dissociation of oceanic methane hydrate as a cause of the carbon isotope excursion at the end of the paleocene isotopic records across the latest paleocene thermal maximum lptm indicate that bottom water temperature increased by more than 4 c during a brief time interval 104 years of the latest paleocene 55 6 ma there also was a coeval 2 to 3 excursion in the 13c of the ocean atmosphere inorganic carbon reservoir given the large mass of this reservoir a rapid 13c shift of this magnitude is difficult to explain within the context of conventional hypotheses for changing the mean carbon isotope composition of the ocean and atmosphere however a direct consequence of warming bottom water temperature from 11 to 15 c over 104 years would be a significant change in sediment thermal gradients and dissociation of oceanic ch4 hydrate at locations with intermediate water depths in terms of the present day oceanic ch4 hydrate reservoir thermal dissociation of oceanic ch4 hydrate during the lptm could have released greater than 1 1 to 2 1 1018 g of carbon with a 13c of approximately 60 the release and subsequent oxidation of this amount of carbon is sufficient to explain a 2 to 3 excursion in 13c across the lptm fate of ch4 in oceanic hydrates must be considered in developing models of the climatic and paleoceanographic regimes that operated during the lptm

biogeographic gradients of middle eocene oligocene calcareous nannoplankton in the south atlantic ocean middle eocene oligocene calcareous nannoplankton have been analyzed quantitatively for eight dsdp and odp sites ranging from the equatorial zone to 65 s latitude in the south atlantic ocean there is a general decrease in calcareous nannoplankton species diversity from the middle eocene through the oligocene and species diversity also decreases towards the higher latitudes similar to findings of other studies the drop of the species diversity of calcareous nannoplankton across the eocene oligocene boundary is not drastic delineation of latitudinal distribution patterns of individual species or groups and r mode cluser analysis permit the classification of warm water taxa coccolithus formosus discoasters helicosphaerids and sphenoliths temperate water taxa coccoliths pelagicus cyclicargoliths floridanus group reticulofenestra bisecta reticulofenestra samodurovii reticulofenestra umbilica and cool water taxa chiasmoliths isthmolithus recurvus and reticulofenestra daviesii the abundance of warm water taxa plummets whereas the abundance of cool water taxa sharply increases across the eocene oligocene boundary at the middle and high latitude sites reflecting a profound cooling event in these areas polar ordination and similarity analyses reveal that steep latitudinal biogeographic gradients had been established at least by the middle eocene the gradient greatly increases near the eocene oligocene boundary indicating more severe and permanent cooling at the high latitudes the biogeographic gradient data of this study conflict with the widely accepted inference from the oxygen isotopic data that the thermal gradients between mid latitudes and high latitudes are low or nearly flat for the paleogene oceans lower surface water salinities in the high latitudes may have lowered the 18o values of the planktonic microfossils but apparently did not have significant effect on latitudinal distribution patterns of calcareous nannoplankton which offers an independent means for estimating latitudinal thermal gradients

abrupt deep sea warming palaeoceanographic changes and benthic extinctions at the end of the palaeocene a remarkable oxygen and carbon isotope excursion occurred in antarctic waters near the end of the palaeocene 57 33 myr ago indicating rapid global warming and oceanographic changes that caused one of the largest deep sea benthic extinctions of the past 90 million years in contrast the oceanic plankton were largely unaffected implying a decoupling of the deep and shallow ecosystems the data suggest that for a few thousand years ocean circulation underwent fundamental changes producing a transient state that although brief had long term effects on environmental and biotic evolution

a blast of gas in the latest paleocene simulating first order effects of massive dissociation of oceanic methane hydrate carbonate and organic matter deposited during the latest paleocene thermal maximum is characterized by a remarkable 2 5 excursion in delta 13c that occurred over approximately 10 4 yr and returned to near initial values in an exponential pattern over approximately 2 x 10 5 yr it has been hypothesized that this excursion signifies transfer of 1 4 to 2 8 x 10 18 g of ch4 from oceanic hydrates to the combined ocean atmosphere inorganic carbon reservoir a scenario with 1 12 x 10 18 g of ch4 is numerically simulated here within the framework of the present day global carbon cycle to test the plausibility of the hypothesis we find that 1 the delta 13c of the deep ocean shallow ocean and atmosphere decreases by 2 3 over 10 4 yr and returns to initial values in an exponential pattern over approximately 2 x 10 5 yr 2 the depth of the lysocline shoals by up to 400 m over 10 4 yr and this rise is most pronounced in one ocean region and 3 global surface temperature increases by approximately 2 degrees c over 10 4 yr and returns to initial values over approximately 2 x 10 6 yr the first effect is quantitatively consistent with the geologic record the latter two effects are qualitatively consistent with observations thus significant ch4 release from oceanic hydrates is a plausible explanation for observed carbon cycle perturbations during the thermal maximum this conclusion is of broad interest because the flux of ch4 invoked during the maximum is of similar magnitude to that released to the atmosphere from present day anthropogenic ch4 sources

