progressive dissolution of fine carbonate particles in pelagic sediments abstract large systematic variations occur in the proportion of coccolith sized carbonate particles relative to other types of carbonate particles within the

antarctic marine temperatures late campanian through early paleocene an oxygen isotope paleotemperature study of benthic foraminifera from the upper campanian through lower paleocene section at seymour island near the coast of antarctica was done in conjunction with careful scanning electron microscope observations to monitor the state of foraminiferal preservation the isotopic compositions of those samples which were deemed to be well preserved were the basis of the conclusion that campanian through paleocene high latitude shelf waters near antarctica had temperatures between approximately 4 5 and 10 5 c temperatures during early and middle maastrichtian time were slightly higher than those of either the late campanian or late maastrichtian the inference of temperate climatic conditions in antarctica is in agreement with paleoclimatic conclusions drawn on the species composition of the planktonic foraminiferal assemblages and the character of the planktonic foraminifera as well as with published conclusions based upon paleobotanical evidence the maastrichtian and campanian water temperatures at seymour island are similar to those inferred from published isotope ratios of pacific late cretaceous benthic foraminifera from low latitudes indicating that campanian through early paleocene deep ocean waters at least in the pacific and perhaps elsewhere as well could have formed by sinking of surface waters in polar regions

late cretaceous sea level changes in tunisia a multi disciplinary approach a multi disciplinary study of sea level and climate proxies including bulk rock and clay mineral compositions carbon isotopes total organic carbon toc sr ca ratios and macro and microfaunal associations reveals seven major sea level regressions in the southwestern tethys during the last 10 million years of the cretaceous late campanian c 74 2 ma 73 4 72 5 ma and 72 2 71 7 ma early maastrichtian 70 7 70 3 ma 69 6 69 3 ma and 68 9 68 3 ma and late maastrichtian 65 45 65 3 ma low sea levels are generally associated with increased terrigenous influx low kaolinite chlorite mica ratios high toc and high sr ca ratios whereas high sea levels are generally associated with the reverse conditions these sea level changes may be interpreted as eustatic as suggested by the global recognition of at least four of the seven major regressions identified 74 2 ma 70 7 70 3 ma 68 9 68 3 ma and 65 45 65 3 ma climatic changes inferred from clay mineral contents correlate with sea level changes warm or humid climates accompany high sea levels and cooler or arid climates generally accompany low sea levels

cycles steps and co2 paleoceanography in the united states from 1983 1986 the field of paleoceanography experienced continued growth during the last three years the first international conference on paleoceanography was held in zurich switzerland in july 1983 and a new journal devoted to the topic paleoceanography american geophysical union washington d c began publication in spring 1986 edited by dr james kennett of the university of rhode island nine legs of the r v glomar challenger concentrated upon paleoceanographic topics legs 71 75 in the south atlantic leg 81 in the north atlantic leg 85 in the equatorial pacific leg 86 in the northwest pacific and leg 90 in the southwest pacific several special symposia and conferences resulted in volumes of collected papers dealing with topics such as climate variability hansen and takahashi 1984 the global carbon cycle sundquist and broecker 1985 catastrophes and earth history berggren and van couvering 1984 orbital insolation and periodicity berger et al 1984 and coastal upwelling suess and thiede 1983 some very useful books have been published which summarize existing information on radiolaria anderson 1983 neogene planktonic foraminifera kennett and srinivasan 1983 calcareous nannofossils haq 1983 1984 and biostratigraphy bolli et al 1983

a stable isotopic record of the maastrichtian ocean climate system south atlantic dsdp site 528 abstract the upper maastrichtian interval of mid latitude south atlantic deep sea drilling project site 528 spans approximately the last 4 million years of the cretaceous the isotopic record of this sequence indicates that relatively large 0 5 1 0 late maastrichtian oxygen and carbon isotopic shifts occurred on geologically short time scales less than 100 500 kyr comparison with previous oxygen isotopic data suggests that in high and mid latitude southern oceans the multimillion year maastrichtian cooling trend largely resulted from geologically rapid climatic steps coincidence of the largest carbon and oxygen isotopic excursions suggests that relatively large and geologically rapid changes in marine and atmospheric carbon content may have directly contributed to the long term cooling of the late cretaceous greenhouse

oxygen and carbon isotopic composition of living planktonic foraminifera from the northeast pacific ocean abstract stable isotopic analyses were performed on the tests of five species of living planktonic foraminifera which are important in paleoclimatic studies of high latitude late cenozoic sequences all but two of the samples used are from horizontal plankton tows of known depths between 0 500 m in the northeastern pacific ocean 50 n 145 w in situ hydrographic seawater stable isotopic and quantitative species distribution data are used in the interpretation of the results all of the species show depletions in both 18 o and 13 c in their calcite tests relative to calcite precipitated in isotopic equilibrium with ambient seawater estimates of the departures from isotopic equilibrium range from 0 35 in globigerinita glutinata to 2 24 in neogloboquadrina pachyderma sinistral with respect to 18 o and from 0 5 in orbulina universa to 4 34 globigerina bulloides with respect to 13 c the 18 o data suggest that primary test growth for individual species is not restricted to the depth interval where highest total standing crop values occur oxygen and carbon isotopic depth rankings for g bulloides n pachyderma and g glutinata reflect the relative magnitude of the vital effect in these species and not necessarily different depth habitats the vital effect for 18 o in these species remains approximately constant with changing temperature water depth while the vital effect for 13 c strongly decreases with increasing depth temperature also does not appear to directly affect the coiling ratios of g bulloides but a significant negative correlation exists between the percentage of sinistrally coiled g glutinata and water temperature

