the flank margin model for dissolution cave development in carbonate platforms the bahama islands contain many abandoned dissolution caves at elevations between two and seven metres above current sea level the development of dissolution caves in tropical carbonate islands is dependent on the position and nature of the freshwater lens lens position is controlled by sea level which in stable carbonate platforms like the bahamas is a function of glacioeustatic sea level still stands caves in the bahamas that are currently subaerial must have developed during past higher sea levels during the late quaternary sea levels higher than present have been relatively short lived and that limits the amount of time that a freshwater lens could be situated at the elevation required for the cave formation the bahama islands are low lying landforms where only aeolian ridges extend to elevations higher than six metres above current sea level past high sea level events greatly reduced the exposed land area of the bahama islands thus also limiting both the catchment for and size of freshwater lenses caves must be younger than the rock in which they are developed most subaerial bahamian caves are found in limestones that are less than 150000 years old development of large dissolution caves under these limitations of time and lens size requires a powerful dissolutional mechanism the mixing of discharging freshwater with tide pulsed incoming marine water under the flanks of emergent dune ridges may have produced the conditions necessary bahamian caves formed by this process are phreatic chambers with complex interconnections and blind tubes their presence demonstrates that significant dissolution can occur rapidly as a result of the mixing of fresh and marine waters beneath small carbonate islands

the influence of tectonics on flank margin cave formation on a passive continental margin naracoorte southeastern australia abstract intensive cave development within the highly porous and permeable eocene middle miocene gambier limestone in southeastern south australia is restricted to a 1 11 km area at naracoorte the caves are overwhelmingly horizontal consisting of large solutional domes connected by smaller passages with bell holes small pendants and large non directional scallops on the walls and ceilings orientation is strongly controlled by nw se joints cave entrances have been opened by subsequent collapse and breakdown is common the caves are located on the kanawinka fault escarpment which was uplifted in the late miocene early pliocene and then overlain by a series of pleistocene carbonate strandline dunes deposited as the sea retreated following a late miocene transgression the coastline lay along the kanawinka escarpment at 0 9 1 1 ma when the caves formed just inland of the shoreline within the zone of enhanced dissolution at the seaward margin of the freshwater lens they have the typical flank margin cave morphology except that joint development adjacent to the fault caused the strong linear orientation parallel to the coastline the beach dune deposited to the west of the kanawinka escarpment shows that sea level had dropped sufficiently to completely drain the caves at 780 880 ka cave development was therefore confined to a period spanning 0 8 1 1 ma continuing gradual uplift through the pleistocene means that the caves are now 100 km inland obscuring the essentially coastal nature of the naracoorte karst speleogenesis at naracoorte reflects the interaction of neotectonics with coastal dissolution and emphasizes the role that tectonism can play in pleistocene karst development even on passive continental margins where glacio eustatic sea level fluctuations are generally ascribed as the dominant role

vorticity flux through the yucatan channel and loop current variability in the gulf of mexico 1 recent observations the canek program candela et al 2002 suggest that potential vorticity pv flux anomaly vfa at yucatan channel may serve as a useful indicator of loop current variability including loop current extension retraction and eddy shedding intuitively anticyclonic vfa extends the loop current into the gulf of mexico and cyclonic vfa causes retraction or even shedding however this intuition is inconsistent with pv conservation the problem is reexamined here by careful analyses of the relation between vfa and loop current variability using 1 the results of a 15 year numerical simulation of shedding specified with simple forcing and 2 canek and satellite observations both model and observations indicate that loop current eddy shedding or retraction tends to occur shortly 1 2 months after the influx of vfa at yucatan has turned anticyclonic and that these events are sometimes preceded by a more prolonged period of influx of cyclonic vfa these findings suggest that contrary to intuition influx of cyclonic vfa tends to extend the loop current into the gulf thus making the loop current more susceptible to retract or shed an eddy and influx of anticyclonic vfa may then trigger retraction or eddy shedding however the loop current s behaviors are much more complex than can be prescribed by these simple rules a much longer observational data set coupled with more refined model experiments and sophisticated analyses is required to further quantify the phenomenon index terms 4520 oceanography physical eddies and mesoscale processes 4255 oceanography general numerical modeling 4576 oceanography physical western boundary currents 4243 oceanography general marginal and semienclosed seas keywords vorticity flux loop current yucatan channel citation oey l y 2004 vorticity flux through the yucatan channel and loop current variability in the gulf of mexico j geophys res 109 c10004 doi 10 1029 2004jc002400

closing the transport budget of the florida straits closing the mean mass budget of the florida straits is fundamental to understanding the source waters of the gulf stream and for constraining ocean simulations and forecasts in a region of complex topography existing transport time series of the inflow through yucatan channel and the outflow at 27 n yield a 9 sv difference in the mean which cannot be reconciled by the two minor inflows between here we present a synthesis of transport estimates from throughout the florida straits using velocity data collected aboard the cruise ship explorer of the seas our transports form a consistent mass budget and conform with the northern outflow from the straits of 32 1 3 3 sv as measured continuously by cable in particular we find an average of 30 0 5 3 sv for the inflow to southern florida straits and estimate that old bahama channel contributes less than an additional 2 sv

observations of the florida and yucatan currents from a caribbean cruise ship abstract the yucatan and florida currents represent the majority of the warm water return path of the global thermohaline circulation through the tropical subtropical north atlantic ocean their transports are quantified and compared by analyzing velocity data collected aboard the cruise ship explorer of the seas from 157 crossings between may 2001 and may 2006 the mean transport of the florida current at 26 n was estimated to be 30 8 3 2 sv 1 sv 106 m3 s 1 with seasonal amplitude of 2 9 sv upstream the yucatan current was estimated from 90 crossings to be 30 3 5 sv with seasonal amplitude of 2 7 sv these two currents are shown to be linked at seasonal time scales hence contrary to former results it was found that transports through the florida straits and the yucatan channel are similar with the implication that only small inflows occur through minor channels between them

flow structure and transport in the yucatan channel 1 the direct ocean current observations across the yucatan channel collected during the canek program allow the best description to date of the exchange between the caribbean sea and the gulf of mexico a net transport of 23 8 1 sv 1 sv 106m3s 1 95 confidence interval flowed through the yucatan channel from the caribbean sea into the gulf of mexico during the period between september 1999 and june 2000 this is about 20 percent less than the 30 sv accepted as the nominal transport of the florida current and less also than the 28 sv assumed for yucatan in closing the transport budgets for caribbean passages the discrepancy may be an imbalance due to fluctuations in the transports through other passages of the system especially the old bahama and northwest providence channels which remain poorly known our data corroborate the principal features of the flow through the yucatan channel the northerly surface yucatan current and its southerly under current off mexico and the southerly surface cuban counter current near cuba but previously unobserved mean currents are found to exist at depth especially on the eastern side of the channel fluctuations seen in the deep flows are related to volume anomalies over the gulf of mexico a transport through the yucatan channel smaller than previously thought has significant implications for the dynamics of the gulf of mexico and its modeling since this transport is the principal forcing of its circulation the circulation budgets in the western subtropical atlantic should be revised considering these new results

