balancing rare earth element distributions in the northwestern mediterranean sea abstract elemental concentrations of rare earth elements ree and isotopic compositions of neodymium end have been measured in three water column profiles in the north western mediterranean sea clear enrichments of ree are observed when comparing to adjacent atlantic waters suggesting ree inputs along the circulation in this area for the first time relative proportions of external sources including submarine groundwater discharges sgd have been quantified for the studied area atmospheric deposition is estimated to be the most important external source for all the ree with an average contribution of 44 followed by diffusion from porewaters which provide a 30 dissolved riverine fluxes account for 11 sgd for 10 and dissolution of remobilized surface sediments the remaining 6 mass balances accounting for seawater transport and identified external sources have been delineated for the three main water masses modified atlantic waters levantine intermediate waters and western mediterranean deep waters they show that the balances of ree in this area are dominated by seawater mass mixing superimposed on this hydrography ree vertical profiles are affected by external sources and biogeochemical cycling dissolved ree are correctly balanced in deep waters whereas substantial missing fluxes are identified in the surface and intermediate water masses additional net lree outputs and hree inputs are required in the surface waters while net output fluxes for all the ree are missing at intermediate waters the most likely process suggested here is an active reversible scavenging consistent with a stronger adsorption of lree compared to hree in the particular case of the redox sensitive cerium the most plausible mechanism to explain the net output missing fluxes is ce 3 removal by particle scavenging via oxidation to insoluble ce 4 estimated ce oxidation rates of 0 33 d 1 in surface waters agree well with previously published values exchange fluxes derived from the isotopic nd mass balance indicate higher nd scavenging in surface compared to intermediate waters

orographic clouds in terrain blocked flows an idealized modeling study abstract idealized numerical simulations of moist strongly stratified flow over topography are used to study the processes that control orographic clouds in terrain blocked flows as a joint function of the nondimensional flow parameter nh u the horizontal topographic aspect ratio and the rossby radius of deformation nh f the simulations show the competition between enhanced upstream condensation in the secondary vertically propagating gravity wave and the reduction of condensation owing to enhanced low level flow deflection as nh u increases above about 1 5 the tendency for flow to be deflected around the barrier reduces cloud formation in the primary gravity wave over the ridge while increasing expands low level clouds over a broader upstream area ice clouds may form aloft in the secondary vertically propagating gravity wave and extend upstream for several hundred kilometers in terrain blocked flows more than half of the condensate mass develops upstream of the barrier in the secondary gravi

231pa 230th fractionation by ocean transport biogenic particle flux and particle type 231pa and 230th are removed from the water column by a process of reversible scavenging which quickly removes 230th to the sediment 231pa is less efficiently scavenged onto particles than 230th and is therefore more effectively transported via advection and diffusion before it reaches the ocean sediment this study combines particle fields dust opal caco3 poc derived from observations with the bern3d intermediate complexity ocean model and an equilibrium scavenging model for isotopes the equilibrium partition coefficient for particulate versus dissolved isotope activity is varied with particle type the model can explain many of the features of the global 231pa and 230th distribution the success of such a simple model at representing the global pattern of 231pa 230th activity ratio supports the use of this proxy in paleoceanographic studies we use the model to address the controversy concerning which particle types are dominant in fractionating 231pa 230th in the ocean the lithogenic dust flux is found to be unimportant for 231pa 230th fractionation the ocean fractionation of 231pa 230th is dominated by the distribution of the caco3 and opal flux we also confirm that opal is a weak scavenger of 230th

exchange of neodymium and its isotopes between seawater and small and large particles in the sargasso sea the concentrations and isotopic ratios of nd were measured in small 1 53 m and large 53 m in situ filtered particles sediment trap material sediment and aerosol samples collected during oligotrophic and productive conditions in the sargasso sea atmospheric input is the main source of exogeneous nd into the sargasso sea based on ndal ratios in trapped material we suggest that up to 50 of atmospheric nd could dissolve at the air sea interface the concentration and isotopic composition of nd vary with both depth and the particle size neodymium concentrations of small and large particles increase with depth from 2 9 12 g g and 5 8 11 8 g g respectively at 40 m the nd signature of large particles is significantly more negative nd 0 13 1 0 2 than that of the small ones nd 0 11 7 0 3 and the particles filtered deeper below 237 m the nd 0 values for small particles match the seawater whereas the nd 0 values of large particles remain less radiogenic these differences are related to the different behaviors of the particulate fractions small particles apparently exchange nd with seawater and then sink rapidly to depth as biologically formed aggregates large particles these aggregates isolate the small particles slowing the exchange with the water to produce different signatures between large particles and seawater since these exchange processes modify the particulate nd signature the shallow radiogenic nd 0 signature observed in the surface and subsurface waters in the nw atlantic is not due to external contributions and is likely of advective origin at depth below 800 m the magnitude of the aggregation disaggregation process varies significantly with season the fraction of small particles repackaged into large aggregates can vary from 0 8 to 80 100 in productive and oligotrophic conditions respectively this seasonal variation may correspond to sinking particles of different zooplanktonic origin vertical fluxes of nd into and out of the sargasso sea as well as exchange fluxes in the water column are examined about 50 of the particulate flux from the surface is remineralized at depth a net scavenging flux of 0 8 10 4 g m2 y is required this value corresponds to a scavenging nd residence time of 1900 y considerably longer than previous estimates of global oceanic residence time of nd on the order of 400 y

the large scale evolution of neodymium isotopic composition in the global modern and holocene ocean revealed from seawater and archive data neodymium isotopic compositions 143nd 144nd or end have been used as a tracer of water masses and lithogenic inputs to the ocean to further evaluate the faithfulness of this tracer we have updated a global seawater end database and combined it with hydrography parameters temperature salinity nutrients and oxygen concentrations carbon isotopic ratio and radiocarbon of dissolved inorganic carbon archive end data are also compiled for leachates foraminiferal tests deep sea corals and fish teeth debris from the holocene period 10 000 years at water depths 1500 m property property plots show clear correlations between seawater end and the other variables suggesting that large scale water mass mixing is a primary control of deepwater end distribution at 200 m basin scale seawater t s end diagrams demonstrate the isotopic evolution of different water masses seawater and archive end values are compared using property property plots and t s end diagrams archive values generally agree with corresponding seawater values although they tend to be at the upper limit in the pacific both positive and negative offsets exist in the northern north atlantic applying multiple regression analysis to deep 1500 m seawater data we established empirical equations that predict the main large scale deepwater end trends from hydrography parameters large offsets from the predicted values are interpreted as a sign of significant local regional influence dominant continental influence on seawater and archive end is observed mainly within 1000 km from the continents generally seawater and archive end values form gradual latitudinal trend in the atlantic and pacific at depths 600 m consistent with the idea that nd isotopes help distinguish between northern southern sourced water contributions at intermediate and deep water depths

tracing past ocean circulation to understand how ocean circulation and climate may change in the future we must first understand how the system operated in the past without man9s influence new inorganic isotopic tracers are now helping to elucidate past ocean circulation patterns but controversies remain regarding the relative influence of ocean circulation and weathering on the isotopic signals

