and u in a number of paleo environmental situations that have been studied before and are therefore rather well constrained the results indicate that attention must be paid to the reference values used to normalize sedimentary as content in geochemical studies the most commonly used references namely the post archean australian shale and average upper crust of earth to be opposed to the average shale tend to overestimate slightly as enrichments as shown by as enrichment factors being quasi systematically larger than 1 whatever the geological setting the results also show that as enrichments are less straightforward compared to those of mo and u when using these elements as redox proxies in addition the depositional milieus that endured the most hydrologically restricted and or reducing euxinic conditions are not those with the highest as enrichments thus arsenic shows a redox sensitive behavior but is not adequate as a redox proxy however as enrichments are correlated with mo enrichments in two distinct types of situations settings impacted 1 by particulate iron shuttling processes and 2 by diagenetic fluid circulation cold seeps in both cases the mo as correlation is induced by the strong relationship between these trace metals and reactive iron fe conveys both as and mo to the sediment where they are trapped thus arsenic has a promising potential to allow recognition of past depositional environments associated with iron shuttling and cold seep circulations lastly high toc high mo low as situations point out possible occurrences of sulfurized organic matter in sediments high mo concentrations indicate reducing sulfidic conditions prone to organic matter accumulation high toc values but low as concentrations indicate that reactive iron was a limiting factor preventing as capture under such conditions free h2s was not associating with iron and could react with organic matter causing its sulfurization

opposing decadal changes for the north atlantic meridional overturning circulation hydrographic properties of the north atlantic ocean have changed significantly over the past decades a combination of changes in seawater density calculated from observed properties of sea water and a numerical ocean model reveals that the strength of the meridional overturning circulation has changed in different directions in the subpolar and subtropical basins respectively

the formation of labrador sea water part ii mesoscale and smaller scale processes abstract in a previous paper clarke and gascard argued that the formation of labrador sea water was taking place in a cyclonic gyre set up each winter in the western labrador sea within the gyre and at its boundaries a number of different scales of organization are believed to be important in the formation processes the longest of these scales is the mesoscale 50 km which appears to be related to topographic rossby waves generated in the labrador current and propagating offshore the next smaller scale is an eddy scale 20 km believed to arise because the mesoscale is baroclinically unstable as shown by applying a two layer model of tang this instability is believed to promote mixing by generating frontal structures and vertical motions along them thus bringing subsurface t s maxima nearer the surface then within the mesoscale and eddy scale structures intense vertical convective cells take place at scales which are probably of the order of 1 km in three dimensions these events are short liv

sr ba in barite a proxy of barite preservation in marine sediments abstract the observation by bertram and cowen j mar res 55 1997 577 593 that the strontium content of marine barite decreased from the water column to the deep sea floor suggested that the sr ba ratio in barite was sensitive to barite dissolution following this observation we have investigated the potential of using the sr ba ratio in barite as a proxy of barite preservation by separating barite crystals from sediment cores collected at different water depths in the equatorial pacific and in the southern ocean our investigations do not reveal significant downcore variations in the sr ba ratios during the holocene period in the two basins and up to a few hundred thousand years in the equatorial pacific however a comparison of the mean sr ba ratios in individual cores suggests that the sr ba ratios in barite decrease with increasing water depth a feature that could be related to dissolution of barite crystals during settling to the deep sea floor and or at the sediment water interface if confirmed the sr ba ratios in barite could be used to infer the intensity of barite dissolution and the state of preservation of barite crystals in sediments such information could be employed usefully in paleoproductivity reconstructions for the purpose of distinguishing between productivity and dissolution signals affecting barite distributions in marine sediments

a twenty year reversal in water mass trends in the subtropical north atlantic temperature and salinity changes have been compared along three repeat sections at 36 n in the north atlantic the principal changes cooling of the upper waters and warming of the intermediate waters observed between 1959 and 1981 were reversed between 1981 and 2005 the controlling mechanisms for the changes over the two time periods differed through the water column neutral density surfaces over the upper 800 m were firstly uplifted and secondly depressed by typically 50 m which is broadly consistent with the changes in thermocline thickness implied by the temporal changes in ekman pumping in contrast the intermediate waters 800 2500 m firstly became warmer and saltier and secondly became cooler and fresher this change in the intermediate waters was controlled by water mass changes along neutral density surfaces suggesting a change in the source waters principally labrador sea water and mediterranean outflow water

trace element and isotope geochemistry of zoned calcite cements lake valley formation mississippian new mexico insights from water rock interaction modelling abstract regionally extensive pre pennsylvanian meteoric zoned calcite cements from the mississippian age lake valley formation new mexico comprise three major zones zones 1 2 and 3 each with a distinct isotope and trace element geochemistry zone 1 has the highest mg 18o and 13c contents zone 2 intermediate values and greatest mn and fe and zone 3 has the lowest trace element 18o and 13c values covariation of c and o isotopes for the three zones define an inverted l shaped trend and covariations of mg mn and mg fe define l shaped trends all suggestive of rock evolution curves resulting from water rock interaction these covariant trends were the impetus for quantitative mass balance modelling of water rock interaction iterative mass balance modelling of covariations of stable isotopes c and o and trace elements mg mn fe of these zoned cements implies that water rock interaction progressively decreased water rock ratios increased during precipitation cementing waters for the oldest cement zone zone 1 resulted from water rock ratios in the range of tens to a few hundred whereas the youngest cement zone 3 resulted from water rock ratios in the 100 s to 1000 s the modelling also implies that differences in geochemistry of the cement zones cannot be explained solely by changes in water rock ratios but require greater 18o and greater ca and mg concentrations in input waters that evolved to zone 1 precipitational waters than those for zones 2 and 3 zones 2 and 3 can reasonably be modelled using input waters with the same isotopic compositions the same ca concentration and for some zone 2 cement the same mg concentrations the minimum mg ca ratios in input waters is constrained by the lower mg plateau in mg mn space and is about the same for all three zones about 1 25 the maximum mg ca ratios about 1 20 occurred in zone 2 input waters mn fe covariations also show an l shaped trend a trend whch fits neither a simple water rock interaction model nor a simple eh model a model is proposed in which eh and limited mn sources determine the amount of fe and mn available in solution to partake in water rock interaction water rock interaction modelling provides one useful approach to quantitatively interpreting isotopic and trace element data from diagenetic carbonates to gain a clearer understanding of evolution of diagenetic fluids

