south china sea isopycnal surface circulation this paper investigates the seasonal variabilities of the south china sea isopycnal surface circulations and of the kuroshio intrusion through the luzon strait using the u s navy s climatological temperature and salinity dataset public domain with 83 8 resolution by the p vector method the representative pattern is a persistent basin scale cyclonic circulation away from the surface and a seasonally varying circulation with a weak anticylonic gyre in the summer and a strong cyclonic gyre in the winter near the surface this pattern is consistent with a classical view of mean cyclonic circulation in large stratified lakes and semienclosed marginal seas by emery and csanady and with a recent numerical simulation using the navy s layered ocean model by metzger and hurlburt the computed monthly volume transport through the luzon strait is negative inflow all year round with a minimum value of 213 7 sv in february strongest intrusion and a maximum value of 21 4 sv in september weakest intrusion the annual mean transport is 26 5 sv intrusion

eocene bipolar glaciation associated with global carbon cycle changes the transition from the extreme global warmth of the early eocene greenhouse climate 55 million years ago to the present glaciated state is one of the most prominent changes in earth s climatic evolution it is widely accepted that large ice sheets first appeared on antarctica 34 million years ago coincident with decreasing atmospheric carbon dioxide concentrations and a deepening of the calcite compensation depth in the world s oceans and that glaciation in the northern hemisphere began much later between 10 and 6 million years ago here we present records of sediment and foraminiferal geochemistry covering the greenhouse icehouse climate transition we report evidence for synchronous deepening and subsequent oscillations in the calcite compensation depth in the tropical pacific and south atlantic oceans from 42 million years ago with a permanent deepening 34 million years ago the most prominent variations in the calcite compensation depth coincide with changes in seawater oxygen isotope ratios of up to 1 5 per mil suggesting a lowering of global sea level through significant storage of ice in both hemispheres by at least 100 to 125 metres variations in benthic carbon isotope ratios of up to 1 4 per mil occurred at the same time indicating large changes in carbon cycling we suggest that the greenhouse icehouse transition was closely coupled to the evolution of atmospheric carbon dioxide and that negative carbon cycle feedbacks may have prevented the permanent establishment of large ice sheets earlier than 34 million years ago between 55 and 34 million years ago earth switched from a warm greenhouse ocean climate system to the icehouse that we now enjoy frustratingly the few oceanographic datasets that exist for this key period are of low resolution tripati et al now present measurements of sediment and foraminiferal geochemistry that provide the first continuous high resolution records for this period the data suggest that northern hemisphere glaciation started 34 million years ago rather than between 10 and 8 million years ago as previously thought

numerical paleoceanographic study of the early jurassic transcontinental laurasian seaway the forces governing marine circulation of a meridional transcontinental seaway is explored with the princeton ocean model the jurassic laurasian seaway which connected the low latitude tethys ocean with the arctic sea is modeled quantitatively the global ocean is found to have a profound influence on seaway dynamics a north south density difference and hence sea level difference of the global ocean was probably the main factor in forcing the seaway flow when the tethys waters were the denser water the net seaway flow was southward and conversely it was northward for denser arctic waters marine bioprovincial boundaries and sediment data indicate that the seaway probably was dominated by boreal faunal groups and reduced salinities several times in the jurassic the model results suggest that this can be explained by southward flowing seaway currents which may have been related to an oceanic thermohaline circulation where no northern high latitude deep convection occurred

a palaeoclimate model for the kimmeridgian abstract most attempts at using numerical general circulation model gcm to simulate mesozoic climates have studied the late cretaceous and have focused on the enigmaof apparently equable global climates however this climate regime lasted throughout the mesozoic and it is of interest to examine other periods we present the results of an integration for the late jurassic using a relatively detailed and high resolution model there is generally good agreement between the model climate and the existing geological data in particular the simulation predicts no permanent ice cover near either pole arid conditions over the southwestern usa seasonally arid climate over southern europe and winter storminess over europe and australia however the surface temperatures over siberia and southeastern gondwanaland drop below zero for a significant part of the winter

