a cenozoic record of the equatorial pacific carbonate compensation depth atmospheric carbon dioxide concentrations and climate are regulated on geological timescales by the balance between carbon input from volcanic and metamorphic outgassing and its removal by weathering feedbacks these feedbacks involve the erosion of silicate rocks and organic carbon bearing rocks the integrated effect of these processes is reflected in the calcium carbonate compensation depth which is the oceanic depth at which calcium carbonate is dissolved here we present a carbonate accumulation record that covers the past 53 million years from a depth transect in the equatorial pacific ocean the carbonate compensation depth tracks long term ocean cooling deepening from 3 0 3 5 kilometres during the early cenozoic approximately 55 million years ago to 4 6 kilometres at present consistent with an overall cenozoic increase in weathering we find large superimposed fluctuations in carbonate compensation depth during the middle and late eocene using earth system models we identify changes in weathering and the mode of organic carbon delivery as two key processes to explain these large scale eocene fluctuations of the carbonate compensation depth

the role of caco3 compensation in the glacial to interglacial atmospheric co2 change the only viable explanations put forth to date for the glacial to interglacial change in atmospheric co2 content suggested from measurements of the co2 content of gas extracted from ice cores involve changes in the ocean s nutrient cycles any nutrient change capable of creating the 80 atm changes in atmosphere co2 pressure suggested by the ice core results also creates significant change in the deep ocean s co3 content evidence from deep sea sediments suggests that these co3 changes are compensated on the time scale of a few thousand years by reductions or increases in amount of caco3 accumulating in deep sea sediments this compensation process has two important consequences first it significantly increases the magnitude of the co2 change per unit of nutrient forcing second it causes a delay in the response of the atmospheric co2 change while the first of these consequences is a boon to those seeking to explain the co2 change the second may prove to be a curse the ice core co2 record shows no evidence of a significant lag between the co2 response and the polar warming in any case it is important that we improve our knowledge of the magnitude and timing of the caco3 preservation events which mark the close of episodes of glaciation and of the dissolution events which mark the onset of these episodes

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

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

the presence of carbonic dominant volatiles during the crystallization of sulfide bearing mafic pegmatites in the north roby zone lac des iles complex ontario mafic pegmatites in the platinum group element pge mineralized roby zone lac des iles complex northwest ontario canada comprise dikes veins and irregular pods of coarse grained magnesiohornblende pyroxene and labradorite andesine with minor biotite apatite fe ti oxides and intercumulus quartz that grades into massive quartz or graphic quartz base metal sulfide vysotskite pd ni s intergrowth at their cores quartz apatite and magnesiohornblende host primary and secondary assemblages of one or two phase carbonic fluid co 2 up to 10 ch 4 minor h 2 o n 2 inclusions that contain ore metals ni cu pd bi te fe rare trails of late stage high salinity aqueous fluid inclusions are secondary in origin and therefore unrelated to the crystallization of the pegmatites assemblages of primary carbonic fluid inclusions show considerable variation in mode and temperature of homogenization reflecting large fluctuations in confining pressure at the time of quartz crystallization of as much as 1 kbar in single quartz crystals and 2 8 kbars all data independent thermobarometric methods constrain conditions for the following two stages of pegmatite formation and carbonic fluid entrapment 1 the crystallization of magnesiohornblende plagioclase intergrowth at t 650 to 850 c and p 1 to 3 kbars and 2 the crystallization of quartz at t 535 to 650 c and p 0 4 to 3 2 kbars setting the maximum depth of emplacement of the lac des iles complex north roby zone magma at 10 to 12 km the results indicate that aqueous dominant volatile phases were absent during the crystallization of pegmatitic gabbroic rocks at the lac des iles complex and that water poor carbonic fluid entrapment persisted to well below solidus conditions a role played by carbonic fluid as a potential transport medium for ligands involved in the precipitation and remobilization of the pge and base metals is strongly suggested and warrants further investigation

changes in sulfides and platinum group minerals with the degree of alteration in the roby twilight and high grade zones of the lac des iles complex ontario canada the lac des iles complex hosts pd deposits with unusually high pd pt and pd ir ratios these high ratios have been attributed to the introduction of pd by late magmatic hydrothermal fluids the presence of hydrous silicates and low temperature sulfide mineral assemblages has been advanced as evidence for fluid overprint this idea has been investigated by documenting the change in silicate sulfide and platinum group mineralogy and texture in samples from the deposit ranging from fresh gabbronorite to extensively altered chlorite actinolite schist in addition whole rock analysis combined with laser ablation analysis of the sulfides was used to determine which phase controlled each of the pge in fresh gabbronorite the sulfide assemblage is igneous pyrrhotite pentlandite chalcopyrite and pd is present mainly in pentlandite and kotulskite pdte inclusions associated with the sulfide minerals all other pge except pt are present in solid solution in pyrrhotite and pentlandite platinum is present as sperrylite ptas2 and montcheite ptte2 inclusions associated with the sulfide minerals these observations suggest that the pge in the fresh gabbronorite were all collected by magmatic sulfide liquid in the chlorite actinolite schist the sulfide assemblage is a low temperature assemblage consisting of chalcopyrite pyrite millerite a minor amount of palladium is present in millerite but most is present as bismuth rich kotulskite and pd arsenides both of which are associated with hydrous silicate all other pge except pt are hosted by pyrite a minor amount of pt is present in pyrite but most is found as sperrylite and montcheite associated with hydrous silicate minerals the pyrite could have formed by fe loss from pyrrhotite resulting in the pyrite inheriting os ir ru and rh and fe loss from pentlandite to form millerite resulting in the millerite inheriting some pd the pge concentrations of the whole rock show there is no direct correlation between the sulfide assemblage the degree of alteration of the silicate minerals and ore grade thus although fluids have clearly altered the sulfide silicate and platinum group mineralogy and their textures it is not clear that these fluids have changed the pge content of the rocks

abyssal circulation driven by near boundary mixing water mass transformations and interior stratification the emerging view of the abyssal circulation is that it is associated with bottom enhanced mixing which results in downwelling in the stratified ocean interior and upwelling in a bottom boundary layer along the insulating and sloping seafloor in the limit of slowly varying vertical stratification and topography however boundary layer theory predicts that these upslope and downslope flows largely compensate such that net water mass transformations along the slope are vanishingly small using a planetary geostrophic circulation model that resolves both the boundary layer dynamics and the large scale overturning in an idealized basin with bottom enhanced mixing along a midocean ridge we show that vertical variations in stratification become sufficiently large at equilibrium to reduce the degree of compensation along the midocean ridge flanks the resulting large net transformations are similar to estimates for the abyssal ocean and span the vertical extent of the ridge these results suggest that boundary flows generated by mixing play a crucial role in setting the global ocean stratification and overturning circulation requiring a revision of abyssal ocean theories

reconstruction of primary productivity from the barium contents in surface sediments of the south atlantic ocean abstract the aim of the present study is an evaluation of the applicability of biogenic barium as a proxy for productivity for this purpose 190 surface sediment samples from the south atlantic ocean were analysed for their barium and aluminium concentrations biogenic barium is estimated by subtracting the calculated terrigenous barium obtained from the terrigenous ba al ratio and the amount of al in the sample from the total ba content in the sample based on the accumulation rates of biogenic barium export production is estimated using three different algorithms proposed by paleoceanography 7 1992 163 global biogeochem cycles 9 1995 289 geomar report 38 1995 105 primary productivity was calculated from these different export productions and compared with measurements of recent primary productivity in the overlying surface waters only the primary productions calculated on the basis of the algorithm of paleoceanography 7 1992 163 yield productivity values comparable to those existing in ocean surface waters this study further reveals that it is not sufficient to use a constant generally applicable organic carbon biogenic barium ratio as is postulated by global biogeochem cycles 9 1995 289 this ratio has to be assessed regionally for the sediments of the cape basin in the eastern south atlantic ocean a new algorithm is developed which gives plausible primary productivities for the overlying surface waters

marked decline in atmospheric carbon dioxide concentrations during the paleogene the relation between the partial pressure of atmospheric carbon dioxide pco2 and paleogene climate is poorly resolved we used stable carbon isotopic values of di unsaturated alkenones extracted from deep sea cores to reconstruct pco2 from the middle eocene to the late oligocene approximately 45 to 25 million years ago our results demonstrate that pco2 ranged between 1000 to 1500 parts per million by volume in the middle to late eocene then decreased in several steps during the oligocene and reached modern levels by the latest oligocene the fall in pco2 likely allowed for a critical expansion of ice sheets on antarctica and promoted conditions that forced the onset of terrestrial c4 photosynthesis

significant southern ocean warming event in the late middle eocene a prominent middle eocene warming event is identified in southern ocean deep sea cores indicating that long term cooling through the middle and late eocene was not monotonic at sites on maud rise and the kerguelen plateau a distinct negative shift in 1 8 o values 1 0 is observed ca 41 5 ma this excursion is interpreted as primarily a temperature signal with a transient warming of 4 c over 600 k y affecting both surface and middle bathyal deep waters in the indian atlantic region of the southern ocean this isotopic event is designated as the middle eocene climatic optimum and is interpreted to represent a significant climatic reversal in the midst of middle to late eocene deep sea cooling the lack of a significant negative carbon isotope excursion as observed during the paleocene eocene thermal maximum and the gradual rate of high latitude warming suggest that this event was not triggered by methane hydrate dissociation rather a transient rise in pco 2 levels is suspected possibly as a result of metamorphic decarbonation in the himalayan orogen or increased ridge arc volcanism during the late middle eocene

organic carbon burial following the middle eocene climatic optimum in the central western tethys we present trace metal geochemistry and stable isotope records for the middle eocene alano di piave section ne italy deposited during magnetochron c18n in the marginal tethys ocean we identify a sim 500 kyr long carbon isotope perturbation event we infer to be the middle eocene climatic optimum meco confirming the northern hemisphere expression and global occurrence of meco interpreted peak climatic conditions are followed by the rapid deposition of two organic rich intervals le 3 toc and contemporaneous positive delta 13 c excursions these two intervals are associated with increases in the concentration of sulphur and redox sensitive trace metals and low concentrations of mn as well as coupled with the occurrence of pyrite together these changes imply low possibly dysoxic bottom water o 2 conditions promoting increased organic carbon burial we hypothesize that this rapid burial of organic carbon lowered global it p co 2 following the peak warming and returned the climate system to the general eocene cooling trend

