oligocene shallow water lacustrine deltas of the baxian sag of bohai bay basin eastern china depositional response during rift to thermal tectonic subsidence transition using cores well logs and other borehole data the results of this study show that the shallow water lacustrine delta has its own unique depositional characteristics of the third member of oligocene dongying formation ed3 in the baxian sag bohai bay basin eastern china during the ed3 stage the rift thermal basin subsidence transition stage the paleoslope was divided into multilevel slopes by faults along the wen an slope with slope angles from approximately 0 19 to 2 02 the paleogeographic conditions low discharge channel and low accommodation controlled the sedimentary characteristics the distributions of the shallow water delta system were controlled by multilevel flexure slopes the delta plain was distributed on the first and second level slope belts and the delta front was distributed on the third level slope belt the high sinuosity fluvial channel of the delta plain was the dominant facies in the whole shallow water delta most sand was deposited in these channels along the second level slope belt therefore not enough sand was present to be transported into the lake shallow water to form mouth bars in the delta front therefore mouth bars of the shallow water delta front were few and the sand beds were thin additionally no more sand was available to be supplied right along to deep lake the lacustrine basin was small and there was insufficient accommodation and sand to develop a subaqueous fan in the delta front

the deep ocean buoyancy budget and its temporal variability abstractdespite slow rates of ocean mixing observational and modeling studies suggest that buoyancy is redistributed to all depths of the ocean on surprisingly short interannual to decadal time scales the mechanisms responsible for this redistribution remain poorly understood this work uses an earth system model to evaluate the global steady state ocean buoyancy and related steric sea level budget its interannual variability and its transient response to a doubling of co2 over 70 years with a focus on the deep ocean at steady state the simple view of vertical advective diffusive balance for the deep ocean holds at low to midlatitudes at higher latitudes the balance depends on a myriad of additional terms namely mesoscale and submesoscale advection convection and overflows from marginal seas and terms related to the nonlinear equation of state these high latitude processes rapidly communicate anomalies in surface buoyancy forcing to the deep ocean locally the deep high latitude changes th

oxygen cycling in the northern benguela upwelling system modelling oxygen sources and sinks abstract this paper elucidates the oxygen dynamics in the northern benguela upwelling system by means of process oriented numerical modelling owing to the complex physical biological interaction in this system a coupled hydrodynamic biogeochemical model is required to grasp the various aspects of the oxygen dynamics we used high resolution atmospheric fields derived from observations to force our model available since 1999 the model results represent a 15 years consistent data set of realistic hydrographic and ecosystem variables including oxygen distribution patterns after a concise description of the main aspects of the model we use the model data to analyse the components contributing to the oxygen dynamics namely the ocean circulation the exchange between ocean and atmosphere as well as the local biogeochemical oxygen cycling in the system we thoroughly validate the model with available field observations and remote sensing data the strengths of coastal upwelling which controls the nutrient supply to the euphotic zone as well as the poleward undercurrent that carries oxygen and nutrients to the shelf in the northern benguela upwelling system are well reproduced in the model among the biological oxygen sinks mineralisation in the sediment respiration of zooplankton and nitrification in the water column are important we also found that vertical migration of zooplankton in response to the oxygen conditions provides a regulating feedback which may prevent a complete deoxygenation of suboxic waters as long as oxygen or nitrate are available in the bottom waters the activities of chemolithoautotrophic sulphur bacteria on the sediment surface keep the redoxcline within the sediment and prevent the release of hydrogen sulphide into the water column by horizontal integration of the simulated ocean atmosphere oxygen flux it can be shown that the kunene upwelling cell between 16 s and 18 s is a boundary between the equatorial ocean characterise by weak oxygen release to the atmosphere and the subtropical benguela upwelling system governed by an enhanced and seasonal varying flux furthermore a comparison of oxygen fluxes controlled by physical transport versus biogeochemical processes shows that the physical processes dominate in the northern benguela upwelling system

