faunal and stable isotopic analyses of benthic foraminifera from the southeast seep on kimki ridge offshore southern california usa abstract we investigated the benthic foraminiferal faunal and stable carbon and oxygen isotopic composition of a 15 cm push core na075 092b obtained on a telepresence enabled cruise to the southeast seep on kimki ridge offshore southern california the seep core was taken at a depth of 973 m in the vicinity of a beggiatoa bacterial mat and vesicomyid clams calyptogena and compared to previously published data of living assemblages from 714 m four reference cores obtained at 1030 m and another one at 739 m all of the reference sites are also from the inner continental borderland but with no evidence of methane seepage no endemic species were found at the seep site and most of the taxa recovered there have been reported previously from other seep or low oxygen environments q and r mode cluster analyses clearly illustrated differences in the faunal assemblages of the seep and non seep sites the living assemblage at southeast seep was characterized by abundant takayanagia delicata cassidulina translucens and spiroplectammina biformis whereas the non seep san pedro basin reference assemblage was comprised primarily of chilostomella oolina and globobulimina pacifica density and species richness were lower at the seep site compared to the non seep site reflecting the harsher living conditions there the dead assemblage at the seep site was dominated by gyroidina turgida compared to cassidulina translucens at the 1030 m non seep site and cassidulina translucens pseudoparrella pacifica and takayanagia delicata at the 739 m non seep site density was three times lower at southeast seep than at the non seep sites of comparable water depth but species richness was 30 higher stable carbon isotopic values were considerably depleted in the seep samples compared to the non seep samples with a progression from lightest to heaviest average 13c values evident at the seep site reflecting microhabitat preference and vital effect the deep infaunal species of globobulimina the shallow infaunal species uvigerina peregrina the epifaunal species cibicidoides wuellerstorfi and the shallow infaunal but aragonite shelled species hoeglundina elegans the 13c values downcore among each benthic species indicates ongoing fluid seepage through at least the last 3800 cal yr b p at southeast seep besides the continual local seepage evidence from 13c values of planktic foraminifera in the seep core suggest two pulses of methane at 3000 and 3700 cal yr b p were released that were large enough to influence much of the water column paired benthic and planktic foraminiferal stable oxygen isotope records provide evidence that there were no paleoenvironmental changes such as increased bottom water temperature or changes in oxygen isotopic composition of bottom and pore waters during this 3800 year record to induce the methane releases instead southeast seep appears to be the result of local faulting providing pathways for fluid to flow to the seafloor at a fault stepover or transpressional bend in the regional strike slip system

nutrient irrigation of the north atlantic abstract the north atlantic as all major oceans has a remarkable duality in primary production manifested by the existence of well defined high and low mean primary production regions the largest region is the north atlantic subtropical gyre nastg an anticyclone characterized by bowl shaped isopycnals and low production the nastg is surrounded at its margins by smaller cyclonic high production regions where these isopycnals approach the sea surface the most extensive cyclonic regions are those at the latitudinal extremes i e the subpolar and tropical oceans though smaller ones do occur at the zonal boundaries in this article we review historical data and present new analyses of climatological data and a selected number of hydrographic cruises in the western northwestern and eastern southeastern boundaries of the nastg with the objective of investigating the importance of upward epipycnal advection of nutrient rich subsurface layers irrigation in maintaining high primary production in the euphotic layers in the north atlantic subpolar gyre naspg irrigation implies intergyre exchange caused by the outcropping extension of the gulf stream gs following the formation of the deep winter mixed layer in the eastern boundary of the nastg irrigation is attained through a permanent upwelling cell which feeds the canary upwelling current cuc in the southeastern corner irrigation occurs in fall when the guinea dome gd is reinforced and in winter when the cuc reaches its southernmost extension other characteristics of the north south extension of the gs cuc are the seasonal nutrient replenishing of subsurface layers spring restratification of naspg and winter relaxation of the gd and the maintenance of high levels of diapycnal mixing during the last phase of nutrient transfer to the euphotic layers off the mid atlantic bight the gs transports a total of about 700 kmol s 1 of nitrate with almost 100 kmol s 1 carried in the surface

oxygen isotope calibration of the onset of ice rafting and history of glaciation in the north atlantic region we report here that dsdp site 552a cored with the hydraulic piston corer on the west flank of rockall bank recovered an undisturbed sequence of alternating white deep sea carbonate oozes and dark coloured layers that are rich in glacial debris oxygen isotope analysis of the sequence together with detailed nannofossil and palaeomagnetic stratigraphy shows that the first major horizon of ice rafting occurred at about 2 4 myr and was preceded by a minor pulse of ice rafting at about 2 5 myr the carbon isotope record shows that the site has been bathed by a water mass of similar characteristics to present day north atlantic deep water at least since 3 5 myr

