chironomid based lateglacial climatic reconstruction for southeast scotland this paper presents the first chironomid based climatic reconstruction for the uk lateglacial obtained from a lake basin in southeast scotland whitrig bog comparison of chironomid lithological geochemical and pollen data reveals a marked vegetation lag behind the warming following deglaciation warm water chironomid taxa e g chironomus had replaced cold water chironomid taxa e g paracladius prior to the arrival of shrubs and trees and when local soils were still poorly developed in addition to clear evidence for the younger dryas stadial chironomid data also reveal two short term cold episodes that punctuate the lateglacial interstadial both of which are also reflected in pollen and lithological data as reversals from open birch scrub woodland to open herbaceous tundra coinciding with inwash of minerogenic matter into the basin 1997 john wiley sons ltd

the eastern tibetan plateau geothermal belt western china geology geophysics genesis and hydrothermal system abstract the eastern tibetan plateau geothermal belt etgb which is located in 98 102 e 28 32 n belongs to the eastern part of the mediterranean himalayan geothermal belt recently about 248 natural hot springs have been found in the etgb 60 of these springs have temperatures of 40 c and 11 springs have temperature above the local water boiling point using the helium isotopic data gravity magnetic and seismic data we analyzed the thermal structure and the relationship between hydrothermal activity and geothermal dynamics of the etgb results show that 1 the 248 springs can be divided into three geothermal fields kangding luhuo geothermal field kgf litang ganzi geothermal field lgf and batang xiangcheng geothermal field bgf the bgf and lgf have hot crust and warm mantle and are characterized by the higher heat flux 66 26 mw m2 and higher ratios of crust derived heat flux to total flux 47 46 60 62 the kgf has cool crust and hot mantle and is characterized by the higher heat flux and lower qc qm 2 there is a relatively 4 6 m higher gravimetric geoid anomaly dome which is corresponding with the etgb and in hydrothermal activity areas of the bgf and lgf there is a northwest southeast trending tensile stress area and the upper middle crust uplift area 3 an abnormal layer exists in the middle lower crust at a depth of 13 30 km beneath the etgb and this layer is 8 10 km thick and is characterized by lower velocity vp 2 5 high conductivity 10 m and high temperature 850 1000 c finally based on the heat source and geological and geophysical background we propose kangding type and batang type hydrothermal system models in the etgb

late glacial fossil midge stratigraphies insecta diptera chironomidae from the swiss alps abstract chironomid midges insecta diptera chironomidae are sensitive indicators of environmental change but relatively few studies have been made of the response of european midge faunas to the high amplitude climatic oscillations of the late glacial in this study late glacial assemblages of chironomid midges from four swiss lakes or former lakes gerzensee 603 m leysin 1230 m regenmoos 1260 m and heremence 2300 m were compared and contrasted the study focused on the response of chironomid assemblages to the beginning and end of the younger dryas cold interval c 12 690 11 485 cal yr bp and to minor cold climatic fluctuations gerzensee oscillation c 13200 12800 cal yr bp and preboreal oscillation c 113 65 11 100 cal yr bp the durations of these climatic fluctuations were defined climato stratigraphically based on oxygen isotope boundaries and the chronology was derived by correlation with grip oxygen isotope records major differences in the composition of the four lakes chironomid assemblages reflected differences in altitude and local environmental conditions nevertheless each lake fauna showed a marked response to the major and minor climatic oscillations demonstrating that large scale temperature change had an overriding influence on the distribution of chironomid midges

the amphi atlantic oscillation a proposed late glacial climatic event a contribution to the north atlantic seaboard programme of igcp 253 termination of the pleistocene abstract numerous palaeoclimatic records from europe greenland and the north atlantic ocean provide evidence for a short term cooling event which preceded the younger dryas stadial of ca 11 10 ka bp the discovery of a similar event in eastern north america the killarney oscillation ko raised the possibility of a single pre younger dryas cooling event that affected the entire north atlantic seaboard this paper reviews evidence for the ko and other pre younger dryas events and discusses the basis for their correlation the informal name amphi atlantic oscillation is proposed as a collective term for the ko and events that correlate with it

on the dynamics of internal waves in a nonlinear weakly nonhydrostatic three layer ocean aspects of the dynamics of internal solitary waves evolving in a three layer ocean are investigated using a new numerical multilayer model that solves the nonlinear weakly nonhydrostatic boussinesq equations and uses high resolution in situ data the model applications refer to two different phenomena frequently observed in the real ocean which can be described using a three layer model rather than a two layer model in the first application the influence of the strength of a shallow seasonal thermocline superimposed on a two layer permanent stratification on the structure of internal solitary waves is studied it is found that while for small to medium wave amplitudes a decrease in the strength of the thermocline yields an increase in the simulated wavelengths for large wave amplitudes this dependence is no longer monotonic in particular in the limiting case of a vanishing thermocline first mode internal solitary wave solutions of the three layer numerical model tend to the analytical internal solitary wave solutions of the miyata equations a two layer model in which the full nonlinearity of the shallow water theory up to first order phase dispersion is retained in the second application that refers particularly to high resolution observations made north and south of the strait of messina in the eurafrican mediterranean basin the generation of internal solitary waves by the evolution of surface and subsurface water jets is investigated the analysis of the in situ data shows in fact that from very energetic surface and subsurface jet like disturbances subject to strong turbulent mixing internal solitary waves emerge as robust quasi nondissipative oceanic features idealized flow conditions aimed at approximating possible initial stages of the observed water jets are imposed to force our numerical model in general good agreement is found between characteristics of observed and simulated wave fields our investigation identifies the observed water jets as peculiar features of the complex ocean dynamics and suggests that layered numerical models can represent helpful tools in understanding fundamental processes inherent in their intricate dynamics