estimating global ocean heat content changes in the upper 1800 m since 1950 and the influence of climatology choice abstractocean heat content anomalies are analyzed from 1950 to 2011 in five distinct depth layers 0 100 100 300 300 700 700 900 and 900 1800 m these layers correspond to historic increases in common maximum sampling depths of ocean temperature measurements with time as different instruments mechanical bathythermograph mbt shallow expendable bathythermograph xbt deep xbt early sometimes shallower argo profiling floats and recent argo floats capable of worldwide sampling to 2000 m have come into widespread use this vertical separation of maps allows computation of annual ocean heat content anomalies and their sampling uncertainties back to 1950 while taking account of in situ sampling advances and changing sampling patterns the 0 100 m layer is measured over 50 of the globe annually starting in 1956 the 100 300 m layer starting in 1967 the 300 700 m layer starting in 1983 and the deepest two layers considered here starting in 2003 and 2004 during the implementation of argo furthermor

propagation pathways of classical labrador sea water from its source region to 26 n 1 more than two decades of hydrography on the abaco line east of the bahamas at 26 n reveals decadal variability in the salinity of classical labrador sea water clsw despite the long distance from its source region in the north atlantic ocean hydrographic time series from the labrador sea and from the abaco line show a pronounced step like decrease in salinity between 1985 and 1995 in the labrador sea and between 1995 and 2010 at the abaco line suggesting a time lag between the two locations of approximately 9 years the amplitude of the anomaly at the abaco line is 50 of the amplitude in the labrador sea a similar time lag and reduction of amplitude is found in the high resolution ofes model in which salinity anomalies can be observed propagating through the deep western boundary current as well as through a broad interior pathway on its way south to the abaco line the clsw becomes 8 standard deviations saltier due to isopycnal mixing with mediterranean outflow water mow climatological data in the north atlantic suggests that the mixing ratio of mow to clsw at the abaco line is 1 4 and that no variability in mow is required to explain the observed variability at the abaco line the data studied here suggest that decadal clsw anomalies stay relatively coherent while getting advected despite the important role of interior pathways

dilution of the northern north atlantic ocean in recent decades declining salinities signify that large amounts of fresh water have been added to the northern north atlantic ocean since the mid 1960s we estimate that the nordic seas and subpolar basins were diluted by an extra 19 000 5000 cubic kilometers of freshwater input between 1965 and 1995 fully half of that additional fresh water about 10 000 cubic kilometers infiltrated the system in the late 1960s at an approximate rate of 2000 cubic kilometers per year patterns of freshwater accumulation observed in the nordic seas suggest a century time scale to reach freshening thresholds critical to that portion of the atlantic meridional overturning circulation

mid 2000s north atlantic shift heat budget and circulation changes prior to the 2000s the north atlantic was the basin showing the greatest warming however since the mid 2000s during the so called global warming hiatus large amounts of heat were transferred in this basin from upper to deeper levels while the dominance in terms of atmospheric heat capture moved into the indo pacific here we show that a large transformation of modal waters in the eastern north atlantic ena played a crucial role in such contrasting behavior first strong winter mixing in 2005 transformed ena modal waters into a much saltier warmer and denser variety transferring upper ocean heat and salt gained slowly over time to deeper layers the new denser waters also altered the zonal dynamic height gradient reversing the southward regional flow and enhancing the access of saltier southern waters to higher latitudes then the excess salinity in northern regions favored additional heat injection through deep convection events in later years

the mechanism of skeletal aragonite neomorphism evidence from neomorphosed mollusks from the upper purbeck formation late jurassic early cretaceous southern england abstract the trace element geochemistry and microtextures of neomorphosed mollusks from the upper purbeck formation late jurassic early cretaceous of southern england suggest that calcite replacement of aragonite occurs by a force of crystallization driven mechanism similar to that of non polymorphic skeletal carbonate replacement reactions such as silicification the purbeck neomorphic calcites are substantially enriched in mg mn and fe and depleted in sr compared to skeletal aragonite indicating that the neomorphic reaction zones were not chemically isolated from the bulk pore waters to a significant degree neomorphic calcite microtextures are fundamentally similar to the replacement microtextures of silicified and celestite replaced fossils in terms of the degree and style of preservation of traces of skeletal microtextures in authigenic crystals and the relationships of authigenic crystal morphology and crystallographic orientation to shell microtexture the neomorphic replacement of aragonite by calcite differs from most non polymorphic replacement reactions in that the calcite cannibalizes aragonite decreases in the intraskeletal pore water calcium carbonate ion activity product caused by calcite precipitation results in aragonite dissolution adjacent to aragonite calcite contacts i e chalkification in some fossils chalkification does not occur in non polymorphic replacements of skeletal carbonate

iodine to calcium ratios in marine carbonate as a paleo redox proxy during oceanic anoxic events periods of globally distributed extreme oxygen depletion so called oceanic anoxic events oaes have been recognized in the mesozoic geological record and appear to be characteristic of episodes of extreme warmth here we explore the application of iodine calcium ratios i ca in marine carbonate as a new geochemical proxy to constrain seawater redox change and provide additional insights into the response of ocean chemistry to ancient climatic warming iodine has long been known as a redox sensitive and biophilic element mainly present as iodate and iodide in seawater iodate converting to iodide under anoxic conditions laboratory experiments growing calcite crystals from solutions spiked with iodate show that this is the ionic species incorporated into the carbonate structure likely substituting for the co 3 2 ion a fall in the i ca ratio measured in carbonates formed in shallow water by marine calcifiers during the early toarcian and cenomanian turonian oaes is interpreted both as a response to a decrease in the iodate iodide ratio in ocean waters and the drawdown of the global iodine inventory under conditions of accelerated organic matter burial the results suggest that i ca ratios in carbonates may be used to monitor seawater oxidation levels throughout earth history

