coupling of the surface and near bottom currents in the gulf of mexico coupling between the surface and near bottom currents in the gulf of mexico gom has been reported in many case studies however geographical variations of this coupling need more examination in this study surface geostrophic currents derived from satellite observed sea surface height and subsurface currents from a collection of deep ocean moorings are used to examine the surface and bottom coupling in different parts of the gom the short period 30 90 days fluctuations generated by the loop current lc and the lc eddies lces have a more vertically coherent structure and stronger deep ocean expressions than the long period fluctuations 90 days in addition the strength of the coupling is modulated by the long period variations of the lc and lce sheddings moreover the surface and bottom coupling varies geographically in the lc region the surface fluctuations along the eastern side of the lc are important in causing the bottom current fluctuations through baroclinic instability under the lc and through traveling topographic rossby waves trws north of the lc in the central deep gom the bottom currents are affected by the upper fluctuations of the northern lc through both local baroclinic instability and remote trw propagation in the northwestern gom the bottom current fluctuations are largely related to the remote surface variability from the west side of the lc by trws propagating northwestward this study will help us better understand mechanisms of the bottom current fluctuations that are important for the dispersal of deep ocean materials and properties

dispersion of a tracer in the deep gulf of mexico a 25 km streak of cf3sf5 was released on an isopycnal surface approximately 1100 m deep and 150 m above the bottom along the continental slope of the northern gulf of mexico to study stirring and mixing of a passive tracer the location and depth of the release were near those of the deep hydrocarbon plume resulting from the 2010 deepwater horizon oil well rupture the tracer was sampled between 5 and 12 days after release and again 4 and 12 months after release the tracer moved along the slope at first but gradually moved into the interior of the gulf diapycnal spreading of the patch during the first 4 months was much faster than it was between 4 and 12 months indicating that mixing was greatly enhanced over the slope the rate of lateral homogenization of the tracer was much greater than observed in similar experiments in the open ocean again possibly enhanced near the slope maximum concentrations found in the surveys had fallen by factors of 104 107 and 108 at 1 week 4 months and 12 months respectively compared with those estimated for the initial tracer streak a regional ocean model was used to simulate the tracer field and help interpret its dispersion and temporal evolution model data comparisons show that the model simulation was able to replicate statistics of the observed tracer distribution that would be important in assessing the impact of oil releases in the middepth gulf

loop current cycle coupled response of the loop current with deep flows abstract although the upper layer dynamics of the loop current and eddies in the gulf of mexico are well studied the understanding of how they are coupled to the deep flows is limited in this work results from a numerical model are analyzed to classify the expansion shedding retraction and deep coupling cycle the loop current cycle according to the vertical mass flux across the base of the loop stage a is the loop reforming period with downward flux and deep divergence under the loop current stage b is the incipient shedding with strong upward flux and deep convergence stage c is the eddy migration with waning upward flux and deep throughflow from the western gulf into the yucatan channel because of the strong deep coupling between the eastern and western gulf the loop s expansion is poorly correlated with deep flows through the yucatan channel stage a is longest and the mean vertical flux under the loop current is downward therefore because the net circulation around the abyssal

shallow water and hypersaline features from the middle proterozoic mt isa sequence fundamental differences of opinion exist about the depositional environment of sediments which host the middle proterozoic1 mt isa cu and pb zn deposits2 3 of northwestern queensland australia the copper host has been repeatedly interpreted as an algal reef2 4 and recently as a sabkha5 whilst models as diverse as saline lakes6 and deep oceanic basins3 7 9 have been proposed for the deposition of both the cu and pb zn ore bodies we now report the discovery of stromatolites halite casts large cross bedded channel deposits and flat pebble conglomerates in sediments closely associated with the ore deposit these sedimentary structures provide evidence of shallow water deposition with intermittent hypersaline and emergent conditions during deposition of the upper mt isa group3 6 sequence the assemblage of sedimentary structures strongly supports a shallow marine or shallow lacustrine depositional model either model is inconsistent with the previously postulated red sea type submarine exhalative mineralization model3 7 9 for mt isa instead we argue that mt isa ore formation took place in a shallow water system possibly aided by the action of evaporite derived brines

numerical paleoceanographic study of the early jurassic transcontinental laurasian seaway the forces governing marine circulation of a meridional transcontinental seaway is explored with the princeton ocean model the jurassic laurasian seaway which connected the low latitude tethys ocean with the arctic sea is modeled quantitatively the global ocean is found to have a profound influence on seaway dynamics a north south density difference and hence sea level difference of the global ocean was probably the main factor in forcing the seaway flow when the tethys waters were the denser water the net seaway flow was southward and conversely it was northward for denser arctic waters marine bioprovincial boundaries and sediment data indicate that the seaway probably was dominated by boreal faunal groups and reduced salinities several times in the jurassic the model results suggest that this can be explained by southward flowing seaway currents which may have been related to an oceanic thermohaline circulation where no northern high latitude deep convection occurred

why can wind delay the shedding of loop current eddies abstract it is first shown that wind in the gulf of mexico can delay the shedding of loop current eddies a time dependent three dimensional numerical experiment forced by a spatially and temporally constant westward wind stress within the gulf is analyzed and then is compared with an otherwise identical no wind run and the result is confirmed with reduced gravity experiments it is shown that the wind produces westward transports over the northern and southern shelves of the gulf convergence in the west and a returned i e eastward upper layer flow over the deep central basin toward the loop current the theory from t pichevin and d nof is then used to explain that the returned flow constitutes a zonal momentum flux that delays eddy shedding mass balance analysis shows that wind also forces larger loop current and rings because the delayed shedding allows more mass to be accumulated in them and produces more efficient mass exchange between the gulf and the caribbean sea it is shown that eddi