os isotope chemostratigraphy applied to organic rich marine sediments from the eocene oligocene transition on the west african margin odp site 959 1 the known temporal relationship between the benthic foraminiferal 18o record and the marine os isotope record is used to reinterpret the absolute chronology and paleoceanographic context of an episode of organic carbon burial on the west african margin ocean drilling program odp site 959 although organic rich sediments require significant corrections for in situ decay of 187re to 187os these results demonstrate the utility of the marine os isotope record for chemostratigraphic correlation of organic rich sediments that are devoid of age diagnostic microfossils with pelagic carbonate sequences revision of the odp site 959 chronology shifts the age assignment of an interval of biosiliceous organic rich sediment deposition from the oligocene to the late eocene and earliest oligocene likely culminating with the first major glaciation of the oligocene oi1 we speculate that enhanced organic carbon burial over much of the west african margin may have contributed to drawdown of atmospheric carbon dioxide before and during the oi1 event and suggest that os isotope chemostratigraphy provides a valuable tool for further exploring this possibility

global carbon cycle perturbation across the eocene oligocene climate transition the eocene oligocene transition eot 34 ma marks a tipping point in the long term cenozoic greenhouse to icehouse climate transition paleorecords reveal stepwise rapid cooling and ice growth across the eot tightly coupled to a transient benthic 13c excursion and a major and permanent deepening of the carbonate compensation depth ccd based on biogeochemical box modeling merico et al 2008 suggested that a combination of 1 glacioeustatic sea level fall induced shelf basin carbonate burial fractionation and 2 shelf carbonate weathering can account for the carbon cycle perturbation but this finding has been questioned alternative proposed mechanisms include increased ocean ventilation decreased carbonate burial increased organic carbon burial increased silicate weathering and increased ocean calcium concentration here we use an improved version of the biogeochemical box model of merico et al 2008 to reevaluate these competing hypotheses and an additional mechanism the expansion of carbon capacitors such as permafrost and peatlands we find that changes in calcium concentration silicate weathering and carbonate or organic carbon burial each yield a response that is fundamentally at odds with the form and or sign of the paleorecords shelf basin carbonate burial fractionation ccd change plus shelf carbonate weathering sequestration of 12c enriched carbon into carbon capacitors and possibly increased ocean ventilation 13c excursion offers the best fit to the paleorecords further work is needed to understand why the eot carbon cycle perturbation is so unique when the forcing mechanisms hypothesized to be responsible cooling and ice growth are not peculiar to this event

unlocking the barite paleoproductivity proxy a new high throughput method for quantifying barite in marine sediments abstract the accumulation rate of barite baso4 in marine sediments is a powerful tracer of paleo export productivity due to the refractory nature of barite in sediments and its ability to record ecosystem wide productivity it has been used to reconstruct past export productivity and to infer the effects of ocean circulation and nutrient supply on ocean ecosystems however the difficulty in generating large datasets of reliable barite accumulation rates has limited the use of this proxy here we present a new method for quantifying barite in marine sediments that promises a dramatic increase in sample throughput while also improving recovery of barite in a wide variety of marine sediments this method relies on selective dissolution of barite using a chelating ligand that avoids liberating ba from silicate phases and it can therefore work reliably on small 250 mg sediment aliquots rigorous evaluation of the method reveals that it quantitatively extracts barite and is largely unaffected by other ba sources due to the relatively simple analytical requirements of this barite extraction method and the small sample amount needed it can also be used to rapidly generate paleoproductivity records both during and after coring expeditions altogether this new technique should expand the study of the marine biologic system in the past by dramatically increasing analytical efficiency and widening the range of questions that are accessible using barite accumulation rate as a paleoproductivity proxy

new evidence for subtropical warming during the late paleocene thermal maximum stable isotopes from deep sea drilling project site 527 walvis ridge the late paleocene thermal maximum lptm was a dramatic short term global warming event that occurred 55 ma warming of high latitude surface waters and global deep waters during the lptm has been well documented however current data suggest that subtropical and tropical sea surface temperatures ssts did not change during the event conventional paradigms of global climate change such as co2 induced greenhouse warming predict greater warming in the high latitudes than in the tropics or subtropics but nonetheless cannot account for the stable tropical subtropical ssts we measured the stable isotope values of well preserved late paleocene to early eocene planktonic foraminifera from south atlantic deep sea drilling project dsdp site 527 to evaluate the subtropical response to the climatic and environmental changes of the lptm planktonic foraminiferal 18o values at site 527 decrease by 0 94 from pre lptm to excursion values providing the first evidence for subtropical warming during the lptm we estimate that subtropical south atlantic ssts warmed by at least 1 4 c on the basis of possible changes in evaporation and precipitation the new evidence for subtropical sst warming supports a greenhouse mechanism for global warming involving elevated atmospheric co2 levels

platinum group minerals in the limoeiro ni cu pge sulfide deposit brazil the effect of magmatic and upper amphibolite to granulite metamorphic processes on pgm formation the limoeiro ni cu platinum group elements pge deposit is a recent discovery associated with an igneous tubular conduit system in northeastern brazil representative ores from the deposit have been used for platinum group minerals pgm identification and for pge in base metal sulfides bms quantification ninety eighty percent of the pgm in the massive sulfide ores is homogeneous pt ni bi bearing merenskyite pdte2 enclosed primarily by pyrrhotite suggesting that it is formed by exsolution from monosulfide solid solution mss merenskyite gradually but systematically becomes poorer in pt and ni with increasing fractionation which is interpreted to reflect a transition to a more evolved sulfide liquid that segregated in the eastern parts of the intrusion in massive sulfide ores merenskyite forms unusually large up to 5000 m2 euhedral grains commonly in contact with spherical silicate inclusions bms hosts 12 16 of the pd with the remainder hosted by pgm which is interpreted to indicate that merenskyite recrystallized from a pge bearing bismuthotelluride metamorphic melt formed during high grade metamorphism sperrylite ptas2 is the second most abundant pgm 18 of pgm in disseminated ore and in contrast to merenskyite occurs mainly as very small median of 25 m2 inclusions in high temperature silicates and oxides interpreted to have crystallized at high temperatures directly from sulfide blebs that formed and were transported within the limoeiro magma conduit

strong sh to love wave scattering off the southern california continental borderland seismic scattering is commonly observed and results from wave propagation in heterogeneous medium yet deterministic characterization of scatterers associated with lateral heterogeneities remains challenging in this study we analyze broadband waveforms recorded by the southern california seismic network and observe strongly scattered love waves following the arrival of teleseismic sh wave these scattered love waves travel approximately in the same azimuthal direction as the incident sh wave at a dominant period of 10 s but at an apparent velocity of 3 6 km s as compared to the 11 km s for the sh wave back projection suggests that this strong scattering is associated with pronounced bathymetric relief in the southern california continental borderland in particular the patton escarpment finite difference simulations using a simplified 2 d bathymetric and crustal model are able to predict the arrival times and amplitudes of major scatterers the modeling suggests a relatively low shear wave velocity in the continental borderland

warm ocean processes and carbon cycling in the eocene sea surface and subsurface temperatures over large parts of the ocean during the eocene epoch 55 5 33 7 ma exceeded modern values by several degrees which must have affected a number of oceanic processes here we focus on the effect of elevated water column temperatures on the efficiency of the biological pump particularly in relation to carbon and nutrient cycling we use stable isotope values from exceptionally well preserved planktonic foraminiferal calcite from tanzania and mexico to reconstruct vertical carbon isotope gradients in the upper water column exploiting the fact that individual species lived and calcified at different depths the oxygen isotope ratios of different species tests are used to estimate the temperature of calcification which we converted to absolute depths using eocene temperature profiles generated by general circulation models this approach along with potential pitfalls is illustrated using data from modern core top assemblages from the same area our results indicate that during the early and middle eocene carbon isotope gradients were steeper and larger through the upper thermocline than in the modern ocean this is consistent with a shallower average depth of organic matter remineralization and supports previously proposed hypotheses that invoke high metabolic rates in a warm eocene ocean leading to more efficient recycling of organic matter and reduced burial rates of organic carbon

seismic scattering near the earth s surface the seismic coda is usually thought to be composed of waves scattered from the heterogeneities in the earth three classes of scattering mechanisms have been recognized repeated specular reflection of primary waves in a uniformly layered structure volume scattering of primary waves from localized volume heterogeneities and scattering of primary waves from irregularities in an otherwise generally layered structure the presence of the earth s surface complicates the description of all these scattering phenomena whenever the scattering obstacles are near or at the surface in this paper i review work which demonstrates the effects of scattering near the earth s surface emphasizing three general areas of investigation scattering of body waves from an irregular free surface scattering of body waves in irregular layers and propagation of surface waves across irregular topography or in irregular wave guides most of the effects of importance have been recognized in model studies of idealized geometries observational evidence in support of the model studies exists but is often inferred few controlled experiments to measure scattering have been performed

comment on changes in sulfides and platinum group minerals with the degree of alteration in the roby twilight and high grade zones of the lac des iles complex ontario canada by mln djon and sj barnes i wish to raise three main issues arising out of a carefulreading of the paper by djon and barnes 2012 1 it employs a fundamentally flawed technique by usingthin sections polished blocks to measure the absoluteand relative abundances of base metal sulfide bms minerals and trace platinum group minerals pgms insilicate whole rocks resulting in errors in calculationsfor mass balance and pge deportment 2 it describes poor analytical methods for electron probemicro analysis epma of pgm and laser ablationinductively coupled plasma mass spectrometry la icp ms analyses of the bms resulting in errors inthe reported concentrations for some elements 3 it shows poor preparation of the manuscript omittingimportant details on which values for pge concentra tions were used in calculations for mass balance andpge deportment and why this makes for the inabilityof the results to be checked and evaluated critically byreaders it is also unfortunate that the authors do not acknowledgeany referees for their efforts which make it impossible forthe reader to judge whether a the referees were knowl edgeable in applied process mineralogy and epma la icp ms and b the authors implemented the obvious rec ommendations that would have been made by such experts because this journal is mainly devoted to the study ofmineral deposits some background is relevant to put theabove criticisms in context studies of pge mass balancesand their deportment in rocks is a well developed techniquein the discipline of applied process mineralogy similarly well established procedures have been developed in theanalytical geochemistry community for in situ analyses ofpges in sulfide minerals by la icp ms nonetheless bothapplied process mineralogy and la icp ms analyses ofminerals are relatively new areas of scientific endeavor formany mineral deposit geologists and academics perhapsexplaining some of the mistakes made applied process mineralogy only evolved internationallywith the first international council for applied mineralogy icam conference in 1981 having been developed in someof the major mining companies and some governmentresearch laboratories e g canmet canada csiro aus tralia and mintek south africa unfortunately there areveryfew universitieswherestudentscanbecomeproficientinappliedandprocessmineralogy mostexpertshavinglearntonthe job schouwstra and smit 2011 there are also very fewbooks devoted to the subject a rare one being by petruk 2000 most case studies being found in conference proceed ings e g canadian mineral processors icam and theminerals metals and material society tms aime ormore recently in the conference of metallurgists e g fordet al 2009 2011 and minerals engineering e g lotter2011 thus proper procedures for pge mass balances anddeportment are not well known outside the applied processmineralogy community secondly la icp ms of mineralswasdevelopedonly20yearsago fromthepioneeringworkofjackson et al 1992 and proper procedures for analyses ofbms has been only widely possible more recently

