refraction and shoaling of nonlinear internal waves at the malin shelf break abstract this paper applies a numerical model to explain the refraction and shoaling of nonlinear internal waves observed at the malin slope for a sequence of tidal cycles in the summer of 1995 the model is first order in dispersion and second order in nonlinearity and is based on the extended korteweg de vries ekdv equation the ekdv model is applied along a set of rays and includes the effect of variable depth the model predicts that an initial long wavelength wave which lies in water of depths between 500 and 900 m develops into a set of internal solitary waves as it passes across the shelf break and onto the continental shelf in agreement with observations the extent of refraction is small because the internal waves are high frequency and in this case the refraction is not strongly dependent on the nonlinear adjustment to phase speed in the observations the internal wave amplitude measured in terms of near surface currents or thermocline displacement initially grows as the wave crosses th

observations of turbulence in a tidal beam and across a coastal ridge during a microstructure survey off california in monterey bay we found a midwater beam of strong turbulence emanating from the shelf break along the ray path of the semidiurnal m2 internal tide within the 50 m thick beam the turbulence kinetic energy dissipation rate e exceeded 10 6 w kg 1 and the diapycnal eddy diffusivity k was 0 01 m2 s 1 the beam extended 4 km off the shelf break several factors suggest that this beam of strong turbulence resulted from the breaking of semidiurnal internal tides the beam appeared to originate from the shelf break which is a potential generation site for semidiurnal internal tides the beam closely followed the ray path of the semidiurnal internal tide the average e off the shelf break varied by a factor of 100 with a semidiurnal tidal periodicity the isopycnal displacement confirmed the presence of semidiurnal internal tides processes associated with the breaking of internal tides are intermittent and sporadic at the same location we also observed equally intense turbulence in a 100 m thick layer of stratified water across the ridge of a sea fan this layer of strong turbulence was separated from the bottom and was clearly not generated by bottom friction although less well resolved in time the strong turbulence above the bottom seemed to vary with the semidiurnal tide and existed at the lee of the ridge where the isopycnal surface dipped and rebounded in a pattern resembling that of internal hydraulic jumps on the basis of the behavior of the density field we believe that the deep mixing was most likely produced by the across ridge current of internal tides the breaking of internal tides at middepth where the richardson number is close to the critical value is likely due to shear instability the presence of the coastal ridge provides an alternative pathway for converting energy from internal tides to turbulence via internal hydraulics multiplying the average e in the midwater beam by the length of the global coastline gives 31 gw only a small fraction of the estimated 360 gw dissipated globally by m2 internal tides our observations suggest that either most internal tides are generated away from shelf breaks or most internal tides generated at shelf breaks propagate away from their generation sites rather than dissipate locally and eventually contribute to pelagic mixing

observations of the internal tide in monterey canyon abstract data from two shipboard experiments in 1994 designed to observe the semidiurnal internal tide in monterey canyon reveal semidiurnal currents of about 20 cm s 1 which is an order of magnitude larger than the estimated barotropic tidal currents the kinetic and potential energy evidenced by isopycnal displacements of about 50 m was greatest along paths following the characteristics calculated from linear theory these energy ray paths are oriented nearly parallel to the canyon floor and may originate from large bathymetric features beyond the mouth of monterey bay energy propagated shoreward during the april experiment itex1 whereas a standing wave that is an internal seiche was observed in october itex2 the difference is attributed to changes in stratification between the two experiments higher energy levels were present during itex1 which took place near the spring phase of the fortnightly 14 8 days cycle in sea level while itex2 occurred close to the neap phase further evide

zonally asymmetric response of the southern ocean mixed layer depth to the southern annular mode interactions between the atmosphere and ocean are mediated by the mixed layer at the ocean surface the depth of this layer is determined by wind forcing and heating from the atmosphere variations in mixed layer depth affect the rate of exchange between the atmosphere and deeper ocean the capacity of the ocean to store heat and carbon and the availability of light and nutrients to support the growth of phytoplankton however the response of the southern ocean mixed layer to changes in the atmosphere is not well known here we analyse temperature and salinity data from argo profiling floats to show that the southern annular mode sam the dominant mode of atmospheric variability in the southern hemisphere leads to large scale anomalies in mixed layer depth that are zonally asymmetric from a simple heat budget of the mixed layer we conclude that meridional winds associated with departures of the sam from zonal symmetry cause anomalies in heat flux that can in turn explain the observed changes of mixed layer depth and sea surface temperature our results suggest that changes in the sam including recent and projected trends attributed to human activity drive variations in southern ocean mixed layer depth with consequences for air sea exchange ocean sequestration of heat and carbon and biological productivity

the record of sea water 187os 186os variation through the cenozoic the variation of sea water 187os 186os during the cenozoic has been determined by analyzing the hydrogenous os released by acidic hydrogen peroxide leaching of layers in an abyssal north pacific pelagic clay core overall sea water 187os 186os has increased from 3 2 at 58 ma to the present day value of 8 6 this pattern is similar to the well known 87sr 86sr evolution of sea water the increase in the proportion of continental os 187os 186os 10 could be due to enhanced weathering rates of black shales associated with the uplift of the himalayas other elements associated with black shale weathering such as u and p should show effects in the sedimentary record

