effects of diagenesis on the isotopic record of late paleogene tropical sea surface temperatures abstract oxygen isotope records of planktonic foraminifera indicate that late eocene and oligocene tropical sea surface temperatures were as much as 8 c lower than present at a time when high latitude sea surface temperatures were higher than present using a numerical model which describes oxygen isotope exchange during burial and recrystallization of deep sea carbonate the effects of diagenesis on bulk carbonate 18 o records for the cenozoic are quantified for four tropical sites most of the observed variations in measured 18 o values at all sites can be accounted for by diagenetic effects there are no systematic trends that support substantial variations in tropical sea surface temperatures beyond diagenetic effects with the possible exception of the early eocene for which the data are consistent with slightly higher sea surface temperatures reconstructions based on oxygen isotope records of planktonic foraminifera which indicate cooler tropical sea surface temperatures for the eocene and oligocene may be artifacts of diagenetic recrystallization as such records are particularly sensitive to diagenetic effects

recent planktonic foraminiferal distribution patterns and their relation to hydrographic conditions of the gulf of tehuantepec mexican pacific abstract the distribution and abundance patterns of planktonic foraminifera in sediments and their relation to ocean dynamics were studied in the gulf of tehuantepec hydrographic and nutrient data outline the contrast between two extreme seasons in the gulf the winter early spring conditions dominated by upwelling and a cyclonic eddy that fertilize the surface waters and summer conditions with the typical stratified water column of the tropical pacific foraminiferal abundances number of individuals g of sediment are related to the ocean dynamics and productivity highest abundances are found in the areas influenced by upwelling and associated front and cold eddy and lower abundances are beneath the areas of influence of the warm core lower productivity eddies the effects of dissolution seem to be important at depths over 1000 m but do not appear to affect critically the foraminiferal remains throughout most of the studied area except near the phosphorite deposits of the oaxaqueno bank dilution by terrigenous materials from riverine inputs seafloor topography and strong transport under the upwelling jet are likely to modify the detailed pattern of foraminiferal abundance found without blurring the major imprint of productivity driven by the upwelling three planktonic foraminiferal assemblages were found reflecting the major oceanographic conditions in the gulf the globigerina bulloides assemblage dominates most of the gulf indicating the overall high productivity of the upwelling influenced surface waters the dynamics of the winter early spring upwelling and associated eddies leave a strong imprint in the planktonic foraminiferal assemblages in the sediments the distribution of the globigerinita glutinata assemblage is tied to the axis of upwelling and the globorotalia menardii neogloboquadrina dutertrei assemblage to the warm equatorial water cores the distribution patterns of these assemblages should help identify quaternary paleoenvironments influenced by upwelling and associated changes in productivity

carbonate dissolution fluctuations in the western equatorial pacific during the late quaternary planktonic foraminiferal test fragmentation in three cores along a depth transect from the western equatorial pacific erdc 93p 1619 m rc17 177 2600 m v28 238 3120 m thompson 1976 were examined for the last 500 kyr at sample intervals from 2 5 to 5 kyr to study the fluctuations of dissolution in the western equatorial pacific the age models were constructed by correlating the 18o records with the specmap stack imbrie et al 1984 results showed that intermediate and deep waters experienced the same patterns of dissolution through climatic cycles fragmentation varied with a greater amplitude and the carbonate ion concentration changed less in the deep than in the intermediate water dissolution has significant variance distributions and coherencies with 18o over the 100 41 and 23 kyr periods of orbital variations dissolution maxima lag ice volume minima by 6 to 20 kyr the dissolution variability was consistent with recent geochemical models which seek to explain the reduction of atmospheric co2 concentration at the last glacial maximum broecker 1982 boyle 1988

atmospheric carbon dioxide and early eocene climate a general circulation modeling sensitivity study abstract the early eocene was the warmest time interval of the past 65 million years we have investigated the hypothesis that the warm climate of the early eocene may have been caused by higher than present levels of atmospheric carbon dioxide co2 we have used an atmospheric general circulation model the ncar genesis model coupled to a land surface model and a mixed layer ocean to examine the sensitivity of early eocene climate to varying levels of atmospheric co2 model cases contained a description of the early eocene earth and included either 300 560 or 1680 ppm atmospheric co2 climate responses to increased atmospheric co2 include 1 increased mean annual global temperature by 2 6 c and decreased latitudinal surface temperature gradients 2 maximum warming at high latitudes especially in the winter season 3 increased mean global precipitation 4 increased high latitude clouds in comparison with geological paleoclimate data the climate response to increased co2 does not appear to explain completely the early eocene latitudinal surface temperature gradient for example with the 1680 ppm co2 case high latitude oceans and continents are minimally warm enough to match paleoclimate data while low latitude regions are overly warm when compared to sea surface temperature reconstructions we conclude that co2 was very likely at least double the present level during the early eocene and contributed to the overall character of early eocene climate however consideration of increased poleward oceanic heat transport and or other factors may be required to produce model results that more closely agree with marine and terrestrial paleoclimate data especially at low latitudes

freshwater export pathways from the bay of bengal abstract observations from surface drifters and argo floats elucidate details of two upper ocean pathways through which freshwater from the bay of bengal bob is advected into the tropical indian ocean and arabian sea as the western route is located along the east coast of india and feeds into the westward northeast monsoon current nmc south of sri lanka during the winter monsoon whereas the eastern path is located along the western margin of sumatra reaching at times as far south as the indonesian throughflow plume near 10 s while the former pathway is highly seasonal and affected by mesoscale variability the latter is a year round feature and may be dominant from an annual perspective the observations do not support the notion of a continuous current system comprised of the nmc and the west india coastal current around the laccadive high in boreal winter that can directly export surface freshwater from the bob to the as further the observations indicate an occasional leakage of low salinity water by a westward coastal current between the eastward southwest monsoon current smc and sri lanka in boreal summer that may be caused by equatorial wave processes the smc which exhibits considerable ekman contributions in contrast to its geostrophically balanced nmc counterpart in boreal winter facilitates the transport of saltier as water into the bob with subsequent spreading into the upper thermocline of the bob setting up an estuary like circulation pattern

paleoclimatic inference from stable isotope profiles of accretionary biogenic hardparts a quantitative approach to the evaluation of incomplete data abstract variation in 18o of invertebrate and vertebrate skeletons has been widely employed to estimate annual means and seasonal ranges of temperature from many geologic settings among incertitudes encountered in employing this approach is the influence of unconstrained noise in environmental signals cessation of hardpart accretion during reproduction and or seasonal temperature extremes biasing of calculated mean temperatures toward seasons of maximum growth rate and dependence on the most extreme 18o values observed for estimating annual temperature range to better constrain paleoclimatic interpretations we describe several applications of a computational approach that address many of these uncertainties it is predicated on the presumption that annual variation in isotope composition across an accretionary skeleton represents sinusoidal variation in temperature and or the composition of ambient fluids the analysis resolves a best fit sinusoid for any portion of the data output consists of determinations of mean annual 18o seasonal range in 18o and sine period which reflects hardpart growth rate the procedure can be employed over some window of values within any data series and can be reiterated to arrive at solutions for all possible windows the technique allows for quantitative interpretation of mean values and annual amplitudes of 18o variation for every window regardless of whether or not that window actually spans a seasonal isotope extreme moreover it affords equal interpretational weight for every analysis in the data set in that mean annual and seasonal variation values estimated for each window are derived from every analysis in the data set it is therefore not necessary to estimate mean annual 18o as simply the arithmetic mean of all analyses and estimates of seasonality can be derived from data within any window rather than depending only on those several analyses that fall at compositional extremes in order to demonstrate the utility this methodology to the interpretation of paleoclimatological data we have applied it to published temperature data from several modern climatological data sets and to published 18o data from a paleogene gulf coast fish otolith a modern arabian sea coral a miocene texan equine tooth and an eocene bivalve from england each yields robust estimates of mean annual temperatures or isotopic compositions and of seasonal ranges in these values in addition unique features of data from each of these examples illustrate the power of this method to shed light on climatological and or biological phenomena that are also unique to each system

planktic foraminifers and hydrography of the eastern and northern caribbean sea the distribution of living planktic foraminifers and their relation to the hydrography of the caribbean sea was investigated in plankton net tows and surface sediment samples taken along the antilles island arc during april may 1996 the planktic foraminiferal community was strongly influenced by spatial variations in salinity that were largely due to the influx of orinoco river water into the southeastern caribbean sea and inflowing sargasso sea water in the north along the antilles island arc globigerinoides ruber was the dominant species in the surface waters throughout in the southeastern caribbean sea where orinoco river outflow influences the planktic community standing stocks of planktic foraminifers 100 m between 4 and 50 specimens m 3 were medium to low the southeastern faunas between tobago and guadeloupe were characterized by increased proportions of neogloboquadrina dutertrei highest standing stocks of 159 specimens m 3 in the upper 20 m of the water column were recorded in the northeastern caribbean sea and the assemblages were characterized by high proportions of globigerinita glutinata associated with cyclonic eddies in the anegada passage where sargasso sea water flows into the caribbean sea low standing stocks of 18 specimens m 3 indicate oligotrophic conditions together with the oligotrophic surface waters the subtropical underwater enters the caribbean sea through the anegada passage in water depths between 100 and 300 m these waters are characterized by higher concentrations of globorotalia truncatulinoides relative to the adjacent water masses comparison of the living planktic foraminiferal fauna with empty test assemblages from the water column and from surface sediments shows that differences in the faunal composition mostly correspond to the distribution of water masses and to the differential dissolution of species in the vicinity of islands globigerinoides ruber reaches higher relative frequencies than in the open ocean pointing towards a higher tolerance of this species towards neritic conditions than in other species

