abrupt changes in deep atlantic circulation during the transition to full glacial conditions 1 six ocean drilling program odp sites in the northwest atlantic have been used to investigate kinematic and chemical changes in the western boundary undercurrent wbuc during the development of full glacial conditions across the marine isotope stage 5a 4 boundary 70 000 years ago sortable silt mean grain size ss measurements are employed to examine changes in near bottom flow speeds together with carbon isotopes measured in benthic foraminifera and planktic foraminiferal fragmentation as proxies for changes in water mass chemistry a depth transect of cores spanning 1 8 4 6 km depth allows changes in both the strength and depth of the wbuc to be constrained across millennial scale events ss measurements reveal that the flow speed structure of the wbuc during warm intervals interstadials was comparable to modern holocene conditions however significant differences are observed during cold intervals with higher relative flow speeds inferred for the shallow component of the wbuc 2 km depth during all cold stadial intervals including heinrich stadial 6 and a substantial weakening of the deep component 3 4 km during full glacial conditions our results therefore reveal that the onset of full glacial conditions was associated with a regime shift to a shallower mode of circulation involving glacial north atlantic intermediate water that was quantitatively distinct from preceding cold stadial events furthermore our chemical proxy data show that the physical response of the wbuc during the last glacial inception was probably coupled to basin wide changes in the water mass composition of the deep northwest atlantic

circulation mixing and production of antarctic bottom water abstract the antarctic source of bottom water to the abyssal layer of the world ocean is examined as well as its large scale flow pattern and ultimate entrainment rate into the deep water above we make use of the available high quality station data in the southern ocean to construct bottom maps of neutral density and mean property maps including chlorofluorocarbon cfc for the abyssal layer underneath a selected neutral density surface the maximum density at the sill depth of drake passage is used to distinguish between the voluminous deep water mass that is a continuous component of the antarctic circumpolar current from the relatively denser bottom water originated along the antarctic continental margins based on water density antarctic bottom water aabw is defined here generically to include all volumes of non circumpolar water of antarctic origin over the shelf regime multiple localized sources of specific aabw types contribute to the abyssal layer of the adjacent antarctic basins characteristics of these dense bottom waters reflect closely those observed on the parent shelf water mass spreading paths of newly formed deep and bottom waters over the slope regime and their subsequent oceanic circulation patterns are analyzed on the basis of global property maps for the aabw layer interior mixing and interbasin exchanges of aabw are deduced from mean characteristic curves following the southern streamline of the antarctic circumpolar current outflow and mixing of aabw from the weddell sea to the argentine basin is depicted using density and cfc distributions of two zonal hydrographic lines recirculation and mixing of deep and bottom waters within the weddell gyre are also detailed using a meridional section along the greenwich meridian the strength of all localized sources of aabw combined is estimated by two independent approaches an estimate of the total production rate of aabw is calculated based on the oceanic cfc budget for the aabw layer offshore of the 2500 m isobath the sum of all downslope inputs of well ventilated bottom water types underneath the top isopycnal must account for the measured cfc content in the bottom layer the resulting total aabw production rate is about 8 sv which is a conservative figure that neglects the loss of cfc bearing waters across the top isopycnal in recent years whereas about 9 5 sv is calculated assuming a well mixed bottom layer making use of their transient nature cfc distributions at the top of the aabw layer indicate that more direct and rapid entrainment of cfc rich bottom waters below occurs over localized areas with relatively strong upwelling rates and enhanced vertical mixing a second more ad hoc but independent oceanic mass budget of the bottom layer is also constructed a typical basin wide rate of deep upwelling of 3 10 7 m s 1 requires 10 sv 1 sv 106 m3 s 1 of newly formed aabw to sink down the slope around antarctica we have also formulated a spatial distribution of deep upwelling on the isopycnal at the top of the aabw it is expressed as a combination of wind topographic and turbulent components which in turn are functions of the isopycnal depth bottom depth and bottom layer thickness this non uniform upwelling field yields about 12 sv of aabw exported across the top isopycnal fortuitously the overall average of upward speed at the top isopycnal 3 7 10 7 m s 1 compares well with previous estimates of deep upwelling in the northern basins a series of likely sites for strong vertical entrainment of aabw are clearly identified in the modeled distribution of deep upwelling consonant with the observed cfc distributions on the top isopycnal altogether regions with relatively high upwelling rates 5 10 7 m s 1 occupy only a quarter of the total areal extent of the top isopycnal but they account for as much as 45 of the total vertical transport

inferring surface water equilibrium calcite δ18o during the last deglacial period from benthic foraminiferal records implications for ocean circulation the ocean circulation modifies mixed layer ml tracer signals as they are communicated to the deep ocean by advection and mixing we develop and apply a procedure for using tracer signals observed upstream by planktonic foraminifera and downstream by benthic foraminifera to constrain how tracer signals are modified by the intervening circulation and by extension to constrain properties of that circulation a history of ml equilibrium calcite 18o 18oc spanning the last deglaciation is inferred from a least squares fit of eight benthic foraminiferal 18oc records to green s function estimated for the modern ocean circulation disagreements between this history and the ml history implied by planktonic records would indicate deglacial circulation changes no deviations from the modern circulation are diagnosed because the two estimates of ml 18oc agree within their uncertainties over the deglaciation but diagnostics suggest data collection and modeling procedures useful for inferring circulation changes uncertainties of benthic derived ml 18oc are lowest in the high latitude regions chiefly responsible for ventilating the deep ocean additional high resolution planktonic records constraining these regions are of particular utility benthic records from the southern ocean where data are sparse appear to have the most power to reduce uncertainties in benthic derived ml 18oc understanding the spatiotemporal covariance of deglacial ml 18oc will also improve abilities of 18oc records to constrain deglacial circulation