ultramafic and mafic rocks from the garret transform fault near 13 30 s on the east pacific rise igneous petrology serpentinized peridotites metagabbros and fresh basaltic rocks were dredged from the garret transform fault near 13 s on the east pacific rise two dredge hauls taken on the northern wall from about 3100 3600 m consisted of aphyric and picritic basalts while peridotites gabbros and moderately phyric basalts were recovered in a single dredge located near the deepest part 4616 4820 m of the transform valley well preserved igneous textures and mineralogical assemblages enable us to differentiate between tectonites including harzburgites and clinopyroxene bearing harzburgites and cumulates consisting of plagioclase dunite troctolites olivine gabbros and ilmenite gabbros the harzburgites are likely to represent deep seated peridotites left after extraction of basaltic melt during upper mantle partial melting of a lherzolite the ultramafic cumulates underwent some deformation and show textural and mineralogical evidences which suggest formation at a minimum depth corresponding to the very lower crust it is also inferred that the composition of the coexisting liquid along with early cumulus crystals has a ratio mg mg fe2 of 0 7 high cao na2o ratios and a low ni content about 150 ppm when compared to similar rock types from atlantic fracture zones subsequent uplift during rifting of the oceanic lithosphere enhanced plastic deformation subsolidus recrystallization and retrogressive metamorphism of the gabbros and the ultramafics

climatic warming of atlantic intermediate waters abstract interdecadal temperature variability of the atlantic ocean is investigated by differencing hydrographic sections taken from the 1920s through the 1990s a comprehensive reanalysis of north atlantic sections and the inclusion of south atlantic sections show that warming seen previously in the north atlantic extends to the south atlantic the largest statistically significant changes occur on pressure surfaces between 1000 and 2000 decibars db over this pressure range and for latitudes between 32 s and 36 n temperatures have warmed by 0 5 c century 1 at 48 n a cooling of 3 c century 1 occurred between the 1950s and 1980s these isobaric temperature trends are decomposed into ones along surfaces of constant neutral density and ones due to the vertical movement of neutral surfaces the two components are associated with different processes in the southern north atlantic 8 36 n the subthermocline warming between the 1950s and 1980s appears to be due primarily to downward displacements of n

strontium and neodymium isotopes in hot springs on the east pacific rise and guaymas basin we have determined the concentrations and isotopic compositions of sr and nd in hydrothermal fluids from 21 n east pacific rise and guaymas basin gulf of california the purest solutions analyzed from 21 n exhibit a small range in sr concentration between individual vents from 5 8 to 8 7 ppm close to normal seawater sr concentrations they exhibit a small range in 87 sr 86 sr from e sr 0 13 4 to 17 7 corresponding to e sr 0 18 2 in the pure hydrothermal end member these results indicate extensive but not complete isotopic exchange with sr in the depleted oceanic crust e sr 0 31 8 and suggest that sr concentrations in these solutions are buffered in contrast the concentration and isotopic composition of nd in solutions show large variations between vents the concentration of nd ranges from 20 to 336 pg g 6 100 times seawater nd concentrations the isotopic composition ranges from e nd 0 3 6 similar to pacific seawater to 7 9 many samples show substantial contributions from morb but all have e nd 0 well below morb at this locality e nd 0 9 7 in spite of very large enrichments in nd concentrations while complete isotopic exchange with water rock 2 or exchange with anomalous oceanic crust can explain the sr data the nd data require exchange with a reservoir having e nd 0 pacific seawater low temperature reactions with metalliferous sediments on the ridge flanks may provide such a source both sr and nd in the guaymas basin solution are very different from21 n e sr 0 11 0 and e nd 0 11 4 and are consistent with the fluid exchanging sr and nd with heated sediments having a substantial component of old continental detritus some irregularities in the nd isotopic data reported here indicate that there must be a problem of contamination for some ultra low level trace elements during sample collection and processing which requires further attention using a simple box model the estimates for hydrothermal nd fluxes are compared with fluxes which would be required to maintain the relatively radiogenic value of e nd 0 3 in the pacific against the influx of more negative antarctic waters e nd 0 9 it is shown that the hydrothermal flux of nd from mid ocean ridges falls far short of that necessary to maintain the isotopic balance this indicates that weathered material from volcanic terranes e nd 0 7 is the most reasonable major source of radiogenic nd in the pacific

iridium in mississippi river suspended matter and gulf of mexico sediment the suggestion1 that a meteorite impact at the end of cretaceous time the cretaceous tertiary boundary caused the extinction of many groups of organisms and left an anomalous iridium concentration in sediments has stimulated interest in both the extinctions and in the geochemistry of ir refs 2 6 the geochemical behaviour of ir is not well understood partly because of the scarcity of concentration data for common rocks soils and waters here we report ir abundances in mississippi river suspended matter mrsm and gulf of mexico gom sediments and suggest that these values may be representative of much of the upper continental crust that accessible to rock weathering these data imply that the processes leading to the well known enrichment of iridium in deep sea sediments7 are similar to those which enrich elements such as ni and co