warm not super hot temperatures in the early eocene subtropics the early eocene ca 55 48 ma encompasses one of the warmest intervals of the past 65 m y and is characterized by an unusually low equator to pole thermal gradient recent proxy studies suggest temperatures well in excess of 30 c even at high latitudes but confl icting interpretations derived from different types of data leave considerable uncertainty about actual early eocene temperatures a robust comparison among new paleotemperature proxies may provide insight into possible biases in their temperature estimates and additional detail on the spatial distribution of temperatures will further resolve the early eocene meridional temperature gradient we use a suite of paleotemperature proxies based on the chemistry of bivalve shell carbonate and associated sedimentary organic matter from the united states gulf coastal plain to constrain climate at a subtropical site during this key interval of earth history oxygen isotope and clumped isotope analyses of shell carbonate and two tetraether lipid analyses of sedimentary organic carbon all yield temperatures of 27 c high resolution intraannual oxygen isotope data reveal a consistent large range of seasonal variation but clumped isotope data suggest that seasonality is due primarily to precipitation not to temperature these paleotemperature estimates are 2 3 c warmer than the northern gulf of mexico today and generally consistent with early eocene temperature estimates from other low and mid latitude locations but are signifi cantly cooler than contemporaneous estimates from high southern latitudes

climate records from a bivalved methuselah arctica islandica mollusca iceland we measured annual shell growth rates of a 374 year old radiometrically confirmed bivalve mollusk specimen of arctica islandica linnaeus this bivalve represents the oldest ever reported individual animal in addition we analyzed 1051 individual powder samples from ontogenetic years two to 40 80 of the entire shell height for isotope analyses oxygen and carbon isotopes exhibit clear intra annual cycles the highest measured carbon isotope values on average 2 73x occurred during summer i e during maximum primary productivity the d 18 oaragonite derived temperature time series cover the period of ad 1496 1533 temperatures calculated from oxygen isotopes ranged from 4 5 to 9 3 8c and exhibit a mean value of 6 2 8c the latter coincides well with the 1854 2003 mean value of 6 81 8c for sea surface temperature between february and september growing season of a islandica neither oxygen nor carbon isotopes exhibit age related unidirectional trends however d 13 caragonite and d 18 oaragonite values fluctuated at decadal periods of four six and eight to nine years nao type periods as well as 12 14 years which may represent teleconnections to cycles in the tropical atlantic annual shell growth is positively correlated to intra annual d 18 oaragonite minima i e warm summer temperatures r 2 0 34 and to intra annual d 13 caragonite minima higher food supply r 2 0 42 using a linear multiregression model 65 of the variation in annual shell growth can be explained by summer temperature and food supply the formation of extremely narrow annual increments coincides with major volcanic eruptions e g tambora 1815 a period of extremely variable growth occurred during the culmination of the little ice age in iceland between ca ad 1550 and 1620 shell growth during ad 1765 1780 however was characterized by very little year to year variability probably as the result of extremely mild climate near the end of the little ice age this study demonstrates that shells of a islandica provide

equable climates during earth history eocene and cretaceous climate model experiments demonstrate that regardless of conditions of warm polar oceans differences in pole to equator surface temperature gradient or topography above freezing surface temperatures in winter for continental interiors at middle to high latitudes cannot be maintained continental interiors will have cold winter temperatures even during globally warm periods unless currently unrecognized forcing factors influenced past climates if model simulations of eocene and cretaceous climates are accurate the term equable as it applies to paleoclimate should be reconsidered

equability continentality and tertiary climate the crocodilian perspective the distributions of fossil crocodilians are used to examine north american continental paleoclimates for four time periods in the cenozoic control groups provide a qualitative means of examining the completeness of the record and thus the validity of crocodilian patterns by analogy with the range of the extant american alligator alligator mississippiensis the patterns imply that mid to high latitude continental interiors during the eocene and miocene did not undergo seasonal temperature extremes as great as those observed in such areas today this is compatible with the paleobotanical data during both the late oligocene and the pleistocene times of major glaciation crocodilians were restricted to more maritime localities

a critical assessment of mollusk 18 o 16 o mg ca and 44 ca 40 ca ratios as proxies for cretaceous seawater temperature seasonality seasonal temperature fluctuations of tethyan coastal water are recorded in a pristine 80 my old rudist shell from turkey in order to critically assess factors other than seawater temperature that might have influenced the shell geochemical record three different paleo temperature proxies 18o mg ca and 44ca were applied in a qualitative manner all three proxies reflect the same cyclical trends and thus yield robust evidence for seasonal fluctuations in late cretaceous surficial seawater temperature this suggests the successful application of the new 44ca temperature proxy to fossil mollusk calcite the direct comparison of the three data sets however demonstrates that all proxies are fraught with problems similar to other studies 18o 16o ratios point to warmer summer temperature maxima than those in comparable costal settings today nevertheless the 18o 16o proxy is subject to environmental factors that might lead to an overestimation of peak temperatures moreover mg ca molar ratios are less sensitive to environmental factors but were strongly affected by the ion regulating capability of the rudist bivalve that responded to the low mg ca ratio of cretaceous seawater similarly uncertainties of the 44ca composition of cretaceous seawater and the complex bio calcification of mollusks presently limit the interpretation of 44ca values in terms of absolute seawater temperature the multiproxy approach applied here however documents that these limitations do not obscure the dominant patterns of seasonal sea surface temperature variations recorded in the biogeochemical rudist archive

eocene seasonality and seawater alkaline earth reconstruction using shallow dwelling large benthic foraminifera abstract intra test variability in mg ca and other trace elements within large benthic foraminifera lbf of the family nummulitidae have been investigated using laser ablation inductively coupled plasma mass spectrometry la icpms these foraminifera have a longevity and size facilitating seasonal proxy retrieval and a depth distribution similar to surface dwelling planktic foraminifera coupled with their abundance in climatically important periods such as the paleogene this means that this family of foraminifera are an important but under utilised source of palaeoclimatic information we have calibrated the relationship between mg ca and temperature in modern operculina ammonoides and observe a 2 increase in mg ca c 1 o ammonoides is the nearest living relative of the abundant eocene genus nummulites enabling us to reconstruct mid eocene tropical sea surface temperature seasonality by applying our calibration to fossil nummulites djokdjokartae from java our results indicate a 5 6 c annual temperature range implying greater than modern seasonality in the mid eocene bartonian this is consistent with seasonal surface ocean cooling facilitated by enhanced eocene tropical cyclone induced upper ocean mixing as suggested by recent modelling results analyses of fossil n djokdjokartae and operculina sp from the same stratigraphic interval demonstrate that environmental controls on proxy distribution coefficients are the same for these two genera within error using previously published test seawater alkaline earth metal distribution coefficients derived from an lbf of the same family raitzsch et al 2010 and inorganic calcite with appropriate correction systematics for secular mg casw variation evans and muller 2012 we use our fossil data to produce a more accurate foraminifera based mg casw reconstruction and an estimate of seawater sr ca we demonstrate that mid eocene mg casw was 2 mol mol 1 which is in contrast to the model most commonly used to correct deep time mg ca data from foraminifera but in agreement with most other paleogene proxy and model data this indicates that mg casw has undergone a substantial 3 4 rise over the last 40 ma

a high resolution study of trace elements and stable isotopes in oyster shells to estimate central asian middle eocene seasonality modern asian climate is characterized by strong seasonality caused by the duality between monsoon dominated conditions in southeastern asia and semi arid to arid conditions in central asia eocene high resolution proxy records which enable the reconstruction of the onset and magnitude of changes in seasonality are lacking to understand in details how and when this climatic turnover pattern occurred here we propose an original method to estimate inter and intra annual variabilities in seawater temperature and salinity recorded by carbonate shell growth increments of the fossil oyster sokolowia buhsii grewingk collected from late lutetian marine strata of the proto paratethys in the southwestern tarim basin western china elemental ratio mg ca mn ca and carbonate stable isotope composition 18o were determined perpendicular to the growth lines of foliated calcite accumulated in the ligamental area during the oyster s lifetime we use temperature dependant mg incorporation to estimate seasonal temperature contrast in the past results suggest a warm annual average temperature 27 28 c with large offset between summer and winter temperatures until t 19 c combining these temperature estimates with stable oxygen isotope analyses from the same growth increments we deconvolve seawater 18osw as a proxy for salinity this suggests an average annual salinity about 34 35 increasing strongly during summer months and decreasing in winter based on these data we conclude that during the middle eocene central asian climate was characterized by a strong intra seasonal variability in both temperature and salinity although the subtidal setting might have contributed to the strong seasonal offsets this still suggests that semi arid to arid conditions prevailed during summer whereas winter was characterized by enhanced rainfall these results are consistent with previous regional palaeoenvironmental data and climate modelling experiments they thus attest for the reliability of the method developed here as a seasonal palaeoclimatic indicator

