gulf stream variability during marine isotope stage 3 we have studied ocean drilling program site 1060 on the blake outer ridge which lies beneath the gulf stream we focus on marine isotope stage 3 60 25 thousand years before present ka sea surface temperatures ssts inferred both from foraminiferal fauna and alkenone ratios as well as counts of iceberg melt out debris and benthic stable isotope analyses enable our record to be interpreted in terms of regional hydrographic changes as well as changing thermohaline circulation thc the observed sst record is consistent with the air temperature record from the greenland ice cores however site 1060 exhibits important differences in detail compared with the ice core record and when compared to other sites within the north atlantic significant longitudinal differences emerge at site 1060 in the western atlantic all greenland stadials gs whether associated with heinrich events hes or not show a similar small amplitude of cooling mean faunal based sstaug during gs is only 1 5 c colder than during greenland interstadials gis in addition during gs the coldest ssts are limited to apparently brief events this is in contrast to several eastern atlantic sites where he stadials exhibit coolings that are enhanced by 2 c compared to other gs and where cold conditions are not restricted to cold pulses but cover 2 ka long intervals furthermore site 1060 ssts remained warm right through each interstadial in contrast to the sustained and uniform cooling trend through interstadials that is consistently observed in greenland indicated by measurements of 18o in ice

antarctic intermediate water properties since 400 ka recorded in infaunal uvigerina peregrina and epifaunal planulina wuellerstorfi benthic foraminifera reconstruction of intermediate water properties is important for understanding feedbacks within the ocean climate system particularly since these water masses are capable of driving high low latitude teleconnections nevertheless information about intermediate water mass evolution through the late pleistocene remains limited this paper examines changes in antarctic intermediate water aaiw the most extensive intermediate water mass in the modern ocean through the last 400 kyr using the stable isotopic composition 18o and 13c and trace element concentration mg ca and b ca of two benthic foraminiferal species from the same samples epifaunal planulina wuellerstorfi and infaunal uvigerina peregrina our results confirm that the most reasonable estimates of aaiw temperature and co2 3 are generated by mg cau peregrina and b cap wuellerstorfi respectively we present a 400 kyr record of intermediate water temperature and co2 3 from a sediment core from the southwest pacific dsdp site 593 40 30 s 167 41 e 1068 m water depth which lies within the core of modern aaiw our results suggest that a combination of geochemical analyses on both infaunal and epifaunal benthic foraminiferal species yields important information about this critical water mass through the late pleistocene when combined with two nearby records of water properties from deeper depths our data demonstrate that during interglacial stages of the late pleistocene aaiw and circumpolar deep water cpdw have more similar water mass properties temperature and 13c while glacial stages are typified by dissimilar properties between aaiw and cpdw in the southwest pacific our new co2 3 record shows short time scale variations but a lack of coherent glacial interglacial variability indicating that large quantities of carbon were not stored in intermediate waters during recent glacial periods

detecting holocene changes in thermohaline circulation throughout the last glacial cycle reorganizations of deep ocean water masses were coincident with rapid millennial scale changes in climate climate changes have been less severe during the present interglacial but evidence for concurrent deep ocean circulation change is ambiguous

a 300 kyr high resolution aridity record of the north african continent new oxygen isotope data and a high resolution carbonate record of a core from the northwest african margin are presented in combination with geochemical zr rb ratio al ba organic carbon and biogenic opal fluxes and sedimentological median grain size parameters to show variations in african continental aridity wind strength and upwelling productivity the carbonate record is diluted by the supply of aeolian dust from the arid saharan region of north africa and is seen to vary with a characteristic sawtooth pattern indicating rapid increases in dust flux followed by gradual declines spectral analysis of the carbonate profile and comparison with specmap stacked oxygen isotope and etp solar radiation profiles shows that the precessional 23 kyr insolation induced african climate system is decoupled from global ice volume climate changes operating on a 100 kyr frequency detailed studies of glacial terminations i ii and iii confirm the presence of rapid short timescale climatic variations in aridity

some key features of the strong motion data from the m 6 0 parkfield california earthquake of 28 september 2004 the 2004 parkfield california earthquake was recorded by an extensive set of strong motion instruments well positioned to record details of the motion in the near fault region where there has previously been very little recorded data the strong motion measurements obtained are highly varied with significant variations occurring over only a few kilometers the peak accelerations in the near fault region range from 0 13 g to over 1 8 g one of the highest acceleration recorded to date exceeding the capacity of the recording instrument the largest accelerations occurred near the northwest end of the inferred rupture zone these motions are consistent with directivity for a fault rupturing from the hypocenter near gold hill toward the northwest however accelerations up to 0 8 g were also observed in the opposite direction at the south end of the cholame valley near highway 41 consistent with bilateral rupture with rupture southeast of the hypocenter several stations near and over the rupturing fault recorded relatively weak motions consistent with seemingly paradoxical observations of low shaking damage near strike slip faults this event had more ground motion observations within 10 km of the fault than many other earthquakes combined at moderate distances peak horizontal ground acceleration pga values dropped off more rapidly with distance than standard relationships at close in distance the wide variation of pga suggests a distance dependent sigma may be important to consider the near fault ground motion variation is greater than that assumed in shakemap interpolations based on the existing set of observed data higher density of stations near faults may be the only means in the near future to reduce uncertainty in the interpolations outside of the near fault zone the variance is closer to that assumed this set of data provides the first case where near fault radiation has been observed at an adequate number of stations around the fault to allow detailed study of the fault normal and fault parallel motion and the near field s wave radiation the fault normal motions are significant but they are not large at the central part of the fault away from the ends the fault normal and fault parallel motions drop off quite rapidly with distance from the fault analysis of directivity indicates increased values of peak velocity in the rupture direction no such dependence is observed in the peak acceleration except for stations close to the strike of the fault near and beyond the ends of the faulting

younger dryas style cooling events at glacial terminations i vi at odp site 658 associated benthic δ13c anomalies constrain meltwater hypothesis high resolution planktonic and epibenthic stable isotope records from ocean drilling program site 658 off northwest africa provide a basis for a detailed study of glacial terminations i vi during the last 650 000 years the duration of the terminations was about one half to one quarter of an orbital precession cycle 5800 10 700 years when its amplitude was high at low amplitudes the terminations lasted longer than half an obliquity cycle 29 000 years marked climatic rebounds similar to the younger dryas each with a duration of 1000 2500 years subdivided all six terminations into distinct steps a b and c important parts of the deglacial steps were as brief as 700 1000 years the speed of climatic change suggests that special associations existed between orbital forcing and inherent instability of the ice sheets in harmony with published models the more rapid pulses of glacial meltwater incursions to the northern north atlantic led to one or more brief short term shut downs of north atlantic deep water formation this process is reflected by pronounced benthic 13c minima that precisely coincide in most cases with the end of the 18o deglaciation steps and immediately terminate with succeeding younger dryas style cooling events thus we conclude that the rebounds resulted from a short term antecedent estuarine circulation regime in the north atlantic except for the younger dryas itself which succeeded the allerod with its well ventilated atlantic deepwater circulation and hence continues to be an enigma

long and short term carbon fluctuations in the eastern mediterranean during the late holocene a high resolution record of carbon isotope changes during the late holocene was obtained in core ga 112 from the easternmost mediterranean over the past 3600 yr a gradual 13 c depletion trend shown by both planktonic and benthic foraminifera corresponds to a global rise in atmospheric co 2 the global and local trends suggest that aridification and biomass destruction in the nile basin played a major role in the global co 2 rise in the late holocene superimposed on the general 13 c trend are four mirror image cycles in 13 c of planktonic and benthic foraminifera higher planktonic 13 c values reflect periods of high productivity off the coast of israel simultaneously decrease in the benthic 13 c values occurred because of degradation of higher organic matter fluxes to the sediment therefore large differences between the two records indicate periods of high productivity the eastern mediterranean productivity fluctuations respond to a periodical replenishment of nutrients to the mixed layer via nile runoff historical data of the nile flood fluctuations for the past 1400 yr show a remarkable coincidence between high and low nile floods and high and low eastern mediterranean productivity levels which are correlated with the periodic monsoonal activity over the nile headwaters

stable isotope fractionation in benthic foraminifera from the peruvian continental margin abstract stable isotope ratios of the carbonate tests of benthic foraminifera are now widely used to reconstruct past changes in ocean circulation and chemistry such studies depend on the accuracy with which changing environmental conditions are recorded and preserved in the tests of foraminifera found in deep sea deposits assessment of this aspect of the method is best accomplished through rigorous study of modern core tops collected from a wide range of depths and bottom water temperatures stable isotope analyses of eighteen taxa of benthic foraminifera from surface sediments of the peru continental margin indicate that most foraminifera are slightly depleted in 18o relative to the benthic foram uvigerina peregrina for at least five taxa we observed subparallel 18 o temperature relationships with slopes nearly equal to that predicted by shackleton 1974 for uvigerina for seven taxa isotopic analysis of six size fractions in the range 210 590 mm reveals that with the exception of u peregrina variation between different size classes for each species is small for 18 o and for 13 c a slight inverse correlation between foraminiferal 18o and 13c content implies a complex interplay of biological and environmental factors which control isotopic composition

upper proterozoic glaciogenic rocks and their stratigraphic significance abstract among more than 300 precambrian tillites mentioned in the literature only 25 can be identified as glacial rocks tillites are known from all continents with the exception of antarctica the uneven stratigraphic distribution of tillites cannot be explained as being due to differences in knowledge roughly synchronous glacial formations and groups form wide regional glaciohorizons they are concentrated in two stratigraphic intervals named glaciocomplexes one such the canadian glaciocomplex consisting of three or four glaciohorizons occurs in the lowermost lower proterozoic in north america and south africa the second glaciocomplex the african containing four or more glaciohorizons is known in the uppermost part of the precambrian in europe asia north and south america africa australia the glaciohorizons and glaciocomplexes reflect oscillation dynamics of glaciations and show a hierarchical structure of glacial events the glaciohorizons and glaciocomplexes were deposited during glacial periods and glacial eras on and marginal to the continents in high and middle paleolatitudes of both hemispheres by comparison with late cenozoic glacial events the duration of the ancient glacioperiods can be roughly estimated at between some millions and a few tens of millions of years within these limits each glaciohorizon can be asynchronous the glaciohorizons have great importance for regional correlations of the precambrian interregional and intercontinental glacial correlations however require radiometric and biostratigraphic controls glacial units can be used in construction of a global stratigrphic scale for the precambrian

