simulation of modern and middle cretaceous marine δ18o with an ocean atmosphere general circulation model 1 we have developed a coupled ocean atmosphere general circulation model the genesis mom model with the ability to transport and fractionate water isotopes in the ocean and atmosphere the model is used to predict modern and cretaceous precipitation and seawater 18o the model reproduces the large scale modern day isotopic distribution in the zonal mean the difference between simulated and observed seawater 18o is within 0 2 in the low and middle latitudes and within 1 at high latitudes in comparison to modern simulated cretaceous surface seawater 18o is systematically depleted by 0 3 at low and middle latitudes these differences are attributed to equilibrium fractionation during surface evaporation at low latitudes and an increased partitioning of 18o from the surface into the deep ocean due to intermediate and deep water formation in subtropical basins in the cretaceous we also find that regional seawater 18o is significantly influenced by the paleobathymetry and the resolution of oceanic gateways boundary conditions that are not well known for the past our simulation of cretaceous seawater 18o has major implications for oxygen isotope paleothermometry we conclude that conventional assumptions of past seawater 18o may lead to an overestimate of cretaceous sea surface temperatures especially at middle and high latitudes

evidence for increased latent heat transport during the cretaceous albian greenhouse warming quantitative estimates of increased heat transfer by atmospheric h2o vapor during the albian greenhouse warming suggest that the intensified hydrologic cycle played a greater role in warming high latitudes than at present and thus represents a viable alternative to oceanic heat transport sphaerosiderite d 18 o values in paleosols of the north american cretaceous western interior basin are a proxy for meteoric d 18 o values and massbalance modeling results suggest that albian precipitation rates exceeded modern rates at both mid and high latitudes comparison of modeled albian and modern precipitation minus evaporation values suggests amplification of the albian moisture deficit in the tropics and moisture surplus in the mid to high latitudes the tropical moisture deficit represents an average heat loss of 75 w m 2 at 108n paleolatitude at present 21 w m 2 the increased precipitation at higher latitudes implies an average heat gain of 83 w m 2 at 458n at present 23 w m 2 and of 19 w m 2 at 758n at present 4 w m 2 these estimates of increased poleward heat transfer by h2o vapor during the albian may help to explain the reduced equator to pole temperature gradients

stratigraphy and paleoenvironmental evolution of the dinosaur rich baruungoyot nemegt succession upper cretaceous nemegt basin southern mongolia abstract portions of the dinosaur rich upper cretaceous baruungoyot nemegt succession are exposed in four geographic areas of the nemegt basin mongolia nemegt altan uul bugiin tsav and hermiin tsav lithostratigraphic correlations of these areas employ marker beds and non random stratigraphic patterns of lithology grain size variation and inferred paleoenvironments correlations suggest a minimum thickness of 350 m for the succession exposures at nemegt altan uul and bugiin tsav form a 100 km east west transect along the northern margin of the basin exposing 265 m of section from east to west the transect exposes higher portions of the succession extending from the uppermost baruungoyot formation and encompassing an almost complete section of the nemegt formation which has a minimum thickness of 235 m and can be consistently divided into three informal members lower middle and upper the lower nemegt is well exposed at nemegt and altan uul and is dominated by fluvial deposits the middle and upper nemegt are well exposed at altan uul 2 and bugiin tsav and consist of alluvial plain paludal lacustrine and fluvial deposits as confirmed by earlier studies the baruungoyot and nemegt formations exhibit an interfingering transition at nemegt the hermiin tsav section is a geographic outlier tens of kilometers west southwest of the northern transect it exposes about 150 m of section that overlaps with but is mostly lower stratigraphically than the northern transect the uppermost hermiin tsav section correlates with the lowermost nemegt section and also exhibits an interfingering contact between the baruungoyot and nemegt formations the remaining section at hermiin tsav comprises sediments of the baruungoyot formation 135 m that were deposited in alluvial fan fluvial paludal lacustrine and eolian environments and can be divided into two informal members designated as lower and upper the distribution of facies through the composite section records changes in paleoenvironments during the late cretaceous that may provide insights into the origins of the dinosaurian biostratigraphy

rediscovery of the type localities of the late cretaceous mongolian sauropods nemegtosaurus mongoliensis and opisthocoelicaudia skarzynskii stratigraphic and taxonomic implications in 1965 the polish mongolian palaeontological expeditions recovered two sauropods from the nemegt formation of the nemegt basin mongolia kielan jaworowska and dovchin 1968 one specimen a nicely preserved complete skull that in 1971 became the holotype of nemegtosaurus mongoliensis was found in central sayr at the nemegt locality the other was found at altan uul iv and is a nearly complete postcranial skeleton lacking only the skull and neck in 1977 this skeleton became the holotype of opisthocoelicaudia skarzynskii nemegtosaurus and opisthocoelicaudia were initially assigned to different sauropod higher taxa dicraeosaurinae and camarasauridae respectively however since the late 1990s both genera have been recognized as members of titanosauria their coincident spatiotemporal distribution and non overlapping skeletal parts have led to the persistent suspicion that they belong to the same species rediscovery of the original quarries and discovery of the postcranial remains attributable to the nemegtosaurus holotype provides the first opportunity to directly compare these two taxa seven additional sites at the nemegt locality preserve sauropod remains including vertebrae humeri femora pelvic elements pedal phalanges and unguals and more than 20 sauropod footprint sites have been mapped none of this material suggests that there is more than one sauropod taxon present in the nemegt formation all localities occur within a discrete stratigraphic interval encompassing the uppermost baruungoyot footprints baruungoyot nemegt interfingering interval nemegtosaurus type and lowermost nemegt formations stratigraphic comparisons indicate the opisthocoelicaudia locality at altan uul iv is within the lower beds of the nemegt formation as sauropod remains are now documented for a total of 34 sites in the nemegt formation a more refined stratigraphic framework may shed new light on the taxonomic inclusiveness of the sample

variable crustal structure along the juan de fuca ridge influence of on axis hot spots and absolute plate motions multichannel seismic and bathymetric data from the juan de fuca ridge jdfr provide constraints on axial and ridge flank structure for the past 4 8 ma within three spreading corridors crossing cleft northern symmetric and endeavour segments along axis data reveal south to north gradients in seafloor relief and presence and depth of the crustal magma lens which indicate a warmer axial regime to the south both on a regional scale and within individual segments for young crust cross axis lines reveal differences between segments in moho two way traveltimes of 200 300 ms which indicate 0 5 1 km thicker crust at endeavour and cleft compared to northern symmetric moho traveltime anomalies extend beyond the 5 15 km wide axial high and coincide with distinct plateaus 32 and 40 km wide and 200 400 m high found at both segments on older crust moho traveltimes are similar for all three segments 2100 100 ms indicating little difference in average crustal production prior to 0 6 and 0 7 ma the presence of broad axis centered bathymetric plateau with thickened crust at cleft and endeavour segments is attributed to recent initiation of ridge axis centered melt anomalies associated with the cobb hot spot and the heckle melt anomaly increased melt supply at cleft segment upon initiation of axial volcano and southward propagation of endeavour segment during the brunhes point to rapid southward directed along axis channeling of melt anomalies linked to these hot spots preferential southward flow of the cobb and heckle melt anomalies and the regional scale south to north gradients in ridge structure along the jdfr may reflect influence of the northwesterly absolute motion of the ridge axis on subaxial melt distribution

global marine gravity from retracked geosat and ers 1 altimetry ridge segmentation versus spreading rate 1 three approaches are used to reduce the error in the satellite derived marine gravity anomalies first we have retracked the raw waveforms from the ers 1 and geosat gm missions resulting in improvements in range precision of 40 and 27 respectively second we have used the recently published egm2008 global gravity model as a reference field to provide a seamless gravity transition from land to ocean third we have used a biharmonic spline interpolation method to construct residual vertical deflection grids comparisons between shipboard gravity and the global gravity grid show errors ranging from 2 0 mgal in the gulf of mexico to 4 0 mgal in areas with rugged seafloor topography the largest errors of up to 20 mgal occur on the crests of narrow large seamounts the global spreading ridges are well resolved and show variations in ridge axis morphology and segmentation with spreading rate for rates less than about 60 mm a the typical ridge segment is 50 80 km long while it increases dramatically at higher rates 100 1000 km this transition spreading rate of 60 mm a also marks the transition from axial valley to axial high we speculate that a single mechanism controls both transitions candidates include both lithospheric and asthenospheric processes

