discovery of new hydrothermal vent sites in bransfield strait antarctica we carried out a search for hydrothermal vents in the central basin of bransfield strait antarctica the zaps zero angle photon spectrometer chemical sensor and instrument package oregon state university ofos ocean floor observation system camera sled and tvg tv grab geomar were used to explore the water column and underlying seafloor these operations were supplemented with a series of dredges hydrothermal plumes over hook ridge at the eastern end of the basin are confined to the e ridge crest and se flank the plumes are complex and sometimes contain two turbidity maxima one widespread feature centered at 1150 m and a smaller more localized but broad maximum at 600 800 m we traced the source of the shallower plume to a sunken crater near the ridge crest using sensors on the zaps instrument package subsequently two tv grabs from the crater brought back hot soupy sediment 42 49 c overlain by hard siliceous crusts and underlain by a thick layer of volcanic ash we also recovered chimney fragments whose texture and mineralogy indicate venting temperatures in excess of 250 c native sulfur and fe sulfides occur in fractures and porous layers in sediment from throughout the area pore water data from the crater site are consistent with venting into a thin sediment layer and indicate phase separation of fluids beneath hook ridge the source of the deeper plumes at hook ridge has yet to be located we also explored a series of three parallel volcanic ridges west of hook ridge called three sisters we detected water column anomalies indicative of venting with the zaps package and recovered hydrothermal barites and sulfides from middle sister we spent considerable time photographing middle sister and hook ridge but did not identify classic vent fauna at either location we either missed small areas with our photography or typical mor vent fauna are absent at these sites

impact of eastern arctic shelf waters on the nansen basin intermediate layers the eurasian shelves supply water to the nansen basin intermediate layers in two ways as buoyancy driven plumes of dense winter water and as permanent inflow of the barents sea branch of atlantic water while the plumes are local and seasonal phenomena the barents sea flow is part of the large scale circulation both interact with atlantic water which enters the arctic ocean through fram strait and moves as a subsurface boundary current eastward along the continental slope during the polarstern cruise ark ix 4 in summer 1993 the fram strait branch was observed as a narrow core within tens of kilometers of the barents sea shelf edge here several patches of cold low salinity water spread across the slope down to about 500 m depth their origin is assumed to be the northern barents sea they mix with the warm saline fram strait branch water fsbw so that the core properties of the latter become modified downstream in the eastern nansen basin the fram strait branch is displaced toward the inner basin by inflow of the barents sea branch of atlantic water bsbw this inflow appears as a broad 200 km wedge extending from 200 to 1300 m depth bsbw is colder and less saline than water of the fram strait branch and it is less dense and less stratified than the ambient water both branches appear to undergo vigorous mixing while spreading eastward so that any eastward continuation of the boundary flow transports about 50 bsbw and 50 fsbw above 600 m and about 80 bsbw and 20 fsbw below that level toward the canadian basin according to available observations the barents and kara seas are the only source areas for shelf waters ventilating the nansen basin below the halocline and these waters constitute a freshwater input rather than a salt input winter shelf water from the laptev sea cannot contribute to layers deeper than the upper halocline

iron and humic type fluorescent dissolved organic matter in the chukchi sea and canada basin of the western arctic ocean 1 the concentrations of dissolved fe d fe total dissolvable fe t fe humic type fluorescence intensity humic f intensity as humic type fluorescent dissolved organic matter and nutrients were vertically determined in the shelf slope and basin regions chukchi sea and canada basin of the western arctic ocean during 1 27 september 2008 in all stations the remarkably high d fe and humic f intensity were found at depths between 25 and 200 m with the subsurface maxima of d fe 1 0 3 2 nm and humic f intensity 4 5 quinine sulfate units in the upper halocline layer upper hl being associated with a prominent nutrient maximum the high d fe and humic f intensity within the upper hl are probably attributed to the fe iii complexation with natural organic ligands such as marine dissolved humic substances resulting from main processes of the brine rejection during sea ice formation and interactions with sediments on the shelves however subsurface maxima 10 50 nm of t fe were found in the lower halocline layer beneath the upper hl of all slope and basin regions and are mainly attributed to the resuspension of sedimentary particles in the shelf region the finding of subsurface iron maxima in the halocline water of all regions may be the first confirmation for the lateral iron transport into the halocline layer from the shelves to the arctic basin

dissolved and particulate fe in a hydrothermal plume at 9 45 n east pacific rise slow fe ii oxidation kinetics in pacific plumes production of fe iii particles in hydrothermal plumes is of fundamental importance to the long term effect of hydrothermal circulation on seawater composition to elucidate the fundamental controls on fe redox kinetics and solution particle partitioning in neutrally buoyant plumes we sampled near field 3 km plume particles at 9 45 n on the east pacific rise in 1996 returning in 1997 to sample both particulate and dissolved phases 0 40 m filter concentrations of dissolved fe varied from 320 to 20 nm in proximal 0 3 km from vent site to distal samples 1 3 km downfield constituting 85 50 of total fe respectively based on vent fluid dilution factors calculated from dissolved mn a mass balance for vent fluid fe at this site indicates that 65 of fe is lost to particulate sulfide settling in the buoyant plume and that particulate fe in distal 1 3 km samples is twice as concentrated as predicted from dilution of particles in proximal plume water these observations are consistent with a calculated fe ii oxidation half time of 3 3 h long enough that fe iii colloid production and aggregation occurs primarily in the neutrally buoyant plume at relatively high dilutions preventing generation of high particulate fe concentrations 11 56 nm observed a general investigation of fe ii oxidation rates in plumes worldwide gives fe ii oxidation half lives as short as 17 min at some atlantic sites and as long as 6 h at some pacific sites the calculations indicate that the distribution of fe particles in plumes depends chiefly on inter basin differences in ambient deep water chemistry primarily ph and dissolved o2 and on local currents driving plume dilution and to a much lesser extent on variations in primary vent fluid composition long term changes in thermohaline circulation or ocean biogeochemistry may therefore alter fe dynamics and minor element fluxes associated with global hydrothermal activity independent of variations in crustal production rates

arctic ocean mn stratigraphy genesis synthesis and inter basin correlation abstract across the arctic ocean late quaternary deep marine sediments are characterized by the occurrence of brownish layers intercalated with yellowish to olive gray sediments these layers show enhanced levels of bioturbation peaks in mn content and typically contain elevated abundances of planktonic and benthic micro and nannofossils it was early surmised that these layers were deposited under interglacial conditions and that their cyclical downcore occurrence could be correlated to the global benthic oxygen isotope curve however the synchronicity of mn layers with interglacial conditions and the underlying mechanisms responsible for their formation remain controversial here we compile and synthesize findings of the last decades with several recent studies that shed light on issues such as the sources of mn to the arctic ocean the processes and pathways for mn to the deep sea the chemical processes active in the sediment and the spatial and temporal distribution of mn rich layers in arctic deep marine sediments budget calculations show that about 90 of mn input to the arctic ocean originates from arctic rivers or coastal erosion two sources effectively shut down during mid to late quaternary glacial intervals by continental ice sheets blocking or re directing the rivers and vast subaerial exposure of the shelf areas thus the strong late quaternary interglacial glacial cyclicity in mn content is clearly an input related signal and only secondarily influenced by chemical processes in the water column and in the sediment on the shelves the mn undergoes repeated geochemical recycling caused by the high organic carbon content in the sediments before it is ultimately exported to the deep basins where scavenging processes in the water column effectively bring the mn to the sea floor in the form of mn oxyhydr oxides the close synchronicity with enhanced bioturbation and elevated micro and nannofossil abundances shows that the mn peaks are preserved at a stratigraphic level closely corresponding to the interglacial intervals however under certain biogeochemical conditions mn oxyhydr oxides may diagenetically become both dissolved and re precipitated deep in the sediments as shown by pore water analyses and x ray radiograph studies dissolution is particularly conspicuous in late quaternary sediments from the lomonosov ridge where in rapidly deposited coarse grained intervals diamictons with elevated total organic carbon toc contents mn appears almost completely removed from within the glacial sediments and also the surrounding interglacial sediments correspondingly bundles of closely spaced mm thick mn rich horizontal bands are observed in sediment otherwise devoid of indicators for interglacial conditions suggesting that these bands were purely formed by diagenetic processes redistributing the mn from deeper sediment layers this type of diagenetic mn redistribution within the sediment can be recognized in xrf core scanner data combined with sedimentological information from x ray radiographs while pore water data are highly promising if clear diagenetic features in the sediment are missing with this increasing ability to recognize intervals where a diagenetic overprint exists in the mn record the recently improved understanding of the mn cycle in the arctic ocean provides a conceptual paleoenvironmental framework in which carefully applied mn stratigraphy can provide a powerful correlation tool when combined with other paleoceanographic proxies and sedimentological data