moored wind temperature and current observations made during coastal ocean dynamics experiments 1 and 2 over the northern california continental shelf and upper slope moored observations of winds currents and temperature made over the northern california shelf and upper slope during the 1981 and 1982 upwelling seasons as part of the coastal ocean dynamics experiment code are described in both field experiments code 1 and code 2 the onset of the upwelling season is triggered by the strengthening of the north pacific high off northern california and signalled by the presence of water colder than 9 c near the bottom over the shelf vertical temperature stratification over the shelf is reduced during active upwelling local winds and subtidal currents over the shelf are strongly polarized in the alongshelf direction and the mean wind stress is directed equatorward response of alongshelf currents to wind forcing is similar at all depths over the shelf the response of the cross shelf current is more complex in the surface layer offshelf flow is significantly and positively correlated with the upwelling favorable alongshelf wind stress beneath this layer a weak return flow exists the thickness of the upper mixed layer varies greatly reaching 60 m during upwelling events thus direct wind forcing affects a substantial fraction of the water over the shelf low frequency wind stress current and temperature fields are adequately described by a few energetic empirical orthogonal functions with simple spatial structure the most energetic mode typically accounts for 75 or more of the variance of wind stress and temperature over the middle and inner shelf the most energetic current mode accounts for 90 or more of the variance is dominated by he alongshelf component and veers to the left with depth the low frequency alongshelf flow fluctuations are quasi barotropic with some vertical shear but no reversal with depth vertical shear in alongshelf current and the cross shelf density gradient obey the thermal wind relation the simple structure of the subdiurnal currents allow estimation of the alongshelf volume transport between the 60 and 130 m isobaths through three cross shelf transects in code 2 volume transport over the shelf is often nearly two dimensional but occasional large differences indicate significant mass exchange between the shelf and the adjacent upper slope correlation of low frequency currents and alongshelf wind stress shows the response of alongshelf current to be maximum near the surface and near midshelf where a 15 cm 1 alongshelf flow lags a 1 dyn cm 2 alongshelf wind stress by the order of 10 hours currents over the upper slope are not significantly correlated with local wind alongshelf transport over the shelf is highly correlated with local wind stress explaining 80 of the variance in the low frequency transport during code 2 volume transport is best correlated with wind stress approximately 30 km to the south winds in the code area during spring and summer are characterized by strong and persistent upwelling favorable winds interrupted by shorter periods of weak winds regression analysis indicates that in the absence of wind a poleward barotropic current jet exists over the shelf with a maximum amplitude over the inner shelf in the code area an upwelling favorable wind counters this jet over the shelf so that the alongshore flow is everywhere equator ward during strong wind events since the maximum response to wind forcing is found at midshelf and near surface the mean current over the upwelling season is strongly sheared in both the vertical and cross shelf directions mean flow over the outer shelf is surface intensified and is directed offshelf and equatorward while the deeper flow at midshelf and through most of the water column over the inner shelf is directed poleward

terrestrial climate evolution in the southwest pacific over the past 30 million years abstract a reconstruction of terrestrial temperature and precipitation for the new zealand landmass over the past 30 million years is produced using pollen data from 2000 samples lodged in the new zealand fossil record electronic database and modern climate data of nearest living relatives the reconstruction reveals a warming trend through the late oligocene to early miocene peak warmth in the middle miocene and stepwise cooling through the late neogene whereas the regional signal in our reconstruction includes a 5 10 northward tectonic drift as well as an increase in high altitude biomes due to late neogene and pliocene uplift of the southern alps the pattern mimics inferred changes in global ice extent which suggests that global drivers played a major role in shaping local vegetation importantly seasonal temperature estimates indicate low seasonality during the middle miocene and that subsequent neogene cooling was largely due to cooler winters we suggest that this may reflect increased subantarctic influence on new zealand vegetation as the climate cooled

exotic seismic phases recorded near mammoth lakes and their use in the delineation of shallow crustal magma anomalies observations of several hundredexotic seismic phases herein defined recorded in and near long valley caldera california have been cataloged i discuss here four classes of such seismograms 1 seismograms with missing s waves 2 seismograms with an unusual pre s phase seen at the single station slk northwest of the caldera 3 seismograms with a strong pre s phase as seen at a number of stations south of the caldera and 4 a very large very slow 2 km sec post s phase seen at the single station benton for each of these phenomena it is not yet possible to pin down an unambiguous and unique theoretical explanation however for each i have presented an explanation summarizing current thinking which involves nonplanar reflections refractions within shallow crustal anomalous zones which can reasonably be supposed to be magma bodies if these explanations are even partially pertinent then the investigation of exotic phases near complex regions like mammoth lakes and other volcanic areas is potentially a way to bring precise resolving power on the nature and geometry of local crustal anomalies

the geophysics of a restless caldera long valley california at 9 33 pdt on the morning of may 25 1980 a strong earthquake of local magnitude ml 6 1 heralded the onset of an earthquake sequence that focused worldwide attention on the major geologic and tectonic fea ture nearest its epicenter the long valley caldera of eastern california this sequence included two additional ml 6 events on may 25 and a fourth ml 6 event on may 27 accompanied by more than 300 ml 3 aftershocks over the next several weeks all of which were located either within or to the south of the caldera uhrhammer ferguson 1980 cramer toppozada 1980 these were not the first major events to occur regionally within the last decade the october 4 1978 bishop event m l 5 7 located some 20 km to the southeast of long valley initiated a sequence of swarm like activity that migrated generally toward the caldera over the next two years ryall ryall 1980 van wormer ryall 1980 in fact van wormer ryall 1980 in a manuscript written prior to the may 1980 earthquakes identified this sequence of events as a