coastal outflow currents into a buoyant layer of arbitrary depth the long wave reduced gravity shallow water equations the semi geostrophic equations are used to study the outflow of a river into the ocean while previous models have studied dynamics driven by gradients in density the focus here is on the effects of potential vorticity anomaly pva the river water is taken to have the same density as a finite depth upper layer of oceanic fluid but the two fluids have different uniform potential vorticities under these assumptions the governing equations reduce to two first order nonlinear partial differential equations which are integrated numerically for a prescribed efflux of river water and pva results are found to depend strongly on the sign of the pva with all fluid turning downstream in the direction of kelvin wave propagation when the river water has positive pva and anticyclonic flow upstream of the river mouth when the pva is negative in all cases a nonlinear kelvin wave propagates at finite speed ahead of the river water away from the river mouth the uniformity of one set of riemann invariants allows for similarity solutions that describe the shape of the outflow as well as a theory that predicts properties of the kelvin wave a range of behaviours is observed including flows that develop shocks and flows that continue to expand offshore the qualitative behaviour of the outflow is strongly correlated with the value of a single dimensionless parameter that expresses the ratio of the speed of the flow driven by the kelvin wave to that driven by image vorticity

dynamics of the atlantic meridional overturning circulation part 1 buoyancy forced response abstract historically a hierarchy of ocean models have been used to investigate the dynamics of basin scale deep meridional overturning circulations mocs near the base of this hierarchy are idealized solutions forced only by a surface buoyancy flux our goal is to provide a complete dynamical description of such base solutions thereby placing the hierarchy on a firmer foundation for this purpose we obtain solutions to two types of models a variable density layer ocean model vlom and an ocean general circulation model coco the former allowing for nearly analytic solutions and the latter for more accurate representation of processes solutions are obtained in an idealized flat bottom basin extending 40 in longitude and from the equator to 60 n and for simplicity density depends only on temperature our standard runs are forced by a surface heating q which is spread uniformly throughout layer 1 in vlom and at depths less than hmin in coco it quickly relaxes upper ocean temperature to a prescribed t y that decreases linearly in the latitude band 30 50 n from 23 c in the south to the temperature of the deep ocean 3 c in the north at the very bottom of our hierarchy are solutions to dynamically simplified versions of the models i e no sub mixed layer entrainment or detrainment in vlom and no mixing and momentum advection in coco that adjust to a steady state without an moc initially q forms an upper layer of thickness h1 hmin and temperature t t y and there is near surface eastward flow across the basin in the latitude band where ty 0 at the eastern boundary kelvin waves cancel this current by adjusting h1 to a nearly parabolic profile he y that thickens poleward and eventually extends to the ocean bottom just south of 50 n subsequently rossby waves propagate across the basin adjusting the solution to a state in which h1 x y he y and t t y above h1 everywhere in the basin after this adjustment the only remaining flows are zonally oriented isopycnal overturning cells within the upper layer caused by thermal wind shear in the latitude band where ty 0 our standard runs which are solutions to the full models necessarily adjust to a steady state with an moc along and near the eastern boundary kelvin wave adjustments still maintain the structure he y and rossby waves begin to carry that structure offshore near 50 n however the rossby waves are strongly damped in vlom the damping is accomplished by a detrainment that prevents h1 from becoming larger than a prescribed maximum value in coco it results primarily from horizontal diffusion which thins h1 by cooling the deep ocean there because of the damping there is an across basin pressure gradient that drives northward geostrophic transport forming the surface branch of the moc furthermore the eastward flowing moc branch is located in a northern boundary layer where the damping is active because there is no wind forcing there is no steady state barotropic flow and the deep response mirrors that in the upper layer in most solutions the upper and deep circulations are closed by diffusive upwelling mostly in the interior ocean and by downwelling primarily at the eastern boundary the exceptions being for two of the extended solutions noted below a useful aspect of vlom is that it allows a closed analytic expression for m h e where m is the moc transport and he is the eastern boundary thermocline depth in the tropics for realistic parameter choices m is essentially proportional to h e 2 in agreement with prior estimates based on ad hoc principles or determined empirically from numerical solutions vlom also provides an approximation for he where is the coefficient of vertical diffusion then m h e describes the approximate dependency of m on and it varies like 2 3 again consistent with prior results in coco solutions m exhibits similar dependencies on he and a consistency traceable to he y being established in both systems by similar processes however the 2 3 relationship is not as precise because upwelling sources other than interior diffusion also contribute significantly to m we also report four solutions that extend our standard runs in straightforward and insightful ways they are solutions in which i the moc eastward branch is the surface flow of nearly isopycnal nearly closed thermal wind cells that extend to the ocean bottom a very different structure than for the northern boundary layer in the coco standard run ii t depends on both x and y and the moc downwelling branch shifts to the northern boundary iii q is weakened enough to allow upper layer temperature advection to impact the response and iv the moc upwelling branch is externally imposed by an exchange of water across the southern boundary of the basin despite the differences among these solutions and the standard runs the underlying processes that generate the moc and determine its strength remain unchanged an indication that the moc processes discussed here have general applicability

