evidence from svalbard for near freezing temperatures and climate oscillations in the arctic during the paleocene and eocene until recently the arctic was assumed to be characterised by relatively warm conditions throughout the early cenozoic however recent investigations on deep sea drilling cores from northern high latitudes including the arctic ocean give apparently contradicting results here we report the intermittent occurrence of certain temperature indicators in the early tertiary sedimentary sequence on svalbard which may represent the first direct northern high latitude record of cold water temperatures for the early cenozoic glendonites calcite pseudomorphs after calcium carbonate hexahydrate and erratics in otherwise fine grained sediments require near freezing temperatures and the presence of at least seasonal sea ice this succession also contains coal seams and other warm climate indicators but not on the same stratigraphical levels these results imply the occurrence of cooling phases episodically during the warm background climate of the paleocene and eocene suggesting that arctic temperature variability was much greater than previously recognized

ikaite precipitation in a lacustrine environment implications for palaeoclimatic studies using carbonates from laguna potrok aike patagonia argentina abstract the monoclinic mineral ikaite caco 3 6h 2 o and its pseudomorphs are potentially important archives for palaeoenvironmental reconstructions natural ikaite occurs in a small temperature range near freezing point and is reported mainly from marine and only rarely from continental aquatic environments ikaite transforms to more stable anhydrous forms of caco 3 after an increase in temperature or when exposed to atmospheric conditions the knowledge about conditions for natural ikaite formation its stable isotope fractionation factors and isotopic changes during transformation to calcite is very restricted here for the first time primary precipitation of idiomorphic ikaite and its calcite pseudomorphs are reported from a subsaline lake laguna potrok aike in southern argentina the calculated stable oxygen isotope fractionation factor between lake water and ikaite derived calcite pai 1 0324 at a temperature of 4 1 c is close to but differs from that of primarily inorganically precipitated calcite pseudomorphs after ikaite rapidly disintegrate into calcite powder that is indistinguishable from m sized calcite crystals in the sediment record of laguna potrok aike suggesting an ikaite origin of sedimentary calcites therefore the holocene carbonates of laguna potrok aike have the potential to serve as a recorder of past hydrological variation

glendonites and methane derived mg calcites in the sea of okhotsk eastern siberia implications of a venting related ikaite glendonite formation mg calcite cemented bioturbation traces glendonite aggregates of idiomorphic bi pyramidal crystals and porous amber colored carbonate concretions were recovered from a methane dominated cold vent area in 380 m water depth at the northern sakhalin slope sea of okhotsk bioturbation traces consist of mg calcite cemented sediment with 13c values between 37 and 46 peedee belemnite pdb which implicate methane as the carbon source glendonite a calcite pseudomorphosis after ikaite caco3 6h2o and amber colored concretions are both composed of varying amounts of calcite and mg calcite with 13c values between 19 and 34 pdb isotope analyses of an ikaite crystal recovered in the vicinity reveals 13c values between 20 and 22 pdb indicating organic matter as the carbon source microscopic investigations of glendonites and amber colored concretions show a porous fabric of a primary calcite phase that is overgrown by a secondary mg calcite cement as ikaite pseudomorphs to porous calcite and as carbon isotope values are the same for the ikaite and the high end member values of glendonite samples the primary calcite phase is suggested to be a former ikaite phase because they share the equal color fabric mineral and isotopic composition with glendonites the amber colored concretions are also suggested to represent calcite that transformed from ikaite a mixture of pseudomorph calcite 13c 20 pdb which originally formed as ikaite from degraded organic matter and mg calcite 13c 43 pdb which crystallized due to the anaerobic oxidation of methane can explain the varying carbon isotope data of the glendonites and the amber colored concretions the growth of ikaite the transformation of ikaite to calcite and the crystallization of mg calcite indicate changing geochemical conditions within a cold vent environment at different times ideal conditions for the ikaite formation are given during the establishment of a cold vent site when upward migrating methane rich fluids enhance the anaerobe decomposition of organic matter which again increases the phosphate and alkalinity concentrations near the sediment surface lower rates of organic matter decomposition during on going venting decrease these high phosphate but also sulphate concentrations and allows other carbonate phases as mg calcite to form this additional carbonate precipitation and the ikaite formation itself lower the high alkalinity and destabilize ikaite which pseudomorphs to porous calcite triggered by the further upward shifting so4 h2s boundary and increasing methane oxidation rates the typical cold vent methane derived carbonate genesis takes place which cements the sediment pore space and induces the secondary mg calcite crystallization within the glendonite fabric taking this scenario into account ikaite formation should be a common process in the beginning of methane dominated vent activity at cold bottom water temperatures glendonite pseudomorphs can be assumed to represent a typical manifestation at fossil and recent cold vents at high latitudes