upper ocean vertical supply a neglected primary factor controlling the distribution of neodymium concentrations of open ocean surface waters neodymium nd isotopes are an important geochemical tool to trace the present and past water mass mixing as well as continental inputs the distribution of nd concentrations in open ocean surface waters 0 100 m is generally assumed to be controlled by lateral mixing of nd from coastal surface currents and by removal through reversible particle scavenging however using 228ra activity as an indicator of coastal water mass influence surface water nd concentration data available on key oceanic transects as a whole do not support the above scenario from a global compilation of available data we find that more stratified regions are generally associated with low surface nd concentrations this implies that upper ocean vertical supply may be an as yet neglected primary factor in determining the basin scale variations of surface water nd concentrations similar to the mechanism of nutrients supply it is likely that stratification inhibits vertical supply of nd from the subsurface thermocline waters and thus the magnitude of nd flux to the surface layer consistently the estimated required input flux of nd to the surface layer to maintain the observed concentrations could be nearly two orders of magnitudes larger than riverine dust flux and also larger than the model based estimation on shelf derived coastal flux in addition preliminary results from modeling experiments reveal that the input from shallow boundary sources riverine input and release from dust are actually not the primary factors controlling nd concentrations most notably in the pacific and southern ocean surface waters

upstream effects of mesoscale mountains abstract the alpine experiment alpex has revealed that low level air is typically diverted around the alps without reaching the mountaintop in pursuit of an understanding of the physical basis of this phenomenon and of its generality we have explored the characteristics of orographic blocking of a rotating continuously stratified quid as revealed in a simple model problem retaining full nonlinear and transient effects hydrostatic dynamics is assumed and the obstacle is taken to be an infinitely long ridge with height h x the key questions treated are the strength of the upstream deceleration of cross mountain flow and the length scale over which the decelerated region extends by means of scale analysis the controlling parameters are found to be the rossby number ro u fl and the froude number fr nhm u where u is the speed of the oncoming flow f is the coriolis parameter l the mountain half width n the brunt vaisala frequency and hm is the maximum mountain height the scale analysis also

a new approach to the nd residence time in the ocean the role of atmospheric inputs concentrations of rare earth elements ree and nd isotopic ratios were analyzed for seawater filtered suspension and sediment trap samples collected in the tropical atlantic ocean eumeli program eutrophic mesotrophic and oligotrophic sites 20 n 18 21 w this is the first ree nd dataset on solution and different sized particles collected at the same site we present direct evidence of the nd isotopic exchange between particulate lithogenic fraction and seawater without significant mass transfer this exchange is probably one of the main factors that simultaneously constrains the nd concentration and isotopic ratio budget we propose a new approach to estimate the residence time of nd in the ocean nd based on isotopic exchange 200 yr nd 1000 yr the exchange requires a partial dissolution of lithogenic nd we estimate that the fraction of soluble nd proportion in atmospheric dust is of the order of 20 based on the isotopic ratios we suggest that the partial dissolution of atmospheric fallout is probably one of the main ree sources of the ocean

seasonal variations of sea ice motion in the canada basin and their implications ice velocities and sea level pressure data from arctic drifting buoys for 1979 85 are used to examine the seasonal variation of sea ice drift in the canada basin a recurring reversal of the mean anticyclonic gyre is demonstrated in late summer in response to changes in atmospheric forcing the identification of this reversal of ice motion is significant for numerical modeling of arctic atmosphere ocean ice interactions

geographically different oceanographic responses to global warming during the cenomanian turonian interval and oceanic anoxic event 2 abstract oceanic anoxic event oae 2 coincided with the cenomanian turonian boundary 93 9 ma and was one of the two most prominent and globally significant of the major mid cretaceous oaes a confluence of global warming major large igneous province volcanism and intensified hydrologic cycling preconditioned the earth system for widespread preservation of organic matter during oae2 however the ultimate necessary ingredient was enhanced nutrient availability in oceanic surface waters here we present new cenomanian turonian interval seawater neodymium isotope data from the proto indian ocean that demonstrates increased water column stratification during the pre and post oae2 interval punctuated by a transient decrease in this stratification immediately prior to the onset of oae2 recorded at ocean drilling program site 763 the direct oceanographic responses to climate change on both longer and short term time scales observed in this region are distinct from those recorded in the northern tropical and southern atlantic basins the transient de stratification of the water column in the eastern proto indian ocean likely did not contribute to the accumulation of organic rich sediments in the region indicating that weathering and or hydrothermal inputs promoted enhanced surface water nutrient levels and hence primary productivity

neodymium isotopic variations in northwest pacific waters abstract four vertical profiles of the concentration and isotopic composition of nd in seawater were obtained in the western north pacific two profiles from the kuroshio current regime showed congruently that although the nd concentration increases gradually with depth its isotopic composition varies significantly with depth depending upon the water mass occupying the water column the high salinity kuroshio waters originating from the north pacific tropical water nptw carry the least radiogenic nd nd 7 4 to 8 7 to this region at 250 m from the western margin continental shelves most likely from the east china sea the nd isotopic compositions in the north pacific intermediate water npiw that occurs at 600 to 1000 m in the subtropical region are fairly uniform at nd 3 7 the profile data from the 38 to 40 n kuroshio oyashio mixed water region off sanriku of honshu japan also suggest that the newest npiw with nd 3 2 is formed there by the mixing of various source waters and the radiogenic component of nd is derived mainly from the oyashio waters in the pacific deep water pdw below 1000 m the nd isotopic composition is neither vertically nor horizontally homogeneous suggesting that it serves as a useful tracer for sluggish deep water circulation as well two profiles from the izu ogasawara trench showed a minimum nd value at 2000 m suggesting that there exists a horizontal advective flow in the vicinity of honshu japan there is some evidence from other chemical properties to support this observation the waters below 4000 m including those within the trench in the subtropical region have nd values of around 5 suggesting that the deep waters are fed from the south along the western boundary ultimately from the antarctic bottom water aabw in the south pacific this extends up to 40 n along the japanese islands in the subarctic region 42 n the waters have more radiogenic nd with nd 4 0 throughout the water column presumably due to the supply of nd by weathering in such igneous provinces as the kuril kamchatska aleutian island chain the lateral inhomogeneity of the nd isotopic composition in pdw suggests that there may be different circulation and mixing regimes in the north pacific basin

the distribution of neodymium isotopes and concentrations in the eastern equatorial pacific water mass advection versus particle exchange the radiogenic isotope composition of the rare earth element ree neodymium nd is a powerful water mass proxy for present and past ocean circulation the processes controlling the nd budget of the global ocean are not quantitatively understood and in particular source and sink mechanisms are still under debate in this study we present the first full water column data set of dissolved nd isotope compositions and nd concentrations for the eastern equatorial pacific eep where one of the globally largest oxygen minimum zones omz is located this region is of particular interest for understanding the biogeochemical cycling of rees because anoxic conditions may lead to release of rees from the shelf whereas high particle densities and fluxes potentially remove the rees from the water column data were obtained between 1 40 n and 16 s along a nearshore and an offshore transect near surface zonal current bands such as the equatorial undercurrent euc and the subsurface countercurrent sscc which are supplying oxygen rich water to the omz are characterized by radiogenic nd isotope signatures end 2 surface waters in the northernmost part of the study area are even more radiogenic end 3 most likely due to release of nd from volcanogenic material deep and bottom waters at the southernmost offshore station 14 s are clearly controlled by advection of water masses with less radiogenic signatures end 7 originating from the southern ocean towards the equator however the deep waters show a clear trend towards more radiogenic values of up to end 2 the northernmost station located in the panama basin shows highly radiogenic nd isotope signatures in the entire water column which indicates that particle scavenging downward transport and release processes play an important role this is supported by relatively low nd concentrations in deep waters 3000 6000 m in the eep 20 pmol kg compared to locations in the northern and central pacific 40 60 pmol kg which suggests enhanced removal of nd in the eep