loop current and deep eddies abstract in contrast to the loop current and rings much less is known about deep eddies deeper than 1000 m of the gulf of mexico in this paper results from a high resolution numerical model of the gulf are analyzed to explain their origin and how they excite topographic rossby waves trws that disperse energy to the northern slopes of the gulf it is shown that north of campeche bank is a fertile ground for the growth of deep cyclones by baroclinic instability of the loop current the cyclones have horizontal vertical scales of about 100 km 1000 2000 m and swirl speeds 0 3 m s 1 the subsequent development of these cyclones consists of two modes a and b mode a cyclones evolve into the relatively well known frontal eddies that propagate around the loop current mode a cyclone can amplify off the west florida slope and cause the loop current to develop a neck that sometimes leads to shedding of a ring this process is shown to be the loop current s dominant mode of upper to deep variability

gulf of mexico circulation within a high resolution numerical simulation of the north atlantic ocean 1 the gulf of mexico circulation is examined from the results of a high resolution 1 12 north atlantic simulation using the miami isopycnic coordinate ocean model the motivation for this paper is twofold first we validate the model s performance in the gulf of mexico by comparing the model fields to past and recent observations and second given the good agreement with the observed gulf of mexico surface circulation and loop current variability we expand the discussion and analysis of the model circulation to areas that have not been extensively observed analyzed such as the vertical structure of the loop current and associated eddies especially the deep circulation below 1500 m the interval between successive model eddy sheddings is 3 to 15 months the eddy diameters range between 140 and 500 km the life span is about 1 year and the translational speeds are 2 3 km d 1 in good agreement with observations areas of high cyclonic eddy occurrence in the model are southwest of florida the loop current boundary and the western campeche bay area the cyclonic eddy diameters range between 50 and 375 km the orbital speeds range between 1 and 55 cm s 1 the translational speeds range between 0 5 and 14 km d 1 and the eddy life spans range between 1 and 3 months the vertical structure of the temperature and salinity of each modeled eddy from the moment it is shed until it disintegrates in the western gulf of mexico is in agreement with the few available observations below 1500 m deep cyclonic eddies are associated with the surface loop current anticyclones the eddy variability is consistent with rossby waves propagating westward and there is bottom intensification of the flow close to steep topography overall we show that this very high horizontal resolution isopycnic coordinate ocean model which is able to produce a quite realistic surface circulation for the north and equatorial atlantic is also able to reproduce well the smaller scale basin wide intricate dynamics such as the gulf of mexico variability

circulation over the continental shelf in the northern gulf of mexico abstract more than 750 surface drifters were deployed over the northern continental shelf in the gulf of mexico gulf from 1993 through 1998 drifters were mostly air deployed on a schedule giving continuous data over much of the texas louisiana and west florida shelves for an entire year the drifter data are analyzed to give descriptive statistical and dynamical views of the northern gulf circulation on synoptic to seasonal scales circulation on both the texas louisiana and west florida shelves is characterized by coherent along shore and across shore modes which explain more than 50 of the variance a pronounced seasonal cycle exists on the texas louisiana shelf but not the west florida shelf both shelves display synoptic signals due to local wind forcing strong connectivity between the shelves occurs during isolated period of strong winds associated with the passage of tropical storms eddies impinging upon the shelf are responsible for moving drifters cross shore offshore flows generally occur prior to reversals in the along shore direction regions with near zero mean velocities but large total energy exist drifters leave these areas and move thorough much of the gulf and into the atlantic within 90 days despite negligible annual mean eulerian velocities

a three dimensional model of density driven circulation in the irish sea abstract a semi implicit version of the princeton ocean model ecomsi was used to simulate the cyclonic gyre that is found in the western irish sea during the spring and the summer mesoscale seasonal density driven circulations such as this are an important component of the long term flow in shelf seas and they pose a challenge to coastal ocean models extensive comparisons are made here with observational data to assess model performance the model successfully reproduced the development of the temperature field and the associated density driven currents throughout seasonal simulations the results demonstrate conclusively that the gyre is density driven and reinforce the dynamical importance of strong nearbed horizontal density gradients maximum baroclinic currents of 0 14 m s 1 were obtained and results showed that the regional kinetic energy due to the residual flow was 20 25 of that due to tidal flow during periods in which density gradients were strongest the model revealed important int

numerical simulation of the gulf stream system the loop current and the deep circulation 1 the loop current and the deep circulation in the gulf of mexico are numerically investigated by a primitive equation sigma coordinate ocean model with realistic surface fluxes obtained from an atmospheric forecast model a deep cyclonic circulation bounded by the deep basin in the eastern gulf of mexico is spun up by the loop current the deep cyclonic circulation is coincident with a southward current of the loop current eastern limb and weakens after loop current ring separation and cessation of the southward current the anticyclonic semienclosed loop current also induces anticyclonic lower layer columnar eddies in the eastern gulf these lower layer eddies decouple from the upper layer loop current the westward translation speed of a loop current ring is about 2 16 5 18 km d 1 the lower layer eddies have a higher speed and lead the rings into the central gulf the time averaged surface circulation of the gulf of mexico basin is anticyclonic mainly because of the transport of anticyclonic vorticity by loop current rings in the surface layer an average lower layer cyclonic circulation occurs along the continental slope of the basin