a description of subtidal pressure field observations on the northern california continental shelf during the coastal ocean dynamics experiment during the coastal ocean dynamics experiment code along the northern california continental shelf in the spring and summer of 1981 and 1982 the first comprehensive effort to obtain all of the observations necessary to infer pressure fluctuations throughout the water column was made this is a description of the subtidal fluctuations in measured bottom pressure internal pressures inferred from moored conductivity and temperature observations and the water column total pressure anomalies computed from a combination of the two components the pressure field during code 2 april july 1982 is found to be more energetic than that in code 1 april july 1981 with more than 70 total pressure variance concentrated at frequencies of less than 15 days 1 the spatial structure of the pressure fluctuation field is characterized by coastal intensification and a tendency for poleward phase propagation like the pressures most of the code across shelf pressure difference variance is found at the lower frequencies with more than 60 of the total across shelf pressure difference variance at frequencies of less than 15 days 1 the code across shelf pressure differences are found to be in geostrophic balance with both alongshelf currents and the total alongshelf transport the alongshelf pressure difference variance is generally found to be concentrated at the lower frequencies much like that of the across shelf pressure differences most of the pressure and pressure difference variance is found to be highly coherent with wind stress the 20 day band pressure variability is apparently related to the response of the pressure field during so called relaxation events the barotropic component of the alongshelf geostrophic transport i e across shelf pressure difference has been found to be almost perfectly coherent with regional wind stress y and to propagate poleward within the code region at the same rate as y and the alongshelf pressure gradient is very important in accelerating the alongshelf flow the 5 day band pressure variability in the code region appears to result from local wind stress fluctuations the alongshelf pressure gradient was found to be of secondary importance relative to the wind in accelerating the alongshelf flow

late miocene turnover of molluscan faunas new zealand taxonomic and ecological reassessment of diversity changes at multiple spatial and temporal scales abstract previous estimates of molluscan biodiversity during the neogene in new zealand have revealed a pattern of significant diversity decline during the latest miocene this study uses an occurrence based dataset derived from published literature to examine this pattern in further detail with both traditional synoptic measures and subsequent sampling standardization synoptic analyses of regional scale data reveal diversity trajectories similar to those previously established and rarefaction techniques demonstrate that the inferred pattern of late miocene diversity decline and early pliocene rebound is only somewhat biased by variations in sampling intensity the pattern is also affected by temporal variations in the preservation of shelf paleoenvironments with representation of highly diverse shallow water facies varying considerably between biostratigraphic stages the sampling and corresponding synoptic genus richness of biogeographic areas within the new zealand region is also uneven within a single sedimentary basin sampled at high temporal resolution wanganui basin new data suggest that late miocene faunas were as diverse as those of the early pliocene contrasting with the pattern of diversity decrease and subsequent increase observed at the regional spatial scale in prior studies however an ecological analysis of the new data demonstrates that turnover and restructuring of benthic communities did take place at the end of the late miocene these findings suggest that spatial scale and temporal resolution are important considerations in determining the magnitude of diversity and ecological change observed in paleontologic studies contemporaneous biodiversity may not be similarly expressed at varying spatial or temporal scales in the fossil record rather regional patterns of diversity change are governed by a complex interplay of not only large scale environmental factors e g temperature control but also independent basin scale processes e g basin subsidence and local sampling intensity

fine scale variability at 140 w in the equatorial pacific in november december 1984 we carried out an intensive 12 day upper ocean sampling program on the equator at 140 w as part of the tropic heat experiment from our observations we constructed hourly averaged profiles of temperature salinity t turbulent kinetic energy dissipation rate and horizontal velocity these data were used to examine the correspondence between hydrographic and velocity fields and to compare the measured turbulent dissipations with the calculated richardson numbers we found that the core of the equatorial undercurrent tracked a density surface t 25 25 on times as short as 1 hour the variability in both hydrographic and velocity fields was greatest at the semidiurnal frequency the supertidal energy was not significantly different from the garrett munk mid latitude level once latitudinal scaling was removed from the garrett munk model parameters horizontal velocity spectra were found to be contaminated by displacement of the background shear turbulent dissipation was dominated by a diurnal cycle with high values of dissipation occurring at night above the undercurrent core shear and buoyancy frequency calculated over 12 m vertical scales were observed to track each other above the core and were dominated by a diurnal period above 40 m and by a semidiurnal period below 40 m when shear and buoyancy frequency were combined to form a richardson number neither diurnal nor semidiurnal cycles were present above the undercurrent core the richardson numbers were uniformly small 0 3 to 0 6