antarctic climate during the middle pliocene model sensitivity to ice sheet variation significant controversy exists surrounding the nature of the antarctic ice sheet during the period of middle pliocene warmth this paper outlines the output from three sensitivity experiments for the middle pliocene using the ukmo gcm and the usgs prism2 data set different east antarctic ice sheet configurations were prescribed in each modelling experiment conforming to a dynamic sea level 35 m higher than at present intermediate pliocene control sea level 25 m higher than at present and stable sea level 12 15 in higher than at present scenario for the nature of the antarctic ice sheet during the middle pliocene all three scenarios would have provided middle pliocene sea levels across the spectrum of estimates provided by known geological data model outputs indicate that surface temperature increases are greatest in the pliocene dynamic experiment climatic conditions for the pliocene control and stable experiments remain harsh over antarctica with surface temperatures rising above freezing mean 4degreesc for a maximum of 2 months per year in contrast mean surface temperatures from the pliocene dynamic experiment rise above freezing mean 10degreesc for 4 months of the year climatic outputs from all of the pliocene experiments were used in a biome model biome 4 for the pliocene control and stable experiments biome 4 predicted the occurrence of exclusively tundra type vegetation on antarctica for the dynamic experiment climatic conditions ameliorated sufficiently to allow biome 4 to predict deciduous taiga montane forests on antarctica thus the results from the dynamic experiment are consistent with reported pliocene nothofagus occurrences on antarctica in the future more sophisticated palaeoclimate modelling studies need to employ atmospheric general circulation models gcms coupled to dynamic ocean and ice sheet models this will allow the gcm to predict rather than prescribe an antarctic ice sheet configuration in equilibrium with reconstructed middle pliocene sea surface temperatures such an approach may also shed light on how the antarctic ice sheet responded to climate variability during the middle pliocene c 2002 elsevier science b v all rights reserved

deep circulation in the late cretaceous oxygen isotope paleotemperatures from inoceramus remains in d s d p cores abstract inoceramus is an epibenthic bivalve which lived in a wide variety of paleoenvironments encompassing a broad range of paleodepths a survey of all cretaceous sediments from deep sea drilling project legs 1 69 and 75 revealed over 500 inoceramus specimens at twenty sites of these 47 well preserved late cretaceous specimens from the south atlantic pacific and indian oceans were analyzed for oxygen and carbon isotopes the specimens exhibit small internal isotopic variability and oxygen isotopic paleotemperatures that are consistent with a deep sea habitat paleotemperatures ranging from 5 to 16 c show that late cretaceous oceans were significantly warmer than the present oceans the data suggest that deep water was formed both by cooling at high latitudes and by evaporation in the subtropics

testing the cretaceous greenhouse hypothesis using glassy foraminiferal calcite from the core of the turonian tropics on demerara rise glassy turonian foraminifera preserved in clay rich sediments from the western tropical atlantic yield the warmest equivalent 18o sea surface temperatures ssts yet reported for the entire cretaceous cenozoic we estimate turonian ssts that were at least as warm as conservative mean 30 c to significantly warmer warm mean 33 c than those in the region today however if independent evidence for high middle cretaceous pco2 is reliable and resulted in greater isotopic fractionation between seawater and calcite because of lower sea surface ph our conservative and warm sst estimates would be even higher 32 and 36 c respectively our new tropical ssts help reconcile geologic data with the predictions of general circulation models that incorporate high cretaceous pco2 and lend support to the hypothesis of a cretaceous greenhouse our data also strengthen the case for a turonian age for the cretaceous thermal maximum and highlight a 20 40 m y mismatch between peak cretaceous cenozoic global warmth and peak inferred tectonic co2 production we infer that this mismatch is either an artifact of a hidden turonian pulse in global ocean crust cycling or real evidence of the influence of some other factor on atmospheric co2 and or ssts a hidden pulse in crust cycling would explain the timing of peak cretaceous cenozoic sea level also turonian but other factors are needed to explain high frequency 10 100 k y instability in middle cretaceous ssts reported elsewhere

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

an ocean modeling study of the cenomanian atlantic equatorial paleo upwelling organic rich sediments and the consequences for a connection between the proto north and south atlantic abstract a reduced gravity ocean modelis used to deter mine the pattern of upwelling in the cenomanian atlantic the deposition of organic rich sediments on the margins ofthe equatorial region is found to be consistent with the pat terns of upwelling in simulations which incorporate only ashallow 300m equatorial connection between the northand south atlantic fracture zone ridges were probably re sponsible for the e ective shallowness of the gateway if adeep equatorial channel is assumed the modeling results areconsistent only with the morerecent turonian sedimentaryrecord we suggest therefore that reduced gravity modelsprovide a mean of predicting areas of the continental mar gins which may be underlain by hydrocarbon rich sedimen tary rocks introduction the equatorial region of the atlantic is a major route forwater transfer between the two hemispheres studies of itssedimentary cover have provided abundant evidence for ma jor environmental changeswithin this critical oceanographicgateway from late jurassic time among the important sed imentary consequences ofcirculation and sea level variationswas the development of petroleum rich sequences along thecontinental margins and in the adjacent deep water basins on the present continental shelves these occur over a widestratigraphic range from the early cretaceous to oligocene reyre 1966 nairn and stehli 1973 akpati 1978 kesse 1984 dumestre and carvalho 1985 herbin et al 1986 koutsoukos et al 1991 while in the deep sea organic richshales ranging in age from albian to late cretaceous havebeen found at several deep sea drilling project dsdp sites figure 1 the deep sea deposits have been attributedto oceanwide anoxic events oaes pedersen and calvert 1990 arthur and sageman 1994 the stratigraphic rangeof the continental margin black shales is much broader thanthe deep sequences however we have to look for othermechanisms apartfrom general oceananoxia to explain this these sequences could be ascribed to enhanced primary pro ductivity arising from upwelling of nutrients into the eu photic zone barron 1985 parrish 1995 parrish 1995 be