the rhine outflow plume studied by the analysis of synthetic aperture radar data and numerical simulations the dynamics of the rhine outflow plume in the proximity of the river mouth is investigated by using remote sensing data and numerical simulations the remote sensing data consist of 41 synthetic aperture radar sar images acquired by the first and second european remote sensing satellites ers 1 and ers 2 over the outflow region of the river rhine most of them show sea surface signatures of oceanic phenomena for example surface current and wind variations ship wakes and oil slicks in particular in 36 of these images pronounced frontal features are visible as narrow zones of mainly enhanced sometimes enhanced reduced radar backscatter that can be associated with the rhine surface front within the area enclosed by the frontal line large zones characterized by a lower radar backscatter than in the outer area are often visible the analysis of the ers sar images suggests that the form and the location of the frontal features are mainly linked to the semidiurnal tidal phase in the outflow region although their variability suggests also that they weakly depend on river discharge residual currents and neap spring tidal cycle in order to test this observational hypothesis the results obtained from the analysis of the ers sar images are compared with the results obtained from the numerical simulation of the hydrodynamics of the rhine outflow region carried out using a two layer frontal model which is based on the nonlinear hydrostatic shallow water equations on an f plane the model is forced by prescribing tidal and residual currents and river discharge at the open boundaries several simulations are performed by varying the values of these forcing parameters the numerical results corroborate the observational conjecture it is found that the form and the location of the simulated interface outcropping lines in the proximity of the river mouth are mainly determined by the semidiurnal tidal phase in the outflow region and that river discharge residual currents and neap spring tidal cycle contribute only secondarily to their determination inserting the simulated surface velocity field into a simple radar imaging model that relates the modulation of the backscattered radar power to the surface velocity convergence in radar look direction narrow elongated bands of enhanced radar backscatter emerge near the model frontal line while patches of low radar backscatter appear within the simulated rhine plume area the consistency of the model results with the results obtained from the analysis of the sar images enables one to infer a mean spatial and temporal evolution of the rhine outflow plume over a semidiurnal tidal cycle from the analysis of spaceborne sar images acquired during different tidal cycles over the rhine outflow area and suggests the possibility of using numerical modeling in conjunction with the analysis of spaceborne measurements for monitoring the oceanic variability in the rhine outflow area

exceptionally steep north south gradients in lake temperatures during the last deglaciation during the transition from the last glacial to the present interglacial climate late glacial period high summer insolation1 combined with the presence of the laurentide ice sheet is thought to have promoted the development of strong summer thermal gradients in north america south of the ice margin2 here we use palaeoecological methods to obtain quantitative evidence for the existence of these gradients our palaeoclimate reconstructions are based on water temperatures inferred from fossil assemblages of aquatic midge larvae in five lakes along a 240 km transect extending from central new brunswick canada to southeastern maine usa we show that the temperature gradient shifted during the killarney oscillation ko and younger dryas yd cooling events and that water temperature differences of 9 and 11 c existed over distances of 55 and 240 km respectively during parts of the late glacial period these gradients are much stronger than the current north south trends of lake summer surface water temperatures for these five lakes and for lakes across the northern tree line the rapid motion of such steep temperature gradients may have affected the progressive development of aquatic and terrestrial ecosystems in the region

coastal circulations driven by river outflow in a variable density 1 layer model a variable density 1 layer model is used to investigate the dynamics of the fresher water plumes generated by river outflow solutions are found in a north south channel and the transport mr and salinity sr of the outflow are specified as boundary conditions along a 25 km wide segment of the western boundary in most cases the river water discharges into a preexisting oceanic mixed layer with thickness h1 when mr is sufficiently low plumes remain coastally trapped immediately after the outflow is switched on a coastal kelvin wave is excited at the river mouth that establishes a southward current of oceanic water along the right hand coast in contrast all the river water first bends to the left as it exits the river mouth and the resulting plume advances northward along the left hand coast at the plume nose some of the fresher water reverses direction and this water together with some oceanic water flows southward on either side of the offshore density front between the fresher and salty waters two processes cause this upstream movement geostrophic adjustment generates the southward frontal current and kelvin wave propagation from the nose thins the layer within the plume thereby establishing the northward geostrophic coastal jet when mr is sufficiently high coastally trapped plumes no longer exist if the rossby number of the outflow is also large enough the river water flows directly offshore and only a portion of it recirculates to form a northward propagating coastal plume the angle at which the outflow leaves the river mouth becomes more southward as mr and sr increase and as h1 decreases the strength of the northward propagating plume is weakened as h1 decreases and sr increases when h1 0 so that there is no ambient oceanic layer there is no northward plume at all likewise the plume is weakened when the model includes entrainment a process that acts to prevent the layer thickness from thinning appreciably