seasonal differences in the current and temperature variability over the northern california shelf during the coastal ocean dynamics experiment a long term moored array was maintained over the northern california continental shelf from april 1981 to april 1983 as part of the coastal ocean dynamics experiment to determine the seasonal differences in the current and water temperature characteristics the array consisted of two midshelf moorings and one upper slope mooring from april 1981 through july 1982 and one midshelf mooring from august 1982 to april 1983 the two summers were characterized by southeastward mean wind stresses upwelling favorable cold water isotherms sloping upward toward the coast and a sheared equatorward mean shelf current the intervening fall and winter were characterized by a weak mean wind stress relatively warm shelf water level isotherms and a more barotropic poleward mean shelf current in contrast to the differences in the characteristics of the means many of the characteristics of the current and temperature variability are the same for the summer and winter the vertical structure of the largest current empirical orthogonal functions eofs for each of the shelf moorings which account for more than 75 of the subtidal variance do not vary with season the current is vertically sheared oriented 15 20 clockwise relative to local isobaths near the surface and along isobaths near the bottom currents at the two shelf moorings alongshore separation 29 37 km are correlated with each other and with the local wind stress and these relationships do not exhibit a seasonal variation denser arrays of wind and current sensors during the two summers indicated that there were strong persistent variations in the wind field over relatively small scales tens of kilometers with corresponding variations in the shelf current field during the summer of 1981 but not during the summer of 1982 over the slope the largest eofs account for 56 72 of the current variance and have a vertical structure which is relatively uniform with depth during the summer fall and winter of 1981 but is strongly sheared in the upper 100 m during the summer of 1982 current observations over the slope are not correlated with either the shelf currents or the local wind stress during any season in contrast the temperature variability as described by eofs does exhibit a seasonal variation in vertical structure with the variability concentrated in the upper 20 30 m in summer and more uniform with depth in winter the near surface temperature variability over the slope is correlated with the shelf temperature variability estimates of the cross shelf heat flux due to the wind driven ekman transport accounts for a large part of the shelf temperature variability observations from the midshelf mooring maintained through the fall and winter of 1982 1983 showed evidence of the 1982 1983 el nino with persistent onshore and poleward currents and water temperatures typically above 12 c

three dimensional circulation in the nw africa coastal transition zone abstract high resolution data collected southeast of the canary islands during late winter 2006 are analyzed to describe the hydrography and three dimensional circulation in the coastal transition zone off nw africa the data are optimally interpolated over a regular grid the geostrophic velocity field is calculated and the q vector formulation of the omega equation is used to compute the quasi geostrophic qg mesoscale vertical velocity the coastal transition zone is divided into upwelling frontal and offshore regions with distinct physical and dynamic characteristics the upwelling region is characterized by cold and weakly stratified waters flowing towards the equator with a poleward undercurrent of approximately 0 05 m s 1 over the continental slope the frontal region exhibits a southwestward baroclinic jet associated with cross shore raising isopycnals the jet transport is close to 1 sv with maximum velocities of 0 18 m s 1 at surface decreasing to 0 05 m s 1 at 300 db vertical sections across the frontal region show the presence of deep eddies probably generated by the topographic blocking of the islands to the southward current as well as much shallower eddies that likely have arisen as instabilities of the baroclinic upwelling jet the qg mesoscale vertical velocity field is patchy estimated to range from 18 to 12 m day 1 with the largest absolute values corresponding to an anticyclonic eddy located south of fuerteventura island these values are significantly larger than estimates for other vertical velocities diapycnal vertical velocities associated with mixing in the frontal region a few meters per day and wind induced vertical velocities non linear ekman pumping arising from the interaction between the wind stress and the background vorticity maximum values of a few meters per day linear ekman pumping due to the divergence of ekman transport a fraction of a meter per day or the coastal constraint in the upwelling region about 0 7 m day 1 however the patchiness in both the qg mesoscale vertical velocity and the non linear ekman pumping velocity cause their integrated vertical transports to be one order of magnitude smaller than either coastal ekman transport 0 08 sv integrated linear ekman pumping 0 05 sv or diapycnal transfer about 0 1 0 2 sv the pattern of the near surface fluorescence field is a good indicator of these different contributions with large homogeneous values in the coastal upwelling region and a patchy structure associated with the offshore mesoscale structures

diapycnal mixing in western boundary currents in a previous study pelegri and csanady 1991 we found upward entrainment and two way exchange between the upper thermocline and surface layers of the gulf stream here we use isopycnic coordinates to analyze the mechanism of diapycnal shear induced mixing in western boundary currents a hydrographic section across the gulf stream off the mid atlantic bight is used for a case study it shows that the upper thermocline layers of the gulf stream are characterized by relatively small 16 m averaged gradient richardson numbers ri analysis of the jacobian j z p with z the depth and p the potential density total vorticity and potential vorticity fields shows that this region has low jacobian values associated with high values of potential vorticity as required theoretically for the case of dominant diapycnal mixing the density tendency wp dp dt is calculated from the vertical gradient of the reynolds density flux the latter parameterized as density eddy diffusivity divided by the jacobian we use munk and anderson s 1948 expression for the eddy diffusivity coefficient modified to conform to data of ueda et al 1981 maintaining a ri 3 2 dependence for large ri from this we obtain an explicit expression for wp in terms of the ri and j distributions the distributions of wp its diapycnal gradient wp p and the diapycnal velocity wd jwp are then calculated regions of high diapycnal convergence large negative wp p values coincide with the location of anomalously low jacobians in agreement with the idea that diapycnal mixing is the consequence of anomalies produced during frontogenesis in some phase of the meanders we suggest that this process taking place intermittently in space and time is responsible for two way exchange in western boundary currents

on the temporal memory of coastal upwelling off nw africa we use a combination of satellite in situ and numerical data to provide a comprehensive view of the seasonal coastal upwelling cycle off nw africa in terms of both wind forcing and sea surface temperature sst response wind forcing is expressed in terms of both instantaneous local and time integrated nonlocal indices and the ocean response is expressed as the sst difference between coastal and offshore waters the classical local index the cross shore ekman transport reproduces reasonably well the time latitude distribution of sst differences but with significant time lags at latitudes higher than cape blanc two nonlocal indices are examined one of them a cumulative index calculated as the backward averaged ekman transport that provides the highest correlation with sst differences reproduces well the timing of the sst differences at all latitudes except near cape blanc the corresponding time lags are close to zero south of cape blanc and range between 2 and 4 months at latitudes between cape blanc and the southern gulf of cadiz the results are interpreted based on calculations of spatial and temporal auto and cross correlations for wind forcing and sst differences at temporal scales of 2 3 weeks the alongshore advection of alongshore momentum compensates for interfacial friction allowing the upwelling jet and associated frontal system to remain active we conclude that the coastal jet plays a key role in maintaining the structure of coastal upwelling even at times of relaxed winds by introducing a seasonal memory to the system in accordance with the atmospheric forcing annual cycle