palaeobotanical evidence for a warm cretaceous arctic ocean the cretaceous period was a time of global warmth1 4 mid cretaceous equatorial temperatures were similar to today s5 but the equator to pole temperature gradient is the subject of some controversy5 7 although it is unlikely that the poles were ice free8 10 fossil evidence3 5 11 12 indicates that near polar temperatures were much higher than they are today little is known moreover about oceanic poleward heat transport and this makes it hard to model the cretaceous climate or to evaluate the extent to which it provides an analogue for a greenhouse world warmed by increased atmospheric co2 alone here we use relationships between leaf physiognomy such as shape and size and modern climate to determine cretaceous climate conditions in the arctic region from fossil leaves we find that the arctic ocean was relatively warm remaining above 0 c even during the winter months this implies that there was significant poleward heat transport during all seasons

sedimentological evaluation of general circulation model simulations for the greenhouse earth cretaceous and jurassic case studies abstract conceptual climate models based on the workings of the present day climate system provided a first order approach to ancient climate systems they are potentially very subjective in character their main drawback was that they involved the relocation of continents beneath a stable atmospheric circulation modelled upon that of the present general circulation models gcms use the laws of physics and an understanding of past geography to simulate climatic responses they are objective in character however they require super computers to handle vast numbers of calculations nonetheless it is now possible to compare results from different gcms for a range of times and over a wide range of parameterisations gcms are currently producing simulated climate predictions which compare favourably with the distributions of climatically sensitive facies e g coals evaporites and palaeosols they have been used effectively in the prediction of oceanic upwelling sites and the distribution of petroleum source rocks and phosphorites parameterisation is the main weakness in gcms e g sea surface temperature orography cloud behaviour sensitivity experiments can be run on gcms which simulate the effects of milankovitch forcing and thus provide insights into possible patterns of climate change both globally and locally i e provide predictions that can be evaluated against the rock record future use of gcms could be in the forward modelling of sequence stratigraphic evolution and in the prediction of the diagenetic characteristics of reservoir units in frontier exploration areas the sedimentary record provides the only way that gcms may themselves be evaluated and this is important because these same gcms are being used currently to predict possible changes in future climate

deep water in the late maastrichtian ocean 1 stable isotopic data from benthic foraminifera indicate the occurrence of at least three deepwater masses in the late maastrichtian ocean given mean oceanic 18ow of 1 0 the temperature of the coolest intermediate depth waters was 5 7 c that of the deepest waters was 10 c and that of the warmest intermediate waters was 13 15 c the cool intermediate depth water mass probably originated in the high latitude southern ocean the deepest waters originated at least partly in the northern atlantic the source region for the warmest intermediate depth water mass is unknown although much of the late maastrichtian deep water was probably preconditioned for winter sinking by low or middle latitude evaporation no more than 11 of late maastrichtian deep water could have been directly actuated by low latitude sea surface evaporation at least in the southern atlantic and indian oceans heat transport by upwelling of deep water was not the primary cause of mild sea surface and coastal temperatures