abrupt hydrographic changes in the equatorial pacific and subtropical atlantic from foraminiferal mg ca indicate greenhouse origin for the thermal maximum at the paleocene eocene boundary 1 the paleocene eocene boundary peb was marked by an extraordinary climatic event hypothesized to originate from a large perturbation to the carbon cycle which fueled global warming the rapid dissociation of oceanic methane hydrates the pattern of surface warming interpreted from existing sea surface temperature records is not consistent with a greenhouse origin for this event which would have fueled sea surface warming globally although oxygen isotope 18o based reconstructions indicate polar warming results for the tropics and subtropics are ambiguous because of uncertainties associated with interpreting planktonic foraminiferal 18o to remedy this we have constructed high resolution temperature records based on mg ca of multiple species of both surface and thermocline dwelling planktonic foraminifera across the peb in the equatorial pacific and subtropical atlantic during the carbon isotope excursion cie surface temperatures increased by 3 5 4 c and thermocline temperatures warmed by 3 c estimates of surface water and thermocline salinity based on paired mg ca and 18o data indicate a pattern of hydrographic changes in the equatorial and subtropical oceans that is different from previously proposed with a more vigorous hydrologic cycle during warming the pattern of warming and salinity changes are consistent with this being a greenhouse induced global warming event and the timing of hydrographic changes relative to the cie supports the hypothesis that gradual warming of intermediate deep waters triggered methane hydrate dissociation

unsaturated quasi linear flow analysis in v shaped domains abstract an explicit essentially 2d solution for steady unsaturated seepage flow from infinity to a corner with boundaries kept at constant suction is obtained for the kirchhoff potential by the method of separation of variables a system of coordinates coinciding with the corner boundaries is selected distributions of the pressure stream lines and velocities are derived non existence of steady flows at certain corner orientations deflection of the incident flow by slanted boundaries and inflection points on the stream lines close to the vertex are discussed one dimensional limit for zones far from the trough is examined refraction and further collimation of the upper 2d flow in the second underlying porous medium with implications to geotechnical capillary barriers is studied a vadose zone originated accretion is matched with a saturated wing which appears on a slanted bedrock mathematically this matching is done by linking the dupuit forchheimer and quasi linear models a tilted water table is shown to entrain the recharging moisture with curvilinear stream lines in the unsaturated zone

gaining and losing sections of horizontal wells the flux along a horizontal well in uniform flow is examined using an analytic three dimensional steady model wells with uniform head and low pumping rates have gaining sections along which water enters the well and losing sections along which water exits such a well may provide a conduit for contaminated groundwater to be drawn into the well conveyed a large distance and injected into an uncontaminated region of an aquifer dimensionless ratios of the well s length l and radius r aquifer thickness h and uniform flow rate u are developed to quantify the minimum pumping rate qmin at which no losing section occurs the ratio qmin ulh is presented as a nomograph usingr h and l h for placement parallel to flow and is 6 r h for placement perpendicular to flow and a parabolic relationship between these limiting cases is developed for placement oblique to flow capture zone geometry is quantified using qmin ulh

on the duration of the paleocene eocene thermal maximum petm 1 the paleocene eocene thermal maximum petm is one of the best known examples of a transient climate perturbation associated with a brief but intense interval of global warming and a massive perturbation of the global carbon cycle from injection of isotopically light carbon into the ocean atmosphere system one key to quantifying the mass of carbon released identifying the source s and understanding the ultimate fate of this carbon is to develop high resolution age models two independent strategies have been employed cycle stratigraphy and analysis of extraterrestrial helium heet both of which were first tested on ocean drilling program odp site 690 these two methods are in agreement for the onset of the petm and initial recovery or the clay layer main body but seem to differ in the final recovery phase of the event above the clay layer where the carbonate contents rise and carbon isotope values return toward background values here we present a state of the art age model for the petm derived from a new orbital chronology developed with cycle stratigraphic records from sites drilled during odp leg 208 walvis ridge southeastern atlantic integrated with published records from site 690 weddell sea southern ocean odp leg 113 during leg 208 five paleocene eocene p e boundary sections sites 1262 to 1267 were recovered in multiple holes over a depth transect of more than 2200 m at the walvis ridge yielding the first stratigraphically complete p e deep sea sequence with moderate to relatively high sedimentation rates 1 to 3 cm ka where a is years a detailed chronology was developed with nondestructive x ray fluorescence xrf core scanning records on the scale of precession cycles with a total duration of the petm now estimated to be 170 ka the revised cycle stratigraphic record confirms original estimates for the duration of the onset and initial recovery but suggests a new duration for the final recovery that is intermediate to the previous estimates by cycle stratigraphy and heet

warming the fuel for the fire evidence for the thermal dissociation of methane hydrate during the paleocene eocene thermal maximum dramatic warming and upheaval of the carbon system at the end of the paleocene epoch have been linked to massive dissociation of sedimentary methane hydrate however testing the paleocene eocene thermal maximum hydrate dissociation hypothesis has been hindered by the inability of available proxy records to resolve the initial sequence of events the cause of the paleocene eocene thermal maximum carbon isotope excursion remains speculative primarily due to uncertainties in the timing and duration of the paleocene eocene thermal maximum we present new high resolution stable isotope records based on analyses of single planktonic and benthic foraminiferal shells from ocean drilling program site 690 weddell sea southern ocean demonstrating that the initial carbon isotope excursion was geologically instantaneous and was preceded by a brief period of gradual surface water warming both of these findings support the thermal dissociation of methane hydrate as the cause of the paleocene eocene thermal maximum carbon isotope excursion furthermore the data reveal that the methane derived carbon was mixed from the surface ocean downward suggesting that a significant fraction of the initial dissociated hydrate methane reached the atmosphere prior to oxidation