assimilation of radiocarbon and chlorofluorocarbon data to constrain deep and bottom water transports in the world ocean a coarse resolution global model with time invariant circulation is fitted to hydrographic and tracer data by means of the adjoint method radiocarbon and chlorofluorocarbon cfc 11 and cfc 12 data are included to constrain deep and bottom water transport rates and spreading pathways as well as the strength of the global overturning circulation it is shown that realistic global ocean distributions of hydrographic parameters and tracers can be obtained simultaneously the model correctly reproduces the deep ocean radiocarbon field and the concentrations gradients between different basins the spreading of cfc plumes in the deep and bottom waters is simulated in a realistic way and the spatial extent as well as the temporal evolution of these plumes agrees well with observations radiocarbon and cfc observations place upper bounds on the northward transports of antarctic bottom water aabw into the pacific atlantic and indian oceans long term mean aabw transports larger than 5 sv sv 10 6 m 3 s 1 through the vema and hunter channels in the south atlantic and net aabw transports across 30 s into the indian ocean larger than 10 sv are found to be incompatible with cfc data the rates of equatorward deep and bottom water transports from the north atlantic and southern ocean are of similar magnitude 15 7 sv at 50 n and 17 9 sv at 50 s deep and bottom water formation in the southern ocean occurs at multiple sites around the antarctic continent and is not confined to the weddell sea a cfc forecast based on the assumption of unchanged abyssal transports shows that by 2030 the entire deep west atlantic exhibits cfc 11 concentrations larger than 0 1 pmol kg 1 while most of the deep indian and pacific oceans remain cfc free by 2020 the predicted cfc concentrations in the deep western boundary current dwbc in the north atlantic exceed surface water concentrations and the vertical cfc gradients start to reverse

north atlantic ventilation of southern sourced deep water in the glacial ocean one potential mechanism for lowering atmospheric co2 during glacial times is an increase in the fraction of the global ocean ventilated by the north atlantic which produces deep water with a low concentration of unused nutrients and thus drives the ocean s biological pump to a high efficiency however the data indicate that during glacial times a water mass low in 13c 12c and 14c c occupied the deep atlantic apparently at the expense of north atlantic deep water nadw this water is commonly referred to as southern sourced because of its apparent entry into the atlantic basin from the south prompting the inference that it was ventilated at the southern ocean surface here we propose that this deep atlantic water mass actually included a large fraction of north atlantic ventilated water the chemical characteristics of which were altered by recirculation in the deep southern and indo pacific oceans in an ocean model sensitivity experiment that reduces antarctic bottom water formation and weakens its overturning circulation we find that a much greater fraction of nadw is transported into the southern ocean without contacting the surface and is entrained and mixed into the southern sourced deep water that spreads into the global abyssal ocean thus north atlantic ventilation takes over more of the ocean interior lowering atmospheric co2 and yet the abyssal atlantic is filled from the south with old water low in 13c 12c and 14c c consistent with glacial data

global ocean heat content in the last interglacial the last interglacial 129 116 thousand years ago ka represents one of the warmest climate intervals of the past 800 000 years and the most recent time when sea level was metres higher than today however the timing and magnitude of the peak warmth varies between reconstructions and the relative importance of individual sources that contribute to the elevated sea level mass gain versus seawater expansion during the last interglacial remains uncertain here we present the first mean ocean temperature record for this interval from noble gas measurements in ice cores and constrain the thermal expansion contribution to sea level mean ocean temperature reached its maximum value of 1 1 0 3 c warmer than modern values at the end of the penultimate deglaciation at 129 ka which resulted in 0 7 0 3 m of thermosteric sea level rise relative to present level however this maximum in ocean heat content was a transient feature mean ocean temperature decreased in the first several thousand years of the interglacial and achieved a stable comparable to modern value by 127 ka the synchroneity of the peak in mean ocean temperature with proxy records of abrupt transitions in the oceanic and atmospheric circulation suggests that the mean ocean temperature maximum is related to the accumulation of heat in the ocean interior during the preceding period of reduced overturning circulation rapid oceanic and atmospheric circulation shifts led to a transient peak in the mean temperature of the ocean at the start of the last interglacial according to noble gas isotope records from an antarctic ice core

a global glacial ocean state estimate constrained by upper ocean temperature proxies abstractwe use the method of least squares with lagrange multipliers to fit an ocean general circulation model to the multiproxy approach for the reconstruction of the glacial ocean surface margo

the little ice age and 20th century deep pacific cooling proxy records show that before the onset of modern anthropogenic warming globally coherent cooling occurred from the medieval warm period to the little ice age the long memory of the ocean suggests that these historical surface anomalies are associated with ongoing deep ocean temperature adjustments combining an ocean model with modern and paleoceanographic data leads to a prediction that the deep pacific is still adjusting to the cooling going into the little ice age whereas temperature trends in the surface ocean and deep atlantic reflect modern warming this prediction is corroborated by temperature changes identified between the hms challenger expedition of the 1870s and modern hydrography the implied heat loss in the deep ocean since 1750 ce offsets one fourth of the global heat gain in the upper ocean

