the roles of co2 and orbital forcing in driving southern hemispheric temperature variations during the last 21 000 yr abstract transient climate model simulations covering the last 21 000 yr reveal that orbitally driven insolation changes in the southern hemisphere combined with a rise in atmospheric pco2 were sufficient to jump start the deglacial warming around antarctica without direct northern hemispheric triggers analyses of sensitivity experiments forced with only one external forcing component greenhouse gases ice sheet forcing or orbital forcing demonstrate that austral spring insolation changes triggered an early retreat of southern ocean sea ice starting around 19 18 ka bp the associated sea ice albedo feedback and the subsequent increase of atmospheric co2 concentrations helped to further accelerate the deglacial warming in the southern hemisphere implications for the interpretation of southern hemispheric paleoproxy records are discussed

glacial interglacial temperature change in the tropical west pacific a comparison of stalagmite based paleo thermometers in the tropics geochemical records from stalagmites have so far mainly been used to qualitatively reconstruct changes in precipitation but several new methods to reconstruct past temperatures from stalagmite material have emerged recently i liquid vapor homogenization of fluid inclusion water ii noble gas concentrations in fluid inclusion water iii the partitioning of oxygen isotopes between fluid inclusion water and calcite and iv the abundance of the 13 c 18 o 16 o clumped isotopologue in calcite we present for the first time a direct comparison of these four paleo thermometers by applying them to a fossil stalagmite covering nearly two glacial interglacial cycles marine isotope stages mis 12 9 and to two modern stalagmites all from northern borneo the temperature estimates from the different methods agree in most cases within errors for both the old and recent samples reconstructed formation temperatures of the recent samples match within 2 sigma errors with measured cave temperatures however slight but systematic deviations are observed between noble gas and liquid vapor homogenization temperatures whereas the temperature sensitivity of fluid inclusion 18 o and clumped isotopes is currently debated we find that the calibration of tremaine et al 2011 for fluid inclusion 18 o and a synthetic calcite based clumped isotope calibration ziegler et al in prep yield temperature estimates consistent with the other methods all methods with the potential exception of clumped isotopes show excellent agreement on the amplitude of glacial interglacial temperature change indicating temperature shifts of 4 5 c this amplitude is similar to the amplitude of mg ca based regional sea surface temperature records when correcting for sea level driven changes in cave elevation our reconstruction of tropical temperature evolution over the time period from 440 to 320 thousand years ago ka adds support to the view that climate sensitivity to varying greenhouse forcing is substantial also in the deep tropics

a study of cleaning procedures used for foraminiferal mg ca paleothermometry the various cleaning steps required for preparation of foraminiferal samples for mg ca and sr ca analysis are evaluated for their relative importance and effects on measured elemental ratios it is shown that the removal of silicate contamination is the most important step for the measurement of mg ca ratios in an example bulk sample mg ca decreases from 10 5 to 2 5 mmol mol 1 during clay removal oxidation of organic material causes a lowering of sample mg ca in the order of 10 or approximately 1 c when converted to temperature use of dilute acid leaching to remove adsorbed contaminants causes partial dissolution of the sample carbonate and a corresponding decrease in mg ca reductive treatment also causes dissolution of the sample and a decrease in the mg ca ratio of up to 10 15 sample preparation for sr ca analysis does not require the same degree of rigor as is necessary for mg ca work the within run reproducibility of the method described here for g ruber in a core top sample from the arabian sea was 1 8 mean sample ratio was 4 72 mmol mol 1 when converted to temperature this becomes 28 0 2 c the equivalent result for sr ca was 0 5 mean ratio 1 44 mmol mol 1

constraints on the magnitude and patterns of ocean cooling at the last glacial maximum observation based reconstructions of sea surface temperature from relatively stable periods in the past such as the last glacial maximum represent an important means of constraining climate sensitivity and evaluating model simulations1 the first quantitative global reconstruction of sea surface temperatures during the last glacial maximum was developed by the climate long range investigation mapping and prediction climap project in the 1970s and 1980s refs 2 3 since that time several shortcomings of that earlier effort have become apparent4 here we present an updated synthesis of sea surface temperatures during the last glacial maximum rigorously defined as the period between 23 and 19 thousand years before present from the multiproxy approach for the reconstruction of the glacial ocean surface margo project5 we integrate microfossil and geochemical reconstructions of surface temperatures and include assessments of the reliability of individual records our reconstruction reveals the presence of large longitudinal gradients in sea surface temperature in all of the ocean basins in contrast to the simulations of the last glacial maximum climate available at present6 7

magnetic and electric fields associated with changes in high pore pressure in fault zones application to the loma prieta ulf emissions we determined the electric and magnetic fields generated during failure of faults containing sealed compartments with pore pressures ranging from hydrostatic to lithostatic levels exhumed fault studies and strain measurement data limit the possible size of these compartments to less than 1 km in extent rupture of seals between compartments produces rapid pore pressure changes and fluid flow and may create fractures that propagate away from the high pressure compartment along the fault face nonuniform fluid flow results from pressure decrease in the fracture from crack generated dilatancy partial blockage by silica deposition and clearing as pressure increases a direct consequence of this unsteady fluid flow may be associated transient magnetic signals caused by electrokinetic piezomagnetic and magnetohydrodynamic effects models of these processes for fault geometries with 1 km high pressure compartments show that electrokinetic effects are several orders of magnitude larger than the other mechanisms the electrokinetic signals produced by this unsteady flow are comparable in magnitude and frequency to the magnetic signals observed prior to the ml 7 1 loma prieta earthquake of october 18 1989 provided fracture lengths are less than 200 m

on the definition of seasons in paleoclimate simulations with orbital forcing 1 orbital forcing is a major driver of climate variability on timescales of 10 000 to 100 000 years changes in the orbital parameters cause variations in the length of the seasons by several days consequently models using a fixed present day calendar result in biased paleoseasons especially in boreal autumn when the vernal equinox is used as an anchor point the bias is estimated for temperatures and precipitation in a transient model simulation over the last 21 000 years and an accelerated simulation over the last 129 000 years the largest differences of up to 4 k occur over the continents in high latitudes precipitation estimates are mostly affected in the low latitudes the time dependent bias is large enough to modify the temporal characteristics of temperature and precipitation indices it is discussed to what extent the bias in one season is distorting comparisons between models and paleoproxies the bias has minor implications for proxy model comparisons in general however proxies of monsoon activity should be compared with fixed angular seasons for process studies and climate sensitivity studies the use of fixed angular seasons is imperative

river floodplain aggradation history and cultural activities geoarchaeological investigation at the yuezhuang site lower yellow river china abstract archaeobotanical research at the yuezhuang and xihe sites of the houli culture in the lower yellow river has found abundant carbonised plant remains including rice millet weed seeds and many other plants 7800 7000 cal bp although studies of the diverse economic practices of the houli people have begun issues such as ecological diversity and relationships between site formation processes with environmental changes are still poorly understood applying soil micromorphology and related methods such as particle size distribution and loss on ignition at yuezhuang this paper presents results of the geoarchaeological investigation and the implications for the reconstruction of site formation processes in relation to river alluvial history a long alluvial sequence is reconstructed consisting of frequent alternations of short periods surface stabilities and succeeding alluviations human occupations corresponded to those short term surface stabilities and are evidenced by the presence of anthropogenic inclusions in thin sections including burned bone fragments and pottery sherds the significances of this study to an ecological approach focusing on environmental changes and cultural adaption are discussed

pollen based continental climate reconstructions at 6 and 21 ka a global synthesis subfossil pollen and plant macrofossil data derived from 14c dated sediment profiles can provide quantitative information on glacial and interglacial climates the data allow climate variables related to growing season warmth winter cold and plant available moisture to be reconstructed continental scale reconstructions have been made for the mid holocene mh around 6 ka and last glacial maximum lgm around 21 ka allowing comparison with palaeoclimate simulations currently being carried out as part of the fifth assessment report ar5 of the intergovernmental panel on climate change the synthesis of the available mh and lgm climate reconstructions and their uncertainties obtained using modern analogue regression and model inversion techniques is presented for four temperature variables and two moisture variables reconstructions of the same variables based on surface pollen assemblages are shown to be accurate and unbiased reconstructed lgm and mh climate anomaly patterns are coherent consistent between variables and robust with respect to the choice of technique they support a conceptual model of the controls of late quaternary climate change whereby the first order effects of orbital variations and greenhouse forcing on the seasonal cycle of temperature are predictably modified by responses of the atmospheric circulation and surface energy balance

