dropstones their origin and significance abstract dropstones are clasts which pose a hydrodynamic paradox or which have an exotic or extra basinal lithology with uncertain provenance recently dropstones have been consistently interpreted as the product of ice rafting and have been used to substantiate the presence of cool climatic phases in the geological record this review illustrates that not all dropstones are reliable as palaeoclimatic indicators dropstones are the product of two distinct entrainment and transport mechanisms by a rafting agent or as a projectile four main processes of transport and formation are identified biological rafting ice rafting floatation and projectiles biological rafting agents include vertebrate gastroliths and other stomach contents vegetational rafting and anthropomorphic activity ice rafting can be the product of ice bergs or seasonal sea river or lake ice floatation of clasts in calm waters has been recorded for stones up to 25 mm in length projectiles are most commonly of volcanic origin given the range of transport and depositional mechanisms reviewed we argue that great care is required in the interpretation of the origin of dropstones

a numerical study on the influence of the mid atlantic ridge on nonlinear first mode baroclinic rossby waves generated by seasonal winds abstract a numerical model simulation investigates the influence of the mid atlantic ridge on nonlinear first mode baroclinic rossby waves generated by seasonal wind fluctuations the north atlantic is simulated by a square box two layer quasi geostrophic qg model the bottom topography is ridge like and compromises the qg approximation and the actual shape of the ridge sponge layers protect all boundaries except the eastern one from wave reflection and eliminate the build up of the western boundary current the model is forced by a purely fluctuating wind stress curl derived from the most significant eofs of the fgge winds a flat bottom and a ridge experiment are compared in both experiments the eastern boundary is an important source of annual period baroclinic rossby waves wave trains having a wavelength of about 1060 km and a westward phase speed around 3 4 cm s 1 propagate energy westward at 3 cm s 1 in the flat bottom experiment a source of directly wind forced baroclinic waves of annual per

mid latitude mesoscale variability neither homogeneous quasi geostrophic turbulence nor the effect of eddies on the interior ocean circulation remains the major focus of mesoscale research as was the case for much of the preceding 20 years following identification of the phenomena concentration on basin wide geographical exploration of eddy properties was rather well established by 1978 over the last few years a promising zero order description and rationalization of the mesoscale field has become available that is eddy energy is largest near strong flows intensification not only in western boundary currents but along their mid latitude open ocean extension roughly as indicated by gyre scale numerical models where eddies develop as a result of instability processes in the mid latitude jet and recirculation regimes and then propagate into the ocean interior our point of view is that mesoscale eddies drive recirculations but do not play a crucial role in the dynamics of the mean flow in the ocean interior in the north atlantic for example the idea is that the downstream increase in transport of the gulf stream is eddy driven but not the flow through the florida straits in addition the fluctuating response to forcing by variable winds may now be widely perceived as forming the horizontally homogeneous background signal in subtropical gyres the time dependent field associated with thermohaline flows at abyssal depths also has a special character

a depositional record of deglaciation in a paleofjord late carboniferous pennsylvanian of san juan province argentina the role of catastrophic sedimentation the combination of high sediment supply rates and ample accommodation within fjords provides high resolution records of deglaciation ancient fjord fills provide the potential for three dimensional views of the evolution of depositional environments in response to changing sediment supply and base level through the deglacial process we describe the fill jejenes formation of a well exposed late carboniferous pennsylvanian glacial valley and its tributaries these deposits record the progressive marine flooding and infilling of topography by glacially derived sediments the geometry of the valley and its tributaries is controlled by the underlying lower paleozoic lithologies a deep valley with steep sides exists where the bedrock is massive limestones and a broader shallower valley exists where the bedrock is generally a fine grained olistostrome the valleys are locally floored with diamictites including both in situ tillites and remobilized diamictites in the trunk valley these are locally overlain by a small shallow water delta the major part of the valley fill consists of a 150 m thick mudstone dominated succession probably generated by plumes of glacial outwash containing numerous dropstones that decrease in abundance down the fjord the mudstones contain numerous thin sandstone and conglomerate turbidites that were supplied laterally via subaqueous gravel fans feeding in from the tributary valleys each of which has a distinctive clast suite related to the local subcrop the entire succession is overlain by 300 m of sandy turbidites of which the upper part includes large mass transport complexes intercalated within the succession in the trunk valley are structureless graded silty mudstones lacking dropstones but with abundant large wood fragments close to the steep western margin of the trunk valley each of these massive mudstones is underlain by a slump or debris flow locally containing meter scale blocks of ordovician limestone from the valley side we interpret these as a consequence of rockfalls from the steeper valley sides triggering debris flows on the subaqueous fjord slopes we suggest that large solitary waves were generated as the rockfalls entered the water traveling along the fjord and stripping vegetation from the shoreline large amounts of mud and silt were thrown into suspension during these events and subsequently settled from suspension to form the structureless graded beds these deposits and other mass flow deposits within the succession emphasize the potential importance of catastrophic sedimentation within deglacial successions

frontogenesis subduction and cross front exchange at upper ocean fronts the subduction of water at upper ocean fronts driven by internal instabilities is investigated a simple analytic model which assumes conservation of potential density and potential vorticity is used to characterize the expected structure of subducted parcels as a function of the surface layer depth and the length scale of the parcel parcels subducted from a deep surface layer will be characterized by anomalously low potential vorticity and anticyclonic circulation while shallow surface layers result in subducted parcels with high potential vorticity and cyclonic circulation a nonlinear isopycnal primitive equation model is used to demonstrate how baroclinic instability and the resulting frontogenesis force the subduction of parcels below and across the front frontogenesis generates vertical velocities of 0 30 m d and ageostrophic cross front flows of 3 to 5 cm s the subduction is achieved by the deep ageostrophic flow which carries water from the surface layer below and across the front the subducted parcels quickly develop a circulation through balanced adjustment anticyclonic for deep surface layers and cyclonic for shallow surface layers the characteristics of parcels subducted in winter conditions closely resemble a class of eddies called submesoscale coherent vortices the horizontal and vertical scales of the vortices are determined by the frontogenetic mechanism and the depth of the surface layer the total permanent subduction rate is estimated to be 20 m yr for frontal subduction driven by frontogenesis although local and temporary subduction can be much larger the subducted anticyclonic vortices are often coupled to upper ocean cyclonic vortices thus forming a baroclinic dipole that propagates at approximately 3 5 cm s and is capable of transporting the anomalous water properties far from the region of formation similarities with observations in the north atlantic subtropical convergence zone and near the gulf stream are discussed

on the maintenance of the subtropical front and its associated countercurrent abstract in the north pacific and atlantic oceans the subtropical countercurrent is an eastward flow across the subtropical gyre at a latitude where a classical wind driven circulation theory would predict a westward flow it is in geostrophic balance with the subtropical front a zonal density front which runs across the ocean basin from previous numerical models it is argued that convergence of ekman transports can hardly be the primary reason for the existence of such a phenomenon and that thermodynamic effects play a crucial role to elucidate how them may be responsible for the frontal structure a very simple analytical model is constructed where the dynamics yield motions consisting of a nondivergent wind driven sverdrup current and a geostrophic thermal flow that is divergent on a beta plane the surface temperature is governed by a nonlinear hyperbolic equation for which the corresponding characteristics intersect separating the basin into two distinct regions limited by a temperature discon

earthquake induced sediment failures on a 0 25 slope klamath river delta california on november 8 1980 a major earthquake magnitude 6 5 to 7 2 occurred 60 km off the coast of northern california a survey of the area using high resolution seismic reflection and side scan sonar equipment revealed the presence of extensive sediment failure and flows in a zone about 1 km wide and 20 km long that trends parallel to the shelf on the very gently sloping c and a prominent 1 to 2 m high seaward facing toe scarp on the outer margin of the terrace this toe scarp is sinuous appears to be nearly continuous for a distance of 20 km and closely parallels the 60 m isobath evidence indicates that the toe scarp is the terminus of lateral spreads and lobes of sediment flows side scan sonar records show evidence of gas vents and small 10 3 0 5 m high pressure ridges formed seaward of and parallel to the sediment flow scarp indicators of liquefaction sand boils and collapse craters are present on the sediment flow terrace extensive sediment failure occurred on a sea floor slope of less than 0 25 and we can unequivocally pinpoint the cause as an earthquake of known location magnitude and time

frontal surveys with a towed profiling conductivity temperature depth measurement package seasoar in april 1986 rv oceanus participated in the frontal air sea interaction experiment fasinex1 in the region 27 29 n 68 71 w the objective was to survey a pronounced oceanic front2 4 and its effect on the oceanic and atmospheric boundary layers although moorings have yet to be recovered and much of the data analysis is as yet only preliminary it is possible to report here the typical density structure of a front as derived from seasoar5 6 fig 1a observations which were analysed within a few hours of collection previously unreported detail is revealed including subducted pycnostads areas of weak vertical density gradient with anomalous temperature salinity signature splitting of the frontal jet and three dimensional structure not apparent in the surface temperature field

the late carboniferous glacial to postglacial transition facies and sequence stratigraphy western paganzo basin argentina abstract namurian early westphalian glacial postglacial deposits have been documented in the paganzo basin argentina but integrated sequence stratigraphic and sedimentological analyses of the glacial postglacial transition are rare in the cuesta de huaco section the glacial postglacial transition encompasses the lower sequence of the existing schemes glacioeustatic changes in sea level controlled the architecture and vertical arrangement of facies the basal sequence boundary is coeval with the onset of glaciation when sea level fell contemporaneous with glacial erosion and bypass of sediment the upper sequence boundary is a high frequency sequence boundary the basal deposits are interpreted as an early transgressive systems tract etst initiated during glacial retreat the interval fines upward contains current reworked diamictites conglomerates and sandstones deposited in a subglacial to proglacial environment facies i ii and ice rafted glaciomarine rhythmites facies iii postglacial brackish marine black shales facies iv represent the late transgressive systems tract ltst micritic limestone beds were deposited during a period of sediment starvation coeval with the maximum marine inundation in the basin mfz it marks a turnaround in the stacking pattern that became coarsening and thickening upward during the overlying highstand systems tract hst it consists of fine grained turbidites facies v and classical turbidites with wave reworked beds at the top facies vi deposited in a shallow deltaic systems intervening postglacial brackish deposits contain an ichnofauna dominated by trackways of arthropods and minor grazing traces preserved in bedding planes that resemble nonmarine ichnocoenoses and differ from the archetypal brackish ichnofaunas even when palynological data support the saline depleted environment

linear instability of a mixed layer front the linear instabilities of a geostrophically balanced frontal jet are computed numerically in an effort to understand the origin of intense small scale cold core features observed in the north atlantic subtropical convergence zones during the frontal air sea interaction experiment fasinex a simple analytic continuously stratified basic state is used to represent the observed frontal structure the most unstable linear modes have e folding timescales of 2 3 days alongfront wavelengths near 70 km and significant asymmetry across the front the results provide indirect evidence that baroclinic instability of the frontal jet is a possible source of the cold core features observed during fasinex