the salinity temperature and δ18o of the glacial deep ocean we use pore fluid measurements of the chloride concentration and the oxygen isotopic composition from ocean drilling program cores to reconstruct salinity and temperature of the deep ocean during the last glacial maximum lgm our data show that the temperatures of the deep pacific southern and atlantic oceans during the lgm were relatively homogeneous and within error of the freezing point of seawater at the ocean s surface our chloride data show that the glacial stratification was dominated by salinity variations in contrast with the modern ocean for which temperature plays a primary role during the lgm the southern ocean contained the saltiest water in the deep ocean this reversal of the modern salinity contrast between the north and south atlantic implies that the freshwater budget at the poles must have been quite different a strict conversion of mean salinity at the lgm to equivalent sea level change yields a value in excess of 140 meters however the storage of fresh water in ice shelves and or groundwater reserves implies that glacial salinity is a poor predictor of mean sea level

on using carbon and oxygen isotope data from glendonites as paleoenvironmental proxies a case study from the permian system of eastern australia abstract glendonites calcite pseudomorphs after ikaite caco3 6h2o feature prominently in fine grained glacially influenced permian marine strata of eastern australia which accumulated in a series of extensional basins that occupied polar to temperate latitudes along the southeastern margin of gondwana because ikaite formation in the marine environment requires near freezing temperatures high alkalinity and elevated concentrations of orthophosphate the presence of glendonites in ancient strata implies a particular array of paleoenvironmental conditions a petrographic and geochemical study was carried out to assess the veracity of isotopic data from glendonites as proxy indicators of ancient ocean chemistry sea floor temperature and diagenesis in thin section glendonites consist of inclusion zoned equant to bladed calcite crystals interpreted as the ikaite replacement phase enclosed in a matrix of calcite and minor chalcedony and pyrite cements carbon and oxygen isotope data show a negative covariance with 18o values ranging from 22 5 to 0 3 and 13c values from 27 7 to 4 5 v pdb of the calcite phases examined the ikaite replacement phase is the most enriched in 18o and most depleted in 13c enclosing cements possess lower 18o and higher 13c values and are interpreted to have formed during later stages of burial diagenesis the 18o values of the ikaite replacement phase do not correspond to formation with permian seawater at near freezing temperatures unless isotopic disequilibrium is assumed the 13c values are similar to the carbon isotope composition of bulk organic matter in the host sediment and suggest that the alkalinity and orthophosphate necessary for ikaite stability were generated in the zone of suboxic to anoxic diagenesis results indicate that although 18o and 13c values from glendonites are useful for understanding early to late diagenetic processes they are not ideal proxies for seawater chemistry and temperature

a review and synthesis of glendonites pseudomorphs after ikaite with new data assessing applicability as recorders of ancient coldwater conditions abstract calcite pseudomorphs after ikaite glendonite are associated with coldwater depositional systems including glaciomarine and deepwater settings as dictated by the limited stability field of ikaite ikaite precipitation is favored by elevated alkalinity and dissolved phosphate conditions encountered commonly in association with organic rich marine sediments where methane oxidation is occurring the rapid recrystallization of ikaite to calcite during slight warming or pressure release results in considerable solid volume loss producing a highly porous crystal mesh preservation of the original ikaite crystal form requires precipitation of diagenetic calcite cement during early burial to prevent compaction and collapse of pseudomorph structures during later burial diagenesis remaining pore space may be filled with deeper burial calcite cement glendonites from the permian of the sydney basin occur in subtidal shelf facies containing glacial dropstones and a normal marine fauna stable oxygen isotope signatures of modern ikaite suggest carbonate precipitation in equilibrium with ambient seawater carbon signatures are usually strongly negative relative to normal marine carbonate consistent with derivation of carbonate from methane oxidation review of published data suggests that while holocene glendonite may provide reliable isotopic records of the conditions of ikaite precipitation precipitation of later calcite cement within the glendonite structure reduces the significance of the isotopic signature as an indicator of primary depositional conditions bulk glendonite samples from the permian sydney basin australia have a broad range of 18 o and 13c 18opdb 5 to 15 13c 8 to 16 in contrast to the narrow range for brachiopod carbonate 18opdb 1 to 5 13c 5 to 7 from the same strata handpicked separates of primary glendonite and secondary calcite also have a wide range of stable isotope values the data from sydney basin glendonites indicate that diagenetic precipitation of calcite has blurred the isotopic signature of primary ikaite replacement calcite at the scale of micosampling done in this study

lateglacial and holocene climatic changes in south eastern patagonia inferred from carbonate isotope records of laguna potrok aike argentina abstract first results of strontium calcium carbon and oxygen isotope analyses of bulk carbonates from a 106 m long sediment record of laguna potrok aike located in southern patagonia are presented morphological and isotopic investigations of m sized carbonate crystals in the sediment reveal an endogenic origin for the entire holocene during this time period the calcium carbonate record of laguna potrok aike turned out to be most likely ikaite derived as ikaite precipitation in nature has only been observed in a narrow temperature window between 0 and 7 c the respective carbonate oxygen isotope ratios serve as a proxy of hydrological variations rather than of palaeotemperatures we suggest that oxygen isotope ratios are sensitive to changes of the lake water balance induced by intensity variations of the southern hemisphere westerlies and discuss the role of this wind belt as a driver for climate change in southern south america in combination with other proxy records the evolution of westerly wind intensities is reconstructed our data suggest that weak shw prevailed during the lateglacial and the early holocene interrupted by an interval with strengthened westerlies between 13 4 and 11 3 ka cal bp wind strength increased at 9 2 ka cal bp and significantly intensified until 7 0 ka cal bp subsequently the wind intensity diminished and stabilised to conditions similar to present day after a period of reduced evaporation during the little ice age strontium isotopes 87 sr 86 sr ratio were identified as a potential lake level indicator and point to a lowering from overflow conditions during the glacial 17 ka cal bp to lowest lake levels around 8 ka cal bp thereafter the strontium isotope curve resembles the lake level curve which is stepwise rising until the little ice age the variability of the ca isotope composition of the sediment reflects changes in the ca budget of the lake indicating higher degrees of ca utilisation during the period with lowest lake level

