an algorithm for automated tsunami warning in french polynesia based on mantle magnitudes we have developed a new magnitude scale mm based on the measurement of mantle rayleigh wave energy in the 50 to 300 sec period range and directly related to the seismic moment through mm log10 m 20 measurements are taken on the first passage of rayleigh waves recorded on scale on broadband instruments with adequate dynamical range this allows estimation of the moment of an event within minutes of the arrival of the rayleigh wave and with a standard deviation of 0 2 magnitude units in turn the knowledge of the seismic moment allows computation of an estimate of the high seas amplitude of a range of expectable tsunami heights the latter combined with complementary data from t wave duration and historical references have been integrated into an automated procedure of tsunami warning by the centre polynesien de prevention des tsunamis cppt in papeete tahiti

tsunami hazard posed to new zealand by the kermadec and southern new hebrides subduction margins an assessment based on plate boundary kinematics interseismic coupling and historical seismicity we assess the tsunami hazard posed to new zealand by the kermadec and southern new hebrides subduction margins neither of these subduction zones has produced tsunami large enough to cause significant damage in new zealand over the past 150 years of well recorded history however as this time frame is short compared to the recurrence interval for major tsunamigenic earthquakes on many of the earth s subduction zones it should not be assumed that what has been observed so far is representative of the long term for each of these two subduction zones we present plate kinematic and fault locking results from block modelling of earthquake slip vector data and gps velocities the results are used to estimate the current rates of strain accumulation on the plate interfaces where large tsunamigenic earthquakes typically occur we also review data on the larger historical earthquakes that have occurred on these margins as well as the global cmt catalogue of events since 1976 using this information we have developed a set of scenarios for large earthquakes which have been used as initial conditions for the comcot tsunami code to estimate the subsequent tsunami propagation in the southwest pacific and from these the potential impact on new zealand has been evaluated our results demonstrate that there is a significant threat posed to the northland and coromandel regions of new zealand should a large earthquake m w 8 5 occur on the southern or middle regions of the kermadec trench and that a similarly large earthquake on the southern new hebrides trench has the potential to strongly impact on the far northern parts of new zealand close to the southern end of the submarine three kings ridge we propose logic trees for the magnitude frequency parameters of large earthquakes originating on each trench which are intended to form the basis for future probabilistic studies

inversion of complex body waves we have developed a method that inverts seismic body waves to determine the mechanism and rupture pattern of earthquakes the rupture pattern is represented as a sequence of subevents distributed on the fault plane this method is an extension of our earlier method in which the subevent mechanisms were fixed in the new method the subevent mechanisms are determined from the data and are allowed to vary during the sequence when subevent mechanisms are allowed to vary however the inversion often becomes unstable because of the complex trade offs between the mechanism the timing and the location of the subevents many different subevent sequences can explain the same data equally well and it is important to determine the range of allowable solutions some constraints must be imposed on the solution to stabilize the inversion we have developed a procedure to explore the range of allowable solutions and appropriate constraints in this procedure a network of grid points is constructed on the i plane where and i are respectively the onset time and the distance from the epicenter of a subevent the best fit subevent is determined at all grid points then the correlation is computed between the synthetic waveform for each subevent and the observed waveform the correlation as a function of and i and the best fit mechanisms computed at each i grid point depict the character of allowable solutions and facilitate a decision on the appropriate constraints to be imposed on the solution the method is illustrated using the data for the 1976 guatemala earthquake

calibrating a viscoelastic sea ice model for wave propagation in the arctic fall marginal ice zone this paper presents a wave in ice model calibration study data used were collected in the thin ice of the advancing autumn marginal ice zone of the western arctic ocean in 2015 where pancake ice was found to be prevalent multiple buoys were deployed in seven wave experiments data from four of these experiments are used in the present study wave attenuation coefficients are calculated utilizing wave energy decay between two buoys measuring simultaneously within the ice covered region wavenumbers are measured in one of these experiments forcing parameters are obtained from simultaneous in situ and remote sensing observations as well as forecast hindcast models cases from three wave experiments are used to calibrate a viscoelastic model for wave attenuation dispersion in ice cover the calibration is done by minimizing the difference between modeled and measured complex wavenumber using a multi objective genetic algorithm the calibrated results are validated using two methods one is to directly apply the calibrated viscoelastic parameters to one of the wave experiments not used in the calibration and then compare the attenuation from the model with measured data the other is to use the calibrated viscoelastic model in wavewatch iii over the entire western beaufort sea and then compare the wave spectra at two remote sites not used in the calibration both validations show reasonable agreement between the model and the measured data the completed viscoelastic model is believed to be applicable to the fall marginal ice zone dominated by pancake ice

seismic moment catalog of large shallow earthquakes 1900 to 1989 we compile a worldwide catalog of shallow depth 70 km and large ms 7 earthquakes recorded between 1900 and 1989 the catalog is shown to be complete and uniform at the 20 sec surface wave magnitude ms 7 0 we base our catalog on those of abe 1981 1984 and abe and noguchi 1983a b for events with ms 7 0 those catalogs however are not homogeneous in seismicity rates for the entire 90 year period we assume that global rates of seismicity are constant on a time scale of decades and most inhomogeneities arise from changes in instrumentation and or reporting we correct the magnitudes to produce a homogeneous catalog the catalog is accompanied by a reference list for all the events with seismic moment determined at periods longer than 20 sec using these seismic moments for great and giant earthquakes and a moment magnitude relationship for smaller events we produce a seismic moment catalog for large earthquakes from 1900 to 1989 the catalog is used to study the distribution of moment released worldwide although we assumed a constant rate of seismicity on a global basis the rate of moment release has not been constant for the 90 year period because the latter is dominated by the few largest earthquakes we find that the seismic moment released at subduction zones during this century constitutes 90 of all the moment released by large shallow earthquakes on a global basis the seismic moment released in the largest event that occurred during this century the 1960 southern chile earthquake represents about 30 to 45 of the total moment released from 1900 through 1989 a frequency size distribution of earthquakes with seismic moment yields an average slope b value that changes from 1 04 for magnitudes between 7 0 and 7 5 to b 1 51 for magnitudes between 7 6 and 8 0 this change in the b value is attributed to different scaling relationships between bounded large and unbounded small earthquakes thus the earthquake process does have a characteristic length scale that is set by the downdip width over which rupture in earthquakes can occur that width is typically greater for thrust events at subduction zones than for earthquakes along transform faults and other tectonic environments

an oscillating trend in phanerozoic non skeletal carbonate mineralogy textural and compositional data on ancient ooids and cements suggest the existence of an oscillating phanerozoic temporal trend in non skeletal carbonate mineralogy the trend shows good correlation with eustatic climatic oscillations proposed by others the most likely mechanism appears to be plate tectonically influenced oscillations in pco2 the vapour pressure of co2 rather than change in oceanic mg ca ratio

impact of atmospheric co2 and galactic cosmic radiation on phanerozoic climate change and the marine δ18o record 1 a new model is developed and applied to simulate the phanerozoic evolution of seawater composition dissolved ca sr dissolved inorganic carbon alkalinity ph 18o marine carbonates sr ca 87sr 86sr 13c 18o atmospheric co2 and surface temperature the marine carbonate records sr ca 87sr 86sr 13c are used to reconstruct changes in volcanic tectonic activity and organic carbon burial over the phanerozoic seawater ph is calculated assuming saturation with respect to calcite and considering the changing concentration of dissolved ca documented by brine inclusion data the depth of calcite saturation is allowed to vary through time and the effects of changing temperature and pressure on the stability constants of the carbonate system are considered surface temperatures are calculated using the geocarb iii approach considering also the changing flux of galactic cosmic radiation gcr it is assumed that gcr cools the surface of the earth via enhanced cloud formation at low altitudes the 18o of marine carbonates is calculated considering the changing isotopic composition of seawater the prevailing surface temperatures and seawater ph repeated model runs showed that the trends observed in the marine 18o record can only be reproduced by the model if gcr is allowed to have a strong effect on surface temperature the climate evolution predicted by the model is consistent with the geological record warm periods cambrian devonian triassic cretaceous are characterized by low gcr levels cold periods during the late carboniferous to early permian and the late cenozoic are marked by high gcr fluxes and low pco2 values the major glaciations occurring during these periods are the result of carbon cycling processes causing a draw down of atmospheric co2 and a coevally prevailing dense cloud cover at low altitudes induced by strong gcr fluxes the two moderately cool periods during the ordovician silurian and jurassic early cretaceous are characterized by both high pco2 and gcr levels so that greenhouse warming compensated for the cooling effect of low altitude clouds the very high jurassic 18o values observed in the geological record are caused by low ph values in surface waters rather than cold surface conditions

in situ observations of wave induced sea ice breakup ocean waves can propagate hundreds of kilometers into sea ice leaving behind a wake of broken ice floes three floe breakup events were observed during the second sea ice physics and ecosystem experiment sipex 2 we show that the three breakup events were likely influenced by ocean waves we compare the observations to a wave induced floe breakup model which includes an empirical wave attenuation model and show that the model underestimates the extent of floe breaking for long period waves