phanerozoic continental drift abstract an account is given of phanerozoic continental drift a series of paleocontinental maps is presented for ten intervals from 600 to 25 my ago post triassic maps were reconstructed using the plate tectonic model based mainly on ocean floor spreading evidence continental edge fits and apparent polar wander apw paths the middle carboniferous triassic maps are less certain lacking ocean floor spreading evidence but continental positions are constrained by the assumptions of minimum relative continental motions the pre carboniferous maps are based on poorly defined apw paths and minimum motions and can only indicate probable configurations during that period the main theme is that the late precambrian pan african pangea has been progressively fragmented during the phanerozoic pieces broken off in the paleozoic have now collided with one another forming the present northern continents which have grown at the expense of pangea except for india fragments broken off in the mesozoic and cenozoic are still unattached and form the present southern continents

carbon isotope offsets between benthic foraminifer species of the genus cibicides cibicidoides in the glacial sub antarctic atlantic epibenthic foraminifer 13c measurements are valuable for reconstructing past bottom water dissolved inorganic carbon 13c 13cdic which are used to infer global ocean circulation patterns epibenthic 13c however may also reflect the influence of 13c depleted phytodetritus microhabitat changes and or variations in carbonate ion concentrations here we compare the 13c of two benthic foraminifer species cibicides kullenbergi and cibicides wuellerstorfi and their morphotypes in three sub antarctic atlantic sediment cores over several glacial interglacial transitions these species are commonly assumed to be epibenthic living above or directly below the sediment water interface while this might be consistent with the small 13c offset that we observe between these species during late pleistocene interglacial periods 13c 0 19 0 31 n 63 it is more difficult to reconcile with the significant 13c offset that is found between these species during glacial periods 13c 0 76 0 44 n 44 we test possible scenarios by analysing uvigerina spp 13c and benthic foraminifer abundances 1 c kullenbergi 13c is biased to light values either due to microhabitat shifts or phytodetritus effects and 2 c wuellerstorfi 13c is biased to heavy values relative to long term average conditions for instance by recording the sporadic occurrence of less depleted deep water 13cdic neither of these scenarios can be ruled out unequivocally however our findings emphasize that supposedly epibenthic foraminifer 13c in the sub antarctic atlantic may reflect several factors rather than being a sole function of bottom water 13cdic which directly bear on the interpretation of extremely light south atlantic 13c values at the last glacial maximum

changes in detrital input ventilation and productivity in the central okhotsk sea during the marine isotope stage 5e penultimate interglacial period abstract by presenting benthic foraminifera isotope profiles and bulk geochemical composition of core sediments we offer a mutiproxy reconstruction of the central okhotsk sea oceanography between 130 to and 115 kyr related to the marine isotopic stage 5e mis 5e sediments from the site mr0604 pc7a have been compared with paleo sea surface temperatures and other records this multiparameter approach allowed to recognize three periods for mis 5e evolution characterized by variations in marine productivity and bottom oxygenation these variations have been ultimately associated with the production of okhotsk sea intermediate water and the presence or absence of nutrient contribution from the pacific deep water into central okhotsk sea aeolian input reconstructed by th sc ratio indicates higher values during the mis 6 and mis 5d compared with the mis 5e eu values indicate an input of detrital material from kurile islands and east kamchatka during the late mis 5e absent during the early mis 5e and glacial periods

the holstein interglaciation time stratigraphic position and correlation to stable isotope stratigraphy of deep sea sediments marine molluscan shells from para type and other loclities of the holsteinian interglaciation were dated by thu and the electron spin resonance esr method to more than 350 000 and 370 000 yr b p beyond the limit of thu dating the high age estimate is corroborated by a kar age of 420 000 yr b p determined from volcanic ash near the base of the ariendorf paleosol in the middle rhine valley believed to be a pedostratigraphic equivalent of the holsteinian shells from the herzeele marine unit iii an equivalent of the wacken domnitz warm stage in northern france and subsequent to the holsteinian revealed ages between 300 000 and 350 000 yr b p a correlation of these two warm stages with marine oxygen isotope stages 11 and 9 on the specmap and cartune time scales is suggested from the benthic oxygen isotope record one may infer that no exceptionally high global sea level rise corresponds to the large transgressions of the holstein sea in northern germany therefore a significant proportion of the transgression was probably the result of an unusually large local glacial isostatic depression caused by the extreme buildup of ice during the preceding elster glaciation stage 12 according to the deep sea record it lasted approximately 50 longer than the subsequent cold stage 10 the outstanding soil formation with braunlehm and the well developed thermal optimum of the holsteinian are tentatively related to a phase of minimum sea ice cover in the norwegian greenland sea as deduced from long benthic carbon isotope records from the central atlantic

multispecies stable isotopes of benthic foraminifers reveal past changes of organic matter decomposition and deepwater oxygenation in the arabian sea 1 the stable isotope composition of one epifaunal and three infaunal benthic foraminiferal species of a sediment core from 1800 m water depth of the western arabian sea was determined to evaluate deepwater oxygenation organic matter remineralization and early diagenetic processes during the past 190 000 years the 18o records reveal species specific metabolic effects susceptibility to changes in carbonate ion concentration and supralysoclinal calcite dissolution the foraminiferal 13c records reveal changes in the stable carbon isotope gradients of pore water dissolved inorganic carbon 13cdic and in the microhabitat depth of infaunal species maximum 13cdic offsets between bottom and pore waters ranged between mean values of 0 8 and 1 2 corresponding to estimates of deepwater oxygen concentration between approximately 1 and 2 7 ml l 1 intervals of improved deepwater oxygenation coincided with high benthic foraminiferal diversity and indicate the admixture of well oxygenated deepwater masses during interglacials during interglacial maxima the 13c difference between epifauna and shallow infauna indicates highest organic matter remineralization rates at times of maximum organic matter fluxes

prolonged warming of the brazil current precedes deglaciations abstract paleoceanographic reconstructions from the brazil current are scarce and lack the required temporal resolution to appropriately represent its variability during key periods of the last glacial interglacial cycles here we present the first high temporal resolution multiproxy reconstruction of the brazil current at 24 s covering the last 185 ka during the last and penultimate glacial periods our mg ca derived sea surface temperature sst record shows a strong cooling at ca 47 and ca 156 ka respectively that is followed by a warming trend from late marine isotope stage mis 3 to mis 1 and from late mis 6 to mis5e respectively importantly the brazil current warmed uninterruptedly towards termination i ii after the low sst at ca 47 and ca 156 ka with no sst minima during the last glacial maximum or penultimate glacial maximum the reason for the strong cooling and the warming trend during late mis 3 and late mis 6 could reside in the favorable obliquity configuration however this mechanism is not sufficient to sustain the warming observed for the rest of the last and penultimate glacial periods we propose that the change in the atlantic meridional overturning circulation amoc as described in the literature from a warm to a cold mode for mis 2 and mis 6 is responsible for the accumulation of warm waters in the subtropical western south atlantic preventing sst minima during the last and penultimate glacial maxima in the region change in benthic 13 c corroborates that a fundamental modification in the amoc mode might have triggered the heat accumulation our data also show a sudden increase in sst and surface salinity during the last glacial descent mis 4 indicating that the western portion of the subtropical gyres may have acted as a heat and salt reservoir while higher latitude climates transited to a glacial background our findings imply that the amoc cold mode induces heat storage in the subtropical western south atlantic and because of that the last two regional sst minima occurred out of phase with the glacial maxima of higher latitudes

a review of the australian new zealand sector of the southern ocean over the last 30ka aus intimate project the australia new zealand region of the southern ocean is influenced by several of the major global water masses of the oceans and is the prime entry point for cold deep waters into the pacific basin during the last glacial there was increased sea ice extent around antarctica as far north as 55 s as well as increased iceberg presence inferred from ice rafted debris evidence from microfossil assemblages suggests that sea surface temperatures sst were up to 7 c cooler consistent with recent estimates of cooling for new zealand derived from glacier modelling and other terrestrial proxies the subtropical front stf subantarctic front saf and polar front pf had migrated north except where the position of the fronts were controlled bathymetrically despite the potential for iron fertilisation by increased dust input into the ocean during the glacial there is limited evidence for higher total biological productivity in the pacific sector of the southern ocean the altered oceanic circulation during the glacial also decreased nutrients in the surface waters and affected the outgassing of co 2 this contributed to an increased storage of co 2 in the deep waters and lowering of the carbonate lysocline during the deglaciation sea ice retreat and sst increased rapidly at 18 ka roughly synchronous with the reinvigoration of deep water circulation in the southern ocean and the release of co 2 stored in the deep waters the gradient in carbon isotopes 13 o benthic between antarctic intermediate water aaiw and lower circumpolar deep water lcdw was greatest at the start of the deglaciation suggesting that the aaiw ventilation preceded lcdw ventilation or there was a significant change in air sea fractionation of 13 o benthic there was a slight enrichment in 18 o planktic decrease in ssts and a reduction in intermediate and deep water circulation between 14 and 12 5 ka bp during the antarctic cold reversal acr coincident with glacier advances in the new zealand southern alps and other terrestrial records of cooling following the acr there was a second more minor release of deep water co 2 most likely related to reinvigoration of north atlantic deep water nadw from 10 ka onwards the modern intermediate and deep water circulation was established air temperatures and ssts reached a maximum in the early holocene with the stf located at its most southerly position and there was a widespread retreat of antarctic ice sheets to their modern position a decline to modern sst and air temperatures in the mid to late holocene followed while millennial cycles overprinted on the sst and 18 o planktic records may be the result of subtle changes in the position and strength of the westerly winds during the holocene

