taphonomic signatures and patterns of test degradation on tropical intertidal benthic foraminifera the preservational condition of benthic foraminifera from tropical intertidal sediments in cleveland bay north queensland australia was examined in order to provide systematic descriptions of taphonomic signatures and semi quantitative estimates of test degradation the primary aim was to improve understanding of the processes of test degradation experienced by intertidal foraminifera during early burial eight common tropical intertidal foraminiferal species were examined arenoparrella mexicana miliammina fusca miliammina obliqua and trochammina inflata from two upper mangrove stations and ammonia aoteana elphidium excavatum clavatum pararotalia venusta and parrellina hispidula from two mudflat stations taphonomic alteration was broadly divided into surface textural features and larger scale structural losses to tests surface alteration of calcareous tests was dominated by the etching and roughening associated with dissolution processes with limited evidence for bioerosion and abrasion both surficial etching and larger scale structural damage were closely related to test architecture with degradation most intense on porous chamber walls as opposed to non porous areas interlocular walls and chamber tips furthermore all calcareous species exhibited consistent pathways of degradation whereby the most recently formed chambers were the most vulnerable to degradation the correspondence between larger scale test loss and these patterns of surface textural alteration suggests calcareous test degradation is primarily driven by dissolution degradation of agglutinated tests contrasts in a number of ways pristine tests of all four species examined exhibited a smooth outer organic coating which may be missing from other specimens the extent to which this initial loss effects further test breakdown is uncertain but appears to differ between species m obliqua and some specimens of a mexicana exhibited structural damage which corresponded to clear cement losses and agglutinant disaggregation more generally agglutinated species displayed fracturing and test breakages which bore no conspicuous relation to cement loss furthermore neither surface alteration nor structural loss affected any part of agglutinated tests preferentially and therefore pathways of degradation were inconsistent across specimens the fact that agglutinated tests degrade in a more arbitrary manner compared with calcareous tests is taken as evidence that their degradation is 1 not entirely controlled by test architecture and 2 at least partially driven by physical mechanical processes we suggest that if agglutinated tests are not already inherently weaker than their calcareous counterparts the loss of organic cements may sufficiently weaken agglutinated tests so as to increase susceptibility to physical damage tests were also graded according to the extent to which they were structurally degraded average taphonomic grades and taphonomic variability i e standard deviation for all species at cocoa creek were statistically invariant with depth contrary to expectations based on the concept of progressive burial through a taphonomically active zone this indicates that shallow sub surface sediments are significantly homogenised and that sediment mixing and infaunal test production imparts a considerable effect on the development of surface and sub surface dead assemblages at the study site

carbonate dissolution and temporal abundances of foraminifera in long island sound sediments the dynamics of benthic foraminifera assemblages can be used to examine carbonate dissolution processes in nearshore sediments and as a general assay of physical chemical factors affecting survival of juvenile benthos abundances of total foraminifera live and dead fluctuate regularly throughout the year in long island sound lis mud deposits with highest numbers in spring summer and lowest in winter essentially all forams disappear each year pore water undersaturation with respect to carbonate minerals coincides with periods of rapid disappearance of forams and suggests that these fluctuations reflect a balance between the rate of production recruitment and the rates of death and dissolution of the calcareous tests of the animals reworking by macrofauna in lis central basin sediments inhibits accumulation or depletion of pore water solutes and is responsible for minimizing pore water carbonate saturation states quantitative estimates of seasonal patterns of foram dissolution with a simple mass balance model give a minimum average annual flux of caz in lis sediments of 6 mmol ca2 m 2 d 1 due solely to foraminifera dissolution abandoned tests have a maximum mean residence time of 86 13 d dissolution precipitation of forams may significantly affect benthic zco fluxes and likely accounts for a large proportion 30 during some seasons or at some locales other organisms with carbonate tests of similar size particularly juvenile bivalves may also be affected by periods of undersaturated pore waters conditions promotinn dissolution of tests may represent an important source of mortality for calcareous meiofauna

stochastic variability of oceanic flows above topography anomalies 1 we describe a stochastic variability mechanism which is genuinely internal to the ocean i e not due to fluctuations in atmospheric forcing the key ingredient is the existence of closed contours of bottom topography surrounded by a stirring region of enhanced eddy activity this configuration leads to the formation of a robust but highly variable vortex above the topography anomaly the vortex dynamics integrates the white noise forcing of oceanic eddies into a red noise signal for the large scale volume transport of the vortex the strong interannual fluctuations of the transport of the zapiola anticyclone 100 sv in the argentine basin are argued to be partly due to such eddy driven stochastic variability on the basis of a 310 years long simulation of a comprehensive global ocean model run driven by a repeated year forcing

hemispheric asymmetry of deep water transport modes in the western atlantic subtropical studies of the atlantic meridional cold water flow show a hemispheric contrast in the dominant southward transport mode below 2000 m in the north atlantic lower deep water ldw 1 8 2 4 c dominates with small transport of middle deep water mdw 2 4 3 2 c while in the south atlantic the opposite is observed we use numerous observations in the western basins of the tropics to show that the transition occurs rapidly near the equator in the western atlantic a meridional section in the central brazil basin suggests zonal flows are responsible for the transition ldw transport from the guiana basin north of the equator flows eastward in the northern brazil basin and is inferred to continue on through the romanche fracture zone into the eastern atlantic an opposing flow of mdw from the eastern tropical atlantic flows toward the western boundary where it bifurcates to supply mdw to the deep western boundary current dwbc of the brazil basin as well as to feed the northward flow of mdw in the guiana basin offshore of the dwbc the magnitude of each of these oppositely directed flows is roughly 7 sv we furthermore speculate that they are connected predominantly by upwelling from ldw to mdw within the low latitude eastern basin the overall deep water transport system below 2000 m in the western basins of the mid and low latitude atlantic is thus found to comprise the following three distinct components 1 a strong dwbc transport of ldw with associated recirculation dominates the guiana basin north of the equator 2 in the northern brazil basin just south of the equator a narrow eastward flow absorbs the ldw and carries it eastward while a somewhat broader westward flow imports mdw into the western basin 3 this mdw flow then bifurcates with the southward branch causing the mdw dominance in the brazil basin where the mdw dominated dwbc and associated recirculations are the third component of the deepwater transport system

streamwater ph alkalinity pco2 and discharge relationships in some forested mediterranean catchments the streamwater chemistry of four catchments at prades and one catchment at montseny ne spain is described and the relationships between streamwater alkalinity ph and pco2 with discharge and that between ph and alkalinity are highlighted at montseny results from a subsurface seepage are also presented the prades and montseny catchments have similar vegetation dense forest of holm oak quercus ilex l and lithology phyllites however the catchments differ strongly in their hydrological behaviour only 8 15 of the rainfall passes to the stream from the two gauged prades catchments whereas the montseny catchment provides 50 of rainfall to the stream hence the mineralization of streamwaters is much higher in the prades catchments all the streams studied show an inverse relationship between alkalinity and discharge although ph also decreases with discharge in the montseny catchment it remains high during high flows in the prades catchments the prades streamwater chemistries are determined by the solubility equilibrium of calcite at high flows alkalinity decreases and as a result of calcite solubility controls this change results in an increase in ph consequently ph and log alkalinity are either negatively correlated or uncorrelated in the prades streams at montseny the relationship between ph and alkalinity is significantly positive calcite solubility controls do not come into play all waters analyzed show an excess pco2 epco2 with respect to atmospheric concentrations the highest epco2 values usually correspond to low flows however study of the variation of epco2 during 15 individual storm events sampled at montseny shows that epco2 increases with discharge at prades the degassing of epco2 in the stream channel produces calcite precipitation

temporal variability of the meridional overturning circulation at 34 5 s results from two pilot boundary arrays in the south atlantic data from two boundary arrays deployed along 34 5 s are combined to produce the first continuous in situ time series observations of the basin wide meridional overturning circulation moc in the south atlantic daily estimates of the moc between march 2009 and december 2010 range between 3 sv and 39 sv 1 sv 106 m3 s 1 after a 10 day low pass filter is applied much of the variability in this 20 month record occurs at periods shorter than 100 days approximately two thirds of the moc variability is due to changes in the geostrophic baroclinic plus barotropic volume transport with the remainder associated with the direct wind forced ekman transport when low pass filtered to match previously published analyses in the north atlantic the observed temporal standard deviation at 34 5 s matches or somewhat exceeds that observed by time series observations at 16 n 26 5 n and 41 n for periods shorter than 20 days the basin wide moc variations are most strongly influenced by ekman flows while at periods between 20 and 90 days the geostrophic flows tend to exert slightly more control over the total transport variability of the moc the geostrophic shear variations are roughly equally controlled by density variations on the western and eastern boundaries at all time scales captured in the record the observed time mean moc vertical structure and temporal variability agree well with the limited independent observations available for confirmation

the effects of multiple stressors on the distribution of coastal benthic foraminifera a case study from the skagerrak baltic sea region abstract coastal ecosystems are subjected to both large natural variability and increasing anthropogenic impact on environmental parameters such as changes in salinity temperature and ph this study documents the distribution of living benthic foraminifera under the influence of multiple environmental stressors in the skagerrak baltic sea region sediment core tops were studied at five sites along a transect from the skagerrak to the baltic sea with strong environmental gradients especially in terms of salinity ph calcium carbonate saturation and dissolved oxygen concentration in the bottom water and pore water we found that living foraminiferal densities and species richness were higher at the skagerrak station where the general living conditions were relatively beneficial for foraminifera with higher salinity and calc in the water column and higher ph and oxygen concentration in the bottom and pore water the most common species reported at each station reflect the differences in the environmental conditions between the stations the dominant species were cassidulina laevigata and hyalinea balthica in the skagerrak stainforthia fusiformis nonionella aff stella and nonionoides turgida in the kattegat and n aff stella and nonionellina labradorica in the oresund the most adverse conditions such as low salinity low calc low dissolved oxygen concentrations and low ph were noted at the baltic sea stations where the calcareous tests of the dominant living taxa ammonia spp and elphidium spp were partially to completely dissolved probably due to a combination of different stressors affecting the required energy for biomineralization even though foraminifera are able to live in extremely varying environmental conditions the present results suggest that the benthic coastal ecosystems in the studied region which are apparently affected by an increase in the range of environmental variability will probably be even more influenced by a future increase in anthropogenic impacts including coastal ocean acidification and deoxygenation

hydrography of the romanche and chain fracture zones the romanche and chain fracture zones rfz and cfz are known as pathways for the lower north atlantic deep water lnadw and the antarctic bottom water aabw from the western trough to the eastern trough of the equatorial atlantic ocean across the mid atlantic ridge we report hydrographic observations describing the evolution of the lnadw and aabw properties during their transit through the equatorial fracture zones to the west of the rfz and cfz sills the lnadw and aabw cores are separated by a deep thermocline pycnocline which marks the transition between the two water masses the deep thermocline is eroded eastward and vanishes in the eastern basin this zonal asymmetry is the signature of a zonal baroclinic pressure gradient associated in each fracture zone with eastward flows of lnadw and aabw below 3800 m depth during the eastward transit through the rfz the near bottom aabw becomes less dense saltier 0 07 and warmer 0 7 c richer in oxygen 0 3 ml l 1 but less rich in silicate 30 mol l 1 simultaneously the lnadw core becomes fresher and colder at a given density and the oxygen maximum characterizing the lnadw core weakens by 0 2 ml l 1 we argue that the property changes within the aabw and lnadw are due to intense vertical mixing in addition to vertical mixing with the aabw it seems likely that isopycnal mixing of the lnadw with the eastern basin deep water contributes to the property evolution of the lnadw exiting the rfz in the cfz evidence is also given of mixing occuring within the aabw and the lnadw a sudden change in the aabw properties observed across the cfz main sill suggests the blocking of the eastward progression of the densest aabw by the cfz main sill however this dense water can reach the eastern basin by flowing northeastward through valleys the sills of which are deeper than thoses of the cfz finally a simple hydraulic control model applied to the rfz and cfz flows predicts a transport of 1 4 0 1 106 m3 s 1 of water colder than 1 9 c across the rfz cfz main sill

a meridional 14c and 39ar section in northeast atlantic deep water 14c 39ar and complementary hydrographic and nutrient data are presented for deep water below 2500 m depth from stations along a meridional section 8 s to 45 n through the romanche trench and along the deep northeast atlantic basins f s meteor cruise 56 leg 5 the large scale 14c distribution along the section is resolved at the 14c data precision of 2 bottom water 14c decreases by 6 from the equator to 45 n and farther up there is a weak 14c minimum 123 over much of the section the 14c data are interpreted as giving a turnover time of about 30 years for the waters below the depth of the 14c minimum 4250 m it is found that water of 1 50 0 05 c potential temperature enters the east atlantic from the west through the romanche trench sill depth about 4000 m and a preliminary value for the inflow rate of 3 6 106 m3 s is deduced this rate greatly exceeds estimated deep inflow rates through the vema fracture zone or across the northern boundary of the east atlantic 39ar data that cover an entire deep ocean circulation system are presented for the first time the observed 14c and 39ar distributions are mutually consistent transit times from the source regions to the equator for water from northern and southern deepwater sources are estimated to be about 170 and 105 years respectively and the 39ar concentration of young antarctic bottom water is deduced as 60 7 modern the 39ar 14c correlation in the ocean appears to be affected by mixing of waters of different age and by more efficient raising of 39ar in the deepwater formation processes