the late lutetian thermal maximum middle eocene first record of deep sea benthic foraminiferal response abstract understanding the role of deep sea biota across global warming events in the past is key to unravel climate system dynamics during periods of increased pco2 levels here we present the first record of the benthic foraminiferal response to a middle eocene transient warming event named the late lutetian thermal maximum lltm 41 52 ma at odp site 702 in the south atlantic ocean changes in benthic foraminiferal assemblages such as a decrease in absolute abundance of certain taxa e g bulimina elongata are correlated with the negative carbon isotope excursion corresponding to the lltm event paleoecological interpretations of the assemblage turnover suggest changes in the type of organic matter arriving to the seafloor during the lltm benthic foraminifera and coarse fraction accumulation rates bfars and cfars decreased across the warming period of the lltm coeval with the negative 18o excursion associated with 2 c deep sea warming we suggest that increased temperatures led to enhanced metabolic rates in heterotroph organisms such as foraminifera triggering a population decline in food limiting environments such as the meso oligotrophic setting of site 702 a similar ecological response and a decrease in export productivity as inferred from decreased cfars and bfars have also been reported across the middle eocene climatic optimum at this site and support the hypothesis that metabolic rates accelerated during warming events in spite of their different magnitude and duration

temperature dependent remineralization and carbon cycling in the warm eocene oceans metabolic rates in heterotrophic bacteria are more sensitive to temperature than rates of primary production e g lopez urrutia et al 2006 regaudie de gioux and duarte 2012 consequently faster bacterial respiration rates in a warmer ocean may result in more efficient remineralization of sinking organic matter higher in the water column with implications for carbon and nutrient cycling during warm climate states this is supported by a series of reconstructed 13cdic depth profiles based on well preserved planktonic foraminifera assemblages from tanzania from the warm eocene epoch 55 5 33 7 ma when global surface and deep ocean temperatures exceeded those of the modern day john et al 2013 these results indicate relatively sharp 13cdic gradients in the upper water column which supports the hypothesis that high metabolic rates in warm eocene oceans led to more efficient recycling of organic matter and reduced burial rates of organic carbon olivarez lyle and lyle 2006 shallower remineralization depths would also cause an upward displacement and intensification of the oxygen minimum zone which is consistent with evidence for a pelagic ecosystem that was focused in a narrow depth range near the surface during the warm early and middle eocene here we use the earth system model cgenie that incorporates a new temperature dependence of remineralization rates to illustrate the potential effects of temperature on particulate organic carbon fluxes and hence vertical 13cdic gradients modeled 13cdic vertical profiles off the coast of tanzania for the eocene agree well with the reconstructed 13cdic profiles supporting our interpretations based on temperature dependent remineralization

scattering of teleseismic p waves by the japan trench a significant effect of reverberation in the seawater column abstract we detected a scattered wave train in data from the high sensitivity seismograph network in japan hi net following the arrival of the near vertically incident p wave generated by the 2009 earthquake mw 7 8 off the south island of new zealand the scattered wave train represented predominantly vertical ground motion at a period of 20 to 50 s and with an apparent velocity of 3 5 km s it propagated cylindrically westward through the kanto area of central japan array analysis showed that the scattered wave train developed beneath the pacific ocean near the boso triple junction southeast of the kanto area a 3d finite difference simulation of seismic wave propagation using a high resolution model incorporating subsurface structure topography and bathymetry revealed that the strong scattered waves that were generated along the japan trench and propagated normal to the trench axis represented multiple reverberations of seismic waves between the seafloor and the pacific plate boundary in addition strong reverberation of acoustic waves in the seawater column above the boso triple junction causes elongated scattered waves which reasonably explains our observations

dynamics of fossil fuel co2 neutralization by marine caco3 a detailed model of the ocean circulation and carbon cycle was coupled to a mechanistic model of caco3 diagenesis in deep sea sediments to simulate the millennium scale response of the oceans to future fossil fuel co2 emissions to the atmosphere and deep sea simulations of deep sea injection of co2 show that caco3 dissolution is sensitive to passage of high co2 waters through the atlantic ocean but caco3 dissolution has a negligible impact on atmospheric pco2 or the atmospheric stabilization co2 emission in the coming centuries the ultimate fate of the fossil fuel co2 will be to react with caco3 on the seafloor and on land an initial caco3 dissolution spike reverses the net sedimentation rate in the ocean until it is attenuated by an enhanced vertical gradient of alkalinity after about 1000 years the magnitude of the initial spike is sensitive to assumptions about the kinetics for caco3 dissolution but subsequent behavior appears to be less model dependent neutralization by seafloor caco3 occurs on a timescale of 5 6 kyr and is limited to at most 60 70 of the fossil fuel release even if the fossil fuel release is smaller than the seafloor erodible inventory of caco3 additional neutralization by terrestrial caco3 restores a balance between caco3 weathering and seafloor accumulation on a timescale of 8 5 kyr while the deficit of seafloor caco3 the lysocline is replenished with an e folding timescale of approximately 18 kyr the final equilibrium with caco3 leaves 7 8 of the fossil fuel co2 remaining in the atmosphere to be neutralized by the silicate rock cycle on a time frame of hundreds of thousands of years

higher temperatures and lower oceanic pco2 a climate enigma at the end of the paleocene epoch one of the largest and most abrupt climatic warming events documented in the geologic record occurred at the end of the paleocene epoch oceanic deep waters warmed to 10 c and high latitude surface waters warmed from 10 c to 20 c within several thousand years this coincided with weakened atmospheric circulation and the extinction of 50 of deep sea benthic foraminiferal species it has been suggested that this warm excursion was forced by higher atmospheric pco2 and greenhouse effects caused by a pulse of hydrothermal activity and or volcanism stable isotopic evidence is presented from two widely separated locations that suggest this warming was associated with a drop in oceanic pco2 rather than an increase oceanic pco2 change across this event was estimated using a model of 13c fractionation in photosynthate organic carbon versus co2aq with solubility constants for co2 and stable isotopic paleotemperature estimates to derive a well preserved record for surface ocean 13c change the organic carbon bound within the calcite lattice of well preserved planktonic foraminifera was extracted for isotopic analysis with allowance for uncertainty in the isotopic differences between phytoplankton and foraminiferal organic matter the initial results indicate a drop in surface ocean pco2 at high and low latitudes from 600 700 parts per million ppm to 200 ppm lower pco2 persisted for at least 10 000 years the duration of the pco2 excursion was long enough for the ocean and atmosphere to have reached a new steady state condition there is no evidence of increased organic carbon burial in the deep sea during this period two alternative explanations are presented to account for such a rapid drop in oceanic pco2 one involves reduced upwelling induced by diminished wind stress as atmospheric circulation weakened in response to climate warming this would have reduced the rate of metabolic co2 recycling into the surface ocean it will be necessary to obtain data from regions outside potential upwelling zones in order to evaluate this the second involves a readjustment of carbonate equilibria in the ocean to higher co3 in the surface ocean particularly at high latitudes where surface waters warmed to approximately 20 c such a shift in carbonate equilibria would have lowered the ocean s capacity to take in co2 if the initial results presented here do accurately reflect a change in the global ocean co2aq the paleocene eocene boundary event may provide clues about the ocean s physical and biological response to rapid large scale perturbations in atmospheric pco2 and to global warming

the global ocean flux of particulate organic carbon areal distribution and magnitude the magnitude and distribution of the particulate organic carbon poc rain rate to the seafloor in the atlantic pacific and indian ocean basins between 61 n and 61 s has been estimated from benthic oxygen flux estimates for water depths 1000 m only the calculation utilizes the extensive data sets of sedimentary organic carbon caco3 and accumulation rate to extrapolate between individual benthic flux measurement sites using an empirically derived correlation between the seafloor oxygen flux and these parameters the poc flux through the 1000 m depth horizon was then estimated from published correlations between sediment trap determined fluxes and water depth total oxygen utilization in the deep ocean is estimated to be 1 2 1014 mol o2 yr 1 a value that agrees well with previous estimates which were based on surface water primary productivity sediment trap and depth relationships and with deep water respiration rates estimated from apparant oxygen utilization aou 14c relationships on the basis of the derived global ocean flux distribution it is concluded that 1 dissolved organic carbon doc inputs are not required to account for estimated deep water respiration rates 2 the majority of the poc input to the deep ocean occurs within 30 of the equator 3 the proportion of primary production that reaches the deep sea does not vary greatly with latitude 4 gyre and continental margin regions contribute roughly equally to the deep poc flux with a relatively minor contribution from the equatorial divergence region 5 of the estimated 7 2 1013 mol c yr 1 of poc that sinks below the 1000 m depth horizon 45 3 3 1013 mol c yr 1 reaches the seafloor where it is oxidized 6 when normalized to basin area average deep flux rates in the atlantic and pacific are similar while highest rates are observed in the indian ocean and 7 the results can be fully reconciled only if the benthic flux of doc is significantly less than the benthic o2 flux

dissolution of calcite in deep sea sediments ph and o2 microelectrode results abstract we present microelectrode profiles of oxygen ph and porosity measured at in situ depth across the sediment water interface from stations above and below the calcite saturation horizon in the equatorial atlantic resistivity electrode data indicate that the diffusion coefficient for solutes is attenuated by nearly a factor of two within the top centimeter of the sediment lattice oxygen and porosity data are used to estimate that the organic carbon respiration rate of the sediment is 10 15 mol cm 2 yr 1 in these locations comparison of the ph data with numerical model results reveals that sedimentary calcite dissolves in response to respiration in the top few centimeters of sediment even above the saturation horizon we calculate that the effective in situ dissolution rate constant for calcite required to explain these data is the neighborhood of 10 100 d 1 although more data are needed to confirm this result it appears to be at least an order of magnitude less than the rate observed in laboratory stirred reactor experiments

biogenic sedimentation in the equatorial pacific carbon cycling and paleoproduction 12 24 ma 1 the equatorial pacific is an important part of the global carbon cycle and has been affected by climate change through the cenozoic 65 ma to present we present a miocene 12 24 ma biogenic sediment record from deep sea drilling project dsdp site 574 and show that a caco3 minimum at 17 ma was caused by elevated caco3 dissolution when pacific plate motion carried site 574 under the equator at about 16 2 ma there is a minor increase in biogenic deposition associated with passing under the equatorial upwelling zone the burial rates of the primary productivity proxies biogenic silica bio sio2 and biogenic barium bio ba increase but biogenic caco3 decreases the carbonate minimum is at 17 ma coincident with the beginning of the miocene climate optimum the transient lasts from 18 to 15 ma bio sio2 and bio ba are positively correlated and increase as the equator was approached corg is poorly preserved and is strongly affected by changing carbonate burial terrestrial 232th deposition a proxy for aeolian dust increases only after the site 574 equator crossing since surface production of bio sio2 bio ba and caco3 correlate in the modern equatorial pacific the decreased caco3 burial rate during the site 574 equator crossing is driven by elevated caco3 dissolution representing elevated ocean carbon storage and elevated atmospheric co2 the length of the 17 ma caco3 dissolution transient requires interaction with a slow part of the carbon cycle perhaps elevated mantle degassing associated with the early stages of columbia river basalt emplacement

climatically forced organic carbon burial in equatorial atlantic and pacific oceans over the past ten years sedimentary geochemists have noted that climate changes associated with pleistocene glaciations have had a pronounced effect on the rate of organic carbon burial found in the tropical oceans1 4 in particular two to five times higher organic carbon accumulation rates have been observed for the 18 kyr bp glacial maximum than for the holocene in several short sediment cores from both oceans see fig 1 here i present 300 kyr time series for organic carbon mass accumulation rate from four sediment cores two each from the equatorial pacific and atlantic and show that orbital forcing of global climate has strongly affected the rate of organic carbon burial in the equatorial oceans