extended cretaceous tertiary boundary extinctions and delayed population change in planktonic foraminifera from brazos river texas high resolution planktonic foraminiferal analysis of three brazos river sections indicates a nearly continuous cretaceous tertiary k t boundary sedimentary record second only to the world s most complete record at el kef tunisia species extinctions occur over an extended period of time and with two major extinction episodes the first extinction episode with 46 of the species extinct occurs at and just below 10 15 cm a short hiatus at the base of a sandy shell hash and clay sand unit which was interpreted by bourgeois et al 1988 to represent a tsunami bed generated by the k t boundary bolide impact the top of this tsunami bed is about 17 20 cm below the k t boundary as defined by the first appearance of tertiary planktonic foraminifera the second extinction phase with 45 of the species extinct occurs 25 cm above the k t boundary zone p0 p1a boundary of the remaining seven surviving cretaceous species six gradually disappear during planktonic foraminiferal subzones p1a and basal p1b no species extinctions or major faunal assemblage changes are directly associated with the k t boundary iridium distribution is ambiguous with one peak in the upper part of the tsunami bed and a second peak at the micropaleontologically defined k t boundary relative abundances of dominant species are stable through the late maastrichtian and only minor abundance changes coincide with the first extinction episode or the k t boundary the first major faunal change in the dominant species group coincides with the second extinction episode and leads to decline and eventual extinction of this group in subzone p1a species disappearing at the two extinction episodes 46 and 45 constitute only a small percentage 8 and 5 of the individuals of the total planktonic foraminiferal population this suggests that weakened species with low numbers of individuals and sensitive to relatively minor environmental changes were primarily affected by these extinction episodes magnetostratigraphy indicates that the first extinction phase began about 310 000 years before the k t boundary and the second extinction phase occurred 50 000 years after the k t boundary this stepped pattern of species extinctions suggests a progressively stressed ecosystem in continental shelf settings which may be related to an observed sea level regression and global cooling the hypothesis of a global catastrophic mass extinction at the k t boundary caused by a large extraterrestrial impact is not supported by the brazos river planktonic foraminiferal data

reorganization of deep ocean circulation accompanying a late cretaceous extinction event deep ocean circulation may be a significant factor in determining global climate1 5 increases in the flux of warm saline waters from low to high latitudes would enhance the poleward transport of heat and thus help maintain the warm conditions at high latitudes typical of globally warm greenhouse periods but controversy exists1 2 as to whether the ocean s thermohaline circulation can transport enough heat to bring about the temperature distributions of these times such as the mid cretaceous and early eocene here we present stable isotope records of ocean temperature and salinity that indicate that bottom waters in late cretaceous oceans of the southern hemisphere became cooler and less saline at the same time about 70 myr ago as widespread biotic changes3 6 8 these findings support the idea that changes in deep ocean circulation can act as a climate switch

past climate and the role of ocean heat transport model simulations for the cretaceous a series of general circulation model experiments using global environmental and ecological simulation of interactive systems genesis were executed to evaluate the sensitivity of simulated mid cretaceous climate to small perturbations in ocean heat transport three experiments were performed 1 mixed layer ocean with no ocean heat transport zeroq 2 ocean heat transport specified as required for genesis to best match modern observations oneq and 3 doubled ocean heat transport twoq the oneq experiment represents an ocean heat transport which is actually about 15 of the values given by carissimo et al 1985 from modern observations as a sensitivity experiment these model simulations represent a doubling of the role of the ocean however relative to the observations they represent small perturbations to the total poleward heat transport in the model with the exception of the tropics no major changes in the structure of the general circulation of the atmosphere resulted from the modification of the ocean heat transport however relatively small increases in ocean heat transport resulted in a number of significant differences between simulations including tropical cooling polar warming weakened equator to pole surface temperature gradients weakened midlatitude jets decreased land sea pressure contrast and decreased midlatitude storminess the experiments indicate that changes in ocean heat transport which are well within the realm of possibility for earth history can have significant climatic impact although ocean heat transport may be a significant factor in explaining cretaceous polar warmth the changes specified in these experiments alone are not sufficient to explain the polar warmth of the cretaceous

seasonal stable isotopic variations in living planktonic foraminifera from bermuda plankton tows abstract seasonal variations in surface water temperature and the 18o 16o ratios of calcite tests of living planktonic foraminifera collected in the upper 10 mare are coincident in the sargasso sea off bermuda the 18o of seasonally restricted globorotalia truncatulinoides and globigerinoides ruber pink and white may be used to determine the seasonal temperature contrast of the oceans in the past a preliminary model based on yearly absolute abundance and isotopic composition of these two species is able to approximate the composite 18o of fossil specimens of these species carbon and oxygen isotopic compositions of most species are size dependent with the largest differences occuring in 13c as a function of size the calcite tests of all living species were depleted in 13c relative to the 13c of total dissolved co2 at 0 and 50 m with no seasonal pattern in 13c being discernible in any species in almost all cases fossil specimens from box core sediments are significantly enriched in 13c and slightly enriched in 18o relative to their counterparts in the living fauna because the sediment populations are generally composed of larger sized specimens compares to the plankton of larger size specimens compared to the plankton