paleotemperatures and ice volume of the past 27 myr revisited with paired mg ca and 18o 16o measurements on benthic foraminifera 1 we explore the applicability of paired mg ca and 18o 16o measurements on benthic foraminifera from southern ocean site 747 to paleoceanographic reconstructions on pre pleistocene timescales we focus on the late oligocene through pleistocene 27 0 ma history of paleotemperatures and the evolution of the 18o values of seawater 18osw at a temporal resolution of 100 200 kyr absolute paleotemperature estimates depend on assumptions of how mg ca ratios of seawater have changed over the past 27 myr but relative changes that occur on geologically brief timescales are robust results indicate that at the oligocene to miocene boundary 23 8 ma temperatures lag the increase in global ice volume deduced from benthic foraminiferal 18o values but the smaller scale miocene glaciations are accompanied by ocean cooling of 1 c during the mid miocene phase of antarctic ice sheet growth 15 13 ma water temperatures cool by 3 c unlike the benthic foraminiferal 18o values which remain relatively constant thereafter temperatures vary by 3 c and reach maxima at 12 and 8 5 ma the onset of significant northern hemisphere glaciation during the late pliocene is synchronous with an 4 c cooling at site 747 a comparison of our 18osw curve to the haq et al 1987 sea level curve yields excellent agreement between sequence boundaries and times of increasing seawater 18o 16o ratios at 12 11 ma in particular when benthic foraminiferal 18o values do not support a further increase in ice volume the 18osw curve comes to a maximum that corresponds to a major mid miocene sea level regression the agreement between the character of our mg ca based 18osw curve and sequence stratigraphy demonstrates that benthic foramaniferal mg ca ratios can be used to trace the 18osw on pre pleistocene timescales despite a number of uncertainties related to poorly constrained temperature calibrations and paleoseawater mg ca ratios the mg ca record also highlights that deep ocean temperatures can vary independently and unexpectedly from ice volume changes which can lead to misinterpretations of the 18o record

high temperatures in the late cretaceous arctic ocean to understand the climate dynamics of the warm equable greenhouse world of the late cretaceous period it is important to determine polar palaeotemperatures the early palaeoceanographic history of the arctic ocean has however remained largely unknown because the sea floor and underlying deposits are usually inaccessible beneath a cover of floating ice a shallow piston core taken from a drifting ice island in 1970 fortuitously retrieved unconsolidated upper cretaceous organic rich sediment from alpha ridge a submarine elevated feature of probable oceanic origin a lack of carbonate in the sediments from this core has prevented the use of traditional oxygen isotope palaeothermometry here we determine arctic palaeotemperatures from these upper cretaceous deposits using tex86 a new palaeothermometer that is based on the composition of membrane lipids derived from a ubiquitous component of marine plankton crenarchaeota from these analyses we infer an average sea surface temperature of approximately 15 degrees c for the arctic ocean about 70 million years ago this calibration point implies an equator to pole gradient in sea surface temperatures of approximately 15 degrees c during this interval and by extrapolation we suggest that polar waters were generally warmer than 20 degrees c during the middle cretaceous approximately 90 million years ago

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

warm palaeotemperatures from high late jurassic palaeolatitudes falkland plateau ecological environmental or diagenetic controls abstract oxygen and carbon isotopes have been determined from late jurassic oxfordian tithonian belemnites and inoceramid bivalves from two deep sea drilling project dsdp sites located on the falkland plateau mean belemnite 18o values derived from well preserved skeletal material were 1 29 from dsdp site 330 and 1 45 from dsdp site 511 assuming a seawater smow value of 1 0 mean palaeotemperatures calculated from the oxygen isotopic composition are 17 2 c and 17 9 c respectively the inoceramid bivalves yielded much lighter 18o values mean 3 58 petrographic and geochemical evidence points to the inoceramid bivalves being altered by diagenesis which accordingly accounts for the observed differences in isotopic values vital effects or the importation of belemnites or inoceramids from another area are considered not to account for the observed isotopic trends the palaeotemperatures interpreted from the belemnites are significantly warmer than other recent estimates of late jurassic temperature from oxygen isotope studies and climate model predictions from similar southern palaeolatitudes we suspect our apparent warmer temperatures are because of a combination of increased freshwater runoff depleting surface waters with respect to 18o and related to the semi enclosed nature of the depositional basin retaining warmth relative to the open ocean of similar latitudes

possible atmospheric co2 extremes of the middle cretaceous late albian turonian 1 atmospheric carbon dioxide co2 estimates for the middle cretaceous mk have a range of 4000 ppm which presents considerable uncertainty in understanding the possible causes of warmth for this interval this paper examines the problem of mk greenhouse forcing from an inverse perspective we estimate upper ocean water temperatures from oxygen isotope measurements of well preserved late albian turonian planktonic foraminifera and compare these against temperatures predicted by general circulation model gcm experiments with co2 concentrations of 500 7500 ppm at least 4500 ppm co2 is required to match maximum temperatures inferred from well preserved planktonic foraminifera approximately 900 ppm co2 produces a good match between the model and the minimum temperature estimates for the mk an ocean model forced by these two extremes in surface conditions brackets nearly all available bottom water temperature estimates for this interval the climate model results support nearly the entire range of mk co2 estimates from proxy data the ocean model suggests possible mk oceanographic changes from deep water formation in the high latitude region of one hemisphere to the other hemisphere in response to changes in atmospheric temperatures and hydrologic cycle strength we suggest that rather than contradicting one another the various proxy co2 techniques especially those with high temporal resolution may capture true variability in co2 concentrations and that mk co2 could have varied by several thousand ppm through this interval

