fluxes of particulate iron from the upper ocean around the crozet islands a naturally iron fertilized environment in the southern ocean despite a large macronutrient reservoir the southern ocean has low levels of chlorophyll primarily due to low iron availability exceptions to this situation are island systems where natural terrestrial iron inputs allow the development of large blooms particulate organic carbon poc and particulate labile and refractory iron analyses were performed on large 53 m particles collected at the base of the mixed layer within such a system the crozet islands and in adjacent high nutrient low chlorophyll hnlc waters biogenic iron was obtained by removal of estimated lithogenic fe from the total fe present we combine these data with 234th measurements to determine downward particulate fe fluxes fluxes of fe ranged from 4 to 301 nmol m 2 d 1 labile not detectable to 50 mol m 2 d 1 biogenic and from 3 to 145 mol m 2 d 1 total and on average were approximately four times larger below the highly productive naturally iron fertilized region than below the adjacent hnlc area downward labile iron fluxes are close to the sum of dissolved terrestrial atmospheric and upwelled iron calculated from the planquette et al 2007 model refractory iron fluxes are 2 orders of magnitude larger and these can only have come from particles advected from the plateau itself the biogenic fe is a substantial fraction 0 76 mean 23 of the total particulate fe to the north of the islands the origin of this fe pool must be dominantly biological conversion from the lithogenic fraction as other supply terms including aeolian deep mixing and lateral advection of dissolved fe are inadequate to account for the magnitude of this fe inclusion of the offshore biologically available fraction of the lithogenic iron flux is therefore required to calculate fully the yield of carbon exported per unit iron injected

removal of thorium 234 by scavenging in the bottom nepheloid layer of the ocean abstract concentrations of234th were measured in deep sea bottom waters to assess the extent of chemical scavenging near the ocean floor at five stations in the eastern tropical pacific where no appreciable bottom nepheloid layer bnl was observed total234th was in secular equilibrium with its parent238u confirming earlier published results in contrast samples from a well developed bnl in the western north atlantic showed a significant depletion of234th due to its removal by scavenging the largest depletions were observed in the two samples closest to the bottom 25 and 64 m above bottom and amounted to 19 of the equilibrium value the results can be used to test models that have been proposed to explain the existence of a bnl it is concluded that only a model which includes local or nearby resuspension of sediment can account for the observations from a steady state model that assumes local resuspension the average residence time of resuspended particles in the bnl is estimated to be 25 days

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

conversion of diatoms to clays during early diagenesis in tropical continental shelf muds in coastal muds downdrift from the amazon river mouth marine diatom frustules are rapidly converted to various forms of authigenic aluminosilicate phases during burial the dominant neoformed crystalline phases have a composition similar to k smectite yield electron diffraction patterns characteristic of clay minerals and exhibit a range of crystal sizes and morphologies including euhedral pseudohexagonal crystals and anhedral flakes replacing biogenic silica a poorly crystalline or microcrystalline k rich and fe rich aluminosilicate material also replaces the siliceous frustules the conversion process is not always complete leaving relics of the original frustule in the resulting authigenic aluminosilicate phases laboratory incubation experiments with cultured diatoms demonstrate that the conversion process occurs in 20 23 months the conversion of biogenic silica to authigenic clays occurs throughout the amazon deltaic deposits and presumably takes place in other comparable depositional settings biogenic silica alteration provides proof for a direct link between the biogeochemical cycle of silica in nearshore environments and the neoformation of cation rich aluminosilicate phases and it may prove to be important for oceanic geochemical cycles as a sink for si k and other elements incorporated in the authigenic aluminosilicates rapid formation of authigenic k smectite may also represent a reaction stage leading to eventual formation of illitic clays during later diagenesis