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

a speleothem based mid holocene precipitation reconstruction for west central florida the mid holocene was the warmest segment of the current interglacial and possessed a weak latitudinal temperature gradient which impacted climate teleconnections and thus precipitation variability

circulation characteristics in three eddy permitting models of the north atlantic a systematic intercomparison of three realistic eddy permitting models of the north atlantic circulation has been performed the models use different concepts for the discretization of the vertical coordinate namely geopotential levels isopycnal layers terrain following sigma coordinates respectively although these models were integrated under nearly identical conditions the resulting large scale model circulations show substantial differences the results demonstrate that the large scale thermohaline circulation is very sensitive to the model representation of certain localised processes in particular to the amount and water mass properties of the overflow across the greenland scotland region to the amount of mixing within a few hundred kilometers south of the sills and to several other processes at small or sub grid scales the different behaviour of the three models can to a large extent be explained as a consequence of the different model representation of these processes

groundwater flow regime within the gambier embayment of the otway basin australia evidence from hydraulics and hydrochemistry a conceptual groundwater flow model for the cainozoic sequence of the gambier embayment of the otway basin south australia is developed using hydraulic head distribution environmental isotopes and hydrochemical data local flow cells occur within the upper sequence of the gambier unconfined aquifer and are recognised by local relief of the water table and as rapid lateral variations in chloride 14c 2h and 18o concentrations indicating that regional flow is not dominant in the upper portion of the unconfined aquifer these localised systems are topographically controlled and have developed in response to undulating stranded coastal dune ridges of the bridgewater formation recharge areas correspond to dune highs while discharge is focused towards the lower lying interdunal regions total dissolved solids concentrations are controlled by evapotranspiration processes during recharge and ion ratios are modified by water rock interactions within the groundwater system groundwaters are more dilute in the southern section of the basin where the surplus of precipitation over evapotranspiration in the winter months is greater than that in the northern section of the basin a regional flow system with interaquifer mixing has developed within the confined dilwyn aquifer system recharge to the dilwyn aquifer has been identified downgradient from the basin margin via downward leakage from an intermediate flow system within the gambier unconfined aquifer to the deeper regional flow system of the confined dilwyn aquifer interaquifer mixing appears to be geologically controlled in the south by the elevated gambier axis and in the north by the kanawinka fault downgradient of the zero head difference line lateral flow appears to be the dominant transport mechanism within the dilwyn aquifer as indicated by constant chloride concentrations monotonic decrease in radiocarbon concentration and more negative 2 and 18 o composition

influence of karst hydrology on water quality management in southeast south australia southeast south australia has large reserves of potable groundwater generally close to the surface european settlement has had a major impact on groundwater quality due to the presence of extensive karst in the unconfined aquifer historically industries such as cheese factories were often sited close to karst features e g caves and sinkholes because they provided a convenient means of waste disposal although most have long since closed they have left a legacy of pollution plumes of varying sizes in mount gambier the main regional centre the presence of both exposed and subterranean karst features provided a perfect system for the disposal of stormwater prior to the provision of a sewerage system within mount gambier all toilet and household wastewaters were disposed to ground these activities and the subsequent problems that began emerging in the 1960s have led to a concerted effort over the last 20 years to change the philosophy of waste disposal and to generate an understanding and responsibility by those who live in the region and depend on groundwater for the major part of their water supply mount gambier s water supply comes from the blue lake groundwater inflow from a highly karstic tertiary limestone aquifer provides 90 of the recharge to the blue lake the lake is a high value resource in a high risk environment and in order to minimize this risk a water quality management plan for the lake is currently being developed

comparisons between a continuous 3 year current meter observation at the sill of the yucatan strait satellite measurements of gulf loop current area and regional sea level from october 1977 through november 1980 a current meter mooring was maintained in the yucatan strait the meter was moored halfway between mexico and cuba 145 m above the sill or in 1895 m of water motions of low frequency 14 1 cycles day are oriented approximately parallel to the isobaths 021 030 true net drift for 3 years is to the ssw at an average velocity of 1 8 cm s sustained southward flows at intervals of 8 months which persisted for several months each have average velocities of 5 cm s with randomly spaced bursts as high as 15 cm s energy in subtidal frequency bands has significant peaks near 38 1 and 19 1 cycles day with a broad band of energy between 300 1 and 200 1 cycles day the latter peak is consistent with the approximately 8 month interval between the southward flow events comparison with weekly areal coverage of the gulf loop current from geostationary operational environmental satellite infrared observations shows little covariation except that 8 months is typical of some anticyclonic eddy generation there is little coherence of sill depth velocities with naples sea level at subtidal frequencies but with miami there is coherence at several frequencies notably 38 1 and 19 1 cycles day in the higher frequencies the principal tidal motions are diurnal and are oriented somewhat across the isobaths toward the northwest 346 349 true with counterrotating o1 and k1 constituents no semidiurnal inertial or fortnightly energy is observed above the background continuum

on the pressure gradient force over steep topography in sigma coordinate ocean models abstract the error in computing the pressure gradient force near steep topography using terms following coordinates is investigated in an ocean model using the family of vertical differencing schemes proposed by arakawa and suarez the truncation error is estimated by substituting known buoyancy profiles into the finite difference hydrostatic and pressure gradient terms the error due to hydrostatic inconsistency which is not simply a space truncation error is also documented the results show that the pressure gradient error is spread throughout the water column and it is sensitive to the vertical resolution and to the placement of the grid points relative to the vertical structure of the buoyancy field being modeled removing a reference state as suggested for the atmosphere by gary reduces the truncation error associated with the two lowest vertical modes by a factor of 2 to 3 as an example the error in computing the pressure gradient using a standard 10 level primitive equation model appl

deep flows in the yucatan channel and their relation to changes in the loop current extension 1 the first attempt to establish a relation between the loop current extension and deep flows in yucatan channel was made by maul et al 1985 it was unsuccessful probably because of the low spatial resolution of their observations from september 8 1999 to june 17 2000 eight moorings with acoustic doppler current profilers current meters and thermometers were deployed across the yucatan channel the data from these arrays were used to compute time series of the transports below the level of the deepest isotherm observed in the florida straits as required by a simple box model that restricts deep exchanges with the gulf of mexico to the yucatan channel the surface extension of the loop current was inferred from 3 day advanced very high resolution radiometer imagery from october to may when temperature gradients were sufficient to map the warm water unambiguously the deep transports appear at first unrelated to the rate of change of the loop current extension but filtering the series with a 20 day running mean increases the correlation between the low pass series to 0 62 and up to 0 83 with a lag of 8 5 days with loop current changes leading the deep flows the cumulative deep transport a quantity that favors lower frequencies is very well related correlations 0 9 to the surface extension of the loop current also with a lag of about a week these lags are not statistically significant but suggest a timescale for internal adjustment processes in the gulf of mexico the empirical orthogonal function of the current best related to the area extension of the loop current represents a unidirectional flow across the entire deep section flowing either toward or from the gulf of mexico and includes a strong expression of the yucatan undercurrent

circulation along the mexican caribbean coast 1 data from an array of seven subsurface upward looking moored acoustic doppler current profilers adcps and four subsurface pressure sensors deployed from august 2002 to august 2003 along the caribbean coast of mexico showed that the currents in the area have a predominant northeastward direction along the coast are coherent within the upper 130 m of the water column and have a general tendency to increase northward reaching magnitudes of 2 4 m s north of cozumel in addition important weeklong reversal periods southward flows are observed around chinchorro bank a vertical current profile eof analysis at each station indicates high coherence within the study area with the first vertical mode at each station explaining at least 69 of variance and current vectors aligned with the coast a second eof analysis carried out for any uniform depth level using current data from all stations shows high coherence in the horizontal as well the first mode explains at least 59 of the variance and has a dominant 3 month long variability comparison between the current patterns along the mexican caribbean coast and in the yucatan channel suggests that dynamics of the entire area might be strongly influenced by the passage of eddies through the region comparison of a singular spectral analysis ssa of the principal components of currents with the pressure difference across the channels supports the idea of eddies modulating current variability numerical model results indicate that high values of the current intensity indexes are associated with eddies the flow along chinchorro and cozumel channels is in geostrophic balance most of the observation time but with week long ageostrophic periods which are predominant off cozumel these events appear to occur when eddies are traversing the region