circulation of the pacific ocean seen in a global ocean model ocean circulation and climate advanced modelling project occam this paper compares observations made in the pacific ocean and the 8 12 year climatology of a global numerical model meridional mass and heat transports and their divergences are calculated and zonal averages compared with the air sea exchange values of doney et al 1998 with mixed success the large scale distribution of sea surface height and near surface currents are shown to be well reproduced by the model but their variance is underestimated severely so in areas of weak variability synoptic wind forcing enhances the latter though only slightly while higher model resolution improves agreement in areas of strong variability model mean transports in the east australian current in the vitiaz strait and in the kuroshio exceed measurements by 10 0 18 sv respectively and variability is underestimated by factors between 2 and 4 near 1000 m and in strong currents the flow is overestimated but over most of the ocean model output does not match either the magnitude or the spatial variability of the observations in contrast the inflow of bottom water and its spreading path throughout both south and north pacific is well described good agreement is found with measured transport through the samoan passage but at 32 s east of the tonga kermadec ridge the model yields only 60 of the observed value the sverdrup balance is shown to hold widely in the model interior utilizing the complete depth integrated vorticity equation it is found that bottom pressure torques balance the advection of planetary vorticity in both surface and bottom intensified western boundary currents

transport of bottom water in the romanche fracture zone and the chain fracture zone abstract two moored arrays deployed in the romanche fracture zone and chain fracture zone in the equatorial atlantic ocean provide two year long time series of current and temperature in the lower north atlantic deep water and the antarctic bottom water total time averaged transport of antarctic bottom water potential temperature 1 9 c across the mid atlantic ridge amounts to 1 22 106 m3 s 1 eastward with a standard deviation of 0 25 106 m3 s 1 a time averaged transport of 0 36 0 23 106 m3 s 1 eastward is found for the lower north atlantic deep water in the 1 9 2 1 c temperature range but this may represent only a fraction of the total flow of this water mass across the ridge contributions of the romanche fracture zone and chain fracture zone to the antarctic bottom water transport are similar while the chain fracture zone has the greater share of lower north atlantic deep water transport semiannual and annual periods are detected in the transport time series and together expl

reconstruction of east west deep water exchange in the low latitude atlantic ocean over the past 25 000 years radiogenic neodymium isotopes have been used as a water mass mixing proxy to investigate past changes in ocean circulation here we present a new depth transect of deglacial neodymium isotope records measured on uncleaned planktic foraminifera from five cores spanning from 3300 to 4900 m on the mauritanian margin in the tropical eastern atlantic as well as an additional record from 4000 m on the ceara rise in the equatorial western atlantic despite being located under the saharan dust plume the eastern atlantic records differ from the composition of detrital inputs through time and exhibit similar values to the western atlantic foraminiferal nd across the deglaciation therefore we interpret the foraminiferal values as recording deep water nd isotope changes all six cores shift to less radiogenic values across the deglaciation indicating that they were bathed by a lower proportion of north atlantic deep water during the last glacial maximum lgm relative to the holocene the eastern atlantic records also show that a neodymium isotope gradient was present during the lgm and during the deglaciation with more radiogenic values observed at the deepest sites a homogeneous water mass observed below 3750 m in the deepest eastern atlantic during the lgm is attributed to the mixing of deep water by rough topography as it passes from the western atlantic through the fracture zones in the mid atlantic ridge this implies that during the lgm the low latitude deep eastern atlantic was ventilated from the western atlantic via advection through fracture zones in the same manner as occurs in the modern ocean comparison with carbon isotopes indicates there was more respired carbon in the deep eastern than deep western atlantic during the lgm as is also seen in the modern atlantic ocean

on climate and abyssal circulation in the atlantic ocean during late pliocene marine isotope stage m2 3 3 million years ago abstract marine isotope stage mis m2 3 3 ma is an isolated cold stage punctuating the benthic oxygen isotope 18o stratigraphy of the warm piacenzian interval of the late pliocene epoch the prominent 0 65 18o increase that defines mis m2 has prompted debate over the extent to which it signals an early prelude to the rhythmic extensive glaciations of the northern hemisphere that characterise the quaternary and raised questions about the forcing mechanisms responsible recent work suggests that co2 storage in the deep atlantic ocean played an important role in these events but detailed reconstructions of deep ocean chemical stratification are needed to test this idea and competing hypotheses here we present new records of the nd isotope composition of fish debris and 13c and b ca ratios of benthic foraminifera from the northwest and southeast atlantic ocean our novel geochemical data show that in contrast to major quaternary glaciations such as mis 2 21 ka and mis 100 2 52 ma the deep north atlantic ocean was weakly chemically stratified during mis m2 we show that southern component water incursion into the atlantic ocean was limited to the deep south atlantic basin during mis m2 and peaked well before 10 15 kyr the atmospheric co2 minimum our findings imply that the deep atlantic ocean was not the principle sink of co2 sequestered from the atmosphere during mis m2 implicating a different co2 storage deep water reservoir mechanism presumably southern component water incursion into the pacific ocean weak chemical stratification in the deep atlantic ocean during mis m2 relative to mis 100 and 2 suggests comparatively active atlantic meridional overturning circulation that suggestion is consistent with the warmth of the high latitude north atlantic during mis m2 surface water temperatures cooled during m2 but only close to holocene values our findings may help to explain the paucity of evidence for extensive early glaciation of the northern hemisphere during m2 but leave open the possibility of ice sheet advance on antarctica

atoll stratigraphy as a record of sea level change problems and prospects stratigraphic hiatuses and solution unconformities in the subsurface of enewetak atoll northern marshall islands record periods of atoll emergence during low stands of sea level changes in sea level are also recorded in the atoll subsurface by variations in the rate of sediment accumulation relative to the subsidence rate of the underlying volcanic edifice past sea levels can be derived from atoll stratigraphy by correcting the present depth of dated subsurface horizons for thermal subsidence and lithospheric flexure since the time of deposition a correction for depositional paleodepth may also be necessary as a result of erosion and nondeposition during periods of emergence the history of sea level derived in this manner is discontinuous past sea levels derived from atoll stratigraphy can only be estimated to within 50 m relative to present sea level owing to uncertainties in the corrections for subsidence and flexure however the minimum magnitude of sea level falls estimated from stratigraphic hiatuses can be estimated to within 10 m owing to limited fossil based age resolution only long term sea level trends can be deduced from sediments dated by means of biostratigraphy based on the biostratigraphic ages of subsurface horizons at enewetak we can discern very little long term change in sea level from late eocene through late oligocene a rise to 110 m above present sea level in the early miocene a long term fall of 170 m through middle and late miocene time and a long term rise of 60 m from the end of the miocene to present resolution of the sea level history recorded beneath mid ocean atolls may be improved by determining the age of shallow marine carbonates by means of strontium isotope stratigraphy our interpretation of past sea levels based on 87sr 86sr chronostratigraphy from enewetak confirms the long term sea level trends inferred from biostratigraphic subsurface ages in addition we interpret three oligocene sea level falls with minimum magnitudes of 30 50 m at 35 33 30 and 25 ma and four miocene sea level falls greater than 30 95 m at 16 14 12 10 and 5 ma these estimates of the timing and magnitude of oligocene and miocene sea level changes derived from enewetak atoll stratigraphy are compared with sea level histories derived from continental margin stratigraphy and from ice volume changes inferred from deep sea foraminifera 18o records

the atlantic deep western boundary current water masses and transports near the equator the distributions and transports of deepwater masses at the western boundary in the tropical atlantic off brazil have been studied on three surveys along 35 degrees w and 5 degrees s and one at 10 degrees s transports are obtained from direct measurements of the velocity fields pegasus profiling system and lowered acoustic doppler current profiler and from geostrophic computations using chlorofluoromethane cfm and hydrographic distributions four water masses could be identified forming the north atlantic deep water nadw system two of these have a high cfm content the shallow upper nadw sunadw and the overflow lower nadw olnadw these exhibit the highest velocity signals at 35 degrees w where distinct flow cores seem to exist most of the southeastward flow of the sunadw centered around 1600 m occurs 320 km offshore between 3 degrees 09 s and 1 degrees 50 s 9 7 3 3 sv farther north in that section a highly variable reversing flow is found in a second velocity maximum the transport of olnadw centered around 3800 m of 4 6 2 6 sv is guided by the parnaiba ridge at 1 degrees 45 s 35 degrees w the water masses located between the two cfm maxima the labrador sea water lsw and the lnadw old water mass lnadw old did not show any persistent flow features however a rather constant transport of 11 1 2 6 sv was observed for these two layers the total southeastward flow of the nadw at 35 degrees w showed a transport of 26 8 7 0 sv if one neglects the reversing sunadw north of 1 degrees 50 s at 5 degrees s the flow of all deepwater masses shows vertically aligned cores the main southward transport occurred near the coast 19 5 5 3 sv the boundary current is limited offshore by a flow reversal present in all three surveys but located at different longitudes at 10 degrees s a southward transport of 4 7 sv was observed in november 1992 however the section extended only to 32 degrees 30 w so that probably a significant part of the flow has been missed an important result is the large transport variability between single cruises as well as variability of the spatial distribution of the flow at 35 degrees w which could lead to large uncertainties in the interpretation of single cruise observations despite these uncertainties we suggest a circulation pattern of the various deepwater masses near the equator by combining our mean transport estimates with other observations

application of the trace element and isotope geochemistry of strontium to studies of carbonate diagenesis carbonate rocks and natural waters exhibit a wide range in the concentration and isotopic composition of strontium this wide range and the quantifiable covariation of these parameters can provide diagnostic tools for understanding processes of fluid rock interaction careful consideration of the uncertainties associated with trace element partitioning sample heterogeneity and fluid rock interaction mechanisms is required to advance the application of the trace element and isotope geochemistry of strontium to studies of diagenesis goundwater evolution ancient seawater chemistry and isotope stratigraphy a principal uncertainty involved in the application of sr concentration variations to carbonate systems is the large range of experimental and empirical results for trace element partitioning of sr between mineral and solution this variation may be a function of precipitation rate mineral stoichiometry crystal growth mechanism fluid composition and temperature calcite and dolomite in ancient limestones commonly have significantly lower sr concentrations 20 70 p p m than would be expected from published trace element distribution coefficient values and sr ca ratios of most modern sedimentary pore waters this discrepancy probably reflects the uncertainties associated with determining distribution coefficient values as techniques improve for the analytical measurement and theoretical modelling of sr concentration and isotopic variations the petrological analysis of carbonate samples becomes increasingly important the presence of even small percentages of non carbonate phases with high rb concentrations and high 87 sr86 sr values such as clay minerals can have significant effects on the measured 87 sr 86 sr values of carbonate rocks due to the decay of 87rb to 87 sr for example a permian marine limestone with 50 p p m sr and 1 p p m rb will have a present day 87 sr 86 sr value that is 2 10 4 higher than its original value this difference is an order of magnitude greater than the analytical uncertainty and illustrates the importance of assessing the need for and accuracy of such corrections a quantitative evaluation of the effects of water rock interaction on sr concentrations and isotope compositions in carbonates strengthens the application of these geochemical tracers geochemical modelling that combines the use of trace elements and isotopes can be used to distinguish between different mechanisms of water rock interaction including diffusive and advective transport of diagenetic constituents in meteoric pore fluids during the recrystallization of carbonate minerals quantitative modelling may also be used to construct diagnostic fluid rock interaction trends that are independent of distribution coefficient values and to distinguish between mixing of mineral end members and fluid rock interaction

