the magnetostratigraphy of leg 73 sediments abstract the main objectiveof dsdp leg 73 was to obtain high quality records of major paleooceanographic events in the south atlantic this was achieved by coringsix sites on the african plate the sediments thus recovered span the cenozoic and five of the six sites proved ideally suited for magnetostratigraphic analysis the results presented in this paper and elsewhere in this volume constitute the first opportunity to extend the direct correlation of the magnetostratigraphic and biostratigraphic time scales into the paleogene in deep sea cores the magnetostratigraphic analyses from dsdp leg 73 sediments are presented in this paper the correlation of the magnetostratigraphy to the magnetic polarity time scale provides tight age depth control for the five sites analyzed allowing the accurate calculation of sediment accumulation rates the data presented here represent a remarkable record of the fine scale polarity history of the earth s magnetic field these data place constraints on the interpretation of small scale marine magnetic anomalies which are modelled equally effectively by field intensity fluctuations as polarity reversals at least some of the tiny wiggles correspond to very short polarity units in the magnetostratigraphic record by assuming an axial geocentric dipole the inclination of the time averaged magnetic field recorded in the sediments can be used to calculate the paleolatitude at which the sediments were deposited combining the age and average inclination information available from the magnetostratigraphy we present paleolatitudes versus time for the leg 73 drill sites

clay organic association as a control on hydrocarbon generation in shale abstract programmed pyrolysis experiments investigating the influence of the mineral matrix on hydrocarbon generation from organic compounds have shown inconclusive results in past studies this study tests the hypothesis that the inhibitory vs catalytic influence of clay minerals is dependent on the physical association of the mineral matrix with organic compounds by comparing natural samples from two shale formations with different mineral organic associations samples from the miocene monterey formation have a greater area of surface contact between organic matter and mineral surfaces when compared to the more particulate texture and discrete nature of the organic matter in the samples from the permian stuart range formation comparison of kerogen extracts to the whole rock containing mineral and organic matter samples during programmed pyrolysis shows higher hydrocarbon generation from isolated kerogen compared to the whole rock sample it was extracted from in both the monterey and the stuart range formation samples the difference between extracted kerogen and whole rock samples is greater and more variable 56 210 mghc gtoc in the stuart range than the monterey formation 85 142 mghc gtoc implying greater hydrocarbon retention by the free mineral surfaces the temperature of maximum hydrocarbon generation rock eval t max is greater in whole rock than kerogen isolates 20 c mean in the monterey formation samples but shows negligible difference 2 c mean in the samples from the stuart range formation standard kerogen typing using rock eval pyrolysis data places the same kerogen as type ii to type iii on a modified van krevelen diagram depending whether it is isolated or pyrolysed with its mineral host this study identifies that not only the bulk mineralogy and kerogen type but also the degree of surface contact of the phases influence hydrocarbon generation

the impact of hydrodynamics authigenesis and basin morphology on sediment accumulation in an upwelling environment the miocene monterey formation at shell beach and mussel rock pismo and santa maria basins central california u s a abstract in the sections at shell beach pismo basin and mussel rock santa maria basin both along the central california coast the miocene monterey formation is composed of laminated biosiliceous organic rich and phosphate rich sediments which are intercalated with carbonates and volcanogenic deposits the presence of small and large scale scours conglomerates gravity flow deposits slumps and condensed intervals reveals the importance of sediment reworking which is related to the presence of bottom currents the general morphology of the basins and recurrent high energy events of likely seismic origin the lithologies reflect strong upwelling enhanced primary productivity and the presence of an oxygen minimum zone which is indicated by ubiquitous lamination a general absence of bioturbation with the rare exception of traces related to the gravity flow displacement of trace makers high pyrite mo and u concentrations and molar ratios of total organic carbon and organic phosphorus toc p org of up to 2000 oxygen depletion was particularly severe during the early langhian and the late serravallian and early tortonian and favored the preservation of organic matter episodes of deposition of organic rich sediment were followed by longer phases of subdued sediment accumulation and early diagenetic phosphogenesis which resulted in the formation of a low porosity less permeable lid in the near surface sediments that assisted in preserving organic matter phosphogenesis occurred throughout the time interval considered approximately 17 5 6 5 ma and phosphate rich sediments formed especially during periods of sedimentary condensation in the langhian and earliest serravallian and the latest tortonian and early messinian a comparison of temporal trends in the type and quantity of deposited sediments between the two sections at shell beach and mussel rock and three sections of the santa barbara basin el capitan state beach naples beach and haskell beach confirms that towards the top of the monterey formation sediments become enriched in biosilica in all three basins the transition into this lithology occurred diachronously during the serravallian in the pismo and santa maria basins and tortonian in the santa barbara basin and was probably related to a diachronous shift to more intense upwelling in all three basins a phase of important condensation and phosphogenesis terminated monterey type sedimentation during the latest tortonian and early messinian in both the santa maria and santa barbara basins the uniform expression of this phase is interpreted as the result of improved connections between the two basins

north pacific late miocene correlations using microfossils stable isotopes percent caco3 and magnetostratigraphy abstract a multidisciplinary approach to stratigraphy based on magnetostratigraphy stable isotopes percent caco 3 and microfossils provides a framework for paleoclimatic and paleoceanographic reconstruction of the equatorial and north pacific a high resolution biochronologic time scale has been achieved through integration of diatom radiolaria coccolith and planktic foraminifer datum levels with direct or indirect correlations to the paleomagnetic time scale over 70 datum levels have been identified between 12 5 and 5 ma from low and middle latitudes resulting in an unprecedented time control this high resolution biostratigraphic control combined with stable isotopic and percent caco 3 analyses permits identification of regional as well as global paleoceanographic events

cycles steps and co2 paleoceanography in the united states from 1983 1986 the field of paleoceanography experienced continued growth during the last three years the first international conference on paleoceanography was held in zurich switzerland in july 1983 and a new journal devoted to the topic paleoceanography american geophysical union washington d c began publication in spring 1986 edited by dr james kennett of the university of rhode island nine legs of the r v glomar challenger concentrated upon paleoceanographic topics legs 71 75 in the south atlantic leg 81 in the north atlantic leg 85 in the equatorial pacific leg 86 in the northwest pacific and leg 90 in the southwest pacific several special symposia and conferences resulted in volumes of collected papers dealing with topics such as climate variability hansen and takahashi 1984 the global carbon cycle sundquist and broecker 1985 catastrophes and earth history berggren and van couvering 1984 orbital insolation and periodicity berger et al 1984 and coastal upwelling suess and thiede 1983 some very useful books have been published which summarize existing information on radiolaria anderson 1983 neogene planktonic foraminifera kennett and srinivasan 1983 calcareous nannofossils haq 1983 1984 and biostratigraphy bolli et al 1983

measurement of tidal and residual currents in the strait of hormuz abstract quantifying the current in the strait of hormuz sh is vital for understanding the circulation in the persian gulf to measure the current in the strait four subsurface moorings were deployed at four different stations close to sh from early november 2012 to the end of january 2013 tidal current were dominant in the sh the tides in the sh were complex partially standing waves and the dominant pattern varied from being primarily semi diurnal to diurnal the phase difference between tidal constituents of current and sea level elevation time series was used as an index to show the partially progressive wave pattern inside the study area at mooring positions 3 and 4 located to the left of sh the phase differences were close to 160 and 100 respectively it indicates partially progressive waves in opposite direction at these stations k 1 and m 2 were the two main constituents at all stations inside the study area at surface the magnitude of semi major axis of ellipses for m 2 constituent was larger than corresponding value for k 1 whereas at the bottom layer the opposite pattern was observed the m 2 rotary coefficients at mooring 1 illustrated that current vector at the bottom layer rotated in opposite direction compared to current vectors at the middle and surface layers the rotation was counterclockwise in the bottom layer while it was clockwise in the surface and middle layers

role of temperature and nutrients in extinction of turritelline gastropods cenozoic of the northwestern atlantic and northeastern pacific abstract turritelline gastropods mesogastropoda turritelline are common to abundant components in many fossil cretaceous cenozoic and recent marine benthic communities but the environmental factors affecting their evolution and extinction are poorly understood this is in large part because today they occur most abundantly in cooler waters associated with upwelling or other high nutrient conditions but thermal tolerances and preferences are unclear for extinct turritelline species turritellines were diverse and abundant throughout the new world for much of the cenozoic beginning in the early neogene through both extinction and range contraction however they started to disappear from higher latitudes on both atlantic and pacific coasts of north and central america the highest rate of extinction took place in the western atlantic in the plio pleistocene when almost all turritelline species in this area became extinct preliminary comparison of the available stratigraphic record suggests that this paleobiogeographic pattern is not an artefact of the record this biogeographic shift coincides with a postulated regional mass extinction among all marine mollusks in the western atlantic at around the same time causes for turritelline extinction however appear to be more complex than the decline in temperature that is cited most often as the probable cause of the western atlantic molluskan extinction event neogene turritellines in the western atlantic appear to have been adversely affected by collapse and or major reorganization of oceanic productivity associated with the formation of the isthmus of panama nutrients thus may have been more important than temperature change in controlling extinction probability in this group

