paired dissolved and particulate phase cu isotope distributions in the south atlantic abstract copper cu is both an essential micronutrient and toxic to photosynthesizing microorganisms at low concentrations its dissolved vertical distribution in the oceans is unusual being neither a nutrient type nor scavenged type element this distribution is attributed to biological uptake in the surface ocean with remineralisation at depth combined with strong organic complexation by dissolved ligands scavenging onto particles and benthic sedimentary input we present coupled dissolved and particulate phase cu isotope data along the uk geotraces south atlantic section alongside higher resolution dissolved and particulate phase cu concentration measurements our dissolved phase isotope data contribute to an emerging picture of homogeneous deep ocean 65cu at about 0 65 relative to nist srm 976 we identify two pools of cu in the particulate phase a refractory lithogenic pool at about 0 and a labile pool accessed via a weak acidic leach at about 0 4 these two pools are comparable to those previously observed in sediments we observe deviations towards lighter 65cu values in the dissolved phase associated with local enrichments in particulate cu concentrations along the continental slopes and in the surface ocean copper isotopes are thus a sensitive indicator of localised particle associated benthic or estuarine cu inputs the measurement of cu isotopes in seawater is analytically challenging and we call for an intercalibration exercise to better evaluate the potential impacts of uv irradiation storage time and different analytical procedures

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

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

a diagnostic gdgt signature for the impact of hydrothermal activity on surface deposits at the southwest indian ridge abstract the impact of hydrothermal activity on wider ocean geochemistry and microbial ecology remains a topic of much interest to explore whether hydrothermal microbial signatures are exported to surrounding marine sediments or if such organisms serve as an important source of sedimentary organic matter we determined the distributions of glycerol dialkyl glycerol tetraether gdgt membrane lipids in surficial normal marine sediments metalliferous sediments and low temperature hydrothermal deposits at newly discovered hydrothermal fields and adjacent areas at the southwest indian ridge swir the gdgts in those samples varied significantly evidently representing a variable influence of the hydrothermal activity gdgt compositions of surficial background sediments in swir were similar to those commonly observed in marine sediments dominated by gdgts associated with marine planktonic archaea and especially gdgt 0 and crenarchaeol in contrast the gdgts of metalliferous sediments strongly impacted by hydrothermal activity and low temperature hydrothermal deposits were markedly different characterized by high relative abundances of isoprenoid gdgts igdgts bearing multiple rings yielding a higher ring index low relative abundances of crenarchaeol and the presence of glycerol monoalkyl glycerol tetraether lipids gmgts so called h tetraethers that were absent in the normal marine sediments sources for these hydrothermal specific tetraether lipids likely include methanogens and anaerobic methanotrophic archaea gdgt 0 and gdgt 1 3 respectively thermoprotei and thermoplasmatales elevated gdgt 3 and 4 and other thermophilic archaea including methanobacteriales gmgts deposits influenced by low temperature hydrothermal activity also contained higher abundances of branched gdgts brgdgts typically attributed to soil bacteria the more distal metalliferous sediments influenced by the neutrally buoyant plume did not contain putative hydrothermal gdgts having the same gdgt distribution as the background sediments this suggests that the neutrally buoyant plume has a limited potential to directly influence the organic matter inputs to surrounding sediments due to a rapidly waning chemosynthetic microbial contribution relative to normal marine contributions as the plume dispersed and was diluted

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

an overview of dissolved fe and mn distributions during the 2010 2011 u s geotraces north atlantic cruises geotraces ga03 abstract high resolution dissolved fe dfe and dissolved mn dmn distributions were obtained using a trace metal clean rosette during the geotraces ga03 zonal transect cruises usgt10 and usgt11 across the north atlantic ocean this manuscript provides a general overview of the dfe as well as dmn and dissolved al dal distributions that reveal several fe inputs at varying depths across the study region elevated dfe concentrations correlate with elevated dal concentrations in the surface waters of the subtropical gyre indicating a significant atmospheric source of fe in contrast there is no apparent significant dust source for mn in the subsurface waters dfe maxima are a result of the remineralization process as revealed by their correspondence with dissolved oxygen minima within the oxygen minimum the ratio of dfe to apparent oxygen utilization aou is lower than would be expected from the measured fe content of surface water phytoplankton suggesting that a significant amount of dfe that is remineralized at depth 63 90 is subsequently scavenged from the water column the rate of remineralization which is based on the slope of dfe aou plot is similar across a wide area of the north atlantic in addition to the remineralization process sedimentary inputs are apparent from elevated dmn signals in the eastern basin particularly near the african coast in the western basin sedimentary input is also occurring along the advective flow path of the upper labrador sea water ulsw as ulsw transits along the north american continental shelf region the largest dfe anomaly 68 nm which also corresponds to a dmn anomaly up to 33 nm is seen in the neutrally buoyant hydrothermal plume sampled over the mid atlantic ridge and that signal is visible for 500 km to the west of the ridge

introduction to physics carbon dioxide trace elements and isotopes in the southern ocean the polarstern expeditions ant xxiv 3 2008 and ant xxiii 3 2006

krill as a central node for iron cycling in the southern ocean 1 in order to establish the potential role of antarctic krill euphausia superba in the recycling of bioactive elements we have quantified the release of iron phosphate and ammonia by these organisms along the antarctic peninsula sector of the southern ocean the experimental results suggested that the presence of krill has a significant impact on ambient iron concentrations as large amounts of this trace element were released by the krill 22 689 nmol fe g dry weight 1 h 1 equivalent to 0 2 to 4 3 nmol fe l 1 d 1 half of this iron release occurred within the first hour of the experiment and differences in iron and phosphate release rates 3 1 to 14 0 mol po43 g dw 1 h 1 seemed to reflect differences in food availability these results identify krill as a major node in iron cycling in the southern ocean potentially influencing iron residence time in the upper water column of this region

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

constraining oceanic dust deposition using surface ocean dissolved al we use measurements of ocean surface dissolved al a global biogeochemical elemental cycling bec ocean model and the global dust entrainment and deposition dead model to constrain dust deposition to the oceans our al database contains all available measurements with best coverage in the atlantic vertical profiles and seasonal data exist in limited regions observations show that surface dissolved al is distributed similarly to the dust deposition predicted by dead and other models there is an equatorial atlantic al maximum that decreases toward higher latitudes there are high al concentrations in the mediterranean sea and the arabian sea and low concentrations in the pacific and the southern ocean the ocean basins maintain more distinct al profiles than fe profiles in the upper ocean consistent with a weaker biological influence on al than fe the bec predicted surface dissolved al compares relatively well with observations the al distribution reflects the combined effects of al input from dust and al removal by particle scavenging and biological uptake by diatoms model observed biases suggest a southward shift of maximum dust deposition compared to current dust model predictions dead appears to overestimate deposition north of 30 n in the pacific and to underestimate deposition south of 30 n observed al concentrations and the ocean model predicted surface al lifetime provide a semi independent method to estimate oceanic dust deposition this technique indicates that dead may overestimate dust deposition to the north equatorial atlantic but underestimate in other atlantic regions the southern ocean and the arabian sea however spatial variations in aerosol al solubility may also contribute to the model observation mismatch our results have implications for all dust borne ocean nutrients including fe and demonstrate the potential of marine geochemical data to constrain atmospheric aerosol deposition fields

relative timing of the storegga submarine slide methane release and climate change during the 8 2 ka cold event this paper highlights the similarity in the timing between the 8 2 ka cold event across the north atlantic region and one of the world s largest underwater slides the storegga submarine landslide that took place on the continental slope west of norway we argue on the basis of a reinterpretation of the age of tsunami deposits that date the slide as well as published ages of sediment directly resting upon the slide surface that the slide occurred between 8100 and 8200 cal yr near the end of the 8 2 ka cold event because sediment exposed at the base of the slide contained less methane gas hydrate c 8200 years ago than exists today and because greenland ice cores do not show an increase in methane at the time of the slide it is argued here that the slide did not release significant volumes of methane to the atmosphere and did not contribute to any change in temperature during or after the 8 2 ka cold event

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

evidence for a composite organic inorganic fabric of belemnite rostra implications for palaeoceanography and palaeoecology carbonate skeletons of fossil marine organisms are widely used to reconstruct palaeoceanographic parameters specifically the geochemistry of jurassic and cretaceous belemnite rostra is traditionally interpreted to represent near sea surface seawater properties more recently an increasing number of workers have reported significant scatter in geochemical data e g 18o 13c element ca ratio when comparing rostra from the same stratigraphic level or within a single belemnite rostrum this scatter is not explained by differential diagenetic overprint alone here we report petrographic evidence on the primary ultrastructure of rostra of megateuthis middle jurassic and belemnitella and gonioteuthis late cretaceous the biogenic ultrastructure consists of a filigree framework of triaxial branches and tetrahedrons of variable size forming a honeycomb like network data presented here suggest that these rostra yielded as much as 50 to 90 primary pore space on the level of a working hypothesis and in analogy with modern cephalopods we propose that the pore space was formerly filled with body fluid and or organic compounds during the life time of these organisms intra rostral porosity was post mortem occluded by earliest diagenetic isopachous calcite cements of a non biogenic origin these may have been precipitated due to increased alkalinity related to the decay of organic matter if this holds true then the resulting fabric represents a composite biogenic abiogenic structure in order to optically separate the two calcite phases forming a single calcite fibre we employed a wide range of state of the art analytical tools to thin sections and ultra thin sections of well preserved specimens pending a verification of these well supported ultrastructural data by means of high resolution geochemical analyses from biogenic and abiogenic phases we suggest that these findings have significance for those using belemnite rostra as archives of their palaeoenvironment

the shelf to basin iron shuttle in the black sea revisited continental shelf sediments are a major source of iron fe for phytoplankton in surface waters in this study we investigate the mechanisms that control release of fe from shelf sediments and its lateral transport shuttling in oxic and hypoxic waters on the northwestern black sea shelf we find that at two coastal stations near the outflow of the danube river high input of organic matter drives strong reductive dissolution of fe oxyhydr oxides henceforth termed fe oxides in surface sediments supporting high rates of fe release to oxygenated bottom waters 0 36 mmol m 2 d 1 we suggest that bioirrigation plays a key role in the release of fe from these sediments at four stations further offshore organic matter deposition is lower resulting in limited mobilization of fe2 in the sediment and low benthic fluxes of fe 0 2 m in the lower part of the water column likely through repeated deposition and resuspension of fe oxides from surface sediments using synchrotron based x ray spectroscopy and sequential chemical extractions we demonstrate that the suspended matter and surface sediments are enriched in easily reducible fe oxides mostly ferrihydrite and fe associated with clay the mobilization of fe in the coastal zone and subsequent lateral transport of these fe bearing particles results in higher ratios of fe al in surface sediments at outer shelf stations ca 1 2 to 2 wt wt 1 than at coastal stations ca 0 5 to 0 9 wt wt 1 however below the sediment surface layer fe al ratios are similar at all stations indicating limited burial of the laterally transported fe our results highlight the critical role of organic matter input associated biological activity and riverine fe input as drivers of fe shuttling on continental shelves we also show that in shelf areas where sediments receive low inputs of organic matter physical transport controls the ultimate fate of the shuttled fe