a modeling study of coastal trapped wave propagation in the gulf of california part ii response to idealized forcing abstract the evolution of remotely forced coastal trapped waves in the gulf of california is studied using a hydrostatic primitive equation model the sea level time variability at a remote station south of the gulf is assumed to propagate northward into the gulf as a mode 1 coastal trapped wave ctw to validate this assumption observations and model results are compared in general sea level fluctuations are reasonably well represented by the model with model data correlations decreasing from 0 76 at topolobampo close to the entrance of the gulf to 0 52 at santa rosalia in the central gulf model data correlations of velocity are lower 0 6 in the gulf ctws propagate northward along the east side with no significant changes south of the sill which is 600 km north of the entrance when incident waves propagating northward in the gulf along the east side arrive at the sill a small fraction of the wave energy enters the northern gulf and is dissipated most of the wave energy is steered at the

the geochemical environment of the wilcherry hill base metal mineralisation south australia high grade lead zinc silver mineralisation occurs in metamorphosed carbonate and calc silicate sequences at wilcherry hill south australia whole rock lithogeochemistry indicates that the host sequence of the mineralisation can be defined and contrasted from others at both prospect and exploration licence scales geochemical haloes are identified on the basis of pb zn and mn variations a saline and possibly evaporitic environment of deposition distal from basin margins is proposed for the host sequence on the basis of alkali element compositions iron formation facies carbonate compositions and comparisons with geochemically similar less metamorphosed sequences with base metal mineralisation in the middle proterozoic of northern australia the combination of geochemical haloes and definition of the depositional environment provide additional criteria for the exploration geologist even in metamorphosed and deformed terrains

geochronology of early to middle proterozoic fold belts in northern australia a review abstract this geochronological review integrates geologically relevant isotopic data from the several early to middle proterozoic fold belts of northern australia a number of firm chronological benchmarks largely established by means of u pb zircon studies now provide a time framework within which to better quantify the tectonostratigraphic history of many of these terranes the apparent worldwide dearth of crustal events in the earliest proterozoic between 2500 and 2000 ma was broken in northern australia with the advent of a major crust forming episode between 1880 and 1850 ma ago these rocks may have evolved from an initial mantle or lower crustal melting and fractionation process about 400 300 ma earlier that is evidenced from sm nd model ages the extent involvement and or degree of assimilation of any pre existing archaean crust is small but whether or not it is negligible or zero is not satisfactorily known the 1880 1850 ma event the barramundi orogeny is well represented in northern australia both lithologically and analytically and the rocks that pre and post date it have a similar tectonic setting over very wide areas of the continent two consistent and widespread elements of this tectonism are regional metamorphism and deformation of the first cycle of supracrustals barramundi orogeny and crystallization of i type k rich felsic magmas closely following and in some cases overlapping with deformational processes in the halls creek inlier the ages of this rapid deep crustal to supracrustal tectonic transition cannot be distinguished within the range 1860 1850 ma this major yet short lived tectonism is mirrored in other fold belts such as pine creek tennant creek and mount isa in which u pb zircon ages give slightly older constraints of 1885 1870 ma 1920 1870 ma and 1885 10 ma respectively the ensuing felsic magmatism in these latter terranes continued for a few tens of millions of years with the crystallization and emplacement of comagmatic volcanic plutonic pairs throughout in the interval 1870 1860 ma in the georgetown and arunta inliers direct evidence of this otherwise ubiquitous event if present is masked by younger high grade metamorphism in the latter however metamorphic crustal components having approximate protolith ages of this order can be inferred from their evolved isotopic signatures the geochronological and geochemical coherency of the extensive early proterozoic 1870 ma magmatism contrasts with that of post 1800 ma magmatism which is less extensive generally anorogenic commonly bimodal in character and varies in age from one terrane to another several major sedimentary basins were being filled at this time major igneous events at 1790 1740 ma 1670 ma and 1500 ma are recognized elongate sublinear volcanic and plutonic belts 1790 1740 ma old are present at mount isa in high grade granitic gneisses of the arunta inlier a few u pb zircon ages and extrapolated rb sr protolith ages are coincident at about 1760 1750 ma indicating that this event may be important in the development of the division 2 sequences of that fold belt the platformal hart dolerite and oenpelli dolerite two of the largest mafic intrusions in the world were emplaced at 1762 25 ma and 1688 13 ma younger felsic plutonism and volcanism gave rise to rapakivi type granites in the mount isa tennant creek and the granites tanami inliers at 1670 ma a time close to that of the aileron deformational metamorphic event in central australia further at 1650 ma there is growing evidence of an unexpectedly coherent hydrothermal episode that reset or disturbed many rb sr ages gave rise to pegmatites and was possibly associated with mineralization in the davenport and eastern arunta inliers discrete middle proterozoic deformational events between 1610 and 1470 ma punctuate the tectonostratigraphic history in the arunta mount isa and georgetown fold belts where they are best documented