advances in marine chemistry 1979 1982 these four years saw advances in many areas further developments in sampling and analytical techniques have opened new avenues of exploration for trace elements and particulate matter the impact of the geosecs expedition was further felt in the field of marine chemistry as the results were still being published a major field effort occurred as a follow on to the geosecs work tto and intensive sampling was performed in the newly discovered submarine hydrothermal vent fields an important and unresolved controversy has arisen regarding the ability to measure preformed co2 in the seawater system in many respects the field of marine chemistry appears to be gaining a momentum spurred by both improvements in analytic techniques and an increasing social and economic relevance

controls on marine carbonate cement mineralogy review and reassessment abstract commonly cited models for controls on variations in carbonate mineralogy are only partly successful in accounting for natural mineralogical trends this limited success may result in part from a failure to recognize or address the ramifications of assumptions inherent to such models in general changes from calcite to aragonite or vice versa and variations in mgco3 incorporation in calcite are interpreted as resulting from 1 kinetic rather than thermodynamic effects 2 the effects of fluid chemistry rather than hydrologic biological or substrate effects 3 the effects of single parameters of fluid chemistry rather than the interactive or aggregate effects of several components and or 4 inorganic rather than organic parameters of fluid chemistry recent laboratory data suggest the necessity of a new approach to modeling controls on mineralogy these data indicate that no single fluid parameter is likely to be a sole or dominant control on carbonate mineralogy in natural environments in some cases thermodynamic stability differences may be as important as kinetic factors in determining mineralogy furthermore the effects of substrate hydrologic and biological factors and of organic compounds cannot be ruled out for most natural situations although at present reliable data are lacking to quantify the influence of these factors on mineralogy future models of controls on carbonate mineralogy need to consider the aggregate and interdependent effects of all of these factors

the removal rates of234th and228th from waters of the new york bight abstract the mean residence time of thorium with respect to non radioactive removal from water was determined as a function of location in three traverses of the new york bight using both 234 th 238 u and 228 th 228 ra correlates well with salinity increasing from about ten days near shore to 70 days at the shelf break it shows a much weaker correlation with suspended matter concentrations both because suspended matter varies in its scavenging efficiency and because salinity is a longer term integrator of scavenging potential s computed from 228 th 228 ra were often higher than those computed from 234 th 238 u either because of the detrital matter present as reflected in the 232 th concentrations or because the water parcels had recently arrived from environments of lower scavenging efficiency anomalous isotopic concentrations found in three adjacent samples can best be explained as the result of an episodic release of 228 ra from bottom sediments at a rate 200 times the normal one

modelled atmospheric temperatures and global sea levels over the past million years the climate has passed through a series of glacials and interglacials over the past million years but the nature of this cyclicity in terms of temperature ice volume and sea level and the underlying causes are not well known bintanja et al use a new method to deduce a one million year time series of these variables the reconstructed records are much longer than other methods have provided for any of these variables individually the most intense glacial stages were 17 c colder than today and most of the continental ice was present in north america strong cooling in the beginning of glacials was found to precede ice sheet build up these findings may shed light on the causes of ice age cycles marine records of sediment oxygen isotope compositions show that the earth s climate has gone through a succession of glacial and interglacial periods during the past million years but the interpretation of the oxygen isotope records is complicated because both isotope storage in ice sheets and deep water temperature affect the recorded isotopic composition1 2 3 4 5 separating these two effects would require long records of either sea level or deep ocean temperature which are currently not available here we use a coupled model of the northern hemisphere ice sheets6 and ocean temperatures forced to match an oxygen isotope record for the past million years compiled from 57 globally distributed sediment cores to quantify both contributions simultaneously we find that the ice sheet contribution to the variability in oxygen isotope composition varied from ten per cent in the beginning of glacial periods to sixty per cent at glacial maxima suggesting that strong ocean cooling preceded slow ice sheet build up the model yields mutually consistent time series of continental mean surface temperatures between 40 and 80 n ice volume and global sea level we find that during extreme glacial stages air temperatures were 17 1 8 c lower than present with a 120 10 m sea level equivalent of continental ice present

dating of sediments using accelerator mass spectrometry abstract an assessment is given of the current status and future prospects for the dating of recent sediments by the direct counting of radionuclides cosmogenic natural terrestrial and artificial using accelerator based mass spectrometers relevant isotopes and equipment are discussed the latter with particular reference to the 3 mv electrostatic accelerator system of the university of toronto inherent difficulties of the new method are outlined and possible applications are identified the ability to obtain radiocarbon dates from very small samples e g 100 g c illustrates the promise of the method