thermal responses to antarctic ice shelf melt in an eddy rich global ocean sea ice model abstractthe response near antarctic waters to freshening by increased glacial melt is investigated using a high resolution 0 1 global ocean sea ice model with realistic antarctic water mass prop

on deep water renewals in indian arm british columbia sensitivity to the production of turbulent kinetic energy caused by horizontal variations in the flow field abstract a two dimensional i e laterally averaged numerical model of the circulation in burrard inlet and indian arm near british columbia canada is used to examine the sensitivity of deep water renewal events in indian arm to the turbulent mixing in the lee of the narrow sills in burrard inlet horizontal variations in the flow field can have an important influence on the production of turbulent kinetic energy near the sills and therefore also on the renewal events in indian arm an ad hoc modification to the expression for the production of turbulent kinetic energy required to obtain an acceptable simulation downstream of second narrows in burrard inlet also results in a reasonable simulation of the observed circulation in indian arm the modified laterally averaged model can reproduce the main features of the circulation away from the narrow sills however it seems that a three dimensional model will be required if the circulation is to be simulated with greater accuracy and without the ad hoc

the simulation of deep water exchange in a fjord indian arm british columbia canada abstract a numerical model is used to simulate deep water renewals that were observed to occur in burrard inlet indian arm over a time period of about 100 days during winter 1984 85 the renewals bottom water flowing from burrard inlet into indian arm occurred or intensified during neap tide and caused a steady increase in the density near the bottom in indian arm the model successfully reproduces the renewal events for a simulation time of at least 85 days it uses a mellor yamada level two turbulence closure scheme for which the local turbulent energy production is balanced by local dissipation and for which the turbulent length scale is prescribed the length scale varies linearly with depth near the surface and bottom and is constrained to never be larger than 1 20 of the water depth and 2 the ozmidov length scale a lower bound is imposed on the vertical diffusion coefficients that depends on the brunt vaisala frequency n its magnitude for a given n is different in burrard inlet and in

dependence of currents and density on the spring neap cycle and the diurnal inequality in burrard inlet british columbia simulations and observations abstract observations of the circulation in a hole near a constriction in burrard inlet are simulated using a two dimensional i e laterally integrated numerical model the model uses a level 2 version of the mellor yamada turbulence closure scheme during spring tides when mixing is at its most intense the density in the hole decreases increases during the large small floods and there is an up inlet current pulse into the hole during each flood regardless of the flood s strength during the large floods in particular the simulation is significantly improved if the explicit influence of horizontal spatial variations on the production of turbulent kinetic energy is taken into account during neap tides the simulated density is much less variable and the currents in the hole are much weaker in agreement with the observations the model differs from the observations in that the simulated current pulses are significantly weaker than the observed pulses possibly because the cross channel averages

a numerical model of the circulation in knight inlet british columbia canada abstract during spring 1988 a period of low freshwater runoff and summer 1989 a period of high freshwater runoff month long observations of velocity temperature and salinity were made throughout the water column in knight inlet both up inlet and down inlet of the sill measurements were made at depths of 2 4 6 9 and 12 m using s4 current meters at depths down to about 200 m using profiling current meters and at depths deeper than 200 m using aanderaa current meters anemometers were deployed at two locations along the inlet a laterally integrated two dimensional numerical model of the inlet that uses the mellor and yamada level 2 5 turbulence closure scheme and that accounts for the combined influence of the winds tides and freshwater runoff has been used to produce 30 day simulations of the velocity and density field in the inlet the vertical coordinate is transformed in the model so that very fine vertical resolution can be attained near the surface even though the tidal range is larg