climatic change and caco3 preservation an 800 000 year bathymetric reconstruction from the central equatorial pacific ocean sixteen deep sea cores from the central equatorial pacific are used to reconstruct a continuous 800 000 year 800 kyr record of bathymetric variations in carbonate preservation as measured by calcium carbonate caco3 content the depth of the sedimentary lysocline has fluctuated markedly in conjunction with late pleistocene climate cycles while the carbonate critical depth ccrd which is the water depth where the sediments contain 10 caco3 has remained relatively constant as a result the depth of the lysocline controls the bathymetric position and thickness of the caco3 transition zone defined as the depth from the lysocline to the ccrd modern and interglacial aged sediments show poor caco3 preservation and thick caco3 transition zones glacial aged sediments show good preservation and deep thin zones due to the deepening of the lysocline detailed comparison of the caco3 preservation and oxygen isotope records from the central equatorial pacific confirms the observation that preservation maxima and minima tend to occur during the latter half of glacial and interglacial stages and on climate transitions rather than during the middle of climatic stages during the nine major glacial stages of the last 800 kyr the lysocline deepened by at least 400 to 800 m this deepening indicates an increase in the abyssal carbonate ion concentration co3 and a depression of the calcite saturation horizon best explained by the deeper presence of a more carbonate saturated water mass the bottom of the transition zone has remained at a relatively constant depth during the brunhes chron indicating a balance between caco3 sedimentation and dissolution in the deepest waters of the central equatorial pacific

the role of uncertainty in estimating lead lag relationships in marine sedimentary archives a case study from the tropical pacific understanding the mechanisms behind any changes in the climate system often requires establishing the timing of events imprinted on the geological record however these proxy records are prone to large uncertainties which may preclude meaningful conclusions about the relative timing of events in this study we put forth a framework to estimate the uncertainty in phase relationships inferred from marine sedimentary records the novelty of our method lies in the accounting of the various sources of uncertainty inherent to paleoclimate reconstruction and timing analysis specifically we use a monte carlo process allowing sampling of possible realizations of the time series as functions of uncertainties in time the climate proxy and the identification of the termination timing we then apply this technique to 15 published sea surface temperature records from the equatorial pacific to evaluate whether we observed any significant changes in the termination timing between the east and the west we find that the uncertainty on the relative timing estimates is on the order of several thousand years and mainly stems from age model uncertainty 90 however even small differences in mean termination timings can be detected with a sufficiently large number of samples improvements in the dating of sediment records provide an opportunity to reduce uncertainty in studies of this kind

epica dome c record of glacial and interglacial intensities abstract climate models show strong links between antarctic and global temperature both in future and in glacial climate simulations past antarctic temperatures can be estimated from measurements of water stable isotopes along the epica dome c ice core over the past 800 000 years here we focus on the reliability of the relative intensities of glacial and interglacial periods derived from the stable isotope profile the consistency between stable isotope derived temperature and other environmental and climatic proxies measured along the edc ice core is analysed at the orbital scale and compared with estimates of global ice volume mis 2 12 and 16 appear as the strongest glacial maxima while mis 5 5 and 11 appear as the warmest interglacial maxima the links between edc temperature global temperature local and global radiative forcings are analysed we show i a strong but changing link between edc temperature and greenhouse gas global radiative forcing in the first and second part of the record ii a large residual signature of obliquity in edc temperature with a 5 ky lag iii the exceptional character of temperature variations within interglacial periods focusing on mis 5 5 the warmest interglacial of edc record we show that orbitally forced coupled climate models only simulate a precession induced shift of the antarctic seasonal cycle of temperature while they do capture annually persistent greenland warmth models fail to capture the warming indicated by antarctic ice core d we suggest that the model data mismatch may result from the lack of feedbacks between ice sheets and climate including both local antarctic effects due to changes in ice sheet topography and global effects due to meltwater thermohaline circulation interplays an mis 5 5 sensitivity study conducted with interactive greenland melt indeed induces a slight antarctic warming we suggest that interglacial edc optima are caused by transient heat transport redistribution comparable with glacial north south seesaw abrupt climatic changes

decadal changes in the aragonite and calcite saturation state of the pacific ocean 1 based on measurements from the woce jgofs global co2 survey the clivar co2 repeat hydrography program and the canadian line p survey we have observed an average decrease of 0 34 yr 1 in the saturation state of surface seawater in the pacific ocean with respect to aragonite and calcite the upward migrations of the aragonite and calcite saturation horizons averaging about 1 to 2 m yr 1 are the direct result of the uptake of anthropogenic co2 by the oceans and regional changes in circulation and biogeochemical processes the shoaling of the saturation horizon is regionally variable with more rapid shoaling in the south pacific where there is a larger uptake of anthropogenic co2 in some locations particularly in the north pacific subtropical gyre and in the california current the decadal changes in circulation can be the dominant factor in controlling the migration of the saturation horizon if co2 emissions continue as projected over the rest of this century the resulting changes in the marine carbonate system would mean that many coral reef systems in the pacific would no longer be able to sustain a sufficiently high rate of calcification to maintain the viability of these ecosystems as a whole and these changes perhaps could seriously impact the thousands of marine species that depend on them for survival

effects of seawater carbonate ion concentration and temperature on shell u mg and sr in cultured planktonic foraminifera we investigate the sensitivity of u ca mg ca and sr ca to changes in seawater co3 and temperature in calcite produced by the two planktonic foraminifera species orbulina universa and globige rina bulloides in laboratory culture experiments our results demonstrate that at constant temperature u ca in o universa decreases by 25 7 per 100 mol co3 k g 1 as seawater co3 increases from 110 to 470 mol kg 1 results from g bulloides suggest a similar relationship but u ca is consistently offset by 40 at the same environmental co3 in o universa u ca is insensitive to temperature between 15 c and 25 c applying the o universa relationship to three u ca records from a related species globigerinoides sacculifer we estimate that caribbean and tropical atlantic co3 was 110 70 mol kg 1 and 80 40 mol kg 1 higher respectively during the last glacial period relative to the holocene this result is consistent with estimates of the glacial interglacial change in surface water co3 based on both modeling and on boron isotope ph estimates in settings where the addition of u by diagenetic processes is not a factor down core records of foraminiferal u ca have potential to provide information about changes in the ocean s carbonate concentration below ambient ph ph 8 2 mg ca decreased by 7 5 o universa t o 16 6 g bulloides per 0 1 unit increase in ph above ambient ph the change in mg ca was not significant for either species this result suggests that mg ca based paleotemperature estimates for the quaternary during which surface ocean ph has been at or above modern levels have not been biased by variations in surface water ph sr ca increased linearly by 1 6 0 4 per 0 1 unit increase in ph shell mg ca increased exponentially with temperature in o universa where mg ca 0 85 exp 0 096 t whereas the change in sr ca with temperature was within the reproducibility of replicate measurements copyright 2004 elsevier ltd

on the nature of lead lag relationships during glacial interglacial climate transitions abstract analysis of leads and lags between different paleoclimate records remains an important method in paleoclimatology used to propose and test hypotheses about causal relationships between different processes in the climate system the robust lead of antarctic temperature over co2 concentration during several recent glacial interglacial transitions inferred from the antarctic ice cores apparently contradicts the concept of co2 driven climate change and still remains unexplained here using an earth system model of intermediate complexity and generic scenarios for the principal climatic forcings during glacial interglacial transitions we performed a suite of experiments that shed some light on the complexity of phase relationships between climate forcing and climate system response in particular our results provide an explanation for the observed antarctic temperature lead over co2 concentration it is shown that the interhemispheric oceanic heat transport provides a crucial link between the two hemispheres we demonstrate that temporal variations of the oceanic heat transport strongly contribute to the observed phase relationship between polar temperature records in both hemispheres it is shown that the direct effect of orbital variations on the antarctic temperature is also significant and explains the observed cooling trend during interglacials in addition an imbedded 18o model is used to demonstrate that during glacial interglacial transitions the temporal evolution of deep calcite marine 18o in different locations and at different depths can considerably deviate from that implied by the global ice volume change this finding indicates that the synchronization of different marine records by means of foraminiferal calcite 18o yield large additional uncertainties based on our results we argue that the analysis of leads and lags alone without a comprehensive understanding and an adequate model of all relevant climate processes cannot provide direct information about causal relationships in the climate system

