effects of sediment supply on surface textures of gravel bed rivers using previously published data from flume studies we test a new approach for quantifying the effects of sediment supply i e bed material supply on surface grain size of equilibrium gravel channels textural response to sediment supply is evaluated relative to a theoretical prediction of competent median grain size d9 50 we find that surface median grain size d50 varies inversely with sediment supply rate and systematically approaches the competent value d9 at low equilibrium transport rates furthermore equilibrium transport rate is a power function of the difference between applied and critical shear stresses and is therefore a power function of the difference between competent and observed median grain sizes d9 and d50 consequently we propose that the difference between predicted and observed median grain sizes can be used to determine sediment supply rate in equilibrium channels our analysis framework collapses data from different studies toward a single relationship between sediment supply rate and surface grain size while the approach appears promising we caution that it has been tested only on a limited set of laboratory data and a narrow range of channel conditions

observational evidence for a southern hemisphere oceanic supergyre 1 a high resolution hydrographic atlas resolves the narrow boundary flow of the western pacific gyre and its pathway around tasmania southern australia and into the indian ocean basin this confirms recent model descriptions of a southern hemisphere supergyre a nested system of subtropical gyres the observations show that the gyre flow is squeezed into a narrow band between tasmania and the antarctic circumpolar current the residue of east australian current transport turns westward around tasmania and leaks into the indian ocean while there is also a limited form of gyre connection between the indian and atlantic systems south of africa with a mean outflow of agulhas current water into the atlantic basin these gyre circulations remain far more discrete the gyre coupling and the east australian current in particular provide the mechanism by which sub antarctic mode water and antarctic intermediate water are distributed between the ocean basins

recent changes in the pacific subtropical cells inferred from an eddy resolving ocean circulation model abstract in this study the subtropical cells stc in the pacific ocean are analyzed using an eddy resolving ocean general circulation model driven by atmospheric forcing for the years 1992 2003 in particular the authors seek to identify decadal changes in the stcs in the model and to compare them with observations in order to understand the consequences of such changes for the equatorial ocean heat and mass budgets the simulation shows a trend toward increasing pycnocline volume transport at 9 n and 9 s across the basin from 1992 to 2003 this increase 4 9 1 0 sv sv 106 m3 s 1 is in qualitative agreement with observations and is attributed primarily to changes in the interior ocean transport which are partially compensated by opposing western boundary transports the subtropical meridional volume transport convergence anomalies in the model pycnocline are found to be consistent with anomalous volume transports in both the observed and modeled equatorial undercurrent as well as with the magni

facies and depositional processes in an upper jurassic to lower cretaceous pelagic sedimentary sequence antarctica the nordenskjold formation oxfordian berriasian age is exposed on the east coast of the antarctic peninsula where it consists of interbedded ash layers and biosiliceous mudstones which accumulated under anaerobic to dysaerobic bottom waters the mudstones were deposited by pelagic settling and the ash layers by pelagic settling from suspension or as fallout from subaerial eruption columns the lower part of the succession accumulated in a basinal setting under anaerobic bottom waters and is characterized by parallel bedding mudstones deposited in this setting preserve abundant zooplankton faecel pellets compaction of these pellets has given rise to a bedding parallel fissility the upper part of the succession accumulated under dysaerobic bottom waters in a slope setting the sequence is wavy bedded and contains abundant evidence of post depositional sediment instability and resedimentation much of which was caused by tectonic activity discrete slide masses are absent from the slope sequence and it appears that slope processes were dominated by creep examination of the mudstones shows that as levels of dissolved oxygen in bottom waters increase pelleted mudstones give way to structureless mudstones before visible bioturbation is noted

kinematics of the pacific equatorial undercurrent an eulerian and lagrangian approach from gcm results abstract three dimensional monthly velocity fields from an ocean general circulation model are used to study the annual mean mass balance of the pacific equatorial undercurrent euc eulerian diagnostics are used to evaluate the various meridional vertical and zonal mass fluxes related to the euc there are several distinct regimes along the equator showing clear asymmetries between the western and eastern parts of the basin and between the northern and southern edges of the euc meridional fluxes are decomposed into pure ekman divergence and geostrophic convergence and it is shown that the asymmetries are mainly related to the spatial structure of the ekman divergence and thus to that of the trade winds lagrangian calculations are used to evaluate accurately the mass transfers between various sections of the euc and between the euc domain and the tropics the authors show that geostrophic convergence only ventilates the upper layers of the euc and that the euc really is a tongue of water flowing