spatiotemporal structure of the east india coastal current from satellite altimetry we use a newly processed altimeter data set to present a hitherto unprecedented description of the spatiotemporal structure of the east india coastal current eicc the data set resolves timescales ranging from a few months to a few years and the high along track resolution yields the first description of the cross shore structure of the current the seasonal cycle dominates the variability but the nonannual timescales have similar energy levels all along the eicc path there are short lived intense intraseasonal bursts in contrast to the seasonal cycle the interannual and intraseasonal components are decorrelated along the coast and possible mechanisms for the decorrelation discontinuity in the flow are discussed in the cross shore direction the current is highly correlated at all timescales the eicc is trapped against the shelf with the current offshore flowing in the opposite direction at most locations the eicc appears as an inherently discontinuous flow taking the form of a few recirculating loops along the eicc path with a typical cross shore spatial scale of 150 200 km the loops are highly variable in direction at all timescales from intraseasonal to interannual this discontinuity of the eicc in space and time implies that the basic pathways and advective timescales for the interbasin exchange of water masses between the bay of bengal and the arabian sea are not robust when the full spatiotemporal variability of the eicc is considered

seasonal changes in the isotopic composition of planktonic foraminifera collected in panama basin sediment traps abstract isotopic analyses have been made on five species of planktonic foraminifera collected in two deployments of parflux mark ii time series sediment traps in the panama basin the automated sampling system on the traps provided 4 one month samples from 29 july to 16 november 1979 and 6 two month samples from december 1979 to november 1980 the 18o values of globigerinoides ruber and globigerinoides sacculifer in this region are primarily affected by a low salinity surface layer that forms during the early winter these species each show a 1 total range in 18o the 18o values of the colder water species globorotalia menardii neogloboquadrina dutertrei and globorotalia theyeri show smaller seasonal changes in 18o the 13c values of g ruber and g sacculifer exhibit small seasonal changes 0 35 and 0 4 respectively despite large seasonal changes in surface water productivity the colder water species exhibit only slightly larger changes in 13c up to 0 55 throughout the year all colder water species exhibit minimum or near minimum 13c values during february and march which is the period of maximum upwelling and primary productivity seasonal variations in the flux of foraminifera in the water column at this location will have only a small effect on the isotopic composition of the sediment assemblage extreme values of 18o and 13c do not occur during the periods which are associated with the high flux of foraminiferal tests

cooler winters as a possible cause of mass extinctions at the eocene oligocene boundary the eocene oligocene boundary at about 33 7 myr ago marks one of the largest extinctions of marine invertebrates in the cenozoic period1 for example turnover of mollusc species in the us gulf coastal plain was over 90 at this time2 3 a temperature change across this boundary from warm eocene climates to cooler conditions in the oligocene has been suggested as a cause of this extinction event4 but climate reconstructions have not provided support for this hypothesis here we report stable oxygen isotope measurements of aragonite in fish otoliths ear stones collected across the eocene oligocene boundary palaeotemperatures reconstructed from mean otolith oxygen isotope values show little change through this interval in agreement with previous studies5 6 from incremental microsampling of otoliths however we can resolve the seasonal variation in temperature recorded as the otoliths continue to accrete new material over the life of the fish these seasonal data suggest that winters became about 4 c colder across the eocene oligocene boundary we suggest that temperature variability rather than change in mean annual temperature helped to cause faunal turnover during this transition

cenozoic seawater sr ca evolution records of seawater chemistry help constrain temporal variations in geochemical processes that impact the global carbon cycle and climate through earth s history here we reconstruct cenozoic seawater sr ca sr casw using fossil conus and turritellid gastropod sr ca combined with an oxygen isotope paleotem perature record from the same samples the gastropod record suggests that sr casw was slightly higher in the eocene 11 4 3 mmol mol than today 8 54 mmol mol and remained relatively stable from the mid to late cenozoic we compare our gastropod cenozoic sr casw record with a published turritellid gas tropod sr casw record and other published biogenic benthic foraminifera fossil fish teeth and inorganic pre cipitate calcite veins sr casw records once the uncertainties with our gastropod derived sr casw are taken into account the sr casw record agrees reasonably well with biogenic sr casw records assuming a seawater ca history derived from marine evaporite inclusions all biogenic based sr casw reconstructions imply decreasing seawater sr through the cenozoic whereas the calcite vein sr casw reconstruction implies increasing sr through the cenozoic we apply a simple geochemical model to examine the implications of divergence among these seawater sr reconstructions and suggest that the interpretation and uncertainties associated with the gastropod and calcite vein proxies need to be revisited used in conjunction with records of carbonate depositional fluxes our favored seawater sr ca scenarios point to a significant increase in the proportion of aragonite versus calcite deposition in shelf sediments from the middle miocene coincident with the proliferation of coral reefs we propose that this occurred at least 10 million years after the seawater mg ca threshold was passed and was instead aided by declining levels of atmospheric carbon dioxide

petrology and palaeoenvironmental significance of authigenic iron rich clays carbonates and apatite in the claiborne group middle eocene ne texas the claiborne group eocene in north east texas consists of clayey sandstones and mudrocks both with variable proportions of dark green to brown clay pellets deposited in a marginal to open marine setting on the gulf coast margin the composition of concretionary carbonate and clay pellets from 5 localities has been investigated using a wide variety of analytical techniques our palaeontological sedimentological c s and stable isotope data support an interpretation of marginal marine facies with limited freshwater input for the claiborne group dark green mature pellets are predominantly associated with transgressive bioturbated marine sediments from the weches formation through to the youngest crockett formation there is a trend from pellets composed mostly of dark green serpentine rich mixed layer clay to those of mostly brown immature nontronite rich mixed layer clay the serpentine is intermediate between odinite and berthierine and may have been originally odinite that has undergone partial transformation to berthierine pellet maturity apparently corresponds with the degree of winnowing and sedimentation rate it does not appear to correspond with global temperature fluctuations though the serpentine rich rather than glauconite rich composition may do siderite cement mostly in the form of concretions post dates the iron rich clay pellets and pre dates calcite cement carbonate and apatite concretions show a wide range of mineral cement textures reflecting variation in sedimentary environment and early diagenetic processes based on water temperatures derived from verneriacardia bivalves a precipitation temperature of 20 c is assumed for the concretionary siderite using this temperature we surmise that the siderite precipitated from marine pore waters with intermittent meteoric water mixing

tropical pacific ocean thermocline depth reconstructions for the last glacial maximum we evaluate the relationship between ten surface ocean 0 300 m hydrographic parameters and the spatial distribution of factor analyzed core top planktonic foraminiferal abundances in the tropical pacific ocean 24 n 24 s for core tops 3800 m the spatial distribution of the first three faunal factor loadings 88 of the variance are most highly correlated to subsurface variability mixed layer depth thermocline depth and resistant species percent rsp however rsp is not related to dissolution but is related to thermocline depth factor i mixed layer species g glutinata g ruber and factor iii g ruber can be distinguished from each other by low abundances of g glutinata in factor iii both assemblages spatially comprise the deep mixed layer region of the western tropical and equatorial pacific ocean but are associated with distinct water mass properties a combination of factor i and iii loadings shows a higher correlation to thermocline depth r 0 70 factor ii loadings dominated by thermocline dwelling species n dutertrei are most significantly correlated with the thermocline depth r 0 73 most factors show only marginally significant correlation to sea surface temperatures ssts indicating that sst is not the primary forcing factor on the planktonic foraminiferal species distributions in the tropical pacific a new transfer function was calculated to predict tropical pacific thermocline depth from planktonic foraminifera abundances using the imbrie kipp method ikm standard deviation of residuals 22 m 1 an additional 5 m error is attributed to low species counts in the core top database the modern analog technique mat was also used to predict thermocline depth standard deviation of residuals 21 m while last glacial maximum lgm thermocline depth changes by ikm and mat were generally within error estimated changes were geographically uniform suggesting an oceanographic response to climate forcing we estimate that the thermocline depth of the lgm was shallower than present by 20 m south of 8 s possibly due to a shift in the south pacific anticyclone to the northeast both the ikm and mat estimate a steeper east west thermocline slope along the equator suggesting that zonal wind stress walker circulation was intensified during the lgm collectively the thermocline estimates for the lgm suggest an equatorward compression of the climate zones in both hemispheres