calcium isotope fractionation in ikaite and vaterite abstract we investigated the isotopic composition of calcium in the metastable calcium carbonate polymorphs vaterite and ikaite the synthetic vaterite precipitates show a smaller degree of ca isotope fractionation than calcite or aragonite at comparable temperatures and revealed no significant temperature sensitivity between 10 and 50 c ikaite the water bearing ca carbonate modification caco 3 6h 2 o was precipitated at 2 c in controlled laboratory experiments and in addition recovered from marine sediments and sea ice synthetic and natural ikaites show similar values of ca isotope fractionation in general ikaite is less depleted in heavy isotopes compared to calcite or aragonite at low temperatures the observed offset of vaterite and ikaite to calcite or aragonite precipitated at similar temperatures is presumably mainly related to differences in precipitation rates and regimes which seem however to be typical for the growth of these carbonate minerals small differences in ca isotope ratios of naturally formed ikaites from different locations seem to be related to different geochemical conditions in the respective sediment settings

geochemistry of ikaite formation at mono lake california implications for the origin of tufa mounds the mineral ikaite caco 3 6h 2 o not previously observed in lake environments precipitates seasonally along the shore of mono lake california where ca hco 3 spring water mixes with cold na co 3 lake water during the winter cold water temperatures and high concentrations of po 4 3 and organic carbon inhibit calcite precipitation allowing the metastable ikaite to form during the spring warming however ikaite decomposes to form calcium carbonate and water occasionally leaving pseudomorphs of the primary precipitate the identification of modern ikaite suggests that both pleistocene and holocene tufas in the mono basin originally precipitated as ikaite this mineral may also form in other lake environments but rapid recrystallization after warming destroys the physical chemical and isotopic evidence of formation and alters the geochemical record

origin and paleoenvironmental significance of calcite pseudomorphs after ikaite in the oligocene creede formation colorado abstract pseudomorphs of calcite are present in lacustrine strata and travertine of the oligocene creede formation the sedimentary moat fill of the creede caldera in the tertiary san juan volcanic field the pseudomorphs previously thought to have formed after gaylussite caco3na2co3 5h2o are interpreted to have formed after ikaite caco3 6h2o on the basis of their modes of occurrence pseudomorph morphology and textural and chemical aspects of the calcite replacement the extent of their exposure and degree of preservation in the creede formation allow elucidation of the depositional conditions in which the ikaite formed and was subsequently pseudomorphically replaced the revised paleoenvironmental interpre ation of the creede formation also has implications for understanding of the late oligocene climate of the southwestern united states formation of ikaite requires water temperatures of 0 3 c supersaturation with respect to calcite and the presence of a chemical inhibitor such as dissolved phosphate to prevent growth of calcite or aragonite shearman and smith 1985 geochemical calculations and hydrogeologic considerations suggest that waters with dissolved phosphate contents sufficient to inhibit calcite growth and stabilize ikaite could have developed in the creede moat lake although a chemical remnant of high phosphate content is not observed in the strata the granular texture of the creede pseudomorphs is common to calcite pseudomorphs after ikaite from many localities a model is proposed in which slow pseudomorphic replacement over a period of a day or more results in sand size calcite grains forme directly from the ikaite this model has important implications for the interpretation of isotopic and chemical data obtained from pseudomorphs and thinolitic tufa

control of sulfate pore water profiles by sedimentary events and the significance of anaerobic oxidation of methane for the burial of sulfur in marine sediments abstract gravity driven mass flow deposits proven by sedimentary and digital echosounder data are indicative for prevailing dynamic sedimentary conditions along the continental margin of the western argentine basin in this study we present geochemical data from a total of 23 gravity cores pore water so 4 is generally depleted within a few meters below the sediment surface by anaerobic oxidation of methane aom the different shapes of so 4 profiles concave kink and s type can be consistently explained by sedimentary slides possibly in combination with changes in the ch 4 flux from below thus mostly representing transient pore water conditions since slides may keep their original sedimentary signature a combined analysis and numerical modeling of geochemical physical properties and hydro acoustic data could be applied in order to reconstruct the sedimentary history we present first order estimates of the dating of sedimentary events for an area where conventional stratigraphic methods failed to this day the results of the investigated sites suggest that present day conditions are the result of events that occurred decades to thousands of years ago and promote a persisting mass transport from the shelf into the deep sea depositing high amounts of reactive compounds the high abundance of reactive iron phases in this region maintains low hydrogen sulfide levels in the sediments by a nearly quantitative precipitation of all reduced sulfate by aom for the total region we estimate a so 4 or ch 4 flux of 6 6 10 10 moles per year into the zone of aom projected to the global continental slope and rise area this may sum up to about 2 6 10 12 moles per year provided that the sulfur is completely fixed in the sediments it is about twice the global value of the recent global sulfur burial in marine sediments of 1 2 10 12 moles per year as previously estimated thus aom obviously contributes very significantly to the regulation of global sulfur reservoirs which is hitherto not sufficiently recognized this finding may have implications for global geochemical models as sulfur burial is an important control factor in the development of atmospheric oxygen levels over time