the velocity and vorticity structure of the agulhas current at 32 s the full depth velocity field of the agulhas current the western boundary current of the southwest indian ocean has been directly measured using a lowered acoustic doppler current profiler ladcp fifteen combined conductivity temperature depth ctd and ladcp stations were occupied across the current at 32 s off the east coast of south africa in february march 1995 as part of the world ocean circulation experiment indian ocean program the deep velocity structure of the agulhas current was found to be very different than previously described using geostrophic estimates in particular ladcp results reveal a v shaped pattern for the level of no motion across the agulhas current and an agulhas undercurrent is observed flowing equatorward below 800 m depth directly beneath the surface core of the poleward flowing agulhas current comparisons of direct and geostrophic velocities suggest that the velocity structure of the agulhas current is essentially geostrophic below about 200 m depth where differences are generally less than estimated errors above these depths the ladcp measured shears and geostrophic shears exhibit differences and velocities can diverge shipboard adcp data support ladcp results near the surface indicating that both instruments are measuring real signals the geostrophic and ladcp measured shears are well matched away from the surface and a depth averaged fit below 200 m between them exhibits small standard deviations the geostrophic volume transport of the agulhas current as referenced to ladcp is 73 sv and is just 3 different from the direct ladcp transport estimate the most recent full depth estimate of agulhas current transport in the literature is given by toole and warren 1993 who estimate a geostrophic volume transport of 85 sv the baroclinic velocity structures from their section and from this work are similar indicating that the difference in the transport estimates is due to the choice of geostrophic reference level and ultimately to the presence of the previously unobserved agulhas undercurrent combined ctd ladcp data are very useful for potential vorticity analysis since velocity and density measurements are simultaneous and coincident the vorticity structure of the agulhas current suggests the presence of a mixing boundary at middepths similar to features observed in the gulf stream the feature appears to be associated with a sharp upturn in isopycnals coincident with the foot of the continental slope the boundary inhibits cross stream mixing of intermediate water masses and may help explain the appearance of a discrete filament of red sea water inshore of antarctic intermediate waters in the same density layer despite intense cross stream shears

mixing in the romanche fracture zone the romanche fracture zone is a major gap in the mid atlantic ridge at the equator which is deep enough to allow significant eastward flows of antarctic bottom water from the brazil basin to the sierra leone and guinea abyssal plains while flowing through the romanche fracture zone bottom water properties are strongly modified due to intense vertical mixing the diapycnal mixing coefficient in the bottom water of the romanche fracture zone is estimated by using the finestructure of ctd profiles the microstructure of high resolution profiler data and by constructing a heat budget from current meter data the finestructure of density profiles is described using the thorpe scaleslt it is shown from microstructure data taken in the bottom water that the ozmidov scale lo is related to lt by the linear relationship lo 5 0 95lt similar to other studies which allows an estimate of the diapycnal mixing coefficient using the osborn relation the thorpe scale and the diapycnal mixing coefficient estimates show enhanced mixing downstream eastward of the main sill of the romanche fracture zone in this region a mean diapycnal mixing coefficient of about 1000 3 1024 m2 s21 is found for the bottom water estimates of cross isothermal mixing coefficient derived from the heat budgets constructed downstream of the current meter arrays deployed in the romanche fracture zone and the nearby chain fracture zone are in agreement with the finestructure estimates of the diapycnal mixing coefficient within the romanche fracture zone although the two fracture zones occupy only 0 4 of the area covered by the sierra leone and guinea abyssal plains the diffusive heat fluxes across the 1 4 8c isotherm in the romanche and chain fracture zones are half that found over the abyssal plains across the 1 88c isotherm emphasizing the role of these passages for bottom water property modifications

sea surface velocities from sea surface temperature image sequences 2 application to the brazil malvinas confluence area an inverse variational model is applied to four exceptionally cloud free sea surface temperature image sequences of the brazil malvinas confluence area for the purpose of estimating sea surface velocity fields the velocity fields are constructed by minimizing a mixed layer integrated form of the heat balance equation while the horizontal divergence and vorticity of the flow field are controlled the source terms involved in the heat balance are determined by fitting a polynomial to diurnal temperature variations as a function of temperature and longitude a sensitivity study of the solution to perturbations of the weights imposed to the constraints on divergence and vorticity as well as of the representation of the source terms yields error fields associated with the velocity a comparison of the estimated velocity fields with available concomitant in situ velocity measurements shows that the fields are realistic errors are of the order of 15 20 in magnitude and 20 25 in direction these errors fall within the error bars of 25 30 in magnitude and of 30 35 in direction except for the summer image series surface velocities of 0 5 0 6 m s 1 are obtained across the malvinas current they are 1 m s 1 in the frontal region in the brazil current overshoot and in warm and cold core rings and vary between 0 3 and 0 8 m s 1 in the brazil current with some hypotheses on the vertical shear of the horizontal flow the transport of the malvinas current is estimated to be 25 5 sv between 41 and 40 s

the geochemistry of carbonate diagenesis the past present and future stable carbon and oxygen isotopes 18o and 13c values and trace elements have been applied to the study of diagenesis of carbonate rocks for over 50 years as valuable as these insights have been many problems regarding the interpretation of geochemical signals within mature rocks remain for example while the 18o values of carbonate rocks are dependent both upon the temperature and the 18o value of the fluid and additional information including trace element composition aids in interpreting such signals direct evidence of either the temperature or the composition of the fluids is required such information can be obtained by analysing the 18o value of any fluid inclusions or by measuring the temperature using a method such as the clumped isotope technique such data speak directly to a large number of problems in interpreting the oxygen isotope record including the well known tendency for 18o values of carbonate rocks to decrease with increasing age unlike the 18o 13c values of carbonates are considered to be less influenced by diagenesis and more a reflection of primary changes in the global carbon cycle through time however many studies have not sufficiently emphasized the effects of diagenesis and other post depositional influences on the eventual carbon isotopic composition of the rock with the classic paradigm that the present is the key to the past being frequently ignored finally many additional proxies are poised to contribute to the interpretation of carbonate diagenesis although the study of carbonate diagenesis is at an exciting point with an explosion of new proxies and methods care should be taken to understand both old and new proxies before applying them to the ancient record

late quaternary barrier and fringing reef development of bora bora society islands south pacific first subsurface data from the darwin type barrier reef system the universally known subsidence theory of darwin based on bora bora as a model was developed without information from the subsurface to evaluate the influence of environmental factors on reef development two traverses with three cores each on the barrier and the fringing reefs of bora bora were drilled and 34 uranium series dates obtained and subsequently analysed sea level rise and to a lesser degree subsidence were crucial for holocene reef development in that they have created accommodation space and controlled reef architecture antecedent topography played a role as well because the holocene barrier reef is located on a pleistocene barrier reef forming a topographic high the pedestal of the fringing reef was pleistocene soil and basalt barrier and fringing reefs developed contemporaneously during the holocene the occurrence of five coralgal assemblages indicates an upcore increase in wave energy age depth plots suggest that barrier and fringing reefs have prograded during the holocene the holocene fringing reef is up to 20 m thick and comprises coralgal and microbial reef sections and abundant unconsolidated sediment fringing reef growth started 8780 50 yr bp accretion rates average 5 65 m kyr 1 the barrier reef consists of 30 m thick holocene coralgal and microbial successions holocene barrier reef growth began 10 030 50 yr bp and accretion rates average 6 15 m kyr 1 the underlying pleistocene reef formed 116 900 1100 yr bp i e during marine isotope stage 5e based on pleistocene age depth and coralgal palaeobathymetry the subsidence rate of bora bora was estimated to be 0 05 to 0 14 m kyr 1 in addition to subsidence reef development on shorter timescales like in the late pleistocene and holocene has been driven by glacioeustatic sea level changes causing alternations of periods of flooding and subaerial exposure comparisons with other oceanic barrier reef systems in tahiti and mayotte exhibit more differences than similarities

modern seawater acidification the response of foraminifera to high co2 conditions in the mediterranean sea abstract the seas around the island of ischia italy have a lowered ph as a result of volcanic gas vents that emit carbon dioxide from the sea floor at ambient seawater temperatures these areas of acidified seawater provide natural laboratories in which to study the long term biological response to rising co 2 levels benthic foraminifera single celled protists are particularly interesting as they have short life histories are environmentally sensitive and have an excellent fossil record here we examine changes in foraminiferal assemblages along ph gradients at co 2 vents on the coast of ischia and show that the foraminiferal distribution diversity and nature of the fauna change markedly in the living assemblages as ph decreases

sr isotopic variation in shallow water carbonate sequences stratigraphic chronostratigraphic and eustatic implications of the record at enewetak atoll sr isotope data from two boreholes within the lagoon at enewetak atoll have been used to evaluate the use of such data to correlate date and monitor sea level change in shallow water carbonate sequences correlative stratigraphic intervals of relatively invariant 87sr separated by abrupt transitions to lower 87sr with increasing depth are recognized in both boreholes conversion of 87sr values to age via calibration with the seawater 87sr trend with age indicates that correlative and synchronous deposition of atoll sediments occurred at 0 4 1 2 and 2 1 ma in contrast a 5 m y hiatus is recognized in one borehole but not the other sr isotope stratigraphy sis is a powerful stratigraphic and chronostratigraphic tool in shallow water carbonate sequences only when significant secular variation of 87sr occurs and retention of depositional 87sr values is demonstrated the latter is best demonstrated when 87sr data are integrated with 18o 13c sr content data and petrographic observations several diagenetically altered intervals have greater 87sr values low 13c values and low sr ca ratios relative to adjacent intervals a combination that is consistent with open system meteoric diagenesis calcite cements from these intervals have early pleistocene 1 2 ma 87sr values despite their occurrence well within the late pliocene 2 1 ma sequence thus local sedimentological and diagenetic processes have produced intralagoon variability in the sis of the two boreholes complicating subsurface stratigraphic correlations the occurrence of anomalously young calcite cement relative to adjacent limestone is a direct response of the interaction of sea level change and meteoric phreatic diagenesis whereby overlying metastable carbonates with greater 87sr values are dissolved during periods of atoll emergence and sea level lowstand liberating sr and soil gas co2 to the pore fluid which is then incorporated into downflow meteoric phreatic diagenetic calcite the stratigraphic relation between the sites of carbonate dissolution and diagenetic calcite precipitation suggest an early pleistocene 1 2 ma sea level fall of between 34 and 64 m moreover the stratigraphic position and inferred age of paleophreatic lens calcite when backtracked for subsidence suggest that early pleistocene 1 2 ma sea level was 72 81 m range of 60 100 m below present sea level the enewetak record of early pleistocene sea level lowstand elevation agrees reasonably well with proxy sea level records inferred from sequence stratigraphy and deep sea foraminiferal 18o data however the enewetak record of the amplitude of early pleistocene sea level change is more consistent with the deep sea foraminiferal 18o proxy than the sequence stratigraphy proxy

nonuniform upwelling in a shallow water model of the antarctic bottom water in the brazil basin a numerical model based on the shallow water equations is developed to represent the flow of antarctic bottom water aabw in the brazil basin southwest atlantic ocean the aim is twofold first an attempt is made to identify in a model that includes both simplified dynamics and realistic bathymetry at 1 68 resolution the impacts of the elevated diapycnal mixing rates near the mid atlantic ridge mar documented by dissipation data of the deep basin experiment dbe to this end different assumptions regarding the distribution of the velocity across the aabw layer interface w are considered second the extent to which the shallow water model can replicate observations relative to aabw circulation in the basin in particular the trajectory and velocity of neutrally buoyant floats released in the aabw during the dbe is examined the model flows are characterized by small rossby numbers except in the northward flowing western boundary current where kinetic energy is largely concentrated to interpret the flows model streamlines are compared with isopleths of linear potential vorticity f h0 of the shallow water theory f is the planetary vorticity and h0 is the layer thickness in the absence of motion the f h0 contours are oriented northwest southeast in the western part of the basin and southwest northeast in the eastern part reflecting the bowl shaped topography of the southern hemisphere basin with a spatially uniform positive w the ubiquitous vortex stretching produces a flow to the southeast consistent with the stommel arons theory this flow occurs in most of the basin interior even in the east where f h0 contours converge to the northeastern end of the basin with strongly positive w near the ridge and zero or slightly negative w elsewhere the flow follows more closely f h0 contours in the western interior and intersects them near the ridge the confinement of the diapycnal mass flux near the mar drastically reduces the southward flow in the interior or even reverses its direction leading to a circulation quite distinct from that of the stommel arons theory the model results compare favorably to some but not all hydrographic estimates of aabw circulation patterns and rates on the other hand the model streamlines and velocities show important differences with respectively the trajectory and the velocity of the floats launched in the aabw layer the prescription of vanishing w in the interior does not systematically improve the fit of the model streamlines to the float trajectories and the model velocities simulated with spatially uniform w or spatially variable w are on average smaller by one order of magnitude than the float velocities a variety of mechanisms which are not included in the numerical experiments may explain the differences between the model results and the float data