simulation of the last 21 000 years using accelerated transient boundary conditions abstract the earth system model of intermediate complexity ecbilt clio has been used for transient simulations of the last deglaciation and the holocene the forcing effects of the ice sheets greenhouse gas concentrations and orbital configurations are prescribed as time varying boundary conditions in this study two key aspects of the transient simulations are investigated which are of broader relevance for long term transient paleoclimate modeling the effect of using accelerated boundary conditions and of uncertainties in the initial state simulations with nonaccelerated boundary conditions and an acceleration factor 10 were integrated these simulations show that the acceleration can have a significant impact on the local climate history in the outcropping regions of the high southern latitudes and the convective regions in the north atlantic the acceleration leads to damped and delayed temperature response to the boundary conditions furthermore uncertainties in the initial state can strongly

orbital and millennial antarctic climate variability over the past 800 000 years a high resolution deuterium profile is now available along the entire european project for ice coring in antarctica dome c ice core extending this climate record back to marine isotope stage 20 2 800 000 years ago experiments performed with an atmospheric general circulation model including water isotopes support its temperature interpretation we assessed the general correspondence between dansgaard oeschger events and their smoothed antarctic counterparts for this dome c record which reveals the presence of such features with similar amplitudes during previous glacial periods we suggest that the interplay between obliquity and precession accounts for the variable intensity of interglacial periods in ice core records

diachronous benthic δ18o responses during late pleistocene terminations 1 benthic 18o is often used as a stratigraphic tool to place marine records on a common age model and as a proxy for the timing of ice volume sea level change however skinner and shackleton 2005 found that the timing of benthic 18o change at the last termination differed by 3900 years between one atlantic site and one pacific site these results suggest that benthic 18o change may not always accurately record the timing of deglaciation we compare benthic 18o records from 20 atlantic sites and 14 pacific sites to evaluate systematic differences in the timing of terminations in benthic 18o analysis of sedimentation rates derived from the alignment of benthic 18o suggests a statistically significant atlantic lead over pacific benthic 18o change during the last six terminations we estimate an average pacific benthic 18o lag of 1600 years for terminations 1 5 slightly larger than the delay expected from ocean mixing rates given that most glacial meltwater probably enters the north atlantic we additionally find evidence of 4000 year pacific 18o lags at approximately 128 ka and 330 ka suggesting that stratigraphic correlation of 18o has the potential to generate age model errors of several thousand years during terminations a simple model demonstrates that these lags can be generated by diachronous temperature changes and do not require slower circulation rates most importantly diachronous benthic 18o responses must be taken into account when comparing atlantic and pacific benthic 18o records or when using benthic 18o records as a proxy for the timing of ice volume change

authigenic 10be 9be ratio signatures of the cosmogenic nuclide production linked to geomagnetic dipole moment variation since the brunhes matuyama boundary geomagnetic dipole moment variations associated with polarity reversals and excursions are expressed by large changes of the cosmogenic nuclide beryllium 10 10 be production rates authigenic 10 be 9 be ratios proxy of atmospheric 10 be production from oceanic cores therefore complete the classical information derived from relative paleointensity rpi records this study presents new authigenic 10 be 9 be ratio results obtained from cores md05 2920 and md05 2930 collected in the west equatorial pacific ocean be ratios from cores md05 2920 md05 2930 and md90 0961 have been stacked and averaged variations of the authigenic 10 be 9 be ratio are analyzed and compared with the geomagnetic dipole low series reported from global rpi stacks the largest 10 be overproduction episodes are related to dipole field collapses below a threshold of 2 10 22 am 2 associated with the brunhes matuyama reversal the laschamp 41 ka excursion and the iceland basin event 190 ka other significant 10 be production peaks are correlated to geomagnetic excursions reported in literature the record was then calibrated by using absolute dipole moment values drawn from the geomagia and pint paleointensity value databases the 10 be derived geomagnetic dipole moment record independent from sedimentary paleomagnetic data covers the brunhes matuyama transition and the whole brunhes chron it provides new and complementary data on the amplitude and timing of millennial scale geomagnetic dipole moment variations and particularly on dipole moment collapses triggering polarity instabilities

magnitude frequency relation for small earthquakes a clue to the origin of ƒmax of large earthquakes in order to test the hyothesis that the max of large earthquakes is due to the source effect and is causally related to the corner frequency of small earthquakes when it becomes constant below magnitude about 3 we constructed the frequency magnitude relation for earthquakes with magnitude range from 1 3 to 4 recorded at a borehole seismograph station operated by the university of southern california at baldwin hills in the middle of the newport inglewood fault a procedure was developed for an accurate estimation of moment magnitude from the measurement of coda amplitude as a function of lapse time the cumulative number of earthquakes per unit time period and area was estimated by finding the detection limit for ts p for each magnitude we found a clear depature of the observed log frequency magnitude relation for m 3 the observed frequency of earthquakes with m 0 5 is almost 10 times less than that expected from the extrapolation of empirical relation for earthquakes with magnitudes larger than 3 we conclude that the observed frequency magnitude relation departs from self similarity for earthquakes with magnitude smaller than about 3 this departure coincides with the widely observed departure of the moment corner frequency relation from self similarity these observations are consistent with the interpretation of max of large earthquakes in terms of the slip weakening instability model in which the critical slip may be a few tenths of a meter to a few meters and the cohesive zone size may be a few hundred meters to a few kilometers

palaeochannels on the north china plain palaeoriver geomorphology abstract variations in the geomorphology of the north china plain are related to differences between river deposits the river deposits from different periods form the various geomorphological features different combinations of palaeochannels form different geomorphological regions different kinds of palaeochannels form different kinds of micro geomorphology during the early glaciation of the late pleistocene the river deposits formed piedmont plains and floodplains by the early holocene the rivers had cut the piedmonts into dissected valleys and deposited alluvial fans at the front edge of the piedmonts to form alluvial plains below by the middle holocene lake sediments covered the alluvial plains and filled in the dissected valleys of the piedmont plains by the late holocene rivers dissected the piedmonts again to form dissected valleys and deposited alluvial fans in the lower reaches to form alluvial plains and deltas at the river mouths

palaeochannels on the north china plain stage division and palaeoenvironments abstract the late pleistocene and holocene palaeochannels in the north china plain were divided into six stages on the basis of seven indicators basal erosion surface and channel lag deposits macropalaeontology organic matter content ground water quality heavy minerals grain size and sedimentary structures they were called the stages i vi palaeochannels from oldest to youngest on the basis of the percentage area and thickness of fluvial sand bodies of the total area and thickness of sediments of the same period there were three palaeochannel development stages or periods of fluvial activity and two palaeoswamp development stages or periods of fluvial inactivity on the north china plain during the late pleistocene and the holocene

disentangling seasonal signals in holocene climate trends by satellite model proxy integration past sea surface temperatures ssts are routinely estimated from organic and inorganic remains of fossil phytoplankton or zooplankton organisms recovered from sea floor sediments potential seasonal biases of paleo proxies were intensely studied in the past however even for the two most commonly used paleo proxies for sst uk0 37 and mg ca ratios a clear global picture does not yet exist in the present study we combine holocene sst trends derived from uk0 37 and mg ca ratios with results from idealized climate model simulations forced by changes in the orbital conguration which represents the major climate driver over the last 10 kyrs such changes cause a spatio temporal redistribution of incoming solar radiation resulting in a modulation of amplitude and phasing of the seasonal cycle considering that the climate signal recorded by a plankton based paleo proxy may be aected by the seasonal productivity cycle of the respective organism we use the modern relationship between sst and marine net primary production npp both obtained from satellite observations to calculate a seasonality index si as an independent constraint to link modeled sst trends with proxy data although the climate model systematically underestimates holocene sst trends we find that seasonal productivity peaks of the phytoplankton based uk0 37 result in a preferential registering of the warm cold season in high low latitudes as it was expected from the si distribution the overall smoother trends from the zooplankton derived mg ca ssts suggest a more integrated signal over longer time averages which may also carry a seasonal bias but the spatial pattern is less clear based on our ndings careful multi proxy approaches can actually go beyond the reconstruction of average climate trends specifically allowing to resolve the evolution of seasonality