molluscan generic diversity of new zealand neogene stages extinction and biostratigraphic events abstract the molluscan generic diversity histogram of new zealand neogene stages almost parallels the trend of published new zealand paleotemperature curves the major exception is very high diversity during the relatively cool pliocene and pleistocene stages attributed to the good preservation at this time of near shore mollusc rich facies diversity was lowest during kapitean late miocene time and probably particularly during late kapitean messinian time 22 9 of molluscan genera became extinct at the end of the preceding tongaporutuan stage three major events can be recognised in the neogene molluscan fauna 1 a thermal maximum during late early and early middle miocene coeval around much of the pacific 2 the terminal miocene event when the most marked neogene extinction occurred and 3 the arrival of a cold water subantarctic fauna in central north island 2 4 m y ago coeval with the onset of major northern hemisphere glaciation

latest miocene benthic δ 18 o changes global ice volume sea level and the messinian salinity crisis oxygen isotope evidence indicates high but variable 18o values in benthic foraminiferal calcite during the latest miocene and earliest pliocene these high values may represent increases in global ice volume and associated sea level fall the 18o record resembles glacial interglacial cycles but with only one third the amplitude of the late pleistocene signal this variability may reflect instability in the antarctic ice sheet and palaeomagnetic correlation points to an isotopic event coinciding with the isolation and desiccation of the mediterranean basin during the latest messinian

constraints on the upper crustal structure of the long valley mono craters volcanic complex eastern california from seismic refraction measurements during the summers of 1982 and 1983 field work was completed on 10 new seismic refraction profiles in the long valley mono craters region located within the technically active zone between the eastern sierra nevada and the basin and range province the four profiles presented here sample the upper 7 10 km of the crust within the western half of long valley cladera the mono craters ring fracture system and the normal crust north and northeast of long valley the entire area shares a common crystalline basement consisting primarily of mesozoic granitic rocks at a depth of 2 km beneath the topographic surface the p wave velocity is uniformly 5 6 km s beneath which the velocity increases with a gradient of about 0 1 s 1 clear secondary arrivals observed on a profile crossing the west part of the caldera support evidence from 1972 seismic refraction profiles for a reflecting boundary at a depth of 7 8 km beneath the west margin of the resurgent dome which may represent the top of a magma chamber structural details resolved in the upper 2 km of the crust lead to the following conclusions 1 p wave velocities in the crystalline basement at depths shallower than 2 km vary from 3 6 to 5 0 km s this variation reflects differences in the degree of fracturing of the upper portion of the basement 2 an apparently homogeneous basement in the upper 7 10 km beneath the mono craters ring fracture system indicates that any extensive magma chamber must be at least 10 km deep there 3 the downdropped crystalline basement beneath the western half of long valley caldera dips genty 5 10 to the northeast apparent offsets along steeply dipping caldera bounding faults are 1 0 1 7 km along the northern western and southern sides of the caldera with largest offsets in the north 4 rocks forming the caldera fill fall into essentially three p wave velocity groups from the surface downward these velocity groups are 100 400 of 1 2 1 8 km s material corresponding to unconsolidated fluvial or lacustrine deposits or highly fractured rhyolite flows 200 400 m of 2 8 3 1 km s material corresponding to sparsely jointed postcaldera rhyolite rhyodacite and basalt flows and approximately 1000 m of 3 9 4 4 km s material corresponding to deposits of bishop tuff

source parameters of the 1980 mammoth lakes california earthquake sequence from the more than 1500 mammoth lakes earthquakes recorded on three component digital seismographs spudich et al 1981 150 were used in an analysis of the locations mechanism and source parameters a composite fault plane solution of nine earthquakes 3 9 m 5 1 defines a right lateral strike slip mechanism on a steeply dipping nearly east west plane striking s75 e or left lateral strike slip on a nearly north south plane striking n10 e vertical cross sections of well located aftershocks indicate possibly three east west planes that coincide with the locations of the four largest earthquakes with ml 6 0 using the spectral analysis of s waves brune 1970 source parameters for 67 earthquakes were determined forty eight had magnitudes greater than or equal to 3 0 seismic moments ranged from 9 20 1018 dyn cm to 2 33 1024 dyn cm earthquakes with seismic moment greater than about 1 0 1021 dyn cm had nearly constant stress drops 50 bars earthquakes with seismic moment less than about 1 0 1021 dyn cm had stress drops that apparently decrease as seismic moment decreases