depth determination for shallow teleseismic earthquakes methods and results the depths of moderate sized shallow earthquakes can be routinely determined to an accuracy of several kilometers using teleseismic data alone making it possible to determine the vertical positions of earthquakes within the lithosphere this capability provides a valuable tool for plate tectonic studies since earthquake depths can be used to constrain lithospheric thermal and mechanical structure at plate boundaries and in intraplate regions two basic techniques are used for depth analyses surface wave spectra can be used to determine focal depths as mode excitation reflects the behavior of the eigenfunctions with depth the primary limitation on such studies stems from lateral heterogeneity of velocity structure the waveforms of body waves are also diagnostic of focal depth which controls the time separation between the direct arrival and near source surface reflections these studies can be limited by a partial trade off between depth and source time function duration the reliability of the body wave modeling approach now in general use is shown by excellent agreement between depths determined by different investigators using different algorithms the depth determination is robust to typical uncertainties in focal mechanism and near source structure the trade off with source time function duration generally does not produce major difficulties for small events ms 6 5 for larger events the trade off can be resolved using a approach in which for a given depth the time function yielding the best fit to a suite of seismograms is found by deconvolution deconvolution at a series of depths yields a misfit function whose minimum indicates the focal depth tests with synthetic data show that the deconvolution process yields reliable depth estimates even given uncertainties in focal mechanism and near source structure it successfully handles multiple sources moderate sized finite sources and horizontally propagating ruptures good results are obtained for vertically propagating ruptures until the fault area becomes so large that waveforms differ significantly from the point source approximation a number of important tectonic results have emerged from studies using these depth determination methods the maximum depth of oceanic intraplate seismicity increases with lithospheric age and is approximately bounded by the 750 c isotherm this depth roughly equals the flexural thickness of the lithosphere but is much less than the depth to the low velocity zone indicated by surface wave dispersion the maximum depth of continental intraplate seismicity is also temperature limited but by a lower temperature these observations are consistent with the rapid weakening of the appropriate rocks with depth predicted by standard temperature dependent rheologies the maximum depth of oceanic transform seismicity corresponds to an isotherm of about 400 c this temperature is lower than would be predicted from the intraplate results and may indicate that transforms are either hotter or weaker than expected the depths of ridge crest earthquakes large enough for teleseismic analysis are extremely shallow 0 8 km the depth distribution of seismicity in continental normal faulting regions provides constraints on the nature of the extension process at subduction zones precise depth determinations can resolve the upper and lower flexural regions in the bending downgoing plate precisely locate the plate interface and map the vertical extent and position of faulting in large earthquakes

the 2011 northern kermadec earthquake doublet and subduction zone faulting interactions 1 a large intraslab earthquake doublet 6 july 2011 mw 7 6 21 october 2011 mw 7 4 occurred in the pacific plate beneath the outer trench slope of the northern kermadec subduction zone seaward of an interseismically coupled region of the megathrust the first large event a shallow 24 km centroid depth normal faulting rupture was followed by intraslab aftershocks within minutes and by aftershocks near the megathrust within hours the second large event a deeper 45 km centroid depth thrust faulting rupture below the northern portion of the first rupture plane was also followed by interplate and intraslab aftershocks the last large interplate activity in northern kermadec involved an underthrusting doublet on 14 january 1976 mw 7 8 7 9 previous studies interpret westward movement of the northern kermadec arc relative to the australian plate from gps measurements to be a result of interseismic coupling on the northern kermadec megathrust a locked plate interface in this region should tend to reduce trench slope extensional stresses coulomb stress change calculations using a finite fault model determined from teleseismic body wave inversions for the normal faulting event in the 2011 doublet favor activation of megathrust faulting coulomb stress changes for the october compressional event appear to reduce interplate thrust activity and for a short time reversed the westward motion of the upper plate the net effect of the doublet is a few bar increase of interplate thrust fault driving stress which may have advanced a future large megathrust event intraslab normal faulting may serve as a harbinger not only a response to large megathrust ruptures

aftershock statistics of major subduction earthquakes abstract large megathrust subduction earthquakes generate prolific aftershock sequences which last over an extended period of time and affect wide spatial areas among those aftershocks the largest ones can cause additional damage and pose significant risks to population and infrastructure therefore modeling aftershock sequences of large subduction earthquakes is of considerable importance for seismic hazard assessment and earthquake risk mitigation it can also play a prominent role in the ground shaking modeling of major mainshock aftershock sequences in this work we analyze statistical properties of aftershock sequences of large subduction earthquakes worldwide which occurred from 1973 to present including recent catastrophic events in sumatra chile and japan we use information provided in the national earthquake information center neic catalog to extract 70 aftershock sequences generated by mainshocks of m 7 0 and above we construct their temporal decay rates and magnitude frequency statistics to model their temporal behavior we estimate the parameters of the modified omori law in the magnitude domain we model the frequency magnitude statistics using the gutenberg richter scaling relationship we also analyze statistically the difference between the magnitude of the mainshock and the corresponding largest aftershock in the sequence and discuss this in terms of bath s law one of the main goals of this work is to investigate the variation in parameter values of the above empirical laws with respect to the magnitude of the mainshock our main finding indicates that most parameters do not depend on the magnitude of the mainshock however they show some variation in values across different subduction settings online material the location and spatial information for elliptical regions of aftershock zones

effect of mg ca ratio in seawater on shell composition in shallow benthic foraminifera 1 the ratio of magnesium to calcium mg ca in caco3 shells of foraminifera is widely used to determine paleotemperatures however mg ca is highly variable within and between species suggesting a strong physiological influence on the incorporation of mg2 into the shells while most field and laboratory calibrations have focused on the effect of temperature we chose to study the effect of ambient mg ca on the calcification process and the final shell composition we cultured two species of symbiont bearing benthic foraminifera amphistegina lobifera and amphistegina lessonii in seawater with different mg ca ratios electron probe analysis of the shell mg ca revealed a positive but not entirely linear correlation with mg ca in the culturing media with slightly different curves for each species partition coefficients of mg2 dmg in the calcite shells showed a decrease by a factor of roughly 2 between the lowest and highest mg ca in the ambient water this was previously demonstrated in inorganic calcite precipitation experiments however the biogenic dmg was significantly lower than the inorganic one suggesting a physiological mechanism that reduces mg ca at the calcification site unlike inorganic experiments that display a dependence of dmg on the kinetics of precipitation the biogenic dmg is not correlated with the rate of calcification both dmg and calcification rates in our experiment were sensitive to the mg ca ratio rather than the concentration of either ca2 or mg2 the largest addition of caco3 was obtained at mg ca of 1 and not at present day seawater ratio mg ca 5 this may reflect the mg ca that prevailed during the eocene mg ca 1 5 when this genus evolved

sea level sediments and the composition of seawater the composition of seawater changed significantly during the course of the phanerozoic in concert with long term changes in sea level which were largely the result of changes in the volume of mid ocean ridges these reflect changes in the rate of seafloor spreading and determine the rate of seawater cycling through mid ocean ridges spencer and hardie 1990 and hardie 1996 proposed that the changes in the cycling rate of seawater through mid ocean ridges have been responsible for the changes in the composition of seawater during the phanerozoic this explanation cannot account for the major changes in the composition of seawater during the cenozoic which was a time of nearly constant seafloor spreading rate however changes in the rate of deposition of shallow water carbonates and their penecontemporaneous dolomitization can explain the cenozoic changes in seawater composition this indicates that sedimentologic parameters have played a major role in the chemical evolution of seawater the more rapid cycling of seawater through mors during the mesozoic can explain semiquantitatively the fairly minor differences between the composition of seawater in the eocene and in the jurassic changes in the composition of seawater during the paleozoic were probably determined both by changes in the rate of dolomite and gypsum anhydrite deposition and by changes in the rate of seawater cycling through mid ocean ridges if the causes of these compositional changes are the same as those during the cenozoic and mesozoic then sedimentologic factors have been significantly more important than the rate of cycling of seawater through mors in shaping the chemical evolution of seawater during the phanerozoic

calcium isotope δ44 40ca variations of neogene planktonic foraminifera measurements of the calcium isotopic composition 44 40ca of planktonic foraminifera from the western equatorial pacific and the indian sector of the southern ocean show variations of about 0 6 over the past 24 myr the stacked 44 40ca record of globigerinoides trilobus and globigerina bulloides indicates a minimum in 44 40casw seawater calcium at 15 to 16 ma and a subsequent general increase toward the present interrupted by a second minimum at 3 to 5 ma applying a coupled calcium carbon cycle model we find two scenarios that can explain a large portion of the observed 44 40casw variations in both cases variations in the ca input flux to the ocean without proportional changes in the carbonate flux are invoked the first scenario increases the riverine calcium input to the ocean without a proportional increase of the carbonate flux the second scenario generates an additional calcium flux from the exchange of ca by mg during dolomitization in both cases the calcium flux variations lead to drastic changes in the seawater ca concentrations on million year timescales our 44 40casw record therefore indicates that the global calcium cycle may be much more dynamic than previously assumed

effects of sedimentary structure and bathymetry near the source on teleseismic p waveforms from shallow subduction zone earthquakes summary the effects of sedimentary layers and non flat bathymetry on teleseismic p waveforms from shallow subduction zone earthquakes are examined by calculating synthetic seismograms the actual bathymetry and shallow sedimentary layers revealed by the seismic refraction studies are incorporated in 2 d velocity models of the oceanic trench region 2 d finite difference calculation is employed to get a complete response of the assumed non flat model structures the result of the modelling of wwssn long period seismograms shows that not only the non flat bathymetry but also thick sedimentary layers are essential to model the synthetic seismograms the lack of non flat bathymetry or sedimentary structure in the structural model often results in unrealistic synthetics in general the paths going across the trench axis are most affected this is caused by the steeply dipping ocean bottom and the thick sedimentary layers at the trench slope observed seismograms of the 1968 kurile thrust event mb 5 5 and the 1967 java normal event mb 6 0 show remarkable large amplitude later arrivals despite their moderate magnitudes a realistic model of the trench structure however reproduces remarkably well this character of later arrivals which shows that it is essential to incorporate the structure our results also indicate that we need precise knowledge on the trench structure to model the structural effects in detail on the gdsn long period seismograms the effect of the sedimentary layers is negligible because the rather narrow band response of the gdsn seismograph lies in a frequency range lower than the affected band however the effect of the non flat bathymetry is significant and can not be neglected

calcite and aragonite precipitation under controlled instantaneous supersaturation elucidating the role of caco3 saturation state and mg ca ratio on calcium carbonate polymorphism abstract for many decades researchers have attempted to clarify the factors controlling the precipitation of calcium carbonate polymorphs and the incorporation of mg into calcite precipitating in natural systems in this study a novel experimental approach delineates the role of instantaneous supersaturation and solution mg ca ratio in calcium carbonate mineralogy and composition the results of this study show that in solutions with different mg ca ratios the transition between the aragonite and the calcite aragonite precipitation fields is controlled by a combination of the saturation state of the solution with respect to caco3 and the mg ca ratio in solution the data show that for increasing solution mg ca ratios progressively higher supersaturation level is required for calcite precipitation the predominance of aragonite at high solution mg ca and low supersaturations is attributed to a relative decrease in calcite growth rates as a result of increasing incorporation of mg2 in the calcite lattice at higher solution mg ca ratios as suggested by abundant experimental work increasing solution mg ca decreases the growth rate of calcite while aragonite growth rates stay unaffected our experiments do demonstrate that despite decreased growth rate the percentage of mgco3 in calcite increases with increasing solution mg ca ratio as calcite growth rates decrease aragonite growth rates stay constant and it becomes the dominant mineral phase in solutions with high mg ca ratio and low supersaturations these findings are relevant to present day mineralogical distributions in carbonate systems and might be the key to elucidate the environmental conditions responsible for mineralogic changes through geologic time the observed dependence of calcium carbonate mineralogy on solution composition and supersaturation suggests that carbonate mineralogy is controlled by kinetics of growth

