antarctic ice sheet melting in the southeast pacific the first oceanographic measurements across a deep channel beneath the calving front of pine island glacier reveal a sub ice circulation driven by basal melting of 10 12 m yr 1 a salt box model described here gives a melt rate similar to that of ice balance and numerical models 5 50 times higher than averages for the george vi and ross ice shelves melting is fueled by relatively warm circumpolar deep water that floods the deep floor of the amundsen and bellingshausen sea continental shelves reaching the deep draft of this floating glacier a revised melt rate for ice shelves in the southeast pacific sector raises circumpolar ice shelf melting to 756 gt yr 1 given prior estimates of surface accumulation and iceberg calving this suggests that the antarctic ice sheet is currently losing mass to the ocean

231pa and 230th contamination at zero age a possible limitation on u th series dating of speleothem material abstract analysis of 67 new zealand speleothem specimens for both 230 th 234 u and 231 pa 235 u by alpha spectrometry showed that in most cases the age concordance between them was excellent however analysis of two growing speleothems less than 100 years old showed apparent near concordant ages of 2 and 3 ka both 230 th and 231 pa had been added to the speleothem contrary to a basic assumption of the dating method in other cases of discordance there was additional evidence that 230 th and sometimes 231 pa had been added to the growing speleothem and probably originated from erosion of old limestone by carbonate rich waters calculation shows that typical 230 th and 232 th contents in carbonate rich waters could easily be deposited in sufficient quantity in growing speleothems in realistic time intervals to produce the amounts found in the straw stalactites the u contents of these speleothem samples were unusually low 42 contained less than 0 1 mg kg 1 but aragonitic samples contained 100 as much u

mapping the u s west coast surface circulation a multiyear analysis of high frequency radar observations signals with phase speeds of o 10 and o 100 to 300 km day 1 and time scales of 2 to 3 weeks the signals with slow phase speed are only observed in southern california it is hypothesized that they are scattered and reflected by shoreline curvature and bathymetry change and do not penetrate north of point conception the seasonal transition of alongshore surfacecirculationforcedbyupwelling favorablewindsandtheirrelaxationiscapturedinfine detail submesoscaleeddies identifiedusingflowgeometry haverossbynumbersof0 1to3 diameters in the range of 10 to 60 km and persistence for 2 to 12 days the hfr surface currents resolve coastal surface ocean variability continuously across scales from

u pb dating of a speleothem of quaternary age we demonstrate that u pb dating is a promising method for secondary carbonate materials of quaternary age and older by obtaining a 206pb 238u age for a speleothem with high u 10 g g 1 and very low pb 10 ng g 1 that is supported by an independent 230th age thermal ionisation mass spectrometry was used to determine the u and pb isotopic ratios and concentrations for subsamples of a stalactite from winnats head cave peak district uk we obtained 206pb 204pb ratios up to 50 and determined a 206pb 238u age of 248 10 ka which is within error of the 207pb 235u age of 333 79 ka and a spectrometric u th age of 255 ka for samples of tertiary and quaternary age the initial state of u series disequilibrium is an important consideration and as with most radiometric dating techniques the mineral must have remained closed to u th pb and all intermediate daughters we show that dense calcite speleothems are ideal in this respect and that no loss of rn has occurred unlike u series disequilibrium methods u pb dating has no upper limit and hence materials of quaternary age older than 0 6 ma can be analysed to investigate landscape development paleoclimate hominid evolution or hydrogeochemistry in carbonate terrains

the circulation and water masses in the gulf of the farallones abstract six adcp and ctd ship surveys of the continental shelf and slope in the vicinity of the gulf of the farallones ca were conducted in 1990 1992 adcp data provide much more detail on the structure of the currents over the slope and shelf in the gulf and reveal a persistent largely barotropic poleward flow with a complex mesoscale flow field superimposed the directly measured currents are not well represented by the geostrophic velocity fields derived from hydrographic casts important upper ocean circulation features include a slope countercurrent scc variable shelf circulation and submesoscale eddy like features the scc was present in all seasons and is believed due to a strong year round positive wind stress curl enhanced by point reyes its flow was poleward throughout the upper 300 m and often surface intensified poleward transport in the upper 400 m was 1 3 sv much greater than previous geostrophic estimates for the california current system constrained to a 500 dbar reference level the shelf circulation was much more variable than the scc and generally exhibited a pattern consistent with classic ekman dynamics responding to synoptic wind forcing submesoscale vortices or eddies often dominated the general flow field these eddies are thought to be generated by the frictional torque associated with current topography interactions their centers typically have a distinct water type associated with either the scc or the southward flowing california current higher spiciness anomalies representing a higher percentage of pacific equatorial water pew were typically found in the core of the scc or within anticyclonic eddies lower bland spiciness anomalies characteristic of a higher percentage of pacific subarctic water psaw were associated with cyclonic eddies while these circulation features were largely barotropic the flow also adjusted baroclinically to changes in the density field as different water types were advected by the general flow field or by mesoscale instabilities in the large scale boundary currents as they interacted with topography despite a seasonal cycle in regional wind and ocean temperature time series there is no obvious seasonal pattern in the circulation most of the temporal variability in the current appears to be due to synoptic and interannual variations in atmospheric forcing because of the very dynamic three dimensional nature of the regional circulation the gulf of the farallones is likely to be a center for active mixing and exchange between the coastal and california current waters relative to most us west coast locales