fossil crocodilians as indicators of late cretaceous and cenozoic climates implications for using palaeontological data in reconstructing palaeoclimate abstract that the earth s climate has cooled over the last 100 million years has been recognized since the early nineteenth century the transition from the hot house world of the cretaceous a time interval without significant polar icesheets to the ice house world in which we now live today the dynamics process responsible for this change are being examined using computer models especially general circulation models gcm s through such work our understanding of the dynamics of the earth system improves and our ability to predict future trends is enhanced but the success of modelling experiments can only be assessed by comparing results with observations the pattern which for palaeoclimate are drawn exclusively from the geological record palaeoclimate interpreted from geological data is invariably based on analogy with the recent the validity of which depends on corroboration from multiple lines of evidence this requires the compilation and investigation of large global datasets of well constrained geological climate proxies this study uses the palaeodistribution of fossil crocodilians to examine the spatial distribution of palaeoclimate during this transition fossil crocodilians have a relatively good fossil record and are climatically limited in the recent they also provide a manageable global dataset with which to investigate other issues that impinge on the use of geologic data for reconstructing palaeoclimate taphonomy sampling effects time averaging tectonics and for fossils palaeobiogeography and evolution as such this study provides a possible template for examining other climate proxies in order to validate and hone palaeoclimatic interpretations an analysis of modern crocodilians indicates that temperature is the principal influence on their global distribution with the coldest month mean temperature cmm of 5 5 c marking the minimum thermal limit for the group corresponding today to a minimum mean annual temperature mat of 14 2 c the duration of warmth during the year partly indicated by the mean annual range of temperature mart is also important as this affects early juvenile development and survival the presence of standing water provides an essential thermal buffer against temperature extremes by analogy the palaeodistribution of fossil crocodilians suggests the following during the late cretaceous and early palaeogene mat s in excess of 14 2 c cmm s 5 5 c permeated throughout mid latitudes and coastal regions in high latitudes during the oligocene the restriction of fossil crocodilians to low latitudes suggests high latitude cooling as indicated by numerous other lines of evidence coeval restriction of crocodilians to coastal regions in mid latitude north america and much of asia consistent with increased seasonality and aridification in continental interiors may reflect local orographic changes as well as global climate change during the miocene fossil crocodilians return to the great plains of north america but do not reoccupy the continental interior of asia by the pliocene crocodilians are again restricted to low latitudes and coastal regions in mid latitudes coincident with further high latitude cooling and aridification and cooling of mid latitude continental interiors minor distributional changes during the holocene may reflect human effects

equatorial sea surface temperatures for the maastrichtian revealed through remarkable preservation of metastable carbonate the classic paleotemperature record based on 18 o data from pelagic foraminiferal calcite suggests that equatorial sea surface temperatures during the maastrichtian 12 20 c were much cooler than today 27 29 c such cool equatorial temperatures contradict basic theories of tropical atmospheric and ocean dynamics we report 18 o data from remarkably well preserved rudist aragonite and magnesian calcite cements of maastrichtian age 69 1 ma from the carbonate platform of wodejebato guyot in the western pacific these data suggest that equatorial sea surface temperatures in the maastrichtian best estimate 27 32 c were at least as warm as today this finding helps reconcile the geologic 18 o record with ocean atmospheric dynamic theory and implies a reduction in the poleward heat flux required by global climate simulations of greenhouse conditions

triassic environments climates and reptile evolution abstract a consideration of all the available data on triassic vertebrate faunas and their stratigraphic location reveals a relatively sudden extinction event among the last of the mammal like reptiles and the herbivorous rhynchosaurs in the norian of the upper triassic this event was apparently quickly followed by the radiation of the dinosaurs also in the norian this conclusion suggests that competition was not the main factor in the initial success of the dinosaurs but opportunistic radiation following the extinction of major reptile groups a global review of triassic sedimentary facies shows that there were climatic and floral changes towards the end of the triassic it is envisaged that increasing aridity in the later triassic resulting from plate motions and particularly affecting gondwanaland and southwestern laurasia brought about floral changes and then the reptile extinctions with the rapid evolution of new floras of conifers and bennettitaleans the dinosaurs came to dominate all terrestrial faunas within the space of only a few million years