ocean surface wave evolvement in the arctic basin 1 recent basin scale changes to the compactness and thickness of arctic sea ice foreshadow that encroaching swells and locally generated waves will exert more influence there in the future indeed it is conceivable that waves may have already hastened the adjustments observed by breaking up ice floes yet waves advancing in sea ice attenuate due to being scattered from ice thickness variations and damped by ice inelasticity turbulence and friction while past research focuses on scattering by unnaturally perfect features in the ice the model reported herein assimilates realistic basin scale swathes of heterogeneous ice and parameterizes damping by way of example we show how an ocean wave train evolves during its passage in an 1670 km long arctic sea ice profile obtained from submarine

the 1986 kermadec earthquake and its relation to plate segmentation to evaluate the tectonic significance of the october 20 1986 kermadec earthquake m w 7 7 we performed a comprehensive analysis of source parameters using surface waves body waves and relocated aftershocks amplitude and phase spectra from up to 93 rayleigh waves were inverted for centroid time depth and moment tensor in a two step algorithm in some of the inversions the time function was parameterized to include information from the body wave time function the resulting source parameters were stable with respect to variations in the velocity and attenuation models assumed the parameterization of the time function and the set of rayleigh waves included the surface wave focal mechanism derived 275 61 156 is an oblique compressional mechanism that is not easy to interpret in terms of subduction tectonics a seismic moment of 4 5 1020 n m a centroid depth of 45 5 km and a centroid time of 13 3 s were obtained directivity was not resolvable from the surface waves the short source duration is in significant contrast to many large earthquakes

biomineralization in perforate foraminifera in this paper we review the current understanding of biomineralization in perforate foraminifera ideas on the mechanisms responsible for the flux of ca2 and inorganic carbon from seawater into the test were originally based on light and electron microscopic observations of calcifying foraminifera from the 1980s onward tracer experiments fluorescent microscopy and high resolution test geochemical analysis have added to existing calcification models despite recent insights no general consensus on the physiological basis of foraminiferal biomineralization exists current models include seawater vacuolization transmembrane ion transport involvement of organic matrices and or ph regulation although the magnitude of these controls remain to be quantified disagreement between currently available models may be caused by the use of different foraminiferal species as subject for biomineralization experiments and or lack of a more systematic approach to study dis similarities between taxa in order to understand foraminiferal controls on element incorporation and isotope fractionation and thereby improve the value of foraminifera as paleoceanographic proxies it is necessary to identify key processes in foraminiferal biomineralization and formulate hypotheses regarding the involved physiological pathways to provide directions for future research

the rupture process and asperity distribution of three great earthquakes from long period diffracted p waves moment tensor source mechanisms for the largest twenty nine shallow earthquakes from 1981 m s 6 5 have been determined using long period rayleigh wave spectra and p wave first motions recorded by the international deployment of accelerograms ida global digital seismic network gdsn and world wide standardised seismic network wwssn these are compared with the centroid moment tensor mechanisms presented by dziewonski and woodhouse which were obtained in a contrasting manner in most cases the source is well represented by a single double couple mechanisms with good agreement of scalar moment and orientation between the two studies apparent mismatches for other cases may be interpreted in terms of source complexity we emphasise the objectivity of comparing moment tensor elements apparent discrepancies in the moment and orientation of double couple fault plane solutions are usually due to differences in the mxz and myz moment tensor elements which are poorly constrained by long period data

the nucleation and rupture process of the 1981 gulf of corinth earthquakes from deconvolved broad band data summary source parameters of the largest three normal faulting earthquakes ms6 6 6 3 6 4 in the 1981 gulf of corinth greece sequence are determined using deconvolved broad band data recorded by arrays and single stations and a 2 d finite source model such a model enables the spatial extent rupture velocity and stress drop of the earthquakes to be determined and geological observations of surface slip can be included as a further constraint on the waveform modelling all three earthquakes were shallow lo km with low stress drops 30 bars and exhibited source complexity the correspondence between the complexity of the earthquake sources and that of the mapped fault breaks implies that the segmentation of surface faulting in greece is representative of faulting at depth tiny initial pulses which correlate across the arrays are seen in the seismograms from the gulf of corinth earthquakes at most stations these initial subevents 1 per cent of the total moment are interpreted as the breaking of small asperities which initiated the main rupture and are used to constrain the attenuation correction t 0 2 s

a model for calcium magnesium and sulfate in seawater over phanerozoic time a theoretical model has been constructed for calculating the concentrations of dissolved calcium magnesium and sulfate in seawater over the past 550 million years phanerozoic time it is demonstrated that the weathering of ca carbonates and silicates by carbonic acid can be generally ignored in the modeling a previous model of the carbon cycle is used to guide input to the oceans of mg from carbonate and silicate weathering by h 2 co 3 similarly a previous model of the sulfur cycle is used to guide input fluxes to the ocean by calcium sulfate weathering and the weathering of ca and mg carbonates and silicates by sulfuric acid the sulfuric acid is derived from the oxidation of pyrite during weathering plus the oxidation of sulfur gases derived from the metamorphic volcanic decomposition of pyrite and caso 4 calcium is removed from seawater as sedimentary carbonates and sulfates so 4 is removed as sedimentary pyrite and caso 4 and mg is removed by exchange for ca via basalt seawater reaction and or dolomitization plus minor burial in sediments with pyrite as anoxic dolomite by adjusting starting conditions modeling results can be found that agree well with results of studies of salt fluid inclusions for variations of ca and so 4 this is especially true of the timing when ca was more abundant in seawater than so 4 and vice versa general agreement was also found with fluid inclusion results for changes in the mg ca ratio thereby distinguishing calcite seas from aragonite seas because of this overall agreement the modeling offers a new perspective on why oceanic ca mg and so 4 have varied over phanerozoic time

measurements of waves in landfast ice using inertial motion units inertial motion units imus are used to perform measurements of waves in water covered by landfast ice close to the ice edge in svalbard the effective noise level of the instruments is assessed in controlled wave tank experiments a set of measurements collected in tempelfjorden svalbard in march 2015 is presented and the ability of the sensors to operate in the field is validated several characteristics of the recorded signals including correlation between the different sensors are analyzed horizontal and vertical motions are of the same order of magnitude a clear transition in the signal properties is observed in relation with changes in incoming wave field and the development of cracks in the ice layer we show that complex physics takes place when waves propagate in landfast ice and that the use of times series containing information on the full three dimensional linear acceleration rather than spectra is required to capture the underlying phenomena

deep time foraminifera mg ca paleothermometry nonlinear correction for secular change in seawater mg ca 1 the mg ca ratio of foraminifera tests is increasingly being utilized as a paleotemperature proxy deep time pre pleistocene mg ca paleothermometry is complicated by the fact that the mg ca ratio of seawater mg casw has undergone considerable secular variation over the cenozoic previous studies have corrected for this by assuming an invariant mg distribution coefficient dmg with mg casw more recent laboratory culturing has shown that this is not the case demonstrating that a power relationship best describes the variation in test mg ca mg catest with mg casw therefore previous corrections are likely to have led to inaccurate temperature reconstructions here we show how the systematics of such a correction should be applied and demonstrate why this provides good evidence that the mg ca ratio of paleogene seawater was lower than previously implied by foraminiferal constraints in agreement with the majority of the proxy mg casw evidence we also demonstrate how it is indirectly possible to constrain the value of h the power component of a mg catest mg casw calibration potentially enabling the appropriate correction of results derived from species where this relationship has not been calibrated however this technique should not be treated as a substitute for culturing the previous erroneous assumptions regarding both 1 the relationship between mg catest and mg caswand 2 the mg ca ratio of seawater at a given time in the past may counteract each other to differing extents as a result previous absolute pre pleistocene paleotemperature estimates derived from mg ca ratios in foraminifera should be treated with caution although relative temperature changes over short 1 ma timescales are likely to be reliable

crystal chemistry and thermodynamic and kinetic properties of calcite dolomite apatite and biogenic silica applications to petrologic problems abstract sedimentary minerals are generally metastable phases that given time and changing environmental conditions recrystallize to more stable phases the actual pathway of stabilization is governed by a host of kinetic factors unfortunately much of the theoretical and experimental work on thermodynamic and kinetic behavior of sedimentary minerals either has not reached field practitioners in sedimentary petrology or has been conducted under conditions that are difficult to extrapolate to natural sedimentary environments in this paper we review and present new data on the basic crystal chemistry thermodynamic and kinetic properties of calcite dolomite apatite and biogenic silica and discuss the relevance of these data to the solution of geological and geochemical problems the crystal chemistry and structure of a given magnesian calcite exert a fundamental control on its solubility and solid solution behavior and this control can be seen most clearly through comparison of synthetic and biogenic phases thus variations in crystal chemistry and structure through solubility control during diagenesis yield a range of possible stabilization pathways whose documentation is the domain of much field based study experimental work involving dolomite has focused on delineation of phase relations in dry and aqueous systems at moderate to high temperatures determination of reaction pathways followed during dolomitization of calcium carbonate and measurement of reaction rate uncertainties reside in the relevance of these data to the classic problem of low temperature dolomite formation we suggest that the effort must now focus on designing experimental systems that effectively mimic natural environments and yield reaction rate data as a function of temperature and solution composition such an example is presented a primary goal in experimental work involving carbonate fluorapatite has been an understanding of the mechanism of formation of this mineral we review the state of this knowledge and also present the results of ongoing dissolution rate experiments the importance of this work is that it bears directly on the understanding of the role carbonate fluorapatite plays in the biogeochemical cycle of p in the oceans many factors influence the solubilities of opaline silica and the silica polymorphs and solubility plays an important role in controlling silica diagenesis a model is presented that relates changes in sediment properties including density and acoustic velocity to the stages of silica diagenesis the model is applied to sediments of deep sea drilling project leg 63 the discussions of the sedimentary phases calcite dolomite apatite and biogenic silica in this paper point to several directions for future experimental research on sedimentary mineral solution reactions these include emphasis on 1 experimental studies of synthetic sedimentary mineral solution reactions to form a foundation for an understanding of natural mineral solution reactions 2 experimental investigations of mineral reactions in aqueous solutions under conditions of composition temperature and pressure similar to the natural conditions of mineral formation and 3 studies of the surface as opposed to bulk properties of sedimentary minerals in aqueous solutions and their role in reactions governing precipitation and dissolution of sedimentary phases