forced ocean response during the frontal air sea interaction experiment a central hypothesis of the frontal air sea interaction experiment fasinex was that the strong gradients in the upper ocean associated with ocean fronts would spatially modulate the response of the ocean to local atmospheric forcing to test this hypothesis measurements of near surface meteorology and upper ocean variability were made for 5 months from an array of moorings and for one of those 5 months from two ships a number of fronts passed through the moored array and the moored meteorological and current meter data were used to examine the response of the upper ocean to atmospheric forcing at subinertial and near inertial frequencies at low frequencies an ekmanlike frictionally driven component in the mixed layer and a more deeply penetrating component thought to be forced by ekman pumping were found strong near inertial response was found in the mixed layer the near inertial motion showed considerable spatial variability in the seasonal thermocline here it was evident that the structure of the front influenced the downward propagating near inertial internal waves data were also obtained by profiling instruments deployed along cross frontal sections these data were used to examine the spatial and temporal variability of the internal waves microstructure and dissipation and the relation of that variability to oceanic fronts and atmospheric events the spectral densities of the components of the internal waves that rotated clockwise with increasing depth were higher in regions of negative relative vorticity than those predicted by garrett and munk munk 1981 and estimates of clockwise and total shear were highest in regions of negative relative vorticity in the strong shear of the ocean front significant anisotropy of the internal wave field was observed and kinetic energy dissipation levels relative to the rate of work by the wind were higher than previously reported

fluvial inertia dominated deltaic deposition in the namurian carboniferous of northern england the namurian upper carboniferous scar house beds of yorkshire northern england are an example of a fluvial dominated deltaic sequence that cannot be adequately described using existing classification schemes for deltas for substantial periods of the scar house delta history inertial processes and hyperpycnal mixing prevailed in the river mouth area due to repeated frequent flooding in the distributary system this generated voluminous density currents which deposited their sandy loads in successively stacked lobes beyond the river mouth bar in the prodelta area the position of a lobe was directly controlled by the position of an active river mouth only during periods of low discharge in the distributary system did homo and hypopycnal mixing take place in these periods frictional and buoyant forces operated and sand was deposited from tractional sheet flow on the mouth bar while mudstone was laid down in the otherwise density current dominated prodelta because of the dominantly hyperpycnal mixing mode the river effluent experienced a low lateral spread causing an elongate delta lobe to form that in geometry can be compared with some recent and ancient bar finger sands important differences exist in terms of dominant depositional processes however most other bar finger sands were controlled by a hypopycnal mixing mode and buoyant forces e g south pass mississippi while the scar house delta was controlled by hyperpycnal mixing and inertial forces this study shows that similar sand body geometries can be generated from different river mouth processes in the future particularly in the field of hydrocarbon exploration there may be a need to classify deltas both in terms of geometry and dominant river mouth processes in that respect the scar house beds represent a fluvial inertia dominated elongate delta

deglacial and postglacial sedimentary architecture in a deeply incised paleovalley paleofjord the pennsylvanian late carboniferous jejenes formation san juan argentina quebrada de las lajas near san juan argentina preserves an early pennsylvanian deglacial postglacial succession in a highly confined paleofjord setting the sedimentary succession records four distinct stages in the evolution of the valley fill stage 1 is represented by the deposits of subglacial diamictites ice contact deltas and related deep water lacustrine environments including several subaqueous channels stage 2 records a glacio eustatic marine transgression and a slow down of the clastic supply into the paleofjord stage 3 records a sandy confined turbidite environment stage 4 consists of a coarse grained delta which represents a significant rejuvenation of the sedimentary system in the paleofjord the transition from stage 1 to stage 2 was abrupt and basinwide and has proven to be a good regional correlation marker in this paleovalley the glacio eustatic rise probably caused floating and consequent rapid melting of the valley glacier this resulted in a paleovalley wide turbidite event that is up to 5 m thick and indicates an overall waning character the rapid sediment emplacement in this event and resulting loading of the paleovalley sediments may have helped cause widespread mass transport events at the stage 1 2 boundary all stages show evidence of mass transport related deposits but stage 1 records the most widespread mass transport with a large spectrum of processes represented including coherently slumped material rafted blocks and completely mixed debris flow deposits these mass transport deposits range from a few meters to over 50 m thick and up to hundreds of meters wide and long most of the large mass transport deposits in the lower part of the fjord fill occurred at the transition to stage 2 implicating a rise in relative sea level as a possible trigger for the slope failures additionally stage 3 deposits were affected by several thrust sense dislocations that have large offsets relative to the scale of the sedimentary succession tens to over 50 m vertically and hundreds of meters laterally strata associated with the dislocations exhibit growth indicating very early movement and they are interpreted as the frontal ramp zones of mass transport deposits the abundance and size of mass transport deposits in stages 1 and 3 helped control sediment pathways throughout the paleofjord

intensive surveys of the azores front 2 inferring the geostrophic and vertical velocity fields the geostrophic and vertical velocity fields are inferred using density and horizontal velocity data from three seasoar acoustic doppler current profiler surveys of the azores front the analysis is a two step procedure consisting of 1 objective analyses to reflect the observed length scales and 2 dynamical adjustments so that the density field is statically stable and the velocity field is in geostrophic balance the vertical velocity is inferred using a version of the quasi geostrophic omega equation in which the stratification is allowed to vary in the horizontal the resulting vertical velocity peaks at 2 10 4 m s 1 at 200 300 m there is a tendency for the denser water to the north of the front to be downwelled while the warmer water to the south is upwelled the implied heat flux exceeds 10 w m 2 near 100 m depth so the upper 100 m is warmed while the lower water column is cooled tending to stratify the upper ocean ageostrophic horizontal flow is toward the dense side of the front at the surface the dominant terms in the density balance are time rate of change and horizontal advection the inferred circulation cells may be an important mechanism of subduction in the upper ocean

a new serpukhovian mississippian fossil flora from western argentina paleoclimatic paleobiogeographic and stratigraphic implications an uppermost mississippian serpukhovian fossil flora from western argentina is described for the first time its particular composition includes both warm climate plants typical from the pennsylvanian of gondwana namely pteridosperms sphenophytes as well as arboreous lycopsids and small lycopsids characteristic of cooler climates of pre serpukhovian times a warm temperate climate is inferred for this association which fills a time gap between those pennsylvanian and mississippian classic floras previously known the presence of tomiodendron nothorhacopteris kellaybelenensis and paracalamites allow the recognition of the paraca floral realm in argentina supporting the existence of a nonglacial paleoclimate period developed just before of the bashkirian moscovian gondwanan glaciation and after a latest visean glaciation it likewise would indicate the paleogeographic position of south west gondwana which would have acceded to a warm temperature latitudinal belt during serpukhovian times the recognition of this floral assemblage has relevant biostratigraphic and lithostratigraphic implications for the western margin of gondwana it defines a new zone for western argentina herein named frenguellia eximia nothorhacopteris kellaybelenensis cordaicarpus cesarii fnc zone which is recorded in the oldest known lithostratigraphic unit from the paganzo basin the loma de los piojos formation nom nov

paleoclimatic significance of the lacustrine carboniferous deposits in northwest argentina abstract the origin and probable paleoclimatic significance of carboniferous lacustrine deposits in northwest argentina are discussed these rocks are developed extensively throughout northwestern argentina but are described in the present paper only from the region of the sistema del famatina five lithofacies have been identified a laminated siltstones and claystones b thinly interbedded mudstones and sandstones c interlayered mudstones and sandstones with sole structures flute marks and tool marks d conglomerates and fine sandstones e sandstones and diamictites these lithofacies are interpreted as lacustrine deposits formed during the final episode of the carboniferous glaciation lithofacies a originated as a suspension load deposit in the central and intermediate parts of the lake the presence of dropstones in this lithofacies suggests coeval ice rafting processes underflow currents probably formed lithofacies b and lacustrine turbidites lithofacies c lithofacies d and e were deposited in marginal environments and represent in some cases shoreline bars and small deltas the age of the lacustrine episode is deduced from paleobotanical information both palynological and megafloristic data suggest that these deposits were formed during the middle carboniferous a palynological assemblage dominated by cristatisporites like spores characterizes these sediments

the three dimensional circulation near the eastern north pacific subtropical front abstract the purpose of our study is to describe and compute the large scale three dimensional circulation near the subtropical front in the eastern north pacific along 31 n this was accomplished through the use of four extensive hydrographic surveys historical wind stress data and also the movement of surface drifters our results indicate that in wintertime surface water sinks on the north side of the front and rises on its south side during the summer however the subtropical salty surface water overflows the frontal area to the north potential vorticity and heat are best conserved in a vertical flow pattern where the annual mean ekman convergence sinks to a depth of 300 m and water upwells throughout the main thermocline the computed horizontal flow below 700 m amounts to less than 0 6 cm s 1 both strength and direction depend greatly on the treatment of noise within the data set and also on the conservation statement that is specified in addition to geostrophic and hydrostatic dynamics a q

descriptive oceanography during the frontal air sea interaction experiment medium to large scale variability medium and large scale oceanographic variability in the sargasso sea is examined during the frontal air sea interaction experiment fasinex focusing primarily on processes that influence the formation of subtropical fronts from fall to spring the mean meridional gradient of meridional ekman transport in the subtropical convergence zone stcz enhances the meridional sea surface temperature ts gradients between 26 o and 32on in the presence of this enhanced mean gradient baroclinic eddies with zonal wavelengths of 800 km and periods of 200 days exert the dominant influence on the formation of subtropical fronts at medium and large scales these eddies generate westward propagating ts anomaly features with the same dominant wavelengths and periods they are confined between 26 o and 32on and have amplitudes that occasionally exceed ioc ts fronts tend to be found within bands 200 km wide that roughly follow the periphery of these anomaly features deformation in the horizontal eddy current field is primarily responsible for the existence of these frontal bands the migration of the strong front originally bracketed by the fasinex moored array was related to the westward propagation of the larger scale eddy anomaly frontal band pattern the moored array was located within a warm anomaly feature during most of the experiment which produced exceptionally warm conditions in the upper ocean these anomalies are confined between 26 o and 32on not only because the relatively large seasonal mean tsy there allows horizontal eddy currents to force strong anomalies but also because the baroclinic eddies with wavelengths of 800 km and periods of 200 days are confined to the stcz large meridional variability exists in many properties of the eddy field much of which can be traced to the influence of the sargasso sea mean current field on eddy variability