seawater density variations in the north atlantic and the atlantic meridional overturning circulation seawater property changes in the north atlantic ocean affect the atlantic meridional overturning circulation amoc which transports warm water northward from the upper ocean and contributes to the temperate climate of europe as well as influences climate globally previous observational studies have focused on salinity and freshwater variability in the sinking region of the north atlantic since it is believed that a freshening north atlantic basin can slow down or halt the flow of the amoc here we use available data to show the importance of how density patterns over the upper ocean of the north atlantic affect the strength of the amoc for the long term trend the upper ocean of the subpolar north atlantic is becoming cooler and fresher whereas the subtropical north atlantic is becoming warmer and saltier on a multidecadal timescale the upper ocean of the north atlantic has generally been warmer and saltier since 1995 the heat and salt content in the subpolar north atlantic lags that in the subtropical north atlantic by about 8 9 years suggesting a lower latitude origin for the temperature and salinity anomalies because of the opposite effects of temperature and salinity on density for both long term trend and multidecadal timescales these variations do not result in a density reduction in the subpolar north atlantic for slowing down the amoc indeed the variations in the meridional density gradient between the subpolar and subtropical north atlantic ocean suggest that the amoc has become stronger over the past five decades these observed results are supported by and consistent with some oceanic reanalysis products

mechanisms of the 40 70 day variability in the yucatan channel volume transport the yucatan channel connects the caribbean sea with the gulf of mexico and is the main outflow region of the caribbean sea moorings in the yucatan channel show high frequent variability in kinetic energy 50 100 days and transport 20 40 days but the physical mechanisms controlling this variability are poorly understood in this study we show that the short term variability in the yucatan channel transport has an upstream origin and arises from processes in the north brazil current to establish this connection we use data from altimetry and model output from several high resolution global models a significant 40 70 day variability is found in the sea surface height in the north brazil current retroflection region with a propagation toward the lesser antilles the frequency of variability is generated by intrinsic processes associated with the shedding of eddies rather than by atmospheric forcing this sea surface height variability is able to pass the lesser antilles it propagates westward with the background ocean flow in the caribbean sea and finally affects the variability in the yucatan channel volume transport

deep flow variability in the vicinity of the yucatan straits from a high resolution numerical simulation 1 the deep flow variability in the vicinity of the yucatan channel between the caribbean sea and the gulf of mexico is examined within a high resolution numerical simulation of the north atlantic ocean we focus on the 6 year integral cycle of loop current lc ring formation and we study the flow regimes both in the yucatan channel and farther north in the lc the circulation in the vicinity of the yucatan channel presents a high variability in the flow regimes and in the shedding period in good agreement with earlier observations the outflow toward the caribbean sea in the yucatan channel is shown to be controlled in part by a regular shift of the lc maximum velocity position in phase with the transport variations the outflow follows the inflow variations independently of the northward extension of the lc our analysis of the growth of the loop is also shown to be in good agreement with the ballooning process proposed by pichevin and nof 1997 and nof and pichevin 2001 to explain the lc ring formation moreover at the end of each cycle of ring formation a sudden deepening of the lc deepest layer occurs together with an intensification of the transport and of the currents in the deep layers beneath the lc this process is shown to be connected with the growth of cyclones in the deep layers they result from the bottom intensified instability of the lc ring and contribute to its separation from the lc

an analysis of loop current frontal eddies in a atlantic ocean model simulation abstractthe loop current frontal eddies lcfes refer to cyclonic cold eddies moving downstream along the outside edge of the loop current in the eastern gulf of mexico they have been observed by in situ measurements and satellite imagery mostly downstream of the campeche bank continental shelf their evolution simulated by a primitive equation and 37 level atlantic ocean general circulation numerical model is described in detail in this study some of the simulated lcfes arise with the passage through the yucatan channel of a caribbean anticyclonic eddy as weak cyclones with diameters less than 100 km near the yucatan channel they then grow to fully developed eddies with diameters on the order of 150 200 km while moving along the loop current edge modeled lcfes have a very coherent vertical structure with isotherm doming seen from 50 to 1000 m depth the caribbean anticyclone and lcfe are two predominant features in this numerical model simulation which account for 22 and 10 respectively

frequency of ring separations from the loop current in the gulf of mexico a revised estimate the most energetic events in the circulation of the gulf of mexico are the separation of large anticyclonic rings from the loop current building on previous work the authors examine all the apparent rings since july 1973 this new dataset includes the satellite altimetry since 1992 providing a set of 34 consecutive ring formations the primary advantage of altimetry is that the data remain available in the summer one finding is that the ambiguity of whether or not a ring has separated is reduced but not eliminated the uncertainty with which separation events can be specified remains approximately 4 weeks even with nearly continuous data primary peaks in the distribution of separation intervals are found at 6 and 11 months with a smaller peak at 9 months if the spectrum is smoothed heavily enough a peak in the distribution can be formed nearer 12 months but this near annual peak is a result more of the smoothing than of the data

ageostrophic fluctuations in cozumel channel 1 the cayman current flows to the west and most of it turns north as it approaches the yucatan coast producing a persistent northwesterly flow on both sides of cozumel island the transport between the yucatan peninsula and cozumel island i e through the cozumel channel is close to 5 sverdrups in the mean with velocities at midchannel ranging from 20 to 180 cm s a recent study of the subinertial flow and pressure difference across cozumel channel by chavez et al 2003 showed the existence of periods lasting over 1 month with large 3 day to 1 week ageostrophic fluctuations the flow was measured again for a year now at four locations around cozumel island including two instruments along the axis of the channel 8 6 km apart thus allowing estimations of the along channel velocity gradients the new measurements reveal that as suggested in the previous study the centripetal or curvature acceleration of the current is the most significant contribution in the departure from geostrophy indeed the curvature is at times so large that the pressure difference implies a geostrophic flow in the direction opposite to that of the actual flow that is the curvature is anticyclonic with amplitude in rossby number larger than unity measures of the intensity of suprainertial variations in pressure differences and velocity show that periods of ageostrophic fluctuations are consistently much richer in high frequency fluctuations than periods of nearly geostrophic behavior nonetheless the large scale reynolds stresses play an insignificant role throughout

improved methodology and new thermoluminescence ages for the dune sequence in south east south australia abstract our thermoluminescence dating technique for quartz extracted from late pleistocene sediments has been improved by the addition of a 33 h 160 c preheat before measurements this yields better plateaux which now encompass the region known as the 325 c tl peak this is consistent with the prediction from isothermal decay studies of the lifetime at ambient temperature of the traps responsible for this peak the preheat does not help resolve problems associated with dose responses above 600 gy some details of the dose response are shown to be better understood with the aid of 3 d tl spectra the improved method has been applied to one former and seven new samples from the stranded beach dune sequence in south east south australia the five ages obtained for the main dune sequence range from 95 6 to 725 100 ka and all are consistent with the expected ages

on the seasonal variability of the currents in the straits of florida and yucatan channel 1 seasonal variability in the major passages of the caribbean are investigated using 5 years of wind and current observations explorer of the seas combined with a 3 year 1 12 simulation seasonal fluctuations in the florida and yucatan passages are both characterized by semiannual cycles with transport maxima in summer and winter and minima in spring and fall in the straits of florida seasonal variability is associated with surface intensified fluctuations of the florida current and can be largely explained by along channel winds and wind stress curl over the atlantic ocean in the yucatan channel seasonal variability is more barotropic and does not covary with wind forcing but rather is associated with fluctuations of an anticyclonic recirculation to the south of the channel upstream the seasonality in the grenada passage also covaries with seasonality in the yucatan and florida passages although the grenada passage carries only a small fraction of the total inflow to the caribbean recent in situ estimates of the mean transport in the yucatan channel differ by 7 sv 30 5 sv explorer of the seas 23 1 sv canek an assessment of sampling errors biases and interannual variability seem to account for no more than 2 sv leaving no satisfactory explanation for the difference in explorer of the seas data flows in the straits of florida and yucatan channel display similar vertical shear structure while canek data exhibit significantly lower shears in the upper 500 m which account for all the transport difference

