interactions between sediment production and transport in the geometry of carbonate platforms insights from forward modeling of the great bank of guizhou early to middle triassic south china abstract carbonate platforms grow through the precipitation transport and final deposition of carbonate sediment out of seawater quantifying the relative contributions of initial production versus subsequent transport in determining the growth rates and geometries of platforms remains a significant challenge in this study stratigraphic forward modeling is used to quantify the roles of sediment production transport and deposition during each growth stage of a permian triassic carbonate platform with a complex growth history parameter optimization and sensitivity analysis show that within the range of reasonable values the morphology of the platform is most sensitive to sediment transport moderately sensitive to maximum carbonate production rate and least sensitive to the productivity depth curve the ramp to high relief steep sloped platform transition during early triassic time can be explained by any factor that limits sediment transport from shallow water areas of high production to the slope and basin reefs may play a role in limiting sediment transport on many platforms but other processes such as early marine cementation or carbonate production along the slope may be equally capable of yielding this shift in platform geometry in this particular case early lithification of ooid and skeletal shoals on the platform margin perhaps facilitated by unusually high carbonate saturation state of seawater may have inhibited sediment transport into the basin prior to the development of a reef on the platform margin later anisian progradation of the platform margin can be explained by the development of a slope factory rather than requiring increased sediment transport from the platform top the development of an escarpment margin in the ladinian is mainly influenced by accommodation in the slope profile created by antecedent anisian topography a general implication from the model results is that the growth of steep sloped carbonate platforms lacking slope factories may often be limited by transport of sediment from the platform top to accommodation on the slope rather than by the intrinsic production capacity of the platform top factory

circulation on the central bering sea shelf july 2008 to july 2010 1 we examine the july 2008 to july 2010 circulation over the central bering sea shelf using measurements at eight instrumented moorings hindcast winds and numerical model results at sub tidal time scales the vertically integrated equations of motion show that the cross shelf balance is primarily geostrophic the along shelf balance is also mainly geostrophic but local accelerations wind stress and bottom friction account for 10 40 of the momentum balance depending on season and water depth the shelf exhibits highly variable flow with small water column average vector mean speeds 5 cm s 1 mean peak speeds in summer 3 6 cm s 1 10 30 cm s 1 are smaller than in winter and fall 6 12 cm s 1 30 70 cm s 1 low frequency flows 1 4 cpd are horizontally coherent over distances exceeding 200 km vertical coherence varies seasonally degrading with the onset of summer stratification because effects of heating and freezing are enhanced in shallow waters warm summers increase the cross shelf density gradient and thus enhance northward transport cold winters with increased ice production and brine rejection increase the now reversed cross shelf density gradient and enhance southward transport although the baroclinic velocity is large enough to influence seasonal transports wind forced ekman dynamics are primarily responsible for flow variations the system changes from strong northward flow with coastal convergence to strong southward flow with coastal divergence for northerly and easterly winds respectively under northerly and northwesterly winds nutrient rich waters flow toward the central shelf from the north and northwest replacing dilute coastal waters that are carried south and west

low frequency current regimes over the bering sea shelf abstract using direct current measurements made during the period 1975 81 we describe the general circulation over the southeastern bering sea and differentiate it by regimes related to depth and forcing mechanisms three regimes are present delineated by water depth z the coastal z 50 m the middle shelf 50 z 100 m and the outer shelf z 100 m these are nearly coincident with previously described hydrographic domains statistically significant mean flow 1 to 10 cm s 1 exists over the outer shelf generally directed toward the northwest but with a cross isobath component flow of similar magnitude 1 6 cm s 1 occurs in the coastal regime paralleling the 50 m isobath in a counterclockwise sense around the shelf mean flow in the middle shelf is insignificant kinetic energy at frequencies 0 5 cycle per day cpd is greater over the outer shelf than in the other two regimes suggesting that oceanic forcing is important there but does not affect the remainder of the shelf kinetic

modeling global sea ice with a thickness and enthalpy distribution model in generalized curvilinear coordinates abstract a parallel ocean and ice model poim in generalized orthogonal curvilinear coordinates has been developed for global climate studies the poim couples the parallel ocean program pop with a 12 category thickness and enthalpy distribution ted sea ice model although the poim aims at modeling the global ocean and sea ice system the focus of this study is on the presentation implementation and evaluation of the ted sea ice model in a generalized coordinate system the ted sea ice model is a dynamic thermodynamic model that also explicitly simulates sea ice ridging using a viscous plastic rheology the ted model is formulated such that all the metric terms in generalized curvilinear coordinates are retained following the pop s structure for parallel computation the ted model is designed to be run on a variety of computer architectures parallel serial or vector when run on a computer cluster with 10 parallel processors the parallel performance of the poim is close to that of a correspon