use of multiple oxygen isotope proxies for elucidating arctic cretaceous palaeo hydrology stable oxygen isotope analysis of siderite and dinosaur tooth enamel phosphate from the campanian maastrichtian prince creek formation alaska usa are analysed to determine the palaeohydrology of the ancient colville basin north of the ancestral brooks range do of freshwater siderites relative to v pdb ranges between 214 86 and 216 21 dinosaur tooth enamel do from three different sites kikak tegoseak pediomys point liscomb range between 3 9 and 10 2 0 dometeoric water are calculated from dosiderite that formed at seasonal temperatures ranging from 22 to 14 5 8c with a mean annual temperature of 6 3 8c at 6 3 8c the dow calculated from siderite ranged between 222 23 and 220 89 v smow ingested water compositions are estimated from dinosaur teeth assuming body temperatures of 37 8c and local relative humidity of 77 5 resulting in values ranging from 228 7 to 220 4 v smow suggesting consumption of meteoric water and orographically depleted runoff from the brooks range the ranges in calculated dometeoric water are compatible between the two proxies and are mutually corroborating evidence of extremely o depleted precipitation at high latitudes during the late cretaceous relative to those generated using general circulation models this depletion is proposed to result from increased rainout effects from an intensified hydrological cycle which probably played a role in sustaining polar warmth supplementary material parameters used for generation of equations compared to kohn 1996 can be found at http www geolsoc org uk sup18642 stable isotopic proxies are invaluable tools for understanding past and current climates pedogenic carbonates siderite and calcite are commonly used to determine the isotopic composition of meteoric water lohmann 1988 hays grossman 1991 ludvigson et al 1998 ufnar et al 2004a suarez et al 2011 when analysed over a range of latitudes the resulting isotopic gradients can be used to determine global isotopic groundwater gradients this gradient is related to the isotopic composition of the precipitation which is itself related to temperature gradients humidity and in some instances orographic effects isotopic studies of the cretaceous are of particular importance because future climatic conditions kiehl 2011 are predicted to approach those pco2 temperature seen in the various greenhouse worlds of the cretaceous several studies on the cretaceous climate have revealed shallow equatorial topole air and ocean temperature gradients wolfe upchurch 1987 amiot et al 2004 jenkyns et al 2004 puceat et al 2007 while others have indicated equator to pole precipitation do gradients that are steeper than the modern climate system ludvigson et al 1998 ufnar et al 2002 suarez et al 2011 this steep gradient has been explained as resulting from increased rainout thereby increasing latent heat transport from the equator to the poles during greenhouse conditions ufnar et al 2004b these conclusions are based on empirical from bojar a v melinte dobrinescu m c smit j eds isotopic studies in cretaceous research geological society london special publications 382 http dx doi org 10 1144 sp382 3 the geological society of london 2013 publishing disclaimer www geolsoc org uk pub ethics by guest on june 17 2013 http sp lyellcollection org downloaded from

did the rifting of the atlantic ocean cause the cretaceous thermal maximum the cretaceous thermal maximum was a major turning point in the history of earth s climate this interval of peak warmth in the turonian has been attributed to very high atmospheric pco2 resulting from rapid outgassing rates although crustal cycling rates peaked in the aptian albian interval on the basis of coupled ocean atmosphere model simulations of the middle cretaceous we hypothesize that the formation of an atlantic gateway could have contributed to the cretaceous thermal maximum differences between prerifting and postrifting climate experiments demonstrate substantial regional oceanographic changes in the north and south atlantic basins that are consistent with oxygen isotopic evidence used to infer a cretaceous thermal maximum the model results help reconcile the paleoclimate record inferred from foraminiferal d 18 o with our understanding of climate dynamics and cretaceous tectonism

oceanographic aspects of the emperor seamounts region effects of the emperor seamount chain on the thermohaline structure and baroclinic flow are investigated on the basis of historical hydrographi data the amplitudes of dynamic height perturbations are 3 to 5 times larger west than east of the chain the intensity of the thermal fronts is stronger west than east of the seamounts near the crest of the southern seamounts strong east west thermohaline fronts and a strong northward baroclinic flow are observed the kuroshio extension west of the seamount chain is a well defined meandering current the axis of which generally lies between 33 and 36 n the available data indicate that the kuroshio extension turns northward and then flows eastward through the gaps of the seamount chain east of the seamounts the kuroshio extension widens threefold and appears to be poorly defined

reevaluation of the oxygen isotopic composition of planktonic foraminifera experimental results and revised paleotemperature equations cultured planktonic foraminifera orbulina universa symbiotic and globigerina bulloides nonsymbiotic are used to reexamine temperature 18o relationships at 15 25 c relationships for both species can be described by linear equations equations for o universa grown under low light ll and high light hl share a slope of 4 80 0 21 c 1 with a hl ll offset of 0 33 due to symbiont photosynthetic activity the effect of co32 on o universa is 0 002 mol 1 kg 1 and is insensitive to temperature for g bulloides ontogenetic effects produce size related trends in temperature 18o whereby larger shells are enriched in 18o relative to smaller specimens the o universa temperature 18o relationships are more accurate than previously published equations for describing plankton tow data our equations do not explain planktonic core top data with the same precision but provide a good fit to benthic cibicidoides data below 10 c temperature 18o relationships for g bulloides provide good agreement with field data for this species from the northeast pacific

a giant sauropod footprint from the nemegt formation upper cretaceous of mongolia abstract an expedition to the nemegt formation in 2007 discovered new footprint sites at the nemegt locality the sites contained natural cast tracks identifiable as those of hadrosaurs tyrannosaurs and sauropods among the sauropod tracks was the best preserved pes print yet described from the late cretaceous of mongolia the footprint is referred to brontopodus sp on the basis of footprint morphology age and potential trackmakers from the same formation size estimations based on the track indicate the trackmaker had an acetabular height of approximately 3 0 3 5 m as such the size of the trackmaker exceeds that of any mongolian dinosaur yet reported from skeletal material

unusual locomotion behaviour preserved within a crocodyliform trackway from the upper cretaceous bayanshiree formation of mongolia and its palaeobiological implications abstract crocodyliform tracks are reported from the upper cretaceous cenomanian santonian bayanshiree formation in southeastern mongolia ten tracks are preserved as natural casts forming a trackway with a quadrupedal gait pattern with a tail trail all tracks are short and wide and dominated by toe traces without plantar impressions pes tracks are characterized by four deep claw impressions and push back marks behind them manus tracks have shallow claw marks and long sub parallel scratch marks behind the preferential association of the scratch marks with only the distal digit impressions and irregular pattern of footfalls suggests that this trackway was made by a bottom walking and punting crocodyliform under water this trackway represents the first crocodyliform swim tracks in the late cretaceous of asia and the first evidence for punting behaviour of a fossil crocodyliform the swim tracks can be divided into two categories such as bottom walking tracks with punting for moving somewhat more quickly and subaqueous walking tracks without punting to be associated with slower underwater speeds the tracks show that crocodylians had adopted a bottom walking behaviour similar to extant crocodylians by cretaceous times

the late cretaceous environment of the arctic a quantitative reassessment based on plant fossils abstract late cretaceous megafossil floras from the palaeo arctic of northeastern russia and northern alaska are reviewed in respect of their age composition structure and floral dynamics palaeofloral correlations and comparisons are made between the two regions nine angiosperm rich predominantly cenomanian to coniacian floras from the palaeo arctic are re evaluated using climate leaf analysis multivariate program clamp calibrated using a global gridded 0 5 0 5 climate data set derived from that used in climate modelling additional floras from lower palaeolatitudes were used to derive latitudinal temperature gradients seven from n america five from around 30 n palaeolatitude in europe and one from kazakhstan the arctic climatic determinations similar to previous estimates support the existence of a northern pacific ocean cold gyre and a warm arctic ocean at palaeolatitudes greater than 80 n floras are insufficiently diverse in woody dicot taxa to use clamp but using clamp derived latitudinal temperature gradients arctic ocean coastal environments at 70 ma and 82 n and which supported a diverse dinosaur magafauna are predicted to have experienced a mean annual temperature of 6 3 2 2 c a warm month mean of 14 5 3 1 c and a cold month mean no colder than 2 0 3 9 c all uncertainties are 2 the new estimates are in good agreement with a wide range of non palaeobotanical climate proxies and render as an outlier warmer temperature estimates for the arctic ocean derived from the tex 86 proxy modelling however shows that land to ocean temperature gradients could have been steep the clamp estimates also suggest high values for humidity and precipitation consistent with sedimentological indicators and coupled with warm temperatures support the existence of a persistent polar cloud cap that helped maintain high terrestrial air temperatures throughout prolonged periods up to 5 months of winter darkness