arsenic incorporation into authigenic pyrite bengal basin sediment bangladesh abstract sediment from two deep boreholes 400 m approximately 90 km apart in southern bangladesh was analyzed by x ray absorption spectroscopy xas total chemical analyses chemical extractions and electron probe microanalysis to establish the importance of authigenic pyrite as a sink for arsenic in the bengal basin authigenic framboidal and massive pyrite median values 1500 and 3200 ppm as respectively is the principal arsenic residence in sediment from both boreholes although pyrite is dominant ferric oxyhydroxides and secondary iron phases contain a large fraction of the sediment bound arsenic between approximately 20 and 100 m which is the depth range of wells containing the greatest amount of dissolved arsenic the lack of pyrite in this interval is attributed to rapid sediment deposition and a low sulfur flux from riverine and atmospheric sources the ability of deeper aquifers 150 m to produce ground water with low dissolved arsenic in southern bangladesh reflects adequate sulfur supplies and sufficient time to redistribute the arsenic into pyrite during diagenesis

the interannual variability of the surface eddy kinetic energy in the labrador sea abstract the variability of the surface eddy kinetic energy eke in the labrador sea is investigated with a suite of numerical integrations using a regional ocean model simulations are performed over the period 1980 2001 and are compared to satellite observations over the last 9 years the surface eke pattern in the basin is dominated by a region along the west coast of greenland where eddies mainly anticyclonic are formed by instability of the main currents flowing over the continental slope consistent with previous idealized results here the interannual changes are linked to the shear of the incoming boundary current system imposed as boundary condition to the model domain the highly variable strength of the east greenland current at the northeast boundary derived from the simple ocean data assimilation soda reanalysis strongly influences the vortex formation in the center of the labrador sea where deep convection occurs a statistically significant portion of the modeled interannual surface eke variability is correlated with the local atmospheric forcing and both heat and wind fluxes play an important role and can be adopted as predictors at a lag of 2 3 months the arctic oscillation index can also be used as a remote indicator of the atmospheric fluxes but with lower skill than local measurements in contrast the north atlantic oscillation index does not correlate significantly with the surface eke at intraseasonal and interannual scales the analysis of altimeter data over the 1993 2001 supports the existence of this asymmetry between the regime locally forced by the atmosphere in the central basin and the regime remotely forced by the incoming boundary current along the west greenland coast those results have important implications for monitoring and predicting the surface eddy kinetic energy variability in the labrador sea

deep ocean warming assessed from altimeters gravity recovery and climate experiment in situ measurements and a non boussinesq ocean general circulation model 1 observational surveys have shown significant oceanic bottom water warming but they are too spatially and temporally sporadic to quantify the deep ocean contribution to the present day sea level rise slr in this study altimetry sea surface height ssh gravity recovery and climate experiment grace ocean mass and in situ upper ocean 0 700 m steric height have been assessed for their seasonal variability and trend maps it is shown that neither the global mean nor the regional trends of altimetry slr can be explained by the upper ocean steric height plus the grace ocean mass a non boussinesq ocean general circulation model ogcm allowing the sea level to rise as a direct response to the heat added into the ocean is then used to diagnose the deep ocean steric height constrained by sea surface temperature data and the top of atmosphere toa radiation measurements the model reproduces the observed upper ocean heat content well combining the modeled deep ocean steric height with observational upper ocean data gives the full depth steric height adding a grace estimated mass trend the data model combination explains not only the altimetry global mean slr but also its regional trends fairly well the deep ocean warming is mostly prevalent in the atlantic and indian oceans and along the antarctic circumpolar current suggesting a strong relation to the oceanic circulation and dynamics its comparison with available bottom water measurements shows reasonably good agreement indicating that deep ocean warming below 700 m might have contributed 1 1 mm yr to the global mean slr or one third of the altimeter observed rate of 3 11 0 6 mm yr over 1993 2008

diachronous evolution of sea surface conditions in the labrador sea and baffin bay since the last deglaciation assessing changes in sea surface conditions due to the effects of past freshwater outflow through baffin bay and davis strait to the labrador sea hereafter referred to as the baffin bay corridor

modelling hydrographic changes in the labrador sea over the past five decades abstract inter annual to inter decadal changes of hydrographic structure and circulation in the subpolar north atlantic are studied using a coarse resolution ocean circulation model the study covers 1949 through 2001 inclusive a time mean state nudging method is applied to assimilate the observed hydrographic climatology into the model the method significantly reduces model biases in the long term mean distribution of temperature and salinity which commonly exist in coarse resolution ocean models by reducing the time mean biases we also significantly improve the model s representation of inter annual to inter decadal variations in the central labrador sea the model broadly reproduces the heat and salt variations of the labrador sea water lsw as revealed by hydrographic observations model sensitivity experiments confirm that the low frequency hydrographic changes in the central labrador sea are closely related to changes in the intensity and depth of deep convection changes in surface heat flux associated with the winter north atlantic oscillation nao index play a major role in driving the changes in t s and sea surface height ssh changes in wind stress play a secondary role in driving these changes but are important in driving the changes in the depth integrated circulation the total changes in both ssh and depth integrated circulation are almost a linear combination of the separate influences of variable buoyancy and momentum fluxes

tracking labrador sea water property signals along the deep western boundary current observations of the deep western boundary current dwbc at line w on the western north atlantic continental slope southeast of cape cod from 1995 to 2014 reveal water mass changes that are consistent with changes in source water properties upstream in the labrador sea this is most evident in the cold dense and deep class of labrador sea water dlsw that was created and progressively replenished and deepened by recurring winter convection during the severe winters of 1987 1994 the arrival of this record cold fresh and low potential vorticity anomaly at line w lags its formation in the labrador sea by 3 7 years complementary observations along the path of the dwbc provide further evidence that this anomaly is advected along the boundary and indicate that stirring between the boundary and the interior intensifies south of the flemish cap finally the consistency of the data with realistic advective and mixing time scales is assessed using the waugh and hall 2005 model framework the data are found to be best represented by a mean transit time of 5 years from the labrador sea to line w with a leading order role for both advection by the dwbc and mixing between the boundary flow and interior waters

