giant middle eocene bryozoan reef mounds in the great australian bight this paper reports the discovery of extensive middle eocene bryozoan reef complexes along the paleoshelf edge of the great australian bight gab the complexes form the earliest carbonate deposit in the gab which is the largest cenozoic cool water carbonate province on earth the bryozoan reef mounds previously misidentifi ed as volcanic bodies were deposited parallel to the shelf margin for more than 500 km along strike individual reef mound complexes are 60 150 km long as wide as 15 km and as thick as 200 m and dwarf all previously described examples superimposed on the distal margin of an underlying paleocene to mid eocene siliciclastic delta complex the reef mounds provide a critical insight into changing paleoenvironments of the australo antarctic gulf ca 43 ma coinciding with global and continent wide climatic and tectonic events the rapid growth and demise of reef mound building bryozoans raises new questions regarding the interplay of southern ocean opening ocean currents and biosphere interactions

the density distributions and the correlations of an earthquake s source parameters the data analysis of the source parameters of five sets of earthquake sequences aftershocks and earthquakes scattered in a region shows that the scalar seismic moment is correlated with the linear size of the fault and the static stress drop we tentatively imply that a correlation also exists between the radius of the faults and the static stress drops and it is suggested that the static stress drop may be decreasing with increasing radius of the source it is shown that the density distribution of the source radius calculated through the source rupture duration obtained from the body wave pulse boatwright 1980 using the time t between the p wave onset and the first zero crossing on the seismogram may be represented by a power law as the density distribution of the stress drops and of the moment which are also computed it is also suggested and tentatively verified that the density distribution of the areas of the broken barriers on the faults is similar to that of the density distribution of the static stress drops it is finally suggested that the seismicity of a region may be studied two dimensionally as a function of the stress drop and the radius of the source instead of the classic b and b0 values concerning the discussion on the range of the values of the static stress drop whether it is almost constant in a seismic region and varies only from one region to another it is seen that in the aftershocks of the 1994 northridge earthquake it covers a range of almost 5 orders of magnitudes finally it is ascertained that the density distribution of the source parameters does not give equipartition of seismic moment release

spatial fingerprint and magnitude of changes in the atlantic meridional overturning circulation during marine isotope stage 3 pronounced millennial scale climate variability during marine isotope stage 3 mis3 is considered to be linked to changes in the state of the atlantic meridional overturning circulation amoc i e a warm interstadial cold stadial state corresponds to a strong weak amoc based on a series of freshwater hosing extraction experiments with the state of the art community climate system model version 3 we construct a global spatial fingerprint of oceanic temperature anomalies in response to amoc changes under mis3 boundary conditions highest sensitivity to amoc changes especially in summer is found in northeastern north atlantic sea surface temperature but a characteristic temperature fingerprint is also found at subsurface levels after testing significance of the linear sea surface temperature sst amoc regressions the model results are combined with paleo sst records to estimate the magnitude of millennial scale dansgaard oeschger amoc variations during mis3 the results suggest a mean difference in amoc strength between interstadial and non heinrich stadial states of 9 2 1 2 sv 1

origin of late pleistocene bryozoan reef mounds great australian bight bryozoan rich biogenic mounds grew periodically on the prograding carbonate slope of the central great australian bight throughout pliocene pleistocene time cores from three odp leg 182 drill sites provide a record of mound growth during the last 300 000 years over a stratigraphic thickness of similar to 150 m these mounds the first such structures described from the modern ocean grew between paleodepths of 100 and 240 m we infer that the upper limit of growth was established by swell wave base and the lower boundary was fixed by an oligotrophic water mass detailed chronostratigraphy based on radiometric and u series dating benthic foraminifer stable isotope stratigraphy and planktonic foraminifer abundance ratios confirms that buildups flourished during glacial lowstands even numbered marine isotope stages but were largely moribund during interglacial highstands and are not extant today mound floatstones are compositionally a mixture of in situ bryozoans comprising 96 genera and characterized by fenestrate flat robust branching encrusting nodular arborescent and delicate branching growth forms the packstone matrix comprises autochthonous and allochthonous sand size bryozoans benthic and planktonic foraminifers serpulids coralline algae sponge spicules peloids and variable glauconite and quartz grains together with mud size ostracods tunicate spicules bioeroded sponge chips and coccoliths intermound allochthonous packstone and local grainstone contain similar particles but they are conspicuously worn abraded blackened and bioeroded an integrated model of mound accretion during sea level lowstands begins with delicate branching bryozoan floatstone that increases in bryozoan abundance and diversity upward over a thickness of 5 10 m culminating in thin intervals of grainstone characterized by reduced diversity and locally abraded fossils mound accumulation was relatively rapid 30 67 cm ky and locally punctuated by rudstones and firmgrounds intermound highstand deposition was comparatively slow 17 25 cm ky and typified by meter scale fining upward packages of packstone and grainstone or burrowed packstone with local firmgrounds overlain by characteristically abraded particles mound growth during glacial periods is interpreted to have resulted from increased nutrient supply and enhanced primary productivity such elevated trophic resources were both regional and local and thought to be focused in this area by cessation of leeuwin current flow together with northward movement of the subtropical convergence and related dynamic mixing

seismic moment distribution revisited i statistical results summary an accumulation of seismic moment data gathered over the previous decade justifies a new attempt at a comprehensive statistical analysis of these data herein more rigourous statistical techniques are introduced their properties investigated and these methods are employed for analysis of large modern data sets several theoretical distributions of earthquake size seismic moment frequency relations are described and compared we discuss the requirements for such distributions and introduce an upper bound or a corner moment for a distribution to have a finite energy or moment flux we derive expressions for probability density functions and statistical moments of the distributions we also describe parameter evaluation in particular how to estimate the seismic moment distribution for the largest earthquakes simulating earthquake size distributions allows for a more rigourous evaluation of distribution parameters and points to the limitations of the classical statistical analysis of earthquake data simulations suggest that several earthquakes approaching or exceeding the corner magnitude mc limit need to be registered to evaluate mc with reasonable accuracy using the harvard catalogue data we compare moment distribution parameters for various temporal spans of the catalogue for different tectonic provinces and depth ranges and for earthquakes with various focal mechanisms the statistical analysis suggests that the exponent b is universal b 0 60 0 65 for all moderate earthquakes the corner moment mc value determined by the maximum likelihood method both in subduction zones and globally is about 10 21 n m corresponding to the corner moment magnitude mc 8 0 for midoceanic earthquakes mc is apparently smaller for spreading ridges it is about 5 8 and for strike slip earthquakes on transform faults it decreases from 7 2 to 6 5 as the relative slip velocity of faults increases we investigate the seismic moment errors both random and systematic and their dependence on earthquake size the relative errors seem to decrease for larger events the influence of moment uncertainties on the parameter estimates is studied whereas the b values do not appear to be significantly influenced by the errors for the corner moment large errors can lead to substantially biased estimates we compare the harvard catalogue results with the earthquake data from instrumental catalogues in the first three quarters of the 20th century several very large earthquakes mi9 occurred around the middle of the century their magnitude values cannot be fitted by a modified gutenberg richter law with mc 8 0 8 5 among other factors this discrepancy can be explained by either substantially higher errors in the earlier magnitude values or by mc being higher for some subduction zones it is unlikely that data available presently or soon will be sufficient to determine the corner magnitude of 9 and above with reasonable precision using purely statistical methods

the deglacial evolution of north atlantic deep convection deepwater formation in the north atlantic by open ocean convection is an essential component of the overturning circulation of the atlantic ocean which helps regulate global climate we use water column radiocarbon reconstructions to examine changes in northeast atlantic convection since the last glacial maximum during cold intervals we infer a reduction in open ocean convection and an associated incursion of an extremely radiocarbon 14c depleted water mass interpreted to be antarctic intermediate water comparing the timing of deep convection changes in the northeast and northwest atlantic we suggest that despite a strong control on greenland temperature by northeast atlantic convection reduced open ocean convection in both the northwest and northeast atlantic is necessary to account for contemporaneous perturbations in atmospheric circulation

carbonate shelf edge off southern australia a prograding open platform margin the southern continental margin of australia is an extensive shelf that has been a site of cool water carbonate deposition since eocene time the platform has no rim and is swept by high energy waves and swells throughout the year the shelf is deep 40 to 100 m and typified by bryozoan rich sediments the shelf margin is a gentle incline that becomes progressively steeper seaward except where it laps down onto offshore terraces the edge of the eucla platform in the great australian bight is used to illustrate that the margin is a series of extensive prograding clinoforms progradation is interpreted to be the result of off shelf sediment transport and in place carbonate production by actively growing deep water bryozoa and sponges this area is a potential model for ancient high energy platform margins during geologic periods when large skeletal reef building metazoans were scarce

source parameters for small events associated with the 1986 north palm springs california earthquake determined using empirical green functions using small events as empirical green functions which include path site and instrument effects on the p waveforms source parameters were estimated for 25 ml 3 4 to 4 4 events associated with the 1986 north palm springs earthquake the static stress drops ranged from 3 to 80 bars for moments of 0 7 to 11 1021 dyne cm there was a spatial pattern to the stress drops of the aftershocks which showed increasing values along the fault plane toward the northwest compared to relatively low values near the hypocenter of the mainshock the highest values were outside the main area of slip and are believed to reflect a loaded area of the fault that still has an higher level of stress which was not released during the main shock the relatively high stress drop of a preshock in 1983 located close to the hypocenter of the main shock is also interpreted as evidence that stress drops of magnitude 3 and 4 events can be used as indicators of the stress level in a particular area