changes in calcareous nannofossil assemblages across the paleocene eocene transition from the paleo equatorial pacific ocean quantitative analyses of selected calcareous nannofossils in deep sea sections recovered from the paleo equatorial pacific odp leg 199 provide new information about biostratigraphy biochronology and the evolutionary history of calcareous nannofossils across the paleocene eocene transition interval the sediment cores from odp leg 199 represent the first continuous paleocene eocene boundary sections ever to be sampled in the central equatorial pacific ocean calcareous nannofossil assemblages are studied to document the distribution of biostratigraphically useful taxa such as ericsonia discoaster fasciculithus rhomboaster and tribrachiatus focus is given to the evolution of the rhomboaster tribrachiatus lineage in the lower eocene interval at site 1215 and on the stratigraphic relationship of these taxa relative to species in the genus fasciculithus critical intervals of north atlantic dsdp site 550 have also been re examined the tribrachiatus digitalis morphotype was described at site 550 from an interval affected by down hole contamination partly originating from within the tribrachiatus orthostylus range the t digitalis morphotype represents an evolutionary transitional form between t contortus and t orthostylus entering the stratigraphic record within the range of the former species and disappearing within the lower part of the range of the latter species the subzonal subdivision of zone np10 hence collapses lithological and colour variability reflecting orbital cyclicity occur in the lower eocene of site 1215 permitting a relative astronomical age calibration of the tribrachiatus taxa the distinct rhomboaster spp discoaster araneus association also occurs in the paleo equatorial pacific ocean together with a marked decrease in diversity of fasciculithus spp site 1220 reveals a short peak abundance of thoracosphaera spp just above the p e boundary interval which probably reflects a stressed surface water environment

modern coccolithophore and carbonate sedimentation along a productivity gradient in the canary islands region seasonal export production and surface accumulation rates abstract coccolithophores one of the main primary and carbonate producers in the surface waters of the canary islands region were investigated to quantify coccolith and coccolith carbonate export fluxes and to determine possible trends in species composition related to different productivity conditions present day fluxes were compared to the long term records of coccolith and carbonate accumulation in holocene sediments underneath the mooring locations coccolithophore flux variations in sediment traps at three stations along an e w transect at approximately 29 n from the upwelling influenced north west african shelf region to the open ocean were recorded from january to september 1997 total coccolith fluxes along the studied transect were highly seasonal with pronounced sedimentation events occurring in february upper traps and march deep traps related to the winter phytoplankton bloom in surface waters while total coccolith flux rates and fluxes of different species at the two oceanic sites lp and estoc were comparable mean 6 4 and 5 4 10 8 coccoliths m 2 d 1 fluxes increased significantly towards the shallower site ebc mean 13 7 10 8 coccoliths m 2 d 1 this gradient points to increased productivity in surface waters at the near shore station probably associated with nutrient rich upwelling filaments detaching from the coast and or the easternmost islands additionally a strong influence of laterally advected coccolith rich material was demonstrated for the deeper sediment traps at the two offshore sites resulting in an increase of mean daily coccolith fluxes by a factor 3 lp and by a factor 2 estoc respectively estimated coccolith carbonate fluxes along the transect were 2 8 g m 2 ebc and 1 2 1 3 g m 2 estoc lp in the upper traps representing 31 33 of the total annual carbonate flux the coccolith carbonate supply was higher in the deeper traps with 63 at lp and 44 at estoc respectively average holocene coccolith and coccolith carbonate accumulation rates derived from surface samples at the mooring locations generally confirm the sediment trap results discrepancies mainly result from near bottom and down slope particle transfer processes which especially influence the site closer to the shelf dissolution processes are likely to affect primarily the deep sediments at the oligotrophic site lp the diverse subtropical coccolithophore assemblages were quite similar in all sediment trap samples from the three mooring sites with three species emiliania huxleyi florisphaera profunda gephyrocapsa ericsonii contributing significantly to the assemblage despite the good correspondence between the assemblage compositions along the transect some trends towards the upwelling influenced site ebc could be observed whereas all gephyrocapsa species mainly g ericsonii respond positively to higher productivity conditions at the near shore station calcidiscus leptoporus and the deep photic zone species f profunda increased in mean relative abundances towards the two offshore sites pointing to a preference for the more stable oligotrophic conditions of the subtropical gyre

phreatic surface flow from a near reservoir saturated tongue steady and transient 2d darcian flows in a saturated tongue adjacent to a reservoir are studied analytically first a stable tongue receiving water from an inclined equipotential reservoir bed and losing moisture through a phreatic surface is considered the hydraulic head is governed by the laplace equation and the complex potential and complex coordinate are determined explicitly by the polubarinova kochina method at an arbitrary bank slopes and evapotranspiration rates in a particular case of a vertical slope the tongue becomes a right angled triangle extending into the layer for the same distance as the dupuit forchheimer model predicts second a saturated dupuit forchheimer flow in the tongue is analyzed under the assumption of evaporation exponentially and linearly decreasing with the depth of a phreatic surface the corresponding non linear ordinary differential equation is integrated twice and predicts the length of the tongue as a function of the reservoir water level third a transient regime is modelled by the boussinesq equation with evaporation uniform in space but varying cyclostationary with time a straight line water table translating upward downward is found to be located always below the water table for steady regimes with an average evaporation