dissolved iron in the southern ocean atlantic sector abstract we report a comprehensive dataset of dissolved iron fe comprising 482 values at 22 complete vertical profiles along a 1 latitudinal section at the zero meridian in addition a shorter high resolution 00 09 surface section of the southernmost part of the transect 66 00 69 35 s is presented within the upper surface mixed layer the concentrations of dissolved fe vary between 0 1 and 0 3 nm an inverse trend versus fluorescence suggests significant fe removal by plankton blooms vertical mixing and upwelling are the most important supply mechanisms of iron from deep waters to the upper surface mixed layer at lower latitude 42 s there is a distinct maximum of 0 6 0 7 nm in the 2000 3000 m depth range due to inflow of north atlantic deep water in one region 55 s elevated dissolved fe found in the surface mixed layer is ascribed to the recent deposition of aeolian dust originating from south america close to the antarctic continent there is an indication of fe supply in surface waters from icebergs in the deep waters there is a strong indication of a hydrothermal plume of dissolved fe and mn over the ridge in the bouvet region 52 56 s in the weddell gyre basin the dissolved fe in the deep water is 0 47 0 16 nm in the eastward flow at 56 62 s and is lower with a value of 0 34 0 14 nm in the westward flow at high 62 69 s latitude at the edge of the continental ice sheet on the prime meridian the continental margin of the antarctic continent appears to be lesser source of dissolved fe than in any other place in the world this is likely because it is unique in being overlain by the extending continental ice sheet that largely prevents biogeochemical cycling

quantifying he fluxes from the mantle using multi tracer data assimilation a global coarse resolution ocean model previously fitted to geostrophic shear estimates and to data of 10 hydrographic parameters and tracers has been used to simulate the 3he and 4he distribution

distinct trends in the speciation of iron between the shallow shelf seas and the deep basins of the arctic ocean the speciation of iron was investigated in three shelf seas and three deep basins of the arctic ocean in 2007 the dissolved fraction 3 nm on the shelves and tdfe 13 5 in the nansen and amundsen basins than in the makarov basin log alpha 13 where the sources of fe and ligands were limited the ligands became nearly saturated with depth in the amundsen and nansen basins favoring fe removal in the deep ocean whereas in the deep makarov basin they became unsaturated with depth still here scavenging occurred although scavenging of fe was attenuated by the presence of unsaturated organic ligands their low reactivity in combination with a lack of sources of fe in the makarov basin might be the reason of a net export of fe to the sediment

iron manganese and lead at hawaii ocean time series station aloha temporal variability and an intermediate water hydrothermal plume trace metal clean techniques were used to sample hawaii ocean time series hot station aloha on seven occasions between november 1998 and october 2002 on three occasions full water column profile samples were obtained on the other four occasions surface and near surface euphotic zone profiles were obtained together with three other published samplings this site may have been monitored for dissolved 0 4 or 0 2 m fe more frequently than any other open ocean site in the world low fe concentrations 2500 m the concentrations we observe 0 4 0 5 nmol kg 1 are significantly lower than some other deep north pacific stations but are similar to values that have been reported for a station 350 miles to the northeast we attribute these low deepwater values to transport of low fe antarctic bottom water into the basin and a balance between fe regeneration and scavenging in the deep water near surface waters have higher fe levels than observed in the lower euphotic zone significant temporal variability is seen in near surface fe concentrations ranging from 0 2 0 7 nmol kg 1 we attribute these surface fe fluctuations to variable dust deposition biological uptake and changes in the mixed layer depth this variability could occur only if the surface layer fe residence time is less than a few years and based on that constraint it appears that a higher percentage of the total fe must be released from north pacific aerosols compared to north atlantic aerosols surprisingly significant temporal variability and high particulate fe concentrations are observed for intermediate waters 1000 1500 m these features are seen in the depth interval where high 3he from the nearby loihi seamount hydrothermal fields has been observed the total fe 3he ratio implies that the hydrothermal vents are the source of the high and variable fe the vertical profile of mn at aloha qualitatively resembles other north pacific mn profiles with surface and intermediate water maxima but there are some significant quantitative differences from other reported profiles the 0 4 m mn concentration is highest near the surface decreases sharply in the upper 500 m then shows an intermediate water maximum at 800 m and then decreases in the deepest waters these concentrations are higher than observed at a station 350 miles to the northeast that shows similar vertical variations it appears that there is a significant mn gradient throughout the water column from hot towards the northeast compared to the first valid oceanic pb data for samples collected in 1976 pb at aloha in 1997 1999 shows decreases in surface waters and waters shallower than 200 m pb concentrations in central north pacific surface waters have decreased by a factor of 2 during the past 25 yr from 65 to 30 pmol kg 1 surface water pb concentrations in the central north atlantic and central north pacific are now comparable we attribute the surface water pb decrease to the elimination of leaded gasoline in japan and to some extent by the u s and canada we attribute most of the remaining pb in pacific surface waters to asian emissions more likely due to high temperature industrial activities such as coal burning rather than to leaded gasoline consumption a 3 year mixed layer time series from the nearby hale aloha mooring site 1997 1999 shows that there is an annual cycle in pb with concentrations 20 higher in winter months this rise may be created by downward mixing of the winter mixed layer into the steep gradient of higher pb in the upper thermocline pb concentrations double between the surface and 200 m from 200 m to the bottom pb concentrations decrease to levels of 5 9 pmol kg 1 near the bottom for most of the water column thermocline and deepwater pb concentrations do not appear to have changed significantly during the 23 yr interval

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

sea ice derived dissolved iron and its potential influence on the spring algal bloom in the bering sea 1 observational and modeling studies in the bering sea indicate that changes in the seasonal ice cover and time of ice retreat influence open water productivity in particular the timing of the spring bloom and its phytoplankton community composition are affected dissolved iron dfe data in the water column and ice cores collected during the 2007 bering ecosystem study best cruise indicate that the melting ice provided substantial dfe to the water column the additional dfe input from melting sea ice could be biologically important along the outer shelf and shelf break where in ice free areas insufficient dfe 20 m variability in sea ice dynamics are likely to result in a varying supply of dfe to the outer shelf and shelf break in early spring and to contribute to the observed changes in the timing and community composition of the spring phytoplankton bloom