the sensitivity of the climate response to the magnitude and location of freshwater forcing last glacial maximum experiments abstract proxy records indicate that the locations and magnitudes of freshwater forcing to the atlantic ocean basin as iceberg discharges into the high latitude north atlantic laurentide meltwater input to the gulf of mexico or meltwater diversion to the north atlantic via the st lawrence river and other eastern outlets may have influenced the north atlantic thermohaline circulation and global climate we have performed last glacial maximum lgm simulations with the ncar community climate system model ccsm3 in which the magnitude of the freshwater forcing has been varied from 0 1 to 1 sv and inserted either into the subpolar north atlantic ocean or the gulf of mexico in these glacial freshening experiments the less dense freshwater provides a lid on the ocean water below suppressing ocean convection and interaction with the atmosphere above and reducing the atlantic meridional overturning circulation amoc this is the case whether the freshwater is added directly to the area of convection south of greenland or transported there by the subtropical and subpolar gyres when added to the gulf of mexico the amoc reduction is less for the smaller freshwater forcings but is not linear with the size of the freshwater perturbation the recovery of the amoc from a slow state is 200 years for the 0 1 sv experiment and 500 years for the 1 sv experiment for glacial climates with large northern hemisphere ice sheets and reduced greenhouse gases the cold subpolar north atlantic is primed to respond rapidly and dramatically to freshwater that is either directly dumped into this region or after being advected from the gulf of mexico greenland temperatures cool by 6 8 c in all the experiments with little sensitivity to the magnitude location or duration of the freshwater forcing but exhibiting large seasonality sea ice is important for explaining the responses the northern hemisphere high latitudes are slow to recover antarctica and the southern ocean show a bipolar response with warming and reduced sea ice this warming continues after the cessation of the freshwater forcing and shows a dependence on the duration of the freshwater forcing equatorward of the expanded sea ice the simulated temperature and salinity anomalies are sensitive to the amount of colder and fresher waters that are advected out of the subpolar north atlantic in the tropical atlantic the recovery of the intertropical convergence zone itcz from its more southerly position during the freshwater forcing is much more rapid than the recovery of the amoc and is more related to the recovery of low latitude surface temperatures than greenland temperature or sea ice these results have implications for using proxy records as indirect measures of the amoc

on the origin and timing of rapid changes in atmospheric methane during the last glacial period we present high resolution records of atmospheric methane from the gisp2 greenland ice sheet project 2 ice core for four rapid climate transitions that occurred during the past 50 ka the end of the younger dryas at 11 8 ka the beginning of the bolling allerod period at 14 8 ka the beginning of interstadial 8 at 38 2 ka and the beginning of interstadial 12 at 45 5 ka during these events atmospheric methane concentrations increased by 200 300 ppb over time periods of 100 300 years significantly more slowly than associated temperature and snow accumulation changes recorded in the ice core record we suggest that the slower rise in methane concentration may reflect the timescale of terrestrial ecosystem response to rapid climate change we find no evidence for rapid massive methane emissions that might be associated with large scale decomposition of methane hydrates in sediments with additional results from the taylor dome ice core antarctica we also reconstruct changes in the interpolar methane gradient an indicator of the geographical distribution of methane sources associated with some of the rapid changes in atmospheric methane the results indicate that the rise in methane at the beginning of the bolling allerod period and the later rise at the end of the younger dryas were driven by increases in both tropical and boreal methane sources during the younger dryas a 1 3 ka cold period during the last deglaciation the relative contribution from boreal sources was reduced relative to the early and middle holocene periods

rapid changes of glacial climate simulated in a coupled climate model abrupt changes in climate termed dansgaard oeschger and heinrich events have punctuated the last glacial period approximately 100 10 kyr ago but not the holocene the past 10 kyr here we use an intermediate complexity climate model to investigate the stability of glacial climate and we find that only one mode of atlantic ocean circulation is stable a cold mode with deep water formation in the atlantic ocean south of iceland however a warm circulation mode similar to the present day atlantic ocean is only marginally unstable and temporary transitions to this warm mode can easily be triggered this leads to abrupt warm events in the model which share many characteristics of the observed dansgaard oeschger events for a large freshwater input such as a large release of icebergs the model s deep water formation is temporarily switched off causing no strong cooling in greenland but warming in antarctica as is observed for heinrich events our stability analysis provides an explanation why glacial climate is much more variable than holocene climate

the corner frequencies and stress drops of intraplate earthquakes in the northeastern united states this article presents the estimation of stress drops for small to middle sized intraplate earthquakes in the northeastern united states the vertical component sg and lg waves of 49 earthquakes were analyzed and their seismic corner frequencies and seismic moments were determined for these events both short period and broadband records were obtained from stations in the region there are eight events each of which has an aftershock good enough to be treated as its empirical green s function and their corner frequencies were estimated from empirical green s function methods for the other events the corner frequencies were directly estimated by the spectral fitting of the vertical component of the sg or lg wave displacement spectrum with the square source spectral model using the available broadband and high frequency short period data and a frequency dependent q correction the static stress drops were then calculated from the corner frequency and seismic moment from our study the source corner frequencies estimated by fitting the lg displacement spectrum with the assumed square source model are more consistent with the corner frequencies measured from empirical green s function deconvolution method than those estimated from the intersection of horizontal low frequency spectral asymptote and a line indicating the 2 decay above the corner frequency the source corner frequencies we estimated proved to be most appropriate for the small to middle sized earthquakes the static stress drops calculated from these corner frequency estimates tend to be independent of seismic moment for events above a certain size for earthquakes with size less than about 2 1020 dyne cm the stress drop tends to decrease with decreasing moment suggesting a breakdown in self similarity below a threshold magnitude a characteristic rupture size of about 100 m is implied for these smaller earthquakes

deterministic ground motion scenarios for engineering applications the case of thessaloniki greece abstract in this article we present a deterministic study to estimate seismic ground motions expected in urban areas located near active faults the purpose was to generate bedrock synthetic time series to be used as seismic input into site effects evaluation analysis and loss estimates for the urban area and infrastructures of thessaloniki northern greece two simulation techniques a full wave method to generate low frequency seismograms 1 hz were used to compute time series associated with four different reference earthquakes having magnitudes from 5 9 to 6 5 and located within 30 km of thessaloniki the propagation medium and different source parameters were tested through the modeling of the 1978 thessaloniki earthquake m 6 5 moreover two different nucleation points were considered for each fault in order to introduce additional variability in the ground motion estimates between the two cases the quasi unilateral rupture propagation toward the city produces both higher median peak ground acceleration pga and peak ground velocity pgv values and higher variability than bilateral ones conversely the low frequency ground motion that is peak ground displacement pgd is slightly influenced by the position of the nucleation point and its variability is related to the final slip distribution on the faults of the reference earthquakes and to the location of the sites with respect to the nodal planes of the radiation pattern to validate our deterministic shaking scenarios we verified that the synthetic peak ground motions pga and pgv and spectral ordinates are within one standard deviation of several ground motion prediction equations valid for the region at specific sites we combined the low and high frequency synthetics to obtain broadband time series that cover the entire frequency band of engineering interest 0 25 hz the use of synthetic seismograms instead of empirical equations in the hazard estimates provides a complete evaluation of the expected ground motions both in frequency and time domains including predictions at short distances from the fault 0 10 km and at periods larger than 2 3 sec

simultaneous determination of site responses and source parameters of small earthquakes along the atotsugawa fault zone central japan velocity seismograms recorded at nine local stations from 102 small earthquakes on the atotsugawa fault zone central japan with seismic moment from 3 10 17 to 3 10 21 dyne cm are analyzed to obtain the s wave spectra a genetic algorithm is applied to determine the earthquake source parameters and site responses simultaneously the stability of both site responses and source parameters are experimentally tested as well as the effects of different q models the resulting source parameters show that the stress drops appear to vary systematically with the location of earthquakes events located on the mozumi fault or the junction of the mozumi and the atotsugawa faults have higher stress drops than those on the creeping section and southernmost part of the atotsugawa fault the relationship between seismic moment and corner frequency constructed by combining our results and those of iio 1986 for other regions in japan shows that a single scaling relation does not apply in a moment range of 10 10 to 10 25 dyne cm a steplike change in scaling relationship occurs between 5 10 18 and 5 10 20 dyne cm corresponding to corner frequencies between 15 and 25 hz this observation suggests that earthquakes are most likely a multihierarchical system divided by characteristic sizes according to aki9s 1980 model a characteristic source dimension 100 200 meters may represent a critical size of the barriers distributed in the fault zone at which the barrier effects are balanced by the dynamic effect of the source process

vertical ground motion in southern spain we quantify the attenuation of ground motion with distance in south ern spain using 6052 velocity recordings from 1107 local and regional earthquakes registered by the andalusianvertical component short period network epicentral dis tances and magnitudes range from 3 to 500 km and from 1 0 to 5 1 respectively the observed peak velocity and the root mean square rms fourier velocity amplitudes with distance are parameterized by excitation distance and site terms for a set of fre quencies ranging from 1 to 12 hz we obtain these terms by performing an iterative damped least squares regression from the excitation term we extract its scaling law with magnitude by using brune s source model the distance terms are fitted by ana lytic functions that depend on geometrical spreading coefficients and a frequency dependent attenuation parameter apart from the analysis of the entire data set we perform two separate analyses of two subdata sets offshore earthquakes alboran data set and inland earthquakes betic data set these data sets have differences in their probed earth structures showing distance terms clearly distinct with higher attenuation in the alboran area q0 100 compared to the betic area q0 200 random vibration theory proved to be a suitable tool to simulate observed peak am plitudes from the obtained spectral scaling laws and signal durations