correlation of late miocene to early pliocene sequences between the mediterranean and north atlantic ocean drilling program odp site 982 in the north atlantic contains a complete latest miocene to early pliocene section that was tuned to the astronomical timescale by correlating the record of gamma ray attenuation gra bulk density to summer insolation at 65 n and the benthic 18o signal to orbital obliquity for the interval from 4 6 to 7 5 ma the astronomical tuning of the site 982 record permits a direct bed to bed correlation to the cyclostratigraphy of messinian sections in the mediterranean krijgsman et al 1999a 2001 the benthic 18o signal at site 982 records a latest miocene glacial period that lasted from 6 26 to 5 50 ma and consisted of 18 glacial to interglacial oscillations that were controlled by the 41 kyr cycle of obliquity although the intensification of glaciation at 6 26 ma may have contributed to the restriction of the mediterranean it preceded the depositional onset of the lower evaporite unit at 5 96 ma by some 300 kyr the transition from stage tg12 to tg11 at 5 5 ma marks the end of the latest miocene glacial period and precedes the miocene pliocene boundary by 170 kyr although benthic 18o values are relatively low and 18o of bulk carbonate reaches a minimum at the miocene pliocene boundary at 5 33 ma there is no single event that would indicate deglaciation and sea level rise as the cause of the reflooding of the mediterranean we conclude that glacioeustatic changes alone were not responsible for either the start or end of evaporite deposition during the messinian suggesting that tectonic or local climate changes in the mediterranean region were the dominant cause s

separation of large scale water storage patterns over iran using grace altimetry and hydrological data extracting large scale water storage ws patterns is essential for understanding the hydrological cycle and improving the water resource management of iran a country that is facing challenges of limited water resources the gravity recovery and climate experiment grace mission offers a unique possibility of monitoring total water storage tws changes an accurate estimation of terrestrial and surface ws changes from grace tws products however requires a proper signal separation procedure to perform this separation this study proposes a statistical approach that uses a priori spatial patterns of terrestrial and surface ws changes from a hydrological model and altimetry data the patterns are then adjusted to grace tws products using a least squares adjustment lsa procedure thereby making the best use of the available data for the period of october 2002 to march 2011 monthly grace tws changes were derived over a broad region encompassing iran a priori patterns were derived by decomposing the following auxiliary data into statistically independent components i terrestrial ws change outputs of the global land data assimilation system gldas ii steric corrected surface ws changes of the caspian sea iii that of the persian and oman gulfs iv ws changes of the aral sea and v that of small lakes of the selected region finally the patterns of i to v were adjusted to grace tws maps so that their contributions were estimated and grace tws signals separated after separation our results indicated that the annual amplitude of ws changes over the caspian sea was 152 mm 101 mm over both the persian and oman gulfs and 71 mm for the aral sea since january 2005 terrestrial ws in most parts of iran specifically over the center and northwestern parts exhibited a mass decrease with an average linear rate of 15 mm yr the estimated linear trends of groundwater storage for the drought period of 2005 to march 2011 corresponding to the six main basins of iran khazar persian and oman gulfs urmia markazi hamoon and srakhs were 6 7 6 1 11 2 9 1 3 1 and 4 2 mm yr respectively the estimated results after separation agree fairly well with 256 in situ piezometric observations

the influence of bacterial activity on phosphorite formation in the miocene monterey formation california abstract authigenic phosphorites from the miocene monterey formation california including an autochthonous phosphatic laminite were analyzed for molecular biomarkers element content and sulfur isotopic composition of associated pyrite and sulfate to evaluate the role of bacterial activity in the precipitation of phosphate minerals the phosphorites formed in a depositional environment typified by upwelling with dynamic bottom currents and hardground formation pyrite enclosed in the phosphorites shows 34 s values as low as 36 5 vcdt which is consistent with bacterial sulfate reduction in a three step extraction phosphorite dissolution extraction procedure molecular fossils of sulfate reducing bacteria di o alkyl glycerol ethers and short chain branched fatty acids i and ai c 15 0 i and ai c 17 0 and 10mec 16 0 were preferentially released from the mineral lattice this suggests that the molecular fossils were tightly bound to carbonate fluorapatite indicating that sulfate reducing bacteria were involved in mineral formation a close association of sulfate reducing bacteria with large sulfide oxidizing bacteria which was previously suggested to favor carbonate fluorapatite precipitation could neither be confirmed nor excluded for the miocene monterey formation phosphorites

compositional controls on early diagenetic pathways in fine grained sedimentary rocks implications for predicting unconventional reservoir attributes of mudstones diagenesis significantly impacts mudstone lithofacies processes operating to control diagenetic pathways in mudstones are poorly known compared to analogous processes occurring in other sedimentary rocks selected organic carbon rich mudstones from the kimmeridge clay and monterey formations have been investigated to determine how varying starting compositions influence diagenesis the sampled kimmeridge clay formation mudstones are organized into thin homogenous beds composed mainly of siliciclastic detritus with some constituents derived from water column production e g coccoliths s depleted type ii kerogen as much as 52 6 total organic carbon toc and others from diagenesis e g pyrite carbonate and kaolinite the sampled monterey formation mudstones are organized into thin beds that exhibit pelleted wavy lamination and are predominantly composed of production derived components including diatoms coccoliths and foraminifera in addition to type iis kerogen as much as 16 5 toc and apatite and silica cements during early burial of the studied kimmeridge clay formation mudstones the availability of detrital fe iii and reactive clay minerals caused carbonate and silicate buffering reactions to operate effectively and the pore waters to be fe ii rich these conditions led to pyrite iron poor carbonates and kaolinite cements precipitating preserved organic carbon being s depleted and sweet hydrocarbons being generated in contrast during the diagenesis of the sampled monterey formation mudstones sulfide oxidation coupled with opal dissolution and the reduced availability of both fe iii and reactive siliciclastic detritus meant that the pore waters were poorly buffered and locally acidic these conditions resulted in local carbonate dissolution apatite and silica cements precipitation natural kerogen sulfurization and sour hydrocarbons generation differences in mud composition at deposition significantly influence subsequent diagenesis these differences impact their source rock attributes and mechanical properties

makran continental margin sedimentation during the late holocene sedimentation in the makran active margin is governed by a complex interaction of atmospheric tectonics and hydrodynamic setting of the northern flank of the gulf of oman the mixed clastic carbo

a numerical investigation of circulation in the arabian gulf a three dimensional hydrodynamic model is developed to study the circulation in the arabian gulf the model contains realistic basin geometries and bathymetries of the arabian gulf and a good portion of the gulf of oman and is driven by monthly climatological winds evaporation and net ocean heat gain in both gulfs and the shatt al arab discharge it is found that the cyclonic circulation in the southern portion of the gulf is primarily driven by the evaporation induced freshening from the strait of hormuz in the northwestern corner of the gulf the shatt al arab discharge maintains the cyclonic circulation which would otherwise be anticyclonic the northwestward intrusion of fresher water along the iranian coast is weakened by northwesterly winds in winter but strengthens and extends almost to the head of the gulf in summer owing to the warming of the gulf of oman waters the development of the summer thermocline in the arabian gulf and diminishing winds the southward coastal current along the arabian coast is most prominent between the head of the gulf and qatar the model also predicts a strong southward coastal jet east of qatar which is primarily wind driven no similar coastal jet can be developed in the gulf of salwa west of qatar

miocene intensification of upwelling along the california margin as recorded in siliceous facies of the monterey formation and offshore dsdp sites

eddy topography interactions and the fate of the persian gulf outflow the persian gulf feeds a warm and salty outflow in the gulf of oman northern arabian sea the salt climatological distribution is relatively smooth in the gulf of oman and the signature of a slope current carrying salty waters is difficult to distinguish hundreds of kilometers past the strait of hormuz in contrast to other outflows of the world ocean this study focuses on the mechanisms involved in the spreading of persian gulf water pgw in the gulf of oman using a regional primitive equation numerical simulation the authors show that the dispersion of pgw occurs through a regime that is distinct from for example the one responsible for the mediterranean outflow dispersion the background mesoscale eddy field is energetic and participates actively to the spreading of pgw remotely formed eddies propagate into the gulf of oman and interact with the topography leading to submesoscales formation and pgw shedding eddy topography interactions are isolated in idealized simulations and reveal the formation of intense frictional boundary layers generating submesoscale coherent vortices scvs interactions take place at depths encompassing the pgw depth thus scvs trap pgw and contribute to its redistribution from the boundaries to the interior of the gulf of oman the overall efficiency of these processes is confirmed by a strong contribution of eddy salt fluxes in the interior of the basin and is quantified using particle statistics it is found to be a highly dispersive regime with an approximated eddy diffusivity of inline image