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

potential productivity and surface circulation in the northern indian ocean during the last glacial to interglacial transition application of a new paleoceanographic model abstract a new paleoceanographic model is presented which approximates concentrations of total po 4 for the upper water column for the recent geologic past using the isotopes of carbon and oxygen from the tests of monospecific assemblages of planktic foraminifera these calculated concentrations of total po 4 are in turn used to estimate relative changes in potential productivity as well as changes in the position and intensity of surface currents for the recent geologic past this new model is based uponthe statistical constancy of the redfield o 2 po 4 ratio in the modern oceans and has been shown to be an accurate and reliable predictor of total po 4 the down core application of this model thus far limited to five core sites in the northern indian ocean has yielded results which are consistent with a number of other studies in characterizing the last glacial maximum in the northern indian ocean as a time of reduced potential productivity and weak surface currents in contrast by 9 ky b p the potential productivity and the surface circulation had increased dramatically in the northern indian ocean conditions in the holocene appear to be very similar to conditions which were in existence during the last glacial maximum the observed general trends in surface circulation and potential productivity during the last 18 000 years in the northern indian ocean suggest a milankovitch type astronomically induced changes in solar insolation orbital forcing

the marine phosphorus cycle phosphorus introduced to the ocean must ultimately be removed if a steady state is to be maintained over geologic time aeolian input is insignificant and there is evidently no hydrothermal contribution rivers dominate p input to the ocean the fluvial p flux is poorly quantified due to the interactions of two factors 1 man s influence on river nutrient fluxes and 2 inherent complexities in understanding the biological and inorganic associations of p in estuarine and coastal waters our best estimate of the natural or pre man p input flux is about 10 x 10 sup 9 moles p cm sup 2 ocean surface year of the identified flux of phosphorus to the sediments about 90 percent is in the form of biogenic debris or its regeneration products the burial of phosphatic fish debris is negligible p removal by direct reaction of phosphate in seawater with sea floor basalts during mid ocean ridge hydrothermal circulation is insignificant p removal by processes such as sorption on clay surfaces or formation of authigenic fe and al phosphate phases is presently unquantified and remains a serious uncertainty in the phosphorus cycle the identified sources and sinks approximately balance yielding a residence time for p in the oceans of about 10 sup 5 yrs

a mesozoic time scale we present an integrated geomagnetic polarity and stratigraphic time scale for the triassic jurassic and cretaceous periods of the mesozoic era with age estimates and uncertainty limits for stage boundaries the time scale uses a suite of 324 radiomenc dates including high resolution 40 ar 39 ar age estimates this framework involves the observed ties between 1 radiometric dates biozones and stage boundaries and 2 between biozones and magnetic reversals on the seafloor and in sediments interpolation techniques include maximum likelihood estimation smoothing cubic spline fitting and magnetochronology

abrupt deep sea warming at the end of the cretaceous climatic and oceanographic variations during the last 2 m y of the maastrichtian inferred from high resolution 10 k y stable isotope analysis of the mid latitude south atlantic deep sea drilling project site 525 reveal a major warm pulse followed by rapid cooling prior to the cretaceous tertiary boundary between 66 85 and 65 52 ma cool but fluctuating temperatures average 9 9 and 15 4 c in intermediate and surface waters respectively this interval is followed by an abrupt short term warming between 65 45 and 65 11 ma which increased temperatures by 2 3 c in intermediate waters and decreased the vertical thermal gradient to an average of 2 7 c this warm pulse may be linked to increased atmospheric pco 2 increased poleward heat transport and the switch of an intermediate water source from high to lowmiddle latitudes during the last 100 k y of the maastrichtian intermediate and surface temperatures decreased by an average of 2 1 and 1 4 c respectively compared to the maximum temperature between 65 32 and 65 24 ma

oceanic mechanisms for amplification of the 23 000 year ice volume cycle situated adjacent to the largest northern hemispher ice sheets of the ice ages the mid latitude north atlantic ocean has an important role in the earth s climate history it provides a significant local source of moisture for the atmosphere and adjacent continents forms a corridor that guides moisture bearing storms northward from low latitudes and at times makes direct contact along its shorelines with continental ice masses evidence of major ice ocean air interactions involving the north atlantic during the last 250 000 years is summarized outflow of icebergs and meltwater initially driven by summer insolation over the ice sheets affects midlatitude ocean temperatures summer heat storage winter sea ice extent and global sea level these oceanic responses in turn influence the winter moisture flux back to the ice sheets as well as ablation of land ice by calving spectral data indicate that the oceanic moisture and sea level feedbacks in part controlled by glacial melt products amplify milankovitch insolation forcing of the volumetrically dominant mid latitude ice sheets at the 23 000 year precessional cycle