the late permian to late triassic great bank of guizhou an isolated carbonate platform in the nanpanjiang basin of guizhou province china the late permian to late triassic great bank of guizhou gbg in southwest china is one of the few isolated carbonate platforms in the world that exposes an essentially complete record of initiation development and drowning across multiple platform to basin transects the platform is exceptionally exposed in cross section at the surface by a faulted syncline that rotated strata to a dip angle of approximately 65 platform development spanned the end permian extinction and triassic recovery that marks the transition from paleozoic to mesozoic styles of carbonate sediment production providing a rare opportunity to assess the impact of global changes in carbonate factory types at a single locality in addition regional basin controls such as differential siliciclastic sediment input and varied antecedent topography provided mechanisms for lateral variability in platform morphology that can be investigated along exposures in several geographic sectors consequently the gbg preserves a record of temporal and spatial variability in platform architecture that offers an unparalleled opportunity to investigate the controls on isolated carbonate platform morphology a better understanding of these mechanisms is critical for improving predictive geologic models in exploration and field development settings the gbg also serves as a key outcrop analog for early triassic oolite reservoirs in the middle east and china the steep microbial boundstone slopes of carboniferous platforms in kazakhstan and the permian platforms of texas and new mexico

factors influencing physical structure and lower trophic levels of the eastern bering sea shelf in 2005 sea ice tides and winds abstract in spring and fall 2005 cross and along shelf transects were sampled to evaluate the influence of physical forcing including sea ice tides and winds on the lower trophic levels of the bering sea ecosystem the hydrography nutrients chlorophyll and zooplankton abundance and species composition were all affected by the presence or absence of sea ice on a north south transect along the 70 m isobath in may shelf waters between 59 n and 62 n were cold and relatively fresh and benthic invertebrate larvae and chaetognaths were a significant fraction of the zooplankton community while to the south the water was warmer saltier and the zooplankton community was dominated by copepods the position of the transition between ice affected and ice free portions of the shelf was consistent among temperature salinity nutrients and oxygen this transition in the hydrographic variables persisted through the summer but it shifted 150 km northward as the season progressed while a transition also occurred in zooplankton species composition it was farther north than the physical chemical transition and did not persist through the summer mooring data demonstrated that the change in the position of the transition in physical and chemical properties was due to northward or eastward advection of water onto and across the shelf from south to north along the 70 m isobath tidal energy decreased resulting in a less sharply stratified water column on the northern portion of the middle shelf as opposed to a well defined two layered system in the southern portion this more gradual stratification in the north permitted a greater response to mixing from winds which were homogeneous from north to south thus the physical and biological structure at any one location over the middle shelf is dynamic over the course of a year and results from a combination of in situ processes and climate mediated regional forcing which is dominated in most years by sea ice

winter currents and hydrographic conditions on the northern central bering sea shelf current observations obtained from the northern bering shelf region in winter 1984 1985 indicate that midwinter circulation patterns differed from those during the rest of the year annual mean circulation in this region is dominated by vigorous northward currents from 10 cm s in shpanberg strait to more than 50 cm s in bering strait these northward currents are accompanied by a weak northwestward coastal flow south of st lawrence island in february april 1985 however flow was weakly 0 5 cm s southward through shpanberg strait and southeastward south of st lawrence island while remaining northward through anadyr and bering straits comparison with current data obtained from previous years suggests that midwinter reversal of flow in shpanberg strait is a recurrent winter feature it generally occurs at about the same time that the winter ice cover undergoes its major advance and it is associated with strong northerly winds northward flow through anadyr strait persists conversely through the winter and is the northward extension of a western intensified northward flow over the bering shelf its source is bering sea water farther south rather than water from the northern central shelf the resultant trapping of shelf water on the northern central shelf coupled with intensive regional ice formation during the same period as the flow reversal led in 1985 to significant about 1 5 brine enrichment this salinity increase agrees qualitatively with historical data which suggest that the northern central bering shelf is the site both of sluggish winter circulation and of elevated salinities due to brine enrichment from ice formation

subinertial currents on the southern califoinia shelf abstract subinertial currents on the southern california shelf are investigated using observations from a current meter array deployed near san diego during the summer fall and winter of 1978 79 this region is characterized by weak winds order 1 2 m s 1 and thus other driving mechanisms for the subinertial currents may be important a simplified depth averaged longshore momentum equation consisting of a balance between current accelerations the adjusted sea level asl gradient and the wind and bottom stress is examined the asl gradient is estimated using sea level and atmospheric pressure observations separated by 350 km a linear parameterization of the bottom stress is used with a drag coefficient of 5 10 4 m s 1 during fall and winter the first order balance of terms in the longshore momentum equation over the inner shelf 15 m depth is between the wind and bottom stress over the outer shelf 60 m the primary balance is between the asl gradient and the bottom stress at midshelf 30 m bo