a planetary wave analysis using the acoustic and conventional arrays in the 1981 ocean tomography experiment abstract using the maximum likelihood estimation method quasi geostrophic wave solutions are fitted to the observations of the 1981 ocean acoustic tomography experiment the experiment occupied a 300 km square area centered at 26 n 70 w over a duration of approximately 80 days the dataset consists of acoustic travel time records moored temperature records and ctd profiles the acoustic data correspond to integral measurements of the temperature or sound speed filed the optimal fit to the data corresponds to three waves in the first baroclinic mode evolving under the presence of a westward mean flow with vertical shear the mean flow is found to be weak approximately 2 cm s 1 but changes the wave periods significantly by producing large doppler shifts the waves are found to be dynamically stable to the mean flow have weak nonlinear interactions with each other and do not form a resonant triad thus they constitute a fully linear solution evidence for the existence of the waves is strongly sup

depositional settings and evolution of a fjord system during the carboniferous glaciation in northwest argentina abstract fjord systems represented by glacial diamictites and postglacial transgressive shales formed in the basins of western argentina during the late carboniferous gondwana glaciation well exposed fjord deposits of the guandacol formation were studied in the loma de los piojos region protoprecordillera where they fill a 2 9 km wide paleovalley with steep side walls and a relatively flat floor the valley cross cuts lower devonian sandstones and mississippian mudstones and sandstones and provides evidence of glacial abrasion including striated pavements and glacial microtopography grooves ridges and striae based on the analysis of seven sedimentary logs eight sedimentary facies in the valley fill were recognized a massive diamictites b laminated mudstones with dropstones c stratified diamictites d clast supported conglomerates and sandstones e deformed diamictites conglomerates and sandstones f folded diamictites g mudstones interbedded with sandstones and h stacked and amalgamated sandstones these sedimentary facies are grouped into two principal facies assemblages that represent different stages of the paleovalley fill assemblage 1 is composed of diamictites facies a c and f laminated mudstones with dropstones facies b and conglomerates facies d and e which represent glacially influenced sedimentation in the paleovalley assemblage 2 represents the paleovalley fill when glacial influence ceased and comprises laminated mudstones interbedded with sandstones facies g and stacked sandstone beds facies h that mostly record deltaic sedimentation stratigraphic relationships plant fossils found in the paleovalley walls and palynological assemblages recovered in mudstones of facies d help to establish an early pennsylvanian age for both the incision and the filling of the paleovalley the studied paleovalley records an exceptional example of the western gondwanan glacial to postglacial transition due to the continuous stratigraphic succession within the paleovalley as well as palynological megafloristic and radiometric data this example provides a complete framework of the late carboniferous postglacial evolution in western gondwana

soft sediment deformation within seismogenic slumps of the dead sea basin abstract the late pleistocene lisan formation preserved next to the dead sea provides exceptional 3 d exposures of folds and faults generated during soft sediment slumping and deformation it is possible to generate a range of four different scenarios associated with overprinting in a single slump event the progressive evolution of slump systems may be broadly categorised into initiation translation cessation relaxation and compaction phases thrust packages typically define piggyback sequences during slump translation with back steepening of imbricate faults leading to collapse of folds back up the regional palaeoslope detailed evaluation of slumped horizons may also permit structures to be traced across apparently separate and distinct slumped units the recognition that slumps may be reworked by younger seismically triggered events suggests that in some cases the seismic recurrence interval may be shorter than previously anticipated

the mean circulation east of the bahamas as determined from a recent measurement program and historical xbt data abstract observational evidence from a two ship synoptic survey from one year long current measurements at four sites and from two independent long term expendable baththermograph xbt data sets is combined to describe the circulation east of the bahamas the results indicate that a weak antilles current actually exists at mid depths about 300 100 m with a northward transport along this boundary of about 4 106 m3 s 1 however both the dynamic height fields and water mass distributions suggest that this current does not represent return flow from the gyre wire sverdrup recirculation but instead is part of the northwestern gulf stream recirculation system west of about 50 w the near surface flow east of the bahamas is more complicated and consists of two isolated anticyclonic circulation cells along the boundary the most intense of these is centered just northeast of abaco island in the northern bahamas the southern weaker cell is centered at about 24 n 71 w in the area just north of puerto r

the energetic surface circulation patterns of the japan east sea abstract in the period of 1988 2001 226 argos fixed drifters were deployed in the japan east sea jes from these and the historical file of temperature at a depth of 100 m 15 m depth circulation and its variances in relationship to the seasonal mean warm and cold water regions were constructed on 0 5 resolutions the strongest seasonal currents were the east korean warm current ekwc the tsushima current tc the north korean cold current nkcc and local eastwards intensifications along the sub polar frontal patterns the tc and nkcc were observed during summer and drifters passed through the soya strait only in summer the sub polar front occurred along 40 n in the northeastern jes a separate front occurred in winter that was associated with the flow of warm water restricted to the southern jes small eddy energy was found in the cold water regime and large eddy energy in the warm water regime satellite altimeter and drifter tracks were used to mark the wonsan eddy found in the east korean bay a yearly late summer occurrence mechanical energy flux from the mean circulation to mesoscale eddies occurred in ekwc tc and the sub polar front in the eastern jes with eddy kinetic energy doubling time of 15 60 days the yearly mean circulation east of the korean coast is organized into a broad eddy filled east sea current that contains weak anticyclonic gyres in the ulleung and yamato basins it accelerates toward the yamato rise and against the eastern coast of the jes the published numerical model solutions show several historical circulation features but fail to capture many of the new structures described by the drifter data

sea surface temperature anomalies planetary waves and air sea feedback in the middle latitudes the mechanisms that contribute to the generation and damping of large scale mid latitude sea surface temperature sst anomalies are discussed the sst anomalies reflect primarily the response of the upper ocean to the changes in air sea fluxes that are associated with daily weather fluctuations heat flux forcing is dominant in the lower middle latitudes while wind driven entrainment may be most effective in the high latitudes advection by anomalous ekman current is generally less important and ekman pumping is negligible the sst anomalies decay in part because of entrainment effects associated with mixed layer deepening and oceanic mixing and in part because of heat exchanges with the atmosphere the three approaches commonly used to model the evolution of sst anomalies are reviewed case studies based on monthly or seasonal anomaly maps of the large scale sst and atmospheric anomalies numerical simulations with one dimensional mixed layer models and stochastic forcing models we stress the similarities in the different approaches and discuss their main advantages and limitations the response of the atmosphere to mid latitude sst anomalies is considered first we discuss the poorly known relationship between sst anomalies and diabatic heating using a crude assumption for the air sea coupling we consider a two layer quasi geostrophic channel model and discuss the stationary wave response to sst anomaly forcing and the resulting air sea feedback it is found that the back interaction of the sst anomalies onto the atmosphere causes a weak sst anomaly damping at large scales and a strong one at small scales the air sea coupling should also act as an eastward propagator for the sst anomalies the response of more realistic linear wave models to prescribed diabatic heating is then reviewed and it is suggested that realistic mid latitude sst anomalies have a weak influence on the atmospheric circulation corresponding to changes in the geopotential height of 10 30 m at most this order of magnitude is consistent with the results of general circulation model experiments and with the limited climate predictability associated with mid latitude sst anomalies

ocean frontal variability in the frontal air sea interaction experiment oceanographic observations during the frontal air sea interaction experiment fasinex in the sargasso sea indicate that upper ocean fronts in the subtropical convergence are strongly surface intensified coherent flow structures which have a preferred orientation and translation speed fronts grow as they propagate in this region such that currents roughly double in strength in a time that they translate by twice their width while currents are dominated by geostrophic momentum balance the rossby number of these flows can reach a few tenths mixed layer water from the cold side of fronts appears to subduct under warm side near surface waters since isolated lenses of water with cold side temperature and salinity characteristics are found embedded in the seasonal thermocline on the warm side of fronts although plausible vertical speeds were observed no actual rates of subduction could be estimated typical frontal widths temperature contrasts horizontal currents vertical shears vertical currents and translation speeds of fronts in the region studied are 20 km 1 c 0 5 m s 1 0 005 s 1 0 0005 m s 1 and 0 2 m s 1 respectively

an upper paleozoic bio chronostratigraphic scheme for the western margin of gondwana abstract the carboniferous and permian fossiliferous sequences of the central western argentina contain abundant plant remains palynomorphs and invertebrates they include a continuous record of large distribution in the paganzo rio blanco calingasta uspallata and san rafael basins the most recent biostratigraphic schemes recognize a floristic succession represented by the biozones archaeosigillaria frenguellia af biozone frenguellia eximia nothorhacopteris kellaybelenensis cordaicarpus cesarii fnc biozone nothorhacopteris botrychiopsis ginkgophyllum nbg biozone interval biozone and gangamopteris biozone the associated palynological record is represented by the biozones reticulatisporites magnidictyus verrucosisporites quasigobbetti mq biozone raistrickia densa convolutispora muriornata dm biozone pakhapites fusus vittatina subsaccata fs biozone and lueckisporites weylandites lw biozone the precise age of the upper paleozoic western gondwanan biozones has been under discussion and remains controversial to date in some regions the main issue hampering an integrated comparison of the gondwanan biozones was its imprecise chronostratigraphic framework however new studies in some argentinian stratigraphic sections bearing floras and faunas have yielded several radiometric ages from these 206 pb 238 u zircon datings it is possible to determine the chronostratigraphic range of many fossiliferous assemblages in this sector of gondwana in this way the af and mq biozones are restricted to the late mississippian and they would be not younger than 335 ma according to radiometric ages 206 pb 238 u ages suggest that the nbg dma and dmb biozones characterize the late serpukhovian glacial deposits and persisted up to the late bashkirian beds containing the interval and dmc biozones have yielded 206 pb 238 u ages of 312 82 0 11 ma and 310 71 0 1 ma which would indicate that both zones characterize the moscovian the remains of gangamopteris biozone found in the paganzo basin overlie basalt levels ranging between 308 6 and 293 6 ma therefore the incoming of the first glossopterids was closely associated to the carboniferous permian boundary in this part of gondwana the data presented in this paper are used for establishing comparisons with other gondwanan biozones constrained by absolute ages

vertical vorticity balance in meanders downstream the agulhas retroflection abstract the agulhas current flows poleward along the western boundary of the southeastern indian ocean where at the southernmost latitude of the african continent it executes a dramatic anticyclonic turn or retroflection to the east since 1978 a large number of drifting buoys have passed through this eastward flowing agulhas return current arc or the zonal frontal boundary between subtropical and subpolar waters of the south indian ocean the spatial distribution of the ensemble averaged near surface velocity along the arc axis reveals a series of steady state meanders of 700 km wavelength and amplitudes that decrease from 170 km in the first meander to 50 km in the following four meanders here an analysis of vorticity balance of the meandering arc speed axis is presented that demonstrates a balance between the term and advection of curvature vorticity this balance implies that the arc axis or frontal region is horizontally nondivergent in agreement with the other observations of flow in t