chemical fractionation of brine in the mcmurdo ice shelf antarctica abstract during the austral summers of 1976 77 and 1978 79 several ice cores were taken from the mcmurdo ice shelf brine zone to investigate its thermal physical and chemical properties this brine zone consists of a series of superimposed brine layers waves that originate at the seaward edge of the ice shelf and migrate at various rates depending upon their age and position in the ice shelf the brine in these layers becomes increasingly concentrated as the waves migrate inland through the permeable ice shelf firn chemical analyses of brine samples from the youngest uppermost brine wave show that it contains sea salts in normal seawater proportions further inland deeper and older brine layers though slightly highly saline s200 are severely depleted in s04 2 na ratio being an order of magnitude less than that of normal seawater analyses of na k ca2 mg2 so4 2 and c1 together with solubility and temperature considerations show that the sulfate depletion is due to selective precipitation of mirabilite na2s041oh2o the location of the inland boundry of brine penetration is closely related to the depth at which the brine encounters the firn ice transition however a small but measurable migration of brine is still occurring in otherwise impermeable ice this is attributed to eutectic dissolution of the ice by concentrated brine as it moves into deeper and warmer parts of the mcmurdo ice shelf

meroplanktonic distribution and circulation in a coastal retention zone of the northern california upwelling system previous studies have shown that settlement of several crab species along the coast north of point reyes 38 00 n 123 00 w occurs primarily during relaxation from upwelling when warm water flows poleward from the gulf of the farallones during 1994 and 1995 we sampled planktonic larval distributions and hydrography both south and north of point reyes during upwelling to test whether high concentrations of crab and rockfish larvae were concentrated in the source of the relaxation flow to the south of point reyes an upwelling plume off point reyes and an upwelling shadow indicated by warmer less saline water in the northern gulf were evident in both years as were frontal regions that marked the boundaries between water types of three different types 1 newly upwelled 2 oceanic and 3 san francisco bay outflow in addition there was a fourth type termed gulf water that was a mixture of these three types concentrations of larvae of cancrid pinnotherid and coastal crabs and rockfishes were high south of point reyes but were low or absent in the newly upwelled water north of the point within the upwelling shadow these meroplankton taxa were associated with different water masses several intertidal crab species and early stage cancrid crabs were concentrated in san francisco bay outflow water and coastal gulf water late stage cancrid crabs early and late stage pinnotherid crabs and rockfishes were concentrated at the frontal region between newly upwelled and gulf water of the taxa examined only rockfishes were found offshore in oceanic water the high concentrations of meroplankton observed suggest that the gulf of the farallones is an important retention area for larvae that settle into coastal populations in the gulf and to the north via poleward transport during upwelling relaxation

on the nature of tidal asymmetry in the gulf of khambhat arabian sea using hf radar surface currents abstract the hourly ocean surface current observations from available high frequency radars hfr have been analyzed to i quantify the tidal constituents ii investigate the role of the bathymetry on shallow water tides and iii identify the nature of tidal asymmetry in the inverted funnel shaped gulf of khambhat gokh on the western shelf of india during may 2012 the hfr observations captured strong currents 2 0 m s 1 showing significant spring neap variations tidal harmonic analysis of the hfr currents showed that the tidal currents at the mouth are dominated by the m2 constituent with amplitude 4 5 times higher than that of k1 among the shallow water constituents m4 dominates the entire gulf with significant amplitudes 10 cm s 1 and gets amplified towards the head of the gulf 30 cm s 1 followed by ms4 comparisons with sea level heights from tide gauges show a higher correlation for the major 0 97 and shallow water 0 96 tidal constituents in terms of the order of amplitudes of the tidal constituents the circulation pattern in the gulf is predominantly driven by tidal currents with the total tidal variance being 90 of the total current variance the major contributions are from the m2 tidal currents 70 90 except at the head where the m4 component contributes significantly up to 40 the interactions with shallow bathymetry are responsible for the amplification of tidal currents in this converging channel with negligible impact from stratification during may the harmonic analysis derived relative surface phase 2m2 m4 and higher m4 m2 amplitude ratio at the head of the gulf reveal that the gulf is highly tidally asymmetric and flood dominant indicating stronger non linear tidal distortions in the nearshore regions a generalized skewness based analysis confirms the flood dominance with positive values of a morphology dependent asymmetry factor and skewness two tidal combinations m2 m4 overtide and m2 s2 ms4 compound tide are identified as the major contributors to the flow velocity skewness in the gokh with mixed mainly semi diurnal tidal regime

hf radar derived origin and destination of surface waters off bodega bay california abstract as an integral part of the west study of the role of wind driven transport in shelf productivity hf radar currents are analyzed to determine typical surface flow patterns off bodega bay in northern california radar derived surface trajectories and surface velocity divergences are used to determine the proximal origins and destinations of surface waters in the area surface trajectory results show a strong bimodality with water over the entire shelf originating in the north under upwelling conditions and waters over the inner mid shelf originating in the south during relaxation conditions outer shelf waters have more variable transport patterns during relaxation conditions with limited equatorward or onshore movements being most typical the destinations of surface waters starting at the outer shelf are predominantly offshore with the majority of particles exiting the radar domain west of pt reyes along the shelf edge in less than 2 days significant proportions of water from the inner mid shelf are exported southward and exit the radar domain inshore or within 20 km of the tip of pt reyes creating possibilities for either nearshore retention in the bodega region or entrainment of water into the gulf of farallons approximately 15 of all trajectories remained in the radar domain for 6 days suggesting that a biologically significant percentage of larvae might be retained in the area for time periods approaching typical larval durations calculations of surface divergence indicate where vertical flux may be significant an extensive area of positive divergence is observed off bodega during upwelling conditions while weakly convergent flow is observed where upwelling flows approach pt reyes positive divergence also is observed during relaxation periods when poleward flow separates from the shore just north of pt reyes estimates of vertical flux in these divergence zones point to a significant contribution of recently upwelled waters to the observed horizontal fluxes at the surface determination of the ultimate source and fate of phytoplankton rich waters requires further analysis of the detailed time dependence of phytoplankton concentration relative to the time dependence of wind forced currents