opposing authigenic controls on the isotopic signature of dissolved iron in hydrothermal plumes iron is a scarce but essential micronutrient in the oceans that limits primary productivity in many regions of the surface ocean the mechanisms and rates of fe supply to the ocean interior are still poorly understood and quantified iron isotope ratios of different fe pools can potentially be used to trace sources and sinks of the global fe biogeochemical cycle if these boundary fluxes have distinct signatures seafloor hydrothermal vents emit metal rich fluids from mid ocean ridges into the deep ocean iron isotope ratios have the potential to be used to trace the input of hydrothermal dissolved iron to the oceans if the local controls on the fractionation of fe isotopes during plume dispersal in the deep ocean are understood in this study we assess the behaviour of fe isotopes in a southern ocean hydrothermal plume using a sampling program of total dissolvable fe tdfe and dissolved fe dfe we demonstrate that 56fe values of dfe 56dfe within the hydrothermal plume change dramatically during early plume dispersal ranging from 2 39 0 05 to 0 13 0 06 2 sd the isotopic composition of tdfe 56tdfe was consistently heavier than dfe values ranging from 0 31 0 03 to 0 78 0 05 consistent with fe oxyhydroxide precipitation as the plume samples age the dfe present in the hydrothermal plume includes stabilised dfe species with potential to be transported to the deep ocean we estimate that stable dfe exported from the plume will have a 56fe of 0 28 0 17 further we show that the proportion of authigenic iron sulfide and iron oxyhydroxide minerals precipitating in the buoyant plume exert opposing controls on the resultant isotope composition of dissolved fe passed into the neutrally buoyant plume we show that such controls yield variable dissolved fe isotope signatures under the authigenic conditions reported from modern vent sites elsewhere and so ought to be considered during iron isotope reconstructions of past hydrothermalism from ocean sediment records

seismic imaging across the eastern ghats belt cuddapah basin collisional zone southern indian shield and possible geodynamic implications abstract the evolutionary nature of the area encompassing cuddapah basin nellore schist belt and the ongole domain of eastern ghats belt south india which contains paleo neoproterozoic imprints of thick sedimentation intense magmatism subduction accretion and possible collision between eastern dharwar craton and east antarctica is still being debated an attempt has been made here to decipher the deep crustal structure and tectonics of this region by reprocessing deep seismic sounding data acquired earlier through the modeling of first arrival refraction and wide angle reflection travel times the derived crustal seismic velocity structure reveals that the intracratonic proterozoic cuddapah basin containing only 4 km thick sediment is bounded by two major faults the moho reaching fault detected on its eastern boundary demarcates cuddapah basin from the nellore schist belt although a deep normal fault is mapped within the nallamalai fold belt but no thrusting signatures are apparent almost all the crustal layers beneath nellore schist belt and the ongole domain of eastern ghats belt show distinct eastward dipping trend conforming to an upthrusted feature suggesting possible presence of a collisional suture besides the areas lying east of cuddapah basin appear to be an accreted orogenic terrain beneath which lower crust has upwarped substantially the entire stretch of the studied region is underplated by unprecedently thick 20 km high velocity 7 0 7 4 km s magma layer above the moho indicating strong crust mantle thermal perturbation and massive subcrustal erosion further an expression of a deep seated mantle thermal anomaly has also been found below the parnapalle region of the sw cuddapah basin beneath which deeper crustal layers have exhumed

fluvial and hydrothermal input of manganese into the arctic ocean abstract a total of 773 samples were analysed for dissolved manganese mn in the arctic ocean aboard r v polarstern during expedition ark xxii 2 from 28 july until 07 october 2007 from tromso norway to bremerhaven concentrations of mn were elevated in the surface layer with concentrations of up to 6 nm over the deep basins and over 20 nm in the laptev sea the general distribution of mn through the water column is consistent with previous studies but there are differences in the absolute concentrations that are most likely related to differences in sample area sampling and filtration the elevated concentrations of mn in the surface layer are related to fresh water input this was visible in the strong negative correlations observed between dissolved mn and salinity the correlation between mn and salinity and the correlation between mn and the quasi conservative trace water mass tracer po4 showed fluvial and melt water input and the pacific and atlantic origin of the surface waters a large portion of the mn delivered by the arctic rivers is removed in the shelf seas and does not pass into the central basins most likely a benthic flux is at the origin of the elevated concentrations of mn near the sediments in the barents and kara seas these elevated concentrations of mn apparently affected the deep basins as well as maxima in the concentrations of mn were observed that corresponded with lowered transmission over the continental slope a maximum in the concentration of mn in the deep basin corresponded with anomalies in light transmission potential temperature and dissolved iron confirming the hydrothermal origin the hydrothermal plume was observed throughout the nansen basin and over the deep gakkel ridge around 2500 m depth and a smaller plume was observed around 3200 m the concentration of mn at the mn maximum around 2500 m depth decreased exponentially consistent with a first order scavenging model the concentrations of mn were extremely low in the deep makarov basin 0 05 nm and slightly higher in the eurasian basin 0 1 nm outside the influence of the hydrothermal activity

structure of the earth s crust and upper mantle below hindustan and the northern part of the indian ocean from geophysical data abstract the crustal cross section of the indian shield is refined on the basis of data obtained in the cooperative indian soviet deep seismic sounding dss research and from the use of a new interpretation technique crustal velocity parameters are studied and the main blocks and faults are identified the hypsometric position of the blocks is determined gravity field interpretation using dss and explosion seismology data has made it possible to characterize the structure of the entire tectonosphere for the area africa hindustan eastern coast of the bay of bengal it is confirmed that the continents have a normal continental crust that passes into the oceanic type under the ocean in the somali trough especially in the bay of bengal sediments are very thick the laccadiv isles have crust which is oceanic in composition the rift zone of the karlsberg ridge has deep seated asthenospheric roots the lithospheric density increases as the distance from the ridge grows the asthenosphere is developed everywhere but it is thinner and denser below the continent than below the ocean

interaction of microbial communities with clastic sedimentation during palaeoproterozoic time an example from basal gulcheru formation cuddapah basin india abstract the siliciclastic basal gulcheru formation 1 8 ga of the proterozoic cuddapah basin preserves abundance of mat induced sedimentary structures like old elephant skin wrinkle structure kinneyia ripples palimpsest ripples etc in the vicinity of pullivendla town kottalu village andhra pradesh india in a low gradient tidal flat deposional setting this is the first report of interaction of microbial communities with clastic sedimentation during palaeoproterozoic time in indian purana stratigraphy and probably from the viewpoint of global proterozoic biosedimentation various types of cracks on bed top hitherto considered as of trace fossil in origin may be considered to be formed on exposed surface due to dessication or under water due to synaeresis in presence of microbial communities

physical speciation of iron in the atlantic sector of the southern ocean along a transect from the subtropical domain to the weddell sea gyre distributions of total dissolvable iron tdfe unfiltered dissolved iron dfe 0 2 m filtered and soluble iron sfe 0 02 m filtered were investigated during the bonus goodhope cruise in the atlantic sector of the southern ocean 34 s 17 e 57 s 0 february march 2008 in the mixed layer mean values of 0 43 0 28 and 0 22 0 18 nmol l 1 were measured for tdfe and dfe respectively in deeper waters tdfe and dfe concentrations were 1 07 0 68 and 0 52 0 30 nmol l 1 respectively dfe concentrations decreased from the north subtropical waters to the south weddell sea gyre in the subtropical domain dusts coming from patagonia and southern africa and inputs from the african continental margin may explain high dfe and tdfe concentrations in surface and intermediate waters results from numerical models gave support to these hypotheses in the antarctic circumpolar current domain estimation of the median advective time of water masses suggests that sediment inputs from the antarctic peninsula south america margin and or south georgia islands could be an important source of fe except in the subtropical domain where 0 4 0 6 nmol l 1 of sfe were observed in the upper 1500 m all stations exhibited values close to 0 1 0 2 nmol l 1 in surface and 0 3 0 5 nmol l 1 in deeper waters for all stations colloidal fe cfe was a minor fraction of dfe in surface waters and increased with depth colloidal aggregation sinking of cfe and assimilation of sfe followed by rapid exchange between the two fractions are suspected to occur

genesis of copper lead mineralization in the regionally zoned agnigundala sulfide belt cuddapah basin andhra pradesh india shallow marine sandstone shale carbonate sedimentary rocks of the paleoproterozoic northern cuddapah basin host copper nallakonda deposit copper lead dhukonda deposit and lead mineralization bandalamottu deposit which together constitute the agnigundala sulfide belt the cu sulfide mineralization in sandstone is both stratabound and disseminated and pb sulfide mineralization occurs as stratabound fracture filling veins and or replacement veins within dolomite systematic mineralogical and sulfur carbon and oxygen isotope studies of the three deposits indicate a common ore fluid that deposited copper at nallakonda copper lead at dhukonda and lead at bandalamottu under progressive cooling during migration through sediments the ore fluid was of low temperature 200 c and oxidized thermochemical reduction of basinal water sulfate produced sulfide for ore deposition it is envisaged that basal red bed and evaporite bearing rift related continental to shallow marine sediments might have acted as the source for the metals rift related faults developed during sedimentation in the basin might have punctured the ore fluid pool in the lower sedimentary succession and also acted as conduits for their upward migration the ore bearing horizons have participated in deformations during basin inversion without any recognizable remobilization