on the fidelity of shell derived δ18oseawater estimates article i nfo 18 oseawater a robustproxyforsurfacesalinity we assessthe fidelity of shell derived 18 oseawater estimates for the surface dwelling foraminifer globigerinoides ruber white using an atlantic meridional coretop transect spanning basin scale temperature and salinity gradients shell derived and observed 18 oseawater values are well correlated r 2 0 77 but a large systematic bias is observed shell mg ca ratios are significantly elevated above values expected from observed and isotopic calcification temperatures in the saline subtropical gyres of both hemispheres this temperature independent shell mg ca ratio variability termed excess mg ca i s highly correlated with surface salinity r 2 0 77 and the observed salinity dependence 27 4 is much higher than indicated by culture studies 6 2 our coretop data are used to develop new atlantic basin temperature and salinity calibration equations that are accurate 1 1 c and 0 20 respectively precise r 2 0 82 and 0 81 respectively and verifiable using previously published data these results are valid for the relatively high salinities of the subtropical atlantic 35 5 37 3 we discover that inclusion of other published data from lower salinity regions b35 indicates little or no excess mg ca taken together these results point to a strongly non linear positive salinity effect on shell mg ca ratios that significantly affects the accuracy of sst and 18

on the difficulty of detecting streaming potentials generated at depth in order to investigate how a streaming potential coefficient measured in the laboratory at a typical scale of 10 cm can be incorporated into a field model with a typical scale of 1 to 10 km we measured the electric field induced by water flows forced at 150 m depth through a 10 m wide granite fractured zone the water flows were obtained by pumping cyclically 10 m of water from a borehole that cut the fractured zone at depth and contemporaneously reinjecting it into another borehole located 50 m away after one day a steady state fluid flow regime was reached with pumping cycles lasting 45 minutes indicating a hydraulic conductivity of 10 5 m s 1 and a specific storage coefficient of 3 25 10 6 m 1 the expected self potential at the surface was an anomaly with two maxima of opposite sign and 2 v amplitude each both located 160 m away from the middle of the borehole heads the signal being divided by two 500 m away from the middle of the borehole heads in agreement with wurmstich and morgan 1994 instead we observed an electrical signal of 8 mv midway between the borehole heads and smaller than 5 mv 33 m away from the borehole heads the discrepancy observed between the data and the model can be explained by fluid flow leakages that occurred close to the water table head represented about 20 of the total water flow and activated smaller but closer electric sources this experiment thus illustrates the practical difficulty of detecting streaming potentials generated at depth it shows in particular that in fractured zones and hence in the vicinity of a major active fault small water flows located distantly from an energetic targeted source but close to some of the electrodes of the network can sometimes drastically distort the shape of the expected anomaly models of possible electrical earthquake precursors therefore turn out to be more speculative than expected

isotopic signals in two morphotypes of globigerinoides ruber white from the south china sea implications for monsoon climate change during the last glacial cycle abstract based on the study of surface and downcore sediment samples from the south china sea scs two morphotypes of globigerinoides ruber white have been differentiated by taxonomic criteria at species and or subspecies level and also by their stable isotopic compositions of oxygen and carbon the two morphotypes g ruber sensu stricto s s and g ruber sensu lato s l represent two groups with different depth habitats with g ruber s s living in the upper 30 m of the water column and g ruber s l living at depths below 30 m the different depth habitats are indicated by the comparison between the present oceanographic data and isotopic signals of the two morphotypes in the surface sediment from the scs application of this information to a hemipelagic sediment core in the northern scs shows that drastic changes existed in the morphotypes isotopic records during the last glacial cycle the isotope difference between the two morphotypes diminished during 18 o stage 2 especially during the last glacial maximum it is inferred that this is the result of intensified monsoon winds which caused mixing of the upper layer of the water column during stage 2 the proportion of g ruber s l increased which is interpreted as a result of the increased productivity due to mixing of the subsurface nutrient rich water into the surface layer

hydrological and vegetation shifts in the wallacean region of central indonesia since the last glacial maximum abstract precipitation is the most important variable of indonesian climate yet there are substantial uncertainties about past and future hydroclimate dynamics over the region this study explores vegetation and rainfall and associated changes in atmospheric circulation during the past 26 000 years in wallacea a biogeographical area in central indonesia wedged between the sunda and sahul shelves and known for its exceptionally high rainforest biodiversity we use terrestrial plant biomarkers from sediment cores retrieved from mandar bay off west sulawesi to reconstruct changes in wallacean vegetation and climate since the last glacial maximum lgm enriched leaf wax carbon isotope 13cwax values recorded in mandar bay during the lgm together with other regional vegetation records document grassland expansion implying a regionally dry and possibly more seasonal glacial climate depleted leaf wax deuterium isotope dwax values in mandar bay during the lgm and low reconstructed precipitation isotope compositions from nearby sites reveal an intensified austral asian summer monsoon circulation and a southward shift of the mean position of the intertropical convergence zone likely due to strong southern hemisphere summer insolation and the presence of large northern hemisphere ice sheets mandar bay 13cwax was anti correlated with dwax during the lgm and the last deglaciation but was positively correlated during most of the holocene indicating time varying controls on the isotopic composition of rainfall in this region the inundation event of the sunda shelf and in particular the opening of the java sea and karimata strait between 9 4 and 11 1 thousand years ago might have provided new moisture sources for regional convection and or influenced moisture source trajectories providing the trigger for shifts in atmospheric circulation and the controls on precipitation isotope compositions from the lgm to the holocene

co2 radiative forcing and intertropical convergence zone influences on western pacific warm pool climate over the past 400 ka abstract the western pacific warm pool wpwp is an important heat source for the atmospheric circulation and influences climate conditions worldwide estimating wpwp sensitivity to past radiative forcing perturbations is important for understanding the magnitudes and patterns of current and projected tropical climate change here we present a new mg ca based sea surface temperature sst reconstruction over the past 400 ka from the bismarck sea off papua new guinea along with benthic foraminiferal 18o records and a transient intermediate complexity earth system model simulation the mg ca sst record exhibits a close similarity with atmospheric co2 content for the whole study period our model analysis demonstrates that greenhouse gas forcing is the primary driver for glacial interglacial sst changes in the entire wpwp region mg ca sst in the bismarck sea also includes a weaker precessional component which covaries with reconstructed and simulated local precipitation and simulated surface currents we propose that orbitally driven latitudinal shifts of the intertropical convergence zone and oceanic heat advection are responsible for this residual sst variability on glacial timescales the reconstructed wpwp surface temperature changes over the past 400 ka are highly correlated with east antarctic air temperature variations the strong effect of greenhouse gas forcings on both records and on global mean temperature variability allows us to determine a scaling factor of 1 1 5 between reconstructed wpwp temperature anomalies and estimates of the global mean temperature

changes in the thermocline structure of the indonesian outflow during terminations i and ii we present centennial records of sea surface and upper thermocline temperatures in core md01 2378 from the timor sea which provide new insights into the variability of the indonesian outflow across the last two glacial terminations mg ca in globigerinoides ruber white s s indicates an overall increase of 3 2 degrees c in sea surface temperature sst over termination i following an early holocene plateau at 11 3 6 4 ka ssts cooled by 0 6 degrees c during the middle to late holocene 6 4 0 7 ka the early holocene warming occurred in phase with increasing northern hemisphere summer insolation coinciding with northward displacement of the intertropical convergence zone enhanced boreal summer monsoon and expansion of the indo pacific warm pool thermocline temperatures pulleniatina obliquiloculata mg ca gradually decreased from 24 5 to 21 5 degrees c since 10 3 ka reflecting intensification of a cool thermocline throughflow the vertical structure of the upper ocean in the timor sea evolved in similar fashion during the holocene and mis5e although the duration of sst plateaux differed 11 3 to 6 4 ka in termination i and from 129 to 119 ka in termination 11 which was probably due to the more intense northern hemisphere summer insolation during mis 5e during both terminations sst increased simultaneously in the southern high latitudes and the tropical eastern indian ocean suggesting virtually instantaneous atmospheric climate feedbacks between the high and low latitudes c 2008 elsevier b v all rights reserved