fe binding dissolved organic ligands near the kerguelen archipelago in the southern ocean indian sector abstract during the ke rguelen o cean and p lateau compared s tudy keops january february 2005 cruise the area southeast of the kerguelen archipelago in the indian sector of the southern ocean was investigated to identify the mechanisms of natural iron fertilization of the kerguelen plateau in this study the organic speciation of fe is described samples were determined immediately on board using competing ligand adsorptive cathodic stripping voltammetry cl adcsv the dissolved organic ligands were always in excess of the dissolved fe concentration increasing the residence time in the water column and the potential availability for phytoplankton the concentration of the dissolved organic ligands ranged from 0 44 to 1 61 n eq of m fe complexation site for fe with an average concentration of 0 91 n eq of m fe s d 0 28 n 113 and a mean logarithm of conditional stability constant log k of 21 7 s d 0 28 n 113 a second weaker dissolved organic ligand group was detected in 32 of the samples with fe binding characteristics at the edge of the detection window of the applied method the occurrence of the highest concentrations of dissolved organic ligands in the wind mixed surface layer and near the sediment at the bottom of the water column indicated that both phytoplankton and the sediment act as sources both sources are in concert with the general conclusions from the keops research on the sources of fe where fe was regenerated organic fe binding ligands were formed in the upper layers and both fe and ligands were supplied by the sediment

western pacific coastal sources of iron manganese and aluminum to the equatorial undercurrent 1 we present results from the first zonal transect of iron aluminum and manganese conducted from the western source region of the equatorial undercurrent euc to the central equatorial pacific trace metals were elevated along the slope of papua new guinea and within the new guinea coastal undercurrent ngcu which is the primary southern hemisphere entry path of water to the euc subsurface maxima in total acid soluble iron aluminum and manganese were evident in the euc these maxima were generally greatest in the western equatorial pacific and decreased in magnitude eastward maxima in iron and aluminum persisted to 140 w maxima in manganese extended to 175 w iron and manganese maxima were deeper 25 75 m than aluminum maxima and located in the lower euc which undergoes less interior ocean mixing than shallower waters the depth of the aluminum subsurface maxima correlated strongly r 0 88 with the depth of the euc velocity maximum surface waters were enriched in aluminum and manganese offshore of papua new guinea surface metal concentrations decreased eastward throughout the western warm pool up to the longitude 180 w of the salinity front detrital sediment input from either direct riverine input or sediment resuspension appeared to be the primary mechanism of supplying metals to the ngcu we estimated eastward fluxes of metals in the euc and found greatest fluxes in the western equatorial pacific between 160 e and 165 e except for aluminum fluxes of aluminum and to a lesser extent manganese increased concurrently with water volume transport in the central equatorial pacific iron transport in the euc remained constant east of the dateline apparently due to the combined effects of dilution by meridional entrainment and scavenging iron was mobilized in a highly active western boundary current region and transported eastward in the lower euc

dissolved trace metals ni zn co cd pb al and mn around the crozet islands southern ocean a phytoplankton bloom shown to be naturally iron fe induced occurs north of the crozet islands southern ocean every year providing an ideal opportunity to study dissolved trace metal distributions within an island system located in a high nutrient low chlorophyll hnlc region we present water column profiles of dissolved nickel ni zinc zn cobalt co cadmium cd lead pb aluminium al and manganese mn obtained as part of the nerc crozex program during austral summer 2004 2005 two stations m3 and m1 were sampled downstream north of crozet in the bloom area and near the islands along with a control station m2 in the hnlc zone upstream south of the islands the general range found was for ni 4 64 6 31 nm zn 1 59 7 75 nm co 24 49 pm cd 135 673 pm pb 6 22 pm al 0 13 2 15 nm and mn 0 07 0 64 nm vertical profiles indicate little island influence to the south with values in the range of other trace metal deprived regions of the southern ocean significant removal of ni and cd was observed in the bloom and zn was moderately correlated with reactive silicate si indicating diatom control over the internal cycling of this metal higher concentrations of zn and cd were observed near the islands pb al and mn distributions also suggest small but significant atmospheric dust supply particularly in the northern region