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

dust sources and deposition during the last glacial maximum and current climate a comparison of model results with paleodata from ice cores and marine sediments mineral dust aerosols in the atmosphere have the potential to affect the global climate by influencing the radiative balance of the atmosphere and the supply of micronutrients to the ocean ice and marine sediment cores indicate that dust deposition from the atmosphere was at some locations 2 20 times greater during glacial periods raising the possibility that mineral aerosols might have contributed to climate change on glacial interglacial time scales to address this question we have used linked terrestrial biosphere dust source and atmospheric transport models to simulate the dust cycle in the atmosphere for current and last glacial maximum lgm climates we obtain a 2 5 fold higher dust loading in the entire atmosphere and a twenty fold higher loading in high latitudes in lgm relative to present comparisons to a compilation of atmospheric dust deposition flux estimates for lgm and present in marine sediment and ice cores show that the simulated flux ratios are broadly in agreement with observations differences suggest where further improvements in the simple dust model could be made the simulated increase in high latitude dustiness depends on the expansion of unvegetated areas especially in the high latitudes and in central asia caused by a combination of increased aridity and low atmospheric co2 the existence of these dust source areas at the lgm is supported by pollen data and loess distribution in the northern continents these results point to a role for vegetation feedbacks including climate effects and physiological effects of low co2 in modulating the atmospheric distribution of dust

dust deposition in the eastern indian ocean the ocean perspective from antarctica to the bay of bengal atmospheric deposition is an important but still poorly constrained source of trace micronutrients to the open ocean because of the dearth of in situ measurements of total deposition i e wet dry deposition in remote regions in this work we discuss the upper ocean distribution of dissolved fe and al in the eastern indian ocean along a 95 e meridional transect spanning the antarctic margin to the bay of bengal we use the mixed layer concentration of dissolved al in conjunction with empirical data in a simple steady state model to produce 75 estimates of total dust deposition that we compare with historical observations and atmospheric model estimates except in the northern bay of bengal where the ganges brahmaputra river plume contributes to the inventory of dissolved al the surface distribution of dissolved al along 95 e is remarkably consistent with the large scale gradients in mineral dust deposition and multiple source regions impacting the eastern indian ocean the lowest total dust deposition fluxes are calculated for the southern ocean 66 60 mg m 2 yr 1 and the highest for the northern end of the south indian subtropical gyre up to 940 mg m 2 yr 1 at 18 s and in the southern bay of bengal 2500 570 mg m 2 yr 1 our total deposition fluxes which have an uncertainty on the order of a factor of 3 5 are comparable with the composite atmospheric model data of mahowald et al 2005 except in the south indian subtropical gyre where models may underestimate total deposition using available measurements of the solubility of fe in aerosols we confirm that dust deposition is a minor source of dissolved fe to the southern ocean and show that aeolian deposition of dissolved fe in the southern bay of bengal may be comparable to that observed underneath the saharan dust plume in the atlantic ocean

distributions sources and transformations of dissolved and particulate iron on the ross sea continental shelf during summer we report water column dissolved iron dfe and particulate iron pfe concentrations from fifty stations sampled across the ross sea during austral summer january february of 2012 concentrations of dfe and pfe were measured in each of the major ross sea water masses including the ice shelf water and off shelf circumpolar deep water despite significant lateral variations in hydrography macronutrient depletion and primary productivity across several different regions on the continental shelf dfe concentrations were consistently low 0 1 nm in surface waters with only a handful of stations showing elevated concentrations 0 20 0 45 nm in areas of melting sea ice and near the franklin island platform across the study region pfe associated with suspended biogenic material approximately doubled the inventory of bioavailable iron in surface waters our data reveal that the majority of the summertime iron inventory in the ross sea resides in dense shelf waters with highest concentrations within 50 m of the seafloor higher dfe concentrations near the seafloor are accompanied by an increased contribution to pfe from authigenic and or scavenged iron particulate manganese is also influenced by sediment resuspension near the seafloor but unlike pfe is increasingly associated with authigenic material higher in the water column together these results suggest that following depletion of the dfe derived from wintertime convective mixing and sea ice melt recycling of pfe in the upper water column plays an important role in sustaining the summertime phytoplankton bloom in the ross sea polynya

iron in east antarctic snow implications for atmospheric iron deposition and algal production in antarctic waters to evaluate the deposition and solubility of aerosol iron in the antarctic seasonal sea ice zone ssiz iron was measured in snow samples collected from three areas in the ssiz prydz bay dumont d urville sea and ross sea and one continental area princess elizabeth land of east antarctica concentrations of total dissolvable iron that soluble at ph 2 ranged from 20 2950 pg g 1 with the lowest concentrations measured in snow from the dumont d urville sea using estimates of snow accumulation rates we calculate atmospheric iron deposition fluxes of 0 017 0 11 mg m 2 yr 1 0 30 2 0 mol m 2 yr 1 which are generally lower than previously published estimates measurements of iron in filtered meltwaters of snow samples from prydz bay and princess elizabeth land suggest that 10 90 of the total atmospheric iron is readily soluble assuming our results to be broadly representative of atmospheric deposition over seasonally ice covered high nutrient antarctic waters we use our mean estimates of atmospheric iron deposition 1 1 mol m 2 yr 1 and solubility 32 to calculate that atmospheric iron potentially supports annual phytoplankton production of 1 1 1012 mole c in the antarctic ssiz which is less than 5 of the estimated total annual primary production in this ocean region

dissolved aluminium in the southern ocean dissolved aluminium al occurs in a wide range of concentrations in the world oceans the concentrations of al in the southern ocean are among the lowest ever observed an all titanium ctd sampling system makes it possible to study complete deep ocean sections of al and other trace elements with the same high vertical resolution of 24 depths as normal for traditional ctd rosette sampling overall 470 new data points of al are reported for 22 full depth stations and 24 surface sampling positions along one transect this transect consisted of 18 stations on the zero meridian proper from 51 degrees 57 s until 69 degrees 24 s and 4 stations somewhat to the northeast towards cape town from 42 degrees 20 s 09 degrees e to 50 degrees 17 s 01 degrees 27 e the actual concentrations of al in the southern ocean were lower than previously reported the concentration of al in the upper 25 m was relatively elevated with an average concentration of 0 71 nm n 22 s d 0 43 nm most likely due to atmospheric input by a suggested combination of direct atmospheric wet and dry input and indirect atmospheric input via melting sea ice below the surface waters there was a distinct al minimum with an average concentration of 0 33 nm n 22 s d 0 13 nm at an average depth of 120 m in the deep southern most weddell basin the concentration of al increased with depth to similar to 0 8 nm at 4000 m and a higher concentration of similar to 1 5 nm in the similar to 4500 5200 m deep weddell sea bottom water over the bouvet triple junction region where three deep ocean ridges meet the concentration of al increased to similar to 1 4 nm at about 2000 m depth over the ridge crest in the deep basin north of the bouvet region the concentration of al increased to higher deep values of 4 6 nm due to influence of north atlantic deep water in general the intermediate and deep distribution of al results from the mixing of water masses with different origins the formation of deep water and additional input from sedimentary sources at sea floor elevations no significant correlation between al and silicate si was observed this is in contrast to some other ocean regions in the southern ocean the supply of al is extremely low and any signal from al uptake and dissolution with biogenic silica is undetectable against the high dissolved si and low dissolved al concentrations here the al si relation in the deep ocean is uncoupled this is due to the scavenging and subsequent loss of the water column of al whereas the concentration of si increases in the deep ocean due to its input from deep dissolution of biogenic diatom frustules settling from the surface layer c 2011 elsevier ltd all rights reserved

cadmium isotope variations in the southern ocean abstract cadmium concentrations and isotope compositions were determined for 47 seawater samples from the high nutrient low chlorophyll hnlc zone of the atlantic sector of the southern ocean the samples include 13 surface waters from a transect of the weddell gyre and 3 depth profiles from the weddell sea and drake passage the southern ocean mixed layer samples from this study and abouchami et al 2011 define a clear but broad hnlc trend in a plot of e cd 114 110 versus cd which is primarily a consequence of isotopic fractionation associated with biological uptake e cd 114 110 is the deviation of the 114cd 110cd ratio of a sample from nist srm 3108 cd in parts per 10 000 the trend is especially apparent in comparison to the large range of values shown by a global set of seawater cd data for shallow depths the southern ocean samples are also distinguished by their relatively high cd concentrations typically 0 2 to 0 6 nmol kg and moderately fractionated e cd 114 110 generally between 4 and 8 that reflect the limited biological productivity of this region detailed assessment reveals fine structure within the hnlc trend which may record differences in the biological fractionation factor different scenarios of closed and open system isotope fractionation and or distinct source water compositions southern ocean seawater from depths 1000 m has an average e cd 114 110 of 2 5 0 2 2se n 16 and together with previous results this establishes a relatively constant e cd 114 110 value of 3 0 0 3 2se n 27 for global deep waters significant isotopic variability was observed at intermediate depths in the southern ocean seawater from 200 m to 400 m in weddell sea has high cd concentrations and e cd 114 110 as low as 1 presumably due to remineralization of cd from biomass that records incomplete nutrient utilization antarctic intermediate water which was sampled at 150 to 750 m depth in the drake passage features a distinct cd isotope signature of e cd 114 110 4 which reflects biological isotope fractionation at the surface and subsequent mixing into the ocean interior taken together our results demonstrate that coupled cd isotope and concentration data provide valuable insights into the distribution and biological cycling of cd in the water column the highly systematic nature of cd isotope signatures may furthermore prove to be of utility for future research in marine geochemistry and paleoceanography