water masses labeled with global fallout 137cs formed by subduction in the north pacific 1 we provide a first cross section of the 137 cs concentration along 165 e longitude in the western north pacific the 137 cs profile is characterized by several subsurface cores with high 137 cs including two 137 cs concentration maxima at 20 n one at 250 m 25 5 and one at 400 500 m 26 0 depths the shallower maximum is in the density range of north pacific subtropical mode water npstmw and the deeper one is in the density range of lighter central mode water lcmw the main 137 cs cores therefore were formed by movements of npstmw and lcmw in the interior ocean during the past four decades the 137 cs has been transported from subarctic region to subtropics and tropics as a result of subduction

cross equator transport of 137cs from north pacific ocean to south pacific ocean beagle2003 cruises abstract the anthropogenic radionuclides such as 137 cs 90 sr 99 tc 129 i and some transuranics are important tracers of transport and biogeochemical processes in the ocean 137 cs with a half life of 30 years a major fission product present in a dissolved form in seawater is a good tracer of oceanic circulation at a time scale of several decades at woce p6 line along 30 s during the beagle cruise in 2003 surface seawater around 80 l was collected a few meters below the ocean surface by a pumping system water column samples from 5 to 20 l were collected using a rosette multisampling system and niskin bottles 137 cs was separated from seawater samples using ammonium phosphomolybdate amp and analysed for 137 cs in low level hpge gamma ray spectrometers results allowed to draw a detailed picture of the distribution of 137 cs in the south pacific ocean along p6 line a 137 cs depth section was depicted from about 160 samples 137 cs concentrations in the subsurface layers ranged from 0 07 0 04 bq m 3 to 1 85 0 145 bq m 3 high in the tasman sea and very low in the eastern region where upwelling occurs water column inventories of 137 cs from surface to 1000 dbar depth ranged from 270 104 to 1048 127 bq m 2 it was concluded that the source of higher 137 cs concentration and inventories in the tasman sea was 137 cs deposited in the mid latitude of the north pacific ocean and transported across the equator during four decades

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

phosphorus accumulation rates in a miocene low oxygen basin the monterey formation pismo basin california abstract phosphorus p limits oceanic productivity on long time scales and therefore determining changes in oceanic p accumulation through time is important for modeling oceanic paleoproductivity we determined p concentrations and accumulation rates at shell beach california a section of phosphatic rich marine sedimentary rocks which includes the widespread phosphatic and siliceous facies of the monterey formation phosphorus concentrations had wide ranges in the major lithologies found in these facies with values in phosphatic shales ranging from 0 36 to 3 9 wt compared to 0 02 to 0 42 wt in dolomitic and siliceous strata phosphorus accumulation rates in mol p cm 2 yr 1 for all values reported here showed significant variability with both sample lithology and position in the section phosphorus accumulation rates were much higher in phosphatic shale strata 1 5 29 than in dolomitic and siliceous strata 0 1 3 1 in both facies furthermore p accumulation rates were generally higher in phosphatic shale strata of the upper siliceous facies 3 1 29 compared to the lower phosphatic facies 1 5 14 mean p accumulation rates calculated using linear sedimentation rate models for each facies and observations of the relative amount of phosphatic shale dolomite and siliceous strata are comparable between the portions of phosphatic and siliceous facies studied this indicates that the two facies with their faunal and sedimentological characteristics considered to reflect major oceanic and climatic changes during the middle miocene are similar in terms of p burial total p accumulation rates are also comparable to other phosphogenic miocene and modern environments we modeled variable sedimentation rates to examine the sensitivity of mean p accumulation rates to the linear sedimentation rate assumption increasing shale sedimentation rates to values above those estimated by linear models yields higher mean p accumulation rates in both facies though they remain comparable in terms of net p burial modeling also revealed that for increased shale sedimentation rates in each facies siliceous sedimentation must be about three times faster than dolomitic strata sedimentation