body wave deconvolution for variable source parameters application to the 1978 december 6 kuriles earthquake summary a method to determine the depth and mechanism of subevents in earthquakes with complex rupture is developed complex body waves are deconvolved using a damped lanczos inversion to retrieve the source time function some constraints on the mechanism and depth of the first subevent are assumed though not required the data set is deconvolved using the green s function for the first subevent to obtain a best fitting source time function this source time function is then windowed in time around the first pulse and the corresponding synthetic seismogram is subtracted from the data this process is repeated on residual data to determine mechanisms and depths of subsequent subevents this method is applied to the 1978 december 6 kuril islands earthquake a complex event which ruptured vertically from 100 to 220km in depth and represents tearing of the pacific plate as it subducts beneath the kuril and honshu arcs using long period wwssn data we found three main subevents with the mechanism o 150 80 and 20 at depths of 120 165 and 210km in this particular case one nodal plane is very well constrained and there is some a priori evidence for significant vertical rupture

rollover of apparent wave attenuation in ice covered seas wave attenuation from two field experiments in the ice covered southern ocean is examined instead of monotonically increasing with shorter waves the measured apparent attenuation rate peaks at an intermediate wave period this rollover phenomenon has been postulated as the result of wind input and nonlinear energy transfer between wave frequencies using wavewatch iii we first validate the model results with available buoy data then use the model data to analyze the apparent wave attenuation with the choice of source parameterizations used in this study it is shown that rollover of the apparent attenuation exists when wind input and nonlinear transfer are present independent of the different wave attenuation models used the period of rollover increases with increasing distance between buoys furthermore the apparent attenuation for shorter waves drops with increasing separation between buoys or increasing wind input these phenomena are direct consequences of the wind input and nonlinear energy transfer which offset the damping caused by the intervening ice

drift of pancake ice floes in the winter antarctic marginal ice zone during polar cyclones high temporal resolution in situ measurements of pancake ice drift are presented from a pair of buoys deployed on floes in the antarctic marginal ice zone during the winter sea ice expansion over 9 days in which the region was impacted by four polar cyclones concomitant measurements of wave in ice activity from the buoys are used to infer that the ice remained unconsolidated and pancake ice conditions were maintained over at least the first 7 days analysis of the data shows i the fastest reported ice drift speeds in the southern ocean ii high correlation of drift velocities with the surface wind velocities indicating absence of internal ice stresses 100 km from the ice edge where remotely sensed ice concentration is 100 and iii presence of a strong inertial signature with a 13 hr period a lagrangian free drift model is developed including a term for geostrophic currents that reproduce the 13 hr period signature in the ice motion the calibrated model provides accurate predictions of the ice drift for up to 2 days and the calibrated parameters provide estimates of wind and ocean drag for pancake floes under storm conditions

slab decoupling in the tonga arc the june 22 1977 earthquake the june 22 1977 earthquake in the southern tonga arc is a large normal faulting event with downdip rupture propagation on a steeply dipping fault plane we use a standard least squares inversion of p and sh waves for the source time function to determine a source consisting of two subevents located at depths of 40 55 and 105 125 km and a total time duration of 50 s the ratios of the spectral amplitudes of the radial modes 0s0 1s0 and 2s0 independently require a centroid depth of at least 100 km at their lower frequencies the body wave analysis suggests a moment of 1 04 1028 and the 0s0 spectral amplitude suggests a value of 1 8 2 0 1028 dyn cm the emerging picture is that of a complete rupture of the sinking lithospheric slab starting from 40 km depth and propagating down to 125 km this indicates that the decoupling of the overriding lithosphere from the slab in this area of the tonga arc takes place by gravitational pull

on the secular variations in the composition of phanerozoic marine potash evaporites in a recent paper l a hardie proposed that the secular changes in the mineralogy of marine nonskeletal limestones and in the mineralogy of marine potash evaporites during the phanerozoic are the result of changes in the composition of seawater caused primarily by fluctuations in the flux of seawater through mid ocean ridges he suggested that even quite small variations 25 in this flux have a profound effect on the composition of seawater we show that the effects of changes in the hydrothermal flux are much smaller than he proposed nevertheless a doubling of the hydrothermal flux could probably alter the composition of seawater sufficiently to affect the mineralogy of marine potash evaporites an alternative explanation for the variations in the mineralogy of these deposits invokes differences in the degree of dolomitization during the evaporation of seawater the apparent near constancy of the k sup content of seawater during the phanerozoic supports this hypothesis it seems likely that during periods of rapid seafloor spreading the rate of seawater cycling is greater than today that sea level is higher that very large carbonate platforms are more abundant and that changes in seawater chemistry together with increases in dolomitization during the evaporation of seawatermore lead to mgso sub 4 free potash deposits the relative importance of these several effects can probably be determined with certainty only when we have analyses of relatively unaltered seawater from the several phanerozoic periods 27 refs 1 fig 1 tab less

comparison of wave propagation through ice covers in calm and storm conditions motivated by a dramatic reduction in arctic sea ice cover interest in the field of wave ice interaction has accelerated over the past few years recent observations have identified that large waves 3 m have a linear attenuation rate rather than the previously assumed exponential rate that is found for small waves this suggests that waves penetrate further into the ice cover than previously expected to explore this further we tested two exponentially decaying wave models contributions from nonlinear and wind generation source terms enabled both models to reproduce the observed regime shift essentially the accumulation of nonlinear and wind energy contributions to long and thus higher amplitude waves can offset the ice damping thus reducing the apparent attenuation this study highlights the relevance of considering frequency dependence when analyzing wave attenuation in sea ice field data

the role of so4 in the switch from calcite to aragonite seas throughout the phanerozoic the primary inorganic marine calcium carbonate mineralogy oscillated between calcite and aragonite reflecting changes in seawater chemistry these variations in seawater composition also appear to have influenced the evolution of calcifying organisms however the processes controlling these mineralogical and biological changes are poorly constrained previous work has focused mainly on the mg ca ratio in seawater as the primary driver here we examine the role of dissolved so 4 in these processes by performing controlled laboratory precipitation experiments and geochemical modeling of evaporite formation we show that an increase in dissolved so 4 decreases the mg ca ratio at which calcite is destabilized and aragonite becomes the dominant caco 3 polymorph our data suggest that the mg ca and so 4 thresholds for formation of calcite seas are significantly lower than previous estimates and are mutually dependent this shows that our understanding of phanerozoic changes in seawater chemistry and the models relating this to primary caco 3 mineralogy need reevaluation 2011 geological society of america

detection and projection of carbonate dissolution in the water column and deep sea sediments due to ocean acidification 1 dissolution of fossil fuel co2 in seawater results in decreasing carbonate ion concentration and lowering of seawater ph with likely negative impacts for many marine organisms we project detectable changes in carbonate dissolution and evaluate their potential to mitigate atmospheric co2 and ocean acidification with a global biogeochemistry model hamocc forced by different co2 emission scenarios our results suggest that as the anthropogenic co2 signal penetrates into ocean interior the saturation state of carbonate minerals will drop drastically with undersaturation extending from the ocean floor up to 100 150 m depth in the next century this will induce massive dissolution of caco3 in the water column as well as the sediment increasing the total alkalinity ta by up to 180 mol kg 1 at the surface and in the ocean interior over the next 2500 years model results indicate an inhomogeneous response among different ocean basins atlantic carbonate chemistry responds faster and starts recovering two millennia after co2 emissions cease which is not the case in the pacific caco3rain stops in the pacific ocean around 2230 using an observation derived detection threshold for ta we project detectable dissolution driven changes only by the year 2070 in the surface ocean and after 2230 and 2500 in the deep atlantic and pacific respectively we show that different model assumptions regarding dissolution and calcification rates have little impact on future projections instead anthropogenic co2 emissions overwhelmingly control the degree of perturbation in ocean chemistry in conclusion ocean carbonate dissolution has insignificant potential in mitigating atmospheric co2 and ocean acidification in the next millennia

teleseismic estimates of radiated seismic energy the e m 0 discriminant for tsunami earthquakes we adapt the formalism of boatwright and choy for the computation of radiated seismic energy from broadband records at teleseismic distances to the real time situation when neither the depth nor the focal geometry of the source is known accurately the analysis of a large data set of more than 500 records from 52 large recent earthquakes shows that this procedure yields values of the estimated energy ee in good agreement with values computed from available source parameters for example as published by the national earthquake information center neic the average logarithmic residual being only 0 26 units we analyze the energy to moment ratio by defining log10 ee m0 for regular earthquakes this parameter agrees well with values expected from theoretical models and from the worldwide neic catalogue there is a one to one correspondence between values of that are deficient by one full unit or more and the so called tsunami earthquakes previously identified in the literature as having exceedingly slow sources and believed due to the presence of sedimentary structures in the fault zone our formalism can be applied to single station measurements and its coupling to automated real time measurements of the seismic moment using the mantle magnitude mm should significantly improve real time tsunami warning

the search for the origin of the planktic foraminifera planktic foraminifera are an extremely abundant important and successful group of marine protists they are particularly useful in reconstructing past environments and for biostratigraphic dating despite their importance the origin of the group is uncertain previous work has suggested that they evolved from a benthic ancestor during the triassic or perhaps the mid jurassic bajocian but a reason for their origination has remained unclear here we present evidence from the toarcian early jurassic of nw europe that the origin of the planktic foraminifera may have been one of the results of the early toarcian oceanic anoxic event this event appears to have been associated with a massive dissociation of gas hydrates and other perhaps related water chemistry changes