estimate of the subglacier dielectric constant of an ice shelf using a ground penetrating step frequency radar the mass balance of the antarctic ice cap its stability and the role of the surrounding ice shelf in bottomwater mass formation is to a large extent dictated by processes associated with subsurface freezing and melting where the submerged ice meets the surrounding ocean it is demonstrated how multifrequency ground penetrating radar data collected at the riiser larsenisen can be used to examine the physical conditions of the ice shelf subsurface the received radar signal from three different frequency intervals 10 30 155 170 and 330 360 mhz range of wavelengths from 15 to 0 5 m in the ice was analyzed by using a plane reflector model it is demonstrated that the data can be successfully used to distinguish between types of ice at the ice ocean interface such as for freezing marine ice melting marine ice melting meteoric ice from the ice cap and melting firn ice the data analysis shows that the subsurface can be regarded as rough on length scales in the order of 1 m

decomposing observations of high frequency radar derived surface currents by their forcing mechanisms decomposition techniques and spatial structures of decomposed surface currents 1 surface current observations from a high frequency radar network deployed in southern san diego are decomposed according to their driving forces pure tides and their neighboring off band energy local winds and low frequency several superposed ocean responses are present as a result of the complicated bottom topography and relatively weak winds off southern san diego as opposed to coastal regions where circulation can be explained by a dominant forcing mechanism this necessitates an application of a statistical decomposition approach surface currents coherent with pure tides are calculated using harmonic analysis locally wind driven surface currents are estimated by regression of observed winds on observed surface currents the dewinded and detided surface currents are filtered by weighted least squares fitting assuming white noise and three colored signal bands low frequency band less than 0 4 cycles per day and near tidal peaks at the diurnal k1 and semidiurnal m2 frequencies the spatial and temporal variability of each part of the decomposed surface currents is investigated in terms of ocean response to the driving forces in addition the spatial correlations of individual components exhibit gaussian and exponential shapes with varying decorrelation length scales

remotely sensed surface currents in monterey bay from shore based hf radar coastal ocean dynamics application radar near surface currents in monterey bay derived from a network of shore based hf radars are presented for august december 1994 and compared with those from april to september 1992 focus is placed on the low frequency 2 to 30 day period motions in the remotely sensed data and on comparison of radar derived currents with moored current and wind observations ship based acoustic doppler current profiler observations satellite based surface temperature imagery and surface drifter velocities the radar derived picture of the late summer mean flow is very similar in the two realizations and is consistent with historical data flow is equatorward in the outer part of the bay poleward in a narrow band nearshore and very sluggish in the middle of the bay low pass filtered time series of radar derived currents are highly correlated with moored current observations and with winds in the outer part of the bay the vector time series are also coherent across a broad frequency band with currents typically in phase between 1 and 9 m depths and with 1 m currents typically 40 60 to the right of the wind overall these results confirm the utility of coastal ocean dynamics applications radar codar type hf radars for the study of coastal surface currents out to ranges 50 km from shore particularly for highly averaged fields data variability and comparison with in situ observations for high frequency 1 to 48 hour period motions point to the need to better characterize and minimize sources of error in the radar observations

the u series ages of carnotites and implications regarding their formation the u series nuclides 230th 234u 238u 227ac 231pa and 210pb were analyzed in up to 75 carnotites from a group of trenches in southwestern israel though 230th234u had the large range of 0 14 to 0 99 its spatial distribution was not random and the ratio never exceeded unity 231pa230th was at least 91 concordant with 230th234u in four of five cases these facts together with the details of the 230th234u distribution especially among ten samples from one small block of rock indicate that 230th234u ages of carnotites are at least a reasonable approximation of true ages the unexpectedly widespread deficiencies in both 227ac and 210pb indicate that although carnotites are nearly closed to the migration of uranium they are open to those of actinium and to lead radon or radium a model of carnotite precipitation is presented which attributes the large range in 230th234u to a continual shift in the site of carnotite precipitation in keeping with a continual change in the geometry of joints this model may apply to other minerals as well

the brine zone in the mcmurdo ice shelf antarctica abstract observations of a 4 4 m high brine step in the mcmurdo ice shelf antarctica show that it has migrated about 1 2 km in 4 years the present brine wave is overriding an older brine soaked layer this migration is proof of the dynamic nature of the step which is the leading edge of a brine wave that originated at the shelf edge after a major break out of the mcmurdo ice shelf the inland boundary of brine penetration is characterized by a series of descending steps that are believed to represent terminal positions of separate intrusions of brine of similar origin the inland boundary of brine percolation is probably controlled largely by the depth at which brine encounters the firn ice transition 43 m however this boundary is not fixed by permeability considerations alone since measurable movement of brine is still occurring at the inland boundary freeze fractionation of the seawater as it migrates throught the ice shelf preferentially precipitates virtually all sodium sulfate and concomitant removal of water by freezing in the pore spaces of the infiltrated firm produces residual brines approximately six times more concentrated than the original seawater

on the accuracy of hf radar surface current measurements intercomparisons with ship based sensors high frequency hf radar systems can provide periodic two dimensional vector current estimates over an area approaching 1000 km as the use of these hf systems has gained wider acceptance a number of attempts have been made to estimate the accuracy of such systems however comparisons of hf radar current estimates with in situ sensors are difficult to interpret since hf systems measure currents averaged over an area of 1 km 2 and to a depth of only 50 cm while in situ sensors measure currents at a point and somewhat greater depths 1 to 10 m previous studies of the accuracy of hf radar technology have thus attributed the differences observed between hf radar and in situ sensors to an unknown combination of vertical shear horizontal inhomogeneity in situ instrument errors and hf radar system errors this study examines the accuracy of hf radar current measurements using data from the 1993 high resolution remote sensing experiment conducted off cape hatteras north carolina data from four shipborne in situ current meters are compared with data from an ocean surface current radar oscr a commercial current measuring radar we attempt to discern the predominant sources of error in these data by using multiple simultaneous measurements from different sensors and by examining the variation of observed current differences as a function of location the results suggest an upper bound on the accuracy of the oscr derived radial currents of 7 to 8 cm s the measurement of near surface currents in the coastal environ ment is an important problem