shelf and open ocean calcareous phytoplankton assemblages across the paleocene eocene thermal maximum implications for global productivity gradients abrupt global warming and profound perturbation of the carbon cycle during the paleocene eocene thermal maximum petm ca 55 ma have been linked to a massive release of carbon into the ocean atmosphere system increased phytoplankton productivity has been invoked to cause subsequent co2 drawdown cooling and environmental recovery however interpretations of geochemical and biotic data differ on when and where this increased productivity occurred here we present high resolution nannofossil assemblage data from a shelf section the u s geological survey usgs drill hole at wilson lake new jersey and an open ocean location ocean drilling program odp site 1209 paleoequatorial pacific these data combined with published biotic records indicate a transient steepening of shelf offshelf trophic gradients across the petm onset and peak with a decrease in open ocean productivity coeval with increased nutrient availability in shelf areas productivity levels recovered in the open ocean during the later stages of the event which coupled with intensified continental weathering rates may have played an important role in carbon sequestration and co2 drawdown

nannofossil assemblage fluctuations during the paleocene eocene thermal maximum at sites 213 indian ocean and 401 north atlantic ocean palaeoceanographic implications the paleocene eocene thermal maximum petm was an abrupt global warming event at f55 ma this event had profound effects on the biosphere quantitative investigations of calcareous nannofossil assemblages were performed across the petm at deep sea drilling project site 213 in the tropical indian ocean and site 401 in the bay of biscay north atlantic ocean at a temperate latitude calcareous nannofossil assemblages from both sites show major changes before during and after the petm fluctuations at site 213 are affected by selective dissolution of the least robust taxa by contrast assemblages in the lower part of the petm at site 401 show less diagenetic alteration and display high abundances of genera such as discoaster fasciculithus and ericsonia these taxa reflect relatively warm and probably oligotrophic surface waters abundances of the genus chiasmolithus an indicator of relatively cool and eutrophic waters decreased dramatically the upper portion of the petm is characterized by an increase in the abundance of toweius spp and zygrhablithus bijugatus interpreted as a return to cooler and more eutrophic conditions the elimination of fasciculithus was probably due to competition with the holococcolith species z bijugatus which occupied the same ecological niche the occurrences of long armed and asymmetrical discoaster species such as discoaster araneus discoaster anartios and discoaster okadai and rhomboaster species such as rhomboaster calcitrapa and rhomboaster cuspis are characteristic of the petm interval d 2004 elsevier b v all rights reserved

relationship between coccolith sr ca ratios and coccolithophore production and export in the arabian sea and sargasso sea coccolithophore caco3 production can account for 20 80 of biogenic carbonate exported from the photic zone and coccoliths are a dominant biogenic carbonate in many deep sea sediments a new method for picking individual coccoliths from sediment traps and sediments for analysis using secondary ion mass spectrometry ion probe allows us to make precise sr ca and mg ca determinations on coccoliths from single species even in samples where material is limited there are large biological effects in sr ca partitioning in coccoliths that have been related to variations in coccolithophore productivity in sediment traps from the sargasso sea at bermuda and arabian sea in the somali basin we can identify sr ca variations in several species that are consistent with inferred seasonal variations in coccolithophore productivity in surface waters in the arabian sea coccolith sr ca ratios in calcidiscus leptoporus and helicosphaera carteri are lowest during the nonproductive intermonsoon they are highest during the upwelling of southwest monsoon and during the nutrient entrainment from strong winds of the northeast monsoon these sr ca variations match seasonal trends in coccolith export flux furthermore sr ca variations in c leptoporus are larger and this species also has the greater variation in export flux between southwest monsoon and intermonsoon seasons at bermuda a 1996 fall bloom driven by passage of a warm mode water eddy induced a large increase in sr ca of c leptoporus coincident with an increase of c leptoporus export over an annual series for 2004 highest sr ca ratios of c leptoporus in the summer months match the typical summer peak in surface standing stock of this species and the stimulation of its productivity by mesoscale cyclonic eddies and eddy eddy interactions high sr ca did not coincide with the highest export of c leptoporus coccoliths likely because cyclonic eddies unlike mode water eddies are dominated by small phytoplankton with low export efficiency these data confirm a relationship between coccolith sr ca ratios and productivity sr ca ratios of the smaller and more slowly sinking emiliania huxleyi at bermuda show very small o4 seasonal sr ca variations in contrast nutrientlimited culture experiments for this species reveal significant 435 increases in sr ca with nitrate stimulated growth

abrupt climate change and transient climates during the paleogene a marine perspective detailed investigations of high latitude sequences recently collected by the ocean drilling program odp indicate that periods of rapid climate change often culminated in brief transient climates with more extreme conditions than subsequent long term climates two examples of such events have been identified in the paleogene the first in latest paleocene time in the middle of a warming trend that began several million years earlier the second in earliest oligocene time near the end of a middle eocene to late oligocene global cooling trend superimposed on the earlier event was a sudden and extreme warming of both high latitude sea surface and deep ocean waters imbedded in the latter transition was an abrupt decline in high latitude temperatures and the brief appearance of a full size continental ice sheet on antarctica in both cases the climate extremes were not stable lasting for less than a few hundred thousand years indicating a temporary or transient climate state geochemical and sedimentolog