seasonal temperature salinity changes and thermocline development in the mid atlantic bight as recorded by the isotopic composition of bivalves stable isotope records across annual growth increments in specimens of the surf clam spisula solidissima from the mid atlantic bight shelf from 10 m and 45 m depths reflect the changes in temperature and nutrient concentrations on the shelf over the year the 18 o and 13 c records from clams at the two depths record well mixed conditions in the water column during the winter months and the development of a thermocline during the summer spring high productivity and a transient salinity excursion in surface waters are also recorded reconstructing the paleoceanography of late cenozoic temperate continental shelves may be possible using stable isotope records from fossil spisula solidissima and other bivalves

a numerical study of the roles of subgyre scale mixing and the western boundary current on homogenization of a passive tracer a numerical model integrated the steady advection diffusion equation by using a kinematic circulation with characteristics of a subtropical gyre i e closed streamlines and western intensification homogenization of the interior concentration increased and the gradients were forced to the boundaries as mixing parameterized as eddy diffusion decreased as the western boundary current intensified the value of the homogenized interior became closer to the southern boundary value this indicated that cross stream mixing was enhanced within the western boundary current tongues of high and low tracer concentration spiraled across streamlines toward the center of the gyre these simulations will be helpful in the interpretation of lateral distributions of geochemical tracers which are being generated by programs such as tto 9 references 6 figures 2 tables

flow and water property structures between the bering sea and fiji in the summer of 1993 an overview is given of the top to bottom flow thermohaline oxygen and nutrient structures between the bering sea and the fiji islands based on high resolution field measurements along 179 e the zonal flow is dominated by a banded mesoscale structure reflecting the highly sheared structure and instabilities of the major ocean currents crossing the date line the major midlatitude currents are 100 200 km wide have maximum speeds of 40 cm s 1 and extend to 2000 m when measured by the 5 cm s 1 isotach el nino conditions in 1993 caused a merger of the north equatorial countercurrent with the equatorial undercurrent leading to a 600 km wide band of equatorial eastward flow 40 60 cm s 1 in the upper 300 m beneath a 400 km wide and 1 2 km deep westward jet 10 30 cm s 1 is found between 1500 and 3500 m the equatorial flow is predominately to the southeast and between 3500 and 5000 m it is toward the northwest consonant with banded shear flow and flow topography interactions the physical and chemical property distributions along 179 e are complicated reflecting the effects of differential property advection mixing and water mass transformation well defined property fronts occur in shear zones between currents of different origin the thermohaline oxygen and nutrient tongues associated with north and south pacific intermediate and deep waters have considerable internal structure indicative of mesoscale processes and contorted flow paths the abyssal flow near the date line indicates northward movement of lower circumpolar water to the hess rise whence it turns westward and north west of the emperor seamounts properties east of this seamount chain are very uniform the deep and abyssal waters of the isolated aleutian basin differ substantially from those in the adjacent pacific by being warmer 0 1 c less saline 0 01 poorer in oxygen 50 mol kg 1 and much richer in silicate 80 mol kg 1 an isolated basin within the wake necker ridge also shows some unusual bottom water characteristics below sill depth

potential vorticity distribution in the north pacific abstract vertical sections and maps of potential vorticity 1f z for the north pacific are presented on shallow isopycnals high potential vorticity is found in the tropics subpolar gyre and along the eastern boundary of the subtropical gyre all associated with ekman upwelling low potential vorticity is found in the western subtropical gyre subtropical mode water in a separate patch near the sea surface in the eastern subtropical gyre and extending around the gyre and near sea surface outcrops in the subpolar gyre the last is analogous to the subpolar mode water of the north atlantic and southern ocean meridional gradients of potential vorticity are high between the subtropical and subpolar gyres at densities which outcrop only in the subpolar gyre lateral gradients of potential vorticity are low in large regions of the subtropical gyre on these isopycnals on slightly denser isopycnals which do not outcrop in the north pacific there are large regions of low potential vorticity gradients

on a simple empirical parameterization of topography catalyzed diapycnal mixing in the abyssal ocean abstract the global spatial distribution of the turbulent diapycnal diffusivity in the abyssal ocean is reexamined in light of the growing body of microstructure data revealing bottom intensified turbulent mixing in regions of rough topography a direct and nontrivial implication of the observed intensification is that the diapycnal diffusivity k is depth dependent and patchily distributed horizontally across the world s oceans theoretical and observational studies show that bottom intensified mixing is dependent upon a variety of energy sources and processes whose contributions to mixing are sufficiently complex that their physical parameterization is premature only rudimentary parameterizations of tidally induced mixing have been attempted although the tides likely provide no more than half of the mechanical energy available for diapycnal mixing in the abyssal ocean here an empirical and still rudimentary parameterization of the spatially variable mean diffusivity k based on a large collection

high resolution maps of khulsan and nemegt localities nemegt basin southern mongolia stratigraphic implications abstract since the discovery of fossil rich exposures at the khulsan and nemegt localities nemegt basin southern mongolia tens of paleontological expeditions returned to these exposures which are considered some of the richest cretaceous units in the world however limited data on the local geology and cartography have been limiting our comprehension on correlations between different sites and the stratigraphic occurrence of vertebrate remains although informative hand drawn maps from the 1940s still represent the sole tool for researchers to provide a framework for locating access path quarries and major geological sections in 2016 we started a project for the realization of high resolution topographic maps of key localities within the nemegt basin based on drone acquired images several tests were performed at pivotal localities such as altan uul 2 and 3 tsagaan khushuu and ulaan khushuu providing partial maps of such localities whereas the nemegt and khulsan localities were fully covered photogrammetric elaboration of high resolution images resulted in digital surface models used to obtain high resolution topographic maps and orthophotos rock cairns used in the 1940s for triangulation were relocated and painted with vivid colors in order to represent reliable ground control points in this study we introduce new topographic maps for both khulsan and nemegt localities as well as comprehensive geological maps in so doing we provide additional stratigraphic and geographic data on the approximately 25 m thick interfingering interval that characterize the transition from the baruungoyot and overlying nemegt formations data presented in this study provide a solid framework in which detailed geological and paleontological investigations can be referred in order to significantly improve our comprehension on the late cretaceous nemegt ecosystems

spatial variability of turbulent mixing in the abyssal ocean ocean microstructure data show that turbulent mixing in the deep brazil basin of the south atlantic ocean is weak at all depths above smooth abyssal plains and the south american continental rise the diapycnal diffusivity there was estimated to be less than or approximately equal to 0 1 x 10 4 meters squared per second in contrast mixing rates are large throughout the water column above the rough mid atlantic ridge and the diffusivity deduced for the bottom most 150 meters exceeds 5 x 10 4 meters squared per second such patterns in vertical mixing imply that abyssal circulations have complex spatial structures that are linked to the underlying bathymetry

on the kuroshio extension near the emperor seamounts in june july 1982 and november 1983 studies were carried out of the vertical structure of the kuroshio extension along 167 e and the path of the current as it approached the emperor seamount chain in addition records from moored current meters at three locations two at 167 e and one in the main gap of the emperor seamount chain were obtained the kuroshio extension in both 1982 and 1983 turned cyclonically meander wave length of 450 km as it approached the chain the axis of the surface current was located in deep water 3 5 km in 1982 and in relatively shallow water 0 5 km in 1983 in 1982 the horizontal temperature gradient decreased and the density surfaces down to 2000 m ascended as the kuroshio extension flowed over the emperor seamounts in neither year was there evidence of current splitting as it crossed the seamounts in 1983 in contrast to 1982 there was no weakening of the horizontal temperature gradient and the kuroshio extension went over a very shallow portion of kinmei seamount 500 m the current measurements made at the time of the hydrographic section show that the instantaneous kuroshio extended to the bottom abyssal eastward current of 2 cm s 1 the deep low frequency eddy kinetic energy values are intermediate between those measured at 152 e and those at 158 w suggesting a large scale eastward decrease in deep eddy activity zonal mean flow near 3500 m at 167 e was essentially zero 0 1 cm s 1 the mean meridional components were larger 2 1 and 0 7 cm s 1 at the southern side of the gap the deep flow was unusually steady ke km 1 and directed northeastward into the eastern basin of the north pacific low ratios o 1 were also observed in the lower thermocline compared with those at 167 e o 10 100 the frequency content of the gap kinetic energy differed from that measured at 167 e the highest frequency band 2 hours p 2 days was the most energetic whereas at 167 e the mesoscale band 20 days p 150 days was the most energetic the flow in the gap resembles in many of its characteristics that observed in two other channel flows the vema channel and the charlie gibbs fracture zone