heinrich events massive late pleistocene detritus layers of the north atlantic and their global climate imprint 1 millennial climate oscillations of the glacial interval are interrupted by extreme events the so called heinrich events of the north atlantic their near global footprint is a testament to coherent interactions among earth s atmosphere oceans and cryosphere on millennial timescales heinrich detritus appears to have been derived from the region around hudson strait it was deposited over approximately 500 250 years several mechanisms have been proposed for the origin of the layers binge purge cycle of the laurentide ice sheet jokulhlaup activity from a hudson bay lake and an ice shelf buildup collapse fed by hudson strait to determine the origin of the heinrich events i recommend 1 further studies of the timing and duration of the events 2 further sedimentology study near the hudson strait and 3 greater spatial and temporal resolution studies of the layers as well as their precursory intervals studies of previous glacial intervals may also provide important constraints

dependence of abrupt atlantic meridional ocean circulation changes on climate background states abrupt decadal climate changes during the last glacial interglacial cycle are less pronounced during maximum glacial conditions and absent during the holocene to further understand the underlying dynamics we conduct hosing experiments for three climate states pre industrial pi 32 kilo years before present ka bp and last glacial maximum lgm our simulations show that a stronger temperature inversion between the surface and intermediate layer in the south labrador sea induces a faster restart of convective processes 32 ka bp lgm pi during the initial resumption of the atlantic meridional overturning circulation amoc a few decades later an amoc overshoot is mainly linked to the advection of warmer and saltier intermediate layer water from the tropical atlantic into the south labrador sea which causes a stronger deep water formation than that before the freshwater perturbation this mechanism is most pronounced during the 32 ka bp weaker during the lgm and absent during the pi

simulated atlantic multidecadal oscillation during the holocene abstractthe atlantic multidecadal oscillation amo and its possible change during the holocene are examined in this study using long term simulations of the earth system model community earth system models cosmos a quasi persistent 55 80 yr cycle characterizing in the north atlantic sea surface temperature is highly associated with the multidecadal variability of the atlantic meridional overturning circulation amoc during the holocene this mode can be found throughout the holocene indicating that the amo is dominated by internal climate variability stronger than normal amoc results in warmer than normal surface temperature spreading over almost the whole north hemisphere in particular the north atlantic ocean during the warm phase of the amo more precipitation is detected in the north atlantic low and high latitudes it also generates a dipolar seesaw pattern in the sea ice anomaly the results reveal that the influence of the amo can be amplified by a more vigorous amoc variability during t

three dimensional seismic imaging of ancient submarine lava flows an example from the southern australian margin this work comprises a part of the great australian bight deepwater marine program gabdmp for funding this project the gabdmp is a csiro research program sponsored by chevron australia the results of which will be made publicly available 3d seismic data was gratefully provided by tgs ihs are thanked for access to seismic interpretation software spectral decomposition was carried out using foster findlay associates geoteric software sverre planke and tracy gregg are thanked for constructive reviews

salt exchange in the indian atlantic ocean gateway since the last glacial maximum a compensating effect between agulhas current changes and salinity variations the import of relatively salty water masses from the indian ocean to the atlantic is considered to be important for the operational mode of the atlantic meridional overturning circulation amoc however the occurrence and the origin of changes in this import behavior on millennial and glacial interglacial timescales remains equivocal here we reconstruct multiproxy paleosalinity changes in the agulhas current since the last glacial maximum and compare the salinity pattern with records from the indian atlantic ocean gateway i aog and model simulations using a fully coupled atmosphere ocean general circulation model the reconstructed paleosalinity pattern in the agulhas current displays coherent variability with changes recorded in the wider i aog region over the last glacial termination we infer that salinities simultaneously increased in both areas consistent with a quasi interhemispheric salt seesaw response analogous to the thermal bipolar seesaw in response to a reduced cross hemispheric heat and salt exchange during times of weakened amoc interestingly these hydrographic shifts can also be recognized in the wider southern hemisphere which indicates that salinity anomalies are not purely restricted to the agulhas current system itself more saline upstream agulhas waters were propagated to the i aog during heinrich stadial 1 hs1 however the salt flux into the south atlantic might have been reduced due to a decreased volume transport through the i aog during the amoc slowdown associated with hs1 hence our combined data model interpretation suggests that intervals with higher salinity in the agulhas current source region are not necessarily an indicator for an increased salt import via the i aog into the south atlantic

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

abrupt north atlantic circulation changes in response to gradual co2 forcing in a glacial climate state glacial climate is marked by abrupt millennial scale climate changes known as dansgaard oeschger cycles the most pronounced stadial coolings heinrich events are associated with massive iceberg discharges to the north atlantic these events have been linked to variations in the strength of the atlantic meridional overturning circulation however the factors that lead to abrupt transitions between strong and weak circulation regimes remain unclear here we show that in a fully coupled atmosphere ocean model gradual changes in atmospheric co2 concentrations can trigger abrupt climate changes associated with a regime of bi stability of the atlantic meridional overturning circulation under intermediate glacial conditions we find that changes in atmospheric co2 concentrations alter the transport of atmospheric moisture across central america which modulates the freshwater budget of the north atlantic and hence deep water formation in our simulations a change in atmospheric co2 levels of about 15 ppmv comparable to variations during dansgaard oeschger cycles containing heinrich events is sufficient to cause transitions between a weak stadial and a strong interstadial circulation mode because changes in the atlantic meridional overturning circulation are thought to alter atmospheric co2 levels we infer that atmospheric co2 may serve as a negative feedback to transitions between strong and weak circulation modes

fault related biogenic mounds in the ceduna sub basin australia implications for hydrocarbon migration abstract the early cenozoic in the bight basin represents a transitional period from the slow to fast oceanic crust spreading of the southern ocean between australia and antarctica this period is characterised by widespread igneous activity and the occurrence of biogenic mound complexes in the proximal part of the ceduna sub basin these mound complexes thrive on local topographic highs exploiting the shut down in siliciclastic sediment supply during the eocene new interpretation of 2d and 3d seismic data from the central ceduna sub basin shows additional undrilled paleocene eocene biogenic mound complexes they display rugose morphology progradational and aggradational internal organisation and high impedance contrast with the surrounding sediments these mounds typically show a clear relationship with underlying reactivated fault segments these faults intersect potential oil mature cretaceous source rock intervals and therefore one plausible mechanism for the development of fault related mound complexes in the central ceduna sub basin relies on natural hydrocarbon seeps along faults supplying nutrients for a benthic chemosynthetic organisms and localised biogenic mound growth the presence of a sub bottom profile anomaly overlaid by a vertical water column acoustic contact in close vicinity of a mound complex support this model the occurrence of seep related biogenic mounds would validate the presence of mature source rock s and hydrocarbon charge in the central ceduna sub basin if confirmed the biogenic mounds would imply fluid migration occurrence until at least the eocene

earthquake source scaling relationships from 1 to 5 ml using seismograms recorded at 2 5 km depth the scaling relationships of earthquake sources less than about magnitude 3 have been the subject of considerable controversy over the last two decades studies of such events have shown a tendency for the constant stress drop self similarity of larger earthquakes to breakdown at small magnitudes and an apparent minimum source dimension of about 100 m has been observed other studies showed that this apparent breakdown in scaling could be an artifact of severe near surface attenuation limiting the spatial resolution of surface data in this study source parameters are determined for over 100 nearby tectonic earthquakes from recordings at a depth of 2 5 km in granite in the cajon pass scientific drill hole southern california comparison of the seismograms recorded at this depth with those at the wellhead clearly demonstrates the effect of the severe attenuation in the upper kilometers of the earth s crust source parameters are calculated by spectral modeling of three component p and s waves assuming four source models based on the brune 2 n 2 model in model l n 2 is fixed and q of p and s waves is determined to be 912 581 1433 and 1078 879 1323 respectively the numbers in parentheses are 1 standard deviation in model 2 qp qs 1000 is assumed and n is allowed to vary the 2 model is a good average for the data set but there is some real scatter supported by the data in model 3 qp qs 1000 is also assumed and 2 is constrained and in model 4 attenuation is ignored and n is allowed to vary source dimensions of less than 10m are observed for all four models 10 times smaller than the proposed minimum no breakdown in constant stress drop scaling is seen in the downhole data approximately ml 1 to 5 5 m0 109 1016 nm the ratio between radiated seismic energy estimated by integrating the velocity squared spectra with adequate signal bandwidth and seismic moment appears to decrease gradually with decreasing moment in the magnitude range 1 to 7 this is not incompatible with a constant stress drop but could result from errors in calculating energy the ratio of the s wave energy to that radiated by the p waves is about 14 after correction for attenuation this low value is consistent with the corner frequency shift of about 1 3 this corner frequency shift is observed for all four source models and therefore is interpreted as being source controlled

extreme deepening of the atlantic overturning circulation during deglaciation glacial terminations during the late pleistocene epoch are associated with changes in insolation they are also punctuated by millennial scale climate shifts characterized by a weakening and subsequent strengthening of the atlantic meridional overturning circulation this ubiquitous association suggests that these oscillations may be a necessary component of deglaciation model simulations have suggested that the period of weakened circulation during these terminal oscillations would be followed by an overshoot of the circulation on its resumption but this phenomenon has not yet been observed here we use radiocarbon measurements of benthic foraminifera and carbonate preservation indices to reconstruct ventilation changes in the deep south atlantic ocean over the past 40 000 years we find evidence for a particularly deep expansion of the atlantic overturning cell directly following the weak mode associated with heinrich stadial 1 our analysis of an ocean general circulation model simulation suggests that north atlantic deep water export during the expansion was greater than that of interglacial conditions we find a similar deep expansion during dansgaard oeschger interstadial event 8 38 000 years ago which followed heinrich stadial 4 we conclude that the rise in atmospheric co2 concentrations and resultant warming associated with an especially weak overturning circulation are sufficient to trigger a switch to a vigorous circulation but a full transition to interglacial conditions requires additional forcing at an orbital scale

