tidal dissipation in the early eocene and implications for ocean mixing 1 the tidally driven vertical diffusivity in the abyssal ocean during the early eocene 55 ma is investigated using an established tidal model a weak tide is predicted in the eocene ocean except in the pacific consequently the integrated global tidal dissipation rate is a mere 1 44tw of which 40 dissipate in the pacific however due to a stronger abyssal vertical stratification the predicted eocene vertical diffusivities are consistently larger than at present the results support the hypothesis that altered tidal dissipation may play a role in explaining the maintenance of past climate regimes especially the anomalously warm temperatures in the southwest pacific in the eocene and the low dissipation rates may be important for lunar evolution history

could early cenozoic thermohaline circulation have warmed the poles the paleocene and eocene epochs provide examples of oceanographic conditions when the earth had a stable climate much warmer than that of the modern world lower cenozoic sediments thus provide a way to investigate how oceanographic processes might respond to extreme warming because high latitude sea surface temperatures were significantly warmer during the early cenozoic while tropical sea surface temperatures were similar to or somewhat less than modern there may have been a much higher poleward oceanic heat transport at that time shackleton and boersma 1981 barron 1987 sloan et al 1995 here i develop a simple ocean thermohaline model to demonstrate that poleward oceanic heat transport could strongly warm the polar regions only if the strength of vertical mixing vertical eddy diffusion in the oceans is sensitive to changes in oceanic density structure if this is true the early cenozoic oceans because they had significantly less density stratification could have had a thermohaline circulation as much as 3 times as strong as that of the modern ocean despite reduced temperature gradients the model also predicts that an optimum bottom water temperature exists for maximum poleward heat transport continued warming of the earth does not continue to increase oceanic heat transport to the poles the hypothesized sensitivity of oceanic vertical mixing to the density gradient should provide a positive feedback to both the transition to ice ages and to a future transition out of them a test of the sensitivity of vertical eddy diffusion to density gradients can be studied through map and depth transects in the horizontal direction high vertical diffusion would be marked by relatively strong bottom water temperature gradients away from bottom water source regions in the vertical direction high vertical diffusion should be indicated by very small temperature gradients

stommel s box model of thermohaline circulation revisited the role of mechanical energy supporting mixing and the wind driven gyration the classical two box model of stommel is extended in two directions replacing the buoyancy constraint with an energy constraint and including the wind driven gyre stommel postulated a buoyancy constraint for the thermohaline circulation and his basic idea has evolved into the dominating theory of thermohaline circulation however recently it is argued that the thermohaline circulation is maintained by mechanical energy from wind stress and tides the major difference between these two types of models is the bifurcation structure the stommel like model has two thermal modes one stable and another one unstable and one stable haline mode whereas the energy constraint model has one stable thermal mode and two saline modes one stable and another one unstable adding the wind driven gyre changes the threshold value of thermohaline bifurcation greatly thus the inclusion of the wind driven gyre is a vital step in completely modeling the physical processes related to thermohaline circulation

records of post cretaceous tertiary boundary millennial scale cooling from the western tethys a smoking gun for the impact winter hypothesis the record of both dinoflagellate cysts and benthic foraminifera across the cretaceous tertiary boundary at el kef tunisia reveals a brief expansion of the boreal bioprovince into the western tethys suggesting that an 2 k y cooling occurred during the earliest danian we show that this prolonged cooling phase is consistent with the oceanographic response to an impact winter