near surface circulation in the south china sea during the winter monsoon 1 original velocity measurements at 15 m depth from surface velocity program drifters are used to calculate the circulation in the south china sea during the winter monsoon the ekman currents are computed with a new method and subtracted from drifter s velocity to calculate the residual circulation which is approximately in geostrophic balance the ekman flow is nearly zonal and comparable to the zonal geostrophic flow in the northern basin the geostrophic flow is cyclonic and extends into the southern luzon strait strong jets occur south of hainan off vietnam and to the south off peninsular malaysia the vietnam jet is concentrated inshore of the 200 m isobath with mean speeds in excess of 1 m s 1 the onshore ekman transport and pumping velocity computed from the wind stress curl offer a qualitative explanation of the existence and behavior of such jets

eocene continental climates and latitudinal temperature gradients global climate during the mesozoic and early cenozoic is thought to have been warmer than at present but there is debate about winter temperatures paleontological data indicate mild temperatures even at high latitudes and in mid latitude continental interiors whereas computer simulations of continental paleoclimates produce winter temperatures closer to modern levels foliar physiognomy and floristic composition of 23 eocene floras from the interior of north america and australia indicate cold month means generally 2 c even where the mean annual temperature mat was

the dynamics of the southwest monsoon current in 2016 from high resolution in situ observations and models abstractthe strong stratification of the bay of bengal bob causes rapid variations in sea surface temperature sst that influence the development of monsoon rainfall systems this stratification

bottom water anoxia inoceramid colonization and benthopelagic coupling during black shale deposition on demerara rise late cretaceous western tropical north atlantic 1 the bulk rock geochemistry and inoceramid isotopic composition from cenomanian to santonian finely laminated organic rich black shales recovered during ocean drilling program leg 207 on demerara rise western tropical north atlantic suggest persistent anoxic free h2s conditions within the sediments and short term variations within a narrow range of anoxic to episodically dysoxic bottom waters over a 15 ma time interval in addition to being organic rich the 50 90 m thick sections examined exhibit substantial bulk rock enrichments of si p ba cu mo ni and zn relative to world average shale these observations point to high organic burial fluxes likely driven by high primary production rates which led to the establishment of intensely sulfidic pore waters and possibly bottom waters as well as to the enrichments of cr mo u and v in the sediments at the same time the irregular presence of benthic inoceramids and foraminifera in this facies demonstrates that the benthic environment could not have been continuously anoxic the 13c and 15n values of the inoceramid shell organics provide no evidence of chemosymbiosis and are consistent with pelagic rain as being a significant food source demerara rise inoceramids also exhibit well defined regularly spaced growth lines that are tracked by 13c and 18o variations in shell carbonate that cannot be simply explained by diagenesis instead productivity variations in surface waters may have paced the growth of the shells during brief oxygenation events suitable for benthic inoceramid settlement these inferences imply tight benthopelagic coupling and more dynamic benthic conditions than generally portrayed during black shale deposition by invoking different temporal scales for geochemical and paleontological data this study resolves recent contradictory conclusions e g sulfidic sedimentary conditions versus dysoxic to suboxic benthic waters drawn from studies of either sediment geochemistry or fossil distributions alone on demerara rise this variability may be relevant for discussions of black shales in general

nutrients plankton and productivity in a warm core ring in the western gulf of mexico argos drift buoy trajectory data showed that a region of anticyclonic circulation about 100 km in diameter was present over the upper continental slope of the nw corner of the gulf of mexico in september october 1988 guided by these data texas am however a maximum of only 36 54 psu at t 25 5 in contrast to as much as 36 88 psu at this density surface in a fresh ring indicated that this feature had spent many months in the western gulf since its separation from the loop current biologically the warm core ring was oligotrophic its surface waters were generally depleted in nitrate to depths of more than 100 m and chlorophyll standing stocks 20 mg m 2 primary productivity 0 4 mg c m 3 h 1 and zooplankton biomass only 4 ml 100 m 3 day and 6 ml 100 m 3 night in the upper 200 m were all extremely low deployments of floating sediment traps within the feature on two consecutive days intercepted fluxes of only 10 20 mg dry weight m 2 d 1 at 50 m and at 100 m by comparison at ring periphery where there was measurable nitrate at 100 m 0 2 1 g at l 1 chlorophyll standing stocks and primary production in the surface mixed layer were 1 5 2 times higher

quantifying carbonate dissolution and calibration of foraminiferal dissolution indices in the somali basin two sediment traps moored off somalia in 1992 1993 collected similar settling fluxes of carbonate and siliceous shells formed by various plankton groups planktic foraminifera showed large seasonal variations with more than 74 of the total planktic foraminifera flux collected during the sw monsoon summer upwelling when globigerina bulloides was dominating along with globigerinita glutinata and neogloboquadrina dutertrei the intermonsoon and ne monsoon assemblages were dominated by globigerinoides ruber we used the trap records as our no dissolution reference for comparison with three boxcore recorders in order to quantify the carbonate dissolution along a depth transect dissolution increases downslope from station 905 to 907 and 915 at depths of 1567 m 2807 m and 4035 m respectively the carbonate fraction of the sediment at station 915 which is located near the ccd is the most affected by dissolution with more than 97 of the planktic foraminifera dissolved here the planktic foraminifera assemblage is strongly modified with thick walled species such as n dutertrei globorotalia tumida and pulleniatina obliquiloculata as the most resistant it is not representative of the settling assemblage the planktic foraminiferal assemblages of the sediment surface at stations 905 and 907 remain similar to the trap assemblages and the foraminifera are well preserved although only 25 of foraminifera are apparently preserved at station 905 and 8 at station 907 those numbers are surprisingly low and infer that only a small fraction of the foraminiferal carbonate production is buried and removed from the carbon cycle this discrepancy between the export and buried flux is partly be due to bio mechanical destruction by benthic processes and to supralysoclinal dissolution due to metabolic co2 generated by the benthic organisms another important factor is the interannual variability of the productivity well known in the arabian sea the calibration of commonly used foraminiferal dissolution indices percentage of foraminiferal fragments percentage of resistant species foraminiferal dissolution index fdx to our data only shows reliable results for high dissolution levels 97 off somalia the most accurate of the proxies is the percentage of foraminiferal fragments compared to the other methods tested i e fdx planktic foraminiferal loss l percentage of radiolarians and diatoms percentage of benthic foraminifera the species assemblage appears to be not significantly modified by dissolution unless the estimated shell loss is high 92 of the arriving shells in our samples this level is expressed in the percentage of fragmentation the percentage of radiolarians and diatoms the percentage of resistant foraminifera species and fdx as 80 35 25 and 1 8 respectively the relative abundance of globigerina bulloides is a valid sw monsoon upwelling proxy only when dissolution is moderate 92 globigerina bulloides and globigerinoides ruber have similar burial efficiencies and susceptibilities to dissolution thus the ratio g bulloides g ruber is a valid proxy for past changes in the intensity of the sw monsoon even in the strongly dissolved samples in our sediment record the ratio g bulloides g ruber indicates that the sw monsoon was stronger in the recent past than in 1992 93

quantifying the paleogeographic driver of cretaceous carbonate platform development using paleoecological niche modeling abstract platform carbonates are a major component of the earth system but their spatial extent through geological time is difficult to reconstruct due to the incompleteness of the geological record sampling heterogeneity and their intrinsic complexity here we use coupled ecological niche modeling and deep time general circulation models to predict the occurrence of platform carbonates at the global scale during the cretaceous specifically niche modeling uses fuzzy logic to predict probable occurrence of platform carbonates as a function of sea surface temperature sea surface salinity primary productivity and water depth the first three parameters derive from cretaceous global paleoclimatic simulations using a coupled ocean atmosphere general circulation model while bathymetry is based on paleogeographical reconstructions model predictions are validated with the well documented and abundant geological data from the aptian the methodologies developed for the aptian are subsequently extended to other cretaceous time intervals the results of the niche model accurately predict the geographic distribution of aptian carbonate platforms if a preference for low open marine productivity levels is assumed for the rudist dominated carbonate factories however if a preference for high productivity levels is assumed the modeling results do not match the reported global distribution of aptian carbonate platforms from the early cretaceous into the late cretaceous sea level rose and the continents on average moved into lower latitudes the model predicts a corresponding increase in the extent of the carbonate platforms mainly due to the increasing extent of shallow water environments available to carbonate development these results indicate that long term sea level rise may have been a major factor responsible for the increase in the area of platform carbonates during the cretaceous

annual patterns within tree rings of the arctic middle eocene ca 45 ma isotopic signatures of precipitation relative humidity and deciduousness the spectacular preservation of middle eocene ca 45 ma wood allows for intra season sampling of stable carbon oxygen and hydrogen in order to reconstruct the paleoseasonal environment of this arctic forest paleolatitude 78 6 1 6 n present latitude 80 n carbon isotopes in bulk organics and cellulose reveal striking annual patterns interpreted as the seasonal switchover from stored to actively acquired carbon associated with deciduous growth in these unusual conifers oxygen and hydrogen stable isotopes of cellulose and cellulose nitrate allow for the calculation of changes in relative humidity and in the isotopic value of plant available water clear annual patterns of increasing relative humidity resulting from tissue growth and concomitant transpiration are apparent as is the systematic increase in the reconstructed oxygen isotope value of environmental water refl ecting progressively increasing temperatures during the growing season