optimum multiparameter analysis of mixing in the thermocline of the eastern indian ocean a method of water mass analysis is developed which optimizes the use of all information contained in a hydrographic data set by solving an overdetermined linear set of mixing equations it requires representation of water masses by a finite number of water types and observations from at least as many oceanographic parameters as water types the procedure to establish the water types find the correct weights for the parameters and solve the mixing equations through minimization of the residuals is described in detail the method is applied to a data set from the eastern indian ocean where indian central water and australasian mediterranean water meet to produce a strong front in the thermocline it is shown that although most of the water from the indonesian archipelago is carried westward north of 11 s contributions from the australasian mediterranean water are found as far south as 25 s particularly along the australian shelf as a result of advection with the leeuwin current

covariances and linear predictability of the atlantic ocean abstract the problem of understanding linear predictability of elements of the ocean circulation is explored in the atlantic ocean for two disparate elements 1 sea surface temperature sst under the storm track in a small region east of the grand banks and 2 the meridional overturning circulation north of 30 5 s to be worthwhile any nonlinear method would need to exhibit greater skill and so a rough baseline from which to judge more complex methods is the goal a 16 year ocean state estimate is used under the assumption that internal oceanic variability is dominating externally imposed changes no evidence exists of significant nonlinearity in the bulk of the system over this time span linear predictability is the story of time and space correlations and some predictive skill exists for a few months in sst with some minor capability extending to a few years sixteen years is however far too short for an evaluation for interannual much less decadal variability although orders of magnitude are likely stably estimated the meridional structure of the meridional overturning circulation moc defined as the time varying vertical integral to the maximum meridional volume transport at each latitude shows nearly complete decorrelation in the variability across about 35 n the gulf stream system if a time scale exists displaying coherence of the moc between subpolar and subtropical gyres it lies beyond the existing observation duration and that has consequences for observing system strategies and the more general problem of detectability of change

rapid export of waters formed by convection near the irminger sea s western boundary the standard view of the overturning circulation emphasizes the role of convection yet for waters to contribute to overturning they must not only be transformed to higher densities but also exported equatorward from novel mooring observations in the irminger sea 2014 2016 we describe two water masses that are formed by convection and show that they have different rates of export in the western boundary current upper irminger sea intermediate water appears to form near the boundary current and is exported rapidly within 3 months of its formation deep irminger sea intermediate water forms in the basin interior and is exported on longer time scales the subduction of these waters into the boundary current is consistent with an eddy transport mechanism our results suggest that light intermediate waters can contribute to overturning as much as waters formed by deeper convection and that the export time scales of both project onto overturning variability

the mean age of ocean waters inferred from radiocarbon observations sensitivity to surface sources and accounting for mixing histories a number of previous observational studies have found that the waters of the deep pacific ocean have an age or elapsed time since contact with the surface of 700 1000 yr numerical models suggest ages twice as old here the authors present an inverse framework to determine the mean age and its upper and lower bounds givenglobaloceandataanalysisproject glodap radiocarbonobservations andthey show that the potential range of ages increases with the number of constituents or sources that are included in the analysis the inversion requires decomposing the world ocean into source waters which is obtained here using the total matrix intercomparison tmi method at up to 2 83 28 horizontal resolution with 11 113 surface sources the authors find that the north pacific at 2500 m depth can be no younger than 1100 yr old which is older than some previous observational estimates accounting for the broadness of surface regions where waters originate leads to a reservoir age correction of almost 100 yr smaller than would be estimated with a two or three water mass decomposition and explains some of the discrepancy with previous observational studies a best estimate of mean age is also presented using the mixing history along circulation pathways subject to the caveats that inference of the mixing history would benefit from further observations and that radiocarbon cannot rule out the presence of extremely old waters from exotic sources the deep north pacific waters are 1200 1500 yr old which is more in line with existing numerical model results

exploring uncertainties in the relationship between temperature ice volume and sea level over the past 50 million years over the past decade efforts to estimate temperature and sea level for the past 50 ma have increased in parallel efforts to model ice sheet changes during this period have been ongoing we review published paleodata and modeling work to provide insights into how sea level responds to changing temperature through changes in ice volume and thermal expansion to date the temperature to sea level relationship has been explored for the transition from glacial to interglacial states attempts to synthesize the temperature to sea level relationship in deeper time when temperatures were significantly warmer than present have been tentative we first review the existing temperature and sea level data and model simulations with a discussion of uncertainty in each of these approaches we then synthesize the sea level and temperature data and modeling results we have reviewed to test plausible forms for the sea level versus temperature relationship on this very long timescale there are no globally representative temperature proxies and so we investigate this relationship using deep sea temperature records and surface temperature records from high and low latitudes it is difficult to distinguish between the different plausible forms of the temperature to sea level relationship given the wide errors associated with the proxy estimates we argue that for surface high latitude southern hemisphere temperature and deep sea temperature the rate of change of sea level to temperature has not remained constant i e linear over the past 50 ma although the relationship remains ambiguous for the available low latitude surface temperature data a nonlinear form between temperature and sea level is consistent with ice sheet modeling studies this relationship can be attributed to 1 the different glacial thresholds for southern hemisphere glaciation compared to northern hemisphere glaciation and 2 the ice sheet carrying capacity of the antarctic continent

mean global ocean temperatures during the last glacial transition little is known about the ocean temperature s long term response to climate perturbations owing to limited observations and a lack of robust reconstructions although most of the anthropogenic heat added to the climate system has been taken up by the ocean up until now its role in a century and beyond is uncertain here using noble gases trapped in ice cores we show that the mean global ocean temperature increased by 2 57 0 24 degrees celsius over the last glacial transition 20 000 to 10 000 years ago our reconstruction provides unprecedented precision and temporal resolution for the integrated global ocean in contrast to the depth region organism and season specific estimates provided by other methods we find that the mean global ocean temperature is closely correlated with antarctic temperature and has no lead or lag with atmospheric co2 thereby confirming the important role of southern hemisphere climate in global climate trends we also reveal an enigmatic 700 year warming during the early younger dryas period about 12 000 years ago that surpasses estimates of modern ocean heat uptake