the sedimentary flux of dissolved rare earth elements to the ocean abstract we determined pore fluid rare earth element ree concentrations in near surface sediments retrieved from the continental margin off oregon and california usa these sites represent shelf to slope settings which lie above within and below the oxygen minimum zone of the northeast pacific the sediments are characterized by varying degrees of net iron reduction with pore fluids from the shelf sites being generally ferruginous and the slope sediments having less pronounced iron reduction zones that originate deeper in the sediment package ree concentrations show maxima in shallow upper 2 10 cm subsurface pore fluids across all sites with concentrations that rise more than two orders of magnitude higher than seawater these pore fluid enrichments highlight the importance of a sedimentary source of rees to the ocean s water column here we use our measurements to estimate the diffusive flux of nd out of ocean sediments resulting in a global flux between 18 and 110 10 6 mol nd yr 1 while we do assume that our pore fluid profiles as well as the very limited data previously published are representative of a wide array of ocean environments this calculated flux can account for the modeled missing nd source flux 76 10 6 mol nd yr 1 in global budgets arsouze et al 2009 pore fluid normalized ree patterns show distinct variation in the middle ree and heavy ree enrichments with sediment depth and amongst sites these patterns show that the heavy ree enrichment of pore fluids at our deep slope site 3000 m water depth is closest to the heavy ree enrichment of seawater this observation supports the view that ree cycling within the upper ten centimeters of deep sea marine sediments as opposed to shallower continental shelf and slope sediments plays a significant role in controlling the integrated global ree flux from the pore fluids and consequently the broad scale ree pattern in seawater

the profile of the rare earth elements in the canada basin arctic ocean we analyzed the dissolved rare earth element ree content of three water column profiles two shelf sites and one deep basin site in the canada basin in order to better constrain the behavior of rees in the arctic ocean dissolved concentrations of the rees in the surface are 1 3 to 1 9 times higher than deep water 500 m concentrations which are constant with depth la 19 23 pm nd 14 17 pm yb 4 0 4 3 pm the dominant source of rees to the surface waters of the canada basin is most likely pacific water flowing through the bering strait and chukchi sea and or the mackenzie river dissolved rees in the intermediate and deep waters are constant and appear to behave conservatively allowing us to investigate this aspect of ree behavior in the oceans calculated deep ocean residence times of the rees in the canada basin range from 450 700 years and match the age of these waters we postulate that these values are likely applicable to global deep ocean reservoirs and that observed deviations from this conservative value can help to constrain non conservative processes acting on the rees this article is protected by copyright all rights reserved

low froude number flow past three dimensional obstacles part i baroclinically generated lee vortices abstract we study the flow of a density stratified fluid past a three dimensional obstacle using a numerical model our special concern is the response of the fluid when the froude number is near or less than unity linear theory is inapplicable in this range of froude number and the present numerical solutions show the rich variety of phenomena that emerge in this essentially nonlinear flow regime two such phenomena which occupy parts i and ii of this study are the formation of a pair of vertically oriented vortices on the lee side and a zone of flow reversal on the windward side of the obstacle the ice vortices have been explained as a consequence of the separation of the viscous boundary layer from the obstacle however this boundary layer is absent by design in the present experiments and lee vortices still occur we argue that a vertical component of vorticity develops on the lee side owing to the tilting of horizontally oriented vorticity produced baroclinically as the isentropes deform in r

simulations of moist nearly neutral flow over a ridge although a fairly common atmospheric condition in orographic rain scenarios there is relatively little known about moist neutral flows over a ridge from theory and modeling presented in this paper are numerical simulations of the orographic flow modification occurring for a two dimensional moist nearly neutral flow over a ridge in the regime where the coriolis force can be neglected if an initially saturated moist neutral flow were to remain everywhere saturated as it flows over an obstacle then the expected solution would be the linear solution because the condition for linearity hill height less than the ambient wind velocity static stability is always met however for higher mountains the solutions indicate the development of areas of unsaturated air with correspondingly larger values of local static stability this internal switching from small to large values of static stability is an inherent nonlinearity which has far reaching consequences for understanding the orographic flow modification in this regime the sensitivity of the solution to the mountain height and to the initial cloud water content is analyzed here the authors find that the solutions fall into three basic categories if the mountain height is small enough a saturated flow can be maintained everywhere given sufficient initial cloud water for tall mountains the atmosphere upwind of the mountain is maintained in a saturated state and transitions to an unsaturated downslope flow on the lee side which has characteristics associated with downslope windstorms for mountains of intermediate height the solutions show the existence of an upwind propagating disturbance that has the effect of desaturating the atmosphere above the mountain

sensitivities of orographic precipitation to terrain geometry and upstream conditions in idealized simulations abstractthis study examines how variations in relatively simple terrain geometries influence orographic precipitation and its spatial patterns of sensitivity to small changes in upstream conditions an idealized three dimensional model is used to simulate a moist flow impinging upon three alpine scale terrain shapes a straight ridge a concave ridge and a convex ridge a variety of simulations are conducted to investigate the sensitivity of precipitation patterns to ridge length and upstream thermodynamic and wind conditions for an impinging flow with a nondimensional mountain height of approximately unity it is found that for the straight and convex ridges the flow response is mostly linear for the conditions examined here and passes over the obstacles with little lateral deflection the concave ridge however exhibits strengthened flow deceleration wave breaking in the lee and flow confluence between the ridge arms the concave ridge also generates substantially more precipitation than the other

study on vertical profiles of rare earth elements by using an ocean general circulation model 1 observed vertical profiles of rare earth elements rees in the north pacific ocean show a systematic change from lighter to heavier rees their source and sink consist of external fluxes coming from the surface and the bottom of the ocean and internal recycling within the ocean in order to evaluate the role of each source and sink in controlling the vertical profiles of rees we conduct numerical simulations of rees by using an ocean general circulation model these simulations demonstrate that the shape of their vertical profiles is not directly related to the external sources from river runoff atmospheric dust deposition and coastal regions but is sensitive to the internal recycling processes within the ocean nutrient like treatment where rees are removed at the surface and released in the deep ocean is suitable for simulating the vertical profiles of lighter rees but not for heavier rees when the irreversible scavenging is considered as a sink term and particle dissolution is taken into consideration as a source term the vertical profiles of heavier rees can be reproduced but those of lighter rees cannot the observed difference in the vertical profiles among rees can be reproduced only when the reversible scavenging process is incorporated into the model only the reversible scavenging process accounts for the observed vertical profiles of different rees in comprehensive manner