microsedimentological characterization using image analysis and μ xrf as indicators of sedimentary processes and climate changes during lateglacial at laguna potrok aike santa cruz argentina palaeoclimatic and paleoenvironmental high latitude records in the southern hemisphere are scarce compared to the northern counterpart however understanding global evolution of environmental systems during sudden climate changes is inseparable from an equivalent knowledge of both hemispheres in this context a high resolution study of lacustrine sediments from laguna potrok aike santa cruz province patagonia argentina was conducted for the lateglacial period using concurrent x ray fluorescence xrf and scanning electron microscope analyses peaks of ca si and mn and occurrences of the green alga phacotus lenticularis have been interpreted as variations in ventilation of the water column from 13 6 to 11 1 ka cal bp during this interval mild climate conditions during the younger dryas are characterized by relatively weak westerlies favouring the formation of a stratified water body as indicated by preserved manganese and ca si peaks and high total organic carbon toc values in this environment water in the epilimnion can reach sufficiently high temperature to allow p lenticularis to grow colder conditions are marked by peaks in ca without p lenticularis and occur during the antarctic cold reversal acr in this lateglacial interval micropumices were also detected in large amount image analysis of thin sections allowed the counting and size measurement of detrital particles and micropumices separately micropumices significantly influence the iron and titanium content hence preventing to use them as proxies of detrital input in this interval

marine cold seeps and their manifestations geological control biogeochemical criteria and environmental conditions characteristics of cold seeps at different geologic settings are the subject of this review primarily based on results of the research consortium sfb 574 criteria are drawn from examples on the erosive convergent margin off costa rica the accretionary margin off chile supplemented by examples from the transform margin of the golf of cadiz and the convergent hikurangi margin off new zealand others are from well studied passive margins of the black sea the golf of mexico the eastern mediterranean sea and the south china sea seeps at all settings transport water and dissolved compounds to the ocean through the seafloor by different forcing mechanism and from different depths of the submerged geosphere 10s of meters to 10s of km the compounds sustain oasis type ecosystems by providing bioactive reductants sulfide methane and hydrogen hereby the interaction between fluid composition flux rates and biota results in a diagnostic hydrocarbon metazoan microbe carbonate association currently well over 100 active sites are known the single most important reaction is microbially mediated anaerobic oxidation of methane with secondary reactions involving s biogeochemistry and carbonate mineral precipitation seep fluids and their seafloor manifestations provide clues as to source depth fluid sediment rock interaction during ascent lifetime and cyclicity of seepage events but less so on the magnitude of return flow at erosive margins cl depleted and b enriched fluids from clay dehydration provide criteria for source depth and temperature the upward material flow generates mud volcanoes at the seafloor above the projected location of dehydration at depth at accretionary margins fluids are derived from more shallow depths by compaction of sediments as they ride on the incoming oceanic plate they are emitted through thrust faults at highly sedimented margins organic rich and evaporite containing strata when present determine the final fluid composition by emitting characteristically gas hydrate derived methane brine associated non methane hydrocarbons or leached elements and their isotopes li 7li b ba from host sediments smectite illite transformation and associated cl depletion from release of interlayer water is a pervasive process at these margins rare earth element pattern in conjunction with redox sensitive metals retained in seep carbonates indicate whether or not they precipitated in contact with oxic bottom water or suboxic fluids clear environmental characterization though currently remains inconclusive more deeply sourced fluids as in transform margins may be characterized by their 87sr 86sr ratios from interaction with oceanic crustal rocks below quantification of flow and reliable estimates of total volatile output from fore arcs remain a challenge to seep research as does understanding the role of geologically derived methane in the global methane cycle

accumulation and properties of soil organic carbon at reclaimed sites in the lusatian lignite mining district afforested with pinus sp abstract the accumulation of organic carbon mainly derived from litter fall and necromass corg recent has been investigated within the forest floor horizons and the mineral topsoil 0 4 cm and 4 10 cm at reclaimed forest stands of the lusatian lignite mining district as well as on an undisturbed forest stand in the general region planted with pinus sylvestris l or pinus nigra arnold recently formed organic carbon corg recent was differentiated from organic carbon derived from lignite and lignite derivatives corg geogenic which are inherent in the dumped substrate at post mining sites by 14 c measurements total organic carbon toc was characterized by 13 c cpmas nmr spectroscopy the storage of toc corg recent corg geogenic and of organic carbon structures was examined we found that the accumulation of corg recent increased with stand age at all investigated stands the results indicate that at the reclaimed stands accumulation of corg recent takes place in the same order of magnitude when compared to the undisturbed stand storage of toc in the mineral topsoil 0 10 cm amounted from 2 6 kg m 2 to 7 0 kg m 2 at the reclaimed stands and to 2 6 kg m 2 at the undisturbed stand at reclaimed stands toc in the mineral topsoil can be attributed mainly to corg geogenic the calculated pools of corg geogenic effect physico chemical soil properties our results indicate that corg geogenic in the substrate may compensate in part the lack of soil organic matter derived from soil development as storage for nutrients and water