quantification of a greenhouse hydrologic cycle from equatorial to polar latitudes the mid cretaceous water bearer revisited article this study aims to investigate the global hydrologic cycle during the mid cretaceous greenhouse by utilizing the oxygen isotopic composition of pedogenic carbonates calcite and siderite as proxies for the oxygen isotopic composition of precipitation the data set builds on the aptian albian sphaerosiderite 18 o data set presented by ufnar et al 2002 by incorporating additional low latitude data including pedogenic and early meteoric diagenetic calcite 18 o ufnar et al 2002 used the proxy data derived from the north american cretaceous western interior basin kwib in a mass balance model to estimate precipitation evaporation fluxes we have revised this mass balance model to handle sphaerosiderite and calcite proxies and to account for longitudinal travel by tropical air masses we use empirical and general circulation model gcm temperature gradients for the mid cretaceous and the empirically derived 18 o composition of groundwater as constraints in our mass balance model precipitation flux evaporation flux relative humidity seawater composition and continental feedback are adjusted to generate model calculated groundwater 18 o

abyssal pathways and the double silica maximum in the northeast pacific basin causes of the double silica maximum in the deep northeast pacific basin nepb are explored using a stochastic lagrangian approach steady state advective fields and diapycnal diffusion are taken

reduced mixing from the breaking of internal waves in equatorial waters in the oceans heat salt and nutrients are redistributed much more easily within water masses of uniform density than across surfaces separating waters of different densities but the magnitude and distribution of mixing across density surfaces are also important for the earth s climate as well as the concentrations of organisms most of this mixing occurs where internal waves break overturning the density stratification of the ocean and creating patches of turbulence predictions of the rate at which internal waves dissipate were confirmed earlier at mid latitudes here we present observations of temperature and velocity fluctuations in the pacific and atlantic oceans between 42 degrees n and 2 degrees s to extend that result to equatorial regions we find a strong latitude dependence of dissipation in accordance with the predictions in our observations dissipation rates and accompanying mixing across density surfaces near the equator are less than 10 of those at mid latitudes for a similar background of internal waves reduced mixing close to the equator will have to be taken into account in numerical simulations of ocean dynamics for example in climate change experiments

paleoclimate reconstruction of the prince creek formation arctic alaska during maastrichtian global warming abstract the upper cretaceous maastrichtian prince creek formation of arctic alaska 82 85 n paleolatitude preserves successions of alluvial paleosols that are used to estimate mean annual precipitation map mean annual temperature mat and meteoric water oxygen isotope composition for the prince creek formation the highest map estimates range between 1000 and 3900 mm yr and the lowest range between 350 and 1200 mm yr the precipitation variability derived from stable carbon isotope analysis occurs on a time scale of 104 years map values agree with previous interpretations from fossil pollen pedological features soil types vegetation composition sedimentological indicators and clamp estimates that suggest high precipitation amounts and high humidity despite the considerable uncertainty with mat proxies our values are consistent with warm month mean temperatures obtained previously from paleobotanical data the 18o of smectite from bentonite beds clusters around 5 0 vsmow the 18o of meteoric water calculated from bentonitic smectite is 23 vsmow assuming a mean annual temperature of 6 3 c which is slightly more 18o depleted than meteoric water calculated from pedogenic siderite in stratigraphically younger beds closer to the brooks range chronostratigraphic correlation with the lower cantwell formation denali national park alaska 64 n paleolatitude suggests higher precipitation rates and highly 18o depleted precipitation in the late cretaceous paleo arctic compared to central alaska these data are consistent with previous studies that suggest a warmer and moister greenhouse earth and an intensified hydrological cycle that enhanced latent heat transport resulting in increased rainout effects

late paleocene arctic coastal climate inferred from molluscan stable and radiogenic isotope ratios abstract characterizing polar climates during past warm intervals is important for understanding greenhouse climate dynamics because high latitude surface temperatures and precipitation patterns are extremely sensitive to global climatic conditions model data comparisons of high latitude climates during past warm intervals cretaceous eocene pliocene are currently at odds specifically simulations of past warm climates produce polar regions characterized by sub freezing temperatures and significant seasonality whereas limited fossil proxy data indicate higher mean annual temperatures and low seasonality i e an equable climate we have constructed a data set to infer northern hemisphere polar marine temperatures during the late paleocene seasonal and mean annual temperature and the oxygen isotopic composition of precipitation are reconstructed for an arctic coastal setting during the thanetian 57 58 ma using fossil shell stable isotope profiles we estimate that coastal water temperatures varied between 10 and 15 c during the seasons of growth presumably spring summer and fall these findings support paleontological evidence implying northern hemisphere polar climates were seasonally warm during the late paleocene in addition estuarine fossil oxygen isotope profiles show periodic excursions to low values as low as 19 vpdb which indicate seasonal pulses of isotopically depleted freshwater

latest cretaceous maastrichtian climate of the koryak upland of north east russia based on a quantitative analysis of a palaeo polar flora we describe fossil plant assemblages from the late maastrichtian kakanaut formation of the koryak upland north east of russia which represent a high 75on palaeolatitude flora the flora contains about 40 species including liverworts horsetails ferns cycadophytes ginkgos conifers and angiosperms angiosperms and conifers predominate and unusually the flora contains typical cretaceous taxa admixed with elements that are more characteristic of the paleocene reconstruction of the palaeoclimate in the kakanaut area was made using the climate leaf analysis multivariate program clamp employing a recently developed calibration that yields 23 different climate variables analysis was made based on 21 morphotypes of woody dicotyledonous plants from the kakanaut flora the analysis indicated a mean annual temperature of 12 2 2 0 c a warmest month mean temperature of 20 6 2 5 c a coldest month mean temperature of 4 8 3 2 c the growing season lasted approximately 7 months during which there was almost 1 m of precipitation this and other indicators relative humidity vapour pressure deficit and potential evapotranspiration all suggest a year round humid regime the winter temperatures suggest occasional mild frosts in this near sea level setting so that at higher elevations freezing conditions would have been more persistent these results throw new light on the living and breeding conditions of diverse latest cretaceous arctic dinosaur populations as represented by numerous skeletal and egg remains associated with the plants

fish tooth δ18o revising late cretaceous meridional upper ocean water temperature gradients the oxygen isotope composition of fossil fi sh teeth a paleo upper ocean temperature proxy exceptionally resistant to diagenetic alteration provides new insight on the evolution of the low to middlelatitude thermal gradient between the middle cretaceous climatic optimum and the cooler latest cretaceous period the new middle cretaceous low to middle latitude thermal gradient agrees with that previously inferred from planktonic foraminifera 18o recovered from deep sea drilling project and ocean drilling program drilling sites although the isotopic temperatures derived from 18o of fish teeth are uniformly higher by 3 4 c in contrast our new latest cretaceous thermal gradient is markedly steeper than those previously published for this period fish tooth 18o data demonstrate that low to middle latitude thermal gradients of the middle cretaceous climatic optimum and of the cooler latest cretaceous are similar to the modern one despite a cooling of 7 c between the two periods our new results imply that no drastic changes in meridional heat transport are required to explain the late cretaceous climate based on climate models such a cooling without any change in the low to middle latitude thermal gradient supports an atmospheric co2 decrease as the primary driver of the climatic evolution recorded during the late cretaceous

late cretaceous terrestrial vegetation a near polar temperature curve quantitative estimates of terrestrial paleotemperatures near the north pole were derived from the physiognomy of the vegetation including leaf margin analysis from rocks of latest albian and late cretaceous age of the north slope of alaska during the latest albian and cenomanian mean annual temperature was approximately 10 3 c during the coniacian mean annual temperature may have been 2 3 c warmer than during the albian cenomanian but no higher than 13 c during the campanian and maastrichtian mean annual temperature would have been about 2 8 c although the ranges for the individual estimates overlap differences among the floras indicate that the relative changes in mean annual temperature did occur

high latitude meteoric δ 18 o compositions from the cenomanian bastion ridge formation axel heiberg island canadian arctic archipelago a palaeoclimate proxy from the sverdrup basin