variability of subantarctic mode water and antarctic intermediate water in the drake passage during the late twentieth and early twenty first centuries a time series of the physical and biogeochemical properties of subantarctic mode water samw and antarctic intermediate water aaiw in the drake passage between 1969 and 2005 is constructed using 24 transects of measurements across the passage both water masses have experienced substantial variability on interannual to interdecadal time scales samw is formed by winter overturning on the equatorward flank of the antarctic circumpolar current acc in and to the west of the drake passage its interannual variability is primarily driven by variations in wintertime air sea turbulent heat fluxes and net evaporation modulated by the el nino southern oscillation enso despite their spatial proximity the aaiw in the drake passage has a very different source than that of the samw because it is ventilated by the northward subduction of winter water originating in the bellingshausen sea changes in aaiw are mainly forced by variability in winter water properties resulting from fluctuations in wintertime air sea turbulent heat fluxes and spring sea ice melting both of which are linked to predominantly enso driven variations in the intensity of meridional winds to the west of the antarctic peninsula a prominent exception to the prevalent modes of samw and aaiw formation occurred in 1998 when strong wind forcing associated with constructive interference between enso and the southern annular mode sam triggered a transitory shift to an ekman dominated mode of samw ventilation and a 1 2 yr shutdown of aaiw production the interdecadal evolutions of samw and aaiw in the drake passage are distinct and driven by different processes samw warmed by 0 3 c and salinified by 0 04 during the 1970s and experienced the reverse trends between 1990 and 2005 when the coldest and freshest samw on record was observed in contrast aaiw underwent a net freshening by 0 05 between the 1970s and the twenty first century although the reversing changes in samw were chiefly forced by a 30 yr oscillation in regional air sea turbulent heat fluxes and precipitation associated with the interdecadal pacific oscillation with a sam driven intensification of the ekman supply of antarctic surface waters from the south contributing significantly too the freshening of aaiw was linked to the extreme climate change that occurred to the west of the antarctic peninsula in recent decades there a freshening of the winter water ventilating aaiw was brought about by increased precipitation and a retreat of the winter sea ice edge which were seemingly forced by an interdecadal trend in the sam and regional positive feedbacks in the air sea ice coupled climate system all in all these findings highlight the role of the major modes of southern hemisphere climate variability in driving the evolution of samw and aaiw in the drake passage region and the wider south atlantic and suggest that these modes may have contributed significantly to the hemispheric scale changes undergone by those waters in recent decades

the velocity structure of the upper ocean in the presence of surface forcing and mesoscale oceanic eddies one goal of the joint air sea interaction experiment jasin was to investigate the structure of the near surface velocity field and to attempt to quantify what fraction of that field was related to the local wind toward that end in the late summer of 1978 two moorings were deployed in the northern rockall trough with oceanographic instrumentation concentrated in the upper 100m of the ocean simultaneous observations were made of the surface winds at each mooring and adjacent to one of the moorings of the velocity field at depths from 79 to 1000m energetic eddy like circulation dominated the velocity field in the jasin area at depths shallower than approximately 800m however both the velocity and the vertical shear of horizontal velocity showed variability that increased with proximity to the surface empirical orthogonal functions computed to separate the velocity data into uncorrelated modes of variability showed that over 97 of the variability in the upper 300m was distributed among only three vertical modes the first function had little depth dependence the second had strong depth independent flow in the depth range of the mixed layer and weak flow in the opposite direction at all depths below and the third had strong flow near the surface strong flow in the opposite direction just below the base of the mixed layer and weaker flow at all other depths function 1 alone provided a near complete description of the velocity variability below 85m where the flows associated with the eddy like circulation and the barotropic semidiurnal tide were the dominant components at 85m and above all three functions were necessary to provide a complete description temporal variability of function 2 was coherent with the local wind stress at the inertial frequency but at lower frequencies resulted in transport in the mixed layer to the southeast that was not coherent with the local wind low frequency temporal variability of function 3 was coherent with the local wind stress at these frequencies the velocity vector of function 3 nearest the surface was directed to the right of the wind stress vector and the velocity vector just below the base of the mixed layer was directed to the left of the wind stress thus forcing by the local wind can account for some but not all of the increased variability found near the surface