simulated resumption of the north atlantic meridional overturning circulation slow basin wide advection and abrupt local convection abstract the resumption process of the north atlantic meridional overturning circulation moc is investigated in a series of freshwater hosing experiments using a comprehensive coupled climate model four different freshwater perturbations are applied to the north atlantic between 50 n and 70 n leading to a substantial weakening of moc and an expansion of winter sea ice cover over the greenland iceland norwegian gin seas deactivating the freshwater forcing leads to a two phase recovery of the moc the first phase is a slow basin wide advection process whereas the second phase is an abrupt decadal scale transition located in the north atlantic the slow basin wide advection process to an intermediate state of the moc is characterized by a restart of the deep water production in the area of the subpolar gyre and the irminger basin however the ice cover over the gin seas remains whereas the surface density gradually increases in the gin seas on a century time scale the length of this intermediate state depends on the strength of freshwater perturbation which determines the magnitude of the meridional density gradient in the north atlantic the second transition phase is triggered by a model specific density threshold reached in the gin seas when passed the moc abruptly intensifies by 60 within 60 80 years the analysis shows that this abrupt intensification only depends on surface salinity in the gin seas the model results reveal that the simulated sea ice retreat in the gin seas and a rapid increase of the greenland air temperature of the second phase of the resumption of the moc are similar in amplitude to temperature proxies observed during dansgaard oeschger events of the last ice age

the interpretation of the b and the b0 values and its implications on the regional deformation of the crust summary after reviewing the model and the interpretation of the negative power laws which represent the statistical distributions of the linear dimension of faults l and of the stress drops p of the earthquakes it is seen that the coefficient of the law log m0 m increases with m for smaller m it is verified that the parameters l and p of california earthquakes are independent and also it is suggested that one may consider a fractal dimension of earthquakes associated with p it is shown how these statistical distributions may allow distribution of slips in the seismic regions to be inferred where all the slips occur approximately in the same horizontal direction from the density distribution of the length of the faults it is found that in california 50 per cent of the regional displacement is due to the faults with linear lengths larger than 63 per cent of the maximum linear length of the faults similar results are obtained using the seismic moment m0 or the magnitude m instead of l in these cases however the density distribution of p is also needed for the exact computation of the displacement assuming that in california the regional displacement has been 5 cm yr 1 as measured with ground observations and space techniques it is tentatively estimated that the displacement due to earthquakes with m0 larger than 1027 1 may be as large as 4 2 cm yr 1 and that a cumulative displacement of at least 170 cm due to earthquakes with m0 larger than 1027 1 may have not been released since the great 1906 san francisco earthquake it is finally discussed how the variation in the density distribution of stress drops may be a precursor to earthquakes

simulation of abrupt climate change induced by freshwater input to the north atlantic ocean temperature records from greenland ice cores1 2 suggest that large and abrupt changes of north atlantic climate occurred frequently during both glacial and postglacial periods one example is the younger dryas cold event broecker3 speculated that these changes result from rapid changes in the thermohaline circulation of the atlantic ocean which were caused by the release of large amounts of melt water from continental ice sheets here we describe an attempt to explore this intriguing phenomenon using a coupled ocean atmosphere model in response to a massive surface flux of fresh water to the northern north atlantic of the model the thermohaline circulation weakens abruptly intensifies and weakens again followed by a gradual recovery generating episodes that resemble the abrupt changes of the ocean atmosphere system recorded in ice and deep sea cores4 the associated change of surface air temperature is particularly large in the northern north atlantic ocean and its neighbourhood but is relatively small in the rest of the world

modelling tempo spatial signatures of heinrich events influence of the climatic background state abstract different sea surface temperature sst reconstructions for the last glacial maximum are applied to a hybrid coupled climate model the resulting oceanic states are perturbed by north atlantic meltwater inputs in order to simulate the effect of heinrich events on the atlantic thermohaline circulation thc and sst the experiments show that both the atlantic sst signature of the meltwater event and the time span of thc recovery strongly depend on the climatic background state data model comparison reveals that the overall spatial signature of sst anomalies is captured much better in the glacial meltwater experiments than in an analogous experiment under present day conditions in particular a breakdown of the modern thc would induce a much stronger temperature drop in high northern latitudes than did heinrich events during the ice age moreover our results suggest that the present day circulation can settle into a stable off mode whereas the glacial thc was mono stable mono stability may serve as an explanation for the recovery of the thc after heinrich event shutdowns during the last glaciation

biogeographic impact of the leeuwin current in southern australia since the late middle eocene abstract the leeuwin current can be tracked from the western margin of the australian continent to the southern margin by the record of fossilized organisms typical of warm water marine environments this transport smudges the normal latitudinal asymmetry in the biotas of opposing oceanic and continental margins in which the eastern margins of oceans are cooler than the western margins and warmer biotas are restricted to lower latitudes in the east the most comprehensive record is in the large benthic foraminifera although fossils of benthic invertebrates nektonic nautiloids and planktonic protists are also informative in addition organic biomarker hydrocarbons in stranded bitumens and resins demonstrate that they have travelled the same route from their ultimate sources in cenozoic sedimentary basins and modern tropical rainforests of the indonesian archipelago the earliest spoor of the current is in the later middle eocene at which time the part deflection of counter gyral circulation in the indian ocean to the southeast was stimulated by the accelerated opening of the oceanic gap between australia and antarctica thus the origin of the leeuwin current is twice the age of the previously suggested origin in the miocene the current turns on and turns off in the great australian bight during the late quaternary in concert with the interglacials and the glacials at scales of 10 5 yr the switch can be seen in the faunal succession of planktonic foraminifera which are consistent with the neritic benthic faunas of the central gulfs both communities show that at the warm peak of the last interglacial the current transported biota across the bight more strongly than it has during the holocene the cenozoic record of the past 40 ma is in the same mode at 10 6 yr scales the relevant fossils are found concurrently at major marine transgressions and warming reversals of the overall fall in global temperature however the fossil pattern is due to transport on the activated leeuwin current not merely to general warming and the spread of friendly environments to higher latitudes

transient simulation of last deglaciation with a new mechanism for bolling allerod warming we conducted the first synchronously coupled atmosphere ocean general circulation model simulation from the last glacial maximum to the bolling allerod ba warming our model reproduces several major features of the deglacial climate evolution suggesting a good agreement in climate sensitivity between the model and observations in particular our model simulates the abrupt ba warming as a transient response of the atlantic meridional overturning circulation amoc to a sudden termination of freshwater discharge to the north atlantic before the ba in contrast to previous mechanisms that invoke amoc multiple equilibrium and southern hemisphere climate forcing we propose that the ba transition is caused by the superposition of climatic responses to the transient co 2 forcing the amoc recovery from heinrich event 1 and an amoc overshoot

southern ocean origin for the resumption of atlantic thermohaline circulation during deglaciation during the two most recent deglaciations the southern hemisphere warmed before greenland at the same time the northern atlantic ocean was exposed to meltwater discharge which is generally assumed to reduce the formation of north atlantic deep water yet during deglaciation the atlantic thermohaline circulation became more vigorous in the transition from a weak glacial to a strong interglacial mode here we use a three dimensional ocean circulation model to investigate the impact of southern ocean warming and the associated sea ice retreat on the atlantic thermohaline circulation we find that a gradual warming in the southern ocean during deglaciation induces an abrupt resumption of the interglacial mode of the thermohaline circulation triggered by increased mass transport into the atlantic ocean via the warm indian ocean and cold pacific ocean water route this effect prevails over the influence of meltwater discharge which would oppose a strengthening of the thermohaline circulation a southern ocean trigger for the transition into an interglacial mode of circulation provides a consistent picture of southern and northern hemispheric climate change at times of deglaciation in agreement with the available proxy records

seismic stratigraphy and geological evolution of the cenozoic cool water eucla platform great australian bight seismic images of the continental margin in the western great australian bight reveal the internal anatomy of a long lived cenozoic cool water carbonate shelf the cenozoic succession is divisible into seven seismic sequences that reflect four depositional phases phase a paleocene middle eocene is a progradational siliciclastic wedge deposited in a depositional sag and represents lowstand and transgressive sedimentation phase b middle eocene earliest middle miocene contains cool water ramp carbonates with biogenic mounds eocene oligocene overlain by a warm water flat topped platform rimmed by the early middle miocene little barrier reef coeval deep water carbonate deposition formed a multi lobed sediment apron this phase was terminated by gentle uplift and tilting throughout southern australia in the late middle miocene phase c late miocene early pliocene represents cool water lowstand wedge and ramp deposition and contains numerous biogenic mounds in the youngest sequence this phase is terminated by an unconformity attributed to marine erosion phase d pliocene quaternary is a thick succession of cool water carbonates with spectacular clinoform ramp geometry that forms most of the modern outer shelf and contains large deep water biogenic mounds this platform the first large cool water carbonate shelf imaged by high quality seismic reflection data demonstrates the interaction between regional tectonic and local and global paleo oceanographic processes as australia drifted northward during the cenozoic the great australian bight moved from high to middle latitudes and the regional oceanographic regime remained cool water largely because of coeval development of the antarctic circumpolar current in the evolving southern ocean short episodes of warm water deposition probably reflect incursions of a proto leeuwin current from the indian ocean whereas growth of the miocene coral algal little barrier reef resulted from a short term global increase in sea surface temperatures this platform dominated by stacked carbonate ramps is most similar to the west florida shelf but contains many more biogenic mounds the western great australian bight carbonate platform is an excellent modern analog for the mesoscale structure of cool water platforms in the older geologic record