effect of a jurassic oceanic anoxic event on belemnite ecology and evolution the toarcian oceanic anoxic event t oae 183 million y ago is possibly the most extreme episode of widespread ocean oxygen deficiency in the phanerozoic coinciding with rapid atmospheric pco2 increase and significant loss of biodiversity in marine faunas the event is a unique past tipping point in the earth system where rapid and massive release of isotopically light carbon led to a major perturbation in the global carbon cycle as recorded in organic and inorganic c isotope records modern marine ecosystems are projected to experience major loss in biodiversity in response to enhanced ocean anoxia driven by anthropogenic release of greenhouse gases potential consequences of this anthropogenic forcing can be approximated by studying analog environmental perturbations in the past such as the t oae here we present to our knowledge the first organic carbon isotope record derived from the organic matrix in the calcite rostra of early toarcian belemnites we combine both organic and calcite carbon isotope analyses of individual specimens of these marine predators to obtain a refined reconstruction of the early toarcian global exogenic carbon cycle perturbation and belemnite paleoecology the organic carbon isotope data combined with measurements of oxygen isotope values from the same specimens allow for a more robust interpretation of the interplay between the global carbon cycle perturbation environmental change and biotic response during the t oae we infer that belemnites adapted to environmental change by shifting their habitat from cold bottom waters to warm surface waters in response to expanded seafloor anoxia

fluxes of dissolved aluminum and manganese to the weddell sea and indications for manganese co limitation the trace metals aluminum al and manganese mn were studied in the weddell sea in march 2008 concentrations of dissolved al al were slightly elevated 0 23 0 35 nmol l 1 in the surface layer compared to the subsurface minimum 0 07 0 21 nmol l 1 observed in the winter water atmospheric deposition is the main source of al to the central weddell sea 22 mu mol m 2 yr 1 and the residence time of dissolved al in the upper mixed layer is similar to 0 8 yr the flux from the shelf and slope regions equals about 50 of the atmospheric input of al to the western weddell sea the highest al in the weddell sea bottom water wsbw is related to the formation of deep water and the associated downward flux is in the range of 3 10 mu mol al m 2 yr 1 the concentrations of dissolved mn mn were depleted in the surface layer likely as a result of biological uptake as indicated by the correlation among mn major nutrients and fluorescence the significant negative relation between the delta mn delta p ratio and the ambient concentration of dissolved iron indicates iron mn co limitation the flux of mn from the continental margin is about 2 2 times greater than atmospheric input 1 1 mu mol m 2 yr 1 the flux of both al and mn from the continental margin indicates melting of continental ice icebergs or direct continental runoff the slightly elevated mn in the wsbw is due to a relatively small flux of 1 mu mol mn m 2 yr 1 associated with wsbw formation

biogeochemical cycling of zinc and its isotopes in the southern ocean abstract we report zn concentration and isotope data for seawater samples from the atlantic sector of the southern ocean collected during the ipy geotraces ant xxiv iii cruise along the greenwich zero meridian data are reported for the full depth range of the water column at three stations as well as a transect of surface samples using a new analytical approach that is presented in detail here zn concentrations increase with depth though due to proximity to upwelling sites surface concentrations are not as low as in some parts of the ocean such as further northward into the sub antarctic zone for two depth profiles south of the polar front zone the physical stratification of the upper water column is reflected in sudden near surface changes in zn concentration with depth in contrast beneath 100 300 m zn concentrations barely change with depth zn isotopic data beneath 1000 m for the southern ocean data presented here as well as published data from the north atlantic and north pacific are strikingly homogeneous with an average 66zn 0 53 0 14 2sd 2se 0 03 n 21 the surface southern ocean is more variable with 66zn ranging from 0 07 to 0 80 between the two is a thin horizon at 40 80 m which in the southern ocean as well as the north atlantic and north pacific is characterised by distinctly light isotopic signatures with 66zn about 0 3 lower than surface waters strong correlations between si and zn concentrations seen here and elsewhere coupled to the lack of any systematic relationship between si and zn isotopes in the southern ocean suggest that the removal of zn associated with diatom opal involves little or no isotopic fractionation regeneration of this zn also explains the homogeneous zn isotopic composition of the global deep ocean so far sampled however the low zn content of opal requires that deep ocean zn does not directly come from the opal phase itself but rather from associated organic material external to the diatom frustule during growth experimental data are consistent with little or no fractionation during incorporation of zn into this material on the other hand the light zinc at 40 80 m is most consistent with the regeneration of an intra cellular pool that both culturing experiments and field data suggest will be isotopically light the data thus imply two processes by which zn is taken up in the surface ocean that these pools have very different regeneration lengthscales and that physical mixing of the oceans cannot eradicate their isotopic signatures finally the deep 66zn ocean value is significantly higher than the current best estimate of the input to the oceans the most obvious candidate for the required light sink is the survival of some of the cellular zn to be buried in sediment

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

dissolved iron and iron ii distributions beneath the pack ice in the east antarctic 120 e during the winter spring transition distributions of dissolved iron dfe and its reduced form fe ii to a depth of 1000 m were investigated under the seasonal pack ice off east antarctica during the sea ice physics and ecosystem experiment sipex 2 sea ice voyage in september october 2012 concentrations of dfe were elevated up to five fold relative to southern ocean background concentrations and were spatially variable the mean dfe concentration was 0 44 0 4 nm with a range from 0 09 to 3 05 nm profiles of dfe were more variable within and among stations than were macronutrients suggesting that coupling between these biologically essential elements was weak at the time of the study brine rejection and drainage from sea ice are estimated to be the dominant contributors to elevated dfe concentrations in the mixed layer but mass budget considerations indicate that estimated dfe fluxes from brine input alone are insufficient to account for all observed dfe melting icebergs and shelf sediments are suspected to provide the additional dfe fe ii was mostly below the detection limit but elevated at depth near the continental shelf implying that benthic processes are a source of reduced fe in bottom waters the data indicate that dfe builds up under the seasonal sea ice cover during winter and that reduction of fe may be hampered in early spring by several factors such as lack of electron donors low biological productivity and inadequate light below the sea ice the accumulated dfe pool in the mixed layer is expected to contribute to the formation of the spring bloom as the ice retreats

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

salinity profiles of antarctic sea ice field data and model results in order to describe and compare sea ice salinity distributions which are of interest in the study of physical and biological ice characteristics as well as ice ocean interaction we have computed composite profiles and fitted third degree polynomials to salinity data of 129 cores from the weddell sea four characteristic profile shapes have been recognized and described through the polynomial coefficients c s i and type profiles the field data have been compared with ideal salinity profiles generated by a simulation scheme based on thermodynamic growth under climatological conditions representative of the weddell sea composite salinity profiles agree well with simulations irrespective of the growth mechanism i e frazil or congelation suggesting that ice properties which depend on salinity or porosity may evolve independent of ice growth conditions analysis of salinity and 18o data in conjunction with the simulations demonstrates that apart from meteorological conditions controlling growth velocity and temperature distribution within the ice flooding and upward brine expulsion are important in raising top salinities as frequently observed low top salinities are typical of ice that has undergone retexturing and differential desalination salinity decreases towards the bottom of a floe are a result of high oceanic heat fluxes and snow cover effects as a consequence of these processes the bulk salinity of weddell sea ice cannot be described by a simple linear age thickness relationship as characteristic of arctic first year ice

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

the distribution and speciation of iron along 6 e in the southern ocean abstract the distribution and speciation of iron was determined along a transect in the eastern atlantic sector 6 e of the southern ocean during a collaborative scandinavian south african antarctic cruise conducted in late austral summer december 1997 january 1998 elevated concentrations of dissolved iron 0 4 nm were found at 60 s in the vicinity of the spring ice edge sie in tandem with a phytoplankton bloom chiefly dominated by phaeocystis sp this bloom had developed rapidly after the loss of the seasonal sea ice cover the iron that fuelled this bloom was mostly likely derived from sea ice melt in the winter ice edge wie around 55 s dissolved iron concentrations were low 0 2 nm and corresponded to lower biological productivity biomass in the antarctic polar front at approximately 50 s a vertical profile of dissolved iron showed low concentrations 0 2 nm however a surface survey showed higher concentrations 1 3 nm and considerable patchiness in this dynamic frontal region the chemical speciation of iron was dominated by organic complexation throughout the study region organic iron complexing ligands l ranged from 0 9 to 3 0 nm fe equivalents with complex stability log k fe l 21 4 23 5 estimated concentrations of inorganic iron fe ranged from 0 03 to 0 79 pm with the highest values found in the phaeocystis bloom in the sie a vertical profile of iron complexing ligands in the wie showed a maximum consistent with a biological source for ligand production and near surface minimum possibly consistent with loss via photodecomposition this work further confirms the role iron that has in the southern ocean in limiting primary productivity

the distribution of fe in the antarctic circumpolar current abstract the large scale distributions of dissolved and total fe in surface and deep waters of the antarctic circumpolar current exhibit strong relationships with hydrography and biological processes the mean dissolved fe concentrations are low in surface waters of the antarctic circumpolar current 0 31 0 49 nm with a minimum of 0 17 nm and higher averaging 1 11 9 nm in the polar frontal region enhanced dissolved surface water concentrations in the polar frontal region are attributed to input from the continental shelf and coincide with phytoplankton spring blooms of large diatoms the effects of sea ice melting and iceberg melting on the fe concentrations were relatively small dissolved deep water concentrations 400 m in the antarctic circumpolar current ranged from 0 4 to 2 8 nm circumpolar deep water has relatively high dissolved fe concentrations in the polar frontal region 0 4 2 8 nm compared with deep waters further to the south 0 6 1 1 nm similarly total dissolvable unfiltered fe concentrations in the upper circumpolar deep water tend to decrease southward from the polar frontal region in the lower circumpolar deep water total dissolvable fe concentrations are higher than in the upper circumpolar deep water due to the existing nepheloid layer and sources on the mid atlantic ridge dissolved and total dissolvable fe concentrations in the antarctic bottom water are higher than those of other water masses in the antarctic circumpolar current consistent with the nepheloid layer as well as diagenetic input from shelf sediments the high nutrient low chlorophyll areas of the antarctic ocean and northeast pacific ocean have different major fe input sources of similar magnitude in the antarctic circumpolar current upward transport of fe is the main input source whereas in the north pacific ocean aerosols are the dominant source