rates of tectonic uplift in the corinth and megara basins central greece we present evidence of the rates of late quaternary tectonic uplift that have affected parts of central greece during this period of active extension and basin formation dual lines of evidence indicate upper pleistocene to holocene uplift rates of the order of 0 3 mm yr 1 for the corinth and megara basins first u series disequilibrium ages of acropora sp corals from uplifted marine sediments are used to derive minimum average rates of vertical displacement since deposition second the geometries of cyclical transgressive sequences and of erosional terraces are consistent with the radiometric evidence and the known history of late quaternary sea level fluctuations two types of uplift are distinguished on the basis of structural relationships 1 fault block rotation about a horizontal axis tilting in response to footwall uplift on the active normal fault bounding the alkyonides gulf and 2 a more regional uplift which affects the corinth basin and peloponnesos to the south the results of u series dating are discussed in the light of initial 234u 238u activity ratios derived from the coral samples which are higher than for average marine waters 1 17 1 31 compared to 1 14 these values may be related to a variable freshwater input to the structurally confined gulf of corinth or alternatively they may reflect a previously higher global 234u 238u activity ratio in marine waters or post mortem enrichment in 234u although the mechanism of the latter is not yet understood

the reliability of uranium series mollusc dates from the western mediterranean basin abstract fossil mollusc shells from western mediterranean raised beach deposits have been dated using u series techniques sub sampling has allowed intra shell isotopic variability to be assessed although most of the calculated ages appear plausible and some internal consistency exists closer scrutiny of the data reveals that the shells have behaved as geochemically open systems and all the ages therefore must be considered suspect some previously published u series mollusc data from the same region may also contain evidence of open system behaviour and are considered equally unreliable simple modelling suggests considerable variation in isotopic uptake behaviour both within and between shells

upper ocean water mass characteristics of the california current summer 1993 abstract two large high resolution upper ocean surveys of the california current region were conducted in the summer of 1993 temperature and salinity were measured from a seasoar vehicle and velocity was measured by a ship borne acoustic doppler current profiler both surveys extended from the continental margin to 128 w and consisted of zonal sections 28 km apart the first survey 7 28 june extended from 39 5 n to 36 25 n and the second 16 august to 1 september extended from 39 0 n to 37 0 n the current field was fairly simple in june showing an equatorward surface jet with only one gentle meander a nearly continuous poleward california undercurrent near the continental margin and two anticyclonic subsurface eddies offshore of the jet by august meanders in the surface jet had strengthened and eddies dominated the flow field large scale trends in the water mass characteristics spiciness along three isopycnal surfaces 26 4 26 0 and 25 6 kg m 3 show that temperature and salinity tend to increase towards the equator and towards shore consistent with poleward advection along the continental margin local minima in spiciness tend to coincide with the equatorward surface jet local maxima in spiciness are associated with subsurface anticyclonic eddies which have a core depth of about 150 m and seem to originate in the california undercurrent over the continental slope at local latitudes we identified several different anticyclonic eddies each with different water mass characteristics all of the eddies we observed had diameters larger than the baroclinic radius of deformation water mass characteristics and migration rates are consistent with formation over the continental margin within the preceding 6 8 months

large scale structure of the june july 1996 marine boundary layer along california and oregon abstract data from surface stations profilers long range aircraft surveys and satellites were used to characterize the large scale structure of the marine boundary layer off of california and oregon during june and july 1996 to supplement these observations june july 1996 averages of meteorological fields from the u s navy s operational coupled ocean atmospheric mesoscale prediction system coamps model were generated for the region model calculations show a broad band of fast northerly surface winds exceeding 7 m s 1 extending along the california oregon coast buoy measured peaks of 7 1 m s 1 off bodega bay 7 2 m s 1 off point piedras blancas and 8 8 m s 1 near point conception were reported mean winds at the buoys located 15 25 km offshore are generally faster than those at coastal stations and all station winds are faster in the afternoon the aircraft and station observations confirm that an air temperature inversion typically marks the top of the marine boundary layer which deepens offs

tide current eddy interaction a seasonal study using high frequency radar observations along the western bay of bengal near 16 n abstract the seasonally reversing boundary currents along the western bay of bengal bob provide a background for studying the rich and complex relationship between tidally driven currents mean current structure and mesoscale eddies a year long high resolution surface current data set from high frequency radars hfr during 2015 along the andhra pradesh coast near 82 e 16 n has been utilized to investigate the interaction of tidal currents with bathymetry and eddies during three seasons january march april and november december the seasonal variability shows the reversibility of boundary currents with speeds of 1 58 1 24 m s 1 during poleward equatorward flow associated with an offshore anticyclonic inshore cyclonic eddy in this region the amplitudes of the tidal constituents from the hfr currents are highly correlated r 0 80 with those from the sea level observations from a nearby tide gauge among the semi diurnal and diurnal tidal constituents m2 5 25 6 51 cm s 1 and k1 2 36 4 32 cm s 1 are the dominant two respectively in all three seasons the tidal variance of 40 70 is observed throughout the domain with highest contribution from the m2 tidal currents the m2 tidal ellipse patterns match well with the mean circulation pattern i e cyclonic anticyclonic during november december march april in the nearshore regions the tidal currents amplify mainly through shallow water tidal constituents m4 and ms4 interacting with bathymetry whereas in the offshore regions they are dominated by m2 which co vary with the mean seasonal circulation pattern the highest amplitude of m2 tidal currents during november december is predominantly due to high stratification along the western bob in the presence of stratification the loss of tidal kinetic energy into turbulent processes is reduced resulting in the amplification of m2 tidal currents the shallow water constituents are also observed with significant amplitudes of 0 50 3 50 cm s 1 in the nearshore region the amplitudes of overtides m3 m4 and s4 associated with an offshore anti cyclonic eddy are higher during march april whereas those for the compound tides mk3 sk3 ms4 2sk5 2mn6 and 2sm6 are associated with an inshore cyclonic eddy dominate during november december