deposition of osmium and other platinum group elements beneath the ultramafic hosted rainbow hydrothermal plume osmium and other platinum group elements pges have been measured in sediments accumulating directly under the rainbow hydrothermal plume at 36 deg n on the mid atlantic ridge 187os 188os and pge concentrations in the sediments of four cores taken 2 25 km from the active vent site reveal evidence of both radiogenic os scavenged from seawater and importantly unradiogenic os released by hydrothermal venting the majority of analyses n 16 yield 187os 188os ratios that fall in a narrow range 0 99 1 06 close to that of modern seawater in these samples os concentrations correlate linearly with hydrothermal v enrichments which are also derived from seawater scavenging a smaller subset of samples characterized by unusually high concentrations of ni and cr derived from ultramafic rock fragments exhibit distinctly lower 187os 188os ratios their ir content is also higher and their pge ratios are more similar to mantle material than the pge patterns of the larger set of samples dominated by seawater scavenged os although the two most proximal cores lack evidence for any similar ultramafic detritus in their surficial sediments 187os 188os ratios in these samples are also lower than that of ambient seawater suggesting they are likely to have been influenced by unradiogenic os from vent fluid incorporated into the plume samples from the most distal core by contrast exhibit 187os 188os ratios indistinguishable from that of seawater compared with background ne atlantic sediments os is enriched four fold in the seawater dominated samples while pd pt and ir are twice the background value burial fluxes of os scavenged by hydrothermal fe in these sediments are 200 400 pg cm 2 kyr 1 up to twice that found on the epr and several times the background bg of 50 pg cm 2 kyr 1 for pt burial fluxes are 1800 3000 pg cm 2 kyr 1 bg ca 1000 pg cm 2 kyr 1 and for pd 2700 4600 pg cm 2 kyr 1 bg ca 800 pg cm 2 kyr 1

mesoscale 50 100 km circulations revealed by inverse and classical analysis of the jasin hydrographic data abstract inverse analysis wunsch 1978 has been applied to two 10 day surveys of an area 15 km consisting of nearly 100 ctd stations in order to determine the velocity field with a horizontal resolution of 45 km reference levels above the main thermocline 1100 m lead to physically implausible circulations below the thermocline the preferred solution conserves mass with bottom velocities not significantly different from zero all casts were repeated after 6 h and the surveys were 20 days apart allowing errors in the reference velocities due to internal waves tides and changes of mass between surveys to be estimated at less than 1 cm s 1 further spatial resolution is obtainable by classical geostrophic analysis contouring dynamic heights with an assumed bottom level of no motion from casts 15 km apart forming triangles 45 km apart two regions of anticyclonic circulation are revealed one a meander the other an eddy the meander and eddy have different water properties and interact as the eddy

scale dependence of environmental and physiological correlates of δ18o and δ13c in the magnesium calcite skeletons of bamboo corals gorgonacea isididae abstract we examine in detail 18 o and 13 c in the calcite internodes of bamboo corals as potential proxies of physiological and environmental variability through a a core top calibration that includes specimens from a wide range of habitats and environmental conditions and b a comparison of high resolution serial point analyses along radial growth axes of a sub set of specimens with each other with instrumental temperature and salinity records with growth rates and with a nominal skeletal proxy for temperature mg ca in the same specimens at the whole of specimen level 18 o and the intercept of the strong within specimen regression of 18 o against 13 c correlates highly with ambient temperatures at slopes that are identical to those reported for other marine biogenic carbonates 0 22 per c 13 c varies predominantly with apparent specimen mean growth rate it also correlates with the slope of the within specimen covariance between 18 o and 13 c which in turn is distributed bi modally among specimens and linked to differences in apparent growth rates within specimens variability in 13 c and to a lesser extent 18 o correlates between specimens collected in the same region and differs between regions implying an environmental effect but the factors involved for either isotope ratio are unclear correlations between 18 o and temperature and mg ca range from positive to negative among specimens and appear to vary over time even within specimens the mismatch between the consistent temperature dependence of 18 o at the whole of specimen level and the mixed relationship within specimens can be reconciled by assuming an unknown temperature dependent factor affecting 18 o during the growth of isidid calcite the contrast between the results of the core top temperature calibration for 18 o which are consistent with studies of other carbonates and the apparently more complex suite of factors affecting both 13 c and 18 o within specimens strongly suggests that calibrations based on a core top approach be applied cautiously to environmental reconstructions based on variations of a nominal proxy within specimens

multidecadal warming and shoaling of antarctic intermediate water antarctic intermediate water aaiw is a dominant southern hemisphere water mass that spreads from its formation regions just north of the antarctic circumpolar current acc to at least 20 s in all oceans this study uses an isopycnal climatology constructed from argo conductivity temperature depth ctd profile data to define the current state of the aaiw salinity minimum its core and thence compute anomalies of aaiw core pressure potential temperature salinity and potential density since the mid 1970s from ship based ctd profiles the results are used to calculate maps of temporal property trends at the aaiw core where statistically significant strong circumpolar shoaling 30 50 dbar decade 1 warming 0 05 0 15 c decade 1 and density reductions up to 0 03 kg m 3 decade 1 are found these trends are strongest just north of the acc in the southeast pacific and atlantic oceans and decrease equatorward salinity trends are generally small with their sign varying regionally bottle data are used to extend the aaiw core potential temperature anomaly analysis back to 1925 in the atlantic and to 1960 elsewhere the modern warm aaiw core conditions appear largely unprecedented in the historical record biennially and zonally binned median aaiw core potential temperatures within each ocean basin are with the notable exception of the subtropical south atlantic in the 1950s 70s 0 2 1 c colder than modern values zonally averaged sea surface temperature anomalies around the aaiw formation latitudes in each ocean and sectoral southern annular mode indices are used to put the aaiw core property trends and variations into context