response of thermohaline circulation to freshwater forcing under present day and lgm conditions responses of the thermohaline circulation thc to freshwater forcing hosing in the subpolar north atlantic ocean under present day and the last glacial maximum lgm conditions are investigated using the national center for atmospheric research community climate system model versions 2 and 3 three sets of simulations are analyzed with each set including a control run and a freshwater hosing run the first two sets are under present day conditions with an open and closed bering strait the third one is under lgm conditions which has a closed bering strait results show that the thc nearly collapses in all three hosing runs when the freshwater forcing is turned on the full recovery of the thc however is at least a century earlier in the open bering strait run than the closed bering strait and lgm runs this is because the excessive freshwater is diverged almost equally toward north and south from the subpolar north atlantic when the bering strait is open a significant portion of the freshwater flowing northward into the arctic exits into the north pacific via a reversed bering strait throughflow which accelerates the thc recovery when the bering strait is closed this arctic to pacific transport is absent and freshwater can only be removed through the southern end of the north atlantic together with the surface freshwater excess due to precipitation evaporation river runoff and melting ice in the closed bering strait experiments after the hosing the removal of the excessive freshwater takes longer and this slows the recovery of the thc although the background conditions are quite different between the present day closed bering strait run and the lgm run the thc responds to the freshwater forcing added in the north atlantic in a very similar manner

response of central european sst to atmospheric pco2 forcing during the oligocene a combined proxy data and numerical climate model approach abstract co 2 induced global warming will affect seasonal to decadal temperature patterns expected changes will be particularly strong in extratropical regions where temperatures will increase at faster rates than at lower latitudes despite that it is still poorly constrained how precisely short term climate dynamics will change in a generally warmer world particularly in nearshore surface waters in the extratropics i e the ecologically most productive regions of the ocean on which many human societies depend specifically a detailed knowledge of the relationship between p co 2 and seasonal sst is crucial to understand interactions between the ocean and the atmosphere in the present investigation we have studied for the first time how rising atmospheric p co 2 levels forced surface temperature changes in central europe paleolatitude 45 n during the mid oligocene from ca 31 to 25 ma a time interval of earth history during which global conditions were comparable to those predicted for the next few centuries for this purpose we computed numerical climate models for the oligocene winter summer annual average assuming an atmospheric carbon dioxide rise from 400 to 560 ppm current level to two times pre industrial levels pal and from 400 to 840 ppm three times pal respectively these models were compared to seasonally resolved sea surface temperatures sst reconstructed from 18 o values of fossil bivalve shells glycymeris planicostalis g obovata palliolum pictum arctica islandica and isognomon maxillata sandbergeri and shark teeth carcharias cuspidata c acutissima and physogaleus latus collected from the shallow water deposits of the mainz and kassel basins germany multi taxon oxygen isotope based reconstructions suggest a gradual rise of temperatures in surface waters upper 30 to 40 m on average by as much as 4 c during the rupelian stage followed by a 4 c cooling during the chattian stage seasonal temperature amplitudes increased by ca 2 c during the warmest time interval of the rupelian stage with warming being more pronounced during summer 5 c than during winter 3 c according to numerical climate simulations the warming of surface waters during the early oligocene required a co 2 increase by at least 160 ppm i e 400 ppm to 560 ppm given that atmospheric carbon dioxide levels predicted for the near future will likely exceed this value significantly the early oligocene warming gives a hint of the possible future climate in central europe under elevated co 2 levels

cenozoic biogenic mounds and buried miocene barrier reef on a predominantly cool water carbonate continental margin eucla basin western great australian bight the southern continental margin of australia is the largest area of cool water carbonate shelf deposition on the globe interpretation of 5495 km of airgun seismic reflection data in the western part of the great australian bight indicates that the 700 m thick cenozoic section of the offshore eucla basin was deposited largely as a prograding cool water middle to high latitude carbonate ramp characterized by widespread development of broad low relief biogenic bryozoan sponge shelf and upper slope mounds the succession also contains a spectacular and extensive 475 km long buried middle miocene barrier reef the miocene little barrier reef parallel to the modern shelf edge this rimmed carbonate platform margin represents an episode of warm water sedimentation during a global climatic optimum probably coupled with strong eastward flow of a proto leeuwin current the late miocene eustatic sea level fall produced an areally restricted debris apron sequence at the foot of the reef escarpment the carbonate platform is capped by a neogene cool water carbonate ramp succession typified by aggradational to sigmoidal sequences punctuated by periods of cold water sea floor erosion interpretation of this succession in the light of global and local tectonic and oceanographic events illustrates the dominant influence of water temperature on carbonate platform and reef growth throughout the cenozoic

north atlantic subsurface temperature response controlled by effective freshwater input in heinrich events abstract the northern north atlantic nna subsurface temperature in response to the slowdown of the atlantic meridional overturning circulation amoc is crucial for ice sheet calving and recovery of the amoc in heinrich events paleoclimate proxies and modeling studies suggest that the nna subsurface exhibits a robust warming during heinrich 1 but with a less clear response during younger dryas yd the mechanism for the potentially different subsurface responses has remained not well understood previous studies show different nna subsurface response depending on hosing at different locations here by examining a suite of water hosing experiments with different hosing regions and intensities we show that regardless of the hosing location nna subsurface temperature response is determined by the effective freshening over the nna deep convective regions through the competition between the warming associated with the suppressed vertical mixing and the cooling associated with the weakened amoc heat transport a weak effective freshening favors advective effect and in turn cooling while a strong effective freshening strengthens the mixing effect and leads to a warming our results suggest that a cooling may occur in the nna subsurface during yd

source parameters of small earthquakes recorded at 2 5 km depth cajon pass southern california implications for earthquake scaling a 2 5 km deep triaxial seismometer at cajon pass in southern california has recorded several hundred earthquakes ml4 0 occurring within the san andreas fault system at 2 5 km seismic background noise is below amplifier sensitivity and the 2 250 hz spectral range of recorded seismic motion is wider and higher than that of most natural event catalogs compared with downhole recorded motion seismic amplitudes at the surface are amplified below 10 hz and severely attenuated above 30 hz we estimate that qs is at least 1000 for wave motion at 2 5 km and below and qp is over 2000 the range of source dimensions in the downhole recorded catalog is 10 m to 70 m ml 2 0 mo 108 nm to ml 2 7 mo 1013 nm the plot of log source radius vs log moment has a straight line trend compatible with earthquake scaling at constant stress drop inferred stress drops are scattered between 1 and 500 bars there is no evidence in the catalog for the proposed minimum source dimension at 100 m when the cajon pass borehole catalog containing some of the smallest recorded natural earthquakes is combined with 800 larger events from previous studies the moment radius trend suggests that natural earthquakes are self similar over a magnitude range m 2 to 8 we suggest that inferences of minimum source dimension are more likely due to bias in bandlimited individual catalogs than to properties of the seismic crust

an introductory perspective on non tropical shelf carbonates abstract this brief account introduces the topic of non tropical shelf carbonate deposits both modern and ancient specific aspects of which are described and discussed in the 22 accompanying papers in this special issue of sedimentary geology non tropical shelves are loosely defined as lying poleward of the present limit of development of hermatypic coral reefs or beyond the mean annual surface water isotherm of about 20 c typically near 30 latitude most geoscientists have traditionally regarded shallow water carbonate formation as a low latitude phenomenon however wherever the rate and extent of terrigenous sediment dilution is small the potential exists for extensive deposits of skeletal carbonate to accumulate on shelves beyond the sub tropics the facies attributes of the modern non tropical carbonates are distinctive and contrast significantly with the structural lithological faunal floral mineralogical and diagenetic character of their tropical counterparts in the rock record non tropical limestones probably occur throughout the phanerozoic but generally remain to be identified and or interpreted as such they are presently described mainly from the ordovician permian and tertiary quaternary periods of major continental glaciations and accentuated latitudinal thermal gradients a uniformitarian approach to the recognition and interpretation of ancient shallow marine limestones requires acceptance of both tropical and non tropical carbonate facies models

the impact of the amoc resumption in the western south atlantic thermocline at the onset of the last interglacial after glacial terminations large amounts of heat and salt were transferred from low to high latitudes which is a crucial phenomenon for the reestablishment of the atlantic meridional overturning circulation amoc however how different glacial terminations evolved in the sub tropics is still poorly documented here we use foraminifera oxygen 18o and carbon 13c stable isotopes to show that the north atlantic heat piracy following the amoc resumption at the early last interglacial affected the thermocline 18o levels of the subtropical western south atlantic because of the cooling imposed by this process glacial 18o persisted in the thermocline for 7 kyr after the onset of the last interglacial dampening the effect of sea level rise usually imprinted on foraminifera 18o during terminations faunal composition and 13c also suggest the existence of a colder and thicker south atlantic central water coeval with the amoc recovery this process apparently did not occur during the last deglaciation

stress drops and radiated energies of aftershocks of the 1994 northridge california earthquake we study stress levels and radiated energy to infer the rupture characteristics and scaling relationships of aftershocks and other southern california earthquakes we use empirical green functions to obtain source time functions for 47 of the larger m 4 0 aftershocks of the 1994 northridge california earthquake m6 7 we estimate static and dynamic stress drops from the source time functions and compare them to well calibrated estimates of the radiated energy our measurements of radiated energy are relatively low compared to the static stress drops indicating that the static and dynamic stress drops are of similar magnitude this is confirmed by our direct estimates of the dynamic stress drops combining our results for the northridge aftershocks with data from other southern california earthquakes appears to show an increase in the ratio of radiated energy to moment with increasing moment there is no corresponding increase in the static stress drop this systematic change in earthquake scaling from smaller to larger m3 to m7 earthquakes suggests differences in rupture properties that may be attributed to differences of dynamic friction or stress levels on the faults

