tree ring δ18o in southwestern china linked to variations in regional cloud cover and tropical sea surface temperature in this paper we present the first annual oxygen isotope 8180 record 1902 to 2004 from the latewood cellulose of trees growing in a temperate moist forest in southwestern china tree ring delta o 18 ranges from 12 8 to 18 6 parts per thousand and averages 15 2 parts per thousand delta o 18 in the latewood negatively correlates with total cloud cover relative humidity and precipitation during the moist months august to october from 1951 to 2004 and to a lesser extent positively correlates with the temperature in june spatial correlation analysis revealed that tree ring latewood delta o 18 is more strongly related to variability in regional cloud cover and precipitation in autumn tree ring delta o 18 negatively correlates with the indices of the indian summer monsoon 1948 to 2004 the western north pacific monsoon 1948 to 2004 and with the east asian summer monsoon 1902 to 2000 suggesting that these monsoons strongly influence the regional climate under global warming of last century we found a strong inverse correlation between tree ring delta o 18 and the southern oscillation index in different periods indicating a complex association between the el nino southern oscillation and the regional climate which in turn affects tree ring delta o 18 correlation with the global sea surface temperature sst indicates that climatic conditions in the indian ocean might play a dominant role in modulating cloud cover and precipitation over the study region during the monsoon seasons we also found a significant correlation between tree ring delta o 18 and sst over the western north pacific ocean our results suggest strong links between tropical oceans and an enso like climate with the oxygen isotope sources and discrimination for trees in the study region c 2011 elsevier b v all rights reserved

new global marine gravity model from cryosat 2 and jason 1 reveals buried tectonic structure gravity models are powerful tools for mapping tectonic structures especially in the deep ocean basins where the topography remains unmapped by ships or is buried by thick sediment we combined new radar altimeter measurements from satellites cryosat 2 and jason 1 with existing data to construct a global marine gravity model that is two times more accurate than previous models we found an extinct spreading ridge in the gulf of mexico a major propagating rift in the south atlantic ocean abyssal hill fabric on slow spreading ridges and thousands of previously uncharted seamounts these discoveries allow us to understand regional tectonic processes and highlight the importance of satellite derived gravity models as one of the primary tools for the investigation of remote ocean basins

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

tropical pacific atlantic ocean interactions at multi decadal time scales analysis of sea surface temperature sst observations suggests a pan oceanic interaction between the tropical pacific and the atlantic ocean at multi decadal time scales such that periods of anomalously high ssts in the tropical pacific are followed by a basin wide sst dipole in the atlantic ocean with a time delay of a few decades the sst anomaly structure in the atlantic ocean is reminscent of variations in the north atlantic thermohaline circulation the two ocean basins are linked through an atmospheric bridge involving anomalous fresh water fluxes based on the observational findings the atlantic thermohaline circulation may strengthen during the next decades in response to the strong decades long increase in tropical pacific sst which will have strong impacts on the climates of north america and europe through changes in the north atlantic oscillation nao

morphology and origin of the osbourn trough the osbourn trough is a 900 km long east west trending gravity low visible in satellite altimetry data which intersects the tonga trench at 25 30 s a recent survey collected gravity magnetic echo sounder and swath bathymetry data on three adjacent north south trending ship tracks centered on the trough the linear gravity low is 20 30 mgal less than the regional value and is accompanied by a flat lying 200 500 m deep sediment filled valley swath bathymetry images reveal several parallel east west trending linear ridges and valleys on either side of the main trough as well as other morphologic features characteristic of relict spreading centers including a prominent inside corner high and possible pseudo fault trace the presence of magnetic anomalies possibly anomalies 33 and 32 suggests that the seafloor here was formed after the end of the cretaceous normal superchron anomaly 34 these data support the conclusion that this trough is a spreading center which stopped spreading in late cretaceous time the existence of this feature has important implications for tectonic reconstructions in this region the osbourn trough could be part of the fossil spreading center between the pacific plate and a fragment of the phoenix plate the bellingshausen plate this would require the seafloor between the osbourn trough and the chatham rise to the south to be a remnant fragment of the bellingshausen plate this remnant may have joined to the pacific plate when the hikurangi plateau entered the gondwana subduction zone at the chatham rise possibly causing the cessation of spreading on the osbourn trough

model evaluation for reconstructing the oxygen isotopic composition in precipitation from tree ring cellulose over the last century the oxygen isotope composition of tree rings is controlled by many factors including temperature amount of precipitation and changes in relative humidity in this study we present a modified leaf water model from dongmann et al radiation and environmental biophysics 11 1974 41 that can be used to calculate the isotopic composition of the source water and thus of precipitation that a tree used during the growing season the calibration of the model was accomplished by comparing a previously measured oxygen isotope tree ring chronology from central switzerland with the swiss network for isotopes in the hydrologic cycle station at bern from 1971 to 1995 and integrating temperature relative humidity data and ring width in particular our efforts focused on understanding the significance of the dampening factor f which we relate to changes in humidity and its variability over both the calibration period 1971 to 1995 and the study period 1913 to 1995 our results indicate that f ranging between 0 27 to 0 49 is variable based on correlation with relative humidity average daily temperature and ring width index using this model we have constructed a record of the oxygen isotope composition of precipitation during the growing season may through september for the last century in central western europe this approach can be potentially used in other locations where isotopic and meteorological data are available to extend records of the isotopic composition of precipitation back in time beyond observational records

pacific north american teleconnection controls on precipitation isotope ratios across the contiguous united states large scale climate teleconnections such as the pacific north american pna pattern strongly influence atmospheric processes and continental climate here we show that precipitation 18o values in the contiguous united states are correlated with an index of the pna pattern the 18o pna relationship varies across the study region and exhibits two prominent modes with positive correlation in the western usa and negative correlation in the east this spatial pattern appears not to reflect variation in local climate variables but rather primarily reflects differences in atmospheric circulation and moisture sources associated with pna our results suggest that strong antiphase variation in paired paleo water 18o proxy records from regions characterized by the two modes of 18o pna correlation especially in the midwest and southwestern usa may provide a robust basis for reconstruction of past variation in the pna pattern

the crustal role of the agulhas plateau southwest indian ocean evidence from seismic profiling summary its key geographical position near the reconstructed centre of the gondwana break up between antarctica south america and africa has brought attention to the agulhas plateau an oceanic plateau in the southwest indian ocean with regard to its crustal nature and origin the majority of previous studies have suggested a dominantly continental origin as part of the project setarap sedimentation and tectonics of the agulhas ridge and agulhas plateau we conducted an extensive seismic survey over the plateau with the aim of solving the questions about its crustal structure origin and role in a plate tectonic reconstruction context in addition to 1550 km of high resolution seismic reflection profiles we recorded deep crustal large offset and wide angle reflection refraction data from an ocean bottom hydrophone obh profile across the southern plateau the reflection data show clear indications of numerous volcanic extrusion centres with a random distribution we are able to date this phase of voluminous volcanism to late cretaceous time a period when numerous other large igneous provinces formed traveltime inversion of the deep crustal obh records reveals an up to 25 km thick crust with velocities between 7 0 and 7 6 km s 1 for the lower 50 70 per cent of its crustal column we do not find indications for continental affinity but rather a predominantly oceanic origin of the agulhas plateau similar to that inferred for the northern kerguelen and ontong java plateaus in late cretaceous time its main crustal growth was controlled by the proximity of spreading centres and by passage over the bouvet hotspot at 80 100 ma