mixed layer thermocline interaction in a three dimensional isopycnic coordinate model abstract the annual buildup and obliteration of the seasonal thermocline and the associated ventilation of the permanent thermocline in a wind and thermally driven ocean basin are simulated numerically the model developed for this purpose is a combination of a single layer model of the oceanic mixed layer based on a simple closure of the turbulence kinetic energy equation and a three dimensional isopycnic coordinate model of the stratified oceanic interior the joint model set in a rectangular ocean basin is forced by annually varying wind stress and radiative plus turbulent heal fluxes approximating zonnaly averaged conditions over the north atlantic special emphasis is placed on the description of the mixed layer detrainment process which requires distributing mixed layer water of continuously variable density among constant density interior layers the truncation errors associated with this process are found to be numerically tolerable the quasi lagrangian character of the model s vertical coo

late glacial climatic oscillations as recorded in swiss lake sediments regional pollen assemblage zones for the late glacial period of the swiss plateau are introduced and defined they include four major zones artemisia juniperus hippophae betula pinus paz with several subzones pollen and oxygen isotope analyses on lacustrine sediments from several lakes in the area reveal four distinct phases of climatic oscillation in the time period of 13 000 9500 yr bp the first oscillation termed the aegelsee fluctuation occurs shortly before 12 000 yr bp and varve counts suggest its duration was ca 100 yr it is characterised by a short decrease in the oxygen isotopes as well as a short increase in nap associated with a depression in birch pollen values the second oscillation which occurs in the 18o record shortly before the deposition of the laacher see tephra ca 11 000 yr bp is termed the gerzensee fluctuation it occurs during a pine dominated phase and its vegetational effects cannot be determined palynologically the most prominent regressive phase is the younger dryas biozone ca 10 700 10 000 yr bp characterised by an increase in heliophilous nap and low 18o values the younger dryas biozone can often be subdivided palynologically into two parts a first part rich in grasses and juniper and a second part with higher filipendula and birch values during the preboreal biozone another distinct oscillation is evidenced only in the oxygen isotope ratios comparison of the swiss oxygen isotope profiles with the greenland dye 3 record suggests that not only the three major shifts in the 18o curves but also the minor ones are closely comparable suggesting some common climatic control

potential vorticity dynamics of coastal outflows abstracta simple quasigeostrophic model is used to examine the outflow from a river estuary or strait into a coastal ocean as shown by johnson et al these quasigeostrophic outflows are accurately described by analytical long wave solutions this paper first uses these solutions and contour dynamics simulations to discuss the behavior of coastal outflows second it extends the model and the long wave theory to consider the effects of ambient currents tides winds or a variable source flux third consideration of the momentum flux at the source is used to understand the turning of the current showing that steady solutions conserve momentum hence resolving the momentum imbalance paradox of pichevin and nof finally a new numerical scheme to compute steady outflow boundaries is developed the model focuses on the key dynamics driven by the source velocity and the generation of vorticity as the buoyant fluid adjusts the simplicity of the model and insight given by the long wave solutions enables

yangtze brackish water plume circulation and diffusion abstract a system of 3 d linearized momentum equations the continuity equation and a simplified equation of state for sea water are analytically solved the solution comprises three parts the first part is a wind driven current the second a jet like current caused by yangtze river outflow and the last a density flow the computed current velocity is obtained by solving an advection diffusion equation of salinity by a finite difference method the results show that the yangtze brackish water plume spreads as a large low salinity tongue at the surface the turning of the tongue axis is mainly controlled by wind stress yangtze run off and bottom topography near the bottom the axis changes little all the year around at about 10 15 m depth there is a sharp halocline in summer but at deeper layers the vertical distribution is almost always uniform the computed salinity distribution agrees fairly well with the observed one

a multiproxy investigation of late glacial climate and vegetation change at pine ridge pond southwest new brunswick canada abstract pollen plant macrofossil chironomid and lithological analyses of late glacial sediment from pine ridge pond all indicate that the warming following deglaciation was punctuated on two separate occasions by a return to colder climes initially by a brief and moderate cold episode the killarney oscillation followed shortly by the younger dryas the killarney oscillation ams 14 c dated at between 11 290 and 10 960 yr b p is characterized by abrupt and simultaneous increases in betula birch pollen and betula glandulosa dwarf birch macrofossils and a decline in tree pollen the younger dryas is distinguished by the reversion of a short lived closed picea spruce forest to a prolonged forest tundra stage ca 10 820 to 9500 yr b p during which macrofossils of arctic alpine plants such as salix herbaces cassiope hypnoides armeria maritima and thalictrum alpinum make their sole late glacial appearance chironomid inferred summer surface water temperatures indicate a cooling of approximately 8 and 12 c during the killarney oscillation and younger dryas respectively and coarse sand analysis indicates increased erosion on the landscape during these same intervals