an eddy resolving numerical model of the ventilated thermocline abstract a three dimensional primitive equation numerical model is used to study the effects of mesoscale eddies within the subtropical thermocline solutions are obtained for an ocean bounded by idealized topography are driven by simple wind and buoyancy forcing at the surface results using an eddy resolving fine grid are compared to those using a noneddy resolving coarser grid relatively little difference is realized in the basic mean flow patterns of the two solutions however more significant differences are seen in the distributions of a passive tracer and the potential vorticity mixing by eddies in the westward flowing sector of the subtropical gyre is quite effective in homogenizing these quantities on isopycnals whereas previous theory has predicted homogenization of potential vorticity on long time scales within recirculating gyres the present model demonstrates homogenization on a much shorter time scale across recirculating ventilating flow boundaries anomalous potential vorticity th

decadal variability of the subtropical front of the western north pacific in an eddy resolving ocean general circulation model 1 we examined decadal variability of the subtropical front stf of the western north pacific by using a north pacific ocean general circulation model ogcm comparing the results of three simulations with different horizontal resolutions in the long term mean fields the eddy resolving model 10 km was able to simulate the distributions of the stf and the associated subtropical countercurrent stcc between 20 n and 30 n better than either the non eddy resolving model 100 km or the eddy permitting model 20 km because it simulated the kuroshio recirculation gyre more realistically the simulated stf intensity exhibited significant decadal scale variations it was stronger in the late 1970s and weaker in the early 1990s during these two periods the simulated mode waters showed corresponding differences in their potential vorticity minima density and paths we also investigated the relationship between the decadal scale stf variability and atmospheric forcing the results suggest that the decadal scale stf variability can be largely explained by changes in the mode waters formed in the western north pacific and advected to north of the stf by the subtropical gyre in response to a change in surface westerly winds that occurred in the mid 1970s

a discussion of flow pathways in the central and eastern equatorial pacific abstract an eddy permitting global ocean model is used to interpret kinematics within the central and eastern equatorial pacific ocean from 160 e to the coast of america because of high levels of variability in this region observational studies of meridional flow are contradictory in particular as to whether the net flow is northward or southward unlike most oceanographic datasets model output can be analyzed at high temporal and spatial resolution providing clues as to real ocean behavior in the model a net southward flow occurs across the equator east of 160 w at most density layers throughout the year in the central pacific from 160 e to 160 w the net flow is northward but varies with season and occurs primarily in the mixed layer this is a key region for the flow of equatorial undercurrent water into the northern hemisphere the three dimensional flow is very complex and seasonally dependent it is vital that these flows are analyzed in an isopycnal framework or else the pathways are ve

simulations of temperature and turbulence structure of the oceanic boundary layer with the improved near surface process an improved model for the oceanic boundary layer is presented in view of the recent observation of the microstructure of the upper ocean including the high dissipation rate near the sea surface in the new model the surface boundary conditions for both the turbulent kinetic energy flux and the roughness length scale are modified the parameterization of stratification effects on turbulence is improved and the convective process is reformulated on the basis of the observation of uniform temperature and velocity profiles within the convective mixed layer evolutions of the profiles of both the dissipation rate and temperature of the observation data patches experiment as well as the time series of the sea surface temperature over the observation days are successfully simulated during a diurnal cycle for the first time it is also shown that the model reproduces various important features of the oceanic boundary layer for example the formation of a diurnal thermocline the profiles of buoyancy flux and the magnitudes of the buoyancy gradients both within the mixed layer and at the diurnal thermocline performance of the model is compared with that of the widely used mellor yamada model

isopycnal mixing in ocean circulation models abstract a subgrid scale form for mesoscale eddy mixing on isopycnal surfaces is proposed for use in non eddy resolving ocean circulation models the mixing is applied in isopycnal coordinates to isopycnal layer thickness or inverse density gradient as well as to passive scalars temperature and salinity the transformation of these mixing forms to physical coordinates is also presented