distinct modes of internal variability in the global meridional overturning circulation associated with the southern hemisphere westerly winds the internal variability of the global meridional overturning circulation gmoc in long term integration of the earth system model community earth system models cosmos is examined in this study two distinct modes of the gmoc which are closely linked to the southern hemisphere westerly winds sww anomalies are found to vary on multidecadaland centennial time scales the dominantmode is characterized by southern ocean dynamics strengthening and poleward shift of the sww associated with a positive phase of the southern annular mode yield ekman induced northward mass transport including a zonally asymmetric response in the southern ocean sea surface temperature and a cooling in the tropical pacific ocean due to large scale upwelling the second mode projects mainly onto the atlantic meridional overturning circulation amoc it is driven by a combination of sww variation and buoyancy forcing based on the relationship between the two modes together with the wind perturbation experiments the authors emphasize that the full amoc response to the sww change takes several centuries in their model the sea surface temperature in northern hemisphere high latitudes is significantly affected in this mode showing a largescale warming their results from a mid holocene experiment imply that both modes are independent from the climate background conditions in the holocene finally the authors argue that the natural modes of gmoc are important to understand trends in ocean circulation with consequences for heat and carbon budgets for past present and future climate

molecular stratigraphy of cores off northwest africa sea surface temperature history over the last 80 ka the molecular stratigraphy of biogeochemical oceanic flux study core 31k 19 n 20 10 w and ocean drilling program hole 658c 20 45 n 18 35 w has been studied for c37 alkenone abundances over the past 80 ka at high resolution circa 200 500 years the derived uk37 sea surface temperature record for both cores shows a range of temperatures from about 18 c during the last glacial to 21 5 c during the early holocene both records also reveal changes in sea surface temperature as much as 2 4 c over a few hundred years which correlate well with similar abrupt climatic changes observed in cores from elsewhere in the ne atlantic associated with heinrich events our results indicate that meltwater produced by these ice rafting events was transmitted southward by the canary current where it had considerable impact on sea surface temperatures in the subtropical eastern atlantic

influence of vertical mixing on the thermohaline hysteresis analyses of an ogcm the thermohaline hysteresis response to varying north atlantic freshwater forcing is studied by means of a three dimensional global ocean general circulation model ogcm the influence of vertical diffusivity is examined using a wide range of mixing coefficients for sufficiently large vertical diffusivity the model shows a pronounced hysteresis behavior so that two equilibrium states of the thermohaline circulation are found one mode with intense deep water formation in the north atlantic on mode and one mode with strongly reduced convective activity off mode by decreasing the diffusivity the two branches of the hysteresis merge in addition the effect of numerical diffusion is analyzed by applying different advection schemes a positive feedback between overturning strength and the numerical diffusivity of upstream advection is found resulting in a reduced stability of the on mode comparing the results with those from zonally averaged models exhibits substantial differences regarding the stability properties of the thermohaline circulation freshwater transports by horizontal gyres have an important effect on the overturning circulation in the ogcm

higher laurentide and greenland ice sheets strengthen the north atlantic ocean circulation during the last glacial interglacial cycle changes in the large scale north atlantic ocean circulation occurred and at the same time topography of the laurentide and greenland ice sheets also varied in this study we focus on detecting the changes of the north atlantic gyres western boundary current and the atlantic meridional overturning circulation amoc corresponding to different laurentide and greenland ice sheet topographies using an earth system model we conducted simulations for five climate states with different ice sheet topographies pre industrial mid holocene last glacial maximum 32 kilo years before present and eemian interglacial our simulation results indicate that higher topographies of the laurentide and greenland ice sheets strengthen surface wind stress curl over the north atlantic ocean intensifying the subtropical and subpolar gyres and the western boundary currents the corresponding decrease in sea surface height from subtropical to subpolar favors a stronger amoc an offshore shift of the gulf stream is also identified during the glacial periods relative to that during the pre industrial due to lower sea levels explaining a weaker glacial gulf stream detected in proxy data meanwhile the north atlantic gyres and amoc demonstrate a positively correlated relation under each of the climate conditions with higher ice sheets

atlantic subsurface temperatures response to a shutdown of the overturning circulation and consequences for its recovery abstract using the coupled climate model of intermediate complexity climber 3 changes in the vertical thermal structure associated with a shutdown of the atlantic meridional overturning circulation amoc are investigated when north atlantic deep water formation is inhibited by anomalous freshwater forcing intermediate depth ventilation can remain active and cool the subsurface water masses i e the cold case however if intermediate ventilation is completely suppressed relatively warm water coming from the south penetrates to a high northern latitude beneath the halocline and induces a strong vertical temperature inversion between the surface and intermediate depth i e the warm case both types of temperature anomalies emerge within the first decade after the beginning of the freshwater perturbation the sign of subsurface temperature anomaly has a strong implication for the recovery of the amoc once the anomalous freshwater forcing is removed while the amoc recovers from the cold case

holocene carbon cycle dynamics based on co2 trapped in ice at taylor dome antarctica a high resolution ice core record of atmospheric co2 concentration over the holocene epoch shows that the global carbon cycle has not been in steady state during the past 11 000 years analysis of the co2 concentration and carbon stable isotope records using a one dimensional carbon cycle model uggests that changes in terrestrial biomass and sea surface temperature were largely responsible for the observed millennial scale changes of atmospheric co2 concentrations

a radiometric calibration of the specmap timescale the astronomical theory of climate change asserts that earth s climate is affected by changes in its orbit which vary the seasonal and latitudinal distribution of solar radiation this theory is the basis of the orbitally tuned specmap timescale a key constraint for this important chronology was the mid point of the penultimate deglaciation initially dated to 127 000 years ago recent work suggests this event may be considerably older casting doubt on the astronomical theory the specmap timescale and the accuracy of orbitally tuned chronologies difficulties with u th coral dating of sea level events have impeded progress on this problem because most corals are not closed systems here we use a new approach to u th dating that corrects for open system behavior and produces a sea level curve of sufficient resolution to confidently correlate with specmap over the last 240 000 years permitting a reassessment of both this critical chronology and a central tenet of climate change theory high precision ages for 24 oxygen isotope events provide a 240 000 year chronology for marine 18o records that is independent of orbital tuning assumptions although there appear to be significant differences between the radiometric and orbitally tuned timescales near the lastglacial maximum and at the marine isotope stage 7 6 boundary a comparison of radiometric and specmap ages for identical isotope events suggest that the specmap timescale is quite accurate and that its errors were in general overestimated despite suborbital complexity orbital cyclicity is clearly evident in our record high amplitude sea level oscillations at periods greater than 20 000 years are very close in phase to summer insolation in the northern hemisphere although sea level changes cannot be uniquely tied to a specific season or latitude of insolation forcing the simplest explanation is that long period high amplitude sea level change is linked to northern hemisphere insolation forcing these results validate the principles of orbital tuning and suggest such timescales are generally robust

late cretaceous climate simulations with different co2 levels and subarctic gateway configurations a model data comparison we investigate the impact of different co2 levels and different subarctic gateway configurations on the surface temperatures during the latest cretaceous using the earth system model cosmos the simulated temperatures are compared with the surface temperature reconstructions based on a recent compilation of the latest cretaceous proxies in our numerical experiments the co2 level ranges from 1 to 6 times the preindustrial pi co2 level of 280 ppm on a global scale the most reasonable match between modeling and proxy data is obtained for the experiments with 3 to 5 pi co2 concentrations however the simulated low high latitude temperatures are too high low as compared to the proxy data the moderate co2 levels scenarios might be more realistic if we take into account proxy data and the dead zone effect criterion furthermore we test if the model data discrepancies can be caused by too simplistic proxy data interpretations this is distinctly seen at high latitudes where most proxies are biased toward summer temperatures additional sensitivity experiments with different ocean gateway configurations and constant co2 level indicate only minor surface temperatures changes 1 c on a global scale with higher values up to 8 c on a regional scale these findings imply that modeled and reconstructed temperature gradients are to a large degree only qualitatively comparable providing challenges for the interpretation of proxy data and or model sensitivity with respect to the latter our results suggest that an assessment of greenhouse worlds is best constrained by temperatures in the midlatitudes

instability of the atlantic overturning circulation during marine isotope stage 3 variations in the strength of the atlantic meridional overturning circulation amoc were involved in the occurrences of dansgaard oeschger d o events during marine isotope stage 3 mis3 the stability of the amoc to north atlantic freshwater perturbations is studied using a comprehensive climate model under mis3 boundary conditions an amoc stability diagram constructed from a series of equilibrium freshwater perturbation experiments reveals a highly nonlinear dependence of amoc strength on freshwater forcing the mis3 baseline state is remarkably unstable with respect to minor perturbations the global climate signal associated with a change in amoc strength is consistent with a transition from an interstadial to a stadial state including an annual mean surface air temperature drop of 8 k in central greenland we suggest that minor freshwater perturbations in the hydrologic cycle e g related to ice sheet processes had the potential to trigger d o type climate shifts associated with a threshold in the atmosphere ocean system