the north pacific a global scale estuary abstract the atmospheric net flow of water from the atlantic to the pacific ocean is supposed to maintain the salinity difference between the two oceans assuming the existence of a subsurface level of no horizontal pressure gradient in the ocean the mean sea level in the northern pacific must be higher than in the arctic ocean this mean sea level difference is supposed to drive the observed mean flow through the bering strait the estimated flow of freshwater through the bering strait is approximately equal to the estimated atmospheric net flow of water from the north atlantic to the north pacific this justifies the formulation of a simple estuary model for the north pacific in which the brackish water exits through the bering strait the salinity difference between the two oceans is shown to be controlled by the topography of the bering strait the estuary model gives residence times for water in the upper layer 1000 m thick of approximately 1000 years and in the lower layer of approximately 400

timing of collision of the north and south china blocks controversy and reconciliation the qinling orogen was formed by the joining of the north and south china blocks but the timing of their integration has been debated for more than a decade the controversies obviously stem from different approaches to reconstruction of the integration history two contrasting lines of evidence yield two different ages for collision of the north and south china blocks middle paleozoic and late triassic the shangdan suture within the qinling was regarded in previous studies as the trace along which the north and south china blocks collided our studies however demonstrate that there are two sutures within the qinling the well documented shangdan suture and the newly discovered mianlue suture we show in this paper that the late proterozoic to early mesozoic evolution of the qinling involved interactions between the north china block the north and south qinling orogens and the south china block the middle paleozoic collision along the shangdan suture as constrained by some evidence accreted only the south qinling orogen to the southern part i e the north qinling of the north china block contemporaneous rifting of the south china block and subsequent drifting separated the south qinling from the south china block during the middle to late paleozoic the separation of the south from the north china blocks is supported by other evidence in particular geomagnetic data evidently it was the late triassic collision of the south china block with the south qinling orogen along the mianlue suture that led to final integration of the north and south china blocks

a numerical study of the circulation of the bering sea basin and exchange with the north pacific ocean abstract a limited area primitive equation three layer hydrodynamic model with realistic coastlines and bathymetry and resolution is used to investigate the circulation of the bering sea basin and the adjacent north pacific ocean the westward flowing alaskan stream to the south of the aleutian island chain is specified as a boundary condition at inflow and outflow ports with a constant throughput of 15 sv sv 1 106 m3 s 1 atmospheric forcing is based an the hellerman and rosenstein monthly climatological wind field the model is spun up over 50 years and the statistics of the final decade are described the general features of the model circulation as discussed below are consistent with available hydrographic and buoy drift observations the model alaskan stream separates from the aleutian island chain near 175 beyond this point there is strong interannual variability associated with meandering and occasional eddy shedding along the northern arm of the western subarctic gyre there is a gen

controls on facies architecture of a large triassic carbonate platform the great bank of guizhou nanpanjiang basin south china abstract the great bank of guizhou gbg is an exceptionally well exposed isolated triassic platform in the nanpanjiang basin of south china the platform is exhumed with its depositional profile preserved and is dissected by a faulted syncline that exposes a complete and uncomplicated cross section providing a unique opportunity to evaluate mechanisms involved in its birth evolution and demise the gbg formed near the southern margin of the yangtze platform during a deepening event that expanded the nanpanjiang basin and drowned the region surrounding the gbg in the latest permian initial accumulation of the gbg began in the latest permian with small reef mounds and open marine skeletal packstones following the end permian extinction cyanobacterial boundstones grew over the bank top during the early triassic the gbg developed a low relief bank profile with mobile oolite shoals at the margin shallow subtidal and peritidal deposits in the interior and gentle slopes dominated by pelagics debris flow deposits and turbidites at the basin margin in the middle triassic anisian the gbg developed a progressively steepening profile rimmed with massive tubiphytes reefs the platform was flat topped with tidal flat deposits across the interior basin margin deposition was dominated by turbidites and debris flow deposits but eventually shifted to avalanche and rock fall deposits as the slopes steepened to the angle of repose in the middle triassic ladinian an erosional escarpment up to 1700 m high developed at the margin platform margin strata are bedded packstones similar to interior strata whereas breccias at the basin margin contain coral boundstone clasts suggesting erosion of reefs from the escarpment a restricted subtidal lagoon formed in the interior producing an atoll like morphology later a flat topped profile was restored as tidal flats spread across the interior in the beginning of the late triassic deepening contributed to termination of the gbg before siliciclastic turbidites and shales were deposited over the platform in contrast with the well known platforms of the dolomites of northern italy the gbg contains abundant muddy carbonates and a progressively steepening bank to reef rimmed and escarpment architecture the italian platforms contain little mud and have angle of repose pinnacle geometries the gbg s larger size increased mud production and protected it from extensive winnowing of mud which in turn resulted in off bank shedding of muddy sediments that were stable on relatively gentle basin margin slopes which progressively steepened and ultimately led to avalanche deposits and a high relief erosional escarpment in contrast the lesser mud content of the dolomites platforms forced avalanche and talus deposition to dominate throughout deposition of basin margins which in turn produced their angle of repose geometries