δ13c values of miocene pacific benthic foraminifera correlations with sea level and biological productivity 13 c 12 c ratios of miocene benthic foraminifera from 22 pacific ocean sites vary with time but are similar at almost all sites in any restricted interval 13 c values are correlated with sea levels inferred from onlap offlap curves reflecting the deposition of greater amounts of organic matter on the continental shelves during transgressions differences in 13 c between sites are correlated with local differences in biological productivity in the overlying surface waters 13 c 12 c values of benthic foraminifera show promise as indicators of marine paleoproductivity

high fertility in the alboran sea since the last glacial maximum based on the glacial to postglacial 13c differences between endobenthic uvigerina peregrina species from the alboran basin and from other mediterranean basins changes in the fertility of the western part of this basin during the last deglaciation are reconstructed as a result of particulate organic carbon poc rain from the highly productive upwelling cell along the northwestern margin of the alboran basin u peregrina is presently depleted by about 1 6 with respect to the measured 13c values of bottom water co2 and by about 0 9 with respect to specimens from other areas of the western mediterranean or from the gulf of cadiz within the mediterranean outflow water the uvigerina 13c difference between the alboran sea and the gulf of cadiz 13c was close to 0 at the beginning of the last deglaciation and during the late glacial time this suggests that highly fertile systems set in the alboran sea near 16 kyr b p two rapid increases in the 13c offset are recorded near 15 kyr and 11 kyr b p fluctuations around 1 1 to 1 2 occurred during the early holocene and a maximum was reached near 9 kyr b p after 4 kyr the 13c offset decreased to its present day average value of 0 9 changes in the intensity of surficial production cannot account for all the observed fluctuations especially in the early holocene time a strong decrease in the intermediate and deep water ventilation of the alboran basin may have occurred near 8 9 kyr in phase with the last stagnant phase in the eastern mediterranean and the deposition of sapropel s1 as a result the redistribution and remineralization at depth of the produced organic matter was incomplete the poc rain reaching the sediment was locally intensified and caused the lowering of the 13c values of endobenthic foraminifers such as u peregrina the benthic 13c signal suggests that the difference between the alboran sea and the gulf of cadiz was at its maximum at the same time an important modification in the water masses structure may have occurred near 9 8 kyr b p the deepening of the permanent pycnocline probably related to a thicker atlantic jet at a stage of high sea level stand is recorded by the replacement of the right coiling n pachyderma dominance coincident with a shallow pycnocline by the g inflata dominance coincident with a deep pycnocline diatom abundances were strongly reduced indicating an important modification of the productive system the glacial postglacial evolution of productivity within the alboran basin was therefore more complex than in the adjacent atlantic ocean and opposite to the global one which displays a general increase in productivity during glacial time although it is the global budget of paleoproductivity that would drive the partitioning of carbon within the ocean local or regional discrepancies with the global glacial interglacial model must be addressed local winds and regional atmospheric pressure systems which are the forcing factors for circulation and exchange with the atlantic control the fertile systems of the alboran basin

recent benthic foraminifera from the continental margin of northwest africa community structure and distribution abstract sediment grab samples were collected at 107 locations along the continental margin of northwest africa these samples form a series of depth transects between the straits of gibraltar and dakar senegal the greater than 250 m size fraction was retained for a census of both the live and dead foraminifera after deleting trace occurrences jaccard and correlation coefficient based cluster analyses were performed to decipher the community structure for this margin the geographic distribution of the four major faunal provinces recognized is conventional in that for both the live and dead assemblages three are related to depth upper slope and shelf middle slope and lower slope and continental rise the biotopes and thanatotopes within these provinces are strongly restricted along vertical or latitudinal boundaries when the data are analysed using jaccard coefficients dendrograms constructed from correlation coefficients emphasize depth related faunal communities dominant species such as cibicides lobatulus trifarina fornasinii planulina ariminensis uvigerina finisterrensis and c wuellerstorfi are generally distributed within a definite depth range along this margin and strongly influence the correlation coefficient based dendrograms other distributions are clearly not depth related but correspond to various environmental variables for example cancris auriculus coarse substrate bolivina subaenariensis oxygen minimum cibicidoides kullenbergi and hoeglundina elegans low organic carbon uvigerina peregrina is also a notable exception to depth dependence in that this dominant species and the province it represents are generally confined to the continental slope south of cape blanc its preference for that region may arise from the high organic carbon and fine grain size of the sediment there from low salinity of the bottom water or from other unknown variables the most important vertical faunal boundary occurs between cape barbas and cape blanc between 22 and 21 n latitude in contrast the canary island ridge intersects the continental margin at a saddle depth of about 1500 m but that physiographic barrier has little effect on provincialism of the deep water benthic foraminifera

sedimentation in glacial environments and the identification of tills and tillites in ancient sedimentary sequences abstract tills and tillites are defined and subdivided into primary tills comprising lodgement tills melt out tills and sublimation tills and secondary tills comprising flow tills and deformation tills they are defined on the basis of their mode of deposition which endows them with their distinctive properties another category of till that of supra till is defined on the basis of its debris source derived supraglacially from valley sides and nunataks which gives these tills a coarse grained character the processes of till deposition and of outwash sedimentation are associated in several recurrent combinations which allow the definition of three principal glacial sediment associations and land systems which define the character of the sequences within which tills tend to occur the criteria which allow tills of different genesis to be identified and to be distinguished from non till diamictons are reviewed there are several features which are uniquely characteristic of till but unfortunately these are few it has been found generally necessary to employ an array of characteristics which though not individually unique to till when taken together can be strong evidence for particular till types the recognition of several typical and repetitive facies sequences which form in the major glacial sedimentary environments can also be important indicators of till genesis

13c record of benthic foraminifera in the last interglacial ocean implications for the carbon cycle and the global deep water circulation the 13c 12c ratios of upper holocene benthic foraminiferal tests genera cibicides and uvigerina of deep sea cores from the various world ocean basins have been compared with those of the modern total carbon dioxide tco2 measured during the geosecs program the 13c difference between benthic foraminifera and tco2 is 0 07 0 04 for cibicides and 0 83 0 07 for uvigerina at the 95 confidence level 13c analyses of the benthic foraminifera that lived during the last interglaciation isotopic substage 5e about 120 000 yr ago show that the bulk of the tco2 in the world ocean had a 13c value 0 15 0 12 lower than the modern one at the 95 confidence level reflecting a depletion compared to the present value of the global organic carbon reservoir regional differences in 13c between the various oceanic basins are explained by a pattern of deep water circulation different from the modern one the antarctic bottom water production was higher than today during the last interglaciation but the eastward transport in the circumpolar deep water was lower

changes in deep and intermediate water properties in the western north atlantic during marine isotope stages 11 12 evidence from odp leg 172 abstract the interval of time represented by marine isotope stages 11 and 12 360 470 ka contains what may be the most extreme glacial and interglacial climate conditions of the late pleistocene it has been suggested that sea level rose by 160 m at the termination of glacial stage 12 this is 30 greater than the sea level rise that followed the most recent glacial maximum there have been few detailed studies of the unique conditions that existed during the stage 11 12 time period because of the lack of high quality core material this problem has been addressed by the collection of high deposition rate cores from sediment drifts in the western north atlantic during ocean drilling project leg 172 benthic foraminiferal 13 c data from cores collected between 4600 and 1800 m were used to reconstruct bathymetric gradients in deep and intermediate water properties for selected time slices during this glacial interglacial cycle during glacial stage 12 the deep western north atlantic was filled by a water mass that was more nutrient enriched than modern antarctic bottom water above 2000 m a more nutrient depleted water mass existed during this glacial stage such an intermediate water mass has been described for more recent glacial periods and presumably forms in a more proximate region of the north atlantic interglacial stage 11 water mass properties closely resemble those of the present day western north atlantic a nutrient depleted water mass 13 c of 0 75 1 0 similar to modern north atlantic deep water existed between 3500 and 2000 m this was underlain by a water mass with lower 13 c values 13 c change of 0 95 from stage 12 to stage 11 this is twice the whole ocean 13 c change reported for the transition from the last glacial maximum to the holocene

response of global deep water circulation to earth s climatic change 135 000 107 000 years ago the response of deep ocean circulation to major climatic events of the past 135 000 years is inferred using carbon 13 analyses of benthic foraminifera from the major ocean basins the results demonstrate that the circulation of the world ocean deep water is very sensitive to climate and that it changes drastically during climatic transitions

pre pleistocene glaciation on earth implications for climatic history of mars the history of ice ages on earth extending back more than 2 ga 109 years has been established by the recognition in strata of many ages of the assemblage of erosional features and deposits generated by glacial activity the most useful indicators are widespread diamictite striated and faceted clasts polished and striated pavements and laminites containing dropstones inferred to be ice rafted the chronology of ancient glaciation is limited by our ability to recognize the results of glacial activity in an incomplete geologic record and by the age resolution attainable with available dating methods ice ages are currently known from the early proterozoic 2 5 2 1 ga ago several intervals in the middle to late proterozoic 1 0 0 57 ga the late ordovician to late silurian 440 415 ma or 106 years possibly latest devonian 360 345 ma permo carboniferous 335 245 ma and late cenozoic 26 ma ago to the present however the timing of pre phanerozoic ice ages occurring before 0 57 ga ago is known only approximately and glacial events would have been shorter than is suggested by the bracketing ages a generally warm climate seems to have prevailed for the remainder of earth history although mesozoic cenozoic seismic stratigraphic evidence suggests that a small ice sheet may have been a persistent feature near the south pole throughout the last 500 ma terrestrial climatic fluctuations occur on several time scales the occurence of ice ages on a time scale of 108 109 years and possibly higher frequency fluctuations 106 107 years appears to be controlled by changes in solar output and atmospheric composition and by the rearrangement of continents and oceans as a result of the motion of lithospheric plates climatic changes on a time scale of 104 105 years are driven by perturbations of the earth s orbital parameters the principal evidence suggesting that significant climate changes have occured on mars consists of widespread dry channels 3 5 0 5 ga and of geologically young dust ice layered terrains in the polar regions 10 ma by analogy with the earth polar layered terrains have probably existed episodically on mars for a considerable time although there is little direct evidence for this factors affecting a potential sedimentary record are the degree to which ice sublimed or melted the effectiveness of eolian destruction of layering and in contrast to the present polar terrains the tendency for ice to flow and slide over its substrate as on earth climate changes on mars have probably been induced by the long term evolution of the atmosphere by changes in solar luminosity and by variations in orbital parameters major tectonic events may have affected martian climate through changes in planetary obliquity