manganese and iron in indian ocean waters abstract the first vertical profiles of dissolved mn and fe for the nw indian ocean are reported the area is characterized by seasonal upwelling and a broad oxygen minimum zone in intermediate waters the dissolved fe profile exhibits a maximum 5 1 nm in the oxygen minimum zone with low values both in surface waters 0 3 nm and deep waters around 1 nm mn concentrations in the surface waters are elevated 2 0 4 3 nm and decrease rapidly in an offshore direction below the first 25 m concentrations decrease dramatically 0 5 1 3 nm indicating removal by oxidation and particle scavenging further down various mn maxima are observed which can be related to hydrographic features sigma 1 1 intermediate water originating from the red sea lost its dissolved o2 while flowing northward along the omani coast and exhibits a strong mn maximum 4 6 6 5 nm coincident with the deep o2 minimum 2 2 at the two inshore stations in the gulf of oman this is overlain by relatively modest mn maxima 2 7 nm related to arabian gulf overflow water 3 3 finally the strong mn maxima 4 4 5 6 nm in the oxygen minimum zone at the two offshore stations are related to yet another watermass below these various maxima concentrations decrease gradually to values as low as 90 pm at 2000 meters depth towards the seafloor concentrations increase again leading to a modest bottom water maximum 0 7 1 5 nm the overall vertical distributions of mn and fe are strikingly similar also in actual concentrations to those previously reported for the eastern equatorial pacific an area also characterized by an extensive o2 minimum zone

pore networks in holocene carbonate sediments abstract permeabilities of holocene carbonate sediments from florida and the bahamas determined for 74 samples by water flow rates in a variable head permeameter range from 0 6 to 57 000 millidarcies porosities range from 40 to 78 percent these parameters are related to depositional texture as follows table the muddiest sediments i e the finest grained have the highest porosities but lowest permeabilities this negative correlation between porosity and permeability is the reverse of the situation found in carbonate rocks even as young as pleistocene high porosity and low permeability in sediments show a strong correlation with percentage of fines 62 m from capillary pressure curves it is inferred that many of the pore throats of muddy carbonate sediments are less than 1 m in diameter at least after drying measured permeabilities are used to calculate cementation rates for simple models of upper phreatic zone cementation the calculated rates would require excessive time to produce the degree of cementation seen in late pleistocene rocks of florida and the bahamas the amounts of rainfall and evaporation are the most important factors in the degree of cementation

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

contribution of resuspended sedimentary particles to dissolved iron and manganese in the ocean an experimental study abstract a number of trace metals play essential roles in marine ecosystem structure and biological productivity until recently it has been argued that phytoplankton access primarily dissolved iron while particulate iron was considered a refractory material with little use biologically and limited interaction with the dissolved pool in order to assess the transfer mechanisms between sediment sourced particulate trace metals and the dissolved pool we conducted a 14 month incubation that reacted resuspended sediments with natural seawater both originating from the kerguelen area keops cruises southern ocean in the dark and at concentrations replicating natural conditions three types of sediments were investigated named biosi biosi ca and basalt mostly composed of i biogenic silica bsio2 ii bsio2 and calcite and iii basaltic fragments respectively the release of dissolved silicon dsi iron dfe and manganese dmn was monitored regularly throughout the incubation as well as living bacteria density and fe organic ligands depending on the origin and composition of the sediment unique dfe and dmn fluxes were observed including a strong decoupling between dfe and dmn the basaltic sediment released up to 1 09 0 04 nmol l 1 of dfe and 0 28 0 09 nmol l 1 of dmn while the biogenic sediments released a higher 3 91 0 04 nmol l 1 and 8 03 0 42 nmol l 1 of dfe and dmn respectively several factors influencing the release and removal of dfe and dmn were discernable at the temporal sampling resolution of the incubation including the structural composition of the sediment bacterial abundance and the formation of manganese oxides the regular sampling over short timescales and the extended sampling over one year proved to be critical to constrain the processes and exchanges that govern the contribution of the particulate to the dissolved pools overall this incubation provides a strong basis for reassessing the role of resuspended sedimentary particles in the marine biogeochemical cycles of fe and mn indeed we show that biogenic silica calcite rich and basaltic particles can contribute substantial dissolved fe and mn to the overlying water column in the future the global extent of this previously overlooked external metal source should be quantified through further process studies and biogeochemical models 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