the fidelity of oxygen and strontium isotope values from shallow shelf settings implications for temperature and age reconstructions abstract the oxygen and strontium isotopic ratios of marine carbonates are widely employed to derive paleotemperature and age respectively while open ocean samples are the standard source for these measures shelf settings can also provide detailed records however the implementation of shelf data for these purposes has been hindered by the perception that local environmental conditions such as freshwater influx confound regional and global signals here we directly evaluate this concern by assessing the spatial variability in the isotopic composition of biogenic carbonate precipitated along the depositional strike of an inner shelf environment data are derived from mollusc shells collected from a stratigraphically restricted transgressive unit in the early eocene 55 ma of the us gulf coastal plain gcp lithofacies and fossil assemblages suggest that an estuary was present in the westernmost study region whereas more typically marine facies predominated elsewhere isotopic composition varies predictably with paleoenvironmental setting shells from the estuary have 18o values and 87sr 86sr ratios that reflect high freshwater input specimens in the eastern gcp however from within and between outcrops separated by up to 400 km all yield similar results serial microsampling reveals congruence not only in mean 18o values but also in winter and summer extremes estimated paleotemperatures mean annual temperature of 26 c agree well with proxy and model evidence for the early eocene and the gcp and 87sr 86sr ratios are consistent with the established early eocene seawater ratio the fidelity of isotopic values relative to environment indicates that shallow shelf records have much to contribute to studies of ancient climate and ocean chemistry

heat transport deep waters and thermal gradients coupled simulation of an eocene greenhouse climate for the first time a coupled general circulation model with interactive and dynamical atmospheric oceanic and sea ice components is used to simulate an eocene 50 ma greenhouse climate we introduce efficient ocean spin up methods for coupled paleoclimate modeling sea surface temperatures ssts and salinities evolve unconstrained producing the first proxy data independent estimates for these eocene climate parameters tropical and extratropical model predicted ssts are warmer than modern values by 3 and 5 c respectively salinity driven deep water formation occurs in the north atlantic and tethys the zonal average overturning circulation is weaker than modern eocene ocean heat transport is 0 6 pw less than modern in the northern hemisphere and 0 4 pw greater in the southern hemisphere the model predicted near modern vertical and meridional eocene temperature gradients imply that the dominant theory for maintaining low gradients increased ocean heat transport is incorrect or incomplete and other mechanisms should be explored

early eocene biotic and climatic change in interior western north america imprecise correlation of the marine and terrestrial fossil records has been a major obstacle to understanding migration and extinction of continental biotas and early cenozoic climate change new sup 40 ar sup 39 ar data from the willwood formation in the bighorn basin of wyoming establish an age of 52 8 plus minus 0 3 ma for earliest lostcabinian late wasatchian faunas and coeval early eocene floras strata just beneath earliest wasatchian faunas can be correlated with the np9 np10 boundary in marine sedimentary units which has an interpolated age of approximately 55 7 ma this new information allows the authors to estimate the durations of the wasatchian approximately 5 m y and the lostcabinian approximately 2 m y and shows that the continental biotas are coeval with the acme of cenozoic warmth inferred from delta sup 18 o measurements of foraminifera from 58 to 50 ma paleoclimate in the continental interior at about 45 degree n was warm and equable but patterns of temperature change inferred from continental floras do not track precisely the marine delta sup 18 o record

arabian sea and bay of bengal exchange of salt and tracers in an ocean model exchanges of mass and salt between the mixed layers in the arabian sea and the bay of bengal are examined in a model of the indian ocean using passive tracers as a tool to map the pathways inflow of high salinity water from the arabian sea into the bay of bengal is significant and occurs after the mature phase of the southwest monsoon freshwater transport out of the bay of bengal is southward throughout the year along the eastern boundary of the indian ocean low salinity water transport into the arabian sea occurs in the somali current during the southwest monsoon closing a clockwise path of water mass transport only a small fraction of low salinity water is advected into the eastern arabian sea from the bay of bengal

oxygen isotope fluctuations in a modern north sea oyster crassostrea gigas compared with annual variations in seawater temperature implications for palaeoclimate studies abstract a total of 181 oxygen isotope values from sequential samples of the left shell of a modern pacific oyster crassostrea gigas that lived on a sub tidal oyster bank in the list basin north sea germany shows periodically varying values between 1 3 and 2 5 in order to test whether these 18 o fluctuations reflect seawater temperature changes the isotope values of the shell were compared to actual seawater temperature variations from the region c gigas serves as an excellent proxy for temperature of palaeoseawater and the results show that the examined oyster precipitated its shell in 18 o equilibrium with the ambient seawater a cessation of the oyster shell calcification starts at water temperatures below 6 c at lower temperatures than previously thought for crassostrea for palaeoclimate investigations the termination of shell production is important because the lowest temperatures might not be represented in the shell higher water temperatures are therefore potentially over represented in time spans when the shell grows faster and mean oxygen isotope values may potentially bias the mean seawater temperatures of annual variations towards higher temperatures

spondylus gaederopus a new mediterranean climate archive based on high resolution oxygen and carbon isotope analyses abstract the presented study evaluates the potential of the mediterranean bivalve spondylus gaederopus linne 1758 as a palaeoclimatic archive its fixosessil life in water depths 18 o and carbon 13 c isotope data obtained from high resolution sampling of a modern s gaederopus from rhodes greece collected alive in 4 m water depth in spring 2002 suggest that the outer calcitic shell layer as well as the inner aragonitic shell layer is precipitated in equilibrium with seawater due to the complexity of the outer calcitic shell layer with its spines and prickles a chronological sampling of this part of the shell is not possible in contrast the inner aragonitic shell layer with its well developed growth bands allows a fast chronologic sampling 18 aragonite growth bands were sampled from the inner shell layer of the studied specimen corresponding to 9 years of growth with 9 10 samples per year carbon stable isotopes 13 c ar yield mean values of 0 70 0 6 and show a remarkable negative shift of about 1 8 from about 1 6 to about 0 2 through time this ontogenetic depletion in 13 c might be related to physiological developments like sexual maturity as it is the case in other bivalves seasonal variations with an average amplitude of 0 85 are superimposed on the observed secular trend these cycles show an increase in amplitude that has not been described before and cannot be explained so far oxygen isotopes 18 o ar exhibit mean values of 1 11 0 5 clearly pronounced seasonal cycles with an average amplitude of 1 45 show the same wavelength as the carbon cycles but run out of phase the 18 o ar correlates well with sea surface temperature and correlation fits best during summer periods deviations between measured and predicted 18 o ar input data sea surface temperature seawater 18 o show that maximal discrepancies occur during winter periods these discrepancies can be best explained by a decrease in local seawater 18 o due to increased freshwater influx on rhodes maxima in precipitation hence river runoff occur during winter months

characteristics of wind generated rings in the eastern tropical pacific ocean eddies are generated in the eastern tropical pacific 3 s 23 n 75 105 w by winds blowing through central american mountain passes from the atlantic we used coastal zone color scanner czcs and advanced very high resolution radiometer avhrr satellite imagery complemented with monthly in situ sea surface temperature and wind series from the comprehensive ocean atmosphere data set coads to study these eddies and their effect on pigment concentrations in the region pigment values in the gulf of tehuantepec generally reach higher values in november march before those in the gulf of papagayo the eddies generated in the gulf of tehuantepec are associated with passages of cold fronts across the gulf of mexico from the north while the eddies off papagayo and panama are associated with increases in trade wind intensity czcs images showed larger numbers of eddies per season than have been previously reported on the basis of in situ and avhrr observations or numerical simulations we counted 13 eddies in 1979 1980 8 in 1984 1985 and 6 in 1985 1986 the eddies transfer both energy and biological constituents from the continental margin to the offshore tropical pacific the eddies frequently moved distances in excess of 1500 km from their point of origin both anticyclonic and cyclonic eddies are generated but in general there are more anticyclones anticyclonic eddies generally moved to the southwest some cyclonic eddies moved to the south and southeast along the central american coast and appeared to be trapped by the cyclonic costa rica thermal dome eddies traveled at speeds varying between 9 and 21 cm s 1 and had diameters of 100 500 km phytoplankton concentrations associated with the eddies varied from 2 to 10 mg m 3 within 70 km of the coast to 1 mg m 3 up to 600 km of the coast between late april and october fewer eddies were observed and phytoplankton concentrations were lower 0 25 mg m 3 and more uniform over the region