waxing and waning lyrical on hiatuses eocene quaternary indian ocean hiatuses as proxy indicators of water mass production the temporal distributions of cenozoic hiatuses in the indian ocean are reconsidered in the light of a new time framework developed by the paleoceanographic indian ocean synthesis on the basis of the temporal distribution of hiatus terminations eight 3 m y time slices were selected for plotting the paleogeographical distribution of hiatus terminations these distributions define areas of potential hiatus development which formed along flow paths of proto antarctic bottom water an analogue of modern antarctic bottom water and proto antarctic intermediate water an analogue of modern antarctic intermediate water expansion and contraction of these areas suggested changes in the volume of these water masses which modified the distibution patterns of erosive deepwater currents and corrosive bottom water consequently the spatial and bathymetric distribution of hiatus formation was altered age depth analysis of hiatuses from sites within post late eocene areas of potential hiatus development was used in conjunction with models of the behavior of unconformity boundaries within fluctuating water masses to construct waxing waning curves for proto antarctic bottom water and proto antarctic intermediate water these curves define volume changes in the production histories of these water masses which were related to the post late eocene glacial history of antarctica since the late oligocene the proto antarctic bottom water waned during intervals of increased glacial intensity whereas the proto antarctic intermediate water waxed during these intervals these relationships reversed during intervals of reduced glacial intensity including intervals where there is no evidence for antarctic glaciation this conflicts with interpretations made by other workers a comparison is made between the production histories of proto antarctric bottom water and northern component water an analogue of north atlantic deep water based on 13c for the miocene to pliocene

pacific ocean and cenozoic evolution of climate 1 the pacific ocean has played a major role in climate evolution throughout the cenozoic 65 0 ma it is a fundamental component of global heat transport and circulation the dominant locus of primary productivity and consequently the largest reservoir for carbon exchange between the oceans and the atmosphere a satisfactory understanding of the cenozoic evolutionary history of the pacific and its impact on global climate is currently data limited nevertheless the large dynamic range of cenozoic conditions sets the stage to greatly expand our understanding of global climate and biogeochemical cycles past earth experiments are particularly useful to understand interactions between climate and geosystems under different greenhouse gas loads we highlight in this review four important problems in which the pacific played a major role the effect of changing geographic boundary conditions on ocean circulation interactions between the carbon cycle and climate the pacific ocean s influence on north american climate and its water cycle and the gradual evolution of climate systems

deformation of ductile inclusions in a multiple inclusion system in pure shear this paper analyzes the deformational behavior of mutually interacting spherical inclusions in a multiple inclusion system considering two physical factors viscosity ratio between inclusion and matrix m and the ratio of inclusion diameter to mean inter inclusion distance a b for a given value of m the strain partitioning between a stiff inclusion and the bulk system i e ratio of their natural extension rates increases non linearly with increasing a b ratios and the gradient of increase becomes steeper when the inter inclusion distance is less than about twice their diameter i e a b about 0 5 the strain distribution within a deformed inclusion is homogeneous when the a b ratio is less than about 0 6 for larger values of a b the internal deformation becomes heterogeneous with the strain increasing or decreasing towards the core in the case of stiff m 1 and soft m 1 inclusions respectively the deformed shape of inclusions in section also shows departure from an ideal ellipse with an increase in the a b ratio stiff inclusions develop shapes similar to that of a super ellipse in contrast to soft inclusions that resemble a sub ellipse the heterogeneity of internal deformation is also reflected in the distortion of passive foliations initially at right angles to the bulk extension direction which become curved with convexity outward and inward respectively within stiff and soft inclusions

neodymium isotopic reconstruction of late paleocene early eocene thermohaline circulation abstract high resolution fish tooth nd isotopic records for eight deep sea drilling project and ocean drilling program sites were used to reconstruct the nature of late paleocene early eocene deep water circulation the goal of this reconstruction was to test the hypothesis that a change in thermohaline circulation patterns caused the abrupt 4 5 c warming of deep and bottom waters at the paleocene eocene boundary the paleocene eocene thermal maximum petm event the combined set of records indicates a deep water mass common to the north and south atlantic southern and indian oceans characterized by mean nd values of 8 7 and different water masses found in the central pacific ocean nd 4 3 and caribbean sea nd 1 2 the geographic pattern of nd isotopic values before and during the petm suggests a southern ocean deep water formation site for deep and bottom waters in the atlantic and indian ocean basins the nd data do not contain evidence for a change in the composition of deep waters prior to the onset of the petm this finding is consistent with the pattern of warming established by recently published stable isotope records suggesting that deep and bottom water warming during the petm was gradual and the consequence of surface water warming in regions of downwelling