vp vs ratio along the voring margin ne atlantic derived from obs data implications on lithology and stress field a total of 13 regional ocean bottom seismograph obs profiles with an accumulated length of 2207 km acquired on the voring margin ne atlantic have been travel time modelled with regards to s waves the vp vs ratios are found to decrease with depth through the tertiary layers which is attributed to increased compaction and consolidation of the rocks the vp vs ratio in the intra campanian to mid campanian layer 1 75 1 8 in the central voring basin is significantly lower than for the layers above and beneath suggesting higher sand shale ratio this layer was confirmed by drilling to represent a layer of sandstone this mid cretaceous anomaly is also present in the northern voring basin as well as on the southern lofoten margin further north the vp vs ratio in the extrusive rocks on the voring plateau is estimated to be 1 85 conformable with mafic basaltic rocks landward of the continent ocean transition cot the vp vs ratio in the layer beneath the volcanics is estimated to be 1 67 1 75 these low values suggest that this layer represents sedimentary rocks and that the sand shale ratio might be relatively high here the vp vs ratio in the crystalline basement is estimated to be 1 67 1 75 in the basin and on the landward part of the voring plateau indicating the presence of granitic granodioritic continental crust in the lower crust the vp vs ratio in the basin decreases uniformly from southwest to northeast from 1 85 1 9 to 1 68 1 73 suggesting a gradual change from mafic gabbroic to felsic granodioritic lower crust significant 3 5 azimuthal s wave anisotropy is observed for several sedimentary layers as well as in the lower crust all these observations can be explained by invoking the presence of liquid filled microcracks aligned vertically along the direction of the present day maximum compressive stress nw se

chronological refinement of an ice core record at upper fremont glacier in south central north america the potential to use ice cores from alpine glaciers in the midlatitudes to reconstruct paleoclimatic records has not been widely recognized although excellent paleoclimatic records exist for the polar regions paleoclimatic ice core records are not common from midlatitude locations an ice core removed from the upper fremont glacier in wyoming provides evidence for abrupt climate change during the mid 1800s volcanic events krakatau and tambora identified from electrical conductivity measurements ecm and isotopic and chemical data from the upper fremont glacier were reexamined to confirm and refine previous chronological estimates of the ice core at a depth of 152 m the refined age depth profile shows good agreement 1736 10 a d with the sup 14 c age date 1729 95 a d the delta sup 18 o profile of the upper fremont glacier ufg ice core indicates a change in climate known as the little ice age lia however the sampling interval for delta sup 18 o is sufficiently large 20 cm such that it is difficult to pinpoint the lia termination on the basis of delta sup 18 o data alone other research has shown that changes in the delta sup 18 o variance are generally coincident with changes in ecm variance the ecm data set contains over 125 000 data points atmore a resolution of 1 data point per millimeter of ice core a 999 point running average of the ecm data set and results from f tests indicates that the variance of the ecm data decreases significantly at about 108 m at this depth the age depth profile predicts an age of 1845 a d results indicate the termination of the lia was abrupt with a major climatic shift to warmer temperatures around 1845 a d and continuing to present day prediction limits error bars calculated for the profile ages are 10 years 90 confidence level thus a conservative estimate for the time taken to complete the lia climatic shift to present day climate is about 10 years suggesting the lia termination in alpine regions of central north america may have occurred on a relatively short decadal timescale c 2000 american geophysical union less

the agulhas plateau structure and evolution of a large igneous province summary large igneous provinces lip are of great interest due to their role in crustal generation magmatic processes and environmental impact the agulhas plateau in the southwest indian ocean off south africa has played a controversial role in this discussion due to unclear evidence for its continental or oceanic crustal affinity with new geophysical data from seismic refraction and reflection profiling we are able to present improved evidence for its crustal structure and composition the velocity depth model reveals a mean crustal thickness of 20 km with a maximum of 24 km where three major units can be identified in the crust in our seismic reflection records evidence for volcanic flows on the agulhas plateau can be observed the middle crust is thickened by magmatic intrusions the up to 10 km thick lower crustal body is characterized by high seismic velocities of 7 0 7 6 km s 1 the velocity depth distribution suggests that the plateau consists of overthickened oceanic crust similar to other oceanic lips such as the ontong java plateau or the northern kerguelen plateau the total volume of the agulhas plateau was estimated to be 4 10 6 km 3 of which about 10 per cent consists of extruded igneous material we use this information to obtain a first estimate on carbon dioxide and sulphur dioxide emission caused by degassing from this material the agulhas plateau was formed as part of a larger lip consisting of the agulhas plateau itself northeast georgia rise and maud rise the formation time of this lip can be estimated between 100 and 94 5 ma

the relationship between seismic velocity and density in the continental crust a useful constraint summary plots of seismic velocity and density of rock samples show that a range of densities is possible for rocks of each seismic velocity and vice versa although a single linear relationship is often assumed in crustal gravity calculations because of the scatter whenever rocks of known seismic velocity are converted to density using this relationship a reduction is made to the resolving power of the resulting gravity calculation if these rocks reach thicknesses of more than a few kilometres then the uncertainties become significant when compared with the size of commonly observed gravity anomalies examples are considered from the north sea mississippi and carolina trough it is concluded that the use of a seismic velocity measurement as the only indication of rock density does not provide a useful constraint when attempting to reproduce observed gravity variations an appropriate model for isostatic compensation is probably the most important factor for successful predictions of crustal structure on the basis of gravity data

light stable isotope systematics of large scale hydrologic regimes in california and nevada surface waters shallow groundwaters and precipitation samples were collected along three traverses which begin at the california coast and are oriented in an east west manner roughly parallel to the atmospheric flow path of meteoric water the hydrogen isotope compositions from short term precipitation records varied as much as 40 at one location and were not representative of the average annual isotopic composition of precipitation the hydrogen isotope ratios of surface waters and shallow groundwaters distinguish segments with isotopic variations that correlate with measured vertical fluxes of meteoric water one coastal segment appears to closely approximate an open system in which precipitation dominates over evapotranspiration most segments are described by rather regular variations in d 3 45 per 100 km which represent different degrees of closure of the hydrologic system caused by variable partitioning of precipitation between runoff and evapotranspiration all partially closed systems imply terrestrial recycling of water a simple model estimates this amount to be about 20 across northern and central california three segments representing the great basin show virtually no geographic variation and appear to represent isotopically closed systems

scratching the surface estimating dimensions of large igneous provinces a study of five major basaltic provinces including oceanic plateaus volcanic passive margins and continental flood basalts shows that they are voluminous constructions of extrusive igneous rock underlain by intrusive rock crustal thickness ranges from 20 to 40 km and lower crust is characterized by high 7 0 7 6 km s seismic velocities volumes and emplacement rates derived for two oceanic plateaus the ontong java and kerguelen broken ridge reveal short lived pulses of increased global crustal production and suggest an origin involving the lower mantle the ontong java rate of emplacement may have exceeded the contemporaneous global production rate of the entire mid ocean ridge system despite the importance off large igneous provinces in studies of mantle dynamics and the global environment scarce age and deep crustal data necessitate intensified efforts in seismic imaging and scientific drilling in a range of such features

a field of volcanoes on the manihiki plateau mud or lava abstract a field of about 100 cones surrounding a 1900 m high seamount was discovered on the northeastern edge of manihiki plateau 10 18 5 s 161 27 5 w during a february 1987 cruise of the r v moana wave in the territorial waters of the cook islands the cones appear as acoustically transparent piercements on single channel seismic reflection profiles collected during this and earlier expeditions to the area seamarc ii sidescan images typically reveal nearly conical steep sided peaks of about 1 km diameter rising several hundred meters above the smooth and featureless plateau surface many of the cones appear to be formed by multiple flow units a few have summit depressions and moats partially surround some of the cones distributed like holes on a dart board individual cones become more densely spaced about a bulls eye located near the eastern edge of the manihiki plateau 50 km southwest of rakahanga island at that location about 40 cones coalesce to form the seamount which is about 25 km in diameter and rises from a plateau depth of 3200 m to a summit at a depth of 1310 m sidescan images show that incised channels trend away from the seamount toward the east where the irregular seafloor in the area truncates tilted e dipping sub bottom reflectors to the south and west the seafloor and sub bottom reflectors are smooth and dip gently to the southwest recent foraminiferal ooze was cored from a satellite cone dredging of the seamount summit recovered middle eocene planktonic foraminifera embedded in burrowed limestone some of the limestone cobbles had manganese crusts coralline fragments and recent foraminifera were also recovered in the same dredge despite the apparent absence of igneous rocks geopotential modelling indicates a basement high at this location if fluid escape rather than magma flow is involved in the genesis of these cones it is localized by faulting associated with basement uplift or the presence of an older igneous intrusion at this time we cannot say with certainty whether the cones are igneous or sedimentary features

