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 hafnium neodymium isotopic composition of atlantic seawater the first full water column hafnium isotopic compositions of atlantic seawater have been obtained at seven locations from the labrador sea to the drake passage despite subpicomolar concentrations in seawater a precision of the hf isotopic measurements of 03 epsilon hf units was achieved an overall epsilon hf range between 3 1 in the labrador sea and 4 4 in antarctic bottom water was determined the distribution of which broadly reflects continental weathering inputs within particular water column profiles significant differences of up to 4 epsilon hf units occur combined with nd isotope data of the same samples it is evident that the hf isotopic composition of seawater is too radiogenic for a given nd isotopic composition and that the largest difference between expected and measured hf isotopic compositions in seawater occurs near the oldest continental crust in the labrador sea this corroborates the previous proposition which was mainly based on ferromanganese crust data that the hf isotopic composition of seawater is controlled by incongruent weathering of continental crust and possibly to some extent by hydrothermal contributions hafnium concentrations in the ocean do not increase along the deep ocean conveyer indicating an oceanic residence time of only a few hundred years which is significantly shorter than previously assumed the hf isotopic composition of past seawater can therefore serve as a proxy for short distance basin scale mixing processes and the regime and intensity of nearby continental weathering processes c 2009 elsevier b v all rights reserved

rare earth element concentrations and nd isotopes in the southeast pacific ocean 1 three vertical profiles of rare earth element concentrations and nd isotopic compositions have been measured in the remote southeast pacific ocean the three stations represent contrasting environments the oligotrophic center of the gyre station gyr the transition zone east of the south tropical front station egy and the peru chile upwelling marked by a pronounced oxygen minimum station upx rare earth concentrations display nutrient like vertical profiles except at upx where surface waters are enriched at this station nd isotopic compositions are clearly more radiogenic than in the open ocean suggesting that boundary exchange process is releasing lithogenic rare earth element from the volcanic andes unexpected radiogenic values end reaching 3 7 are also observed at 2000 m at station gyr in the upper circumpolar deep water that commonly have end values around 6 exchange processes related to hydrothermal activity are suspected to produce this increase in end in the vicinity of the east pacific rise these results provide some guidance for higher resolution studies planned in this region by the international geotraces program

the hafnium and neodymium isotope composition of seawater in the atlantic sector of the southern ocean we present the first combined dissolved hafnium hf and neodymium nd concentrations and isotope compositions of deep water masses from the atlantic sector of the southern ocean eight full depth profiles were analyzed for hf and twelve for nd hafnium concentrations are generally depleted in the upper few hundred meters ranging between 0 2 pmol kg and 0 4 pmol kg and increase to relatively constant values of around 0 6 pmol kg in the deeper water column at the stations north of the polar front pf nd concentrations increase linearly from about 10 pmol kg at depths of 200 m to up to 31 pmol kg close to the bottom indicating particle scavenging and release within the weddell gyre wg however nd concentrations are essentially constant at 25 pmol kg at depths greater than 1000 m the distributions of both elements show a positive correlation with dissolved silicon implying a close linkage to diatom biogeochemistry hafnium essentially shows invariant isotope compositions with values averaging at ehf 4 6 whereas nd isotopes mark distinct differences between water masses such as modified north atlantic deep water nadw end 11 to 10 and antarctic bottom water aabw end 8 6 to 9 6 but also waters locally advected via the agulhas current can be identified by their unradiogenic nd isotope compositions mixing calculations suggest that a small fraction of nd is removed by particle scavenging during mixing of water masses north of the pf nevertheless the nd isotope composition has apparently not been significantly affected by uptake and release of nd from particles as indicated by mixing calculations a mixing envelope of an approximated north pacific and a north atlantic end member shows that nd isotope and concentration patterns in the lower circumpolar deep water lcdw can be fully explained by 30 70 percentage contributions of these respective end members

dissolved redox sensitive elements re u and mo in intense denitrification zone of the arabian sea the concentrations of redox sensitive elements rhenium uranium and molybdenum have been measured in the suboxic water column of the arabian sea to determine their response behavior to intense oxygen minima and denitrifying conditions in the water column north of 12 n within the core of the intense oxygen minimum zone omz of the arabian sea the dissolved oxygen levels drop to values as low as 5 m accompanied by the presence of secondary nitrite maxima snm indicating the occurrence of denitrification in the water column the distributions of re u and mo in the arabian sea show that their dissolved concentrations in the suboxic layer are indistinguishable from those in the overlying and underlying oxic waters suggesting that there is no discernible removal of these elements from the suboxic denitrifying layers in contrast the lateral and vertical distribution of dissolved re u and mo concentrations vary as a function of salinity suggesting their conservative behavior the salinity normalized 35 re u and mo concentrations in the arabian sea are 40 pmol kg 13 8 nmol kg and 114 nmol kg respectively these concentrations are nearly identical to their abundances in the bay of bengal a basin adjacent to the arabian sea characterized by high freshwater influx and fluvial sediments the similarity in concentration suggests that the large variability in the biogenic and detrital particulate fluxes and the suboxic denitrifying conditions between these two oceanic regions do not affect the concentrations of re u and mo and that the prevailing biogeochemical conditions in these regions are inadequate for their removal from the water column

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

nd and pb isotope variability in the indus river system implications for sediment provenance and crustal heterogeneity in the western himalaya abstract the indus river system is the only major drainage system in the western himalaya and erodes not only the high himalaya but also topographically high regions within and north of the indus suture zone most notably the karakoram ion microprobe analysis of pb isotopes in detrital k feldspar grains taken from the tributaries of the indus together with bulk nd isotope analysis of those same sediments is here used to identify distinct sediment source regions these span the very radiogenic nanga parbat and associated lesser himalaya the relatively radiogenic intermediate high himalaya the unradiogenic ladakh and kohistan batholiths and intermediate values in the hindu kush karakoram and lhasa block the range of compositions reflects differing degrees of recycling of older continental crust during petrogenesis k feldspars from the ladakh and kohistan batholiths are less radiogenic than the laterally equivalent gangdese granite of tibet interpreted to reflect the preferential recycling of accreted oceanic arc units within the western transhimalaya prior to india asia collision similarly the zanskar high himalaya are less radiogenic than their equivalents in nepal isotope values from pleistocene indus fan sediment are compatible with a dominant source in the karakoram with additional important contributions from the arc batholiths and high himalaya reflecting both the area and modern rates of tectonic uplift within the drainage basin in contrast radiogenic grains are common in the lower reaches of the modern indus river possibly as a result of the damming of the main river channel where it reaches the foreland

characteristics and formation of eastern south pacific intermediate water 1 newly gathered hydrographic data from the eastern south pacific is combined with other high quality data mainly woce to reassess the properties and boundaries of the eastern south pacific intermediate water espiw to date the espiw has been only poorly described the espiw core is found off central and northern chile between the coast and 90 w and 20 38 s located at 50 400 m of depth its temperature varies between 11 13 c salinity ranges from 34 1 34 3 and its sigma t lies between 25 75 26 25 kgm 3 espiw spreads with the subtropical gyre circulation and can be traced to at least 150 w formed through the process of subduction southeastward of the wind driven gyre circulation the espiw communicates surface properties of the waters off central chile to tropical latitudes

hydrothermal contribution to the oceanic dissolved iron inventory mineral dust and marine sediment resuspension are generally considered the primary sources of the nutrient iron to the oceans numerical model results suggest that iron released by hydrothermal activity is also an important source of dissolved iron particularly in the southern ocean iron limits phytoplankton growth and hence the biological carbon pump in the southern ocean1 models assessing the impacts of iron on the global carbon cycle generally rely on dust input and sediment resuspension as the predominant sources2 3 although it was previously thought that most iron from deep ocean hydrothermal activity was inaccessible to phytoplankton because of the formation of particulates4 it has been suggested that iron from hydrothermal activity5 6 7 may be an important source of oceanic dissolved iron8 9 10 11 12 13 here we use a global ocean model to assess the impacts of an annual dissolved iron flux of approximately 9 108 mol as estimated from regional observations of hydrothermal activity11 12 on the dissolved iron inventory of the world s oceans we find the response to the input of hydrothermal dissolved iron is greatest in the southern hemisphere oceans in particular observations of the distribution of dissolved iron in the southern ocean3 chever et al manuscript in preparation bowie et al manuscript in preparation can be replicated in our simulations only when our estimated iron flux from hydrothermal sources is included as the hydrothermal flux of iron is relatively constant over millennial timescales14 we propose that hydrothermal activity can buffer the oceanic dissolved iron inventory against shorter term fluctuations in dust deposition

sr and nd isotopes in river sediments from the ganga basin sediment provenance and spatial variability in physical erosion 1 sr and nd concentrations and isotope compositions in sediment of the ganga river from gangotri to rajmahal and its tributaries have been measured to determine provenance and the spatial variability in physical erosion among the ganga subbasins sr and nd in silicates range from 37 to 138 and from 10 to 36 g g with 87sr 86sr and nd of 0 7474 0 8428 and 25 5 to 15 5 respectively the results suggest that 65 of ganga mainstream sediments are derived from the higher himalayan crystallines highlighting intense physical erosion in this region the 87sr 86sr values of sediments in the gangetic plain show nearly identical trends during two seasons with a sharp and significant decrease at barauni downstream of gandak confluence this brings out the major impact of the sediment contribution from the gandak to the ganga mainstream model calculation suggests that about half of the ganga sediment at rajmahal is sourced from the gandak the erosion rates in the himalayan subbasins of the ganga range between 0 5 and 6 mm a where a is years with the gandak having the highest erosion rate high relief and intense precipitation over the headwater basins of the gandak appear to drive the rapid and focused erosion of this basin the results of this study and those in literature suggest that the eastern syntaxis brahmaputra the western syntaxis indus and the gandak have much higher physical erosion rates than the other himalayan basins focused erosion in the hot spots of these river basins contributes significantly to the global riverine sediment budget and influence regional tectonics