rapid freshening of the deep north atlantic ocean over the past four decades the overflow and descent of cold dense water from the sills of the denmark strait and the faroe shetland channel into the north atlantic ocean is the principal means of ventilating the deep oceans and is therefore a key element of the global thermohaline circulation most computer simulations of the ocean system in a climate with increasing atmospheric greenhouse gas concentrations predict a weakening thermohaline circulation in the north atlantic as the subpolar seas become fresher and warmer1 2 3 and it is assumed that this signal will be transferred to the deep ocean by the two overflows from observations it has not been possible to detect whether the ocean s overturning circulation is changing but recent evidence suggests that the transport over the sills may be slackening4 here we show through the analysis of long hydrographic records that the system of overflow and entrainment that ventilates the deep atlantic has steadily changed over the past four decades we find that these changes have already led to sustained and widespread freshening of the deep ocean

diagenesis in pleistocene 80 to 500 ka corals from the ironshore formation implications for paleoclimate reconstruction abstract fossil corals provide a unique opportunity for paleoclimate research because they can be dated and they incorporate climate controlled seawater proxies into their aragonitic skeletons during growth coral skeletons however can only produce reliable environmental information if they have not been diagenetically altered an issue that becomes increasingly probable as the age of the corals increase although commonly used analytical techniques such as thin section scanning electron microscopy and x ray diffraction can highlight obvious mineralogical changes subtle changes in the trace element and isotopic composition of the skeletons may not be evident this premise is assessed by examining orbicella annularis and montastrea cavernosa corals from the pleistocene ironshore formation units a f on grand cayman 80 500 ka to determine the diagenetic effects on both physical and chemical properties of corals in the ironshore formation the corals in units a and c were altered in a semi open diagenetic system by seawater diluted by meteoric water which resulted in chemical diagenesis that changed the elemental and isotopic composition of the corals even though their aragonitic skeletons show no obvious signs of change in contrast the limestones in unit b have been pervasively recrystallized in an open diagenetic system by meteoric waters that caused both chemical and physical changes the corals in units d to f however underwent minimal diagenesis and show no evidence of alteration for altered corals from the ironshore formation elevated mg ca and low sr ca ratios provide evidence of subtle chemical diagenetic changes even in corals that have retained their primary aragonitic skeleton thus corals that are formed of 95 wt aragonite show no evidence of cementation and have mg ca ratios 8 0 mmol mol 1 18o values 5 7 and 13c values 3 0 are ideal candidates for paleoclimate reconstruction adoption of these criteria shows that the corals from units d to f can be used to calculate sea surface temperatures sst whereas those from units a to c cannot be used for this purpose the calculated sst and the corresponding temperature profiles derived from the corals in units d to f are consistent with global sst reconstructions during the pleistocene unit d corals record an overall increase in sst which is consistent with elevated temperatures associated with marine isotope stage mis 5e whereas units e and f record overall cooling which is consistent with the end of the peak interglacials of mis 5c and 5a respectively

a fossil coral perspective on western tropical pacific climate 350 ka 1 the nature of tropical climate variability 350 ka is addressed using 18o and sr ca records from a modern and a fossil coral from vanuatu southwestern tropical pacific ocean modern el nino events at vanuatu produce positive coral 18o and sr ca anomalies similar anomalies observed in the fossil coral records suggest that el nino was operative 350 kyr ago seasonal variations in coral sr ca a sea surface temperature sst proxy have the same amplitude in both corals whereas seasonal 18o variations are smaller in the fossil coral than in the modern coral this is consistent with displacement of the south pacific convergence zone toward the southwest during the boreal summer 350 ka mathematical modeling results preclude warmer sst and higher sss at vanuatu during this time but permit the surface ocean to be 2 c cooler and 0 2 psu fresher than today assessing the potential of variations in late quaternary seawater sr ca remains the largest obstacle to accurately reconstructing tropical sst using pristine fossil corals

long term coordinated changes in the convective activity of the north atlantic the north atlantic is a peculiarly convective ocean the convective renewal of intermediate and deep waters in the labrador sea and greenland iceland sea both contribute significantly to the production and export of north atlantic deep water thus helping to drive the global thermohaline circulation while the formation and spreading of 18 degree water at shallow to intermediate depths off the us eastern seaboard is a major element in the circulation and hydrographic character of the west atlantic for as long as time series of adequate precision have been available to us it has been apparent that the intensity of convection at each of these sites and the hydrographic character of their products have been subject to major interannual change as shown by aagaard 1968 clarke et al 1990 and meincke et al 1992 for the greenland sea in the ows bravo record from the labrador sea eg lazier 1980 et seq and at the panulirus hydrostation s site in the northern sargasso off bermuda eg jenkins 1982 talley and raymer 1982 this paper reviews the recent history of these changes showing that the major convective centres of the greenland and labrador seas are currently at opposite convective extrema in our postwar record with vertical exchange at the former site limited to 1000 m or so but with labrador sea convection reaching deeper than previously observed to over 2300 m as a result greenland sea deep water has become progressively warmer and more saline since the early 70 s due to increased horizontal exchange with the arctic ocean through fram strait while the labrador sea water has become progressively colder and fresher over the same period through increased vertical exchange most recently convection has become deep enough there to reach into the more saline nadw which underlies it so that cooler but now saltier and denser lsw has resulted