pliocene pleistocene evolution of sea surface and intermediate water temperatures from the southwest pacific over the last 5 million years the global climate system has evolved toward a colder mean state marked by large amplitude oscillations in continental ice volume equatorward expansion of polar waters and strengthening temperature gradients have been detected however the response of the mid latitudes and high latitudes of the southern hemisphere is not well documented despite the potential importance for climate feedbacks including sea ice distribution and low high latitude heat transport here we reconstruct the pliocene pleistocene history of both sea surface and antarctic intermediate water aaiw temperatures on orbital time scales from deep sea drilling project site 593 in the tasman sea southwest pacific we confirm overall pliocene pleistocene cooling trends in both the surface ocean and aaiw although the patterns are complex the pliocene is warmer than modern but our data suggest an equatorward displacement of the subtropical front relative to present and a poleward displacement of the subantarctic front of the antarctic circumpolar current acc two main intervals of cooling from 3 ma and 1 5 ma are coeval with cooling and ice sheet expansion noted elsewhere and suggest that equatorward expansion of polar water masses also characterized the southwest pacific through the pliocene pleistocene however the observed trends in sea surface temperature and aaiw temperature are not identical despite an underlying link to the acc and intervals of unusual surface ocean warmth 2 ma and large amplitude variability in aaiw temperatures from 1 ma highlight complex interactions between equatorward displacements of fronts associated with the acc and or varying poleward heat transport from the subtropics

deglacial whole ocean δ13c change estimated from 480 benthic foraminiferal records terrestrial carbon storage is dramatically decreased during glacial periods due to cold temperatures increased aridity and the presence of large ice sheets on land most of the carbon released by the terrestrial biosphere is stored in the ocean where the light isotopic signature of terrestrial carbon is observed as a 0 32 0 7 depletion in benthic foraminiferal 13c the wide range in estimated 13c change results from the use of different subsets of benthic 13c data and different methods of weighting the mean 13c by volume we present a more precise estimate of glacial interglacial 13c change of marine dissolved inorganic carbon using benthic cibicidoides spp 13c records from 480 core sites more than 3 times as many sites as previous studies we divide the ocean into eight regions to generate linear regressions of regional 13c versus depth for the late holocene 0 6 ka and last glacial maximum 19 23 ka and estimate a mean 13c decrease of 0 38 0 08 2 for 0 5 5 km estimating large uncertainty ranges for 13c change in the top 0 5 km below 5 km and in the southern ocean we calculate a whole ocean change of 0 34 0 19 this implies a terrestrial carbon change that is consistent with recent vegetation model estimates of 330 694 gt c additionally we find that a well constrained surface ocean 13c change is essential for narrowing the uncertainty range of estimated whole ocean 13c change

kinematic inversion of the 2004 m 6 0 parkfield earthquake including an approximation to site effects the 2004 m 6 0 parkfield earthquake yielded one of the largest amounts of near source strong ground motion seismic data ever we invert strong motion seismograms to obtain a model for the space time distribution of coseismic slip on the fault to reduce noise in the inversion we take into account local amplifications that affect each station by using records of the 1983 m 6 5 coalinga earthquake site amplification correlates well with large peak ground velocities registered during the 2004 parkfield mainshock the inversion for a kinematic rupture model yields a nonunique solution we therefore analyze various rupture models that explain the data equally well our preferred rupture model identifies a primary zone of high slip surrounding the hypocenter where the maximum slip is 57 cm a secondary slip area over which contours are not well resolved is located northwest of the hypo center the rupture speed is highly heterogeneous we infer an average rupture ve locity of 2 8 km sec close to the hypocenter and of 3 3 km sec in the secondary region of large slip to the northwest of the hypocenter by correlation of our rupture model with both microseismicity and velocity structure we identify six patches on the fault plane that behave in seismically distinct ways online material kinematic rupture model parameters

response of deep ocean circulation to initiation of northern hemisphere glaciation 3 2 ma carbon isotopic records from benthic foraminifera are used to map patterns of deep ocean circulation between 3 and 2 million years ago the interval when significant northern hemisphere glaciation began the 18o and 13c data from four atlantic sites 552 607 610 and 704 and one pacific site 677 show that global cooling over this interval was associated with increased suppression of north atlantic deep water nadw formation however the relative strength of nadw production was always greater than is observed during late pleistocene glaciations when extreme decreases in nadw are observed in the deep north atlantic our data indicate that an increase in the equator to pole temperature gradient associated with the onset of northern hemisphere glaciation did not intensify deepwater production in the north atlantic but rather the opposite occurred this is not unexpected as it is the warm high salinity characteristic rather than the low temperature of thermocline waters that is critical to the deepwater formation process in this region today

introduction to the special issue on the 2004 parkfield earthquake and the parkfield earthquake prediction experiment the 28 september 2004 m 6 0 parkfield earthquake a long anticipated event on the san andreas fault is the world s best recorded earthquake to date with state of the art data obtained from geologic geodetic seismic magnetic and electrical field networks this has allowed the preearthquake and postearthquake states of the san andreas fault in this region to be analyzed in detail analyses of these data provide views into the san andreas fault that show a complex geologic history fault geometry rheology and response of the nearby region to the earthquake induced ground movement although aspects of san andreas fault zone behavior in the parkfield region can be modeled simply over geological time frames the parkfield earthquake prediction experiment and the 2004 parkfield earthquake indicate that predicting the fine details of future earthquakes is still a challenge instead of a deterministic approach forecasting future damaging behavior such as that caused by strong ground motions will likely continue to require probabilistic methods however the parkfield earthquake prediction experiment and the 2004 parkfield earthquake have provided ample data to understand most of what did occur in 2004 culminating in significant scientific advances

variation of deepwater convection in the western mediterranean sea gulf of lion during the last 28 ka abstract the oxygen and carbon isotopes record from fossil foraminifera in deep sea sediments are commonly used as proxy for global thermohaline and productivity changes the last 28 ka record of oxygen and carbon isotopes are characterized by a slow transfer of isotopic signal from surface to deep mediterranean at the beginning of heinrich events h2 and h1 and during the bolling allerod these changes in deep waters properties occur some 180 years later indicating a decrease of ventilation in the beginning of these events the slowing of the thermohaline convection is more marked in the early holocene characterized by less than 500 years of lag time between the isotopic signals

stable isotope fractionation in live benthic foraminifera from the southern california borderland live specimens of benthic foraminifera have been analyzed from surface sediment samples collected from 108 to 1134 m depth in the southern california borderland the temperature and isotopic composition of the ambient water and dissolved inorganic carbon have also been measured to permit comparison of foraminiferal compositions to expected equilibrium values the species analyzed break down into four groups which reflect the influence of mineralogy aragonite vs calcite biological fractionation vital effect and microhabitat effects on isotopic composition the aragonitic hoeglundina elegans show an enrichment in 18o relative to equilibrium calcite of 0 41 0 in shallower water increasing to at least 1 06 0 in deeper water the 13c enrichment of h elegans relative to the dissolved inorganic carbon dic is also depth dependent increasing from 1 27 0 at 108 m to 2 13 0 at 940 m this depth dependence results from the change in composition of the dic the 13c composition of h elegans remains constant with depth for some unknown reason one possible explanation is that the change in composition of the dic is balanced by an increase in hoeglundina hco 3 fractionation with decreased temperature the 13c values of the cassidulina species are almost identical to those of the ambient dissolved inorganic carbon dic and reflect the decrease in the 13c of the dic with depth the 13c values of species not in 18o equilibrium vary independently of the changing composition of the dic there is a correlation between 13c and 18o among coeval species consistent with the model which explains vital effect as the result of incorporation of isotopically light metabolic co2 into the shell the magnitude of disequilibrium is relatively constant for 18o but not for 13c suggesting that in isotopic stratigraphy studies it may be difficult to calibrate the 13c of different species as has been done with 18o there appears to be a relationship between taxonomic group and vital effect the foraminifera in approximate 18o equilibrium with the water including species of cassidulina bolivina uvigerina and globobulimina are members of the family cassidulinidae or superfamily buliminacea those not in 18o equilibrium including species of pyrgo quinqueloculina triloculina and lenticulina belong to the families miliolidae and vaginulinidae no disequilibrium species have been found as yet in the low oxygen environments of the borderland this observation and published findings on the ultrastructure of benthic foraminifera suggest that isotopic behavior may be related to a foraminifer s ability to exchange gases rapidly with its ambient water