determination of earthquake source mechanisms using teleseismic 30 140 s waves the january 17 1994 northridge earthquake complete seismic waveforms with periods between 30 and 140 s recorded at teleseismic distances 10 are used to determine the source mechanism of the january 17 1994 northridge earthquake ms 6 8 an algorithm called the earth simplifying transformation est is applied to the mainshock primary event data to calibrate and remove propagation effects of earth s lateral and radial heterogeneities that are not predicted by a reference earth model the procedure involves frequency domain division of each pair of observed and synthetic waveforms for an auxiliary event with a well constrained source mechanism in proximity to the primary event with the synthetics being computed for a reference earth model if the auxiliary event source mechanism is correct the differences between the data and synthetics represent the residual effects of the earth s structure that are not predicted by the earth model the frequency dependent deconvolution filters are convolved with the corresponding observed signals for the primary event the resulting waveforms are then used to determine the source mechanism of the primary event by forward modeling and by centroid moment tensor inversion with excellent fits to the complete waveforms being achieved the resulting solution for the northridge event has a centroid depth of 12 1 km and a mechanism with strike 115 dip 40 and rake 95 with 5 uncertainty for each parameter the est procedure holds promise for reliable source inversion for small earthquakes in a region calibrated by large events with well determined source parameters

variability in diatom and silicoflagellate assemblages during mid pliocene glacial interglacial cycles determined in hole u1361a of iodp expedition 318 antarctic wilkes land margin the earth is currently experiencing climatic changes that will result in similar environmental conditions to those experienced during the mid pliocene 5 3 3 6 million years ago ma such as similar atmospheric co2 concentrations elevated sea surface temperature and higher sea levels due to polar ice melt studying the temporal distribution of antarctic diatoms and silicoflagellates from this epoch provides insights into environmental conditions and sea ice configurations during that time and remains the only way to realistically estimate future phytoplankton community responses and southern ocean sea ice extent during large scale transient changes of similar magnitude to that anticipated by anthropogenic causes in this study we identified and quantified diatoms and silicoflagellates in a sediment core section obtained from the antarctic wilkes land margin iodp expedition 318 hole u1361a spanning four glacial and interglacial cycles around the gauss gilbert geochron boundary 3 6 ma between about 3 69 and 3 56 ma two major abundance peaks around 79 66 and 76 86 mbsf representing time intervals around 3 65 ma and 3 58 ma respectively were identified both peaks temporally match previously determined high productivity warm intervals interglacials diatom and silicoflagellate assemblages in these two interglacial periods differed the abundance peak in the older sediments is dominated by the pennate diatoms fragilariopsis barronii rouxia naviculoides and rouxia antarctica indicative of seasonal meltwater associated stratification the abundance peak in the younger sediments is composed principally of chaetoceros resting spores suggesting higher productivity strong stratification and prolonged ice free open water conditions analysing highly abundant diatoms and environmental indicator species from this iodp site in relation to the previously determined palaeo productivity proxy ba al allowed us to refine the age model our study provides orbital scale insights into the variability of antarctic diatom and silicoflagellate assemblages during the mid pliocene thereby offering a reference for future predictions of extant diatom responses to ongoing climate change

multiple episodes of sand injection leading to accumulation and leakage of hydrocarbons along the san andreas san gregorio fault system california abstract the presence of sand injections has been shown to enhance the likelihood of hydrocarbon traps within siliciclastic successions through the development of large interconnected networks of sills and dykes sand injection complexes provide a volume of porous and permeable rocks within the low permeability host units overall the formation of sand injection complexes requires extensive fracturing and hydrofracturing which can be particularly pronounced when sand injections are coupled with brittle tectonic deformation in some circumstances this process may threaten the integrity of the reservoir top seal thereby preventing further hydrocarbon accumulation studying exceptional exposures along the coastal area of santa cruz in california we report evidence for top seal failure associated with injection episodes two distinct sand injection episodes are proposed the first event datable to the late miocene resulted in large volumes of sand being emplaced within the top seal units and was followed by accumulation of hydrocarbons within the newly injected sandstones later a series of brittle tectonic events associated with the san andreas san gregorio fault system caused remobilization and accumulation of sand along newly formed fault planes our case study documents this combination of pervasive brittle deformation and sandstone injection along fault structures which can ultimately disrupt the integrity of a host unit leading top seal failure and leakage of hydrocarbons

phosphogenesis and organic carbon preservation in the miocene monterey formation at naples beach california the monterey hypothesis revisited the middle part of the miocene monterey formation at naples beach west of santa barbara california is predominantly composed of organic rich mudstone interstratified with phosphatic laminae minor lithologies include volcanic ash dolomite porcelanite and chert and condensed phosphatic beds sediments dated as 14 3 13 5 ma have average total organic carbon toc values around 8 5 wt and organic carbon oc accumulation rates are around 565 mg cm2 k y sediments dated as 13 5 13 ma are characterized by average toc values of 12 6 wt and oc accumulation rates of around 1130 mg cm2 k y the interval between 13 and 10 6 ma is marked by condensation average toc values are around 8 6 wt and oc accumulation rates diminished to around 55 mg cm2 k y the last interval studied is dated as 10 6 9 4 ma and average toc values are around 6 wt whereas oc accumulation rates rose again to 320 mg cm2 k y the presence of erosional surfaces angular unconformities and reworked clasts and nodules suggests that bottom current activity and gravity flow deposition have been instrumental in sediment accumulation the phosphatic laminae were precipitated at a very early stage of diagenesis during periods of nonsedimentation they formed less permeable sedimentary lids and may as such have contributed to enhanced oc preservation between 13 and 10 6 ma the thus formed phosphatic laminae were frequently subjected to subsequent sediment winnowing and reworking resulting in the formation of condensed phosphatic beds calculated p c molar ratios suggest that 1 the measured section is highly enriched in phosphorus p relative to oc 2 regeneration of organic p from organic matter decomposition was negligible and 3 the source of p was external likely upwelled bottom water rich in inorganic p in spite of good preservation conditions and correspondingly high toc contents the overall oc accumulation rates are moderate in comparison to those of actual high productivity areas which is mainly due to the episodic character of depositional processes and the intervening long periods of nondeposition and sediment reworking they preclude this section and by extrapolation the monterey formation in general from being an important oc sink during the middle miocene alternatively large oc sinks were probably created on the continent lignite deposits and in sedimentary depocenters which received increasing amounts of detrital sediments due to a combination of climate change spreading of grasslands and the increasing importance of mountain chains such as the himalaya the associated high nutrient fluxes may have been involved in the backstepping and drowning of carbonate platforms and in the generation of widespread phosphat rich deposits during the late early and early middle miocene

hydrology and circulation in the strait of hormuz and the gulf of oman results from the gogp99 experiment 1 strait of hormuz in october and early november 1999 the gogp99 experiment collected hydrological currentmeter tide recorder thermistor and drifting buoy data near the strait of hormuz data analysis provides the water mass structure in the strait persian gulf water pgw core is banked against the omani coast while indian ocean surface water iosw lies near the iranian coast these water masses are most often covered by a homogeneous surface layer thermohaline characteristics of the pgw core decrease substantially downstream from the persian arabian gulf to the gulf of oman pgw and iosw thermohaline characteristics and distribution also exhibit notable changes at periods shorter than a month as shown by repeated hydrological sections the tidal signal measured south of the strait by moored adcp and thermistor chains has predominant semi diurnal m2 and s2 and diurnal k1 components and possesses a complex vertical structure tidal intensification near the surface pycnocline is associated with noticeable internal waves at subtidal timescale mooring recordings confirm the water mass variability observed in the repeated hydrological sections the mixed layer also deepens substantially during the 1 month period finally trajectories of surface buoys drogued at 15 m exhibit reversals over periods characteristic of changes in wind direction

modeling of circulation in the arabian gulf and the sea of oman skill assessment and seasonal thermohaline structure hindcast simulations of the arabian gulf and the sea of oman using the regional ocean modeling system roms are quantitatively evaluated with basin wide hydrographic data and time series measurements the model shows comparable skill in reproducing moored observations of current velocities structure in upper and bottom depths the skill in simulating observed temperature is higher of 0 93 scale 0 1 in upper depths compared to 0 52 in bottom depths model results are sensitive to parameterization of water clarity a lower sensitivity was noticed to kpp gls and my2 5 turbulence closures when coastal turbid water parameterization is used accuracy of the model in reproducing seasonal and spatial variations of temperature and salinity increased by 25 compared to the clear water case whereas only 10 increase was noticed when applying kpp turbulent closure the model reproduces well anticlockwise circulation in the gulf a stronger surface inflow of fresher water to the arabian gulf through the strait of hormuz is simulated in summer compared to winter conditions mainly due to upper layer horizontal gradient of density between the arabian gulf and the sea of oman less seasonal variability of outflow between 0 15 and 0 20 m s 1 at 50 m to bottom depth around the strait of hormuz was noticed in the model results modeled surface layer stratification is stronger in summer than winter and varies spatially in the arabian gulf with highest stratification near the strait of hormuz overall the stratification in shallow water area of the arabian gulf remains low throughout the year