diagenesis of mollusc aragonite and the role of fluid reservoirs abstract biogenic carbonate minerals are widely used as archives in paleoenvironmental research providing substantial information for past depositional and diagenetic regimes however nearly all biogenic carbonates undergo post mortem diagenetic alteration to variable degrees diagenetic features are essentially caused by complex fluid solid interaction including recrystallization and neomorphosis of shell architecture and related geochemical resetting a common conception is that a given primary shell texture is replaced by a secondary fabric via micro scale dissolution reprecipitation reactions that may reach geochemical and or isotopic equilibrium with the diagenetic fluid here we document that the process of petrographic and geochemical alteration of a biogenic carbonate archive progresses stepwise and the re equilibration processes can be separated in space and time more specifically attached and bound aqueous fluids within the shell organic matter and fluid inclusions likely play a crucial role in the early stages of alteration within a relatively rock buffered system degradation of organics was observed via decreased sulfur concentration and decreased fluorescence in this early stage of alteration the conversion of micro scale aragonite biominerals to metastable diagenetic calcite meso crystals is documented by raman spectroscopy electron backscatter diffraction ebsd and a decrease in strontium concentrations further stabilization to larger neomorphosed calcite crystals resulted from re equilibration with external fluids and was evidenced by ebsd oxygen isotope data and further reduction of strontium spatial chemical and isotope data were used to decipher the impact of fluid availability and transfer behavior i e carbonate buffered versus diagenetic fluid buffered and isotope and element exchange behavior and analyzed in context to textural alteration features these data suggest that during diagenesis the evolution to more sustainable diagenetically induced fabrics is accompanied by individual reaction steps traced by elemental and isotopic signatures kinetics and thus degree of diagenetic alteration of biominerals at a given exposure to physicochemical alteration conditions is initially strongly controlled by the micro to nano scale internal architecture governing the availability and transfer of aqueous fluids results shown here have significance for those concerned with biogenic carbonate archives and have wider implications for a mechanistic understanding of carbonate diagenesis

distribution of arsenic iii arsenic v and total inorganic arsenic in porewaters from a thick till and clay rich aquitard sequence saskatchewan canada abstract inorganic arsenic species were measured in the porewaters collected from eighteen piezometers installed between 3 and 91 4 m below ground in a thick till and clay rich aquitard sequence located in southern saskatchewan to investigate the distribution of and controls on arsenic speciation in the sequence aqueous concentrations of as v as iii and total as are in the range of 0 31 97 0 71 21 and 3 2 98 ppb respectively profiles of as iii and as v concentration distribution with depth broadly track that of total as erratic increases to 15 2 m then more uniform concentrations to 88 m aqueous arsenic is accumulated at the upper redox transition zone 6 14 m the alkaline porewater at 91 4 m contains the highest concentrations of as v and total as which might result from the facilitated desorption of arsenate from the host solid due to decrease of positive surface charge of the oxides in alkaline solution the ratio of as v as iii is greater than unity in the uppermost oxidized porewater 3 m less than unity from 4 6 to 71 6 m and greater than unity in the lowest four porewaters 76 2 to 91 4 m in the 3 m porewater low as iii but high as v as iii is due to the oxidized nature of the near surface weathered till the high as v as iii in the deepest porewater at 91 4 m likely results from the enhanced and heterogeneous oxidation of as iii to as v on clay mineral surfaces in the alkaline solution total as and arsenic speciation may not be controlled by as fe or mn concentrations in the host till or clay dissolved as v and total as positively covary with aqueous chloride whereas dissolved as iii is independent of aqueous chloride aqueous as iii and to a less extent as v and total as are positively correlated with dissolved mn in the till in the clay aqueous as v and total as show strong negative covariation with mn however aqueous as iii as v and total as exhibit almost no correlation with total dissolved fe in the till the as v as iii ratio has strong negative correlation with dissolved mn but positive covaration with dissolved chloride generally good agreement between the redox potentials eh calculated from aqueous as v and as iii concentrations and those measured by a pt electrode throughout most of the unoxidized till suggests the suitability of using as v as iii redox couple as a redox indicator for the studied aquitard system however large negative bias of the calculated eh from the measured eh in the oxidized till upper unoxidized till and the clay is attributed to errors associated with the field measurements of eh

trace element behavior and redox facies in core shales of upper pennsylvanian kansas type cyclothems the black shale submember of core shales of pennsylvanian kansas type cyclothems is highly enriched in redox sensitive trace elements tes relative to the overlying gray shale submember as well as to many other modern and ancient organic rich deposits controls on trace element behavior in the black shale can be inferred from trace element enrichment factors efs relative to gray shale and the relationship of tes to total organic carbon toc most tes conformed to one of two patterns 1 mo u v zn and pb exhibited moderate efs and strong covariation with toc in samples having 10 wt toc and 2 cu ni cr and co exhibited low efs and moderate to strong covariation with toc in all samples these patterns are inferred to represent different responses to benthic redox conditions the first pattern is characteristic of tes of strong euxinic affinity i e those taken up in solid solution by fe sulfide or involved in other reactions catalyzed by free h2s and resident mainly in authigenic phases whereas the second pattern is characteristic of tes of weak euxinic affinity i e those not strongly influenced by the presence of free h2s and resident mainly in the organic carbon or detrital fractions of the sediment these inferences allowed development of a multiproxy technique for assessing redox facies in black shale samples euxinic conditions were considered to have existed if at least two of four redox indicator trace elements mo u v zn showed euxinic levels of enrichment and nonsulfidic anoxic conditions were inferred otherwise the validity of the procedure is indicated by 1 agreement among all four redox indicators for a large majority of samples 69 of 185 2 among samples yielding a mixed redox signal a systematic sequence of te enrichment v zn mo u and 3 for tes of weak euxinic affinity reduced variance among samples representing each redox facies sequential enrichment may be a response to differential redox thresholds for accumulation e g v or postdepositional remobilization of trace elements e g u and may provide a basis for finer assessment of redox conditions in low oxygen paleoenvironments than permitted by simple classification schemes the multiproxy procedure for redox facies analysis developed in this study is likely to be more reliable than widely used single proxy indicators based on trace elements e g mo authigenic u or v v ni or c s fe systematics e g s toc or dop d 2004 elsevier b v all rights reserved

importance of density compensated temperature change for deep north atlantic ocean heat uptake the efficiency with which the oceans take up heat has a significant influence on the rate of global warming an analysis of observations of heat uptake into the deep north atlantic shows that the propagation of density compensated temperature anomalies is an important mechanism for this heat uptake and depends on high salinity in the subpolar gyre