source and site characteristics of earthquakes that have caused exceptional ground accelerations and velocities abstract this study investigates the characteristics of the free field strong motion records that have yielded the 100 largest peak accelerations and the 100 largest peak velocities in a relatively complete database of accelerograms recorded through the summer of 2007 the peak is defined as the maximum zero to peak amplitude of the acceleration or velocity vector during the strong shaking this compilation includes 35 records with peak acceleration greater than 1 g 980 cm sec 2 and 40 records with peak velocities greater than 100 cm sec the results sample an estimated 150 000 instrument years of strong motion recordings the geometric mean of the two horizontal components of acceleration or velocity as used in many ground motion prediction equations is typically 0 76 times the magnitude of this vector peak accelerations in the top 100 come from earthquakes as small as magnitude 4 8 while velocities in the top 100 all come from earthquakes with magnitude 5 7 or larger these records are dominated by crustal earthquakes with thrust oblique thrust or strike slip mechanisms normal faulting mechanisms in crustal earthquakes constitute under 5 of the records in the databases searched and an even smaller percentage of the 100 largest acceleration or velocity records all national earthquake hazard reduction program site categories have contributed exceptional records in proportions similar to the extent that they are represented in larger databases

carbon and oxygen isotopic disequilibria of recent deep sea benthic foraminifera abstract the carbon and oxygen isotopic compositions of 149 samples of benthic foraminifera from deep sea core tops indicate that none of the nine species studied secrete calcium carbonate in isotopic equilibrium with ambient bottom water uvigerina pyrgo murrhina and oridorsalis tener are the closest to 18o equilibrium with average deviations about 0 4 while planulina wuellerstorfi and p murrhina are the closest to 13c equilibrium with average deviations about 1 p wuellerstorfi shows the most systematic relationship between 13c and bottom water apparent oxygen utilization the intraspecific variabilities in 18o and 13c suggest that estimates of bottom water paleotemperatures can be made to a precision of 0 7 c while estimates of past apparent oxygen utilization aou can be made to 35 mol kg based on intraspecific comparisons of the recent samples with fossils no temporal changes in the degree of either 18o or 13c disequilibrium have been detected for planulina wuellerstorfi uvigerina oridorsalis tener and globocassidulina subglobosa

direct assessment of stable isotope variability in planktonic foraminifera populations abstract a large number of tests of three species of planktonic foraminifera globigerinoides sacculifer orbulina universa and pulleniatina obliquiloculata were analyzed for stable oxygen and carbon isotopes in a western equatorial pacific box core estimates of population variance were calculated using a statistical technique known as the jackknife these estimates were used to generate sampling curves which provide the number of foraminiferal tests required in an isotopic analysis when precision and reliability criteria are specified the jackknife results have important sampling implications 1 a large number of foraminiferal tests are required to obtain statistically reliable isotope data for example given a machine precision standard deviation of 0 09in0 417 tests g sacculifer 355 420 m are required to obtain a 18 o precision of 0 1in0 with 90 reliability 2 variance is a function of test diameter with greater variance being found in larger size fractions 3 variance is dependent on foraminiferal species 4 variance differences between glacial and interglacial samples are not significant 5 in the size interval 600 900 m a systematic relationship is not seen between size and 18 o or 13 c 6 replicate analysis is a practical method of improving isotope data quality size and species related variance differences are probably related to a number of factors including depth habitat seasonal production of tests species vertical migrations and vital and or symbiosis caused effects knowledge of data variance permits error assessment in sediment unmixing analyses and optimization of spectral estimates

regional and global benthic δ18o stacks for the last glacial cycle although detailed age models exist for some marine sediment records of the last glacial cycle 0 150 ka age models for many cores rely on the stratigraphic correlation of benthic 18o which measures ice volume and deep ocean temperature change the large amount of data available for the last glacial cycle offers the opportunity to improve upon previous benthic 18o compilations such as the lr04 global stack not only are the age constraints for the lr04 stack now outdated but a single global alignment target neglects regional differences of several thousand years in the timing of benthic 18o change during glacial terminations here we present regional stacks that characterize mean benthic 18o change for 8 ocean regions and a volume weighted global stack of data from 263 cores age models for these stacks are based on radiocarbon data from 0 to 40 ka correlation to a layer counted greenland ice core from 40 to 56 ka and correlation to radiometrically dated speleothems from 56 to 150 ka the regional 18o stacks offer better stratigraphic alignment targets than the lr04 global stack and furthermore suggest that the lr04 stack is biased 1 2 kyr too young throughout the pleistocene finally we compare global and regional benthic 18o responses with sea level estimates for the last glacial cycle

multiscale site response mapping a case study of parkfield california the scale of previously proposed methods for mapping site response ranges from global coverage down to individual urban regions typically spatial coverage and accuracy are inversely related we use the densely spaced strong motion stations in parkfield california to estimate the accuracy of different site response mapping methods and demonstrate a method for integrating multiple site response estimates from the site to the global scale this method is simply a weighted mean of a suite of different estimates where the weights are the inverse of the variance of the individual estimates thus the dominant site response model varies in space as a function of the accuracy of the different models for mapping applications site response models should be judged in terms of both spatial coverage and the degree of correlation with observed amplifications performance varies with period but in general the parkfield data show that 1 where a velocity profile is available the square root of impedance sri method outperforms the measured v s 30 30 m divided by the s wave travel time to 30 m depth and 2 where velocity profiles are unavailable the topographic slope method outperforms surficial geology for short periods but geology outperforms slope at longer periods we develop new equations to estimate site response from topographic slope derived from the next generation attenuation nga database

changes in the advection of antarctic intermediate water to the northern chilean coast during the last 970 kyr 1 the antarctic intermediate water aaiw is a key player in global scale oceanic overturning processes and an important conduit for heat fresh water and carbon transport the aaiw past variability is poorly understood mainly due to the lack of sedimentary archives at intermediate water depths we present records of benthic stable isotopes from sediments retrieved with the seafloor drill rig marum mebo at 956 m water depth off northern chile geob15016 27 29 48 s 71 07 58 w that extend back to 970 ka the sediments at this site are presently deposited at the boundary between aaiw and pacific deep water pdw for previous peak interglacials our results reveal similar benthic 13c values at site geob15016 and of a newly generated stack of benthic 13c from various deep pacific cores representing the average pdw this suggests unlike today the absence of aaiw at the site and the presence of nearly pure pdw in contrast more positive 13c values at site geob15016 compared to the stack imply a considerable aaiw contribution during cold phases of interglacials and especially during glacials besides we used three short sediment cores to reconstruct benthic 13c values from the aaiw core during the last glacial and found a 13c signature similar to today s assuming that this was the case also for the past 970 kyr we demonstrate that sea level changes and latitudinal migrations of the aaiw formation site can only account for about 50 of the full range of past 13c increases at site geob15016 during cold periods other processes that could explain the remaining of the positive 13c anomalies are increases in glacial aaiw production and or deeper convection of the aaiw with respect to preceding interglacials

accelerator mass spectrometry radiocarbon stratigraphies in deep labrador sea cores paleoceanographic implications foraminiferal accelerator mass spectrometry ams 14c ages and benthic planktonic age differences in surface layer sediments of labrador sea are influenced by bioturbation and by changes in the relative abundance of foraminiferal species carrying the 14c signal using benthic mixing models we demonstrate that inverse benthic planktonic age differences can be generated when the effect of benthic mixing and abundance change exceeds apparent age differences between surface water and deep water ams 14c ages obtained put constraints on the timing of major paleoceanographic changes in the basin notably on the history of the western boundary undercurrent which was clearly reinitiated during the mid deglaciation and intensified during the last 2 3 ka

the role of vertical chemical fractionation in controlling late quaternary atmospheric carbon dioxide the 30 decrease in atmospheric carbon dioxide during glacial maxima must be driven by some change in the chemical circulation of the ocean here a new model for late quaternary co2 variability is presented which resolves some problems occurring in previous models including the timing of carbon dioxide response and changes in the oxygen content of the deep ocean the primary driving factor in this model is a rearrangement of chemical distributions in the ocean whereby labile nutrients and metabolic co2 are concentrated in deep waters rather than in intermediate waters as observed in the modern ocean this new bottom heavy chemical structure does not affect atmospheric carbon dioxide directly instead co2 induced acidity lowers the deep ocean carbonate ion concentration and temporarily increases carbonate dissolution rates oceanic alkalinity then rises until the deep ocean carbonate ion is restored to its steady state value the resulting increase in oceanic alkalinity draws co2 out of the atmosphere into the ocean alkalinity and atmospheric co2 lag several thousand years behind the change in oceanic chemical structure this delayed response is determined by the limited rate of continental weathering and deep ocean carbonate dissolution relative to the oceanic alkalinity inventory it is proposed that characteristic deglacial and preglacial states of the ocean are leading factors driving glacial interglacial climate changes this concept reinterprets the carbon isotope contrast between surface water and deep waters 13c p b as due to a shift of light metabolic carbon from intermediate waters into deep waters the process is illustrated here by a simple equilibrium five box ocean model the observed intermediate depth nutrient depletion is not sufficient in itself to determine which of several possible mechanisms are operating and some mechanisms are not as effective in changing atmospheric co2 as others the largest response is seen from deepening the regeneration cycle of organic carbon the least response is seen from converting north atlantic deep water into intermediate water

gulf stream intensification after the early pliocene shoaling of the central american seaway abstract the shoaling of the central american seaway cas around 4 6 ma million years ago is thought to have enhanced the gulf stream strengthening the atlantic meridional overturning circulation and potentially influencing the evolution of pliocene climate paleoclimate records indicate a buildup of heat and salt in the caribbean and changes in the formation of north atlantic deep water nadw associated with a major step in the shoaling of the cas at 4 6 ma however so far direct evidence supporting an intensification of the gulf stream is scarce here we report new north atlantic early pliocene 5 3 3 9 ma records of sea surface temperature sst reconstructed using the u 37 k and tex86 paleotemperature indices based on new sediment trap measurements near the study site we suggest that in this particular region the two paleothermometers record sst during different seasons spring for u k 37 and summer for tex86 at 4 6 and 4 2 ma our results indicate substantial increases in sst and salinity during summer but not spring pointing to a significant intensification of the gulf stream and its extension the north atlantic current after the shoaling of the cas the divergence of the u 37 k and tex86 temperature trends in those intervals suggests that the gulf stream intensification contributed to the strong north atlantic seasonality that is observed today