contrasting geochemical cycling of hafnium and neodymium in the central baltic sea the central baltic sea is a marginal brackish basin which comprises anoxic bottom waters and is surrounded by geological source terrains with a wide variety of compositions and ages this allows the investigation of water mass mixing using radiogenic isotope compositions of nd and hf as well as their geochemical cycling across varying redox conditions in the water column in this study we present the distribution of nd and hf concentrations and their isotopic compositions for 6 depth profiles and 3 surface water sites obtained during a cruise in the central baltic sea onboard the rv oceania as a part of the international geotraces program the results obtained indicate that nd isotopes effectively trace the mixing between more radiogenic saline waters from the south and unradiogenic fresh waters from the north which helps to understand the reliability of nd isotopes as water mass tracer in the open ocean in surface waters nd shows higher concentrations and less radiogenic isotope compositions at the northern stations which are progressively diluted and become more radiogenic to the south consistent with the counterclockwise circulation pattern of central baltic sea surface waters in contrast to the variable nd concentrations hf shows much less variability at the gotland deep station the nd concentrations of the euxinic waters are higher by a factor 10 than those of the overlying oxygen depleted waters whereas hf only shows small concentration variations this indicates faster removal of hf from the water column than nd moreover the dissolved hf isotope signatures document great variability but no consistent mixing trends our explanation is that hf has a lower residence time than nd and also that the hf isotope signatures of the sources are highly heterogeneous which is attributed to their differing magmatic and tectonic histories as well as incongruent post glacial weathering around the central baltic sea

contour mapping of arctic basin ice draft and roughness parameters a data base of ice draft and roughness parameters has been constructed for selected portions of the arctic ocean based upon analysis of under ice draft distribution data acquired by inverted echo sounder systems on submarines from the voyages of 12 submarines which traversed the alaskan canadian and central arctic regions of the arctic ocean during the summer and winter seasons a series of mean ice draft and deep draft keel statistics was calculated for 50 km segments along each submarine track contour maps of the mean ice draft its standard deviation the mean keel draft and the spatial frequency of ice keels were constructed they show that the greatest ice drafts the roughest ice and the greatest number of deep draft keels are found off the north coasts of the canadian archipelago and greenland due to ice convergence on these land barriers

rare earth element association with foraminifera abstract neodymium isotopes are becoming widely used as a palaeoceanographic tool for reconstructing the source and flow direction of water masses a new method using planktonic foraminifera which have not been chemically cleaned has proven to be a promising means of avoiding contamination of the deep ocean palaeoceanographic signal by detrital material however the exact mechanism by which the nd isotope signal from bottom waters becomes associated with planktonic foraminifera the spatial distribution of rare earth element ree concentrations within the shell and the possible mobility of ree ions during changing redox conditions have not been fully investigated here we present ree concentration and nd isotope data from mixed species of planktonic foraminifera taken from plankton tows sediment traps and a sediment core from the nw atlantic we used multiple geochemical techniques to evaluate how where and when rees become associated with planktonic foraminifera as they settle through the water column reside at the surface and are buried in the sediment analyses of foraminifera shells from plankton tows and sediment traps between 200 and 2938 m water depth indicate that only 20 of their associated nd is biogenically incorporated into the calcite structure the remaining 80 is associated with authigenic metal oxides and organic matter which form in the water column and remain extraneous to the carbonate structure remineralisation of these organic and authigenic phases releases ions back into solution and creates new binding sites allowing the nd isotope ratio to undergo partial equilibration with the ambient seawater as the foraminifera fall through the water column analyses of fossil foraminifera shells from sediment cores show that their ree concentrations increase by up to 10 fold at the sediment water interface and acquire an isotopic signature of bottom water adsorption and complexation of ree3 ions between the inner layers of calcite contributes significantly to elevated ree concentrations in foraminifera the most likely source of ree ions at this stage of enrichment is from bottom waters and from the remineralisation of oxide phases which are in chemical equilibrium with the bottom waters as planktonic foraminifera are buried below the sediment water interface redox sensitive ion concentrations are adjusted within the shells depending on the pore water oxygen concentration the concentration of ions which are passively redox sensitive such as ree3 ions is also controlled to some extent by this process we infer that a the nd isotope signature of bottom water is preserved in planktonic foraminifera and b that it relies on the limited mobility of particle reactive ree3 ions aided in some environments by micron scale precipitation of mnco3 this study indicates that there may be sedimentary environments under which the bottom water nd isotope signature is not preserved by planktonic foraminifera tests to validate other core sites must be carried out before downcore records can be used to interpret palaeoceanographic changes

composition of rare earth elements in settling particles collected in the highly productive north pacific ocean and bering sea implications for siliceous matter dissolution kinetics and formation of two ree enriched phases abstract settling particles were sampled monthly for 1 year using an automated time series sediment trap positioned at similar depths at two sites of high diatomaceous productivity in the north pacific ocean and bering sea the particles were analyzed for rare earth elements rees by inductively coupled plasma mass spectrometry icp ms with and without chemical treatment of the bulk samples to isolate siliceous fractions the ree composition of the bulk samples is explained largely by the contribution of two distinct components i carbonate with a higher ree concentration a negative ce anomaly and lighter ree lree enrichment ii opal with a lower ree concentration a weaker negative ce anomaly and heavier ree hree enrichment the siliceous fractions of settling particles are characterized by high si al ratios 30 190 reflecting high diatom productivity at the studied sites the la al ratio of the siliceous fraction is close to that of the upper crust but the lu al and lu la ratios are significantly higher than those of the upper crust or airborne particles indicating the presence of excess hrees in the siliceous fraction diatoms are believed to be important carriers of hrees the ce anomaly eu anomaly slope of the ree pattern and ree of the siliceous fraction vary exponentially with decreasing total mass flux they can be well reproduced according to the differential dissolution kinetics of elements in the order of ce

rare earth elements in early diagenetic foraminifer coatings pore water controls and potential palaeoceanographic applications abstract rare earth element ree distributions in the ocean bear the fingerprints of several key environmental processes including vertical particle organic carbon fluxes water column pore water oxygenation and ocean transports the use of fossil ree analyses in the service of palaeoceanography as redox water transport or nutrient cycling proxies has long been a tantalizing possibility here we demonstrate the application of a novel laser ablation microanalysis approach for the rapid and accurate measurement of the ree composition of early diagenetic coatings on fossil foraminifera by applying this new method to a range of core top and multi core samples we show that authigenic ree enrichments on planktonic foraminifer surfaces reefs reflect a primary seawater signature that becomes overprinted during sediment burial due to early diagenetic processes that control the flux of rees to pore fluids thus light rees lrees and eventually middle rees mrees are generally enriched in foraminifer coatings relative to seawater while ce anomalies ce ce recorded in surface sediments are typically more positive than local seawater values and are further eroded during burial with the onset of anoxic conditions in the sediment similar patterns have previously been observed in pore fluid measurements indeed we show that mn and fe concentrations measured in foraminifer coatings track the availability of these elements in pore water indicating that they are not associated with a secondary oxide phase we propose that these elements along with rees are instead adsorbed directly from pore fluids in contrast u in authigenic coatings tracks the removal of this element from solution under sub oxic conditions supporting the use of u ca in foraminifer coatings as a redox proxy although our results confirm a significant early diagenetic influence on reefs we also demonstrate the potential utility of ce enrichment relative to expected seawater values as a palaeo oxygenation proxy we support this proposal with down core measurements of u ca and ce enrichment spanning the last deglaciation in the sub antarctic atlantic as well as a global array of lgm measurements which are found to co vary with parallel estimates of radiocarbon ventilation age consistent with a widespread drop in oxygen suggesting an increase in the efficiency of the biological pump our results suggest that laser ablation reefs measurements may hold some promise for palaeoceanographic reconstruction in particular through a shift in emphasis away from the reconstruction of primary seawater signals to the analysis of diagenetic impacts that are sensitive to changing hydrographic conditions