nanpanjiang basin a window on the tectonic development of south china during triassic assembly of the southeastern and eastern asia abstract as the largest siliciclastic sink in the south china block the triassic nanpanjiang basin is generally thought of as a foreland basin related to indosinian collision between the south china and indochina blocks our basin analysis spanning an eight years period provides details of lopingian to middle triassic stratigraphic fill and tectonic subsidence of the basin field observation and sedimentological analyses reveal that the basin was not filled by a monotonous turbidite system and suggest instead the development of five primary depositional units constituted by deep water turbidite systems mass transport deposits condensed drapes shallow water isolated carbonate platforms and volcano volcaniclastic rocks the stratigraphic completeness of the basin the coexistence of widespread but localized carbonate platforms within axially filled deep water basin tectonically generated cyclothems of transverse mass transport deposits along intrabasinal faults and basin fill of extrusive rocks of bimodal composition together apparently call in question the claim that crustal shortening prevailed during the late permian to pre norian triassic patterns of basin fill differential tectonic subsidence and very high subsidence rate of the region adjacent to master fault are more closely match the pattern expected for extensional to transtensional basin in a back arc setting the crustal extension in the southwestern south china was not consistent with hypothesized indosinian collision between south china and indochina blocks but more likely developed in response to northwestward subduction of the paleo pacific plate our results combined with regional considerations lead to a new model for the triassic tectonic evolution of south china during triassic assembly of the southeastern and eastern asia

observations of the aleutian north slope current bering sea 1996 2001 1 cyclonic circulation dominates flow in the bering sea basin the eastward flowing aleutian north slope current ansc flows along the north slope of the aleutian islands turning northwestward in the southeast corner of the basin to form the bering slope current bsc during the period 1997 to 2007 a pair of hydrographic lines was occupied 14 times in the southeastern portion of the basin one transect was across the ansc and the second was across the bsc in addition a series of five yearlong moorings was deployed in a water depth of 1000 m in the ansc and a single yearlong mooring was deployed to the northeast in a water depth of 2200 m at the primary mooring site strong variability in temperature and salinity occurred at fortnightly and annual periods while strong variability in the currents occurred at fortnightly and semiannual periods the mean geostrophic flow relative to 1500 m calculated from the 14 occupations of the hydrographic lines was 3 1 106 m3 s 1 in the ansc and 3 3 106 m3 s 1 in the bsc a significant barotropic component measured by the current meters adds 3 106 m3 s 1 to the transport

on exchange of water between the gulf of alaska and the bering sea through unimak pass we present the first long term current and bottom pressure observations from unimak pass alaska and adjacent locations on the gulf of alaska and bering sea shelves vector mean current recorded between march and august 1980 was 12 cm s toward 284 t or onto the bering sea shelf however magnitude decreased from 20 cm s to 6 cm s between the first and second halves of the record at shorter periods 3 10 days current fluctuations in the pass were strongly coherent k2 0 7 with the pressure difference measured along the axis of the pass and this was coherent with geostrophic wind estimates the results indicated that wind induced sea level perturbation was the dominant forcing mechanism for fluctuations relations among current bottom pressure pressure difference and geostrophic wind time series also showed that dynamic variaton on the gulf of alaska shelf was primarily responsible for current fluctuations in the pass hydrographic data indicated that a baroclinic current existed along the gulf of alaska coast and this flow became the long term mean flow through the pass we suggest that this feature was the extension of the kenai current the historic supposition that water is transported from the gulf of alaska into the bering sea was verified however the waters are of coastal origin rather than from the alaskan stream

construction of an oceanic island insights from the el hierro canary islands 2011 2012 submarine volcanic eruption eight consecutive swath bathymetry data sets were obtained to monitor the submarine eruption that occurred from 10 october 2011 to 5 march 2012 south of el hierro island in the canary islands an increase in seismic activity since july 2011 preceded the onset of the eruption which was marked by seismic tremor and stained waters the first bathymetry 15 d after the eruption started depicts a cone topping at 205 m depth growing on a preexisting valley recurrent mapping shows changes in the morphology and depth of the cone allowing us to identify collapses and calculate eruptive volumes and rates which peaked at 12 7 10 6 m 3 d 1 of non dense rock equivalent ndre on 29 30 october the final cone consists of at least four vents along a north northwest south southeast lineation with the shallowest summit at 89 m depth the total accumulated volume was 329 10 6 ndre m 3 of which one third formed the cone similar cones have been identified on the submerged flanks of the island with volumes ranging from 6 to 1000 10 6 ndre m 3 as in many other volcanic islands large scale landslides play an important role in the evolution of el hierro a giant flank landslide el golfo 13 134 ka 150 180 km 3 mobilized in a single event a volume equivalent to 450 550 eruptions of the size of the reported one showing striking differences in the construction and destruction rates of the island this study is relevant for future monitoring programs and geohazard assessment of new submarine eruptions