origin of atoll dolomites distinguished by geochemistry and crystal chemistry kita daito jima northern philippine sea abstract kita daito jima is a carbonate island located at the northwestern region of the philippine sea 25 55 6 57 6 n 131 16 9 19 8 e dolomites extend from the island surface to a depth of 100 m below the ground surface mbgs strontium isotope stratigraphy indicates that subsurface units c1 0 49 7 mbgs and c2 49 7 103 4 mbgs were dolomitized at 5 5 ma and 2 0 ma respectively and that island surface dolomites are products of dolomitization at 1 6 2 0 ma x ray diffraction analysis indicates that the island surface and borehole dolomites comprise variable mixtures of four and three dolomite crystal phases respectively each of these phases is distinguished by a different ca and mg content three textural types can be recognized in the kita daito jima dolomites fabric preserving crystalline nonmimetic cnm crystalline mimetic cm and fabric preserving microsucrosic ms cnm dolomites contain more calcian phases whereas ms dolomites commonly are richer in more stoichiometric phases backscattered electron images indicate that calcian dolomite phases were precipitated earlier than the more stoichiometric dolomite phases and that there is no significant hiatus between the phases although they are diachronous both the island surface and borehole cores dolomites show linear relationships between whole rock 18o composition and mg contents and between whole rock trace element concentrations sr and na and mg contents these covariances result from phase mixing not stoichiometric effects deconvolution of whole rock isotopic and elemental compositions based on the relative abundance of phases reveals that each phase has a distinct chemical and isotopic composition oxygen isotopic compositions of the island surface and borehole dolomites suggest that all dolomite phases formed in seawater and that dolomitization primarily occurred during glacio eustatic sea level lowstands and cooler ocean temperatures

impact of the gravity field and steady state ocean circulation explorer goce mission on ocean circulation estimates 2 volume and heat fluxes across hydrographic sections of unequally spaced stations 1 accurate geoids are expected to improve our knowledge of the dynamic sea surface height ssh as a mirror of the dynamic state of the oceans the dedicated gravity field and steady state ocean circulation explorer goce mission will lead to a highly accurate geoid model with a resolution of degree and order 200 we examine the impact of this mission on the assessment of large scale oceanic mass and heat transports via its expected error characteristics we do so applying a linear box inverse model and a nonlinear section inverse model to hydrographic data and to synthetic ssh data the results are compared to those obtained when substituting the error estimates of the gravity recovery and climate experiment grace mission and the present day earth gravitational model 1996 for the box inverse model we find an average reduction in transport uncertainties of about 9 for grace geoid error covariances and about 17 for goce over the hydrography only solution in both grace and goce these average percentage improvements are significantly increased when model error is excluded summarizing our results and those of the companion parts of this study we conclude that the grace mission reduces the marine geoid uncertainties such that altimetry may become useful for the study of the steady state ocean circulation the goce mission will improve the accuracy of the circulation estimates significantly on the large scales and introduce higher accuracy on shorter wavelengths as well furthermore it will enable us to study individual ocean currents

the high supply current dominated continental margin of southeastern south america during the late quaternary the continental margin off the la plata estuary se south america is characterized by high fluvial sediment supply and strong ocean currents high resolution sediment acoustic data combined with sedimentary facies analysis ams 14c ages and neodymium isotopic data allowed us to reconstruct late quaternary sedimentary dynamics in relation to the two major sediment sources the la plata estuary and the argentine margin sediments from these two provinces show completely different dispersal patterns we show that the northward trending la plata paleo valley was the sole transit path for the huge volumes of fluvial material during lower sea levels in contrast material from the argentine margin sector was transported northwards by the strong current system despite the large sediment volumes supplied by both sources wide parts of the shelf were characterized by either persistent non deposition or local short term depocenter formation the location and formation history of these depocenters were primarily controlled by the interplay of sea level with current strength and local morphology the high sediment supply was of secondary importance to the stratigraphic construction though locally resulting in high sedimentation rates thus the shelf system off the la plata estuary can be considered as a hydrodynamic controlled end member

growth demise and dolomitization of miocene carbonate platforms on the marion plateau offshore ne australia abstract strontium isotope stratigraphy has been used to examine the timing of depositional events and dolomitization in two miocene carbonate platforms cored by ocean drilling program odp leg 194 just seaward of the great barrier reef the results provide firm constraints for correlating surfaces and depositional stages between the two platforms and thereby relating seismic sequences previously defined in the off platform sediments to the lithostratigraphic units described from cores in the seismically transparent platform top sites oyster bearing beds at the base of both platform successions yield early oligocene ages 29 31 ma thus dating initial transgression of the marion plateau s volcanic basement there followed a period of slow accumulation of shallow water grainstones rich in quartz and phosphate grains in late oligocene time 29 23 ma seismic megasequence a the main growth of the carbonate platforms took place in early to late miocene time 23 7 ma comprising five depositional sequences the first four of these seismic megasequence b are common to both platforms and terminated with a possible karst surface at 10 7 ma different sedimentologic expression of this megasequence in the two platforms reflects contrasting progradational versus aggradational geometries in the locations studied the final growth stage seismic megasequence c occurred only in the southern platform and terminated at 6 9 ma both platform demise events 10 7 and 6 9 ma approximately coincide with falls in global sea level combined with longer term trends of decreasing water temperature sr isotope ages of dolostones increase with depositional age and older dolostones in the southern platform have more coarsely crystalline and fabric destructive textures than overlying younger dolostones these relationships are consistent with dolomitization by normal seawater shortly after deposition and overprinting of multiple times of dolomite recrystallization and cementation in the deeper strata

spatial variability of turbulent mixing in the abyssal ocean ocean microstructure data show that turbulent mixing in the deep brazil basin of the south atlantic ocean is weak at all depths above smooth abyssal plains and the south american continental rise the diapycnal diffusivity there was estimated to be less than or approximately equal to 0 1 x 10 4 meters squared per second in contrast mixing rates are large throughout the water column above the rough mid atlantic ridge and the diffusivity deduced for the bottom most 150 meters exceeds 5 x 10 4 meters squared per second such patterns in vertical mixing imply that abyssal circulations have complex spatial structures that are linked to the underlying bathymetry

extremely long kelvin helmholtz billow trains in the romanche fracture zone in the atlantic ocean the densest water mass antarctic bottom water aabw can only cross the mid atlantic ridge from its southwestern to northeastern basins in limited because deep conduits at the southwestern entrance of one of these the equatorial romanche fracture zone aabw crosses a sill at 4550 m depth in a 7 km narrow channel before plunging into the deep at the sill slope the rapidly flowing aabw causes shear induced turbulent mixing with the overlying water masses we present an excerpt of 1 hz sampled half yearlong moored observations from 99 high resolution temperature sensors that demonstrate and quantify the turbulence details on top of quasi steady shear flow an internal tide modulates the mixing together they constitute a means for an extremely long train of 250 consecutive kelvin helmholtz billows in a day that vary between 5 and 100 m in vertical scale

circulation and water mass modification in the brazil malvinas confluence abstract the confluence between the brazil current and the malvinas current the brazil malvinas confluence bmc in the argentine basin is characterized by a complicated thermohaline structure favoring the exchanges of mass heat and salt between the subtropical gyre and the antarctic circumpolar current acc analysis of thermohaline properties of hydrographic sections in the bmc reveals strong interactions between the acc and subtropical fronts in the subantarctic front subantarctic mode water samw antarctic intermediate water aaiw and circumpolar deep water cdw warm become saltier by 0 4 0 08 0 3 0 02 and 0 6 c 0 1 respectively in the subtropical gyre aaiw and north atlantic deep water have cooled freshened by 0 4 0 07 and 0 7 c 0 11 respectively to quantify those acc subtropical gyre interactions a box inverse model surrounding the confluence is built the model diagnoses a subduction of 16 4 sv 1 sv 106 m3 s 1 of newly formed samw and aaiw under the subtro

turbulent mixing in a deep fracture zone on the mid atlantic ridge abstractmidocean ridge fracture zones channel bottom waters in the eastern brazil basin in regions of intensified deep mixing the mechanisms responsible for the deep turbulent mixing inside the numerous midocean fracture zones whether affected by the local or the nonlocal canyon topography are still subject to debate to discriminate those mechanisms and to discern the canyon mean flow two moorings sampled a deep canyon over and away from a sill contraction a 2 layer exchange flow accelerated at the sill transports 0 04 0 10 sv 1 sv 106 m3 s 1 up canyon in the deep layer at the sill the dissipation rate of turbulent kinetic energy e increases as measured from microstructure profilers and as inferred from a parameterization of vertical kinetic energy cross sill density and microstructure transects reveal an overflow potentially hydraulically controlled and modulated by fortnightly tides during spring to neap tides e varies from o 10 9 to o 10 10 w kg 1 below 3500 m around the 2 layer inte

evolution of the deep western boundary current of antarctic bottom water in the brazil basin abstract a synthesis of woce and other hydrographic data shows that the deep western boundary current of antarctic bottom water has a double core structure and that it is differentially modified during its northward transit through the brazil basin at 25 s it descends about 200 m while continuing equatorward as a paired double core current over the relatively broad sloping topography of the western region the downslope core is faster 4 6 cm s 1 versus 3 cm s 1 and is coincident with the high density core equatorward of 19 s the cores begin to diverge and by 15 s the velocity cores have separated and the high speed pattern has inverted between 13 and 11 s the colder slower flowing branch around 3 cm s 1 deepens by 350 m with a noticeable decrease in the vertical stratification of overlying water characteristics subsequently it continues to the equator toward the romanche chain fracture zones the warmer faster flowing branch around 8 cm s 1 proceeds to the equator along the continent

directly dating geologic events u pb dating of carbonates 1 carbonates are ubiquitous forming in a variety of settings including caves soils the oceans during burial from hydrothermal fluids and along faults u pb dating of carbonates is applicable to almost the entire geologic time scale with results from pleistocene speleothems showing great promise for dating records 1 ma old here we review studies of u pb dating of carbonates from a range of depositional and diagenetic environments and consider published results with regard to stratigraphic associations and the behavior of u and pb in various fluids we detail the steps required to select suitable samples summarize current laboratory techniques and provide directions for improvement of analytical protocols the u pb dating of carbonates has tremendous potential for dating events of geologic interest and is virtually untapped

the diabatic deacon cell abstract southern ocean air sea fluxes from the coads dataset are examined for compatibility between buoyancy gain and northward ekman transport an analysis in density classes points to an upwelling of upper circumpolar deep water and subsequent buoyancy gain from air sea exchange as water flows northward in the ekman layer the upper circumpolar deep water layer is too shallow to admit southward geostrophic flow along topography and an eddy mass flux mechanism for southward transport in this layer to replenish the upwelling is advanced based on observed large scale potential vorticity gradients estimates of the strength and vertical structure of the meridional flow are given using repeated hydrographic sections and a new climatology

nutrient mineralization rates and ratios in the eastern south atlantic the physical and biogeochemical components of nutrients and inorganic carbon distributions along woce line a14 are objectively separated by means of a constrained least squares regression analysis of the mixing of eastern south atlantic water masses contrary to previous approaches essentially devoted to the intricate south atlantic circulation this work is focused on the effects of circulation on nutrients and carbon biogeochemistry with special emphasis on the stoichiometry and the rate of mineralization processes combination of nutrient and apparent cfc age anomalies derived from the mixing analysis indicate faster mineralization rates in the equatorial 12 10 2 mol p kg 1 yr 1 and subequatorial 5 3 10 2 mol p kg 1 yr 1 than in the subtropical 4 3 10 2 mol p kg 1 yr 1 regime at the south atlantic central water sacw depth range lower rates are obtained in the antarctic intermediate water aaiw domain 3 0 10 2 mol p kg 1 yr 1 significant variation with depth of o2 c n p anomalies indicates preferential mineralization of proteins in thermocline waters as compared with the reference redfield composition

large scale mass transports water mass formation and diffusivities estimated from world ocean circulation experiment woce hydrographic data 1 a global inversion is used to estimate the oceanic mass transports and vertical diffusivities based on a subset of hydrographic data from the world ocean circulation experiment woce and java australia dynamic experiment the analysis is based on the linear inverse box model of ganachaud and wunsch 2000 that consistently combines the transoceanic sections a globally consistent solution is obtained for a depth independent adjustment to the thermal wind field the freshwater flux divergences the ekman transport and the advective and diffusive dianeutral fluxes between layers a detailed error budget permits calculation of statistical uncertainties taking into account both the nonresolved part of the solution and the systematic errors due to the temporal oceanic variability the horizontal structure of the transports for different density classes is analyzed regionally during the woce period 1985 1996 net meridional transports are estimated with 16 2 sv 106 m3 s of north atlantic deep water nadw being produced in the northern north atlantic moving southward entraining antarctic bottom water aabw and antarctic intermediate water increasing in volume transport to 23 3 sv at 30 s in the southern ocean 21 6 sv of bottom water was formed from lower circumpolar deep water which corresponds approximately to the lower nadw density range bottom water inflows nadw aabw mixture to the atlantic indian and pacific oceans are estimated at 6 1 3 11 4 and 7 2 sv respectively in the indian and pacific oceans this water returns southward at deep and intermediate levels property anomaly conservation constraints permit estimation of dianeutral diffusivities in deep layers with a global average of 3 7 0 7 cm2s 1 north of 30 s