pleistocene coastal stratigraphy sea level highstands and neotectonism of the southern australian passive continental margin a review located in a tectonically stable intraplate setting and in the far field of former ice sheets the southern australian passive continental margin represents a globally important region for quantifying sea level during pleistocene highstands the stratigraphical record of the southern australian margin is dominated by geographically extensive coastal barrier estuarine and peritidal landforms of bioclastic temperate carbonate affinity a function of regional aridity siliciclastic successions dominate the eastern australian coastline despite the generally high level of tectonic stability regional contrasts are evident in the elevation of pleistocene shoreline deposits that largely relate to pre quaternary geotectonic setting the most complete record of pleistocene highstand deposits occurs in the murray basin coorong coastal plain region and indicates that interglacial sea level highstands for at least the past 11 interglacials did not deviate by more than 6 m from present sea level the pleistocene marginal marine record of southern australia is dominantly represented by coastal successions deposited during marine oxygen isotope stages 5e and 7 equating with relative sea level maxima of 2 6 m and greater than 1 m above present sea level apsl respectively intertidal facies of late pleistocene interstadial successions rarely occur above present sea level the most reliable record of glacio eustatic ice equivalent sea level is registered on coastlines developed on stable precambrian cratons such as the gawler craton eyre peninsula where a consistent elevation of 2 m apsl is registered for over 500 km for the last interglacial shoreline 125 ka copyright 2002 john wiley sons ltd

climatology of ocean features in the gulf of mexico using satellite remote sensing data a climatology of various ocean features in the gulf of mexico gom was developed using the combination of satellite remote sensing and in situ data that spanned periods as long as 32 years twelve separate statistics were created some of which described characteristics of the loop current while others are involved with warm core rings that separate from the loop current and cold core rings these statistics examined the frequency with which the loop current was found in the gom the orientation of the loop current the frequency of intrusion of loop current water onto the west florida shelf and into the gom common water region ring separation period from the loop current ring dissipation ring speed ring path frequency of ring water in the western gom and the frequency of warm and cold core rings wcrs and ccrs respectively in the gom the results indicate that ccrs were principally responsible for mass and heat redistribution in the eastern gom egom and wcrs are responsible for mass and heat redistribution in the western gom wgom the average period for wcr separation from the loop current was 11 months and the range from 5 to 19 months wcrs moved through the wgom most often using the central path i e their trajectory was found between 24 and 26 n latitude and they decreased to about 55 of their initial size when they reach the western wall of the gom ccrs were most often found in the egom and their frequency of occurrence in the egom surpassed that of wcrs anywhere in the gom

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

the stranded beach dune sequence of south east south australia a test of thermoluminescence dating 0 800 ka the remarkable sequence of stranded beach dunes in south east south australia deposited during the past 800 ka has provided us with a rare set of samples for testing thermoluminescence sediment dating methods here we report thermoluminescence ages obtained from quartz separated from the dunes and compare them with accepted ages for the high sea levels responsible for the dunes the independent ages of the dunes were obtained from earlier work by schwebel which has been extended and refined by modelling the dune formation using sea level variations derived from the oceanic 18o record the work is unusual in extending thermoluminescence dating to an 800 ka sequence with modest geological control of the age the agreement between thermoluminescence and geological ages is satisfactory for eight dunes with ages in the range 120 800 ka quartz is not usually thought to be useful for thermoluminescence dating in this time span two factors contribute to our success the first is that the dose rates are low about 0 5 gy ka 1 or one quarter of that typical of sediments the second is that the thermoluminescence vs dose response continues to rise monotonically above the saturation region at doses above 300 gy

spatial patterns of convection in south florida abstract although they are a fairly consistent feature the sea breeze and lake breeze convergence lines and the associated convection over south florida during the summer may vary considerably from one day to the next daily radar maps indicate a few basic recurring patterns analyses of radiosonde data show significant differences corresponding to the different patterns in the local thermodynamic parameters most notably the mixing ratio changes in the synoptic scale wind field correspond closely to changes in the observed radar patterns and the local thermodynamic conditions explanation of the formation and development of the different patterns of convection is given in terms of the complex interaction between the regional synoptic peninsular and local scale circulations

late quaternary vegetation and climate change in southeastern australia palynological evidence from marine core e55 6 abstract palynological analysis of core e55 6 obtained from off shore western victoria provides a record of vegetation and climate change in the southeastern south australian and western victorian region spanning much of the last 125 000 yr an accompanying oxygen isotope record provides a chronology for the sequence the pollen record suggests that maximum effective precipitation occurred during the height of the last interglacial oxygen isotope substage 5e with wet sclerophyll forest and rainforest widespread in the region effective precipitation appears to have decreased during substage 5d promoting the expansion of dry sclerophyll communities then increased slightly during substage 5c with the limited re occurrence of wetter forest types climatic conditions gradually became drier from substage 5b with the replacement of eucalypt dominated forest by more open heath and mallee type communities in the arid glacial conditions of isotopic stage 4 a brief phase of increased effective precipitation occurred during the interstadial stage 3 with limited expansion of eucalyptus followed by a steady decline in effective precipitation and the expansion of open heath and grass communities pollen is very sparse in the top section of the core making environmental interpretation difficult nevertheless it appears that grass and heath communities dominated the region during stage 2 there is no clear record of the holocene due to the presence of mudflow sediments in the top of the core the pollen evidence also suggests that continental shelf exposed as sea levels fell was colonised by a mosaic of coastal vegetation including myrtaceae dominated scrub eucalypt and casuarina woodland asteraceae and chenopodiaceae dominated heath and grassland the charcoal record expressed as a ratio to pollen concentration gives evidence of increased burning during the height of the last interglacial period most likely in response to increased fuel loads with the expansion of eucalypt dominated forest this record also indicates a second phase of increased burning commencing in stage 2 which gives possible evidence for increased anthropogenic activity in the region

on the seasonal variability and eddies in the north brazil current insights from model intercomparison experiments the time dependent circulation of the north brazil current is studied with three numerical ocean circulation models which differ by the vertical coordinate used to formulate the primitive equations the models are driven with the same surface boundary conditions and their horizontal grid resolution isotropic 1 3 at the equator is in principle fine enough to permit the generation of mesoscale eddies our analysis of the mean seasonal currents concludes that the volume transport of the north brazil current nbc at the equator is principally determined by the strength of the meridional overturning and suggests that the return path of the global thermohaline circulation is concentrated in the nbc models which simulate a realistic overturning at 24 n of the order of 16 18 sv also simulate a realistic nbc transport of nearly 35 sv comparable to estimates deduced from the most recent observations in all models the major part of this inflow of warm waters from the south atlantic recirculates in the zonal equatorial current system but the models also agree on the existence of a permanent coastal mean flow to the north west from the equator into the carribean sea in the form of a continuous current or a succession of eddies important differences are found between models in their representation of the eddy field the reasons invoked are the use of different subgrid scale parameterisations and differences in stability of the nbc retroflection loop because of differences in the representation of the effect of bottom friction according to the vertical coordinate that is used finally even if differences noticed between models in the details of the seasonal mean circulation and water mass properties could be explained by differences in the eddy field nonetheless the major characteristics mean seasonal currents volume and heat transports appears to be at first order driven by the strength of the thermohaline circulation