buoyancy driven current during cooling periods in ise bay japan 1 the cooling effect on buoyancy driven current is studied in the coastal embayment of ise bay japan by applying knowledge derived from studies of convection in a rotating fluid this convection process is highly sensitive to the presence of inhomogeneities in the preexisting stratification and to differential buoyancy loss on freshwater input the bay water is divided into two regions that differ in their response to the cooling from the surface one region represents a river plume which in effect shields the deeper regions from the cooler surface in the other region convective mixing is active although the mixed water forms and becomes extensive in this convection region the mixed water hardly develops in the river plume region the subsequent differential deepening of the mixed water causes gravitational circulation and yields a mixed water lens which has a reversed dome shape and rotates anticyclonically in a thermal wind balance in the mixed water lends nonvanishing stratification remains because of the rotational effect the location of the mixed water lens and associated anticyclonic circulation determines the basin wide circulation during cooling periods

river forced estuarine plumes abstract the development maintenance and dissipation of river forced estuarine plumes with and without seaward sloping bottom are studied by use of a three dimensional primitive equation model inside the estuary discussion is focused on how the coriolis force induces lateral asymmetries in the circulation four physical processes dictate the transient as well as the quasi steady circulation in moderately stratified estuaries 1 upper layer convergence during the transient spinup phase 2 upward entrainment leading to the two layer steady circulation pattern 3 upward stretching of the lower layer vortex during the spindown period and 4 in the presence of a seaward bottom slope the left bounded tendency of the landward undercurrent for all phases of development deviations from the laterally averaged circulation pattern caused by these processes are discussed over the shelf various types of plumes are defined according to the visual appearance of the surface salinity field the four types of p

the preboreal oscillation around the nordic seas terrestrial and lacustrine responses the occurrence of an early preboreal climatic cooling oscillation pbo in lacustrine and glacial records from northwest europe iceland and greenland is reviewed and documented the often subtle response of the proxy records to this oscillation in combination with its short duration make it difficult to detect owing to its chronostratigraphic position between the 10 000 9900 and 9600 9500 14 c plateaux c 11 300 11 150 calendar yr bp it is also difficult to 14 c date with precision we find that the vegetation response to the pbo varies between sites and regions in contrast to the pioneer vegetation in iceland and southern sweden the expanding birch pine forest in germany denmark was more susceptible to deteriorating growing conditions the combined lacustrine tree ring and glacial records imply that the pbo was characterised by cool and humid conditions throughout northwestern and central europe this is documented by vegetation changes decreased aquatic production increased soil erosion increased 2 h and 13 c content in tree rings readvances or stillstands of the ice sheet in norway and finland and ingression of brackish water into the baltic icelandic proxy records from lake sediments and glacial moraines imply cooler conditions than during the previous preboreal period but not as extreme as during the younger dryas greenland records suggest that the early preboreal was characterised by ice readvances as an effect of cool climate and increased precipitation in relation to the younger dryas it was not until the end of the pbo that climate was warm enough to melt the land based ice sheet this preboreal oscillation found on both sides of the nordic seas is interpreted as an effect of increased freshwater forcing on the thermohaline circulation in the nordic seas which is implied by a simultaneous and distinct rise in the atmospheric 14 c 12 c ratio a slow down of the thermohaline circulation may tempor arily have pushed the polar front further south 1997 by john wiley sons ltd preboreal oscillation thermohaline circulation lacustrine records glacial records chronology

chironomid evidence for late glacial climatic reversals in maine previously published pollen studies from maine have not identified any late glacial reversals despite evidence for them from adjacent areas the distribution and abundance of midge flies are strongly correlated with summer surface water temperatures we analyzed fossils of larval midge flies from the sediments of two ponds trout and tilley from maine each site reveals a major and a minor oscillation during which inferred summer surface water temperatures fell by 7 13 c and 2 1 2 6 c respectively we tentatively correlate these events with the younger dryas cooling and killarney oscillation reported from adjacent maritime canada where they have been ams 14c dated at 10 770 10 000 and 11 160 10 910 yr b p respectively a third oscillation occurs at the northernmost site tilley pond and may represent the effects of a local ice advance in northern maine