the three dimensional overturning circulation of the southern ocean during the woce era a box inverse model of the southern ocean during the world ocean circulation experiment is constructed to investigate the three dimensional structure of the regional overturning circulation in that era the model has many features in common with various preceding inverse studies but also contains several novel elements that make it well suited for addressing many of the significant uncertainties that surround the circulation at present the net overturning circulation of the southern ocean is found to consist of two well defined cells of similar strength the upper cell consists of a northward transport of 18 8 5 5 sv of surface mode and intermediate waters lighter than the 27 5 kg m 3 isoneutral and an equivalent southward flow in the approximate 27 5 27 9 kg m 3 neutral density range encompassing the bulk of the upper circumpolar deep water the lower cell involves the northward export of 18 6 0 9 sv of antarctic bottom water and lower circumpolar deep water denser than 28 08 kg m 3 and an opposing transport in the lighter classes of that water mass substantial structural differences between the overturning circulations of the atlantic indian and pacific basins are indicated by the model s solution overall the diagnosed southern ocean circulation shares many qualitative and some quantitative features with previous inverse estimates particularly as regards the large scale depth integrated lateral circulation and associated energy fluxes in the subtropics and in the antarctic circumpolar current and the strength of the upper overturning cell however it also suggests several significant adjustments to current views of the regional circulation most notable amongst these are the subpolar circulation of the southern ocean is more vigorous and zonally interconnected than generally thought the associated lower overturning cell is more intense than indicated by most preceding estimates contrary to common perception sub surface mixing processes play a role of comparable importance to air sea ice exchanges of buoyancy in underpinning the dianeutral closure of the southern ocean overturning even at shallow mode and intermediate water levels and the connection between north atlantic deep water formation and southern ocean upwelling is fundamentally three dimensional such that deep waters from the north atlantic must upwell dianeutrally before being returned to the permanent pycnocline of the northern oceans

hydraulie control and flow separation in a multi layered fluid with applications to the vema channel abstract observations from a recent field experiment in the vema channel are briefly described these show a remarkable change in the configuration of isopycnal surfaces within the channel and the development of thick nearly homogeneous regions near the bottom which are capped by sharp vertical gradients contrary to previous speculation that these bottom boundary layer result from enhanced vertical mixing a dynamical mechanism is explored this involves the hydraulic adjustment of an inertial semi geostrophic flow to the channel geometry first an active two layer flow in a rectangular geometry is studied to show that internal flow separation can occur when the flow is accelerated sufficiently by a narrowing channel almost always this separation accompanies hydraulic control the slowest upstream moving kelvin wave is stopped and upstream and downstream states are not symmetric with respect to the channel width an active three layer flow with a variable bottom profile is then presented as a more

the flow of antarctic bottom water into the brazil basin the total transport of antarctic bottom water across the rio grande rise including the western boundary the vema channel and the hunter channel is estimated from hydrographic measurements across these pathways the contribution of the vema channel is greatest at 3 9 106 m3 s 1 which is very close to earlier estimates the western boundary current contribution is 2 0 106 m3 s 1 and that of the hunter channel 0 7 106 m3 s 1 the lower values outside the vema channel are offset by the important source of mass they form to the lower density classes of bottom water about 40 of the flow is concentrated in the highest density class representing the source of weddell sea deep water to the brazil basin the flow structure is characterized by horizontal and vertical recirculation

mg and sr uptake in benthic foraminifera ammonia aomoriensis based on culture and field studies abstract trace elements incorporated in foraminiferal test are commonly used as paleoproxies however the incorporation of trace elements is controlled by more than one environmental parameter we conducted one year sampling from june 2014 to may 2015 in the qingdao intertidal flat the yellow sea and retrieved surface samples in the jiaozhou bay 3 9 6 8 m water depth the yellow sea in february 2015 as well as performed a laboratory culture experiment under temperature 6 24 c and salinity 24 33 psu by combining 18oc values of field a aomoriensis parameters controlling mg ca and sr ca ratios of ammonia aomoriensis were investigated under constant seawater chemistry temperature dominates the magnesium incorporation into a aomoriensis test by an exponential increase of 5 1 per c mg ca 1 0980 0 2073 e0 0510 0 0097 t mg ca 0 5565 0 3897 0 1279 0 0242 t 2 4 24 c including field samples whereas temperature has no significant effect on strontium uptake calcite sr ca of a aomoriensis is primarily explained by mg ca value 3 per mmol mol salinity variations are of subordinate importance for both mg and sr content in the test of a aomoriensis mg ca raises linearly with approximately 2 per salinity unit and sr ca increases 1 per salinity unit importantly biological mechanism might be an inestimable factor perturbing mg and sr response to environmental parameters in natural waters complicating the paleoclimate reconstruction

a review of the ecological and taphonomic controls on foraminiferal assemblage development in intertidal environments intertidal foraminifera from surface sediments are commonly used as a high resolution indicator of sea level change the integrity of this approach is based upon the assumption that surface assemblages are similar in composition to their buried fossil counterparts this assumption may in some cases be inappropriate due to subsurface or infaunal production and taphonomic alteration here we review the current understanding of foraminiferal production and taphonomic loss in intertidal environments and examine the extent to which these processes can affect the development of foraminiferal assemblages in intertidal environments as a sediment layer undergoes burial dead tests are added at a rate proportionate to the standing crop at that depth as a consequence test accumulation within the layer is proportionate to the depth integrated standing crop depending on the nature of its vertical living distribution the upper 1 cm of sediment may therefore not adequately characterise a given species total input instead a comparison of each species contribution to the entire depth integrated living community may offer a better a priori estimate of relative input to the sediment column this provides an improved base line for identifying true taphonomic trends downcore the potential for infauna to create discrepancies between surface and subsurface assemblages may be minimised however where 1 reproduction is concentrated near to the sediment surface transforming an apparent infaunal standing crop into an effective epifaunal production 2 the living fauna is composed similarly at all depths of production and or 3 intense bioturbation homogenises the upper sediment layers the likely decline in the intensity of taphonomic processes with depth may mean that the foraminiferal production from different depths may not experience taphonomic processes uniformly consequently in addition to their possible gradual enrichment due to subsurface production infaunal species may be preferentially preserved by virtue of their production closer to the base of the taphonomically active zone additionally homogenisation of the sediment column by reworking may mix temporally and perhaps environmentally distinct faunas affecting the stratigraphic integrity of the sediment deposit the most important taphonomic processes in intertidal environments are those associated with early diagenesis while the organic cements of agglutinated taxa may be directly oxidised the associated changes in the saturation state of porewaters with respect to calcium carbonate may affect calcareous species the type of diagenetic reaction operating within the sediment provides a quantitative control on agglutinated test degradation but a largely qualitative control on calcareous preservation in addition calcareous test preservation is dependent upon the rate with which organic matter is supplied while agglutinated test preservation is independent of organic matter concentrations although the specific morphological pathways of test degradation for calcareous species are well understood the stages under which agglutinated tests are lost are less clear the combined but varying influences of production infaunal and species composition taphonomic processes and bioturbation may create complex pathways in the transition from live to dead to fossil assemblages understanding the extent to which infauna taphonomic loss and sediment reworking affect assemblage development in different intertidal environments is essential in order to interpret the fossil record

eocene to early miocene growth of enewetak atoll insight from strontium isotope data the margin of enewetak atoll contains 1 260 to 1 405 m of cenozoic carbonates above a volcanic basement previous biostratigraphic studies on two deep wells e1 and f1 yielded conflicting results on the ages of tertiary strata on enewetak and on the presence of oligocene strata strontium isotope ratios support relatively continuous carbonate sedimentation from late eocene to early miocene 23 ma carbonate deposition on the atoll margin started with rapid aggradation during much of the late eocene followed by gradual seaward progradation of depositional facies during the latest eocene oligocene and early miocene the only distinct break in sedimentation from late eocene to early miocene was observed at 850 m in the e1 well here an unconformity formed by subaerial exposure separates backreef upper eocene grainstones from lower oligocene carbonates no contemporaneous subaerial exposure surface and unconformity were observed in the f1 well because correlative rocks were deposited in a slope environment extensive diagenesis occurred in upper eocene oligocene and lower miocene strata at the atoll margin where sea water circulated through in response to thermal convection and tidal pumping the main diagenesc processes are 1 aragonite dissolution 2 radiaxial calcite cementation 3 compaction in slope deposits and 4 dolomitization aragonite dissolution is pervasive below 375 m in the f1 well radiaxial calcite cement is common at 375 825 m in the f1 well compaction related fracturing and pressure solution are common in poorly cemented packstones and grainstones deposited in a slope environment and now buried more than 1 100 m deep dolomite is common in slope carbonates at 1 320 m in the f1 well and in reefal carbonates at 1 245 m in the e1 well stable carbon and oxygen isotope data support formation of radiaxial calcite and dolomite in cool sea water radiaxial calcite cement and dolomite have distinctly higher 87sr 86sr ratios than does adjacent depositional carbonate strontium isotope ratios of radiaxial calcite cements indicate precipitation at burial depths of 100 350 m the absence of meteoric cements and association of radiaxial calcite cement with aragonite dissolution suggest that aragonite dissolution also occurred in moderately deep sea water strontium isotope ratios in dolomites indicate dolomitization by sea water at burial depths greater than 950 m marine diagenesis is dependent on the saturation state of sea water relative to aragonite calcite and dolomite shallow sea water supersaturated with respect to aragonite and high magnesium calcite hmc precipitates aragonite and hmc moderately deep sea water undersaturated with respect to aragonite and hmc super saturated with respect to low magnesium calcite lmc dissolves aragonite converts hmc to lmc and precipitates lmc including radiaxial calcite deep sea water under saturated with respect to calcite supersaturated with respect to dolomite dissolves calcite and precipitates dolomite the intensity of marine diagenesis depends on the amount of sea water circulating through the platform or atoll margin

bottom water throughflows at the rio de janeiro and rio grande fracture zones bottom water throughflows at the rio de janeiro fracture zone 22 s and rio grande fracture zone 26 s of the mid atlantic ridge are identified from hydrographic anomalies observed along 9 w in the angola basin the throughflow water is supplied by a meridional band of cold and fresh water lying against the western flank of the ridge

intense mixing of antarctic bottom water in the equatorial atlantic ocean the spreading of antarctic bottom water the densest global scale water mass is highly constrained by ocean floor topography in the atlantic ocean the mid atlantic ridge confines this water mass mainly to the western basins the bottom waters in the eastern basins being renewed by flows through gaps in the ridge1 one such gap is the romanche fracture zone a large offset of the ridge which straddles the equator it has been observed2 that sills within this fracture zone block the passage of waters colder than 0 9 c warmer less dense waters passing over the sills appear to cascade downslope where they are modified by mixing here we present direct measurements which quantify these processes the flow is vertically sheared and exhibits remarkably intense turbulence comparable to that seen at the ocean surface in the presence of winds of l0ms 1 this turbulence mixes the densest waters passing through the fracture zone with the warmer overlying waters so that the coldest waters exiting this region have been warmed by 0 6 c during transit topographic obstructions and turbulent mixing together thus determine the properties of the flows renewing the deepest waters of the atlantic ocean s eastern basins

strontium isotope stratigraphy and paleomagnetic age constraints on the evolution history of coral reef islands northern south china sea understanding the history of the response of coral reefs to past climate changes can provide valuable information for predicting the future response of modern reefs however dating such ancient biotic carbonate is still challenging because of its sensitivity to diagenetic alteration processes scarcity of well preserved fossils and low magnetic mineral content there have been a long debates about the origin and evolutionary history of coral reefs in the northern south china sea mainly due to the lack of direct and reliable age constraints this provides us with a good opportunity to verify the practicability of different dating approaches especially the strontium sr isotope analysis of bulk carbonate here we retrieved a 972 55 m long core from the xisha islands to provide a credible chronologic constraint on the carbonate platform evolution the lithostratigraphy strontium isotope stratigraphy and magnetostratigraphy were analyzed throughout the whole reef sequence the lithostratigraphic results show that the 873 55 m reef sequence developed on an ancient volcaniclastic basement and experienced multiple evolutionary phases the sr 87 sr 86 results of all 100 bulk carbonate samples vary from 0 708506 to 0 709168 and show a monotonic increase with decreasing depth except for a few outliers trace element criteria and stable isotope delta o 18 and delta c 13 methods were applied to these bulk carbonate samples and results imply that the primary or near primary seawater sr 87 sr 86 values were likely preserved although different degrees of diagenetic alteration occurred in addition the paleomagnetic results indicate 10 normal polarity and eight reversed polarity magnetozones based on the sr 87 sr 86 ratios of the selected 58 samples and paleomagnetic reconstruction of polarity reversals the bottom of the reef sequence is dated to 19 6 ma and the observed polarity chronozones extend from chron c6 19 722 18 748 ma at 866 60 m to present at the top based on the new data we propose a new chronologic framework for the evolutionary history of the reef islands where 1 the reefs initiated in the early miocene 19 6 ma and were drowned until 16 26 ma 2 during 16 26 10 66 ma lagoon to lagoon slope environments prevailed 3 the lagoon environment progressively transformed into a reef crest environment from 10 66 to 4 36 ma and 4 36 to 1 59 ma and 4 the reef started to be drowned again during 1 59 0 ma our study provides a new and reliable chronologic constraint on the general evolutionary history of the reef islands in the northern south china sea furthermore the sr 87 sr 86 results from bulk carbonate indicate that strontium isotope stratigraphy is a powerful dating tool only when rigid sample selection sequential leaching procedures and strict trace element and isotopic criteria are applied