on the total input of antarctic waters to the deep ocean a preliminary estimate from chlorofluorocarbon measurements 1 deep ocean inventories of dissolved chlorofluorocarbon 11 cfc 11 along representative sections off antarctica provide the first estimate of the overall strength of all dense water sources in the southern ocean their formation rates are reported for three density layers that span the main water masses involved in the lower limb of the thermohaline circulation thc the bottom layer is supplied via sinking of antarctic bottom water aabw produced at a few continental shelves the middle layer receives the offshore injection of ventilated modified circumpolar deep water mcdw produced along much of the lengthy antarctic slope front the top layer is ventilated by northward export of antarctic surface water into the upper circumpolar deep water of the antarctic circumpolar current average southern ocean inputs to the upper two layers of the deep ocean for the 1970 1990 period are derived on the basis of the cfc 11 distributions along meridional sections the mean cfc 11 saturations of all water mass ingredients and the inferred mixing leading to production of dense source waters about 5 4 1 7 sv 1 sv 10 6 m 3 s 1 of near freezing shelf water ventilate the bottom layer and 4 7 1 7 sv and 3 6 1 3 sv of cold antarctic surface water ventilate the middle and top layers therefore the total contribution of ventilated southern ocean waters to the lower limb of the global thc is about 14 sv this is close to the about 17 sv estimated for north atlantic near surface sources from cfc 11 inventories their entrainment of 7 4 2 4 sv of cfc poor subsurface lower circumpolar deep water during the formation and sinking of aabw and mcdw raises the total southern ocean input to the deep ocean to about 21 sv

abyssal water carbon 14 distribution and the age of the world oceans the carbon 14 distribution in the abyssal waters of the world oceans indicates replacement times for pacific indian and atlantic ocean deep waters more than 1500 meters deep of approximately 510 250 and 275 years respectively the deep waters of the entire world ocean are replaced on average every 500 years

40ar39ar dating of glauconites measured 39ar recoil loss from well crystallized specimens abstract nine glauconite samples with relatively high k concentrations and which appear to be well crystallized using normal x ray diffraction techniques have been studied using the 40 ar 39 ar method the glauconite 40 ar 39 ar apparent ages exceed their k ar rb sr and in most cases stratigraphic ages by substantial amounts 40 ar 39 ar release spectra sometimes yield plateaus but these apparent ages have no geological significance the results indicate that 39ar is lost by recoil from mineral grains during neutron irradiation consistent with previously reported observations the amount of 39ar loss was measured by isotope dilution for four samples and varied from 29 to 17 in contrast radiogenic 40ar is quantitatively retained during irradiation the very fine blades which make up glauconite grains yield the mineral susceptible to large amounts of 39ar loss and unsuitable for 40 ar 39 ar dating

seasonal changes in beach topography and beach volume in delaware abstract a beach study was conducted along a shore segment of the delaware coast from march 1982 through to april 1983 results indicate that beach topography and beach volume varied with changes in wave climatic regimes the regimes in turn were generally in phase with the winter and summer seasons because both the magnitude and frequency of storm waves were higher during winter than in summer the winter beach shape was concave upward following the winter storms of 1981 1982 swells rebuilt the beach in two stages from march through to august 1982 in the first stage the beach vertically accreted aggraded and in the second it laterally accreted prograded the aggrading stage involved the welding of a swash bar to the foreshore thereafter swash overtopping caused deposition on and landward of the bar in time the swash bar attained a berm and swale topography the prograding stage started when the swash could no longer overtop the berm crest which confined deposition to the foreshore this stage occurred following a minor or moderate storm event that shifted the berm crest upward and landward or during a neap tidal stage that occurred after the construction of a spring tide berm between march and the end of august 1982 60 m 3 of sediments per 1 m of beach were deposited on the shore of this value 67 was attributed to aggradational processes while the remaining 33 was attributed to progradational processes swells as well as storm waves caused vertical accretion storm waves contributed 20 of the total sediment volume deposited on the beach when the shore was at its maximum sediment volume for 1982 the beach topography was convex upward an inverse relationship existed between the mean monthly sediment volume and the mean monthly surge variability the surge level was used as an index of wave conditions high surge levels were associated with large waves while low surge levels were associated with small waves when surge variability was high during the winter sediment volume on the beach was low and conversely when surge variability was low in summer sediment volume was high correlation analysis showed that 80 of the variance of the mean monthly sediment volume was explained by the mean monthly surge variability

least squares multiple tracer analysis of water mass composition we present an inverse method that uses measurements of the concentration of several tracer variables to find the mixture of source water types that best describes in a weighted least squares sense the composition of the water sample the solution includes two physically realistic constraints first that all sources together must sum to 100 and second that no source is present in negative amounts these constraints improve the statistical stability of the solution the method is particularly valuable in regions involving strong mixing among a relatively large number of source water types in contrast to conventional ts analysis more water types can be considered the assumption of mixing along isopycnals is unnecessary and sensitivity to errors in individual tracer measurements is reduced by averaging the influence of a larger number of tracers we demonstrate the method using data from two oceanographic regions analysis of summer data from the continental margin off vancouver island british columbia canada confirms and quantifies the importance of deep upwelling of california undercurrent water onto the continental shelf it also identifies localized outer shelf filaments of low salinity water originating from the vancouver island coastal current finally we reanalyze the north african data of tomczak and confirm his interpretation of diapycnal mixing at the frontal boundary between north atlantic central water and south atlantic central water masses