middle late cretaceous climate of the southern high latitudes stable isotopic evidence for minimal equator to pole thermal gradients a detailed 18 o and 13 c stratigraphy has been generated from analysis of well preserved albian early maastrichtian foraminifera from deep sea drilling project dsdp sites 511 and 327 falkland plateau 58 s 62 s paleolatitude in the southern south atlantic and cenomanian and coniacian santonian foraminifera from dsdp site 258 naturaliste plateau 58 s paleolatitude in the southern indian ocean these results when combined with previously published maastrichtian stable isotope data from ocean drilling program odp site 690 weddell sea 65 s paleolatitude provide new insight into the climatic and oceanographic history of the southern high latitudes during middle late cretaceous time the planktonic foraminifer 18 o curves reveal a gradual warming of surface waters from the albian through the cenomanian followed by extremely warm surface waters from the turonian through the early campanian long term cooling of surface waters began in the late early campanian and continued through the end of the maastrichtian the benthic foraminifer 18 o record generally parallels changes in the oxygen isotopic curves defined by shallow dwelling planktonic foraminifera the vertical oxygen and carbon isotopic gradients were relatively low during the albian cenomanian high from the turonian early campanian and then low during the late campanian and maastrichtian foraminiferal oxygen isotopic data from published sources and this study are averaged for each site corrected for latitudinal changes in salinity based on modern day surface water values and plotted versus paleolatitude for the late albian coniacian santonian and late maastrichtian differences between lowand high latitude surface water paleotemperatures are estimated at 14 c during the late albian and late maastrichtian but the coniacian santonian reconstruction reveals only a 0 4 c latitudinal temperature gradient uncertainty regarding cretaceous salinity gradients and possible diagenetic alteration of 18 o values introduce error into our estimates of paleolatitudinal thermal gradients however apparent low equator to pole temperature differences could indicate much higher poleward heat transport than at present

oxygen and carbon isotopic composition and biogeographic distribution of planktonic foraminifera in the indian ocean five planktonic foraminiferal assemblages were encountered along a north south transect in the indian ocean with the following dominant species globorotalia truncatulinoides in the southern subtropical assemblage globigerinoides ruber globigerinella aequilateralis and globorotalia menardii in the northern subtropical assemblage globigerinoides sacculifer and pulleniatina obliquiloculata in the tropical assemblage neogloboquadrina dutertrei and globigerina bulloides in the tropical upwelling assemblage and globigernoides conglobatus in the tropical arabian sea assemblage oxygen and carbon isotopic analyses were performed on three surface dwelling species of planktonic foraminifera in tropical and subtropical waters 22 30 c the 18o of globigerinoides ruber and g sacculifer varies with surface water temperature and the slope of the isotope temperature regression line is similar to that of epstein et al 1953 for marine molluscs however foraminiferal 18o values are significantly lighter than those of molluscs indicating isotopic disequilibrium comparison between plankton tows taken within and below the mixed layer at the same stations shows that g ruber has similar low 18o values in both sets suggesting that it secretes its shell within the mixed layer by contrast g sacculifer has slightly higher 18o values below than within the mixed layer because it continues to secrete calcite below the thermocline no significant 18o variations with shell size were found on the other hand 13c values were strongly size dependent i e the smaller the size the lighter the 13c comparison of living g ruber and g sacculifer with recent specimens from the surface sediment shows that the living foraminifera are generally lighter in 18o than the fossils supporting independent observations that the latter have secreted additional calcite during gametogenesis when the organisms settle freely from the euphotic zone for about 12 h and pass through waters lower in temperature than the epipelagic waters where the foraminifera form the bulk of their shells

north american nonmarine climates and vegetation during the late cretaceous abstract analyses of physiognomy of late cretaceous leaf assemblages and of structural adaptations of late cretaceous dicotyledonous woods indicate that megathermal vegetation was an open canopy broad leaved evergreen woodland that existed under low to moderate amounts of rainfall evenly distributed through the year with a moderate increase at about 40 45 n many dicotyledons were probably large massive trees but the tallest trees were evergreen conifers megathermal climate extended up to paleolatitude 45 50 n mesothermal vegetation was at least partially an open broad leaved evergreen woodland perhaps a mosaic of woodland and forest but the evapotranspirational stress was less than in megathermal climate some dicotyledons were large trees but most were shrubs or small trees evergreen conifers were the major tree element some mild seasonality is evidenced in mesothermal woods precipitational levels probably varied markedly from year to year northward of approximately paleolatitude 65 n evergreen vegetation was replaced by predominantly deciduous vegetation this replacement is presumably related primarily to seasonality of light the southern part of the deciduous vegetation probably existed under mesothermal climate comparisons to leaf and wood assemblages from other continents are generally consistent with the vegetational climatic patterns suggested from north american data limited data from equatorial regions suggest low rainfall late cretaceous climates except probably those of the cenomanian had only moderate change through time temperatures generally appear to have warmed into the santonian cooled slightly into the campanian and more markedly into the maastrichtian and then returned to santonian values by the late maastrichtian the early eocene was probably warmer than any period of the late cretaceous latitudinal temperature gradients were lower than at present for the campanian and maastrichtian a gradient of about 0 3 c 1 latitude is inferred equability was high a mean annual range of temperature of about 8 c is inferred for paleolatitude 51 56 n during the campanian most late cretaceous plants evolved in a climate characterized by absence of freezing and low to moderate amounts of precipitation a brief low temperature excursion and a major long lasting increase in precipitation occurred at the cretaceous tertiary boundary in megathermal climates these events selected for plants that could exist in rainforest environments in mesothermal climates deciduousness and contamitant structural adaptations were selected the events at the cretaceous tertiary boundary had a major and long lasting impact on the evolution of land plants and their ecosystems low precipitation at low to middle late cretaceous latitudes is suggested to be the result of high levels of atmospheric co2 which in turn are probably related to inability of warm saline oceans to store large amounts of carbon conditions appear to have rapidly changed at the cretaceous tertiary boundary when oceanic circulation and stratification may have been fundamentally altered after the boundary the oceans were apparently able to store much greater amounts of carbon and the oceans withdrew large amounts of co2 from the atmosphere in turn more precipitation fell at low to middle latitudes the resulting high biomass vegetation formed a second major carbon reservoir to keep atmospheric co2 low relative to the late cretaceous changes in oceanic and atmospheric circulation probably resulted from some factor external to the ocean atmosphere system