biological and physical controls on n2 o2 and co2 distributions in contrasting southern ocean surface waters we present measurements of pco2 o2 concentration biological oxygen saturation o2 ar and n2 saturation n2 in southern ocean surface waters during austral summer 2010 2011 phytoplankton biomass varied strongly across distinct hydrographic zones with high chlorophyll a chl a concentrations in regions of frontal mixing and sea ice melt pco2 and o2 ar exhibited large spatial gradients range 90 to 450 atm and 10 to 60 respectively and covaried strongly with chl a however the ratio of biological o2 accumulation to dissolved inorganic carbon dic drawdown was significantly lower than expected from photosynthetic stoichiometry reflecting the differential time scales of o2 and co2 air sea equilibration we measured significant oceanic co2 uptake with a mean air sea flux 10 mmol m 2 d 1 that significantly exceeded regional climatological values n2 was mostly supersaturated in surface waters mean n2 of 2 5 while physical processes resulted in both supersaturation and undersaturation of mixed layer o2 mean o2phys 2 1 box model calculations were able to reproduce much of the spatial variability of n2 and o2phys along the cruise track demonstrating significant effects of air sea exchange processes e g atmospheric pressure changes and bubble injection and mixed layer entrainment on surface gas disequilibria net community production ncp derived from entrainment corrected surface o2 ar data ranged from 40 to 300 mmol o2 m 2 d 1 and showed good coherence with independent ncp estimates based on seasonal mixed layer dic deficits elevated ncp was observed in hydrographic frontal zones and stratified regions of sea ice melt reflecting physical controls on surface water light fields and nutrient availability

chemical and isotopic architecture of the belemnite rostrum abstract macrofossil calcite is of great importance for quantitative reconstructions of palaeoenvironment and palaeoseasonality the calcite rostra of belemnites jurassic to cretaceous marine invertebrates are especially suited for such investigations because they are comparatively large and are structured by growth bands despite their use in chemostratigraphic and palaeoenvironmental studies much of the internal variability of geochemical signatures in rostra is poorly understood here multiple profiles through a belemnite rostrum of passaloteuthis bisulcata 183 myr old were analyzed for 13c and 18o values as well as mg ca sr ca and mn ca ratios geochemical signatures of the central 1 2 mm of the profiles indicate diagenetic cementation along the apical zone for which original porosity of up to 40 can be inferred the overall 13c and 18o values of the other well preserved parts of the belemnite fluctuate by 1 per mil but are nearly uniform within single growth bands in contrast sr ca and mg ca in the well preserved parts show growth rate and crystal shape related variability close to the central apical zone strongly bent calcite crystals are enriched in mg up to 70 and sr up to 50 through the remainder of the rostrum higher calcite precipitation rate can account for mg depletion of 15 and sr enrichment of 15 with respect to co genetic calcite precipitated at a slower rate no indication for temperature control on mg ca or sr ca is detected in the investigated specimen overall the new findings indicate that 13c and 18o analyses of belemnite rostra produce consistent results regardless of the sampling area within the rostrum and that growth rate effects on element incorporation are minor with respect to the control exerted by secular changes in seawater composition through time additionally the central part of the rostrum where strong calcite crystal bending is observed should be avoided for sampling when studying elemental composition of the calcite for palaeoenvironmental reconstructions

mollusc shell microstructures and crystallographic textures abstract x ray diffraction is used to characterise textures of the aragonite layers of shells from monoplacophoras bivalves cephalopods and gastropods textures vary in strength pattern and through the thickness of the shells the texture patterns exhibited in the studied taxa which can be quantitatively described by a limited number of parameters are compared with the microstructure types observed with scanning electron microscopy whereas for simple crystallite arrangements such as nacres there is a good correspondence between texture and microstructure this is often not the case in more complex microstructures such as in crossed lamellar layers morphologically similar microstructures may have different crystallographic textures and the same textures may be found in microstructures with different morphology these two kinds of measurements are shown to be complementary since they provide non redundant information for many taxa which suggests that they may be valuable phylogenetic indicators

radiaxial fibrous calcites a new look at an old problem abstract marine radiaxial fibrous and fascicular optic calcites are very common but poorly understood pore filling cements in paleozoic and mesozoic marine neritic and upper bathyal limestones the main diagnostic feature of these cements is their converging or diverging crystal c axis respectively the reasons for this anomalous texture are at present unknown another controversy is due to the relative lack of occurrences in cenozoic strata and their apparent absence in quaternary marine limestones despite these uncertainties marine fibrous cements are thought by some to be amongst the best proxies for the geochemistry of ancient oceans because of the absence of metabolic effects during their precipitation applying electron backscatter diffraction analysis we here for the first time document radiaxial fibrous and subordinate fascicular optic fibrous biominerals from well preserved jurassic and cretaceous low mg calcite belemnite rostra the finding of fibrous biogenic calcites in combination with the recent description of holocene and modern fibrous calcites in stalagmites represents in the view of the authors a significant advance in carbonate research here these findings are placed in their wider processes oriented context and the significance of biogenic and speloan fibrous calcite for their marine counterparts is assessed comparing the physico chemical and organomineralic properties of different precipitation sites indicates that the diagnostic variations in the crystal c axis orientation are not related to a specific nucleation environment or substratum in contrast preliminary crystallographic analyses suggest that kinetic factors during nucleation or subtle gradients in the statistical replacements of ca 2 by mg 2 in the crystal structure may lead to local strain resulting in converging or diverging crystal c axes

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

soluble iron inputs to the southern ocean through recent andesitic to rhyolitic volcanic ash eruptions from the patagonian andes patagonia due to its geographic position and the dominance of westerly winds is a key area that contributes to the supply of nutrients to the southern ocean both through mineral dust and through the periodic deposits of volcanic ash here we evaluate the characteristics of fe dissolved into soluble and colloidal species from volcanic ash for three recent southern andes volcanic eruptions having contrasting features and chemical compositions contact between cloud waters wet deposition and end members of andesitic hudson volcano and rhyolitic chaiten volcano materials was simulated results indicate higher fe release and faster liberation rates in the andesitic material fe release during particle seawater interaction dry deposition has higher rates in rhyolitic type ashes rhyolitic ashes under acidic conditions release fe in higher amounts and at a slower rate while in those samples containing mostly glass shards fe release was lower and faster the 2011 puyehue eruption was observed by a dust monitoring station puyehue type eruptions can contribute soluble fe to the ocean via dry or wet deposition nearly reaching the limit required for phytoplankton growth in contrast the input of fe after processing by an acidic eruption plume could raise the amount of dissolved fe in surface ocean waters several times above the threshold required to initiate phytoplankton blooms a single eruption like the puyehue one represents more than half of the yearly fe flux contributed by dust

isotopic analysis of coexisting late jurassic fish otoliths and molluscs implications for upper ocean water temperature estimates ophosphate of fi sh teeth are abstract the 18 o compositions of well preserved jurassic fi sh otoliths from wootton bassett uk provide upper ocean paleotemperatures that are comparable with those derived from the iso topic analysis of fitooth phosphates providing independent scrutiny of such paleotempera tures 18 o otolith temperatures in excess of 30 c also rival temperatures associated with the middle cretaceous thermal maximum the negative carbon isotopes of the otoliths may point to a freshwater infl uence and potentially migratory nature of the fi sh however given the large departures from equilibrium fractionation toward more negative carbon values reported from modern marine fi sh we consider our temperature interpretations to be robust and representa tive of the marine depositional environment depleted 13 c values we believe suggest that the otoliths examined in this study belong to fiwith high metabolic rates

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

free drifting icebergs as sources of iron to the weddell sea abstract in recent years glaciers on the antarctic peninsula have retreated resulting in loss of mass from ice shelves and increased supply of icebergs to the southern ocean free drifting icebergs may serve as an important source of fe to surrounding waters we measured concentrations of dissolved fe and fe content of suspended particulate material via flow injection chemiluminescence and icp ms respectively in the waters surrounding several icebergs during cruises to the scotia and weddell seas in june 2008 and march 2009 surface dissolved fe dfe concentrations varied from 0 58 to 2 92 nm and were elevated up to 60 at some stations 10 km from the icebergs indicating general fe enrichment in the lower salinity surface layer however surface dfe within 1 km of the iceberg was similar to that measured at depths below the draft of the iceberg a feature that may result from upwelling of circumpolar deep water caused by basal melting at the face of the iceberg iron concentrations in ice collected following calving events were highly variable 4 600 nm but were elevated above concentrations in seawater particulate fe normalized to particulate p in suspended particulate material was up to 20 fold higher within 0 6 km of two large tabular icebergs but no enrichment was observed at two smaller icebergs iron phosphorus ratios of suspended particulate material were also higher in deeper 40 m waters compared to shallow ca 15 m waters at the iceberg face iron release appeared to be episodic producing a spatially heterogeneous environment around icebergs this source term may increase in coming years as antarctic ice shelves degrade further potentially impacting the ecology and biogeochemistry of low fe waters of the southern ocean

dissolved fe in the upper waters of the pacific sector of the southern ocean the concentration of dissolved fe was determined in upper ocean waters along 170 degreesw between 53 and 72 degreess during four cruises between october 1997 and march 1998 as part of the us jgofs southern ocean antarctic polar frontal zone cruises fe concentrations were extremely variable in both space and time as a result of advection of meso scale eddys through the region observed values ranged from a maximum of 0 34 nm at 64 degreess in november next to the retreating ice edge to 0 075 nm in march at 71 degreess in the northern ross sea gyre in general the highest average mixed layer fe concentrations and the largest seasonal changes were observed in the two frontal zones at similar to 60 degreess and similar to 64 degreess formation of deep mixed layers during winter and the entrainment of sub surface waters enriched in fe is the primary source of this element to surface waters in this region of the southern ocean additionally upwelling of circumpolar deep water in the circumpolar current along its northern boundary at the polar front and its southern boundary at the southern antarctic circumpolar current front is an important mechanism supplying fe to surface waters in these areas throughout the summer comparison of integrated fe concentrations and th derived poc export and n drawdown all suggest that the maximum changes in these properties are comparable to those that would be predicted by fe availability fe concentrations determined by shipboard flow injection analysis measures et al mar chem 50 1995 3 were significantly higher than those found in replicate samples determined by shored based flameless atomic absorption spectrophotometry after preconcentration by chelation solvent extraction johnson et al mar chem 57 1997 137 the concentration differences which appear to be restricted to the upper 200 300 m do not appear to arise from different sampling or handling processes but instead are believed to result from the different sensitivity of the methods to organic fractions of fe in seawater c 2001 elsevier science ltd all rights reserved