evidence of surface water oligotrophy during the paleocene eocene thermal maximum nannofossil assemblage data from ocean drilling program site 690 maud rise weddell sea 1 nannoplankton assemblages at ocean drilling program site 690 maud rise weddell sea experienced an abrupt and dramatic transformation at the onset of the paleocene eocene thermal maximum petm at 55 m y the major assemblage shift suggests a change from colder more productive surface waters to warmer more oligotrophic conditions significant restructuring of assemblages during the later part of the petm indicates that nannoplankton communities were not stable and that surface water conditions changed although they remained warm and oligotrophic combined with benthic foraminiferal assemblage data nannoplankton assemblage results suggest increased sequestration of nutrients in shelf environments and starvation of the open ocean although the petm was a short lived event it appears to have had long term effects on nannoplankton leading to the extinction of fasciculithus a dominant paleocene genus

orbital climate forcing of δ13c excursions in the late paleocene early eocene chrons c24n c25n 1 high resolution stable carbon isotope records for upper paleocene lower eocene sections at ocean drilling program sites 1051 and 690 and deep sea drilling project sites 550 and 577 show numerous rapid 40 60 kyr duration negative excursions of up to 1 we demonstrate that these transient decreases are the expected result of nonlinear insolation forcing of the carbon cycle in the context of a long carbon residence time the transients occur at maxima in earth s orbital eccentricity which result in high amplitude variations in insolation due to forcing by climatic precession the construction of accurate orbital chronologies for geologic sections older than 35 ma relies on identifying a high fidelity recorder of variations in earth s orbital eccentricity we use the carbon isotope records as such a recorder establishing a robust orbitally tuned chronology for latest paleocene earliest eocene events moreover the transient decreases provide a means of precise correlation among the four sites that is independent of magnetostratigraphic and biostratigraphic data at the 105 year scale while the eccentricity controlled transient decreases bear some resemblance to the much larger amplitude carbon isotope excursion cie that marks the paleocene eocene boundary the latter event is found to occur near a minimum in the 400 kyr eccentricity cycle thus the cie occurred during a time of minimal variability in insolation the dominant mechanism for forcing climate change on 104 year scales we argue that this is inconsistent with mechanisms that rely on a threshold climate event to trigger the paleocene eocene thermal maximum since any threshold would more likely be crossed during a period of high amplitude climate variations

analytic element solutions for seepage towards topographic depressions abstract point and line singularities are superposed with incident unidirectional saturated and unsaturated flows the resulting isobars of 3d laplacian or advective dispersion equation fields model either seepage face dimples and rills on a tilted hillslope or an undulated top of the vadose zone above a stagnant water table the reconstructed shapes of isobars are conchoidal i e convex concave all flow characteristics drawdowns velocity and kirchhoff potential distributions dimple sizes are calculated either explicitly or by elementary computer algebra routines

determination of critical head in soil piping one of the main mechanisms of failure of levees is a phenomenon called piping which generally begins with the formation of a sand boil at the leeward side of the levee and has been frequently observed to proceed upstream along the base of the levee through a slit formation the issue of most important concern is to estimate the critical head that could promote the occurrence of piping considering the flow through porous media and coupling it with bernoulli s equation and a critical tractive stress condition a model is developed for the critical head using appropriate transformations the proposed model takes on a form which supports bligh s empirical findings another model based on critical velocity is also developed to estimate the critical head the functional form of these two models is evaluated using the critical head versus porosity data from a number of laboratory studies conducted in the netherlands these models were found to perform better than did terzaghi s model

coccolith sr ca records of productivity during the paleocene eocene thermal maximum from the weddell sea 1 a major perturbation of the global carbon cycle 55 million years ago believed to result from release of 1000 2000 gt of c from methane hydrates correlates with an intense but transient greenhouse warming event known as the paleocene eocene thermal maximum petm the rapid 105 years recovery of global temperatures reflects important negative feedbacks in the climate system and carbon cycle enhanced marine productivity may be one important feedback but indicators for productivity changes have yielded conflicting results here we use a new independent indicator sr ca in coccolith carbonate which covaries with the productivity of coccolithophorid algae to investigate the biotic response in the most complete petm deep sea record which was recovered at odp site 690 in the weddell sea in the dominant coccolithophorid genus toweius a large 40 sr ca increase immediately after the gas hydrate release signals a dramatic productivity increase productivity levels remained high for 60 000 years but decreased to pre event levels by 120 000 years after the gas hydrate release productivity levels during the petm are higher than observed at any other time in our 400 000 year record other coccolithophorid genera chiasmolithus and discoaster show a brief modest 25 sr ca increase increase in productivity that lags behind the methane event by 50 000 years and is within the range of productivity variation elsewhere in the record the timing of the toweius productivity increase agrees well with os isotope records of globally increased weathering intensity which may have provided higher nutrient fluxes to stimulate algal productivity if this type of productivity response occurred globally it would also be consistent with the timing of c drawdown that may have returned temperatures to near pre event levels