anomalous phase association of ree in ferromanganese crusts from indian mid oceanic ridges evidence for large scale dispersion of hydrothermal iron abstract ferromanganese crusts collected at selected locations along the 7000 km long stretch of carlsberg central indian and southwest indian ridges are studied for bulk geochemical composition and distribution of rare earths and yttrium in major geochemical phases exchangeable carbonate mn oxide fe oxyhydroxide and residual silicate the crusts are dominated by vernadite with traces of quartz and calcite a high concentrations of major fe mn trace co ni cu zn and rare earth elements indicates that these crusts are hydrogenous in nature however the negative or no cerium anomalies in the shale normalized ree pattern indicates that some of these crusts are of mixed type hydrogenous and hydrothermal irrespective of their nature mixed or hydrogenous the phase distribution of ree y shows 70 83 of total ree y are associated with fe oxyhydroxide phase whereas only about 17 30 are associated with mn oxide phase such phase distribution is expected in mixed type crusts because it is a combination of hydrothermal where 90 of the total ree y is associated with only fe oxyhydroxide phase and hydrogenous processes where 50 of the total ree y is associated with only fe oxyhydroxide phase conversely the hydrogenous crusts also shows similar phase distributions 70 83 association with fe oxyhydroxide phase which is certainly different from typical hydrogenous crusts where both fe oxyhydroxide and mn oxide phases host equal amounts 50 each the large scale dispersion of hydrothermal particulate iron along the indian ocean ridges is likely to contribute an additional fe bound ree y pool to these crusts the positive yttrium anomaly in mn oxide phase of all these crusts substantiates the hydrothermal contribution

dissolved iron in the arctic ocean important role of hydrothermal sources shelf input and scavenging removal arctic ocean waters exchange with the north atlantic and thus dissolved iron dfe in the arctic has implications for the global fe cycle we present deep water 250 m dfe concentrations of the central arctic ocean nansen amundsen and makarov basins the dfe concentration in the deep waters varies considerably between these basins with the lowest dfe concentrations 0 2 0 4 nm in the makarov basin higher concentrations similar to 0 45 nm in the amundsen basin and highest concentrations similar to 0 6 0 7 nm in the nansen basin atlantic input from the shelf seas and slopes enhances the dfe concentration in the nansen basin moreover hydrothermal activity at the gakkel ridge causes a significant and widespread enrichment of dfe in the eurasian basins at a depth of 2000 3000 m below this maximum the important role of scavenging and absence of input sources are reflected in a strong relation with dissolved mn dmn and in very low 3000 m amundsen and makarov basins the depth profiles of dfe in the arctic ocean notably in the makarov basin deviate from the dfe distribution pattern observed in other parts of the world ocean

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

dissolved fe and al in the upper 1000 m of the eastern indian ocean a high resolution transect along 95 e from the antarctic margin to the bay of bengal a high resolution section of dissolved iron dfe and aluminum dal was obtained along 95 e in the upper 1000 m of the eastern indian ocean from the antarctic margin 66 s to the bay of bengal 18 n during the u s climate variability and predictability clivar co2 repeat hydrography i08s and i09n sections february april 2007 in the southern ocean low concentrations of dal

seismic imaging of the proterozoic cuddapah basin south india and regional geodynamics abstract cuddapah basin has been believed to be one of the largest intra cratonic proterozoic sedimentary basins of india situated in the eastern part of the dharwar craton of the south indian shield which is magmatically infested and contain thick column of sediments its overall sedimentary thickness as well as the nature of crustal evolution has remained enigmatic based on deep seismic sounding and other geological studies in the past it was perceived that this basin may contain as much as 10 12 km thick sediments the results of our present analysis derived up to a depth of 12 km reveals five layered upper crust associated with velocities i 4 50 km s ii 5 20 5 30 km s iii 5 50 5 80 km s iv 5 85 6 00 km s and v 6 40 km s out of which second and third layers correspond to upper and lower cuddapah sediments the results suggest the presence of only 4 0 km thick sediments in the deepest part of the basin below the nallamalai fold belt which has its implications in the developmental history of the basin a thermal driving force was invoked by earlier workers to account for estimated 10 12 km thick sediments however the present estimate of only 4 km basement depth in the cuddapah basin shows that the role of the thermal driving force may be marginal particularly in the deeper eastern cuddapah as isostatic subsidence due to sedimentary accumulation alone is enough to explain the basin depth further a basement sag of about 10 km would have logically needed lateral extension of the order of several hundreds of kilometers however as our present estimate of the sediment thickness gets reduced from earlier 10 km to only 4 km the size of the basin 44 500 km 2 would be in conformity with isostatic subsidence due to sedimentary accumulation hypothesis the structural features derived from present analysis like maximum depth observed near the thrust suture on the basin margin from where it decreases away from it its association of shallow marine sediments the arcuate shape of the basin along with its areal dimension resembles foreland basin between continent continent collisions

crustal structure of the west bengal basin india from deep seismic sounding investigations summary basement and sub basement crustal configuration of parts of the west bengal basin has been delineated from inverse and forward modelling of refraction and wide angle reflection data obtained along two east west profiles a beliatorburdwan bangaon profile 1 about 180 km long and b gopali tamluk port canning profile 2 about 140 km long the study has revealed the existence of four groups of prominent refractors velocities 1 7 2 1 km s 2 7 3 2 km s 3 74 2 km s and 4 6 5 3 km s overlying the crystalline basement with a velocity of 5 8 6 2 km s rajmahal traps velocity 4 6 5 3 km s averaging 4 8 km s l occur beneath the base of the tertiary sediments in the middle parts of the profiles the presence of sub trappean gondwanas is also indicated from the wide angle reflection modelling supported by deep well lithological information in general depth to the basement is found to increase from west to east with a maximum depth of around 10 to 11 km at the extreme eastern parts of the profiles a basement upwarp with a sharp flexure west of bishnupur on profile 2 in combination with the fault west of shantipur on profile 1 possibly brings into focus the regionally extending nne ssw hinge zone a low velocity layer lvl of about 2 to 3 km thickness velocity 5 6 5 8 km s has been inferred in the upper crust in this area in general the thickness of the upper including the sedimentary column and the middle 6 4 6 6 km s velocity parts of the crust is found to be larger thickness varying between 22 and 27 km than the lower crustal column interval velocity 6 8 7 0 km s l with a thickness of 5 to 10 km the moho lies at varying depths of 36 to 26 km along profile 1 with a prominent domal feature of about 40 km width between satgachia and west of shantipur in the middle part of profile 2 the moho occurs at depths of 32 to 34 km with a mild flexure east of tamluk configuration of the moho indicates that the crust is more akin to continental in nature in the western and middle parts of the basin whereas significantly thinned continental crust is indicated in the eastern and southeastern parts