the periglacial climate and environment in northern eurasia during the last glaciation this paper summarizes the results of studies of the late weichselian periglacial environments carried out in key areas of northern eurasia by several queen teams european science foundation esf programme quaternary environment of the eurasian north the palaeoglaciological boundary conditions are defined by geological data on timing and extent of the last glaciation obtained in the course of the eu funded project eurasian ice sheets these data prove beyond any doubt that with the exception of the northwestern fringe of the taymyr peninsula the rest of the eurasian mainland and severnaya zemlya were not affected by the barents kara sea ice sheet during the last glacial maximum lgm inversed modelling based on these results shows that a progressive cooling which started around 30 ka bp caused ice growth in scandinavia and the northwestern areas of the barents kara sea shelf due to a maritime climate with relatively high precipitation along the western flank of the developing ice sheets in the rest of the eurasian arctic extremely low precipitation rates less than 50 mm yr 1 did not allow ice sheet growth in spite of the very cold temperatures palaeoclimatic and palaeoenvironmental conditions for the time prior to during and after the lgm have been reconstructed for the non glaciated areas around the lgm ice sheet with the use of faunal and vegetation records permafrost eolian sediments alluvial deposits and other evidences the changing environment from interstadial conditions around 30 ka bp to a much colder and drier environment at the culmination of the lgm at 20 15 ka bp and the beginning of warming around 15 ka bp have been elaborated from the field data which fits well with the modelling results

simulation of mesoscale variability in the gulf of mexico sensitivity studies comparison with observations and trapped wave propagation abstract a primitive equation gulf of mexico model was used to examine variability of the loop current lc and loop current eddies lce realistic results were obtained for a certain range of values of the horizontal mixing coefficient eddy paths were west and southwestward eddy propagation speeds from 3 to 5 km day 1 the ratio of minor to major eddy axes about 0 8 eddy shedding periods from 200 to 500 days eddy lifetimes from 100 to 200 days eddy sizes from 200 to 400 km and eddy swirl transports as fractions of the specified inflow of 30 sv were from 0 55 to 0 85 on the other hand the maximum vertical deepening of the 20 c isotherm was 15 to 50 less than that observed resulting in weaker near surface currents of about 0 65 m s 1 in comparison to observed values of 0 88 to 1 7 m s 1 a strong correlation between eddy shedding and decreasing or reversing lower layer below 750 m transport in the yucatan channel is found in the western gulf current variability is produced by eddy arriva

impact of caribbean cyclones on the detachment of loop current anticyclones 1 the western boundary current in the north atlantic is characterized by an intense flow reaching 2 5 ms 1 at the surface that enters the caribbean sea through the lesser antilles passages crosses the entire caribbean and enters the gulf of mexico through the yucatan channel where it is known as the loop current a characteristic feature of the loop current is eddy shedding events i e the detachment of large anticyclonic eddies at irregular intervals moored current measurements between january 2005 and july 2009 in the loop current the yucatan channel and the caribbean coastal waters of mexico i e the western cayman sea along with aviso altimetry are used to evidence the northward propagation of cyclonic anomalies along the caribbean coast of mexico and the marked eastward displacement of the loop current at 23 n latitude just before several anticyclonic eddy shedding events after entering the gulf of mexico these cyclonic anomalies might initiate or enhance existing campeche bank cyclonic eddies which are related to many of the loop current detachment events sixteen of the twenty one detachments that occurred during the study period 76 are related to the cyclonic eddies in the western caribbean sea six of them were not reattached again to the loop current observations thus clearly indicate that cyclonic eddies in the western cayman sea contribute significantly to the loop current eddy shedding process which is complex and in principle not unique

deep eddy energy and topographic rossby waves in the gulf of mexico abstract observations suggest the hypothesis that deep eddy kinetic energy eke in the gulf of mexico can be accounted for by topographic rossby waves trws it is presumed that the trws are forced by loop current lc pulsation loop current eddy lce shedding and perhaps also by lce itself although the hypothesis is supported by model results such as those presented in oey the existence of trws in the model and how they can be forced by larger scale lc and lces with longer period vacillations have not been clarified in this paper results from a 10 yr simulation of lc and lces with double the resolution of that used by oey are analyzed to isolate the trws it is shown that along an east to west band across the gulf approximately over the 3000 m isobath significant eke that accounts for over one half of the total spectrum is contained in the 20 100 day periods bottom energy intensification exists in this east west band with vertical decay scales of about 600 300 m decreasing westward the de

deep currents in the bay of campeche abstractdata from five moorings deployed in the bay of campeche during november 2007 july 2008 are used to analyze subinertial motions of waters below 1000 m depth to the authors knowledge this is the first time such a comprehensive observational program of direct deep current measurements has been carried out in the region the mean currents are in agreement with a cyclonic circulation at 1000 m depth however this cyclonic pattern is not so clearly defined at deeper levels only at the deepest mooring located at 3500 m depth are the mean currents uniform all the way to the bottom over the bay of campeche s smooth western slope currents show features compatible with topographic rossby waves having vertical trapping scales thicker than 700 m periods between 5 and 60 days and horizontal wavelengths of 90 140 km in contrast the eastern slopes are characterized by rough topography and motions with periods longer than 28 days decrease toward the bottom suggesting a substantial reduction in the l

late pleistocene and holocene ice wedge activity on the blackstone plateau central yukon canada ice wedge activity can be used to reconstruct past environmental conditions we investigated the moisture source and timing of ice wedge formation on the blackstone plateau a section of permafrost exposed ice wedges that developed at two distinct depths the first set formed syngenetically and penetrated alluvial silts from the top of permafrost the second set truncated by an erosional or thaw contact was found solely in icy muddy gravels 3 1 m depth the 18o and d excess records of the ice wedges suggest that they formed from freezing of snow meltwater whose isotopic composition evolved during meltout the 14cdoc results suggest that climate was favorable to ice wedge growth between 32 000 30 000 and 14 000 12 500 cal yr bp but there was likely a hiatus during the last glacial maximum due to climate being too dry during the early to mid holocene ice wedges were inactive as a result of warmer and wetter climate ice wedge re initiated around 6360 cal yr bp with a peak in activity between 3980 and 920 cal yr bp a period characterized by cool and moist climate overall timing of ice wedge activity was broadly consistent with the climate and vegetation evolution in the western arctic