evidence of glacial abrasion in the calingasta uspallata and western paganzo basins mid carboniferous of western argentina abstract evidence of glacial abrasion is present in the basal part of the carboniferous section of the calingasta uspallata and paganzo western argentina where subglacial and proximal glacial marine diamictites with pebbly dropstone shales constitute the dominant facies association intraformational striated pavements are exposed in the hoyada verde and leoncito formations of the calingasta uspallata basin marine invertebrate fossils levispustula zone in associated shales indicate a mid carboniferous age for both units a single layer striated boulder pavement is superbly exposed in the hoyada verde formation local a axis clast imbrication in the underlying bouldery diamictite and strong parallel striae on the flattened upper surfaces of boulders indicate a subglacial origin for the pavement paleo ice flow directions have an nne ssw strike the leoncito intraformational pavement is shaped on bioturbated fine grained sandstones with plant remains glacial striations are straight and parallel with subcircular cross sections dome like features are present in the surface which is covered in turn by a sandy bouldery diamictite four striated surfaces are present in the western paganzo basin three of them pavements at the san juan river valley loma de los piojos and agua hedionda are developed on basement rocks they contain parallel to subparallel striations nailhead striations crescentic gouges impact marks and furrows the pavements are overlain by thin up to 1 5 m laterally discontinuous diamictite beds with striated clasts some of them bullet shaped paleo ice flow directions are n ne directed an intraformational pavement is also present at the san juan river valley section it is carved on the top of the basal diamictite and exhibits furrows probably caused by subglacial soft sediment grooving the dispersion of paleo ice flow directions in the calingasta uspallata and paganzo basins indicates i regional slopes toward the north into a brackish water embayment and northwest into the open marine conditions ii glacial erosion by ice grounded below sea level and confined to the margins of the basins

towed thermistor chain observations of fronts in the subtropical north pacific a thermistor chain was towed 1400 km through the eastern north pacific subtropical frontal zone in january 1980 the observations resolve surface layer temperature features with horizontal wavelengths of 0 2 200 km and vertical scales of 10 70 m the dominant features which have horizontal wavelengths of 10 100 km amplitudes of 0 2 1 0 c and random orientation likely arise from baroclinic instability associated with them is a plateau below 0 1 cpkm in the horizontal temperature gradient spectrum strong temperature fronts o 1 2 c 3 10 km are observed near 33 n 31 n and 27 n temperature variability is partially density compensated by salinity with the fraction of compensation increasing northward there is evidence of vertical mixing during high winds temperature at 15 m depth is roughly normally distributed around the climatological surface mean with a standard deviation of approximately 0 5 c the standard deviation would correspond to an adiabatic meridional displacement of 80 100 km in the mean gradient horizontal temperature gradient at 15 m depth has maximum values in excess of 0 25 c 100 m and kurtosis near 80 in the band 0 10 1 cpkm the 15 m gradient spectrum is inversely proportional to wave number consistent with predictions from geostrophic turbulence theory while the spectrum at 70 m depth has additional variance that is consistent with garrett munk internal wave displacements

geosat and advanced very high resolution radiometer observations of oceanic planetary waves adjacent to the hawaiian islands geosat observations of the central north pacific ocean show westward propagating mesoscale features with length scales 500 km time scales 105 155 days and observed zonal phase speeds commensurate with those of nearly nondispersive baroclinic rossby waves advanced very high resolution radiometer derived sea surface temperatures observed during april 1988 showed a cusp shaped pattern north of the hawaiian islands congruent with concurrent geosat derived sea level height anomalies it is believed that the cusp shaped pattern is the surface manifestation of a baroclinic rossby wave the observed wavelength of the cusp shaped pattern was 560 km it had an observed meridional extent horizontal amplitude of 200 300 km and an inferred zonal propagation speed of 0 052 m s 1 the westward propagating sea level height structure was observed to amplify as it approached 150 w reaching amplitudes of 0 06 0 08 m in the vicinity of the cusp shaped feature these waves are believed to be locally forced by the topography either as the result of eastward flow over the submerged island ridge or as a result of baroclinic instability during periods of westward flow

variability and frontogenesis in the large scale oceanic frontal zones sea surface temperature sst from weekly global advanced very high resolution radiometer data for the period of 1982 1992 and estimates of the surface forcing due to wind stress and net heat flux are used to investigate a global monthly climatology of large scale oceanic frontal zones ofzs the variability of sst gradient in several frontal zones and the meridional frontogenesis in the north pacific subpolar frontal zones are identifiable in the sst gradient field throughout the whole year while subtropical frontal zones appear as seasonal phenomena in the northern hemisphere the magnitude and position of subtropical fronts were found to vary synchronously in both hemispheres with maximum intensity in november to march during this period subtropical fronts in the northern hemisphere become clearly identifiable separate features while in the southern hemisphere their southern boundaries tend to merge with the subpolar front in the northern hemisphere the northward shift of the subtropical frontal zones during late boreal spring results in a merger of the subpolar and subtropical zones by august in the southern hemisphere subtropical fronts separate from the subpolar front during this period and become clearly distinguishable though less intense singular spectrum analysis of the 11 year time series of sst gradient in several ofzs revealed a seasonal signal as well as interannual variations that in the equatorial zone are related to el nino events the amplitude of the annual cycle is comparable in the subtropical and subpolar north pacific but the subtropics leads the subpolar zone by about 4 months combined forcing due to wind stress and net surface heat flux was found to be sufficient to describe most of the observed frontogenesis variability in north pacific midlatitudes on seasonal timescales but not on shorter timescales in the subtropical zone the ekman convergence alone was not sufficient to provide the observed frontogenesis frontolysis on seasonal time scales in fact when the maximum frontogenesis associated with ekman convergence occurs in late spring early summer this is counteracted by the frontolytic effect of ekman pumping and the dominating frontolytic effect of surface heat forcing in summer ekman convergence is more important in the subpolar area where it is enhanced by the smaller frontogenetic effect of both ekman pumping and surface heat forcing surface forcing due to wind stress and heat flux considered in this study does not explain the high amplitude intraseasonal frontogenesis variations especially in the subpolar region

the three dimensional structure of an upper ocean vortex in the tropical pacific ocean in the equatorial pacific ocean easterly trade winds and the earth s rotation combine to drive surface currents away from the equator thereby causing cold nutrient rich subsurface water to upwell the front1 that forms between this upwelled water and warmer waters north of the equator is sometimes visible as a spectacular line in the sea 2 between 2 and 6 n westward propagating cusp shaped disturbances observed along this front3 have been attributed to the effect of dynamical instabilities in the system of zonal equatorial currents4 11but the connection between these phenomena remains unclear here we report extensive measurements from shipboard sensors satellite and drifting buoys which reveal the three dimensional structure of an anticyclonic eddy or vortex 500 km in diameter and centred at 4 n we suggest that cusp shaped disturbances of the front are caused by trains of large amplitude vortices which are driven by instability of the mean zonal shear we show that these vortices not only play an important role in the meridional transport of heat salt and momentum but are also associated with regions of intense horizontal convergence along the front where dramatic concentrations of marine life are observed

reassessment of mid carboniferous glacial extent in southwestern gondwana rio blanco basin argentina inferred from paleo mass transport of diamictites abstract late paleozoic glacial diamictites occur in many localities in western argentina indicating that the region was strongly affected by glaciation during the mid carboniferous late serpukhovian early bashkirian in most instances these diamictites are found in steeply walled paleovalley settings in the andean precordillera this study presents new data from a locality north of the precordillera that suggests an additional distinct volume of ice existed in the region during the carboniferous the glacigenic diamictites in the rio blanco basin were ultimately emplaced as gravity flows precluding inferences of paleo ice volume fold nose orientation and soft sediment groove orientations within the diamictites indicate that the deposits were emplaced from north to south suggesting that glacial ice was most likely not sourced from the proto precordillera at this locality requiring the need for another ice center to the north of the basin diamictite facies indicates that the sediment was initially supplied to the study area by a warm based glacier

iceberg drop dump and grounding structures from pleistocene glacio lacustrine sediments scotland abstract dropstone dump and grounding structures resulting from the melt out of debris contained in floating and grounded icebergs are described from a pleistocene ice marginal glacio lacustrine sequence in scotland dropstones display bending penetration rucking and complete rupture of stratum occurring beneath them and onlap above them with the degree of deformation varying as a function of the size shape and axial disposition of the clast and of the sediment type into which they fell dump structures are conical mounds of gravel or diamict formed by the break up and overturning of dirt laden icebergs and the consequent release of large quantities of debris to the lake floor grounding structures are caused by the grounding of icebergs the down warping of underlying lake floor se iment and the subsequent in situ melt out of contained debris to form isolated troughs of diamict

applications of ichnology in lacustrine sequence stratigraphy potential and limitations abstract in comparison with their marine counterparts lacustrine ichnofaunas have not been extensively used in sequence stratigraphy application of trace fossils in continental sequence stratigraphy cannot be based simply on the extrapolation of marine sequence stratigraphy marine substrate controlled ichnofacies in particular the firmground glossifungites ichnofacies develop in stable and cohesive substrates reflecting erosive exhumation of the sediment in contrast in lacustrine sequences substrate controlled ichnofossils only rarely indicate erosional exhumation because they are commonly related to desiccation of water bodies the tripartite division of overfilled balanced fill and underfilled lakes provides a comprehensive framework to evaluate the potential and limitations of lacustrine ichnofaunas in sequence stratigraphy based on a number of case studies spanning the three lake basin types a model of trace fossil distribution in overfilled balanced fill and underfilled basins is proposed overfilled lake basins contain well developed softground trace fossils mermia and skolithos ichnofacies and the softground suite of the scoyenia ichnofacies that are useful to delineate parasequences and parasequence sets fluvial discharge into overfilled lakes usually generates density currents that oxygenate lake bottoms allowing the establishment of epifaunal and infaunal communities additionally these are freshwater lakes where no stress due to hypersalinity occurs leading to the development of a relatively diverse benthos land plant derived organic matter is the prime source of nutrients favoring the development of a deposit feeding benthic fauna in permanently subaqueous low energy zones firmground suites are rare because such large lakes usually do not experience desiccation abundant firmground trace fossil suites of the scoyenia ichnofacies occur in balanced fill lakes but softground assemblages are usually depauperate lowstand deposits contain abundant and widespread ichnofaunas commonly meniscate trace fossils and arthropod trackways of the scoyenia ichnofacies lake hydrology is closed during lowstands and salinity usually increases imposing a stress factor on the lake biota and therefore softground ichnofaunas are depauperate ichnofaunas from turbidite systems in balanced fill lakes are less abundant and diverse than those from overfilled lacustrine turbidites freshwater conditions are common during transgression but dysaerobic conditions may prevail imparting a stress factor on the benthic biota in hydrologically closed lakes the scoyenia ichnofacies is widespread but the mermia ichnofacies is commonly absent or impoverished the scoyenia ichnofacies is associated with lowstand desiccated substrates in underfilled lakes the density of arthropod trackways may be high forming tracked omission surfaces some of these omission surfaces may represent sequence boundaries expressed by co planar surfaces of lowstand and subsequent flooding rapid changes in depositional conditions reflecting desiccation during vertical aggradation can lead to the formation of composite ichnofabrics that reflect successive bioturbation events