three agulhas rings observed during the benguela current experiment a field program to study the circulation of the benguela current and its extension into the southeastern atlantic ocean has completed the survey and instrument deployment phase we report here new observations of three agulhas rings north and west of cape town south africa three mesoscale anticyclonic rings initially identified by means of topex poseidon altimetry were surveyed with expendable bathythermographs conductivity temperature depth oxygen profiles direct current measurements from a lowered acoustic doppler current profiler a hull mounted acoustic doppler current profiler and satellite tracked surface drifters characteristics of the rings are presented and their origins are discussed two are typical agulhas rings surveyed at different times after their generation the third agulhas ring has an anomalous water mass structure whose most likely origin is the subtropical front

geochronology and subsurface stratigraphy of pukapuka and rakahanga atolls cook islands late quaternary reef growth and sea level history eustatic sea level cycles superposed on thermal subsidence of an atoll produce layers of high sea level reefs separated by erosional unconformities coral samples from these reefs from cores drilled to 50 m beneath the lagoons of pukapuka and rakahanga atolls northern cook islands give electron spin resonance esr and u series ages ranging from the holocene to 600 000 yr b p subgroups of these ages and the stratigraphic position of their bounding unconformities define at least 5 periods of reef growth and high sea level 0 9000 yr b p 125 000 180 000 yr b p 180 000 230 000 yr b p 300 000 460 000 yr b p 460 000 650 000 yr b p only two ages fall within error of the last interglacial high sea level stand 125 000 135 000 yr b p this paucity of ages may result from extensive erosion of the last intergracial reef in addition post depositional isotope exchange may have altered the time ages of three coral samples to apparent ages that fall within glacial stage 6 for the record to be preserved vertical accretion during rising sea level must compensate for surface lowering from erosion during sea level lowstands and subsidence of the atoll erosion rates 6 63 cm 1000 yr can therefore be calculated from reef accretion rates 100 400 cm 1000 yr subsidence rates 2 6 cm 1000 yr and the duration of island submergence 8 15 of the last 600 000 yr the stratigraphy of coral ages indicates island subsidence rates of 4 5 2 8 cm 1000 yr for both islands a model of reef growth and erosion based on the stratigraphy of the cook islands atolls suggests average subsidence and erosion rates of between 3 6 and 15 20 cm 1000 yr respectively

marine geophysical investigation of the chain fracture zone in the equatorial atlantic from the pi lab experiment the chain fracture zone is a 300 km long transform fault that offsets the mid atlantic ridge we analyzed new multibeam bathymetry backscatter gravity and magnetic data with 100 multibeam bathymetric data over the active transform valley and adjacent spreading segments as part of the passive imaging of the lithosphere asthenosphere boundary pi lab experiment analyses of these data sets allow us to determine the history and mode of crustal formation and the tectonic evolution of the transform system and adjacent ridges over the past 20 myr we model the total field magnetic anomaly to determine the age of the crust along the northern ridge segment to better establish the timing of the variations in the seafloor fabric and the tectonic magmatic history of the region within the active transform fault zone we observe four distinct positive flower structures with several en echelon fault scarps visible in the backscatter data we find up to 10 mgal residual mantle bouguer anomaly in the region of the largest positive flower structure within the transform zone suggesting crustal thickening relative to the crustal thinning typically observed in fracture zones in the atlantic the extensional compressional features observed in the chain transform are less pronounced than those observed further north in the vema st paul and romanche and may be due to local ridge segment adjustments

monsoon influenced variations in plankton community structure and upper water column stratification in the western bay of bengal during the past 80 ky abstract to enhance our understanding of the forcing factors of marine biological community structure in the bay of bengal we studied proxies for biogenic carbonate and silicate production in the western bay of bengal and compared them with proxies for upper ocean stratification and strength of the indian summer monsoon ism specifically we investigated the record in a sediment core from the western bay of bengal that extended to approximately 80 ky before the present bp the records of globigerinoides ruber sensu stricto 18o minus neogloboquadrina dutertrei 18o 18or d were used to investigate changes in upper ocean stratification we reconstructed variations in mass accumulation rates mars of caco3 and biogenic silica bsi to discuss plankton community structure greater difference between globigerinoides ruber sensu stricto 18o and neogloboquadrina dutertrei 18o during the marine isotope stage mis 1 and 5a indicate intervals with less saline and more stratified conditions in contrast the relatively small difference between both planktic foraminiferal 18o during mis 2 and 4 indicates diminished stratification during these periods elevated carbonate production during mis 2 and 4 demonstrated by the increase in caco3 mar could have been driven by lower freshwater influx to the western bay of bengal resulting from lower ism precipitation and thus the increased mixing and upwelling of deep nitrate into the photic zone the relative increase in bsi mar during periods of high ism precipitation and decreased salinity of surface waters suggests a limited recovery in biological siliceous production under interglacial conditions possibly due to enhanced fluvial sio4 delivery to the ocean fluctuations of 18or d during mis 3 indicate that freshwater stratification was moderate and insufficient to restrict upwelling this might have induced moderate biogenic silica and carbonate productions during this period

a decomposition of the atlantic meridional overturning a decomposition of meridional overturning circulation moc cells into geostrophic vertical shears ekman and bottom pressure dependent or external mode circulation components is presented the decomposition requires the following information 1 a density profile wherever bathymetry changes to construct the vertical shears component 2 the zonal mean zonal wind stress for the ekman component and 3 the mean depth independent velocity information over each isobath to construct the external mode the decomposition is applied to the third generation hadley centre coupled ocean atmosphere general circulation model hadcm3 to determine the meridional variability of these individual components within the atlantic ocean the external mode component is shown to be extremely important where western boundary currents impinge on topography and also in the area of the overflows the sverdrup balance explains the shape of the external mode moc component to first order but the time variability of the external mode exhibits only a very weak dependence on the wind stress curl thus the sverdrup balance cannot be used to determine the external mode changes when examining temporal change in the moc the vertical shears component allows the time mean and the time variable upper north atlantic moc cell to be deduced at 25 s and 50 n a stronger dependency on the external mode and ekman components between 8 and 35 n and in the regions of the overflows means that hydrographic sections need to be supplemented by bottom pressure and wind stress information at these latitudes at the decadal time scale variability in ekman transport is less important than that in geostrophic shears in the southern hemisphere the vertical shears component is dominant at all time scales suggesting that hydrographic sections alone may be suitable for deducing change in the moc at these latitudes

marine paleoclimatic proxies a shift from qualitative to quantitative estimation of seawater parameters abstract understanding past climate during contrasting boundary conditions can help in assessing imminent climate changes marine sediments offer a vast archive of past climate various indirect methods called proxies are used to infer principal climate parameters like temperature salinity productivity monsoon intensity ocean circulation seawater ph and others from the marine sediments the relationship between a climate parameter and marine paleoclimate proxy may vary from region to region additionally the marine proxies are often affected by more than one climate parameter thus making it difficult to assess the change in any particular parameter from a single proxy diagenetic alteration can also significantly affect the parameter proxy relationship a growing emphasis now is on quantifying changes in key climatic parameters in the past proxies for quantitative estimation of seawater temperature runoff sea level and ph are now fairly well established similar robust quantitative proxies for dissolved oxygen concentration and productivity are however still being developed additionally the uncertainty associated with quantitative estimation of past climate has to be reduced therefore continuous efforts are being made to develop novel paleoclimate proxies and to evaluate existing proxies in different regions of the world oceans

origins and variability of the benguela current a subset of the benguela sources and transports best 1992 1993 data is analyzed to study the magnitude and variability of the large scale transports in the area the data consist of inverted echo sounder series and conductivity temperature depth stations the mean 16 month transport values for the upper 1000 m indicate that of the 13 sv northward transport within the benguela current 50 is derived from the central atlantic which from geometry may be chiefly south atlantic water 25 comes from the indian ocean which may be chiefly agulhas water and the remaining 25 may be a blend of agulhas and tropical atlantic water a simple schematic of the transport pattern with a somewhat restricted corridor for agulhas eddies translation is envisioned to the west of the eddy corridor flows the south atlantic source for the benguela current to the east is the agulhas indian ocean source the corridor is breached by south atlantic and indian water as the transient eddy field stirs these water masses

oceanic fluxes on the woce a11 section abstract the most southerly woce one time section in the south atlantic designated a11 was occupied in january 1993 the cruise track lay across the cool subantarctic zone of the circumpolar current in the west and the warm subtropical gyre in the east in this paper estimates of the flux of heat salt oxygen and other tracers across the section are presented a brief description of the distribution of physical and chemical properties is followed by a determination of the flux in the surface ekman layer direct measurements of current shear made from a shipborne adcp and estimates from cruise wind data and climatological data all yield a flux of 5 1 sv sv 106 m3 s 1 equatorward when combined with geostrophic estimates relative to a level near 3500 dbar or the bottom where shallower an initial guess for the flow field is derived this initial guess is combined with absolute currents derived from the adcp when the ship is underway unrealistic aspects of the circulation are found and we conclu

natural dissolution of modern shallow water benthic foraminifera taphonomic effects on the palaeoecological record comparison of the living and dead assemblages of benthic foraminifera from the coastal areas of the skagerrak kattegat reveals that although there are considerable similarities in terms of the presence absence of species there are major differences in relative abundance at species level furthermore the relative abundance of calcareous tests in the living assemblages is considerably higher than that of the dead assemblages average values of 67 and 30 respectively since the environments are microtidal there is little transport of foraminiferal tests due to tidal currents so there are no introduced exotic species although there is local transport caused by waves and wave induced currents however the major taphonomic process appears to be dissolution of calcareous tests this is manifested through etching and breakage of test walls leading to complete decalcification which leaves a residue of organic linings of certain taxa e g ammonia beccarii and a marked increase in abundance of agglutinated tests in the dead assemblages although dissolution is normal in marsh settings throughout the world the skagerrak kattegat area is unusual in the intensity of dissolution in the subtidal zone whereas most of the calcareous species occur throughout the investigated depth range except marsh two of the subtidal agglutinate species eggerelloides scaberand ammotium cassis show upper depth limits consequently the agglutinated foraminifera are better indicators than calcareous foraminifera of upper depth limits in these shallow subtidal environments 1999 elsevier science b v all rights reserved

multiple oscillatory modes of the argentine basin part ii the spectral origin of basin modes in this paper the spectrum of barotropic basin modes of the argentine basin is shown to be connected to the classical rossby basin modes of a flat bottom constant depth rectangular basin first the spectrum of basin modes is calculated for the argentine basin by performing a normal mode analysis of the barotropic shallow water equations then a homotopy transformation is performed that gradually morphs the full bathymetry geometry through a flat bottom configuration into a rectangular basin following the eigenmodes through this transition establishes a connection between most of the basin modes and the classical rossby basin modes of a rectangular geometry in particular the 20 day mode of the argentine basin is identified with the lowest order mode of classical theory sensitivity studies show that the decay rate of each mode is controlled by bottom friction but that it is insensitive to lateral friction lateral friction strongly impacts the oscillation frequency in addition the modes are found to be only slightly sensitive to the presence of a background flow

the mis 11 paradox and ocean circulation role of millennial scale events the role of millennial scale climate variability in supplementing the astronomical forcing of glacial interglacial transitions remains a major unresolved question here we compare the occurrence and character of terminal ice rafting events in both the north and south atlantic during the last deglaciation termination i ti and during the transition between marine isotope stages mis 12 and 11 or termination v tv we show that tv experienced a massive terminal ice rafting event in the north atlantic that was more intense and longer lasting than heinrich event 1 h1 of the last deglaciation this massive ice rafting event was linked to cold stadial conditions and reduced deep water formation in the north atlantic in parallel with warming at high southern latitudes similar to the bipolar seesaw pattern exhibited during h1 over the last deglaciation we propose that the particular intensity and duration of the tv ice rafting event resulted from the especially large volume of northern hemisphere ice sheets during mis12 in turn the unusually long duration and large amplitude of tv likely resulted from the exceptionally prolonged collapse of the amoc during the tv heinrich stadia and from a subsequent transient amoc overshoot with respect to later mis11 interglacial circulation furthermore we suggest that the intense heinrich stadial of tv contributed to the deglaciation primarily via meridional heat transport anomalies that would have enhanced the incipient warming arising from relatively weak insolation forcing and only secondarily via co2 release