benthic foraminiferal δ13c and accumulation rates of organic carbon uvigerina peregrina group and cibicidoides wuellerstorfi the glacial to interglacial 13c records of the benthic foraminifera cibicidoides wuellerstorfi and the uvigerina peregrina group from deep sea cores cannot be adjusted by a generally valid constant the 13c values of the u peregrina group largely correlate with the accumulation rates of organic carbon suggesting a local habitat effect those of c wuellerstorfi vary independently with respect to the carbon flux and record fluctuations in the 13c of the ambient bottom water isotopic composition

the late palaeozoic gondwana glaciation the glacial deposits of gondwana are today spread over one whole hemisphere on the re assembled gondwana continents they still occupy an area exceeding that of the pleistocene glaciation the onset of the glaciation in the different areas has not yet been dated satisfactorily the earliest lower and middle carboniferous glacial beds occur in the andean belt and in eastern australia where high mountains may have existed at that time during stephanian sakmarian time when the pole wandered over antarctica large ice sheets reached sealevel in all the major depositories palaeotopographical reconstructions allow the conclusion that some of the ice centres were supported by uplands which reached altitudes of up to 1 500 m above sealevel depending on their palaeotopographical positions the glacigenic sediments exhibit the full facies range to be expected between glaciated uplands and glaciomarine environments there are indications that ice may have flowed from africa into the parana basin and from antarctica into the great karoo basin and into australia at least 12 advances and retreats have been recognized in the parana basin closer to the ice centres the record is less complete the retreats were probably more of an interstadial than an interglacial nature there is some evidence that the final deglaciation proceeded in stages from south america over africa to antarctica the ice centres were fed by moist air from the pacific ocean and the tethys

chronology of earth s glacial and tectonic record the glacial record yields a pattern of ice ages that shows distinctive characters for different periods however ages of deposits generally provide constraints on the time sequence which because of uncertainties are still too wide to be used critically for or against any regular or cyclic history it seems better to assume no periodicity until such can be argued models for cyclic mechanisms with a longer period than the milankovitch cycle that have been proposed include major chancge in tilt of earth s spin axis galactic year and tectonic cycles evolutionary tectonic changes or changes in atmospheric co 2 are more likely to have been contributing factors but the late proterozoic vendian varangian ice ages with at least equatorial glaciation remain enigmatic

stable isotope composition of late cretaceous benthic foraminifera from the southern south atlantic biological and environmental effects abstract the stable carbon and oxygen isotope composition of different benthic foraminiferal species of the latest campanian and earliest maastrichtian from ocean drilling project hole 690c weddell sea southern south atlantic 1800 m paleowater depth have been investigated the total range of measured isotope values of all samples exceeds 4 for 13c and 1 1 for 18o carbon isotope values of proposed deep infaunal species are generally similar or only slightly lower when compared to proposed epifaunal to shallow infaunal species interspecific differences vary between samples probably reflecting temporal changes in organic carbon fluxes to the sea floor constantly lower 13c values for pullenia marssoni and pullenia reussi suggest the deepest habitat for these species the strong depletion of 13c values by up to 3 within lenticulinids may be attributed to a deep infaunal microhabitat strong vital effects or different feeding strategy when compared to other species or modern lenticulinids the mean 18o values reveal a strong separation of epifaunal to shallow infaunal and deep infaunal species epifaunal to shallow infaunal species are characterized by low 18o values deep infaunal species by higher values this result possibly reflects lower metabolic rates and longer life cycles of deep infaunal species or the operating of a pore water co32 effect on the benthic foraminiferal stable isotopes pyramidina szajnochae shows an enrichment of oxygen isotopes with test size comprising a total of 0 6 between 250 and 1250 m shell size although 13c lacks a corresponding trend these data likely represent the presence of changes in metabolic rates during ontogenesis these results demonstrate the general applicability of multi species stable isotope measurements of pristine cretaceous benthic foraminifera to reconstruct past microhabitats and to evaluate biological and environmental effects on the stable isotope composition

lithofacies types and vertical profile models an alternative approach to the description and environmental interpretation of glacial diamict and diamictite sequences abstract increased knowledge of modern glacial depositional environments has resulted in rapidly evolving classifications of glacial tills these are based to a large degree on theoretical considerations of likely depositional processes the classifications are sophisticated and more advanced than the establishment of simple field criteria whereby individual till facies can be identified in quaternary and pre quaternary successions this situation is compounded in many quaternary terrains by the continued description of tills in terms of laboratory derived analytical data only reflecting a traditional interest in stratigraphic correlation rather than reconstruction of depositional environment detailed sedimentological logging of lithofacies is rarely undertaken there is thus considerable confusion as to what is being described or sampled when analytical data are presented for many pleistocene tills the same remarks apply to pre pleistocene tillites a lithofacies code is presented here for the rapid description and visual appraisal of field sequences or drill cores containing unconsolidated diamicts or lithified diamictites the term till is not used as it has a strict genetic definition referring to direct aggregation and deposition by glacier ice use of a four part code in conjunction with codes already published for fluvial sediments allows fundamental field properties to be depicted independent of genetic terminology and provides a firm basis for subsequent environmental interpretation and analytical work the value of this approach is illustrated by comparing a representative suite of vertical profiles of diamict assemblages deposited by modern grounded glaciers with a classic late pleistocene glacigenic sequence at scarborough bluffs ontario

ontogenetic effects on stable carbon and oxygen isotopes in tests of live rose bengal stained benthic foraminifera from the pakistan continental margin abstract we determined the stable oxygen and carbon isotopic composition of live rose bengal stained tests belonging to different size classes of two benthic foraminiferal species from the pakistan continental margin samples were taken at two sites with water depths of about 135 and 275 m corresponding to the upper boundary and upper part of the core region of the oxygen minimum zone omz for uvigerina ex gr uvigerina semiornata and bolivina aff bolivina dilatata 13c and 18o values increased significantly with increasing test size in the case of uvigerina ex gr u semiornata 13c increased linearly by about 0 105 for each 100 m increment in test size whereas 18o increased by 0 02 to 0 06 per 100 m increment for bolivina aff b dilatata the relationship between test size and stable isotopic composition is better described by logarithmic equations a strong positive linear correlation is observed between 18o and 13c values of both taxa with a constant ratio of 18o and 13c values close to 2 1 this suggests that the strong ontogenetic effect is mainly caused by kinetic isotope fractionation during co2 uptake our data underline the necessity to base longer 18o and 13c isotope records derived from benthic foraminifera on size windows of 100 m or less this is already common practice in down core isotopic studies of planktonic foraminifera

stable oxygen and carbon isotopes of live benthic foraminifera from the bay of biscay microhabitat impact and seasonal variability we determined the stable oxygen and carbon isotopic composition of live rose bengal stained benthic foraminifera n150 am size fraction of seven taxa sampled along a downslope transect between 140 to 2000 m water depth in the bay of biscay at the five stations hoeglundina elegans cibicidoides pachydermus uvigerina peregrina uvigerina mediterranea preferentially occupy shallow infaunal niches whereas melonis barleeanus and uvigerina elongatastriata occupy an intermediate infaunal microhabitat and globobulimina spp live in a deep infaunal niche close to the zero oxygen boundary when compared with d 18 o values of calcite formed in equilibrium with bottom waters u peregrina forms its test in close equilibrium with bottom water d 18 o all other foraminiferal taxa calcify with a constant offset to calculated equilibrium calcite there is no systematic relationship between the foraminiferal microhabitat depth and the dd 18 o between foraminiferal and equilibrium calcite we calculated correcting factors for the various taxa which are needed for constructing multispecies based oxygen isotope records in paleoceanographic studies of the study area the d 13 c values of foraminiferal taxa investigated in this study do neither record bottom water d 13 cdic in a 1 1 relationship nor with a constant offset but appear to be mainly controlled by microhabitat effects the increase of d 13 c values of shallow infaunal taxa with increasing water depth reflects the decrease of the exported flux of organic carbon along the bathymetric transect and early diagenetic processes in the surface sediment this is particularly the case for the shallow infaunal u peregrina the d 13 c values of deep infaunal globobulimina spp are much less dependent on the exported organic matter flux we suggest that the dd 13 c between u peregrina and globobulimina spp can shed light on the various pathways of past degradation of organic detritus in the benthic environments at a station in 550 m water depth where periodic eutrophication of sediment surface niches was demonstrated previously we performed a two year seasonal survey of the isotopic composition of foraminiferal faunas no marked seasonal changes of the stable carbon isotopic composition of shallow intermediate and deep infaunal foraminiferal taxa were observed thus the d 13 c values of foraminiferal individuals belonging to the n150 am fraction may result from rather long term calcification processes lasting for several weeks or months which limit the impact of ephemeral 12 c enrichment of shallow infaunal niches on the isotope chemistry of adult individuals during eutrophic periods only highly opportunistic taxa reproducing or calcifying during

global deepwater circulation between 2 4 and 1 7 ma and its connection to the onset of northern hemisphere glaciation we have generated an early pleistocene benthic isotopic record for the ocean drilling program odp site 807 2804 m from the western equatorial pacific between 2 4 and 1 7 ma the benthic 13c of this site and a few other deep pacific sites was consistently higher than the southern ocean site mv0502 4jc 4286 m pointing to a reversal relative to the current gradient and hence implying a different circulation regime we reconstructed the deep water mass distribution of this interval using a collection of benthic isotope records from 15 pacific and 10 atlantic sites and a 13c 18o mixing model a two end member mixing regime between the north atlantic deep water nadw and the antarctic bottom water aabw with properties very different from today was identified the southern ocean showed strong signs of stratification and aabw with low benthic 13c but high 18o values reached out to other basins only below 4000 m in contrast nadw ventilated most of the ocean interior contributing 70 to the pacific deep water pdw volumetrically our model results also reveal a strong remineralization effect at the bottom sites of the pacific and the atlantic suggesting significant accumulation of respired carbon in the bottom water between 2 4 and 1 7 ma we propose that such a circulation pattern was initiated by the reversal of salinity gradient between aabw and nadw from 3 0 to 2 4 ma possibly linked to antarctic sea ice expansion and reduced southward heat transport during the onset of northern hemisphere glaciation nhg