226ra and 228ra in the mixing zones of the pee dee river winyah bay yangtze river and delaware bay estuaries 226ra and 228ra have non conservative excess concentrations in the mixing zones of the pee dee river winyah bay estuary the yangtze river estuary and the delaware bay estuary laboratory experiments using pee dee river sediment indicate desorption of 226ra to increase with increasing salinities up to 20 in winyah bay desorption from river borne sediments could contribute almost all of the increases for both isotopes desorption adds only a portion of the excess 228ra measured in the yangtse river and adjacent shelf waters and delaware bay in the yangtze river the mixing zone extends over a considerable portion of the continental shelf where 228ra is added to the water column by diffusion from bottom sediments while 226ra concentrations decrease from dilution diffusion of 228ra from bottom sediments in delaware bay primarily occurs in the upper part of the bay 22 water where fine grained sediments predominate a diffusive flux for 228ra of 0 33 dpm cm 2 year was determined for delaware bay

calcium carbonate hexahydrate from organic rich sediments of the antarctic shelf precursors of glendonites large euhedral crystals of calcium carbonate hexahydrate were recovered from a shelf basin of the bransfield strait antarctic peninsula at a water depth of 1950 meters and sub zero bottom water temperatures the chemistry mineralogy and stable isotope composition of this hydrated calcium carbonate phase its environment of formation and its mode of precipitation confirm the properties variously attributed to hypothetical precursors of the glendonites and thereby greatly expand their use in paleoceanographic interpretation

importance of submarine landslides for non steady state conditions in pore water systems lower zaire congo deep sea fan abstract most concentration profiles of sulfate in continental margin sediments show constant or continuously increasing gradients from the benthic boundary layer down to the deep sulfate reduction zone however a very marked change in this gradient has been observed several meters below the surface at many locations which has been attributed to anoxic sulfide oxidation or to non local transport mechanisms of pore waters the subject of this study is to investigate whether this feature could be better explained by non steady state conditions in the pore water system to this end data are presented from two gravity cores recovered from the zaire deep sea fan the sediments at this location can be subdivided into two sections the upper layer about 10 m thick consists of stratified pelagic deposits representing a period of continuous sedimentation over the last 190 kyr it is underlain by a turbidite sequence measuring several meters in thickness which contains large crystals of authigenic calcium carbonate ikaite caco3 6h2o ikaite 13c values are indicative of a methane carbon contribution to the co2 pool radiocarbon ages of these minerals as well as of the adjacent bulk sediments provide strong evidence that the pelagic sediments have overthrust the lower section as a coherent block therefore the emplacement of a relatively undisturbed sediment package is postulated pore water profiles show the depth of the sulfate methane transition zone within the turbiditic sediments by the adaptation of a simple transport reaction model it is shown that the change in the geochemical environmental conditions resulting from this slide emplacement and the development towards a new steady state are fully sufficient to explain all features related to the pore water profiles particularly so42 and dissolved inorganic carbon dic the model shows that the downslope transport took place about 300 yr ago

natural radionuclides in waters of the new york bight the half removal time of228th from the surface waters by settling particles tc does not change much with season except in the winter when regenerated228th as well as210pb and210po were transported back to the surface water from the bottom water and or near shore sediments the removal of228th and210pb from the surface waters of new york bight by phytoplankton zooplankton fecal pellet route is not important in the shelf but is important in the slope areas the removal of210po is almost entirely associated with the phytoplankton zooplankton fecal pellet pathway throughout the new york bight

pore fluid constraints on the temperature and oxygen isotopic composition of the glacial ocean pore fluids from the upper 60 meters of sediment 3000 meters below the surface of the tropical atlantic indicate that the oxygen isotopic composition 18 o of seawater at this site during the last glacial maximum was 0 8 0 1 per mil higher than it is today combined with the 18 o change in benthic foraminifera from this region the elevated ratio indicates that the temperature of deep water in the tropical atlantic ocean was 4 c colder during the last glacial maximum extrapolation from this site to a global average suggests that the ice volume contribution to the change in 18 o of foraminifera is 1 0 per mil which partially reconciles the foraminiferal oxygen isotope record of tropical sea surface temperatures with estimates from barbados corals and terrestrial climate proxies