evaluating mg ca in belemnite calcite as a palaeo proxy the mg ca sr ca 18o and 13c compositions are given for well preserved specimens of ten belemnite species genera from three stratigraphic intervals the data help assess the use of these proxies for palaeo oceanography samples are from dorset uk pliensbachian 5 species cambridgeshire uk callovian 1 species and the vocontian basin se france valanginian 4 genera in none of these belemnite populations at species or genera level does mg ca correlate with 18o neither do values of 18o correlate with mg ca along a microsampled radial profile across a single specimen of cylindroteuthis puzosiana callovian the use of mg ca is therefore considered to be unreliable as a palaeo temperature indicator for these belemnite species and genera

dissolved iron in the vicinity of the crozet islands southern ocean the annual phytoplankton bloom occurring north of the crozet plateau provides a rare opportunity to examine the hypothesis that natural iron fertilization can alleviate high nutrient low chlorophyll hnlc conditions normally associated with the southern ocean therefore during crozet natural iron bloom and export experiment crozex a large multidisciplinary study performed between november 2004 and january 2005 measurements of total dissolved iron dfe0 2 m were made on seawater from around the islands and atmospheric iron deposition estimated from rain and aerosol samples dfe concentrations were determined by flow injection analysis with n n dimethyl p phenylenediamine dihydrochloride dpd catalytic spectrophotometric detection dfe concentrations varied between 0 086 and 2 48 nm with low values in surface waters enrichment of dissolved iron 1 nm at close proximity to the islands suggests that the plateau and the associated sediments are a source of iron waters farther north also appear to be affected by this input of coastal and shelf origin although dissolved iron concentrations decrease as a function of distance to the north of the plateau with a gradient of 0 07 nm km 1 at the time of sampling using lateral and vertical diffusion coefficients derived from ra isotope profiles and also estimates of atmospheric inputs it was then possible to estimate a dfe concentration of 0 55 nm to the north of the islands prior to the bloom event which is sufficient to initiate the bloom the lateral island source being the largest component a similar situation is observed for other sub antarctic islands such as kerguelen south georgia that supply dissolved iron to their surrounding waters thus enhancing chlorophyll concentrations

a study of sulphur enrichment in the humic fraction of marine sediments during early diagenesis abstract the evolution of the sulphur content of humic acids extracted from a near shore sediment core was investigated special attention was taken to avoid s contamination of the humic materials during extraction the s c ratios increased continuously with depth to values which strongly suggest s addition to the humic matrix during early diagenesis by reactions between organic matter and h2s or its oxidation products their light isotopic composition supports this view however subsequent isotopic exchange has obscured the mechanism initially involved since a large fraction of the enrichment occurred above the sulphidic zone redox boundaries such as the interface of anoxic microniches within more oxidized zones or the sulphidic suboxic boundary of the sediment column must have been important sites for s addition bioturbation by increasing the contact between sedimentary zones of a different redox regime will likely enhance such processes

the stabilisation and transportation of dissolved iron from high temperature hydrothermal vent systems iron fe binding phases in two hydrothermal plumes in the southern ocean were studied using a novel voltammetric technique this approach reverse titration competitive ligand exchange adsorptive cathodic stripping voltammetry showed that on average 30 21 of dissolved fe in the hydrothermal plumes was stabilised by chemically labile binding to ligands the conditional stability constant log k fel of the observed complexes was 20 61 0 54 mean 1 sd for the two vent sites intermediate between previous measurements of deep ocean ligands 21 4 23 kondo et al 2012 and dissolved weak estuarine ligands 20 gerringa et al 2007 our results indicate that approximately 7 5 of all hydrothermal fe was stabilised by complexation with ligands furthermore 47 26 of the dissolved fe in the plume existed in the colloidal size range 0 02 0 2 m our data suggests that a portion 7 5 of hydrothermal fe is sufficiently stabilised in the dissolved size fraction 0 2 m to make an important impact on deep ocean fe distributions lateral deep ocean currents transport this hydrothermal fe as lenses of enhanced fe concentrations away from mid ocean ridge spreading centres and back arc basins

estimates of atmospheric processed soluble iron from observations and a global mineral aerosol model biogeochemical implications 1 desert dust deposition to the ocean may be a significant source of biogeochemically important elements specifically iron the bioavailability of iron in the oceans requires it to be in a soluble form and because atmospheric iron in desert dust is typically insoluble understanding the atmospheric processes that convert insoluble iron to more soluble forms is essential understanding these relationships is especially important in remote ocean regions where iron may be the limiting nutrient observations of soluble iron from 2001 cruise based aerosol measurements over the atlantic and pacific oceans ranged from 0 to 45 mean of 4 9 in the fine mode 2 5 m in diameter and 0 to 87 mean of 2 10 in the coarse mode we test two simple hypotheses of soluble iron enhancement in the atmosphere using a global model of mineral aerosols the first method assumes that iron solubility increases as iron is exposed to solar radiation approximating photoreduction reactions that are important pathways for enhancement of soluble iron in the presence of acidic solutions the second process imitates cloud processing of iron by increasing the amount of soluble iron when the mineral aerosol comes into contact with a cloud both methods resulted in similar average magnitudes of percent soluble iron compared to observations but did not capture specific events or have sufficient variability perhaps because the model does not include aerosol interactions between species other than mineral dust or other processes that may be important

microbial mats as bioreactors populations processes and products microbial mats are dynamic and complex ecosystems exhibiting spatial and temporal heterogeneity the physical chemical environment is typified by steep gradients and distinct microenvironments these microenvironments support a great diversity of species with a wide range of metabolic processes these processes often result in coupled reactions and biogeochemical cycles and produce important end products such as trace gases and mineral precipitates the latter can impact the composition and character of the sediment imparting a biosignature these biosignatures can be preserved in the rock record and are useful in the interpretation of fossil record on earth and possibly as an indication of life on other planetary bodies the modern marine stromatolites of the exuma cays bahamas provide an ideal system for studying the populations processes and products in a microbial ecosystem using a multidisciplinary approach in order to acquire redox energy microbial populations need to carry out metabolic reactions at rates faster than the equivalent chemical abiotic reactions as such microbes can be viewed as bioreactors that preferably oxidize carbon to co2 to maximize the energy yield the study of the microbial role in carbonate sedimentation and lithification in these stromatolites provides a picture of microbial mats as bioreactors producing a biosignature

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

fluxes and distribution of dissolved iron in the eastern sub tropical north atlantic ocean aeolian dust transport from the saharan sahel desert regions is considered the dominant external input of iron fe to the surface waters of the eastern sub tropical north atlantic ocean to test this hypothesis we investigated the sources of dissolved fe dfe and quantified dfe fluxes to the surface ocean in this region in winter 2008 surface water dfe concentrations varied between 1 5 nm correlated positively with apparent oxygen utilization aou and showed the importance of organic matter remineralization as an dfe source as a consequence vertical diffusive mixing formed an important fe flux to the surface ocean in this region even surpassing that of a major dust event

high resolution al and fe data from the atlantic ocean clivar co2 repeat hydrography a16n transect extensive linkages between atmospheric dust and upper ocean geochemistry 1 trace element sampling and shipboard flow injection analysis during the june august 2003 climate variability and predictability clivar co2 repeat hydrography a16n transect has produced a high resolution section of dissolved fe and al in the upper 1000 m of the atlantic ocean between 62 n and 5 s using the surface water dissolved al and the model of aluminum for dust calculation in oceanic waters madcow model we have calculated the deposition of mineral dust to the surface ocean along this transect and compare that to dissolved fe concentrations the lowest mean mineral dust depositions of 0 2 g m 2 a 1 are found to the north of 51 n a region which also exhibits characteristics of biological fe limitation through its low dissolved surface water fe 0 1 nm and residual macronutrients e g nitrate 2 m to the south of this region mean dust deposition increases by an order of magnitude reaching 3 g m 2 a 1 at 10 n underneath the saharan dust outflow surface water fe values also increase along this section to 1 nm distinct minima in fe concentrations at the depth of the chlorophyll maximum in the vertical profiles between 18 and 4 n illuminate the role that active biological uptake plays in fe cycling an extensive subsurface zone of enhanced dissolved fe concentrations 1 5 nm underlying this region is a result of the biological vertical transport and remineralization of the surface water fe and is coincident with the intermediate nutrient maximum and oxygen minimum of this region elevated concentrations of dissolved al in subsurface waters seen between 30 and 20 n coincide with the domain of the subtropical mode waters stmw which result from the sinking of surface waters in late winter in regions imprinted by dust deposition the magnitude of the al enrichment observed in this water mass implies that the predominant source to the stmw is from the more dust impacted western atlantic with only limited contributions from the stmw formation region near madeira a deeper subsurface al enrichment 30 45 n is associated with the outflow from the mediterranean another heavily dust impacted basin these two regions of al enrichment show the widespread geochemical connection between atmospheric transport processes and the north atlantic and underscore its susceptibility to imprinting by atmospherically borne materials natural as well as anthropogenic