geochemical and sedimentologic variations in inter annually laminated sediments from santa monica basin abstract laminated sediments were recently discovered in the center of santa monica basin california continental borderland and extend from the present day to at least the little ice age ca 1600 a d unlike the annual varves observed in santa barbara basin the light dark lamination couplets observed in 210 pb dated cores from the center of santa monica basin occur at 3 to 6 year intervals very similar in length to the el nino southern oscillation enso phenomena the mechanisms that control the temporal patterns of laminations in this basin are unknown potential causal mechanisms of lamination formation in santa monica basin include 1 changes in the flux of terrigenous vs marine organic carbon and detritus 2 surface water processes which affect marine productivity and organic carbon flux to the sediments and 3 deep water processes which affect oxygen renewal and preservation of organic matter within the basin a box core from the central portion of santa monica basin was analyzed using a suite of geochemical sedimentary and micropaleontologic techniques in order to a investigate which if any of these mechanisms has contributed to the occurrence of laminations and b reconstruct proxy records of climate change samples were extracted from this core at 1 mm increments and provide a temporal resolution of 1 3 years per sample a resolution which is comparable in length to the thickness of individual laminae within the core geochemical and micropaleontologic analyses of core samples provide paleoclimatic and paleoceanographic records which are comparable to and extend beyond historical regional and global climate records in addition to direct comparisons between these records spectral analysis was used to investigate whether there were similar patterns of variability that would implicate dominant forcing functions in the historic and proxy records herein we present preliminary results of records from ca 1860 to the present our results suggest that organic carbon fluxes are the dominant factors that affect lamination variability input of organic carbon is primarily a function of primary productivity and to a lesser extent a function of percentage of terrestrial input thus 1 and 2 are both mechanisms of lamination formation stability of 3 only allows preservation of the record of these variations variations in southern california rainfall appear to be linked to decadal scale variations in downcore density profiles and thus cause variations in the thickness and character of the laminations in the deepest portions of this basin thus filtered density records can be used to reconstruct general paleo rainfall trends which compare well with historic rainfall records variations in the isotopic composition of total organic carbon toc are compared to historic enso and climate records and primarily reflect changes in the relative contribution of marine organic carbon to the basin variations in the carbon isotopic composition of n pachyderma mirror changes in the sedimentary 13 c toc record from santa monica basin and suggest that primary productivity is the primary control on the flux of organic carbon to the sediments and exerts a strong influence on the interannual variability in lamination composition variations in paleo sea surface temperatures generated from the oxygen isotopic composition of n pachyderma correlate well with historical sst records and suggest potential usage as a proxy for general paleosst patterns oxygen sensitive assemblages of benthic foraminifera bolivina argentea and b spissa have been used to identify potential large scale flushing events and construct a historical record of variations in deep water oxygen levels spectral analysis of regional historic records indicate dominance of short term enso length and long term decadal patterns of climate variability the short term enso signal is not dominant in the santa monica proxy records however strong decadal length signals are identified in all of the proxy records and suggest that the dominant forcing mechanisms in santa monica basin may be decadal in length

agulhas plateau sw indian ocean new evidence for excessive volcanism a new set of seismic reflection and refraction lines has been interpreted regarding the basement and crustal structure of the southern agulhas plateau a large number of extrusion centres were identified lava flows dip away from those extrusion centres and form subparallel stratified sequences we interpret those extrusion centres as the result of excessive volcanism in course of the separation of the southern agulhas plateau from the maud rise since the sedimentary layers appear to be little affected by the volcanism that episode obviously ceased before onset of sedimentation in late cretaceous times we have not found evidence for continental fragments within overthickened predominantly oceanic crust we therefore propose that the agulhas plateau belongs to the world wide suite of large igneous provinces lip of predominantly oceanic origin

drought reconstructions for the continental united states abstract the development of a 2 lat 3 long grid of summer drought reconstructions for the continental united states estimated from a dense network of annual tree ring chronologies is described the drought metric used is the palmer drought severity index pdsi the number of grid points is 154 and the reconstructions cover the common period 1700 1978 in producing this grid an automated gridpoint regression method called point by point regression was developed and tested in so doing a near optimal global solution was found for its implementation the reconstructions have been thoroughly tested for validity using pdsi data not used in regression modeling in general most of the gridpoint estimates of drought pass the verification tests used in addition the spatial features of drought in the united states have been faithfully recorded in the reconstructions even though the method of reconstruction is not explicitly spatial in its design the drought reconstructions show that the 1930s dust bow

winter precipitation isotope slopes of the contiguous usa and their relationship to the pacific north american pna pattern this study compares the synoptic dynamic relationship between two phases of the pacific north american pna pattern and winter precipitation isotopes at 73 sites across the contiguous usa we use the spatial pattern of isotope slope the rate of changes in precipitation isotope ratios with distance to identify features in the seasonal precipitation isotope fields related to climatic patterns pna positive and pna negative our results show relationships between zones of high isotope slopes and the spatial position of the polar jet stream and juxtaposition of air masses associated with the pna pattern during a positive pna winter zones of high isotope slope in the eastern usa shift southward this change is coincident with a southward displacement of the polar jet stream in this region which leads to a greater frequency of polar air masses and 18o depleted isotope values of precipitation in the region in the western usa zones of high slope shift eastward during the positive pna winter associated with more frequent penetration of tropical air masses that bring 18o enriched precipitation to the region differences in 18o temperature relationships between the pna positive and negative winters and contrasting 18o temperature behaviors in the eastern and western usa provide support for the role of variation in moisture source and transport as a control on the isotopic patterns these findings highlight the importance of synoptic climate driven by pna pattern in determining the spatial patterns of precipitation isotopes and provide constraints on paleo water isotope interpretation and modern isotope hydrological processes

annual precipitation in the yellowstone national park region since ad 1173 cores and cross sections from 133 limber pine pinus flexilis james and douglas fir pseudotsuga menziesii mirbel franco at four sites were used to estimate annual july to june precipitation in the yellowstone national park region for the period from ad 1173 to 1998 examination of the long term record shows that the early 20th century was markedly wet compared to the previous 700 yr extreme wet and dry years within the instrumental period fall within the range of past variability and the magnitude of the worst case droughts of the 20th century ad 1930s and 1950s was likely equaled or exceeded on numerous occasions before ad 1900 spectral analysis showed significant decadal to multidecadal precipitation variability at times this lower frequency variability produces strong regime like behavior in regional precipitation with the potential for rapid high amplitude switching between predominately wet and predominately dry conditions over multiple time scales strong yellowstone region precipitation anomalies were almost always associated with spatially extensive events spanning various combinations of the central and southern u s rockies the northern u s southern canadian rockies and the pacific northwest 2007 university of washington all rights reserved

evidence for 18 6 year lunar nodal drought in western north america during the past millennium analysis of 38 tree ring chronologies yields evidence for enhanced drought conditions every 18 6 years in the north american interior for the past millennium cross spectra between a drought area index and 26 temperature records confirm the analysis of currie 1979 1981d as regards a lunar nodal mn term in these data discussion of the mn tidal constituent which appreciably modulates amplitude and phase of four main constituents m2 k1 o1 mf is presented and implications for agriculture are surveyed

reduction in himalayan snow accumulation and weakening of the trade winds over the pacific since the 1840s 1 in 1884 blanford suggested that summer rainfall over northwest india was anti correlated with snow cover during the preceding winter and spring in the western himalaya walker elaborated on this suggestion in his seminal work on predictors of the indian summer monsoon a body of work that forms the basis of our understanding of how eurasia influences this monsoonal circulation recently a number of studies have questioned the existence of this relationship or have proposed a more complex coupling between eurasian snow cover including the himalaya and the indian summer monsoon here we present a 196 year record of snow accumulation from a himalayan ice core that contains a decreasing trend in accumulation that began in the 1840s indian summer monsoon rainfall shows no evidence of such a trend and we argue that this reduction in snow accumulation is associated with a long term weakening of the trade winds over the pacific ocean citation zhao h and g w k moore 2006 reduction in himalayan snow accumulation and weakening of the trade winds over the pacific since the 1840s geophys res lett 33 l17709