observations of change in the southern ocean the southern ocean has been in a state of disequilibrium with its atmosphere and cryosphere during recent decades ocean station and drifting float observations have revealed rising temperatures in

how is the ocean filled 1 the ocean surface rapidly exchanges heat freshwater and gases with the atmosphere but once water sinks into the ocean interior the inherited properties of seawater are closely conserved previous water mass decompositions have described the oceanic interior as being filled by just a few different property combinations or water masses here we apply a new inversion technique to climatological tracer distributions to find the pathways by which the ocean is filled from over 10 000 surface regions based on the discretization of the ocean surface at 2 by 2 resolution the volume of water originating from each surface location is quantified in a global framework and can be summarized by the estimate that 15 of the surface area fills 85 of the ocean interior volume ranked from largest to smallest the volume contributions scaled by surface area follow a power law distribution with an exponent of 1 09 0 03 that appears indicative of the advective diffusive filling characteristics of the ocean circulation as demonstrated using a simple model this work quantifies the connection between the surface and interior ocean allowing insight into ocean composition atmosphere ocean interaction and the transient response of the ocean to a changing climate

seasonal variation of mid foreshore sediments at a delaware beach abstract from march 1982 through april 1983 at a delaware beach there was a modest but significant relation between the first three moments of mid foreshore sediment distributions and surge variability based on monthly averages as surge variability increased from summer to winter that is as the magnitude and frequency of storm waves increased the mean grain size increased sorting improved and skewness became more positive the reverse was also noted from winter to summer the results of stepwise regression analysis showed that mean particle size was highly influenced by the percentage of fine sands between 2 25 and 2 75 fines which was relatively high in summer and low in winter sorting was most sensitive to the extent of the coarse tail in a sediment sample as this tail was extended sorting became poorer the extent of the coarse tail and the percentage of fines explained most the variance of skewness as the coarse end of a sediment sample was extended and as the percentage of fines increased skewness became more negative

dilution of the northern north atlantic ocean in recent decades declining salinities signify that large amounts of fresh water have been added to the northern north atlantic ocean since the mid 1960s we estimate that the nordic seas and subpolar basins were diluted by an extra 19 000 5000 cubic kilometers of freshwater input between 1965 and 1995 fully half of that additional fresh water about 10 000 cubic kilometers infiltrated the system in the late 1960s at an approximate rate of 2000 cubic kilometers per year patterns of freshwater accumulation observed in the nordic seas suggest a century time scale to reach freshening thresholds critical to that portion of the atlantic meridional overturning circulation

rates and mechanisms of water mass transformation in the labrador sea as inferred from tracer observations time series of hydrographic and transient tracer 3h and 3he observations from the central labrador sea collected between 1991 and 1996 are presented to document the complex changes in the tracer fields as a result of variations in convective activity during the 1990s between 1991 and 1993 as atmospheric forcing intensified convection penetrated to progressively increasing depths reaching 2300 m in the winter of 1993 over that period the potential temperature salinity s properties of labrador sea water stayed nearly constant as surface cooling and downward mixing of freshwater was balanced by excavating and upward mixing of the warmer and saltier northeast atlantic deep water it is shown that the net change in heat content of the water column 150 2500 m between 1991 and 1993 was negligible compared to the estimated mean heat loss over that period 110 w m 2 implying that the lateral convergence of heat into the central labrador sea nearly balances the atmospheric cooling on a surprisingly short timescale interestingly the 3h 3he age of labrador sea water increased during this period of intensifying convection starting in 1995 winters were milder and convection was restricted to the upper 800 m between 1994 and 1996 the evolution of 3h 3he age is similar to that of a stagnant water body in contrast the increase in and s over that period implies exchange of tracers with the boundaries via both an eddy induced overturning circulation and along isopycnal stirring by eddies with an exchange coefficient of o 500 m2 s 1 the authors construct a freshwater budget for the labrador sea and quantitatively demonstrate that sea ice meltwater is the dominant cause of the large annual cycle of salinity in the labrador sea both on the shelf and the interior it is shown that the transport of freshwater by eddies into the central labrador sea 140 cm between march and september can readily account for the observed seasonal freshening finally the authors discuss the role of the eddy induced overturning circulation with regard to transport and dispersal of the newly ventilated labrador sea water to the boundary current system and compare its strength 2 3 sv to the diagnosed buoyancy forced formation rate of labrador sea water

southwest pacific ocean water mass changes between 1968 69 and 1990 91 abstract water mass changes are estimated in the southwest pacific ocean by comparing a meridional hydrographic section along 170 w between 60 s and the equator occupied in 1968 69 during the southern cross cruise and again in 1990 during a noaa climate and global change cruise another comparison is made using a hydrographic section along 35 s between the date line and 169 w occupied in 1969 during usns eltanin cruise 40 and again in 1991 during a mapkiwi cruise the most robust change consists of cooling and freshening on isopycnals with peak differences exceeding 1 0 c 0 25 pss at the base of the subtropical thermocline the cooling and freshening starts above the stratification minimum of the subantarctic mode water and persists to below the salinity minimum of the antarctic intermediate water amplitudes are largest at 48 s near where these water masses subduct and decay toward 20 s near the axis of the subtropical gyre this change is likely the result of surface warming and or freshening