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

high resolution record of export production in the eastern equatorial pacific across the eocene oligocene transition and relationships to global climatic records 1 understanding changes in export production through time provides insight into the response of the biological pump to global climate change particularly during periods of rapid climate change in this study we consider what role changes in export production may have had on carbon sequestration and how this may have contributed to the onset of the eocene oligocene transition eot in addition we consider if these export production variations are dominantly controlled by orbitally driven climate variability to accomplish these objectives we report changes in export production in the eastern equatorial pacific eep from site u1333 across the eot reconstructed from a high resolution record of marine barite accumulation rates bar bar fluctuations suggest synchronous declines in export production associated with the two step increases in oxygen isotopes that define the transition the reduction in productivity across the eot suggests that the biological pump did not contribute to carbon sequestration and the cooling over this transition we also report a previously undocumented peak in eep export productivity before the eot onset this peak is consistent with export production proxies from the southern ocean potentially implying a global driver for this precursor event we propose that this enhanced export production and the associated carbon sequestration in the late eocene may have contributed to the pco2 drawdown at the onset of antarctic glaciation

biogenic sediment regimes in the neogene equatorial pacific iodp site u1338 burial production and diatom community abstract the equatorial pacific experienced significant changes in productivity and microfossil assemblage since 16 million years ago ma we compiled a record of those changes from iodp site u1338 using a reconnaissance of diatom assemblages and high resolution xrf scan chemical profiles 1 2 kyr spacing productivity and caco3 dissolution intervals are defined by sediment component ratios in particular opal clay opal baso4 and caco3 baso4 or caco3 clay there are large abrupt changes in export production in the miocene especially compared to the pleistocene and pliocene and average levels of export production are higher throughout the miocene compared to the pliocene and pleistocene using diatom assemblages and bulk sediment composition the u1338 sediment record is divided into several distinct deposition regimes 1 a middle miocene regime 13 2 ma marked by low diatom numbers and a few short lived productivity intervals 2 a carbonate crash regime distinguished by an older substage 13 2 10 2 ma with relatively high abundances of productivity related diatoms and common productivity related depositional intervals interspersed with caco3 dissolution intervals and a younger carbonate crash substage 10 2 8 0 ma with weaker brief productivity intervals high caco3 dissolution and moderately high numbers of upwelling diatom species 3 the biogenic bloom regime 8 0 4 5 ma marked by extended periods of high opal and caco3 deposition with a maximum between 7 0 and 6 4 ma and 4 a pliocene modern regime 4 5 0 ma with lower productivity and high cyclic caco3 dissolution changes in production and dissolution result from reorganizations of nutrient supply to the equatorial pacific not by higher wind driven upwelling we propose that nutrients were more accessible in the miocene because of a combination of factors including higher organic matter degradation in the upper water column and deep intermediate nutrient pathways that efficiently recycled nutrients to upwelling zones closure of the central american seaway was likely a prime cause of the biogenic bloom

chemical accumulation variations under the peru current during the past 130 000 years the titanium to aluminum ratio in core v19 29 is correlated with aluminosilicate accumulation rates this correlation may be due to pleistocene eolian transport fluctuations which alter the mean grain size of sedimented eolian material the relation between aluminum accumulation rate and ti al established from accumulation rates integrated over 11 000 50 000 year intervals can be inverted to compute a high resolution record of aluminosilicate and calcium carbonate accumulation rates over the past 130 000 years carbonate accumulation rates are closely related to the oxygen isotope record in the core with a phase lag and damping constant that is compatible with the response time shown to be only 6000 years of calcium carbonate in the ocean carbonate sedimentation at this site responds to several processes independently correlated with climatic change the relative importance of these processes for carbonate sedimentation at this site can be constrained by the record in this core and other lines of evidence 15 of the increased carbonate deposition at this site during glacial periods may be due to diminished nadw north atlantic deep water formation 10 is due to carbonate productivity decreases in the north atlantic 25 may be due to a diminished shallow sea carbonate sink and the residual 50 must be due to a local productivity increase these assignments are consistent with observations on carbonate paleoceanography in the north atlantic aluminosilicate accumulation rate variations correlate with the record of eolian quartz deposition near northwest africa and in a general way with the climatic record but in detail the record differs substantially from the oxygen isotope record and may provide independent evidence on the nature of climate dynamics

upper mantle structures beneath usarray derived from waveform complexity tomographic imaging of the crust and upper mantle beneath the western united states has greatly improved with the addition of usarray data these models display many detailed images of both fast and slow blobs penetrating into the transition zone to study such features we apply a newly developed technique called multipath detector analysis to the sh waveform data the method simulates each observed body waveform by performing a decomposition by s t c s t 9lr 2 where s t is the synthetics for a reference model time separation 9lr and amplitude ratio c are needed to obtain a high cross correlation between a simulated waveform and data the travel time of the composite waveform relative to the reference model synthetics is defined as t a simulated annealing algorithm is used to determine the parameters lr and c we also record the amplitude ratio amp between the synthetics for the reference model relative to the data generally large lr values are associated with low amp s whereas the conventional tomography yields a travel time correction t our analysis yields an extra parameter lr which describes the waveform complexity with the array we can construct a mapping of the gradient of lr with complexity patterns a horizontal structure introduces waveform complexity along the distance profile in plane multipathing an azimuthally orientation lr pattern indicates a vertical structure with out of plane multipathing using such maps generated from artificial data we can easily recognize features produced by dipping fast structures and slow structures dss many of these features display organized waveform complexity that are distinctly directional indicative of dipping sharp edges here we process the array data for events arriving from various azimuths and construct maps of multipathing patterns the similarity between tomographic features and complexity maps is striking when features are dipping such as the slab structures beneath the cascade range and nevada strong complexity is observed from southeastern events arriving along these ray paths with split pulses separated up to 6 s for both this requires extended slab segments to at least 600 300 km with a 4 8 per cent velocity jump along the edges one of the most dramatic set of dss observations is associated with a slow northwest dipping conduit beneath yellowstone that extends into the transition zone a number of forward modelling experiments are included for the strongest patterns formed by sharpening present tomographic images

new mineralogical and isotopic constraints on main zone hosted pge mineralisation at moorddrift northern bushveld complex the northern limb of the bushveld complex south africa contains a number of occurrences of platinum group element pge mineralisation within main zone rocks whereas the rest of the complex has pge depleted main zone units on the farm moorddrift cu ni pge sulphide mineralisation is hosted within the upper main zone in a layered package of gabbronorites mottled anorthosites and thin pyroxenites our observations indicate that a 10 m thick reef style package of mineralisation has been extensively disturbed forming a mega breccia which in some localities may distribute mineralised rocks over intersections of over 300 m the sulphides are made up of pyrrhotite pentlandite and chalcopyrite heavily altered around their margins and overprinted by secondary pyrite platinum group mineral assemblages typical of primary magmatic deposits with pt and pd tellurides and sperrylite are present in the reef style package whereas there is a decrease in tellurides and an increase in antimonides in the disturbed package interpreted to be related to hydrothermal recrystallization during veining and brecciation sulphur isotopes show that all sulphides within the mineralised package on moorddrift have a crustal signature consistent with local country rock sediments of the transvaal supergroup we interpret the mineralisation at moorddrift as a primary sulphide reef likely produced as a result of the mixing of crustally contaminated magmas in the upper main zone which has been locally disrupted post crystallisation at present there are no firm links between moorddrift and the other known pge occurrences in the main zone at the aurora and waterberg projects although the stratigraphic position of all may be similar and thus intriguing nonetheless they do demonstrate that the main zone of the northern limb of the bushveld complex unlike the eastern and western limbs can be considered a fertile unit for potential pge mineralisation

production and accumulation of calcium carbonate in the ocean budget of a nonsteady state present day production of caco3 in tne world ocean is calculated to be about 5 billion tons bt per year of which about 3 bt accumulate in sediments the other 40 is dissolved nearly half of the carbonate sediment accumulates on reefs banks and tropical shelves and consists largely of metastable aragonite and magnesian calcite deep sea carbonates predominantly calcitic coccoliths and planktonic foraminifera have orders of magnitude lower productivity and accumulation rates than shallow water carbonates but they cover orders of magnitude larger basin area twice as much calcium is removed from the oceans by present day carbonate accumulation as is estimated to be brought in by rivers and hydrothermal activity 1 6 bt suggesting that outputs have been overestimated or inputs underestimated that one or more other inputs have not been identified and or that the oceans are not presently in steady state one missing calcium source might be groundwater although its present day input is probably much smaller than that of rivers if as seems likely caco3 accumulation presently exceeds terrestial and hydrothermal input this imbalance presumably is offset by decreased accumulation and increased input during lowered sea level shallow water accumulation decreases by an order of magnitude with a 100 m drop in sea level while groundwater influx increases because of heightened piezometric head and the diagenesis of metastable aragonite and magnesian calcite from subaerially exposed shallow water carbonates

eocene biogenic silica accumulation rates at the pacific equatorial divergence zone 2 the eocene biosiliceous oozes of the tropical pacific are an easily recognizable sediment type having a reddish brown color and sugary texture these sediments are dominated by radiolarian tests with traces of terrigenous debris hydrothermal oxides a few diatoms and little if any carbonate the paucity of carbonate is a result of the very shallow pacific calcite compensation depth ccd of the eocene 3300 m rea and lyle 2005 and references therein the dominance of radiolarian tests over those of diatoms is an enigma in that diatoms usually dominate siliceous rich sediments of the oligocene and neogene the opal rich character of these eocene sediments is commonly associated with the development of cherts within the sections 3 these unusual characteristics of eocene radiolarian oozes have prompted some authors to puzzle over how so much silica could have been delivered to the sea floor during