experimental assessment of the purity of α cellulose produced by variations of the brendel method implications for stable isotope δ13c δ18o dendroclimatology 1 stable isotope dendroclimatology using cellulose has unique potential to deliver multimillennial scale sub annually resolved terrestrial climate records however lengthy processing and analytical methods often preclude such reconstructions variants of the brendel extraction method have reduced these limitations providing fast easy methods of isolating cellulose in some species here we investigate application of standard brendel sbrendel variants to resinous soft woods by treating samples of kauri agathis australis ponderosa pine pinus ponderosa and huon pine lagarastrobus franklinii varying reaction vessel temperature boiling time and reagent volume numerous samples were visibly under processed and fourier transform infrared spectroscopic ftir investigation showed absorption peaks at 1520 cm 1 and 1600 cm 1 in those fibers suggesting residual lignin and retained resin respectively replicate analyses of all samples processed at high temperature yielded consistent 13c and 18o despite color and spectral variations spectra and isotopic data revealed that cellulose 13c can be altered during processing most likely due to chemical contamination from insufficient acetone removal but is not systematically affected by methodological variation reagent amount temperature and extraction time all influence 18o however and our results demonstrate that different species may require different processing methods ftir prior to isotopic analysis is a fast and cost effective way to determine cellulose extract purity furthermore a systematic isotopic test such as we present here can also determine sensitivity of isotopic values to methodological variables without these tests isotopic variability introduced by the method could obscure or create climatic signals within a data set

an annually resolved bristlecone pine carbon isotope chronology for the last millennium abstract we present the first near millennium length annually resolved stable isotope record from bristlecone pines pinus longaeva d k bailey the carbon isotope ratios from the cellulose of seven trees from the white mountains of california corrected for anthropogenic changes in atmospheric chemistry are used to reconstruct growing season june through august precipitation back to ad 1085 extremely negative isotope results are strongly correlated with proposed severest el nino events over the last 500 yr and similar values in the first half of the millennium are used to reconstruct a further 13 strong el nino events concentrated in the 12th century and the mid 13th and 14th centuries ring width chronologies from adjacent sites in the white mountains demonstrate a high degree of decadal covariance with the 13c series although there are several periods of notable divergence

pacific absolute plate motion since 145 ma an assessment of the fixed hot spot hypothesis 1 using the geometry and ages from 12 pacific seamount chains we have determined two new absolute plate motion models that now extend our self consistent and high resolution models with covariance estimates back to 145 ma the wk08 a model maps the full uncertainty in the age progressions into uncertainties in rotation opening angles yielding a relatively smooth plate motion model the wk08 g model relaxes the mapping of age uncertainties in order to better isolate secondary geometry changes seen along many coregistered chains both models have been used to assess the viability of the fixed hot spot hypothesis in the pacific in determining the models we found that only a small group of age samples had to be discarded on the grounds that they were discordant with the dominant trends we were able to connect plate motions for pre and post emperor age intervals by including the ratak gilbert ellice and musicians trails in our analysis however as no active hot spot locations exist for the older chains their inclusion adds additional model parameters both age and geometry misfits increase with age reflecting the observed increase in age uncertainties and the general widening of trails secondary and short lived changes in absolute plate motion mapped in wk08 g appear to correlate with the timing and sense of motion of known pacific rim tectonic events analysis of interchain distances between coeval samples from the hawaii and louisville chains suggests possible discrepancies during the older emperor stage that are compatible with predictions of hot spot drift we computed a new apparent polar wander path for the pacific and found a high degree of correspondence with paleomagnetically derived paths as long as solutions allowing for anomalous skewness were included in the latter our polar wander path suggests that there might have been some true polar wander during the emperor stage complemented by a smaller amount of hot spot drift than otherwise required we show that chain geometries and ages combined with future paleolatitude determinations from additional sites and chains could enable an observation based description of both hot spot and plate motions without relying on predictions of hot spot drift derived from mantle flow calculations

history of the cretaceous osbourn spreading center the osbourn trough is a fossil spreading center that rifted apart the manihiki and hikurangi plateaus during cretaceous time previous models of the osbourn spreading center are based on data collected near the trough axis and therefore only constrain the history of the osbourn spreading center during the last few ma of spreading our data set includes multibeam data collected northward to the manihiki plateau allowing us to examine seafloor morphology created during the entire active period of the osbourn spreading center as well as several additional multibeam data sets that provide the opportunity to examine the relationship between the osbourn paleospreading center and the cretaceous pacific phoenix ridge the axial gravity of the trough is similar to the gravity found at other extinct slow intermediate spreading rate ridges magnetic field measurements indicate that spreading at the trough ceased during chron c34 abyssal hill trends indicate that spreading during the early history of the osbourn spreading center occurred at 15 20 the east west component of this spreading explains the modern east west offset of the manihiki and hikurangi plateaus spreading rotated to 2 5 prior to extinction abyssal hill rms amplitudes show that a decrease in spreading rate from 7 cm yr to 2 6 cm yr full spreading rate occurred 2 6 ma prior to ridge extinction our data analysis is unable to determine the exact spreading rate of the osbourn spreading center prior to the slowing event the temporal constraints provided by our data show that the osbourn spreading center ceased spreading prior to 87 ma or 93 ma depending on whether the manihiki and hikurangi plateaus rifted at 115 ma or 121 ma our model resolves the conflict between regional models of osbourn spreading with models based on trough characteristics by showing that spreading at the osbourn spreading center was decoupled from pacific phoenix spreading

another nail in the plume coffin at least one chain of hot spot volcanoes is not caused by a plume rising up from the core mantle boundary calling for a reexamination of the plume hypothesis

recent and dramatic changes in pacific storm trajectories recorded in δ18o from bristlecone pine tree ring cellulose 1 a 300 year stratigraphy of annual cellulosic 18ovsmow is presented for the long lived bristlecone pine pinus longaeva from the white mountains of california the 18ovsmow stratigraphy exhibits two distinctive characteristics a bidecadal oscillation during the 20th century with peak excursions of 4 and a dramatic 9 shift in mean 18o values in the mid 19th century the bidecadal 18o variability during the 20th century does not correlate well with the bidecadal pattern of drought recurrence as reflected in the palmer drought severity index geochemical modeling of the cellulose 18ovsmow indicates local climate conditions particularly humidity and rainfall amount should have been important influences on the cellulose 18o variability but these influences cannot explain the larger bidecadal excursions or the shift in values during the mid 19th century the large isotope variations must reflect sustained shifts in the frequency of subtropical versus polar storms that affect the isotopic composition of rainfall at the site the mid 19th century isotopic shift correlates with the major climate shift across the northern hemisphere as documented in a wide range of proxy records we hypothesize that the large isotopic shift in the 19th century represents the hydrologic response to a regime shift in mean wintertime atmospheric circulation that changed storm trajectories brought about by a more southerly position of the midlatitude jet increased trade wind strength and a change in the frequency of the pacific decadal oscillation the extent to which the hydrologic changes influenced the growth behavior of the high altitude bristlecone pine in the white mountains remains an important unanswered question

evidence for late eocene emplacement of the malaita terrane solomon islands implications for an even larger ontong java nui oceanic plateau 1 most tectonic models for the solomon islands arc invoke a miocene collision with the ontong java plateau ojp to halt cessation of pacific plate subduction initiate australian plate subduction and emplace the malaita terrane which shares the characteristic basement age and geochemistry of ojp existing paleomagnetic evidence however required the malaita terrane to have been fixed to the arc from at least the late eocene new sampling has yielded a paleomagnetic pole from aptian albian limestones and mudstones that falls between the apparent polar wander paths for the australian plate and ojp confirming the extended period of residence of the malaita terrane on the arc arc derived turbidities within late eocene through miocene limestones on malaita and santa isabel and related clasts in broadly contemporary sandstones and conglomerates on santa isabel also attest to early emplacement modeling the emplacement at 35 ma satisfies both the paleomagnetic data and the sediment provenance continuing the reconstruction to 125 ma leaves the malaita terrane far from ojp at the time of plateau formation ojp is now understood to have formed as part of a larger ontong java nui also comprising the hikurangi and manihiki plateaus separated by spreading during the cretaceous restoring the separation of the known elements and invoking an additional triple junction unites the now largely subducted malaita terrane with the rest of ontong java nui subduction of substantial areas of the ontong java nui plateau with little geological signal other than a reduction in arc volcanism is a corollary