late pliocene variations in the carbon isotope values of north atlantic benthic foraminifera biotic control of the isotopic record abstract analyses of benthic foraminifera carbon isotope values were made in 172 samples from the late pliocene at dsdp site 548 which is located in the northeast atlantic on the continental slope southwest of ireland 1253 m water depth the carbon isotope record is quite stable from about 3 4 to 2 5 ma and contrasts with the record at site 552a in the north atlantic 2311 m water depth which is much more variable for this time period the carbon record at site 548 is also consistently more negative than that of site 552a after 2 5 ma the benthic carbon isotope record of uvigerina at site 548 becomes extremely variable with large negative deviations these isotopic variations might be associated with paleoceanic circulation changes caused by glaciation between 2 5 and 2 ma however paired analyses of uvigerina and cibicidoides species for 38 samples within the glacial interval yield carbon isotopic records which are quite different from one another the uvigerina record contains larger negative deviations than does the cibicidoides record also the isotopic difference between uvigerina and cibicidoides increases during glaciations and in a long term trend from 2 5 to 2 0 ma the lack of covariance between the uvigerina and cibicidoides carbon isotope records indicates that after 2 5 ma at site 548 biotic factors influenced the benthic isotopic record

nonlinear attenuation and rock damage during strong seismic ground motions strong seismic waves cause nonlinear behavior in the shallow subsurface in fractured rocks seismologists use low amplitude signals from small repeating earthquakes to measure s wave velocity decrease after strong motion the 2004 parkfield california earthquake provides examples of such velocity changes in fractured sandstone with an s wave velocity of 300 m s 1 this nonlinear behavior occurred around the wave number depth of the incident waves 30 m for the 10 s 1 dominant angular frequency on a velocity seismogram the low amplitude s wave velocity gradually recovered with the logarithm of time the attenuation of strong waves in general depends nonlinearly on their amplitude high dynamic stress triggered small very shallow earthquakes at sites including parkfield the theoretical frictional behavior of a fractured medium with heterogeneous prestress relates these phenomena failure occurs in the highly prestressed domains causing small earthquakes and opening mode cracks the energy to dilate the cracks dissipates a significant fraction of the incoming seismic energy the local high porosity domains close with the logarithm of time as expected from the aging law of rate and state friction increasing the s wave velocity the domain model indicates that nonlinear effects increase gradually over a range of dynamic coulomb stresses as observed and as included in the widely used masing rules the linker and dieterich 1992 relationship provides the maximum sustainable dynamic coefficient of friction needed to utilize the masing rules this parameter is the coefficient of friction at a laboratory normal traction plus a constant 0 15 times the logarithm of the ratio of field normal traction to the laboratory normal traction it is helpful to relate s wave velocity to starting frictional strength as coefficient of friction near the quarter wavelength depth determines nonlinear behavior then the dynamic coefficient of friction and equivalently the maximum sustainable acceleration at the dominant frequency depend weakly on s wave velocity for example the coefficient of friction at an angular frequency of 10 s 1 is less than 1 5 for rocks ranging from parkfield sandstone to intact granite

glacial deep water geometry south atlantic benthic foraminiferal cd ca and δ13c evidence a depth transect of cores from 1268 to 3909 m water depth in the western south atlantic are ideally situated to monitor the interocean exchange of deep water and variations in the relative strength of northern and southern sources of deep water production benthic foraminiferal cd ca and 13c data suggest that glacial north atlantic intermediate water gnaiw extended at least as far south as 28 s in the western south atlantic the core of nutrient depleted water was situated at 1500 m above and below water masses with higher nutrient concentrations when examined in conjunction with published paired cd ca and 13c from intermediate depth cores from other basins it appears that the extent of gnaiw influence on the intermediate waters of the world s oceans was less than suggested previously differentiating among possible pathways for the glacial deep ocean 3 km requires a better understanding of the controls on cd ca and 13c values of benthic foraminifera

glacial events of the past and their geological significance abstract traces of glaciations are unevenly distributed in the stratigraphic column and exhibit rhythmicity of several ranks this rhythmicity makes it possible to establish the corresponding hierarchy of climatic events in descending order glacio and thermo eras glacial and interglacial periods and epochs as well as smaller events which appear to be compared to the most important climatic fluctuation during the pleistocene the direct factors causing initiation and termination of glaciations were climatic fluctuations the palaeolatitudinal position of the continents controlled a degree of asymmetry and perhaps a certain diachronism of glaciations in different hemispheres during the glacial periods in high and middle latitudes of the earth the glacial and cold temperate climates either were predominant or alternated the thermo eras and at least some interglacial periods were characterized by warm temperate and warm climates at high and middle latitudes glaciations have been numerous and important geological events they affected all outer spheres of the earth from asthenosphere to atmosphere they apparently stimulated the biological evolution too the study of ancient glaciations is important from both the scientific and economical points of view

early carboniferous onset of gondwanian glaciation and neo tethyan rifting in south tibet at least four diamictite bearing intervals of early carboniferous age containing faceted pebbles trapezoidal cobbles and boulders up to 1000 m3 in volume have been recognized and traced for over 200 km along the tethys himalayan zone of south tibet from east of everest to west of shishapangma these largely glacio marine sediments intercalated within the rakyang formation which overlies lower tournaisian limestones and underlies lower bashkirian black shales were deposited during the visean to serpukhovian shore ice thus began to form in this region of northern gondwana several tens of million years earlier than previously thought this glacial event occurred at middle southern latitudes and was triggered by basin inversion and tectonic uplift in the first stages of neo tethyan rifting as documented by the close association of diamictites with olistoliths and olistostromes in lower carboniferous units after a transgressive interglacial episode in the bashkirian a much more widespread glaciation occurred in the latest carboniferous and was shortly followed by continental break up and opening of neo tethys in the late early permian

exceptional ground motions recorded during the 26 april 2008 mw 5 0 earthquake in mogul nevada abstract an unusually shallow swarm of earthquakes in mogul a suburb in west reno nevada started 28 february 2008 and continued for several months temporary instruments in the epicentral region constrained event depths and locations and provided onscale recordings of the strong ground motions and supplemented a network of over 21 permanent advanced national seismic system anss strong motion stations deployed throughout the metropolitan reno area by the end of august the swarm had produced over 200 earthquakes with magnitude m l greater than 2 0 the largest earthquake in the sequence occurred at 06 40 utc on 26 april 2008 11 40 p m on 25 april local time with magnitude m l 4 7 m w 5 0 and a hypocentral depth of about 3 1 km in the m w 5 0 mainshock mean horizontal peak ground acceleration exceeded 0 6 g at three stations the strongest peak vector acceleration was 1164 cm sec 2 or about 1 19 g at the station mogl 0 4 km from the epicenter at a frequency of about 3 hz the mean horizontal peak velocity exceeded 12 cm sec at the four nearest stations and the peak vector velocity at the strongest was 54 cm sec the duration of the strongest shaking was about 2 sec at these stations the observed peak accelerations and peak velocities decreased more rapidly with distance than predicted to values below the median predictions at most stations in the reno metropolitan area the shallow source depth is to some degree a likely contributing factor to these unusual observations the motions in the residential neighborhood near the epicenter are significantly greater than the seismic forces required by the 1985 uniform building code zone 3 that was in effect when the mogul neighborhood was developed but damage to the wood frame structures in the neighborhood was minimal

palynology of the circum mediterranean triassic phytogeographical and palaeoclimatological implications following a tentative evaluation of palynological information from ladinian and more particularly karnian successions there seems to be every indication that qualitative and quantitative compositional differences of palynological assemblages could well be applied in testing concepts of triassic phytogeography and palaeoclimatology

on the upper precambrian sinian suberathem in china abstract this paper gives a general outline of the upper precambrian sinian suberathem in china including its geographic distribution development stratigraphic sequence and classification the sinian suberathem with a time range of 1950 615 ma constitutes the greater part of the proterozoic it is characterized by the development of stromatolites appearance of eukaryotes and the presence of metazoa in its upper part its sedimentological characteristics are quite similar to those of the overlying paleozoic on the basis of the biological evolution isotopic dating and stages of tectonic development the sinian suberathem can be divided into four systems in ascending order the changcheng ca 1950 1400 ma jixian ca 1400 1000 ma qingbaikou ca 100 800 ma and sinian ca 800 615 ma systems the stratotype for the first three systems is located in jixian county and the type section for the sinian system in the yangzi gorges area the contact between the sinian and cambrian systems is in some places a continuous transition with abundant small shelly fauna above the precambrian cambrian boundary e g in the yangzi gorges yunnan and sichuan with regard to sedimentological characteristics the rocks of the sinian suberathem may be subdivided into three main facies such as 1 carbonate facies of stable region 2 volcanic sedimentary facies of mobile zones and 3 argillo arenaceous carbonate facies of transitional zones progress in the study on the succession of the sinian suberathem has been made in recent years in regard to palaeontology stratigraphy isotopic geochronology magnetostratigraphy and palaeoglaciology they provide important evidence for the stratigraphic correlation of the upper precambrian of china and other continents