climate model sensitivity to atmospheric co2 levels in the early middle paleogene this study examines the sensitivity of the slab ocean version of the national center for atmospheric research climate system model with revised eocene geography orography and vegetation to changing carbon dioxide co2 levels we compare model results with temperature proxies from the geologic record for the early middle paleogene we ran three modeling experiments with co2 levels at 500 1000 and 2000 ppm and all with atmospheric methane levels of 3 5 ppm surface temperatures in the two higher co2 scenarios are warmer than those of the 500 ppm scenario the largest warming with increasing co2 occurred in the high latitudes particularly in the northern hemisphere during the wintertime compared to the 500 ppm case arctic wintertime temperatures increased by 10 c for the 1000 ppm scenario and 20 c for the 2000 ppm scenario the 1000 and 2000 ppm scenarios produced mean annual and cold month mean temperatures in mid and high latitudes that are much more compatible with the climate interpretations from eocene flora especially for data from the southern hemisphere tropical sea surface temperatures ssts in the 2000 ppm scenario however are still 4 c higher than the warmest temperatures inferred from proxy data the better match between temperatures in the high co2 modeling scenario and high latitude climate interpretations is consistent with the idea that the co2 levels during the eocene were high at least 3 4 times the pre industrial value of 280 ppm but the discrepancies in the tropics suggest that sst estimates from proxies are too low or that the models lack some tropical cooling mechanism that was important at this time

modeling the calcite lysocline a numerical model of calcite dissolution in contact with sediment pore water is used to predict the depth and shape of the calcite lysocline in the deep sea model results are compared with lysocline data from 13 regions in the atlantic pacific and indian oceans the model lysocline shape is sensitive to the calcite dissolution rate constant the calcite organic carbon and refractory material rain rates and the rates of oxic versus anoxic organic carbon degradation in the sediment the model is able to reproduce the observed lysocline within the constraints of the sediment trap and calcite accumulation data using a calcite dissolution rate constant of 30 100 d 1 a molar ratio of organic carbon to calcite rain rates of 0 5 1 0 and an initial caco3 fraction of 90 excluding organic carbon this rate constant is consistent with microelectrode results presented by archer et al 1989 the model predicts that 30 50 of the calcite rain to the sea floor at the saturation horizon dissolves in response to organic carbon respiration consistent with previous modeling studies the range in the best fit value of the organic inorganic carbon rain rates arises from model sensitivity to uncertainty in the rate of anoxic carbon degradation in the sediment and in the rain rate of refractory material rather than from scatter in the data lysocline data from the western equatorial atlantic are anomalous to the rest of the data this anomaly may be explained by high rates of refractory material sedimentation from the amazon river

in situ measurements of calcium carbonate dissolution rates in deep sea sediments benthic fluxes of alkalinity carbon dioxide and oxygen have been measured using an in situ incubation chamber at three sites manop sites c and s and pacflux site sc in the central equatorial north pacific at two carbonate rich sites c and sc a budget for oxygen alkalinity and tco2 fluxes indicate a net caco3 dissolution rate of approximately 0 4 mmol m 2 day 1 this rate is only 20 of previous estimates but is consistent with a dissolution rate constant predicted from laboratory experiments with deep sea sediments and derived from in situ flux measurements in sediments of the southern california borderland organic matter oxidation in the sediment column provides the acid for 60 100 of the calcium carbonate dissolution occurring at these sites with the remainder derived from undersaturated bottom water at a low carbonate site s no carbonate dissolution in the sediment or on the sea floor is apparent although sediment traps indicate a rain of caco3 through 3400 m the rates of remineralization relative to resuspension or erosion at this site must differ for organic carbon and calcium carbonate so that carbonate grains reaching the sea floor are physically removed by erosion or resuspension before they dissolve while organic carbon is largely oxidized before it can be physically removed

anomalous surface waves associated with deep earthquakes generated at an ocean ridge summary broad band seismograms observed at regional distances from deep earthquakes display large amplitude rayleigh and love waves with a predominant period of about 20 s although deep earthquakes in laterally homogeneous structures do not generate such surface waves since the propagation direction of the surface waves inferred from particle motion is approximately radial and the group velocity of the surface waves observed at each station is similar it can be assumed that the surface waves have travelled close to the great circle paths back projection allows us to determine the region in which these surface waves are generated manyof the zones from which the surface waves appear to originate are located close to the norfolk ridge where crustal structure has strong lateral heterogeneity this suggests that the surface waves are generated by the interaction of body waves from the deep earthquakes with this strongly heterogeneous crustal structure in order to investigate the eiect of such heterogeneity in crustal structure on seismic wave elds we have modelled the p sv wave eld using a pseudospectral method the results show that surface waves such as those observed can be generated by ridge structures and indicate that sedimentary layer thickness plays a very important role we suggest that such unexpected surface waves from deep earthquakes may prove useful for delineating heterogeneity in shallow structure

radiolarian stratigraphy near the eocene oligocene boundary three sites from the equatorial pacific odp 1218 iodp u1333 and u1334 are judged to have a complete stratigraphic sequence across the eocene oligocene boundary the sections of all three sites from 40 ma to 30 ma have been sampled and the samples merged into a single composite section with an average sample spacing 20 kyr a total of 76 radiolarian species species groups and specific variant forms provide a detailed radiolarian stratigraphy across this climatically important boundary altogether 47 eocene radiolarian species had their last appearance between 40 ma and the end of the final step of the eocene oligocene climate transition many of them in discreet episodes of extinction that grew in magnitude as the transition was approached first appearance datums appear to cluster at the base of the cool down from the middle eocene climate optimum and near the base of the oligocene following a maximum in radiolarian last appearances and coincident with relatively abundant diatoms there appears to be little relationship between paleoproductivity as measured by barite accumulation rates and both first and last appearances of radiolarians diatoms are not common in the eocene and their blossoming in the oligocene is preceded by the major episodes of radiolarian extinctions in the oligocene radiolarian extinctions appear to be associated with low to moderate diatom abundance whereas species first appearances seem to be associated with moderate to high diatom abundance neither paleoproductivity nor a competition for the dissolved silica a resource necessary for diatom frustule and radiolarian test construction appears to control the episodic extinction of radiolarians in the eocene or the more dispersed loss of species in the oligocene

global cenozoic paleobathymetry with a focus on the northern hemisphere oceanic gateways abstract the evolution of the northern hemisphere oceanic gateways has facilitated ocean circulation changes and may have influenced climatic variations in the cenozoic time 66 ma 0 ma however the timing of these oceanic gateway events is poorly constrained and is often neglected in global paleobathymetric reconstructions we have therefore re evaluated the evolution of the northern hemisphere oceanic gateways i e the fram strait greenland scotland ridge the central american seaway and the tethys seaway and embedded their tectonic histories in a new global paleobathymetry and topography model for the cenozoic time our new paleobathymetry model incorporates northeast atlantic paleobathymetric variations due to iceland mantle plume activity updated regional plate kinematics and models for the oceanic lithospheric age sediment thickness and reconstructed oceanic plateaus and microcontinents we also provide a global paleotopography model based on new and previously published regional models in particular the new model documents important bathymetric changes in the northeast atlantic and in the tethys seaway at eocene oligocene transition 34 ma the time of the first glaciations of antarctica believed to be triggered by the opening of the southern ocean gateways i e the drake passage and the tasman gateway and subsequent antarctic circumpolar current initiation our new model can be used to test whether the northern hemisphere gateways could have also played an important role modulating ocean circulation and climate at that time in addition we provide a set of realistic global bathymetric and topographic reconstructions for the cenozoic time at one million year interval for further use in paleo ocean circulation and climate models

scattering of teleseismic body waves by the lateral crustal heterogeneity at the pacific trench of mexico we examine the scattered field generated at the pacific trench of mexico upon the incidence of teleseismic body waves and the waveguide properties associated with the structure of the subduction zone in this study we analyze seismic records from a portable array perpendicular to the trench that show a distinctive phase with a phase velocity of graphic 1 following body wave phases this signal is better observed following phases with high incident angles such as ps sp and ss arriving from the ocean side of the trench and for events at teleseismic distances with magnitudes larger than m w 7 0 although weak scattered signals were detected for events down to m w 6 2 and for direct p and s phases we found that the lateral transition between the dipping slab and continental crust with an inclined boundary formed by the subducting slab at the trench generates a strong discontinuity that scatters seismic waves generating a secondary field with amplitude comparable to the incident wave this phase appears for incident body wave arrivals with characteristic wavelength comparable to the thickness of the continental crust analysis of the observed scattered field shows that the trapped waves are vertically polarized surface waves numerical modeling suggests that the impedance contrast at the trench and the geometry of the subducting slab form a waveguide like structure that efficiently generates and transmits trapped seismic waves along the continental margin 1 embed inline graphic 1 gif

a data driven model of the global calcite lysocline gridded maps of sediment calcium carbonate calcite concentration and overlying water saturation state archer 1996 are combined with maps of benthic oxygen fluxes and sediment accumulation rates from jahnke 1996 and cweink 1986 to drive a diagenetic model of calcium carbonate preservation in deep sea sediments the only model input for which we cannot draw a detailed map is the rain rate of calcite to the seafloor so i use the model to calculate the calcite rain rate required to simulate the observed distribution of calcite concentration on the seafloor the predictive power of the model can be checked by searching for input parameters to which the model is sensitive and comparing the model requirements with independent data the model is sensitive to the ratio of organic carbon to calcite rain rates the rain ratio and within the constraint of pelagic sediment trap rain ratio data is unable to reproduce the calcite field without respiratory dissolution the promotion of calcium carbonate dissolution by the oxic degradation of organic carbon however relative to variability in sediment trap data the required model rain ratio is insensitive to the extent of anoxic respiration the stoichiometric ratio of o c during respiration the bioturbation rate the dissolution rate constant the effect of borate chemistry and small offsets in the saturation state for caco3 the model is sensitive to the accumulation rate of non caco3 material and predicts an atlantic pacific difference in non caco3 rain rate which is consistent with observations the model predicts that the dissolution flux of caco3 from sediments is 25 40 1012 mol yr 1 roughly half of the total deep sea caco3 dissolution rate estimated from the water column alkalinity distribution broecker and peng 1987 archer and maier reimer 1994 wollast 1994 the model also predicts that only 20 30 of the flux of caco3 to the seafloor globally escapes dissolution