spatial distribution of dissolved neodymium and end in the bay of bengal role of particulate matter and mixing of water masses abstract the concentration and isotope composition of dissolved nd have been measured in the water column along an 87 e transect gio1 section of international geotraces program in the bay of bengal bob to investigate the effect of water mass mixing and nd release from particulate matter in determining these properties the concentration of nd in surface waters of the bob shows a north south decreasing non linear trend 46 to 22 pmol kg with salinity whereas its depth profiles typically show a high value in surface waters a minimum 15 to 23 pmol kg in the shallow subsurface 50 200 m followed by a gradual increase with depth the nd concentration of bob waters is generally higher than that in nearby oceanic basins on the other hand the e nd values in the bob are less radiogenic compared to those reported for other regions of the global oceans except baffin bay the north atlantic subpolar gyre and the niger delta margin and show a greater variation in the upper water column surface waters of the southernmost profile 6 n show a more radiogenic e nd value 8 which decreases to 15 in the northernmost profile 20 n close to the values for dissolved and particulate phases of the ganga brahmaputra g b rivers this latitudinal trend is most likely a result of variations in mixing proportion between the more radiogenic indonesian throughflow surface waters iw and unradiogenic bob low salinity water the former s signature being more clearly discernible in surface waters of the two southernmost profiles 6 n and 8 5 n attempts to balance the nd budget in the water column based on an inversion model suggest that in addition to water masses other source s is required the strength of which is estimated to vary from 1 to 65 of the measured nd concentration the calculations also show that the e nd of this additional source s has to be in the range of 16 2 typical of g b river sediments these observations coupled with the north south distribution of dissolved nd and e nd indicate that this additional source is release from particulate phases supplied by the g b river system the calculations also bring out the presence of hot spots of nd release excess nd near the sediment water interface along the northern slope of the bay indicating supply of nd from continental margin sediments this study underscores the significant role of dissolved particulate nd from the ganga brahmaputra river system in contributing to the dissolved nd budget of the global oceans

deep structure of the u s atlantic continental margin offshore south carolina from coincident ocean bottom and multichannel seismic data we present the results of a combined multichannel seismic reflection mcs and wide angle ocean bottom seismic profile collected in 1988 across the carolina trough on the u s atlantic continental margin inversion of vertical incidence and wide angle travel time data has produced a velocity model of the entire crust across the continent ocean transition the margin consists of three structural elements 1 rifted continental crust comprising 1 4 km of post rift sedimentary rocks overlying a 30 34 km thick subsedimentary crust 2 transitional crust a 70 to 80 km wide zone comprising up to 12 km of postrift sedimentary rocks overlying a 10 to 24 km thick subsedimentary crust and 3 oceanic crust comprising 8 km of sedimentary rocks overlying an 8 km thick crystalline crust the boundary between rifted continental and transitional crust marked by the brunswick magnetic anomaly represents an abrupt change in physical properties with strong lateral increases in seismic velocity density and magnetic susceptibility the transitional crust contains mid crustal seaward dipping reflections observed on the mcs section and has seismic velocities of 6 5 6 9 km s in the midcrust and 7 2 7 5 km s in the lower crust modeling of potential field data shows that transitional crust also produces the prominent margin parallel gravity anomaly and the brunswick and east coast magnetic anomalies these observations support the interpretation that the transitional crust was formed by magmatism during continental breakup the prodigious thickness up to 24 km of igneous material rivals that interpreted on continental margins of the north atlantic e g hatton bank and voring plateau which formed in the vicinity of the iceland hotspot these observations when combined with other transects across the margin confirm previous suggestions that the u s atlantic margin is strongly volcanic and further imply that the magmatism was not the result of a long lived mantle plume

large igneous province on the us atlantic margin and implications for magmatism during continental breakup rifted continental margins commonly include sections of igneous rock more than twice as thick as normal oceanic crust explanations for this voluminous magmatic accretion during rifting include plume models1 3 which require a deep seated thermal or chemical anomaly in upwelling mantle and non plume models4 7 which call on broad shallow thermal anomalies and or rapid upwelling of mantle through the melting zone new seismic models from two transects across the continent ocean transition on the us atlantic margin8 10 confirm the presence of a 20 25 km thick igneous section here we argue that the similarity of the crustal structure on these and two previous transects spanning 1 000 km of the margin and the association of thick igneous crust with the east coast magnetic anomaly11 imply that the thick igneous section extends along the entire margin and may have a volume of as much as 3 2 106 km3 the distribution of volcanic and plutonic rocks details of the seismic structure and lack of independent evidence for a hotspot are difficult to reconcile with plume models and suggest that non plume processes created the thick igneous crust

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

early deglacial 19 17 ka strengthening of the northeast monsoon 1 earlier studies that mostly relied on bulk 14c dating indicated a weaker southwest monsoon swm and a stronger than present northeast monsoon nem during the last glacial maximum lgm 18000 14c years or 21000 calendar years ago we have analyzed a sediment core from the equatorial indian ocean where planktonic foraminifera were dated by accelerator mass spectrometry ams 14c 18o analysis of three species of foraminifera viz globigerinoides ruber globigerinoides sacculifer and globorotalia menardii reveals that the nem strengthened during the early deglacial period 15000 14c years ago or 18000 calendar years ago relative to the present and not during the lgm as surmised earlier

late pleistocene variability of arabian sea summer monsoon winds and continental aridity eolian records from the lithogenic component of deep sea sediments the modern indian ocean summer monsoon is driven by differential heating between the asian continent and the indian ocean to the south this differential heating produces a strong pressure gradient which drives southwest monsoon winds during june july and august satellite and meteorological observations aerosol measurements sediment trap studies and mineralogical studies indicate an atmospheric mode of transport for modern lithogenic sediments in the northwest arabian sea analyses of lithogenic grain size and mass accumulation rate mar records from the owen ridge indicate that eolian transport has been the primary mode of transport for the past 370 kyr visual inspection shows that the mar record is positively correlated with global ice volume as indicated by the marine 18o record in contrast the grain size record varies at a much higher frequency showing little correlation to either the mar or the 18o records spectral analyses confirm these relationships indicating that the lithogenic grain size and mar records are coherent only over the precession band whereby the grain size leads the mar by 124 8 kyr we conclude that an eolian transport mechanism is the only mechanism that allows for this phase difference and at the same time is supported by comparison of the grain size and mar with independent eolian records we use lithogenic grain size as a paleoclimatic indicator of summer monsoon wind strength and lithogenic mar as a paleoclimatic indicator of source area aridity these interpretations are supported by comparison of the lithogenic records to independent indicators of wind strength globigerina bulloides upwelling record and aridity a loess record from central china such comparisons indicate high coherence and zero phase relationships our work supports the findings of previous studies which have documented the link between monsoon strength and the earth s axial precession cycles both the lithogenic mar and the grain size records have high coherency with precessional insolation maximum lithogenic mar source area aridity is in phase with 18o global ice volume and leads maximum precessional insolation by 88 6 kyr we attribute this lead to the influence of glacial conditions on the aridity and therefore the deflation potential of the source areas maximum lithogenic grain size summer monsoon wind strength lags maximum precession by 148 9 kyr we attribute this lag both to the influence of global and or local ice volume and to the availability of latent heat from the southern hemisphere indian ocean the two of which combine to determine the strength of the indian ocean monsoon

sea surface salinity variability during the indian ocean dipole and enso events in the tropical indian ocean an ocean reanalysis that covers the period from 1871 2008 is used to analyze interannual variability of sea surface salinity sss in the tropical indian ocean the reanalysis sss and the sss anomaly patterns during indian ocean dipole iod and el nino southern oscillation enso events are compared with patterns from argo sss data the mean seasonal sss variation is large in the northern bay of bengal compared to variations in the arabian sea and equatorial indian ocean during a positive iod event positive sss anomalies are found along the sumatra coast due to the combination of wind driven upwelling of subsurface high salinity waters enhanced evaporation and anomalous surface circulation the opposite is true to a lesser extent during negative iod events a dipole mode index for salinity dmis based on sss data and a new index based on the average of salinity in a region off the coast of sumatra is introduced to monitor sss variability during iod and enso events the impact of concomitant el nino events on a positive iod event is large with freshening a negative sss anomaly in the equatorial indian ocean and salting positive sss anomaly off the southern sumatra coast the impact of intense freshening reaches into the southwestern tropical indian ocean the impact of concomitant la nina with negative iod is also large with an intense freshening in the southeastern arabian sea and salting off the northern sumatra coast

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

rare earth elements in the nw indian ocean abstract dissolved rare earth element ree distributions have been determined at three stations in the high productivity nw indian ocean nwio upwelling zone dissolved ree distributions within the well oxygenated surface waters and deep portions of the water column are similar to those reported previously from other open ocean locations at depth dissolved ree concentrations are intermediate between those of the atlantic and pacific oceans consistent with the continuous regeneration and enrichment of the strictly trivalent rees in and the progressive oxidative removal of ce from the deep ocean within the mid depth oxygen minimum zone dissolved ree concentrations exhibit a notable enrichment superimposed upon these typical oceanic profiles further dissolved ce concentrations are preferentially enriched within the suboxic horizon compared to the rest of the series indicating the reduction of insoluble ce iv to dissolved ce iii at these depths by analogy with our previous studies of ree distributions in anoxic basins we propose that the more modest enrichments of the strictly trivalent rees observed in the nwio suboxic zone must derive from uptake through scavenging within the well oxygenated portions of the water column and regeneration from sediments and settling particles within the more reducing conditions of the oxygen minimum zone

qanat hazard in iranian urban areas explanation and remedies this article explains the qanat hazard in iranian urban areas each qanat consists of an underground gallery tunnel which conveys groundwater to the surface and several to tens of vertical wells shafts which provide access to the gallery it is estimated that about 10 000 km qanats with 300 000 wells lie under iranian urban areas their number under urban areas of the other countries containing it seems to be significant as well in iran subsidence and other problems related to shafts and galleries of hidden qanats impose millions of dollars damage annually despite the importance of the qanat hazard it has not yet received enough attention from scholars in this article qanat hazard as a special kind of geological hazard is explained from such aspects as the causes the extents the impacts and the various remedies to combat this hazard remedies to abate this hazard should include hazard assessment risk assessment and risk reduction phases generally the most efficient strategy is to detect qanats using aerial photos maps or inquiring local people and construct the buildings in hazard prone areas with spread footing foundations however this is not applicable in all occasions so depending on conditions some other strategies which are provided in the text may be more effective