tide induced mixing in the amazon frontal zone the freshwater discharge from the amazon river produces a bottom salinity front on the amazon shelf that extends many hundreds of kilometers along the shelf between the 10 and 20 m isobaths strong cross shelf tidal currents cause advective excursions of the front of more than 20 km and supply the major source of kinetic energy for mixing on the shelf this mixing is manifested in spring neap variations in the frontal structure and position with weaker stratification and seaward migration of the front during periods of strong tidal currents and stronger stratification and landward migration during neap tides mixing appears to be driven by shear instability based on local estimates of gradient richardson number and bulk estimates of the water column stability maximum mixing occurs during ebb when vertical shear is greatest suspended sediment reaches such high concentrations in the frontal zone that it makes a significant contribution to the stratification thus increasing the stability of the flow and reducing the effectiveness of tide induced mixing

three dimensional gravity modeling of the geologic structure of long valley caldera a 48 mgal gravity low coincides with long valley caldera and is mainly attributed to low density caldera fill gravity measurements by unocal geothermal have been integrated with u s geological survey data vastly improving gravity station coverage throughout the caldera a strong regional gravity trend is mainly attributed to isostasy a best fitting based on regional control of basement densities airy heiskanen isostatic model was used for the regional correction a three dimensional multiple unit gravity modeling program with iterative capabilities was developed to model the residual gravity the density structure of long valley caldera and vicinity was modeled with 22 discrete density units most of which were based on geologic units information from drill hole lithologies surface geology and structural geology interpretations constrain the model some important points revealed by the three dimensional gravity modeling are that 1 the volume of ejected magma associated with the bishop tuff eruption is greater than previously thought 2 the caldera structure is strongly influenced by precaldera topography and the extensions of major active faults 3 the main west ring fracture is coincident with the inyo domes mono craters fracture system 4 a relatively low density region probably underlies the caldera and 5 a silicic magma chamber may underlie devils postpile

crustal refraction profile of the long valley caldera california from the january 1983 mammoth lakes earthquake swarm seismic refraction profiles recorded north of mammoth lakes california using earthquake sources from the january 1983 swarm complement earlier explosion refraction profiles and provide velocity information from deeper in the crust in the area of the long valley caldera eight earthquakes from a depth range of 4 9 to 8 0 km confirm the observation of basement rocks with seismic velocities ranging from 5 8 to 6 4 km sec extending at least to depths of 20 km the data provide further evidence for the existence of a partial melt zone beneath long valley caldera and constrain its geometry this evidence is in the form of pronounced secondary arrivals which we interpret as waves that have propagated through a volume with low q the magma chamber and reflected from the lower boundary of the southern edge of this volume at depths of 18 to 20 km

relaxation from upwelling in the coastal ocean dynamics experiment a relaxation of the upwelling system on the northern california shelf occurs when upwelling favorable winds decay or reverse observations from the coastal ocean dynamics experiment are used to investigate this process with emphasis on the near surface temperature evolution models of relaxation warming are tested for the surface layer 0 30 m over midshelf with the result that the surface heat flux and poleward alongshelf advection can account for the observed temperature behavior onshore advection of the upwelled isopycnal field is a relatively unimportant contribution the warming patterns that are observed and which provide the gradients for the advective process have wedgelike shapes warmest inshore and in the south of the experimental area these patterns appear to be related to a topographic influence of point reyes possibly through the generation of gradients in the wind field remote advection of warm water from as far south as san francisco occasionally occurs as well the nature of the relaxation mechanism has general implications a new warm saline nutrient rich water mass may be formed in the surface layer since the warming processes are not the reverse of the cooling an important asymmetry is present it causes time variable upwelling to generate conditions very different from steady upwelling a new upwelling front is created during each event with upwelled water seaward of it and reversed alongshelf flow contributes to the warming and exchange mechanisms the system cannot be described or understood without the irreversible processes during upwelling and relaxation or without a mixed layer

exposed coasts vs sheltered bays contrast between new zealand and japan in the molluscan record of temperature change in plio pleistocene cyclothems abstract cyclothems in the omma formation on the japan sea coast of central honshu each contains two ecostratigraphic datums the appearance and disappearance datums of warm water molluscs cold water molluscs occur both below in early tst and above in late hst and possibly rst warm water ones which occur in late tst and early hst in contrast no new zealand cyclothems in the main plio pleistocene basins contain both cold and warm water faunas in one cycle cyclothems in the petane group central hawke s bay and in the castlecliff section wanganui basin contain entirely eurythermal and warm water molluscs throughout cyclothems in south wairarapa have entirely eurythermal and cold water molluscs throughout the subantarctic zygochlamys delicatula fauna even in hsts of some cycles this contrast demonstrates the importance of exposure of the deposition site to strong coastal currents for the maximum faunal expression of temperature change the omma formation was deposited in an open site on the japan sea coast where currents transported larvae of a wide variety of molluscs northwards and southwards in response to temperature oscillations the main new zealand cyclothemic successions were deposited in large embayments sheltered from the influence of coastal currents the maximum faunal expression within one cyclothem of plio pleistocene temperature change can be expected in only those few deposition sites that satisfy the optimum requirements deposition of reasonably complete sequences at least tsts hsts and rsts preserved in an exposed coastal site influenced by strong currents from both the north and south on the inner shelf in the temperate regions between ca 30 and 60 north and south near the north south oriented coast of a large continent