decadal water mass variations along 20 w in the northeastern atlantic ocean abstract water mass variations in the northeastern atlantic ocean along 20 w are analyzed with pentadal resolution over the past 15 years using data from four repeat occupations of a meridional hydrographic section running south from iceland the section was sampled in 1988 1993 1998 and 2003 the results are interpreted in the context of changes in air sea forcing ocean circulation and water properties associated with the north atlantic oscillation nao the nao index oscillated around zero from 1984 to 1988 was strongly positive from 1989 to 1995 after which it shifted to lower positive and occasionally negative values from 1996 to 2003 previously published studies suggest that after the 1995 1996 shift of the nao the subpolar gyre largely retreated to the northwest in the northeastern atlantic ocean resulting in an increasingly southeastern character of local water masses with time water property changes extending from the subpolar mode water spmw just below the seasonal pycnocline through the density range shared by mediterranean outflow water and subarctic intermediate water saiw along 20 w are consistent with changes in wind driven ocean circulation and air sea heat flux associated with shifts in the nao especially after accounting for ocean memory after periods of lower nao index the spmw is warmer saltier and lighter at these same times large increases of apparent oxygen utilization aou and potential vorticity are found at the spmw base consistent with spmw ventilation to lighter densities during lower nao index periods deeper and denser in the water column the cold fresh and dense saiw signature within the permanent pycnocline that was most strongly present in 1993 near the culmination of a period of high nao index is much reduced in 1988 and 1998 in 2003 after a prolonged period of lower nao index increasing influence of warmer saltier subtropical waters is clear within the permanent pycnocline the deep penetration of the changes implies that they are caused primarily by circulation changes resulting from nao associated wind shifts but changes in air sea heat flux could also have played a role

application of an internal tide generation model to baroclinic spring neap cycles 1 a numerical internal tide generation model is used to study the behavior of baroclinic spring neap cycles in open basins and channels the motivation for this study comes from an observation on tidal currents in faeroe shetland channel which is briefly described a surprisingly large baroclinic semidiurnal tidal signal is found in the lower part of the water column above the slope on the shetland side concurring with barotropic neap tides the numerical model results indeed show that the baroclinic spring neap cycle may have a phase shift with respect to the barotropic spring neap cycle and that the phase of the baroclinic cycle may vary strongly within short distances it is also shown that even small changes in the background conditions e g stratification can provoke a large phase shift in the baroclinic cycle a possible connection to intermittency is discussed

a core top screen for trace element proxies of environmental conditions and growth rates in the calcite skeletons of bamboo corals isididae abstract we test for trace element proxies in the high magnesium calcite fraction of bamboo coral internodes by comparing environmental conditions and growth rates to the specimen mean compositions of 73 corals that were live caught at depths ranging from 3 to 3950 m and collected from habitats ranging from tropical coral reefs to the antarctic slope comparisons were done at a large geographic scale lgs and for a well sampled area south of australia across depths at a single site in order to help separate the effects of environmental variables that co vary at one spatial scale but not the other thirty seven trace elements were measured using solution based sector field icp ms of which seventeen were significantly detected in more than a third of the specimens only eight element calcium ratios correlated significantly with any environmental variable at the large geographic scale and only four did so at the local level at the lgs the highest correlation was between ambient temperature and mg ca which accounted for 89 of the variance across specimens spanned all four isidid sub families and was independently significant in the two best sampled sub families the predictive geometric mean relationship is t c 23 9 2 46 0 34 0 25 mg ca mmol mol spanning a temperature range of 1 9 to 26 8 c mg ca ratios from 58 6 to 155 1 mmol mol and an uncertainty rms of 2 78 c the numbers in parentheses are 95 cis the slope of the regression does not differ significantly from that of abiotic high mg calcites which suggests that the temperature dependent incorporation of mg into the carbonate results from kinetic reactions at the crystal surface analysis at the sh scale for the sub set of specimens for which we had data suggests is also affected by growth rates there were no obvious trace element correlates at either spatial scale of salinity or oxygen levels that could not be accounted for by covariance between these environmental parameters and in most cases temperature single and multiple correlation analyses also confirm previous suggestions that ba ca in bamboo coral calcite is a proxy for seawater barium and hence refractory nutrients suggest that sr ca is influenced by specimen mean mg ca ratios and water temperature as well as possibly seawater sr ca and falsify for bamboo corals p ca as well as p cd and cd ca as a proxy for seawater phosphate levels the predictive relationship between isidid skeletal mean ba ca and seawater silicate concentrations appears to be linear and is given by silicate mol kg 1 56 7 20 8 9217 1632 ba ca mmol mol spanning a silicate range of 0 5 to 120 mol kg 1 a ba ca range of 0 0042 to 0 0195 mmol mol and with an uncertainty rms of 33 1 mol kg 1 mn ca differences among specimens and sites are highly significant and appear to reflect seawater mn suggesting a proxy for this micronutrient the compilation of growth rate data across 34 specimens indicates a wide range of growth rates even among con familial specimens from within a single habitat and suggests both ambient temperature and food availability underlie at least part of this variability