mg and sr distribution in carbonate rocks from the maastrichtian danian boundary of the danish subbasin and the north sea central graben abstract examination of the mg and sr concentrations in carbonate rocks in a number of sections provides the basis for the establishment of two geochemical facies within the region studied 1 a basinal facies including the axial part of the danish subbasin and the north sea central graben indicating relatively stable geochemical conditions and 2 an eastern marginal facies in the danish subbasin reflecting unstable geochemical conditions and distinguished by partial cementation and increasing mg and sr concentrations towards the northeastern limits of the basin a slight microtextural variation in the chalk between the basinal and marginal facies indicates that the origin and composition of the biogenic carbonate components strongly influence the bulk rock geochemistry the elemental distribution reveals a negative correlation between the mg and sr concentrations in the topmost maastrichtian chalk expressed by increasing mg and decreasing sr upwards towards the maastrichtian danian boundary this relation occurs in both geochemical facies and in all sections studied and is believed to have been governed by changing physicochemical conditions in the late maastrichtian sea

siderophore promoted transfer of rare earth elements and iron from volcanic ash into glacial meltwater river and ocean water abstract the rare earth elements ree are a group of trace elements that have short marine residence times and that in river lake and marine surface waters are typically associated with organic and inorganic particles explosive volcanic eruptions such as the 2010 eruptions of eyjafjallajokull volcano in iceland produce volcanic ash particles which can be an important source of iron and other nutrients for aquatic organisms to become bioavailable however this iron needs to be solubilized by complexing agents such as siderophores a well studied example of such a chelator is the biogenic siderophore desferrioxamin b dfob based on results from incubation experiments with glacial meltwater rich river waters from southern iceland which are rich in suspended volcanic ash and that had been incubated with and without dfob respectively we here show that siderophores not only enhance the release of iron but also promote the mobilization of ree from these particles in the presence of dfob partial dissolution of volcanic ash and presumably other lithic particles produces a flux of dissolved ree into ambient waters that is characterized by depletion of the light ree over the middle ree and by selective enrichment of cerium due to the formation of dissolved ce iv dfob complexes in siderophore rich environments this siderophore bound ree flux has the potential to modify the concentrations and distribution of the dissolved ree and of the isotopic composition of dissolved nd in glacial meltwaters river waters and seawater and might be a component of the boundary effects between shelf sediments and seawater which are assumed to account for the missing nd flux to seawater thermodynamic data further suggest that siderophore promoted element mobilization could also be important for other polyvalent trace elements such as hf

iron fluxes from the shelf regions near the south shetland islands in the drake passage during the austral winter 2006 abstract spatial distributions of dissolved iron fe manganese mn and aluminum al in the upper 500 m of the water column near the antarctic peninsula ap during the 2006 austral winter are consistent with diagenetically produced sedimentary sources and are somewhat higher than data obtained in this region during the 2004 austral summer in contrast surface phytoplankton abundances were 6 7 times lower relative to the 2004 austral summer near the south shetland islands elevated levels of dissolved al fe and mn were found corresponding to high loads of resuspended material above the shelf as indicated by the transmissometer signal despite these high levels of trace metals phytoplankton abundances in this area were lower than in the offshore antarctic circumpolar current acc waters offshore acc stations had low concentrations of fe but up to five times greater abundance of phytoplankton the difference in phytoplankton abundance between the regions seems largely driven by light availability as indicated by mixed layer depths the elevated trace metal concentrations near king george island in the bransfield strait bs correspond to the flow path of the bransfield current this enriched plume can also be seen exiting the bs between clarence and elephant islands into the ona basin where it mixes with high nutrient low trace metal concentration acc waters leading to high productivity in this region and further downstream in the scotia sea during the growing season