brucite chimney formation and carbonate alteration at the shinkai seep field a serpentinite hosted vent system in the southern mariana forearc brucite carbonate chimneys were discovered from the deepest known 5700 m depth serpentinite hosted ecosystem the shinkai seep field ssf in the southern mariana forearc textural observations and geochemical analysis reveal three types i iii of chimneys formed by the precipitation and dissolution of constitutive minerals type i chimneys are bright white to light yellow have a spiky crystalline and wrinkled surface with microbial mat and contain more brucite these formed as a result of rapid precipitation under high fluid discharge conditions type ii chimneys exhibit white to dull brown coloration tuberous textures like vascular bundles and are covered with grayish microbial mats and dense colonies of phyllochaetopterus this type of chimney is characterized by inner brucite rich and outer carbonate rich zones and is thought to have precipitated from lower fluid discharge conditions than type i chimneys type iii chimneys are ivory colored have surface depressions and lack living microbial mats or animals this type of chimney mainly consists of carbonate and is in a dissolution stage stable carbon isotope compositions of carbonates in the two types i and ii of active chimneys are extremely 13c enriched up to 24 1 which may reflect biological 12c consumption under extremely low dissolved inorganic carbon concentration in alkaline fluid type iii chimneys have 13c compositions indicating re equilibration with seawater our findings demonstrate for the first time that carbonate chimneys can be form below carbonate compensation depth and provide new insights about linked geologic hydrologic and biological processes of the global deep sea serpentinite hosted vent systems this article is protected by copyright all rights reserved

an ikaite record of late holocene climate at the antarctic peninsula abstract calcium carbonate can crystallize in a hydrated form as ikaite at low temperatures the hydration water in ikaite grown in laboratory experiments records the 18 o of ambient water a feature potentially useful for reconstructing 18 o of local seawater we report the first downcore 18 o record of natural ikaite hydration waters and crystals collected from the antarctic peninsula ap a region sensitive to climate fluctuations we are able to establish the zone of ikaite formation within shallow sediments based on porewater chemical and isotopic data having constrained the depth of ikaite formation and 18 o of ikaite crystals and hydration waters we are able to infer local changes in fjord 18 o versus time during the late holocene this ikaite record qualitatively supports that both the medieval warm period and little ice age extended to the antarctic peninsula

potential of ikaite to record the evolution of oceanic δ18o a challenge in the quest to understand the sensitivity of the climate system is the separation of the competing effects of ice volume or sea level salinity and temperature on foraminiferal 18o we present precipitation experiments on the mineral ikaite a hydrated form of calcium carbonate found in organic carbon rich deep marine sediments that show that the hydration waters within the ikaite crystal capture the 18o of seawater 18 osw with a fractionation factor of 1 0029 0 0002 the 18osw measures the volume of continental ice with an overprint of local salinity isolation of 18osw by analysis of the hydration waters of sedimentary ikaite preserved at temperatures 4 c could be exploited to create a record of sea level during the pleistocene preliminary data of 18osw from hydration waters of ikaite at the last glacial maximum agree with estimates from modeling of pore waters that antarctic bottom water was 1 4 0 2 heavier 2006 geological society of america

the solubility and stabilization of ikaite caco3 6h2o from 0 to 25 c environmental and paleoclimatic implications for thinolite tufa we determined the solubility of ikaite from 0 to 25 c to model its saturation state in natural waters and test the hypothesis that it is the precursor of the calcite pseudomorphs in thinolite tufa of quaternary lake lahontan reversible solubility at buffered p co 2 yields the following expression for the dissolution constant of ikaite log k ikaite 0 15981 2011 1 t where t circ k and 0 circ c leq t leq 25 circ c derived standard state properties are delta g ikaite circ 2541 9 kjmol 1 pm 0 66 delta h ikaite circ 2973 4 kjmol 1 pm 1 02 s ikaite circ 306 6 jt 1 mol 1 pm 1 2 modeling shows that ikaite is undersaturated at all temperatures in seawater and in alkaline lakes but that it rapidly approaches saturation near 0 c its precipitation in near freezing marine sediments requires large additions of hco 3 to pore fluids from the diagenetic decomposition of organic matter its crystallization in tufas of alkaline lakes howeve

mixing and cycling of uranium thorium and 210pb in puget sound sediments abstract activity profiles of excess 234 th excess 210 pb 232 th 230 th 234 u and 238 u and 228 232 th ratios determined in eight box cores of sediment from six sites in central puget sound provide new insights into the dynamic nature of solid phase mixing in surface sediments the exchange of 228 ra and other soluble species across the sediment water interface and the cycling of u th and 210 pb in this coastal zone comparison of excess 234 th inventories in sediments with its production rate in the overlying water column indicates a mean residence time of at most 14 days for particles in the central puget sound water column surface sediment horizons with excess 234 th have no excess 228 th which might be used to ascertain sediment accumulation rates over the past decade instead deficiencies of 228 th due to loss of soluble 228 ra from pore water to the overlying water persist to 20 30 cm revealing that exchange of soluble chemicals between pore and overlying waters reaches these depths in the extensively bioturbated sediments of puget sound solid phase u isotope concentrations tend to increase by up to a factor of two with depth in sediments as a result of dissolved u being biologically pumped down into sediments where it is partially removed when conditions become mildly reducing 232 th and 230 th activities and 230 232 th ratios are constant with depth in sediments indicating constant detrital phase compositions and essentially no authigenic 230 th steady state 210 pb depositional activities in and fluxes to puget sound sediments average only about onehalf those for sediments of the open washington coast north of the columbia river mouth primarily because of a much lower supply of dissolved 210 pb in sea waters adverting into puget sound excess 234 th profiles in sediments reveal much more detail about the depth dependency dynamic nature and recent history of solid phase mixing processes than excess 210 pb profiles at least six of eight 234 th profiles show that mixing within the 210 pb defined surface mixed layer is depth dependent in three profiles 234 th derived mixing rates are fastest several centimeters below the sediment water interface indicating greater macro benthic activity at these depths depth dependent mixing coefficients derived from the best fit of a four layer advection diffusion decay model to the 234 th data are consistent with 210 pb profiles determined for the same sediments strongly suggesting that 234 th and 210 pb are mixed equivalently and in a multilayered manner