thin bedded diamictites in the glaciomarine hoyada verde formation carboniferous calingasta uspallata basin western argentina a discussion on the emplacement condition of subaqueous cohesive debris flows abstract thin bedded 0 5 20 cm diamictites are present in the glaciomarine sequence of the hoyoda verde formation carboniferous of the calingasta uspallata basin the sharp non erosive contacts the high mud content and the wide range in clast size suggest that the thin bedded diamictites have been deposited as subaqueous debris flows bed thickness bth versus maximum clast size mcs plots show a strong positive correlation 0 95 proving that the flows had a close balance between capacity and competence and were laminar the cohesive factor also deduced from the bth mcs plots indicates that the flows can be interpreted as cohesive debris flows the widespread presence of inversely graded or massive beds and low bth mcs values mean bth mcs 2 71 standard deviation 0 33 suggest relatively concentrated competent debris flows with minor water intake in contrast to other more frequent examples of more dilute water rich subaqueous debris flows with lower competence relative to flow thickness

glacimarine processes at grounding line fans and their growth to ice contact deltas abstract grounding line fans originate from subglacial and basal stream tunnels at grounding lines of glaciers terminating in a marine environment during melt seasons discharge forms a turbulent jet beyond the efflux over the initial zone of flow establishment in the jet it may remain in contact with the sea floor for up to 13 4 d d tunnel diameter along a runout distance if velocity is constant plug flow in this zone deposits marine outwash sediment commonly having chaotic texture and graded and welded contacts texture may vary rapidly because of discharge pulses and the jet may move laterally to produce sheet or cut and fill geometries imbricate gravel is deposited near the efflux then farther out are sheet or weakly channelized finer grained gravels and sands in some instances a migrating barchanoid bar forms at the detachment zone and forms large scale trough cross beds beyond the detachment zone the turbulent jet becomes vertical and sediment cascades from it in a veil this sediment is added to by flows from continuous failures of bed load sediment in the detachment zone resulting deposits are interstratified sediment gravity flows and thick coarse end members of cyclopsams the jet changes to a plume when inertial forces become less than buoyancy forces turbulent vorticies within the jet can re entrain particles into a buoyant plume the plume remains vertical although continuously spreading until reaching neutral buoyancy fan depocentres have been observed to accumulate at over 10 6 m 3 a 1 in temperate glacial areas eventually at quasi stable grounding lines fans may aggrade to sea level to form ice contact deltas at incipient deltas when the delta plain is intertidal coarse sediment is redistributed to the prodelta with each tidal cycle intense prodelta rhythmites mark the transition of a fan into a delta

variability of the climatic oceanic frontal zones and its connection with the large scale atmospheric forcing abstract global satellite sea surface temperature sst measurements and ncep ncar reanalysis wind data for the period of 1982 2009 have been used to study the seasonal and interannual variability of the main climatic oceanic frontal zones ofz subpolar subtropical and equatorial associated with the large scale atmospheric forcing the seasonal variability of the ofz is manifested in variations of their intensity magnitude of the meridional gradient of sst and latitudinal position of the cores defined as areas of maximum sst gradient the maximum intensity of the subpolar ofz is observed in summer of the corresponding hemisphere while subtropical ofz are intensified synchronously in both hemispheres during boreal winter subtropical ofz cores in both hemispheres shift synchronously to the south north during the winter summer of the northern hemisphere which is caused by the seasonal meridional migration of the areas of the maximum convergence of ekman transport all subpolar and subtropical ofz reveal a pronounced quasi decadal 7 10 years variability manifested in the variations of their intensity and latitudinal position of the zones cores strengthening of the sst gradient is accompanied by a displacement of the zones cores to the north in both hemispheres for subpolar ofz while subtropical ofz cores migrate to the poles in this situation positive correlations between the maximum magnitude of the meridional gradient of zonally averaged sst and meridional shear of zonal wind which is an estimate of the ekman convergence intensity were found for all subpolar and subtropical ofz variability of the latitudinal position of subpolar ofz cores is associated with the ekman advection variability due to zonal wind variations strengthening of zonal wind results in a shift of subpolar ofz cores to the south north in the northern southern hemispheres a period of the variability of the north pacific equatorial ofz is 4 5 years and is determined by the variability of the enso system during the el nino events the sharp decrease of the intensity of the equatorial ofz take place

effects of horizontal advection on upper ocean mixing a case of frontogenesis abstract the wind stress on the ocean surface induces horizontal advection and vertical mixing two mechanisms which are capable of changing the surface water density advection and mixing can enhance or partially destroy the effects of each other frontogenesis due to convergent ekman transports forced by a wind stress field is one example a bulk model for the study of advection and mixing in such circumstances is constructed from a one dimensional model continuity of mass requires that water masses either downwell convergence or escape laterally confluence this distinction leads to a study of two extreme cases of frontogenesis each herein treated separately the model reduces to two coupled highly nonlinear prognostic equations for the mixed layer buoyancy and mixed layer depth scaling of the equations leads to the definition of a mixing parameter a nondimensional number which measures the relative importance of advection and mixing for large scale ocean frontogenesis this parameter is of th

field evidence of the viscous sublayer in a tidally forced developing boundary layer field observations of boundary layer development within a tidally forced estuary revealed evidence of an observable viscous sublayer evidence is provided by several independent measures of the flow field including hydrodynamic smoothness an immobile bed and characteristic velocity constant stress and higher order moment structures this investigation reports what may be the second comprehensive observation of the viscous sublayer in a marine environment and what could be the first observation of a momentum balance that includes the viscous sublayer within a shallow estuarine environment hydrodynamic observations were made in a straight channel within the great bay estuary of new hampshire over a flat sandy mud with low water depth of 1 5 m at the sampling location beyond quantifying the role of the benthic boundary layer in nutrient dynamics these observations are useful to provide insight into very near boundary stress estimates leading to incipient motion in estuarine and coastal environments

models of glaciomarine sedimentation and their application to the interpretation of ancient glacial sequences abstract this paper argues that glaciomarine environments can be regarded as special glacially influenced types of continental margin environments e g continental shelf slope rise and basin plain knowledge of the stratigraphic architecture and typical sedimentary sequences of non glacial margins is becoming well known but remains limited for those that have been glacially modified the principal influences on sedimentation in these environments relate to the glacial sediment input controlled by relief of basin margin glacier thermal regime and ice flow dynamics and depositional environments influence of traction currents substrate relief and proximity to nearby ice margins typical ranges of sedimentation rates can be established for glacially influenced continental margin environments and these may provide a framework for ancient sequences starvation of sediment supply to glacially influenced continental margins is common the nature of sub ice shelf sedimentation a model that has been applied to many ancient glacial sequences is critically reviewed the significance of such sedimentation in the rock record has probably been exaggerated because of oversimplistic interpretations of diamictite sequences existing process models of glaciomarine sedimentation derived from study of modern environments are sometimes difficult to employ in investigation of ancient sedimentary sequences because simple lithofacies criteria and typical vertical profiles are not available to aid in interpretation in addition compositional data emphasized by many workers for distinguishing glaciomarine from continental glacial diamict ite s frequently fingerprint sediment source and not mode of deposition the importance of facies analysis methods for isolating depositional environments is illustrated by three examples of ancient glaciomarine sequences these are the early proterozoic gowganda formation 2 3 ga of northern ontario canada the late proterozoic port askaig formation 670 ma of scotland and ireland and the late cenozoic yakataga formation 20 ma to recent of the gulf of alaska these examples illustrate the significance of detailed genetic studies of ancient glacial rocks in the interpretation of palaeogeographic and tectonic settings diamictite units in ancient glaciomarine sequences cannot be easily interpreted in terms of climatic or ice advance retreat cycles because of the varied controls on diamict accumulation and diamictite preservation in marine basins

formerly aragonitic limestones associated with tillites in the late proterozoic of death valley california abstract the upper proterozoic virgin spring and sour dough limestones occur within the glaciogenic kingston peak formation of the death valley region eastern california the virgin spring limestone is black thinly laminated and consists of microscopic spheroids and scattered ooids contained within coarse neomorphic spar an original aragonite mineralogy is inferred and this is supported by high contents of strontium up to 3 650 ppm thin sandstone beds occur within the limestone and their features suggest a storm origin the sour dough limestone has been metamorphosed and deformed but shows similar sedimentary structures and a high sr content both limestones are interpreted as deeper water outer shelf deposits and their sedimentation is related to a sea level rise through deglaciati n the virgin spring limestone has a typical marine 13c signature average 2 0 pdb but the 18o is very negative 15 8 pdb the latter is attributed more to the burial diagenetic calcitization of an originally aragonitic sediment than to precipitation from 18o depleted seawater

lithofacies types and vertical profile models an alternative approach to the description and environmental interpretation of glacial diamict and diamictite sequences abstract increased knowledge of modern glacial depositional environments has resulted in rapidly evolving classifications of glacial tills these are based to a large degree on theoretical considerations of likely depositional processes the classifications are sophisticated and more advanced than the establishment of simple field criteria whereby individual till facies can be identified in quaternary and pre quaternary successions this situation is compounded in many quaternary terrains by the continued description of tills in terms of laboratory derived analytical data only reflecting a traditional interest in stratigraphic correlation rather than reconstruction of depositional environment detailed sedimentological logging of lithofacies is rarely undertaken there is thus considerable confusion as to what is being described or sampled when analytical data are presented for many pleistocene tills the same remarks apply to pre pleistocene tillites a lithofacies code is presented here for the rapid description and visual appraisal of field sequences or drill cores containing unconsolidated diamicts or lithified diamictites the term till is not used as it has a strict genetic definition referring to direct aggregation and deposition by glacier ice use of a four part code in conjunction with codes already published for fluvial sediments allows fundamental field properties to be depicted independent of genetic terminology and provides a firm basis for subsequent environmental interpretation and analytical work the value of this approach is illustrated by comparing a representative suite of vertical profiles of diamict assemblages deposited by modern grounded glaciers with a classic late pleistocene glacigenic sequence at scarborough bluffs ontario