topographic rossby waves in the gulf of mexico abstract observations of topographic rossby waves trw using moored current meters bottom pressure gauges and lagrangian rafos floats are investigated for the deep basin of the gulf of mexico recent extensive measurement programs in many parts of the deep gulf which were inspired by oil and gas industry explorations into ever deeper water allow more comprehensive analyses of the propagation and dissipation of these deep planetary waves the gulf of mexico circulation can be divided into two layers with the 800 1200 m upper layer being dominated by the loop current lc pulsations and shedding of large diameters 300 400 km anticyclonic eddies in the east and the translation of these lc eddies across the basin to the west these processes spawn smaller eddies of both signs through instabilities and interactions with topography and other eddies to produce energetic surface layer flows that have a rich spectrum of orbit periods and diameters in contrast current variability below 1000 m often has the characteristics of trws with periods ranging from 10 100 days and wavelengths of 50 200 km showing almost depth independent or slightly bottom intensified currents through the weakly stratified lower water column these fluctuations are largely uncorrelated with simultaneous upper layer eddy flows trws must be generated through energy transfer from the upper layer eddies to the lower layer by potential vorticity adjustments to changing depths of the bottom and the interface between the layers therefore the lc and lc eddies are prime candidates as has been suggested by some model studies model simulations have also indicated that deep lower layer eddies may be generated by the lc and lc eddy shedding processes in the eastern gulf the highest observed lower layer kinetic energy was north of the campeche bank under the lc in a region that models have identified as having strong baroclinic instabilities part of the 60 day trw signal propagates towards the sigsbee escarpment a steep slope at the base of the northern continental slope and the rest into the southern part of the eastern basin higher energy is observed along the escarpment between 89 w and 92 w than either under the northern part of the lc or further south in the deep basin because of radiating trws from the western side of the lc in the northern part of the lc evidence was found in the observations that 20 30 day trws were connected with the upper layer through coherent signals of relative vorticity the 90 phase lead of the lower over the upper layer relative vorticity was consistent with baroclinic instability along the sigsbee escarpment the trws are refracted and reflected so that little energy reaches the lower continental slope and a substantial mean flow is generated above the steepest part of the escarpment rafos float tracks show that this mean flow continues along the escarpment to the west and into mexican waters this seems to be a principal pathway for deepwater parcels to be transported westward away from the slope rafos floats tend to oscillate in the same general area as if primarily responding to the deep wave field little evidence of westward translating lower layer eddies was found in both the float tracks and the moored currents in the western gulf the highest deep energy levels are much less than in the central gulf and are found seaward of the base of the slope otherwise the situation is similar with trws propagating towards the slope probably generated by the local upper layer complex eddy field being reflected and forcing a southward mean flow along the base of the mexican slope amplitudes of the lower layer fluctuations decay from the northwest corner towards the south

kuroshio in the luzon strait 1 three acoustic doppler current profilers adcps were deployed in the central luzon strait to monitor current velocity the profilers were deployed from 1997 to 1999 with the duration of deployment varying by location the observed current velocities indicated that the kuroshio flowed consistently into the south china sea further information provided by composite shipboard adcp data showed that the kuroshio intruded into the luzon strait through the deepest channels 20 5 n most of the intruded component made a loop and flowed out of the northern luzon strait but a branch of the kuroshio intruded into the south china sea while the current velocity obtained from mooring data did not show seasonal variation significant intraseasonal variation ranging from several to 100 days was found the seasonal reversal of monsoonal winds i e northeasterly in winter and southwesterly in summer did not cause noticeable variation in current velocity the miami isopycnic coordinate ocean model together with monthly wind data provided by the european centre for medium range weather forecasts was used to interpret the observed current velocity validation of the model results by the adcp data showed that the model can explain the seasonal and interannual variations in the observed velocity fields for example the model reproduced the branch of the kuroshio that consistently intruded into the south china sea the modeled velocity showed slight seasonal variation in the central luzon strait although the large interannual signal could have hindered the seasonal timescale fluctuation the interaction between the kuroshio and south china sea cyclonic flow caused variation in current velocities in both the luzon strait and the northern sector of the south china sea the model results also indicated that the kuroshio axis bent clockwise within the luzon strait and flowed into and out of the south china sea through the central and northern luzon strait respectively this pattern is similar with that shown by composite shipboard adcp data in summer the kuroshio looped west of the luzon strait with a small intruding branch confined to the northwestern south china sea in winter the intruding branch of the kuroshio extended west and into the interior of the south china sea the net zonal transport of inflow and outflow across the luzon strait calculated from the model results was primarily westward with the maximum varying from 4 8 to 6 5 sv eastward transport was found occasionally in summer in some years with a maximum from 0 3 to 2 2 sv while the kuroshio intruded consistently into the south china sea transport out of the south china sea was also observed in summer the current on the northern south china sea shelf break contributed to the outflow variation in zonal transport was caused by variation in the sea surface height ssh west of northern luzon caused by wind stress curl ekman transport driven by monsoonal winds and the strength of the kuroshio off the luzon strait had little impact on the intrusion which varied with fluctuation of the ssh west of northern luzon