a reduced gravity isopycnal ocean model hindcasts of el nino abstract a global isopycnal ocean model is presented for the study of interannual to interdecadal variability in the global ocean the model treats the primitive equations on a sphere with a generalized vertical coordinate this coordinate is designed to represent a turbulent well mixed surface layer and nearly isopycnal deeper layers disappearing isopycnics are treated through the quasi isopycnal technique in which the coordinate separates from the isopycnic in order to maintain a minimum layer thickness a reduced gravity treatment is made with the deepest interface at a mean depth of 2300 m coastal topography is represented but the reduced gravity treatment precludes the use of variable bottom depth the model is used for hindcast studies of el nino during the decade from 1982 through 1991 using a combination of climatological wind forcing and wind anomalies derived from various sources in order to carry out the hindcast experiments a technique is developed for constructing a mean climatological

structure and eastward extension of the changjiang river plume in the east china sea 1 the hydrographic structure and offshore extension of freshwater plume discharged from the changjiang also known as the yangtze river in the northern east china sea were investigated by analyzing conductivity temperature depth ctd data and drifter trajectories collected during the summers of 1997 and 1998 from june to early september when southerly winds prevail the plume tends to move northeast in the chinese coastal area and then separates from the coastal zone to travel eastward over 400 km offshore across the western shelf of the northern east china sea during other seasons when northerly winds prevail the plume is confined to the chinese coast in the summer the plume in the midshelf confined to a thin surface layer 10 to 15 m thick extends eastward in the form of patches of low salinity water rather than spreading as a tongue shaped pattern from the changjiang mouth the eastward movement of patches in the western shelf is primarily due to upwelling favorable southerly winds upon reaching the vicinity of cheju do an island in the middle of northern east china sea the patches are advected to the korea tsushima strait by either the cheju warm current or a northward flowing mean current of the kuroshio branch current and then finally flow into the east japan sea

the upstream spreading of bottom trapped plumes it is well known that numerical simulations of freshwater discharges produce plumes that spread in the direction opposite to that of the propagation of coastally trapped waves the upstream direction the lack of a theory explaining these motions in unforced environments deemed the numerical results suspect thus it became a common practice in numerical studies to add a downstream mean flow to arrest the development of the upstream perturbation this approach is generally unjustified and it remains a matter of interest to determine if the upstream displacement produced by models is a geophysical phenomenon or a consequence of erroneous assumptions in the model setup in this article the results of highly idealized numerical experiments are used to investigate these matters it is shown that this phenomenon is associated with the geostrophic adjustment of the discharge and that upstream motion is endemic to the baroclinic structure of bottom trapped plumes it is also shown that downstream displacements are generated by the cross shelf barotropic pressure gradient generated by the propagation of coastally trapped waves sensitivity experiments indicate that the speed of upstream propagation and the density structure of the plume are affected by bottom friction the slope of the bottom and the magnitude of the density anomaly bottom friction in particular slows down the progression of the plume and changes its density structure producing a more homogeneous downstream region and a more stratified upstream region

the role of wind on the detachment of low salinity water in the changjiang estuary in summer in july 2006 and the role of wind on detaching the lsw in particular are explored with a three dimensional numerical model the real case simulation and the sensitivity experiments results show that wind plays a crucial role in the detachment events and is highlighted in three aspects first wind is the most important dynamic factor in the two detachment processes of the lsw wind mixing wind driven northward current and wind induced upwelling are three driving forces on detaching the lsw which increase the salinity in the upper layer in the detachment region along the 30 m isobath and separate the offshore lsw from the nearshore main body of lsw the diagnostic analysis further indicates that the increase of salinity in the detachment region is mainly due to northward current which transports high salinity water from the south second a critical wind speed namely a southeasterly wind above 8 0 m s is found to be related to the timing of the detachment events a sensitivity experiment further confirms this critical wind speed and no detachment occurs when the wind speed is below 8 0 m s third the southwesterly wind plays a key role in the magnitude of the spatial size of the detached lsw before the detachment occurs a persistent southwesterly wind induces northeastward expansion of the lsw and consequently forms larger lsw offshore after detachment which is verified by another sensitivity experiment with modified wind direction

chironomidae insecta diptera succession in żabieniec bog and its palaeo lake central poland through the late weichselian and holocene abstract subfossil chironomidae assemblages were studied in a sediment sequence from abieniec bog in central poland the climate history and habitat changes in the palaeo lake were reconstructed from these assemblages currently no chironomid based climate calibration set is available from poland and so past mean july air temperatures were inferred from chironomid climate calibration data sets from norway russia and switzerland during the late weichselian the three calibration functions from these data sets provided similar temperature inferences but there was some divergence in the reconstructions for the younger dryas and holocene in the late pleniglacial inferred summer air temperature was relatively low 8 12 c and the lake was oligotrophic at about 16 5 ka bp temperature rapidly rose to 15 c and assemblage diversity substantially increased during the interstadial temperature stayed at this level in the younger dryas july air temperature was only 1 2 c lower than in the interstadial as inferred from the norwegian calibration data set whereas the russian and swiss calibration functions did not indicate any temperature decrease from the beginning of the holocene taxa typical of meso eutrophic conditions dominated there was an increased abundance of phytophilous species and the assemblage composition was also influenced by changes in water level palaeotemperature reconstructions differed in their values from 8 0 to 8 7 ka bp inferences based on the swiss and russian data sets indicated a cold oscillation while reconstructions based on the norwegian data set did not show any temperature decrease after 2 5 ka bp assemblage diversity and head capsule concentrations decreased in the last millennium semi terrestrial taxa dominated except from late medieval to early modern times when shallow water species reappeared