dissolved aluminium cycling in the northern equatorial and subtropical gyre region of the indian ocean abstract dissolved aluminium hereafter dal concentrations have been determined on 34 full vertical water column profiles sampled along the two separate geotraces india transects gi 01 and gi 06 to understand the biogeochemical controls on dal distribution in the northern the bay of bengal the andaman sea and the arabian sea equatorial and subtropical gyre region of the indian ocean al released due to the partial dissolution of and or al desorption from the suspended lithogenic sediments supplied in a huge amount to the bay of bengal bob waters by the ganga brahmaputra g b river system indian peninsular rivers and sediment resuspension from the continental shelf and slope predominantly controls the dal distribution in the bob and results in an overall increase in the dal concentrations throughout the water column towards the northern bob and the eastern coast of india considering the steady state balance between the dal input from the lithogenic sediment flux in the upper water column and first order scavenging removal of dal the fractional solubility of al from the lithogenic sediments in the bob surface waters is estimated to be in the range of 1 1 4 7 advection of indonesian sea surface waters through the strait of malacca and dal input from the partial dissolution of resuspended terrigenous sediments sourced from the insular shelf of the nicobar islands set major controls on the dal distribution in the surface and upper thermocline waters of the southern andaman sea and the southern bob region near the nicobar islands rapid renewal of and vertical mixing in the deeper waters 1000 m relative to scavenging removal of dal results in near uniform dal concentrations 3 7 nm in the deeper waters at the center of the southern andaman sea in the south eastern arabian sea the continental outflow of mineral dust and advection of dal enriched bay of bengal surface waters control the dal distribution in the surface water layer dal in the surface waters of the equatorial indian ocean during the late winter sampling period of the gi 06 cruise is predominantly determined by the mixing between dal rich surface waters of the southern bob and relatively dal depleted surface waters of the southern arabian sea under the influence of the northeast monsoon current the scavenging residence time of dal in the deep waters of the equatorial indian ocean is estimated using a 1 d scavenging advection diffusion model and found to be in the range of 92 141 years deposition of australian dust and advection of indonesian throughflow water translates to the dal enrichment in the upper water column 3500 m advects across the ninety east ridge from the western australian basin to bring the dal rich waters to the northern end of the central indian ocean 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

temporal variations in 87sr 86sr and ɛnd in sediments of the southeastern arabian sea impact of monsoon and surface water circulation sr and nd isotopic composition of silicate fractions of sediments have been measured in two well dated gravity cores from the eastern arabian sea archiving a depositional history of 29 and 40 ka the 87 sr 86 sr and e nd in the northern core ss 3104g 12 8 n 71 7 e ranges from 0 71416 to 0 71840 and 8 8 to 12 8 these variations are limited compared to those in the southeastern core ss 3101g 6 0 n 74 0 e in which they vary from 0 71412 to 0 72069 and 9 0 to 15 2 respectively this suggests that the variation in the relative proportions of sediments supplied from different sources to the core ss 3104g are limited compared to core ss 3101g the 87 sr 86 sr and e nd profiles of ss 3101g exhibit two major excursions ca 9 ka and 20 ka coinciding with periods of holocene intensified monsoon phase imp and the last glacial maximum lgm respectively with more radiogenic 87 sr 86 sr and lower e nd during these periods these excursions have been explained in terms of changes in the erosion patterns in the source regions and surface circulation of the northern indian ocean resulting from monsoon intensity variations the intensification of north east ne monsoon and associated strengthening of the east indian coastal current in southwest direction during lgm transported sediments with higher 87 sr 86 sr and lower e nd from the western bay of bengal to the arabian sea in contrast enhanced south west sw monsoon at 9 ka facilitated the transport of sediments from the northern arabian sea particularly indus derived to the southeastern arabian sea this study thus highlights the impact of monsoon variability on erosion patterns and ocean surface currents on the dispersal of sediments in determining the sr and nd isotopic composition of sediments deposited in the eastern arabian sea during the last 40 ka

crustal thickness anomalies in the north atlantic ocean basin from gravity analysis gravity derived crustal thickness models were calculated for the north atlantic ocean between 76 n and the chain fracture zone and calibrated using seismically determined crustal thickness about 7 of the ocean crust is 7 km thick and is interpreted to have been affected by excess magmatism thin crust probably reflects reduced melt production from relatively cold or refractory mantle at scales of up to hundreds of kilometers along the spreading axis by far the most prominent thick crust anomaly is associated with iceland and adjacent areas which accounts for 57 of total crustal volume in excess of 7 km much smaller anomalies include the azores 8 cape verde islands 6 canary islands 5 madeira 4 and new england great meteor seamount chain 2 all of which appear to be associated with hot spots hot spot related crustal thickening is largely intermittent suggesting that melt production is episodic on time scales of tens of millions of years thickened crust shows both symmetrical and asymmetrical patterns about the mid atlantic ridge mar axis reflecting whether melt anomalies were or were not centered on the mar axis respectively thickened crust at the bermuda and cape verde rises appears to have been formed by isolated melt anomalies over periods of only 20 25 myr crustal thickness anomalies on the african plate generally are larger than those on the north american plate this most likely results from slower absolute plate speed of the african plate over relatively fixed hot spots

water masses in the humboldt current system properties distribution and the nitrate deficit as a chemical water mass tracer for equatorial subsurface water off chile abstract three sections are used to analyze the physical and chemical characteristics of the water masses in the eastern south pacific and their distributions oceanographic data were taken from the scorpio may june 1967 piquero may june 1969 and krill june 1974 cruises vertical sections of temperature salinity dissolved oxygen nitrate nitrite phosphate and silicate were used to analyze the water column structure five water masses were identified in the zone through t s diagrams subantarctic water subtropical water equatorial subsurface water antarctic intermediate water and pacific deep water their proportions in the sea water mixture are calculated using the mixing triangle method vertical sections were used to describe the geographical distributions of the water mass cores in the upper 1500 m several characteristic oceanographic features in the study area were analyzed the shallow salinity minimum displacement towards the equator the equatorial subsurface salinity maximum associated with a dissolved oxygen minimum zone and a high nutrient content displacement towards the south and the equatorward intermediate antarctic salinity minimum associated with a dissolved oxygen maximum the nitrate deficit generated in the denitrification area off peru and northern chile is proposed as a conservative chemical tracer for the equatorial subsurface waters off the coast of chile south of 25 s

implications of the deep circulation and ventilation of the indian ocean on the renewal mechanism of north atlantic deep water in the indian ocean sector of the great ocean conveyor scheme the north atlantic deep water nadw replacement is realized by the transformation of the sinking circumpolar deep water cdw from the southern ocean to a prevailingly upward flow in the northern indian ocean this water mass transformation scenario has been studied by using hydrographie data including potential temperature salinity dissolved oxygen and nutrients in a water mass mixing model and by calculation of dianeutral velocity the model comprises a mixing system of three major deep water masses nadw cdw and north indian deep water this third water mass is introduced as a virtual water mass to represent the aged cdw the assumption is feasible as the artificial water mass can be eliminated on the deepest n 28 12 neutral surface characterized by isopycnal mixing the experiment is fulfilled when a conservative variable initial phosphate po40 is introduced and all conservative parameters are used in the mixing scheme the n 28 12 surface provides a major isopycnal transition path of cdw to the northern indian ocean and thus cdw is transformed to an upward flow dominant dianeutral up welling is detected on all four neutral surfaces north of 30 s showing increasingly strong dianeutral velocity toward shallower surfaces with the water mass mixing pattern and spreading path dianeutral circulation and dynamical information of the acceleration potential 10 m2 s 2 mapped on neutral surfaces a schematic of deep water circulation and ventilation of the indian ocean emerges from this study the contribution of nadw is largely limited to the southwest indian ocean the northward cdw is found mainly in two paths one in the western indian ocean apparent between 2000 and 3000 m through the western crozet and madagascar basins and farther north into the somali basin and arabian basin and another in the central indian basin apparent below 3000 m where ridge blocking becomes effective in the west and nadw salinity reaches a maximum while the major path switches from west to the central basin in the deeper layer 3000 3500 m the flow in the western indian ocean reverses southward north of the southeast indian ridge the deep path bifurcates from which point the eastern branch feeds the deep western boundary flow in the west australian basin except for part of the transformed cdw which is contributed to the upward flow in the north the return flow of cdw is found on the eastern side of these basins

rare earth elements rees in the tropical south atlantic and quantitative deconvolution of their non conservative behavior this study presents new concentration measurements of dissolved rare earth elements drees along a full depth east west section across the tropical south atlantic 12 s and uses these data to investigate the oceanic cycling of the rees enrichment of drees associated with the redox cycling of fe mn oxides is observed in the oxygen minimum zone omz off the african shelf for deeper waters a multi parameter mixing model was developed to deconvolve the relative importance of physical transport i e water mass mixing from biogeochemical controls on the dree distribution in the deep atlantic this approach enables chemical processes involved in ree cycling not apparent from the measurements alone to be distinguished and quantified results show that the measured dree concentrations below 1000 m are dominantly controlled 75 by preformed ree concentrations resulting from water mass mixing this result indicates that the linear correlation between drees and dissolved si observed in atlantic deep waters results from the dominantly conservative behavior of these tracers rather than from similar chemical processes influencing both drees and si minor addition of drees 10 of dnd and 5 of dyb is observed in the deep 4000 m brazil basin resulting from either remineralization of particles in situ or along the flow path greater addition of drees up to 25 for dnd and 20 for dyb is found at 1500 m and below 4000 m in the angola basin near the african continental margin cerium anomalies suggest that different sources are responsible for these dree addition plumes the 1500 m excess is most likely attributed to dree release from fe oxides whereas the 4000 m excess may be due to remineralization of calcite higher particulate fluxes and a more sluggish ocean circulation in the angola basin may explain why the dree excesses in this basin are significantly higher than that observed in the brazil basin hydrothermal venting over the mid atlantic ridge acts as a regional net sink for light rees but has little influence on the net budget of heavy rees the combination of dense ree measurements with water mass deconvolution is shown to provide quantitative assessment of the relative roles of physical and biogeochemical processes in the oceanic cycling of rees