observations of seasonal exchange through the straits of hormuz and the inferred heat and freshwater budgets of the persian gulf the exchange between the persian arabian gulf and the indian ocean is investigated using hydrographic and moored acoustic doppler current profiler data from the straits of hormuz during the period december 1996 to march 1998 the moored time series records show a relatively steady deep outflow through the strait from 40 m to the bottom with a mean speed of approximately 20 cm s a variable flow is found in the upper layer with frequent reversals on timescales of several days to weeks the annual mean flow in the near surface layer is found to be northeastward out of the persian gulf in the southern part of the strait suggesting a mean horizontal exchange with the indian ocean that is superimposed on the vertical overturning exchange driven by evaporation over the gulf the salinity of the deep outflow varies from 39 3 to 40 8 psu with highest outflow salinities occurring in the winter months december march the annual mean deep outflow through the strait is estimated to be 0 15 0 03 sv calculation of the associated heat and freshwater fluxes through the strait yields estimates for the annual heat loss over the surface of the gulf of 7 4 w m2 and an annual water loss e p r of 1 68 0 39 m yr these values are shown to be in relatively good agreement with climatological surface fluxes derived from the southampton oceanography centre global flux climatology after known regional biases in the radiative budget are taken into account

what processes control the net currents through shallow straits a review with application to the bohai strait china we review the key processes controlling the net water circulation in shallow straits the circulation is mainly barotropic driven by the difference in mean sea level and tides on either side of the strait the wind the meandering of the currents in the adjoining seas the bathymetry including the shape and width of the mouths and the presence of narrows shoals sills islands and lateral embayments as the oceanography forcing can be non synchronised on either side of the strait the resulting net currents through the strait may appear chaotic we apply these findings to the net circulation through the bohai strait in china using local wind remote sensing data of currents and sea level and a hydrodynamic model the net currents through the bohai strait were episodic they were largest during winter storms when the wind generated a cyclonic coastal current in the northern yellow sea that flowed across the width of the bohai strait like the luzon strait this current meandered and a branch of the current intruded into the northern bohai strait along the deeper channel the wind set up in the bohai sea and the wind driven longshore current in the southern bohai sea generated a seaward flow through the southern bohai strait somewhat like in irbe strait as with the straits of the seto inland sea stagnation occurred in some embayments as in the torres strait the islands in the southern bohai strait retarded the net flow and increased the width of the outflow zone these flows were also modulated at very long periods 60 days by long waves in the yellow sea possibly generated by meandering of the kuroshio current that created an additional sea level slope through the strait the transit time in the bohai strait was 60 and 10 days respectively during calm weather and winter storms the residence time in the bohai sea was estimated to be about 1 68 years by the loicz model and 1 56 years by the hydrodynamic model and the influence of the river runoff including the yellow river was negligible

a mid permian chert event widespread deposition of biogenic siliceous sediments in coastal island arc and oceanic basins abstract radiolarian and conodont of permian siliceous rocks from twenty three areas in teh the circum pacific and mediterranean regions reveal a widespread permian chert event during the middle leonardian to wordian radiolarian and or sponge spicule rich siliceous sediments accumulated beneath high productivity zones in coastal island arc and oceanic basins most of these deposits now crop out in fault bounded accreted terranes biogenic siliceous sediments did not accumulate in terranes lying beneath infertile waters including the marine sequences in terranes of northern and central alaska the permian chert event is coeval with major phosphorite deposition along the western margin of pangea phosphoria formation and related deposits a well known analogue for this event is middle miocene deposition of biogenic siliceous sediments beneath high productivity zones in many parts of the pacific and concurrent deposition of phosphatic as well as siliceous sediments in basins along the coast of california interrelated factors associated with both the miocene and permian depositional events include plate reorientations small sea level rises and cool polar waters

comparison of monterey formation kerogens from the salinas basin and santa barbara area california abstract unweathered monterey kerogens from surface samples and wells in the santa barbara area and the salinas basin approximately 125 miles apart are oil prone good to excellent potential oil source rocks deposited under marine anoxic to suboxic conditions the kerogens in the surface samples are somewhat similar when viewed through the microscope and the differences result from the depositional conditions anoxic vs suboxic and the original organic matter that formed the amorphinite alginite vs exinite the bitumens extracted from these samples have similar carbon isotope values and gas chromatography fingerprints in the santa barbara area mudstones from the lower calcareous facies of the monterey formation contain greater than 90 fluorescent marine amorphinite ii kerogen that is oil prone type ii and mixed type ii and iii based on rock eval and toc analysis in the salinas basin kerogens from the calcerous sandholdt member of the monterey formation equivalent to the lower calcareous facies also contain greater than 90 amorphous highly oil prone amorphinite ii the upper siliceous monterey formation in the santa barbara area also contains large amounts of oil prone amorphinite ii and is compared to the weathered siliceous hames member in the salinas basin that contains a large amount of alginite the kerogens in the lower calcerous facies in both areas are thermally immature but contain solid bitumen and or oil droplets in the residues at low levels of vitrinite reflectance and tai mean r o values from 0 3 to 0 4 and tai values from 2 2 to 2 5

neogene stratigraphy paleoceanography and paleobiogeography in northwest south america and the evolution of the panama seaway abstract the atrato basin in the pacific coastal region of nw south america colombia exhibits stratigraphic and biostratigraphic characteristics similar to other neogene pacific coastal basins of southern central america and northern south america an evaluation of the neogene stratigraphy and foraminiferal biostratigraphy with emphasis on paleoceanographic and paleobiogeographic phenomena indicate the following 1 previous to the middle miocene well aerated deep and open oceanic conditions and free and active water circulation prevailed along the steep continental margins of nw south america 2 during the early middle miocene right after the neogene hiatus nh 2 15 2 ma tectonic disturbances triggered the initial uplift of the panama sill bottom water circulation foraminiferal and sedimentation changes are observed in both the pacific and caribbean coastal areas of nw south america 3 during the middle miocene coinciding with the neogene hiatus nh 3 12 9 11 8 ma an abrupt paleobathymetric change from lower to middle bathyal depths indicates a major uplift of the panama sill to about 1000 m reflecting the middle miocene tectonic disturbances in nw south america 4 during the late middle miocene immediately following this uplift a distinctive pacific benthic foraminiferal fauna abruptly appeared and extended from ecuador to california because these assemblages do not occur in the adjacent caribbean region a circulation barrier between the atlantic and pacific oceans as a result of intensification of the cool marginal california current is proposed anoxic middle to upper bathyal environments prevailed under well aerated cool surface waters in the pacific coastal areas of nw south america 5 during the latest miocene immediately following the neogene hiatus nh 6 7 0 6 3 ma surface water circulation between the caribbean and the pacific was re established and the previous influence of the california current disappeared a rapid filling and shallowing of the basin to mostly neritic depths is indicated along the pacific and caribbean coastal basins of colombia as well as a progressive increase in similarity between the coastal pacific and caribbean benthic biotas this shallowing in the early late miocene also appears to have been associated with the earliest terrestrial interchange of ground sloths to north america and raccoons and their allies to south america 6 immediately following early pliocene time the panamanian isthmus became completely emergent providing a terrestrial environment favourable for intermingling of terrestrial faunas and floras between north and south america i correlate this pliocene uplift with the neogene hiatus nh 8 3 7 3 1 ma four regional unconformities associated with tectonic disturbances in the nw corner of south america have also been recognized and correlated with neogene hiatuses recorded from the oceans early middle miocene middle miocene late miocene and early pliocene

a hycom modeling study of the persian gulf 2 formation and export of persian gulf water 1 the circulation and water mass transformation processes in the persian gulf and the water exchange with the indian ocean through the strait of hormuz are studied using the hybrid coordinate ocean model hycom model results suggest that intruding indian ocean surface water iosw is transformed into hypersaline waters with salinity 41 practical salinity unit by the fresh water loss in the northern end of the gulf and in the southern shallow banks during wintertime intense heat loss from sea to air leads to the formation of cold and saline waters both in the northern gulf and in the southern gulf dense waters formed in the southern gulf have higher salinity and spill into the axial deep trough of the gulf as a sporadic bottom outflow in winter which leads to high salinity pulses in the strait as observed whereas in summer their buoyancy is increased due to heating and they are exported as a warm yet salty intermediate depth flow through the strait dense waters formed in the northern gulf propagate toward the strait along the axial trough throughout the year correspondingly there are two branches of seasonal overturning circulation in density classes the northern branch peaking in august with strength of 0 13 sv and the southern branch peaking in february and december with strength of 0 08 sv these two branches outflow together feed a seasonally varying deep outflow through the strait with an annual mean volume transport of 0 12 sv

the sensitivity of the southwest monsoon phytoplankton bloom to variations in aeolian iron deposition over the arabian sea 1 a coupled 3 d biophysical ocean general circulation model is used to investigate how aeolian iron deposition affects the arabian sea ecosystem two separate aeolian iron deposition fields derived from the giss and gocart atmospheric transport models have been applied as surface boundary conditions the model results exhibit widespread biogeochemical sensitivity to the choice of deposition field with gocart deposition sw monsoon phytoplankton blooms in the western and central arabian sea are enhanced and exhibit greater realism the central arabian sea bloom is supported by supplemental input of horizontally advected iron from a pool that undergoes a yearlong progression that begins in the gulf of oman where the difference in aeolian iron enrichment between the two deposition fields is most prevalent the gocart enhanced blooms result in a more pronounced shift toward netplankton an increase in euphotic zone export flux of up to a 20 during the sw monsoon and an additional annual biogenic export of 3 5 tgc the potential ramifications of regional n cycle alteration through stimulation of n2 fixation that is promoted by significant aeolian mineral flux needs to be explored the canonical thinking that the northern arabian sea is invariably iron replete is now being challenged by both our model results and recent observational studies as well our results indicate that arabian sea iron concentrations are strongly modulated by the specific nature of aeolian mineral deposition thus climate or land use influences on dust mobilization could exercise leading order controls on regional biogeochemical variability metabolic status and air sea exchanges of co2