petrological and geochemical characterization of proterozoic ophiolitic melange nellore khammam schist belt se india abstract the ophiolitic melange occurs close to a major fault within the metavolcanics of kanigiri area in the western margin of the khammam nellore schist belt andhra pradesh india the unique feature of kanigiri melange is the occurrence of ophiolitic bodies of various sizes most of which display petrological and geochemical characteristics typical of supra subduction zone oceanic crust the ophiolitic melange is composed mainly of blocks of variably deformed and metamorphosed pillow basalts serpentinized ultramafic rocks meta gabbros cherts and pelagic sediments in a pervasive scaly argillite matrix the melange has a tectonic contact with a granite intrusion and numerous thrust faults cut across the melange exposures primary magmatic features such as drainage cavities in pillow basalts magmatic layering in gabbros and clinopyroxene cumulates in ultramafic rocks are well preserved in low strain domains mafic components enclosed in the melange are characterized by low pressure secondary mineral assemblages retrograded from amphibolite down to greenschist facies as commonly observed in subducted and exhumed orogens all amphiboles in the studied fragments are calcic and cluster in the range from winchite actinolite to hornblende amphibole compositions are characterized by al 2 o 3 2 4 13 8 feo 5 13 k 2 o 0 04 0 7 and x mg 0 67 0 77 the metabasalt and wherlite samples exhibit light rare earth element lree enriched patterns and negative high field strength element hfse zr and ti consistent with a suprasubduction zone geodynamic setting a notable feature of both metabasalt and wherlite samples is their pronounced negative ce anomaly and a positive eu anomaly as observed in a number of modern island arc suites as the petrological features and the geochemical characteristics of the remnant fragments we analyzed in this study are reminiscent of their phanerozoic ophiolite counterparts we suggest that these rocks were derived from a proterozoic oceanic plate belonging to a suprasubduction ophiolite assemblage subduction zone geochemical signatures and ophiolite like crustal lithologies in the study region are consistent with the accretion of juvenile oceanic fragments to the pre existing continental blocks through a forearc continent collision

geochemical and iron isotopic insights into hydrothermal iron oxyhydroxide deposit formation at loihi seamount abstract low temperature hydrothermal vents such as those encountered at loihi seamount harbor abundant microbial communities and provide ideal systems to test hypotheses on biotic versus abiotic formation of hydrous ferric oxide feox deposits at the seafloor hydrothermal activity at loihi seamount produces abundant microbial mats associated with rust colored feox deposits and variably encrusted with mn oxyhydroxides here we applied fe isotope systematics together with major and trace element geochemistry to study the formation mechanisms and preservation of such mineralized microbial mats iron isotope composition of warm 2 s depleted hydrothermal fluids yielded 56 fe values near 0 1 indistinguishable from basalt values suspended particles in the vent fluids and feox deposits recovered nearby active vents yielded systematically positive 56 fe values the enrichment in heavy fe isotopes between 1 05 and 1 43 relative to fe ii in vent fluids suggest partial oxidation of fe ii during mixing of the hydrothermal fluid with seawater by comparing the results with experimentally determined fe isotope fractionation factors we determined that less than 20 of fe ii is oxidized within active microbial mats although this number may reach 80 in aged or less active deposits these results are consistent with fe ii oxidation mediated by microbial processes considering the expected slow kinetics of abiotic fe oxidation in low oxygen bottom water at loihi seamount in contrast feox deposits recovered at extinct sites have distinctly negative fe isotope values down to 1 77 together with significant enrichment in mn and occurrence of negative ce anomalies these results are best explained by the near complete oxidation of an isotopically light fe ii source produced during the waning stage of hydrothermal activity under more oxidizing conditions light fe isotope values of feox are therefore generated by subsurface precipitation of isotopically heavy fe oxides rather than by the activity of dissimilatory fe reduction in the subsurface overall fe isotope compositions of microbial mats at loihi seamount display a remarkable range between 1 2 and 1 6 which indicate that fe isotope compositions of hydrothermal fe oxide precipitates are particularly sensitive to local environmental conditions where they form and are less sensitive to abiotic versus biotic origins it follows that feox deposits at loihi seamount provides important modern analogues for ancient seafloor fe rich deposits allowing for testing hypotheses about the biogeochemical cycling of fe isotopes on early earth

particle dynamics in the rising plume at piccard hydrothermal field mid cayman rise processes active in rising hydrothermal plumes such as precipitation particle aggregation and biological growth affect particle size distributions and can exert important influences on the biogeochemical impact of submarine venting of iron to the oceans and their sediments however observations to date of particle size distribution within these systems are both limited and conflicting in a novel buoyant hydrothermal plume study at the recently discovered high temperature 398 c piccard hydrothermal field mid cayman rise we report optical measurements of particle size distributions psds we describe the plume psd in terms of a simple power law model commonly used in studies of upper and coastal ocean particle dynamics observed psd slopes derived from spectral beam attenuation and laser diffraction measurements are among the highest found to date anywhere in the ocean and ranged from 2 9 to 8 5 beam attenuation at 650 nm ranged from near zero to a rarely observed maximum of 192 m 1 at 3 5 m above the vent we did not find large 100 m particles that would settle rapidly to the sediments instead beam attenuation was well correlated to total iron suggesting the first order importance of particle dilution rather than precipitation or dissolution in the rising plume at piccard our observations at piccard caution against the assumption of rapid deposition of hydrothermal particulate metal fluxes and illustrate the need for more particle size and composition measurements across a broader range of sites globally

basement structure of the cuddapah basin from gravity anomalies abstract an attempt has been made to understand the complex nature of gravity anomalies over the cuddapah basin and their relationship with geology structure and tectonics the gravity anomalies could delineate the approximate boundaries of the basin which is characterized by a steep gravity gradient on its eastern margin and gentle gradients on all its other sides prominent gravity lineaments which probably represent faults separate sub basins within the main basin previous studies have indicated that the southwestern gravity high is related to a basic body and that the macherla high is thought to be due to a greenstone belt the gravity high near kurnool also appears to be due to a greenstone belt which might extend into the basin beneath the sedimentary rocks with the exception of these highs the gravity picture of the cuddapah basin is a broad low of about 35 mgal in amplitude regression analysis between residual gravity and basement depths inferred from aeromagnetic interpretation and deep seismic sounding dss data suggest a probable density contrast of about 0 07 g cm 3 between the basement and the cuddapah rocks p wave velocities from dss data support this view with a negative density contrast of about 0 05 0 10 g cm 3 between the basement and the sedimentary rocks from the residual gravity the basement structure map of the cuddapah basin has been prepared by using an effective density contrast of 0 07 g cm 3 the results indicate that the thickest pile of sedimentary rocks about 10 km occurs in the nallamalai sub basin at many locations the basement depths obtained in the present analysis corraborate those obtained from the analysis of other data

quantitative evaluation of iron transport processes in the sea of okhotsk abstract comprehensive observations of the iron fe distribution in the western sea of okhotsk were conducted and revealed the existence of two fe transport processes in the sub polar marginal sea one transport process is fe loading from the amur river and transport by the east sakhalin current esc and the other is fe transport by the intermediate water part of which was reported by nishioka et al 2007 here we report on quantitative evaluations of these two fe transport processes the surface dissolved fe diss fe and low salinity water distribution clearly indicate the influence of fe discharge from the amur river and the fe that is transported by the east sakhalin current the amounts of total dissolvable fe td fe and diss fe that cross the surface of the northeast sakhalin coastal area are estimated at 9 0 108 1 3 109 g yr 1 and 1 0 108 1 5 108 g yr 1 respectively although the esc surface transport system along the sakhalin coast is effective the length scale estimation of td fe transport indicated that only 1 5 of the fe at the mouth of the amur river reached 52 n which may be due to scavenging by biological particulates high fe anomalies were observed at the bottom of the continental shelf and the shelf break along the sakhalin coast the extremely low temperature and low n water indicate that fe resuspension due to the reducing properties of sediment occurred on the shelf and that the fe was introduced to dense shelf water dsw by tidal mixing we estimate that the amounts of td fe and diss fe involved in the dsw on the continental shelf are 8 8 1010 2 5 1011 g yr 1 and 2 3 109 6 6 109 g yr 1 respectively length scale estimates of td fe transport indicate that 20 of the td fe on the continental shelf remained in the kuril basin thus the td fe in the intermediate water was efficiently transported to the kuril basin these results indicate that two orders of magnitude more fe is derived from the continental shelf by the intermediate water than by surface water and that fe is transported a greater distance by intermediate water than by the surface layer additionally the fe that reached the kuril straits was mixed by intensive tidal mixing and influenced the vertical profiles of the water columns on both sides of the kuril straits in the kuril basin and the oyashio region our quantitative evaluation also indicates other fe inputs around the kuril strait