earlier history of the 70 ma old canary hotspot based on the temporal and geochemical evolution of the selvagen archipelago and neighboring seamounts in the eastern north atlantic major element trace element and sr nd pb isotope data combined with 40ar 39ar age determinations of volcanic rocks from the selvagen islands and neighboring seamounts in the eastern north atlantic reveal the earlier history of the 70 ma old canary hotspot a basanitic to phonolitic late shield stage intrusive complex 29 ma is exposed on selvagem pequena the evolution of selvagem grande can be divided into three magmatic phases a tephritic to phonolitic late shield stage intrusive complex 24 26 ma and two rejuvenated or post erosional stages 8 12 and 3 4 ma consisting of alkali basalt basanite and rare phonolite during the early to mid miocene volcanic hiatus 12 24 ma the top of the volcano was beneath sea level as evidenced by marine carbonate sediments 13 24 ma dated through correlation of 87sr 86sr with the seawater sr isotope curve the geochemistry of the shield stage lavas indicates that they derive from plume sources whereas the post erosional lavas are derived from metasomatized lithospheric sources five sampled seamounts to the east and northeast of the islands range in composition from alkali basalt and basanite to phonolite samples from dacia conception bank and lars were dated at 9 17 and 68 ma respectively geochemical data suggest that the dredged samples come from the post erosional stage of volcanism and therefore the dates represent minimum ages for the seamount volcanoes the elevation of erosional platforms formed at wave base decrease from selvagen grande 100 m above sea level to lars seamount 900 m below sea level suggesting a southwest to northwest age progression and that all of these seamounts are older than the selvagen islands trace element and sr nd pb isotopic composition of the selvagen islands and neighboring seamounts are consistent with their origin from the canary plume interaction of the weak canary mantle plume with a slow moving plate appears to be responsible for generating a 450 km wide irregular hotspot track extending 800 km from the youngest canary island of hierro in the southwest to lars seamount in the northeast

interhemispheric controls on deep ocean circulation and carbon chemistry during the last two glacial cycles changes in ocean circulation structure together with biological cycling have been proposed for trapping carbon in the deep ocean during glacial periods of the late pleistocene but uncertainty remains in the nature and timing of deep ocean circulation changes through glacial cycles in this study we use neodymium nd and carbon isotopes from a deep indian ocean sediment core to reconstruct water mass mixing and carbon cycling in circumpolar deep water over the past 250 thousand years a period encompassing two full glacial cycles and including a range of orbital forcing building on recent studies we use reductive sediment leaching supported by measurements on isolated phases foraminifera and fish teeth in order to obtain a robust seawater nd isotope reconstruction neodymium isotopes record a changing north atlantic deep water nadw component in the deep indian ocean that bears a striking resemblance to northern hemisphere climate records in particular we identify both an approximately in phase link to northern hemisphere summer insolation in the precession band and a longer term reduction of nadw contributions over the course of glacial cycles the orbital timescale changes may record the influence of insolation forcing for example via nadw temperature and or antarctic sea ice extent on deep stratification and mixing in the southern ocean leading to isolation of the global deep oceans from an nadw source during times of low northern hemisphere summer insolation that evidence could support an active role for changing deep ocean circulation in carbon storage during glacial inceptions however mid depth water mass mixing and deep ocean carbon storage were largely decoupled within glacial periods and a return to an interglacial like circulation state during marine isotope stage mis 6 5 was accompanied by only minor changes in atmospheric co2 although a gradual reduction of nadw export through glacial periods may have produced slow climate feedbacks linked to the growth of northern hemisphere ice sheets carbon cycling in the glacial ocean was instead more strongly linked to southern ocean processes

lead concentrations in the northeast pacific evidence for global anthropogenic perturbations lead concentrations were determined by isotope dilution mass spectrometry in 34 surface and deep water samples collected in the northeast pacific between hawaii and california and off the california coast using a deep water sampler protected against fouling by contamination from the ship and hydrowire measured concentrations lie more than one order of magnitude below previously published open ocean values and they show that in most cases 90 or more of the total lead is in a dissolved form lead concentrations are about 10 fold higher in surface and thermocline waters than in deep waters values drop as low as 1 ng kg 5 pmol kg below 3500 m depth lead profiles thus appear different compared to those of most trace metals which show enrichment in deep waters compared to surface concentrations lead concentrations in surface waters increase from 5 to 15 ng kg 25 to 75 pmol kg along a transect starting from a location 200 km off the california coast and continuing towards the center of the north pacific gyre this increase is congruent with that observed for 210 pb concentrations in the same waters sampled at the same time lead is supplied to the open north pacific largely from the atmosphere at a rate of about 60 ng cm 2 yr which exceeds the prehistoric oceanic output flux of authigenic lead recorded in pelagic sediments about tenfold this excess originates from emissions from smelters and combustion of leaded gasoline overwhelming natural lead inputs that entered the ocean during prehistoric time probably largely through rivers vertical lead concentration profiles below the surface mixed layer are probably not in steady state there concentrations must be increasing in response to the increase of anthropogenic inputs because the estimated lead residence times are more than 20 years in the thermocline and about 80 years in deep waters based on an estimated 10 fold input and concentration increase since the mid eighteenth century in the surface mixed layer in the central northeast pacific it is calculated that the 10 ng kg average concentration between 100 and 900 m is 2 to 5 times larger and the 1 8 ng kg average concentration between 900 and 5000 m depth is about 2 times larger than it was in the mid eighteenth century profiles of lead concentrations in the north atlantic are expected to be shifted generally to larger values by a factor of 2 to 3 compared to those in the north pacific because of the effects of greater industrial lead contamination while lead concentration profiles in the south pacific are expected to be shifted generally to lower values compared to the north pacific by about this same factor because of the effects of lesser industrial lead contamination

neogene rejuvenation of central appalachian topography evidence for differential rock uplift from stream profiles and erosion rates abstract the persistence of topography within ancient orogens remains one of the outstanding questions in landscape evolution in the eastern north american appalachians this question is manifest in the outstanding problem of whether topographic relief is in a quasi equilibrium state decaying slowly over many millennia or whether relief has increased during the late cenozoic here we present quantitative geomorphic data from the nonglaciated portion of the susquehanna river drainage basin that provide insight into these end member models analysis of channel profiles draining upland catchments in the northern valley and ridge appalachian plateau blue ridge and piedmont provinces reveals that a large number of streams have well defined knickpoints clustered at 300 600 m elevation but not systematically associated with transitions from weak to resistant substrate cosmogenic 10 be inventories of modern stream sediment indicate that erosion rates are spatially variable ranging from 5 30 m myr above knickpoints to 50 100 m myr below knickpoints overall channel gradients normalized for drainage area scale linearly with catchment averaged erosion rates collectively regionally consistent spatial relationships among erosion rate channel steepness and knickpoints reveal an ongoing wave of transient channel adjustment to a change in relative base level reconstructions of relict channel profiles above knickpoints suggest that higher rates of incision are associated with 100 150 m of relative base level fall that accompanied epierogenic rock uplift rather than a change to a more erosive climate or drainage reorganization channel response timescales imply that the onset of relative base level change predates 3 5 ma and may have begun as early as 15 ma we suggest that adjustment of the channel network was likely driven by changes in mantle dynamics along the eastern seaboard of north america during the neogene

neodymium concentration and isotopic composition distributions in the southwestern indian ocean and the indian sector of the southern ocean abstract neodymium concentration and isotopic composition profiles were determined for two stations in the crozet basin in the southwestern indian ocean and one station in the indian sector of the southern ocean the station located in the northern part of the crozet basin showed very similar nd concentrations sio2 and dissolved oxygen profiles to those previously reported for the closest station in the madagascar basin however the station in the northern part of the crozet basin and the previously studied station in the madagascar basin exhibited clearly different nd isotopic values at water depths of approximately 400 m which was attributed to a strong influence of the agulhas return current on the crozet basin station and or a large contribution of the south equatorial current to the madagascar basin the nd isotopic profile at er 14 in the indian sector of the southern ocean was similar to those of stations in the atlantic sector of the southern ocean at depths above 2000 m conversely variable nd isotopic compositions were observed in the indian and atlantic sectors of the southern ocean at depths below 2000 m suggesting the importance of local nd to determination of the nd isotopic composition of deeper depths the pb isotopic compositions which are strongly controlled by anthropogenic pb showed different features in vertical profile from nd isotopic compositions at all stations the nd isotopic composition profiles of stations from the crozet basin showed a clear peak corresponding to antarctic intermediate water whereas a clear peak corresponding to subantarctic mode water was observed for pb isotopic vertical profiles a combined nd and pb isotopic composition study of seawater may clarify the contribution of natural and anthropogenic sources to pb in the ocean this article is part of a special issue entitled cycles of trace elements and isotopes in the ocean geotraces and beyond edited by tim m conway tristan horner yves plancherel and aridane g gonzalez