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

facies characteristics of middle pleistocene saalian ice margin subaqueous fan and delta deposits glacial lake leine nw germany abstract the blocking of major river valleys in the leinebergland area by the early saalian scandinavian ice sheet led to the formation of a large glacial lake referred to as glacial lake leine where most of the sediment was deposited by meltwater at the initial stage the level of glacial lake leine was approx 110 m a s l the lake level then rose by as much as 100 m to a highstand of approx 200 m a s l two genetically distinct ice margin depositional systems are described that formed on the northern margin of glacial lake leine in front of the retreating scandinavian ice sheet the bornhausen delta is up to 15 m thick and characterized by a large scale tangential geometry with dip angles from 10 28 reflecting high angle foreset deposition on a steep delta slope foreset beds consist of massive clast supported gravel and pebbly sand alternating with planar parallel stratified pebbly sand deposited from cohesionless debris flows sandy debris flows and high density turbidity flows the finer grained sandy material moved further downslope where it was deposited from low density turbidity currents to form massive or ripple cross laminated sand in the toeset area the freden ice margin depositional system shows a more complex architecture characterized by two laterally stacked sediment bodies the lower part of the section records deposition on a subaqueous ice contact fan the upper part of the freden section is interpreted to represent delta slope deposits beds display low to high angle bedding 3 30 and consist of planar and trough cross stratified pebbly sand and climbing ripple cross laminated sand the supply of meltwater transported sediment to the delta slope was from steady seasonal flows during higher energy conditions 2 d and 3 d dunes formed migrating downslope and passing into ripples during lower energy flow conditions thick climbing ripple cross laminated sand beds accumulated also on higher parts of the delta slope

paraglacial slope instability in scottish fjords examples from little loch broom nw scotland lateglacial holocene fjord sediments in little loch broom preserve evidence of extensive slope instability the major area of reworking is in the outer loch and mid loch sill region where ice contact ice proximal deposits of the lateglacial assynt glacigenic formation have been disrupted by sliding and mass flow processes linked to the little loch broom slide complex and the adjacent badcaul slide mass failure was instigated about14 13 ka bp and is probably the response of the landscape to deglaciation immediately following the removal of ice support during glacial retreat an initial phase of translational sliding was followed by rotational sliding as revealed by the superimposition of scalloped shaped slumps on a larger scale rectilinear pattern of failure paraglacial landscape readjustment may have also been enhanced by episodic seismic activity linked to glacio isostatic unloading in the inner fjord evidence of holocene mass failure includes the ardessie debris lobe and a discrete intact slide block preserved within the postglacial basinal deposits the former is a localised accumulation linked to a fluvial catchment on the adjacent an teallach massif these mass transport deposits may represent an ongoing response to paraglacial processes albeit much reduced relative to the major slides in terms of sediment supply to the fjord

air sea fluxes and surface layer turbulence around a sea surface temperature front the observed effects of sharp changes in sea surface temperature sst on the air sea fluxes surface roughness and the turbulence structure in the surface layer and the marine atmospheric boundary layer are discussed in situ flux and turbulence observations were carried out from three aircraft and two ships within the fasinex framework three other aircraft used remote sensors to measure waves microwave backscatter and lidar signatures of cloud tops descriptions of the techniques intercomparison of aircraft and ship flux data and use of different methods for analyzing the fluxes from the aircraft data are described changing synoptic weather on three successive days yielded cases of wind direction both approximately parallel and perpendicular to a surface temperature front for the wind perpendicular to the front wind over both cold to warm and warm to cold surface temperatures occurred model results consistent with the observations suggest that an internal boundary layer forms at the sst

facies and architecture of a carboniferous grounding line system from the guandacol formation paganzo basin northwestern argentina abstract new outcrops of middle carboniferous glacigenic deposits found in the guandacol formation western paganzo basin are described in this paper the study locality of los pozuelos creek northwestern argentina includes coarse grained diamictites rhythmites laminated pebbly mudstones and shales that represent an expanded column of the gondwanic glaciation in this region thirteen lithofacies recorded at the measured section have been grouped into three facies associations facies association i is composed of coarse grained massive and stratified diamictites lithofacies dmm dms dmg dcs laminated siltstones with dropstones fld and interstratified sandstones and mudstones fl sr these rocks represent both tillites and resedimented diamictites closely associated to small water bodies where laminated siltstones with dropstones and stratified sandstones and mudstones were deposited facies association ii comprises couplets of matrix supported thinly bedded diamictites dmld and laminated mudstones with dropstones fld this facies association results from the combination of three different processes subaqueous cohesionless debris flows coeval rainout of ice rafted debris and settling of fine grained particles from supension finally facies association iii is made up of laminated mudstones without dropstones thin marl levels and scarce fine to very fine grained sandstones this assemblage clearly suggests sedimentation in a deep marine environment below the wave base the architecture of the glacigenic deposits has been investigated using photomosaic panels the geometry of the depositional bodies and facies suggest that los pozuelos creek outcrops exhibit a well preserved three dimensional example of a grounding line system in particular three different subenvironments of a morainal bank were interpreted a bank front a bank core and a bank back the bank front assemblage is characterized by coarse grained mainly resedimented diamictites grading laterally to prograding clinoforms composed of interbedded matrix supported thinly bedded diamictite and mudstones the bank core assemblage is formed by a stacking of coarse grained diamictites where at least five major erosional surfaces bounding four multistory diamictite bodies can be recognized finally the bank back assemblage corresponds to discontinuous intervals of striated lodgement till and coarse grained resedimented diamictites showing important post depositional deformation the retrogradational stacking of the morainal banks indicate an overall glacial retreat and a glacioeustatic sea level rise erosional surfaces at the base of each morainal bank suggest intervening short term episodes of ice advance the new data presented here confirm the existence of true tillites in western paganzo basin and suggest several at least four pulses of glacial advance and retreat during the namurian glaciation in the region and permit a more refined interpretation of the glacial deposits in the huaco area

a numerical study of the nonlinear stability of the eastern ocean circulation nonlinear unstable waves in the eastern ocean basin are analyzed using a three layer quasi geostrophic numerical model the upper two layers are forced to maintain a mean circulation in the absence of mesoscale motion the waves are produced by initial small perturbations added to the mean flow two experiments focused on the eastern ocean basin and differing only by mean flow strength are performed a region of high eddy kinetic energy is formed in the southern region but the eastern and northern regions are vacant of eddies because of the energy efflux by westward and southwestward propagating unstable waves regional energetics are calculated to highlight the differences between the eastern and southern regions two dominant waves are found in the southern region waves with a period of 120 days propagate to the west and form several wave trains parallel to the southern boundary longer period waves with a period of 200 days propagate to the southwest comparisons with observed eddies in the northeast pacific are discussed besides baroclinic instability it is found that the energy flux by propagating waves is very important in the finite amplitude stability of the eastern ocean general circulation

mid carboniferous deglaciation of the protoprecordillera argentina recorded in the agua de jaguel palaeovalley abstract the agua de jaguel formation near uspallata mendoza province argentina was deposited within a palaeovalley along the southeastern margin of the calingasta uspallata basin adjacent to the protoprecordillera the basal glacigenic sequence of the formation was deposited in the serpukhovian early bashkirian near the beginning of the late palaeozoic ice age the sequence is composed of diamictite conglomerate sandstone and mudrock and records four depositional stages within a palaeofjord 1 morainal bank deposition by a wet based tidewater glacier 2 glacial retreat succession where ice retreated up the fjord out of the immediate area allowing iceberg deposition of dropstones and dump deposits 3 continued glacial retreat with ice receding onto land allowing a shoreface to develop within the palaeovalley and 4 transgression across the shoreface and resumption of iceberg deposition the thickness and facies of this succession are similar to deposits within modern alaskan fjords housing temperate tidewater glaciers comparison of the agua de jaguel formation with alaskan fjords indicates that sequence stratigraphy used for low latitude deposits must be applied with caution as glacimarine ice retreat within a fjord produces strata surfaces that are easily misidentified as flooding surfaces resulting from changes in water depth likewise the transgression during stage 4 is significant as it indicates a rise in sea level that occurred during glaciation of the protoprecordillera thus suggesting that the transgression between stages 3 and 4 was not driven by input of glacial meltwater additionally the sediment geochemistry suggests that the bottom waters of the palaeovalley were anoxic which may help explain the absence of bioturbation in the sequence as well as in other ancient glacimarine palaeovalleys the deglaciation succession and transgression are also recorded in the nearby hoyada verde and tramojo formations so it is proposed that all three formations record one glacial event in the protoprecordillera overlying fluvial and shallow marine strata in the agua de jaguel hoyada verde and tramojo formations show no indication of continued glaciation in the protoprecordillera following stage 4 and equivalent strata the deglaciation succession of the agua de jaguel formation affirms the emerging concept that the late palaeozoic ice age was characterized by alpine glaciers ice caps and small ice sheets that were not massive enough to have driven eustatic fluctuations of 100 m as previously understood and that ice never covered westernmost gondwana during later lpia events

facies architecture and grounding line fan processes of morainal banks during the deglaciation of coastal maine submarine jet processes are inferred from glaciomarine facies exposed in gravel pits in southwestern coastal maine the geometry and distribution of fan facies depend on 1 the proximity to the grounding line and stream effluxes 2 the angle of jet trajectory from glacier conduits and 3 sediment remobilization processes syndepositional glaciotectonic deformation further augments morainal bank formation through pushing and squeezing of fan sediments at the grounding line complex process sediment interactions along the temperate tidewater margin of the laurentide ice sheet are recorded in the facies architecture of sedimentary sequences in morainal banks morainal bank accumulation was governed by rapid fluvial deposition and outwash jet dynamics that controlled the spatial distribution of sedimentary facies near the grounding line meltwater dynamics change rapidly where sediment laden fresh water is discharged at or near the sea floor turbulent mixing with ambient sea water and discharge fluctuations cause rapid changes in flow competence accompanied by the dumping of bed load gravel and sand at the apices of grounding line fans in the morainal banks jet trajectory relative to the morainal bank slope determines whether a jet will make contact with the morainal bank gravel and sand remain in bed load traction as long as the jet is in contact with the morainal bank bed load dumping and settling of the coarse suspended load occurs where buoyant forces in the jet overcome momentum forces or where the jet is deflected by the morainal bank below these buoyant jets backflow eddies can produce currents that drive ripple migration toward the grounding line abrupt facies changes record fluctuations in jet discharge and trajectory and sediment redistribution by sediment gravity flows initiated near the grounding line

stratigraphy and palynology of a late paleozoic glacial paleovalley in the andean precordillera argentina fil limarino carlos oscar consejo nacional de investigaciones cientificas y tecnicas oficina de coordinacion administrativa ciudad universitaria instituto de geociencias basicas aplicadas y ambientales de buenos aires universidad de buenos aires facultad de ciencias exactas y naturales instituto de geociencias basicas aplicadas y ambientales de buenos aires argentina