submarine columns of ikaite tufa in the small ikka fjord in southwestern greenland we have studied remarkable submarine tufa columns forming over alkaline springs by abiotic precipitationof the metastable cold water mineral ikaite caco3 6h2o 1 3 the columns which support a rich marine life are up to 20 m high with annual growth of more than 50 cm we wish to nominate the locality which seems to be unique for classification as a geological world heritage site

ikaite pseudomorphs in the zaire deep sea fan an intermediate between calcite and porous calcite translucent brown aggregates of calcium carbonate crystals have been found in cores from the zaire deep sea fan west equatorial africa the aggregates are well preserved but very friable upon storage they become yellowish white and cloudy and release water chemical mineralogical xrd petrographical crystal morphological and stable isotope data demonstrate that the crystals have passed through three phases 1 an authigenic carbonate phase probably calcium carbonate which is represented by the external habit of the present crystals 2 a translucent brown ikaite phase caco 3 6h 2 o unstable at temperatures above 5 c and 3 a phase consisting of calcite microcrystals that are poorly cemented and form a porous mass within the crystal form of the morphologically unchanged first phase the transformation from the first phase into ikaite was probably a kinetic replacement the transformation from ikaite into the third phase occurred because of storage at room temperature the presence of ikaite is indicative of a low temperature anaerobic organic carbon rich marine environment ikaite is probably the precursor of a great number of porous calcite pseudomorphs and possibly also of many marine authigenic microcrystalline carbonate nodules

stable isotope fractionation factors of water in hydrated saline mineral brine systems hydrogen and oxygen isotope fractionation factors of water between water of crystallization of carnallite bischofite and tachyhydrite and the mother solutions were determined from the isotopic activity ratios of the mother solutions a in the temperature range of 10 40 c deuterium is depleted and 18o enriched in the water of crystallization of all these minerals no clear temperature dependence can be observed the published fractionation factors in the literature which were all determined from the isotopic concentration ratios of the mother solutions c were corrected to a using the salt effect coefficients it is proposed that only the a values can be applied to the natural settings

early permian seasonality from bivalve δ18o and implications for the oxygen isotopic composition of seawater oxygen isotope values of sequentially microsampled accretionary carbonate from the thick shelled calcitic bivalve eurydesma from the early permian of southeastern australia vary seasonally over 6 yr of growth paleotemperature constraints derived from coeval glendonite and ice rafted clasts in combination with published biome data indicate near freezing winter conditions however paleotemperatures calculated from oxygen isotope data are too warm unless the 18 o value of seawater approached 4 associated stenohaline brachiopods and lack of covariance with 13 c argue against significantly reduced salinity and published 18 o data from across australia suggest that conditions recorded by this bivalve were typical of the gondwanan high latitudes the negative 18 o value of seawater implied by these data reflects in part the expected meridional gradient in marine seawater composition related to latitudinal variation in evaporation and precipitation in permian oceans but is also consistent with previous suggestions of a secular increase in the oxygen isotopic composition of ocean water through the phanerozoic

on the structure and origin of major glaciation cycles 2 the 100 000 year cycle climate over the past million years has been dominated by glaciation cycles with periods near 23 000 41 000 and 100 000 years in a linear version of the milankovitch theory the two shorter cycles can be explained as responses to insolation cycles driven by precession and obliquity but the 100 000 year radiation cycle arising from eccentricity variation is much too small in amplitude and too late in phase to produce the corresponding climate cycle by direct forcing we present phase observations showing that the geographic progression of local responses over the 100 000 year cycle is similar to the progression in the other two cycles implying that a similar set of internal climatic mechanisms operates in all three but the phase sequence in the 100 000 year cycle requires a source of climatic inertia having a time constant similar to 15 000 years much larger than the other cycles similar to 5 000 years our conceptual model identifies massive northern hemisphere ice sheets as this larger inertial source when these ice sheets forced by precession and obliquity exceed a critical size they cease responding as linear milankovitch slaves and drive atmospheric and oceanic responses that mimic the externally forced responses in our model the coupled system acts as a nonlinear amplifier that is particularly sensitive to eccentricity driven modulations in the 23 000 year sea level cycle during an interval when sea level is forced upward from a major low stand by a milankovitch response acting either alone or in combination with an internally driven higher frequency process ice sheets grounded on continental shelves become unstable mass wasting accelerates and the resulting deglaciation sets the phase of one wave in the train of 100 000 year oscillations whether a glacier or ice sheet influences the climate depends very much on the scale the interesting aspect is that an effect on the local climate can still make an ice mass grow larger and larger thereby gradually increasing its radius of influence