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

fractionation of 230th 231pa and 10be induced by particle size and composition within an opal rich sediment of the atlantic southern ocean this study centers on the question how sensitive are 231pa 230th and 10be 230th to sediment composition and redistribution the natural radionuclides 231pa 230th and 10be recorded in deep sea sediments are tracers for water mass advection and particle fluxes we investigate the influence of oceanic particle composition on the element adsorption in order to improve our understanding of sedimentary isotope records we present new data on particle size specific 231pa and 10be concentrations an additional separation step based on settling velocities led to the isolation of a very opal rich phase we find that opal rich particles contain the highest 231pa and 10be concentrations and higher 231pa 230th and 10be 230th isotope ratios than opal poor particles the fractionation relative to 230th induced by the adsorption to opal rich particles is more pronounced for 231pa than for 10be we conclude that bulk 231pa 230th in southern ocean sediments is most suitable as a proxy for past opal fluxes the comparison between two neighboring cores with rapid and slow accumulation rates reveals that these isotope ratios are not influenced significantly by the intensity of sediment focusing at these two study sites however a simulation shows that particle sorting by selective removal of sediment winnowing could change the isotope ratios consequently 231pa 230th should not be used as paleocirculation proxy in cases where a strong loss of opal rich material due to bottom currents occurred

diatoms preserved in surface sediments of the northeastern kerguelen plateau abstract an island mass effect was observed from the sedimentary distribution of diatoms on the northeastern kerguelen plateau five new samples placed in context to species distributions previously reported from the permanently open ocean zone pooz revealed a plateau community dominated by three species taxa fragilariopsis kerguelensis thalassionema nitzschioides f nitzschioides and chaetoceros hyalochaete resting spores intermediate abundances of thalassiosira antarctica were unique to the plateau sediment signature as were increased abundances of eucampia antarctica v antarctica the off plateau sediment sample contained typical pooz sediment distributions dominated by f kerguelensis thalassiosira lentiginosa and thalassiothrix antarctica the role of deposition from the surface waters to the sediments was investigated by comparison to the diatom thanatocoenose observed in surface waters these results suggest that the use of sediment abundances of c hyalochaete resting spores and f kerguelensis to determine past productivity events such as wind sourced iron enrichment of the southern ocean at the last glacial maximum is not straightforward the elevated abundance of t nitzschioides f nitzschioides on the plateau did not indicate an iron deplete regime but the converse for the evaluation of paleo productivity hypotheses for the open southern ocean we suggest caution in the use of subantarctic and kerguelen plateau sediment signatures and emphasize that there is a need to also study antarctic coastal and especially sea ice melt water stimulated blooms

iron sources and dissolved particulate interactions in the seawater of the western equatorial pacific iron isotope perspectives this work presents iron isotope data in the western equatorial pacific marine aerosols and top core margin sediments display a slightly heavy fe isotopic composition 56 fe of 0 33 0 11 2sd and 0 14 0 07 respectively samples reflecting the influence of papua new guinea runoff sepik river and rabaul volcano water are characterized by crustal values in seawater fe is mainly supplied in the particulate form and is found with a 56 fe between a0 49 and 0 34 0 07 the particulate fe seems to be brought mainly by runoff and transported across continental shelves and slopes aerosols are suspected to enrich the surface vitiaz strait waters while hydrothermal activity likely enriched new ireland waters dissolved fe isotopic ratios are found between a0 03 and 0 53 0 07 they are almost systematically heavier than the corresponding particulate fe and the difference between the signature of both phases is similar for most samples with 56 fe dfe pfe 0 27 0 25 2sd this is interpreted as an equilibrium isotopic fractionation revealing exchange fluxes between both phases the dissolved phase being heavier than the particles suggests that the exchanges result in a net nonreductive release of dissolved fe this process seems to be locally significantly more intense than fe reductive dissolution documented along reducing margins it may therefore constitute a very significant iron source to the ocean thereby influencing the actual estimation of the iron residence time and sinks the underlying processes could also apply to other elements