global environmental changes preceding the cretaceous tertiary boundary early late maastrichtian transition stable carbon oxygen and strontium isotope data from maastrichtian planktic and benthic foraminifera from southern high latitude ocean drilling program sites 690 750 and 761 reveal major changes in climate and ocean chemistry during the early to late maastrichtian transition some 4 to 6 m y prior to the cretaceous tertiary k t boundary the 18o results suggest accelerated cooling resulting in the lowest marine temperatures of the late cretaceous the late maastrichtian rise in the seawater 87sr 86sr ratio begins at the time of this change and suggests increased rates of continental weathering and or runoff the 13c values show a negative shift of 0 5 followed by a positive shift of 1 these 13c fluctuations may reflect change in deep water chemistry with cooling variation in reduced carbon storage in coastal areas caused by eustatic sea level fluctuation and increased surface water productivity these findings contradict the common representation of stable and climatically equable environmental conditions in the latest cretaceous before the k t boundary event

paleo oceanographic utility of oxygen isotopic measurements on planktic foraminifera indian ocean core top evidence abstract isotopic analyses have been performed on narrow size ranges of seven species of planktic foraminifera picked from 43 core top locations in the indian ocean comparison of observed 18o for each species with calculated profiles of equilibrium 18o at each location yield three distinct depth habitat preferences for surface dwelling species globigerinoides ruber and globigerina bulloides observed oxygen isotopic compositions are in close agreement with the seasonal range of calculated 18o for calcite precipitated in surface waters observed 18o values for orbulina universa neogloboquadrina dutertrei and pulleniatina obliquiloculata are consistently enriched relative to calculated 18o for surface conditions in the northern indian ocean test precipitation for o universa n dutertrei and p obliquiloculata occurs over a narrow range of temperature 22 c 24 c with no systematic relationship with sea water t in contrast globorotalia inflata and g truncatulinoides observed 18o apparently reflect temperature and salinity variation along the 26 8 t isopycnal

maastrichtian climate productivity and faunal turnovers in planktic foraminifera in south atlantic dsdp sites 525a and 21 abstract stratigraphic faunal and isotopic analyses of the maastrichtian at dsdp sites 525a and 21 in the south atlantic reveal a planktic foraminiferal fauna characterized by two major events an early late maastrichtian diversification and end maastrichtian mass extinction both events are accompanied by major changes in climate and productivity the diversification event which occurred in two steps between 70 5 and 69 1 ma increased species richness by a total of 43 and coincided with the onset of major cooling in surface and bottom waters and increased surface productivity the onset of the terminal decline in maastrichtian species richness began at 67 5 ma and the first significant decline in surface productivity occurred at 66 2 ma coincident maximum cooling to 13 c in surface waters and the reduction of the surface to deep temperature gradient to less than 5 c major climatic and moderate productivity changes mark the mass extinction and the last 500 kyr of the maastrichtian between 200 and 400 kyr before the k t boundary surface and deep waters warmed rapidly by 3 4 c and cooled again during the last 100 kyr of the maastrichtian surface productivity decreased only moderately across the k t boundary species richness began to decline during the late maastrichtian cooling and by k t boundary time the mass extinction had claimed 66 of the species viewed within the context of maastrichtian climate and productivity changes the k t mass extinction could have resulted from extreme environmental stress even without the addition of an extraterrestrial impact

variability in late cretaceous climate and deep waters evidence from stable isotopes abstract strong climatic and temperature fluctuations mark the late campanian and maastrichtian as indicated by stable isotope records from the equatorial pacific site 463 and middle and high latitude south atlantic sites 525 689 and 690 the first major global cooling decreased intermediate water temperatures iwt by 5 6 c between 73 70 ma at the same time sea surface temperature sst decreased by 4 5 c in middle and high latitudes intermediate waters iw temporarily warmed by 2 c in low and middle latitudes between 70 68 5 ma global cooling resumed between 68 5 65 5 ma when iwt decreased by 3 4 c and sst by 5 c in middle latitudes about 450 ka before the cretaceous tertiary boundary rapid global warming increased iwt and sst by 3 4 c though sst in the tropics changed little during the last 200 ka of the maastrichtian climate cooled rapidly with iwt and sst decreasing by 2 3 c during the global cooling at 71 70 ma and possibly at 67 65 5 ma the sources of cold intermediate waters in the equatorial pacific indo pacific and south atlantic were derived from the high latitude north pacific in contrast during the global climate warming between 65 2 65 4 ma the middle latitude south atlantic was closest to the source of iw production and implies that the low latitude tethys played a major role in global climate change climate changes sea level fluctuations and associated restricted seaways appear to be the most likely mechanisms for the alternating sources of iw production

late cretaceous oceans and the cool tropic paradox oxygen isotopic proxies of paleo sea surface temperatures ssts suggest that maastrichtian about 66 million years ago tropical ssts were lower than those of today they also demonstrate that maastrichtian latitudinal sst gradients were much lower than those of the present the low maastrichtian sst gradients indicate that meridional heat transport was much greater or latitudinal differences in the balance of radiation to and from the sea surface were much less extreme during the latest cretaceous than they are today or that both conditions were true these findings challenge traditional interpretations of greenhouse late cretaceous climates