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

oxygen isotope analyses and deep sea temperature changes implications for rates of oceanic mixing since the first measurements were made more than thirty years ago1 analysis of oxygen isotopes in foraminifera from deep sea sediments has gained widespread use as a palaeoclimatic and stratigraphic indicator isotopes stages are commonly used to define the ice ages2 but controversy still remains regarding the relative contributions of temperature and ice volume change to the down core 18o record for the past decade temperature has commonly been considered a trivial portion of the signal3 recent reports however suggest that as much as one third of the measured 18o variations can be ascribed to cooler glacial maximum temperatures4 5 this interpretation requires mean deep ocean temperatures 0 c through much of late quaternary time here we explore some of the consequences of this hypothesis for the heat budget of the deep sea and conclude that either thermohaline overturn must have been faster than at present or that cooling of the deep ocean at the glacial maximum may have been overestimated

similar rates of modern and last glacial ocean thermohaline circulation inferred from radiochemical data today the ocean thermohaline circulation transports half of the 231pa produced by radioactive decay in the atlantic ocean water column to the southern ocean this export respectively imparts low and high 231pa 230th ratios to the surface sediments of these oceans ocean sediments from the last glacial maximum bear a similar isotopic fingerprint implying that advection of north atlantic deep intermediate water into the circumpolar deep water of the southern ocean occurred at a similar or slightly higher rate during the last glacial period

seismic and geologic evidence for early paleogene deepwater circulation in the western north atlantic previous studies of paleogeography global climate and foraminiferal stable isotopes have suggested that paleogene deepwater circulation was significantly different from that of today extracting details of deepwater history from the western north atlantic has been hampered by oligocene erosion and the lack of ideally located drill holes we report the discovery of a seismic disconformity on the sw bermuda rise that we have tied to a late paleocene erosional event in deep sea drilling project dsdp boreholes from this region distribution of this new seismic marker reflector ab indicates that it was formed by cyclonically circulating bottom water entering the western north atlantic from the south we attribute this vigorous deep circulation to a southern ocean source analogous to the effects of modern antarctic bottom water this interpretation is supported by isotopic comparisons that show the paleocene southern ocean was enriched in 13c relative to the pacific we distinguish reflector ab from the overlying reflector au on the basis of superposition and ages obtained at dsdp sites and piston cores using one of the cores we have estimated that the youngest age for reflector au is earliest oligocene 36 6 34 0 ma while its oldest age has been previously established as late eocene laminated sediments beneath reflector ab are enriched in organic carbon indicating that the early paleocene deep western north atlantic was occasionally anoxic these low oxygen levels may have been the result of sluggish deep circulation and or low latitude production of warm saline deep water wsdw sediments immediately above reflector ab show that deposition resumed on the western bermuda rise site 387 by the latest paleocene to earliest eocene biochron np10 57 2 0 6 ma while deposition resumed on the central bermuda rise site 386 during the late paleocene erosion nondeposition continued across much of the bermuda rise widespread resumption of pelagic deposition in the early eocene is consistent with 13c evidence for reduced southern ocean influence at this time however lower eocene sediments record well oxygenated conditions and 13c and 18o comparisons indicate that there were two early eocene deepwater sources the southern ocean and wsdw pak and miller this issue