distribution of dissolved iron during the natural iron fertilization experiment keops kerguelen plateau southern ocean abstract the southern ocean is the largest high nutrient low chlorophyll hnlc region of the world ocean it is now well recognized that the low biological productivity in this region is mainly due to the limitation of phytoplankton growth by iron however in the core of the southern ocean a massive bloom occurs annually above the kerguelen plateau in the context of keops kerguelen plateau and ocean compared study we investigated the three dimensional distribution of dissolved iron dfe concentrations southeast of the island we show that in surface waters dfe was low and not significantly different above and outside the plateau 0 090 0 034 and 0 073 0 014 nm respectively by contrast below 150 m major differences in vertical profiles of dfe were observed the deep waters above the plateau were clearly enriched with dfe concentrations up to 0 6 nm near the seafloor the regeneration from sinking biogenic material and the input from the sediments are very likely the major processes delivering dfe to the deep water the deep iron rich reservoir existing above the plateau was responsible for the natural iron fertilization of the surface water by two different mechanisms i winter mixing provided 5 times more dfe to the surface waters above the plateau than outside and ii enhanced vertical gradients of dfe and elevated vertical diffusivity resulted in an 8 fold higher diapycnal diffusive flux the natural iron fertilization presented major differences from artificial iron fertilization experiments carried out in the southern ocean the amount of dfe required to stimulate the biological activity is much less and the mode of addition is clearly different the quantification of the excess of dfe supplied in the naturally fertilized area leads to the conclusion that the natural iron fertilization is 10 150 times more efficient to export carbon below 200 m than in artificial fertilization experiments the bloom above the kerguelen plateau was contingent to iron fertilization but it was also sustained by continuous input of major nutrients thus the natural fertilization described here mimics quite well glacial period scenarios where iron fertilization of the southern ocean might have occurred from below

winter and summer distributions of copper zinc and nickel along the international geotraces section gipy05 insights into deep winter mixing abstract first measurements of labile dissolved copper ldcu and dissolved zinc dzn and nickel dni in the atlantic sector of the southern ocean in winter are compared with summer data at reoccupied stations in order to better understand the winter reset state and supply of these trace metals to support productivity in summer vertical profiles of zinc behaved similarly to silicate si and increased from sub nanomolar surface concentrations to 8 nmol kg 1 in bottom waters copper profiles also resembled si and were typically 1 nmol kg 1 in surface waters and increased to 3 nmol kg 1 at depth first summer nickel data reported from this transect displayed comparatively higher surface concentrations of 4 6 nmol kg 1 increasing more rapidly to local intermediate depth maximums between 6 5 and 7 0 nmol kg 1 similar to phosphate po4 trace metal seasonality was most apparent in the mixed layer where the average of winter concentrations within the mixed layer exceeded summer values by approximately 0 2 nmol kg 1 for ldcu 1 2 nmol kg 1 for dzn and 0 3 nmol kg 1 for dni owing to low utilization under unfavourable growth conditions for phytoplankton in an effort to estimate the winter reserve two scenarios were considered scenario 1 accounted for in situ mixed layer depths mld where the winter reserve inventory was calculated by subtracting the summer depth integrated metal inventory surface to summer mld from the winter equivalent surface to winter mld scenario 2 assumed a constant mixed layer taken as the depth of the maximum winter mixed layer where summer depth integrated metal inventories surface to maximum winter mld were subtracted from the winter equivalents surface to maximum winter mld results for scenario 1 were predominantly dependent on the mixed layer depth which varied spatially and seasonally scenario 2 showed a southwards increase in the winter reserve inventory suggesting a greater role for entrainment at higher latitudes in this region this is however heavily dependent on other physical processes controlling vertical trace metal supply e g diapycnal diffusion ekman upwelling downwelling zinc r2 0 75 and copper r2 0 73 were strongly correlated with si throughout the study implicating diatoms as strong controllers of their biogeochemical cycling nickel was more strongly correlated with po4 in the upper water column r2 0 75 as compared to the whole water column r2 0 52 while in the deep ocean nickel appears to correlate with si although more deep ocean data is needed to confirm this trace metal to major nutrient ratios were higher in winter suggesting reduced micronutrient requirement relative to macronutrients under stressed but low productivity conditions 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

iron from melting glaciers fuels the phytoplankton blooms in amundsen sea southern ocean iron biogeochemistry dissolved iron dfe and total dissolvable fe tdfe were measured in january february 2009 in pine island bay as well as in the pine island and amundsen polynyas amundsen sea southern ocean iron fe has been shown to be a limiting nutrient for phytoplankton growth even in the productive continental shelves surrounding the antarctic continent however the polynyas of the amundsen sea harbor the highest concentrations of phytoplankton anywhere in antarctica here we present data showing the likely sources of fe that enable such a productive and long lasting phytoplankton bloom circumpolar deep water cdw flows over the bottom of the shelf into the pine island bay where dfe and tdfe were observed to increase from 0 2 to 0 4 nm dfe and from 0 3 4 0 to 7 14 nm tdfe respectively at the southern end of pine island bay the cdw upwelled under the pine island glacier bringing nutrients including fe to the surface and melting the base of the glacier concentrations of dfe in waters near the pine island glacier and the more westward lying crosson dotson and getz ice shelves varied between 0 40 and 1 31 nm depending on the relative magnitude of upwelling turbulent mixing and melting these values represent maximum concentrations since associated ligands which

234th in surface waters distribution of particle export flux across the antarctic circumpolar current and in the weddell sea during the geotraces expedition zero and drake abstract as part of the geotraces polarstern expedition antxxiv 3 zero and drake we have measured the vertical distribution of 234th on sections through the antarctic circumpolar current along the zero meridian and in drake passage and on an ew section through the weddell sea steady state export fluxes of 234th from the upper 100 m derived from the depletion of 234th with respect to its parent 238u ranged from 621 105 to 1773 90 dpm m 2 d 1 this 234th flux was converted into an export flux of organic carbon ranging from 3 1 to 13 2 mmol c m 2 d 1 2 1 9 0 mmol c m 2 d 1 using poc 234th ratio of bulk respectively 50 m suspended particles at the export depth 100 m non steady state fluxes assuming zero flux under ice cover were up to 23 higher in addition particulate and dissolved 234th were measured underway in high resolution in the surface water with a semi automated procedure particulate 234th in surface waters is inversely correlated with light transmission and pco2 and positively with fluorescence and optical backscatter and is interpreted as a proxy for algal biomass high resolution underway mapping of particulate and dissolved 234th in surface water shows clearly where trace elements are absorbed by plankton and where they are exported to depth quantitative determination of the export flux requires the full 234th profile since surface depletion and export flux become decoupled through changes in wind mixed layer depth and in contribution to export from subsurface layers in a zone of very low algal abundance 54 58 s at the zero meridian confirmed by satellite chl a data the lowest carbon export of the acc was observed allowing fe and mn to maintain their highest surface concentrations an ice edge bloom that had developed in december january in the zone 60 65 s as studied during the previous leg had caused a high export flux at 64 5 s when we visited the area 2 months later february march the ice edge bloom had then shifted south to 65 69 s evident from uptake of co2 and dissolved fe mn and 234th without causing export yet in this way the parallel analysis of 234th can help to explain the scavenging behavior of other trace elements

slow spreading submarine ridges in the south atlantic as a significant oceanic iron source low levels of the micronutrient iron limit primary production and nitrogen fixation in large areas of the global ocean measurements in the south atlantic suggest that slow spreading submarine ridges serve as a significant oceanic iron source in these waters

the transport of the weddell gyre across the prime meridian abstract current meter observations from instruments moored from 1996 to 2001 are used to determine the structure and the volume transport of the weddell gyre on the greenwich meridian the record length mean volume transport is 45 sv to the east within the northern and 56 sv to the west within the southern limb of the weddell gyre thus 11 sv must leave the gyre circulation west of the greenwich meridian and enter it east of it the deficit occurs with 8 sv mainly in the circumpolar deep water cdw warm deep water wdw layer surface waters and weddell sea deep water wsdw contribute 2 and 3 sv respectively in contrast to this 3 sv more of weddell sea bottom water wsbw flow in the northern limb to the east than in the southern limb to the west which suggests a wsbw formation rate of about 3 sv in the western weddell sea in the southern boundary of the antarctic circumpolar current acc a volume transport of 35 16 sv was found using geostrophic calculations adjusted with two measurements of the absolute velocity the large heat content of the northern limb points to an extensive heat exchange between the weddell sea and the world ocean west of the prime meridian hence the heat transport as well as the volume transport suggest that the water masses of the weddell gyre are not exclusively replaced in its eastern part but that there is a significant exchange of water masses to the west of the prime meridian

atmospheric transport of iron and its deposition in the ocean the atmospheric transport of continental weathering products is responsible for much of the mineral material and fe entering the open ocean and is probably the dominant source of nutrient fe in the photic zone in regions where other nutrients are present in high concentrations the flux of fe from the atmosphere may be a limiting factor in primary productivity due to the larger source regions for dust north of the equator 8 times more atmospheric fe is deposited in the northern hemisphere than in the southern hemisphere the mineral aerosol and fe transport and deposition are highly variable due to the episodic nature of dust generation and its transport and deposition processes between 10 and 50 of the total atmospheric fe entering the world ocean appears to dissolve i e it will pass through a 0 4 m pore size filter rapidly when the mineral matter enters the ocean much of the atmospheric fe is present as fe ii apparently produced as a result of photochemical reduction reactions taking place during atmospheric transport this readily soluble fe ii should be available immediately for use as a nutrient by phytoplankton atmospheric transport from the continents is estimated to supply 3 times as much dissolved fe to the oceans as that delivered via rivers

the natural iron fertilization experiment keops kerguelen ocean and plateau compared study an overview when the first scientific voyages went to the southern ocean high levels of living biomass were observed in the vicinity of islands hart 1942 was the first to mention that the abundant biomass might be due to the release of oligoelements like iron from the island this hypothesis however remained unverified for more than half a century because of the experimental difficulties in properly manipulating water with subnanomolar iron concentrations when john martin formulated the iron hypothesis martin 1990 and provided the first supporting evidence of it he also suggested using the chlorophyll plume observed westward of the galapagos island in the equatorial pacific as a natural iron fertilization experiment

modulation of the southern ocean cadmium isotope signature by ocean circulation and primary productivity article i nfo article history the high nutrient low chlorophyll hnlc southern ocean plays a key role in regulating the biological pump and the global carbon cycle here we examine the efficacy of stable cadmium cd isotope fractionation for detecting differences in biological productivity between regions our results show strong meridional cd isotope and concentration gradients modulated by the antarctic fronts with a clear biogeochemical divide located near 56 s the coincidence of the cd isotope divide with the southern boundary of the antarctic circumpolar current acc together with evidence for northward advection of the cd signal in the acc demonstrate that cd isotopes trace surface ocean circulation regimes the relationships between cd isotope ratios and concentrations display two negative correlations separating the acc and weddell gyre into two distinct cd isoscapes these arrays are consistent with rayleigh fractionation and imply a doubling of the isotope effect due to biological consumption of cd during water transport from the weddell gyre into the acc the increase in magnitude of cd isotope fractionation can be accounted for by differences in the phytoplankton biomass community composition and their physiological uptake mechanisms in the weddell gyre and acc thus linking cd isotope fractionation to primary production and the global carbon cycle 2011 elsevier b v all rights reserved