diagenetic effects on uranium isotope fractionation in carbonate sediments from the bahamas abstract uranium isotope variations 238u recorded in sedimentary carbonate rocks are a promising new proxy for the extent of oceanic anoxia through geological time however the effects of diagenetic alteration on the u isotopic composition in carbonate sediments which are crucial to understand the accurate reconstruction of marine 238u are currently poorly constrained here we examine the effects of the aragonite to calcite transition in the pleistocene key largo limestone of south florida and assess the effects of vadose meteoric phreatic meteoric and phreatic marine diagenesis on u isotope fractionation in carbonate sediments from the bahamas transect including the well studied clino unda and odp site 1006 drill cores our results suggest that early diagenetic processes in bahamas carbonate sediments fractionate u isotopes by an average of 0 27 0 14 1 sd heavier than contemporaneous seawater downcore variations of 238u in slope and basin sediments display little if any correlation with u concentration and common geochemical indicators of diagenesis 13c 18o mn sr mg ca sr ca enrichments of redox sensitive elements or rare earth elements anomalies we propose two possible mechanisms to interpret the positive change in the 238u during carbonate diagenesis authigenic enrichment of isotopically positive u iv in carbonates and preferential incorporation of isotopically positive aqueous u vi species into carbonates these processes likely operate during early syndepositional diagenesis on the banktop further diagenesis during deeper burial is limited by the low solubility of u iv under reducing pore water conditions the early diagenetic behavior of u isotopes in bahamas carbonate sediments is likely broadly representative of carbonate diagenesis in the geological past we suggest that the mean diagenetic offset determined in this study be applied when reconstructing seawater 238u from ancient carbonates furthermore early diagenesis induces significant statistical variability in sediment 238u values pointing to the need for large high resolution data sets in order to average out stochastic variations in individual bulk sediment samples

micro sized dolomite inclusions in ferroan calcite cements developed during burial diagenesis of kimmeridgian reefs northern iberian basin spain burial diagenesis of the upper jurassic torrecilla reef complex is recorded by a complex paragenetic sequence initiated with emplacement of ferroan calcite cements and followed by the precipitation of ferroan saddle dolomite ferroan calcite cements contain micro sized dolomite inclusions mdis elemental and isotopic compositions of mdis are virtually indistinguishable from those of ferroan saddle dolomite cements in contrast to other scenarios for the formation of microdolomite inclusions that invoke either a magnesian calcite precursor or incomplete dedolomitization the paragenetic relations of mdis to their host ferroan calcite and their geochemical composition implies formation by fine scale burial replacement of ferroan calcite by fluids associated with the emplacement of ferroan saddle dolomite petrographic observations and mass balance considerations suggest that it is unlikely that fe and mg incorporated into ferroan dolomite could have been derived from the cannibalization of the reefal host rock rather dolomitizing fluids were likely associated with the hydrothermal low grade metamorphic event that affected the cameros basin during the middle to late cretaceous interaction of these fluids with preexisting burial cements produced mdis in the ferroan calcites

stable isotope variations in the neoproterozoic beck spring dolomite and mesoproterozoic mescal limestone paleokarst implications for life on land in the precambrian proterozoic karst events lowered 13c values by as much as 11 for the 800 ma beck spring dolomite california and as much as 8 5 for the 1 1 ga mescal limestone central arizona relative to the originally deposited carbonate the 13c changes are attributed to input of 13c depleted organic co2 derived from photosynthetic organisms that colonized the ancient land surface the large isotopic shift and its presence at two separate localities suggest that proterozoic karst surfaces were colonized by significant photosynthetic communities with phytomasses possibly approaching those of today

skeletal aragonite neomorphism in plio pleistocene sandy limestones and sandstones hollywood florida usa abstract the basic mechanics of the neomorphism of aragonitic shells to calcite are generally understood but fundamental questions remain concerning the details of the process completely and partially neomorphosed aragonitic skeletal fragments recovered in cores of plio pleistocene limestones and sandstones from hollywood florida provide some insights into the process skeletal aragonite neomorphism occurred in a volume for volume manner across solution films which resulted in the preservation of ghosts of fine scale microstructures neomorphic calcite crystals that replaced skeletal aragonite in at least some instances inherited their crystallographic orientation from adjoining calcite cement crystals rather than from the host shell microstructure some neomorphic calcite crystals inherited the optical orientation of nearby echinoderm ossicles however host shell microstructure commonly controlled the direction of migration of the neomorphic replacement front anisotropies in shell solubility influenced the directional rates of growth of neomorphic calcite crystals as evidenced by the strong tendency for the boundaries between neomorphic calcite and aragonite to parallel or coinicide with shell microstructural features no examples were observed where neomorphic calcite replaced aragonite along euhedral crystal faces such as commonly occurs during dolomitization and the replacement of limestone by megaquartz

variability in early vadose carbonate diagenesis in sandstones abstract early carbonate diagenesis in calcareous and siliciclastic sandstones in the vadose environment is reviewed and shown to be more extensive than generally recognized and more importantly highly variable in character both spatially and temporally spatial variability is classed into three hierarchical scales macro regional meso sediment body and micro individual and groups of pores dependent and independent variables relating to the diagenesis are shown to vary according to scale at the macro scale the independent variables are tectonic activity climate sea level and lithofacies at the meso scale they include location of the sediment body relative to the watertable and sea level and exposure to sea spray plant cover water balance relationships texture and allochem content micro scale independent variables are the chemistry amounts and mobility of the pore waters and individual particle microstructures and mineralogies dependent variables at one scale are shown to exist as independent variables at the next more detailed scale the infinitely complex combinations of variables operating over different time scales explain the observed and characteristic variability in diagenetic processes and products within the vadose zone

shell beaches to beachrock diagenetic stable isotopic trends abstract modern shell accumulations on padre island texas gulf coast are composed of pristine aragonite whereas laterally adjacent pleistocene beachrock on the mainland shores of laguna madre are made up of the same taxa but display a range of mixtures of aragonite and diagenetic low mg calcite cements and pedogenic crusts associated with the beachrock are 100 low mg calcite stable isotopic values for shells composed of 0 15 20 45 75 and 90 calcite display high correlations between the 18o values and mineralogy r2 0 95 and 13c values and mineralogy r2 0 87 the highly correlated changes in the stable isotopic compositions and mineralogy of the skeletal material are also evident in the data from the analyses of the pure calcite cements and pedogenic crusts changes in stable isotopic composition of the shells are the result of the early diagenetic alteration of the original aragonitic composition to low mg calcite