latitudinal temperature trends in the northern hemisphere during the early cretaceous valanginian hauterivian abstract we present the first detailed stable isotope record 13c 18o for the valanginian lower cretaceous of the southern boreal realm the observations are based on the geochemical analysis of 286 belemnite rostra from stratigraphically well dated sections in northwest germany a major positive carbon isotope excursion cie of 2 in the early late valanginian documents a perturbation of the carbon cycle this positive cie which is well known as the weissert event in the tethys is also displayed in composite carbon isotope records based on published and own data from three different palaeolatitudes 35 39 65 north these findings suggest that the environmental changes indicated by the cie in the early late valanginian are synchronous thereby pointing to a global control the combined oxygen isotope data sets show long term fluctuations of up to 7 c with a cooling in the late valanginian for both the southern and the arctic part of the boreal realm whilst tethyan data document only a ca 1 c cooling based on a reliable bio and chemostratigraphic correlation between the different realms this study highlights the amplitude of the environmental perturbations in the valanginian and supports the idea that a combination of regional and global factors caused such shifts

carbon and oxygen isotopic composition of holocene reefal carbonates carbon and oxygen isotopic compositions have been determined for holocene reefal carbonate grains and cements in samples from enewetak bikini bermuda and belize to identify components that exhibit systematic isotopic fractionation relationships these findings are compared with fractionation relationships determined from experimentally precipitated low magnesium calcite lmc aragonite and high magnesium calcite hmc to determine if these relationships are observed in naturally precipitated carbonates compositional variation within individual samples is extreme up to 6 in 13 c pdb and 3 in 18 o pdb experimental fractionation relationships fail to predict the range of observed compositions aragonite cements are enriched 1 0 to 1 4 in 13 c and 1 5 to 2 0 in 18 o relative to calcite equilibrium compositions hmc cements are enriched by 0 3 to 0 4 in 13 c and by 1 8 to 1 9 to 18 o for carbon these results are in agreement with the experimental work of rubinson and clayton for oxygen our results suggest that fractionation factors of both aragonite and hmc may have been underestimated skeletal components exhibit inconsistent fractionation relative to inorganically precipitated marine cements suggesting that marine cement compositions are more reliable indicators of the physicochemical conditions of precipitation than co occurring skeletal carbonates

hydrothermal helium plumes in the pacific ocean hydrothermal activity along the global mid ocean ridge system and at active seamounts introduces a 3 he rich signal into the deep ocean basins which can be used to trace patterns of ocean circulation and mixing this hydrothermal helium signal is especially strong in the pacific ocean where the spreading rate of the ridges is the greatest in several areas of the pacific the hydrothermal activity is of sufficient strength to produce intense helium plumes which clearly define the regional circulation among these are 1 a pair of helium plumes at 2500 m depth which extend westward from the east pacific rise at 10 n and 15 s into the interior of the pacific basin 2 a helium plume at 2000 m depth extending southwest from sources on the juan de fuca ridge in the northeast pacific and 3 a plume at 1100 m depth emanating from loihi seamount at 20 n which extends eastward from hawaii to the coast of mexico the flow field implied by the helium distribution appears to be in reasonable agreement with reid s 1997 steric height analysis for the pacific

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

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

life at the top of the greenhouse eocene world a review of the eocene flora and vertebrate fauna from canada s high arctic early middle eocene ca 53 38 ma sediments of the eureka sound group in canada s arctic archipelago preserve evidence of lush mixed conifer broadleaf rain forests inhabited at times by alligators turtles and diverse mammals including primates tapirs brontotheres and hippo like coryphodon this biota reflects a greenhouse world offering a climatic and ecologic deep time analog of a mild ice free arctic that may be our best means to predict what is in store for the future arctic if current climate change goes unchecked in our review of the early middle eocene arctic flora and vertebrate fauna we place the arctic fossil localities in historic geographic and stratigraphic context and we provide an integrated synthesis and discussion of the paleobiology and paleoecology of these eocene arctic forests and their vertebrate inhabitants the abundance and diversity of tapirs and plagiomenids both rare elements in midlatitude faunas and the absence of artiodactyls early horses and the hyopsodontid condylarth hyopsodus well represented at midlatitude localities are peculiar to the eocene arctic the eocene arctic macrofloras reveal a forested landscape analogous to the swamp cypress and broadleaf floodplain forests of the modern southeastern united states multiple climate proxies indicate a mild temperate early middle eocene arctic with winter temperatures at or just above freezing and summer temperatures of 20 c or higher and high precipitation at times this high precipitation resulted in freshwater discharge into a nearly enclosed arctic ocean basin sufficient to cause surface freshening of the arctic ocean supporting mats of the floating fern azolla fluctuating arctic ocean sea level due to freshwater inputs as well as tectonics produced temporary land bridges allowing land plants and animals to disperse between north america and both europe and asia

deep currents in the central subarctic pacific ocean abstract sections of closely spaced ctd stations along longs 165 w 175 w and 175 e in combination with 14 month current records from the central longitude define two deep nearly zonal currants with speed increasing upward in the subarctic pacific one flows eastward above the aleutian rise and aleutian trench and appears to be a concentration of geostrophic flow forced by the bottom topography the other flows westward along the aleutian island arc and is the northern boundary current predicted by deep circulation theory both currents reach to the sea surface the boundary current being simply the deep part of the alaskan stream the current records were too few to permit better than rough estimates of volume transports but to the extent that they could be combined with thermal wind calculations they suggest at 175 w 1 a transport of 28 106 m3 s 1 for the alaskan stream of whch 5 106 m3 s 1 was found below 1500 m and 2 a transport of around 20 1o6 m3 s 1 for the eastward jet of wh

the internal wave driven meridional overturning circulation abstractthe upwelling diapycnal limb of the ocean s meridional overturning circulation is driven by divergence of diabatic turbulent buoyancy fluxes w b across density surfaces a global assessment of zonally averaged internal wave driven turbulent diapycnal buoyancy fluxes from a strain based finescale parameterization is used to infer mean diapycnal transports in the interior and near the bottom boundary bulk interior diabatic transports dominate above 2500 m depth buoyancies b g n 0 0 267 m s 2 neutral densities n 27 9 kg m 3 upwelling at 10 11 sv 1 sv 106 m3 s 1 2 5 and 3 4 sv in the indian pacific and atlantic respectively but are weak in the abyss boundary water mass transformations peak at 18 25 sv 4 6 10 14 and 4 5 sv in the indian pacific and atlantic near buoyancy b 0 268 m s 2 n 28 1 kg m 3 4500 m depth between bottom and lower deep waters consistent with published 20 30 sv global antarctic bottom water aabw transport estimates interior transpor

the climatological distribution of potential vorticity over the abyssal ocean climatological maps of the large scale potential vorticity field q along isopycnals are diagnosed for the abyssal waters over the global ocean the inferred patterns of q vary with density the basin and hemisphere at middepths the distribution of q is controlled by the background planetary vorticity gradient on deeper isopycnals there are regions where q contours deviate from latitude circles and even regions of nearly uniform q these different regimes appear to be robust features over the interior of ocean basins as the standard error is found to be relatively small there the nearly uniform q occurs in the deep waters of the north pacific and possibly in the bottom waters of the western north atlantic and north pacific the nearly uniform q has a low magnitude in each case as well as a relatively low variability for the deep waters of the north pacific this nearly uniform q signal appears to be formed when a single water mass enters the basin from a low latitude source

revised and synthetic apparent polar wander paths of the african eurasian north american and indian plates and true polar wander since 200 ma we have reviewed paleomagnetic data available for the eurasian african north american and indian plates over the last 200 ma selection criteria are those generally accepted with an emphasis on evidence for lack of remagnetization accurate dating and proper structural analysis this results in 23 35 51 and 2 poles for eurasia africa north america and india respectively we believe that this limited set of higher quality data is more likely to reveal key features of apparent polar wander apw paths than averaging of larger data sets involving less stringent selection criteria we propose and describe revised apw paths but more importantly we next use relative motion models to transfer all data in a common reference frame we find good agreement between transferred data when they are averaged separately for each plate in independent 20 ma windows this is a check on consistency of paleomagnetic data kinematic models and of the geocentric dipole hypothesis transferred data from all plates are averaged in 20 ma windows to generate synthetic apw paths for all plates studied these synthetic paths are in agreement with the original revised apw paths that use only data from a single plate moreover both geographic and time resolution are improved spatial confidence intervals are of the order of 5 the synthetic paths display interesting features such as a previously ill recognized apw loop for eurasia paleomagnetic and hotspot apw are next compared and a determination of true polar wander tpw is derived we find significant tpw amounting to over 20 in the last 200 ma tpw appears to be episodic with a standstill between 180 and 110 ma there is general agreement with a previous study of livermore et al 1984 the tpw standstill appears to correlate with a time of decreasing reversal frequency ending with the cretaceous long normal superchron other periods of fast tpw would seem to correspond to increasing reversal frequency however it is suggested that the major tpw hairpin at 50 ma might correspond to the collision of india with eurasia tentative correlations with core or mantle indicators can be understood as a result of couplings between the core mantle and lithosphere we believe primarily related to episodic evolution of the d layer