aftershock stress release along active fault planes of the 1984 round valley california earthquake sequence applying a time domain stress drop method abstract the 23 november 1984 m l 5 8 round valley earthquake is one in a series of moderate m l 6 earthquakes to have occurred in the bishop mammoth lakes california area since 1978 this earthquake and its aftershock sequence occurred within a dense seismic network and hypocentral location quality is excellent in a previous study we determined that the round valley sequence involved faulting on a conjugate set of fault planes one a near vertical plane striking n30 e the mainshock fault plane showing principally left lateral strike slip motion and another subperpendicular to the mainshock fault plane striking n40 w and dipping 55 ne exhibiting dominantly right lateral strike slip this conjugate fault plane conforms to a postulated extension of the hilton creek fault and is the only significant activity on this structure in the 12 year bishop mammoth lakes earthquake sequence source dimensions and stress drops for 87 aftershocks m l 2 8 to 4 2 of the round valley sequence have been determined using an adaptation of the initial p wave pulse width time domain deconvolution technique of frankel and kanamori 1983 the aftershock sequence is confined to a limited volume of crust we have shown that site and instrument effects and not whole path attenuation control the minimum pulse widths for this limited region the determination of a site minimum pulse width rather than a minimum pulse width for each source receiver pair as in the frankel and kanamori study makes the deconvolution procedure practical for processing the large numbers of events in an aftershock sequence with the large data set available for the round valley aftershock sequence patterns of the stress drop along the active fault planes can be seen in detail source radii systematically increase with magnitude from about 100 m for events near magnitude 3 0 to 500 m for events near magnitude 4 0 static stress drops range from 10 to 200 bars and are not strongly correlated with magnitude or depth the stress release pattern reveals a broad stress drop low 10 bars for aftershocks within the mainshock fault plane that is consistent with other evidence of the rupture surface of the round valley mainshock higher stress release occurs above and below the mainshock rupture surface and on the shallower conjugate fault plane further distant from the rupture surface of the mainshock stress drops decrease to average values on the conjugate fault surface stress drops are seen to be high in areas that may be interpreted as off fault clusters with respect to the mainshock rupture surface

oligocene and miocene carbonate platform development in the browse basin australian northwest shelf abstract extensive 2d and 3d seismic reflection data calibrated by wells provide new insights into the lateral extent morphology internal architecture and age of carbonate platforms in the subsurface of the browse basin australian northwest shelf nws the oldest carbonate build ups are interpreted as a giant bryozoan build up complex of oligocene age 34 03 27 8 ma in the late burdigalian tropical reef growth began and numerous reef rimmed carbonate platforms progressively coalesced into an extensive barrier reef from the mid langhian to the early tortonian the browse basin contained an elongate along margin barrier reef system over 500 km long this barrier reef possibly extended in the southwest into the northern carnarvon basin after the early tortonian reefs on top or landward of this major barrier reef system were smaller and less connected this significant reduction in area covered by reef rimmed platforms likely resulted from cooling following the mid miocene climate optimum and relatively high subsidence rates the reef rimmed carbonate platforms that formed between the late burdigalian and the early tortonian are very similar throughout the browse basin platform development after the early tortonian was regionally diverse high subsidence rates in the northern browse basin are interpreted to have promoted the development of thick aggrading platforms lower subsidence in the south led to thinner more widespread platforms recurrently shifting location in response to eustatic change the final phase of reef decline around 6 ma coincides with an increase in current driven drift sedimentation current related winnowing of sediments from the lagoons and slopes of the remaining carbonate platforms likely contributed to their final drowning

source parameters of microearthquakes in southeastern sicily italy we computed the source parameters of 135 local earthquakes that occurred in southeastern sicily italy between 1994 and 2001 magnitudes ranged from 0 6 to 2 5 the source parameters were determined from the spectral analysis of p waves after corrections for attenuation and site effects p wave quality qp and site s factors are known in the two frequency ranges 3 9 hz and 16 27 hz giampiccolo et al 2003 because the correction for qp and s over the whole spectrum could not be performed a new approach to estimate spectral parameters was applied we defined the new notion of holed spectrum to specify a spectrum lacking corrected spectral amplitude values within a certain frequency range whereas we referred to a whole spectrum to specify when the entire analyzed frequency band was used a detailed statistical analysis showed that dealing with the holed spectrum did not lead to significant differences in the estimate of spectral parameters displacement holed spectra corrected by the attenuation and site response were then used to estimate source parameters seismic moments ranged from 1017 to 1020 dyne cm and source dimensions from 150 to 500 m in general the stress drop values obtained analyzing p wave spectra were very low because they mainly span the range of 0 05 5 bars

evidence for general instability of past climate from a 250 kyr ice core record recent results1 2 from two ice cores drilled in central greenland have revealed large abrupt climate changes of at least regional extent during the late stages of the last glaciation suggesting that climate in the north atlantic region is able to reorganize itself rapidly perhaps even within a few decades here we present a detailed stable isotope record for the full length of the greenland ice core project summit ice core extending over the past 250 kyr according to a calculated timescale we find that climate instability was not confined to the last glaciation but appears also to have been marked during the last interglacial as explored more fully in a companion paper3 and during the previous saale holstein glacial cycle this is in contrast with the extreme stability of the holocene suggesting that recent climate stability may be the exception rather than the rule the last interglacial seems to have lasted longer than is implied by the deep sea specmap record4 in agreement with other land based observations5 6 we suggest that climate instability in the early part of the last interglacial may have delayed the melting of the saalean ice sheets in america and eurasia perhaps accounting for this discrepancy

static stress drop in the 1994 northridge california aftershock sequence we use time domain pulse widths to estimate static stress drops for 279 ml 2 5 to 4 0 aftershocks of the 17 january 1994 mw 6 7 northridge california earthquake the stress drops obtained range from 0 02 to 40 bars with a log average of 0 75 bar error bars computed for our estimates are typically a factor of 5 indicating that the three order of magnitude scatter in stress drops is not solely a result of measurement errors and that there is a significant amount of heterogeneity in the static stress drops of the aftershocks stress drops might be expected to increase with depth since a fault can maintain a higher shear load at higher confining pressures we observe an increase in log average stress drop at about 15 km depth which is statistically significant at the 80 confidence level the increase is due primarily to a lack of lower stress drop events below this depth and may be controlled by material properties since the northridge aftershocks are observed to intersect an anomalously high velocity body at around this depth hauksson and haase 1997 an apparent increase in stress drop with magnitude is also observed over the entire magnitude range of the study although whether this trend is real or an artifact of attenuation of high frequencies in the upper crust is unresolved

secular changes in colony forms and bryozoan carbonate sediments through geological history ever since their first radiation in the ordovician bryozoans have contributed significantly to carbonate sedimentation most of the numerous colony forms developed by bryozoans have evolved repeatedly in different taxonomic groups and vary in their sediment producing potential there are nine basic bryozoan colony forms encrusting dome shaped palmate foliose fenestrate robust branching delicate branching articulated and free living the proportion of these morphotypes in bryozoan faunas period by period is shown to change significantly through the phanerozoic notable patterns include i steady increase in the number and proportion of encrusting species through time interrupted by a transient drop in the late palaeozoic ii post triassic decrease in robust branching colonies iii rise in the proportion of fenestrate colonies through the palaeozoic followed by their absence in the triassic and jurassic rarity in the cretaceous and reappearance in smaller proportions in the cenozoic and iv scarcity of articulated colonies and absence of free living colonies until the cretaceous most palaeozoic bryozoan sediments come from two architecturally distinct groups of colonies i domal delicate branching robust branching and palmate and ii fenestrate the former generate coarse particles both as sediment and components of stromatoporoid coral reefs in the early and mid palaeozoic whereas the delicate lacy fans of the latter create both prolific coarse sediment and form the cores of late palaeozoic deep water sub photic biogenic mounds nearly all post palaeozoic bryozoan sediments comprise cyclostomes and cheilostomes with many of the same growth forms but with the addition of free living colonies and significant numbers of articulated colonies the latter produced sand and mud sized bryozoan sediment via disarticulation for the first time in contrast to the palaeozoic post palaeozoic bryozoans generated sediment varying more widely across the grain size spectrum from mud to sand to gravel this article highlights the need to consider evolutionary changes in carbonate producing organisms when interpreting facies changes through time

global glacial isostasy and the surface of the ice age earth the ice 5g vm2 model and grace abstract the 100 kyr quasiperiodic variation of continental ice cover which has been a persistent feature of climate system evolution throughout the most recent 900 kyr of earth history has occurred as a consequence of changes in the seasonal insolation regime forced by the influence of gravitational n body effects in the solar system on the geometry of earth s orbit around the sun the impacts of the changing surface ice load upon both earth s shape and gravitational field as well as upon sea level history have come to be measurable using a variety of geological and geophysical techniques these observations are invertible to obtain useful information on both the internal viscoelastic structure of the solid earth and on the detailed spatiotemporal characteristics of glaciation history this review focuses upon the most recent advances that have been achieved in each of these areas advances that have proven to be central to the construction of the refined model of the global process of glacial isos

impact of weddell sea shelf progradation on antarctic bottom water formation during the miocene the weddell sea is a main location of bottom water formation and thus an important component of global ocean circulation in this study we examine the ocean and climatic responses to a shelf progradation induced by ice sheet advance and glacially transported sediments during the miocene using a general circulation model our investigations show that relative to a miocene standard bathymetry a farther southerly placed shelf break as reconstructed in a state of the art bathymetry for the weddell sea enables enhanced antarctic bottom water aabw formation and gyre transport during the middle miocene for both relatively high and low atmospheric co2 concentrations furthermore co2 sensitivity experiments show that an atmospheric co2 decline for a setup with the southerly placed shelf break of a new bathymetry has only a minor impact on aabw formation while the standard setup shows an increase in combination these impacts may explain the pronounced deep water formation in the southern high latitudes from the middle miocene to the late miocene

on the strong ground motion attenuation in spain in the last two decades all earthquake hazard studies in spain have been done using the attenuation deduced from the isoseismal maps of the most important earthquakes however it is well known that the preferred parameter to measure the size of any shock is magnitude and consequently the knowledge of acceleration as a function of magnitude and distance is basic to any new hazard determination the installation of a strong motion network in spain with more than a hundred digital instruments set up in the last 15 years made possible the recording of more than 447 shocks in the moment magnitude range of 1 3 m 6 3 however only 149 shocks were processed corresponding to magnitudes greater than 3 and a distance of less than 100 km values of the maximum horizontal acceleration recorded on firm soil permitted us to make a regression analysis which has been compared with similar previously published relationships additionally the southwestern part of spain is also affected by a marine source area of different very low attenuation but there are not enough recordings to attempt a regression analysis in this case the only strong motion data gathered for the area was checked against the two intensity attenuation relationships available after conversion of maximum intensity to moment magnitude and intensity to acceleration showing a reasonable behavior of the newest intensity attenuation law gathered for the area