historical sam variability part i century length seasonal reconstructions seasonal reconstructions of the southern hemisphere annular mode sam index are derived to extend the record before the reanalysis period using station sea level pressure slp data as predictors two reconstructions using different predictands are obtained one jones and widmann jw based on the first principal component pc of extratropical slp and the other fogt on the index of marshall a regional based sam index visbeck is also considered these predictands agree well post 1979 correlations decline in all seasons except austral summer for the full series starting in 1958 predictand agreement is strongest in spring and summer hence agreement between the reconstructions is highest in these seasons the less zonally symmetric sam structure in winter and spring influences the strength of the sam signal over land areas hence the number of stations included in the reconstructions reconstructions from 1865 were therefore derived in summer and autumn and from 1905 in winter and spring this paper examines the skill of each reconstruction by comparison with observations and reanalysis data some of the individual peaks in the reconstructions such as the most recent in austral summer represent a full hemispheric sam pattern while others are caused by regional slp anomalies over the locations of the predictors the jw and fogt reconstructions are of similar quality in summer and autumn while in winter and spring the marshall index is better reconstructed by fogt than the pc index is by jw in spring and autumn the sam shows considerable variability prior to recent decades

the study of molybdenites through the187re 187os chronometer we determined the re and os concentrations in 11 molybdenites of various ages 30 2700 m y and from various areas no common osmium has been detected and os was found to be purely radiogenic therefore by comparing the concentrations we were able to determine 187 re 187 os ages for most samples these ages are in good agreement with those measured in surrounding rocks and probably correspond to the age of mineralization however two or three re os ages seem unreliable being probably related to some rhenium leaching through later metamorphic and or hydrothermal events this shows that the petrographic characteristics of ores and the type of crystallization of mos 2 are important in choosing samples suitable for dating re and os determinations combined with careful petrographic investigations may give important clues on the genesis and evolution of molybdenum ores

parallel decadal variability of inferred water temperatures for northern and southern hemisphere intermediate water masses we use a novel proxy growth rates of long lived deep water fish orange roughy to reconstruct inferred water temperatures of intermediate water masses in both northern and southern hemispheres since the mid 1800s the data are consistent with instrumental records showing long term warming in the northern hemisphere but also indicate decadal variability of intermediate depth temperatures that is coherent across the two hemispheres this variability correlates with the dominant subpolar annular mode in each hemisphere and implies a bihemispheric oceanic response to external forcing that influences the properties of intermediate depth water masses

internal tide generation at a shelf break by an oblique barotropic tide observations and analytical modeling an analytical model has been developed to describe the generation of a linear interfacial wave over a steep ocean margin by a barotropic tide propagating toward the shelf break with a variable angle of incidence the stratification is reduced to a two layer system and the model uses step like shelf geometry in both shallow and deep regions an open boundary is assumed this implies particularly that there is no reflection at the coast the model is forced with the amplitude and direction of an incident barotropic poincare wave propagating toward the shelf break with this forcing the model gives the amplitude direction of propagation and wavenumber of both barotropic and baroclinic poincare waves transmitted onto the shelf and reflected into the deep region in the vicinity of the shelf break after comparison with baines 1973 model our model is compared with internal tide observations made in july 1996 on the malin shelf within the u k land ocean interaction study shelf edge study program the observations are from moored thermistor chains and acoustic doppler current profilers sited at two locations one near the shelf break and the other 47 5 km onto the shelf observations at this latter mooring are not described by the generation model because of nonlinear changes and damping as the internal wave propagates through shallow water baroclinic displacements of the thermocline of 8 m amplitude were observed close to the shelf break and total baroclinic energy was estimated at 2 4 j m3 during neap tide and 3 j m3 during spring tide both amplitude and energy of the shoreward propagating internal tide waves are compared with the model using a barotropic forcing taken from bibliographical data good agreement with observations is found during neap tide when the density structure is close to being two layer for an incident barotropic tide of 1 m amplitude and propagation direction on a bearing of 23 t t means from true north in a clockwise sense

decadal spinup of the south pacific subtropical gyre abstract an increase in the circulation of the south pacific ocean subtropical gyre extending from the sea surface to middepth is observed over 12 years datasets used to quantify the decadal gyre spinup include satellite altimetric height the world ocean circulation experiment woce hydrographic and float survey of the south pacific a repeated hydrographic transect along 170 w and profiling float data from the global argo array the signal in sea surface height is a 12 cm increase between 1993 and 2004 on large spatial scale centered at about 40 s 170 w the subsurface datasets show that this signal is predominantly due to density variations in the water column that is to deepening of isopycnal surfaces extending to depths of at least 1800 m the maximum increase in dynamic height is collocated with the deep center of the subtropical gyre and the signal represents an increase in the total counterclockwise geostrophic circulation of the gyre by at least 20 at 1000 m a comparison of woce and