circulation on the western south atlantic continental shelf 1 numerical process studies on buoyancy 1 buoyancy driven currents are investigated in the western south atlantic ocean where a major river plume la plata interacts with a minor one patos lagoon a series of simulations were performed with a three dimensional free surface numerical model to better understand the processes which control both plumes evolution and their interaction the simulations are focused on the importance of turbulent mixing to the evolution of the la plata plume and its downshelf penetration toward the patos lagoon satellite observations and historical data show that the la plata plume has a tendency to expand along the river southern margin before it turns north in the direction of coastal trapped waves propagation our results on the other hand show that in the absence of the tides and the wind this plume tends to leave the estuary attached to its northern margin downstream unless the model parameters are tuned to produce unrealistically high turbulent mixing we then address the role of each parameter that controls mixing and show that by tuning the model parameters we can get plumes similar to those observed in nature however the plumes produced in the experiments with excessively high mixing parameters showed unbounded southward upstream expansion by introducing the tides we show that the plumes produced in the presence of tidal stirring and normally set mixing parameters are more realistic suggesting that tidal stirring is more effective than artificially tuned turbulent mixing on causing the plume lateral expansion

dynamics of andaman sea circulation and its role in connecting the equatorial indian ocean to the bay of bengal circulation in the bay of bengal bob is driven not only by local winds but are also strongly forced by the reflection of equatorial kelvin waves ekws from the eastern boundary of the indian ocean the equatorial influence attains its peak during the monsoon transition period when strong eastward currents force the strong ekws along the equator the andaman sea lying between the andaman and nicobar island chains to its west and indonesia thailand and myanmar to the south east and north is connected to the equatorial ocean and the bob by three primary passages the southern 6 n middle 10 n and northern 15 n channels we use ocean circulation models together with satellite altimeter data to study the pathways by which equatorial signals pass through the andaman sea to the bob and associated dynamical interactions in the process the mean coastal circulation within the andaman sea and around the islands is primarily driven by equatorial forcing with the local winds forcing a weak sea level signal on the other hand the current forced by local winds is comparable to that forced remotely from the equator our results suggest that the andaman and nicobar islands not only influence the circulation within the andaman sea but also significantly alter the circulation in the interior bay and along the east coast of india implying that they need to be represented accurately in numerical models of the indian ocean

the interaction of estuarine and shelf waters a model and applications abstract an analytical model is developed to describe the steady flow in an estuary shelf interaction region where the system is treated as a two layer density stratified flow the motion is expanded in terms of the relative thickness of the vertical ekman layer the zero order flow is geostrophic in each layer balancing of order one quantities reduces the system to two vorticity equations relating the pressure field with the displacement of the interface and the bottom topography an explicit solution is obtained for the case of linear offshore sloping bottom the flow behavior of the estuarine plume depends on the vertical structure of the flow at the river mouth the bottom slope and the ambient coastal flow under certain conditions a front exists as an offshore boundary of the plume these results are compared with observations for the changjiang river estuary in china and both the chesapeake bay and savannah river estuaries in the united states

an early holocene pollen mollusc and ostracod sequence from lake marl at llangorse lake south wales uk an integrated analysis of molluscs ostracods and pollen is presented from early holocene lake marl at llangorse lake powys south wales the mollusc and ostracod records reflect a littoral enviro

oxygen isotopes of lake marl at gerzensee and leysin switzerland covering the younger dryas and two minor oscillations and their correlation to the grip ice core the ratio of oxygen isotopes is a temperature proxy both in precipitation and in the calcite of lacustrine sediments the very similar oxygen isotope records from greenland ice cores and european lake sediments during the last glacial termination suggest that the drastic climatic changes occurred quasi simultaneously on an extra regional probably hemispheric scale in order to study temporal relations of the different parameters recorded in lake sediments for example biotic response times to rapid climatic changes a precise chronology is required in unlaminated lake sediments there is not yet available a method to provide a high resolution chronology especially for periods with radiocarbon plateaux alternatively an indirect time scale can be constructed by linking the lake stratigraphy with other well dated climate records new oxygen isotope records from gerzensee and leysin with an estimated sampling resolution of between 15 and 40 years match the greenlandic isotope record in many details under the assumption that the main variations in temperature and thus in oxygen isotopes occurred about simultaneously in greenland and switzerland we have assigned a time scale to the lake sediments of gerzensee and leysin by wiggle matching their stable isotope records with those of greenland ice cores which are among the best dated climatic archives we estimate a precision of 20 to 100 years during the last glacial termination