eocene spiculites and spongolites in southwestern australia not deep not polar but shallow and warm siliceous spongolite and spiculite are generally interpreted as deep and or cold water deposits largely because modern analogs are found mostly in cold and or deep water environments however extensive shallow water biosiliceous accumulations are present in late eocene age deposits of southern western australia the attributes and paleoenvironmental setting of these accumulations frame the specific climatic and or oceanographic constraints that allow such shallow neritic sediments to form the generally fine grained siliciclastic biosiliceous sediments accumulated in a nearshore shallow water setting around numerous islands and offshore from a warm temperate rainforest covered upland sponges compose a lithistid hexactinellid assemblage of mesozoic tethyan affinity confined to deep water in the modern ocean that migrated into neritic paleoenvironments during late eocene time lithistids dominated shoreface environments and were reworked into sponge conglomerate beaches while hexactinellids flourished offshore in muddy subshoreface environments these deposits also contain common soft demosponge spicules and a rare but otherwise normal marine calcareous biota the biosiliceous sediments grade offshore into bryozoan rich marls and limestones sponges outcompeted the calcareous benthos in these inner shelf environments because of elevated amounts of land derived nutrients that included high dissolved silica and a calm hydrodynamic setting these deposits suggest that neither temperature nor water depth are critical factors for prolific sponge colonization the rarity of such deposits in the rock record likely reflects the necessity for the coincidence of all of these factors or they are misinterpreted

past co2 changes and tropical sea surface temperatures the relationship between past co2 variations and tropical climate change on time scales of millions of years is reviewed explanations for cretaceous and early cenozoic climate change often involve higher atmospheric co2 levels climate models predict that such increases should have been associated with warmer tropical sea surface temperatures ssts however sparse mid cretaceous 18o based sst estimates from low latitude calcareous plankton are 1 0 1 5 heavier than predicted initial evaluations indicate that changes in salinity may not alleviate model data discrepancies for calcareous 18o and that interpretation of altered latitudinal 18o gradients in terms of increased poleward heat transport due to warm saline bottom water wsbw formation would require very large levels of wsbw production at least 60 sv calcareous 18o records may not always record true sst patterns as 18o analyses from phosphatic groups which are less sensitive to diagenesis indicate ssts 5 c higher this latter conclusion is supported by a number of other fossil groups which indicate temperatures warmer than those estimated from calcareous 18o in order to more rigorously test the paleo co2 hypothesis and indeed the models used to forecast future climates it is desirable to intensify investigations of past climate change in low latitudes in order to determine whether these preliminary conclusions stand the test of further scrutiny

enhanced circulation during a warm period the early pliocene is the most recent interval in which equilibrium oceanic conditions can be studied in the context of global warmth relative to today to characterize thermohaline circulation during this warm period 4 4 3 1 ma we combined new benthic foraminiferal isotopic data from the southeast atlantic with published data and reconstructed pacific and atlantic ocean nutrient distributions the data indicate enhanced ventilation of the deep atlantic and intermediate pacific during the early pliocene enhanced ventilation implies that delivery of surface water to high latitudes in western boundary currents of north pacific and atlantic subtropical gyres was probably also enhanced future modeling of this warm period needs to reconcile reduced meridional surface temperature gradients with enhanced subtropical gyre and thermohaline circulation

nd isotopic structure of the pacific ocean 70 30 ma and numerical evidence for vigorous ocean circulation and ocean heat transport in a greenhouse world the oceanic meridional overturning circulation moc is a crucial component of the climate system impacting heat and nutrient transport and global carbon cycling past greenhouse climate intervals present a paradox because their weak equator to pole temperature gradients imply a weaker moc yet increased poleward oceanic heat transport appears to be required to maintain these weak gradients to investigate the mode of moc that operated during the early cenozoic we compare new nd isotope data with nd tracer enabled numerical ocean circulation and coupled climate model simulations assimilation of new nd isotope data from south pacific deep sea drilling project and ocean drilling program sites 323 463 596 865 and 869 with previously published data confirm the hypothesized moc characterized by vigorous sinking in the south and north pacific 70 to 30 ma compilation of all pacific nd isotope data indicates vigorous distinct and separate overturning circulations in each basin until 40 ma simulations consistently reproduce south pacific and north pacific deep convection over a broad range of conditions but cases using strong deep ocean vertical mixing produced the best data model match strong mixing potentially resulting from enhanced abyssal tidal dissipation greater interaction of wind driven internal wave activity with submarine plateaus or higher than modern values of the geothermal heat flux enable models to achieve enhanced moc circulation rates with resulting nd isotope distributions consistent with the proxy data the consequent poleward heat transport may resolve the paradox of warmer worlds with reduced temperature gradients