climates of the last three interglacials in subtropical eastern australia inferred from wetland sediment geochemistry abstract records of australian climate during marine isotope stages 5 and 7 130 71 and 243 191 ka are rare preventing detailed assessments of long term climate drivers and ecological responses across the continent over glacial interglacial timescales this study presents a geochemistry based palaeoclimate record from fern gully lagoon on north stradbroke island also known as minjerribah in subtropical eastern australia which records climates in mis 7a c mis 5 and much of the holocene in addition to mis 4 71 57 ka and parts of mis 6 mis 3 and mis 2 191 130 57 29 and 29 14 ka indicators of inorganic sedimentation from a 9 5 m sediment core focussed on high resolution estimates of sediment geochemistry supported by x radiography inorganic content and magnetic susceptibility were combined with a chronology consisting of six radiocarbon 14c and thirteen single grain optically stimulated luminescence osl ages hiatuses occurred at 178 153 ka 36 21 ka and 7 2 ka and likely result from the wetland drying low values of locally sourced aeolian materials indicate a wet mis 7a c and early mis 6 before a relatively dry mis 5 inorganic flux during the holocene was up to four times greater than during mis 5 consistent with long term interglacial drying observed in other regions most notably in central australia this study highlights the importance of employing a combination of multiple dating approaches and calibrated geochemical proxies to derive climate reconstructions and to identify depositional complexities in organic rich wetland records

compiling the map of shallow buried palaeochannels on the north china plain abstract the 4 methods used in compiling the shallow buried palaeochannel maps are as follows geohydrologic electrical resistivity areo electro magnetism and drilling methods on the north china plain the drilling method was used mainly accompanied by the geohydrologic and the electrical resistivity methods before compiling the map detailed studies of typical palaeochannels were undertaken of palaeochannel sediments their ages and relation to the storage of shallow groundwater quantity and quality this provides the theoretical foundation for compiling the map of a large area and for dividing the palaeochannels then data from drilling samples were collected and each drilling hole divided into zones 1 and 2 and marked on the base map the boundaries of zones 1 and 2 were drawn on the base map from the map of the shallow buried palaeochannels we can conclude that the shallow buried palaeochannel zones and shallow groundwater zones are identical with the sand bodies of stage i iii and iv palaeochannels

response of planktic foraminiferal size to late quaternary climate change 1 geographical size distribution within entire holocene foraminiferal assemblages is related to global environmental gradients such as temperature primary productivity and environmental variability this study demonstrates that these correlations are also recognizable in late quaternary assemblages from three locations in the south atlantic on temporal and latitudinal scales the size response to temporal paleoenvironmental changes during glacial interglacial cycles mimics the geographic holocene size variability the amplitude of size variability is directly related to the amplitude of the climatic fluctuations as shown by the stable size temperature relationship over time the documented changes in the assemblage size are caused by species replacement and intraspecific size variability the relative importance of these processes depends on the environmental setting species have been shown to reach their maximum size and abundance under certain optimum conditions and decrease in size if environmental conditions differ from these optima we confirm that late quaternary species sizes were largest at paleotemperatures identical to holocene ones

paleochannel controlled earth fissures in daming north china plain and their implication for underground paleogeomorphology abstract earth fissures are a geologic phenomenon that mainly affects the medium with shallow surface soil and mainly developed in the quaternary sediment cover in the yellow river qinghe river zhanghe river shallow buried paleochannel band hqz qh2 ii band on the north china plain 93 earth fissures are developed among them 29 fissures are evolved in the daming zone in the upper reaches of the paleochannel band thus the zone belongs to a densely grouped fissure area this study through a series of field trenching and surveying revealed that these earth fissures have unique plane distribution rules and profile structure features of short length several meters to several hundred meters shallow depth smaller than 10 m and good correspondence to daming paleochannels these basic characteristics reveal that unlike other tectonic earth fissures daming earth fissures are a new and unknown type of fissures i e paleochannel controlled earth fissures theoretical analysis of their features showed that they were formed due to the actions of gravity primary joint factors and groundwater pumping activities and controlled by ancient river factors including paleochannels sediments and groundwater among them the process of mode i can be summed up as self gravity action tensile cracks surface water scouring earth fissures the process of mode ii is primary join surface water infiltration piping cave in earth fissures the process of mode iii is groundwater extraction aquifer compression inhomogeneous ground subsidence earth fissures these formation mechanisms of paleochannel induced earth fissures can be used to predict the fine distribution of shallow buried paleochannels and the overall migration process of the rivers thus this kind of earth fissures is of great significance for understanding the underground paleogeomorphology buried paleochannel of the north china plain and other alluvial plains of the world

progressive shoaling of the equatorial pacific thermocline over the last eight glacial periods the depth of equatorial pacific thermocline is diagnostic of the main modes of tropical climates past estimates of pacific thermocline dynamics have been reconstructed either for the last glacial maximum or on longer timescales at low resolution here we document a new high resolution set of reconstructed past sea surface and subsurface waters temperatures from the southwestern subequatorial pacific core md05 2930 in the gulf of papua over the last 800 ka we used two morphotypes of globigerinoides ruber known to live at different water depths to reconstruct past stratification we estimated calcification temperature of each morphotypes by mg ca paleothermometry our subequatorial pacific thermocline paleotemperature record indicates a response of the thermocline to both direct orbital forcing and glacial interglacial changes our stratification record shows a systematic shallower glacial thermocline whereas sea surface temperatures are characterized by precessional forcing the record is indicative of a progressive long term shoaling of the thermocline during the glacial stages during the late pleistocene the shoaling of the subequatorial pacific thermocline is consistent with regional estimates an enhanced south pacific shallow overturning wind driven circulation could have driven this progressive shoaling we speculate that this late pleistocene glacial shoaling of the thermocline could be related to an increase in the amplitude of the obliquity

a conceptual model for the response of tropical rainfall to orbital variations tropical rainfall to first order responds to variations in earth s orbit through shifts of the intertropical convergence zone itcz and changes in zonally averaged rainfall intensity here a conceptual model is developed that represents both processes and their response to orbital insolation variations the model predicts the seasonal evolution of tropical rainfall between 30 s and 30 n insolation variations impact seasonal rainfall in two different ways thermodynamically leading to variations in rainfall intensity through modulation of the water vapor content of the atmosphere and dynamically leading to shifts of the itcz through modulation of the global atmospheric energy budget thermodynamic and dynamic effects act together to shape the annual mean response of tropical rainfall to changes in earth s orbit the model successfully reproduces changes in annual mean rainfall inferred from paleo proxies across several glacial interglacial cycles it illuminates how orbital precession and variations of earth s obliquity affect tropical rainfall in distinct ways near the equator and farther away from it with spectral signatures of precession and obliquity variations that shift with latitude it also provides explanations for the observed different phasings of rainfall minima and maxima near the equator and away from it for example the model reproduces a phase shift of 10 ka between rainfall records from caves in northern borneo 4 n and from china approximately 30 n the model suggests that such phase shifts arise through a different weighting of itcz shifts and variations in rainfall intensity thus providing insight into the mechanisms that drive tropical rainfall changes on orbital time scales

on the reported magnetic precursor of the 1989 loma prieta earthquake among the most frequently cited reports in the science of earthquake prediction is that by fraser smith et al 1990 and bernardi et al 1991 they found anomalous enhancement of magnetic field noise levels prior to the 18 october 1989 loma prieta earthquake in the ultra low frequency range 0 0110 10 001 hz from a ground based sensor at corralitos ca just 7 km from the earthquake epicenter in this analysis we re examine all of the available corralitos data 21 months from january 1989 to october 1990 and the logbook kept during this extended operational period we also examine 1 0 hz 1 s data collected from japan 0 0167 hz 1 min data collected from the fresno ca magnetic observatory and the global kp magnetic activity index the japanese data are of particular importance since their acquisition rate is sufficient to allow direct comparison with the lower frequency bands of the corralitos data we identify numerous problems in the corralitos data evident from both straightforward examination of the corralitos data on their own and by comparison with the japanese and fresno data sets the most notable problems are changes in the baseline noise levels occurring during both the reported precursory period and at other times long before and after the earthquake we conclude that the reported anomalous magnetic noise identified by fraser smith et al and bernardi et al is not related to the loma prieta earthquake but is an artifact of sensor system malfunction 2008 elsevier b v all rights reserved

modeling obliquity and co2effects on southern hemisphere climate during the past 408 ka abstractthe effect of obliquity and co2 changes on southern hemispheric climate is studied with a series of numerical modeling experiments using the earth system model of intermediate complexity loch vecode ecbilt clio agism model loveclim and a coupled general circulation model model for interdisciplinary research on climate miroc it is shown in time slice simulations that phases of low obliquity enhance the meridional extratropical temperature gradient increase the atmospheric baroclinicity and intensify the lower and middle troposphere southern hemisphere westerlies and storm tracks furthermore a transient model simulation is conducted with loveclim that covers the greenhouse gas ice sheet and orbital forcing history of the past 408 ka this simulation reproduces reconstructed glacial interglacial variations in temperature and sea ice qualitatively well and shows that the meridional heat transport associated with the orbitally paced modulation of middle troposphere westerlies and storm tr