eddy energy and shelf interactions in the gulf of mexico sea surface height anomaly data from satellite are continuously available for the entire gulf of mexico surface current velocities derived from these remotely sensed data are compared with surface velocities from drifting buoys the comparison shows that satellite altimetry does an excellent job resolving gulf eddies over the shelf rise depths between 200 and 2000 m if the proper length scale is used correlations between altimeter and drifter derived velocities are statistically significant r 0 5 when the surface slope is computed over 125 km indicating that remotely sensed sea surface height anomaly data can be used to aid the understanding of circulation over the shelf rise velocity variance over the shelf rise from the altimetry data shows regions of pronounced eddy energy south of the mississippi outflow south of the texas louisiana shelf and in the northwest and northeast corners of the gulf these are the same locations where surface drifters are most likely to cross the shelf rise suggesting gulf eddies promote cross shore flows this is clearly exemplified with both warm and cold eddies finally the contribution of gulf eddies and wind stress to changes in the mean circulation are compared results indicate that the eddy generated vorticity flux to the mean flow is greater than the contribution from the surface wind stress curl especially in the region of the loop current and along the shelf rise base in the western gulf future modeling efforts must not neglect the role of eddies in driving gulf circulation over the shelf rise

first direct dating of late pleistocene ice wedges by ams we present the first direct dating by 14 c accelerator mass spectrometry of three late pleistocene syngenetic icewedges from the seyaha cross section they are representative of permafrost with multistage ice wedges from the north of western siberia the most important result is the clear vertical age stratification of the ice i e the old ice is located beneath the young this shows that a timescale can be assigned to these ice wedges penetrating down into the permafrost the age of the ice shows a depth of not more than 3 5 m for frost cracking water penetrated into the icewedges at that depth the lower part of the ice wedges from the seyaha cross section has been dated between 21 000 and 14 000 bp fl 2000 elsevier science b v all rights reserved

deep current variability near the sigsbee escarpment in the gulf of mexico abstract observations of deep currents from a closely spaced array deployed at the base of the sigsbee escarpment south of the mississippi delta are dominated by energetic short period 10 days topographic rossby waves over a 2 yr interval distinct trains of waves occurred with differing characteristic periods wavelengths and horizontal energy distribution usually initiated with a burst of large amplitude current fluctuations that slowly decay over the next 2 3 months two of the wave trains were associated with the shedding and westward passage of major loop current anticyclones however one event occurred when upper layer currents were quiescent this latter wave train showed that bottom trapped topographic wave motions can be traced to within 300 m of the surface in a 2000 m water column ray tracing showed that a likely source region of the short period waves was the west side of an extended loop current the data and ray paths suggest that through refraction and reflection the steep es

lithogeochemical exploration for shale hosted lead zinc deposits case studies from the mcarthur river and mt isa districts northern australia the large lead zinc deposits of middle proterozoic age in northern australia occur in sediments interpreted as having been deposited under saline shallow emergent conditions significant alkaline diagenesis is evident from the presence of abundant k feldspar and locally albite alkali element compositions clearly distinguish the sediments of the mineralised shallow emergent locations both from those of more permanent water cover lacustrine or lagoonal and from those close to basin margins the key variables for identifying the geochemical contrasts are the levels of k rb and na and the ratios of k al and k rb these geochemical parameters can be used in conjunction with the levels of the target and indicator elements to detect whether mineralisation may be present in a favourable geological environment two case studies of the application of whole rock geochemistry in base metal exploration are given for the glyde river sub basin mcarthur basin and the western succession mt isa block

the fox permafrost tunnel a late quaternary geologic record in central alaska the fox permafrost tunnel which penetrates 110 m into frozen sediments of gold stream valley provides a continuous exposure of fossiliferous silt and alluvium above schistose bedrock deposition of fluvial gravel was followed by a long interval of loess accretion and permafrost aggradation that was punctuated by episodes of thaw and of gullying and redeposition of silt imbricated sandy gravel above the bedrock contains lenses of finer alluvium that contain wood fragments and some rooted stumps radiocarbon dates indicate that the gravel is older than 40 ka but absence of mature soil and weathering profiles at its upper contact indicates that fluvial activity must have continued until shortly before loess accretion began at the tunnel site silt is the most widespread depositional unit in the tunnel this deposit is of eolian origin loess but some has been redeposited by slope processes the silt units contain abundant ground ice as pore filings lenses wedges and buried pond ice loess accretion was interrupted by a period when little loess accumulated and when large ice wedges formed in the lower loess unit and subsequently were truncated by thaw loess began forming sometime before 40 ka and was rapidly accreting by 39 ka under xeric conditions with open vegetation a sharply decreased rate of loess accretion associated with local erosion and thaw between about 36 and 30 ka is marked by anomalous cation concentration values lenses of buried sod fossils indicative of moist to wet substrates and truncated ice wedges beneath small frozen ponds or streamlets that occupied ice wedge troughs a later episode of rapid loess influx under drier conditions began after 30 ka and coincided with glacial advances of late wisconsin age in the adjoining alaska range large ice wedges also formed in the upper loess unit but only their bases are exposed in the tunnel and their history of development is uncertain fanlike deposits of poorly sorted debris near the tunnel portal formed between about 12 5 and 11 ka during deep erosion of loess slopes under moister conditions the deposits locally form two subunits the younger over whelmed a stand of tall willows on the floor of goldstream valley between about 11 3 and 11 1 ka the older may have formed about 1 000 yr earlier stratigraphic records elsewhere in central alaska indicate variable middle wisconsin environments followed by colder and drier conditions that began between 30 and 25 ka and persisted until perhaps 12 5 ka widespread loess erosion and redeposition subsequently occurred under moister and probably warmer conditions renewed early holocene loess deposition may have been widespread but its exact environmental controls are uncertain our data challenge three generally accepted concepts of late quaternary periglacial processes in central alaska we contend that 1 many ice wedge systems may have formed under interstadial conditions rather than full glacial conditions 2 episodes of rapid loess influx may have been partly out of phase with episodes of glacier expansion and 3 redeposition of loess by solifluction sheetwash and gully formation may have been episodic and required conditions moister than those under which the loess initially accreted