core top evaluation of benthic foraminiferal isotopic ratios for paleo oceanographic interpretations abstract the benthic foraminifera cibicides wuellerstrofi oridforsalis tener and pyrgo rotalaria from twelve core tops in the norwegian greenland sea and c wuellerstorfi o tener and o umbonatus from four core tops on the rio grande rise were analysed for oxygen and carbon isotopes the norwegian greenland sea data yield statistically discrete means for both 18o and 13c for each species the interregional comparison of our data to published data from the east pacific rise shows that c wuellerstorfi 18o and 13c variations reflect oceanographic differences between sites whereas the data on oridorsalis and pyrgo do not we conclude that c wuellerstorfi is a reliable sensor of bottom water conditions whereas other taxa are of unproven utility supportive biological studies and the lack of positive covariance of 18o to 13c among deep sea benthic taxa lead us to reject models calling for incorporation of metabolic co2 to explain the isotopic variation among deep sea benthic foraminifera we propose a within sediment microhabitat hypothesis to explain the 13c variations among taxa

direct ventilation of the north pacific did not reach the deep ocean during the last deglaciation 1 despite its tremendous size the deep north pacific has received relatively little attention by paleoceanographers it was recently suggested that the deep north pacific was directly ventilated by dense waters formed in the subarctic pacific during heinrich stadial 1 hs1 of the early deglaciation here we present new redox sensitive trace metal data from a sediment core at 2393 m in the subarctic pacific in comparison with previously published data from elsewhere in the region the combined picture shows no sign of ventilation during the early deglaciation in any available core from water depths of 2393 m and deeper while the deepest core to display clear signs of enhanced ventilation during hs1 was raised from 1366 m water depth thus it appears likely that although the north pacific was well ventilated to intermediate depths during hs1 the deep ocean did not receive a significant input of dense waters from a local source but remained isolated from the surface waters above

note on the very high acceleration fault zone 16 record from the 2004 parkfield earthquake a very high acceleration recording was obtained at station fault zone 16 near parkfield california during the m 6 0 parkfield earthquake of 28 september 2004 this note documents key aspects of the station the instrument and the record a preliminary reconstruction of the record is performed to produce an estimate of the true acceleration which is then integrated to obtain the estimated velocity the strong motion accelerograph at fault zone 16 is deployed at a soil site in a light fiberglass housing common in the parkfield array postearthquake testing indicates that the accelerograph operated normally instrument shake table tests indicate that the recorded acceleration is relatively accurate even at the high accelerations involved in this record that is the very high accelerations in the record are a reasonably accurate reflection of the accelerations that occurred at the site during the parkfield earthquake although the peak motion was not recorded the record itself has several unusual features the trace was lost at the top edge of the film where the excursion went beyond the recordable part of the film most unusually the traces of two accelerometers recorded on top of one another during the positive highest amplitude part of the record the accelerograph did not record the peak accelerations of the components which occurred during this time an additional aspect is that for the largest amplitude component the negative part of the acceleration was affected by momentary stalling of the recording film during the strongest shaking the constraint for the mean of the acceleration over the whole record to be zero and detailed analysis of the time trace leads to a reconstruction of the record the peak acceleration on this component is over 1 8 g and most likely over 2 g the peak velocity is estimated to be about 80 cm sec the other horizontal component goes off the film at the same time combined the horizontals yield a fault normal acceleration of over 2 2 g and most likely over 2 5 g this record is a challenge to interpret an important practical lesson is that given what has been learned about near fault accelerations any instrument deployed in the region should have a recording capacity well in excess of 2 g

stable carbon isotopes in marine porewaters abstract we present centimeter scale porewater 13 c profiles from four sites in the central equatorial pacific ocean which reveal steep porewater 13 c gradients up to 1 0 cm 1 at the deep sea sediment water interface we describe the processes controlling porewater carbon isotopic composition and incorporate them into a model of the deep sea benthic carbon cycle our measured 13 c profiles are then used to estimate carbon rain rates at two of these sites manop sites c and s the 13 c data yield organic carbon rain rates of 10 mol c cm 2 yr 1 at site c and 3 mol c cm 2 yr 1 at site s these carbon rain rates agree with recent carbon rain estimates based on sediment trap data and porewater nitrate profiles but are a factor of 2 lower than estimates based on millimeter scale porewater oxygen profiles our model results indicate that changes of the same magnitude in organic carbon rain rate and bottom water composition o 2 co 2 and 13 c have comparable effects on the carbon isotopic composition of surficial porewaters this suggests the need to consider the effects of benthic carbon cycling on the stable carbon isotope record preserved in deep sea benthic foraminifera tests

variability in mid depth ventilation of the western atlantic ocean during the last deglaciation negative stable carbon isotopic excursions have been observed throughout most of the mid depth 1000 3000 m atlantic ocean during heinrich stadial 1 hs1 and the younger dryas yd although there is an agreement that these mid depth excursions were in some way associated with a slowdown of the atlantic meridional overturning circulation amoc there is still no consensus on the precise mechanism s here we present benthic stable carbon and oxygen isotopic 13c and 18o records from five cores from the western equatorial atlantic wea together with published benthic isotopic records from nearby cores we produced a wea depth transect 800 2500 m we compare hs1 and yd data from this transect with data from previously published north and south atlantic cores and demonstrate that the largest negative 13c excursions occurred in the wea during these times moreover our benthic 18o records require the presence of two water masses flowing from the southern ocean bisected by a northern component water ncw given that 18o is a conservative water mass tracer we suggest that 13c was decoupled from water mass composition and does not correspond to simple alternations between northern and southern sourced waters instead 13c behaved non conservatively during hs1 and the yd consistently with our new 231pa 230th record from the wea transect that allowed the reconstruction of amoc strength we hypothesize that the negative 13c excursions reflect an increase in the residence time of ncw in response to a weakened amoc allowing for a marked accumulation of 13c depleted respired carbon at the mid depth wea

carbonate ion effect on mg ca sr ca and stable isotopes on the benthic foraminifera oridorsalis umbonatus off namibia abstract we investigate the influence of carbonate system parameters carbonate ion concentration co32 carbonate ion saturation co32 on the trace element and stable isotope ratios in the endobenthic foraminifera oridorsalis umbonatus data from modern core top samples from the namibian continental slope suggest that the shell composition of this species is influenced by the chemistry of the pore water for these organic rich sediments the impact of ocean bottom water properties on both pore water and shell chemistry is surprisingly small sr ca correlates positively with co32 and to a lesser extent with co32 which is opposed to previous results a co32 decrease of 10 mol kg leads to an increase of 0 05 mmol mol in sr ca we observe a correlation between shell 18o corrected for temperature and 18o seawater and co32 however the variability of the corrected 18o is close to the analytical limit no clear dependences were observed for 13c and mg ca

environmental distribution of recent benthic foraminifera on the northeast united states continental slope several bathymetrically consistent recent benthic foraminiferal biofacies have been recognized from the continental slope south east of cape cod faunal assemblages are dominated by globobulimina bulimina upper slope less than 1 000 m and uvigerina peregrina lower slope uppermost rise water depths between 1 000 and 2 500 m the globobulimina bulimina assemblage coincides with the oxygen minimum zone this agrees with the occurrence of globobulimina in mediterranean sapropels organic rich sediments deposited under anoxic conditions previous studies have noted the association of u peregrina with bathyal water depths deep water temperatures of 3 to 4 c and water of low oxygen content however correlations between abundance of u peregrina and water depth or temperature are not the same everywhere and no correlation with dissolved oxygen in the water column is seen on the united states continental slope and rise the highest abundances of u peregrina coincide with maxima of organic carbon and silt within the slope sediments this suggests that the distribution of u peregrina in this region may be influenced more by low oxygen in the sediments rather than by low oxygen content of the overlying water

sampling statistic limitations on benthic foraminifera chemical and isotopic data abstract analyses of benthic foraminiferal isotopic and chemical properties are typically done on a small number of individuals often 5 10 because benthic sediment mixing produces a mix of individuals whose properties were determined at times encompassing several thousand years a sampling of several individuals does not adequately represent the average mixture a quantitative statistical analysis shows that this effect places a fundamental limit on measurement precision in cores especially where rapid environmental changes occur over short vertical distances the fundamental parameters defining this limit are the rate of change of the property per unit distance and the effective mixing depth in cores found in the vema channel rio grande rise region where sedimentation rates are about 1 cm ka 1 and mixing depths are about 3 cm a single sampling of six individuals can produce a result that has an expected one sigma standard deviation of 6 25 of the observed range precision can be improved by using more individuals or running more replicate analyses but the result only improves as the square root of the number of individuals or replicates this effect is illustrated by cd ca and isotopic data from low 0 7 cm ka 1 and moderate 1 5 cm ka 1 sedimentation rate cores although precision is compromised the most in low sedimentation rate cores this effect contributes to imprecision in high sedimentation rate cores as well

stable isotope composition of benthic foraminifera from the equatorial pacific when ranked according to deviation from isotopic equilibrium deep sea benthic foraminifera exhibit no correlation between the rankings for oxygen and for carbon both rank sequences are stable from east to west in the equatorial pacific fertility independent and from glacial to post glacial time independent records for the past 15 000 yr suggest marked changes in deep sea circulation during this time interval

production of brief extreme ground acceleration pulses by nonlinear mechanisms in the shallow subsurface 1 a brief pulse of extreme acceleration 20 m s 2 was recorded at station fz16 during the 2004 mw 6 0 parkfield california earthquake the sustained acceleration at the dominant frequency is a factor of 2 below the maximum here we show that the pulses of extreme acceleration might originate in the shallow subsurface rather than on the main fault plane two nonlinear mechanisms can feasibly convert low frequency energy of the incident wave into high frequency pulses with extreme acceleration 1 dynamic stress carried by strong seismic waves causes small shallow cracks to slip in secondary earthquakes 2 the elasticity of the shallow subsurface is nonlinear the relationship between dynamic shear stress and strain is linear at small strains at the large strains associated with strong ground motion shear deformation locks compliant cracks by bringing their asperities into contact the locking increases the instantaneous shear modulus of the cracked rock computations indicate that both mechanisms produce high accelerations in the later part of the strong ground motion these testable hypotheses imply that brief pulses of extreme acceleration are likely not a property of the main fault and hence not harbingers of prolonged pulses of extreme acceleration