possible focal mechanism change during reactivation of a previously ruptured subduction zone and stress tensor implications summary body waveform inversion methods usually assume a constant double couple source or a combination of such subevents previous studies suggest that the source rupture of mature sources in terms of coupling along smooth subduction zones are usually resolved on this assumption however for events where the source area overlaps previously ruptured zones the conventional inversion methods fail to resolve the source process for such events the subduction coupling may vary between the mature source area and the previously ruptured zone causing a variation in the focal mechanism too we study the implications on the stress tensor of the coexistence of two such focal mechanisms using a major aftershock of the 1985 chilean earthquake m 6 0 the 1978 kurile m 7 6 and 1980 santa cruz islands m 7 7 earthquakes for the first event we use the two different sets of focal parameters obtained by a study which describes a focal mechanism change during the process the epicentres of the latter two large events are located in the spots which had remained unbroken in the preceding large events e g the 1963 and 1969 kurile earthquakes and the 1966 santa cruz is earthquake respectively for each event one of the focal mechanism solutions shows a substantial strike slip component the stress tensors are examined under the constraints that the shear stress is parallel to the slip vector and a friction law is satisfied two particular families of stress tensors examined are 1 the tensors that are optimally orientated with respect to the mature source area and 2 the tensors that have a vertical principal stress direction the first type of tensors can fully account for the observed slip orientation only for the chile aftershock but it comes close to the observed one in the case of the kurile island event and would indeed reactivate the decoupled area at a reasonably low stress level the second type of tensors can be compatible with the two observed slip orientations in all cases however for the santa cruz is and kurile is earthquakes the friction law which should be satisfied on each plane requires too high a stress deviation

gravity waves propagating into an ice covered ocean a viscoelastic model 1 a viscoelastic model is proposed to describe the propagation of gravity waves into various types of ice cover the ice ocean system is modeled as a homogeneous viscoelastic fluid overlying an inviscid layer both layers have finite thickness the viscosity is imagined to originate from the frazil ice or ice floes much smaller than the wavelength and the elasticity from ice floes which are relatively large compared to the wavelength a compact form of the dispersion relation is obtained under proper limiting conditions this dispersion relation can be reduced to several previously established models including the mass loading model the viscous layer model and the thin elastic plate model the full dispersion relation contains several propagating wave modes under the ice cover the following two criteria are used to select the dominant wave mode 1 wave number is the closest to the open water value and 2 attenuation rate is the least among all modes the modes selected from those criteria coincide with the ones discussed in previous studies which are shown to be limiting cases in small or large elasticity regimes of the present model in the intermediate elasticity regime however it appears that there are three wave modes with similar wavelengths and attenuation rates implications of this intermediate elasticity range remain to be seen the general viscoelastic model bridges the gap among existing models it also provides a unified tool for wave ice modelers to parameterize the polar regions populated with various types of ice cover

large earthquakes in the tonga region associated with subduction of the louisville ridge subduction of the louisville ridge influences both interplate and intraplate seismicity in the southern tonga region 22 s 26 s five earthquakes with diverse mechanisms and seismic moments greater than 1 1027 dyn cm have occurred in this region since 1975 these include two outer rise one underthrusting and two intermediate depth events all of which occurred in close proximity to the subducting ridge in order to understand better the nature of these events and to determine the role played by the louisville ridge in the subduction process detailed rupture models have been determined for each earthquake by body and surface wave analysis three events occurred at shallow depths near the oblique intersection of the louisville ridge and the tonga are these are the compressional thrust outer rise event of october 11 1975 mw 7 4 the tensional normal outer rise event of october 10 1977 mw 7 4 and the subsequent underthrusting event on december 19 1982 mw 7 5 the latter being the largest documented interplate event in tonga the intermediate depth events of june 22 1977 d 70 km mw 8 1 and april 13 1980 d 160 km mw 7 6 both have normal fault mechanisms however the 1977 event has a downdip tension axis whereas the 1980 event has a downdip compression axis the 1977 event is unusual due to its large size and the fact that most intermediate depth activity in tonga involves downdip compression the body wave radiation for the 1977 event indicates concentrated rupture in the depth range 70 90 km near the downdip projection of the louisville ridge it appears that the louisville ridge perturbs the regional stress regime at both intermediate and shallow depths in the slab the ridge appears to be a buoyant feature that produces locally strong interplate coupling to the north of its junction with the tonga trench which accounts for the 1982 thrust event and the preceding 1975 compressional outer rise event located seaward of the thrust rupture zone south of the ridge intersection the plate interface appears to be less strongly coupled tensional stresses due to slab pull are communicated to shallow depths resulting in the october 10 1977 mw 7 4 tensional outer rise event the locally enhanced interplate coupling along with a downdip stress barrier to the intraplate compressional stresses that arise from deep resistance to the slab subduction are two effects of the ridge that appear to explain the accumulation of in plate tension in the region of the june 22 1977 event the april 13 1980 downdip compressional event reflects a return to in plate compression following the great 1977 rupture which relaxed the tensional stress the unusual stress regime of the subducting ridge and its oblique trajectory down the plate are thus responsible for the diversity of large earthquake occurrence in the southern tonga arc

the attenuation rates of ocean waves in the marginal ice zone during field operations in the greenland and bering seas in 1978 1979 and 1983 a number of experiments were carried out in which wave energy was measured along a line of stations running from the open sea deep into an icefield wave buoys in the water and accelerometer packages on floes were the instruments employed with airborne vertical photography to supply information on floe size distribution it was found that the decay of waves is exponential with a decay coefficient which generally increases with frequency except for a roll over at the highest frequencies the observations can be fitted reasonably well to a theory of one dimensional scattering

the long term impact of magnesium in seawater on foraminiferal mineralogy mechanism and consequences foraminifera are unicellular protists primarily known for their calcium carbonate shells that provide an extensive fossil record this record ranging from cambrian to present shows both major shifts and gradual changes in the relative occurrence of taxa producing different polymorphs of carbonate here we present evidence for coupling between shifts in calcite versus aragonite producing species and periods with respectively low and high seawater mg ca throughout the phanerozoic during periods when seawater mg ca is 2 mol mol low mg calcite producing species dominate the foraminiferal community vice versa high mg calcite and aragonite producing species are more abundant during periods with relatively high seawater mg ca this alteration in dominance of the phase precipitated is due to selective recovery of groups producing the favorable polymorph after shifts from calcite to aragonite seas in addition relatively high extinction rates of species producing the mineral phase not favored by the seawater mg ca of that time may be responsible for this alteration these results imply that the current high seawater mg ca will in the long term favor prevalence of high mg and aragonite producing foraminifera over calcite producing taxa possibly shifting the balance toward a community in which calcite production is less dominant

comparison of viscoelastic type models for ocean wave attenuation in ice covered seas continuum based models that describe the propagation of ocean waves in ice infested seas are considered where the surface ocean layer including ice floes brash ice etc is modeled by a homogeneous viscoelastic material which causes waves to attenuate as they travel through the medium three ice layer models are compared namely a viscoelastic fluid layer model currently being trialed in the spectral wave model wavewatch iii and two simpler viscoelastic thin beam models all three models are two dimensional a comparative analysis shows that one of the beam models provides similar predictions for wave attenuation and wavelength to the viscoelastic fluid model the three models are calibrated using wave attenuation data recently collected in the antarctic marginal ice zone as an example although agreement with the data is obtained with all three models several important issues related to the viscoelastic fluid model are identified that raise questions about its suitability to characterize wave attenuation in ice covered seas viscoelastic beam models appear to provide a more robust parameterization of the phenomenon being modeled but still remain questionable as a valid characterization of wave ice interactions generally

mm a variable period mantle magnitude this paper lays the theoretical groundwork for a variable period mantle magnitude mm based on the measurement of the spectral amplitude x of very long period rayleigh waves we retain the concept of magnitude by restricting ourselves to single station measurements ignoring the focal mechanism and the exact depth of the shallow earthquakes considered our measurements are made at a series of periods in all cases greater than 40 s and the largest value is retained this procedure effectively avoids the well known interference effects leading to saturation of magnitude scales defined at a fixed period two corrections are used a period dependent distance correction cd and a source correction cs also period dependent compensating for the variation of the excitation of rayleigh waves with period both of these corrections are fully predictable on the basis of standard surface wave excitation and dispersion theory the result is a formula of the type mm log10 x cd cs c0 in which all coefficients including the constant c0 are justifiable on sound theoretical grounds the analysis of a data set of 256 records from the broadband seismograph at papeete tahiti the ultra long period system at pasadena and stations of the geoscope network shows that the mean error in the estimation of the seismic moment is on the order of 0 1 0 2 units of magnitude with the standard deviation at each station also on the order of 0 2 units of magnitude no significant trend with either distance period or station can be identified the method can also be transposed to the time domain under some simple assumptions which are justifiable theoretically for typical teleseismic distances across the pacific basin both versions of the method lend themselves well to automation thus by providing a real time estimate of the seismic moment of distant earthquakes mm has considerable potential for tsunami warning purposes its concept can easily be extended to love waves and also to intermediate and deep earthquakes

echinoderm skeletal preservation calcite aragonite seas and the mg ca ratio of phanerozoic oceans abstract the alternation between abiotic calcite and aragonite precipitation in shallow seawater and the oscillation of seawater mg ca ratio throughout the phanerozoic are both popular hypotheses echinoderms with well preserved stereom provide new empirical evidence that supports both these hypotheses analyses are reported from 29 specimens cambrian to eocene age containing ossicles preserved either as mg calcite 3 3 to 8 mole mgco3 or as mixed calcite and dolomite 5 to 12 5 mole mgco3 echinoderms with high mole mgco3 occur in the early cambrian and late carboniferous to triassic low values come from the silurian and jurassic to cretaceous the average composition of echinoderms with preserved stereom does not fall below 3 5 mol mgco3 during the phanerozoic and reaches its highest mean value of 16 0 mol mgco3 today an empirical partition coefficient of 0 03182 for modern tropical echinoids is used to indicate the mg ca ratio of ancient seawater from the mg ca ratio of fossil stereom some assumptions are involved and a likely error is calculated from the mg2 variation of modern echinoids high mean seawater mg ca ratios are calculated for early cambrian 3 3 and the late carboniferous to triassic 2 3 but never reached today s value of 5 2 low mg ca ratios 1 1 are indicated from jurassic to cretaceous echinoderms the 29 echinoderm samples plot close to first order mg ca seawater oscillations derived from geochemical models and mg ca ratios determined from fluid inclusions but considerable discrepancies exist when shorter 106 myr time intervals are considered further data and improved understanding of mg partitioning is required before accurate secular variation in the mg ca of seawater can be determined from echinoderms however they are an underused resource in this context and provide an excellent seawater archive