semidiurnal internal tide in jasin observations and simulation temperature was observed in the upper 80 m by moored thermistor chains at three locations in rockall channel west of scotland isotherms were interpolated and a 1 week period of exceptionally energetic tidal oscillations was analyzed the moored array horizontal separations ranging from 6 to 20 km was used as an antenna to determine the dominant horizontal wavelength and direction of propagation of the internal tide within the array rockall bank 100 km to the southeast was identified as the source of the internal tide the semidiurnal internal tide generated by the interaction of the surface tide with rockall bank was simulated by use of a model due to prinsenberg and rattray the model predicts generation of the internal tide at the shelf break and propagation seaward as energetic beams which lie along internal wave characteristics some energy is trapped near the surface in association with the pycnocline there is substantial structure in the velocity and vertical displacement fields most of the total energy of the internal tide is in the first vertical mode however at particular depths vertical modes as high as 4 horizontal wavelengths of 25 km dominate the high degree of spatial variability in the modeled internal tide illustrates the potential for error when basing a description of the tide on sparse observations there is good agreement between the modeled vertical displacements and the 1 week period of energetic oscillations of isotherm depth observed at the moorings in addition there is good agreement between the model and the tidal velocity variance measured during the same week at depths ranging from 10 to 1000 m and distances ranging from 50 to 130 km from rockall bank richardson numbers associated with the vertical shear of the modeled internal tide range down to values less than 2

internal waves in jasin the internal wavefield during the joint air sea interaction jasin experiment was monitored by moored current meters and moored and towed thermistor chains the observations were concentrated in the upper ocean near the centre of rockall trough but velocity measurements were also made near topographic features and throughout the water column observed spectra are compared with results from the deep ocean as represented by the garrett munk gm model of the spectral continuum and are generally found to have spectral levels equal to or greater than the gm spectrum the greatest deviation from the gm spectrum occurs at high frequencies and wavenumbers where the observed spectra often exhibit a spectral shoulder and high vertical coherence these features also found in other upper ocean spectra are explained by a model composed of three vertically standing modes the spatial variation of internal wave variance is related to topography variance is highest near rough topography the ratio of variance in the semidiurnal tidal band to variance in a band in the continuum is approximately constant the possibility of a dynamical link between the two frequency bands requires further investigation the semidiurnal internal tide varies temporally and spatially rockall bank is identified as the source of an energetic beam of tidal oscillations during a one week period

an exchange window for the injection of antarctic intermediate water into the south pacific antarctic intermediate water aaiw occupies the intermediate horizon of most of the world oceans formed in the southern ocean it is characterized by a relative salinity minimum with a new denser in situ national oceanographic data center dataset the authors have reanalyzed the export characteristics of aaiw from the southern ocean into the south pacific ocean these new data show that part of the aaiw is exported from the subpolar frontal region by the large scale circulation through an exchange window of 10 width situated east of 90 w in the southeast corner of the pacific basin this suggests the origin of this water to be in the antarctic circumpolar current a set of numerical modeling experiments has been used to reproduce these observed features and to demonstrate that the dynamics of the exchange window is controlled by the basin scale meridional pressure gradient the exchange of aaiw between the southern and pacific oceans must therefore be understood in the context of the large basin scale dynamical balance rather than simply local effects

antarctic intermediate water and subantarctic mode water formation in the southeast pacific the role of turbulent mixing abstract during the 2005 austral winter late august early october and 2006 austral summer february mid march two intensive hydrographic surveys of the southeast pacific sector of the southern ocean were completed in this study the turbulent kinetic energy dissipation rate diapycnal diffusivity and buoyancy flux jb are estimated from the ctd o2 and xctd profiles for each survey enhanced of o 10 3 to 10 4 m2 s 1 is found near the subantarctic front saf during both surveys during the winter survey enhanced was also observed north of the subduction front the northern boundary of the winter deep mixed layer north of the saf in contrast the summer survey found enhanced across the entire region north of the saf below the shallow seasonal mixed layer the enhanced below the mixed layer decays rapidly with depth a number of ocean processes are considered that may provide the energy flux necessary to support the observed diffusivity the observed buoyancy flux 4 0 10 8 m2 s 3 surr

estimation of continental 187os 186os values by using 187os 186os and 143nd 144nd ratios in marine manganese nodules abstract the relationship between 187os 186os and 143nd 144nd in different manganese nodule fields is used to determine the 187os 186os ratio of the continental terrains bounding the major ocean basins the atlantic ocean drainages yield 187os 186os of about 11 the pacific ocean between 25 and 36 and the western indian ocean 20 by assuming a two component continental crust composed of ultramafic rocks high os concentration low 187os 186os and granite with only radiogenic 187os produced in accessory re bearing molybdenite the ultramafic contribution to weathering is about 0 2 some or most of this may come from the alteration of oceanic ultramafics

nonreflecting internal wave beam propagation in the deep ocean using linear internal wave theory for an ocean stratified by both density and current several background profiles are identified for which internal wave beams can propagate without any internal reflection these special profiles are favorably compared with available oceanic data