a modeling study of shelf circulation off northern california in the region of the coastal ocean dynamics experiment 2 simulations and comparisons with observations 1 this is the second part of a modeling study of wind forced flow on the continental shelf off northern california in the region 37 40 n of the coastal ocean dynamics experiment code gan and allen 2002 analyzed the shelf flow response to idealized wind stress forcing in a process oriented study the study here applies forcing from observed winds and heat flux for april may 1982 and compares the model results with moored current and temperature measurements the princeton ocean model pom is used in a three dimensional limited area domain with a high resolution curvilinear grid approximately 1 km horizontal spacing 60 vertical levels and realistic coastline and bottom topography the objectives of the study are to simulate the response of the shelf circulation field to time varying observed wind stress and heat flux to compare model results with oceanographic observations to establish confidence in the model and to subsequently analyze the model fields and the model dynamical balances to help understand the behavior of the observed flow the model variables show overall good agreement with corresponding observations similar to the conclusions by gan and allen 2002 it is found that the alongshore variability of upwelling is mainly controlled by the interaction of the wind forced shelf flow with the coastline and bottom topography different dynamical regimes in the regions north and south of the coastal capes formed by pt reyes and pt arena and in the more uniform region between these capes are identified and investigated the results demonstrate that the coastal capes play a dominant role in causing alongshore variability of the upwelling flow including the setup of an alongshore pressure gradient that forces northward currents during relaxation of southward upwelling favorable winds an analysis of the balance of terms in the equation for potential temperature indicates that across shore temperature advection is the major contributor to the cooling of coastal water during upwelling with a larger magnitude to the south of the capes to the north of the capes however alongshore temperature advection is the dominant contributor to the colder water near the coast

227th230th dating method methodology and application to chinese speleothem samples abstract an improved version of the analytical and computational procedure for the 227 th 230 th dating method is described in detail this method is applicable to the range of 30 300 ka and to most speleothem samples with 0 1 ppm u and relatively free from detrital contamination 230 th 232 th 20 provided sufficient amount of sample is available fourteen chinese speleothem samples and one coral standard were analysed in parallel with two u series methods for the comparison between 230 th 234 u and 227 th 230 th close concordance of within 1 was found for all 18 age sets between 230 th 235 u and 231 pa 235 u within 1 for 16 instances and the remaining two between 1 and 1 5 replicate analyses give consistent results the isotopic ratios of two young calcites showed no abnormality which tends to negate the possibility of excess 227ac as suggested by gascoyne 1985 these results point to the usefulness of the 227 th 230 th as a stringent check of the validity of 220 th 234 u dating and to the reliability of cave calcites as pleistocene temporal markers

near field zooplankton ice face biota and proximal hydrography of free drifting antarctic icebergs abstract a small rov was used to collect plankton make video surveys and take hydrographic measurements in close proximity to six free drifting antarctic icebergs the icebergs studied ranged in size from 32 km in length large icebergs have a greater scale of influence than do smaller ones and iceberg mediated differences in the hydrographic characteristics of their surrounding water depend on the scale sampled irrespective of size temperature generally decreased in close proximity to an iceberg while salinity increased chlorophyll a was often lower in the surface waters near the iceberg relative to the surface waters further away tabular icebergs typically had 3 distinct underwater features shelf side and bottom ablation pockets were a common feature of subsurface ice the ice itself is a dynamic and seemingly harsh environment with relatively few macrofauna living on it those that do inhabit the ice face are either highly specialized or highly mobile species composition of zooplankton within 40 m of an iceberg did not change relative to distance however biomass was generally greater within 5 m of an iceberg than it was 15 to 40 m distant

an empirical model of the tidal currents in the gulf of the farallones abstract candela et al 1990 1992 showed that tides in an open ocean region can be resolved using velocity data from a ship mounted adcp we use their method to build a spatially varying model of the tidal currents in the gulf of the farallones an area of complicated bathymetry where the tidal velocities in some parts of the region are weak compared to the mean currents we describe the tidal fields for the m 2 s 2 k 1 and o 1 constituents and show that this method is sensitive to the model parameters and the quantity of input data in areas with complex bathymetry and tidal structures a large amount of spatial data is needed to resolve the tides a method of estimating the associated errors inherent in the model is described

diurnal period wind stress and current fluctuations over the continental shelf off northern california diurnal period wind stress and current fluctuations measured over the continental shelf off northern california during the coastal ocean dynamics experiment in the summers of 1981 and 1982 are examined the diurnal currents are strongly surface intensified with amplitudes of up to 20 cm s 1 at depths of less than 35 m the diurnal currents are nonstationary and their amplitude is well correlated with the amplitude modulation of the local diurnal wind stress beneath the surface layer the diurnal current vectors rotate clockwise with ellipse semi major axes of 1 to 3 cm s 1 a mixed layer model driven with diurnal wind stress and surface heat flux produces currents similar to those observed in the upper water column the deeper currents are consistent with the combination of a freely propagating kelvin and first mode coastal trapped wave and over the inner shelf with the interior flow forced by the diurnal wind stress in the presence of a coast