spreading of the labrador sea water to the irminger and iceland basins 1 labrador sea water lsw is a principal convectively formed water mass of the subpolar north atlantic spna using extensive oceanographic archives we demonstrate striking changes in spna caused by massive lsw production during 1987 1994 and document recent salinification and warming imminently bringing spna to the state last time seen in the 1960s two prominent lsw classes are spreading across spna since the 1980s the first record dense deep and voluminous class has been progressively built by intense winter convection through 1987 1994 even though most of this lsw has left spna its remnants are still present there the second shallower class strengthens in 2000 over subsequent years its core becomes slightly thicker and deepens the anomalous signals acquired by these lsw classes in their formation region arrive in the irminger and iceland basins with the characteristic delays of two and five years for deeper lsw and a year and four years for shallower lsw

the subpolar mode water of the north atlantic ocean abstract the warm waters of the subtropical and subpolar basins of the north atlantic have tight regional temperature salinity relationships and are conventionally called the regional central waters a volumetric census of the temperature salinity characteristics of the north atlantic by wright and worthington 1970 shows that waters characterized by certain segments of the t s relationships have large volumes compared to those of other segments volumetric mode waters such mode waters appear as layers with increased vertical separation between isopycnals pycnostads the present study reports on the existence of pycnostads in the central and eastern north atlantic these subpolar mode waters are formed by deep winter convection in the subpolar north atlantic and participate in the upper water circulation of the northern north atlantic the seasonal outcropping of the pycnostads occurs within and adjacent to the north atlantic current the irminger current the east and west greenland currents and

the regime shift of the 1920s and 1930s in the north atlantic abstract during the 1920s and 1930s there was a dramatic warming of the northern north atlantic ocean warmer than normal sea temperatures reduced sea ice conditions and enhanced atlantic inflow in northern regions continued through to the 1950s and 1960s with the timing of the decline to colder temperatures varying with location ecosystem changes associated with the warm period included a general northward movement of fish boreal species of fish such as cod haddock and herring expanded farther north while colder water species such as capelin and polar cod retreated northward the maximum recorded movement involved cod which spread approximately 1200 km northward along west greenland migration patterns of warmer water species also changed with earlier arrivals and later departures new spawning sites were observed farther north for several species or stocks while for others the relative contribution from northern spawning sites increased some southern species of fish that were unknown in northern areas prior to the warming event became occasional and in some cases frequent visitors higher recruitment and growth led to increased biomass of important commercial species such as cod and herring in many regions of the northern north atlantic benthos associated with atlantic waters spread northward off western svalbard and eastward into the eastern barents sea based on increased phytoplankton and zooplankton production in several areas it is argued that bottom up processes were the primary cause of these changes the warming in the 1920s and 1930s is considered to constitute the most significant regime shift experienced in the north atlantic in the 20th century

hydrographic changes in the labrador sea 1960 2005 abstract the labrador sea has exhibited significant temperature and salinity variations over the past five decades the whole basin was extremely warm and salty between the mid 1960s and early 1970s and fresh and cold between the late 1980s and mid 1990s the full column salinity change observed between these periods is equivalent to mixing a 6 m thick freshwater layer into the water column of the early 1970s the freshening and cooling trends reversed in 1994 starting a new phase of heat and salt accumulation in the labrador sea sustained throughout the subsequent years it took only a decade for the whole water column to lose most of its excessive freshwater reinstate stratification and accumulate enough salt and heat to approach its record high salt and heat contents observed between the late 1960s and the early 1970s if the recent tendencies persist the basin s storages of salt and heat will fairly soon likely by 2008 exceed their historic highs the main process responsible for the net cooling and freshening of the labrador sea between 1987 and 1994 was deep winter convection which during this period progressively developed to its record depths it was caused by the recurrence of severe winters during these years and in its turn produced the deepest densest and most voluminous labrador sea water lsw1987 1994 ever observed the estimated annual production of this water during the period of 1987 1994 is equivalent to the average volume flux of about 4 5 sv with some individual annual rates exceeding 7 0 sv once winter convection had lost its strength in the winter of 1994 1995 the deep lsw1987 1994 layer lost communication with the mixed layer above consequently losing its volume while gaining heat and salt from the intermediate waters outside the labrador sea while the 1000 2000 m layer was steadily becoming warmer and saltier between 1994 and 2005 the upper 1000 m layer experienced another episode of cooling caused by an abrupt increase in the air sea heat fluxes in the winter of 1999 2000 this change in the atmospheric forcing resulted in fairly intense convective mixing sufficient to produce a new prominent lsw class lsw2000 penetrating deeper than 1300 m this layer was steadily sinking or deepening over the years following its production and is presently overlain by even warmer and apparently less dense water mass implying that lsw2000 is likely to follow the fate of its deeper precursor lsw1987 1994 the increasing stratification of the intermediate layer implies intensification in the baroclinic component of the boundary currents around the mid depth perimeter of the labrador sea the near bottom waters originating from the denmark strait overflow exhibit strong interannual variability featuring distinct short term basin scale events or pulses of anomalously cold and fresh water separated by warm and salty overflow modifications regardless of their sign these anomalies pass through the abyss of the labrador sea first appearing at the greenland side and then about a year later at the labrador side and in the central labrador basin the northeast atlantic deep water 2500 3200 m originating from the iceland scotland overflow water reached its historically freshest state in the 2000 2001 period and has been steadily becoming saltier since then it is argued that lsw1987 1994 significantly contributed to the freshening density decrease and volume loss experienced by this water mass between the late 1960s and the mid 1990s via the increased entrainment of freshening lsw the hydrostatic adjustment to expanding lsw or both