northward abyssal transport through the samoan passage and adjacent regions a conductivity temperature depth hydrographic survey in january february 1994 and a 17 month deployment of current meter moorings from september 1992 to march 1994 were carried out to determine the volume transport water mass characteristics and diathermal fluxes of northward flowing abyssal waters in the samoan passage and adjacent regions of the south pacific ocean geostrophic calculations relative to 1 2 c potential temperature indicated northward transport of 7 8 sv in the samoan passage 1 1 sv through a gap in robbie ridge and 2 8 sv along the eastern flank of the manihiki plateau all of the total of 11 7 sv of northward geostrophic transport was in waters colder than 1 1 c the northward transport distribution was bimodal in temperature with a cold mode of 3 6 sv in the range 0 65 0 70 c occurring entirely in the samoan passage and a warm mode of 3 0 sv in the range of 0 80 0 85 c occurring mainly along the manihiki plateau within the samoan passage 7 1 sv of the northward transport was below 4000 m where the geostrophic calculation was confirmed by an equal estimate of transport from current meters during the simultaneous 3 day period the 17 month mean transport from the moored array was 6 0 sv 0 5 by using the observed temporally varying flow within the samoan passage together with the hydrographic snapshot across the region an estimate of the total mean northward transport of 10 6 sv 1 7 was obtained estimates of the flow across near bottom potential temperature surfaces indicate extraordinarily high rates of mixing with heating of the abyssal layer up to 20 w m 2 corresponding to diffusivities up to 10 1 m2 s 1

the abyssal and deep circulation of the northeast pacific basin abstract three dimensional abyssal and deep circulation of the region to the east and north of the emperor seamount chain hawaiian ridge is determined from a compilation of ctd and argo float data using a new overdetermined inverse technique for the geostrophic reference velocity and diapycnal lateral mixing coefficients the northeast pacific basin is primarily sourced from its northern boundary at a rate of 3 5 sv across 47 n below 3000 m bottom water in the western subarctic gyre recirculates cyclonically between the emperor seamount chain and 155 w bottom water east of 155 w takes a more direct path southward along the flank of a broad topographic slope in the deep water a ridge of potential vorticity lying along the mendocino fracture zone separates circulation systems north and south of 40 n the region has very weak diapycnal and lateral mixing and an aspect ratio for the overturning circulation that is correspondingly flat with bottom water parcels rising less than 1 km during their long transit from the aleutian trench to the latitude of hawaii

isotope paleontology growth and composition of extant calcareous species abstract isotope paleontology uses the isotopic composition of fossil remains of organisms to make inferences about the physical surroundings of growth of the organisms especially temperature and to obtain clues about life history and modes of growth in calcareous fossils oxygen isotopes are mainly used in the former and carbon isotopes in the latter however since physical surroundings and organism response are intimately associated both types of information are contained in each of the isotopic signals to explore the potential of isotope paleontology and to provide a basis for reconstruction a broad range of extant organisms has been studied taking the pioneering work of epstein and associates as a starting point results are summarized for a representative sampling of these studies with emphasis on work at the laboratories of the authors from the mid seventies to the present the organisms considered are nannoplankton benthic algae planktonic and benthic deep sea foraminifera larger foraminifera sponges corals bryozoans polychaetes arthropods bivalves gastropods cephalopods and vertebrates fish otoliths the survey broadly suggests that regarding oxygen isotopes materials tend to be precipitated close to equilibrium with the surrounding seawater as postulated by urey and that for carbon isotopes disequilibrium is the rule life spans growth rates differential seasonal growth and age of reproductive activity can be extracted under favorable circumstances from individual shells and skeletal parts in detail the interpretation of isotope records of individual shells is quite complicated and simple models will fail to give satisfactory results in many or most cases

global abyssal mixing inferred from lowered adcp shear and ctd strain profiles abstract internal wave wave interaction theories and observations support a parameterization for the turbulent dissipation rate e and eddy diffusivity k that depends on internal wave shear vz2 and strain z2 variances its latest incarnation is applied to about 3500 lowered adcp ctd profiles from the indian pacific north atlantic and southern oceans inferred diffusivities k are functions of latitude and depth ranging from 0 03 10 4 m2 s 1 within 2 of the equator to 0 4 0 5 10 4 m2 s 1 at 50 70 diffusivities k also increase with depth in tropical and subtropical waters diffusivities below 4500 m depth exhibit a peak of 0 7 10 4 m2 s 1 between 20 and 30 latitudes where semidiurnal parametric subharmonic instability is expected to be active turbulence is highly heterogeneous though the bulk of the vertically integrated dissipation e is contributed from the main pycnocline hotspots in e show some correlation with small scale bottom roughness and near bottom flow at sites where st

large scale mass transports water mass formation and diffusivities estimated from world ocean circulation experiment woce hydrographic data 1 a global inversion is used to estimate the oceanic mass transports and vertical diffusivities based on a subset of hydrographic data from the world ocean circulation experiment woce and java australia dynamic experiment the analysis is based on the linear inverse box model of ganachaud and wunsch 2000 that consistently combines the transoceanic sections a globally consistent solution is obtained for a depth independent adjustment to the thermal wind field the freshwater flux divergences the ekman transport and the advective and diffusive dianeutral fluxes between layers a detailed error budget permits calculation of statistical uncertainties taking into account both the nonresolved part of the solution and the systematic errors due to the temporal oceanic variability the horizontal structure of the transports for different density classes is analyzed regionally during the woce period 1985 1996 net meridional transports are estimated with 16 2 sv 106 m3 s of north atlantic deep water nadw being produced in the northern north atlantic moving southward entraining antarctic bottom water aabw and antarctic intermediate water increasing in volume transport to 23 3 sv at 30 s in the southern ocean 21 6 sv of bottom water was formed from lower circumpolar deep water which corresponds approximately to the lower nadw density range bottom water inflows nadw aabw mixture to the atlantic indian and pacific oceans are estimated at 6 1 3 11 4 and 7 2 sv respectively in the indian and pacific oceans this water returns southward at deep and intermediate levels property anomaly conservation constraints permit estimation of dianeutral diffusivities in deep layers with a global average of 3 7 0 7 cm2s 1 north of 30 s

evidence for enhanced mixing over rough topography in the abyssal ocean the overturning circulation of the ocean plays an important role in modulating the earth s climate but whereas the mechanisms for the vertical transport of water into the deep ocean deep water formation at high latitudes and horizontal transport in ocean currents have been largely identified it is not clear how the compensating vertical transport of water from the depths to the surface is accomplished turbulent mixing across surfaces of constant density is the only viable mechanism for reducing the density of the water and enabling it to rise however measurements of the internal wave field the main source of energy for mixing and of turbulent dissipation rates have typically implied diffusivities across surfaces of equal density of only approximately 0 1 cm2 s 1 too small to account for the return flow here we report measurements of tracer dispersion and turbulent energy dissipation in the brazil basin that reveal diffusivities of 2 4 cm2 s 1 at a depth of 500 m above abyssal hills on the flank of the mid atlantic ridge and approximately 10 cm2 s 1 nearer the bottom this amount of mixing probably driven by breaking internal waves that are generated by tidal currents flowing over the rough bathymetry may be large enough to close the buoyancy budget for the brazil basin and suggests a mechanism for closing the global overturning circulation

abyssal upwelling and downwelling driven by near boundary mixing abstracta buoyancy and volume budget analysis of bottom intensified mixing in the abyssal ocean reveals simple expressions for the strong upwelling in very thin continental boundary layers and the interior near boundary downwelling in the stratified ocean interior for a given amount of antarctic bottom water that is upwelled through neutral density surfaces in the abyssal ocean between 2000 and 5000 m up to 5 times this volume flux is upwelled in narrow turbulent sloping bottom boundary layers while up to 4 times the net upward volume transport of bottom water flows downward across isopycnals in the near boundary stratified ocean interior these ratios are a direct result of a buoyancy budget with respect to buoyancy surfaces and these ratios are calculated from knowledge of the stratification in the abyss along with the assumed e folding height that characterizes the decrease of the magnitude of the turbulent diapycnal buoyancy flux away from the seafloor these strong diapycnal upward and downwa