the paradox of drowned carbonate platforms and the origin of cretaceous pacific guyots geochemical stratigraphic and palaeolatitudinal data from deep boreholes drilled through pacific guyots flat topped seamounts help to explain the drowning of these cretaceous shallow water carbonate platforms that once thrived through the accumulation of biogenic and inorganic calcium carbonate sediment in mid oceanic regions the platforms drowned sequentially over a 60 million year interval while they were being transported northward by pacific plate motion through a narrow equatorial zone 0 10 s such platforms were apparently resistant to the effects of cretaceous oceanic anoxic events although the mechanism responsible for drowning remains unknown the tropics have not always been the refuge for atolls that they are today

millennial scale holocene hydrological changes in the northeast atlantic new insights from la grande vasiere mid shelf mud belt a mid to late holocene paleohydrological reconstruction from the northeast atlantic is proposed through the study of a high resolution sedimentary record from the northern continental shelf of the

response of south atlantic deep waters to deglacial warming during terminations v and i abstract new deep sea core data from the atlantic sector of the southern ocean covering mis12 to mis10 and the last deglaciation show a clear lag of the changes in deep water properties with respect to changes in surface conditions the development of a chronology based on the correlation of southern ocean sea surface temperature with air temperature over antarctica allows the quantification and comparison of phase lags within the marine records during termination v tv and termination i ti deglacial changes in the south atlantic are interpreted as the response to changes in the state of the atlantic meridional ocean circulation amoc the warming of south atlantic surface waters and air temperature over antarctica at the beginning of both tv and ti is attributable to a reduction in interhemispheric heat transport due to the weakening of the amoc comparison of our results with climber 2 simulations indicates that the response of bottom waters seen in the benthic isotopic records delayed with respect to south atlantic surface warming can be explained by the increased inflow of north atlantic deep water nadw to the south atlantic site at the time of the amoc recovery reconstructed sea surface temperature at our south atlantic site exhibits a cold spell at the end of tv resembling the antarctic cold reversal of the last deglaciation the presence of cold spells during tv and ti may be explained by the fact that the recovery of the amoc took place early during the termination in both cases the sequence of events is similar during both terminations however the magnitude of the phase shifts between south atlantic surface and deep waters conditions differs from one termination to the other suggesting variations in the magnitude and duration of the amoc perturbation

strontium isotope stratigraphy of kita daito jima atoll north philippine sea implications for neogene sea level change and tectonic history abstract a detailed chronology of a 432 m core from kita daito jima an atoll on the philippine sea plate has been obtained by strontium isotope stratigraphy the atoll carbonate extends to late oligocene age the top 100 m plio pleistocene section of the core has been dolomitized and dolomite also extends to middle miocene sediments sr isotopes identify two dolomitization events at 2 and 5 ma atoll growth appears to have been continuous between 18 8 and 24 3 ma and the fit of the growth history to a standard model provides a successful confirmation of darwin s subsidence theory the atoll growth appears to have commenced about 42 ma ago 6 ma after volcanism producing a 2 km column of atoll carbonate in agreement with bathymetry the subsidence model defines an apparent loss of 360 m of the sedimentary record since the early middle miocene boundary the amount in excess of the 100 m associated with sea level fall is attributed to plio pleistocene uplift at rates of 20 30 m ma associated with the forebulge of the philippine sea plate prior to its subduction uplift rates have also been estimated using a the heights of dated last interglacial coral reefs on kita daito jima and nearby minami daito jima 17 m ma and 29 m ma b sr isotope ages of calcites from surface samples on minami daito jima 21 m ma and c contrasts in elevation with okino daito jima 100 km away 22 m ma the locations of hiatuses and ages of dolomitization indicate sea level falls of 80 m at 17 16 ma 30 m at 16 15 ma 125 m at 11 ma and 90 m at 5 ma and at 2 ma the data have been combined with those from enewetak atoll to produce a curve of sea level change for the neogene

benthic foraminiferal response to changes in mining pattern a case study from the zuari estuary goa india being sensitive to environmental changes foraminifera have been extensively used to monitor pollution level in the marine environment including the effect of mining in coastal areas in the goa state of india the rejects from opencast mining on land largely find their way to the estuaries as washout during monsoon additionally the mormugao port at the mouth of the zuari estuary is the hub of activities due to the transport of ore from hinterland areas by barges and its subsequent loading for export on the directive of the supreme court of india all the mining related activities abruptly stopped throughout india including that in goa in 2012 and got reinstated in 2015 therefore it provided a fit case to test the effectiveness of benthic foraminifera as an indicator of environmental impact due to mining activities a total of ten surface sediment samples from five locations in zuari estuary were collected from a depth range of 4 5 8 5 m in the years of 2013 and 2016 and were analyzed for both the living stained and dead benthic foraminifera the year 2013 represents a time interval immediately after the closure of extensive mining activity and the sampling during 2016 represents minimal mining the living benthic foraminiferal abundance was higher 19 54 g sediment during 2013 and decreased substantially during 2016 3 22 g sediment suggesting an adverse effect of activities associated with mine closure on benthic foraminifera additionally the relative abundance of ammonia was also significantly low during the year 2016 the temporal variation in dead foraminifera was however different than that of the living foraminifera the differential response was attributed to the terrigenous dilution as a result of change in sedimentation rate therefore we conclude that living foraminifera correctly incorporate the changes in mining pattern and may be used as an effective tool to monitor the impact of mining we further suggest that the potential counter effect of terrigenous dilution on total and living benthic foraminiferal population should be considered while interpreting temporal variations in foraminiferal abundance in marginal marine settings

tracing lower north atlantic deep water across the equator water whose ultimate source is the overflow at the denmark strait can be traced using maps of salinity dissolved oxygen and silica concentration on deep density surfaces south along the american continent to at least 5 s several property extrema whose resolution is at the limit of accuracy of the measurements occur on these density surfaces which nevertheless may indicate areas of stronger mixing along the crest of the mid atlantic ridge transport estimates for that part of the southward flow within 600 km of the western boundary near 10 n suggest that 10 3 106 m3 s 1 of lower north atlantic deep water moves south there the total southward deep water transport near 10 n is estimated to be closed to 25 106 m3 s 1

multiple oscillatory modes of the argentine basin part i statistical analysis observations of the sea surface height in the argentine basin indicate that strong variability occurs on a time scale of 2030 days the aim of this study is to determine the physical processes responsible for this variability first results are presented from two statistical techniques applied to a decade of altimetric data a complex empirical orthogonal function ceof analysis identifies the recently discovered dipole mode as the dominant mode of variability a principal oscillation pattern pop analysis confirms the existence of this mode which has a period of 25 days the second ceof displays a propagating pattern in the northern argentine basin plus a rotating dipole in the southwest corner the pop analysis identifies both patterns as individual modes with periods of 30 and 20 days respectively second the barotropic normal modes of the argentine basin are studied using a shallow water model capturing the full bathymetry of the basin coherences between the spatial patterns of these modes and altimeter data suggest that several of the basin modes are involved in the observed variability this analysis implies that the 20 day mode detected by recent bottom pressure measurements is a true barotropic mode however the 25 day variability as found in altimeter data cannot be directly attributed to the excitation of a free rossby basin mode this study indicates that the results of several apparently conflicting observations of the flow variability in the argentine basin can be reconciled by assuming that multiple basin modes are involved

eastward flow through the mid atlantic ridge at 11 n and its influence on the abyss of the eastern basin abstract the dilute antarctic bottom water of the north atlantic eastern trough is supplied from the western trough through fractures in the mid atlantic ridge in particular the influence on eastern trough property distributions of flow through the romanche and vema fracture zones near the equator and 11 n respectively has been noted previously here new observations are reported that document the abyssal circulation of the northeastern atlantic basins gambia abyssal plain south canary basin and north canary basin in particular the dominance of vema influence the absence of romanche influence and the existence of a system of deep western boundary currents and estimated transport deep isopycnals slope steeply across the vema s eastern end near 39 w corresponding to a geostrophic transport through the vema of 2 1 to 2 3 106 m3s 1 colder than 2 0 c this is half or more of the estimated bottom water that flows north across the equator into the subtropical western north atlantic this transp

evolution of deepwater mixing and weathering inputs in the central atlantic ocean over the past 33 myr the isotopic composition of nd in present day deep waters of the central and northeastern atlantic ocean is thought to fingerprint mixing of north atlantic deep water with antarctic bottom water the central atlantic romanche and vema fracture zones are considered the most important pathways for deep water exchange between the western and eastern atlantic basins today we present new nd isotope records of the deepwater evolution in the fracture zones obtained from ferromanganese crusts which are inconsistent with simple water mass mixing alone prior to 3 ma and require additional inputs from other sources the new pb isotope time series from the fracture zones are inexplicable by simple mixing of north atlantic deep water and antarctic bottom water for the entire past 33 myr the distinct and relatively invariable nd and pb isotope records of deep waters in the fracture zones appear instead to have been controlled to a large extent by contributions from saharan dust and the orinoco amazon rivers thus the previously observed similarity of nd and pb isotope time series from the western and eastern north atlantic basins is better explainable by direct supply of labrador seawater to the eastern basin via a northern pathway rather than by advection of north atlantic deep water via the romanche and vema fracture zones

the record of pliocene sea level change at enewetak atoll abstract detailed seismic stratigraphy lithostratigraphy and chemostratigraphy indicate that atoll wide subaerial exposure surfaces major disconformities developed during major sea level lowstands form prominent seismic reflectors and are coincident with biostratigraphic breaks in the plio pleistocene on enewetak atoll sea level models based on the stratigraphic position and age of major disconformities suggest a maximum sea level highstand elevation of 36 m above present sea level and a maximum sea level lowstand elevation of 63 m below present sea level for the pliocene

structure of the deep spillway in the western part of the romanche fracture zone structure of the deep spillway was studied on the basis of conductivity temperature depth lowered acoustic doppler current profiler and mooring measurements in 2011 2014 in the romanche fracture zone 22 27 22 32 w the spillway exists quasi permanently in the regime of hydraulic control overflow and consists of two flows in the layer 1 20 c deeper than 4 150 m the first flow enters the fracture from the south through a gap in the southern wall the second flow is directed to the east along the narrow valley of the fracture the sill depths of these passages are 4 570 and 4 430 m respectively the depths over the surrounding ridges are shallower than 4 100 m both flows descend to the local depression of the fracture with 5 000 m depth bottom potential temperatures over both sills were 0 51 c and the measured velocities were 20 40 cm s when the flows descend down the slope they accelerate in supercritical regime maximal measured velocities were up to 65 cm s analysis of the 189 day time series of velocities on the mooring deployed in the flow descending from the gap showed a very high level of fluctuation energy 10 times greater than the energy of the barotropic tide at this point the only energy source of these fluctuations is the available potential energy of the deep thermocline in the west atlantic transforming to the kinetic energy of the deep spillway the total transport of the bottom water below 1 2 c based on the lowered acoustic doppler current profiler measurements is estimated at 0 29 0 35 sv which agrees with the predicted values

radiogenic isotopes systematics and applications to earth surface processes and chemical stratigraphy radiogenic isotopes have wide application to chemical stratigraphy geochronology provenance studies and studies of temporal changes in earth surface processes this paper briefly reviews the principles of radiogenic isotope geochemistry and the distribution of a number of elements of interest in the environment and then uses this information to explore the range of applications to chemical stratigraphy and other fundamental subjects of sedimentary geology many of these applications center on the reconstruction of secular variations in paleoseawater isotope signals these seawater isotope curves can be used for stratigraphic correlation and to assess changes through earth history in processes such as tectonic uplift climate change biogeochemical cycling ocean circulation crustal growth and surface water evolution understanding the modern biogeochemical cycle of the element isotope system of interest is essential for gaining the maximum information regarding the operation of ancient cycles the main sources of uncertainty for reconstructing seawater isotope curves involve diagenetic alteration sample impurities and errors in age assignments rigorous sample selection criteria and pretreatment methods are keys to reconstructing the most accurate seawater isotope curves applications are discussed for the rb sr sm nd la ce lu hf re os u th pb k ar and cosmogenic isotope systems d 2003 elsevier b v all rights reserved