the potential of chironomid insecta diptera larvae in archaeological investigations of floodplain and lake settlements the head capsules of chironomids insecta diptera are well preserved in sediments and can be recognised to a high taxonomic level usually genus and sometimes species work on lake sediments has shown that they can be accurate indicators of water temperature oxygen regimes and nutrient status particularly total phosphorus and chlorophyll a as well as heavy metal pollution no systematic chironomid analyses however have previously been undertaken on archaeological deposits in order to address this we assessed the use of chironomids in three types of archaeological deposit firstly a lake core at the edge of a lake settlement crannog secondly a palaeochannel infill adjacent to a multi period settlement site and lastly a roman well deposit from a floodplain environment the chironomid assemblages are shown to vary significantly both between and within the sites and reflect the immediate environment and the adjacent area the lake sediment assemblage reflects the construction of the crannog through elevated levels of organic detritus wood and woody debris the palaeochannel assemblage reveals changing natural conditions and nutrient enrichment probably associated with settlement during the saxon period the well assemblage is taxonomically restricted and indicative of organic debris dead plant material animal dung and possibly human effluent deposited after abandonment of the well dry storage of the palaeochannel and well sediments for several years did not appear to affect the concentration or state of preservation of the head capsules the chironomid reconstructions are shown to provide an additional indicator of human activity which has the potential to provide quantitative data on the character of aquatic environments associated with archaeological sites

estuary plumes and fronts in shelf waters a layer model abstract a layer model that treats fronts as discontinuities is developed to study the steady state behavior of shallow estuary plumes on the continental shelf the complete range of earth rotation effect is evaluated from small scale or nonrotating plumes kelvin number equal zero to large scale rotating plumes kelvin number equal order one supercritical flow is assumed in the outlet channel and the method of characteristics is used to compute the flow downstream nonrotating plumes have strong boundary fronts and concentrate their greatest layer depth and mass transport offshore near the front but form no coastal current rotating plumes have boundary fronts that weaken soon after discharge form a turning region where coriolis action deflects the flow toward shore and subsequently set up a coastal current soon after its formation this coastal current is bounded offshore by a strong front called the coastal front across which the momentum balance changes from nearly inertial in the turning regi

tongue shaped frontal structure and warm water intrusion in the southern yellow sea in winter 1 in winter a thermohaline front forms at the yellow sea ys entrance where the warm and saline cheju warm current cwc water meets cold coastal water the frontal structure as well as the northwestward intrusion of the warm water was investigated by analyzing conductivity temperature depth ctd data tracks of drifting floats moored current data and satellite images the cwc water advances westward as a tongue with its tip heading westward across the ys entrance not intruding northward along the deepest part of the ys trough whereas a secondary warm water band is developed northwestward along the western flank of the trough floats in the warm tongue moved northwestward across the western frontal zone where the frontal structure was weak reflecting the northwestward intrusion along the 50 70 m isobaths through the frontal zone currents in the trough do not always meet the upwind flow theory that in an elongated basin the wind driven flow is upwind in the deep channel but rather show the predominance of the southward downwind flow model experiments show that on the western flank of the trough both the southeastward tide induced residual flow and the southeastward flow due to the nonlinear effect between tide and wind are generated at the same time thus the intermittent intrusion of the cwc across the western frontal zone may be closely associated with the predominance of the upwind flow over the southeastward nonlinear interacted flow

biotic responses to rapid climatic changes abstract qualitative and quantitative changes in fossil flora and fauna have been used in many studies to infer climatic change here we ask a different question how do flora and fauna respond to climatic changes such as rapid warming or cooling as an independent proxy for paleotemperature we take the ratio of oxygen isotopes in biogenically precipitated lake marl and in ostracod shells this introductory paper describes the project design and the five sites on an altitudinal transect from 600 m to about 2300 m asl in the western swiss alps as cases of climatic cooling and warming we use the beginning and end of the younger dryas as major changes and the gerzensee and preboreal oscillations as minor changes at the two sites of gerzensee and leysin these changes are recorded in stable isotope ratios and there the time scales can be derived by correlations to the grip ice core schwander et al 2000 von grafenstein et al 2000 biotic responses to climate changes are treated in individual papers using pollen wick 2000 plant macrofossils tobolski and ammann 2000 and remains of chironomids brooks 2000 beetles and other insects lemdahl 2000 and chydorid cladocera hofmann 2000 they are followed by a synthesis focusing on quantification of biotic responses ammann et al 2000 in addition a reconstruction of summer temperatures for the allerod and the younger dryas at gerzensee is provided by lotter et al 2000

coastal flows driven by a local density flux a two layer model with a rigid lid and a flat bottom on an f plane is employed to study a flow field driven by a density flux through the sea surface or the coast for example freshwater discharged from a river the negative positive density flux into the upper layer is represented by the water beneath over the interface changing from the lower upper layer to the upper lower layer that is entrainment of the lower upper layer by the upper lower layer the subinertial flow pattern constrained by the coast has two components one is a baroclinic eddy nearby that matches the entrainment region and the other is a forced internal kelvin wave along the appropriate half of the coast