a global analysis of sverdrup balance using absolute geostrophic velocities from argo using observations from the argo array of profiling floats the large scale circulation of the upper 2000 decibars db of the global ocean is computed for the period from december 2004 to november 2010 the geostrophic velocity relative to a reference level of 900db is estimated from temperature and salinity profiles and the absolute geostrophic velocity at the reference level is estimated from the trajectory data provided by the floats combining the two gives the absolute geostrophic velocity on 29 pressure surfaces spanning the upper 2000db of the global ocean these velocities together with satellite observations of wind stress are thenusedtoevaluatesverdrupbalance thesimplecanonicaltheoryrelatingmeridionalgeostrophictransport to wind forcing observed transports agree well with predictions based on the wind field over large areas primarily in the tropics and subtropics elsewhere especially at higher latitudes and in boundary regions sverdrup balance does not accurately describe meridional geostrophic transports possibly due to the increased importance of the barotropic flow nonlinear dynamics and topographic influence thus while it provides an effective framework for understanding the zero order wind driven circulation in much of the global ocean sverdrup balance should not be regarded as axiomatic

a coupled climate model simulation of the last glacial maximum part 2 approach to equilibrium the climate of the last glacial maximum lgm is simulated with a coupled climate model the simulated climate undergoes a rapid adjustment during the first several decades after imposition of lgm boundary conditions as described in part 1 and then evolves toward equilibrium over 900 model years the climate simulated by the coupled model at this period is compared with observationally based lgm reconstructions and with lgm results obtained with an atmosphere mixed layer slab ocean version of the model in order to investigate the role of ocean dynamics in the lgm climate global mean surface air temperature and sea surface temperature sst decrease by about 10 c and 5 6 c in the coupled model which includes ocean dynamics compared to decreases of 6 3 and 3 8 c in slab ocean case the coupled model simulates a cooling of about 6 5 c over the tropics which is larger than that of the climap reconstruction 1 7 c and larger than that of the slab ocean simulation 3 3 c but which is in reasonable agreement with some recent proxy estimates the ocean dynamics of the coupled model captures features found in the climap reconstructions such as a relative maximum of ocean cooling over the tropical pacific associated with a mean la nina like response and lead to a more realistic sst pattern than in the slab model case the reduction in global mean precipitation simulated in the coupled model is larger 15 than that simulated with the slab ocean model 10 in conjunction with the enhanced cooling some regions such as the usa and the mediterranean region experience increased precipitation in accord with proxy paleoclimate evidence the overall much drier climate over the ocean leads to higher sea surface salinity sss in most ocean basins except for the north atlantic where sss is considerably lower due to an increase in the supply of fresh water from the mississippi and amazon rivers and presumably a decrease in salt transport by the weakened north atlantic overturning circulation the north atlantic overturning stream function weakens to less than half of the control run value the overturning is limited to a shallower depth less than 1000 m and its outflow is confined to the northern hemisphere in the southern ocean convection is much stronger than in the control run leading to a stronger overturning stream function associated with enhanced antarctic bottom water formation as a result southern ocean water masses fill the entire deep ocean the antarctic circumpolar current acc transport through the drake passage increases by about 25 the acc transport despite weaker zonal winds is enhanced due to changes in bottom pressure torque the weakening of the overturning circulation in the north atlantic and the accompanying 30 decrease in the poleward ocean heat transport contrasts with the strengthening of the overturning circulation in the southern ocean and a 40 increase in heat transport as a result sea ice coverage and thickness are affected in opposite senses in the two hemispheres the lgm climate simulated by the coupled model is in reasonable agreement with paleoclimate proxy evidence the dynamical response of the ocean in the coupled model plays an important role in determining the simulated and undoubtedly the actual lgm climate

the relative roles of diapycnal and isopycnal mixing on subsurface water mass conversion abstract fluid motion in the sea is known to occur predominantly along quasi horizontal neutral surfaces but the very small diapycnal i e across isopycnal velocities often make a significant contribution to the conversation equations of heat salt and tracer by eliminating the diapycnal advection term between the conservation equations for i heat and ii salt an equation is derived for the rate of change lagrangian derivative of potential temperature on a neutral surface which has terms caused by a turbulent mixing along isopycnal surfaces i e isopycnal mixing b diapycnal turbulent mixing and c double diffusive convection bemuse of the nature of the isopycnal reference frame the diapycnal mixing terms do not take their expected forms for example the diapycnal turbulent mixing term is proportional to the diapycnal eddy diffusivity d multiplied by the curvature of the s curve d2s d 2 rather than the usual form d x x if the s curve is locally straight small scale turbulen

reconstructing the paleohydrology of a cretaceous alaskan paleopolar coastal plain from stable isotopes of bivalves abstract as global mean annual temperatures continue to rise modern arctic climates are changing at an incredibly fast rate to predict changing climate dynamics a number of researchers have been focused on characterizing arctic climate from ancient greenhouse worlds such as the cretaceous and eocene characterization of these climates requires analysis of a variety of proxy materials here we use bivalve shells identified as nucula aff nucula percrassa conrad from the cretaceous early maastrichtian prince creek formation in combination with isotope data from previous lithologic and isotopic studies to characterize a cool house cretaceous climate bounded by greenhouse climates mid cretaceous thermal maximum and late paleocene climate bivalves were analyzed by powder x ray diffraction pxrd cathodoluminescence cl and thin section petrography to determine mineralogy and integrity of shells pxrd analysis indicates that shells are composed of primary aragonite and not secondary calcite thin section and cl images reveal well preserved shell morphology including daily growth lines and no luminescent patches or coarsening of crystal sizes to indicate diagenetic alteration recrystallization aragonite carbon isotopic composition 13carag range from 0 45 to 3 00 vpdb and average 1 58 aragonite oxygen isotopic composition 18oarag range from 10 48 to 15 42 vpdb and average 12 83 using temperatures from 4 5 c to 12 5 c the salinity 18owater relationship of a modern arctic setting from torres et al 2011 and the water aragonite equation of grossman and ku 1986 reveal salinity ranges between 8 and 17 7 ppt using these salinity ranges and temperatures n percrassa precipitated shell aragonite from water that ranged between 18owater 14 41 vsmow at 12 5 c and 16 23 at 4 5 c shell growth was in equilibrium with water that represents a coastal mixed water setting such as an estuary when combined with previous studies the mixture of fresh marine water represents a 50 50 to 72 28 mixture and ranged between 14 41 and 16 23 during spring to summer months

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

buoyancy forcing by turbulence above rough topography in the abyssal brazil basin abstract observations of turbulent dissipation above rough bathymetry in the abyssal brazil basin are presented relative to regions with smooth bathymetry dissipation is markedly enhanced above rough topography of the mid atlantic ridge with levels above bathymetric slopes exceeding levels observed over crests and canyon floors furthermore mixing levels in rough areas are modulated by the spring neap tidal cycle internal waves generated by barotropic tidal flow over topography are the likely mechanism for supplying the energy needed to support the observed turbulent dissipation a model of the spatial and temporal patterns in the turbulent dissipation rate is used to constrain the diapycnal advection in an inverse calculation for the circulation in an area of rough bathymetry this inverse model uses both beta spiral and integrated forms of the advective budgets for heat mass and vorticity and contains sufficient information to resolve the full three dimensional flow the inverse model solution re

dinosaur tracks at the nemegt locality paleobiological and paleoenvironmental implications abstract the nemegt locality is one of the most famous dinosaur localities in mongolia ever since the site was discovered in 1946 it yields abundant dinosaur skeletons however little attention had been given to dinosaur footprints at the locality the only nemegt dinosaur footprint study focused on descriptions of the footprints gave only a few taxonomic implications and provided no comparison with other dinosaur tracksites this study reports newly recorded dinosaur footprints hadrosaurs sauropods and theropods at the nemegt locality during the nemegt educational expedition of 2016 a single footprint bearing horizon that extends several kilometres was examined within the nemegt formation to determine the ichno taxonomic assemblage of the nemegt dinosaurs a significant difference was identified between taxonomic compositions based on skeletal remains and ichno taxonomic compositions based on footprints although the vast majority of the skeletal elements collected in the area belong to theropods the footprints suggest that the nemegt locality was dominated by herbivorous dinosaurs this suggests that the previously inferred tarbosaurus dominant taxonomic composition at the nemegt locality is a result of a preservational bias the size distribution of the newly studied footprints suggest that the nemegt hadrosaurs had an adult dominant and multigenerational population structure comparisons with dinosaur tracksites at the cantwell alaska usa and tremp spain formations show that the population structure and body sizes of the nemegt hadrosaurs were similar to those of the high latitude cantwell hadrosaurs it suggests that the nemegt area was more open and had higher plant productivity than the tremp area