refining the extraction methodology of carbonate associated sulfate evidence from synthetic and natural carbonate samples sulfur and oxygen isotope analyses of trace and whole mineral sulfate are valuable in investigating diagenetic processes and the microbial communities that produced them seawater anoxia and paleoclimate oxygen isotopes are particularly useful in that they may also record alterations to the original isotope ratio be it from post depositional processes or oxidation of sulfide minerals during the chemical extraction procedure here we rigorously test several common methodological procedures of extracting carbonate associated sulfate cas for sulfur and oxygen isotope analyses in order to generate a method that will extract only the cas while preserving associated organic reduced sulfur and sulfides for analysis the results of these experiments on synthetically generated carbonates demonstrate that our proposed protocol sufficiently removes all non cas sulfate and does not result in oxidation of included sulfides analytical reproducibility standard deviation of synthetic carbonates is 0 1 1 for 34s and 0 3 1 for 18o extractions of low pyrite high organic matter geologic samples from the monterey formation across a range of facies types demonstrate a reproducibility 1 of 0 4 0 7 for 34s and 0 8 1 3 for 18o resulting from sample heterogeneity 34s and 18o from monterey formation samples do not demonstrate oxidation of organic matter suggesting our proposed protocol will preserve organic sulfur a high pyrite concentration jet rock concretion demonstrates that additional sulfate can be produced during the non cas leaching processes from oxidation of pyrite we show that pyrite from the jet rock concretion ceases to oxidize when the sample is leached under an anoxic environment

miocene stable isotope record a detailed deep pacific ocean study and its paleoclimatic implications deep sea drilling project site 289 in the western equatorial pacific has yielded an extremely detailed record of the carbon and oxygen isotopic changes in the miocene deep ocean the isotopic record reflects major changes in paleoclimate and paleoceanography probably dominated by a major phase of antarctic ice cap growth the transition from a relatively unglaciated world to one similar to today occurred between 16 5 x 10 6 and 13 x 10 6 years before the present with the greatest change occurring between approximately 14 8 x 10 6 and 14 0 x 10 6 years before the present

the influence of shale depositional fabric on the kinetics of hydrocarbon generation through control of mineral surface contact area on clay catalysis abstract accurately assessing the temperature and hence the depth and timing of hydrocarbon generation is a critical step in the characterization of a petroleum system clay catalysis is a potentially significant modifier of hydrocarbon generation temperature but experimental studies of clay catalysis show inconsistent or contradictory results this study tests the hypothesis that source rock fabric itself is an influence on clay mineral catalysis as it controls the extent to which organic matter and clay minerals are physically associated two endmember clay organic fabrics distinguish the source rocks studied 1 a particulate fabric where organic matter is present as discrete 5 m particles and 2 a nanocomposite fabric in which amorphous organic matter is associated with clay mineral surfaces at sub micron scale high resolution electron imaging and bulk geochemical characterisation confirm that samples of the miocene monterey formation california are representative of the nanocomposite source rock endmember whereas samples from the permian stuart range formation south australia represent the particulate source rock endmember kinetic experiments are performed on paired whole rock and kerogen isolate samples from these two formations using open system non isothermal pyrolysis at three different heating rates 0 7 2 and 5 k min to determine the effects of the different shale fabrics on hydrocarbon generation kinetics extrapolation to a modelled geological heating rate shows a 20 c reduction in the onset temperature of hydrocarbon generation in monterey formation whole rock samples relative to paired kerogen isolates this result is consistent with the monterey formations s nanocomposite fabric where clay catalysis can proceed because reactive clay minerals are intimately associated with organic matter by contrast there is no significant difference in the modelled hydrocarbon generation temperature of paired whole rock and kerogen isolates from the stuart range formation this is consistent with its particulate fabric where relatively large discrete organic particles have limited contact with the mineral matrix and the clay minerals are mainly diagenetic and physically segregated within pores while heating rate may have a control on mineral matrix effects this result shows that the extent to which organic matter and clay minerals are physically associated could have a significant effect on the timing of hydrocarbon generation and is a function of the depositional environment and detrital vs diagenetic origin of clay minerals in source rocks

character and dynamics of the red sea and persian gulf outflows historical hydrographic data and a numerical plume model are used to investigate the initial transformation dynamics and spreading pathways of red sea and persian gulf outflow waters where they enter the indian ocean the annual mean transport of these outflows is relatively small 0 4 sv but they have a major impact on the hydrographic properties of the indian ocean at the thermocline level because of their high salinity they are different from other outflows in that they flow over very shallow sills depth 200 m into a highly stratified upper ocean environment and they are located at relatively low latitudes 12 n and 26 n furthermore the red sea outflow exhibits strong seasonal variability in transport the four main results of this study are as follows first on the basis of observed temperature salinity t s characteristics of the outflow source and product waters we estimate that the red sea and persian gulf outflows are diluted by factors of 2 5 and 4 respectively as they descend from sill depth to their depth of neutral buoyancy the high dilution factor for the persian gulf outflow results from the combined effects of large initial density difference between the outflow source water and oceanic water and low outflow transport second the combination of low latitude and low outflow transport and associated low outflow thickness results in ekman numbers for both outflows that are o 1 this indicates that they should be thought of as frictional density currents modified by rotation rather than geostrophic density currents modified by friction third different mixing histories along the two channels that direct red sea outflow water into the open ocean result in product waters with significantly different densities which probably contributes to the multilayered structure of the red sea product waters in both outflows seasonal variations in source water and oceanic properties have some effect on the t s of the product waters but they have only a minor impact on equilibrium depth fourth product waters from both outflows are advected away from the sill region in narrow boundary currents at least during part of the year at other times the product water appears more in isolated patches

the relationship of diagenesis with a complex microbial ecosystem in the phosphatic interval of the miocene monterey formation evidence from stable isotopes and mineralogy abstract a combination of evidence from mineralogy sulfur and oxygen stable isotope ratios from early diagenetic carbonate associated sulfate cas and structurally substituted sulfate in phosphate both termed cas here and carbon and oxygen stable isotope ratios from carbonate describe a complex redox system and complex microbial ecosystem within the phosphate rich interval of the monterey formation 34s and 18o of cas are lower than miocene seawater sulfate as reconstructed from marine evaporite and barite minerals combined with mineralogical speciation modeling and mineralogical observations isotopically low cas isotope values suggest mixing from three isotopically characterized sulfate pools two isotopically higher sulfate pools one with the composition of miocene seawater sulfate and a second isotopically evolved porewater modified by sulfate reducing microbes srm and a third isotopically lower porewater sulfate pool resulting from the oxidation of h2s produced by srm by sulfide oxidizing bacteria sob high carbonate 13c and diagenetic dolomite validates prior claims of methanogenesis differences in mineralogy are consistent with differences in isotope ratios e g higher 13c in dolomites suggesting products from a vertical distribution of oxic to anoxic redox environments and associated ecosystems are preserved these mineralogical and isotopic fluctuations repeat in various facies changes suggesting that redox environments fluctuated over time this interpretation is supported by prior sedimentologic analysis which interpreted that deposition of the phosphatic interval of the monterey formation was influenced by gravity deposition processes promoted by tectonic activity gravity deposition would serve to transport more oxygenated waters to the deep water depositional environment and support microbially mediated sulfide oxidation at depth whereby h2s generated by srm in the absence of sufficient iron could diffuse upward to a more oxygenated zone near the suboxic oxic boundary h2s oxidation would decrease porewater ph slightly and inhibit the preservation of carbonate minerals and promote precipitation of phosphate increasing depth in sediments generates successively more reducing conditions promoting sulfate reduction which may have been coupled with the anaerobic oxidation of methane and carbonate mineral precipitation the most reducing conditions would support methanogenesis and dolomite production after consumption of the majority of sulfate

magnetostratigraphy of the late neogene purisima formation santa cruz county california abstract the magnetic polarity zonation of a late neogene sedimentary sequence in santa cruz county california has provided a chronologic framework for studies of the sedimentologic and tectonic processes involved in an episode of basin formation in the vicinity of the san andreas fault system in central coastal california the zonation is based on the analysis of samples from 79 horizons in a 300 m thick section of the purisima formation and a portion of the overlying aromas formation although rock magnetic studies support the hypothesis that the primary carrier of the remanence is magnetite many samples contain a secondary overprint which cannot be completely removed by alternating field demagnetization nevertheless systematic analysis of the behavior of the samples during demagnetization has led to an unambiguous determination of the polarity of each horizon and to the development of a magnetic polarity zonation containing thirteen magnetozones these magnetozones can be correlated to the magnetic polarity time scale using biostratigraphic constraints provided by diatoms in the lower portion of the section and invertebrates and vertebrates in the upper portion the studied section is found to span the interval from the epoch 5 epoch 6 boundary 6 07 mya to the matuyama gauss boundary 2 47 mya with a hiatus corresponding to the upper part of the gilbert epoch 4 5 mya to 3 5 mya this hiatus does not coincide with major regressions in the global sea level curve and is interpreted as a period of tectonic uplift the compression which generated this uplift was probably caused by interplay between the san andreas fault east of the study area and the san gregorio hosgri fault west of it