temporal relationships of carbon cycling and ocean circulation at glacial boundaries evidence from high sedimentation rate south atlantic deep sea cores indicates that global and southern ocean carbon budget shifts preceded thermohaline circulation changes during the last ice age initiation and termination and that these were preceded by ice sheet growth and retreat respectively no consistent lead lag relationships are observed during abrupt millennial warming events during the last ice age allowing for the possibility that ocean circulation triggered some millenial climate changes at the major glacial interglacial transitions the global carbon budget and thermohaline ocean circulation responded sequentially to the climate changes that forced the growth and decline of continental ice sheets

neodymium isotopic composition and concentration in the western north atlantic ocean results from the geotraces ga02 section the neodymium nd isotopic composition of seawater is commonly used as a proxy to study past changes in the thermohaline circulation the modern database for such reconstructions is however poor and the understanding of the underlying processes is incomplete here we present new observational data for nd isotopes and concentrations from twelve seawater depth profiles which follow the flow path of north atlantic deep water nadw from its formation region in the north atlantic to the northern equatorial atlantic samples were collected during two cruises constituting the northern part of the dutch geotraces transect ga02 in 2010 the results show that the different water masses in the subpolar north atlantic ocean which ultimately constitute nadw have the following nd isotope characteristics upper labrador sea water ulsw end 14 2 0 3 labrador sea water lsw end 13 7 0 9 northeast atlantic deep water neadw end 12 5 0 6 northwest atlantic bottom water nwabw end 11 8 1 4 in the subtropics where these source water masses have mixed to form nadw which is exported to the global ocean upper nadw is characterised by end values of 13 2 1 0 2sd and lower nadw exhibits values of end 12 4 0 4 2sd while both signatures overlap within error the signature for lower nadw is significantly more radiogenic than the traditionally used value for nadw end 13 5 due to the dominance of source waters from the nordic seas nwabw and neadw comparison between the concentration profiles and the corresponding nd isotope profiles with other water mass properties such as salinity silicate concentrations neutral densities and chlorofluorocarbon cfc concentration provides novel insights into the geochemical cycle of nd and reveals that different processes are necessary to account for the observed nd characteristics in the subpolar and subtropical gyres and throughout the vertical water column while our data set provides additional insights into the contribution of boundary exchange in areas of sediment resuspension the results for open ocean seawater demonstrate at an unprecedented level the suitability of nd isotopes to trace modern water masses in the strongly advecting western atlantic ocean

towards explaining the nd paradox using reversible scavenging in an ocean general circulation model abstract the isotopic composition of the rare earth element neodymium nd has the potential to serve as water mass tracer because it is naturally tagged by continental sources with distinct ages and lithologies however in order to understand the limitations of this approach we need to know more about the physical and biogeochemical processes controlling the distribution of nd in the modern ocean for example nd isotope ratios behave quasi conservatively while concentrations in the water column generally increase with depth showing a broadly nutrient like behaviour we define this decoupling of nd concentrations and isotopic compositions as the nd paradox for the first time we model nd concentrations and isotopic compositions simultaneously and address the hypothesis that the nd paradox can be explained by a combination of lateral advection and reversible scavenging we impose a reversible scavenging model of nd removal from the ocean on the ocean circulation fields from the mit general circulation model using the transport matrix method we conclude that reversible scavenging is an active and important component in the cycling of nd in the ocean in the absence of an adequate alternative explanation reversible scavenging should be considered a necessary component in explaining the nd paradox

intensification and variability of ocean thermohaline circulation through the last deglaciation neodymium isotope ratios in the authigenic ferromanganese oxide component in a southeastern atlantic core reveal a history of the global overturning circulation intensity through the last deglaciation from a minimum during the last glacial maximum lgm north atlantic deep water nadw began to strengthen between 18 and 17 kyr cal bp approximately 2000 3000 years before the bolling warming it exhibits a gradually increasing baseline intensity that plateaus in the early holocene tracks increasing northern hemisphere insolation and parallels atmospheric co2 concentration millennial scale fluctuations are superimposed on this baseline nadw increase corresponding to events in northern hemisphere climate records the millennial excursions show sharp increases associated with the pre bolling retreat of continental glaciers and the bolling warming itself a decrease with allerod cooling and a recovery through the younger dryas and early holocene the data confirm a close link between deep ocean circulation and north atlantic climate changes there is no clear linkage with meltwater pulses indicating that rapid meltwater additions did not trigger observable mode changes in nadw production however rapid changes in north atlantic sea ice cover show a strong relationship with the millennial perturbations of nadw flux to the deep southern ocean the data indicate that the baseline intensity of nadw reaching the cape basin is paced by northern hemisphere insolation and that north atlantic sea ice coverage acts as a major amplifying link between the oceans and the atmosphere d 2004 elsevier b v all rights reserved

investigation of orographic precipitation over an isolated three dimensional complex topography with a dense gauge network radar observations and upslope model abstractthis study uses a dense rain gauge network radar observations and an upslope model to document the detailed aspects of precipitation over da tun mountain dt of northern taiwan under pre

rare earth elements in pore waters of marine sediments abstract the rare earth elements rees were measured in pore waters of the upper 25 cm of sediment from one site off peru and three sites on the california margin the pore water ree concentrations are higher than sea water and show systematic down core variations in both concentration and normalized pattern from these analyses and from comparison to other chemical species measured dissolved fe mn ba oxygen nitrate phosphate it is suggested that pore water rees can be grouped into three categories those that are from an fe source those that are from a poc source and cerium oxide rees from the fe source appear where anoxia is reached they have a distinctive middle ree mree enriched pattern the concentrations in this source are so elevated that they dominate ree trends in the fe oxide reduction zone the net result of flux from the poc source is relative enrichment of heavy rees hrees over light rees lrees reflecting remineralizing poc and complexation with doc a common linear ree pattern seen in both oxic and anoxic sediments is associated with this poc source as well as a hree enriched pattern that is seen in surficial sediments at the peru site overall the pore water results indicate that mn oxides are not an important carrier of rees in the oceans a ree biogeochemical model is presented which attempts to reconcile ree behavior in the water and sediment columns of the oceans the model proposes that poc fe oxide and ce oxide sources can explain the ree concentration profiles and relative abundance patterns in environments ranging from oxic sea water to anoxic pore water the model is also consistent with our observation that the ce anomaly of pore water does not exceed unity under any redox condition

on the dynamics of hawaiian cloud bands comparison of model results with observations and island climatology abstract this paper presents a detailed comparison study of three dimensional model results with an aircraft wind field mapping for the island of hawaii model runs were initialized using an aircraft sounding from 1 august 1985 and detailed predictions from the model are compared with observations from that day the strength and location of the upwind convergence zone were well simulated as well as the strong deflection and deceleration of the flow around the island and the geometry and location of the upstream cloud bands the good agreement between the model results and observations supports the results of our previous study in which we show that the flow pattern and associated cloud processes around the island of hawaii can be understood by considering the flow of a stably stratified fluid around a large three dimensional obstacle model runs with different wind directions showed that increasing northerly tradewind flow resulted in the band clouds moving closer to the shore line and the large scale