ratio of 36cl cl in ground ice of east siberia and its application for chronometry abundance of the cosmogenic nuclide chlorine 36 36cl was measured together with the chloride cl concentration in different horizons of quaternary permafrost samples collected from various types of ground ice in the northeastern part of siberia the 36cl cl in 32 samples ranged in value from 2 4 10 14 to 1 4 10 12 nonetheless after a few extreme values were excluded these 36cl cl ratios provided a local permafrost chronometry the general concordance of the modeled ages with geological expectations and other chronological methods supports the potential power of the proposed dating method however the large observed change in ratios from higher to lower values during the transition from last glacial maximum to holocene climatic conditions remains unexplained an attempt to make use of the corresponding beryllium 10 10be absolute concentrations in the same samples failed because input of 10be attached to particulate matter into permafrost is unknown further 36cl cl serial measurements of modern precipitation and fossil ground ice are needed to refine this dating method into a practical tool with a clear protocol

near surface currents in desoto canyon 1997 99 comparison of current meters satellite observation and model simulation this study evaluates a data assimilated model simulation of near surface circulation in desoto canyon dsc gulf of mexico with emphasis on analyzing moored current meter observations and comparing them with satellite data and model results the study period is for two years from april 1997 to april 1999 the model results are from a high resolution gulf of mexico model forced by analyzed wind and surface heat flux two types of data are used to deduce near surface circulation moored current meters at 13 locations in the dsc and satellite sea level anomaly the moored currents are mapped through multivariate objective analysis to produce surface currents and surface geopotentials against which satellite and model derived sea surface heights and geostrophic currents are compared coupled patterns between the observations model results and satellite data are obtained using the singular value decomposition svd analysis there are two dominant modes a single eddy mode in which currents are concentrated at the foot of the canyon and an eddy pair mode in which one eddy is at the foot of the canyon and the other a counterrotating eddy is over the head of canyon mode 1 appears to be associated with the mesoscale eddy traveling around the loop current crest and trough and mode 2 is associated with the intrusion of loop current crest and trough over the west florida shelf the observed and model currents are in good agreement about the means and variances the model currents also appear to be well constrained by the steep topography however the model velocity field contains only the first mode the satellite derived velocity field on the other hand contains both the first and second modes though the satellite field does not adequately resolve the velocity structures over the slope

geochemistry of evaporite bearing series a tentative guide for the identification of metaevaporites literature on metasedimentary rocks indicates that former evaporites have been assumed where brines are present as fluid inclusions or minerals such as scapolite tourmaline and lazurite which are considered as evidence of equilibria with brines very few works take into account the chemical composition of rocks because chemical data on evaporite bearing sedimentary series are scarce

modeling the baroclinic circulation in the area of the sicily channel the role of stratification and energy diagnostics 1 aspects of the circulation of the sicily channel region are studied with a high resolution primitive equation sigma coordinate model this work is an attempt to study the process governing the purely baroclinic dynamics and its sensitivity to seasonal stratification thus no atmospheric forcing is used two numerical experiments are analyzed using as initial conditions diagnostic velocity fields derived from the winter and summer climatological hydrologies the quasi steady state is characterized by circulation patterns in the depth range of the modified atlantic water maw and the levantine intermediate water liw strongly controlled by mesoscale eddies and topography seasonal difference is found in the surface current which exhibits the major variability on the african side downstream of adventure bank and the ionian slope where the absolute maximum occurs the intermediate circulation instead does not show relevant seasonal differences liw enters through the two passages south of malta plateau and preferentially flows along the sicilian shelf edge exiting over the northern sill its pathway is strongly controlled by subsurface cyclonic and anticyclonic cells the results are in good agreement with observations an energy diagnostics is applied to model results and sheds important light on dynamical characteristics of the mesoscale eddy field and indicates seasonal differences in the energetic exchange with the mean flow the analysis of the mean mke and eddy eke kinetic energy the transfer terms between energy compartments and the eddy momentum flux divergence indicates how eddies are strongly energetic in summer and exchange energy more efficiently with the mean flow in the quasi steady state maw volume transport and mke and eke fluctuations are strongly correlated this result suggests that mesoscale motions can control up to 40 of volume transport variability