density distribution functions and correlations of earthquake parameters abstract the statistical analysis of the source parameters of 9 earthquake sets of different types aftershocks scattered events swarms and of different seismic regions shows that the density distribution function ddf of the linear dimension l of a fault is represented by a negative power law as well as the ddf of the static stress drop and of the scalar seismic moment mo it is then suggested and tentatively verified that also the ddf of the root mean square ground acceleration defined as a function of l and may be represented by a negative power law and that at least in the cases examined it scales like the ddf of it is seen that the variability of the static stress drop is significant from one region to another as is well known but it seems remarkable also in the same seismic region in particular in california varies by several orders of magnitude and in the different sets of events of a given region as observed again for california it is hypothesized that a correlation although weak between the stress drop and the linear dimension of a fault exists and the analyses seem not to contradict that may be a decreasing function of l finally it is suggested that the seismicity of a region may be represented two dimensionally as a function of the ddf of the stress drop and of the linear dimension of a fault instead of the classic b and bo values

intermediate depth warming in the tropical atlantic related to weakened thermohaline circulation combining paleoclimate data and modeling results for the last deglaciation 1 benthic foraminiferal oxygen isotope ratios from two sediment cores recovered at 426 and 1299 m water depth in the eastern and western tropical atlantic show that a slowdown of the thermohaline circulation thc during heinrich event h1 and the younger dryas was accompanied by rapid and intense warming of intermediate depth waters millennial scale covariations of low paleosalinities in the subpolar north atlantic with decreased benthic oxygen isotope ratios in the eastern tropical atlantic throughout the past 10 000 years suggest that thc weakening might be related to middepth warming during the holocene period as well climate model experiments simulating a strong reduction of the thc in the atlantic ocean under present day and glacial conditions reveal that the increase of temperature in the middepth tropical and south atlantic is a common feature for both climatic states caused by a reduced ventilation of cold intermediate and deep waters in conjunction with downward mixing of heat from the thermocline from the similarity of the paleoclimatic records with the model simulations we infer that the characteristic pattern of temperature change in the atlantic ocean related to weakened thermohaline circulation can serve as an indicator of present day and future thc slowdown

determination of rupture duration and stress drop for earthquakes in southern california a simple technique is developed for determining the rupture duration and stress drop of earthquakes between magnitudes 3 5 and 4 0 using the time between the p wave onset and the first zero crossing 1 2 on seismograms from local seismic networks this method is applied to 10 main shocks in southern california to investigate regional variations in stress drop the initial pulse widths of 65 foreshocks or aftershocks of these events were measured values of 1 2 for small earthquakes below about magnitude 2 2 are generally observed to remain constant with decreasing magnitude in four sequences studied the relative pulse width of a particular main shock m 3 5 at a given station is found to be correlated with the relative pulse width of its aftershocks recorded at that station these observations are interpreted to signify that the waveforms of these small events m 2 2 are essentially the impulse response of the path between the source and receiver values of 1 2 determined from small foreshocks and aftershocks are therefore subtracted in effect deconvolved from those of each main shock to obtain an estimate of the rupture duration of the main shock which is corrected for path effects significant variations in rupture duration and stress drop are observed for the main shocks studied aftershock locations and azimuthal variations in 1 2 both indicate that the rupture zone of one earthquake expanded unilaterally a factor of 10 variation in stress drop is calculated for two adjacent events of similar seismic moments occurring 1 hr apart on the san jacinto fault system the first event in this pair had the highest stress drop of the events studied 860 bars and was followed within 8 months by a magnitude 5 5 earthquake 2 km away

variability of crustal attenuation in the northeastern united states from lg waves high quality digital seismograms from eight pairs of collocated earthquakes in the northeastern united states were analyzed to determine accurate source spectrum corner frequencies this was accomplished by applying the empirical green s function method to regional pg and lg or sg phases recorded by vertical component seismographs of the u s national seismographic network usnsn and the lamont doherty cooperative seismographic network lcsn stations the frequency band used was 0 5 16 hz for usnsn and 1 30 hz for lcsn records the source spectrum corner frequencies for the eight larger earthquakes of the event pairs magnitudes between mb lg 2 5 4 1 range from about 4 3 to 16 3 hz based on the comer frequencies obtained independently from the empirical green s function analysis sg or lg wave displacement amplitude spectra up to 30 hz were used to determine the crustal average q factors along 87 event station paths these paths crossed diverse tectonic features in the northeastern united states and were in the epicentral distance range of 41 to 1394 km we found that within the northeastern united states the crustal average qlg we obtained was frequency dependent and showed spatial variability which correlated fairly well with the major tectonic features in the region our attenuation measurements indicated low lg attenuation in the adirondack mountains with exposed precambrian grenville basement with qlg 905 f0 40 high lg attenuation in the central appalachian province with qlg 561 586 f0 46 0 47 and an intermediate lg attenuation in northern new england appalachians with q 705 f0 41

roles of sea ice surface wind feedback in maintaining the glacial atlantic meridional overturning circulation and climate abstractduring glacial periods climate varies between two contrasting modes the interstadials and stadials these climate changes are often associated with drastic reorganizations of the atlantic

sediment waves with a biogenic twist in pleistocene cool water carbonates great australian bight abstract sediment waves composed of fine grained carbonate ooze with in place bryozoans are a characteristic element of the pleistocene of the great australian bight gab the low amplitude and strongly elongate sediment waves are up to 10 km long 1 km wide 40 m high and oriented sub parallel to contours immediately off the shelf slope break they are asymmetrical showing up slope migration and mainly occur in trains the sediment waves were drilled during odp leg 182 in 1998 and were interpreted as biogenic reef mounds new high quality seismic and multibeam bathymetry data were acquired on the galathea 3 expedition in 2006 allowing description of the morphology and internal architecture of the sediment waves in unprecedented detail leading to an alternative interpretation of their formation most sediment waves were initiated by preferential deposition on the landward side of irregular erosion surfaces sediment wave accretion took place under the influence of density driven currents which decelerated up the landward dipping flanks and accelerated down the seaward dipping flanks of the sediment waves the currents are interpreted as dense water cascades formed by summer evaporation and strong winter cooling by analogy with oceanographic processes in the present day gab the lithological composition varied with climate and sea level but sediment wave formation did not sediment waves formed and accreted during both glacials and interglacials in contrast to the previous interpretations which involved growth in glacial periods only bryozoans influenced the depositional environment by adding sediment trapping fine grained particles and stabilizing the muddy sea floor this caused the sediment waves to gain a more prominent sea floor relief than most muddy siliciclastic sediment waves formed by similar depositional processes the interpretation of the sediment waves as purely biogenic build ups is rejected and the sediment waves are most appropriately described as biogenically influenced sediment waves

quaternary bryozoan reef mounds in cool water upper slope environments great australian bight bryozoan reef mounds are common features in the geological record occurring within mid ramp slope paleoenvironments especially in paleozoic carbonate successions but until now have not been recorded from the modern ocean recent scientific drilling in the great australian bight ocean drilling program leg 182 has confirmed the existence of shallow subsurface bryozoan reef mounds in modern water depths of 200 350 m these structures have as much as 65 m of synoptic relief and occur both as single mounds and as mound complexes they are unlithified have a floatstone texture and are rich in delicate branching encrusting and or nodular arborescent flat robust branching fenestrate and articulated zooidal bryozoan growth forms the muddy matrix is composed of foraminifers serpulids fecal pellets irregular bioclasts sponge spicules and calcareous nannofossils the 14c accelerator mass spectrometry dates of 26 6 35 1 ka indicate that the most recent mounds the tops of which are 7 10 m below the modern seafloor flourished during the last glacial lowstand but perished during transgressive sea level rise this history reflects changing oceanographic current patterns strong upwelling during lowstands and reduced upwelling and lowered trophic resources during highstands large specimens of benthic foraminifers restricted to the mounds confirm overall mesotrophic growth conditions the mounds are similar in geometry scale general composition and paleoenvironments to older structures but lack obvious microbial influence and extensive synsedimentary cementation such differences reflect either short term local conditions or long term temporal changes in ocean chemistry and biology

large scale reorganization of ocean currents offshore western australia during the late quaternary abstract the history of coastal surface currents in the eastern indian ocean over the last 130 kyr has been studied through the application of the fi 2 transfer function to planktic foraminifera in deep sea cores in a n s transect offshore western australia the concept of sea surface temperature sst gradient residuals is the amount by which the sea surface temperature gradient of a given time differs from that in the modern sea the sst gradient residuals for several episodes of climate extremes in the late quaternary the last glacial maximum 20 kyr b p the last interglacial maximum 122 120 kyr b p and at the end of the penultimate glaciation 130 kyr b p indicate that areas north of 18 s off western australia have changed very little during the extremes in climate over the last 130 kyr while south of 18 s there have been significant changes in surface water temperatures large areas of anomalously cool surface water were established off north west cape 22 s 24 s during both glacial and interglacial extremes these reflect the increased influence of the west australian current on the surface water circulation during the last glacial maximum and at the end of the penultimate glaciation cold sea surface temperature anomalies were established near to the coast indicating that the leeuwin current did not warm the coastal zone as it does today during the last interglacial maximum the leeuwin current flowed as an intensified current in a narrow zone close to the coast but did not significantly warm surface waters offshore as far as 20 25 s where a zone of cold water was maintained