ocean gyre circulation changes associated with the north atlantic oscillation abstract observational evidence is presented for interannual to interdecadal variability in the intensity of the north atlantic gyre circulation related to the atmospheric north atlantic oscillation nao patterns a two point baroclinic pressure difference between the subtropical and subpolar gyre centers an oceanic analogue to the much used sea level pressure slp based atmospheric nao indices is constructed from time series of potential energy anomaly pea derived from hydrographic measurements in the labrador basin and at station s near bermuda representing the upper 2000 db eastward baroclinic mass transport between the two centers the transport index indicates a gulf stream and north atlantic current that gradually weakened during the low nao period of the 1960s and then intensified in the subsequent 25 years of persistently high nao to a record peak in the 1990s the peak to peak amplitude difference was 15 20 megatons per second mt s 1 with a 43 yr mean of about 60 mt s 1 a change of 25 33

interannual variability of the northwestern iberia deep ocean response to large scale north atlantic forcing the oceanic hydrography of the north easternmost region of the north atlantic subtropical gyre has been monitored since 2003 by three sections extending between 100 and 200 nautical miles from the spanish nw and n coast into the atlantic and the bay of biscay the sections were occupied twice a year from 2003 to 2010 annually after that and measure the whole water column 5000 m correlation of series in the vertical and among sections autocorrelation and estimates of the effect of the noise induced by the mesoscale field all indicate that observed signatures are robust changes of water masses at the regional scale the hydrographic time series are not characterized by smooth trends but instead by shifts that persist through consecutive cruises the most notable features include a shift to more saline central waters around 2005 after which they remained stable and a decrease in thermohaline properties of the labrador sea water from autumn 2008 to 2010 years with a strong winter north atlantic oscillation nao index are characterized by shifts in thermohaline properties across most of the intermediate levels with the most notable event being the warming and increasing salinity that followed the large nao index drop of 2010 the observations are consistent with current understanding of the large scale functioning of the north atlantic which predicts a northeastward expansion of subtropical temperate waters in the eastern boundary as a response to nao forcing the observed variability is discussed in relationship to large scale circulation

dating and characterization of polymorphic transformation of aragonite to calcite in pleistocene bivalves from rhodes greece by combined shell microstructure stable isotope and electron spin resonance study absolute dating of diagenesis is a challenging yet significant problem reconstructing the depositional and diagenetic history of a late pleistocene coralligene type red algal reef and overlying maerl red algal sand from the plimiri coastal cliff se island of rhodes greece is enabled using a combination of microstructure stable isotope analyses and electron spin resonance of large bivalve shells partially altered by diagenesis these shells consisting of both original shell aragonite and polymorphic transformed rims now consisting of neomorphic spar provide the opportunity to date the primary age when the shells were precipitated as well as the age of their polymorphic transformation the contamination of samples presented a significant problem for interpreting ages based on data from electron spin resonance esr alone however sample contamination was evaluated with quantitative xrd providing the opportunity to apply corrections which increased reliability of the ages the carbon and oxygen stable isotope values and the neomorphic spar microtexture suggested that the polymorphic transformation at plimiri took place in a meteoric environment with a high and increasing fluid rock ratio the electron spin resonance dates combined with the vertical sedimentary evolution allowed to assign the formation of the red algal reef to the marine isotope stages 6 to 5e transgressive event ca 135 to 120 ka and to identify meteoric diagenetic phases during possibly the marine isotope stage 5d and the upper marine isotope stage 5c to lower 3 the use of electron spin resonance dating of neomorphic spar and age correction for sample contamination is presented herein for the first time and the results suggest that it might provide a useful tool to date late pleistocene diagenesis

estimation of se vi se iv ratio in water by the ratio recorded in barite 1 it is possible that the distribution behaviors of redox sensitive elements such as selenium se between authigenic minerals and water can provide information on the oxidation state of the element in the coexistent water during mineral deposition considering the similar chemical characteristics of se iv and se vi oxyanions we propose that the se vi se iv ratio in a particular precipitate such as barite may enable us to estimate the se vi se iv ratio in the coexistent water the coprecipitation experiments of se with barite coupled with the determination of the oxidation state of se both in the aqueous phase and in barite were conducted by se k edge x ray absorption near edge structure and high performance liquid chromatography connected to inductively coupled plasma mass spectrometry respectively to investigate the influence of the oxidation state of se on its immobilization into barite at ph 4 0 and 8 0 the results showed that the se vi se iv ratio in barite was correlated with the se vi se iv ratio in water which in turn can provide physicochemical and biogeochemical information related to the se vi se iv ratio in water in the environment where barite precipitated

skeletal aragonite neomorphism quantitative modelling of a two water diagenetic system abstract the neomorphism of skeletal aragonite occurs by the simultaneous dissolution of aragonite and precipitation of calcite along thin solution films which may have an associated zone of partly dissolved aragonite chalky zone it has been proposed that pore waters at neomorphic calcite aragonite contact zones neomorphic fronts may be partly isolated from bulk pore waters and thus retain primary geochemical signatures to varying degrees iterative computer programs were developed that simulate aragonite neomorphism in two water diagenetic systems using stable isotope and trace element data neomorphism of aragonitic mollusks from the purbeck group of southern england late jurassic to early cretaceous was associated with a decrease in strontium concentration from approximately 5100 ppm to 500 ppm modelling results indicate a high bulk water rock ratio and minimal if any isolation of the neomorphic front waters for the purbeck group mollusks and also for some pleistocene corals partial isolation of neomorphic front waters from bulk pore waters is uncommon based on published data on the geochemistry of neomorphic calcites however partial isolation does occur in some thick low porosity shells such as the gastropod strombus gigas pleistocene process based modelling of fluid rock interaction provides a means for better interpreting trace element and stable isotope data in diagenetic carbonates sensitivity analysis results indicate that water rock ratios cannot be determined at much better than order of magnitude accuracies because of uncertainties over initial pore water composition fractionation factors and distribution coefficients

labrador sea water property variations in the northeastern atlantic ocean 1 labrador sea water lsw property variations are analyzed using data from four hydrographic sections occupied along 20 w from iceland south toward the equator in 1988 1993 1998 and 2003 lsw between the azores biscay rise and the rockall plateau steadily becomes deeper colder fresher denser and thicker over the 15 year time series lsw apparent oxygen utilization aou remains unchanged during this time period the changes analyzed are consistent with previously published spreading rates of 8 years for lsw from the labrador sea to 20 w and emphasize the long reach of decadal lsw variability