surface currents in the canary basin from drifter observations satellite tracked drifting buoys deployed in the canary basin as part of the subduction experiment between july 1991 and october 1993 and the french semaphore experiment during october 1993 were used to obtain a description of surface currents and temperature in the canary basin the study focuses on surface water convergence eddy energy production and heat transport the azores current associated with the subtropical convergence zone is clearly visible at 34 n and bifurcates around 22 w with the major branch of the current circling the madeira plateau and joining the canary current along the continental slope eddy kinetic energy maxima are found along the azores current the mean current revealed a region of maximum convergence north of the azores current around longitude 29 w occurring with a negative heating anomaly and positive work done by the reynolds stress the southward meridional temperature fluxes in the ekman layer 0 50 m between 37 w and the african and european coast are estimated between 0 076 0 022 l015 w produced by mean southward volume transport in our study area the residual between local surface heat fluxes and horizontal convergence of heat implies a vertical heat convergence process associated with mesoscale temperature and flow fields

generation of annual rossby waves in the north pacific by the wind stress curl abstract the rossby wave field generated by the annual cycle of the observed wind stress curl over the north pacific ocean 15 n 53 100 w 175 e has been obtained through numerical integration of the linearized reduced gravity vorticity equation in spherical coordinates the dominant source region of rossby waves is adjacent to the eastern boundary between 20 44 n more specifically this source is shown to be made up essentially of two distinct parts a southern region off california baja california which was first identified by white and saur and a northern region corresponding to a generation area first proposed by mysak in addition a second midocean generation region has been identified over the central north pacific from 35 to 45 n 150 to 160 w the behavior of the model is strongly affected by wave refraction due to the variation of phase velocity with latitude as described in schopf et al as waves emanate from the eastern boundary they are refracted such that the wavenumber vector init

a paleoclimatic review of southern south america during the late paleozoic a record from icehouse to extreme greenhouse conditions abstract this paper provides a review of the late mississippian to permian paleoclimatic history for southern south america based on lithologic indicators biostratigraphic information and chronostratigraphic data the region is divided into three major types of basins 1 eastern intraplate basins e g parana basin 2 western retroarc basins e g paganzo basin and 3 western arc related basins e g rio blanco basin four major types of paleoclimatic stages are recognized in these basins 1 glacial late visean early bashkirian 2 terminal glacial bashkirian earliest cisuralian 3 postglacial cisuralian early guadalupian and 4 semiarid arid late guadalupian lopingian the glacial stage began in the late visean and continued until the latest serpukhovian or early bashkirian in almost all of the basins in southern south america during the bashkirian earliest cisuralian terminal glacial stage glacial deposits disappeared almost completely in the western retroarc basins e g paganzo basin but glaciation persisted in the eastern basins e g parana and sauce grande basins a gradual climatic amelioration postglacial stage began to occur during the earliest permian when glacial deposits completely disappeared across all of south america during this interval glacial diamictites were replaced by thick coal beds in the parana basin while north south climatic belts began to be delineated in the western basins which were likely controlled by the distribution of mountain belts along the panthalassan margin of south america towards the late permian climatic belts became less evident and semiarid or arid conditions dominated in the southern south america basins eolian dunes playa lake deposits and mixed eolian fluvial sequences occur in the parana basin and in the western retroarc basins volcanism and volcaniclastic sedimentation dominated along the western margin of south america at that time the stratigraphic record obtained in southern south america supports a long duration transition from icehouse to extreme greenhouse conditions

the influence of explosive volcanism on fluvial sedimentation the deschutes formation neogene in central oregon abstract the upper miocene to lower pliocene deschutes formation of central oregon is a sequence of interstratified volcanic and sedimentary rocks as much as 700 m thick largely derived from the adjacent cascade range the formation is correlative with the early high cascade eruptive episode that included voluminous pyroclastic eruptions and culminated in the development of an intra arc graben in the central oregon high cascades facies associations and paleocurrent data define three depositional settings 1 the eastward sloping arc adjacent alluvial plain was the depositional site by sheetfloods debris flows and hyperconcentrated flood flows their deposits from 10 to 70 m thick sequences separated by erosion surfaces with up to 60 m of relief widespread superimposed paleosols overlie these facies and constitute the upper 10 to 50 m of the section sedimentation was episodic with pulses of rapid aggradation corresponding to periods of explosive volcanism and abundant sediment supply separated by periods of nondeposition when streams incised to reestablish grade as sediment loads diminished 2 a gravel bedload river flowed northward through the basin at the foot of the alluvial plain and is represented by channel fill conglomerates and overbank sandstones and siltstones 3 a thin sequence derived from older tertiary highlands was deposited on the east side of the basin and was little affected by cascade volcanism extensive development of thick superimposed paleosols reflects the inactive nature of the eastern basin margin as a sediment source deschutes formation deposition records the response of a fluvial system to large volcanism induced sediment loads popular facies models do not adequately allow for the influence of volcanism on fluvial systems because sediment is mobilized episodically and on a scale unparalleled in nonvolcanic settings

numerical modeling of meander and eddy formation in the azores current frontal zone abstract numerical experiments with an 11 level primitive equation finite difference model in a periodic channel are performed to analyze the properties of unstable finite amplitude disturbances in an idealized azores current release of available potential energy due to baroclinic instability occurs preferentially on scales of about 100 km with a theoretical growth time of 8 days at larger times the combined effect of friction and nonlinear transfer between internal and external depth integrated mode and the distribution of energy among different wavenumbers of the initial disturbance determine the scale of the meandering jet cold water tongues with a meridional scale of several hundred km found in satellite images and hydrographic surveys east of the azores are prescribed as initial disturbances they develop into pairs of troughs and ridges dominated by cyclonic vortices on the poleward flank of the jet phase propagation is downstream at 2 4 km day 1 extremely strong frontogenetic enhancement o

experimental study of the grain flow fluid mud transition in debris flows abstract we have performed a series of laboratory experiments that clarify the nature of the transition between fluid mud and grain flow behavior the surface velocity structure and the speed of the nose of debris flows in channels with semicircular cross sections were measured with several cameras and visual tracers while the mass flow rate was recorded using a load cell at the exit chamber other rheological tests were used to calculate independently the yield strength and matrix viscosity of the debris flow mixture shear rates were varied by nearly an order of magnitude for each mixture by changing the channel radius and slope shear rates were significantly higher than expected 6 55 s 1 given the modest slopes examined 10 7 15 2 the large values were primarily a result of the concentration of shear into narrow bands between a central nondeforming plug and the sidewall as a result the shear rate of interest was calculated by using the width of the shear band and the plug velocity as oppose

high precision u pb calibration of carboniferous glaciation and climate history paganzo group nw argentina the duration and geographic extent of carboniferous glacial events in southern gondwana remain poorly constrained despite recent evidence for a more dynamic glacial history than previously considered we report 10 high precision 2 0 1 u pb ages for the permian carboniferous paganzo group nw argentina that redefi ne the chronostratigraphy of the late paleozoic paganzo and rio blanco basins and signifi cantly refi ne the timing of glacial events and climate shifts in the western region of southern gondwana radiometric calibration of the paganzo group indicates three pulses of carboniferous glaciation in the mid visean the late serpukhovian to earliest bashkirian and between the latest bashkirian to early moscovian an abrupt shift in depositional style from high sinuosity single storied fl uvial deposits and clay rich paleosols to low sinuosity multi storied feldspathic fluvial deposits inter calated with eolianites and calcic paleosols is constrained to the latest moscovian and earliest kasimovian these constraints indicate a relatively abrupt climate shift from humid subhumid to nonseasonal semiarid regional climate conditions that occurred signifi cantly earlier than previously inferred early permian this period of high latitude aridity was contemporaneous with a shift to dryland depositional environments and a major vegetation regime shift documented throughout the pangean paleotropics in the pennsylvanian

field and laboratory observations of bed stress and associated nutrient release in a tidal estuary abstract nutrient release driven by sediment resuspension in a shallow coastal estuarine system is examined with field observations of bed stress and bed elevation coupled with laboratory erosion experiments on sediment cores two field experiments were conducted over near cohesive muddy sand sediments in the great bay estuary new hampshire in the first deployment boundary layer development during typical summer tidal forcing was observed while the second deployment occurred under enhanced wind forcing of tropical storm irene in situ bed stress and erosion depths were estimated with a profiling acoustic doppler velocimeter sediment cores were subjected to eromes erosion chamber experiments to determine erosion depth and nutrient release as a function of applied shear stress results show erosion depths are consistent with in situ observations over shear stresses ranging from 0 10 n m 2 incipient motion to 0 35 n m 2 resuspension events erosion chamber experiments showed that ammonium release up to 2 mmol m 2 increased with bed stress in both spring and summer however phosphate release was more variable with no phosphate release during resuspension in spring and a variable phosphate flux ranging 0 5 2 mmol m 2 in summer increased hydrodynamic forcing during a storm event in the summer generated shear stresses up to 0 58 n m 2 during flood tides that exceeded the threshold for sediment motion and resulted in erosion of the seabed eromes results predict there was concomitant release of nutrients into the water column from the muddy sediments of the bay and the release of dissolved inorganic nitrogen and phosphate was up to 10 and 65 respectively of the summer monthly riverine input of these nutrients results indicate qualitatively that in shallow tidally dominated estuaries fine grained sediment beds may be a source of nutrients that are particularly important during storms that enhance near bed shear stresses

large scale sst variability in the western north atlantic subtropical convergence zone during fasinex part i description of sst and wind stress fields abstract we describe properties of large scale fluctuations in the wind field represented by two analyses fnoc and noaa atoll and in the sst field represented by maps derived from 5 day composite avhrr images within an 11 longitude by 10 latitude domain during fasinex january through june 1986 fnoc and atoll wind and wind stress time series were highly correlated with each other 0 8 over the entire domain and they were also highly correlated with time series measured at the fasinex site 0 89 at periods of 2 13 days clockwise energy exceeded anticlockwise energy by an order of magnitude while the energy was nearly partitioned equally at periods of 13 40 days mean atoll winds were everywhere more eastward than mean fnoc winds probably in part because the atoll fnoc analyses are intended to represent 850 mb 19 5 m winds the 850 mb winds are expected to be more eastward due to the thermal wind balance with the mean southward air temperature gradient the sst maps represented large s