mid cretaceous tectonic evolution of the tongareva triple junction in the southwestern pacific basin the trace of the ridge ridge ridge triple junction that connected the pacific farallon and phoenix plates during mid cretaceous time originates at the northeast corner of the manihiki plateau near the tongareva atoll for which the structure is named the triple junction trace extends 3250 km south southeast to and beyond a magnetic anomaly 34 bight it is identified by the intersection of nearly orthogonal abyssal hill fabrics which mark the former intersections of the pacific phoenix and pacific farallon ridges a distinct trough is commonly present at the intersection a volcanic episode from 125 to 120 ma created the manihiki plateau with at least twice its present volume and displaced the triple junction southeast from the nova canton trough to the newly formed manihiki plateau almost simultaneously the plateau was rifted by the new triple junction system and large fragments of the plateau were rafted away to the south and east the tongareva triple junction originated ca 119 ma when carbonate sedimentation began atop the manihiki plateau subsequent spreading rates on the pacific phoenix and pacific farallon ridges averaged 18 20 cm yr until 84 ma

multiphase magmatic and tectonic evolution of a large igneous province evidence from the crustal structure of the manihiki plateau western pacific the manihiki plateau a large igneous province lip in the western pacific has been proposed to be emplaced as part of the greater ontong java event during the early cretaceous shortly after its formation the manihiki plateau fragmented into multiple sub provinces plate tectonic reconstructions ignore this fragmentation treating the manihiki plateau as a single crustal block by analyzing two seismic refraction wide angle reflection profiles crossing the two largest sub provinces of the manihiki plateau we provide new insight into their deep crustal structure and magmatic evolution our data indicate that the high plateau and the western plateaus were emplaced as a single unit during an initial phase of massive magmatic activity but later magmatic stages altered the individual sub provinces considerably the high plateau has a crustal thickness of 20 km and its p wave velocity distribution is comparable to previously surveyed oceanic lips strong secondary magmatic phases are visible by eruptive centers and former magmatic pathways in the middle and lower crust the western plateaus which have a crustal thickness decreasing gradually from 17 3 km east to 9 2 km west experienced smaller amounts of magmatism mainly along fault zones and on local seamounts therefore we propose a distinct development of the two main sub provinces of the manihiki plateau after their initial joint emplacement the high plateau experienced voluminous multi phase magmatic accretion and extrusion whereas the thinner western plateaus exhibit only relatively minor magmatic growth such a large difference in the evolution process has not been reported from any other oceanic lip so far

crustal and upper mantle seismic structure and lithospheric flexure along the society island hotspot chain summary four wide angle and refraction lines have been shot along the society island hotspot track a 280 km long profile covers oceanic crust to the east of the islands the active hotspot region and the apron of tahiti the other profiles cover the region between moorea and huahine and the western archipelago of huahine raiatea bora bora and adjacent oceanic crust traveltime modelling provided lateral variations in crustal structure along the hotspot chain removal of the contribution of the uppermost low velocity layer which represents the volcanic edifices and debris suggests that the islands and atolls sit on normal oceanic crust and are surrounded by a large volcaniclastic apron seismic profiles running between raiatea and huahine and between raiatea and moorea cover a region where extreme down bending due to volcanic loading is expected a nearly flat crust mantle boundary indicates regional isostasy and clearly supports a stiff plate seismic structural models have been compared with calculated boundaries based on simple 3 d elastic plate models a good fit to the seismic crust mantle boundary was obtained for models with an effective elastic thickness of the lithosphere of 20 25 km these values are in accordance with a model in which the elastic thickness depends on the thermal age of the lithosphere and therefore contradict models that suggest that the region of french polynesia has been thermally rejuvenated amplitude modelling of crustal and upper mantle arrivals suggests that crust on the hotspot trail has been modified with respect to the pre hotspot crust to explain the observations we suggest that during the ongoing late stage volcanic activity the lower crust has been intruded by sills and some melts are trapped in the crust mantle boundary region if late stage volcanism and plutonism continue prolonged crustal growth may form a large underplate or subcrustal plutonic core complex along the hotspot chain

non annual laminations and expansion of anoxic basin floor conditions in santa monica basin california borderland over the past four centuries sediments from box cores in the deep portion of santa monica basin have been examined by x radiography and the upper 10 20 cm are characterized by laminations 1 5 mm in thickness age dating of 9 cores by 210pb analysis has shown that accumulation rates on the central basin floor have been remarkably constant during the past century averaging 16 0 0 4 mg cm2 yr densitometer analysis of the x radiography films from 7 cores and spectral analysis of the resulting time series indicates that most lamination couplets have a periodicity in the 3 7 year range a range matching that of the el nino southern oscillation periodicity the median periodicity appears to have decreased slightly during the past 3 centuries from 7 0 years during 200 300 yrs b p to 5 2 yrs during 0 100 yrs b p this trend could be due to a decreasing sedimentation rate an increasing forcing frequency or an increasingly faithful response of the basin in more recent years multiple processes have contributed to creation of the laminations in santa monica basin the principal factors appear to be 1 variations in porosity due to the relative abundance of organic filaments probably formed by beggiatoa mats and 2 compositional variations that reflect variations in carbonate lithogenous ratios and in grain size both of these are expected to respond to enso events the presence of near anoxic bottom waters has prevented bioturbation permitting laminations to be preserved basin bottom waters became nearly anoxic about 350 years ago at the onset of warming as the little ice age waned expansion of the near anoxic area during the past century may have been augmented by 20th century anthropogenic effects the style of these non annual laminations in santa monica basin matches that of the annual laminations in the adjacent santa barbara basin and demonstrates the need for caution in interpreting all laminations as representing annual varves

organic matter provenance and paleoenvironment in the cretaceous on the manihiki plateau south pacific abstract three holes at site 317 on the high manihiki plateau were drilled in 1973 as part of the deep sea drilling project dsdp this plateau is of special interest because of its organic rich shale formation during its early history potentially linking paleo depositional conditions and water depth or land exposure a multi tracer approach was used to analyze target organic rich layers of hole 317a core 16 sections 2 and 3 from the early cretaceous this included bulk elemental and stable carbon isotope compositions of specific chemical classes lipids humic acids kerogen as well as individual biomarkers separated by thin layer chromatography and analyzed by gas chromatography mass spectrometry the major natural product contributions found in the core sediments were derived from three primary sources algal low molecular weight c22 aliphatic lipids phytosterols diterpenoids algal and bacterial derived compounds were observed at the shallowest layers of the core sample 680 30 m below sea floor and decreased with increasing core depth terrestrial inputs increased down core and peaked between 680 33 and 680 70 m below sea floor this trend coincides with a thick sapropel layer and agrees with the oceanic anoxic event oae in the early cretaceous indicating deposition in a shallow water environment in proximity to land e g atoll

reconstructing benthic carbon oxidation rates using δ13c of benthic foraminifers abstract in non bioturbated organic rich marine sediments the concentration and carbon isotope gradient of total dissolved carbon dioxide co2 primarily reflects the rate of carbon oxidation and co2 diffusion within the sediment pore waters here we investigate whether the calcium carbonate secreted by benthic foraminifers that inhabit discrete depths within the sediments record the pore water 13c co2 gradient and hence can be used as proxies to reconstruct a history of carbon oxidation change the distribution and live abundance of bolivina argentea s l bolivina subadvena s l and buliminella tenuata inhabiting the dysoxic marine sediments along the california margin is similar among sites that differ in co2 gradient by up to a factor of three bolivina argentea inhabits the sediments at the sediment water interface whereas b subadvena s l is most abundant at depths of between 2 and 4 mm buliminella tenuata is most abundant at deeper depths of between 4 and 6 mm the 13c of calcite precipitated by these species matches the 13c of the pore water co2 at the depth of their maximum live abundance indicating that each species has a preferred depth for calcification the 13c difference between the species increases as the rate of carbon oxidation increases these results indicate the carbon isotopic difference between these species in fossil assemblages can be used to estimate changes in the rate of carbon oxidation