deep inflow into the mozambique basin more than 200 conductivity temperature depth ctd stations were worked around the southwest indian ridge and del cano rise as part of the world ocean circulation experiment a selection of these data provides information about the inflow of bottom water into the mozambique basin the basin is closed below 3000 m yet the inflow is significantly large of order 1 sv 1 sv 106 m3 s 1 estimates of the basin scale upwelling at 4000 m suggest that the vertical velocity is also large 10 10 5 cm s 1 or more an order of magnitude greater than global ocean estimates examination of the characteristics of the bottom water in the mozambique and agulhas basins and the prince edward fracture zone shows that bottom water enters the mozambique basin from the agulhas basin and also directly from the enderby basin most of the transport enters the mozambique basin via the agulhas basin where two regions of northward flow below 4000 m are found the major flow on the eastern flank of the mozambique ridge is through and above the deep extending 5900 m trench that connects the agulhas and mozambique basins the second weaker flow enters the transkei basin along the deep eastern flank of the agulhas plateau then turning east into the mozambique basin the only source of bottom water to the agulhas basin is the enderby basin but a more direct route between the enderby and mozambique basins exists via the prince edward fracture which extends deeper than 4000 m throughout its length and links the two basins directly across the southwest indian ridge full depth ctd stations trace the changing characteristics of the deep and bottom water in the fracture and moored current meter data show the strength and persistence of the throughflow strong mixing with the overlying deep water elevates the salt content of the bottom water by comparison with the other water in the mozambique basin thus two distinct bottom waters of the mozambique basin originate in the same place the enderby basin and their different characteristics are solely a function of the routes they have taken and the processes encountered along the different pathways

effect of salinity induced ph alkalinity changes on benthic foraminifera a laboratory culture experiment the salinity of coastal waters in the vicinity of seasonally fresh water fed estuaries changes tremendously and reportedly affects the living calcite secreting organisms like foraminifera as well as their dead remains the precise mechanism of adverse effect of such seasonal salinity changes on calcite secreting organisms is however not clear the seasonal fresh water influx from the estuaries also affects the ph and alkalinity of the coastal seawater therefore to understand the effect of salinity induced ph alkalinity variations on benthic foraminifera living specimens of rosalina globularis were subjected to different salinity additionally water samples were collected from an estuary during both monsoon and post monsoon season to understand the relationship between salinity ph and total alkalinity ta the ph decreased with decreasing salinity during both the seasons a similar decrease in ta with decreasing salinity was also observed but only till 20 psu salinity below which the ta increased with decreasing salinity even though the maximum growth was reported in specimens kept at 35 psu salinity growth of specimens maintained at 25 psu salinity was same specimens kept at 10 psu and 15 psu salinity however were much smaller and turned opaque within two days of lowering the salinity and later on their tests dissolved within 24 and 43 days respectively no specimen reproduced at 10 psu and 15 psu salinity while only a few specimens 3 reproduced at 20 psu salinity as compared to 10 20 psu salinity 60 reproduction was observed in specimens subjected to 25 40 salinity the specimens maintained at 20 psu salinity took twice the time to reach maturity than those subjected to 2540 psu salinity since a big drop in ph was observed at 10 15 psu salinity ph 7 2 and 7 5 respectively while the alkalinity was still higher we suggest that fresh water influx induced drop in ph adversely affects calcification and reproduction in benthic foraminifera the response is however not linear as beyond a certain limit a further increase in ph does not affect benthic foraminifera rather they respond to salinity as per their salinity tolerance range it is further inferred that the time required to reach reproductive maturity increases at the extreme salinity tolerance limits dissolution of calcareous foraminifera below 20 psu salinity suggests that salinity induced changes control the carbonate inventory in the coastal regions subjected to seasonal fresh water influx

the distribution of neodymium isotopes and concentrations in the eastern tropical north atlantic abstract dissolved neodymium nd and its radiogenic isotope composition 143nd 144nd expressed as end belong to the key parameters of the international geotraces program which aims to investigate the processes controlling the distribution of trace elements and their isotopes in the global ocean we present nd isotope and concentration nd data from eleven full depth water column profiles from the eastern sub tropical atlantic ocean between 2 n and 29 n and from the romanche fracture zone sampled during meteor cruise m81 1 geotraces cruise ga11 in february march 2010 the end signatures range from 12 9 in upper north atlantic deep water unadw at the equator to 8 1 in the mixed layer near the canary islands nd concentrations range from 11 9 pmol kg observed within the equatorial undercurrent to 40 2 pmol kg in antarctic bottom water aabw in the romanche fracture zone large variations in surface water nd isotope compositions 12 7 end 8 1 and concentrations 15 7 pmol kg nd 27 7 pmol kg are caused by partial dissolution of saharan dust particles between 2 n and 13 n and volcanic island weathering canaries between 25 n and 29 n in contrast to dust inputs which predominantly affect the nd concentrations and isotope compositions of surface waters and underlying south atlantic central water sacw contributions originating from the canary islands affect the nd isotope composition of the entire surrounding water column without significantly altering nd concentrations thus confirming the concept of boundary exchange in its strictest sense the results confirm that the composition of lower north atlantic deep water lnadw end 12 1 in the abyssal plains of the eastern north atlantic is exclusively set by the mixing ratio of lnadw and antarctic bottom water aabw upper north atlantic deep water unadw in contrast is characterized by end signatures between 12 7 and 12 0 between 2 n and 10 n whereas further north it is clearly affected by admixture of mediterranean water mw and radiogenic inputs from the canary islands and likely also the cape verde islands this article is part of a special issue entitled cycles of trace elements and isotopes in the ocean geotraces and beyond edited by tim m conway tristan horner yves plancherel and aridane g gonzalez

mineralization of biogenic materials in the water masses of the south atlantic ocean i assessment and results of an optimum multiparameter analysis abstract this is the first of two manuscripts dealing with the circulation mixing ventilation and organic matter mineralization of the south atlantic ocean sao the present work quantifies the complex mixing of water masses in the sao using a constrained least squares regression optimum multiparameter omp analysis the omp based on temperature salinity silicate and the conservative parameter no was applied on two world ocean circulation woce lines a17 and a14 in the western and eastern sao respectively the constrained omp sensitivity to sources of error in the end member characteristics measured parameters equation weights and oxygen to nitrogen mineralization ratio rn was carefully assessed using perturbation tests perturbation of rn was the only test that changed significantly the mixing proportions although by less than 5 the constrained omp method allowed defining the realm and identifying the core of flow of each water mass to study its circulation the evolution of its chemical composition and eventually to separate the contribution of physical and biogeochemical processes relevant specific outputs of this first manuscript are 1 north of the south equatorial current the silicate maximum is primarily composed of antarctic intermediate water aaiw rather than circumpolar deep water cdw 2 the two degree discontinuity tdd experiences a dramatic meridional change of water masses composition being dominated by north atlantic deep water nadw north of the vema channel and by cdw southwards 3 the 50 proportion horizon of weddell sea deep water wdsw with a of 0 3 c at the entry of the sao defines the upper limit of the wsdw realm more properly than the classical isopycnals of 46 04 or 46 06 4 where the proportion of wsdw is around 75

marine carbonate factories a global model of carbonate platform distribution platform carbonates are a major component of the earth system but their spatial distribution through geological times is difficult to reconstruct due to the incompleteness of geological records sampling heterogeneity and their intrinsic complexity beyond this complexity carbonates are not randomly distributed in the world oceans neither in the modern nor in the past and thus global trends exist in the present review we focus on the understanding of the spatial distribution of carbonate production at a global scale we use a deterministic approach which focuses on discriminating components stratigraphic architectures and environmental features to relate shallow water carbonate production to oceanographic parameters the work is based on extensive literature reviews on carbonate platforms ecological niche modelling coupled with deep time general circulation models is used to calibrate a predictive tool of carbonate factory distribution a carbonate factory function is set up that is based on sea surface oceanographic parameters temperature salinity and primary productivity the model was tested using remote sensing and in situ oceanographic data of modern times while outputs of paleoceanographic models are utilized for lower aptian cretaceous modelling the approach allows determining four neritic carbonate factories that are called the marine biochemical photozoan photo c and heterozoan factories the model finely simulates the global distribution of lower aptian and modern carbonate platforms carbonate factories appear to thrive for specific ranges along the environmental gradient of carbonate saturation this conceptual scheme appears to be able to provide a simple universal model of paleoclimatic zones of shallow water marine carbonates

renewal rates of east atlantic deep water estimated by inversion of 14c data the renewal of the deep water of the east atlantic and its large scale internal circulation are studied on the basis of the distributions of potential temperature silicate co2 and 14c an isopycnal multibox model including advection mixing and sources and sinks is set up and described tracer data are input for the model and balance equations for the various properties for the boxes of the model serve as constraints for the determination of water fluxes mixing coefficients and source parameters extremal values for various model parameters that are consistent with the tracer data satisfy the balance equations within the estimated tolerances are calculated by linear programming techniques 14c data are seen to be valuable in determining absolute flow rates model results confirm the importance of the romanche facture zone for the renewal of east atlantic deep water eastward flows through the romanche fracture zone were found to be between 2 6 and 5 1 sv flows through the vema fracture zone amount to at most 20 of the romanche fracture zone inflow contributions of antarctic bottom water at the southern end of the east atlantic walvis ridge and of iceland scotland overflow water at the northern end are very small 5 of equatorial inflow diapycnal mixing coefficients are between 1 and 10 cm2 s and values for the dissolution rates of silicate and carbon are in the expected range

reef talus a popular misconception reef fronts have traditionally been regarded as comprising debris derived by contemporaneous erosion of the reef however evidence from wave transport indicates that on present day reefs the bulk of the debris generated in this way accumulates in the back reef area with only finer grained sediment carried off reef by retreating flows or by overwash nevertheless in contrast to this observation fore reef debris slopes are commonly considered characteristic of phanerozoic reefs this apparent error reflects the conflation of processes defining contemporary growth and accretion of the reef and the corresponding long term accretion of the carbonate platform on which it rests present day reefs are commonly although not exclusively additions to long lived carbonate platforms growth of the latter is intermittent and has been moderated by changes in sea level that for recent reefs have been on time scales of less than 100 ka during low sea level stands growth ceases or is translated downslope and earlier deposits are subject to lithification and subaerial erosion similar changes are applied on a larger scale to the aggrading growth of carbonate platforms but the bulk accretion of these includes quite different processes and reflects far longer timescales during low sea level stands the margins of platforms commonly become unstable with instability reflected in slope failure and in the shedding of blocks ranging from metres to kilometres in diameter associated with the generation of debris flows and turbidites it is argued that these are the materials that are commonly described as reef talus in ancient structures although their formation is largely independent of any contemporary reef growth difficulties arise where the reef and the platform are treated as a single functional entity it is important to recognize the conceptual distinction between them reef talus is a misleading description of the debris predominantly generated by platform erosion and slope failure

planktonic foraminiferal area density as a proxy for carbonate ion concentration a calibration study using the cariaco basin ocean time series 1 biweekly sediment trap samples and concurrent hydrographic measurements collected between march 2005 and october 2008 from the cariaco basin venezuela are used to assess the relationship between co32 and the area densities a of two species of planktonic foraminifera globigerinoides ruber pink and globigerinoides sacculifer calcification temperatures were calculated for each sample using species appropriate oxygen isotope 18o temperature equations that were then compared to monthly temperature profiles taken at the study site in order to determine calcification depth ambient co32 was determined for these calcification depths using alkalinity ph temperature salinity and nutrient concentration measurements taken during monthly hydrographic cruises the a which is representative of calcification efficiency is determined by dividing individual foraminiferal shell weights 0 43 g by their associated silhouette areas and taking the sample average the results of this study show a strong correlation between a and ambient co32 for both g ruber and g sacculifer r2 0 89 and 0 86 respectively confirming that co32 has a pronounced effect on the calcification of these species though the a for both species reveal a highly significant p 0 001 relationship with ambient co32 linear regression reveals that the extent to which co32 influences foraminiferal calcification is species specific hierarchical regression analyses indicate that other environmental parameters temperature and po43 do not confound the use of g ruber and g sacculifer a as a predictor for co32 this study suggests that g ruber and g sacculifer a can be used as reliable proxies for past surface ocean co32

interannual variations in the atlantic meridional overturning circulation and its relationship with the net northward heat transport in the south atlantic 1 variability of the atlantic meridional overturning circulation amoc and its effect on the net northward heat transport nht in the south atlantic are examined using a trans basin expendable bathythermograph xbt high density line at 35s ax18 the time mean amoc is 17 9 2 2 sv during 2002 2007 although the geostrophic transport dominates the time mean amoc both geostrophic and ekman transports are important in explaining the amoc variability the contributions of geostrophic and ekman transports to the amoc show annual cycles but they are out ofphase resultinginweakseasonalvariabilityoftheamoc the nht variability is significantly correlated with the amoc where a 1 sv increase in the amoc would yield a 0 05 0 01 pw increase in the nht partition of transport into the western and eastern boundaries and interior suggests that to quantify changes in the amoc and nht it is critical to monitor all three regions citation dong s s garzoli m baringer c meinen andg goni 2009 interannualvariations intheatlanticmeridionaloverturningcirculationanditsrelationship with the net northward heat transport in the south atlantic geophys res lett 36 l20606 doi 10 1029 2009gl039356