three dimensional groundwater flow to a lake an explicit analytical solution steady darcian groundwater flow near a hemispherical lake contacting a confined homogeneous aquifer of semi infinite depth is studied analytically by the method of separation of variables the lake bottom is modeled either as an equipotential the dirichlet boundary or as a surface with a thin sediment skin the robin boundary the lake disturbs an incident uniform flow such that three regimes gaining losing and flow through are possible depending on the ambient velocity aquifer conductivity lake diameter the bottom head sediment thickness and conductivity in case of silted beds explicit expressions for the specific discharge and stream function are derived inflow and outflow rates are calculated implications for other equipotential surfaces placed in ambient fields are discussed

unsaturated seepage and subterranean holes conspectus and exclusion problem for circular cylindrical cavities this paper introduces the general theory of water exclusion from or entry into subterranean holes from steady uniform downward unsaturated seepage buried holes serve as obstacles to the flow and so increase water pressure at parts of the hole surface when downward seepage is fast enough and or the hole is large enough water pressure increases to the point where a seepage surface forms and water enters the hole contrary to the conventional picture drawn from capillary statics hydrodynamics shows that the larger the hole the more vulnerable it is to water entry cavity shape is important also applications include optimal design of configurations of tunnels and underground repositories e g for nuclear wastes against entry of seepage water the theory also embraces the disturbance of seepage flows by buried impermeable obstacles such as stones and structures the quasi linear exclusion problem for circular cylindrical cavities is solved both exact solutions and simple asymptotic results are found and graphs and tables presented the moisture field about the cavity exhibits upstream and downstream stagnation points and retarded regions roof drip lobes in which the moisture content and downward flow velocity are augmented by water essentially deflected from the cavity roof and the dry shadow region of reduced moisture content and flow velocity essentially sheltered by the cavity a practical consequence is that we can establish for any given combination of downward seepage velocity cavity radius saturated hydraulic conductivity k1 and sorptive number whether or not seepage water will enter a cylindrical cavity

a chrysophyte based quantitative reconstruction of winter severity from varved lake sediments in ne poland during the past millennium and its relationship to natural climate variability abstract chrysophyte cysts are recognized as powerful proxies of cold season temperatures in this paper we use the relationship between chrysophyte assemblages and the number of days below 4 c db4 c in the epilimnion of a lake in northern poland to develop a transfer function and to reconstruct winter severity in poland for the last millennium db4 c is a climate variable related to the length of the winter multivariate ordination techniques were used to study the distribution of chrysophytes from sediment traps of 37 low land lakes distributed along a variety of environmental and climatic gradients in northern poland of all the environmental variables measured stepwise variable selection and individual redundancy analyses rda identified db4 c as the most important variable for chrysophytes explaining a portion of variance independent of variables related to water chemistry conductivity chlorides k sulfates which were also important a quantitative transfer function was created to estimate db4 c from sedimentary assemblages using partial least square regression pls the two component model pls 2 had a coefficient of determination of r cross 2 0 58 with root mean squared error of prediction rmsep based on leave one out of 3 41 days the resulting transfer function was applied to an annually varved sediment core from lake abinskie providing a new sub decadal quantitative reconstruction of db4 c with high chronological accuracy for the period ad 1000 2010 during medieval times ad 1180 1440 winters were generally shorter warmer except for a decade with very long and severe winters around ad 1260 1270 following the ad 1258 volcanic eruption the 16th and 17th centuries and the beginning of the 19th century experienced very long severe winters comparison with other european cold season reconstructions and atmospheric indices for this region indicates that large parts of the winter variability reconstructed db4 c is due to the interplay between the oscillations of the zonal flow controlled by the north atlantic oscillation nao and the influence of continental anticyclonic systems siberian high east atlantic western russia pattern differences with other european records are attributed to geographic climatological differences between poland and western europe low countries alps striking correspondence between the combined volcanic and solar forcing and the db4 c reconstruction prior to the 20th century suggests that winter climate in poland responds mostly to natural forced variability volcanic and solar and the influence of unforced variability is low

a transient rise in tropical sea surface temperature during the paleocene eocene thermal maximum the paleocene eocene thermal maximum petm has been attributed to a rapid rise in greenhouse gas levels if so warming should have occurred at all latitudes although amplified toward the poles existing records reveal an increase in high latitude sea surface temperatures ssts 8 to 10 c and in bottom water temperatures 4 to 5 c to date however the character of the tropical sst response during this event remains unconstrained here we address this deficiency by using paired oxygen isotope and minor element magnesium calcium ratios of planktonic foraminifera from a tropical pacific core to estimate changes in sst using mixed layer foraminifera we found that the combined proxies imply a 4 to 5 c rise in pacific sst during the petm these results would necessitate a rise in atmospheric pco 2 to levels three to four times as high as those estimated for the late paleocene