the salinity contrast between the atlantic and pacific oceans during glacial time in today s ocean the salinity of low latitude surface waters in the pacific is on the average 1 per mil lower than in the atlantic oxygen isotope records for planktonic foraminifera suggest that an even larger salinity deficit may have existed for pacific surface water during glacial time if so the transport of water vapor from the atlantic to the pacific must have been as strong as or even stronger to balance the tendency toward salt buildup the atlantic would have had to export during glacial time waters saltier than it received from the other oceans

planktonic foraminifera differential dissolution and the quaternary stable isotope record in the west equatorial pacific differential dissolution affects the isotopic composition of different species of planktonic foraminifera in different ways in the two species studied here in cores from ontong java plateau the less resistant species globigerinoides sacculifer is more readily affected at a shallower depth than the more resistant species pulleniatina obliquiloculata 2 9 versus 3 4 km but shows a smaller and less predictable response to partial dissolution 0 2 to 0 3 per mil versus 0 6 to 0 7 per mil comparison of isotopic values from the last glacial period with those from the late holocene indicates that the apparent dissolution effect is considerably reduced during the last glacial presumably due to reduced dissolution intensity during glacial time a change in the level of the lysocline of about 400 m is suggested in the published isotope records from pacific cores v28 238 and v28 239 the dissolution generated difference in 18o noted previously by shackleton and opdyke 1976 is seen to describe a mid brunhes dissolution maximum between 300 and 500 thousand years ago this mid brunhes dissolution excursion is well known from the pacific and the indian ocean

tectonic forcings of maastrichtian ocean climate evolution a global compilation of deep sea isotopic records suggests that maastrichtian ocean climate evolution tvas tectonically driven during the early maastrichtian the atlantic intermediate deep ocean was isolated from the pacific indian and southern oceans deep water formed in the high latitude north atlantic and north pacific at the early late maastrichtian boundary a major reorganization of oceanic circulation patterns occurred resulting in the development of a thermohaline circulation system similar to that of the modem oceans a combination of isotopic and plate kinematic data suggests that this event was triggered by the final breaching of tectonic sills in the south atlantic and the initiation of north south flow of intermediate and deep water in the atlantic the onset of laramide tectonism during the mid maastrichtian led to the concurrent draining of major epicontinental seaways together these events caused cooling increased latitudinal temperature gradients increased ventilation of the deep ocean and affected a range of marine biota

opening the carbon isotope vital effect black box 2 quantitative model for interpreting foraminiferal carbon isotope data interpretation of carbon isotope records from late quaternary planktonic foraminifers are confounded due to the presence of a significant physiological component in the carbon isotopic signal a quantitative carbon isotope qc model is presented which relates the carbon isotopic composition of a foraminiferal shell to the physiological processes of respiration and symbiont photosynthesis and to the 13c value of seawater co2 the qc model is calibrated with physiological and stable isotopic data from laboratory experiments with living planktonic foraminifers model simulations of chamber and shell 13c values with the symbiont bearing foraminifers orbulina universa and globigerinoides sacculifer suggest 1 variations in symbiont density and photosynthetic rate light level or habitat depth are the primary physiological parameters controlling intraspecific carbon isotopic variability in these species 2 respiration has little effect on the 13c of o universa and 3 each chamber in a multichambered foraminiferal test will have a distinct 13c value depending on its position in the test whorl size 13c value relationships reported for g sacculifer from fossil assemblages can be explained as a function of increasing symbiont density during ontogenetic development

the mode and mechanism of the last deglaciation oceanic evidence changes in ocean temperature carbonate productivity and ice rafted detritus in the north atlantic suggest that half of the northern hemisphere ice volume at the last glacial maximum had disappeared by 13 000 yr b p despite the still extensive limits of the ice sheets this early thinning of the ice sheets occurred during a time when summer insolation values were slowly rising but when pollen evidence south of the ice margins indicates cold dry air masses we infer that this rapid early ice disintegration 16 000 13 000 yr b p was caused by oceanic mechanisms 1 rising sea level causing increased calving along ice margins 2 the chilling of the sea surface by icebergs and meltwater reducing moisture extraction by the atmosphere and transport to the ice sheets and 3 winter freezing of the low salinity meltwater layer suppressing local moisture extraction and the regional influx of moisture bearing storms from lower latitudes in winter and hence starving the ice sheets these oceanic feedback mechanisms were strongest from 16 000 to 13 000 yr b p and weaker but still active from that date until the end of deglaciation at 6000 yr b p

geochemical evidence for suppression of pelagic marine productivity at the cretaceous tertiary boundary the normal biologically productive ocean is characterized by a gradient of the 13c 12c ratio from surface to deep waters here we present stable isotope data from planktonic and benthic micro fossils across the cretaceous tertiary boundary in the north pacific which reveal a rapid and complete breakdown in this biologically mediated gradient the fluxes of barium a proxy for organic carbon and caco3 also decrease significantly at the time of the major marine plankton extinctions the implied substantial reduction in oceanic primary productivity persisted for 0 5 myr before the carbon isotope gradient was gradually re established in addition the stable isotope and preservational data indicate that environmental change including cooling began at least 200 kyr before the cretaceous tertiary boundary and a peak warming of 3 c occurred 600 kyr after the boundary event