modeled and observed intra ring δ18o cycles within late holocene bristlecone pine tree samples abstract the oxygen isotope ratio of alpha cellulose produced by bristlecone pine trees from the white mountains of california was measured for three different 10 year tree ring sections at near weekly resolution to investigate how the growing season climate cycle influences the annual to inter annual isotopic variability of whole ring samples we selected sections of wood that grew under periods of generally reduced 155 172 bc and increased ad 1106 1122 ad 1827 1834 growth to assess whether or not the environmental parameters that are responsible for ring width variability including water availability also influence the intra annual cellulosic isotope variability each annual ring is characterized by a parabolic function of intraseasonal 18 o change that reflects humidity and temperature dependent fractionations of h 2 18 o utilized by the tree during the growth period subtle shifts in the shape and amplitude of the seasonal 18 o cycle are attributed to changing growing season length but the differences are not large enough to bias a whole ring isotopic value we model the isotope fractionations based on growing season climate variables and tree physiology and find that the measured 18 o is in close agreement with the model predicted values the model retains no information on previous winter conditions and thus confirms that these trees draw upon an isotopically homogenized water source the intraseasonal 18 o cycle arises entirely from fractionations due to summer season temperature and humidity a persistent issue with dendroclimatic reconstructions is addressing seasonal biases in the record we find that in this environment where growth and precipitation are separated by many months we are able to capture distinct information on both seasons by coupling average annual values with information on sub seasonal variability

tectonic evolution of the pacific phoenix farallon triple junction in the south pacific ocean analysis of multibeam and gravity data reveals the tectonic history of the mid cretaceous 119 107 ma penrhyn basin in the equatorial south pacific ocean the basin formed during a period of heightened geodynamic activity and cessation of magnetic reversals similarities in the geometry of the tongareva triple junction and the rodriguez triple junction in the indian ocean make this study an interesting comparison between modern and ancient tectonics changes in abyssal hill trends during the formation of the basin suggest either a change in the location of the euler pole describing the relative motion between the pacific and farallon plates or a significant period of oblique spreading interaction between the local stress field associated with the break up of the manihiki plateau and the regional stress field controlling major plate motions complicated the tectonic evolution of the penrhyn basin construction of velocity triangles from abyssal hill trends and measurements of the triple junction trace suggests that the triple junction oscillated between ridge ridge ridge and ridge ridge fault configurations at least two reorganizations in the geometry of the triple junction occurred within 10 ma of the initial rifting of the manihiki plateau both changes in triple junction geometry coincide with discontinuities in the triple junction trace and result in right lateral displacements of the triple junction trace changes in the bathymetric expression of the triple junction trace suggest a period of triple junction propagation controlled by rift propagation shortly after the change in euler pole location

toward forward modeling for paleoclimatic proxy signal calibration a case study with oxygen isotopic composition of tropical woods a forward model of the oxygen isotopic composition 18o of wood cellulose is parameterized for time series prediction in tropical environments and driven with meteorological data observed at la selva biological research station costa rica for 1985 2001 monthly resolution model results correlate modestly r 0 34 p 0 05 with observed isotopic data with higher correlation r 0 45 p 0 01 over the earliest 10 years of comparison and nonsignificant correlation over the most recent 6 years of record analysis of model output for la selva suggests that isotopic variations are strongly controlled by rainfall amount the model simulates an analogous but stronger than observed negative isotopic anomaly associated with positive july september rainfall anomalies during el nino southern oscillation enso warm phase event years simulated tree isotope data for the global tropics suggest that a network of well replicated data series from selected locations may resolve the large scale precipitation anomaly pattern associated with enso

isotopic composition of throughfall in pine plantation and native eucalyptus forest in south australia summary knowledge of the isotopic composition in precipitation is of importance for studies using isotopic composition as hydrological tracers to investigate recharge sources of groundwater hydrograph separation and paleoclimate reconstruction in catchments with vegetation cover major water isotope inputs are throughfall instead of precipitation thus it is necessary to know how much precipitation isotopic composition is altered by vegetation canopy and how this alteration varies with different vegetation covers however few studies have examined these issues with continuous monitoring and for typical vegetation covers in south australia in this study we investigate the stable isotopic composition of throughfall over two vegetation surfaces pine plantation and native eucalyptus forest with bulk precipitation and throughfall samples collected from september 2009 to october 2010 with an average 18 day interval together with intra event precipitation samples collected at a nearby location from september 2009 to february 2013 we synthesized a conceptual framework for throughfall isotopic composition including the effects of intra event selection and inter event selection and partial evaporation using d 18 o and d excess the results indicate that the selection processes either within individual events or between events or both contribute to throughfall isotopic composition over the two vegetation covers with less important but observed effects from partial evaporation pine plantation site with a denser vegetation cover has experienced larger alteration in throughfall isotopic composition the significance of the difference between throughfall and precipitation isotopic compositions for groundwater sources hydrograph separation and paleoclimate reconstruction studies are also discussed 2014 elsevier b v all rights reserved

influence of the pacific decadal oscillation on the climate of thesierra nevada california and nevada mono lake sediments have recorded five major oscillations in the hydrologic balance between a d 1700 and 1941 these oscillations can be correlated with tree ring based oscillations in sierra nevada snowpack comparison of a tree ring based reconstruction of the pacific decadal oscillation pdo index d arrigo et al 2001 with a coral based reconstruction of subtropical south pacific sea surface temperature linsley et al 2000 indicates a high degree of correlation between the two records during the past 300 yr this suggests that the pdo has been a pan pacific phenomena for at least the past few hundred years major oscillations in the hydrologic balance of the sierra nevada correspond to changes in the sign of the pdo with extreme droughts occurring during pdo maxima four droughts centered on a d 1710 1770 1850 and 1930 indicate pdo related drought reoccurrence intervals ranging from 60 to 80 yr

isotopic evidence for the origin of the manihiki and ontong java oceanic plateaus abstract pb nd and sr isotopic results for lavas of the cretaceous ontong java and manihiki oceanic plateaus fall well within the modern day oceanic island or hotspot field the data provide no evidence of old continental basements but indicate a major involvement of kerguelen type or em i like mantle in the sources of both plateaus which appear to have probably been formed at least in part by hotspots however the presently active hotspots that pacific plate reconstructions suggest might have been possible plateau sources lack kerguelen type isotopic compositions either these hotspots did not participate in the formation of the two plateaus or if they did kerguelen type material must have been volumetrically much more important early in their existence two hypotheses for the origins of these plateaus which involve hotspot sources are consistent with the sparse available geochemical geochronological and geophysical data the first holds that the plateaus formed cataclysmically in association with surfacing plume heads the second posits a relatively steady but robust hotspot at or near a ridge crest and requires a much longer period of formation a near ridge origin appears to be indicated by evidence that most of the pacific plateaus were built largely on relatively young ocean crust however we suggest that a near ridge origin is also compatible with the plume head concept in that plume heads appear very likely to become associated with spreading axes through their influence on rift propagation which should be substantially greater than for ordinary hotspots in either case the lack of hotspot tracks seamount chains attached to the two plateaus would be a consequence of ridge migration or rift propagation in a near ridge setting

onset of the mid cretaceous greenhouse in the barremian aptian igneous events and the biological sedimentary and geochemical responses basalts and biostratigraphy dated at 125 120 ma from the ontong java and manihiki plateaus in the western pacific evidence the largest volcanic event in earth history in at least the past 160 m y the intervening nova canton trough rifted at about 121 118 ma and a number of guyots and seamounts formed concurrently or slightly later geological events that probably were responses to these volcanic tectonic events occurred in the following chronostratigraphic order biotic fluctuations began at about 122 5 ma at about 122 0 ma 87sr 86sr began to decline slowly metal concentrations of co mn pb yb and cu in sediments peaked at about 121 5 121 2 ma changes in planktonic communities and sedimentation culminated in a nannoconid crisis just prior to 120 5 ma and in the selli black shale oae la at about 120 5 119 5 ma a sharp drop in 13c occurred at the beginning of the selli event and rebounded into a longer positive excursion that reached a peak after the selli event at about 119 5 118 5 ma at 120 5 ma 87sr 86sr declined rapidly and reached a minimum at about 116 113 ma we speculate that the intensity of these latter responses suggests a corresponding peak in volcanic tectonic activity at about 121 119 ma