iron from melting glaciers fuels phytoplankton blooms in the amundsen sea southern ocean phytoplankton characteristics and productivity the phytoplankton community composition and productivity in waters of the amundsen sea and surrounding sea ice zone were characterized with respect to iron fe input from melting glaciers high fe input from glaciers such as the pine island glacier and the dotson and crosson ice shelves resulted in dense phytoplankton blooms in surface waters of pine island bay pine island polynya and amundsen polynya phytoplankton biomass distribution was the opposite of the distribution of dissolved fe dfe confirming the uptake of glacial dfe in surface waters by phytoplankton phytoplankton biomass in the polynyas ranged from 0 6 to 14 mg chl a l 1 with lower biomass at glacier sites where strong upwelling of modified circumpolar deep water from beneath glacier tongues was observed phytoplankton blooms in the polynyas were dominated by the haptophyte phaeocystis antarctica whereas the phytoplankton community in the sea ice zone was am ix ofp antarctica and diatoms resembling the species distribution in the ross sea water column productivity based on photosynthesis versus irradiance characteristics averaged 3 00 g c m

environmental versus biological controls on mg ca variability in globigerinoides ruber white from core top and plankton tow samples in the southwest pacific ocean 1 laser ablation inductively coupled plasma mass spectrometry was used to analyze the individual chambers from tests of foraminiferal fossil and plankton tow globigerinoides ruber from the southwest pacific ocean from latitudes 3 s to 42 s the variability of mg ca between chambers of an individual intraindividual and individuals of the same population interindividual is such that when converted to temperature the extent of intra individual and interindividual variability appears to exceed that attributable to either calcification or seasonal temperature variability the pooled mean chamber mg ca from each core top and plankton tow site demonstrates a significant p 0 05 positive correlation with temperature we derive chamber specific calibrations where mg cach f 2 0 798 exp0 070 t mg cach f 1 0 891 exp0 067 t and mg cach f 0 590 exp0 072 t we do not observe any bias between the two morphotypes gs ruber ruber and gs ruber pyramidalis the chamber specific calibrations potentially offset mg ca based temperature reconstructions if used on bulk whole test mg ca or applied to misidentified chambers nevertheless these calibrations can be used to reliably estimate sea surface temperature although there is a general overriding temperature control on mg ca we show that removal of the effect of temperature at each site reveals a lognormal mg ca distribution this suggests that mg ca variability at each site is also affected by biological mechanism s that may control the distribution of interindividual mg ca in addition other te ca data al ca and mn ca from laser ablation trace element depth profiles can be used to identify detrital or diagenetic phases that may bias the trace element ca signal

dissolved manganese in the atlantic sector of the southern ocean the first comprehensive dataset 492 samples of dissolved mn in the southern ocean shows extremely low values of 0 04 up to 0 64 nm in the surface waters and a subsurface maximum with an average concentration of 0 31 nm n 20 s d 0 08 nm the low mn in surface waters correlates well with the nutrients po4 and no3 and moderately well with si oh 4 and fluorescence furthermore elevated concentrations of mn in the surface layer coincide with elevated fe and light transmission and decreased export th 234 u 238 deficiency and fluorescence it appears that mn is a factor of importance in partly explaining the hnlc conditions in the southern ocean in conjunction with significant controls by the combination of fe limitation and light limitation no input of mn from the continental margins was observed this is ascribed to the protruding continental ice sheet that covers the shelf and shuts down the usual biological production microbial breakdown and sedimentary geochemical cycling the low concentrations of mn in the deep ocean basins 0 07 0 23 nm were quite uniform but some elevations were observed the highest deep concentrations of mn were observed at the bouvet triple junction region and coincided with high concentrations of fe and are deemed to be from hydrothermal input the deep basins on both sides of the ridge were affected by this input in the deep weddell basin the input of weddell sea bottom water appears to be the source of the slightly elevated concentrations of mn in this water layer c 2010 elsevier ltd all rights reserved

shell structure patterns and trends of oxygen and carbon stable isotopes in modern brachiopod shells this study investigates 13c and 18o variations in the shells of modern brachiopods representing all extant groups of calcite precipitating brachiopods collected live from 8 locations sem examinations determined the ultrastructural characteristics of each species prior to isotope analyses 13c and 18o analyses of shell carbonate were carried out with samples representing disparate morphological features and ultrastructural shell layers of both ventral and dorsal valves generally 18o values from the fibrous secondary or prismatic tertiary shell layers of the articulated terebratulida and rhynchonellida species were in oxygen isotopic equilibrium with ambient seawater isotopic temperatures extrapolated from these values are close to measured annual mean seawater temperatures 18o values were relatively unaffected by shell specialisation the only exception was antarctic species liothyrella uva which did not have a complete tertiary shell layer typical of this genus and had 18o values of the innermost layer strongly correlated with 13c and mostly not in oxygen isotopic equilibrium with ambient seawater with the exception of the rhynchonellid notosaria nigricans the outer primary layer material was depleted in 13c and 18o and highly variable inclusion of this material even as part of a whole shell sample could lead to misinterpretation of seawater temperature therefore only fossil secondary layer material should be used the anomalous articulated thecideidine brachiopod thecidellina barretti is composed of mainly primary shell material and was not in oxygen isotope equilibrium 18o values from the laminar secondary layer material of the inarticulated craniida are highly variable therefore these species are not recommended for use as palaeoenvironmental proxies this study suggests caution when employing fossil brachiopod shells with similar ultrastructures to modern craniid and thecideidine brachiopods the carbon isotope composition is highly variable in all of the brachiopods studied analysis of samples from specialised regions of the secondary shell layer show a pattern of depletion in 13c relative to non specialised secondary material the carbon isotope variability is independent of 18o and is repeated in most of the articulated species regardless of geographical location this is possibly a vital effect produced by metabolic prioritisation

cenomanian palaeotemperatures derived from the oxygen isotopic composition of brachiopods and belemnites evaluation of cretaceous palaeotemperature proxies sixty low magnesium calcite samples from cenomanian articulate brachiopods belemnites and oysters from the epicontinental shelf sea of europe were geochemically and microscopically studied in order to evaluate their preservation and potential as carriers of palaeoenvironmental information the sampled localities in northern spain germany and southern england cover the transition between subtropical 25 30 n and temperate 33 38 n climates mean cenomanian salinity adjusted palaeotemperatures of diagenetically unaltered terebratulid and rhynchonellid brachiopods are 25 5 1 3 c in spain and 19 4 1 9 c in southern england the resulting low to mid latitude meridional temperature gradient of 0 7 c per degree latitude is similar to the gradient today and suggests modern heat transport values for cenomanian low latitudes oxygen isotopic composition of unaltered specimens of the upper cenomanian belemnite praeactinocamax plenus mean 0 2 is enriched in 18o by 1 in comparison to brachiopod shells correspondingly upper cenomanian palaeotemperatures derived from belemnite calcite 13 0 1 3 c underestimate modelled mid latitude sea surface temperatures by 6 c since p plenus occurs as boreal pulse fauna during a short interval in the late cenomanian its heavy oxygen isotopic composition can be attributed either to migration from a cooler and or deeper water mass or to unknown vital effects

shallow marine ironstones formed by microaerophilic iron oxidizing bacteria in terminal paleoproterozoic abstract the microbial origin of precambrian iron formations is debated due to the lack of direct fossil evidence in order to reveal the genesis of ironstones under low oxygen levels integrative studies of sedimentology petrography mineralogy and geochemistry were conducted on the intertidal to shallow subtidal ooidal and stromatolitic ironstones from the terminal paleoproterozoic chuanlinggou formation ca 1 65 1 64 ga of north china using microscopy sem eds icp oes icp ms and mc icp ms techniques mineralogical study shows that the fe rich mineral is predominantly hematite that resulted from dehydration of amorphous fe oxyhydroxide during diagenesis petrographic observation indicates that the iron was oxidized and precipitated from seawater rather than sourced from terrestrial detritus basinward increases of the ironstone abundance eu anomalies from 1 39 to 1 56 and 56fe values of the ironstones from 0 5 to 1 0 suggest that the iron was mainly sourced from seafloor hydrothermal fluids and partially oxidized and precipitated in shallow subtidal to intertidal environments the common existence of fe oxide coated sheaths spiral stalks residual extracellular polymer substances eps and other biogenic fabrics indicates that microaerophilic iron oxidizing bacteria feob may have played an important role in precipitating the chuanlinggou ironstones the extremely low oxygen concentrations implied by the proliferation of microaerophilic feob in the shallow waters the weak positive ce anomalies 0 94 1 12 and low mn concentrations in the ironstones are broadly consistent with the previous result of a cr isotope study thus the establishment of a microaerophilic feob genetic model for the widespread chuanlinggou ironstones in north china provides new insight into the origin of precambrian iron formations and the redox evolution of ocean atmosphere systems during the boring billion

iron and manganese diagenesis in deep sea volcanogenic sediments and the origins of pore water colloids abstract volcanogenic sediments are typically rich in fe and mn bearing minerals that undergo substantial alteration during early marine diagenesis however their impact on the global biogeochemical cycling of fe and mn has not been widely addressed this study compares the near surface 0 20 cm below sea floor cmbsf aqueous no 3 and solid phase reactive fe distributions between two volcanogenic sediment settings 1 a deep sea tephra rich deposit neighbouring the volcanically active island of montserrat and 2 mixed biosiliceous volcanogenic sediments from abyssal depths near the volcanically inactive crozet islands archipelago shallow penetration of o2 aq into montserrat sediments was observed 5 cmbsf and largely controlled by the oxidation of organic matter dissolved fe and mn distributions in montserrat pore waters were lowest in the surface oxic layer 0 3 m fe 32 m mn with maxima 20 m fe 200 m mn in the upper 1 15 cmbsf unlike montserrat fe and mn in crozet pore waters were ubiquitously partitioned between 0 2 m and 0 02 m filtrations indicating that the pore water distributions of fe and mn in the traditionally termed dissolved size fraction are dominated by colloids with respective mean abundances of 80 and 61 plausible mechanisms for the origin and composition of pore water colloids are discussed and include prolonged exposure of crozet surface sediments to early diagenesis compared to montserrat favouring nano particulate goethite formation and the elevated dissolved si concentrations which are shown to encourage fine grained smectite formation in addition organic matter may stabilise authigenic fe and mn in the crozet pore waters we conclude that volcanogenic sediment diagenesis leads to a flux of colloidal material to the overlying bottom water which may impact significantly on deep ocean biogeochemistry diffusive flux estimates from montserrat suggest that diagenesis within tephra deposits of active island volcanism may also be an important source of dissolved mn to the bottom waters and therefore a source for the widespread hydrogenous mnox deposits found in the caribbean region