the ocean circulation in the southern hemisphere and its climatic impacts in the eocene abstract opening of southern ocean gateways may have had a controlling influence on the evolution of global climate the largest step in the history of cenozoic climate from an eocene greenhouse toward the modern glaciated state is correlated with opening of a deep water connection between the southern indian and southern pacific oceans this study synthesizes results from previous work assesses the possibility that ocean heat transport was much greater than modern during the globally warm eocene and explores the sensitivity of polar climate to large changes in ocean heat transport the magnitudes of these sensitivities are compared with those due to greenhouse gas concentration changes we find that ocean heat transport was unlikely to have been sufficiently greater than modern during the eocene to explain the change in the climate specifically in order to have significantly affected antarctic climate ocean heat transport changes would have had to change by an order of magnitude much greater than the largest change produced in our simulations in coupled climate model simulations changes in co2 concentrations from 1120 to 560 ppm supported by proxy records lead to significant antarctic responses in the absence of ocean heat transport changes the results show that antarctic snow accumulation is primarily controlled by changes in summer temperature not precipitation and that snow did not remain on antarctica during summer months in eocene even at low greenhouse gas concentrations greenhouse gas concentration changes and subsequent processes such as ice albedo and weathering feedbacks were more likely to have been the primary cause of antarctic glaciation than ocean heat transport changes

paleocene to eocene benthic foraminiferal isotopes and assemblages implications for deepwater circulation early paleogene warm climates may have been linked to different modes and sources of deepwater formation warm polar temperatures of the paleocene and eocene may have resulted from either increased atmospheric trace gases or increased heat transport through deep and intermediate waters the possibility of increasing ocean heat transport through the production of warm saline deep waters wsdw in the tethyan region has generated considerable interest in addition general circulation model results indicate that deepwater source regions may be highly sensitive to changing basin configurations to decipher deepwater changes we examined detailed benthic foraminiferal faunal and isotopic records of the late paleocene through the early eocene 60 to 50 ma from two critical regions the north atlantic bay of biscay site 401 and the pacific shatsky rise site 577 these records are compared with published data from the southern ocean maud rise site 690 islas orcadas rise site 702 during the late paleocene similar benthic foraminiferal 18o values were recorded at all four sites this indicates uniform deepwater temperatures consistent with a single source of deep water the highest 13c values were recorded in the southern ocean and were 0 5 more positive than those of the pacific we infer that the southern ocean was proximal to a source of nutrient depleted deep water during the late paleocene upper paleocene reflector ab was cut on the western bermuda rise by cyclonically circulating bottom water also suggesting a vigorous source of bottom water in the southern ocean a dramatic negative excursion in both carbon and oxygen isotopes occurred in the latest paleocene in the southern ocean this is a short term 100 kyr globally synchronous event which also is apparent in both the atlantic and pacific records as a carbon isotopic excursion of approximately 1 faunal analyses from the north atlantic and pacific sites indicate that the largest benthic foraminiferal faunal turnover of the cenozoic was synchronous with the isotopic excursion lending support to the hypothesis that the extinctions were caused by a change in deepwater circulation we speculate that the southern ocean deepwater source was reduced or eliminated at the time of the excursion during the early eocene southern ocean 13c values remained enriched relative to the north atlantic and pacific however the southern ocean was also enriched in 18o relative to these basins we interpret that these patterns indicate that although the southern ocean was proximal to a source of cool nutrient depleted water the intermediate to upper deep water sites of the north atlantic and pacific were ventilated by a different source that probably originated in low latitudes i e wsdw