iterative deconvolution of complex body waves from great earthquakes the tokachi oki earthquake of 1968 abstract a method of body wave inversion is developed in an attempt to extract the information about asperities or barriers in a fault zone a sequence of point sources each being characterized with the seismic moment the onset time and the location are iteratively derived from observed records at multi stations where the two dimensional extent of the source location is taken into account a modification is made of the iterative method of kikuchi and kanamori on the formulation of inversion procedure to facilitate the computation using this method we analyse long period p waves of the tokachi oki earthquake of 1968 mw 8 2 and obtain several significant subevents with time durations of 10 s their spatio temporal distribution shows that the rupture process consists of three characteristic stages a a stage of introductory rupture b a stage of main rupture and c a stage of aftershocks the main rupture takes place in the form of clustering around a few sites of the fault plane the largest subevent occurs in the northwestern corner the stress drop associated with this event is estimated to be 200 bars one order of magnitude higher than the stress drop averaged over the entire fault plane the sum of the seismic moments of the individual subevents amounts to 2 3 1028 dyn cm which approximately coincides with the one estimated from the analysis of long period surface waves this implies that the source of the tokachi oki earthquake consists of several major subevents with time durations of 10 s in addition to other minor subevents

mm use of a variable period mantle magnitude for the rapid one station estimation of teleseismic moments broadband records of the first passage of rayleigh waves at papeete tahiti from large circum pacific earthquakes are used to recover in real time their seismic moments the magnitude concept is used at periods varying from 50 to 300 s adequate corrections are made for distance and period typical standard deviations are 0 2 orders of magnitude on mo this mantle scale mm can be extended continuously with no additional corrections over 4 orders of magnitude it can be measured in the frequency or time domains and we describe briefly the automation of the method with obvious applications in tsunami warning

evolution of the mg ca ratio of cretaceous seawater implications from the composition of biological low mg calcite abstract for the evaluation of variations in the cretaceous seawater mg ca ratio 12 shells of rudist bivalves ranging in age from the late barremian 112 2 ma to the early campanian 81 4 ma have been analysed for intra shell variations in chemical mg sr fe mn and isotopic 18 o 13 c compositions of low mg calcite preservation of fibrous prismatic ultrastructure low fe and mn concentrations as well as sr concentrations within the range of marine biological calcite indicate only very minor diagenetic alteration in all studied shells mg concentrations and 18 o values show a more or less well defined inverse covariance this pattern is similar to the conditions observed in modern skeletal calcite and interpreted to result from a combination of a temperature effect and an unidentified metabolic control on the incorporation of mg into calcite average mg concentrations in rudist calcite are significantly lower than those of modern bivalves and increase from the barremian albian to the campanian while slopes of 18 o mg regressions are similar to those of modern bivalves assuming that the mg incorporation is linearly dependent on the mg ca ratio of seawater and that mg incorporation into calcite of modern bivalve mollusks follows the same metabolic pathway than in their extinct cretaceous relatives the mg ca molar ratio of cretaceous seawater increased from 1 in the late barremian to 3 in the early campanian this trend matches previous model predictions of seawater composition and experimental results from fluid inclusions in halite a very low mg ca ratio of seawater is confirmed here to have occurred before the onset of the significant mid cretaceous increase of seafloor production rates in the late barremian uncertainties in the secular variations of seafloor spreading are discussed as hydrothermal alteration of young oceanic crust is an important driver of changes in the seawater mg ca ratio

low magnesium calcite produced by coralline algae in seawater of late cretaceous composition abstract shifts in the mg ca ratio of seawater driven by changes in midocean ridge spreading rates have produced oscillations in the mineralogy of nonskeletal carbonate precipitates from seawater on time scales of 108 years since cambrian time skeletal mineralogies of anatomically simple organisms functioning as major reef builders or producers of shallow marine limestones have generally corresponded in mineral composition to nonskeletal precipitates here we report on experiments showing that the ambient mg ca ratio actually governs the skeletal mineralogy of some simple organisms in modern seas coralline algae produce skeletons of high mg calcite 4 mol mgco3 we grew three species of these algae in artificial seawaters having three different mg ca ratios all of the species incorporated amounts of mg into their skeletons in proportion to the ambient mg ca ratio mimicking the pattern for nonskeletal precipitation thus the algae calcified as if they were simply inducing precipitation from seawater through their consumption of co2 for photosynthesis presumably organic templates specify the calcite crystal structure of their skeletons in artificial seawater with the low mg ca ratio of late cretaceous seas the algae in our experiments produced low mg calcite 4 mol mgco3 the carbonate mineral formed by nonskeletal precipitation in those ancient seas our results suggest that many taxa that produce high mg calcite today produced low mg calcite in late cretaceous seas

impact of biomineralization processes on the mg content of foraminiferal shells a biological perspective the mg ca ratio in foraminiferal shells is widely used as a proxy for paleotemperatures nevertheless it seems that the basic mg content of foraminifera is determined by biological factors as can be concluded from the large inter species and intrashell variability and the frequent deviations from inorganic behavior this paper discusses three possible ways by which foraminifera can control or modify the mg content in their shell 1 involvement of organic matrix in the precipitation process that may alter the partition coefficient of mg in biogenic calcite 2 controlled conversion of transient amorphous phases to calcite and 3 modification of the mg concentration in the parent solution from which the crystals precipitate the first two mechanisms are probably responsible for the precipitation of high mg calcite phases whole shell or sublayers while the third mechanism leads to the formation of low mg calcite phases we propose a model adapted from epithelial cells that allows massive mg2 removal from the biomineralization site this model is especially relevant to the planktonic and deep benthic low mg foraminifera that are frequently used for paleotemperature reconstructions we discuss the possible biological roles of mg in the shell in terms of the calcite polymorph conservation the in vivo chemical stability of the shell the functions of mg as a stabilizer of transient phases and as a controlling agent of the precipitation process several temperature sensitive biological processes that may influence the mg ca ratio of the shell are suggested and a model that combines biogenic and inorganic considerations is presented the model uses mg heterogeneity in the shell together with temperature response biologic and inorganic of biomineralization processes to account for the deviation of planktonic foraminifera from inorganic calcite at equilibrium with seawater

secular oscillations in the carbonate mineralogy of reef building and sediment producing organisms driven by tectonically forced shifts in seawater chemistry the primary mineralogy of oolites and early marine carbonate cements led sandberg nature 305 1983 19 22 to divide the phanerozoic eon into three intervals of aragonite seas and two intervals of calcite seas hardie geology 24 1996 279 283 has shown that these oscillations together with synchronous oscillations in the mineralogy of marine potash evaporites can be explained by secular shifts in the mg ca ratio of seawater driven by changes in spreading rates along mid ocean ridges the hardie model also predicts that high mg calcite should precipitate along with aragonite as it does in today s aragonite sea we have uncovered oscillations in the carbonate mineralogy of hypercalcifying organisms ones that have produced massive skeletons large reefs or voluminous bodies of sediment that correspond to sandberg s aragonite seas and calcite seas and that are predicted by the hardie model particular groups of corals sponges and algae appear to have been dominant reef builders only when favored by an appropriate mg ca ratio in seawater in early and middle paleozoic calcite seas calcite i reefs were dominated by calcitic tabulate heliolitid and rugose corals and calcitic stromatoporoids in contrast during the period of late paleozoic early mesozoic aragonite seas aragonite ii aragonitic groups of sponges scleractinian corals and phylloid algae as well as high mg calcitic red algae were principal reef builders during late cretaceous time at the acme of calcite ii massive rudists displaced aragonitic hermatypic corals in today s aragonite sea aragonite iii scleractinian corals are again dominant reef builders along with high mg calcitic coralline algae major sediment producing algae exhibit temporal patterns similar to those of reef builders calcitic receptaculitids flourished during calcite i whereas aragonitic dasycladaceans did not become dominant rock formers until aragonite ii during calcite ii calcitic nannoplankton formed massive coccolith chalks in warm shallow seas of the late cretaceous after the mg ca ratio of seawater had reached a very low value and calcium concentration a very high value as the mg ca ratio of seawater rose and calcium concentration fell during the cenozoic era individual coccoliths on average became less massive and encrusted cells less thickly by pliocene time during aragonite iii the prominent genus discoaster secreted only narrow rayed coccoliths that covered less than 25 of the cell surface also during aragonite iii the aragonitic green alga halimeda emerged as the dominant skeletal sediment producer in reef tracts the influence of seawater chemistry on skeletal secretion appears to have been especially strong for morphologically simple taxa that exert relatively weak control over their own calcification such groups include algae sponges corals and bryozoans morphological simplicity also permits these groups to adopt vegetative or colonial modes of growth that confer success in competition for space on reefs this linkage in addition to the basic chemical demands of hypercalcification has given the mg ca ratio of seawater strong control over the success of individual reef building taxa more generally this ratio appears to have strongly influenced evolutionary changes in the skeletal mineralogy of sponges and cheilostome bryozoans throughout their history we conclude that throughout phanerozoic time a chain of causation has extended from mid ocean ridge processes via seawater chemistry to the mineralogical and biological composition of reef communities and bioclastic carbonate deposits