river runoff sea ice meltwater and pacific water distribution and mean residence times in the arctic ocean hydrographic and tracer data collected during ark iv 3 fs polarstern in 1987 arctic91 ib oden and aos94 ccgs louis s st laurent expeditions reveal the evolution of the near surface waters in the arctic ocean during the late 1980s and early 1990s salinity nutrients dissolved oxygen and 18 o data are used to quantify the components of arctic freshwater river runoff sea ice meltwater and pacific water the calculated river runoff fractions suggest that in 1994 a large portion of water from the pechora ob yenisey kotuy and lena rivers did not flow off the shelf closest to their river deltas but remained on the shelf and traveled via cyclonic circulation into the laptev and east siberian seas river runoff flowed off the shelf at the lomonosov ridge and most left the shelf at the mendeleyev ridge arctic91 and aos94 pacific water fraction estimates of upper halocline water the traditionally defined core of the pacific water mass document a decrease in extent compared to historical data the front between atlantic water and pacific water shifted from the lomonosov ridge location in 1991 to the mendeleyev ridge in 1994 the relative age structure of the upper waters is described by using the 3 h 3 he age the mean 3 h 3 he age measured in the halocline within the salinity surface of 33 1 0 3 is 4 3 1 7 years and that for the 34 2 0 2 salinity surface is 9 6 4 6 years lateral variations in the relative age structure within the halocline and atlantic water support the well known cyclonic boundary current circulation

deep dissolved iron profiles in the eastern north atlantic in relation to water masses concentrations of dissolved iron dfe 0 2 m were determined at two stations in the biscay abyssal plain north east atlantic in march 2002 dfe concentrations in the surface layer 0 23 0 34 nm were typical of winter conditions in this area at 1000 m dfe concentrations increased to 0 62 0 86 nm this feature is consistent with the production of dfe by remineralization of the biogenic material however at this depth mediterranean outflow water mow could be an additional source of dfe below 2500 m dfe concentrations were constant 0 75 0 04 nm an interesting feature of the profiles was the intermediate maximum of dfe 1 19 1 12 nm around 2000 m associated with the labrador sea water lsw we suggest that the iron enrichment of lsw occurred when this water mass reached the continental margin likely in the vicinity of the goban plateau vertical distributions were highly dependent on water masses encountered

gravity study along the kavali udipi deep seismic sounding profile in the indian peninsular shield some inferences about the origin of anorthosites and the eastern ghats orogeny abstract the crustal section along a 600 km long profile across the indian peninsular shield between kavali on the east coast and udipi on the west coast running approximately along 14 n latitude can be represented by a generalised three layer crustal model in accordance with the interpretation of gravity data along this profile based on the structural picture obtained from deep seismic soundings dss kaila et al 1979 these three crustal layers are an upper layer of density 2 70 g cm 3 corresponding to an average p wave velocity v p of 6 2 km sec an intermediate layer of density 2 75 g cm 3 v p 6 5 km sec and a deeper layer of density 2 85 g cm 3 v p 6 8 km sec crust of varied thicknesses and comprising the above three layers sits in general on upper mantle rocks of 3 3 g cm 3 corresponding to v p 8 2 km sec the regional gravity anomaly pattern along the profile can convincingly be explained as being due to the combined effect of intracrustal structural features and the configuration of the moho boundary as developed through tectonic activities along a number of faults detected by dss in the eastern portion of the profile corresponding to the cuddapah basin there exists an additional deep crustal layer of density 3 05 g cm 3 v p 7 2 km sec and an emplacement of highdensity material at shallow depths along weak zones on the eastern margin of the cuddapah basin this magmatic high density mass at shallow depth may extend as a linear subsurface feature along the entire eastern ghats belt as evidenced by the continuity of the similar gravity anomaly pattern and may be responsible for the eastern ghats orogeny and uplift this feature may be responsible for the plutonic activity to which the origin of anorthosite rocks found along the eastern ghats can be associated in the western part of the cuddapah basin the basaltic layer has thickened considerably with its top reaching a shallow depth of about 8 km this thickening of the basaltic layer is considered responsible for the generation of numerous dykes and sills in this region

micro and macronutrients in the southeastern bering sea insight into iron replete and iron depleted regimes abstract surface transects and vertical profiles of macronutrients dissolved iron d fe and dissolved manganese d mn were investigated during august 2003 in the southeastern bering sea we observed iron limited hnlc surface waters in the deep basin of the bering sea 15 20 mol kg nitrate 0 07 nmol kg d fe and 1 0 nmol kg d mn nitrate limited iron replete surface waters over the shelf

evidence of an extensive spread of hydrothermal dissolved iron in the indian ocean abstract ocean scale transect observations covering the entire water depth enable a comprehensive picture of the chemistry including the circulation and biogeochemical cycling of elements in seawater the large scale investigation of dissolved iron fe took place through the japanese geotraces study and here we report a basin scale full depth section profile of dissolved fe in the indian ocean from the arabian sea to the southern ocean the data clearly shows the hydrothermal fe distributed over 3000 km distance in the deep layer centered at a depth of approximately 3000 m around the central indian ridge segment and a large part of the dissolved fe from the hydrothermal sources was in the real soluble fraction rather than the colloidal fraction in the intermediate water in the north arabian sea another dissolved fe rich water mass existed where fe was enriched by remineralization processes from settling particles and or adjacent reducing sediments and preserved in the suboxic water the basin scale section profile indicates that there are several sources supplying dissolved fe to deep waters such as the hydrothermal sources and terrestrial fe input with a persistent condition in the oxygen minimum zone omz between the northern subtropical section though few fe sources were apparent in the southern ocean combining our size fractionated fe data with numerical modeling study suggests that the fe physical chemical form in seawater differs between the sources and is a key factor for controlling residence time and explaining the large scale distributed hydrothermal fe

the cuddapah salient a tectonic model for the cuddapah basin india based on landsat image interpretation abstract analysis of geologic geophysical data and lineaments derived from landsat image interpretation has revealed a pattern of tectonic inheritance of archean structural elements by the folded and thrusted eastern margin of the middle late proterozoic cuddapah basin in india a structural pattern set by deep crustal faults in the archean and intracratonic basin fabric is apparent in both sedimentary and tectonic trends in the basin the lineaments represent broad zones of en echelon and parallel alignments that appear to have nucleated on deep crustal faults which were reactivated as structural uplifts lateral and frontal ramps and transverse tear faults the major zones recognized are the northeast trending veldruti guntur lateral ramp to the north and the northwest trending cuddapah nellore transverse tear fault to the south east west directed compression during the eastern ghats latest proterozoic orogeny was apparently confined within these converging lineament zones that effectively buttressed the west verging thrust fronts block uplift along the ne trending veldruti guntur lateral ramp acted as a boundary to east to west thrust translation the northeastern ends of folds and thrusts were pinned down with relative displacement being clockwise and greater increasing to the southwest the lack of a lateral ramp or basement buttress to the south resulted in the development of the left lateral cuddapah nellore transverse tear fault steep imbricate thrust ramps in the foreland resisted further movement westward the resulting convex to the west arcuate nallamalai and vellikonda thrust fronts broadly paralleled by the east coast gravity high anomaly kaila and bhatia 1981 is herein named the cuddapah salient