sea ice thickness distribution in the greenland sea and eurasian basin may 1987 upward sonar data from a 3400 km track in the greenland sea and the eurasian basin of the arctic ocean obtained by a british submarine in may 1987 have been statistically analyzed mean ice thicknesses in the greenland sea show significant melting with downstream distance at an average rate of 0 38 m per degree of latitude equivalent to about 2140 km3 yr 1 of freshwater input between 80 n and 75 n in the region north of fram strait between 82 n and 80 n there is remarkable consistency between mean ice drafts in 1987 and in three previous cruises 1976 1979 1985 while between greenland and the north pole there was a significant thinning in 1987 relative to 1976 in fram strait the mean ice draft shows evidence of thinning within the region of influence of a semipermanent eddy ice draft distributions show that the probability density function of deformed ice follows a negative exponential distribution and that the change of shape of the distribution with downstream distance in the greenland sea is due to preferential melting of thicker ice pressure ridge draft distributions also fit a negative exponential while their spacings fit a lognormal distribution lead width distribution follows a power law with an exponent of 1 45 for narrow leads and 2 50 for wider leads if leads are defined as having a 1 m maximum draft 1 67 and 2 76 for a 0 5 m maximum draft lead spacings follow a negative exponential distribution for moderate spacings 400 1500 m but with an excess of lead pairs at small and very large spacings

new insights into cycling of 231pa and 230th in the atlantic ocean abstract we use the bern3d model of intermediate complexity to examine the marine cycle of isotopes 231pa and 230th and the relationship between the particle bound ratio pa p th p and changes in the formation of the north atlantic deep water nadw model parameters describing reversible scavenging of isotopes by organic particles opal calcite and resuspended sediments were systematically varied and alternative sink parametrisations explored it proves difficult to simultaneously achieve a good agreement with observations of dissolved and particle associated concentrations of 231pa and 230th pa d th d pa p th p as well as the particle bound ratio pa p th p within the classical concept of reversible scavenging alone agreement between simulated and observed pa d th d and estimates of mean ocean residence times is improved by taking into account simplified representations of additional sinks at the sea floor bottom scavenging and at continental boundaries boundary scavenging we also find improved agreement between model and data by increasing lateral advection in particular for pa d these results point to the importance of sink processes that act in addition to reversible scavenging to shape the steady state distribution of 231pa and to a lesser degree of 230th in transient experiments in which the strength of the atlantic meridional overturning circulation amoc is periodically turned on and off we find a strong statistical relationship between variations in amoc strength and pa p th p at great depths in the northwest atlantic region these conclusions are robust across the range of sink parametrisations that are consistent with estimates in the mean ocean residence time of 231pa and 230th our results indicate that the relationship between pa p th p and amoc strength may not be fundamentally affected by uncertainties in sink processes at least on the large spatial and temporal scale considered here and support the idea that changes in pa p th p in sediments of the northwest atlantic are indicative of changes in amoc strength taking into account our simplified approach our results indicate that the relationship between pa p th p and amoc strength in the deep northwest atlantic is not affected by boundary scavenging or bottom scavenging our results thus support the idea that changes in pa p th p in sediments of the northwest atlantic are indicative of changes in amoc strength

simulations of temperature and turbulence structure of the oceanic boundary layer with the improved near surface process an improved model for the oceanic boundary layer is presented in view of the recent observation of the microstructure of the upper ocean including the high dissipation rate near the sea surface in the new model the surface boundary conditions for both the turbulent kinetic energy flux and the roughness length scale are modified the parameterization of stratification effects on turbulence is improved and the convective process is reformulated on the basis of the observation of uniform temperature and velocity profiles within the convective mixed layer evolutions of the profiles of both the dissipation rate and temperature of the observation data patches experiment as well as the time series of the sea surface temperature over the observation days are successfully simulated during a diurnal cycle for the first time it is also shown that the model reproduces various important features of the oceanic boundary layer for example the formation of a diurnal thermocline the profiles of buoyancy flux and the magnitudes of the buoyancy gradients both within the mixed layer and at the diurnal thermocline performance of the model is compared with that of the widely used mellor yamada model

tracing papua new guinea imprint on the central equatorial pacific ocean using neodymium isotopic compositions and rare earth element patterns abstract the nd isotopic composition ic and rare earth patterns of hydrodynamic structures of the equatorial pacific ocean were characterized along 140 w the nd ic of antarctic intermediate water aaiw and of the lower layer of the equatorial undercurrent euc at 140 w 13 c water are much more radiogenic at the equator than at their origin in the south equatorial current 12 s revealing that these water masses have been in contact with the highly radiogenic papua new guinea png slope in both cases only a small fraction less than 9 of the sediment deposited on the png slope is required to be exchanged or dissolved to explain these nd ic variations whereas the hydrographic properties of the same water masses remain unchanged this confirms the usefulness of this tracer to identify pathways of water masses these results emphasize the importance of jets in transporting lithogenic material into the subsurface layers of remote areas where aeolian inputs are particularly weak and corroborate the previous results on fe and al maximum in this area m l wells g k vallis e a silver nature 398 1999 601 604 the nd ic of the upper layer of the euc contrasts strongly to that of the subpycnocline layer indicating that the equatorial upwelling only affects the surface waters and is not effective between 120 and 150 m we calculate that the nd imprint of the png input is likely to vanish from this surface layer as it traverses the basin due to the replacement of upwelled waters by non radiogenic ones

rare earth element ree silicic acid complexes in seawater to explain the incorporation of rees in opal and the leftover rees in surface water new interpretation of dissolved ree distribution profiles in light of a new finding that diatom opal carries rare earth elements rees at an amount exceeding that which would explain the rees si ratio in open ocean columns the complex formation of rees with silicic acid and subsequent incorporation of the complex into diatom opal has been explored reported complex formation constants of euh3sio42 and an empirical linear relationship of the constants with hydrolysis constants were employed in the species calculation the calculation reveals that ree silicic acid complex is the dominant species of dissolved rees especially in deep layers of the pacific and the atlantic oceans the degree of complex formation varies depending on dissolved silica concentration ph and pco2 assuming that only rees in the form of reeh3sio42 which is diffused advected from deep water to surface water together with dissolved silica are incorporated into diatom opal a ree incorporation theory has been developed the theory links the intake of rees and silica by diatoms in surface water and their concentrations in deep water and presents two distribution coefficients ds of rees in diatom opal conventional d against surface water and columnar d against deep water as functions of ph and dissolved silica concentration the theory successfully explains the significant ree concentration level leftover rees in the surface water of the oceans and reproduces a concentration of rees in diatom opal that is consistent with that observed in diatom opal in the north pacific ocean the ree composition of oceanic deep water is largely explained by two fractionation processes ree incorporation into opal and carbonate oxide scavenging of rees