an interpretation of trends in grain size measures abstract the mean grain size sorting and skewness of a sedimentary deposit are dependent on the sediment grain size distribution of its source and the sedimentary processes of i winnowing erosion ii selective deposition of the grain size distribution in transport and iii total deposition of the sediment in transport if a source sediment undergoes erosion and the resultant sediment in transport is deposited completely the deposit must be finer better sorted and more negatively skewed than the source this trend is referred to as case i the lag remaining after erosion on the other hand must be coarser better sorted and more positively skewed case ii if sediment in transport undergoes selective deposition the resultant deposit can either be finer case iiia or coarser cas iiib than the source but the sorting will be better and the skew more positive although exceptions to these trends may occur they suggest that comparison of one sediment must be made with another for the proper identification of the sedimentary process and therefore it is not possible for a single grain size distribution to identify the depositional environment the trends also suggest that the skewness of a grain size distribution has been widely misinterpreted and implies neither the truncation of one of the tails nor the mixing of more than one mode rather a skewed sediment is the natural result of the sedimentary process in a system of related environments these trends can be used to identify both the probable source and the probable deposit and by inference the net sediment transport paths among sedimentary deposits such an analysis provides a rapid understanding of the sedimentary processes identifies patterns of erosion and accretion and may suggest transport processes

convection with rotation in a neutral ocean a study of open ocean deep convection abstract the intensity and scale of the geostrophically adjusted end state of the convective overturning of a homogeneous rotating ocean of depth h at a latitude where the coriolis parameter is f induced by surface buoyancy loss of magnitude b0 are studied by numerical experiment the experiments are related to observations and laboratory studies of open ocean deep convection a numerical model based on the nonhydrostatic boussinesq equations is used the grid spacing of the model is small enough that gross aspects of convective plumes themselves can be resolved yet the domain of integration is sufficiently large to permit study of the influence of plumes on the large scale and geostrophic adjustment of the convected water numerical simulations suggest that cooling at the sea surface is offset by buoyancy drawn from depth through the agency of convective plumes these plumes efficiently mix the water column to generate a dense chimney of fluid which subsequently breaks up through the mechanism of bar

quantifying antarctic bottom water and north atlantic deep water volumes 1 a near global census of antarctic bottom water aabw and north atlantic deep water nadw is essayed through a nonnegative least squares analysis of conservative and quasi conservative seawater properties aabw thickness generally decreases from south to north modulated by ocean bathymetry likewise nadw thickness generally decreases from north to south in the atlantic ocean nadw dominates below the thermocline of the atlantic ocean at least as far south as the subtropical gyre of the south atlantic with a lesser but still significant influence around the entire antarctic circumpolar current in the indian ocean and in the pacific ocean however in the pacific and indian oceans aabw dominates below the thermocline in addition measurable quantities of aabw reach into the abyssal north atlantic on both sides of the mid atlantic ridge the census results suggest that aabw occupies roughly twice the volume of nadw in the three main oceans and that aabw is in contact with roughly twice the area of the deep main ocean floor compared with nadw however these results are somewhat sensitive to choices of water masses their values of seawater properties and the weightings of the seawater properties used in the analysis

the influence of air and sea exchange on the carbon isotope distribution in the sea we explore here the influence of the temperature dependence of isotope fractionation between atmospheric co2and ocean co2 on the distribution of carbon isotopes in the ocean this is accomplished by an analysis of departures from the expected redfield tie between po4 and 13c we find that for the surface ocean the temperature influence largely compensates for the biologic influence in the deep ocean the temperature influence imprinted at the sites of deepwater formation reduces somewhat the biologically induced difference between the carbon isotope ratios for deep waters produced in the northern atlantic and in the antarctic these same features are reproduced in the hamburg ocean model in order to assess the impact of changes in the ratio of ocean mixing rate to wind speed we have made a model run in which co2 exchange rates between air and sea were everywhere doubled as expected the influence of the thermodynamic effect on the oceanic carbon isotope distribution is magnified

characterizing transport between the surface mixed layer and the ocean interior with a forward and adjoint global ocean transport model the theory of first passage time distribution functions and its extension to last passage time distribution functions are applied to the problem of tracking the movement of water masses to and from the surface mixed layer in a global ocean general circulation model the first passage time distribution function is used to determine in a probabilistic sense when and where a fluid element will make its first contact with the surface as a function of its position in the ocean interior the last passage time distribution is used to determine when and where a fluid element made its last contact with the surface a computationally efficient method is presented for recursively computing the first few moments of the first and last passage time distributions by directly inverting the forward and adjoint transport operator this approach allows integrated transport information to be obtained directly from the differential form of the transport operator without the need to perform lengthy multitracer time integration of the transport equations the method which relies on the stationarity of the transport operator is applied to the time averaged transport operator obtained from a three dimensional global ocean simulation performed with an ogcm with this approach the author i computes surface maps showing the fraction of the total ocean volume per unit area that ventilates at each point on the surface of the ocean ii partitions interior water masses based on their formation region at the surface and iii computes the three dimensional spatial distribution of the mean and standard deviation of the age distribution of water

radiocarbon based circulation age of the world oceans 1 the distributions of deep ocean 14c data are often used to illustrate the rate of deep ocean circulation the associated conventional 14c ages show a difference of 1000 years between the north atlantic and the southern ocean and a difference of another 1000 years between the southern ocean and the north pacific these differences may be interpreted directly and mistakenly as the timescale of circulation the characterization of the deep ocean circulation being millennial is common using objectively gridded natural 14c data of key et al 2004 i recast 14c in terms of circulation by accounting for 1 long surface ocean reservoir 14c ages and 2 two sources of deep water formed in the north atlantic and around antarctica the new distribution of circulation 14c ages is more consistent with the deep ocean being characterized by a centennial timescale than a millennial timescale also the role of the southern sourced deep water is now made more obvious by accounting for the two important controls on oceanic 14c that are not well known outside the field of chemical oceanography the new map will be useful as an illustration of global deep ocean circulation to the wider scientific community and as a pedagogical tool to new students in earth sciences and oceanography