infrared surveillance of crater lakes using satellite data abstract under optimum circumstances thermal infrared data recorded from satellites can measure water surface temperatures to accuracies of a few tenths of a degree celsius such techniques are applied here to evaluate volcanic crater lake temperatures at present band 6 of the landsat thematic mapper tm is the most pertinent sensor in this respect although its nominal 120 120 m footprint only permits useful measurements of circular lakes exceeding 340 m in diameter in addition the radiative properties of the atmosphere between sensor and target at the instant of observation should be well characterised in order to make confident measurements of surface temperatures with single band infrared data an analysis is presented of three tm band 6 images of the crater lake at poas volcano costa rica recorded on february 6 1986 march 13 1987 and may 10 1988 in the february 1986 scene the band 6 derived water surface temperature is 36 c which is 3 c less than a field measurement made in the same month since the satellite measurement was integrated over some 14 400 m 2 of the lake surface while the field measurement was obtained at a single point below the surface the former may be more representative of surface heat losses subsequent tm data reveal an increasing discrepancy between contemporaneous field and satellite observations probably because the lake diameter had decreased to 250 m by march 1987 and to less than 200 m by mid 1988 greatly reducing the likelihood of obtaining a pure lake pixel the advanced spaceborne thermal emission and reflection radiometer aster which is earmarked for orbit on the first of nasa s earth observing system satellite platforms later this decade has five discrete spectral bands in the thermal infrared region and will produce data composed of 90 90 m pixels these specifications could enable the determination of water surface temperatures of 250 m diameter crater lakes by algorithms that implicitly account for atmospheric effects

the cenozoic ocean circulation based on ocean general circulation model results abstract a series of ocean general circulation model gcm experiments for paleocene eocene miocene and present day continental geography with atmospheric forcing prescribed from atmospheric gcm experiments is utilized to investigate the changes in surface and deep water ocean circulation through the cenozoic the experiments illustrate a number of similarities with previous observation based reconstructions although the timing of the development of particular gyre systems and the nature of the high southern latitude circulation are generally different than previous interpretations in addition the model results suggest substantial changes in the sites of deep water formation including a middle eocene subtropical source because of a number of experimental limitations the experiments should be considered largely as a sensitivity analysis of the role of changing geography in modifying the ocean circulation

warm saline bottom water in the ancient ocean considerable isotopic evidence indicates that oceanic bottom water was much warmer in the geological past a simple convection model driven by multiple turbulent buoyant plumes and observations of present deep water formation have led to the development of a theory for the formation of warm saline bottom water it is suggested that changes in the size and configuration of marginal seas in net evaporation zones due to lithospheric plate motions and eustatic sea level change caused these seas to become sources of warm saline bottom water evidence from the palaeotemperature record and palaeogeography during the late cretaceous is used to reinforce the hypothesis climatic and chemical consequences of the formation of warm saline bottom water are discussed

the rate and consequences of sr diagenesis in deep sea carbonates we have used a diffusion advection reaction model for sr exchange during deep sea carbonate diagenesis to determine the rate and consequences of sr exchange between porewaters and bulk carbonate at six dsdp sites 590b 575 593 516 305 and 289 where the required sr concentration and isotopic composition data for the interstitial waters are available from the literature the model can reproduce both the sr2 and 87sr 86sr profiles in the porewaters at each of the sites by adjusting the rate of sr exchange due to solution reprecipitation as a function of sediment age we find that the rate of solution reprecipitation at all of the sites is highest for the youngest sediment 1 10 m y and decreases by about an order of magnitude over the first 10 m y of sediment age the effect of this exchange on the properties of the bulk carbonate is to reduce the sr content by 5 25 depending primarily on the sedimentation rate and shift the 87sr 86sr by as much as 0 00004 from the value the sediment had when first deposited isotopic shifts of this magnitude are large compared to present analytical uncertainties and therefore should be corrected for when using bulk carbonate 87sr 86sr for stratigraphic correlation the average sr loss in the carbonate sections studied is about 15 from which we conclude that the sr flux from carbonate sediments to the overlying ocean is of the order of 15 of the riverine sr flux we also show that the isotopic composition of the diagenetic sr flux is at all times quite close to the contemporaneous seawater value and therefore this flux plays a very minor role in the overall sr budget that determines the sr isotopic composition of seawater the range of sr losses from bulk carbonate due to diagenesis that we calculate is too small to account for the typical decrease in sr content seen in pelagic carbonates as a function of age about 70 over the first 100 m y we conclude that this decrease is not the result of diagenesis and must involve some changing property of the ocean itself

do planktic foraminifera accurately record shifts in the carbon isotopic composition of seawater σco2 abstract both the carbon isotopic composition of seawater and physiological vital effects such as respiration and symbiont photosynthesis influence the 13 c value of foraminiferal calcite the symbiont bearing planktic foraminifera orbulina universa was grown in a series of laboratory experiments to determine whether vital effects differentially obscure the 13 c signal such that changes in the 13 c of seawater co 2 cannot be quantitatively evaluated foraminifera were cultured under three different irradiance levels to elicit a full range of symbiont photosynthetic effects and in seawater with 13 c values ranging between 1 77 ambient and 5 76 power regression analysis of isotope data from individual shells plotted against culture irradiance yields three curves which are nearly parallel but are offset by the difference between the carbon isotopic composition of the culture waters when irradiance groups are combined and o universa 13 c values are plotted against seawater 13 c three parallel linear regressions are obtained with slopes ranging between 0 93 and 0 96 because the slopes are near unity it is concluded that the 13 c of o universa accurately tracks changes in the carbon isotopic composition of seawater regardless of the magnitude of its physiological vital effect o universa oxygen isotope data show that individuals maintained in the low and medium irradiance groups secrete their shells in isotopic equilibrium according to established paleotemperature equations in contrast individuals grown under high irradiance levels maximum symbiont photosynthetic rates are on average 0 35 depleted in 18 o relative to equilibrium symbiont enhanced calcification rates in the high light group may be responsible for the observed 18 o difference