pangaean climates megamonsoons of the megacontinent the climate for a highly idealized geographic representation of the megacontinent of pangaea corresponding to the period 250 200 m y ago is explored using a low resolution atmospheric general circulation model that is coupled to a static mixed layer ocean of constant depth with a provision for sea ice formation and decay soil moisture is included as a predicted variable on the continent because there are large uncertainties about key factors that might influence the pangaean climate sensitivity experiments are used to examine the climate for two different mean elevations 0 and 1000 m two different snowcover prescriptions and two different levels of implied greenhouse heating and solar luminosity modern co2 concentration and modern solar luminosity fivefold increase in modern co2 concentration and a 1 decrease in modern solar luminosity in all of the experiments the large bipolar land masses of laurasia and gondwanaland joined near the equator in the west and separated by the tethys sea in the east exhibit extreme continentality with hot summers cold winters and large scale summer and winter monsoon circulations year round or seasonal aridity is simulated for all but the eastern coastal regions the tropical western coast and the regions poleward of 40 latitude the simulated climate of the idealized pangaean continent has many features that correspond qualitatively with geologic evidence for tropical warmth and aridity in the late permian and triassic however the model results serve mainly to indicate the importance of various climate forming factors geography topography heating detailed comparisons will require new experiments with better models and more accurate geologic boundary conditions

paleocurrent reconstruction of the deep pacific inflow during the middle miocene reflections of east antarctic ice sheet growth today the deep western boundary current dwbc east of new zealand is the most important route for deep water entering the pacific ocean large scale changes in deep water circulation patterns are thought to have been associated with the development of the east antarctic ice sheet eais close to the main source of bottom water for the dwbc here we reconstruct the changing speed of the southwest pacific dwbc during the middle miocene from 15 5 12 5 ma a period of significant global ice accumulation associated with eais growth sortable silt mean grain sizes from ocean drilling program site 1123 reveal variability in the speed of the pacific inflow on the timescale of the 41 kyr orbital obliquity cycle similar orbital period flow changes have recently been demonstrated for the pleistocene epoch collectively these observations suggest that a strong coupling between changes in the speed of the deep pacific inflow and high latitude climate forcing may have been a persistent feature of the global thermohaline circulation system for at least the past 15 myr furthermore long term changes in flow speed suggest an intensification of the dwbc under an inferred increase in southern component water production this occurred at the same time as decreasing tethyan outflow and major eais growth between 15 5 and 13 5 ma these results provide evidence that a major component of the deep thermohaline circulation was associated with the middle miocene growth of the eais and support the view that this time interval represents an important step in the development of the neogene icehouse climate

extreme polar warmth during the cretaceous greenhouse paradox of the late turonian δ18o record at deep sea drilling project site 511 1 oxygen isotope data for upper turonian planktonic foraminifera at deep sea drilling project site 511 falkland plateau 60 s paleolatitude exhibit an 2 excursion to values as low as 4 66 vienna peedee belemnite standard pdb coincident with the warmest tropical temperature estimates yet obtained for the open ocean the lowest planktonic foraminifer 1 8 o values suggest that the upper ocean was as warm as 30 32 c this is an extraordinary temperature for 60 s latitude but is consistent with temperatures estimated from apparently coeval mollusc 1 8 o from nearby james ross island 65 s paleolatitude glassy textural preservation a well defined depth distribution in site 511 planktonics low sediment burial temperature 32 c and lack of evidence of highly depleted pore waters argue against diagenesis even solid state diffusion as the cause of the very depleted planktonic values the lack of change in benthic foraminifer 1 8 o suggests brackish water capping as the mechanism for the low planktonic 1 8 o values however mixing ratio calculations show that the amount of freshwater required to produce a 2 shift in ambient water would drive a 7 psu decrease in salinity the abundance and diversity of planktonic foraminifera and nannofossils high planktonic benthic ratios and the appearance of keeled foraminifera argue against lower than normal marine salinities isotope calculations and climate models indicate that we cannot call upon more depleted freshwater 1 8 o to explain this record without more late turonian data especially from outside the south atlantic basin we can currently only speculate on possible causes of this paradoxical record from the core of the cretaceous greenhouse