stratification on the eastern bering sea shelf revisited abstract the timing and magnitude of stratification can have profound influences on the marine ecosystem on the eastern bering sea shelf in the absence of strong wind mixing stratification can be initiated by the melting of seasonal sea ice or by springtime warming of the surface temperature and salinity both influence the stratification of the eastern bering sea shelf with their relative importance varying spatially and temporally in the northern middle shelf domain north of 60 n salinity stratification is often as important as temperature stratification on the southern middle shelf while the influence of temperature on stratification dominates during summer the influence of salinity stratification plays a role in the interannual variability mooring 2 m2 56 9 n 164 1 w has been deployed at 70 m depth in the southern middle shelf domain since 1995 data from this mooring show that stratification typically begins to set up in may and to break down in september october but these dates can vary by 30 d while no trend is found in the timing of the spring setup the fall stratification breakdown exhibited a trend toward later breakdown 2 d later per year from 1996 to 2009 results suggest that it may be difficult to forecast stratification on the eastern bering sea shelf from climate models as simple indices of wind mixing or heat fluxes are not correlated with stratification contrary to intuition the strength of summer stratification is not correlated with depth averaged temperature warm years such as 2000 and 2001 can have low stratification and cold years such as 2007 can have very high stratification this decoupling of stratification and temperature has implications for forecasting the ecosystem in the face of climate change as we cannot assume that projections of a warmer climate simply imply higher stratification in the future

transport through unimak pass alaska we examined inflow through unimak pass 200 m deep which is the only major connection between the shelves of the north pacific ocean and the eastern bering sea geostrophic transport was generally northward from the gulf of alaska into the bering sea the flow through the pass appeared to be modulated by the seasonal cycle of freshwater discharge on shorter time scales transport also was affected by semi daily variations in tidal mixing this effect was significant and not anticipated near bottom currents measured from moorings were maximum during winter and significantly correlated r 0 7 with the alongshore winds although the flow through unimak pass transported some nutrients from the north pacific ocean the gulf of alaska shelf is not the major source of nutrients to the bering sea shelf

observations of topographic planetary waves in the bering slope current using the geosat altimeter topographic planetary waves associated with the downstream leg of the bering slope current are observed in measurements of sea surface height anomalies acquired by the geosat altimeter during 1987 and 1988 the waves are most prominent from may to august 1987 during which time the estimated wave period and wavelength are about 72 days and 103 km respectively the direction of propagation is roughly north northeast

aleutian basin of the bering sea thermohaline oxygen nutrient and current structure in july 1993 an overview is given of the surface to bottom thermohaline oxygen nutrient and baroclinic flow structures in the aleutian basin of the bering sea and the adjacent north pacific based on high resolution field measurements in july 1993 a basic four layer vertical structure is observed in the upper 1500 m the 30 m top layer is warm low in salinity and nutrients and high in oxygen beneath it a 100 to 150 m thick temperature minimum layer is found believed to be a remnant of winter convection this is followed by a 300 m thick warm layer in which the main halocline oxycline and nutricline are located below it lies a layer of minimum oxygens and maximum nitrates and phosphates centered at a depth of 900 m in the bering sea but rising to 400 m south of the aleutians this basic structure is disrupted in the vicinity of amchitka pass due to strong tidal mixing the deep and abyssal waters of the aleutian basin differ substantially from those at comparable depth in the adjacent pacific by being warmer 0 1 c less saline 0 01 less dense 0 01 kg m3 poorer in oxygen 50 mol kg and richer in silicates 80 mol kg nitrates 1 0 mol kg and phosphates 0 3 mol kg the highest silicate concentrations 240 mol kg occur at the foot of the bering shelf unusual hydrographic conditions exist in an isolated tidal mixing basin in amchitka pass where the bottom mixed layer is 600 m thick 0 7 c warmer 0 14 less saline and 21 mol kg less oxygenated than at comparable depths outside baroclinic currents indicate strong deep jetlike flows on both sides of the aleutian ridge weak shallow eddies in the middle of the aleutian basin and somehat enhanced flows near the bering shelf edge the alaska stream in july 1993 was 100 km wide had a double core with a top speed of 0 54 m s and had a westward volume transport of 38 sv with 14 sv below 1000 dbar the north aleutian current had a speed of 0 2 m s and an eastward transport of 10 sv with 4 sv below 1000 dbar off the bering slope both eastward and westward flows were observed with volume transports near 7 sv