effect of subseabed salt domes on tidal residual currents in the persian gulf geological studies in the persian gulf pg have revealed the existence of subseabed salt domes with suitable filtering of a high resolution pg seabed topography it is seen that the domes leave their signature in the seabed i e numerous hills and valleys with amplitudes of several tens of meters and radii from a few up to tens of kilometers it was suspected that the shark skin of the pg seabed may affect the tidal residual flow the interaction of tidal dynamics and these obstacles was investigated in a nonlinear hydrodynamic numerical tidal model of the pg the model was first used to characterize flow patterns of residual currents generated by a tidal wave passing over symmetric elongated and tilted obstacles thereafter it was applied to the entire pg the model was forced at its open boundary by the four dominant tidal constituents residing in the pg each tidal constituent was simulated separately results i e tidal residual currents in the pg as depicted by lagrangian trajectories reveal a stationary flow that is very rich in eddies each eddy can be identified with a topographic obstacle this confirms that the tidal residual flow field is strongly influenced by the nonlinear interaction of the tidal wave with the bottom relief which in turn is deformed by salt domes beneath the seabed different areas of maximum residual current velocities are identified for major tidal constituents the pattern of trajectories indicates the presence of two main cyclonic gyres and several adjacent gyres rotating in opposite directions and a strong coastal current in the northern pg

a multi basin redox reconstruction for the miocene monterey formation california usa abstract deposition of the miocene monterey formation into numerous basins provides an ideal opportunity to study how preservation of geochemical signatures varies within and among basins as a function of local and global climatic and oceanic conditions this study presents commonly employed redox indicators including iron fe speciation and redox sensitive trace metal concentrations mo u v to constrain paleoredox conditions from three monterey locations the santa barbara basin the santa maria basin and the san joaquin basin the fe speciation geochemistry of the santa barbara and santa maria basin sediments are consistent with a wide range of redox conditions from suboxic to euxinic these results in combination with associated phosphorites and trace metal enrichment patterns indicate oscillatory redox conditions perhaps with a chemocline that fluctuated above the sediment water interface on seasonal or multi year timescales overall these sections were deposited in environments similar to modern phosphorite forming and upwelling dominated oxygen minimum zone settings like the peru margin geochemical evidence indicates that the san joaquin basin was generally more restricted and more stably anoxic compared to the other two basins perhaps more analogous to the modern cariaco basin at least for the studied interval iron speciation in the san joaquin basin reveals anoxia and euxinia over the entirety of the studied interval although trace metal concentrations are generally at the low end of those typical of anoxic euxinic conditions consistent with a restricted connection with the open ocean the one exception is an interval c 11 6 million years ago ma with elevated concentrations of redox sensitive elements that may represent a decrease in basin restriction or an increase in water column sulfide concentrations the present day california margin does not achieve euxinic conditions in similar basinal settings comparable with these monterey sections suggesting fundamental differences for the miocene california margin that may carry implications for global scale oxygen deficiency in miocene oxygen minimum zones

upper ocean currents in the northern arabian sea from shipboard adcp measurements collected during the 1994 1996 u s jgofs and onr programs abstract a large upper ocean velocity data set was obtained using a shipboard acoustic doppler current profiler adcp on seventeen rv t g thompson cruises during the jgofs and onr expedition to the northern arabian sea from september 1994 through january 1996 seven of the cruises followed a large area survey track centered over the arabian basin four cruises conducted seasoar surveys on either side of the findlater jet axis and six cruises were for the deployment and maintenance of moored instrumentation together providing some 380 cruise days and 96 000 track kilometers of coverage the adcp data extended over the upper 250 400 m of the water column depending upon the temporal spatial distributions of acoustic scatterers the velocity data revealed several items that differed significantly from the historical perspective maximum current magnitudes in this area varied from more than 1 m s 1 along the arabian coast to 10 20 cm s 1 well offshore perhaps the most important result was the complete dominance of the velocity field by eddies that had offshore correlation length scales of roughly 100 km a spectral peak at around 300 km and kinetic energies that ranged from 70 to more than 90 of the total kinetic energy the total kinetic energy was highest within about 300 km of the shore and decreased significantly in magnitude and vertical extent offshore within the coastal region the temporal variability was such that currents of 50 cm s 1 or more could completely reverse within a two week period seemingly independent of any local atmospheric forcing mean and seasonal velocities also differed from historical results there was a large anti cyclonic feature located for most of the year south of ras ash shabatat 58 e which intensified during the southwest monsoon there was a strong jet like current off ras al hadd 22 n which also intensified during the southwest monsoon although itflowed southwestward against the wind in contrast to the historical ship drift data which indicated that the surface currents followed the monsoonal winds the adcp data over the upper 200 400 m was highly variable with overall seasonal means that were often directed against the wind except within 100 200 km of the arabian coast the mean currents were generally toward the southwest with a mean transport in the upper 150 m between the coast and 10 n of approximately 9 10 6 m 3 s 1

paleoceanographic implications of miocene deep sea hiatuses miocene paleoceanographic evolution exhibits major changes resulting from the opening and closing of passages the subsequent changes in oceanic circulation and development of major antarctic glaciation the consequences and timing of these events can be observed in variations in the distribution of deep sea hiatuses sedimentation patterns and biogeographic distribution of planktic organisms the opening of the drake passage in the latest oligocene to early miocene 25 20 ma resulted in the establishment of the deep circumpolar current which led to thermal isolation of antarctica and increased global cooling this development was associated with a major turnover in planktic organisms resulting in the evolution of neogene assemblages and the eventual extinction of paleogene assemblages the erosive patterns of two widespread hiatuses ph 23 0 22 5 ma and nh 1 20 18 ma indicate that a deep circumequatorial circulation existed at this time characterized by a broad band of carbonate ooze deposition siliceous sedimentation was restricted to the north atlantic and a narrow band around antarctica a major reorganization in deep sea sedimentation and hiatus distribution patterns occurred near the early middle miocene boundary apparently resulting from changes in oceanic circulation beginning at this time deep sea erosion occurred throughout the caribbean hiatus nh 2 16 15 ma suggesting disruption of the deep circumequatorial circulation and northward deflection of deep currents and or intensification of the gulf stream sediment distribution patterns changed dramatically with the sudden appearance of siliceous ooze deposition in the marginal and east equatorial north pacific by 16 0 to 15 5 ma coincident with the decline of siliceous sedimentation in the north atlantic this silica switch may have been caused by the introduction of norwegian overflow water into the north atlantic acting as a barrier to outcropping of silica rich antarctic bottom water the main aspects of the present oceanic circulation system and sediment distribution pattern were established by 13 5 to 12 5 ma hiatus nh 3 coincident with the establishment of a major east antarctic ice cap antarctic glaciation resulted in a broadening belt of siliceous ooze deposition around antarctica increased siliceous sedimentation in the marginal and east equatorial north pacific and indian oceans and further northward restriction of siliceous sediments in the north atlantic periodic cool climatic events were accompanied by lower eustatic sea levels and widespread deep sea erosion at 12 to 11 ma nh 4 10 to 9 ma nh 5 7 5 to 6 2 ma nh 6 and 5 2 to 4 7 ma nh 7

miocene benthic foraminiferal isotope records a synthesis abstract 18 o 16 o and 13 c 12 c ratios of miocene benthic foraminifera from a number of atlantic pacific and indian ocean dsdp sites 71 77b 206 208 238 279 289 296 329 357 and 366a have been compiled these provide a rather detailed history of miocene deep water especially in the pacific ocean bottom water temperatures rose during the early miocene and then declined rapidly during the middle miocene this decline was accompanied by an increase in antarctic glaciation late miocene bottom temperatures and antarctic ice volumes are inferred to be similar to today s but exhibited some fluctuation the early miocene ocean was less thermally stratified at intermediate and abyssal depths while the late miocene deep ocean had a thermal structure generally similar to the modern ocean foraminiferal carbon isotope ratios at most of the sites varied quasi sympathetically throughout the miocene these variations must reflect comparable variations in the mean 13 c 12 c of marine hco 3 however the causes of such variations are not yet clear

on the mechanisms of episodic salinity outflow events in the strait of hormuz abstract observations in the strait of hormuz 26 26 n 56 08 e during 1997 98 showed substantial velocity fluctuations accompanied by episodic changes in the salinity outflow events with amplitude varying between 1 and 2 psu on time scales of several days to a few weeks these events are characterized by a rapid increase in salinity followed by an abrupt decline the mechanisms behind these strong pulses of salinity events are investigated with a high resolution 1 km hybrid coordinate ocean model hycom with particular reference to the year 2005 in accordance with the observations the simulated salinity events are characterized by strong coherence between the enhanced flows in zonal and meridional directions it is inferred that most of the simulated and observed outflow variability is associated with the continuous formation of strong mesoscale cyclonic eddies whose origin can be traced upstream to around 26 n 55 5 e these cyclonic eddies have a diameter of about 63 km and have a remnant of p