can increased poleward oceanic heat flux explain the warm cretaceous climate the poleward transport of heat in the mid cretaceous 100 ma is examined using an idealized coupled ocean atmosphere model the oceanic component consists of two zonally averaged basins representing the proto pacific and proto indian oceans and models the dynamics of the meridional thermohaline circulation the atmospheric component is a simple energy and moisture balance model which includes the diffusive meridional transport of sensible heat and moisture the ocean model is spun up with a variety of plausible cretaceous surface temperature and salinity profiles and a consistent atmosphere is objectively derived based on the resultant sea surface temperature and the surface heat and freshwater fluxes the coupled model does not exhibit climate drift multiple equilibria of the coupled model are found that break the initial symmetry of the ocean circulation several of these equilibria have one cell northern or southern sinking thermohaline circulation patterns two main classes of circulation are found circulations where the densest water is relatively cool and is formed at the polar latitudes and circulations where the densest water is warm but quite saline and the strongest sinking occurs at the tropics in all cases significant amounts of warm saline bottom water are formed in the proto indian basin which modify the deepwater characteristics in the larger proto pacific basin temperatures in the deep ocean are warm 10 17 c in agreement with benthic foraminiferal oxygen isotope data the poleward transport of heat in the modeled cretaceous oceans is larger than in some comparable models of the present day thermohaline circulation and significantly larger than estimates of similar processes in the present day ocean it is consistently larger in the polar sinking cases when compared with that seen in the tropical sinking cases but this represents an increase of only 10 the largest increase over present day model transports is in the atmospheric latent heat transport where an increased hydrological cycle especially in the tropical sinking cases contributes up to an extra 1 pw of poleward heat transport better constraints on the oceanic deepwater circulation during this period are necessary before the meridional circulation can be unambiguously described

equatorial ocean circulation in an extremely warm climate 1 the warm climates of the early paleogene and the associated diminished near surface winds should have resulted in a reduction in near surface ocean circulation one check on this deduction is the delineation of biogenic sediments associated with an equatorial current system of the early eocene pacific a latitudinal seismic reflection transect across the tropical pacific along early paleogene ocean crust reveals a basal high amplitude reflection package that we take to be the lower eocene section this unit varies in thickness by a factor of about two with the thickest portion forming a low mound some 3 4 north of the 56 ma paleoequator this mound may represent the position of a divergence generated in the frontal region between two currents flowing in opposite directions and its position suggests that the wind driven equatorial circulation of the early eocene was one without a pronounced equatorial divergence

stable isotopes in late middle eocene to oligocene foraminifera oxygen and carbon isotope ratios in eocene and oligocene planktonic and benthic foraminifera have been investigated from atlantic indian and pacific ocean locations the major changes in eocene oligocene benthic foraminiferal oxygen isotopes were enrichment of up to l in 18o associated with the middle late eocene boundary and the eocene oligocene boundary at locations which range from 1 to 4 km paleodepth although the synchronous eocene oligocene 18o enrichment began in the latest eocene most of the change occurred in the earliest oligocene the earliest oligocene enrichment in 18o is always larger in benthic foraminifera than in surface dwelling planktonic foraminifera a condition that indicates a combination of deep water cooling and increased ice volume planktonic foraminiferal 18o does not increase across the middle late eocene boundary at our one site with the most complete record deep sea drilling project site 363 walvis ridge this pattern suggests that benthic foraminiferal 18o increased 40 m y ago because of increased density of deep waters probably as a result of cooling although glaciation cannot be ruled out without more data stable isotope data are averaged for late eocene and earliest oligocene time intervals to evaluate paleoceanographic change average 18o of benthic foraminifera increased by 0 64 from the late eocene to the early oligocene 18o maximum whereas the average increase for planktonic foraminifera was 0 52 this similarity suggests that the eocene oligocene boundary 18o increase was caused primarily by increased continental glaciation coupled with deep sea cooling by as much as 2 c at some sites average 18o of surface dwelling planktonic foraminifera from 14 upper eocene and 17 lower oligocene locations when plotted versus paleo latitude reveals no change in the latitudinal 18o gradient the oligocene data are offset by 0 45 also believed to reflect increased continental glaciation at present there are too few deep sea sequences from high latitude locations to resolve an increase in the oceanic temperature gradient from eocene to oligocene time using oxygen isotopes