carbon and oxygen isotopic records of benthic foraminifera from the northeast indian ocean implications on glacial interglacial atmospheric co2 changes abstract we present here continuous records of 18o and 13c in benthic foraminifera extending well into the last ice age in two piston cores from the andaman sea sill depth 1 3 km and the bay of bengal 3 km these show that contrary to the previous reports the glacial to interglacial shift in 13c at mid depths in the northeast indian ocean was indistinguishable from the mean oceanic 13c change negating a more vigorous renewal of intermediate waters globally during the glacial time the corresponding 13c shift in deep waters is estimated to be about 50 larger than that reported previously jointly with some recent data from the pacific our results indicate a modest glacial holocene shift in the intermediate to deep water chemical gradients in the indo pacific as a whole implying that it was perhaps not the dominant mechanism for the glacial interglacial atmospheric co2 variations also in conflict with previous work our measurements suggest significant cooling of both the intermediate and deep waters during the glacial time the high resolution records from the andaman sea help reconstruct paleoenvironmental changes at intermediate depths during the last deglaciation rapid increases in 13c occurring in two stages during the early deglaciation appear to have been caused by the fluctuations in the north atlantic deep water production a negative excursion in 13c during the mid deglaciation is ascribed to enhanced nutrient regeneration at mid depths associated with the greatly intensified summer monsoon around the pleistocene holocene boundary

a warm equable cretaceous the nature of the problem abstract the nature of the problem of warm equable paleoclimates is defined by investigating the mid cretaceous period the problem consists of three components 1 defining precisely the climatic state during any specified interval of geologic time 2 specifying the external climatic forcing factors which may have been important and 3 understanding the climatic response to any specific modifying influence these components are characterized by limitations of critical importance in understanding paleoclimates the nature of the problem of a warm cretaceous is defined both qualitatively and quantitatively within these limits

evidence for thermohaline circulation reversals controlled by sea level change in the latest cretaceous fluctuations in oxygen 18 o and carbon 13 c isotope values of benthic foraminiferal calcite from the tropical pacific and southern oceans indicate rapid reversals in the dominant mode and direction of the thermohaline circulation during a 1 m y interval 71 70 ma in the maastrichtian at the onset of this change benthic foraminiferal 18 o values increased and were highest in low latitude pacific ocean waters whereas benthic and planktic foraminiferal 13 c values decreased and benthic values were lowest in the southern ocean subsequently benthic foraminiferal 18 o values in the indo pacific decreased and benthic and planktic 13 c values increased globally these isotopic patterns suggest that cool intermediate depth waters derived from high latitude regions penetrated temporarily to the tropics the low benthic 13 c values at the southern ocean sites however suggest that these cool waters may have been derived from high northern rather than high southern latitudes correlation with eustatic sea level curves suggests that sea level change was the most likely mechanism to change the circulation and or source s of intermediate depth waters we thus propose that oceanic circulation during the latest cretaceous was vigorous and that competing sources of intermediate and deep water formation linked to changes in climate and sea level may have alternated in importance

dynamics of meltwater discharge from northern hemisphere ice sheets during the last deglaciation during the last ice age ice sheets covered large portions of north america europe asia and the arctic ocean the ice sheets were composed of meteoric water enriched in the light isotope of oxygen 16o leaving oceanic seawater correspondingly enriched1 2 in 18o the volume of past continental ice sheets during the last glacial maximum 18 000 yr ago has been estimated from terrestrial evidence of ice limits3 glaciological modelling4 the 18o of foraminifera from deep sea cores5 6 and sea level evidence from raised coral terraces7 8 oxygen isotope studies of planktonic foraminifera reveal that 18o shifts during deglaciations in areas near sources of ice meltwater like the gulf of mexico and labrador sea baffin bay are often larger than the corresponding average global oceanic shift9 11 and that these variations reflect the timing of ice decay without the ocean mixing lag contained in both distal and benthic 10o variations12 we show here that geographically distinct planktonic 18o gradients can be related to the volume of meltwater discharged through specific meltwater outlets and thus to the initial volume of the ice sheets at the commencement of deglaciation and to the subsequent dynamics of ice sheet decay

comparison of isotopic composition of planktonic foraminifera in plankton tows sediment traps and sediments planktonic foraminifera from plankton tows sediment traps and sediments in the central north atlantic were studied in order to understand what determines their oxygen and carbon isotope composition a clear separation of species and genera on a 18o vs 13c plot for all samples suggests that their isotopic composition is controlled to a certain degree by biological factors within a species population the globorotaliids show a positive linear correlation between 18o and 13c while the shallow dwelling spinose species mostly globigerinoides species do not show a definite trend the latter species when collected in plankton tows often show slight negative deviations from isotopic equilibrium with respect to oxygen all species deviate from carbon isotope equilibrium by 1 5 to 6 these deviations from equilibrium are probably caused by incorporation of isotopically light metabolic co2 into the skeleton which is enhanced by the activity of symbiotic algae during their ontogeny the average weight per individual of most species increases which indicates that calcification continues to a depth of about 100 m this additional skeleton roughly 50 by weight is isotopically heavier because temperatures are lower and photosynthesis of symbiotic algae stops below the photic zone therefore the skeleton of foraminifera collected in sediment traps below 400 m has an overall oxygen isotope composition that seems to be in equilibrium for caco3 deposited in the upper 100 m