hydrology and circulation in the strait of hormuz and the gulf of oman results from the gogp99 experiment 2 gulf of oman art no c12038 hydrological adcp and drifting buoy data obtained during the gogp99 experiment in october and early november 1999 are analyzed to describe the persian gulf water pgw core and the regional circulation in the gulf of oman the warm and salty pgw core flows out of the strait of hormuz heading southeastward unto 25degrees20 n 57degreese approximately from there it cascades down the continental slope veers southwestward and joins the omani coast near 24degrees50 n 56degrees50 e to form a slope current this pgw current has then thermohaline maxima on isopycnal sigma 0 26 5 near 220 m depth its thermohaline characteristics decrease along its progression to ra s al hadd and then offshore into the arabian sea but maintain a sharp contrast with surrounding waters outflow variability at the strait of hormuz can be related to downstream fluctuations of the thermohaline maxima in the pgw core at gulf scale and over a 2 to 3 week period moreover several mechanisms baroclinic instability flow intermittency cape effects are examined to explain the widening of this pgw core upstream and downstream of ra s al hamra in the eastern part of the gulf of oman the regional circulation is a cyclonic gyre the circulation in the western part of the gulf is more complex with the outflow of pgw and southeastward currents in the upper 250 m near the omani coast and a recirculation of upwelled waters near ra s jagin on the iranian coast the large cyclonic gyre occupies at least the upper 300 m of the water column and undergoes little variation over a month the pgw outflow in the northern arabian sea is southward and located 50 100 km from the coast it borders a shallower northward current located offshore

bioturbated oxygenation event beds in siliceous facies monterey formation miocene california abstract predominatly laminated marine diatomaceous sequences deposited in oxygen deficient neogene basins typically contain bioturbated intervals that reflect episodes of improved benthic oxygenation excellent exposures of the siliceous facies of the miocene monterey formation near lompoc central california provided an opportunity to assess the ichnology and sedimentology of 200 such event beds in their general paleogeographic paleoclimatic and sea level context and hence to evaluate the character and causes of associated oxygenation episodes four recurring event bed types type i iv are distinguished on the basis of ichnologic characteristics these types fall into two general groups delineated on the basis of sedimentologic attributes primarily texture group 1 beds type i only have 1 homogeneous bioturbate primary strata that are more clastic rich and much coarser than surrounding laminated diatomites and 2 vertically extensive piped zones characterized by firmground thalassinoides paradoxicus glossifungites ichnofacies these characteristics indicate that group 1 events involve coincident increases in bottom current intensity clastic input and benthic oxygenation some group 1 beds may be the product of turbidity current transport of sediments trauma resistant crustaceans and allochtonous waters however most group 1 beds more likely record climate and sea level mediated migratio of incipient bank top conditions down the flank of a submergent topographic high group 2 beds types ii iii and iv are characterized by primary strata that are only slightly coarser and more clastic rich than surrounding laminites ichnofabrics and trace fossil assemblages which are dominated by burrows of deposit feeders thalassinoides suevicus meniscate backfilled structures and chondrites reflect normal softground substrates and quiet water pelagic deposition zoophycos ichnofacies differences in ichnologic parameters bed thickness adn presence diversity size and vertical extent of discrete burrows in primary strata and or piped zones among the bed types within this group reflect differences in magnitude duration and to a lesser extent frequency of oxygenationepisodes coincident increases in oxygenation and clastic content recorded by group 2 beds are attributed to e1 nino like climatic events gross temporal patterns in the intensity and frequency of these climatic events appear to be linked to the phases of a third order sea level cycle whereas shorter term variations 100 120 ka may have been mediated by milankovitch cyclicity relationships established between bioturbation events and relative water depth are of potential use in reconstructing basin paleogeography and or recognizing the signal of sea level change in the monterey formation and other neogene siliceous sequences

seasonal spreading of the persian gulf water mass in the arabian sea the characteristics of the subsurface salinity maximum associated with the persian gulf water mass pgw are used to quantify the spreading and mixing of pgw in the thermocline of the arabian sea based on a bimonthly climatology of temperature and salinity examination of the seasonal cycles of heat and freshwater fluxes in the persian gulf region indicates that pgw forms as a result of elevated evaporative cooling in conjunction with reduced insolation during winter maps are presented of the distributions of depth salinity and geostrophic flow on 26 5 which nearly coincides with the core of the pgw after intense mixing in the strait of hormuz the property fields suggest that warm 17 c and high salinity 36 2 psu pgw enters the arabian sea to form a subsurface salinity extremum between 200 and 300 m we have found variability in the distribution of pgw in the arabian sea associated with monsoonal changes in the arabian sea circulation during the winter monsoon there is southward spreading of pgw along the western boundary during summer it is not present lateral mixing with low salinity water from the bay of bengal in the region south of 10 n and along the west coast of india during winter accounts for changes in the characteristics of pgw along these paths associated with the findlater jet during summer the entire thermohaline structure is vertically displaced along the coasts of somalia and arabia ekman convergence in the central arabian sea accounts for deepening of the pgw either lateral or vertical mixing would cause changes in pgw properties in these regions during this time pgw spreads predominantly southward along the central arabian sea as indicated by a tongue of high salinity

a sedimentological model of organic matter preservation and phosphogenesis in the miocene monterey formation at haskells beach goleta central california abstract at haskells beach west of santa barbara ca u s a the upper part of the miocene monterey formation is predominantly composed of organic rich mudstone which is interstratified with phosphatic laminae and lenses minor lithologies consist of dolomite volcanic ash porcelanite chert and condensed phosphate these sediments date from the end of the serravallian and almost the entire tortonian 11 05 7 85 ma based on calcareous nannofossils and the 13 c org record which correlates well with the global record sediments have total organic carbon values between 2 75 and 9 15 wt average value 6 48 wt n 61 rock eval analyses show the dominance of type ii kerogen the sediment accumulation rate varied between 5 9 and 84 7 m ma correspondingly organic carbon accumulation rates range between 0 08 and 1 43 g cm 2 ky average value 0 48 g cm 2 ky total phosphorus contents in the organic rich mudstone vary between 0 001 and 3 48 wt and c org p org ratios show high values of up to 4727 average value 2232 whereas c org p total values are low up to 185 average value 52 this indicates that early diagenetic organic matter degradation was a source of phosphate in phosphogenesis in addition other sources of phosphate were necessary in order to explain the abundance of phosphate relative to organic matter such as the transfer of dissolved inorganic phosphate into the sediments slumps angular unconformities erosive surfaces reworked clasts and nodules and condensed phosphatic layers suggest that hydrodynamic conditions were important and likely variable leading to frequent erosion and sediment reworking under these circumstances organic matter was predominantly delivered during gravity flow events which were followed by longer periods of low sediment accumulation and phosphogenesis of the uppermost sediment layer associated pore occlusion by phosphate minerals may have considerably enhanced the preservation of organic matter during the early late miocene a progressive change is observed from the mixed accumulation of organic phosphate biosilica and carbonate sediments to the predominant accumulation of biosilica rich sediments this change is related to more intense upwelling a shift of the upwelling center to the californian coastline and a leveling out of basin topography leading to a more even spread of biosilica

paleoceanographic and tectonic controls on deposition of the monterey formation and related siliceous rocks in california abstract the timing of paleoceanographic and tectonic events that shaped the deposition of the monterey formation of california and related siliceous rocks has been determined by application of a refined biochronology the base of the monterey at 17 5 ma coincides with rising global sea level and a switch in biogenous silica deposition from the caribbean and low latitude north atlantic to the north pacific major polar cooling which began at 15 ma postdates the base of the monterey by more than 2 ma and cannot be invoked to cause the deposition of diatomaceous sediments occurring in the lowermost monterey later polar cooling in the early late miocene however apparently caused increased upwelling and deposition of purer diatomites in the upper monterey the top of the monterey at about 6 ma coincides with a major sea level drop and is commonly marked by an unconformity equivalent unconformities are widespread around the rim of the north pacific and typically separate more pelagic sediments from overlying sediments with a greater terrigenous component above the monterey diatoms persist in california sediments to 4 5 4 0 m y where their decline coincides with increased deposition of diatoms in the antarctic carbon isotope records in the pacific and indian oceans record storage of 12 c in the monterey formation and equivalent organic rich sediments around the rim of the north pacific a 1 0 excursion in 13 c beginning at 17 5 ma coincides with rising sea level and probably reflects storage of organic material in monterey like marginal reservoirs a reverse 1 0 shift at 6 2 ma closely approximates the top of the monterey and may represent erosion of these marginal reservoirs and reintroduction of stored organic carbon into the ocean atmosphere system initiation of transform faulting and extension in the california margin in the latest oligocene and early miocene caused the subsidence of basins which later received monterey sediments a major tectonic event centered at 10 9 ma which included rotation of the santa barbara basin and a change in pacific plate motion is recorded by an unconformity and or interval of compressed sediments in many monterey sections another change in plate motion at about 6 ma may be expressed by the angular discordance observed in many sections across the unconformity at the top of the monterey