on the processes controlling shelf basin exchange and outer shelf dynamics in the bering sea abstract we use a 9 km pan arctic ice ocean model to better understand the circulation and exchanges in the bering sea particularly near the shelf break this region has historically been undersampled for physical chemical and biological properties very little is known about how water from the deep basin reaches the large shallow bering sea shelf to address this we examine here the relationship between the bering slope current and exchange across the shelf break and resulting mass and property fluxes onto the shelf this understanding is critical to gain insight into the effects that the bering sea has on the arctic ocean especially in regard to recent indications of a warming climate in this region the bering sea shelf break region is characterized by the northwestward flowing bering slope current previously it was thought that once this current neared the siberian coast a portion of it made a sharp turn northward and encircled the gulf of anadyr in an anticyclonic fashion our model results indicate a significantly different circulation scheme whereby water from the deep basin is periodically moved northward onto the shelf by mesoscale processes along the shelf break canyons along the shelf break appear to be more prone to eddy activity and therefore are associated with higher rates of on shelf transport the horizontal resolution configured in this model now allows for the representation of eddies with diameters greater than 36 km however we are unable to resolve the smaller eddies

lower triassic oolites of the nanpanjiang basin south china facies architecture giant ooids and diagenesis implications for hydrocarbon reservoirs lower triassic platforms in the nanpanjiang basin contain extensive oolites interior oolites are stacked in meter scale cycles arranged into larger coarsening upward sequences oolites thicken toward margins to include grainstones up to 50 m 164 ft thick and contain giant ooids up to 1 cm 0 4 in and composite coated grains cross bedding ripples and abraded ooids indicate deposition in high energy shoals apparent layer cake correlation across interiors indicates amalgamation of shoals thinner interior lenses represent spillover lobes ooids are interpreted to have originally been bimineralic with cortices of radial or micritic fabrics high magnesium calcite alternating with coarse pseudospar or brickwork originally aragonite distorted ooids formed by brittle compaction of micritic cortices around voids are interpreted to have been dissolved aragonite abundant potential nuclei indicate that limited supply was not a factor contributing to the large ooid size high energy and abnormally high seawater caco3 saturation are interpreted to be causes of the giant ooids most previous reports of giant ooids come from the neoproterozoic a period of increasing surface water oxygenation and high caco3 saturation caused by a minimal skeletal carbonate precipitation we interpret similar seawater chemistry in the aftermath of the end permian extinction to explain the genesis of the giant ooids in the early triassic the genesis of bimineralic ooids during an early triassic period of rapidly increasing pco2 and low indicates that an increasing ca mg ratio was the primary mechanism driving the change from aragonite to calcite seas the architecture textures and diagenesis of the lower triassic oolites of the nanpanjiang basin provide useful analogs for coeval reservoirs in sichuan and the middle east

early triassic calcimicrobial mounds and biostromes of the nanpanjiang basin south china stanley s model 1988 proposed that a permiantype reef fauna survived the early triassic reefless period in yet undiscovered refuges in the ancestral pacific ocean and then reappeared as the builders of middle triassic reefs flugel 1994 in contrast suggested that the middle triassic reefbuilding fauna are not holdovers from the permian but bear only a superficial resemblance to permian fossils recent publications reflect a consensus that the early triassic lacked reefs and reef mounds although some authors acknowledged the possibility that reef like structures may have existed in poorly explored areas such as south china and russia senowbari daryan et al 1993 flugel 1994 it is shown herein that calcimicrobial framework mounds and biostromes existed in the early triassic in the nanpanjiang basin of south china organic framework in this paper refers to a three dimensional biologically constructed network of calcified fossils that forms a rigid mass and supports an interconnected network of internal cavities that were open during accumulation although the calcimicrobial frameworks discussed herein are much smaller than frameworks of modern metazoan reefs the term framestone is more appropriate for these fabrics than other reef rock terms such as bindstone or bafflestone embry and klovan 1971 these calcimicrobial mounds and biostromes are important as the first organic framestones documented from the early triassic

tidal currents in the st lawrence island region 1 vertical and spatial variability of tidal currents in the northern part of the bering sea near st lawrence island were examined using observations made at 17 new and historical current meter mooring locations the semidiurnal currents dominate over the diurnal currents semidiurnal currents exhibit a seasonal modulation with currents being somewhat stronger during the summer and fall when the density structure displays two layer stratification diurnal currents exhibit a weak semiannual modulation examination of the vertical structure of tidal currents shows that maximum semidiurnal currents are observed in the upper or middle layers down to a depth of about 20 m and below this depth the energy of the semidiurnal currents decreases rapidly however the energy of diurnal band currents remains almost constant with depth decreasing only in close proximity to the bottom rotary spectral analysis applied to the records shows further differences the m2 clockwise cw component of rotation dominates in the upper and middle water column but the counterclockwise component ccw dominates near the bottom interpretation of these observed results points to the different bottom boundary layers bbl for the cw and ccw motions in addition to the role of density stratification in organizing the bbl we compare results of a vertically averaged two dimensional model to the observationally derived tidal ellipse parameters and show that the barotropic formulation provides a first order description of the tidal regime within the domain