scattering from a fault interface in the coso geothermal field large amplitude secondary arrivals are modeled as scattering anomalies near the coso california geothermal field polarization and ray tracing methods determine the orientation and location of the scattering body two models are proposed for the scatterer 1 a point scatterer located anywhere in a one dimensional 1 d layered velocity model and 2 a dipping interface between two homogeneous half spaces each model is derived by non linear grid search inversion for the optimal solution which best predicts observed travel times in each case the models predict a nearly vertical scatterer southwest of stations s4 and y4 each southeast of sugarloaf mountain a large rhyolite dome the interface model includes five unknown parameters describing the location and orientation of the interface in addition to the s wave velocity of the half space the s wave velocity 3 25 km s agrees with independently derived 1 d models in this area the large amplitude vertical impedance contrast interface coincides with steep gradients of heat flow measured near the surface and with structural boundaries observed in surface geology the reflector is most probably the sharp boundary between the northern part of the field where there is significant fluid flow and the southern part where hydrothermal fluids are absent the interface coincides with geological boundaries and faults recently observed in this region most likely representing the hydrothermal barrier which channels hot fluids northward

globorotalia planktic foraminifera at the miocene pliocene boundary in new zealand abstract mid latitude assemblages of globorotalia in the late miocene and early pliocene of new zealand are dominated by the g miozea complex and its derivative taxa most of which appear rather suddenly in the basal pliocene the most uninterrupted sequence present in dsdp site 284 on the challenger plateau is closely matched in the north island mangapoike river section which is correlated by biostratigraphy geomagnetic polarity and a fission track date with blind river in the south island k ar dates of 5 2 m y and 5 3 m y for basalt associated with basal pliocene fossiliferous deposits in the chatham islands support the location of the miocene pliocene boundary at or close to the gilbert chron 5 boundary the isotopic record indicates that there were one or more periods of oceanic instability accompanied by cooling and polar ice accumulation in the late miocene immediately before the marked phase of evolutionary radiation of globorotalia in the early pliocene

upper ocean shear and density variability at the equator during tropic heat abstract a four and one half day time series of upper ocean shear and density observations was collected in the tropical pacific ocean in november 1984 the measurements were made on the equator at 139 50 w during a period when the equatorial undercurrent was well developed and 20 30 day period velocity fluctuations were prominent shear observations were collected with a ship mounted acoustic doppler velocity profiler density data were obtained from a loosely tethered microstructure instrument the mean shear profile during the series strongly reflected the structure of the undercurrent however the meridional component contributed significantly to the magnitude of the total shear the mean richardson number was large near the undercurrent core but fell to values less than 0 5 25 m above and below the core and was below 0 25 in the upper 40 m for most of the sample period buoyancy frequency varied on a diurnal time scale in the upper 50 m owing to the solar heating cycle but a compensating diurnal

an s to p converted phase recorded near long valley mono craters region california we examine and model the arrival time of a large secondary seismic arrival recorded in the long valley mono craters region of east central california zucca et al 1987 and peppin 1987 both previously reported on different features of this same arrival using both arrays of sources and receivers we demonstrate that the arrival is an s to p converted phase as first suggested by lewis and peppin 1988 backprojection of the observed travel times allows us to constrain the location of the converting material to a southeast dipping zone between 7 and 16 km depth and 5 km on either side of the topographic margin of the caldera the analysis demonstrates the power of source and receiver array combinations when analyzing seismic arrivals in complicated environments

regional biotic turnover dynamics in the plio pleistocene molluscan fauna of the wanganui basin new zealand sampling gaps and variable preservation greatly complicate attempts to interpret patterns of biotic change from the fossil record this study investigates whether observed patterns of first and last occurrences of mollusc species can be explained by poor or uneven sampling of a diverse 800 species plio pleistocene marine fauna from the wanganui basin north island new zealand estimates of sampling completeness are high ranging from 78 to 98 mean 88 despite several sampling gaps in the succession stratigraphic permutation tests suggest that most of the apparent peaks in the local first and last appearances of species are caused by uneven sampling however peaks of last occurrences of species during the late pliocene 2 5 2 0 ma and of first occurrences in the middle pleistocene 0 75 0 5 ma cannot be classified as artefacts and appear to represent real biological events a wide early pleistocene gap in the stratigraphic section in the basin prevents the precise estimation of the magnitude duration or timing of these biotic transitions mechanisms for the biotic change remain elusive better palaeoenvironmental control and detailed ecological study of selected molluscan clades are required to test alternative causal hypotheses however similar turnover episodes have been documented from the temperate and tropical western atlantic suggesting a global biotic perturbation on shallow shelves in response to plio pleistocene global environmental change

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

hydrographic observations along the code central line off northern california 1981 abstract repeated ctd observations were made along a single section spanning the continental shelf off northern california at 38 40 n during 1981 the section consisted of nine standard stations between 1 and 46 km from the shore in water depths between 40 and 1700 m the shelf break was at a depth of 150 m about 25 km from shore the section was occupied 17 times between 13 april and 3 august and twice in december and a similar section had been occupied in february during the april august period winds were strong and persistently favorable for upwelling isotherms isohalines and isopycnals in the upper 200 in sloped persistently upward toward the coast and coldest saltiest and densest surface waters almost always occurred at the most inshore nation variations in wind strength caused changes in the surface layer over the entire shelf stronger winds were associated with lower temperatures and higher salinities subsurface temperatures increased gradually between april and august we were unable to