eocene oligocene ocean de acidification linked to antarctic glaciation by sea level fall one of the most dramatic perturbations to the earth system during the past 100 million years was the rapid onset of antarctic glaciation near the eocene oligocene boundary some 34 million years ago this climate transition was accompanied by a deepening of the calcite compensation depth the ocean depth at which the rate of calcium carbonate input from surface waters equals the rate of dissolution but the mechanism linking glaciation to the deepening of calcite compensation depth remains unclear merico et al use a global biogeochemical box model to test competing hypotheses put forward to explain the eocene oligocene transition they find that only shelf to deep sea carbonate partitioning can explain the observed changes in both carbon isotope composition and calcium carbonate accumulation at the sea floor this work sheds new light on the mechanisms linking glaciation and ocean acidity change during this important climate transition a global biogeochemical box model is used to test competing hypotheses put forward to explain the eocene oligocene transition it is found that only shelf to deep sea carbonate partitioning is capable of explaining the observed changes in both carbon isotope composition and calcium carbonate accumulation at the sea floor this work sheds new light on the mechanisms linking glaciation and ocean acidity change across the climate transition of the cenozoic one of the most dramatic perturbations to the earth system during the past 100 million years was the rapid onset of antarctic glaciation near the eocene oligocene epoch boundary1 2 3 34 million years ago this climate transition was accompanied3 by a deepening of the calcite compensation depth the ocean depth at which the rate of calcium carbonate input from surface waters equals the rate of dissolution changes in the global carbon cycle4 rather than changes in continental configuration5 have recently been proposed as the most likely root cause of antarctic glaciation but the mechanism linking glaciation to the deepening of calcite compensation depth remains unclear here we use a global biogeochemical box model to test competing hypotheses put forward to explain the eocene oligocene transition we find that of the candidate hypotheses only shelf to deep sea carbonate partitioning is capable of explaining the observed changes in both carbon isotope composition and calcium carbonate accumulation at the sea floor in our simulations glacioeustatic sea level fall associated with the growth of antarctic ice sheets permanently reduces global calcium carbonate accumulation on the continental shelves leading to an increase in pelagic burial via permanent deepening of the calcite compensation depth at the same time fresh limestones are exposed to erosion thus temporarily increasing global river inputs of dissolved carbonate and increasing seawater 13c our work sheds new light on the mechanisms linking glaciation and ocean acidity change across arguably the most important climate transition of the cenozoic era

dwarfing of ostracodes during the paleocene eocene thermal maximum at dsdp site 401 bay of biscay north atlantic and its implication for changes in organic carbon cycle in deep sea benthic ecosystem abstract the paleocene eocene thermal maximum petm has been held up as a past analog to future environmental change and presents the opportunity to study climate impacts on marine communities during the petm deep sea benthic foraminifers decreased their body size and increased their productivity metabolic rates and food consumption in response to abruptly increasing temperature and changing surface water productivity here we find that three species of marine ostracodes part of the multicellular benthos also experienced a reduction in body size in response to petm warming in the northeast atlantic positive correlations between ostracode body size and benthic foraminiferal oxygen isotope data indicate that reduced body sizes were caused by high temperature during the petm dwarfing of ostracodes during the petm interval suggests that their food consumption rates and lifetimes were less than those of ostracodes in the pre petm interval this interpretation is based upon previous studies that show that food consumption and ostracode lifetimes both decrease as ostracodes increase their growth rates under higher temperatures estimates of body volume temperature and individual abundance suggest a decline in lifetime metabolic rate in ostracode individuals during the core of the petm in addition there is also a decrease in biomass flux in the whole ostracode community at this time the decline in biomass flux at the community level suggests major changes in the energy flow and carbon cycling in deep sea benthic ecosystem and the reduction of organic carbon flux between the ostracode community and sediments during the petm the decline in ostracode carbon flux stands in contrast with previous interpretations that carbon cycling by benthic foraminifera increased during the petm hence our data suggest that the benthic community response to the petm was not uniform between different taxonomic groups

an atlas of the distribution of calcium carbonate in sediments of the deep sea historical observations of the concentration of calcium carbonate in global deep sea sediments are compiled and compared with a new gridded field of seawater co3 concentration to reveal regional variations in the calcite lysocline the most obvious mode of variability of the calcite lysocline is the thickness of the lysocline defined here as the difference in overlying water carbonate saturation co3 between high and low calcite sediments with a thicker lysocline in the atlantic than in the pacific i attribute this variation to differences in the delivery rate of terriginous material a recent model for the lower glacial atmospheric pco2 proposed to change the relationship between the depth of the lysocline and the co3 of the water column by changing the rain rate ratio of organic carbon to calcite production the rain ratio model archer and maier reimer 1994 i search the data set for analogs to the proposed glacial world by looking for a link between the regional climate at the sea surface and the depth of the lysocline below the co3 at the carbonate compensation depth ccd in the tropics appears to be 10 20 mol kg 1 co3 more undersaturated than in high latitudes but this is smaller than the 40 mol kg 1 shift required by the model in addition the general resemblance of the glacial lysocline to the present day requires that the proposed shift in co3 at the ccd be globally uniform rather than locally variable as climate forcing would probably generate i conclude that the rain ratio model would probably require some globally uniform perturbation during glacial time such as a change in ocean si content if it is to explain the entire pco2 decrease observed in the glacial atmosphere finally i grid the sedimentary data to estimate that the inventory caco3 which is available to neutralize fossil fuel co2 is approximately 1600 gt carbon a quantity which may be exceeded by fossil fuel release in the next several centuries

redox controlled carbon and phosphorus burial a mechanism for enhanced organic carbon sequestration during the petm abstract geological records reveal a major perturbation in carbon cycling during the paleocene eocene thermal maximum petm 56 ma marked by global warming of more than 5 c and a prominent negative carbon isotope excursion of at least 2 5 within the marine realm the entire event lasted about 200 000 yr and was associated with a massive release of light carbon into the ocean atmosphere system over several thousands of years here we focus on the terminal stage of the petm during which the ocean atmosphere system rapidly recovered from the carbon cycle perturbation we employ a carbon cycle box model to examine the feedbacks between surface ocean biological production carbon oxygen phosphorus and carbonate chemistry during massive co 2 release events such as the petm the model results indicate that the redox controlled carbon phosphorus feedback is capable of producing enhanced organic carbon sequestration during large carbon emission events the locale of carbon oxidation ocean vs atmosphere does not affect the amount of carbon sequestered however even though the model produces trends consistent with oxygen excess accumulation rates of organic carbon 1700 pg c during the recovery stage export production and 13 c data it fails to reproduce the magnitude of change of sediment carbonate content and the ccd over deepening during the recovery stage the ccd and sediment carbonate content overshoot during the recovery stage is muted by a predicted increase in caco 3 rain nonetheless there are indications that the caco 3 export remained relatively constant during the petm if this was indeed true then an initial pulse of 3 000 pg c followed by an additional slow leak of 2 500 pg c could have triggered an accelerated nutrient supply to the surface ocean instigating enhanced organic carbon export consequently increasing organic carbon sequestration resulting in an accelerated restoration of ocean atmosphere biogeochemistry during the termination phase of the petm

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

equatorial pacific productivity changes near the eocene oligocene boundary there is general agreement that productivity in high latitudes increased in the late eocene and remained high in the early oligocene evidence for both increased and decreased productivity across the eocene oligocene transition eot in the tropics has been presented usually based on only one paleoproductivity proxy and often in sites with incomplete recovery of the eot itself a complete record of the eocene oligocene transition was obtained at three drill sites in the eastern equatorial pacific ocean odp site 1218 and iodp sites u1333 and u1334 four paleoproductivity proxies that have been examined at these sites together with carbon and oxygen isotope measurements on early oligocene planktonic foraminifera give evidence of ecologic and oceanographic change across this climatically important boundary export productivity dropped sharply in the basal oligocene 33 7 ma and only recovered several hundred thousand years later however overall paleoproductivity in the early oligocene never reached the average levels found in the late eocene and in more modern times changes in the isotopic gradients between deep and shallow living planktonic foraminifera suggest a gradual shoaling of the thermocline through the early oligocene that on average affected accumulation rates of barite benthic foraminifera and opal as well as diatom abundance near 33 5 ma an interval with abundant large diatoms beginning at 33 3 ma suggests an intermediate thermocline depth which was followed by further shoaling a dominance of smaller diatoms and an increase in average primary productivity as estimated from accumulation rates of benthic foraminifera

climate impact of late quaternary equatorial pacific sea surface temperature variations magnesium calcium data from planktonic foraminifera in equatorial pacific sediment cores demonstrate that tropical pacific sea surface temperatures ssts were 2 8 0 7 c colder than the present at the last glacial maximum glacial interglacial temperature differences as great as 5 c are observed over the last 450 thousand years changes in sst coincide with changes in antarctic air temperature and precede changes in continental ice volume by about 3 thousand years suggesting that tropical cooling played a major role in driving ice age climate comparison of sst estimates from eastern and western sites indicates that the equatorial pacific zonal sst gradient was similar or somewhat larger during glacial episodes extraction of a salinity proxy from the magnesium calcium and oxygen isotope data indicates that transport of water vapor into the western pacific was enhanced during glacial episodes

convection of north pacific deep water during the early cenozoic the history of deep water formation and abyssal flow is poorly known but important to establish in order to develop a better understanding of changes in oceanic mass heat salt and nutrient transport north atlantic high latitude regions currently are the dominant deep water producers but paleogeographic constraints proxy interpretations and physical models have suggested other modes for the past such as those characterized by high latitude pacific sources subtropical sources or widespread nonlocalized sources here we present new north pacific late cretaceous paleogene nd isotope data from fossil fish debris and detrital silicates combined with results of coupled climate model simulations to test these hypothesized circulation modes the data and model simulations support a circulation mode characterized by high latitude bipolar pacific convection deep convection in the north pacific and likely the south pacific was most intense during the relatively cool portion of the late cretaceous paleocene and waned prior to the peak global warmth of the early eocene ca 52 ma