the seasonal alongshore pressure gradient on the west coast of the united states the long term mean steric height 0 500 dbar data of reid and mantyla 1976 are added to relative monthly mean adjusted sea level data to obtain a seasonal time series of quasi absolute large scale 300 km sea surface elevation along the west coast of the united states from 48 n to 33 n north of 38 n the elevation slope reverses sign seasonally so that the resulting pressure gradient force is southward from october to june and northward from july to september south of 38 n the pressure gradient force is northward except during january at all latitudes and during february in the interval from 38 n to 35 n maximum northward force occurs during august and september at all latitudes the relative contributions to sea level elevation slope by seasonal heating and cooling freshwater effluent effects the alongshore component of coastal wind stress and deep ocean currents are investigated both seasonal heating and cooling and freshwater contributions to large scale elevation slope are relatively insignificant 10 in every month at all latitudes wind stress forcing determined with the barotropic steady frictional model of csanady 1978 is significant north of point conception 35 n for both the long term mean slope and its seasonal oscillation remote contributions are particularly important in the pacific northwest south of san francisco 38 n empirical evidence suggests that deep ocean currents contribute significantly to coastal elevation slope in summer and fall and in the mean deep ocean currents may also affect elevation slope along the whole coast during spring causing elevated sea level toward the north

observations of platelet ice growth and oceanographic conditions during the winter of 2003 in mcmurdo sound antarctica 1 platelet ice is the name given to ice crystals that nucleate in the ocean and grow either at depth or loosely attached to the ice water interface related to the proximity of ice shelves it is known to form in supercooled seawater this study details the conditions for its growth during the austral winter of 2003 in mcmurdo sound antarctica a key finding is that the presence of platelet ice in the sea ice cover is conclusively linked to the time history of the appearance of ice crystals in the water column monitored using the strength of the backscattered signal from an acoustic doppler current profiler as a proxy generally these crystals appeared from mid may as water near the interface became supercooled this near surface supercooling appears to be related to a simultaneous abrupt change in the structure of the upper 250 m of the water column from one that behaved dynamically and contained both the warmest and coolest measured temperatures to one in which the water was essentially isothermal near its surface freezing temperature near surface ocean temperature was also affected by tidal mixing and by an increase in the thickness and density over the course of winter of the surface mixed layer created by salt rejection during ice growth these processes allowed cold water trapped by buoyancy in a band at the base of the mixed layer in early winter to gain access to the ice water interface by midwinter this band of cold water probably had its origin beneath the mcmurdo ice shelf

uranium series dating of quaternary deposits abstract this is a review of u series dating methods as applicable to terrestrial sedimentary materials alpha counting techniques allow the dating of carbonates and phosphates with a precision of 5 to 10 over the time range from 1 ka to 350 ka atom counting methods mass spectrometry and ams substantially increase precision and may increase the range problems of contamination and open system behavior are discussed correction for detrital contaminant is demonstrated in the dating of speleothem from a cave in italy

subtidal currents over the central california slope evidence for offshore veering of the undercurrent and for direct wind driven slope currents abstract in february 1991 an array of six current meter moorings was deployed for one year across the central california outer shelf and slope the main line of the array extended 30 km offshore of the shelf break out to water depths of 1400 m a more sparsely instrumented line displaced 30 km to the northwest extended 14 km offshore though shorter the northern line spanned similar water depths because the gradient of the topography steepened in the northern region a poleward flow pattern typical of the california undercurrent was seen across both lines in the array over most of the year the poleward flow was surface intensified in general the portion of the undercurrent that crossed the southern line had larger amplitudes and penetrated more deeply into the water column than the portion that crossed the northern line transport over the year ranged from 0 to 2 5 sverdrups sv poleward across the southern line 0 to 1 sv poleward across the northern line we suggest the difference in transport was caused by topographic constraints which tended to force the poleward flow offshore of the northern measurement sites the slope of the topography steepened too abruptly to allow the poleward flow to follow isobaths when currents were strong when current velocities lessened a more coherent flow pattern was seen across both lines in the array in general the poleward flow patterns in the undercurrent were not affected by local winds or by the local alongshore pressure gradient nor was a strong seasonal pattern evident rather unexpectedly a small but statistically significant fraction of the current variance over the mid and outer slope was driven by the surface wind stress an alongshelf wind stress caused currents to flow along the slope parallel to the wind field down to depths of 400 m below the surface and out to distances of 2 rossby radii past the shelf break the transfer functions were weak 3 4 cm s per dyn cm 2 but comparable to wind driven current amplitudes of 4 6 cm s per unit wind stress over the middle shelf equatorward alongshelf winds also caused water from 200 300 m over the slope to upwell onto the shelf as the surface water moved offshore

uranium series chronology and environmental applications of speleothems an increasing number of scientists recognize the value of speleothems1 as often extremely well preserved archives of information about past climate vegetation hydrology sea level nuclide migration water rock interaction landscape evolution tectonics and human action well constrained data are required to document past changes reconstruct past patterns and predict future responses of the earth system at a wide range of spatial and temporal scales speleothems are particularly useful in this regard because they can be found in many locations of the globe sampled at high resolution and reliably dated using high precision uranium series techniques speleothems are bodies of mineral material formed in caves as the result of chemical precipitation from groundwater flowing or dripping in a cave most speleothems are composed of calcite formed by slow degassing of co2 from supersaturated groundwater but aragonite and gypsum forms are also common particularly near cave entrances where evaporative effects are important a host of different speleothem types decorate the walls ceilings and floors of caves and their mineralogy and morphology is a function of fluid flow and chemistry of waters feeding a particular location as well as the ambient conditions temperature chemistry light in the air or water filled void subaerial forms include the familiar stalagmites stalactites draperies flowstones subaqueous forms include rimstone pools rafts mammillary calcite wall coatings and dog tooth spar for an extensive review of the types of speleothem that have been observed see hill and forti 1997 speleothems are used in a multitude of ways to explore past environmental conditions perhaps the most fundamental of which is their very presence or absence deposition of speleothems relies on sufficient water supply and soil co2 to enable dissolution and transport of reactants in the vadose zone to underlying caves in arid or glacial times conditions may not have been favorable for speleothem formation