internal wave observations from the arctic environmental drifting buoy a free drifting buoy serving as an ice anchor and flotation sphere for a 125 m instrumented mooring line was deployed in the arctic pack ice by the r v polarstern in august 1987 at the northernmost point achieved by the arktis iv expedition current measurements were made from this arctic environmental drifting buoy aedb using a 150 khz acoustic doppler current profiler adcp attached to the mooring line at a depth of 16 m below the flotation sphere with the transducers facing downward velocity profiles spanning depths between 35 and 327 m with 15 m resolution were collected at half hour intervals over a period of 216 days while the buoy drifted from its starting point near 86 n 22 e to about 70 n 16 w the full experimental record was separated into three sections corresponding to periods of the drift spent in the nansen basin over the yermak plateau and in the greenland sea velocity time series and spectra were computed and results for the three analysis sections were compared spectra in the nansen basin were found to have energy levels significantly less than those typical for mid latitudes roughly one third of the canonical garrett munk gm level and a spectral slope between and 2 5 that was significantly flatter than that expected from the gm model between 83 n and 81 n as the buoy passed over the yermak plateau internal wave energy increased to levels comparable to gm isolated energetic near inertial wave packets with upward group velocity were observed in this portion of the record presumably generated by interaction of the barotropic tide with the bottom topography of the plateau estimates of the upward energy flux from these near inertial packets were comparable to the downward fluxes from typical surface sources interpretation of the greenland sea section was complicated by adcp sampling problems and a lack of argos fixes but the available data showed internal wave spectral levels that were intermediate between those of the nansen basin and yermak plateau and no evidence of upward propagating near inertial energy

extracting the internal tide from data methods and observations from the mixed layer dynamics experiment several methods are developed for analyzing data containing a highly variable internal tide in particular the methods are aimed at the analysis of moored observations with relatively few measurements in the vertical the analysis depends upon an elliptical decomposition that is a generalization of the familiar rotary decomposition the technique is applied to velocity and temperature observations in the upper ocean made during the mixed layer dynamics experiment mildex in the northeast pacific ocean about 700 km west of santa barbara california during october november 1983 the observed propagation direction and amplitude of the internal tide was highly variable in time it was anticipated that the wave could be propagating from the continental shelf where it is presumed to be generated however most of the time the internal tide appears to be propagating parallel to the coast this result suggests the importance of density and velocity structure at mesoscale and frontal scale in affecting the propagation of the internal tide

summary of the jasin 1978 field experiment jasin was designed to observe the physical processes causing mixing and to quantify aspects of the heat and momentum budgets in mid latitude oceanic and marine atmospheric boundary layers the multiplicity of processes to be sampled necessitated a large experiment and jasin involved 14 ships and 3 aircraft with more than 50 teams of investigators from 9 countries the experiment took place from july to september 1978 in the north rockall trough an area of deep water several hundred kilometres off the west coast of scotland hydrographic surveys revealed eddies 100 km across and intensive measurements on smaller scales revealed fronts in the confluence zones of the eddy field the development of the mixing layer and seasonal thermocline internal and inertial wave fields and the ekman response to winds are all complicated by the fronts and eddies the atmospheric boundary layer on scales of 200 km was non steady and inhomogeneous surface generated turbulence occupied the subcloud layer and transfers through the cloud layer occurred on scales greater than 50 km or intermittently possible driving factors were the variability in surface fluxes near the oceanic mesoscale eddies radiative processes in the cloud layer and condensation processes the lifting of warm sector boundary layer air from widely differing sources into the free atmosphere at a front resulted in well mixed moist layers that exhibited near thermal wind equilibrium

187os 186os in marine manganese nodules and the constraints on the crustal geochemistries of rhenium and osmium during their formation marine manganese or more properly ferromanganese oxide nodules include and commonly concentrate elements dissolved in seawater this attribute makes them especially valuable recorders of the isotopic composition of elements supplied to the oceans having radiogenic isotopes for these can be used in exploring crustal composition and evolution1 5 from measurements of 187os 186os ratios in marine manganese nodules and comparison with the 143nd 144nd ratios of the same nodules we have calculated the os isotopic composition and the osmium and rhenium concentrations of the weatherable portion of the continental crust together with the proportions of ultra mafic and granitic rock that constitute this crustal mass

internal tide radiation from mendocino escarpment abstract strong semidiurnal internal tides are observed near mendocino escarpment in full depth profile time series of velocity temperature and salinity velocity and density profiles are combined to estimate the internal tide energy flux divergence of this flux demonstrates that its source is the barotropic tide interacting with the escarpment a baroclinic energy flux of 7 kw m 1 radiates from the escarpment corresponding to 3 of the 220 kw m 1 fluxing poleward in the surface tide energy and energy flux are concentrated in packets that emanate from the flanks of the ridge surmounting the escarpment and one site 90 km north of the escarpment coherent beamlike structure along semidiurnal ray paths remains identifiable until the first surface reflection beyond the first surface reflection north of the escarpment the energy flux drops by 2 kw m 1 and beams are no longer discernible turbulence as inferred from finescale parameterizations is elevated by over two orders of magnitude relative to th