late paleocene early eocene climate changes in southwestern wyoming paleobotanical analysis the warmest global temperatures of the cenozoic era occurred in early eocene time following a warming trend that started in late paleocene time the greater green river basin of southwestern wyoming is one of the best areas in the rocky mountains for paleobotanical investigation of the paleocene eocene climatic transition intensive sampling has resulted in the recovery of an estimated 189 species of plant macrofossils from the tiffanian clarkforkian wasatchian and bridgerian land mammal ages the leaf morphologies and taxonomic affinities of these fossils were used in combination with other indicators to evaluate paleocene eocene climates following cool humid conditions in the tiffanian the clarkforkian was humid and subtropical and several plant families with modern tropical affinities appeared however as in the tiffanian clarkforkian floras had low diversity and were dominated by a single species in the birch family mean annual temperature mat rose from an estimated 12 c in the tiffanian to 19 c in the clarkforkian while mean annual precipitation map for the tiffanian and clarkforkian is estimated to have been 130 150 cm little fossil plant material is preserved from the latest clarkforkian or the earliest wasatchian which is thought to have contained an interval of cooling and drying followed by renewed warming by the middle wasatchian the time of the cenozoic thermal maximum the inferred mat was about 21 c and the map was near 140 cm a second influx of plant families with tropical affinities appeared in the area and diversity increased significantly but most plant families known from the clarkforkian persisted species turnover from the clarkforkian to the wasatchian was greater than 80 a second turnover of more than 80 of species but not families from the wasatchian to the early bridgerian accompanied drying and increased seasonality of precipitation the early bridgerian mat is inferred to have been near 20 c and the map to have been about 80 cm except for the tiffanian and possibly portions of the early wasatchian paleoclimates during the study interval were predominantly frost free although the moderating influence of the green river lake system has been suggested as a possible explanation for mild eocene winters in wyoming this study shows that virtually frostfree climates existed in the area prior to and independent of significant lake development

paratropical floral extinction in the late palaeocene early eocene the palaeocene eocene thermal maximum petm at c 55 8 ma marks a transient c 100 ka duration interval of rapid greenhouse warming that had profound effects on marine and terrestrial biota plant communities responded rapidly with major compositional turnover the long term effects on tropical vegetation communities that stem from the brief period of global warming are unclear we present pollen data from the paratropical us gulf coast eastern mississippi western alabama and georgia which had background palaeogene mean annual temperatures of 26 27 c sporomorph data pollen and spores demonstrate that taxonomic diversity increases over c 1 ma in the late palaeocene but this trend is replaced with the first occurrences of taxa that mark the early eocene by a pronounced extinction into the early eocene c 20 of the palynoflora taxonomic diversity also decreases by up to 38 in the early eocene the timing of the extinction is not clearly resolved but may be restricted to the earliest part of the early eocene two richness estimators chao 2 and jackknife 2 both demonstrate that late palaeocene samples contain significantly more taxa than those in the early eocene extinction on the us gulf coast proves that ancient tropical ecosystems were highly susceptible to changes in diversity mediated directly or indirectly by environmental change even during equable greenhouse climates in the early palaeogene

climatic influences on the paleogene evolution of alkenones application of the alkenone paleotemperature proxy uk 37 for marine sediments is typically constrained by three factors i an absence of alkatrienones in sediments deposited where ocean temperatures exceed 28 c ii loss of alkenones in thermally altered sediments and iii poor preservation of alkenone signals due to oxidative degradation in addition there appears to be a temporal limit on the occurrence of alkatrienones which are conspicuously absent in all alkenone containing sediments from the early aptian to the immediate aftermath of the early eocene climatic optimum eeco when they first appeared in arctic ocean sediments compilation of reported and previously unpublished alkenone distributions for the paleogene coupled with assessment of co occurring calcareous nannoplankton genera within the noelaerhabdaceae provide evidence that evolutionary developments in alkenone occurrences include biosynthetic responses likely triggered by climate change the timing of emergence of alkatrienones post eeco and their subsequent appearance at all latitudes during the middle eocene accompanies expansion of the calcareous nannoplankton genus reticulofenestra coincident with significant climate driven changes in oceanic conditions including i modification of trophic structure associated with weakened thermal stratification ii higher productivity facilitated by enhanced nutrient influx and iii changes in seasonality initially at high latitudes related to greater latitudinal temperature gradients collectively these changes would serve to favor eurythermal eurytrophic algae like reticulofenestra with a biomechanism to store energy through production of lipid bodies rich in alkenones during episodes of higher nutrient availability this ability likely enhanced the viability of this marine haptophyte when nutrients were limiting ultimately ensuring its evolutionary success

characteristics of the near surface currents in the indian ocean as deduced from satellite tracked surface drifters part i pseudo eulerian statistics using the 1985 2013 record of near surface currents from satellite tracked drifters the pseudo eulerian statistics of the near surface circulation in the indian ocean io are analyzed it is found that the distributions of the current velocities and mean kinetic energy mke in the io are extremely inhomogeneous in space and nonstationary in time the most energetic regions with climatologic mean velocity over 50cms 21 and mke over 500cm 2 s 22 are found off the eastern coast of somalia with maxima of over 100cms 21 and 1500cm 2 s 22 and the equatorial io associated with the strong annually reversing somalia current and the twice a year eastward equatorial jets high eddy kinetic energy eke is found in regions of the equatorial io western boundary currents and agulhas return current with a maximum of over 3000cm 2 s 22 off the eastern coast of somalia the lowest eke 500cm 2 s 22 occurs in the south subtropical gyre between 308 and 408s and the central eastern arabian sea annual and semiannual variability is a significant fraction of the total eke off the eastern coast of somalia and in the central eastern equatorial io in general both the mke and eke estimated in the present study are qualitatively in agreement with but quantitatively larger than estimates from previous studies these pseudo eulerian mke and eke fields based on the most extensivedrifterdatasettodate arethemostpreciseinsituestimatestodateandcanbeusedtovalidatesatellite and numerical results

evolution of early cenozoic marine temperatures the equator to high southern latitude sea surface and vertical temperature gradients are reconstructed from oxygen isotope values of planktonic and benthic foraminifers for the following five time intervals late paleocene early eocene early middle eocene late eocene and early oligocene paleotemperatures are calculated using standard oxygen isotope temperature equations with adjustments to account for 1 variations in sea water 18o related to changes in global ice volume over time and 2 latitudinal gradients in surface water 18o these reconstructions indicate that sea surface temperatures sst of the southern oceans in the early eocene were as high as 15 c whereas temperatures during the late paleocene and early middle eocene reached maximum levels of 10 12 c by the late eocene and early oligocene high latitude sst had declined to 6 and 4 c respectively for most of the early paleogene low latitude sub tropical temperatures remained constant and well within the range of holocene temperatures 24 ndash 25 c but by the late eocene and early oligocene declined to values in the range of 18 to 22 c the late paleogene apparent decline in tropical temperatures however might be artificial because of dissolution of near surface foraminifera tests which biased sediment assemblages toward deeper dwelling foraminifera moreover according to recent plate reconstructions it appears that the majority of sites upon which the late eocene and early oligocene tropical temperatures were previously established were located either in or near regions likely to have been influenced by upwelling global deepwater temperature on average paralleled southern ocean sst for most of the paleogene we speculate based on the overall timing and character of marine sea surface temperature variation during the paleogene that some combination of both higher levels of greenhouse gases and increased heat transport was responsible for the exceptional high latitude warmth of the early eocene

gastropod carbonate δ18o and δ13c values record strong seasonal productivity and stratification shifts during the late eocene in england high resolution 18o and 13c measurements obtained from the gastropod clavilithes macrospira provide the most detailed record of seasonal change in temperature range 14 c seawater chemistry and bottom water ventilation yet obtained from late eocene strata type bartonian ca 40 ma the 18o oscillations suggest a linear rate of long term growth and rapid growth in spring early summer coherence analysis shows that 13c patterns vary from being closely in phase with respect to annual 18o oscillations to being antiphase with a phase shift toward a spring or more rarely an autumnal 13c peak these patterns are attributed to unstable seasonal productivity and or the development of a seston rich bottom layer in which the 13c gradients arising from seasonal eutrophication were perturbed by spring storms such episodes may have led to the decline and extinction of oligotrophic marine biota with photosymbionts including nummulites in the late eocene

a summer monsoon pump to keep the bay of bengal salty the bay of bengal receives a large influx of freshwater from precipitation and river discharge outflow of excess freshwater and inflow of saltier water is required to prevent the bay from freshening relatively fresh water flows out of the bay along its boundaries and inflow of saltier water occurs via the summer monsoon current smc which flows eastward from the arabian sea into the bay this saltier water however slides under the lighter surface water of the bay maintaining the salt balance of the bay therefore demands upward mixing of this saltier subsurface water here we show that an efficient mechanism for this mixing is provided by upward pumping of saltier water in several bursts during the summer monsoon along the meandering path of the smc advection by currents can then take this saltier water into the rest of the basin allowing the bay to stay salty despite a large net freshwater input