ocean circulation and exchanges through the northern bering sea 1979 2001 model results abstract we have developed and run a model with sufficiently high resolution 9 km and 45 levels and a large enough spatial domain to allow for realistic representation of flow through the narrow and shallow straits in the northern bering sea this is potentially important for quantification of long term mean and time dependent ocean circulation and water mass and property exchanges between the pacific and arctic oceans over a 23 year interval 1979 2001 mean transport through bering strait is estimated to be 0 65 sv comparison of our model results with published observations indicates that ocean circulation is not only variable at seasonal to interdecadal scales but it is also responsive to short term atmospheric forcing one of such events occurred during the winter of 2000 2001 with reversed oceanic flow in some areas and much reduced sea ice cover analyses of eddy kinetic energy fields identify some high biological productivity regions of the chirikov basin coincident with persistent high energy up to 2700 cm 2 s 2 in the surface layer and up to 2600 cm 2 s 2 at mid depth throughout the annual cycle model output in the bering strait region is validated against several time series of moored observations of water mass properties comparison with shipboard observations of near bottom salinity from late winter through autumn indicates that the model reasonably represents the major water mass properties in the region the modeled vertical water column structure in the northern bering sea allows increased understanding of the mechanisms of water transformation and transport northward through bering strait into the chukchi and beaufort seas we conclude that the long term model results for the northern bering sea provide important insights into the ocean circulation and fluxes and they are a useful frame of reference for limited observations that are short term and or cover only a small geographic region

northward flow in the bering and chukchi seas the ocean circulation on the bering and chukchi sea shelves is investigated using a barotropic numerical model in the presence of the winter seasonal wind stress from the northeast observed northward transport through bering strait of 0 6 sv for the 8 month winter season 1981 1982 can be driven by a sea level difference of 0 4 m between the pacific and arctic oceans this sea level difference between basins is in agreement with hydrographic estimates in the absence of wind stress a 0 4 m sea level difference drives a northward transport through bering strait of 1 1 sv maximum transport through bering strait is geostrophically limited not frictionally or inertially limited major qualitative circulation features of the region are evident in the simulations westward intensification of the northward transport across the bering sea shelf is confirmed with the major transport occurring in the relatively deep gulf of anadyr in the absence of wind anadyr strait contributes 72 of the northward transport through bering strait with northeasterly winds there is a net clockwise circulation around saint lawrence island within the 20 m isobath norton and kotzebue sounds are little influenced by the general circulation northward transport in the chukchi sea bifurcates in the vicinity of point hope the predominant branch is directed toward the northwest in a broad canyon feature south of herald shoal and the balance becomes the alaskan coastal current between cape lisburne and point barrow

characteristics of currents over the continental slope of the eastern bering sea between september 1989 and 1990 twenty six current records were collected by instruments on eight moorings located in pribilof and zhemchug canyons and at a site midway between these features these records provide the first long term eulerian measurements from the slope and mid slope of the eastern bering sea results from the current records together with water property observations permit a characterization of the bering slope current moderate flow 2 to 18 cm s 1 followed the bathymetry toward the northwest and existed primarily in the upper 300 m wind and current energy increased in winter but vector mean current did not increase at all sites wind forcing accounted for only a small fraction of the current fluctuations at one mid slope location in pribilof canyon bathymetry resulted in rectification of the strong daily tidal current estimates of heat and salt fluxes indicate some significant shoreward transport however this flux did not occur preferentially in the canyons

circulation in the bering sea 1982 83 based on satellite tracked drifter observations abstract a satellite tracked drifting buoy deployed unintentionally in the bering sea in 1982 completed a circuit of that basin in about one year during its cyclonic passage around the bering sea it experienced many different flow regimes ranging from steady alongshelf motion at the shelf break to highly variable tidal flow on the shelf itself the buoy trajectory differs from previous descriptions of the deep bering sea circulation because it moved southwestward in the central bering sea rather than along the western boundary as other depictions have suggested many of the bering sea mesoscale eddies reported earlier were evident indicating that possibly these eddies are permanent features the forces which caused the buoy to move between the various flow regimes are unclear but the data suggest an annual period for the deep bering sea circulation

variability of physical and chemical characteristics along the 70 m isobath of the southeastern bering sea abstract from observations of ice cover temperature salinity currents and nitrate it is evident that along shelf variability was significant over the middle shelf of the eastern bering sea but less distinct than that observed in the cross shelf domains along the 70 m isobath three zones were evident in the summer the southeastern cold pool centered at 57 n an intermediate zone consisting of warmer water with weaker stratification and the northern cold pool extending northward from 58 n small scale 20 km horizontal features that persisted for months were common nutrient concentrations were related to salinity and were replenished more uniformly over the southern shelf than north of the pribilof islands although mean currents were weak 1 cm s 1 short energetic advective events impacted the temperature and salinity structure