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

reconciling discrepancies between uk37 and mg ca reconstructions of holocene marine temperature variability significant discrepancies exist between the detrended variability of late holocene marine temperatures inferred from mg ca and uk37 proxies with the former showing substantially more centennial scale variation than the latter discrepancies exceed that attributable to differences in location and persist across various calibrations indicating that they are intrinsic to the proxy measurement we demonstrate that these discrepancies can be reconciled using a statistical model that accounts for the effects of bioturbation sampling and measurement noise and aliasing of seasonal variability the smaller number of individual samples incorporated into mg ca measurements relative to uk37 measurements leads to greater aliasing and generally accounts for the differences in the magnitude and distribution of variability an inverse application of the statistical model is also developed and applied in order to estimate the spectrum of marine temperature variability after correcting for proxy distortions the correction method is tested on surrogate data and shown to reliably estimate the spectrum of temperature variance when using high resolution records applying this inverse method to the actual mg ca and uk37 data results in estimates of the spectrum of temperature variance that are consistent this approach provides a basis by which to accurately estimate the distribution of intrinsic marine temperature variability from marine proxy records

a 23 000 year record of surface water ph and pco2 in the western equatorial pacific ocean the oceans play a major role in defining atmospheric carbon dioxide co2 levels and although the geographical distribution of co2 uptake and release in the modern ocean is understood little is known about past distributions boron isotope studies of planktonic foraminifera from the western equatorial pacific show that this area was a strong source of co2 to the atmosphere between approximately 13 800 and 15 600 years ago this observation is most compatible with increased frequency of la nina conditions during this interval hence increased upwelling in the eastern equatorial pacific may have played an important role in the rise in atmospheric co2 during the last deglaciation

low frequency magnetic field measurements near the epicenter of the ms 7 1 loma prieta earthquake the authors report the results of measurements of low frequency magnetic noise by two independent monitoring systems prior to the occurrence of the m sub s 7 1 loma prieta earthquake of 17 october 1989 their measurements cover 25 narrow frequency bands in the more than six decade frequency range 0 01 hz 32 khz with a time resolution varying from a half hour in the ulf range 0 01 10 hz to one second in the elf vlf range 10 hz 32 khz the ulf system is located near corralitos about 7 km from the epicenter the elf vlf system is located on the stanford campus about 52 km from the epicenter analysis of the elf vlf system is located on the stanford campus about 52 km from the epicenter analysis of the elf vlf data has revealed no precursor activity that they can identify at this time however the ulf data have some distinctive and anomalous features first a narrow band signal appeared in the range 0 05 0 2 hz around september 12 and persisted until the appearance of the second anomalous feature which consisted of a substantial increase in the noise background starting on 5 october and covering almost the entire frequency range of the ulf system third there was an anomalousmore dip in the noise background in the range 0 2 5 hz starting one day ahead of the earthquake finally and perhaps most compelling there was an increase to an exceptionally high level of activity in the range 0 01 0 5 hz starting approximately three hours before the earthquake there do not appear to have been any magnetic field fluctuations originating in the upper atmosphere that can account for this increase further while the systems are sensitive to motion seismic measurements indicate that there were no significant shocks preceding the quake thus the various anomalous features in the data and in particular the large amplitude increase in activity starting three hours before the quake may have been magnetic precursors less

assessing influence of diagenetic carbonate dissolution on planktonic foraminiferal mg ca in the southeastern arabian sea over the past 450 ka comparison between globigerinoides ruber and globigerinoides sacculifer 1 the influence of supralysoclinal calcite dissolution on the mg ca thermometer over the last 450 ka is assessed using globigerinoides ruber and globigerinoides sacculifer from a core site in the eastern arabian sea the studied site is characterized by precession cycled paleoproductivity changes that have induced calcite dissolution in the sediments although the core still contains 40 80 caco3 during high productivity periods the narrow sized test weights of both foraminiferal species tend to decrease with increasing mn ca ratio indicating corrosive pore water conditions scanning electron microscope observations show that g sacculifer maintains a better preserved test ultrastructure than g ruber microprobe mapping reveals that mg rich bands in g ruber chamber walls are preserved despite reduced ca content assuming that the low test weight and offset in mg ca temperature between g sacculifer and g ruber are exclusively produced by calcite dissolution the bias in mg ca temperature determination can be estimated at around 1 c comparable to uncertainty of this thermometry despite the evidence for test dissolution foraminiferal mg ca seems to preserve initial temperature signals under the studied conditions

calibration of mg ca thermometry in planktonic foraminifera from a sediment trap time series 1 paired mg ca and 18o measurements on planktonic foraminiferal species g ruber white g ruber pink g sacculifer g conglobatus g aequilateralis o universa n dutertrei p obliquiloculata g inflata g truncatulinoides g hirsuta and g crassaformis from a 6 year sediment trap time series in the sargasso sea were used to define the sensitivity of foraminiferal mg ca to calcification temperature habitat depths and calcification temperatures were estimated from comparison of 18o of foraminifera with equilibrium calcite based on historical temperature and salinity data when considered together mg ca mmol mol of all species except two show a significant r 0 93 relationship with temperature t c of the form mg ca 0 38 0 02 exp 0 090 0 003 t equivalent to a 9 0 0 3 change in mg ca for a 1 c change in temperature small differences exist in calibrations between species and between different size fractions of the same species o universa and g aequilateralis have higher mg ca than other species and in general data can be best described with the same temperature sensitivity for all species and pre exponential constants in the sequence o universa g aequilateralis g bulloides g ruber g sacculifer other species this approach gives an accuracy of 1 2 c in the estimation of calcification temperature the 9 sensitivity to temperature is similar to published studies from culture and core top calibrations but differences exist from some literature values of pre exponential constants different cleaning methodologies and artefacts of core top dissolution are probably implicated and perhaps environmental factors yet understood planktonic foraminiferal mg ca temperature estimates can be used for reconstructing surface temperatures and mixed and thermocline temperatures using g ruber pink g ruber white g sacculifer n dutertrei p obliquiloculata etc the existence of a single mg thermometry equation is valuable for extinct species although use of species specific equations will where statistically significant provide more accurate evaluation of mg ca paleotemperature

mindanao dome variability over the last 160 kyr episodic glacial cooling of the west pacific warm pool we present sea surface upper thermocline and benthic delta 18 o data as well as temperature and paleoproductivity proxy data from the international marine global change study program images core md06 3067 6 degrees 31 n 126 degrees 30 e 1575 m water depth located in the western equatorial pacific ocean within the flow path of the mindanao current our records reveal considerable glacial interglacial and suborbital variability in the mindanao dome upwelling over the last 160 kyr dome activity generally intensified during glacial intervals resulting in cooler thermocline waters whereas it substantially declined during interglacials in particular in the early holocene and early marine oxygen isotope stage mis 5e when upwelling waters did not reach the thermocline during mis 3 and mis 2 enhanced surface productivity together with remarkably low sst and low upper ocean thermal contrast provide evidence for episodic glacial upwelling to the surface whereas transient surface warming marks periodic collapses of the mindanao dome upwelling during heinrich events we attribute the high variability during mis 3 and mis 2 to changes in the el nino southern oscillation state that affected boreal winter monsoonal winds and upper ocean circulation glacial upwelling intensified when a strong cyclonic gyre became established whereas el nino like conditions during heinrich events tended to suppress the cyclonic circulation reducing ekman transport thus our findings demonstrate that variations in the mindanao dome upwelling are closely linked to the position and intensity of the tropical convection and also reflect far field influences from the high latitudes