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

oxygen isotope evidence for a stronger winter monsoon current during the last glaciation a variety of palaeoclimate data from the northern indian ocean has shown that the asian summer monsoon was weaker during the last glacial maximum 18 000 years ago than it is today1 5 it has also been inferred from these data that the winter monsoon was stronger at that time5 here we present evidence that the transport of low salinity water from the bay of bengal to the arabian sea caused by the winter monsoon6 was higher during the last glacial maximum this inference is based on a negative excursion up to about 1 in magnitude in the oxygen isotope ratios of three planktonic foraminiferal species detected in a sediment core from the arabian sea by high resolution 1 2 cm sampling our results place an upper limit of about 4 000 years on the length of time during which the winter monsoon was stronger than today

impact of anthropogenic pb and ocean circulation on the recent distribution of pb isotopes in the indian ocean abstract pb and pb isotope ratios in the modern ocean have been altered significantly by anthropogenic pb inputs over the past century most studies of anthropogenic pb in the ocean have focused on the north atlantic and north pacific oceans and the impact of anthropogenic pb inputs to the indian ocean and processes controlling the distribution of pb in the indian ocean are poorly known this study presents the pb and pb isotopic composition 206 pb 207 pb 208 pb 207 pb of 11 deep stations from the indian ocean japanese geotraces cruise kh 09 5 from the bay of bengal and arabian sea to the southern ocean 62 s the pb isotope ratios of the indian ocean range 1 140 1 190 for 206 pb 207 pb and 2 417 2 468 for 208 pb 207 pb with lower ratios appearing in the shallow waters of the northern indian ocean and higher ratios appearing in the deep layers of the southern ocean this result agrees with a previous study on pb concentrations echegoyen et al 2014 showing that the indian ocean particularly its northern part is largely perturbed by anthropogenic pb inputs 206 pb 207 pb and 208 pb 207 pb of the indian sector southern ocean are still lower than natural pb showing this region was also affected by anthropogenic pb anomalously low or high 206 pb 207 pb and 208 pb 207 pb were observed in the thermocline and shallow waters of the southern indian ocean and the arabian sea which are ascribed to water mass distribution e g subantarctic mode water and evolving pb isotope ratios of this region as dominant anthropogenic pb sources change 206 pb 207 pb and 208 pb 207 pb in the bay of bengal are higher than those in the arabian sea which might be the result of the anthropogenic pb inputs from different provenance or seawater exchanging pb isotopes with natural particles derived from rivers and or sediments at the basin boundaries

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

variations in eastern mediterranean hydrology during the last climatic cycle as inferred from neodymium isotopes in foraminifera abstract the nd isotopic compositions end of mixed planktonic foraminifera have been analyzed in two sediment cores collected in the nile deep sea fan in order to reconstruct past end of the eastern mediterranean deep water emdw and to assess the relative contributions of nile discharge and modified atlantic water maw inflow to the eastern mediterranean sea hydrology as well as their potential control on anoxic events over the last climatic cycle the two foraminiferal end records are similar and display an increase in end values during the african humid periods superimposed on this precession forced variability insolation received by the earth at low latitudes the record of variations in foraminiferal end indicates a 2 unit decrease in end during the interglacial marine isotope stages mis 5 and 1 compared to glacial mis6 4 3 and 2 the end results suggest that the long term glacial to interglacial changes in nd isotopic composition of emdw were not entirely induced by variations in nile river discharge and saharan dust inputs decreases in end during mis5 and mis1 interglacials indicate an increase in the contribution of unradiogenic maw to the eastern mediterranean sea related to high sea level stands and greater seawater exchange between the north atlantic and mediterranean basins in addition radiogenic seawater end values observed during african humid periods and sapropel events are associated with an intensification of nile discharge and an increase in residence time of deep water masses in the eastern mediterranean sea which induces an increase in the interaction between deep water masses and radiogenic sediments along the margin of the eastern mediterranean sea results confirm that an intensification of the hydrological exchanges between the western and eastern mediterranean basins during high sea level stand and the subsequent higher proportion of atlantic water in the levantine basin may have preconditioned the eastern mediterranean sea to sapropel depositions during the last climatic cycle

bermuda and appalachian labrador rises common non hotspot processes other than the corner rise new england seamounts and associated white mountains most postbreakup intraplate igneous activity and topographic uplift in the western north atlantic and eastern north america do not readily conform to simple hotspot models for example the bermuda rise trends normal to its predicted hotspot trace on continental crust cretaceous eocene igneous activity is scattered along a northeast trending belt 500 1000 km west of and paralleling the continent ocean boundary corresponding activity in the western atlantic generated seamounts preferentially clustered in a belt 1000 km east of the boundary the eocene volcanism on bermuda is paired with coeval magmatism of the shenandoah igneous province and both magmatic belts are associated with northeast trending topographic bulges the appalachian labrador rise to the west and the bermuda rise eocene to the east the above observations suggest the existence of paired asthenosphere upwelling paralleling and controlled by the deep thermal contrast across the northeast trending continental margin such convection geometry apparently fixed to the north american plate rather than to hotspots is consistent with recent convection models by b hager the additional importance of plate kinematic reorganizations causing midplate stress enhancement is suggested by episodic igneous activity ca 90 100 ma and 40 45 ma

from the subtropics to the central equatorial pacific ocean neodymium isotopic composition and rare earth element concentration variations 1 neodymium isotopic compositions end and rare earth element ree concentrations were measured for filtered surface to deep waters 112 samples in the southern tropical pacific the relatively detailed picture of these tracer distributions allowed us to refine the areas where oceanic end variations occur end values increase for most of the water masses flowing from samoa to the solomon sea and in the papua new guinea png area as already observed furthermore water masses arriving from the eastern equatorial pacific 200 550 m depth also revealed radiogenic values possibly acquired in the vicinity of the south american coasts and galapagos islands these end variations affect the whole water column the most likely process causing such variations is boundary exchange between the numerous radiogenic slopes margins located in this area and seawater flowing past dissolution of atmospheric deposition and or diffuse streaming of volcanic ash are also suggested to explain the radiogenic end observed at the surface in the png area interestingly a positive europium eu anomaly characterizes the normalized ree patterns of most of the studied water masses this anomaly is consistent with the ree patterns of sediment and rock samples that are potential sources for the local waters such consistency reinforces the hypothesis that lithogenic sources play a major role in the oceanic ree budget thanks to boundary exchange the data set presented here is a good basis for further sampling that will be realized in the framework of the ongoing geotraces program www geotraces org

a boundary exchange influence on deglacial neodymium isotope records from the deep western indian ocean the use of neodymium nd isotopes to reconstruct past water mass mixing relies upon the quasi conservative behaviour of this tracer whereas recent studies in the modern oceans have suggested that boundary exchange involving the addition of nd from ocean margin sediments may be an important process in the nd cycle here we suggest that the relative importance of water mass advection versus boundary exchange can be assessed where the deep western boundary current in the indian ocean flows past the madagascan continental margin a potential source of highly unradiogenic nd foraminiferal coatings and bulk sediment reductive leachates are used to reconstruct bottom water nd isotopic composition end in 8 holocene age coretops with excellent agreement between the two methods these data record spatial variability of 4 end units along the flow path of circumpolar deep water end 8 8 in the deep southern inflow upstream of madagascar which evolves towards end 11 5 offshore northern madagascar whereas end 7 3 where deep water re circulates in the eastern mascarene basin this variability is attributed to boundary exchange and together with measurements of detrital sediment end an isotope mass balance suggests a deep water residence time for nd of 400 yr along the madagascan margin considering deglacial changes a core in the deep inflow upstream of madagascar records end changes that agree with previous reconstructions of the circumpolar deep water composition in the southern ocean consistent with a control by water mass advection and perhaps indicating a longer residence time for nd in the open ocean away from local sediment inputs in contrast sites along the madagascan margin record offset end values and reduced glacial interglacial variability underlining the importance of detecting boundary exchange before inferring water mass source changes from nd isotope records the extent of madagascan boundary exchange appears to be unchanged between the holocene and late glacial periods while a consistent shift towards more radiogenic end values at all sites in the late glacial compared to the holocene may represent a muted signal of a change in water mass source or composition

tracing the influence of the trans european suture zone into the mantle transition zone cratons with their thick lithospheric roots can influence the thermal structure and thus the convective flow in the surrounding mantle as mantle temperatures are hard to measure directly depth variations in the mantle transition zone mtz discontinuities are often employed as a proxy here we use a large new data set of p receiver functions to map the 410 km and 660 km discontinuities beneath the western edge of the east european craton and adjacent phanerozoic europe across the most fundamental lithospheric boundary in europe the trans european suture zone tesz we observe significantly shorter travel times for conversions from both mtz discontinuities within the craton caused by the high velocities of the cratonic root by contrast the differential travel time across the mtz is normal to only slightly raised this implies that any insulating effect of the cratonic keel does not reach the mtz in contrast to earlier observations in siberia we do not find any trace of a discontinuity at 520 km depth which indicates a rather dry mtz beneath the western edge of the craton within most of covered phanerozoic europe the mtz differential travel time is remarkably uniform and in agreement with standard earth models no widespread thermal effects of the various episodes of caledonian and variscan subduction that took place during the amalgamation of the continent remain only more recent tectonic events related to alpine subduction and quarternary volcanism in the eifel area can be traced while the east european craton shows no distinct imprint into the mtz we discover the signature of the tesz in the mtz in the form of a linear region of about 350 km width with a 1 5 s increase in differential travel time which could either be caused by high water content or decreased temperature taking into account results of recent s wave tomographies raised water content in the mtz cannot be the main cause for this observation accordingly we explain the increase equivalent to a 15 km thicker mtz by a temperature decrease of about 80 k we discuss two alternative models for this temperature reduction either a remnant of subduction or an indication of downwelling due to small scale edge driven convection caused by the contrast in lithospheric thickness across the tesz any subducted lithosphere found in the mtz at this location is unlikely to be related to variscan subduction along the tesz though as eurasia has moved significantly northward since the variscan orogeny

relationship between observed upper mantle structures and recent tectonic activity across the southeastern united states the lithospheric structure of the southeastern united states is a product of earlier episodes of continental collision and breakup the region is located in the interior of the north american plate away from active plate margins however there is ongoing tectonism in the region with multiple zones of seismicity uplifting arches and cenozoic intraplate volcanism the mechanisms controlling this activity and the state of stress remain enigmatic two important factors are plate strength and preexisting inherited structures here we present new tomographic images of the upper mantle beneath the southeastern united states revealing large scale structural variations in the upper mantle examples include the relatively thick lithospheric mantle of stable north america that abruptly thins beneath the paleozoic appalachian orogeny and the slow upper mantle of the proterozoic reelfoot rift our results also indicate fast seismic velocity patterns that can be interpreted as ongoing lithospheric foundering this provides a viable explanation for seismicity uplifting and young intraplate volcanism we postulate that not only tectonic inheritance but also continuing lithospheric foundering may control the ongoing activity of the region long after it became a passive margin based on distinct variations in the geometry and thickness of the lithospheric mantle and foundered lithosphere we propose that piecemeal delamination has occurred beneath the region throughout the cenozoic removing a significant amount of reworked deformed mantle lithosphere ongoing lithospheric foundering beneath the eastern margin of stable north america explains significant variations in thickness of lithospheric mantle across the former grenville deformation front