mechanisms of intense alpine rainfall abstract numerical studies by the authors and others of the 1994 piedmont flood show that the orographically modified flow was a critical element for the production of extraordinary rainfall to uncover the precise mechanism of orographic rainfall occurring in full physics mm5 simulations of the 1994 piedmont flood the authors carried out simulations with the same real data initial and boundary conditions but with the real orography replaced by an idealized one with excellent agreement between real and idealized orography on the rainfall rate versus time in the piedmont area analysis of the idealized orography simulation provides a clear picture of the model s mechanism of orographically induced rainfall as noted in previous studies of the 1994 piedmont case a moist saturated airflow has a reduced effective static stability and tends to flow over the mountains while an unsaturated airstream is stable and tries to flow around toward the left in the northern hemisphere in the 1994 piedmont case t

orographic effects on precipitating clouds 1 precipitation over and near mountains is not caused by topography but rather occurs when storms of a type that can occur anywhere deep convection fronts tropical cyclones form near or move over complex terrain deep convective systems occurring near mountains are affected by channeling of airflow near mountains capping of moist boundary layers by flow subsiding from higher terrain and triggering to break the cap when low level flow encounters hills near the bases of major mountain ranges mesoscale convective systems are triggered by nocturnal downslope flows and by diurnally triggered disturbances propagating away from mountain ranges the stratiform regions of mesoscale convective systems are enhanced by upslope flow when they move over mountains in frontal cloud systems the poleward flow of warm sector air ahead of the system may rise easily over terrain and a maximum of precipitating cloud occurs over the first rise of terrain and rainfall is maximum on ridges and minimum in valleys if the low level air ahead of the system is stable blocking or damming occurs shear between a blocked layer and unblocked moist air above favors turbulent overturning which can accelerate precipitation fallout in tropical cyclones the tangential winds encountering a mountain range produce a gravity wave response and greatly enhanced upslope flow depending on the height of the mountain the maximum rain may occur on either the windward or leeward side when the capped boundary layer of the eye of a tropical cyclone passes over a mountain the cap may be broken with intense convection resulting

the geochemical balance of the rare earth elements and neodymium isotopes in the oceans profiles of ree concentrations and neodymium isotope measurements in the western indian ocean are consistent with published data from the other major oceans ree concentrations show a strong hydrographic control the influence of intermediate water masses is particularly significant surface water concentrations vary with salinity paniculate rees are less than 5 of dissolved concentration except for ce where up to 20 of total rees are present as 0 4 m particles in contrast to dissolved profiles concentration profiles of paniculate rees including ce all increase with depth ree concentrations correlate with silica over all but the deepest waters although in detail correlations are complex the neodymium isotopic composition of indian ocean seawater avg nd 0 8 3 is intermediate between that for the atlantic and pacific oceans comparison of ree data from the major oceans shows that the hrees behave more like si than do the lrees sm nd ratios are near constant for all oceans whereas ernd ratios vary between the atlantic indian and pacific oceans the fractionation of the rees in surface seawaters can be explained by fractionation factors relative to silica from 0 12 for la to 0 05 for er use of a seven box model shows that the interoceanic variations in neodymium isotopic compositions and nd concentrations cannot be reconciled unless particle water exchange is invoked the degree of exchange required is consistent with particle residence times of 1 10 yr

limits on conservative behavior of nd isotopes in seawater assessed from analysis of fish teeth from pacific core tops abstract neodymium nd isotopes have become an accepted water mass tracer for paleoceanographic reconstructions however high rates of radiogenic nd input from volcanic islands arcs in the western equatorial pacific wep and the subarctic north pacific sanp can significantly alter the isotopic composition of ambient seawaters leading to questions about the conservative nature of nd isotopes in the pacific here we present the first comprehensive study of nd isotopes preserved in core top fossil fish teeth debris from 31 sites in the pacific to define the vertical and horizontal distributions of seawater nd isotopes and to test the reliability of nd isotopes as a water mass tracer in the pacific we found that nd isotopic values of northward flowing lower circumpolar deep water lcdw are significantly modified in the western central equatorial pacific and the sanp as a result of local radiogenic inputs from young circum pacific island arcs consequently modified lcdw with 5 end is created in the central equatorial pacific while recirculated north pacific deep water npdw acquires a radiogenic nd isotope value 2 end in the sanp nd isotopic ratios of fish teeth debris in the central north pacific plotted against salinity or phosphate concentration from the overlying bottom water produce a mixing envelope between modified lcdw and npdw indicating that these nd isotopic values represent the southern and northern sourced end member values for the central north pacific and that mixing of these water masses defines vertical profiles of nd isotopes in this region in the eastern equatorial pacific eep three water masses modified lcdw npdwsanp and npdwwestern pacific combine to produce nd isotopic values that reflect this conservative mixture therefore nd isotopes behave as a conservative water mass tracer in the central north pacific and the eep but high rates of lithogenic inputs from young circum pacific island arcs compromise the conservative behavior of nd isotopes in the wep and sanp

modeling the distribution of nd isotopes in the oceans using an ocean general circulation model nd isotopic compositions of authigenic phases in marine archives are increasingly used as a tracer of past changes in ocean circulation such applications assume that water masses are tagged with distinct nd isotope compositions in source regions and that away from these regions the nd isotope ratios observed in deep waters mainly reflect water mass mixing however the degree to which the simple assumption of quasi conservative mixing reflects the complicated reality of general circulation in the oceans is not well understood here we present numerical simulations of the nd isotope distribution in seawater using an offline ocean general circulation model ogcm treating the nd isotopic composition of seawater as a conservative tracer nd isotope data from modern surface waters are used to generate an interpolated map of nd isotope compositions for the entire surface ocean this map is treated as a fixed surface boundary condition that is propagated into the interior ocean by the advective diffusive transport of the ocean model until a steady state is reached this treatment of nd isotopes was chosen because it mimics the behavior of well known and well understood conservative tracers such as potential temperature and salinity the model results for all non surface grid points are then compared to published data this simple approach produces nd isotope estimates for north atlantic deep water that are consistent with observations but produces values lower than observed in the deep pacific and southern oceans indicating the need for a source of radiogenic nd directly to the deep pacific ocean sensitivity tests show this to be a robust result by fixing the return flow of the pacific ocean to the southern ocean with nd isotope ratios that are consistent with modern observations the model results are brought into close agreement with a majority of the available data with the addition of a deep pacific source of radiogenic nd more than half of the simulated values from the interior ocean fall within one e unit of the corresponding observations our results thus indicate that the deep pacific ocean requires a source of radiogenic nd in addition to inputs to the surface ocean and that when the deep waters of the north atlantic and north pacific are set with realistic values a majority of intermediate areas are consistent with quasi conservative mixing of these two end members

further sensitivities of orographic precipitation to terrain geometry in idealized simulations abstractthis study examines how variations to the nondimensional mountain height and the horizontal aspect ratio of a straight ridge and a concave ridge influence orographic precipitation an idealized three dimensional model is used to simulate a moist flow impinging upon these two ridges with 0 66 2 0 and 1 0 8 0 the concave ridge generates substantially more precipitation than the straight ridge via an established precipitation enhancing funneling mechanism near the ridge vertex when the flow is unblocked based on previous work it was hypothesized that when the approaching flow becomes blocked the strength of the precipitation enhancement by the concave ridge relative to the straight ridge becomes negligible this study reveals that if is sufficiently large to induce flow reversal on the windward slope then a secondary circulation develops that is strengthened by the concave ridge with a subsequent enhancement of precipitation it is also shown that the competing effects of the ridg