early diagenetic influences on iron transformations in a freshwater lake sediment abstract iron transformations in a calcium carbonate rich fresh water sediment were studied by analyzing the relevant constituents of both interstitial water and solid matter analysis of interstitial water shows that the observed redox sequence no 3 nh 4 mno 2 mn ii feooh fe ii so 2 4 s ii is roughly in agreement with that predicted by the gibbs free energy for the corresponding reactions in contrast to marine sediments these redox transitions occur in the uppermost sediments i e at depths of 0 4 cm deeper in the sedimentary sequence the depth profile for dissolved iron exhibits a steady non linear increase up to 400 mol dm 3 in this anoxic zone according to thermodynamic predictions iron ii minerals such as iron sulfide siderite and vivianite should precipitate while fe iii oxides should be completely dissolved however microscopic analysis showed that fe iii oxides were present throughout the studied sediment furthermore scanning electron microscope energy dispersive spectroscopy analysis suggests the presence of iron sulfide could be verified but not that of siderite or vivianite these observations indicate kinetic control of iron transformations we have investigated the importance of kinetic control of iron distribution in anoxic sediments using a diagenetic model for dissolved iron ii a rough estimate of time scales for dissolution and precipitation rates was made by imposing limiting boundary conditions using the calculated rate constant we established that more than 1000 years would be required for the complete dissolution of fe iii oxides which is agreement with our observations and experimental data from the literature calculated precipitation rates of fe ii for a given mineral phase such as siderite yield a maximum value of 3 g feco3 g 1 dry sediment yr 1 such low rates would explain the absence of siderite and vivianite finally it can be inferred from the mn t fe t ratio in the sediments that this ratio depends on the redox conditions of the sediment water interface at the time of deposition thus this ratio can be used as paleo redox indicator in lacustrine sediments

calcium isotope record of phanerozoic oceans implications for chemical evolution of seawater and its causative mechanisms a total of 280 brachiopods of ordovician to cretaceous age complemented by published data from belemnites and planktonic foraminifera are used to reconstruct the evolution of calcium isotope composition of seawater 44 40casw over the phanerozoic the compiled 44 40casw record shows a general increase from 1 3 nist srm 915a at the beginning of the ordovician to 2 at present superimposed on this trend is a major long term positive excursion from the early carboniferous to early permian as well as several short term mostly negative oscillations a numerical model of the global cycles of calcium carbon magnesium and strontium was used to estimate whether the recorded 44 40casw variations can be explained by varying magnitudes of input and output fluxes of calcium to the oceans the model uses the record of marine 87sr 86sr ratios as proxy for seafloor spreading rates a record of oceanic mg ca ratios to estimate rates of dolomite formation and reconstructed atmospheric co2 discharge and erosion rates to estimate continental weathering fluxes the model results indicate that varying magnitudes of the calcium input and output fluxes cannot explain the observed 44 40casw trends suggesting that the isotope signatures of these fluxes must also have changed as a possible mechanism we suggest variable isotope fractionation in the sedimentary output flux controlled by the dominant mineralogy in marine carbonate deposits i e the oscillating calcite aragonite seas the ultimate control of the calcium isotope budget of the phanerozoic oceans appears to have been tectonic processes specifically variable rates of oceanic crust production that modulated the hydrothermal calcium flux and the oceanic mg ca ratio which in turn controlled the dominant mineralogy of marine carbonates hence the 44 40casw as to the causes of the short term oscillations recorded in the secular 44 40casw trend we tentatively propose that these are related to variable rates of dolomite formation and or to changing chemical composition of the riverine flux in particular and ratios induced by variable proportions of silicate vs carbonate weathering rates on the continents

effects of near source bathymetry on teleseismic p waveforms teleseismic p waveforms from submarine earthquakes show water reverberations that are often poorly modeled by synthetic seismograms this study suggests that considerable misfit results from the non horizontal nature of the seafloor in the epicentral region and examines this effect for a planar dipping water crust interface geometric ray theory synthetics calculated for a double couple source show that p waveforms are extremely sensitive to seafloor orientation because of the large impedance contrast across the boundary seafloor dips as small as 0 5 significantly modify the ray paths affecting the take off angle at the source reflection and transmission coefficients at the interface geometric spreading and travel time to test the applicability of such modeling p waveforms from the march 29 1976 cocos ridge intraplate earthquake were studied the waveforms many of which show prominent water multiples poorly modeled with flat lying bathymetry were inverted for the best fitting planar ocean bottom orientation using a grid search technique synthetics computed for the best fitting seafloor orientation match the data much better than synthetics for a flat lying structure and reproduce the observed azimuthal dependence of water multiple amplitudes the derived ocean bottom dip angle and direction are in agreement with bathymetric charts suggesting p waveforms provide constraints on the seafloor orientation in the epicentral region green s functions incorporating the effects of bathymetry should provide better resolution of the source parameters of submarine earthquakes

bathymetric effects on body waveforms from shallow subduction zone earthquakes and application to seismic processes in the kurile trench resolution of earthquake source characteristics is limited by structural complexities in the source region this study explores the effects of dipping near source bathymetry and structure on long period teleseismic body waveforms from shallow subduction zone earthquakes ray theory synthetics calculated for shallow double couple sources and velocity structures incorporating planar dipping interfaces suggest that p waveforms are most sensitive to water depth and sea bottom orientation for sources beneath a substantial water layer the seafloor dip of the inner trench slope can give rise to prominent later arrivals and waveform complexity not found on synthetics calculated for horizontal bathymetry sediment thickness and the dip of the sediment crust and crust mantle interfaces generally have lesser effects the high amplitude arrivals result largely from changes in the source takeoff angles of the reverberations these arrivals present difficulties for source depth and time function determination from p waveforms and may cause spurious complexity in the derived pattern of earthquake moment release sh waveforms show little effect of sea bottom orientation or local structure for shallowly dipping thrust faulting events suggesting that sh waveform analysis can stabilize source parameter studies with respect to unknown or incompletely parameterized bathymetry and structure effects of nonhorizontal structure are observed in the p waveforms from shallow kurile trench events ms 5 8 7 2 which show prominent later arrivals not observed on sh waveforms synthetics calculated for a dipping water crust interface provide a better fit to these arrivals than those calculated for a horizontal interface suggesting that the p waveforms show systematic effects of seafloor dip the synthetics are highly sensitive to the assumed orientation of the seafloor the data are fit best for seafloor orientations consistent with the dip of the inner trench slope the distorting effect of the water layer gives rise to systematic differences in p wave complexity between shallow events near the seismic front which occur beneath a thick water layer and show numerous later arrivals and deeper arcward events which occur beneath a thin water layer and show simple waveforms large reverberations in the p waveforms of the october 20 1963 and june 10 1975 kurile tsunami earthquakes have previously been used as evidence for a long source duration and a change in focal mechanism during rupture however sh waveforms suggest simple source time functions with durations of 25 and 43 s inversion of p and sh waveforms and amplitudes yields shallowly dipping thrust mechanisms with no conclusive evidence for a previously proposed steepening of the fault dip during rupture the large p wave reverberations cannot be fit using a point source and a horizontal seafloor detailed modeling of the 1963 event as an upward propagating rupture extending through low velocity sediments to the ocean bottom combined with the effects of the dipping seafloor allow the reverberation amplitudes to be matched the anomalous tsunami excitation appears to be related to the location of the sources at shallow depths within low velocity sediments

circum pacific seismic potential 1989 1999 the seismic potential for 96 segments of simple plate boundaries around the circum pacific region is presented in terms of the conditional probability for the occurrence of either large or great interplate earthquakes during the next 5 10 and 20 years i e 1989 1994 1989 1999 and 1989 2009 this study represents the first probabilistic summary of seismic potential on this scale and involves the comparison of plate boundary segments that exhibit varying recurrence times magnitudes and tectonic regimes presenting these data in a probabilistic framework provides a basis for the uniform comparison of seismic hazard between these differing fault segments as well as accounting for individual variations in recurrence time along a specific fault segment and uncertainties in the determination of the average recurrence time

along strike variability of rupture duration in subduction zone earthquakes 1 subduction zone earthquakes exhibit a wide spectrum of rupture times that reflect conditions on the megathrust fault tsunami earthquakes are examples of slower than expected ruptures that produce anomalously large tsunamis relative to the surface wave magnitude one model explaining tsunami earthquakes suggests slip within patches of low rigidity material at shallow depths heterogeneous fault conditions such as having patches of low rigidity material surrounded by higher strength material should produce heterogeneous earthquake rupture parameters here we investigate along strike variation in rupture duration for 427 shallow thrust earthquakes mw 5 0 7 0 in the peru chile alaska tonga kuril izu and java sumatra subduction zones to explore how heterogeneous seismic and tectonic characteristics such as differences in sediment type thickness and roughness of subducting bathymetry affect earthquake properties earthquake source parameters including rupture durations are estimated using multi station deconvolution of teleseismic p and sh waves to solve for earthquake source time functions and all events are relocated using additional depth phase information we classify events into shallow 26 km and deep 26 km and 61 km groups based on the overall mean depth and focus on the longest duration events with moment normalized rupture durations of 1 standard deviation above the mean duration for each group we find long duration events at all depths within the study regions except peru and chile we find no correlation with incoming sediment thickness or type and limited spatial correlation with regions of past tsunami earthquakes regions of observed afterslip and subducting bathymetric features

effect of ambient mg ca ratio on mg fractionation in calcareous marine invertebrates a record of the oceanic mg ca ratio over the phanerozoic the mg ca ratio of seawater has changed significantly over the phanerozoic primarily as a function of the rate of ocean crust production echinoids crabs shrimps and calcareous serpulid worms grown in artificial seawaters encompassing the range of mg ca ratios that existed throughout the phanerozoic exhibit a direct nonlinear relationship between skeletal and ambient mg ca specimens grown in seawater with the lowest mg ca 1 changed their mineralogy to low mg calcite 4 mol mgco3 suggesting that these high mg calcareous organisms would have produced low mg calcite in the cretaceous when oceanic mg ca was lowest 1 these results support the empirical evidence that the skeletal chemistry of calcareous organisms has varied significantly over the phanerozoic as a function of the mg ca of seawater and that the mg ca of unaltered fossils of such organisms may be a record of oceanic mg ca throughout the phanerozoic mg fractionation algorithms which relate skeletal mg ca seawater mg ca and temperature were derived from these and other experiments they can be used to estimate paleoceanic mg ca ratios and temperatures from fossil skeletal mg ca of the organisms evaluated paleoceanic mg ca ratios recalculated by using the echinoderm mg fractionation algorithm from published fossil echinoid mg ca crinoid mg ca and paleotemperature data are consistent with other estimates and models of oceanic mg ca over the phanerozoic