analysis of ontong java plateau palaeolatitudes evidence for large scale rotation since 123 ma summary we have discovered evidence of a previously unrecognized large scale rotation of the ontong java plateau ojp recorded in its basement palaeolatitudes when palaeolatitude differences computed among ocean drilling program sites 807 and 1183 1187 are plotted versus their present day site latitude differences a systematic 2 1 slope bias is evident while it is possible to resolve this bias by introducing ad hoc tilt corrections at all six sites drilling records indicate relatively undisturbed conditions at sites 1183 and 1185 1187 of the possible causes of the bias only whole plateau rotation resolves it while honouring the majority of published palaeolatitudes this implies that only sites 807 and 1184 palaeolatitudes both questioned in the literature are erroneous a 9 northward dip previously reported at site 1184 appears to stem from inclined deposition rather than post emplacement deformation we also estimate an 8 southward tilt correction at site 807 to make the data set self consistent based on the six sites analysed we find that ojp may have experienced 40 of clockwise rotation since its formation at 123 ma in contrast available pacific absolute plate motion apm models predict less than 10 of rotation if our analysis is correct it suggests that the plateau moved independently of the pacific plate early in its history or that pacific apm models for the lower cretaceous are unreliable while our corrections to sites 807 and 1184 combined with 40 rotation resolve the internal inconsistencies the mean palaeolatitude value of ontong java remains largely unchanged and is still anomalous with respect to the pacific apparent polar wander path at 123 ma

the manihiki plateau a key to missing hotspot tracks a neogene magmatic reactivation of the manihiki plateau a large igneous province lip in the central pacific is studied using seismic reflection data igneous diapirs have been identified exclusively within a narrow wnw ese striking corridor in the southern high plateau hp which is parallel to the neogene pacific plate motion and overlaps with an extrapolation of the society islands hotspot path the igneous diapirs are characterized by a narrow width 5 km penetration of the neogene sediments and they become progressively younger towards the east 23 10 ma the magmatic source appears to be of small lateral extent which leads to the conclusion that the diapirs represent neogene hotspot volcanism within a lip and thus may be an older previously unknown extension of the society islands hotspot track 4 5 ma comparing hotspot volcanism within oceanic and continental lithosphere we further conclude that hotspot volcanism within lip crust has similarities to tectonically faulted continental crust

temporal stability in bristlecone pine tree ring stable oxygen isotope chronologies over the last two centuries the absolutely dated bristlecone pine pinus longaeva tree ring chronology spans almost 9000 years offering great potential for inferring past environmental change existing ring width chronologies have been widely used to produce some of the most influential millennial length temperature reconstructions for the northern hemisphere a recently published 18o record from two bristlecone pine trees growing at methuselah walk in the white mountains of california showed a dramatic decrease in 18o between ad 1850 and 1920 c 13 interpreted as indicating a major shift in pacific storm tracks over the past 300 years here we present new bristlecone pine 18o time series from 15 trees at three white mountains sites including two series from methuselah walk whilst occasional high interannual variability is observed in our 18o series none of our chronologies exhibit an equivalent pronounced or sustained twentieth century decrease suggesting the earlier results are anomalous and may require palaeoclim

evidence for 18 6 year mn signal in temperature and drought conditions in north america since ad 1800 evidence for the 18 6 year lunar nodal mn term in air temperature is found at 30 stations in eastern north america since ad 1800 the mean discrepancy in epoch between maxima in temperature and maxima in the drought area index dai for the western united states vis a vis the maxima in the mn tide is 0 9 and 0 1 yr respectively also a cluster of 9 stations in western canada yields the 18 6 yr term which is out of phase with stations in eastern north america and is indicative of a standing tidal wave in the atmosphere this suggests that enhanced drought conditions in the western united states are neither recurrent nor rhythmic on a time scale of 20 yr but rather periodic with a period of 18 6 yr finally the rocky mountain system is seen as an influence for atmospheric tidal phenomena at epochs of maximum in the mn tide as well as for maxima in the temperature records and the dai

seismic imaging of upper crustal structure using travel times from the passcal ouachita experiment a first arrival travel time inversion applied to the 1986 passcal ouachita experiment has been used to image upper crustal structure twenty one shot points every 10 km were recorded along two 100 km long segments with 400 seismographs on each segment a splined velocity model parameterization allowed for the inversion of laterally inhomogeneous models but not velocity discontinuities over 800 travel times were used in the inversion with a variable data covariance weighting the multiple source nature of the experiment design allowed the use of reciprocity relationships among 21 shot points to enhance data correlation a succession of models with velocities specified at 30 90 171 and 221 nodes were inverted for whose horizontal node spacing decreased from 100 to 12 5 km in the final 221 node model vertical node spacings of 3 0 and 1 5 km were used the results of the inversions indicate changes in depth of isovelocity lines which are interpreted as triassic fault structure based on nearby well data the final rms travel time residual is 0 045 s resolution using first arrivals deteriorates rapidly below 9 km depth three distinct velocity gradients can be correlated with geologic units surface exposed cretaceous and jurassic sediments with velocities from 3 0 tomore 3 5 km s extend to 1 5 km depth triassic rift fill sediments which do not outcrop have inverted velocities ranging from 3 5 to 4 75 km s between depths of 1 5 3 0 km paleozoic sediments are imaged by a decreased velocity gradient below a depth of 3 0 km lack of resolution at depths greater than 9 km necessitates detailed modeling of wide angle reflected phases to further constrain deeper crustal structure less

evidence for a rheologically strong chemical mantle root beneath the ontong java plateau shear wave splitting measurements in conjunction with studies of shear wave velocity structure indicate that the ontong java plateau ojp large igneous province lip has a thick compositionally distinct root that diverts asthenospheric mantle flow beneath the pacific plate the ojp the largest of earth s lips stands 2 km above adjacent pacific abyssal plains and is composed of mantle plume derived volcanics erupted at 122 and 90 ma surface wave tomography of the plateau reveals a seismically slow upper mantle root that extends approximately to 300 km depth the thickness and juxtaposition of the plateau and the mantle root imply that the ojp is the preserved head of a rising mantle plume formed in situ when the lip erupted thus it is a far traveled body currently moving northwestwards with the pacific plate shear wave splitting at four seismic stations along the northern margin of the ojp varies systematically the fast axis of seismic anisotropy at three stations on the ne ojp margin trend nw parallel to hotspot defined pacific absolute plate motion at a fourth station on the nw margin of the plateau the fast shear wave trend is ne upper mantle flow directions delineated by the shear wave splitting could thus represent mantle flow diverted around the leading northwestern face of the rheologically strong chemically distinct ojp root in sum the plateau and its deep root appear to be similar to continental tectosphere except for contrasting seismic velocities fl 2001 elsevier science b v all rights reserved

high resolution stratigraphy and the response of biota to late cenozoic environmental changes in the central equatorial pacific ocean manihiki plateau an undisturbed 16 m late pliocene pleistocene sediment core spanning 2 6 myr of deposition was recovered from the manihiki plateau by the german research vessel sonne in 1990 this core 34kl complements the heavily disturbed late pliocene pleistocene core sections of dsdp site 317 and is well suited for stratigraphic correlation the sediments consist of calcareous microfossils 93 97 caco3 minor portions of siliceous microfossils and detrital minerals all important calcareous microfossil zones could be identified and correlated with the magnetostratigraphic and isotope stratigraphic events stages and periods due to the high degree of silica dissolution the late quaternary radiolarian buccinosphaera invaginata zone is the only siliceous fossil zone which could be identified an interval with globigerinoides gomitulus pink was found within the middle pleistocene which is clearly distinguished from the globigerinoides ruber pink interval of the late pleistocene the magnetostratigraphic gauss matuyama and matuyama brunhes boundaries as well as the olduvai and jaramillo events were clearly identified the 180 curve displays the 100 kyr milankovitch and the 41 kyr laplace cyclicity periods the beginning of the laplace period and the last occurrence of the calcareous nannofossil discoaster brouweri which marks the end of the pliocene fall within the base of the olduvai event there is also a marked drop in sedimentation rates around this time which seems to be a regional phenomenon prominent 3 5 khz subbottom reflectors at 8 ms and 15 ms reflection time are related to lithologic changes near the mid pleistocene revolution mpr and the beginning of the laplace period or the pleistocene respectively it is possible to trace these reflectors laterally to the eroded eastern edge of the manihiki plateau where they can be tied to older strata