implications for the creation of warm saline deep water late paleocene reconstructions and global climate model simulations a global warming trend began during the late paleocene that culminated in the early eocene with the highest global temperatures of the cenozoic we have reconstructed late paleocene surficial boundary conditions and modeled atmospheric conditions using the goddard institute for space studies general circulation model version ii giss gcm ii these experiments were conducted to test the hypothesis that warm saline deep water formed during the late paleocene and to understand atmospheric circulation near the beginning of a period of global warming the warming is attributed primarily to increased sea surface temperatures at high latitudes the sensitivity of the climate to ocean temperature was tested using two sea surface temperature distributions each delimited latitudinally by oxygen isotope values but with different east west gradients the simulations discussed here contain several features unique among warm climate experiments the first experiment p 1 used latitudinally constant zonal sea surface temperatures the zonally distributed sea surface temperatures strengthen the general circulation of the atmosphere in particular hadley cell circulation is intensified leading to extremes of precipitation in the equatorial region and extreme evaporation across subtropical oceans the unusual results prompted a second experiment with modern east west sea surface temperature gradients superimposed and referred to as p gradient p grad the east west gradients in the sea surface temperature field exert a strong influence on the general atmospheric circulation but the extreme zonality prevails under extreme zonal conditions it is possible to create a model where evaporation is in excess of precipitation by as much as 3 mm day if this occurred in restricted areas in a generally warmer ocean such as the late paleocene eastern tethys ocean and parts of the south atlantic ocean it should be possible to create very saline water which could become a component in warm saline deep water formation

radiocarbon age of last glacial pacific deep water one of the most important projects envisaged ever since the possibility emerged of making tandem accelerator mass spectrometric radiocarbon determinations has been that of investigating changes in the radiocarbon age of the deep ocean1 initial attempts to achieve this2 were thwarted by difficulties imposed by bioturbation because these workers used core v28 238 with an accumulation rate of only 1 5 cm kyr 1 thus emphasizing the need to work in a core with a higher accumulation rate working in the glacial section of core tr163 31b with an accumulation of 10 cm kyr 1 we show here that the ventilation age of pacific deep water was about 500 years greater in last glacial times than it is today

on the mid pleistocene transition to 100 kyr glacial cycles and the asymmetry between glaciation and deglaciation times 1 a mechanism is proposed for the mid pleistocene transition from a dominant periodicity of 41 kyr to 100 kyr in glacial oscillations the same mechanism is shown to also explain the asymmetry between the long glaciation and short deglaciation phases of each cycle since that transition versus the symmetry of the 41 kyr oscillations prior to the transition these features arise naturally within the framework of the sea ice switch glacial cycle mechanism of gildor and tziperman 2000 as a result of the gradual cooling of the deep ocean during the pleistocene this cooling results in a change of the relation between atmospheric temperature and the rates of accumulation and ablation of continentals ice sheets it is this latter change that leads to the activation of the sea ice switch and therefore to the initiation of the 100 kyr oscillations the gradual glaciation and rapid deglaciations during these oscillations occur because the mean value of the ice sheet ablation is not far from the maximum rate of snow accumulation during warm periods this proximity of mean ablation and maximum accumulation rates is shown to be also a consequence of the mid pleistocene gradual cooling of the deep ocean index terms 3344 meteorology and atmospheric dynamics paleoclimatology 1620 global change climate dynamics 3309 1640 global change remote sensing 4267 oceanography general paleoceanography keywords climate dynamics glacial cycles mid pleistocene transition 100 kyr 41 kyr