analysis of 137cs concentration in the pacific using a lagrangian approach 1 a hindcast of the 137cs concentration in seawater is conducted using a 0 5 1 global ocean general circulation model a significant amount of 137cs concentration appears in the subtropical gyre in the south pacific even though the source of 137cs is limited to the northern hemisphere the pathway from the north pacific to the south pacific is examined using the lagrangian approach the 137cs in the south pacific water is brought by the water that enters the equator through the interior pathway and the mindanao current from the subtropical gyre in the north pacific the water then flows along the equatorial undercurrent and spreads to the south pacific through the ekman transports at the surface a cross section of 137cs along 165 e is examined by the lagrangian approach and categorized based on the source region the maximum 137cs concentration in 1975 comes from the formation region of the eastern subtropical mode water emw along the 24 7 0 surface while the origin of the 137cs maximum in 2002 spreads over the central mode water cmw and the tropical water tw along the 25 8 0 surface the change of the maximum 137cs concentration from the water of emw origin to the waters of cmw origin and tw origin is explained by the difference in the time evolution of 137cs in the ventilated region the 137cs concentration decreases much more slowly in the formation regions of cmw and tw than in that of emw

subtropical mode water in the northeast pacific basin a new type of mode water in the upper thermocline of the eastern subtropical north pacific is identified and examined using data from world ocean circulation experiment high resolution repeat expendable bathythermograph xbt section px37 and archives of historical xbt data this water mass labeled eastern subtropical mode water is characterized by a subsurface potential vorticity minimum and is located east of hawaii northeast pacific basin in a density range of 24 25 4 it is a distinct water mass from the classical subtropical mode water stmw of the western pacific eastern stmw is formed as a relatively deep late winter mixed layer associated with the subtropical subpolar water mass boundary near 25 30 n 135 140 w and is capped and subducted into the permanent thermocline along a section between san francisco and honolulu eastern stmw production is seen in every year for which there is adequate data in this section the volume of eastern stmw formed each winter and the temperature of the potential vorticity minimum are similar during the periods 1970 1979 and 1991 1997

progradational sequences in miocene shoreline deposits southeastern caliente range california abstract an exceptionally well exposed marine nonmarine transition in middle miocene strata exists in the southeastern caliente range california about 50 individual progradational sequences form a succession that ranges in thickness from approximately 1000 m where predominantly nonmarine to more than 2500 m where predominantly marine paleogeographic evidence in basalt flows near the top of the succession and in overlying fluvial deposits indicates that these middle miocene strata were deposited across a north northwest trending shoreline a complete progradational sequence typically is several meters to a few tens of meters thick and includes strata that represent three intertonguing stratigraphic units individual sequences generally rest on a thin gravel deposit interpreted as a transgressive lag on an erosional surface the gravel is overlain by structureless siltstone or fine grained sandstone deposited at water depths where the rate of faunal mixing exceeded that of production of structures by physical processes these rocks grade upward into bedded fine sandstone deposited closer to shore where physical processes exceeded bioturbation crossbedded lenses of coarse sand or fine gravel in the upper part of this facies suggest the presence of fairly long period surface waves the bedded fine sandstone is sharply ove lain by a cross bedded coarse sandstone facies that is interpreted as a combined offshore bar rip channel surf zone assemblage cross strata dip dominantly offshore suggesting substantial deposition from rip currents a secondary shoreparallel mode of cross strata direction suggests longshore currents produced by surface waves from the northwest the crossbedded coarse grained sandstone grades upward into planar bedded medium grained sandstone that is interpreted as a beach foreshore this facies grades upward through structureless medium grained sandstone into nonmarine or lagoonal red and green mudstone of the caliente formation the middle miocene succession was deposited in a subsiding basin that was otherwise remarkably stable tectonically the position of the strand line differed no more than a few kilometers through a period of 1 to 3 m y the average duration of the transgressive regressive cycles a few tens of thousands of years together with their distribution in groups of three or four in the lower two thirds of the succession is consistent with the pattern of long term climatic cycles produced by periodicity of the earth s solar orbit and may be related to eustatic sea level changes attendant to the development of the antarctic ice cap changes in the pattern of progradation in the upper part of the succession and nearby basaltic eruptions may have been precursors to the onset of movement along th san andreas fault in this area 12 14 m y ago

fecal pellet flux to modern bottom sediment of santa barbara basin california based on sediment trapping fecal pellets constituted more than 60 of the material collected during 45 days of deployment of a suitcase type sediment trap in santa barbara basin the flux was 660 g m 2 yr 1 of which 22 g m 2 yr 1 was carbon flux pellet transport can account for about one half of the sediment flux to the central basin floor including the supply of terrigenous matter the clearing activities of pellet producing plankton have important implications for sedimentation and fertility in the coastal ocean