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

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

thickness distribution of antarctic sea ice 1 ship based observations are used to describe regional and seasonal changes in the thickness distribution and characteristics of sea ice and snow cover thickness around antarctica the data set comprises 23 373 observations collected over more than 2 decades of activity and has been compiled as part of the scientific committee on antarctic research scar antarctic sea ice processes and climate aspect program the results show the seasonal progression of the ice thickness distribution for six regions around the continent together with statistics on the mean thickness surface ridging snow cover and local variability for each region and season a simple ridge model is used to calculate the total ice thickness from the observations of level ice and surface topography to provide a best estimate of the total ice mass including the ridged component the long term mean and standard deviation of total sea ice thickness including ridges is reported as 0 87 0 91 m which is 40 greater than the mean level ice thickness of 0 62 m analysis of the structure function along north south and east west transects revealed lag distances over which sea ice thickness decorrelates to be of the order of 100 300 km which we use as a basis for presenting near continuous maps of sea ice and snow cover thickness plotted on a 2 5 5 0 grid

physical anatomy of fronts and surface waters in the acc near the 6 w meridian during austral spring 1992 small scale features of the antarctic circumpolar current acc along a meridional section at 6 w between the polar front and the acc weddell gyre boundary front are discussed using data collected during the austral spring cruise ant x 6 of r v polarstern organized within the framework of the european igbp jgofs southern ocean the section covered three distinct fronts namely the polar front the southern polar front also southern acc front and the acc weddell gyre boundary front physical measurements during repeated transects over a period of 6 weeks in october november revealed a large variability in the polar frontal region indicating meandering and eddy shedding the positions of the southern polar front and the acc weddell gyre boundary front were observed to be far more stable than that of the polar front a possible reconstruction of the meandering flow field near the polar front based upon the physical observations is presented details in the flow field coincide with the spatial distribution of a number of biological parameters such as phytoplankton biomass and species and photosynthetic pigments although a causal relationship between them is likely biomass enhancement cannot be understood simply in terms of macronutrients from deeper layers entering the euphotic zone as substantiated for other oceanic frontal regions because macronutrients do not limit phytoplankton blooms this process however can be important for the micronutrient iron evidence is presented that the antarctic zone of the acc can be subdivided into a number of spheres of influence related to the fronts interleaving of water is apparent between positions within such a region but not between the regions

biogeochemical cycling of dissolved zinc along the geotraces south atlantic transect ga10 at 40 s the biogeochemical cycle of zinc zn in the south atlantic at 40 s was investigated as part of the uk geotraces program to date there is little understanding of the supply of zn an essential requirement for phytoplankton growth to this highly productive region vertical zn profiles displayed nutrient like distributions with distinct gradients associated with the water masses present surface zn concentrations are among the lowest reported for the world s oceans 2 0 97 n 460 our results suggest that the use of a global zn si relationship would lead to an underestimation of dissolved zn in deeper waters of the south atlantic by utilizing si and a new tracer zn our data indicate that the preferential removal of zn in the southern ocean prevented a direct return path for dissolved zn to the surface waters of the south atlantic at 40 s and potentially the thermocline waters of the south atlantic subtropical gyre the importance of zn for phytoplankton growth was evaluated using the zn soluble reactive phosphorus srp relationship we hypothesize that the low zn concentrations in the south atlantic may select for phytoplankton cells with a lower zn requirement in addition a much deeper kink at 500m in the zn srp ratio was observed compared to other oceanic regions key points dissolved zinc biogeochemical cycle investigated in the south atlantic ocean 2014 american geophysical union all rights reserved

natural iron fertilization of the atlantic sector of the southern ocean by continental shelf sources of the antarctic peninsula in large parts of the southern ocean primary production is limited due to shortage of iron fe we measured vertical fe profiles in the western weddell sea weddell scotia confluence and antarctic circumpolar current acc showing that fe is derived from benthic fe diffusion and sediment resuspension in areas characterized by high turbulence due to rugged bottom topography our data together with literature data reveal an exponential decrease of dissolved fe dfe concentrations with increasing distance from the continental shelves of the antarctic peninsula and the western weddell sea this decrease can be observed 3500 km eastward of the antarctic peninsula area downstream the acc we estimated dfe summer fluxes into the upper mixed layer of the atlantic sector of the southern ocean and found that horizontal advection dominates dfe supply representing 54 15 of the total flux with significant vertical advection second most important at 29 13 horizontal and vertical diffusion are weak with 1 2 and 1 1 respectively the atmospheric contribution is insignificant close to the antarctic continent but increases to 15 10 in the remotest waters 1500 km offshore of the acc translating southern ocean carbon fixation by primary producers into biogenic fe fixation shows a twofold excess of new dfe input close to the antarctic continent and a one third shortage in the open ocean fe recycling with an estimated fe ratio of 0 59 is the likely pathway to balance new dfe supply and fe fixation

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

the distribution of dissolved zinc in the atlantic sector of the southern ocean the distribution of dissolved zinc zn was investigated in the atlantic sector of the southern ocean in the austral autumn of 2008 as part of the ipy geotraces expedition zero drake research focused on transects across the major frontal systems along the zero meridian and across the drake passage there was a strong gradient in surface zinc concentrations observed across the antarctic polar front along both transects and high zinc levels were found in surface waters throughout the southern ocean vertical profiles for dissolved zinc showed the presence of local minima and maxima in the upper 200 m consistent with significant uptake by phytoplankton and release by zooplankton grazing respectively highest deep water zinc concentrations were found in the centre of the weddell gyre associated with central intermediate water ciw a water mass which is depleted in o2 elevated in co2 and is regionally a cfc minimum our data suggests that the remineralization of sinking particles is a key control on the distribution of zn in the southern ocean disappearance ratios of zinc to phosphate zn p in the upper water column increased southwards along both transects and based on laboratory studies they suggest slower growth rates of phytoplankton due to iron or light limitation zinc and silicate were strongly correlated throughout the study region but the disappearance ratio zn si was relatively uniform overall except for the region close to the ice edge on the zero meridian

soil abrasion and eolian dust production implications for iron partitioning and solubility 1 eolian dust is a source of iron for phytoplankton in many ocean areas and there are complex pathways of atmospheric processing from soil to ocean overlooked parts of the pathways are the impact of large 10 m grains including a role as proxies for the behavior of smaller grains and the effect of multiple cycles of uplift and abrasion in the dust source region partitioning readily released acid leachable and refractory and dissolution rates of iron were determined for an artificial dust produced by abrading an australian soil untreated soil abraded soil after production of the artificial dust and a natural australian eolian dust sample taken during a dust storm readily released iron is not created during abrasion and therefore the amount of readily released iron in a dust or dust derived soil depends on processing events since the dust or soil last experienced an abrasion event our study develops a method for the partitioning of iron within airborne dusts and appears to be the first to consider the effect of multiple uplift events on iron partitioning

key role of organic complexation of iron in sustaining phytoplankton blooms in the pine island and amundsen polynyas southern ocean primary productivity in the amundsen sea southern ocean is among the highest in antarctica the summer phytoplankton bloom in 2009 lasted for 470 days in both the pine island and amundsen polynyas such productive blooms require a large supply of nutrients including the trace metal iron fe the organic complexation of dissolved fe was investigated in the amundsen sea during the spring of 2009 to better understand the potential role of ligands in enhancing the local stock of dissolved fe the main sources of fe and ligands to the amundsen sea are thought to be melting sea ice and the circumpolar deep water cdw which is modified mcdw on the continental shelf and upwells beneath the coastal glaciers and ice shelves upwelling of relatively warm mcdw is also responsible for the rapid melting of the pine island glacier pig and surrounding ice shelves resulting in additional release of fe into surface waters at upwelling stations near ice shelves organic ligands were nearly saturated with fe thus enhancing the stock of fe and its availability to the phytoplankton community however ligands had little capacity to buffer additional fe input from glacial melt in these coastal upwelling regions much of the glacial fe supply is lost due to vertical export of fe via scavenging and precipitation conversely within the phytoplankton bloom in the nearby coastal polynyas the uptake of fe combined with the production of organic matter enhanced the abundance of relatively unsaturated organic ligands capable of stabilizing additional fe supplied from glacial melt these unsaturated dissolved organic ligands combined with the continuous input of fe dissolved and particulate from glacial melt appear to favor the solubilization of fe thus increasing the stock of bioavailable fe and fueling the phytoplankton bloom

the relationship between cadmium and phosphate in the atlantic ocean unravelled abstract cadmium cd is not generally considered a nutrient element but behaves like a nutrient in the oceans and might play an important role in ocean biology after all the relationship between cd and the nutrient phosphate po4 has been studied for over 40 yrs but the debate on the driving mechanism and reason behind the kink a change in the steepness of the slope is ongoing using new data of high accuracy and spatial resolution covering the west atlantic ocean from north to south in combination with a robust extended optimum multiparameter eomp water mass model we show that mixing between different water masses is the dominant factor explaining the observed correlation and its kink regeneration of cd via remineralisation explains the smaller scale variability notably in the surface ocean observations imply the availability of cd in surface waters determines the cd uptake and thus the cd po4 remineralisation ratio this ratio is variable between different ocean regions notably between the northern and southern high latitude oceans due to their role in deep water formation both the northern and southern high latitude oceans are a driving factor in the atlantic and global cd and po4 relation outside the atlantic ocean the classical kink is not expected but the relationship is by no means linear most likely this is due to the interaction between low latitude surface waters and subsurface waters from high latitude origin but more data are required to assess this in detail

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