an atlantic lead over pacific deep water change across termination i implications for the application of the marine isotope stage stratigraphy globally synchronous changes in glacioeustatic sea level provide a particularly useful stratigraphic reference in the study of glacial interglacial climate change and form the basis for the marine isotope stage mis system which posits a dominant glacioeustatic signal in benthic foraminferal 18o however benthic 18o strictly does not represent a pure sea level record and it is shown here that due to local changes in deep water hydrography the mis 2 1 boundary i e benthic 18o change occurred 4000 years later in the deep eastern equatorial pacific than in the deep northeast atlantic this discrepancy is too large to be attributed entirely to the pacific lag that may be expected due to the mixing time of the ocean basins instead multiple proxies including benthic foraminiferal mg ca suggest that the large offset in benthic 18o most probably resulted from a late rise in deep water temperature at the pacific site and a series of coupled deep water temperature and 18o changes at the northeast atlantic site these findings have important implications for the application of the mis stratigraphy and the interpretation of benthic 18o records in general as they show that benthic 18o fluctuations and mis boundaries from different hydrological settings may be significantly diachronous these results call into question the leads and lags that we might infer from a naive interpretation of benthic 18o as a sea level proxy with a direct bearing on the mechanisms that we may propose to explain glacial interglacial climate transitions

precession modulation of the south pacific westerly wind belt over the past million years the southern westerly wind belt sww interacts with the antarctic circumpolar current and strongly impacts the southern ocean carbon budget and antarctic ice sheet dynamics across glacial interglacial cycles we investigated precipitation driven sediment input changes to the southeast pacific off the southern margin of the atacama desert over the past one million years revealing strong precession 19 23 ka cycles our simulations with 2 ocean atmosphere general circulation models suggest that observed cyclic rainfall changes are linked to meridional shifts in water vapor transport from the tropical pacific toward the southern atacama desert these changes reflect a precessional modulation of the split in the austral winter south pacific jet stream for precession maxima we infer significantly enhanced rainfall in the southern atacama desert due to a stronger south pacific split jet with enhanced subtropical subpolar jets and a weaker midlatitude jet conversely we derive dry conditions in northern chile related to reduced subtropical subpolar jets and an enhanced midlatitude jet for precession minima the presence of precessional cycles in the pacific sww and lack thereof in other basins indicate that orbital scale changes of the sww were not zonally homogeneous across the southern hemisphere in contrast to the hemispherewide shifts of the sww suggested for glacial terminations the strengthening of the jet is unique to the south pacific realm and might have affected winter controlled changes in the mixed layer depth the formation of intermediate water and the buildup of sea ice around antarctica with implications for the global overturning circulation and the oceanic storage of atmospheric co2

north atlantic midlatitude surface circulation changes through the plio pleistocene intensification of northern hemisphere glaciation the north atlantic current nac transports warm salty water to high northern latitudes with important repercussions for ocean circulation and global climate a southward displacement of the nac and subarctic front which separate subpolar and subtropical water masses is widely suggested for the last glacial maximum lgm and may have acted as a positive feedback in glacial expansion at this time however the role of the nac during the intensification of northern hemisphere glaciation inhg at 3 5 to 2 5 ma is less clear here we present new records from integrated ocean drilling program site u1313 41 n spanning 2 8 2 4 ma to trace the influence of subarctic front waters above this mid latitude site we reconstruct surface and permanent pycnocline temperatures and seawater 18 o using paired mg ca 18 o measurements on the planktic foraminifers globigerinoides ruber and globorotalia crassaformis and determine abundances of the subpolar foraminifer neogloboquadrina atlantica we find that the first significant glacial incursions of subarctic front surface waters above site u1313 did not occur until 2 6 ma at no time during our study interval was sub surface reorganization in the midlatitude north atlantic analogous to the lgm our findings suggest that lgm like processes sensu stricto cannot be invoked to explain interglacial glacial cycle amplification during inhg they also imply that increased glacial productivity at site u1313 during inhg was not only driven by southward deflections of the subarctic front we suggest that nutrient injection from cold core eddies and enhanced glacial dust delivery may have played additional roles in increasing export productivity in the midlatitude north atlantic from 2 7 ma

isopycnal mixing in ocean circulation models abstract a subgrid scale form for mesoscale eddy mixing on isopycnal surfaces is proposed for use in non eddy resolving ocean circulation models the mixing is applied in isopycnal coordinates to isopycnal layer thickness or inverse density gradient as well as to passive scalars temperature and salinity the transformation of these mixing forms to physical coordinates is also presented

near field high resolution strain measurements prior to the october 18 1989 loma prieta ms 7 1 earthquake high resolution strain recordings were made in deep boreholes throughout california prior to during and following the october 18 1989 ms 7 1 loma prieta earthquake the nearest dilational strainmeters sensitivity 1010 and 3 component tensor strainmeters sensitivity 10 9 were 37 km to 42 km respectively from the main shock high quality data including details of strain offsets were recorded on both instruments through the earthquake these data have been searched for indications of short intermediate and long term strain redistribution and or fault slip that might have indicated imminent rupture short and intermediate term changes in both tensor strain and dilational strain several nanostrain if any during the minutes to months before the earthquake are at least 1000 times smaller than that generated by the earthquake itself if short term preseismic slip did occur at the nucleation point of the earthquake during the previous week and if the type of slip is similar to that during the earthquake its moment could not be more than 1024 dyne cm stated another way slip equivalent to that expected for a m 5 3 earthquake could have occurred in the hypocentral region without the strainmeters detecting it at these distances and azimuthal positions long term changes appear to have occurred in mid 1988 and mid 1989 these changes were both followed by ml 5 earthquakes in the hypocentral region on june 27 1988 and august 8 1989 respectively and since they correspond approximately to changes in geodetic strain rate over the epicenter may indicate precursory strain redistribution in the epicentral region minor postseismic strain recovery 14 occurred in the month following the main shock

interlaboratory comparison study of mg ca and sr ca measurements in planktonic foraminifera for paleoceanographic research thirteen laboratories from the usa and europe participated in an intercomparison study of mg ca and sr ca measurements in foraminifera the study included five planktonic species from surface sediments from different geographical regions and water depths each of the laboratories followed their own cleaning and analytical procedures and had no specific information about the samples analysis of solutions of known mg ca and sr ca ratios showed that the intralaboratory instrumental precision is better than 0 5 for both mg ca and sr ca measurements regardless whether icp oes or icp ms is used the interlaboratory precision on the analysis of standard solutions was about 1 5 and 0 9 for mg ca and sr ca measurements respectively these are equivalent to mg ca based temperature repeatability and reproducibility on the analysis of solutions of 0 2 c and 0 5 c respectively the analysis of foraminifera suggests an interlaboratory variance of about 8 rsd for mg ca measurements which translates to reproducibility of about 2 3 c the relatively large range in the reproducibility of foraminiferal analysis is primarily due to relatively poor intralaboratory repeatability about 1 2 c and a bias about 1 c due to the application of different cleaning methods by different laboratories improving the consistency of cleaning methods among laboratories will therefore likely lead to better reproducibility even more importantly the results of this study highlight the need for standards calibration among laboratories as a first step toward improving interlaboratory compatibility

ultra low frequency electromagnetic measurements associated with the 1998 mw 5 1 san juan bautista california earthquake and implications for mechanisms of electromagnetic earthquake precursors abstract ultra low frequency ulf 0 01 10 hz magnetic field anomalies prior to m 6 0 earthquakes have been reported in various regions of the world here we test whether smaller magnitude earthquakes have associated ulf anomalies by using continuous measurements made 9 km above and 2 km ne of the epicenter of the m w 5 1 8 12 98 san juan bautista ca earthquake half hour spectral averages of the magnetic field data in nine different ulf frequency bands show no long term days to weeks magnetic field anomaly prior to the earthquake in addition magnetic and electric field polarization shows no anomalous behavior clearly associated with seismic activity an 0 02 nt increase in activity for 2 h prior to the earthquake is close to the background noise levels precluding identification of a precursor we present scaling calculations to show if precursory ulf anomalies are related to the size of the earthquake the observed 0 02 nt increase is the approximately expected magnetic anomaly prior to the san juan bautista sbj earthquake based on the anomaly observed prior to the 1989 loma prieta lp earthquake our reexamination of previously proposed dilatant conductive and piezomagnetic mechanisms for ulf precursors shows that these effects are consistent with the observations prior to the sjb earthquake based on the observations i e lack of a strong precursor in contrast previously proposed electrokinetic and magnetohydrodynamic mhd mechanisms do not appear to be appropriate for this particular earthquake this analysis further supports the hypothesis that precursory ulf signals are related to the size of the earthquake