observed interaction between low and high frequency motions off the coasts of peru and california abstract datasets taken near the coasts of peru and california have been analyzed to explore the evidence of a correlation between the high frequency period 4 day motions a large part of the high frequency current is consistent with internal wave dynamics they have a near 180 phase change across the water column there is also evidence of a clockwise veering with depth presumably due to frictional effects no correlation of the vertical reynolds stress vw and vertical shear vz is found the horizontal stress uv is found to be negatively correlated with the horizontal shear vx only when averaged over time and space scales larger than those of the mean velocity field the implied eddy viscosity is of order h 105 cm2 5 1 it is suggested that the relaxation time for the wave field to lose asymmetry is larger than the time for the wave to propagate across a typical scale of the mean shear field due to this the fluctuating field may locally behave like a negati

evidence of a critical richardson number in moored measurements during the upwelling season off northern california evidence is found for a cutoff gradient richardson number of ri 0 25 in the moored measurements of temperature and current obtained during the second coastal ocean dynamics experiment code 2 conducted off northern california during the upwelling season of march august 1982 the cutoff at ri 0 25 was noticed even when the instruments were separated by depth intervals as large as 40 m or when the time series having a sampling interval of 7 5 min were averaged over an hour during several strong wind events which tended to increase the mean shear ri 0 25 occurred in the main thermocline beneath the surface mixed layer over the shelf on the other hand several instances were found when a low ri was not directly related to any wind event suggesting that superposition of various waves can locally generate unstable conditions the deeper water over the shelf and slope was generally stable with ri 0 25 these results suggest that in coastal areas with strong currents the intensification of mean vertical shear seems to be very important in bringing about kelvin helmholtz type instabilities as compared with the open ocean without strong currents where superposition of internal waves is believed to be primarily responsible for causing the instabilities because the density structure almost everywhere in the ocean is in the form of steps and because the overall richardson number across vertical scales as large as 20 m are frequently near critical it follows that appreciably thick regions in the ocean frequently remain on the brink of kelvin helmholtz instability even though the actual mixing may take place within thin interfaces between relatively homogeneous layers a small increase of the overall shear then greatly increases the frequency of billow events and vertical mixing and a small decrease of the overall shear greatly decreases such activity it is suggested that in numerical circulation models the richardson number be constantly checked and vertical mixing be used to maintain the richardson number above a minimum value of 0 25

mesoscale surveys over the shelf and slope in the upwelling region near point arena california repeated mesoscale surveys of a 40 km wide 100 km long coastal region near point arena california were conducted during the upwelling season april august in 1981 and 1982 each survey included conventional conductivity temperature depth casts at standard locations over the continental shelf and slope between 38 n and 39 10 n and continuous operation of a doppler acoustic log to obtain velocity profiles in the 20 to 150 m depth range synoptic surveys covered the entire grid in 2 3 days winds were strongly favorable for upwelling during the three 1981 surveys and were weak or variable during the three 1982 surveys surface temperature and salinity fields reflect the influence of both the seasonal winds and day to day variations in the wind persistently low surface salinities offshore reflect the general southward advection of subarctic waters and sporadic low salinities over the inner shelf reflect north ward advection of local runoff through an intermittent narrow countercurrent along the coast circulation patterns during all but one of the surveys were very complex and included meandering equatorward flow cyclonic and anticyclonic eddies and inshore countercurrents the simple two dimensional equatorward baroclinic coastal jet usually associated with coastal upwelling was observed during only one of our surveys overall average fields are relatively simple they show broad equatorward surface flow a very weak inshore countercurrent and a definite poleward undercurrent at the shelf break average temperature salinity and density fields are generally congruent with the average flow pattern average isotherms and isohalines are not strictly parallel to the coastline south of the coastline bend at point arena they diverge gradually from the coast comparison of average sections calculated from 10 matched pairs of central and arena lines separated by 50 km shows there are systematic differences between them warmer fresher waters lie nearer shore and in shallower water off point arena than on the central line this suggests that the surface waters flowing past point arena have sufficient southward momentum to cross isobaths comparison of average velocity sections on these two lines shows some differences in structure since the variability is large these may not be significant comparison of the measured and geostrophic average shears suggests there is a significant ageostrophic component in the upper layers above 40 m it may be the signature of an average wind driven ekman spiral

basement structure and implications for hydrothermal circulation patterns in the western moat of long valley caldera california detailed surface mapping subsurface drill hole data and geophysical modeling are the basis of a structural and hydrothermal model for the western part of long valley caldera six fault zones are recognized in the western caldera with dominant orientations of north northwest and northeast sub parallel to regional fault trends in the surrounding sierran basement the internal structural geometry of the cores of 12 exogenous domes inside and outside the caldera suggests that the domes erupted at the intersections of these principal fault trends rather than along the axis of a single dike gravity modeling and subsurface data from deep geothermal wells indicate that the floor of the caldera is segmented into a number of discrete fault blocks with varying offsets one of the northeast trending fault zones designated discovery fault in this paper appears to be part of the original sierran embayment that existed before caldera collapse recent hydrothermal alteration occurs along discovery fault strands and composite vertical offset of intracaldera volcanic units across the entire fault zone may be as much as 400 m field relationships geophysical interpretations and interpretaions of drill hole data suggest that this fault is a fundamental flaw in the western caldera the preexisting tectonic framework of the basement rocks controlled the configuration of the western caldera floor and through it the location of postcollapse eruptive centers these deep basement structures may also provide the high fracture density which controls circulation in the present geothermal system of long valley