the south east karst province of south australia the south east karst province of south australia is an extensive area of low relief with dolines cenotes uvalas and a variety of cave types developed in the soft porous flat lying tertiary gambier limestone and also as syngenetic karst in the overlying calcarenite dunes of the pleistocene bridgewater formation the most spectacular surface karst features are the large collapse dolines especially those that extend below the water table to form cenotes shallow swampy hollows occur in superficial quaternary sediments these are an enigmatic feature of the bool region where all gradations appear to occur between definite karst dolines and nonkarstic hollows some depressions may be polygenetic involving a combination of 1 primary depositional hollows on coastal flats or in dune fields 2 deflation and 3 karst solution and subsidence there are extensive underwater cave systems in the southern part of the province and the bulk of the cave development there may well lie below the present water table although these systems would have been at least partly drained during the lower sea levels of the last glacial period systematic variations within the province reflect differences in the parent rock types the extent and nature of the cover and most importantly the hydrology in particular the depth to the water table and its gradient

the influence of the atlantic warm pool on the florida panhandle sea breeze 1 in this paper we examine the variations of the boreal summer season sea breeze circulation along the florida panhandle coast from relatively high resolution 10 km regional climate model integrations the 23 year climatology 1979 2001 of the multidecadal dynamically downscaled simulations forced by the national centers for environmental prediction department of energy ncep doe reanalysis ii at the lateral boundaries verify quite well with the observed climatology the variations at diurnal and interannual time scales are also well simulated with respect to the observations we show from composite analyses made from these downscaled simulations that sea breezes in northwestern florida are associated with changes in the size of the atlantic warm pool awp on interannual time scales in large awp years when the north atlantic subtropical high becomes weaker and moves further eastward relative to the small awp years a large part of the southeast u s including florida comes under the influence of relatively strong anomalous low level northerly flow and large scale subsidence consistent with the theory of the sverdrup balance this tends to suppress the diurnal convection over the florida panhandle coast in large awp years this study is also an illustration of the benefit of dynamic downscaling in understanding the low frequency variations of the sea breeze

cenozoic eucla basin and associated palaeovalleys southern australia climatic and tectonic influences on landscape evolution sedimentation and heavy mineral accumulation abstract the eucla basin including the vast nullarbor plain lies on the margins of the yilgarn musgrave and gawler cratons in southern australia and owes its distinctive landscape to a unique set of interactions between eustatic climatic and tectonic processes over the last 50 ma understanding of the history of the basin and the palaeovalleys that drained from the surrounding cratons are important because they contain major mineral deposits and the sediments derived from them contain remobilised gold uranium and heavy minerals in particular a remarkably preserved palaeoshoreline sequence along the north eastern margin of the eucla basin is highly prospective for heavy mineral placer deposits the record of marine marginal marine estuarine fluvial and lacustrine environments as constrained mainly by an extensive borehole dataset reflects major depositional events during the palaeocene early eocene middle late eocene oligocene early miocene middle miocene early pliocene and pliocene quaternary these events reflect the key role of eustatic sea level variation which during highstands inundated the craton margins flooding palaeovalleys to up to 400 km inboard of the present coastline however a systematic eastward migration of the depocentre across the eucla basin during the neogene together with apparent flow reversals in a number of palaeovalley systems draining the gawler craton suggest that the eucla basin has also been subject to differential vertical movements expressed as a west side up east side down tilting of 100 200 m this differential movement forms part of a broader north down southwest up dynamic topographic tilting of the australian continent associated with relatively fast 6 7 cm yr northward plate motion since fast spreading commenced in the southern ocean at 43 ma we suggest that the evolving dynamic topography field has played a key role in facilitating development of placer deposits largely through multistage eastward reworking of near shore sequences during highstand transgressive cycles on a progressively tilting platform under the influence of persistent westerly weather systems

new evidence of sea level lowstands and paleoenvironment during mis 6 and 4 in the cantabrian coastal karst the cobiheru cave north iberia the geomorphological evolution of the cobiheru cave shows the influence of the non carbonate coastal mountain ranges on coastal karst evolution as well as the temporal distribution of the cold adapted fauna sites in the cantabrian coast geomorphological observation and u th dating lead to the construction of an evolution model the model comprises two episodes of cave deposition occurred at ca 60 70 and 130 150 ka linked to cold climate conditions global sea level lowstands and the erosion of alluvial fans that covered the karst moreover the comparison between the cobiheru record and some raised beaches identified in previous studies sets the beginning of the sea level lowering in the cantabrian sea during the mis 5 4 transition two palaeoenvironments are inferred based on finding equus ferus and elona quimperiana a wet deciduous forest would have been developed on the emerged marine terrace of the cobiheru cave since at least the middle pleistocene and an open landscape with scarce vegetation would have been present at ca 65 ka the erosional event identified in the cobiheru cave helps to understand the temporal distribution of cold adapted mammals located in the asturias region the probable sites of cold adapted fauna developed in caves and alluvial fans would have disappeared after 65 ka therefore palaeontological and palaeoclimate research based on cold adapted mammals suggests the occurrence of an hiatus in the palaeontological record prior to 50 ka this article is protected by copyright all rights reserved

a model study of the vertically integrated transport variability through the yucatan channel role of loop current evolution and flow compensation around cuba 1 in the paper a model study of the vertically integrated transport variability through the yucatan channel role of loop current evolution and flow compensation around cuba by lin et al journal of geophysical research 114 c08003 doi 10 1029 2008jc005199 2009 in the last sentence of paragraph 31 the word westward in drives enhanced westward should be eastward

500 ka precipitation record from southeastern australia evidence for interglacial relative aridity 230 th 234 u dating of speleothems from southeastern australia documents changes in effective precipitation over the past 500 k y at a temporal resolution not previously achieved results show that the highest effective precipitation for the southeastern interior of australia occurred during stadials and cool interstadials of the past four glacial cycles interglacials and warm interstadials as well as glacial maxima are comparatively arid we suggest that lower regional temperatures over the continent and changes in atmospheric circulation stronger walker circulation produced the observed periods of increased effective precipitation

chronometric calibration of a comparative time scale for the mesozoic and paleozoic the relationship between radiometric and biostratigraphic ages is analyzed by local empirical methods and illustrated in chronograms for the mesozoic and paleozoic stages the chronograms allow estimates for stage boundaries and their errors consequently the ages for epoch boundaries and their errors are discussed which for several reasons may not be identical with the age and error of the oldest stage of an epoch

an eddy permitting model of the atlantic circulation evaluating open boundary conditions as part of the french clipper project an eddy permitting model of the atlantic circulation has been run for 22 years the domain has open boundaries at drake passage and at 30 e from africa to antarctica the simulated mean circulation as well as the eddy activity is satisfactory for a 1 3 model resolution and the meridional heat transport at 30 s is within the range estimated from observations we use the mixed open boundary algorithm of barnier et al 1998 which has both a radiation condition and a relaxation to climatology the climatological boundary forcing strongly constrains the solution in the whole domain the model heat balance adjusts through the surface heat flux retroaction term more than the open boundaries the radiation phase velocities calculated within the algorithm are analyzed this shows quite surprisingly that both the eastern and western boundaries have a similar behavior regardless of the preferred directions for advection mainly eastward and wave propagation mainly westward our results confirm that open boundary algorithms behave differently according to the dynamics of the region considered the passive boundary condition that penduff et al 2000 applied successfully in the north eastern atlantic does not work in the present south atlantic model we emphasize the need for a careful prescription of the climatology at the open boundary for which a new approach based on synoptic sections is implemented