qanat is not a hazard comments are presented on the article by abbasnejad et al environ earth sci 75 1306 2016 dealing with qanat and hazards in iran my rebuttal starts from the direct attribution of the described hazards to qanat and addresses the importance in the correct use of terminology for geological hazards all of the problems pointed out in iran subsidence sinkholes pollution have to me an anthropogenic origin and cannot be directly ascribed to qanat eventually i present some additional elements to highlight the remarkable importance of qanat systems and their influence on the development of similar underground structures in many countries of the mediterranean basin this remarks the relevance of qanat as cultural heritage sites and the need for their preservation and valorization

rey th u solute dynamics in the critical zone combined influence of chemical weathering atmospheric deposit leaching and vegetation cycling mule hole watershed south india the source and proportion of rey th and u exported by groundwater and by the ephemeral stream along with the elemental proportions passing through vegetation have been assessed in the sub humid tropical forested czo of mule hole southern india the study relies on a pluri annual hydro geochemical monitoring combined with a hydrological model the significant difference between the soil input si and output so solute fluxes mmol km2 yr of lree si so 13250 1500 hree 1930 235 th 64 12 and u 63 25 indicates a strong uptake by roots carried by canopy and forest floor processes the contribution of atmospheric dust leaching can reach about 60 of lree and 80 of hree at the watershed scale the u solute flux exported by groundwater 180 mmol km2 yr mainly originates from the breakdown of primary u bearing accessory minerals and dominates by a factor of 25 the stream flux the precipitation of authigenic u bearing phases and adsorption onto fe oxides and oxyhydroxides plays a significant role for limiting the u mobility in the groundwater the plagioclase chemical weathering is efficiently traced by the positive eu anomaly the very low rey to nil th contents are explained by the precipitation of authigenic phases in the stream flow dominated by the overland flow 87 of the yearly stream flow the solute exports in mmol km2 yr of rey 1080 for lree and 160 for hree and of th 14 dominate those by groundwater their mobility is enhanced by chelation with organic ligands produced by forest floor and canopy processes

seasonal variations in dissolved neodymium isotope composition in the bay of bengal abstract constraining the dissolved neodymium nd cycle in the ocean is paramount for using nd isotopic composition e nd as a tracer to reconstruct deep sea paleocirculations or continental weathering on different time scales dissolved end has been measured in seawater samples from six hydrological stations collected along 89 e north south transect in the bay of bengal bob in order to assess the impact of seasonal freshwater and sediment discharges from the continental river systems seawater samples collected in this study during june 2012 reveal more radiogenic end a difference of 2 epsilon units for the upper 2000 m and 0 5 epsilon unit below 2000 m and 3 8 pmol kg lower nd concentrations than the reported values of nearby seawater samples collected in november 2008 these observations are most plausibly explained by a seasonal variations in dissolved nd concentrations and end in the bob induced by seasonal variations in the freshwater and sediment discharges from the ganges brahmaputra g b river system however we cannot entirely exclude the possibility of spatial differences given that the water stations collected in this study are not exactly the same positions collected in november 2008 a two box model suggests 1 the particulate nd inputs from the g b river system mainly control the seasonal shift of end observed in the bob seawater and 2 a very rapid nd exchange exists between lithogenic particles and seawater at least on the scale of a few months seasonal changes in seawater end may also occur in other marginal seas and in the outflows of major rivers and these need to be taken into account when using the end proxy in the ocean

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

processes controlling the distribution and cycling of manganese in the oxygen minimum zone of the arabian sea abstract vertical and horizontal distributions of dissolved and particulate manganese were investigated in the arabian sea northwestern indian ocean during the 1995 spring intermonsoon period march april us jgofs process cruise 2 tn045 the region is characterized by an intense basin wide oxygen minimum zone omz that strongly influences the manganese distribution in the omz two distinct dissolved mn d mn maxima were observed at depths of 200 300 m and 600 m respectively the latter peak displayed concentration maxima of approximately 6 nanomolar and was largely confined to stations north of 19 n latitude stations n2 n7 this mid depth maximum was associated with the low oxygen core of the omz o 2 saager et al 1989 geochimica et cosmochimica acta 53 2259 2267 this signal was largely absent at stations along the southern transect likely due to oxidative scavenging of d mn to the suspended particulate phase mid depth particulate mn maxima at some southern stations stations s4 s11 appear to be remnants of this feature the upper d mn maximum 200 300 m depth was more widely distributed than the 600 m peak with d mn concentrations of 3 to as high as 8 nm at most stations east of about 62 e longitude the signal was everywhere correlated with the secondary nitrite maximum at stations within the main denitrification zone delineated by naqvi 1991 nepheloid layers presumably bacterial also were associated with this depth interval particulate mn profiles displayed corresponding concentration minima and low mn al and reactive refractory mn ratios for this same depth interval suggesting reductive dissolution of mn oxyhydroxides these observations imply that in situ microbially mediated processes may be the predominant source of d mn in the upper omz while horizontal advection is more important deeper in the water column

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

anomalous topography in the western atlantic caused by edge driven convection 1 the western atlantic region contains a long wavelength intraplate topography anomaly that is defined by the ne sw trending bermuda rise and two adjacent topography lows using numerical experiments we test the hypothesis that the anomalous topography may be the surface response to edge driven convection a primary edge driven convection cell and secondary flow circulation develops at a modeled continent ocean plate margin and induces subsidence at the continent ocean margin an off shore peak plateau of high topography on the ocean plate and distal ocean plate subsidence unlike hot spots the edge driven convection cell and associated topography migrate with moving surface plates the flow cell and wavelength of topography is broadened with continent ward motion of the lithosphere relative to the mantle whereas a migration in the ocean ward direction suppresses the formation of the edge driven convection cell and surface topography the wavelength of observed anomalous topography in the western atlantic and estimates of plate motions relative to a fixed hot spot reference frame are consistent with the former

dispersal patterns for hydrothermal plumes in the south pacific using manganese as a tracer abstract manganese profiles over the spreading axis of the east pacific rise epr between 22 15 s and 19 25 s disclose a series of plumes which are formed by buoyant emanations of hot hydrothermal vent fluids the plume ceilings or anomaly maxima can occur several hundred meters above the sea floor these plumes are dispersed laterally and are detectable as mid depth manganese anomalies 2000 km from the spreading axis along this section the plumes are dispersed mainly westward but at 30 s the plumes are advected eastward the asymmetrical dispersal pattern inferred from these data is coincident with the asymmetrical distribution of metalliferous sediments about the epr which suggests that plumes generated by high temperature venting play a dominant role in the formation of these sediments

erosion as a driving mechanism of intracontinental mountain growth in nature mountains can grow and remain as localized tectonic features over long periods of time 10 m y by contrast according to current knowledge of lithospheric rheology and neglecting surface processes any intracontinental range with a width that exceeds that which can be supported by the strength of the lithosphere should collapse within a few tens of millions of years for example assuming a quartz dominated crustal rheology the relief of a range initially 3 km high and 300 400 km wide is reduced by half in about 15 m y as a result of lateral spreading of its crustal root we suggest that surface processes might actually prevent such a subsurface collapse removal of material from topographic heights and deposition in the foreland oppose spreading of the crustal root and could eventually drive a net influx of material toward the orogeny we performed a set of numerical experiments in order to validate this hypothesis a section of a lithosphere with a brittle elasto ductile rheology initially loaded by a mountain range is submitted to horizontal shortening and to surface processes if erosion is intense material is removed more rapidly than it can be supplied by crustal thickening below the range and the topography is rapidly smoothed for example a feature 3 km high and 300 400 km wide is halved in height in about 15 m y for an erosion coefficient k 10 3 m 2 yr the erosion rate is of the order of a few 0 1 mm yr this regime might be called erosional collapse if erosion is not active enough the crustal root spreads out laterally and subsurface collapse occurs in the third intermediate regime removal of the material by erosion is dynamically compensated by isostatic rebound and inward flow in the lower crust so that the range can grow in this mountain growth regime the range evolves toward a characteristic graded shape that primarily depends on the erosion law the erosion rate may be high e g 0 5 0 9 mm yr close to the rate of tectonic uplift e g 0 7 1 1 mm yr and few times higher than the rate of topographic uplift 0 15 0 2 mm yr these experiments show that surface processes can favor localized crustal shortening and participate in the development of an intracontinental mountain surface processes must therefore be taken into account in the interpretation and modeling of long term deformation of continental lithosphere conversely the mechanical response of the lithosphere must be accounted for when large scale topographic features are interpreted and modeled in terms of geomorphologic processes

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

susceptibility mapping of instability related to shallow mining cavities in a built up environment anthropogenic activities and urbanization frequently spread over areas underlain by unstable karst ground or man made cavities leading to potential risk situations for buildings infrastructure and population the roof of the cavities may rapidly propagate upwards eventually resulting in progressive ground settlement and or sudden collapse these processes are frequently accelerated or triggered by various human activities e g overloading water recharge water table decline in this paper the susceptibility to instability of artificial cavity networks under an urban area in apulia region southern italy was assessed and evaluated here there is dense network of underground quarries excavated for the extraction of massive calcarenite for building and ornamental stone that are currently affected by severe instability problems identifying the zones of the cavities most prone to instability is of great practical importance susceptibility models have been developed analyzing the statistical relationships between the cavity sections with evidence of instability and a number of predisposing factors mainly related to the 3d geometry of the voids roof thickness and the presence of overloads the models produced by the discriminant analysis and the logistic regression approaches were independently and quantitatively evaluated through the construction of roc curves although the two models are characterized by different input data treatment as the logistic regression allows using continuous and discrete variables or any combination of both types even if they do not have a normal distribution the roc curves highlighted for both methods a satisfactory congruence between the model results and the observed data consequently from the model performance analysis the two models were evaluated comparable in terms of result reliability the methodology should be considered as a general first level analysis for near surface underground cavities aimed at identifying critical cave sectors that can be the focus of more detailed analyses especially those associated with sensitive zone related to the presence of buildings roads and frequent presence of human activity