modeling the neodymium isotopic composition with a global ocean circulation model abstract for the first time modeling of the neodymium nd isotopic composition expressed as end is performed in an ocean global circulation model opa orca2 0 model in the interest of simplicity nd concentration is not explicitly included and end is modeled as a passive tracer recent studies suggest that dissolved particulate exchanges between continental margin sediments and seawater termed boundary exchange be could be the dominant source sink terms that determine the distribution of neodymium isotopes in the global ocean to test this hypothesis we only included this be source sink term in the model be was parameterized as a relaxing term that forces end of seawater to the isotopic composition of the continental margin over a characteristic exchange time sensitivity tests were made using different exchange times and parameterizations the model reproduces most of the general trends of end composition in seawater at global scale inter basin gradient composition of some of the main water masses these results suggest that be process may account for the major sources and sinks of oceanic nd while indicating that the characteristic time of interaction between seawater and margins varies from about half a year in surface waters to several years at depth the disparities between the model and observations might reflect the typical shortcomings of utilizing a coarse resolution ocean model circulation fields or neglected sources of neodymium such as dissolution of aeolian inputs or dissolved river loads

mechanisms controlling export production at the lgm effects of changes in oceanic physical fields and atmospheric dust deposition 1 using a biogeochemical ocean model that includes the iron cycle we carry out preindustrial control ctl and glacial last glacial maximum lgm climate simulations focusing on changes in export production ep the model successfully reproduces general trends of a paleoclimate reconstruction of ep at the lgm except over the atlantic ocean by conducting a series of sensitivity simulations we investigate the mechanism controlling ep at the lgm in each basin in the southern ocean the model successfully reproduces the dipole pattern of the paleoreconstruction the higher latitude decrease and lower latitude increase of ep it is found that the lower latitude increase of ep comes from iron fertilization effects by enhanced dust deposition while the higher latitude decrease of ep is caused by the reduction of surface shortwave due to spreading of sea ice there we also find that increased dust input in other basins remotely affects ep in the southern ocean in the pacific ocean the model suggests that iron fertilization effects are dominant in open ocean regions in the atlantic ocean the model simulates overall reduction of ep whereas the paleoreconstruction suggests the increase in some regions we propose that the atlantic response is strongly affected by distribution of iron limitation in a control climate in our ctl simulation the biological production is limited not by iron but by phosphate in the atlantic ocean which leads to the decrease of ep in spite of the significant increase of dust deposition there it is implied that the accurate evaluation of iron limitation in the present ocean is critical for evaluating changes in ep and associated reduction of atmospheric co2 concentration at the lgm

modelling nd isotopes with a coarse resolution ocean circulation model sensitivities to model parameters and source sink distributions the neodymium nd isotopic composition nd of seawater is a quasi conservative tracer of water mass mixing and is assumed to hold great potential for paleoceanographic studies here we present a comprehensive approach for the simulation of the two neodymium isotopes 143nd and 144nd using the bern3d model a low resolution ocean model the high computational efficiency of the bern3d model in conjunction with our comprehensive approach allows us to systematically and extensively explore the sensitivity of nd concentrations and nd to the parametrisation of sources and sinks previous studies have been restricted in doing so either by the chosen approach or by computational costs our study thus presents the most comprehensive survey of the marine nd cycle to date our model simulates both nd concentrations as well as nd in good agreement with observations nd covaries with salinity thus underlining its potential as a water mass proxy results confirm that the continental margins are required as a nd source to simulate nd concentrations and nd consistent with observations we estimate this source to be slightly smaller than reported in previous studies and find that above a certain magnitude its magnitude affects nd only to a small extent on the other hand the parametrisation of the reversible scavenging considerably affects the ability of the model to simulate both nd concentrations and nd furthermore despite their small contribution we find dust and rivers to be important components of the nd cycle in additional experiments we systematically varied the diapycnal diffusivity as well as the atlantic to pacific freshwater flux to explore the sensitivity of nd concentrations and its isotopic signature to the strength and geometry of the overturning circulation these experiments reveal that nd concentrations and nd are comparatively little affected by variations in diapycnal diffusivity and the atlantic to pacific freshwater flux in contrast an adequate representation of nd sources and sinks is crucial to simulate nd concentrations and nd consistent with observations the good agreement of our results with observations paves the way for the evaluation of the paleoceanographic potential of nd in further model studies

low froude number flow past three dimensional obstacles part ii upwind flow reversal zone abstract the present paper contains a continuation of our study of the flow of a density stratified fluid past three dimensional obstacles for froude number o 1 linear theory large froude number and potential flow type theory small froude number are both invalid in this range which is of particular relevance to natural atmospheric flows past large mesoscale mountains the present study was conceived to provide a systematic investigation of the basic aspects of this flow thus we have excluded the effects of friction rotation nonuniform ambient flow and the complexity of realistic terrain in part i of this study we focused on the pair of vertically oriented vortices forming on the lee side when the froude number decreases below 0 5 approximately and argued that their formation may be understood in terms of nonlinear aspects of inviscid gravity waves i e without invoking traditional arguments on the separation of the friction boundary layer herein we examine the zone of flow reversal on

neodymium budget in the modern ocean and paleo oceanographic implications the oceanic nd budget is calculated using a steady state 10 box model and a compilation of field data this is the first attempt to propose consistent estimates of the nd fluxes entering the ocean as well as indicating possible nd sources and the proportion of nd fluxes exchanged between dissolved and particulate fractions with presently available nd data the best estimates give a total nd influx of 9 x 10 9 g yr which leads to an oceanic nd residence time of 500 years from modeling tests we suggest that the authigenic nd scavenged by particulates is 100 remineralized in the deep ocean the total exchanged nd flux may be as high as 2 x 10 10 g yr the epsilon nd 0 values of the influxes are 22 11 1 and 4 for the north atlantic surface atlantic north pacific and surface indo pacific regions respectively atmospheric and riverine nd fluxes are insufficient to explain the magnitude and regional variability of calculated nd influxes and epsilon nd 0 we propose continental margins as an additional source supplying nd to the ocean using the model calibrated for nd we examine the sensitivity of deep water epsilon nd 0 to variations of nd inputs to the ocean deep water nd concentrations and epsilon nd 0 vary with the changes in nd influxes and their epsilon nd 0 as nd sources to the ocean may change during glacial interglacial periods the epsilon nd 0 shifts recorded in ferromanganese nodules and crusts do not necessarily reflect changes in paleoceanic circulation the effects of continental erosion should be considered in reconstructing patterns of ocean circulation using nd isotopes

precipitation over concave terrain abstract many topographic barriers are comprised of a series of concave or convex ridges that modulate the intensity and distribution of precipitation over mountainous areas in this model based idealized study stratiform precipitation associated with stratified moist airflow past idealized concave ridges is investigated with a focus on windward blocking flow confluence and the associated precipitation enhancement it is found that flow confluence and precipitation enhancement by a concave ridge are controlled by the nondimensional ridge height m m nmhm u where nm is the moist buoyancy frequency hm is the maximum ridge height and u is the wind speed based on which three dynamical regimes can be defined in the linear regime m 0 4 a flow confluence zone is present over the upwind slope of the ridge vertex where precipitation is significantly enhanced the precipitation enhancement is due to the additional updraft driven by the horizontal flow convergence with a considerable contribution fr