distinguishing the influence of diagenesis on the paleoecological reconstruction of nannoplankton across the paleocene eocene thermal maximum an example from the kerguelen plateau southern indian ocean abstract the paleocene eocene thermal maximum petm ca 55 ma is an abrupt profound perturbation of climate and the carbon cycle associated with a massive injection of isotopically light carbon into the ocean atmosphere system as such it provides an analogue for understanding the interplay between phytoplankton and climate under modern anthropogenic global warming conditions however the accompanying enhanced dissolution poses uncertainty on the reconstruction of the affected ecology and productivity we present a high resolution record of bulk isotopes and nannofossil absolute abundance from ocean drilling program odp site 1135 on the kerguelen plateau southern indian ocean to quantitatively constrain for the first time the influence of dissolution on paleoecological reconstruction our bulk carbonate isotope record closely resembles that of the classic petm site at odp site 690 on the opposite side of the antarctic continent and its correlation with those from odp sites 690 1262 and 1263 records allows recognition of 14 precessional cycles upsection from the onset of the carbon isotopic excursion cie this together with a full range of common discoaster araneus and an abundance crossover between fasciculithus and zygrhablithus bijugatus indicates the presence of the petm at site 1135 a poorly known record with calcareous fossils throughout the interval the strong correlation between the absolute abundances of chiasmolithus and coccolith assemblages reveals a dominant paleoecological signal in the poorly preserved fossil assemblages while the influence of dissolution is only strong during the cie this suggests that r selected taxa can preserve faithful ecological information even in the severely altered assemblages studied here and therefore provide a strong case for the application of nannofossils to paleoecological studies in better preserved petm sections the inferred nannoplankton productivity drops abruptly at the cie onset but rapidly increases after the cie peak both of which may be driven by nutrient availability related to ocean stratification and vertical mixing due to changed sea surface temperatures

coccolithophores in the equatorial atlantic ocean response to seasonal and late quaternary surface water variability abstract the present study was initiated to ascertain the significance of coccolithophores as a proxy for paleoceanographic and paleoproductivity studies in the equatorial atlantic data from a range of different samples from the plankton surface sediments as well as sediment cores are shown and compared with each other in general the living coccolithophores in the surface and subsurface waters show considerable variation in cell numbers and distribution patterns cell densities reached a maximum of up to 300 103 coccospheres l in the upwelling area of the equatorial atlantic here emiliania huxleyi is the dominant species with relatively high cell numbers whereas umbellosphaera irregularis and umbellosphaera tenuis are characteristic for oligotrophic surface waters although they are observed in high relative abundances these species only occur in low absolute numbers the lower photic zone is dominated by high abundances and considerable cell numbers of florisphaera profunda the geographical distribution pattern of coccoliths in surface sediments reflects the conditions of the overlying surface water masses however abundances of the oligotrophic species umbellosphaera irregularis and umbellosphaera tenuis are strongly diminished causing an increase in relative abundance of the lower photic zone taxa florisphaera profunda and gladiolithus flabellatus during the past 140 000 years the surface water circulation of the equatorial atlantic has changed drastically as can be seen from changes in the coccolithophore species composition absolute coccolith numbers as well as coccolith accumulation rates significant increases in coccolith numbers and accumulation rates is observed in the southern equatorial atlantic during the last glacial interval oxygen isotope stages 2 4 which we attribute to enhanced upwelling intensities and advection of cool nutrient rich waters at this site in the western equatorial atlantic we observe an opposite trend with decreasing numbers of coccoliths during glacial periods which probably is caused by a deepening of the thermocline

calcareous nannofossil paleoceanography of the cretaceous greenhorn sea two distinctive laterally traceable bentonite beds were used to construct three isochronous time slices through the marine sediments of the upper cretaceous greenhorn cyclothem of the western interior basin calcareous nannofossil assemblages from these time slices were analyzed from 40 localities to examine the paleoceanographic conditions in the basin deposition of the lower time slice x bentonite approximately corresponded to the time at which free communication between the basin and open oceanic systems first occurred the most striking trend is the presence of common to abundant nannofossils in the center of the basin and their absence from the eastern and western margins this indicates that open oceanic conditions conducive to large standing crops of calcareous nannoplankton existed only in a narrow centrally located channel conditions at the basin margins were probably unsuitable for large populations due to salinity constraints multivariate analyses indicate two distinct biofacies northern and southern which are interpreted to represent distinct surface water masses the geometry of the water mass boundary suggests that the northern surface water mass actively flowed southward into or over the relatively passive southern water mass the upper time slice hl 3 bentonite samples the nannofossil distributions at or near the maximum transgression of the greenhorn sea in this time slice nannofossils occur beyond the limits of the study area except in proximity to the frontier delta system diversities are significantly higher indicating water mass conditions more similar to those in open oceanic settings multivariate analyses indicate three distinct surface water masses northern southern and western the northern and southern water masses exhibit relationships similar to those during the x bentonite time slices the interaction between the northern and southern water masses promoted vertical stratification of the water column and resultant sediment anoxia the western biofacies may be indicative of a surface water mass with significant contributions from nearby fresh water influx