the energetics and tidally induced reverse renewal in a two silled fjord a laterally integrated two dimensional numerical model is used to examine the influence of the m2 tide on the circulation in the saguenay fjord a two silled fjord with a large inner and a small outer basin located on the north shore of the st lawrence estuary it is found that the m2 tide is more vigorous in the outer than in the inner basin and that more vertical mixing occurs in the outer basin therefore the density at depth in the outer basin decreases faster than it does in the inner basin and the resulting horizontal pressure gradient causes a bottom flow of water from the inner to the outer basin across the inner sill this reverse renewal is evident in both the available observations and the simulation according to the model much of the m2 energy withdrawn from the surface tide is fed into the internal tide significant tidal energy is also advected by the mean flow velocity approximately 25 of the net energy flux into the fjord is dissipated within 2 km of the outer sill because of the baroclinic pressure i e the total pressure but with the influence of the surface displacement removed the subtidal circulation is associated with very large energy fluxes within the fjord these fluxes are much larger than the net rate at which tidal energy enters the fjord and they are greater than the subtidal advective energy flux they represent a large redistribution of energy within the fjord and their horizontal divergence along the fjord is almost in balance with the time rate of change of potential energy when a flux richardson number is calculated for the inner basin below sill depth a value of 0 075 is obtained which is close to values found for other fjords

late quaternary paleohydrology of the central atacama desert lat 22 24 s chile in northern chile precipitation in the high andes 3500 m recharges groundwater systems that flow down the pacific slope and feed large aquifers in the hyperarid atacama desert wetlands which are often found along the base of the andes mark locations where the water table intersects the land surface at these locations paleo wetland deposits which are present as terraces between 3 and 20 m above modern wetlands record past water table heights along the andean front and are used to reconstruct changes in groundwater discharge paleo wetland deposits in the central atacama desert lat 22 24 s record an episode 15 4 9 ka of high water tables followed by an episode 8 3 ka of moderately high water tables elevated water tables result from increased groundwater discharge and ultimately from enhanced recharge in the andes the concordance of results from three separate hydrologic systems suggests that changes in groundwater discharge and recharge are regional and reflect climatic fluctuations this interpretation is supported by close agreement with other paleoclimatic records in the region the periods of greater groundwater discharge were separated by episodes 9 8 and 3 0 ka of significant groundwater lowering and stream incision implying greatly diminished discharge the central atacama and andes lat 22 24 s receive precipitation mainly from moist air masses transported from the amazon basin by the south american summer monsoon sasm increases in groundwater recharge are therefore thought to reflect an increase in the frequency and or moisture content of sasm air masses crossing the andes fluctuations in sasm precipitation have previously been linked to summer insolation in the southern hemisphere the wettest period in the central atacama 15 4 9 ka however coincides with a minimum in austral summer insolation at 10 ka suggesting that regional summer insolation is not a dominant influence on the sasm instead intensification of the sasm may be linked to extraregional forcings such as the walker circulation

yanai waves in the western equatorial indian ocean 1 observations and models have shown the presence of intraseasonal fluctuations in 20 30 day and 10 20 day bands in the equatorial indian ocean west of 60 e weio their spatial and temporal structures characterize them as yanai waves which we label low frequency lfyw and high frequency hfyw yanai waves respectively we explore the dynamics of these intraseasonal signals using an ocean general circulation model modular ocean model and a linear continuously stratified model yanai waves are forced by the meridional wind y everywhere in the weio most strongly during the monsoon seasons they are forced both directly in the interior ocean and by reflection of the interior response from the western boundary interference between the interior and boundary responses results in a complex surface pattern that propagates eastward and has nodes yanai waves are also forced by instabilities primarily during june july in a region offshore from the western boundary 52 55 e at that time eddies generated by barotropic instability of the southern gyre are advected southward to the equator there they generate a westward propagating cross equatorial flow field veq with a wave number frequency spectrum that fits the dispersion relation of a number of yanai waves and these waves are efficiently excited typically yanai waves associated with several baroclinic modes are excited by both wind and eddy forcing and typically they superpose to create beams that carry energy vertically and eastward along ray paths the same processes generate lfyws and hfyws and hence their responses are similar differences are traceable to the property that hfyws have longer wavelengths than lfyws for each baroclinic mode