autonomous underwater vehicle measurements of surface wave decay and directional spectra in the marginal sea ice zone in march 2003 several autonomous underwater vehicle auv missions were carried out under sea ice in the western bellingshausen sea data from the upward looking acoustic doppler current profiler adcp on the autosub auv indicate a strongly oscillating horizontal velocity of the ice due to ocean swell swell period height direction and directional spread have been computed every 800 m from the ice edge to 10 km inward for three missions exponential period dependent attenuation of waves propagating through sea ice was observed mean period increased with distance from the ice edge the wave field refracted during propagation the directional wave spread does not seem to relate to distance from the ice edge although higher frequencies tended to be more spread if suitably deployed an ordinary adcp may be used with this technique to study both scalar and directional properties of waves in open or ice covered water

use of the mantle magnitude m m for the reassessment of the moment of historical earthquakes the mantle magnitudemm is used on a dataset of more than 180 wavetrains from 44 large shallow historical earthquakes to reassess their moments which in many cases had been previously estimated only on the basis of the earthquake s rupture area we provide 27 new or revised values ofmo based on the spectral amplitudes of surface waves recorded at a number of stations principally uppsala and pasadena among them and most significantly we document a large low frequency component to the source of the 1923 kanto earthquake the low frequency seismic moment is 2 9 1028 dyn cm in accord with geodetic observations on the other hand we revise downwards the seismic moment of the 1906 ecuador event which did not exceed 6 1028 dyn cm

active tectonic studies in the united states 1987 1990 the techniques and instrumentation used in active tectonic studies are discussed and recent results are reviewed it is suggested that a critical mass of data on several particular regions has been accumulated making possible critical debates and attempts to assess earthquake hazards particular attention is given to studies of the pacific northwest region basin and range deformation studies and distributed deformation and hidden earthquake sources also included is a comprehensive bibliography for the period

a wave based model for the marginal ice zone including a floe breaking parameterization 1 the marginal ice zone miz is the boundary between the open ocean and ice covered seas where sea ice is significantly affected by the onslaught of ocean waves waves are responsible for the breakup of ice floes and determine the extent of the miz and floe size distribution when the ice cover is highly fragmented its behavior is qualitatively different from that of pack ice with large floes therefore it is important to incorporate wave ice interactions into sea ice ocean models in order to achieve this goal two effects are considered the role of sea ice as a dampener of wave energy and the wave induced breakup of ice floes these two processes act in concert to modify the incident wave spectrum and determine the main properties of the miz a simple but novel parameterization for floe breaking is derived by considering alternatively ice as a flexible and rigid material and by using current estimates of ice critical flexural strain and strength this parameterization is combined with a wave scattering model in a one dimensional numerical framework to evaluate the floe size distribution and the extent of the miz the model predicts a sharp transition between fragmented sea ice and the central pack thus providing a natural definition for the miz reasonable values are found for the extent of the miz given realistic initial and boundary conditions the numerical setting is commensurate with typical ice ocean models with the future implementation into two dimensional sea ice models in mind

global omori law decay of triggered earthquakes large aftershocks outside the classical aftershock zone 1 triggered earthquakes can be large damaging and lethal as evidenced by the1999 shocks in turkey and the 2001 earthquakes in el salvador in this study earthquakes with ms 7 0 from the harvard centroid moment tensor cmt catalog are modeled as dislocations to calculate shear stress changes on subsequent earthquake rupture planes near enough to be affected about 61 of earthquakes that occurred near defined as having shear stress change 0 01 mpa the ms 7 0 shocks are associated with calculated shear stress increases while 39 are associated with shear stress decreases if earthquakes associated with calculated shear stress increases are interpreted as triggered then such events make up at least 8 of the cmt catalog globally these triggered earthquakes obey an omori law rate decay that lasts between 7 11 years after the main shock earthquakes associated with calculated shear stress increases occur at higher rates than background up to 240 km away from the main shock centroid omori s law is one of the few time predictable patterns evident in the global occurrence of earthquakes if large triggered earthquakes habitually obey omori s law then their hazard can be more readily assessed the characteristic rate change with time and spatial distribution can be used to rapidly assess the likelihood of triggered earthquakes following events of ms 7 0 i show an example application to the m 7 7 13 january 2001 el salvador earthquake where use of global statistics appears to provide a better rapid hazard estimate than coulomb stress change calculations

phanerozoic trends in skeletal mineralogy driven by mass extinctions changes in ocean chemistry that favoured the precipitation of aragonite or calcite are thought to have influenced the skeletal mineralogy of marine calcifyers an investigation of the original skeletal mineralogy of large numbers of marine taxa suggests that the selective recovery of marine organisms from mass extinctions has a much greater influence on the overall percentage of aragonitic organisms than the mg ca ratio of the oceans marine calcifying organisms that produce sediments and build reefs generally have skeletons and shells that are composed of either aragonite or calcite long term changes in the estimated mg ca ratios of sea water tend to correspond to changes in the prevailing mineralogy of these creatures1 2 high mg ca ratios are expected to favour the spread of aragonitic organisms whereas calcitic taxa are thought to benefit from low mg ca ratios3 4 5 6 here we test these patterns throughout the phanerozoic eon and assess the relative impacts of changing ocean chemistry and mass extinctions on the evolutionary success of calcifying organisms we find that mass extinctions are more important in regulating long term patterns of skeletal mineralogy than the mg ca ratios of the global oceans furthermore selective recovery from mass extinctions is usually more important than selective extinction in driving the phanerozoic pattern of skeletal mineralogy but even in the recovery phase there is no clear connection between changes in the dominance of aragonite or calcite and the mg ca ratio of the oceans thus providing further evidence for the complexity of biotic recoveries7

effect of different seawater mg2 concentrations on calcification in two benthic foraminifers magnesium incorporated in foraminiferal calcite mg cacc is used intensively to reconstruct past seawater temperatures but in addition to temperature the mg cacc of foraminiferal tests also depends on the ratio of mg and ca in seawater mg casw the physiological mechanisms responsible for these proxy relationships are still unknown this culture study investigates the impact of different seawater mg2 on calcification in two benthic foraminiferal species precipitating contrasting mg cacc ammonia aomoriensis producing low mg calcite and amphistegina lessonii producing intermediate mg calcite foraminiferal growth and test thickness were determined and mg ca was analyzed using laser ablation inductively coupled plasma mass spectrometry la icp ms results show that at present day seawater mg casw of 5 both species have highest growth rates reflecting their adaptation to modern seawater element concentrations test thickness is not significantly affected by different mg casw the relationship between mg casw and mg cacc shows a distinct positive y axis intercept possibly reflecting at least two processes involved in foraminiferal biomineralization the associated mg partition dmg changes non linearly with increasing mg casw hence suggesting that the dmg is best described by an exponential function approaching an asymptote

auger spectroscopy determination of the surface most adsorbed layer composition on aragonite calcite dolomite and magnesite in synthetic seawater

total moment spectra of fourteen large earthquakes total moment spectra mt m where m is the moment rate tensor are computed for 14 large earthquakes recorded by the international deployment of accelerometers ida network using the scalar moment retrieval method proposed by silver and jordan 1982 for each event we obtain estimates of mt averaged over the 10 disjunct 1 mhz intervals in the low frequency band 1 11 mhz typical ida record sets from events with mt 0 2 a 1 a 1027 dyne cm yield standard errors on the 1 mhz averages that are generally less than 20 our multiple band estimates of mt are usually consistent with comparable single band values found by other investigators from the total moment spectra we derive the zero frequency static moment mt 0 and the characteristic source duration c 2 var f t where f t is the time function of the moment rate tensor assumed to be the same for all components the parameter c formally depends on the second degree temporal spatial and mixed spatial temporal moments of an extended source but calculations with realistic source geometries indicate that the interpretation of tc strictly in terms of the second temporal moment leads to very little error a plot of c against shows considerable scatter some events lie significantly above the empirical scaling curve of kanamori and given 1981 slow earthquakes and some below fast earthquakes examples of the former include all three deep focus events analyzed here as well as the 1970 colombia and 1963 peru bolivia deep focus earthquakes whose total moment spectra are calculated from the moment tensor solutions of gilbert and dziewonski 1975 an example of the latter is the great sumbawa earthquake of august 9 1977 24 3 a which is inferred to have a relatively shallow spatial centroid 20 km and a nearly flat moment spectrum suggesting that the faulting was confined to the upper more brittle portion of the oceanic lithosphere three other large earthquakes tonga june 22 1977 23 2 a kuril islands december 6 1978 3 6 0 2 a and tumaco december 12 1979 25 2 a exhibit moment spectra which significantly decrease toward higher frequencies indicating larger values of c the aftershocks of both the tonga and kuril islands events are distributed over a considerable range of depths consistent with rupture into the lower more ductile portions of the oceanic lithosphere we speculate that the characteristic source duration may be causally related to the depth of coseismic rupturing within the lithosphere

effects of an explosive polar cyclone crossing the antarctic marginal ice zone antarctic sea ice shows a large degree of regional variability which is partly driven by severe weather events here we bring a new perspective on synoptic sea ice changes by presenting the first

rupture characteristics of the 1982 tonga and 1986 kermadec earthquakes source time functions are obtained for the december 19 1982 tonga and october 20 1986 kermadec earthquakes from deconvolution of p waves using a model including a significant dip of the ocean bottom in such a geometry the amplitudes of subsequent water multiples are large and irregular as a result we can model these two events as consisting of a single pulse of short duration 23 s in the case of the 1982 event and 19 s for the 1986 one despite complex teleseismic waveshapes this is in contrast to inversions using flat layered models which required very complex source time functions which were mutually inconsistent at different stations the anomalously large tsunami generated by the 1982 event is modeled as the result of propagation of the rupture into the sedimentary wedge at the trench rather than due to a long lived complex source time function the latter being also incompatible with the total lack of excitation of the earth s normal modes in the low frequency limit for the 1986 event we derive a source duration 19 s very short in relation to its moment 8 1027 dyn cm this earthquake a high stress drop rupture featuring a unique combination of strike slip and thrust motion on a plane dipping oceanwards of the trench is interpreted as expressing internal deformation of the subducting pacific slab at a depth of 40 km under the compressional stresses resulting from the collision