southern bay of bengal currents and salinity intrusions during the northeast monsoon shipboard velocity and hydrographic profiles collected in december 2013 along with drifter observations satellite altimetry global ocean nowcast forecast products and coupled model simulations were used to examine the circulation in the southern bay of bengal as part of ongoing international research efforts in the region the observations captured the southward flowing east india coastal current eicc off southeast india and east of sri lanka the eicc was approximately 100 km wide with speeds exceeding 1 m s 1 in the upper 75 m east of the eicc a subsurface intensified 300 km wide northward current was observed with maximum speeds as high as 1 m s 1 between 50 m and 75 m the eicc moved low salinity water out of the bay and the subsurface northward flow carried high salinity water into the bay during typical northeast monsoon conditions during a time period when the central equatorial indian ocean was experiencing a westerly wind burst related to the madden julian oscillation mjo event while the northward subsurface high salinity flow has previously been observed during the southwest monsoon it was observed during the northeast monsoon the observations are consistent with northward high salinity subsurface flow in numerical model solutions the analysis suggests that direct forcing along the equator may play a significant role for high salinity intrusions east of sri lanka

intra annual isotopic variation in venericardia bivalves implications for early eocene temperature seasonality and salinity on the u s gulf coast abstract stable isotope compositions were determined for 166 microsamples of aragonite from the bivalve venericardia hatcheplata collected from the early eocene hatchetigbee formation in southwestern alabama these were milled from two transects one across the left valve hinge plate and one along the growth axis amplitude and spacing of about nine years of seasonal variation is very regular with peaks and troughs occurring at equal intervals and reaching consistent compositions except for some attenuation in both parameters during the last three years of life assuming an ice free world with an ocean 18o value of about 1 0 and using the aragonite water fractionation equation of grossman and ku 1986 isotope derived paleotemperatures are somewhat warmer 31 c than temperatures presently recorded anywhere on the earth s surface and exhibit significantly greater seasonality 12 c than regions with the warmest mean temperatures it is therefore likely that these very negative and extremely seasonal 18o values reflect the influence of seasonal discharge of 18o depleted river water into the eocene gulf of mexico comparison of these data with 1 mean annual temperature versus seasonal temperature variation from modern climates 2 isotopic compositions reported from coeval molluscs and 3 isotopic compositions of global meteoric precipitation and united states rivers suggest that mean annual temperature along this portion of the eocene gulf coast was in fact about 26 c and varied seasonally from a winter low of about 25 c to a summer high of 27 c differences between these temperatures and those derived from direct conversion of oxygen isotope values reflect the influence of seasonal influx of fresh 18o value of 4 7 water during deposition of this portion of the hatchetigbee formation ambient water 18o values varied between winter values of about 1 0 to less than 3 5 during the summer freshwater discharge served to seasonally depress salinity to 10 to 16 ppt along this part of the gulf coast the early eocene was perhaps the warmest time interval of the past 65 million years primarily manifest as lower equator to pole temperature gradients in this context an eocene mean annual temperature of 26 c is not much higher than modern surface water temperatures of about 24 c at 29 30 n immediately off the modern alabama coast seasonal temperature variation of 2 to 3 c about a mean of 26 c however is significantly lower than that off coastal alabama 19 to 30 c and occurs only along modern equatorial coasts at latitudes less than 19 this implies that early eocene tropical conditions extended well beyond modern latitudinal limits

the response of the surface circulation of the arabian sea to monsoonal forcing abstracttwo decades of drifter and satellite data allow the authors to describe the seasonal evolution of the surface circulation of the arabian sea which reverses annually with the indian monsoon winds this study finds several features that advance current understanding most significantly northward flow appears along the length of the western boundary together with a weak anticyclone at 6 n a precursor to the great whirl as early as march or april one or two months before the southwest monsoon winds this circulation is driven by planetary waves which are initiated by wind curl forcing during the previous southwest monsoon leading the authors to speculate that there is an oceanic mechanism through which one monsoon may precondition the next second the authors find that the eastward south equatorial counter current secc is present year round fed by the northward east african coastal current eacc during the southwest monsoon the eacc overshoots the equator and splits feeding both northwa

seasonal climatic fluctuations in the late triassic tropics high resolution oxygen isotope records from aragonitic bivalve shells cassian formation northern italy abstract three megalodontoid bivalves from the upper triassic cassian formation n italy dolomites were sampled for 13 c and 18 o sclerochronology n 270 with more than 1000 described invertebrate species the cassian formation has one of the best records of an early mesozoic tropical fauna in addition the cassian formation is one of the very few triassic occurrences with original aragonite preservation with all studied shells consisting of pristine aragonite the presence of aragonite and crossed lamellar as well as fibrous prismatic shell microstructures shown for the first time for triassic megalodontoids suggests absence or minimal impact of diagenetic alteration the 13 c values range from 3 6 to 5 8 and show a distinct cyclicity in two studied shells whereas a third shell shows no obvious cyclicity in one bivalve specimen the cycles are somewhat offset from 18 o cycles and in the other specimen 18 o and 13 c curves are inversely correlated seasonal variation in freshwater runoff including nutrient input and subsequent changes in plankton productivity during dry and wet seasons may explain 13 c cyclicity 18 o values show a pronounced cyclicity within each of the studied shells varying from 3 6 to 1 4 the variations in 18 o suggest a pronounced seasonality in late triassic tropical shallow waters of the western tethys with inferred seasonal temperature changes ranging from 24 to 32 c influx of fresh water during the rainy seasons mega monsoon or upwelling might also explain part of the variation in 18 o the presented data suggest that the diverse cassian fauna lived under conditions characterized by warm sea surface waters with a pronounced seasonality similar conditions are reported for some modern tropical settings

possible role of oceanic heat transport in early eocene climate increased oceanic heat transport has often been cited as a means of maintaining warm high latitude surface temperatures in many intervals of the geologic past including the early eocene although the excess amount of oceanic heat transport required by warm high latitude sea surface temperatures can be calculated empirically determining how additional oceanic heat transport would take place has yet to be accomplished that the mechanisms of enhanced poleward oceanic heat transport remain undefined in paleoclimate reconstructions is an important point that is often overlooked using early eocene climate as an example we consider various ways to produce enhanced poleward heat transport and latitudinal energy redistribution of the sign and magnitude required by interpreted early eocene conditions our interpolation of early eocene paleotemperature data indicate that an approximately 30 increase in poleward heat transport would be required to maintain eocene high latitude temperatures this increased heat transport appears difficult to accomplish by any means of ocean circulation if we use present ocean circulation characteristics to evaluate early eocene rates either oceanic processes were very different from those of the present to produce the early eocene climate conditions or oceanic heat transport was not the primary cause of that climate we believe that atmospheric processes with contributions from other factors such as clouds were the most likely primary cause of early eocene climate

a comparison of eocene climate model results to quantified paleoclimatic interpretations abstract the integration of climate model results and geologic information offers considerable potential for deriving greater insight into the geologic record in this study climate model results and quantified climatic interpretations derived from proxy data are compared to assess model capabilities and to examine proxy data interpretations atmospheric general circulation model experiments were used to produce a range of possible representative eocene climate states based on current knowledge of the eocene record the climate model experiments incorporate two idealized endmembers of eocene ocean surface temperature distributions characterized by very different latitudinal gradients model results are compared to quantified interpretations of the climate of early eocene north america in an attempt to identify one of the sea surface temperature distributions as more likely to have existed during the eocene the comparisons do not produce a conclusive match between inferred paleoclimatic information and any single case of model results but some interesting insights become apparent model predictions of mean annual temperature and mean annual precipitation compare favorably to interpretations from geologic evidence but there are large differences between model results and interpreted paleoclimatic parameters of minimum surface temperature and mean annual temperature range several possible causes for these differences are discussed

application of calcite mg partitioning functions to the reconstruction of paleocean mg ca abstract calcite mg ca is usually assumed to vary linearly with solution mg ca that a constant partition coefficient describes the relationship between these two ratios numerous published empirical datasets suggests that this relationship is better described by a power function we provide a compilation of these literature data for biotic and abiotic calcite in the form of calcite mg ca f solution mg ca h where f and h are empirically determined fitting parameters describing the slope and deviation from linearity respectively of the function this is equivalent to freundlich sorption behavior controlling mg incorporation in calcite using a power function instead of a partition coefficient lowers phanerozoic seawater mg ca estimates based on echinoderm skeletal material by on average 0 5 mol mol from previous estimates these functions can also be used to model the primary skeletal calcite mg ca of numerous calcite phases through geologic time such modeling suggests that the mg ca of all calcite precipitated from seawater has varied through the phanerozoic in response to changing seawater mg ca and that the overall range in mg ca measured among various calcite phases would be greatest when seawater mg ca was also high e g aragonite seas and lowest when seawater mg ca was low e g calcite seas it follows that during times of calcite seas when the seawater mg ca is presumed to have been lower deposition of calcite with low mg contents would have resulted in a depressed drive for diagenetic stabilization of shelfal carbonate and in turn lead to greater preservation of crystal and skeletal microfabrics and primary chemistries in biotic and abiotic calcites