eddy mediated transport of warm circumpolar deep water across the antarctic shelf break the antarctic slope front asf modulates ventilation of the abyssal ocean via the export of dense antarctic bottom water aabw and constrains shoreward transport of warm circumpolar deep water cdw toward marine terminating glaciers along certain stretches of the continental shelf particularly where aabw is exported density surfaces connect the shelf waters to the middepth circumpolar deep water offshore offering a pathway for mesoscale eddies to transport cdw directly onto the continental shelf using an eddy resolving process model of the asf the authors show that mesoscale eddies can supply a dynamically significant transport of heat and mass across the continental shelf break the shoreward transport of surface waters is purely wind driven while the shoreward cdw transport is entirely due to mesoscale eddy transfer the cdw flux is sensitive to all aspects of the model s surface forcing and geometry suggesting that shoreward eddy heat transport may be localized to favorable sections of the continental slope

a generalized transport theory water mass composition and age abstract a general theory to describe and understand advective and diffusive ocean transport is reported it allows any passive tracer field with an atmospheric source to be constructed by superposing sea surface contributions with a generalized green s function called the boundary propagator of the passive tracer equation the boundary propagator has the interpretation of the joint water mass and transit time distribution from the sea surface the theory thus includes the classical oceanographic idea of water mass analysis and extends it to allow for a distribution of transit times from the sea surface the joint water mass and transit time distribution contains complete information about the transport processes in the flow it captures this information in a more accessible way than using velocity and diffusivity fields however at least for the case of sequestration and transport of dissolved material by the ocean circulation the boundary propagator is thus the natural quantity to consider when discus

the subpolar mode water of the north atlantic ocean abstract the warm waters of the subtropical and subpolar basins of the north atlantic have tight regional temperature salinity relationships and are conventionally called the regional central waters a volumetric census of the temperature salinity characteristics of the north atlantic by wright and worthington 1970 shows that waters characterized by certain segments of the t s relationships have large volumes compared to those of other segments volumetric mode waters such mode waters appear as layers with increased vertical separation between isopycnals pycnostads the present study reports on the existence of pycnostads in the central and eastern north atlantic these subpolar mode waters are formed by deep winter convection in the subpolar north atlantic and participate in the upper water circulation of the northern north atlantic the seasonal outcropping of the pycnostads occurs within and adjacent to the north atlantic current the irminger current the east and west greenland currents and

lagrangian pathways of upwelling in the southern ocean the spatial and temporal variability of upwelling into the mixed layer in the southern ocean is studied using a 1 10 ocean general circulation model virtual drifters are released in a regularly spaced pattern across the southern ocean at depths of 250 500 and 1000 m during both summer and winter months the drifters are advected along isopycnals for a period of four years unless they outcrop into the mixed layer where lateral advection and a parameterization of vertical mixing is applied the focus of this study is on the discrete exchange between the model mixed layer and the interior localization of interior mixed layer exchange occurs downstream of major topographic features across the indian and pacific basins creating hotspots of outcropping minimal outcropping occurs in the atlantic basin while 59 of drifters outcrop in the pacific sector and in drake passage the region from 140 w to 40 w a disproportionately large amount even when considering the relative basin sizes due to spatial and temporal variations in mixed layer depth the lagrangian trajectories provide a statistical measure of mixed layer residence times for each exchange into the mixed layer the residence time has a rayleigh distribution with a mean of 30 days the cumulative residence time of the drifters is 261 194 days over a period of four years these results suggest that certain oceanic gas concentrations such as co 2 and 14 c will likely not reach equilibrium with the atmosphere before being re subducted

total matrix intercomparison a method for determining the geometry of water mass pathways abstract ocean tracer distributions have long been used to decompose the deep ocean into constituent water masses but previous inverse methods have generally been limited to just a few water masses that have been defined by a subjective choice of static property combinations through air sea interaction and upper ocean processes all surface locations are potential sources of distinct tracer properties and thus it is natural to define a distinct water type for each surface site here a new box inversion method is developed to explore the contributions of all surface locations to the ocean interior as well as the degree to which the observed tracer fields can be explained by a steady state circulation with unchanging surface boundary conditions the total matrix intercomparison tmi method is a novel way to invert observations to solve for the pathways connecting every surface point to every interior point in the limiting case that the circulation is steady and that five conservative tracers are perf

reduced ventilation and enhanced magnitude of the deep pacific carbon pool during the last glacial period it has been proposed that the ventilation of the deep pacific carbon pool was not significantly reduced during the last glacial period posing a problem for canonical theories of glacial interglacial co2 change however using radiocarbon dates of marine tephra deposited off new zealand we show that deep 2000 m 2000 m and shallow sub surface ocean atmosphere 14c age offsets i e reservoir or ventilation ages in the southwest pacific increased by 1089 and 337 yrs respectively reaching 2689 and 1037 yrs during the late glacial a comparison with other radiocarbon data from the southern high latitudes suggests that broadly similar changes were experienced right across the southern ocean if like today the southern ocean was the main source of water to the glacial ocean interior these observations would imply a significant change in the global radiocarbon inventory during the last glacial period possibly equivalent to an increase in the average radiocarbon age 2 km 2 km of 700 yrs 700 yrs simple mass balance arguments and numerical model sensitivity tests suggest that such a change in the ocean s mean radiocarbon age would have had a major impact on the marine carbon inventory and atmospheric co2 possibly accounting for nearly half of the glacial interglacial co2 change if confirmed these findings would underline the special role of high latitude shallow sub surface mixing and air sea gas exchange in regulating atmospheric co2 during the late pleistocene