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

turning ocean mixing upside down abstractit is generally understood that small scale mixing such as is caused by breaking internal waves drives upwelling of the densest ocean waters that sink to the ocean bottom at high latitudes however the observational evidence that the strong turbulent fluxes generated by small scale mixing in the stratified ocean interior are more vigorous close to the ocean bottom boundary than above implies that small scale mixing converts light waters into denser ones thus driving a net sinking of abyssal waters using a combination of theoretical ideas and numerical models it is argued that abyssal waters upwell along weakly stratified boundary layers where small scale mixing of density decreases to zero to satisfy the no density flux condition at the ocean bottom the abyssal ocean meridional overturning circulation is the small residual of a large net sinking of waters driven by small scale mixing in the stratified interior above the bottom boundary layers and a slightly larger net upwelling driven b

theropod trackways associated with a gallimimus foot skeleton from the nemegt formation mongolia abstract a theropod tracksite was discovered in the nemegt formation maastrichtian at bugiin tsav mongolia by the korea mongolia international dinosaur project in 2009 a total of 67 tracks 14 trackways one didactylous 13 tridactylous and 12 isolated tracks belonging to four ichnomorphotypes were mapped on a single horizon this indicates at least four different theropod trackmakers lived in the same area at the same time this tracksite consists of laminated gray mudstone yellowish brown siltstone couplets interbedded with eolian yellowish brown sandstone deposited on a distal floodplain abundant footprints with v shaped profiles cross section within in the vertical section indicate that dinosaurs repeatedly walked across in this area before the discovery of the tracks the site was illegally excavated by fossil poachers a widespread problem in the gobi desert during excavation of the track horizon a clenched inclined gallimimus foot skeleton was found in the mudstone extended down 20 cm below the track bearing sandstone layer the occurrence of tracks closely associated with body fossils is unusual and taphonomically intriguing it is possible that the foot skeleton represents an animal that died in its tracks however the depth of the foot in mud is probably too shallow for the animal to have been mired sedimentological and taphonomic evidence also suggests that the pes of gallimimus may have passed straight through the track bearing sandstone layer the inclined right pes indicates that the body lay on its left side on the substrate during decomposition in the mud all digits were flexed but the distal phalanges were stuck and anchored in the stiff lower mud consequently as more proximal phalanges were able to accommodate flexing they were pulled away and dislocated from the anchored distal phalanges subsequent trampling by dinosaurs in the track bearing sandstone would have further distorted the underlying foot

some preliminary results concerning deep northern boundary currents in the north pacific abstract fourteen month velocity records from five moorings along long 175 w in combination with ctd and nutrient data distinguish two pronounced quite steady deep zonal currents near the northern margin of the north pacific one flows westward at speeds of 1 3 cm s 1 along the slope of the aleutian island arc and appears to be the northern boundary current required by deep circulation theory the other flows eastward at about 1 2 cm s 1 just to the south above the aleutian trench and upper aleutian rise and carries water that is slightly lower in temperature and dissolved silica and slightly higher in salinity and dissolved oxygen than that to the north or south we believe that this eastward jet represents an extreme distortion of a level bottom interior flow pattern as forced by the meridional variation in bottom slope on the southern flank of the aleutian rise which imposes a varying effective beta on the system a simple model of this effect is discussed

is the south pacific helium 3 plume dynamically active it is suggested that the hydrothermal vents of the south pacific rise produce a beta governed circulation at mid depth and that perhaps the associated plume of excess3he lupton and craig 1 points westward because of the dynamics of this circulation rather than as a passive tracer

jiggling the tropical thermostat in the cretaceous hothouse modern open ocean sea surface temperatures rarely exceed 28 29 8c and the same has been thought to represent a rough maximum for past tropical climates however new isotopic estimates from the uppermost cenomanian in the tropical western north atlantic suggest that mixed layer temperatures reached 33 34 8 c 62 8c during the middle cretaceous hothouse uppermost cenomanian tropical sea surface temperatures may have been as much as 4 7 8c warmer than the highest modern mean annual temperatures such extreme conditions suggest that warm tropical oceans could have driven substantially intensified atmospheric heat transport near the cenomanian turonian boundary the tropical thermostat was set higher than today challenging the hypothesis of tropical climate stability

idealized solutions for the energy balance of the finescale internal wave field abstract recent fine and microstructure observations indicate enhanced finescale shear and strain in conjunction with bottom intensified turbulent dissipation above rough bathymetry in the brazil basin such observations implicate the bottom boundary as an energy source for the finescale internal wave field simple analytical and numerical solutions to an equation governing the spatial and temporal evolution of the finescale wave field are described here the governing equation implicitly treats the effects of wave breaking on the vertical propagation of internal waves through a flux representation of nonlinear transports associated with internal wave wave interactions these solutions identify the rate of dissipation of turbulent kinetic energy with downscale energy transports at high vertical wavenumber resulting in an estimate of dissipation versus depth the sensitivity of the turbulent dissipation depth profile to various environmental parameters is examined observed dissipation profiles and shear

a summertime rainy season in the arctic forests of the eocene the discovery of exceptionally well preserved fossil wood revealed that extensive forests existed north of the arctic circle during the eocene ca 45 55 ma subsequent paleobotanical studies led researchers to suggest eastern asia as a modern analog based on the distribution of nearest living relatives during the last decade proxy based reconstructions of mean annual paleoprecipitation productivity and relative humidity have led workers to characterize the climate of the arctic forests as similar to today9s temperate forests of the pacific northwest using a new model we reconstructed the seasonal timing of paleoprecipitation from high resolution intra ring carbon isotope measurements of fossil wood we showed that the eocene arctic forests experienced on average 3 1 times more precipitation during summer than winter entirely dissimilar to the pacific northwest where summer precipitation is only one half to one sixth of the winter precipitation this new result shows that although mean annual climate conditions may have been similar to the mean annual conditions the pacific northwest consideration of seasonality implies that the temperate forests of eastern asia represent the best overall modern analog for the eocene arctic forests

a nonconservative β spiral determination of the deep circulation in the eastern south pacific abstract the horizontal mean circulation and diapycnal flux divergence field in the south pacific between tahiti and the east pacific rise are obtained from a nonconservative spiral inverse method applied to high quality hydrographic data the diapycnal flux divergence term is found to be an essential part of the deep vorticity balance and proper resolution of this term is critical to the success of the spiral calculation the subthermocline circulation in this region of the south pacific consists of three vertical regimes between the thermocline and approximately 1800 2000 m a cyclonic circulation pattern exists a zone of minimum motion is found between 1800 and 2000 m below this zone northward flow along the rise and westward flow in the north indicate an anticyclonic gyre centered on 15 s that extends approximately 1000 2000 km to the west of the east pacific rise the deep vorticity balance associated with this flow system is primarily between meridional advection of planetary vorticity and

an estimate of absolute geostrophic velocity from the density field in the northeastern pacific ocean a pair of hydrographic sections 35 sup 0 n 155 sup 0 w were analyzed to compute absolute velocity by using a variation of the technique by stommel and schott 1977 absolute velocity is determined from an integrated form of the potential vorticity equation by a technique suggested by davis 1978 this study is the first application of this technique that allows a direct comparison between the uncertainty in estimating a smooth density field and the amount of imbalance in the system of model equations because the amount of incompatibility imbalance in the system of equations is far smaller than is allowed by the uncertainty in defining the smooth field the model equation is considered adequate for this set of data below 400 m the nearly constant zonal isopycnal slope indicates that potential vorticity is uniform on isopycnal surfaces since the method depends on resolving flow directions from the intersection of isopycnals and surfaces of constant potential vorticity the absolute velocity is indeterminate in this region the model equation does however constrain the structure of the meridional density field and requires a poleward shift in the latitude which successively deeper isopycnals reach their maximum depth the fact that this poleward translation can be predictedmore over several degrees of latitude suggests potential vorticity is uniform over a substantial portion of the north pacific subtropical gyre this poleward translation of the density field is an aspect of subtropical density fields in general and occurs in conjunction with a translation in the field of geopotential anomaly it is directly related to the curvature in the deep portion of the beta spiral less