hf radar observations of surface circulation off bodega bay northern california usa 1 two high frequency radar stations codar were installed along the northern california coast in may 2001 comparisons of radar data with acoustic doppler current profiler adcp current data and near surface drifter tracks indicate considerable agreement with minimum rms differences of order 0 05 0 15 m s and average drifter hf radar track separation rates of 5 3 km d radar data resolve the three main sources of intraseasonal current variability in the area 1 upwelling relaxation dynamics 2 tidal and diurnal forcing and 3 inertial currents subtidal fluctuations are the largest component of variability accounting for 45 75 of the variance wind driven dynamics are the dominant source of this subtidal variability 67 of subtidal variability both upwelling and relaxation periods exhibit consistent patterns of surface velocity with nearshore currents being slower and more poleward than offshore currents which are strongly equatorward analysis of tidal and inertial variability indicate that current fluctuations are polarized toward clockwise rotation and are generally weaker and more linearly polarized near the coast m2 tidal current ellipses switch direction of rotation at the shelf break suggesting the presence of internal tidal waves currents in all frequency bands are deflected and accelerated around pt reyes and there are indications of increased current variability and changes in flow direction near cordell bank the presence of considerable cross shore and alongshore gradients in the strength and direction of surface flow patterns and in particular weak poleward currents over the inner shelf could have important consequences for plankton retention in the area

an analysis of hf radar measured surface currents to determine tidal wind forced and seasonal circulation in the gulf of the farallones california united states 1 a complete year of hourly 3 km resolution high frequency radar measured surface currents covering the gulf of the farallones were analyzed with the following three primary objectives 1 describe the seasonal surface circulation 2 identify tidal currents and 3 determine the influence of wind forcing three predominant seasonal circulation regimes were identified relaxation storm and upwelling the relaxation period exhibited mean poleward flow over the slope variable equatorward flow over the shelf and cyclonic and anticyclonic eddies south of pt reyes the storm period mean flow was variable and exhibited evidence of coastally trapped buoyancy flow from the mouth of the san francisco bay the upwelling period exhibited equatorward flow throughout the gulf with regions of intensified flow at the northern and southern regions over the slope the tidal variance ranged from 4 to 60 was highest around the mouth of the bay decreased past the shelf and its spatial pattern reflected the combined influence of the k1 and m2 tidal current amplitudes k1 ellipses typically rotated clockwise throughout the gulf and decreased in amplitude past the shelf m2 ellipses were comparably more variable in orientation and magnitude harmonic tidal analyses of buoy wind data over 4 month time periods showed significant k1 amplitudes which did not appear when the analysis was done for the entire year this indicates that harmonic tidal analyses on surface currents are probably more effective at disassociating diurnal sea breeze driven currents when performed over long periods of time such as a year

thermohaline steps induced by melting of the erebus glacier tongue a vertically stable step like thermohaline structure is observed throughout a continuous 400 m conductivity temperature depth ctd profile taken near the erebus glacier tongue mcmurdo sound antarctica the pattern is best developed between the sea surface and 250 m depth the interval corresponding to that of the irregular underwater profile of the glacier tongue the steps average 17 m in thickness and typically display discontinuities of 0 1 c in temperature 0 04 in salinity and 3 5 10 4 g cm 3 in density the observations are compared with theory and laboratory experiments of cell development and lateral flow near ice melting into vertically stratified salt water at this location subsurface seawater is inferred to remain above the in situ freezing point year round and contains sufficient heat to account for much of the glacier tongue thinning by basal melting an adequate volume of meltwater would result to produce the measured salinity steps we discuss related observations and some implications of this process for ocean circulation and biological productivity in the antarctic

generation of harmonics by sea breeze in nontidal water bodies abstract the sea breeze introduces harmonics of its diurnal cycle into water bodies which can be notable for strong sea breeze and microtidal and nontidal conditions the harmonics can be of the same magnitude as those produced by bottom friction and dominate those produced by nonlinear terms in the equations of motion a closed form analytic solution of the linearized depth averaged equations of motion including friction is discussed for the situation of a sea breeze blowing on an idealized one dimensional basin of constant depth the solution reveals the generation of odd harmonics introduced by the quadratic wind stress and role of linearized friction sea breeze forcing on the idealized basin is numerically modeled and agreement with the analytic solution is found the numerical model is then run with quadratic bottom friction and nonlinear terms to compare relative contributions to the generation of harmonics harmonics of the water motion are distinguished as forced or arising from the wind for

microstructure and electrical properties of marine ice and its relationship to meteoric ice and sea ice a 215 m ice core has penetrated the central part of the ronne ice shelf 76 59 s 52 16 w the core consisted of meteoric ice above 152 8 m depth below this the ice was bubble free and of seawater origin the salinity of the layer below 152 8 m depth is less than 0 05 ppt very much lower than typical sea ice the ice represents an unusual source of ice intermediate in salinity and some physical properties between meteoric ice and sea ice the structure of the ice from four different depths where salinities vary by a factor of 4 has been investigated using a scanning electron microscope sem the fabric and grain structures are unusual and seem to depend on the impurity concentration in the ice chemical impurity localization has also been investigated the dielectric properties of the ice show that the ice has a transitional behavior from the linear dependence of conductivity on chloride concentration found in meteoric ice to the less predictable sea ice behavior the behavior may be interpreted in terms of the structure of the ice the higher salinity samples show convoluted grain boundaries small grain size and brine inclusions there are indications that the brine inclusions were liquid at temperatures between 10 c and 30 c by contrast the lower salinity samples possess larger grain sizes and show no evidence of brine inclusions all samples show brine concentrated at triple grain junctions and also along two grain boundaries in higher salinity samples the dielectric properties of the lower salinity samples are well described by a jaccard mechanism with l defects created in proportion to salinity that also describes the behavior of meteoric ice higher salinity samples exhibit lower conductivity than would be seen if l defects continued to be created in proportion to salinity the dielectric and structural data are consistent with a solubility limit of about 300 m for cl in the ice lattice