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

enhanced particle fluxes and heterotrophic bacterial activities in gulf of mexico bottom waters following storm induced sediment resuspension abstract bottom nepheloid layers bnls in the deep sea transport and remobilize considerable amounts of particulate matter enhancing microbial cycling of organic matter in cold deep water environments we measured bacterial abundance bacterial protein production and activities of hydrolytic enzymes within and above a bnl that formed in the deep mississippi canyon northern gulf of mexico shortly after hurricane isaac had passed over the study area in late august 2012 the bnl was detected via beam attenuation in ctd casts over an area of at least 3 5 km 2 extending up to 200 m above the seafloor at a water depth of 1500 m a large fraction of the suspended matter in the bnl consisted of resuspended sediments as indicated by high levels of lithogenic material collected in near bottom sediment traps shortly before the start of our sampling campaign observations of suspended particle abundance and sizes throughout the water column using a combined camera ctd system marine snow camera msc revealed the presence of macroaggregates 1 mm in diameter within the bnl indicating resuspension of canyon sediments a distinct bacterial response to enhanced particle concentrations within the bnl was evident from the observation that the highest enzymatic activities peptidase glucosidase and protein production 3 h leucine incorporation were found within the most particle rich sections of the bnl to investigate the effects of enhanced particle concentrations on bacterial activities in deep bnls more directly we conducted laboratory experiments with roller bottles filled with bottom water and amended with experimentally resuspended sediments from the study area macroaggregates formed within 1 day from resuspended sediments by day 4 of the incubation bacterial cell numbers in treatments with resuspended sediments were more than twice as high as in those lacking sediment suspensions cell specific enzymatic activities were also generally higher in the sediment amended compared to the unamended treatments the broader range and higher activities of polysaccharide hydrolases in the presence of resuspended sediments compared to the unamended water reflected enzymatic capabilities typical for benthic bacteria our data suggest that the formation of bnls in the deep gulf of mexico can lead to transport of sedimentary organic matter into bottom waters stimulating bacterial food web interactions such storm induced resuspension may represent a possible mechanism for the redistribution of sedimented oil fallout from the deepwater horizon spill in 2010

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

trace metal mg ca and sr ca analyses of single coccoliths by secondary ion mass spectrometry here we present the first multi species comparison of modern and fossil coccolith trace metal data obtained from single liths we present both trace metal analyses sr ca mg and al and distribution maps of individual paleogene fossil coccoliths obtained by secondary ion mass spectrometry sims we use this data to determine the effects of variable coccolith preservation and diagenetic calcite overgrowths on the recorded concentrations of strontium and magnesium in coccolith calcite the analysis of coccoliths from deep ocean sediments spanning the eocene oligocene transition demonstrates that primary coccolith calcite is resistant to the neomorphism that is common in planktonic foraminifera from similar depositional environments instead where present diagenetic calcite forms distinct overgrowths over primary coccolith calcite rather than replacing this calcite diagenetic overgrowths on coccoliths are easily distinguished in sims analyses on the basis of relatively higher mg and lower sr concentrations than co occurring primary coccolith calcite this interpretation is confirmed by the comparable sims analyses of modern cultured coccoliths of coccolithus braarudii further with diagenetic calcite overgrowth being the principle source of bias in coccolith based geochemical records we infer that lithologies with lower carbonate content deposited below the palaeo lysocline are more likely to produce geochemical records dominated by primary coccolith calcite than carbonate rich sediments where overgrowth is ubiquitous the preservation of primary coccolith carbonate in low carbonate lithologies thus provides a reliable geochemical archive where planktonic foraminifera are absent or have undergone neomorphism