intensive mixing along an island chain controls oceanic biogeochemical cycles 1 the subarctic pacific is a high nutrient low chlorophyll hnlc region in which phytoplankton growth is broadly limited by iron fe availability however even with fe limitation the western subarctic pacific wsp has significant phytoplankton growth and greater seasonal variability in lower trophic levels than the eastern subarctic pacific therefore differences in fe supply must explain the west to east decrease in seasonal phytoplankton growth the fe flux to the euphotic zone in the wsp occurs at a moderate value in that it is significantly higher than its value on the eastern side yet it is not sufficient enough to cause widespread macronutrient depletion that is hnlc status is maintained although we recognize several fe supply processes in the wsp the mechanisms that account for this moderate value of fe supply have not previously been explained here we demonstrate the pivotal role of tidal mixing in the kuril islands chain kic for determining the moderate value a basin scale meridional fe section shows that fe derived from sediments in the sea of okhotsk is discharged through the kic into the intermediate water masses 800 m of the western north pacific the redistribution of this fe rich intermediate water by intensive mixing as it crosses the kic is the predominant process determining the ratio of micronutrient fe to macronutrients e g nitrate in subsurface waters this ratio can quantitatively explain the differences in surface macronutrient consumption between the western and eastern subarctic as well as the general formation and biogeochemistry of hnlc waters of the subarctic north pacific

discovery of abundant hydrothermal venting on the ultraslow spreading gakkel ridge in the arctic ocean submarine hydrothermal venting along mid ocean ridges is an important contributor to ridge thermal structure and the global distribution of such vents has implications for heat and mass fluxes from the earth s crust and mantle and for the biogeography of vent endemic organisms previous studies have predicted that the incidence of hydrothermal venting would be extremely low on ultraslow spreading ridges ridges with full spreading rates 2 cm yr 1 which make up 25 per cent of the global ridge length and that such vent systems would be hosted in ultramafic in addition to volcanic rocks here we present evidence for active hydrothermal venting on the gakkel ridge which is the slowest spreading 0 6 1 3 cm yr 1 and least explored mid ocean ridge on the basis of water column profiles of light scattering temperature and manganese concentration along 1 100 km of the rift valley we identify hydrothermal plumes dispersing from at least nine to twelve discrete vent sites our discovery of such abundant venting and its apparent localization near volcanic centres requires a reassessment of the geologic conditions that control hydrothermal circulation on ultraslow spreading ridges

the continental margin is a key source of iron to the hnlc north pacific ocean here we show that labile particulate iron and manganese concentrations in the upper 500m of the western subarctic pacific an iron limited high nutrient low chlorophyll hnlc region have prominent subsurface maxima between 100 200 m reaching 3 nm and 600 pm respectively the subsurface concentration maxima in particulate fe are characterized by a more reduced oxidation state suggesting a source from primary volcagenic minerals such as from the kuril kamchatka margin the systematics of these profiles suggest a consistently strong lateral advection of labile mn and fe from redox mobilized labile sources at the continental shelf supplemented by a more variable source of fe from the upper continental slope this subsurface supply of iron from the continental margin is shallow enough to be accessible to the surface through winter upwelling and vertical mixing and is likely a key source of bioavailable fe to the hnlc north pacific

multi stage deformation in the nallamalai fold belt cuddapah basin south india implications for mesoproterozoic tectonism along southeastern margin of india abstract the common occurrence of small scale refolded folds deformed lineations and overprinting of foliation in the northern nallamalai fold belt nfb within the intracratonic cuddapah basin south india suggest three phases of deformation d 1 d 2 and d 3 during the late paleoproterozoic to neoproterozoic d 1 structures are represented by tight to isoclinal folds a slaty cleavage and local development of mylonites d 2 structures include ne trending tight to open folds f 2 with variable plunge indicating control of large domal structures and a steep crenulation cleavage developed in phyllites and other schistose rocks the above structures are overprinted by e w trending d 3 folds and cleavage which affect mesoproterozoic rocks of the srisailam formation uppermost nallamalai group in the e w trending vami konda range and metasediments of the palnad area thought to be equivalent of the neoproterozoic kurnool group taking into account the ages of intrusive vellaturu granite 1575 ma which is post d 2 deformation in the nfb and the chelima lamproite 1400 ma which intrudes the folded nallamalai rocks we suggest that the earlier episodes of multiple deformation in the nfb represent either late paleoproterozoic or early mesoproterozoic nw se compression in this part of the east gondwana the e w fold thrust structures affecting the srisailam quartzite and adjacent metasediments in the palnad area represent late mesoproterozoic and or neoproterozoic event the granite gneisses and schists of the nellore schist belt bordering the nfb are affected by both early and later events and thrust over rocks of the nallamalai group we propose that early deformation in the nfb lying southwest of the eastern ghats and roughly parallel to the present southeastern coast of india was unrelated to and occurred prior to the main deformation in the eastern ghats which is generally correlated with the 1000 ma old grenville event alternatively in view of the complex protracted evolution of the eastern ghats and published geochronological data supporting pre grenvillian tectonism particularly in the western charnockite zone of the eastern ghats d 1 and d 2 deformation in the nfb may be linked to this older 1600 1400 ma tectonic disturbance in the eastern ghats

hydrothermal fe cycling and deep ocean organic carbon scavenging model based evidence for significant poc supply to seafloor sediments abstract submarine hydrothermal venting has recently been identified to have the potential to impact ocean biogeochemistry at the global scale this is the case because processes active in hydrothermal plumes are so vigorous that the residence time of the ocean with respect to cycling through hydrothermal plumes is comparable to that of deep ocean mixing caused by thermohaline circulation recently it has been argued that seafloor venting may provide a significant source of bio essential fe to the oceans as the result of a close coupling between fe and organic carbon in hydrothermal plumes but a complementary question remains to be addressed does this same intimate fe corg association in hydrothermal plumes cause any related impact to the global c cycle to address this scor interridge working group 135 developed a modeling approach to synthesize site specific field data from the east pacific rise 9 50 n hydrothermal field where the range of requisite data sets is most complete and combine those inputs with global estimates for dissolved fe inputs from venting to the oceans to establish a coherent model with which to investigate hydrothermal corg cycling the results place new constraints on submarine fe vent fluxes worldwide including an indication that the majority of fe supplied to hydrothermal plumes should come from entrainment of diffuse flow while this same entrainment is not predicted to enhance the supply of dissolved organic carbon to hydrothermal plumes by more than 10 over background values what the model does indicate is that scavenging of carbon in association with fe rich hydrothermal plume particles should play a significant role in the delivery of particulate organic carbon to deep ocean sediments worldwide

the purana basins of southern cratonic province of india a case for mesoproterozoic fossil rifts abstract since its cratonization in the palaeoproterozoic southern peninsular india witnessed the development of a number of large intracratonic sedimentary basins traditionally referred to as purana basins spanning in age from late palaeoproterozoic through neoproterozoic the localization of these intracratonic basins namely pranhita godavari pg chattisgarh and cuddapah basins is apparently controlled by pre existing sutures and or weak zones the pg basin and the cuddapah basin host unconformity bound thick sediment dominated successions attesting to several cycles of fluvial shallow marine to shelf slope basin sedimentation deposition was punctuated by block uplifts resulting in local hiatuses and or volcanic upheavals leading to intercalation of thin but persistent basaltic flows and acid tuffs and ignimbrites basin margin deep faults apparently played a role in the facies distribution in these basins based on these features we propose that these basins initiated as continental rifts which however never opened up into a full fledged ocean basin but links with open seaway are evident from frequent occurrence of deposits representing tidal and storm influence particularly in upper part of the chattisgarh succession spatial distribution of facies and sediment thickness in the cuddapah and pg basins suggest that an open seaway existed to the east of the south indian cratonic province during the mesoproterozoic while similar criteria point to the existence of an open seaway north of the chattisgarh basin development history including nature of inversion suggest that the southern cratonic province of india existed as a single large continental mass since the mesoproterozoic in spite of episodes of supercontinent build up and fragmentation involving india and east gondwana during the proterozoic