petrology of indus river sands a key to interpret erosion history of the western himalayan syntaxis the indus river has been progressively transformed in the last decades into a tightly regulated system of dams and channels to produce food and energy for the rapidly growing population of pakistan nevertheless indus river sands as far as the delta largely retain their distinct feldspar and amphibole rich composition which is unique with respect to all other major rivers draining the alpine himalayan belt except for the brahmaputra both the indus and brahmaputra rivers flow for half of their course along the india asia suture zone and receive major contributions from both asian active margin batholiths and upper amphibolite facies domes rapidly exhumed at the western and eastern himalayan syntaxes compositionofindussandschangesrepeatedlyandmarkedlyinladakhandbaltistan indicatingoverwhelmingsedimentflux from each successive tributary as the syntaxis is approached provenance estimates based on our integrated petrographic mineralogical data set indicate that active margin units karakorum and transhimalayan arcs provide 81 of the 250f50 10 6 t ofsedimentsreachingthetarbelareservoireachyear partitioningofsuchfluxamongtributariesandamongsourceunitsallowsus to tentatively assess sediment yields from major subcatchments extreme yields and erosion rates are calculated for both the karakorum belt up to 12 500f4700 t km 2 year and 4 5f1 7 mm year for the braldu catchment and nanga parbat massif 8100f3500t km 2 yearand3 0f1 3mm year thesevaluesapproachdenudationratescurrentlyestimatedforsouthkarakorum and nanga parbat crustal scale antiforms and highlight the major influence that rapid tectonic uplift and focused glacial and fluvial erosion of young metamorphic massifs around the western himalayan syntaxis have on sediment budgets of the indus system detailed information on bulk petrography and heavy minerals of modern indus sands not only represents an effective independent method to constrain denudation rates obtained from temperature time histories of exposed bedrock but also

rare earth elements in saanich inlet british columbia a seasonally anoxic basin rare earth element and manganese distributions have been investigated in saanich inlet british columbia a seasonally anoxic basin redox cycling of ce and mn takes place across an oxic suboxic boundary approximately 20 m shallower than the o2h2s interface the remaining strictly trivalent ree undergo scavenging above this oxic suboxic boundary and regeneration from dissolving host phases below it these processes result in pronounced removal of ce from solution above the oxic suboxic boundary due to oxidative precipitation along with preferential uptake of the lighter trivalent ree during scavenging below the oxic suboxic boundary regeneration of particulate ree into solution leads to a less pronounced ce depletion and a less pronounced hree enrichment in the anoxic bottom waters dissolved ree concentrations in the sediment pore waters exhibit an approximately ten fold increase across the seawater sediment interface but then decrease with increasing depth indicating removal from solution during later diagenesis calculated diffusive fluxes of the ree and mn from the sediments into the overlying anoxic water column are insufficient to account for the accumulated trace metal enrichments observed in the water column we propose an annual redox cycle for saanich inlet in which flushing causes extensive oxidative precipitation and scavenging of trace elements from the water column each autumn the same material is rapidly regenerated from the underlying near surface sediments when the basin next turns anoxic

the mechanism for antarctic intermediate water renewal in a world ocean model abstract realistic representation of the low salinity tongue of antarctic intermediate water aaiw has been achieved in a coarse resolution ocean general circulation model the authors find that this water mass is not generated by direct subduction of surface water near the polar front instead the renewal process is concentrated in the southeast pacific ocean off southern chile the outflow of the east australian current progressively cools by heat loss to the atmosphere and freshens by assimilation of polar water carried north by the surface ekman drift during its slow movement across the south pacific toward the aaiw formation zone further deep warm advection near chile enables more convective overturn resulting in very deep mixed layers from which aaiw is fed into the south pacific and also into the malvinas current along with this isolated region of aaiw renewal the model relies on alongisopycnal mixing of fresh surface water from the polar front to capture a realistic circumpolar tongue

subpolar mode water formation traced by neodymium isotopic composition 1 the formation of subpolar mode water spmw is documented by combining neodymium isotopic composition nd ic as a conservative tracer with salinity temperature and o2 concentration nd ic reveals a more pronounced eastward extension of the labrador current particularly its subarctic intermediate water component than the other parameters nd ic also suggests that waters flowing through the denmark strait do not significantly contribute to the spmw formation a two end member mixing involving subarctic intermediate water and maybe ultimately labrador current water and north atlantic central water is proposed to explain spmw formation these results provide important insight into the processes controlling the nd ic in the north atlantic subpolar gyre which could provide a means for reconstructing the northward extension of the gulf stream in the past

seasonal spreading of the persian gulf water mass in the arabian sea the characteristics of the subsurface salinity maximum associated with the persian gulf water mass pgw are used to quantify the spreading and mixing of pgw in the thermocline of the arabian sea based on a bimonthly climatology of temperature and salinity examination of the seasonal cycles of heat and freshwater fluxes in the persian gulf region indicates that pgw forms as a result of elevated evaporative cooling in conjunction with reduced insolation during winter maps are presented of the distributions of depth salinity and geostrophic flow on 26 5 which nearly coincides with the core of the pgw after intense mixing in the strait of hormuz the property fields suggest that warm 17 c and high salinity 36 2 psu pgw enters the arabian sea to form a subsurface salinity extremum between 200 and 300 m we have found variability in the distribution of pgw in the arabian sea associated with monsoonal changes in the arabian sea circulation during the winter monsoon there is southward spreading of pgw along the western boundary during summer it is not present lateral mixing with low salinity water from the bay of bengal in the region south of 10 n and along the west coast of india during winter accounts for changes in the characteristics of pgw along these paths associated with the findlater jet during summer the entire thermohaline structure is vertically displaced along the coasts of somalia and arabia ekman convergence in the central arabian sea accounts for deepening of the pgw either lateral or vertical mixing would cause changes in pgw properties in these regions during this time pgw spreads predominantly southward along the central arabian sea as indicated by a tongue of high salinity

effects of vertical boundaries on infinite prandtl number thermal convection summary the physics of thermomechanical coupling of the continental lithosphere and its surrounding mantle is studied using a simple hydrodynamic model in which a fluid is heated from below and is bounded by rigid side walls rayleigh numbers up to 106 are considered a series of finite element stability analyses is employed to characterize systematically the nature of convective instability in such a system the marginal stability of a bounded fluid is increased not only by the rigid boundary condition on side walls but also by heat conduction across side walls the planform of convection at the marginal state is 3 d having convective rolls aligned perpendicular to side walls the characteristics of non linear convection at supercritical rayleigh numbers are investigated by first calculating 2 d steady state solutions and then applying 2 d and 3 d stability analyses the 2 d stability analysis shows that the presence of side walls significantly reduces the transition rayleigh number for time dependent convection and the 3 d stability analysis shows that heat conduction through side walls strongly prefers 3 d convective motion finally the characteristics of 3 d convection are analysed through the 3 d single mode approximation both 2 d and 3 d single mode solutions demonstrate that conducting side walls reduce the strength of convection at low rayleigh numbers but have a negligible influence at higher rayleigh numbers we therefore propose that the basal topography of the continental lithosphere can modulate the convective planform efficiently in the upper mantle

impact of water mass mixing and dust deposition on nd concentration and e nd of the arabian sea water column abstract the concentration and isotopic composition e nd of dissolved nd have been measured in the sub oxic denitrifying water column of the eastern arabian sea to explore the impact of water mass mixing and release from particles dissolved nd in the north eastern arabian sea is more radiogenic e nd 7 to 10 compared to its south eastern part e nd 11 to 15 suggesting contribution of nd from the bay of bengal bob the vertical profile of nd typically show higher values in surface waters 15 8 27 8 pmol kg followed by minima 12 18 pmol kg in the subsurface waters 200 300 m and a gradual increase with depth thereafter the nd concentration does not seem to show any changes in the sub oxic layers suggesting no impact of the sub oxic denitrifying conditions in this oceanic region on the biogeochemistry of nd the enrichment of nd in surface waters can be explained either by supply from high nd low salinity waters from the bob to the arabian sea via the east india coastal current eicc or alternatively the nd surface excess can be result of release from aeolian dust depositing over the sea surface inverse modeling computations suggest that in addition to nd contributed from water mass mixing some additional excess nd nd xs is required to balance the nd inventory in the water column there is significant nd xs in the surface waters of the north eastern arabian sea with e nd 6 similar to that of dust depositing over the arabian sea the fractional solubility of nd released from the aeolian dust was estimated to be varying from 3 to 17 for excess nd inventory per unit area nd xs of 20 g m 2 with nd ranging from 1 to 3 years this study highlights the significance of aeolian dust deposition in controlling the abundance and distribution of nd in the arabian sea the western arm of the northern indian ocean lying in the proximity to the arid landmass and characterized by high lithogenic aeolian dust deposition

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

neodymium isotopic composition of the oceans a compilation of seawater data a global compilation of the neodymium isotopic composition of seawater is presented with 880 data points it confirms the gradual end increase for intermediate deep water masses from the northwest north atlantic via the austral and indian oceans to the pacific this confirms the usefulness of this tracer for studying large scale oceanic circulation the compilation stresses the need for documenting the oceans south of 30 s from which less than 4 of the data are derived the associated neodymium concentrations display heterogeneous vertical gradients among major oceanic basins in addition to particle remineralization along the global thermohaline circulation the database suggests that basin size differences also contribute to that heterogeneity

dissolved silicon and its isotopes in the water column of the bay of bengal internal cycling versus lateral transport abstract the concentration of dissolved si and its isotope composition are measured in the bay of bengal bob region of the northern indian ocean the isotope data are the first data set from the northern indian ocean the measurements are made in eight depth profiles closely along the 87 e transect gio1 section of the international geotraces program and in a few samples from the northern shelf of the bay dissolved si in the water column varies from 0 6 to 152 5 mol kg whereas the 30si data cover a range 1 2 to 3 6 the depth profiles of dissolved si show generally lower values in the surface increasing with depth whereas the pattern reverses in the case of 30si these vertical distribution patterns of si and 30si are similar to those reported in other oceanic regions and suggestive of the significant role of biological processes in governing si biogeochemistry in the upper layers top 1500 m in contrast dissolved si in near surface waters of the northern shelf and the southernmost station is exceptionally high these results indicate a continental supply of dissolved si from the ganga brahmaputra river system g b and submarine groundwater discharge sgd to the shelf region and an intrusion of high salinity waters from the arabian sea in the southern bay the 30si values of 1 34 0 10 for deep bottom waters of the bob depth 1500 m are similar to those reported for the deep southern ocean and indicate the dominant control of water mass mixing the dissolved si concentrations in the bottom waters of the bob are generally higher than those of the water mass endmembers which suggest the need for an additional source of si in situ particle dissolution and or benthic release in the central bay seem to be the potential candidate the annual si budget in the top 100 m of the bob seems to suggest that meso scale eddies frequently occurring during non monsoon periods can supply at the most 2 6 g si m2 year which is about 33 of the si requirement to support new production in the bay the supply of dissolved si 1 3 0 5 1011 mol year from the g b river system and sgd has been calculated based on the distributions of dissolved si concentration and 30si in the northern shelf waters a comparison of this supply with the reported si flux upstream of the estuarine zone indicates about 40 removal of dissolved si in the g b estuary the mass balance of si isotopes in the deep waters indicates that the dissolution of diatoms is the main cause of excess si in the bay