a new estimate of the holocene lowstand level of lake titicaca central andes and implications for tropical palaeohydrology new evidence from piston cores and high resolution seismic reflection data shows that water levels in lake titicaca were as much as 100 m below the present level during the early to mid holocene between 6 and 3 8 14c kyr bp climatological and modelling studies indicate that lake titicaca rainfall depends on convective activity in upwind amazonia the lake level data therefore suggest a drier amazon basin during this time this view is bolstered by an excellent match between the titicaca lake level curve and decreased methane concentrations in greenland ice previously ascribed to drying of low latitude wetlands blunier et al 1995 the postglacial history of lake titicaca fits a global pattern of lake level change in the tropics characterized by opposite phasing between the southern and northern hemispheres this pattern is most likely the result of orbital controls over the intensity of summer insolation

tropical climate changes at millennial and orbital timescales on the bolivian altiplano tropical south america is one of the three main centres of the global zonal overturning circulation of the equatorial atmosphere generally termed the walker circulation1 although this area plays a key role in global climate cycles little is known about south american climate history here we describe sediment cores and down hole logging results of deep drilling in the salar de uyuni on the bolivian altiplano located in the tropical andes we demonstrate that during the past 50 000 years the altiplano underwent important changes in effective moisture at both orbital 20 000 year and millennial timescales long duration wet periods such as the last glacial maximum marked in the drill core by continuous deposition of lacustrine sediments appear to have occurred in phase with summer insolation maxima produced by the earth s precessional cycle short duration millennial events correlate well with north atlantic cold events including heinrich events 1 and 2 as well as the younger dryas episode at both millennial and orbital timescales cold sea surface temperatures in the high latitude north atlantic were coeval with wet conditions in tropical south america suggesting a common forcing

the influence of the spring neap tidal cycle on currents and density in burrard inlet british columbia canada abstract tidal mixing through two constrictions at the entrance to a fjord type estuary in british colombia canada is studied from a mooring programme in the spring of 1995 and from ship born adcp measurements in the spring of 1997 time series from the moorings show that during spring tides currents at depth are as high as 1 5 m s 1 small floods bring outside water through the narrows relatively unmixed which sinks down to depth in contrast large floods result in intrusions of highly mixed water up to 1 kg m 3 lower in density during neap tides currents at depth are generally small density decreases slowly and turbulent vertical diffusion is believed to be the dominant process at depth analysis of vertical diffusion near the bottom at one station during neap tides produces estimates of the vertical eddy diffusivity which are somewhat higher than those from similar studies in other b c fjords results from the adcp study reveal the presence of strong vertical velocities downstream of the narrows during large floods possibly associated with hydraulic jumps the flow through the narrows at such times is indeed supercritical with respect to the first baroclinic mode

energy fluxes due to the surface and internal tides in knight inlet british columbia abstract a laterally integrated two dimensional nonlinear numerical model is used to examine the flux of m2 tidal energy in knight inlet the simulated flux of tidal energy into the inlet is somewhat smaller than that estimated using the change in phase of the m2 tidal height along the inlet a method that does not account for the effect of the internal tide on the surface elevation the simulated energy flux into the inlet is close to the energy flux of the internal tide away from the sill determined from observations using an acoustic doppler current profiler adcp the net flux due to the internal tide is significantly less than 1 2 of the rate at which energy is removed from the surface tide earlier linear models of the internal tide produced energy fluxes that agreed with those estimated from the phase change of the tidal height but were larger than the fluxes that could be found in the observations the reason for this discrepancy is not that these simple models neglected nonlinear effects b