evidence from en echelon cross grain ridges for tensional cracks in the pacific plate sea floor topography in the pacific is mainly aligned with original spreading directions1 but is overprinted by alignments created by mid plate processes spreading produces abyssal hills and fracture zones and mid plate volcanism generates seamounts isolated or in chains a different category of topography the cross grain discovered in geoid height data collected by the seasat radar altimeter2 comprises linear troughs and swells spaced 200 km apart oblique to fracture zones and abyssal hills but parallel to the hawaiian chain three models have been proposed for the cross grain small scale convection organized into longitudinal rolls by the shear of the pacific plate2 compressive buckling3 and lithospheric boudinage resulting from plate wide tensile stresses4 5 none of the previously available data ruled out any of these models here we report multi beam bathymetric data revealing long narrow en echelon ridges along the cross grain interpreted as evidence of tension cracks in the pacific plate

relative humidity recorded in tree rings a study along a precipitation gradient in the olympic mountains washington usa abstract humidity is one of the fundamental variables controlling the energy balance of the climate and thus its reconstruction represents a significant aspect of paleoclimate studies we here report a study of oxygen and hydrogen isotopic compositions of tree ring cellulose along a precipitation gradient in the olympic mountains of washington usa to examine whether and how the relative humidity is recorded in the cellulose according to the physically based model described in this paper the relationship between d and 18 o of cellulose should have the same slope as that in the relationship between d and 18 o in the source water 8 8 for the local meteoric water if there is no systematic variation in the mean relative humidity among study sites and no physiologic differences among trees however our isotopic analyses of cellulose yielded a slope of 17 4 significantly greater than the slope of the local meteoric water line we show that to produce such a slope a positive covariation between the relative humidity and the d and 18 o in the source water is required across the precipitation gradient this work suggests that the d vs 18 o relationship in tree rings can be a useful tool for paleohumidity reconstruction

a 20 000 year record of ocean circulation and climate change from the santa barbara basin much of the evidence for climate driven fluctuations in ocean circulation during the past 20 000 years has come from studies of the north atlantic region1 6 the extent to which such interactions have occurred in other ocean basins and any associated teleconnec tions between basins is poorly understood here we present high resolution palaeoclimate and palaeoceanographic records from a 20 000 year sedimentary sequence from the santa barbara basin on the eastern margin of the north pacific ocean the sequence shows oscillations of the benthic environment between low oxygen conditions laminated sediments during periods of warm climate and higher oxygen conditions non laminated bioturbated sediments during cool intervals age differences between coexisting benthic and planktonic foraminifers indicate climate related changes in the age and source and hence oxygen content of basin bottom waters relatively young bottom waters are associated with the cooler intervals and are considered to reflect high proportions of intermediate waters derived from proximal sources conversely older bottom waters are associated with the warmer intervals and were derived from more distal sources these climate driven variations in ocean circulation appear to be synchronous with the main ocean climate fluctuations in the north atlantic region1 6 suggesting that a tight coupling mechanism operates between the two basins

paleocene pacific plate reorganization mirrored in formation of the suvarov trough manihiki plateau the suvarov trough is a graben structure that deviates from the danger islands troughs within the manihiki plateau a large igneous province lip located in the central pacific new high resolution seismic reflection data provide evidence that the graben formed in two phases during the paleocene 65 45 ma in a first phase extension occurred in south westward direction pulling apart the northern part of the suvarov trough and a parallel trending unnamed trough in a second phase a change of extensional force direction occurred from southwest to west northwest forming the southern part of the suvarov trough that extends onto the high plateau the formation of the suvarov trough is accompanied by a series of normal fault systems that apparently formed simultaneously comparing the seismic results to existing pacific paleo strain reconstructions the timing of increased strain and local deformation direction fits well to our findings we thus suggest that the multiple strike directions of the suvarov trough represent an extensional structure that was caused by the major stepwise pacific plate reorganization during the paleocene

stable isotope composition of waters in the great basin united states 1 air mass trajectories 1 isentropic trajectories calculated using the noaa climate monitoring and diagnostics laboratory s isentropic transport model were used to determine air parcel origins and the influence of air mass trajectories on the isotopic composition of precipitation events that occurred between october 1991 and september 1993 at cedar city utah and winnemucca nevada examination of trajectories that trace the position of air parcels backward in time for 10 days indicated five distinct regions of water vapor origin 1 gulf of alaska and north pacific 2 central pacific 3 tropical pacific 4 gulf of mexico and 5 continental land mass deuterium d and oxygen 18 18o analyses were made of precipitation representing 99 of all cedar city events similar analyses were made on precipitation representing 66 of the precipitation falling at winnemucca during the same period the average isotopic composition of precipitation derived from each water vapor source was determined more than half of the precipitation that fell at both sites during the study period originated in the tropical pacific and traveled northeast to the great basin only a small proportion traversed the sierra nevada the isotopic composition of precipitation is determined by air mass origin and its track to the collection station mechanism of droplet formation reequilibration within clouds and evaporation during its passage from cloud to ground the rayleigh distillation model can explain the changes in isotopic composition of precipitation as an air mass is cooled pseudo adiabatically during uplift however the complicated processes that take place in the rapidly convecting environment of cumulonimbus and other clouds that are common in the great basin especially in summer require modification of this model because raindrops that form in the lower portion of those clouds undergo isotopic change as they are elevated to upper levels of the clouds from where they eventually drop to the ground

superplumes and ridge interactions between ontong java and manihiki plateaus and the nova canton trough the initial pulse of volcanism on the ontong java and manihiki plateaus began prior to 123 124 ma and had largely ceased by about 122 ma whereas the intervening pacific phoenix spreading ridge probably was disrupted between 120 and 115 ma by formation of the nova canton trough rift system plateau formation may have resulted from a large plume head that rose beneath each of the two plateau sites during the plateau eruption phase these two plumes spread beyond the plateaus and within the asthenosphere they eventually coalesced beneath the intervening spreading ridge where the nova canton trough rift system is now located at about the time volcanism ceased on the plateaus the two plumes combined to form the nova canton trough rift system by reheating the nascent lithosphere near the ridge crest and widening the plate boundary from the usual 1 10 km to a much broader region the present rift system is a maximum of 500 km wide and much of this area may have formed by normal faulting and crustal accretion across the broadened plate boundary as plate divergence continued eventually coherent spreading resumed somewhere south of the nova canton trough rift system

intrabasement reflections of the ontong java plateau implications for plateau construction 1 the early cretaceous ontong java plateau ojp in the western equatorial pacific earth s most voluminous large igneous province lip is characterized by intrabasement seismic reflections to investigate the nature of such reflections we have analyzed new and all older multichannel seismic mcs reflection data from the ojp using an instantaneous phase velocity analysis technique and synthetic seismograms intrabasement reflections are most prevalent on the main ojp especially on its crest on mcs data the reflections 1 are semicontinuous and subparallel to the top of igneous basement 2 in places have the opposite phase of seafloor reflections and 3 have an average frequency of 20 hz we calculate synthetic seismograms using impedance contrasts between massive lava and pillow lava flows obtained from downhole logs at ojp scientific drill sites and show that these lithologies can produce intrabasement reflections similar to those observed in the mcs data alternatively to evaluate the possibility of sediment sedimentary rock interbeds causing the intrabasement reflections we use published early cretaceous sedimentation rates determined from ojp drill sites and published estimates for the duration of massive ojp volcanism to calculate a range of possible sedimentary interbed thicknesses the range proves to be below the detection limit of the mcs data therefore we conclude that the intrabasement reflections arise from alternating relatively thin lava flows produced at low effusion rates and relatively thick massive flows generated at high effusion rates both originating from vents and fissures on the ojp probably on its crest