widespread miocene deep sea hiatuses coincidence with periods of global cooling high resolution biostratigraphic analyses of miocene deep sea cores reveal eight intervals of widespread hiatuses in the world ocean at 23 0 22 5 20 0 18 0 16 0 15 0 13 5 12 5 12 0 11 0 10 0 9 0 7 5 6 2 and 5 2 4 7 m y ago in complete sections these hiatuses correspond to intervals of cool faunal and floral assemblages rapid enrichment of 18 o and sea level regressions these factors suggest that miocene deep sea hiatuses result from an increased intensity of circulation and corrosiveness of bottom currents during periods of increased polar refrigeration

neogene paleoceanographic events recorded in an active margin setting humboldt basin california abstract recognition of north pacific paleoceanographic events in the marginal humboldt eel river basin of northern california enables correlation of stratigraphic sections and development of a chronostratigraphy paleoclimatically related coiling shifts in neogloboquadrina pachyderma ehrenberg and benthic foraminiferal datums form the basis of the chronostratigraphy benthic foraminiferal datums are defined by the occurrence of selected benthic species and abundance maxima of benthic biofacies the compiled chronostratigraphy is used to refine reconstructions of the depositional history of humboldt basin paleoceanographic events recognized by the distribution of benthic foraminiferal biofacies are used to infer paleoceanographic history along the northeastern pacific margin the similarity in coiling curves of n pachyderma from the marine sequence at dsdp site 173 and the coastal centerville beach section of humboldt basin and at other independently dated sites along the northeastern pacific margin demonstrates that matching records of climatic oscillations is a reliable method of correlating marine sequences benthic fauna from the centerville beach section vary in phase with climatically related coiling shifts in n pachyderma in particular these data show an increase in displaced neritic fauna during inferred warm intervals and resurgence of deeper bathyal fauna during inferred cool events similar data are observed from the inland eel river section demonstrating that benthic foraminiferal trends recognized at centerville beach can be identified elsewhere in humboldt basin this in phase benthic response to climatic fluctuations probably results from changes in vertical depth range of many benthic species in response to paleoclimatically related vertical changes in water mass position depositional histories reconstructed for two key sites in southern humboldt basin indicate low rates of sediment accumulation during early basin filling with hemipelagic sediments initiation of turbidite sedimentation in the early pliocene resulted in a sharp increase in rate of sediment accumulation this increase in rate of sediment accumulation is partially a response to tectonic uplift in the northern coast ranges and may be an effect of realignment of motion between the pacific and north american plates at about this time the inland site shoaled more rapidly during turbidite sedimentation as a result of a higher rate of sediment accumulation the rate of sediment accumulation increased again at this site in the late pliocene during deposition of shelf and nearshore facies the eel river region subsided concurrent with deposition of these shallow water deposits

carbonaceous and phosphate rich sediments of the miocene monterey formation at el capitan state beach california u s a abstract the organic and phosphate rich interval of the monterey formation at el capitan state beach west of santa barbara california u s a late early to early late miocene in age is composed of a carbonaceous marl toc contents between 1 2 and 23 2 wt with intercalated phosphate rich laminae lenses and layers subordinate lithologies include ash layers dolomitized horizons and siliceous beds we distinguished five lithological units 1 a gray marl unit lacking major phosphate accumulations 16 3 ma average toc content 2 by weight average sedimentation rate 75 m my average toc accumulation rate 0 19 mg cm2 yr 2 a black marl unit including light colored phosphatic laminae lenses and discrete particles 16 3 14 5 ma average toc content 7 5 by weight average sedimentation rate 20 m my average toc accumulation rate 0 19 mg cm2 yr 3 a red marl unit including light colored phosphatic laminae lenses and commonly reworked particles 14 5 12 7 ma average toc content 15 by weight average sedimentation rate 20 m my 14 5 13 3 ma and 2 m my 13 3 12 7 ma respectively average toc accumulation rate 0 39 mg cm2 yr 14 5 13 3 ma and 0 04 mg cm2 yr 13 3 12 7 ma respectively 4 a unit of complex and condensed phosphatic beds interbedded with red marl 12 7 10 8 ma average sedimentation rate 3 m my and 5 a black marl unit with intercalated phosphatic laminae and lenses 10 8 ma average sedimentation rate 9 m my average toc accumulation rate 0 09 mg cm2 yr phosphogenesis and accumulation of phosphate were dynamic processes which started with local phosphogenesis leading to the formation of phosphatized particles as well as stratigraphically bound phosphogenesis leading to the formation of phosphate laminae and lenses phases of subsequent sediment reworking resulted in the concentration of phosphate particles in phosphate rich layers and repeated phases of sediment reworking and phosphogenesis ultimately resulted in the formation of the complex phosphate condensed horizons preservation of organic matter was favored by high productivity rates and by the development of dysaerobic bottom water conditions the dynamic sedimentary environment likely led to the formation of early diagenetic phosphatic lids which may have sealed off subjacent organic rich layers as well as to the rapid deposition of entire layers in the form of mud flows thereby eventually enhancing the potential of organic matter preservation our new age data suggest that at the el capitan state beach section the intervals characterized by high toc values and maximum toc accumulation rates red marl as well as significant quantities of in situ phosphates appeared in the late middle miocene i e during and after the major cooling phase at around 14 5 ma this implies that deposition of phosphate and organic carbon continued well after this cooling phase thereby underlining the observation that preservation of organic carbon in the monterey formation is not only dependent on climate change during the mid miocene but also on regional conditions

oceanic germanium silicon ratios evaluation of the potential overprint of temperature on weathering signals 1 diatom remains indicate the oceanic ge si ratio mmol mol has varied temporally ranging from miocene values of 0 9 to last glacial maximum lgm values of 0 55 with the present value of 0 69 these ratios lie between those for the primary sources for these elements continental weathering ge si 0 5 and hydrothermal fluids ge si 11 previous explanations for temporal variation have focused on variations in the relative strength of the primary inputs alternatively the cause may be temporal variation in the relative strength of the two sinks for ge opal and a nonopal sink found in margin sediments the importance of the latter depends on the rate of opal rain to the seafloor in margin environments as temperature decreases opal dissolution rates in the water column decrease permitting a larger fraction of the opal rain to reach the seafloor before dissolving this increases the rate of ge uptake into nonopal phases a model calculation predicts that a decrease of 3 5 c in lgm ocean temperature should increase opal rain to the margin seafloor by a factor of 1 5 an increase of 3 5 ci n miocene temperature should decrease rain by a factor of 0 6 the predicted changes for ge uptake in the nonopal sink can account for essentially all of the temporal ge si variation recorded in diatoms the absence of larger changes constrains silicate weathering rates relative to the present as 106 16 during the lgm and 88 12 during the mid miocene 15 20 ma however additional uncertainty exists because some factors of potential importance remain unconstrained index terms 0330 atmospheric composition and structure geochemical cycles 1050 geochemistry marine geochemistry 4835 4850 1886 hydrology weathering 1625 4845 oceanography biological and chemical nutrients and nutrient cycling 4267 oceanography general paleoceanography keywords germanium silicon weathering

formation and circulation of dense water in the persian arabian gulf 1 the nature and circulation of water masses in the persian arabian gulf hereinafter referred to as the gulf is investigated by examination of a historic database of hydrographic observations the densest water forms in winter at the northern end of the gulf rather than along the warmer southern and western coasts with the exception of small amounts of water directly above the seafloor most water flowing out of the gulf mixes across a density front that separates gulf deep water within the gulf from the indian ocean surface water iosw contrary to previous inferences the seasonally variable incursion of iosw into the gulf peaks in late spring this timing may be due to seasonal changes in sea surface slope driven by variations in evaporation rate in order to explain mooring results published elsewhere that show relatively small seasonal changes in the volume flux through the strait of hormuz hereinafter referred to as the strait we suggest that this flux is driven by the difference between the density of gulf deep water in the interior of the basin and water at comparable depths outside the gulf this density difference varies less than 15 during the year high rates of vertical mixing in the strait extend about 200 km westward in response to topographic constriction of tidal flows by islands and shoals

internal tides over a shelf break analytical model and observations abstract data collected on cruise ondine 85 organized by the service hydrophique et oceanographique de la marine at two points p1 and p6 near the continental shelf break of the bay of biscay show very large amplitudes of internal tides these waves exhibit a strong nonlinear character of the semidiurnal evolution of the thermocline depth during spring tide the internal oscillations can reach 80 meters in order to get an analytical solution for the interface depth variation near the top of the shelf break the two layer nonlinear model of generation and propagation of internal tides developed by maze is linearized in the present paper taking account of several monochromatic tides waves m2 s2 n2 k2 in the forcing term comparison between this analytical solution and data can be done over a six week period such a comparison shows that that the scale of the interface level and the time variation of the interface are quite well reproduced by the analytical model