combined active passive retrievals of ocean vector wind and sea surface salinity with smap in this paper we introduce the combined active passive cap data product for the soil moisture active passive mission we develop the algorithms for a radiometer only salinity product a radar only vector wind product and a cap vector wind and salinity product we show that the performance of the radiometer only salinity product nears but is still inferior to the aquarius salinity accuracy performance when aggregated on a monthly timescale then we show that the radar only vector wind product has reasonable accuracy away from the nadir track while suffering from inadequate measurement geometry in the middle of the swath finally we demonstrate that the cap salinity and vector wind performance is superior to individual algorithms and provides wind vectors nearly as good as rapidscat for low to moderate winds and possibly superior to traditional scatterometers for wind speeds larger than 12 5 m s

strontium to calcium ratios in the marine gastropod conus ermineus growth rate effects and temperature calibration here we investigate the potential of sr ca ratios in the marine gastropod conus ermineus for reconstructing seawater temperatures we present annually resolved records of sr ca and 18o for four shells collected alive from the flower garden banks national marine sanctuary in the gulf of mexico our results show that variations in sr ca and 18o covary with the in situ seasonal temperature cycle sr ca and temperature are positively correlated in contrast with the inverse relationship found in inorganically precipitated aragonite the seasonal sr ca variability is superimposed on a long term trend of increasing sr ca with age both the seasonal and long term ontogenetic changes in sr ca are associated with variations in growth rate defined here as the shell linear extension rate ler the seasonal variability in ler is superimposed on a long term decrease with ontogeny thus the covariance of sr ca ratios with temperature and ler suggests that sr incorporation is likely driven by temperature influence on growth rate rather than by thermodynamic effects unlike the seasonal variability the ontogenetic effect is characterized by inverse covariation between sr ca and ler suggesting that sr ca variability is not controlled by growth rate alone but probably by two different biomineralization mechanisms one related to temperature and the other related to age we use the seasonal sr ca signal of four shells to construct a temperature calibration to minimize the ontogenetic effects we separate the records into juvenile and adult growth stages and calculate the sr ca temperature t relationships juvenile sr ca mmol mol 1 0 042 0 008 t c 0 24 0 21 r2 0 66 adult sr ca mmol mol 1 0 072 0 014 t c 0 05 0 34 r2 0 68 applying the calibration to a single specimen provides mean annual temperature estimates within 1 c of the in situ temperature record but resolves the seasonal variability only within 3 5 c the large error in the seasonal estimates reflects the high variability among specimens to reduce the uncertainty on seasonal temperatures we propose combining records from multiple shells to generate an average temperature record the potential of this approach needs however to be validated in other locations

seasonality in the north sea during the allerod and late medieval climate optimum using bivalve sclerochronology seasonal temperature patterns may have changed through time in response to current global warming however the temporal resolution of available proxy records is not sufficient to quantify paleotemperature seasonality prior to anthropogenic forcing of the climate in the present study we reconstructed seasonal and inter annual temperature patterns of the north sea during the last 140 years the allerod interglacial and the late medieval climate optimum using sclerochronological and 18oaragonite data from bivalve shells arctica islandica on average the climate during 1278 1353 ad was ca 1 1 c colder and seasonality was ca 60 less than today during the allerod long term temperatures remained about 3 2 c below present values and absolute summer and winter anomalies were ca 4 and 2 7 c respectively however seasonality was statistically indistinguishable from today long term average temperatures compare well with existing data for the late medieval and allerod but detailed information on seasonality during the studied time intervals has never been presented before our data also demonstrated that annual instrumental and 18oaragonite derived temperatures did not always match this difference is explained by 1 nao driven salinity changes which influence the temperature estimation from 18oaragonite and 2 food driven changes in growth rates portions of the shell that formed more rapidly are overrepresented in carbonate samples our study indicated that individual bivalve shells can open discrete near century long ultra high resolution windows into the climate past such information can be vital for testing and verifying numerical climate models

planktic foraminiferal and sea surface temperature record during the last 1 myr across the subtropical front southwest pacific planktic foraminiferal faunas and modern analogue technique estimates of sea surface temperature sst for the last 1 million years myr are compared between core sites to the north odp 1125 178 faunas and south dsdp 594 374 faunas of the present location of the subtropical front stf east of new zealand faunas beneath cool subtropical water stw north of the stf are dominated by dextral neogloboquadrina pachyderma globorotalia inflata and globigerina bulloides whereas faunas to the south are strongly dominated by sinistral n pachyderma 80 95 in glacials with increased g bulloides 20 50 and dextral n pachyderma 15 50 in interglacials beneath subantarctic water or saw canonical correspondence analysis indicates that at both sites sst and related factors were the most important environmental influences on faunal composition greater climate related faunal fluctuations occur in the south significant faunal changes occur through time at both sites particularly towards the end of the mid pleistocene climate transition mis18 15 e g decline of globorotalia crassula in stw disappearance of globorotalia puncticulata in saw and during mis8 5 interglacial sst estimates in the north are similar to the present day throughout the last 1 myr to the south interglacial ssts are more variable with peaks 4 7 c cooler than present through much of the early and middle pleistocene but in mis11 mis5 5 and early mis1 peaks are estimated to have been 2 4 c warmer than present these high temperatures are attributed to southward spread of the stf across the submarine chatham rise along which the stf appears to have been dynamically positioned throughout most of the last 1 myr for much of the last 1 myr glacial sst estimates in the north were only 1 2 c cooler than the present interglacial except in mis16 mis8 mis6 and mis4 2 when estimates are 4 7 c cooler these cooler temperatures are attributed to jetting of saw through the mernoo saddle across the chatham rise and or waning of the stw current to the south glacial sst estimates were consistently 10 11 c cooler than present similar to temperatures and faunas currently found in the vicinity of the polar front one interpretation is that these cold temperatures reflect thermocline changes and increased circumpolar surface water spinning off the subantarctic front as an enhanced bounty gyre along the south side of the chatham rise for most of the last 1 myr the temperature gradient across the stf has been considerably greater than the present 4 c during glacial episodes the stf in this region did not migrate northwards but instead there was an intensification of the temperature gradient across it interglacials 4 11 c glacials 8 14 c

winter and summer temperatures of the early middle eocene of france from turritella δ18o profiles the mean annual range of temperature is from a climatological point of view at least as important as the mean annual temperature in order to examine intra annual temperature variations in the warm early cenozoic we have analyzed stable oxygen and carbon isotopes along the transect of growth on excellently preserved specimens of the gastropod turritella imbricataria and the bivalve venericardia imbricata from sedimentary rocks of early middle eocene age ca 46 ma in the paris basin turritella shell growth is fast throughout the year and the isotopic records give the first detailed information about early middle eocene seasonal variations the oxygen isotope profiles indicate winter temperatures of about 14 c and summer temperatures of up to 28 c i e a seasonality indistinguishable from the present situation but an annual temperature some 10 c higher our results contradict the opinion that the climate during this period was more equable than that of today

reevaluation of conflicting eocene tropical temperature estimates molluskan oxygen isotope evidence for warm low latitudes oxygen isotope data from planktonic foraminifera for the warm eocene epoch suggest that tropical sea surface temperatures ssts may have been cooler than at present such data have stimulated various explanations involving e g major changes in ocean heat transport however the planktonic data disagree with terrestrial climate proxies which suggest significantly warmer low latitude temperatures we examined this discrepancy by analyzing seasonal oxygen isotope variations in shallow marine mollusks from the mississippi embayment results indicate that mean annual ssts decreased from 26 27 c in the early eocene to 22 23 c in the oligocene agreeing well with temperatures inferred from terrestrial climate proxies these cooling trends with more significant winter cooling 5 c than summer cooling 3 c are consistent with the predicted consequences of decreasing atmospheric co 2 concentration through the paleogene suggesting that atmospheric co 2 change was a major controlling factor for paleogene climate change that winter sst estimates from the mollusks agree well with the foraminiferal sst estimates suggests that planktonic foraminiferal growth in low latitudes occurred mainly during the cooler winter months throughout the eocene we hypothesize that the unusual hydrography of eocene oceans shifted foraminiferal productivity primarily to winter biasing foraminiferal sst estimates of mean annual ssts

eocene equator to pole surface ocean temperatures a significant climate problem eocene surface ocean paleotemperature data which illustrate a reduced equator to pole temperature gradient cooler tropical sea surface temperatures and a relatively small global temperature warming 2 c present a significant climatic enigma if the reconstructions are correct such a temperature distribution can be achieved through greater poleward heat transport by the ocean however the mechanism for a greater oceanic role is uncertain in addition the results from climate models for conditions of a substantially greater poleward heat transport by the oceans indicate a weak atmospheric circulation and highly seasonal continental interior climates the weak atmospheric circulation is consistent with the record of continent derived eolian sediment recovered in deep sea cores however the eocene paleobotanical evidence from continental interiors indicates a very mild seasonality the lack of consistency between model results oceanic data and terrestrial data defines the nature of the problem of eocene climates the solution must involve reinterpretation of at least one major source of information