hydrogeologic processes in saline systems playas sabkhas and saline lakes abstract pans playas sabkhas salinas saline lakes and salt flats are hydrologically similar varying only in their boundary conditions thus in evaluating geochemical processes in these systems a generic water and solute mass balance approach can be utilized a conceptual model of a coastal sabkha near the arabian gulf is used as an example to illustrate the various water and solute fluxes analysis of this model suggests that upward flux of ground water from underlying formations could be a major source of solutes in the sabkha but contribute only a small volume of the water local rainfall is the main source of water in the modeled sabkha system with a surprisingly large recharge to rainfall ratio of more than 50 the contribution of seawater to the solute budget depends on the ratio of the width of the supratidal zone to the total width and is generally confined to a narrow zone near the shoreline of a typical coastal sabkha because of a short residence time of water steady state flow is expected within a short time 50 000 years the solute composition of the brine in a closed saline system depends largely on the original composition of the input water the high total ion content in the brine limits the efficiency of water rock interaction and absorption because most natural systems are hydrologically open the chemistry of the brines and the associated evaporite deposits may be significantly different than that predicted for hydrologically closed systems seasonal changes in temperature of the unsaturated zone cause precipitation of minerals in saline systems undergoing evaporation thus during the hot dry season months minerals exhibit retrograde solubility so that gypsum anhydrite and calcite precipitate evaporation near the surface is also a major process that causes mineral precipitation in the upper portion of the unsaturated zone e g halite and carnallite provided that the relative humidity of the atmosphere is less than the activity of water the slope of the fresh brine water interface in saline lake systems is shallower than in fresh seawater interface because of the greater density difference between the fresh brine water bodies the interface between sabkha brines and seawater slopes seaward unlike normal marine fresh water systems that slope landward moreover the brine seawater interface does not achieve steady state because it is pushed toward the sea by the sabkha s brine

calcareous nannofloral response to termination ii at 45 n 25 w northeast atlantic abstract termination ii glacial to interglacial transition from oxygen isotope stage 6 to stage 5 is considered to be one of the most rapid and abrupt climatic changes during the late quaternary our high resolution geochemical and nannofloral study of the interval from 140 to 100 ka in the northeast atlantic core t90 9p 45 17 5 n 25 41 3 w shows that termination ii 135 125 ka occurred in two steps of drastic changes interrupted by a short period of stability and followed by at least 25 ka of relatively stable interglacial conditions traditionally referred to as the eemian age substage 5 5 a primary productivity proxy based on coccolith accumulation rate number cm 2 ka 1 shows higher values during the eemian than during glacial stage 6 and interglacial substage 5 4 with the maximum values 70 10 9 coccoliths cm 2 ka 1 at 123 122 ka the coccolith assemblage was dominated by two morphotypes of gephyrocapsa alternating in dominance under different climatic conditions gephyrocapsa muellerae was more abundant in colder periods whereas small gephyrocapsa dominated in the eemian emiliania huxleyi syracosphaera pulchra and florisphaera profunda increased in the eemian whereas coccolithus pelagicus and helicosphaera carteri decreased small gephyrocapsa together with emiliania huxleyi are associated with periods of higher primary productivity the pelagic sedimentary record of termination ii in core t90 9p includes a 5 cm thick layer enriched in ice rafted material a heinrich layer in contrast to termination i where such a heinrich layer h1 is associated with the first meltwater pulse of the deglaciation the record of core t90 9p suggests that the heinrich event of termination ii h11 occurred during the second stage of deglaciation 129 4 127 1 ka it is characterised by accumulation of ice rafted debris and low coccolithophore diversity the coincident apparent drop in coccolith accumulation rate could be explained either by changes in primary productivity due to reduction in salinity and light or by dilution by ice rafted material five models are applied for the deposition of the heinrich layer with changing thickness 3 cm and duration 1000 500 and 250 yr these scenarios result in a lowered constant or even slightly increased primary productivity during this event

the source and fate of massive carbon input during the latest paleocene thermal maximum lithologic faunal seismic and isotopic evidence from the blake nose subtropical western north atlantic links a massive release of biogenic methane 55 5 million years ago to a warming of deep ocean and high latitude surface waters a large perturbation in the combined ocean atmosphere carbon cycle the largest of the past 90 million years a mass extinction event in benthic faunas and a radiation of mammalian orders the deposition of a mud clast interval and seismic evidence for slope disturbance are associated with intermediate water warming massive carbon input to the global exogenic carbon cycle pelagic carbonate dissolution a decrease in dissolved oxygen and a benthic foraminiferal extinction event these events provide evidence to confirm the gas hydrate dissociation hypothesis and identify the blake nose as a site of methane release

release of methane from a volcanic basin as a mechanism for initial eocene global warming a 200 000 yr interval of extreme global warming marked the start of the eocene epoch about 55 million years ago negative carbon and oxygen isotope excursions in marine and terrestrial sediments show that this event was linked to a massive and rapid approximately 10 000 yr input of isotopically depleted carbon it has been suggested previously that extensive melting of gas hydrates buried in marine sediments may represent the carbon source and has caused the global climate change large scale hydrate melting however requires a hitherto unknown triggering mechanism here we present evidence for the presence of thousands of hydrothermal vent complexes identified on seismic reflection profiles from the voring and more basins in the norwegian sea we propose that intrusion of voluminous mantle derived melts in carbon rich sedimentary strata in the northeast atlantic may have caused an explosive release of methane transported to the ocean or atmosphere through the vent complexes close to the palaeocene eocene boundary similar volcanic and metamorphic processes may explain climate events associated with other large igneous provinces such as the siberian traps approximately 250 million years ago and the karoo igneous province approximately 183 million years ago