application of the 227th230th method to dating pleistocene carbonates and comparison with other dating methods the 227th230th dating method is described in detail and its usefulness investigated by comparing ages of sixteen pleistocene carbonates mainly cave deposits with those determined by the 231pa235u and 230th234u methods the 227th230th ages are found to be critically dependent on corrections for decay of 227th prior to alpha counting and ingrowth of daughter isotopes of 232th derived from clastic detritus of nineteen sets of ages determined for the sixteen samples good agreement is found for only seven sets differences are attributed to low u content of some samples and the possibility of excess 227th in the calcite of samples younger than 50 ky possibly due to the coprecipitation of 231pa during formation calculated negative 227th230th ages may be a direct result of this process and the fact that unlike the other methods the activity ratio is non zero at zero age nevertheless the 227th230th is found to be a useful alternative dating technique for carbonates which are between 50 and 300 ky because no spiking is required it also serves as a check for partial concordancy with ages dated by the other methods

surface circulation at the strait of gibraltar a combined hf radar and high resolution model study observations from a high frequency radar system and outputs from a high resolution operational ocean model working at the strait of gibraltar have been analyzed and compared during the period february 2013 to september 2014 in order to evaluate their capability to resolve the surface circulation of the region the description of the mean circulation patterns has been statistically assessed showing good agreement particularly in the central region of the strait corresponding with the atlantic jet aj stream although some short scale features are not reproduced by the model in the frequency domain very high concordance is observed tidal maps of diurnal and semidiurnal constituents are in good agreement with previous observations the analysis of the model and radar response to the wind forcing reveals that the low resolution of the model wind forcing field and its deeper superficial level smoothes the wind effect on the simulated currents the first three eof modes account for the 86 of model and radar variances the coincidence between the observed and simulated patterns is very significant for the first two modes which account for the mean velocity field and the latitudinal shifting of the aj consequence of the flow topography interaction the third mode captures the wind induced circulation and greater discrepancies are found in this case results underline the complementary character of both systems radar observations improve the model description resolving short scale processes while the model completes the radar information when the time or spatial coverage is poorer

palaeoclimate determination from cave calcite deposits calcite deposits formed in limestone caves have been found to be an excellent repository of palaeoclimatic data for terrestrial environments the very presence of a relict deposit indicates non glacial conditions at the time of formation and both 14c and uranium series methods can be used to date the deposit and hence the age of these climatic conditions variations in 13c and 18o content of the calcite in 2h and 18o content of fluid inclusions in trace element concentrations and more recently in pollen assemblages trapped in the calcite are all potentially available as synchronous palaeoclimatic indicators previous work has tended to concentrate mainly on abundance of deposits as a palaeoclimatic indicator for the last 300 000 years this literature is briefly reviewed here together with the theory and methods of analysis of the u series and stable isotopic techniques the combined use of u series ages and 13c and 18o variations in cave calcites illustrates the potential for palaeoclimate determination previously unpublished results of stable isotopic variations in dated calcites from caves in northern england indicate the level of detail of stable isotopic variations and time resolution that can be obtained and the complexity of interpretation that may arise tentative palaeoclimatic signals for the periods 90 125 ka and 170 300 ka are presented more comprehensive studies are needed in future work especially in view of the difficulty in obtaining suitable deposits and the ethics of cave deposits conservation

tidal currents seaward of the northern california continental shelf current measurements obtained from a sparse array of moorings deployed over the slope and the adjacent deep sea basin off northern california for 4 to 14 months have been analyzed for their tidal constituents the m2 tidal currents were the strongest tidal constituent containing 50 to 75 of the total current variance in the four major tidal bands the semimajor axis of the m2 constituent ranged from 2 to 4 cm s 1 and tended to be aligned with the local topography internal tides which were usually present in the m2 band were often the dominant cross slope current component on the middle slope at least a portion of the internal tidal current field had a steady phase that slowly changed over 1 to 2 months the semimajor axes of the diurnal barotropic ellipses had amplitudes ranging from 0 7 to 1 2 cm s 1 and were oriented both parallel and perpendicular to the local topography these tidal current measurements suggest that the barotropic diurnal currents propagate poleward as a combination of kelvin and continental shelf waves and that the barotropic m2 tides propagate poleward primarily as a kelvinlike wave battisti and clarke s 1982 model which uses coastal sea level data to predict m2 tidal currents agrees reasonably well with the observations presented here indicating that the model can be used to predict the m2 currents seaward of the middle slope off northern california

measurements of total alkalinity calcium and sulfate in natural sea ice we report precise measurements of salinity chlorinity alkalinity calcium and sulphate in various types of sea ice collected at the canadian expedition to study the alpha ridge cesar ice camp in the arctic ocean and in both first year and multiyear ice collected in fram strait several of the samples showed some relative enrichment of alkalinity and sulphate compared to what would be observed in seawater of the same salinity the relative enrichment was quite varied and did not correspond quantitatively with what has been observed in sea ice produced in the laboratory our results indicate that the temperature and salinity history of sea ice must be crucial in determining the relative composition of salts in natural sea ice and that quantitative geochemical predictions based on the composition of sea ice produced in the laboratory or on a particular specimen of natural sea ice must be made with caution