deep sea paleotemperature record of extreme warmth during the cretaceous oxygen isotope analyses of well preserved foraminifera from blake nose 30 n paleolatitude north atlantic and globally distributed deep sea sites provide a long term paleotemperature record for the late albian maastrichtian interval that is difficult to reconcile with the existence of significant cretaceous ice sheets given reasonable assumptions about the isotopic composition of cretaceous seawater our results suggest that middle bathyal water temperatures at blake nose increased from 12 c in the late albian through middle cenomanian to a maximum of 20 c during the latest cenomanian and earliest turonian bottom waters were again 12 c during the middle campanian and cooled to a minimum of 9 c during the maastrichtian correlative middle bathyal foraminifera from other ocean basins yield paleotemperature estimates that are very similar to those from blake nose comparison of global bottom water temperatures and latitudinal thermal gradients suggests that global climate changed from a warm greenhouse state during the late albian through late cenomanian to a hot greenhouse phase during the latest cenomanian through early campanian then to cool greenhouse conditions during the mid campanian through maastrichtian

paleoclimate of the kimmeridgian tithonian late jurassic world ii sensitivity tests comparing three different paleotopographic settings moore g t sloan l c hayashida d n and umrigar n p 1992 paleoclimate of the kimmeridgian tithonian late jurassic world ii sensitivity tests comparing three different paleotopographic settings palaeogeogr palaeoclimatol palaeoecol 95 229 252 topography and location of continents largely determine present day climate we conclude that in the geologic past paleotopographic expression was equally important however in the geologic record paleotopography is difficult to assess and compile because it is largely a self destructive environment without record and is rarely addressed in the literature an objective of this study is to test the sensitivity of paleoclimate to paleotopography by comparing three different late jurassic scenarios paleotopography influences many paleoclimate parameters to varying degrees to test the sensitivity of paleoclimate to modeled paleotopography for simulations incorporating a late jurassic reconstruction we ran three simulations using the same boundary conditions of paleogeography land and ocean and atmospheric co2 concentration 4x the pre lndustrial level 1120 ppm one simulation contained mountain ranges of variable height to 3 kin in another all the mountain ranges were reduced to 1 km highlands the third simulation used a constant 500 m height for all land grid cells the sensitivity tests indicate that paleotopography is an important boundary condition without realistic paleotopography flat or idealized continents surrounded by bodies of water do not produce realistic pateoclimate results we conclude that in paleogeographic reconstructions the location and extent of mountain ranges and highlands should be recognized and given suitable elevations consistent with their plate tectonic origins settings and geologic ages

palaeobiogeography of the early cretaceous corals abstract a compilation of the geographical distribution of about 1000 species of corals from the early cretaceous valanginian to cenomanian is presented after the reefal regression during the latest jurassic no corals appear in the berriasian and only a few species are known from the valanginian and hauterivian in many regions it is impossible to distinguish pre barremian stages many of the pre barremian corals reported are hauterivian in age the pre barremian displays an explosion of the scleractinia more than 300 species extended through europe africa and north and south america during the aptian and albian coral distribution was about the same as during the pre barremian but during the albian the number of species decreased and the proportion of ahermatypic forms increased because of pronounced endemism during the albian faunal similarity no longer existed between the americas and europe during the cenomanian the madreporaria nearly disappeared from north america but were still well represented in europe half of the known cenomanian coral species are ahermatypic and they appear to be distributed on the two sides of the hermatypic buildup along the tethyan realm

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

paleoclimate of the kimmeridgian tithonian late jurassic world i results using a general circulation model abstract the kimmeridgian tithonian 154 7 145 6 ma middle and late late jurassic was a time of expanded continental rifting increased sea floor spreading and a relatively high eustatic sea level stand these processes collectively caused the fragmentation and flooding of the megacontinent pangea as well as the alteration of the global paleoclimate using a version of the community climate model ccm from the national center for atmospheric research we report two kimmeridgian tithonian paleoclimate seasonal simulations with geologically inferred paleotopography one using a co 2 concentration of 280 ppm pre industrial level and the other 1120 ppm increasing the co 2 four fold warms virtually the entire planet the greatest warming occurs over the higher latitude oceans and the least over the equatorial and subtropical regions simulation of a warmer planet with an elevated greenhouse effect fits the distribution of paleoclimatically sensitive faunas floras and sedimentary rocks model results indicate that sea ice was restricted to the high latitudes of the boreal and austral seas making landfall only in restricted areas the trade winds bring heavy rainfall in december january february to eastern gondwana and in june july august to the tethys sea margins a strong june july august monsoon occurs over southeast asia the distribution of coals correlates to precipitation sufficient to maintain gymnosperm forests and coastal areas where water saturated sediments are a result of eustatic high stands of sea level evaporites are localized to areas of negative precipitation evaporation runoff is restricted to regions of intense precipitation overall the 1120 ppm co 2 simulation provides a reasonable paleoclimate for the kimmeridgian tithonian and provides a standard until a ccm with oceanic heat transport a coupled atmospheric oceanic model or one with a finer grid cell configuration is available the results need further scrutiny in areas with more detailed geologic information