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

evidence for deep water production in the north pacific ocean during the early cenozoic warm interval the deep ocean circulation is responsible for a significant component of global heat transport in the present mode of circulation deep waters form in the north atlantic and southern oceans where surface water becomes sufficiently cold and dense to sink polar temperatures during the warmest climatic interval of the cenozoic era approximately 65 to 40 million years myr ago were significantly warmer than today and this may have been a consequence of enhanced oceanic heat transport however understanding the relationship between deep ocean circulation and ancient climate is complicated by differences in oceanic gateways which affect where deep waters form and how they circulate here i report records of neodymium isotopes from two cores in the pacific ocean that indicate a shift in deep water production from the southern ocean to the north pacific approximately 65 myr ago the source of deep waters reverted back to the southern ocean 40 myr ago the relative timing of changes in the neodymium and oxygen isotope records indicates that changes in cenozoic deep water circulation patterns were the consequence not the cause of extreme cenozoic warmth

local amplification of rayleigh waves in the continental united states observed on the usarray abstract we develop a method based on ratios of amplitudes measured at adjacent stations to determine local amplification of surface waves across an array of seismic stations we isolate the effects of local structure from those of the earthquake and propagation by systematic averaging of ratios corresponding to many sources we apply the method to data recorded on the usarray for the years 2006 2011 and determine amplification factors at each station of the array for rayleigh waves at periods between 35 s and 125 s local amplification factors are spatially coherent and display variations of 10 at a period of 125 s and greater variations at shorter periods maps of local amplification exhibit spatial correlation with topography and geologic structures in the western and central united states at long periods the observed amplification factors correlate well with predictions from a regional crust and mantle model of north america at short periods correlations are weaker suggesting that the local amplification factors can be useful for constraining shallow structure better

vostok ice core provides 160 000 year record of atmospheric co2 direct evidence of past atmospheric co2 changes has been extended to the past 160 000 years from the vostok ice core these changes are most notably an inherent phenomenon of change between glacial and interglacial periods besides this major 100 000 year cycle the co2 record seems to exhibit a cyclic change with a period of some 21 000 years

role of a strong oxygen deficient zone in the preservation and degradation of organic matter a carbon budget for the continental margins of northwest mexico and washington state rates of organic carbon oxidation in marine sediments were determined for the continental margins of northwest mexico and washington state with the goal of assessing the role of oxygen in the preservation of organic matter on a margin with a strong oxygen deficient zone and on a typical western continental margin total carbon oxidation rates including rates for individual electron acceptors o2 no3 and so4 were determined at depths ranging from 100 to 3000 m on both margins carbon oxidation rates were generally higher on the washington margin than on the mexican margin the relative importance of the different electron acceptors varied across the two margins and was related primarily to the availability of o2 and no3 from the overlying water the relative contribution of o2 consumption increased in deeper sediments 2000 m as aerobic processes began to dominate the total carbon oxidation rate denitrification rates were highest in washington sediments however denitrification represented a larger fraction of the total carbon oxidation rate in the mexican sediments 40 for mexico vs 30 for washington sulfate reduction accounted for as much as 79 of the total carbon oxidation rate in shallow sediments and less than 20 in deep sediments on both margins the offshore trends in carbon oxidation rate appeared to be related to the organic carbon input rate pore water o2 and no3 penetration depths were shallowest in nearshore stations and increased offshore regeneration ratios of c n p reveal non redfield behavior on both margins carbon budgets for the two margins demonstrate that off mexico a much greater percentage of the organic matter produced in the surface ocean reached the sediments 15 vs 8 for mexico and washington respectively on the mexican margin 8 of the primary production escaped oxidation in the surface sediments to be permanently buried as compared with only 1 2 of the primary production on the washington margin this suggests that oxygen deficient conditions on mexican margin are linked to enhanced carbon preservation

geochemical cycles in an ocean general circulation model preindustrial tracer distributions a state of the art report is given of the hamburg model of the oceanic carbon cycle the model advects geochemical tracers important to the carbon cycle by the currents of a general circulation model the geochemical cycling is driven by a michaelis menten type production kinetics the model is an extension of the bacastow and maier reimer 1990 model it is based on a more realistic current field and includes a mechanism of lysocline sediment interaction principal variables are co2 alkalinity phosphate oxygen and silicate the carbon variables are defined for 12c 13c and 14c separately in addition to these carbon isotopes 39a and 18o of dissolved oxygen are predicted the model predicts realistic global patterns of tracer distribution in the equatorial eastern pacific however the structures are exaggerated due to a strong upwelling which is a common feature of coarse resolution models of the general circulation of the ocean

missing organic carbon in eocene marine sediments is metabolism the biological feedback that maintains end member climates 1 ocean chemistry is affected by pco2 in the atmosphere by increasing the dissolution of solid calcium carbonate and elevating the dissolved inorganic carbon concentrations in seawater positive feedbacks between the ocean and atmosphere can maintain high atmospheric pco2 and affect global climate we report evidence for changes in the oceanic carbon cycle from the first high quality organic carbon corg data set of eocene sediments beneath the equatorial pacific upwelling region leg 199 of the ocean drilling program eocene corg mass accumulation rates mars are 10 times lower than holocene rates even though expected corg mars estimated from biogenic barium mars an indicator of biological production equal or exceed modern fluxes what happened to the missing corg recent advances in ecology and biochemical kinetics show that the metabolism of nearly all animals marine and terrestrial is positively correlated by first principles to environmental temperatures the approximately 10 c abyssal temperature difference from eocene to holocene should have radically reduced pelagic corg burial as we observe we propose that higher basal metabolism and nutrient utilization recycling rates in the eocene water column and surface sediments precluded corg sediment burial in the pelagic ocean increased rates of metabolism nutrient utilization and lowered corg sedimentation caused by increased temperature may have acted as a biological feedback to maintain high atmospheric pco2 and hothouse climates conversely these same parameters would reverse sign to maintain low pco2 when temperatures decrease thereby maintaining icehouse conditions during cold climate regimes

the lac des iles palladium deposit ontario canada part i the effect of variable alteration on the offset zone the recently discovered offset zone of the mine block intrusion of the lac des iles complex hosts palladium mineralization with unusually high pd pt and pd ir ratios in rocks that range from relatively unaltered norite to amphibolites and chlorite actinolite talc schist quantitative assessment of the effect of progressive alteration using mineral modes was done using total silicate h2o as a monitor of reaction progress moles h2o added to form alteration minerals per 100 g of rock major mineral modal variations define three reaction regions 1 0 00 0 03 characterized by epidote clinozoisite formation and some amphibole 2 0 03 0 23 characterized by formation of chlorite amphibole quartz muscovite sericite and calcite after plagioclase pyroxene and 3 0 23 0 28 characterized by the formation of talc after earlier formed amphibole epidote occurs as an incongruent product from the destruction of plagioclase that is itself lost as the reaction proceeds pyroxene is altered at about twice the rate of plagioclase resulting in pyroxene rich protoliths to be more altered than those relatively enriched in plagioclase major elements variations largely reflect variations in the plagioclase pyroxene ratio of the protolith but compositional trends suggest a loss of na with reaction progress the base metal sulfides chalcopyrite pyrrhotite and pentlandite show decreasing abundance with reaction progress forming pyrite magnetite as an intermediate reaction product that also is lost as the reaction proceeds millerite is overall low but increases slightly a more limited data set on the platinum group minerals suggests that platinum group element pge arsenides increase whereas pge sulfides and pge bi tellurides decrease with reaction progress assuming ore element concentrations in the protolith were constant and similar to relatively fresh norites pd increases modestly by 5 whereas pt decreases by about 65 in the most altered rocks similarly cu au and s decrease by 60 82 and 94 respectively in the most altered rocks the antithetical behavior of pd and the fact that pd enrichment is not seen in altered dikes suggest that the pd originally was enriched in the more melanocratic protoliths that are most extensively altered and that pd also was lost in part these results are consistent with the mineralization having been a high temperature event that predated the amphibolite greenschist alteration

noble metal enrichment processes in the merensky reef bushveld complex we have analysed sulphides silicates and chromites of the merensky introduction reef for platinum group elements pges re and au using laser the enrichment of noble metals in layered gabbroic ablation inductively coupled plasma mass spectrometry and synthetic intrusions to form stratiform merensky type ore horizons pyrrhotite standards annealed with known quantities of noble metals is an extremely efficient yet poorly understood process os ir and ru reside in solid solution in pyrrhotite and pentlandite metal enrichment must be related to the formation of rh and part of the reef s pd in pentlandite whereas pt au re magmatic layering as the ore horizons form an integral and some pd form discrete phases olivine and chromite often part of the magmatic stratigraphies of their host insuspected to carry os ir and ru are pge free all phases analysed trusions metal concentration is also related to the prescontain noble metals as discrete micro inclusions with diameters ence of magmatic sulphides because the noble metals are either dissolved in base metal sulphides or occur as typically 100 nm inclusions in sulphides commonly have the discrete noble mineral phases intergrown with sulphides element combinations os ir pt and pt pd au inclusions in vermaak hendriks 1976 ballhaus ryan 1995 olivine and chromite are dominated by pt au pd few inclusion ballhaus ulmer 1995 spectra can be related to discrete noble metal phases and few there is considerable controversy as to where the inclusions have formed by sub solidus exsolution rather some metals came from and how metal enrichment worked pge inclusions notably those in olivine and chromite are earlyfor a stratiform platinum group element pge deposit magmatic nuggets trapped when their host phases crystallized we inside the magmatic stratigraphy of a layered intrusion suggest that the silicate melt layer that preceded the merensky reef there are two possibilities either the metals were derived was pge oversaturated at early cumulus times experiments from the melt column above the ore horizon or they came combined with available sulphide silicate partition coefficients sugfrom the magma equivalent to the cumulate package gest that a silicate melt in equilibrium with a sulphide melt underlying the ore owing to the large density contrast containing the pge spectrum of the merensky ore would indeed be between silicate and sulphide melt a popular view is that oversaturated with respect to the least soluble noble metals sulphide the metals were enriched by gravitational settling of melt apparently played little role in enriching the noble metals in sulphide melt i e out of the magma column above the the merensky reef rather its role was to immobilize a pre existing ore campbell et al 1983 barnes naldrett 1985 in situ stratiform pge anomaly in the liquid stratified magma naldrett et al 1987 on the other hand it is well chamber established that gravitational crystal settling plays little role in producing magmatic layering and magmatic stratigraphies mcbirney noyes 1979 morse 1986 campbell 1987 and this cannot remain without consequence for stratiform noble metal deposits a third alternative is noble metal enrichment by late

coupled greenhouse warming and deep sea acidification in the middle eocene 1 the middle eocene climatic optimum meco is an enigmatic warming event that represents an abrupt reversal in long term cooling through the eocene in order to further assess the timing and nature of this event we have assembled stable isotope and calcium carbonate concentration records from multiple deep sea drilling project and ocean drilling program sites for the time interval between 43 and 38 ma revised stratigraphy at several sites and compilation of 18o records place peak warming during the meco event at 40 0 ma chron c18n 2n the identification of the 18o excursion at sites in different geographic regions indicates that the climatic effects of this event were globally extensive the total duration of the meco event is estimated at 500 ka with peak warming lasting 100 ka assuming minimal glaciation in the late middle eocene 4 6 c total warming of both surface and deep waters is estimated during the meco at the study sites the interval of peak warming at 40 0 ma also coincided with a worldwide decline in carbonate accumulation at sites below 3000 m depth reflecting a temporary shoaling of the calcite compensation depth the synchroneity of deep water acidification and globally extensive warming makes a persuasive argument that the meco event was linked to a transient increase in atmospheric pco2 the results of this study confirm previous reports of significant climatic instability during the middle eocene furthermore the direct link between warming and changes in the carbonate chemistry of the deep ocean provides strong evidence that changes in greenhouse gas concentrations exerted a primary control on short term climate variability during this critical period of eocene climate evolution