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

hafnium and neodymium isotopes in surface waters of the eastern atlantic ocean implications for sources and inputs of trace metals to the ocean we present hafnium hf and neodymium nd isotopic compositions and concentrations in surface waters of the eastern atlantic ocean between the coast of spain and south africa these data are complemented by hf and nd isotopic and concentration data as well as rare earth element ree concentrations in saharan dust hafnium concentrations range between a maximum of 0 52 pmol kg in the area of the canary islands and a minimum value of 0 08 pmol kg in the southern angola basin neodymium concentrations also show a local maximum in the area of the canary islands 26 pmol kg but are even higher between 20n and 4n reaching maximum concentrations of 35 pmol kg these elevated concentrations provide evidence of inputs from weathering of the canary islands and from the partial dissolution of dust from the sahara sahel region the inputs from ocean island weathering are also reflected in radiogenic hf and nd isotopes the hf isotopic compositions of dust samples themselves are highly variable ranging between ehf 20 and 0 6 the combined hf and nd isotopic compositions of dust plot close to the terrestrial array during periods of appreciable dust load in the atmosphere during low atmospheric dust loading combined hf and nd isotopic compositions similar to seawater are observed most of the variability can be explained in terms of variable degrees of zircon loss from the dust samples which in turn is linked to sorting during atmospheric transport to the eastern atlantic ocean and possibly presorting by sedimentary redistribution on the continent in addition increasing relative proportions of radiogenic clay minerals with decreasing grain size may contribute to the radiogenic hf isotopic compositions observed while the nd isotopic composition in the surface ocean reflects the nd isotopic composition of the saharan dust adjacent to the sahara sahel region the release of hf from that dust appears to be incongruent and results in surface ocean hf isotopic compositions which are 10 ehf more radiogenic than the bulk dust radiogenic hf appears to be released from clays and possibly from trace apatite rare earth element patterns of dust samples indicate the presence of apatite but provide no evidence for ferromanganese grain coatings suggesting that such coatings are insignificant in the release of hf and nd from saharan dust to the surface ocean the nd isotopic composition of the surface waters becomes less radiogenic south of the equator most likely reflecting the release of nd from congo river sediments the release of hf from saharan dust and the congo river sediments however does not produce distinct hf isotopic signatures in the surface ocean implying that the mobile fraction of hf integrated over large continental areas is isotopically uniform the hf isotopic uniformity in the surface ocean means that the limited variability in deep water isotopic compositions is consistent with a short deep water residence time and reflects homogenous continental inputs rather than efficient deep water homogenization

on the origins of deep and bottom waters of the indian ocean the characteristics of the deep and bottom waters of the indian ocean when illustrated on potential density anomaly surfaces indicate that the waters enter from both the atlantic and pacific oceans the paths of spreading are constrained by the complex topography and characteristics are seen to be altered by exchange with the overlying and underlying water and with the sediments especially in the northern indian ocean the weddell sea contributes to the densest waters found in the western basins and the ross sea and adelie coast to the densest waters found in the eastern basins both dense water varieties are altered by and incorporated in the less dense water above initially water carried by the circumpolar current then water from the north atlantic and finally by deep water whose characteristics are derived in the northern indian ocean contact with the sediments increases the silica content of the bottom water in the southern ocean in the northern indian ocean the sediments alter the silica of the water at the bottom and together with enhanced salinity from diffusion of saline overflows from the marginal seas above imprint unique markers to the deep water that flows back to the south at middepths the series of ridges between madagascar and australia confine the flow to a series of gyres that carry characteristics from the circumpolar current equatorward and the northern indian ocean characteristics southward within the circumpolar current low oxygen deep water from the pacific is carried across the atlantic and into the indian ocean south of africa part flows around the cyclonic weddell sea gyre and part extends across the southern ocean water from another pacific source can be seen near 2000 m extending westward from the tasman sea south of aus tralia and across the indian ocean and perhaps to the aghulas current region southeast of africa in this study we show some maps of deep and bottom water characteristics of the indian ocean which may be used in a qualitative sense to infer pathways of spreading of water below a depth of about 2000 m the indian ocean has numerous ridges and basins figure 1 that severely restrict possible pathways of deep and bottom wa ter flow in the following we will begin by looking at char acteristics at the bottom of the ocean to reveal the path ways of spreading of the densest bottom waters from basin to basin then a series of six potential density anomaly surfaces at progressively shallower depths from about 4000 m up to about 2000 m will be shown to see what character istics influence the deep waters and how pathways of flow are constrained by the bathymetry of the indian ocean the choice of the specific density levels table 1 was based primarily on various property extrema shown by the 18os atlantis ii cruise 93 colored sections that accompany warren s 1981 detailed discussion of the major features of the central indian ocean between madagascar and aus tralia the sections approximately midway between antarctica and the northern indian ocean boundaries are well positioned to show features originating from both the north and the south as well as some brought into the indi an ocean by the antarctic circumpolar current the full ocean area isopycnal maps provide essential evidence on the origins and fates of features seen in the sections and

episodic cenozoic tectonism and the development of the nw european passive continental margin the north atlantic margins are archetypally passive yet they have experienced post rift vertical movements of up to kilometre scale the cenozoic history of such movements along the nw european margin from ireland to mid norway is examined by integrating published analyses of uplift and subsidence with higher resolution tectono stratigraphic indicators of relative movements including results from the stratagem project three episodes of epeirogenic movement are identified in the early mid and late cenozoic distinct from at least one phase of compressive tectonism two forms of epeirogenic movement are recognised referred to as tilting coeval subsidence and uplift rotations 1 over distances of 100s of kilometres and sagging strongly differential subsidence rotations up to 4 over distances 100 km each epeirogenic episode involved relatively rapid 10 ma km scale tectonic movements that drove major changes in patterns of sedimentation to find expression in regional unconformity bounded stratigraphic units early cenozoic tilting late paleocene to early eocene c 60 50 ma caused the basinward progradation of shelf slope wedges from elongate uplifts along the inner continental margin and from offshore highs mid cenozoic sagging late eocene to early oligocene c 35 25 ma ended wedge progradation and caused the onset of contourite deposition in deep water basins late cenozoic tilting early pliocene to present 4 0 5 ma again caused the basinward progradation of shelf slope wedges from uplifts along the inner margin including broad dome like features and from offshore highs the early mid and late cenozoic epeirogenic episodes coincided with atlantic plate reorganisations but the observed km scale tectonic movements are too large to be accounted for as flexural deflections due to intra plate stress variations mantle lithosphere interactions are implied but the succession of epeirogenic episodes of differing form are difficult to reconcile with the various syn to post rift mechanisms of permanent and or transient movements proposed in the hypothetical context of a plume beneath iceland the epeirogenic movements can be explained as dynamic topographic responses to changing forms of small scale convective flow in the upper mantle tilting as coeval upwelling and downwelling above an edge driven convection cell sagging as a loss of dynamic support above a former upwelling the inferred cenozoic succession of epeirogenic tilting sagging and tilting is proposed to record the episodic evolution of upper mantle convection during ocean opening a process that may also be the underlying cause of plate reorganisations the postulated episodes of flow reorganisation in the ne atlantic region have testable implications for epeirogenic movements along the adjacent oceanic spreading ridge and conjugate continental margin as well as on other atlantic type passive margins

rare earth element transport in the western north atlantic inferred from nd isotopic observations the isotopic composition of nd in the water column from several western north atlantic sites and formational areas for north atlantic deep water shows extensive vertical structure at all locations in regions where a thermocline is well developed large isotopic shifts 2 to 3 units are observed across the base of the thermocline regions without a thermocline are characterized by much more gradual shifts in isotopic composition with depth in general the data reveal an excellent correlation between the nd isotopic distribution in the western north atlantic water column and the distribution of water masses identified from temperature and salinity characteristics nadw as identified from t s properties is also characterized by a well defined isotopic composition having nd 0 13 5 0 5 this signature is associated with waters identified as nadw from high latitudes near formational areas in the labrador sea down to the equatorial region the isotopic signature of nadw would appear to be formed by a blend of more negative waters originating in the labrador sea nd 0 18 and more positive waters originating in the overflows from the norwegian and greenland seas nd 0 8 to 10 and is consistent with classical theories on the formation of nadw the isotopic signature of nadw is propagated southward to the equator where it is gradually being thinned out by mixing from above and below with more radiogenic nd associated with northward spreading antarctic intermediate and bottom waters the preservation of the isotopic signature of nadw over these large distances indicate that the ree undergo extensive lateral transport the isotopic composition of nd is largely conservative over the time scales of mixing within the atlantic in spite of the intrinsic nonconservative behavior of neodymium nd concentration gradients generally show surface waters to be depleted in nd relative to deep waters which must require vertical transport processes however isotopic differences in the water column preclude the local downward transport of ree from the surface into underlying deep waters as a simple explanation of the concentration gradient the apparent decoupling of ree in nadw from overlying local surface waters and the increasing concentration with depth provide a conflict with simple vertical transport mechanisms that is not yet resolved