tectonics in the cuddapah fold thrust belt in the indian shield andhra pradesh india and its implication on the crustal amalgamation of india and rayner craton of antarctica during neoproterozoic orogenesis neoproterozoic orogenesis in east antarctica and india led to the amalgamation of northern prince charles mountains rayner complex of antarctica with the krishna province of india along the present eastern coast of india with the development of 990 900 ma old fold thrust belt the frontal part of the fold thrust belt henceforth called the cuddapah fold thrust belt cftb recognized in the intercratonic palaeoproterozoic neoproterozoic cuddapah basin includes two frontal thrust sheets carried by the eastern velikonda and the western nallamalai thrusts along with a part of the undeformed foreland constituting frontal part of a larger fold thrust belt now fragmented and separated in different continents of gondwanaland therefore the intercratonic deformation now preserved in the palaeoproterozoic neoproterozoic cuddapah basin is related to the collision of the indian shield to the antarctic block during the amalgamation of the rodinia supercontinent cftb is dominated by quasi plastic deformational structures representing exhumed deeper level fault propagation folding related to the velikonda thrust while the nallamalai thrust represents the forelandward thrust of the cftb dominated by elastico frictional deformation structures

dissolved iron anomaly in the deep tropical subtropical pacific evidence for long range transport of hydrothermal iron abstract dissolved iron profiles along a north south transect along 158 w in the tropical pacific show evidence of two deepwater anomalies the first extends from station aloha 22 78 n to the equator at 1000 1500 m and lies below the maximum apparent oxygen utilization and nutrient n p concentrations the feature is not supported by vertical export processes but instead corresponds with the lateral dilution field of 3 he derived from the loihi seamount hawaii though a sediment source associated with the hawaiian island chain cannot be entirely ruled out the second deeper 2000 3000 m anomaly occurs in tropical south pacific waters 7 s and also does not correlate with the depths of maximum nutrient concentrations or apparent oxygen utilization but it does coincide closely with 3 he emanating from the east pacific rise more than 5000 km to the east we hypothesize that these anomalies represent the long range 2000 km transport of hydrothermal iron residuals stabilized against scavenging by complexation with excess organic ligands in the plume source regions such trace leakage of hydrothermal iron to distal plume regions would have been difficult to identify in most hydrothermal vent mapping studies because low analytical detection limits were not needed for the proximal plume regions these findings suggest that hydrothermal activity may represent a major source of dissolved iron throughout the south pacific deep basin today as well as other regions having high mid ocean spreading rates in the geologic past in particular we hypothesize that high spreading rates along the south atlantic and southern ocean mid oceanic ridges combined with the upwelling ventilation of these distal hydrothermal plumes may have increased ocean productivity and carbon export in the southern ocean assessing the magnitude and persistence of dissolved hydrothermal iron in basin scale deep waters will be important for understanding the marine biogeochemistry of iron and potentially on ocean productivity and climate change during the geologic past

structural trends in the cuddapah basin from deep seismic soundings dss and their tectonic implications abstract structural trends in the upper proterozoic cuddapah basin at the basement level and at the moho level have been discussed based on deep seismic sounding dss studies results of dss studies along the alampur koniki profile profile 2 of fig 1 crossing the northern part of the cuddapah basin have been discussed in detail these results combined with the results of the kavali paranpalle section of the kavali udipi dss profile profile 1 of fig 1 kaila et al 1979 crossing the basin on its southern flank along with geological data and earthquake epicentral locations are used to explain the structural trends of the area it has been shown that the cuddapah basin was first created in its western part by downfaulting of the crustal block between faults 7 and 14 towards the west and fault 6 in the east fig 1 subsequently the eastern part was downfaulted against fault 6 before the commencement of upper cuddapah sedimentation further downfaulting towards the north along fault 5 created the srisailam block minor scale downfaulting between faults 7 and 13 in the west and fault 6 in the east and fault 8 in the north gave rise to the kurnool sub basin at a later stage similar downfaulting east of fault 9 and north of fault 5 gave rise to the palnad sub basin both these sub basins received kurnool sediments after the close of kurnool sedimentation the blocks between faults 4 and 6 along profile ii and between 11 and 6 along profile i were uplifted at the basement level thus giving rise to the nallamalai hills and iswarakuppam dome fig 1 the low angle thrust fault 3 on the eastern margin of the cuddapah basin might be a post cuddapah phenomenon the low angle thrust fault 2 probably occurred in the post dharwar period faults 1 17 and 10 near the east coast of india seem to be comparatively younger probably of mesozoic time along which the coastal block is downfaulted giving rise to the sedimentary basins

dissolved iron in the arctic shelf seas and surface waters of the central arctic ocean impact of arctic river water and ice melt key points dfe in the arctic shelves and surface is linked to freshwater and alkalinity fluvial input main contributor to high dfe low alkalinity in central arctic remineralisation and biological depletion determine dfe in the arctic shelf seas abstract concentrations of dissolved 10 nm in the bottom waters of the laptev sea shelf may be attributed to either sediment resuspension sinking of brine or regeneration of dfe in the lower layers a significant correlation r2 0 60 between salinity and dfe is observed using 18o salinity nutrients and total alkalinity data the main source for the high 2 nm dfe concentrations in the amundsen and makarov basins is identified as eurasian river water transported with the transpolar drift tpd on the north american side of the tpd the dfe concentrations are low 4 above the shelf and low 4 off the shelf

physical and biogeochemical controls on the variability in surface ph and calcium carbonate saturation states in the atlantic sectors of the arctic and southern oceans polar oceans are particularly vulnerable to ocean acidification due to their low temperatures and reduced buffering capacity and are expected to experience extensive low ph conditions and reduced carbonate mineral saturations states in the near future however the impact of anthropogenic co2 on ph and will vary regionally between and across the arctic and southern oceans here we investigate the carbonate chemistry in the atlantic sector of two polar oceans the nordic seas and barents sea in the arctic ocean and the scotia and weddell seas in the southern ocean to determine the physical and biogeochemical processes that control surface ph and high resolution observations showed large gradients in surface ph 0 10 to 0 30 and aragonite saturation state ar 0 2 to 1 0 over small spatial scales and these were particularly strong in sea ice covered areas up to 0 45 in ph and 2 0 in ar in the arctic sea ice melt facilitated bloom initiation in light limited and iron replete dfe 0 2 nm regions such as the fram strait resulting in high ph 8 45 and ar 3 0 along the sea ice edge in contrast accumulation of dissolved inorganic carbon derived from organic carbon mineralisation under the ice resulted in low ph 8 05 and ar 1 1 in areas where thick ice persisted in the southern ocean sea ice retreat resulted in bloom formation only where terrestrial inputs supplied sufficient iron dfe 0 2 nm such as in the vicinity of the south sandwich islands where enhanced ph 8 3 and ar 2 3 were primarily due to biological production in contrast in the adjacent weddell sea weak biological uptake of co2 due to low iron concentrations dfe 0 2 nm resulted in low ph 8 1 and ar 1 6 the large spatial variability in both polar oceans highlights the need for spatially resolved surface data of carbonate chemistry variables but also nutrients including iron in order to accurately elucidate the large gradients experienced by marine organisms and to understand their response to increased co2 in the future

seismic properties of the central indian shield we use broadband seismic data at hyderabad to investigate average crustal properties of the central indian shield crustal receiver functions p to sv conversions based on data of excellent quality and azimuthal coverage show essentially no signal on the transverse component indicating laterally homogeneous structures near this station a joint analysis of receiver functions and the dispersion of fundamental mode rayleigh waves result in a simple model for the shear wave speed v s with a moderate gradient of 0 010 0 028 km sec km in the crust the moho is sharp with a contrast of approximately 0 7 km sec in v s across a small thickness of only 0 4 km measured from the middle of the moho region the crust is 30 34 km thick with an average v s of 3 58 0 10 km sec by modeling the timing and waveforms of sp and sspmp phases sv to p conversions we estimate the average crustal poisson9s ratio to be 0 26 0 01 this value is comparable to that found in the tanzanian craton which is also of archean age both values being somewhat lower than the global average of 0 29 0 02 for shield regions that include both proterozoic and archean crust a low poisson9s ratio and a slow v s in the crust indicate that on average archean crust beneath the central indian shield is intermediate to felsic in composition somewhat less mafic than globally averaged precambrian crust