an early to middle pleistocene palynological record from the volcanic crater of pejark marsh western plains of victoria southeastern australia abstract a discontinuous 70 m sediment core was extracted from the volcanic crater of pejark marsh to temporally extend the existing quaternary record of vegetation and environments from the western plains of victoria the sequence was fission track dated to the early middle pleistocene transition both the sediments and the aquatic pollen indicate a general lake shallowing and progressive increase in drying and peat deposition events the major dry land pollen taxa are similar to those that dominate the late quaternary records from the area and indicate the alternation of regionally dominant sclerophyll forest during wetter periods and steppe or open woodlands during drier periods a major feature of the pollen record is the presence of a number of regionally extinct taxa in the basal half of the record some of these taxa including araucaria canthium and microcachrys represent major range extensions of previously considered regionally extinct taxa into the pleistocene tentative correlation with the marine oxygen isotope record suggests that the sequence may extend from isotope stages 30 to 17 with major changes within the record relating to the transition from the higher frequency lower amplitude orbitally forced climatic cycles of the early pleistocene to the lower frequency higher amplitude cycles of the middle late pleistocene

new quartz sar osl ages from the stranded beach dune sequence in south east south australia a sequence of stranded coastal barriers in south east south australia preserves a record of sea level variations over the past 800 ka huntley et al quat sci rev 12 1993a 1 quat sci rev 13 1994a 201 attempted to test thermoluminescence tl dating methods and found good agreement between quartz tl ages with independent ages for these dunes we investigate the accuracy of the single aliquot regenerative dose sar procedure radiat meas 32 2000 57 over an extended age range of 0 250 ka by comparing sar osl ages determined on quartz extracts from these dunes with the existing chronology we show that robe ii range is 60 ka and that robe iii is 100 ka old not surprisingly the osl ages increase monotonically from the robe ii range to the west naracoorte range for the younger dunes 240 ka the sar osl ages agree with the expected ages within 1 errors whereas for the older dunes the sar ages are consistent with independent ages within 2 error limits we consider these results to be very promising and lend support to the large number of quartz sar osl ages being presented in the literature where such comparisons with independent chronology are not usually possible

hydrography of the gulf of mexico using autonomous floats abstractfourteen autonomous profiling floats equipped with ctds were deployed in the deep eastern and western basins of the gulf of mexico over a four year interval july 2011 august 2015 produ

volcanogenic origin of cenotes near mt gambier southeastern australia abstract the cenotes near mt gambier are circular cliffed collapse dolines containing water table lakes up to 125 m deep floored by large rubble cones they lie in a flat coastal plain composed of mid tertiary limestone most of the deepest cenotes are concentrated in two small areas located along trends sub parallel to the main joint direction in the limestone the cenotes do not connect to underwater phreatic passages and water chemistry data confirm that they are not part of an interconnected karst network they formed by collapse into large chambers up to 1 million m 3 that extended 125 m or more below the land surface several cenotes have actively growing stromatolites on the sub vertical walls that started growing at 8000 years bp the caves that collapsed to form the deep mt gambier cenotes are much larger than shallow and deep phreatic caves in the area and do not connect into deep phreatic systems they were not formed by freshwater seawater mixing responsible for many of the well known yucatan cenotes because they are not associated with locations of the mixing zone during previous high sea levels and are much larger than caves presently forming along the mixing zone near mt gambier instead dissolution was most likely due to a process whereby acidified groundwater containing large amounts of volcanogenic co 2 ascended up fractures from the magma chambers that fed the pleistocene holocene volcanic eruptions in the area deep reservoirs of volcanogenic co 2 occur nearby cave dissolution could have been due to release of co 2 during the mt gambier eruption 28 000 years ago followed by collapse to form cenotes during the low sea levels of the last glacial maximum 20 000 years ago the cenotes then flooded 8000 years ago as sea level rose and stromatolites began to grow on the walls

further thermoluminescence dates from the dune sequence in the southeast of south australia abstract our thermoluminescence dating technique has been applied to several new samples from the remarkable sequence of stranded beach dunes in southeast south australia that were formed during the past 800 ka we show that robe iii is probably 100 ka as suggested by schwebel and not 80 ka as we suggested earlier a sample from the west dairy dune is shown to belong to 18 o stage 7 in accordance with schwebel s original suggestion and not stage 5 as he suggested later a new west naracoorte sample yielded acceptable data and an age consistent with formation just after the brunhes matuyama magnetic reversal at 780 ka as required by palaeomagnetic measurements two more samples from the woakwine dune show that our reproducibility is consistent with our derived errors

a cretaceous and jurassic geochronology an integrated geomagnetic polarity and geologic time scale for the jurassic and cretaceous periods is presented based on various methods according to the availability of definitive isotopic ages an age calibrated sea floor spreading model is used to interpolate the ages of the kimmeridgian to barremian and the campanian to maestrichtian stages numerical age estimates for the aptian to santonian stage boundaries follow published isotopic age determinations the hypothesis of equal duration of ammonite zones is employed as a vernier to apportion time for the hettangian to oxfordian stages the new scale results in ages of 208 ma for the base of the jurassic 144 ma for the jurassic cretaceous boundary and 66 5 ma for the top of the cretaceous the integrated biostratigraphic magnetostratigraphic and geochronometric record serves as a working hypothesis for geologic correlation of jurassic and cretaceous strata

slowing of the atlantic meridional overturning circulation at 25 n the atlantic meridional overturning circulation carries warm upper waters into far northern latitudes and returns cold deep waters southward across the equator its heat transport makes a substantial contribution to the moderate climate of maritime and continental europe and any slowdown in the overturning circulation would have profound implications for climate change a transatlantic section along latitude 25 n has been used as a baseline for estimating the overturning circulation and associated heat transport here we analyse a new 25 n transatlantic section and compare it with four previous sections taken over the past five decades the comparison suggests that the atlantic meridional overturning circulation has slowed by about 30 per cent between 1957 and 2004 whereas the northward transport in the gulf stream across 25 n has remained nearly constant the slowing is evident both in a 50 per cent larger southward moving mid ocean recirculation of thermocline waters and also in a 50 per cent decrease in the southward transport of lower north atlantic deep water between 3 000 and 5 000 m in depth in 2004 more of the northward gulf stream flow was recirculating back southward in the thermocline within the subtropical gyre and less was returning southward at depth

potential role of atlantic warm pool induced freshwater forcing in the atlantic meridional overturning circulation ocean sea ice model simulations recent studies have indicated that the multidecadal variations of the atlantic warm pool awp can induce a significant freshwater change in the tropical north atlantic ocean in this paper the potential effect of the awp induced freshwater flux on the atlantic meridional overturning circulation amoc is studied by performing a series of ocean sea ice model experiments our model experiments demonstrate that ocean response to the anomalous awp induced freshwater flux is primarily dominated by the basin scale gyre circulation adjustments with a time scale of about two decades the positive negative freshwater anomaly leads to an anticyclonic cyclonic circulation overlapping the subtropical gyre this strengthens weakens the gulf stream and the recirculation in the interior ocean thus increases warm cold water advection to the north and decreases cold warm water advection to the south producing an upper ocean temperature dipole in the midlatitude as the freshwater salty water is advected to the north atlantic deep convection region the amoc and its associated northward heat transport gradually decreases increases which in turn lead to an inter hemispheric sst seesaw in the equilibrium state a comma shaped sst anomaly pattern develops in the extratropical region with the largest amplitude over the subpolar region and an extension along the east side of the basin and into the subtropical north atlantic based on our model experiments we argue that the multidecadal awp induced freshwater flux can affect the amoc which plays a negative feedback role that acts to recover the amoc after it is weakened or strengthened the sensitivity of amoc response to the awp induced freshwater forcing amplitude is also examined and discussed