contribution of seasonal sub antarctic surface water variability to millennial scale changes in atmospheric co2 over the last deglaciation and marine isotope stage 3 the southern ocean is thought to have played a key role in past atmospheric carbon dioxide co2 atm changes three main factors are understood to control the southern ocean s influence on co2 atm via their impact on surface ocean pco2 and therefore regional ocean atmosphere co2 fluxes 1 the efficiency of air sea gas exchange which may be attenuated by seasonal or annual sea ice coverage or the development of a shallow pycnocline 2 the supply of co2 rich water masses from the sub surface and the deep ocean which is associated with turbulent mixing and surface buoyancy and or wind forcing and 3 biological carbon fixation which depends on nutrient availability and is therefore influenced by dust deposition and or upwelling in order to investigate the possible contributions of these processes to millennial scale co2 atm variations during the last glacial and deglacial periods we make use of planktonic foraminifer census counts and stable oxygen and carbon isotope measurements in the planktonic foraminifera globigerina bulloides and neogloboquadrina pachyderma sinistral from marine sediment core md07 3076q in the sub antarctic atlantic these data are interpreted on the basis of a comparison of core top and modern seawater isotope data which permits an assessment of the seasonal biases and geochemical controls on the stable isotopic compositions of g bulloides and n pachyderma s based on a comparison of our down core results with similar data from the southeast atlantic cape basin we infer past basin wide changes in the surface hydrography of the sub antarctic atlantic we find that millennial scale rises in co2 atm over the last 70 ka are consistently linked with evidence for increased spring upwelling and enhanced summer air sea exchange in the sub antarctic atlantic parallel evidence for increased summer export production would suggest that seasonal changes in upwelling and air sea exchange exerted a dominant influence on surface pco2 in the sub antarctic atlantic these results underline the role of southern ocean dynamics in particular their seasonal variations in driving millennial scale variations in co2 atm

tracer transport timescales and the observed atlantic pacific lag in the timing of the last termination 1 the midpoint of the last termination occurred 4 000 years earlier in the deep atlantic than the deep pacific according to a pair of benthic foraminiferal 18o records seemingly implying an internal circulation shift because the lag is much longer than the deep radiocarbon age here a scenario where the lag is instead caused by regional surface boundary condition changes delays due to oceanic transit timescales and the interplay between temperature and seawater 18o 18ow is quantified with a tracer transport model of the modern day ocean circulation using an inverse method with individual green functions for 2 806 surface sources a time history of surface temperature and 18owis reconstructed for the last 30 000 years that is consistent with the foraminiferal oxygen isotope data mg ca derived deep temperature and glacial pore water records thus in the case that the ocean circulation was relatively unchanged between glacial and modern times the interbasin lag could be explained by the relatively late local glacial maximum around antarctica where surface 18ow continues to rise even after the north atlantic 18owfalls the arrival of the signal of the termination is delayed at the pacific core site due to the destructive interference of the still rising antarctic signal and the falling north atlantic signal this scenario is only possible because the ocean is not a single conveyor belt where all waters at the pacific core site previously passed the atlantic core site but instead the pacific core site is bathed more prominently by waters with a direct antarctic source

how much deep water is formed in the southern ocean three tracers are used to place constraints on the production rate of ventilated deep water in the southern ocean the distribution of the water mass tracer po4 phosphate star in the deep sea suggests that the amount of ventilated deep water produced in the southern ocean is equal to or greater than the outflow of north atlantic deep water from the atlantic radiocarbon distributions yield an export flux of water from the north atlantic which has averaged about 15 sv over the last several hundred years cfc inventories are used as a direct indicator of the current production rate of ventilated deep water in the southern ocean although coverage is as yet sparse it appears that the cfc inventory is not inconsistent with the deep water production rate required by the distributions of po4 and radiocarbon it has been widely accepted that the major part of the deep water production in the southern ocean takes place in the weddell sea however our estimate of the southern ocean ventilated deep water flux is in conflict with previous estimates of the flux of ventilated deep water from the weddell sea which lie in the range 1 5 sv possible reasons for this difference are discussed

millennial scale glacial meltwater pulses and their effect on the spatiotemporal benthicδ18o variability 1 ratios of oxygen isotope values obtained from foraminiferal calcite are one of the most established paleoceanographic proxies they are used in the context of estimating variations in ice volume ocean temperature and salinity and provide a means to date marine sediment cores across different ocean basins our study addresses the question how the 18o of the deglacial meltwater signal propagates into the interior ocean when large scale millennial scale reorganizations of the atlantic meridional overturning circulation amoc are present analyzing a series of idealized tracer injection experiments conducted with an earth system model we find that a substantial weakening of the amoc leads to a massive delay in the export of the glacioeustatic oxygen isotope signal into the deep ocean whereas the atlantic pacific lag in benthic oxygen isotope signals is not increased furthermore it is shown that an amoc cessation causes a decoupling of 18o propagation time and water mass age in particular in the deep pacific our results lend further support to the notion that benthic oxygen isotope records obtained from stacks are not a useful global chronostratigraphic tool during periods of millennial scale global ocean circulation changes the regionally varying delay effect of the deglacial sea level signal studied here adds onto existing uncertainties in the interpretation and decomposition of benthic oxygen isotope in terms of sea level temperature and hydrographic variations