seismomagnetic effect generated by the october 1989 ml 7 1 loma prieta california earthquake a differentially connected array of proton magnetometers operated within the epicentral region of the october 18 1989 ml 7 1 loma prieta earthquake for 12 years from 1974 to 1986 the closest magnetometer station was located 7 3 km from the epicenter of the earthquake and within 3 km of the site where anomalous ulf magnetic noise measurements were observed following the earthquake the magnetometers were reinstalled with sensors replaced in the original undisturbed sensor holders comparison of pre 1986 total intensity magnetic field data with data obtained during the months following the earthquake indicate local offsets of about 1 nt may have been generated at stations nearest the epicenter tests on other continuous differenced data from 1983 to present indicate that offsets determined could be biased by as much as 0 7 nt the offsets can be approximately fit with a simple seismomagnetic model of the earthquake for which 1 9 m of right lateral and 1 3 m of dip slip southwest side up occurred on a fault patch between 6 km and 18 km deep and 45 km long the total rock magnetization is assumed to be 1 5 a m since the offset has persisted following the earthquake an alternate explanation in terms of electokinetic effects is unlikely even though transient ground water flow occurred following the earthquake comparison of pre 1986 and similar post seismic total magnetic field noise does not indicate any change caused by aliasing of ulf 0 01 hz 10 hz magnetic noise in the vicinity of the loma prieta earthquake

analysis of ultralow frequency electromagnetic field measurements associated with the 1999 m 7 1 hector mine california earthquake sequence we installed two electromagnetic em monitoring systems in the im mediate aftermath of the 16 october 1999 hector mine earthquake to search for possible continuing ultralow frequency ulf em activity due to the mainshock as well as for any precursory or coseismic em signals that might be associated with large aftershocks we installed the first portable monitoring system 2 5 days after the m 7 1 hector mine earthquake at a location 16 km southeast of the epicenter and 2 km east of the surface rupture a second system was installed on 29 october 1999 10 km northwest of the epicenter and within 100 m of the surface rupture our continuous measurements of multiple component magnetic field electric field and ground motion span the low frequencies appropriate for recording possible em sig nals generated at seismogenic depths and were carried out during 3 months following the mainshock continuous magnetic field measurements at observatory em stations operating in california are used as remote reference sites to remove global atmo spheric signals which helps isolate local terrestrial sources of interest our analysis of preseismic ulf em variations the coseismic response the 2 month long magnetic field power spectra and electric field polarization shows no anomalous behavior clearly associated with seismic activity

comparison of ultra low frequency electromagnetic signals with aftershock activity during the 1989 loma prieta earthquake sequence abstract ultra low frequency 0 01 to 10 0 hz magnetic field fluctuations near the epicenter of the 1989 loma prieta earthquake rose sharply immediately before the earthquake following indications of increased disturbance during the previous 12 days the magnetic activity remained much higher than the pre earthquake background level for 6 weeks following the mainshock these observations suggest a causal relationship between the earthquake failure process and the magnetic signals a search for similar precursory electromagnetic signals associated with aftershocks of this earthquake yields negative results specifically no correlation appears to exist between the amplitude of the electromagnetic activity and the frequency or magnitude of aftershocks following the mainshock either a threshold earthquake magnitude larger in this case than m l 5 5 may be necessary to generate precursory electromagnetic signals or the continued generation of magnetic signals related to the mainshock may have masked signals generated by the larger aftershocks

hemispheric roles of climate forcings during glacial interglacial transitions as deduced from the vostok record and lln 2d model experiments the vostok ice contains fingerprints of atmospheric greenhouse trace gases antarctic temperature northern hemisphere temperature and global ice volume sea level changes during the last glacial interglacial cycles and thus allows us to investigate the sequences of these climatic events in particular during the transitions from full glacial to interglacial conditions the use of the updated co2 record presented here and a reexamination of the sea level proxy confirm that the succession of changes has been similar through each of the four marked transitions found at vostok antarctic air temperature and co2 increase in parallel and almost synchronously while the rapid warmings over greenland take place during the last half of their change and coincide with the marked decay in continental ice volume the vostok results thus emphasize a fundamental difference between south and north in terms of climate dynamics our results confirm the role of co2 as an important amplifier of the glacial interglacial warming in the south it appears also that the marked warming observed at high northern latitudes lagging behind the co2 increase by several thousand years is roughly synchronous with the decay of the northern ice sheets suggesting a major role of climatic feedback due to this decay such a climatic scenario is supported by sensitivity experiments performed with the lln 2 d model forced by the northern hemisphere insolation and co2 model results indicate that the decay of the northern ice sheets and the northern hemisphere temperature depend primarily on the northern summer insolation these results nevertheless could be affected if mechanisms specific to the southern hemisphere appear to play a major role in driving the northern hemisphere climate the model also helps to constrain the time response of ice volume to insolation and co2 changes

assessing divergent sst behavior during the last 21 ka derived from alkenones and g ruber mg ca in the equatorial pacific equatorial pacific sst reconstructions derived from mg ca ratios in planktonic foraminifera globigerinoides ruber and from alkenone producing coccolithophorids record different trends throughout the holocene and the last deglaciation we set forth the hypothesis that their diverging behavior may be related to different seasonal sensitivities which result from the annually varying production rates of alkenone producing coccolithophorids and of g ruber using a series of transient paleoclimate model simulations forced with the time varying forcing history over the last 21 ka a good qualitative agreement is found between simulated boreal winter temperatures and alkenone sst reconstructions as well as between simulated boreal summer temperatures and reconstructed mg ca based sst variations pronounced features in the reconstructions that can be readily explained by the conjectured seasonal biases include the mismatch in middle to late holocene temperature trends and the different onsets of deglacial climate change in the eastern equatorial pacific the analysis presented here further suggests that through combinations of mg ca and alkenone sst reconstructions information can be gained on annual mean temperature changes and the amplitude of the seasonal cycle in sst our study concludes by discussing potential weaknesses of the proposed model derived seasonal bias interpretation of tropical pacific sst proxies in terms of present day core top data sediment trap studies and satellite based observations of chlorophyll

interlaboratory comparison study of calibration standards for foraminiferal mg ca thermometry an interlaboratory study of mg ca and sr ca ratios in three commercially available carbonate reference materials bam rs3 cmsi 1767 and ecrm 752 1 was performed with the participation of 25 laboratories that determine foraminiferal mg ca ratios worldwide these reference materials containing mg ca in the range of foraminiferal calcite 0 8 mmol mol to 6 mmol mol were circulated with a dissolution protocol for analysis participants were asked to make replicate dissolutions of the powdered samples and to analyze them using the instruments and calibration standards routinely used in their laboratories statistical analysis was performed in accordance with the international standardization organization standard 5725 which is based on the analysis of variance anova technique repeatability rsdr an indicator of intralaboratory precision for mg ca determinations in solutions after centrifuging increased with decreasing mg ca ranging from 0 78 at mg ca 5 56 mmol mol to 1 15 at mg ca 0 79 mmol mol reproducibility rsdr an indicator of the interlaboratory method precision for mg ca determinations in centrifuged solutions was noticeably worse than repeatability ranging from 4 5 at mg ca 5 56 mmol mol to 8 7 at mg ca 0 79 mmol mol results of this study show that interlaboratory variability is dominated by inconsistencies among instrument calibrations and highlight the need to improve interlaboratory compatibility additionally the study confirmed the suitability of these solid standards as reference materials for foraminiferal mg ca and sr ca determinations provided that appropriate procedures are adopted to minimize and to monitor possible contamination from silicate mineral phases

millennial scale glacial meltwater pulses and their effect on the spatiotemporal benthicδ18o variability 1 ratios of oxygen isotope values obtained from foraminiferal calcite are one of the most established paleoceanographic proxies they are used in the context of estimating variations in ice volume ocean temperature and salinity and provide a means to date marine sediment cores across different ocean basins our study addresses the question how the 18o of the deglacial meltwater signal propagates into the interior ocean when large scale millennial scale reorganizations of the atlantic meridional overturning circulation amoc are present analyzing a series of idealized tracer injection experiments conducted with an earth system model we find that a substantial weakening of the amoc leads to a massive delay in the export of the glacioeustatic oxygen isotope signal into the deep ocean whereas the atlantic pacific lag in benthic oxygen isotope signals is not increased furthermore it is shown that an amoc cessation causes a decoupling of 18o propagation time and water mass age in particular in the deep pacific our results lend further support to the notion that benthic oxygen isotope records obtained from stacks are not a useful global chronostratigraphic tool during periods of millennial scale global ocean circulation changes the regionally varying delay effect of the deglacial sea level signal studied here adds onto existing uncertainties in the interpretation and decomposition of benthic oxygen isotope in terms of sea level temperature and hydrographic variations