analysis of flow variability in the yucatan channel 1 the structure and variability of the velocity and temperature fields in yucatan channel are analyzed using data from an eight mooring array deployed from august 1999 to june 2000 the area averaged kinetic energy and transport fluctuations spectra show that the extrema of these quantities do not coincide and that flow variability is dominated by highly energetic processes with weak transport contributions transport fluctuations peak in the 20 40 and 5 10 day period bands but show no clear correlation with the local wind stress forcing empirical orthogonal function eof analysis of the along channel velocity component shows that approximately 55 of the total velocity variance is retained in the first two eofs which depict tripolar the center of the channel is out of phase with the sides and dipolar structures a multivariate complex eof analysis of low passed temperature and velocity components suggests the tripole dipole structures are the components of irregular oscillations of the flow related to the northwestward propagation of anticyclones and cyclones through the channel the weak transport signal in these modes is consistent with the eddies being advected by the mean flow in contrast to other western boundary current regions the passage of eddies provides the predominant explanation for the variability in the yucatan channel however the processes controlling transport variability remain unclear

mountain building along a passive margin late neogene tectonism in southeastern victoria australia the hoddle ranges maximum elevation of 750 m above sea level lie along the southeastern australian passive margin detailed geological geomorphological studies of the southern margin of the ranges focusing on a fault block of oligocene miocene sedimentary rocks have constrained the landscape evolution in the mid cretaceous this area changed from a subduction zone accumulating volcanogenic sediments to a passive low relief margin which was crossed by north flowing rivers in the paleocene the eruption of basaltic volcanics formed a low divide which diverted these rivers towards the northeast so that sediments deposited on either side of the divide contain different heavy mineral assemblages in the middle late miocene early pliocene the area was subjected to a period of relatively rapid mountain building the kosciuszko uplift as broadly nw se oriented compression created the hoddle ranges at an uplift rate of 0 15 mm a uplift was not uniform a small southern block was uplifted only 200 m and its surface has acted as a local base level for the agnes river which flows across it with a major knickpoint on the southern side the southeastern highlands to the north were uplifted by up to 700 1000 m during the kosciuszko uplift similar to the maximum increase in elevation of the hoddle ranges 600 m the kosciuszko uplift tectonism occurred at rates greater than typical of passive margins and belies australia s reputation as a tectonically stable continent

light attenuation as a control for microbiogeomorphic features implications for coastal cave speleogenesis san salvador bahamas is a carbonate island with dozens of flank margin caves formed in the phreatic zone by fresh seawater mixing within the freshwater lens these caves have no direct connection with the sea and form at or close to the tidally influenced fluctuating water table after sea level fall in their subaerial parts caves are enlarged mainly by rock dissolution and by erosion close to the water level condensation corrosion and breakdown processes for understanding the geomorphological features observed in these caves and how they are related to light attenuation we investigated three sampling sites in the tidally influenced zone of lighthouse cave which has been re invaded by seawater during the holocene sea level highstand a freshwater lens no longer exists within or adjacent to the cave rock samples were collected above and below the internal lake shores close to the entrance and in the twilight and dark zones of this cave light and electron microscopy examinations were conducted for detecting microbial cells as well as bioconstruction and bioweathering features in addition a high precision laser scanner was used for characterising sample microtopography our data showed that the microtopography and geomorphology of the lake shore samples cave entrance are dominated by bioweathering whereas the samples of the twilight and dark zones are controlled by a combination of both bioweathering and bioconstructive processes depending on light availability bioconstructive structures such as semi planar lamination at the fluctuating water level of the lighthouse cave show that dissolution due to water mixing of sea and freshwater in the holocene is no longer the most important speleogenetic process we propose that the geomorphological evolution is strongly influenced by the degree of rock diagenesis more than the initial mechanism of speleogenesis

shallow caves and blowholes on the nullarbor plain australia flank margin caves on a low gradient limestone platform abstract the nullarbor plain of southern australia is a very extensive limestone platform with relatively few large caves for its size but contains thousands of blowholes sub circular vertical shafts up to 1 2 m in diameter which often connect to similar sized sub horizontal passages recent detailed systematic surveys of large areas of the nullarbor plain have provided new distribution data showing that blowholes and associated shallow caves are concentrated in a 25 30 km wide band located 75 km inland the known density of these features up to 43 25 km2 underestimates the cave porosity because the strong draughts blowing from many of the blowholes indicate that they connect to extensive cave systems of small passages these shallow caves are relict phreatic features their entrances blowholes were opened as the land surface was lowered by denudation the band of blowholes and caves is located along the late miocene 6 ma shoreline across the nullarbor when there was a eustatic stillstand the caves formed in the zone of enhanced dissolution at the seaward margin of the freshwater lens along the carbonate coastline and can therefore be regarded as flank margin caves on a low gradient limestone platform a flank margin setting relatively unknown prior to this study the width of the band of flank margin caves which is substantially greater than previously documented for this cave type reflects the very low gradient of both the ground surface and water table together with the influence of tidal fluctuations and regression of the shoreline flank margin cave development stopped when the sea retreated rapidly in the late miocene early pliocene due to a period of tilting and uplift the band of flank margin caves has high permeability and substantial porosity and would therefore form an excellent largely overlooked type of palaeokarst petroleum reservoir

an inland facies controlled eogenetic karst of the carbonate reservoir in the middle permian maokou formation southern sichuan basin sw china abstract carbonate karst is one of the research highlights in the field of carbonate reservoir geology here we report on a new type of karst formed in the middle permian maokou formation southern sichuan basin sw china i e inland facies controlled eogenetic karst which is different from the previously defined telogenetic karst this karst is eogenetic as the formation was buried at shallow depths prior to being subaerially exposed for a period of 7 8 myr in the paleo continental region of the upper yangtze uplift subaerial exposure may have been caused by a sea level regression during the tungwu orogeny which gave rise to a depositional hiatus over a broad area the top of the maokou formation is commonly marked by a weathered crust and an unconformable relationship with overlying layers below the surface the maokou formation contains sediments deposited by an underground drainage the geological setting can be inferred from an inland karst far from coastline the subsurface karst interval consists mainly of coarse grained limestone and micrite with the former occurring in shoal facies deposited in a high energy depositional environment and the latter in non shoal facies deposited in a low energy environment both of them were interbedded with in variable thicknesses the coarse grained limestone layers with high porosity and permeability acted as inception horizons more favourable for the development of karst than the micritic layers with low porosity and permeability therefore in places where both coarse grained limestone and micrite are present the karst is considered to be facies controlled the primary permeability of the coarse grained limestone combined with the permeability provided by faults and fractures provides sufficient channels for karst water formation of the karst system was characterized by contemporaneous development at multiple levels as controlled by the stratigraphic position of coarse grained shoal facies the karst reservoir therefore developed in both karst highland and karst transitional zone area between the karst highland and karst basin according to this model of karstification hydrocarbon exploration should focus on karst highlands located on palaeohighs and in synclines located far from fault zones

yucatan channel flow observations versus clipper atl6 and mercator pam models 1 the statistical properties of the flow structure in the yucatan channel s main section based on 2 years of continuous observations august 1999 to june 2001 are compared with those simulated by the ocean parallelise opa primitive equation model in two different configurations the atl6 configuration from the clipper project the whole atlantic domain with a 1 6 resolution and the prototype atlantique mediterranee pam configuration from the mercator project the north atlantic domain with 1 12 resolution while the observed 2 year mean transport into the gulf of mexico is 23 06 sv atl6 has a 5 year mean of 27 49 sv and pam has a 3 year mean of 29 06 sv apart from this discrepancy in the mean transport both simulations are able to reproduce well in structure and magnitude details of the mean current and its variability features like the yucatan current core and the deep countercurrents in the yucatan and cuban sides are both well reproduced as is the presence of a minimum surface current variability at the center of the channel the two principal empirical modes of current variability which are related to the passage of eddies through the channel are also reproduced by the simulations the observed and simulated transports above and below the 6 c isotherm show no coherency at any frequency except for a significant coherent peak at a period around 20 days which we interpret as a first baroclinic kelvin mode between the two layers as in the observations the shedding of eddies by the loop current in the simulations is preceded by periods of diminished negative horizontal vorticity flux into the gulf of mexico