characteristics and variability of the inner front of the southeastern bering sea the inner front of the southeastern bering sea shows marked spatial variability in frontal characteristics created by regional differences in forcing mechanisms differences in forcing mechanisms sea ice advance retreat and storm strength and timing and early spring water properties result in strong interannual variability in biological chemical and physical features near the front we have developed a simple model based on surface heat flux and water column mixing to explain the existence of cold belts cont shelf res 19 14 1999 1833 associated with such fronts hydrography fluorescence and nutrient observations show that pumping of nutrients into the euphotic zone occurs and this can prolong primary production at the inner front the effectiveness of this process depends on two factors the existence of a reservoir of nutrients in the lower layer on the middle shelf and the occurrence of sufficient wind and tidal energy to mix the water column

impact of differential tectonic subsidence on isolated carbonate platform evolution triassic of the nanpanjiang basin south china the nanpanjiang basin of south china contains four exceptionally well exposed isolated triassic carbonate platforms detailed mapping of two dimensional transects and description of stratigraphic sections allow the reconstruction of facies architecture sequence stratigraphy and evolution of the platforms biostratigraphy magnetic susceptibility profiles and volcanic ash horizons allow chronostratigraphic correlation and thus a basinwide evaluation of mechanisms controlling platform evolution a comparison of platform architecture demonstrates that southerly platforms have substantially greater thickness backstepping geometry pinnacle development and earlier drowning that resulted from greater tectonic subsidence proximal to a probable convergent margin along the southern perimeter of the basin felsic volcanics thicken southward and contributed to the termination of the southernmost platform indicating the development of a volcanic arc along the southern margin of the south china tectonic block the northernmost isolated platform had greater longevity and lesser accumulation and lacks backstepping and pinnacle phases of development basin margin intertonguing relationships or lack thereof demonstrate that earlier siliciclastic influx into the basin to the south and concurrent starved basin conditions to the north impacted the evolution of platform margin geometries comparative analysis of platform evolution shows that the timing and rates of tectonic subsidence controlled the timing of platform termination by drowning backstep geometries pinnacle development and overall platform thickness the timing of siliciclastic basin fill dictated differences in platform margin geometries such as slope angle relief above basin floor and the presence or absence of basinward platform progradation despite the dramatic differences in platform architecture eustatic sea level fluctuations imparted a basinwide sequence stratigraphic signal

spatial and temporal characteristics of the wind forcing of the bering sea abstract the surface wind stress over the bering sea is estimated for the period 1946 90 from sea level pressure analyses empirical relationships between the geostrophic wind and the surface wind and a bulk aerodynamic formula the focus is on the propagation and variability of the stress and the curl of the stress as a function of frequency the stress at high frequencies 0 1 cpd is dominated by northward and eastward propagating disturbances with mean wavelengths of 2500 and 10 000 km respectively at periods of 10 100 days the mean propagation is near zero there are however significant interannual variations in the zonal propagation wind driven ocean transports estimated by the sverdrup method for the deep bering basin account for 6 sv or roughly one half of the observed transport within the western boundary current along the kamchatka peninsula a low pass filtered retaining periods greater than 18 months time series of the sverdrup transport exhibits a standard deviation of 25 of th

some controls on flow and salinity in bering strait 1 during 1993 1994 steric forcing of flow through bering strait represented a northward sea level drop of 0 7 m from the bering sea basin to the adjacent deep arctic ocean of which 2 3 was due to the salinity difference between the basins seasonal variability of steric forcing appears small 0 05 m in contrast to large seasonal wind effects interannual changes in steric forcing may exceed 20 however and warm inflow from the north atlantic accumulation of freshwater in the southwest canada basin and temperature and salinity changes in the upper bering sea have all contributed to recent changes the mean salinity balance in bering strait is primarily maintained by large runoff to the bering shelf dilute coastal inflow from the gulf of alaska and on shelf movement of saline and nutrient rich oceanic waters from the bering sea basin in bering strait therefore both the throughflow and its salinity are affected by remote events

observations of ice thickness and frazil ice in the st lawrence island polynya from satellite imagery upward looking sonar and salinity temperature moorings 1 for the 1999 winter this paper examines the behavior of the bering sea st lawrence island polynya using a combination of advanced very high resolution radiometer avhrr radarsat synthetic aperture radar sar meteorological data over winter moored upward looking sonars uls and seabird salinity temperature sensors we define a thermal ice thickness from the avhrr retrieval of ice surface temperature combined with meteorological observations and a heat flux model south of the island we compare the uls and thermal thicknesses for congelation and frazil ice when the satellites observe congelation ice over the ulss the uls and thermal ice thicknesses generally agree when sar observes langmuir plumes over the ulss which indicate frazil ice formation the ulss show scatterers at 5 20 m depths in the water column and the seawater temperatures are either within 0 01 c of freezing or are slightly supercooled this suggests that during frazil events crystals either nucleate at depth or are transported to depth by the langmuir circulation the combination of the sar imagery and uls observations also allow measurement of the pack ice advection velocity the polynya width and the downwind frazil accumulation thickness giving widths of 10 to 30 km and thicknesses of 0 1 0 2 m substitution of these observed values with the heat flux into the pease polynya model yields polynya widths that approximately agree with the observed