ocean surface topography measured by the geosat radar altimeter during the frontal air sea interaction experiment an objective analysis oa technique was used to analyze geosat geodetic mission residual sea height anomalies rsha for the frontal air sea interaction experiment fasinex conducted in the western north atlantic preprocessing of the geosat data included removal of a mean sea surface and orbit error and corrections for tides wave height inverse barometer and ionospheric and dry tropospheric effects geosat data were not corrected for water vapor central to the analysis was the computation of a spatially anisotropic time dependent autocorrelation function directly from the geosat data results show a single autocorrelation function peak having a diameter of 270 km at 0 day time lag a 15 month time series of rsha topography was constructed at 10 day intervals forming a set of 47 oa maps these maps show a field of topographic features propagating to the west at 4 km d 1 the features exhibited spatial and temporal scales of 200 km and 50 days respectively the root mean square rms of the oa derived feature amplitudes fluctuated slowly between 0 05 and 0 09 m with a period of 200 days over the 15 month interval these fluctuations appeared to be related to the passage of large scale northeast southwest trending sea surface temperature sst anomaly features reported for fasinex which were surface manifestations of large scale first mode baroclinic rossby waves the rms amplitude of the oa derived features was maximal minimal during periods of negative positive sst anomaly when the depths of the mixed layer and main thermocline in the upper ocean shoaled deepened the fluctuations also appeared to be correlated with the structure of the field periods of decreased feature amplitudes corresponded to a closely packed structure while during times of increased amplitudes the field structure became zonal with regions of alternating sign during fasinex january june 1986 the field was characterized by the closely packed structure and decreasing feature amplitudes this corresponded to the period of positive sst anomaly and high upper ocean heat content reported for fasinex

overview of the frontal air sea interaction experiment fasinex a study of air sea interaction in a region of strong oceanic gradients from 1984 to 1986 the cooperative frontal air sea interaction experiment fasinex was conducted in the subtropical convergence zone southwest of bermuda the overall objective of the experiment was to study air sea interaction on 1 to 100 km horizontal scales in a region of the open ocean characterized by strong horizontal gradients in upper ocean and sea surface properties ocean fronts provided both large spatial gradients in sea surface temperature and strong jetlike flows in the upper ocean the motivation for and detailed objectives of fasinex are reviewed then the components of the field program are summarized finally selected results are presented in order to provide an overview of the outcome of fasinex

mesoscale eddies northeast of the hawaiian archipelago from satellite altimeter observations 1 enhanced mesoscale eddy activity northeast of the hawaiian archipelago was investigated by using the high pass filtered satellite altimetric sea surface height ssh data of the past 16 years the level of eddy kinetic energy eke shows significant interannual variations which appear well correlated to the large scale atmospheric wind forcing associated with the pacific decadal oscillation index the eke levels in the area along the subtropical front zone in 1997 1998 and 2003 2005 for example were three times as large as those in the low eke years spectral analyses in the 3 latitude by 5 longitude subregions revealed the dominant mesoscale periods ranging from 90 days near 18 n to 180 days near 36 n a 3 layer quasi geostrophic model constrained by world ocean atlas 2005 climatologies was used to explore instability of the regional circulation the analysis shows a geographical match between baroclinic instability strength and the observed rms ssh variability and a temporal match between seasonally varying instability strength and the observed seasonal eke modulation and suggests that baroclinic instability by the vertically sheared regional mean circulation provides the energy source for the enhanced eddy variability northeast of the hawaiian archipelago

the subarctic and northern subtropical fronts in the eastern north pacific ocean in spring abstract the subarctic and subtropical frontal zones of the eastern north pacific ocean were surveyed in june for five consecutive years starting in 1972 these surveys from the basis for a description of the complex frontal distributions and their year to year differences the fronts appear as surface outcroppings of haloclines the subarctic halocline where salinity increases with depth and the subtropical halocline where the opposite prevails between the fronts lies a transition zone where strong vertical gradients of salinity are generally absent an examination of the northern boundary of subtropical waters in this new dataset reveals the presence of two major fronts in the subtropical frontal zone in addition to the front commonly identified as the subtropical front 18 c and 34 8 is a northern subtropical front that forms the northern boundary of the subtropical halocline in the eastern north pacific it falls some 2 to 3 of latitude north of the subtropical front and is the same front observ

large scale sst variability in the western north atlantic subtropical convergence zone during fasinex part ii upper ocean heat balance and frontogenesis abstract we analyzed the influence of wind deriven horizontal heat advection on the large scale o 1000 km wavelength variability of both the upper ocean mixed layer heat content and the subtropical frontal zone sfz within an 11 by 10 domain in the western north atlantic ocean during fasinex january through june 1986 by estimating heat advection due to both ekman transport and interior geostrophic sverdrup minus ekman transport from a slab mixed layer heat balance equation using satellite derived sea surface temperature ts and wind analysis maps it was found that these processes could not account for the observed variability in either beat content or the sfz the annual cycle of surface vertical heat flux had the dominant influence on the heat content even when the average heat balance was analyzed during a 4 month time interval when the net influence of the annual cycle was nearly zero mid january to mid may 1986 westward propagating ts spatial anomaly features with peak to peak scales

on the geographical variability of the upper level mean and eddy fields in the north atlantic and north pacific abstract all available historical expendable bathythermograph data are used to compute means and standard deviations in temperature for the upper 500 m in the north atlantic and north pacific to take advantage of marked spatial differences in data coverage a variable grid scheme is employed both surface and subsurface annual mean temperature distributions agree well with published maps of these quantities climatological mean temperature salinity and salinity depth curves are used to infer salinities for the mean temperature profiles in order to compute 0 500 db inferred dynamic height and its standard deviation these mean curves are also used to compute eddy potential energy at 300 m the maps of mean annual inferred dynamic height agree well with traditional dynamic height maps and appear similar to the maps of mean temperature at 400 m the north atlantic eddy potential energy distribution is similar to an earlier calculation maps of the standard deviations in inferred dynamic height also represent

evidence for wind driven current fluctuations in the western north atlantic two subsurface current meter moorings were deployed for 20 months along 70 w in a low energy portion of the western north atlantic the resulting data were compared with estimates of the wind stress curl in an attempt to seek a relationship between currents below the mixed layer and meteorological forcing at subinertial frequencies currents and temperature tend to be significantly coherent with the curl and are most coherent with the curl at remote locations usually more than 500 km away from the mooring and generally to the east coherences generally decrease with increasing frequency the current response is surface intensified a linear stratified model for stochastically wind forced rossby waves in a flat bottomed ocean is presented as an attempt to rationalize the results the effort was not entirely successful so that it appears that a more realistic model perhaps including bottom topography and mean currents will be needed to rationalize these observations fully

sediment transport partitioning in the swash zone of a large scale laboratory beach abstract swash zone sheet flow and suspended sediment transport rates are estimated on a coarse sand beach constructed in a large scale laboratory wave flume three test cases under monochromatic waves with wave heights of 0 74 m and wave periods of 8 and 12 2 s were analyzed sediment flux in the sheet flow layer exceeds several hundred kg m 2 s 1 during both uprush and backwash suspended sediment flux is large during uprush and can exceed 200 kg m 2 s 1 instantaneous sediment flux magnitudes in the sheet layer are nearly always larger than those for suspended sediment flux however sediment transport rates those integrated over depth indicate that suspended load transport is dominant during uprush for all cases and during the early stages of backwash except in the case for the 12 2 s wave case when the foreshore was steeper results could not be obtained for an entire swash event and were particularly truncated during backwash when water depths fell below the elevation of the lowest current meter

animal substrate interactions in an early miocene wave dominated tropical delta delineating environmental stresses and depositional dynamics tacata field eastern venezuela abstract the miocene tacata reservoirs of the eastern venezuela basin contain deposits that accumulated as a result of the progradation of a wave dominated delta complex in a tropical setting integration of ichnologic and sedimentologic data helps to detect different stress factors allowing distinction between deltaic and associated along strike strandplain shoreface successions fluvial discharge was repeatedly interrupted by periods of storm wave reworking and suspension fallout leaving diagnostic ichnologic signatures in the deposits repeated storms rank among the most important controlling factors on the front of the tacata deltas lateral especially on the updrift side to the river mouths wave activity caused nearly continuous accretion of the associated strandplains evidence of tidal influence is essentially restricted to distributary channel and particularly interdistributary bay deposits although elements of the skolithos ichnofacies e g skolithos are present they tend to occur in subordinate numbers as a result of water turbidity distributary channel deposits are sparsely bioturbated but the presence of certain ichnotaxa e g ophiomorpha allows distinction from freshwater fluvial channels ichnofabrics from interdistributary bay deposits display all the characteristics expected from brackish water settings e g low ichnodiversity presence of monospecific suites and are also typically sparsely bioturbated teichichnus and planolites commonly associated with synaeresis cracks are dominant ichnotaxa in these fine grained low energy protected brackish water settings in contrast delta front and prodelta deposits contain some ichnotaxa that typically do not occur in brackish water settings such as chondrites and phycosiphon preservation of very thin storm layers is probably more common in wave dominated deltas than in strandplain systems because deltaic stresses preclude the establishment of an abundant infauna that otherwise would have completely reworked such thin sandstone layers amalgamated thick bedded storm deposits are typically unburrowed or contain deep vertical ophiomorpha scolicia ichnofabrics seem to be restricted to the fully marine parts of strandplain deposits and are therefore useful to detect possible delta asymmetry along depositional strike or vertical changes in degree of deltaic influence

westward propagating sst anomaly features in the sargasso sea 1982 88 abstract sea surface temperature ts maps of the region from 59 5 to 75 5 w 22 5 to 33 5 n containing the western north atlantic subtropical convergence zone stcz were derived from avhrr 2 images the 7 year mean annual cycle was removed and the maps were filtered in space and time to represent anomaly variability with wavelengths 220 km and periods 50 days warm and cold anomaly features were observed cast of 71 w between 26 and 32 n that propagated westward at 3 4 km day 1 and that occasionally exceeded 1 c in amplitude they are generally strong and persistent from fall to spring and are only marginally detectable during summer during 1981 82 1982 83 and 1985 86 individual features could be followed through the entire fall spring interval during 1983 84 1986 87 and 1987 88 they could typically be followed for 2 4 months and during 1984 85 for only 1 2 months the features were anisotropic during all fall spring intervals except 1986 87 and they had characteristic wavelengths of 80

mixed layers and fronts in simple ocean circulation models abstract a three dimensional regime with a differentially heated mixed layer on top of an ideal fluid interior is considered in a situation which corresponds to the interior of the well known wind driven model by stommel 1948 although the transport field in this case is continuous and simple the same is not necessarily true for the density and velocity fields if the mixed layer is weakly coupled to the atmosphere a front is generated at the line of a maximum downwelling another front is expected at the line of a zero downwelling

a study of the variability of ocean currents in the northwestern atlantic using satellite altimetry abstract altimeter data obtained from geos 3 during the three year period 1975 78 for a region of the western north atlantic which includes a portion of the gulf stream system and part of the open ocean area of the subtropical gyre are analyzed by a new technique which utilizes all the points along the satellite tracks the physical phenomenon studied are the time variable but almost geostrophic currents or mesoscale eddies so that geoid errors contaminate the scientific signal minimally and the dynamical interpretation is direct results presented include the spatial distribution of geostrophic eddy kinetic energy and examples of a synoptic map of the eddy field april 1977 and of a time series at a point these results are compared to and synthesized with a diverse and selected set of existing measurements and observations obtained in situ by a variety of instrumental techniques the agreement is generally good and the altimeter data analyzed provides new information on features in the map of mean e