cyclic patterns in the paleozoic and mesozoic implications for time scale calibrations the analysis of both physical and biological data from the devonian strata of new york state reveals the existence of two robust cyclic patterns one cycle with a duration of 4 5 5 7 m y and a larger cycle of approximately twice this wavelength at 11 3 13 6 m y depending upon the absolute time scale used in the wavelength calculation the analysis of sedimentation rates from the jurassic likewise reveals a cycle with a temporal spacing of 4 to 6 m y a cycle with a periodicity virtually identical to the shorter cycle detected in the devonian the data further suggest the existence of cycles at 2 3 m y and 30 m y intervals though these periodicities approach the lower and upper limits of resolution of the data base the potential correlation of cyclic patterns has considerable implication for the development of new chronological time scales and global chronostratigraphic resolution current radiometric time scales have a resolution which is still above the stage level for most of the pre cenozoic in estimating the ages of stage boundaries most time scales are based on either the assumption of equal stage durations or the assumption of equal biostratigraphic zone durations and the subsequent linear interpolations between control tie points operating under the working hypothesis that a regular periodic signal exists in the data the above listed devonian cycles are brought into a more uniform periodicity by transforming the time scale itself yielding an alternatively calibrated timescale which is neither equal stage nor equal zone in structure

optical dating using inclusions within quartz grains a sequence of stranded beach dunes in the southeast of south australia which resulted from the advance and retreat of the sea over a tectonically rising land surface during the past 800 ka has been securely dated by geological means and successfully used to test thermoluminescence dating based on quartz we have now obtained a series of promising results from the same sequence with a test of optical dating on inclusions within the quartz grains the innovative aspect of the measurements is the use of infrared irradiation to stimulate emission from the inclusions rather than conventional stimulation of the quartz itself by light of shorter wavelength satisfactory ages were found for seven dunes covering the time span 0 400 ka

eddy development and motion in the caribbean sea eddy motion in the caribbean sea is described on the basis of sea level anomalies deduced from ers 1 altimetry data corrected with topex poseidon data during the 15 months of the exact repeat mission october 1992 to december 1993 both cyclones and anticyclones were observed in the satellite data as anomalies originating in the venezuelan basin or entering the caribbean through the antillean passages mainly the st lucia channel anegada passage and north of trinidad the diameter of the eddies ranged from a few tens of kilometers to 700 km advection speeds were typically 20 30 cm s 1 and the eddies were energetic kinetic energy 0 6 m2 s 2 their lifetime of 3 4 months was determined in general by their interaction with topography most eddy activity was eroded and disappeared at the central american rise area although a few eddies crossed into the cayman sea through the chibcha channel some eddies also entered the cayman sea from outside the caribbean through the windward passage the panama colombia gyre was evident only during the tropical rainy season a large cyclonic eddy was formed there during the period of maximum precipitation when strong meridional salinity and wind speed gradients occurred eddy production in the central caribbean appears to be associated with the interaction of the meandering caribbean current and the strong wind curl

mid pleistocene cave fills megafaunal remains and climate change at naracoorte south australia towards a predictive model using u th dating of speleothems abstract the limestone caves of the naracoorte region in south australia contain extensive deposits of megafauna rich sediments and intercalated cave formation speleothems high precision thermal ionisation mass spectrometry tims u th dating of flowstones directly associated with several large deposits reveals a distinct cyclicity in the timing of sediment and flowstone depositional events in the naracoorte caves this pattern parallels a cyclical alternation of wet phases and intervening periods with a water deficit over the last 500 ka ayliffe et al 1998 geology 26 147 dates from flowstone interlayers in the fossil deposits coincide with the massive speleothem growth events which characterise wet phases hiatuses in flowstone deposition correlatable through several cave systems imply that water deficits were initiated by regional aridity during full glacial and then extended into the succeeding warmer wetter interglacials clastic deposits in caverns with restricted entrance shafts correlate with hiatuses suggesting many of these deposits contain fauna representative of full glacial and interglacial climates caverns with small openings have often been sealed from the surface and dating has constrained the length of accumulation episodes in several fossil deposits one to less than 20 ka the hydrological regimes and environmental conditions inferred from the timing of speleothem deposition have been used to develop a model for cyclic sediment and bone accumulation in the caverns at naracoorte over the last 400 ka the giant victoria fossil chamber deposit accumulated prior to 200 ka and because its entrance is large it may contain faunas representative of all climatic phases there has been no apparent change in faunal diversity at naracoorte over at least three glacial interglacial cycles of the middle pleistocene

shallow burial dolomitization and dedolomitization of mid cenozoic cool water calcitic deep shelf limestones southern australia abstract oligocene to mid miocene deep shelf bryozoan rich limestones across southern australia are variably altered to gray to orange ca rich medium crystalline sucrosic dolomite degree of replacement ranges from scattered rhombs to complete dolostone units several tens of meters thick and many kilometers in areal extent the locale and timing of dolomitization are tightly constrained to shallow burial and mid to late miocene dolostone varies from friable to dense and well lithified dolomitization is fabric specific muddy sediments are preferentially replaced calcite bryozoans and brachiopods form biomolds geochemistry suggests that dolomitization was predominantly by seawater limestone interaction but admixing of continental possibly meteoric groundwater is required by data on stable and radiogenic isotopes and trace elements sr isotopes confirm a mid miocene age for the dolomite if precipitated from seawater with no inherited limestone values dolomite crystals have undergone variable degrees of dissolution and meteoric calcite cement has locally filled the resultant rhombic voids dissolution began in the crystal cores implying some sort of metastability and expanded outward until in some ins ances the whole dolomite crystal was dissolved leaving dolomolds in otherwise unaffected limestone this dolomite occurrence well constrained by regional geology shows that widespread porous and permeable fabric destructive medium crystalline sucrosic dolostone can form in the shallow subsurface soon after sediment deposition such dolomite however may be metastable in the presence of variably mixed continental marine waters and newly formed crystals can undergo dedolomitization soon after precipitation

observing global ocean topostrophy 1 recent publications have evaluated topostrophy f v d where is f coriolis v is velocity and d is gradient of total depth as a means of comparing models circulations some results are striking comparing four global models two with modest grid size and two with fine grids merryfield and scott 2007 show that finer grid models are characterized by more positive especially at greater depths and higher latitudes among nine arctic ocean models holloway et al 2007 find in three of the models quite distinct from the other six a result shown to depend upon subgrid eddy parameterization from different choices of numerical method within the same model penduff et al 2007 show that improved numerical representations support more positive can these model results be compared with observations a global compilation has been prepared from 17120 current meter records spanning 83087 current meter months the compilation tends to confirm modeling progress achieved by finer resolution improved parameterizations and better representations a new characterization of global ocean circulation emerges with suggestive dynamical insights

the potential vorticity flux through the yucatan channel and the loop current in the gulf of mexico 1 two year long time series of current and density structure measurements across the yucatan channel s main section allow the calculation of the time dependent potential vorticity flux between the gulf of mexico and the caribbean sea which is characterized by alternating periods of positive cyclonic and negative anti cyclonic vorticity influx periods of negative cumulative vorticity influx are related to the loop current extending into the gulf of mexico whereas periods of positive cumulative vorticity influx relate to a loop current retraction sometimes coincident with the shedding of an anti cyclonic eddy