correlation of upper pleistocene sediments in northern west siberia abstract a geochronometric database comprising 121 optically stimulated luminescence and 59 radiocarbon dates plus u th date on peat from 24 key sections in northern west siberia is presented and discussed these data have been obtained during russian norwegian joint research for the past 15 years and are augmented by reports on radiocarbon dated mammoth carcasses in west siberia together they provide the basis for revising the regional stratigraphic scheme and for correlation to the european quaternary chronostratigraphy and marine oxygen isotope record the geochronologic correlation of sedimentary formations across west siberia involves classical stratotypes of fluvial shallow limnic and temperate marine sediments of the karginsky horizon ca 130 ka which was previously attributed to mis 3 the older kazantsevo marine formation is thus assigned a middle pleistocene age the uppermost glacial sedimentary complex containing glacial ice was deposited by shelf based ice sheets between ca 100 and 60 ka bp the postglacial pleistocene sediments are mostly ice bound loess like deposits and sink hole silts containing numerous mammoth carcasses that are radiocarbon dated to between ca 42 and 25 ka bp there are no traces of glacial activity on the siberian plains during mis 2 a period for which palaeoclimatic proxies suggest a cold and dry environment this synthesis indicates that the prior usage of the siberian correlation horizons of kazantsevo and karginsky as equivalents of the eemian and middle pleniglacial is stratigraphically invalid

refined proterozoic evolution of the gawler craton south australia through u pb zircon geochronology abstract through the application of both conventional u pb zircon analyses and small sample u pb isotopic analyses the nature and timing of tectonic events leading to the formation of the gawler craton have been defined more precisely constraints on deposition of early proterozoic iron formation bearing sediments have been narrowed down to the period 1960 1847 ma deformed acid volcanics including the economically important moonta porphyry have zircon ages of 1790 and 1740 ma the voluminous acid gawler range volcanics and correlatives to the east were erupted over a short interval at 1592 2 ma and were intruded by anorogenic granites at 1575 ma small sample zircon analyses proved to be an extremely valuable adjunct to conventional analyses generally yielding more concordant data which forced a curved discordia through an upper intercept slightly younger than from a conventional straight line discordia

energetic topographic rossby waves in the northern south china sea abstracttopographic rossby waves trws are reported to make a significant contribution to the deep ocean current variability on the northern south china sea nscs continental slope trws with pe

an algorithm to detect isolated anomalies in three dimensional stratified data fields with an application to density fields from four deep basins of the baltic sea 1 a new approach to describe the mesoscale variability caused by eddies in terms of the integral properties of all eddies contained in a certain ocean volume is suggested for this purpose a pattern recognition algorithm to detect isolated anomalies in three dimensional stratified data fields was developed and is introduced in detail an application to 12 eddy resolving density fields acquired in the framework of the german russian project mesodyn in four deep basins of the baltic sea namely the arkona basin the bornholm basin the stolpe furrow and the eastern gotland basin demonstrates that the algorithm works properly the most remarkable finding of this application is that the volume fraction occupied by the isolated anomalies or eddies is constant it amounts to about 12 of the total volume for each data field no matter whether the stratification corresponds to a summer or a winter situation many possible applications of the pattern recognition are proposed to document its general usefulness finally the main features of the algorithm and possible extensions are discussed extensively

numerical simulations of a buoyancy driven coastal countercurrent off vancouver island abstract a three dimensional prognostic numerical model has been developed to study the ocean circulation around vancouver island british columbia in a series of simulations the model is applied to examine the role of buoyancy forcing in the dynamics of the summer coastal countercurrent found off the west coast of vancouver island the forcing is provided by the fraser river discharge into the strait of georgia an estuarine circulation establishes itself in juan de fuca strait from which a distinctive right bounded current is formed and advances along the coast sensitivity studies are conducted to determine the robustness of this current to initial conditions opposing wind enhanced vertical mixing and grid resolution finally various characteristics of the numerically modeled coastal flow are compared with observations

the postglacial pleistocene of the northern russian mainland abstract the paper summarizes the results of recent studies of late pleistocene postglacial geological events which occurred in the flatlands of northern russia stretching from the timan ridge to the laptev sea coast the available sedimentary record includes thawed and perennially frozen subaerial sediments and in places lacustrine and fluvial formations hundreds of geochronometric measurements by radiocarbon and luminescence techniques place this record within the time span of 50 11 ka bp which confirms an early mid weichselian age of the underlying glacial complex first established by the queen programme the spectrum of proxies includes sedimentary facies pollen data plant macrofossils oxygen isotope values megafauna remains insect assemblages traces of dna paleosols and permafrost properties together they indicate a continental progressively deteriorating climate with very cold winters and warmer than present summers through the second half of the late pleistocene minor climatic fluctuations are largely due to slightly changing humidity during mis 3 these changes are more pronounced in periglacial european russia in the vicinity of the barents kara ice sheet where the mid weichselian biotic maximum contrasts with conditions in the late weichselian polar desert in siberia the periglacial environments were more stable and beneficial for biota inspite of the increased continentality the recent data accumulated by various researchers are incompatible with the conventional correlation of the karginsky interglacial strata of siberia with mis 3 or any part of the european pleniglacial

observations of intermittent deep currents and eddies in the gulf of mexico 1 intense currents having speeds between 10 and 40 cm s 1from 1000 m below the surface to the bottom have been measured in the loop current lc region and in the western gulf of mexico wgm the observations come from moored current meters sampling from the near surface to the bottom at 3300 3500 m and from august 2008 to august 2010 ten intermittent intensified currents are documented these events last 10 to 30 days and take place in the region just between the surface intensified anticyclonic cyclonic features as deduced from altimetry and measured currents in the wgm they occur between the cores of anticyclone cyclone pairs in the eastern gulf of mexico egm they occur in the loop current edge between its anticyclonic circulation and a neighboring cyclone during each event the analysis shows an increase in the barotropic contribution to the current in the loop current region these events are often associated with intensification of cyclonic vorticity in the deep layer