three dimensional nature of flow near a sill velocity and density sections across knight inlet british columbia demonstrate that lateral recirculations are a first order feature of the flow in the lee of the sill the flow over this sill has been used as a typical example of two dimensional hydraulics with a lower layer that thins and accelerates as it moves downstream below an almost stagnant layer that widens downstream creating a distinctive wedge shape however we find that rather than being stagnant the velocity in this wedge shaped layer is actually quite large consisting of a swiftly recirculating dipole vortex during flood tide and a monopole vortex during ebb tide though we may have missed the matching half of a dipole with our sampling during ebb the recirculations during flood tide carry an amount of water equal to 25 of the tidal flux while the monopole during ebb tide carries 20 of the tidal flux these recirculations bias along channel estimates of volume flux especially in the middle wedge shaped layer and demonstrate that accurate volume fluxes in the lee wave are only possible if three dimensional surveys are made our three dimensional survey shows that there is a net isopycnal convergence of water in the middle layer at a rate adequate to close the volume budget of the flow without recourse to diapycnal fluxes we also calculate the strength of the vorticity in the recirculations observed during flood tide and attribute their formation to boundary layer separation

the role of upstream waves and a downstream density pool in the growth of lee waves stratified flow over the knight inlet sill abstract observations and modeling simulations are presented that illustrate the importance of a density contrast and the upstream response to the time dependence of stratified flow over the knight inlet sill repeated sections of velocity and density show that the flow during ebb and flood tides is quite different a large lee wave develops early in flood tide whereas lee wave growth is suppressed until the second half of ebb tide there is a large upstream response that displaces as much water as accumulates in the lee wave one that is large enough to also block the flow at a depth roughly consistent with simple dynamics there is a large density contrast between the seaward and landward sides of the sill and a salty pool of water is found in the seaward basin that is not found landward the interface with this salty pool demarks the point of flow separation during ebb initially suppressing the lee wave and then acting as its lower boundary a simple two dimensional numerical model of the inlet wa

tidally forced internal wave mixing in a k e model framework applied to fjord basins abstract a simple method for including tidally forced internal wave mixing in a two equation turbulence closure framework the k e model is presented the purpose is to model the vertical mixing in the basin waters of stagnant sill fjords an internal wave energy iwe term of the form an where n is the buoyancy frequency and a is a weighted average of the locally available iwe is added to the equation for the turbulent kinetic energy tke the total available iwe f is given by the energy flux from the barotropic tide to baroclinic internal waves and a is determined assuming that all the available iwe is transferred to tke namely f an dv where the integral is taken over the entire volume of the fjord comparisons with observations from two scandinavian fjords show that the model successfully describes the vertical mixing in the basin water further the buoyancy term in the equation for dissipation of tke e is found to be irrelevant during stable stratification that is the empirical param

a numerical study of the tidal circulation and buoyancy effects in a scottish fjord loch torridon 1 the tidal and buoyancy driven circulation in loch torridon a scottish fjord is investigated using a three dimensional hydrostatic primitive equation model the predictions from the model have been quantitatively compared to available data gathered between 1998 and 2001 the model performed well in reproducing the tidal characteristics and density evolution of the fjord over the 3 month simulation period results show that tidal currents are dominated by the constraint imposed on the flow by the shallow sill separating the upper and middle basins the flow is strongly accelerated during flood and ebb tides and significant residual currents are generated that may influence exchange and residence times of the middle basin a strong baroclinic response to the flow over the sill is predicted throughout the fjord with a propagating linear m2 tide displacing isopycnals vertically by up to 32 m at the sill the formation of stationary lee waves on both flood and ebb tides is predicted with the wave generated during flood tide being notably larger as the growth of the ebb wave is inhibited by deep dense water this allows more energy to transfer into the seaward propagating internal tide as the tidal flow weakens the lee waves propagate over the sill and upstream estimates of the total vertical turbulent buoyancy flux in the fjord are made and the distribution of mixing over a tidal cycle is shown vertical mixing is seen to be highly spatially and temporally variable and strongly linked to the presence and dissipation of lee waves near the sill