co 2 record in the byrd ice core 50 000 5 000 years bp the analysis of air in polar ice cores revealed 30 lower co2 values during glacial periods than during interglacial periods at present this is confirmed by results from six different ice cores two from greenland and four from antarctica1 5 in all cores the co2 change coincides with the change in the isotopic composition of the ice expressed as either the 18o or d ratio both are indicators for the mean annual surface temperature6 to investigate the relationship between atmospheric co2 concentration changes with changes in climate the atmospheric co2 concentration during and at the end of the last glaciation has to be known in detail to achieve this we have studied a great number of samples from the deep ice core from byrd station westantarctica drilled in 1968 these measurements allow us to reconstruct the atmospheric co02 concentration in the time period 50 000 15 000 yr bp in great detail

expanded oxygen minimum zones during the late paleocene early eocene hints from multiproxy comparison and ocean modeling anthropogenic warming could well drive depletion of oceanic oxygen in the future important insight into the relationship between deoxygenation and warming can be gleaned from the geological record but evidence is limited because few ocean oxygenation records are available for past greenhouse climate conditions we use i ca in benthic foraminifera to reconstruct late paleocene through early eocene bottom and pore water redox conditions in the south atlantic and southern indian oceans and compare our results with those derived from mn speciation and the ce anomaly in fish teeth we conclude that waters with lower oxygen concentrations were widespread at intermediate depths 1 5 2 km whereas bottom waters were more oxygenated at the deepest site in the southeast atlantic ocean 3 km epifaunal benthic foraminiferal i ca values were higher in the late paleocene especially at low oxygen sites than at well oxygenated modern sites indicating higher seawater total iodine concentrations in the late paleocene than today the proxy based bottom water oxygenation pattern agrees with the site to site o2 gradient as simulated in a comprehensive climate model community climate system model version 3 but the simulated absolute dissolved o2 values are low 35 mol kg while higher o2 values 60 100 mol kg were obtained in an earth system model grid enabled integrated earth system model multiproxy data together with improvements in boundary conditions and model parameterization are necessary if the details of past oceanographic oxygenation are to be resolved

early oligocene glaciation and productivity in the eastern equatorial pacific insights into global carbon cycling the onset of sustained antarctic glaciation across the eocene oligocene transition eot marks a pivotal change in earth s climate but our understanding of this event particularly the role of the

the occurrence of platinum group element and gold minerals in the bon accord ni oxide body south africa two samples from the enigmatic ni oxide body of bon accord barberton greenstone belt south africa have been investigated with the hydroseparation technique to obtain heavy mineral concentrates the concentrates contain abundant pt pd and gold minerals never reported before from the bon accord ni oxide body the grains occur as 1 minute inclusions 3 m in trevorite ideally nife3 o4 and 2 larger 5 70 m free aggregates liberated from the host phase the first group comprises several pgm compounds of pd sb pd sb as pd cu sb pt sb pt as s ru as s ru s along with free grains of ni fe as the second consists of sperrylite ptas2 members of the sobolevskite kotulskite series and electrum these results are in good agreement with previous analyses of pge au in bulk rock paragenetic relationships indicate that the pgm and electrum are of secondary origin probably generated during low temperature metamorphism of the ni rich mineralization they have a terrestrial origin and are related with a low sulfidation regime that usually accompanies hydrothermally driven serpentinization of mafic ultramafic bodies the ligands in the newly formed pgm as sb bi te and o probably proceed from the same source of the hydrothermal solutions in this model the metals ni pge au were original components of the primary mineral assemblage of the bon accord precursor whereas as sb bi te and o might have been contributed by the metasomatizing fluids during near surface evolution of the ore body the data on the high grade heavy mineral concentrates obtained by hydroseparation have provided new knowledge about the mineral deportment of pd pt and au

unlocking the ice house oligocene miocene oxygen isotopes eustasy and margin erosion oxygen isotope records and glaciomarine sediments indicate at least an intermittent presence of large continental ice sheets on antarctica since the earliest oligocene circa 35 ma the growth and decay of ice sheets during the oligocene to modern ice house world caused glacioeustatic sea level changes the early eocene was an ice free greenhouse world but it is not clear if ice sheets existed during the middle to late eocene doubt house world benthic foraminiferal 18o records place limits on the history of glaciation suggesting the presence of ice sheets at least intermittently since the earliest oligocene the best indicator of ice growth is a coeval increase in global benthic and western equatorial planktonic 18o records although planktonic isotope records from the western equatorial regions are limited subtropical planktonic foraminifera may also record such ice volume changes it is difficult to apply these established principles to the cenozoic 18o record because of the lack of adequate data and problems in stratigraphic correlations that obscure isotope events we improved oligocene to miocene correlations of 18o records and erected eight oxygen isotope zones oi1 oi2 mi1 mi6 benthic foraminiferal 18o increases which are associated with the bases of zones oil circa 35 8 ma oi2 circa 32 5 ma and mil circa 23 5 ma can be linked with 18o increases in subtropical planktonic foraminifera and with intervals of glacial sedimentation on or near antarctica our new correlations of middle miocene benthic and western equatorial planktonic 18o records show remarkable agreement in timing and amplitude we interpret benthic planktonic covariance to reflect substantial ice volume increases near the bases of zones mi2 circa 16 1 ma mi3 circa 13 6 ma and possibly mi5 circa 11 3 ma possible glacioeustatic lowerings are associated with the 18o increases which culminated with the bases of zone mi4 circa 12 6 ma and mi6 circa 9 6 ma although low latitude planktonic 18o records are required to test this these inferred glacioeustatic lowerings can be linked to seismic and rock disconformities for example we link 12 oligocene early late miocene inferred glacioeustatic lowerings with 12 of the sequence boundaries inferred eustatic lowerings of haq et al 1987

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

the middle eocene climatic optimum meco a multiproxy record of paleoceanographic changes in the southeast atlantic odp site 1263 walvis ridge the middle eocene climatic optimum meco 40 ma was a transient period of global warming that interrupted the secular cenozoic cooling trend we investigated the paleoceanographic paleoenvironmental and paleoecological repercussions of the meco in the southeast atlantic subtropical gyre ocean drilling program site 1263 tex86 and 18o records support an 4 c increase in surface and deepwater temperatures during the meco there is no long term negative carbon isotope excursion cie associated with the early warming consistent with other sites and there is no short term negative cie 50 kyr during the peak of the meco in contrast to what has been observed at some sites this lack of a cie during the peak of the meco at site 1263 could be due to poor sediment recovery or geographic heterogeneity of the 13c signal benthic and planktic foraminiferal mass accumulation rates markedly declined during meco indicating a reduction of planktic foraminiferal production and export productivity vertical 13c gradients do not indicate major changes in water column stratification and there is no biomarker or micropaleontological evidence that hypoxia developed we suggest that temperature dependency of metabolic rates could explain the observed decrease in foraminiferal productivity during warming the kinetics of biochemical reactions increase with temperature more so for heterotrophs than for autotrophs steady warming during meco may have enhanced heterotroph i e foraminiferal metabolic rates so that they required more nutrients these additional nutrients were not available because of the oligotrophic conditions in the region and the lesser response of primary producers to warming the combination of warming and heterotroph starvation altered pelagic food webs increased water column recycling of organic carbon and decreased the amount of organic carbon available to the benthos

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

export productivity and carbonate accumulation in the pacific basin at the transition from a greenhouse to icehouse climate late eocene to early oligocene 1 the late eocene through earliest oligocene 40 32 ma spans a major transition from greenhouse to icehouse climate with net cooling and expansion of antarctic glaciation shortly after the eocene oligocene e o boundary we investigated the response of the oceanic biosphere to these changes by reconstructing barite and caco3 accumulation rates in sediments from the equatorial and north pacific ocean these data allow us to evaluate temporal and geographical variability in export production and caco3 preservation barite accumulation rates were on average higher in the warmer late eocene than in the colder early oligocene but cool periods within the eocene were characterized by peaks in both barite and caco3 accumulation in the equatorial region we infer that climatic changes not only affected deep ocean ventilation and chemistry but also had profound effects on surface water characteristics influencing export productivity the ratio of caco3 to barite accumulation rates representing the ratio of particulate inorganic c accumulation to corg export increased dramatically at the e o boundary this suggests that long term drawdown of atmospheric co2 due to organic carbon deposition to the seafloor decreased potentially offsetting decreasing pco2 levels and associated cooling the relatively larger increase in caco3 accumulation compared to export production at the e o suggests that the permanent deepening of the calcite compensation depth ccd at that time stems primarily from changes in deep water chemistry and not from increased carbonate production

ocean science ancient burial at sea a study reveals cyclic changes in the rate of burial of biogenic calcium carbonate at the pacific ocean floor 43 million to 33 million years ago as earth exited a warm greenhouse state to become an ice capped planet see article p 609 the carbonate compensation depth the oceanic depth at which carbonate is dissolved reflects the amount of carbon dioxide present in the atmosphere and thus gives clues about climate on geological timescales this paper reports a detailed reconstruction of the carbonate compensation depth in the equatorial pacific over the past 53 million years the compensation depth is found to track ocean cooling deepening from 3 0 3 5 kilometres during the early cenozoic 56 53 million years ago to 4 6 kilometres today rapid fluctuations observed in the carbonate compensation depth around 46 34 million years ago could be explained in part by changes in weathering and in the type of organic carbon supplied to the sea floor

arrival angle anomalies across the usarray transportable array abstract we construct composite maps of surface wave arrival angle anomalies using clustered earthquakes and an array method for measuring wave front geometry this results in observations of arrival angles covering the entire footprint of the usarray transportable array during 2006 2010 bands of arrival angle deviations in the propagation direction indicate the presence of heterogeneous velocity structure both inside and outside of the array we compare the observed patterns to arrival angles predicted using two global tomographic models the mantle model s362ani and the surface wave dispersion model gdm52 we use both ray theory based prediction methods and measurements on synthetic data calculated using a spectral element method both models and all prediction methods produce similar mean arrival angles and long wavelength patterns of anomalies which are similar to the observations predicted short wavelength features generally do not agree with the observations the spectral element method produces some complexity that is not obtained using the ray theory based methods this predicted complexity is similar in character to the observed patterns but does not match them

cenozoic deep sea temperatures and global ice volumes from mg ca in benthic foraminiferal calcite a deep sea temperature record for the past 50 million years has been produced from the magnesium calcium ratio mg ca in benthic foraminiferal calcite the record is strikingly similar in form to the corresponding benthic oxygen isotope 18o record and defines an overall cooling of about 12 c in the deep oceans with four main cooling periods used in conjunction with the benthic 18o record the magnesium temperature record indicates that the first major accumulation of antarctic ice occurred rapidly in the earliest oligocene 34 million years ago and was not accompanied by a decrease in deep sea temperatures