chert in the pacific biogenic silica and hydrothermal circulation abstract data on sections drilled by dsdp and odp in the pacific have been compiled for 187 sites 105 of which contain chert the spatial pattern of siliceous deposits in the pacific generally follows the pattern of biologic productivity there is some evidence that enhanced vertical diffusivity in the ocean during the eocene warm climate gave rise to siliceous deposits on and near bathymetric highs and basin margins the most common occurrence of chert is in eocene and older sections however cherts do occur in sections as young as 7 ma in the sites investigated over half of the youngest chert occurrences in sedimentary sections are within 150 m of basement nearly all the chert occurrences on crust younger than 60 ma are within 150 m of basement the deficit in heat flow over ocean crust younger than 60 ma is explained as the result of heat advection by hydrothermal waters circulating in the upper part of the ocean crust these waters appear to dissolve biogenic silica and deposit it as chert in the lower parts of sedimentary sections diffusion of these waters into the lower sediment section is enhanced by small scale faulting this faulting may be associated with intra plate stresses that develop during ridge jumps and reorientations of plate motion the relatively warm bottom waters of the early cenozoic may have also enhanced the dissolution of biogenic silica during hydrothermal circulation in the upper oceanic crust and basal sediment section

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

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

pacific ocean intermediate and deep water circulation during the pliocene abstract new benthic foraminiferal stable isotopic records of northeast pacific intermediate water odp site 1014 1177 m and mid depth water odp site 1018 2476 m were compared to isotopic records of deep water in the tropical pacific odp site 849 3851 m for the reconstruction of vertical profiles of nutrient and physical properties from the early pliocene to the early pleistocene approx 5 1 4 ma our data indicate that for the entire interval there was enhanced north pacific intermediate water ventilation relative to today and a similar to modern circulation pattern with northward flowing pacific bottom water pbw beneath its southward flowing return flow however the core of maximally aged return flow resided as deep as 2500 m as compared to 1500 m today probably due to the strengthened intermediate water flow less apparent aging of deep water along its path before 2 7 ma indicates that thermohaline overturning may have been more rapid in the warm period of the early pliocene in addition prior to 2 7 ma foraminiferal oxygen isotopic values at mid depth sites are higher than at deep sites a reversed vertical gradient relative to today in both the atlantic and pacific oceans we suggest that nadw was warmer and more saline than today and that it influenced mid depth waters throughout the atlantic and pacific oceans enhanced pliocene formation of warmer saltier intermediate water in the north pacific and deep water in the north atlantic may have been a result of higher than modern high mid latitude sea surface temperatures evaporation and salinity

the climate of the eocene ocean oxygen isotope palaeotemperature estimates are presented for a number of deep sea sediment samples of eocene age covering a wide geographical area these are plotted on a geographical reconstruction for 50 ma the latitudinal temperature gradient at that time was less than half its present value surface temperature at high latitudes was about 10 c and at low latitudes little over 20 c it is concluded that ocean currents must have contributed a greater proportion of the poleward transport of heat than they do at present

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

sea floor hydrothermal activity links climate to tectonics the eocene carbon dioxide greenhouse two important findings of recent ocean floor drilling in the southeast pacific deep sea drilling project leg 92 are i that sea floor hydrothermal activity may fluctuate through time by as much as an order of magnitude and ii that episodes of greatest hydrothermal flux correspond to times when ridge transform plate boundaries are undergoing major changes in their configuration rather than to known times of increased spreading rate or volcanism evidence is presented here in support of the hypothesis that heightened hydrothermal activity induced by the eocene tectonic activity caused a global greenhouse effect which may represent the long sought after historical analog to the carbon dioxide induced global warming expected to occur by the middle of the next century

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

advanced inversion methods for airborne electromagnetic exploration airborne electromagnetic aem surveys can contribute substantially to geologic mapping and target identification if good quality multifrequency data are produced properly evaluated and displayed a set of multifrequency em data is transformed into a set of apparent resistivity a and centroid depth zp values which then are plotted as a sounding curve these a zp curves commonly provide a smoothed picture of the vertical resistivity distribution at the sounding site we have developed and checked methods to enhance the sensitivity of sounding curves to vertical resistivity changes by using new definitions for apparent resistivity and centroid depth one of these new sounding curves with enhanced sensitivity to vertical resistivity contrasts is plotted from nb zs values derived from differentiation of the a f curve with respect to the frequency f this approach is similar to the niblett bostick transform used in magnetotellurics it not only enhances vertical changes in resistivity but also

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