mesozoic climates general circulation models and the rock record abstract general circulation models gcms use the laws of physics and an understanding of past geography to simulate climatic responses they are objective in character however they tend to require powerful computers to handle vast numbers of calculations nevertheless it is now possible to compare results from different gcms for a range of times and over a wide range of parameterisations for the past present and future e g in terms of predictions of surface air temperature surface moisture precipitation etc gcms are currently producing simulated climate predictions for the mesozoic which compare favourably with the distributions of climatically sensitive facies e g coals evaporites and palaeosols they can be used effectively in the prediction of oceanic upwelling sites and the distribution of petroleum source rocks and phosphorites models also produce evaluations of other parameters that do not leave a geological record e g cloud cover snow cover and equivocal phenomena such as storminess parameterisation of sub grid scale processes is the main weakness in gcms e g land surfaces convection cloud behaviour and model output for continental interiors is still too cold in winter by comparison with palaeontological data the sedimentary and palaeontological record provides an important way that gcms may themselves be evaluated and this is important because the same gcms are being used currently to predict possible changes in future climate the mesozoic earth was by comparison with the present an alien world as we illustrate here by reference to late triassic late jurassic and late cretaceous simulations dense forests grew close to both poles but experienced months long daylight in warm summers and months long darkness in cold snowy winters ocean depths were warm 8 c or more to the ocean floor and reefs with corals grew 10 of latitude further north and south than at the present time the whole earth was warmer than now by 6 c or more giving more atmospheric humidity and a greatly enhanced hydrological cycle much of the rainfall was predominantly convective in character often focused over the oceans and leaving major desert expanses on the continental areas polar ice sheets are unlikely to have been present because of the high summer temperatures achieved the model indicates extensive sea ice in the nearly enclosed arctic seaway through a large portion of the year during the late cretaceous and the possibility of sea ice in adjacent parts of the midwest seaway over north america the triassic world was a predominantly warm world the model output for evaporation and precipitation conforming well with the known distributions of evaporites calcretes and other climatically sensitive facies for that time the message from the geological record is clear through the phanerozoic earth s climate has changed significantly both on a variety of time scales and over a range of climatic states usually baldly referred to as greenhouse and icehouse although these terms disguise more subtle states between these extremes any notion that the climate can remain constant for the convenience of one species of anthropoid is a delusion although the recent rate of climatic change is exceptional

a review of mesozoic climates there is overwhelming evidence based on the distribution of distinctive sediments and fossils and oxygen isotope data that the climate of the mesozoic world was appreciably more equable than that of today with no polar ice caps but precise quantitative data are not available except for an episode of late cretaceous cooling there is no good documentation of any significant change in global temperature distributions through the era the distribution of coals and evaporites together with other criteria indicates a pattern of humid arid and zones appreciably different in important respects from that of today during the triassic and jurassic western pangaea in low to middle latitudes was largely arid but in the early cretaceous the lands on the margin of the newly opening central atlantic and western tethys experienced a humid climate by late cretaceous times arid zones had become very restricted in extent because of insufficient suitable data attempts at climatic modelling have had only modest success and only to a limited extent can the major long term changes in climate between the permian and the present be explained in terms of changing geography the most probable explanation of mesozoic equability is an increased atmospheric co 2 content a number of enigmas remain such as the existence of flourishing forests in polar palaeolatitudes whereas for the late cenozoic short term climatic changes can be related successfully to variations in the geometry and mechanics of the earth sun system there is a long way to go before comparable success can be claimed for the mesozoic

dc trains and pc3s source effects in mid latitude geomagnetic transfer functions magnetotelluric mt data from two sites 150 and 300 km southeast of san francisco california geomagnetic dipole latitude 43 degrees l approximately 1 9 show that the usual mt assumption of spatially uniform external magnetic fields is violated to a significant degree in the period range 10 30 s inter station transfer functions exhibit large systematic temporal variations which are consistent with a combination of two distinct sources electromagnetic noise due to the san francisco bay area rapid transit bart dc electric railway and pc3 geomagnetic pulsations there is a suggestion in the data that some of the pc activity may actually be excited by bart

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