Robustness of fossil fish teeth for seawater neodymium isotope reconstructions under variable redox conditions in an ancient shallow marine setting

Fossil fish teeth from pelagic open ocean settings are considered a robust archive for preserving the neodymium (Nd) isotopic composition of ancient seawater. However, using fossil fish teeth as an archive to reconstruct seawater Nd isotopic compositions in different sedimentary redox environments and in terrigenous‐dominated, shallow marine settings is less proven. To address these uncertainties, fish tooth and sediment samples from a middle Eocene section deposited proximal to the East Antarctic margin at Integrated Ocean Drilling Program Site U1356 were analyzed for major and trace element geochemistry, and Nd isotopes. Major and trace element analyses of the sediments reveal changing redox conditions throughout deposition in a shallow marine environment. However, variations in the Nd isotopic composition and rare earth element (REE) patterns of the associated fish teeth do not correspond to redox changes in the sediments. REE patterns in fish teeth at Site U1356 carry a typical mid‐REE‐enriched signature. However, a consistently positive Ce anomaly marks a deviation from a pure authigenic origin of REEs to the fish tooth. Neodymium isotopic compositions of cleaned and uncleaned fish teeth fall between modern seawater and local sediments and hence could be authigenic in nature, but could also be influenced by sedimentary fluxes. We conclude that the fossil fish tooth Nd isotope proxy is not sensitive to moderate changes in pore water oxygenation. However, combined studies on sediments, pore waters, fish teeth, and seawater are needed to fully understand processes driving the reconstructed signature from shallow marine sections in proximity to continental sources

The potential of sedimentary foraminiferal rare earth element patterns to trace water masses in the past

Dissolved rare earth element (REE) concentration data from intermediate and deep seawater form an array characterized by higher middle REE enrichments (MREE/MREE*) in the North Atlantic and a progressive increase in heavy-to-light REE ratios (HREE/LREE) as water masses age. The REEs in foraminifera are fractionated towards higher MREE/MREE* and lower HREE/LREE relative to seawater. Calculations based on a scavenging model show that the REE patterns in uncleaned core-top foraminifera resemble those adsorbed onto calcite, particulate organic material, and hydrous ferric oxides but the full extent of the REE fractionation measured in foraminifera was not reproduced by the model. However, differences in the HREE/LREE, MREE/MREE* ratios and the cerium anomaly between ocean basins are preserved and are in agreement with the seawater REE distribution. Under oxic conditions, the HREE/LREE and MREE/MREE* compositions of uncleaned foraminifera at the sediment/seawater boundary are preserved during burial but the cerium anomaly is sensitive to burial depth. In suboxic sedimentary environments, all uncleaned foraminiferal REE concentrations are elevated relative to core-top values indicating addition of REEs from pore waters. The HREE/LREE ratio is highest when sedimentation rates were greatest [Lippold et al., 2009] and when high Fe/Ca ratios in the uncleaned foraminifera indicate that Fe was mobile. In sediments that have not experienced suboxic conditions during burial, uncleaned foraminifera preserve the seawater signal taken up at the sediment/seawater interface and are therefore suggested to be a suitable archive of changes in the REE signal of past bottom waters. This article is protected by copyright. All rights reserved

Science-based restoration monitoring of coastal habitats, Volume Two: Tools for monitoring coastal habitats

Healthy coastal habitats are not only important ecologically; they also support healthy coastal communities and improve the quality of people’s lives. Despite their many benefits and values, coastal habitats have been systematically modified, degraded, and destroyed throughout the United States and its protectorates beginning with European colonization in the 1600’s (Dahl 1990). As a result, many coastal habitats around the United States are in desperate need of restoration. The monitoring of restoration projects, the focus of this document, is necessary to ensure that restoration efforts are successful, to further the science, and to increase the efficiency of future restoration efforts

Sediment Bacterial Communities in Nutrient Cycling and in the History of the Baltic Sea

The Baltic Sea has experienced fresh-, brackish, oxic and hypoxic water phases and its deepest bottom areas are naturally hypoxic. Recently, eutrophication has caused spreading of hypoxic areas and internal feedback mechanisms, such as the release of phosphorus (P) and nitrogen (N) nutrients from sediment to water, which sustains hypoxia. Bacteria participate in release of nutrients by mineralizing organic matter or by altering the sediment s ability to retain nutrients. In deeper sediment layers, most microbes are inactive, dead or only their DNA is preserved, representing the remains of the preceding sedimentary communities. This work investigated variation in bacterial communities in the northeastern Baltic Sea sediments along the gradients of chemical forms of P and elements related to its cycling, as well as organic matter and some properties of the upperlying water column such as oxygen concentrations. The results were discussed from the standpoint of nutrient recycling, which sustains the eutrophic conditions of the Baltic Sea. In addition, a sediment core covering the last 8000 years were investigated to determine whether historical phases of the Baltic Sea can be inferred from bacterial community data and this kind of data could be used as a palaeomicrobiological tool. Current and historical bacterial communities were studied using terminal restriction fragments length polymorphism and sequencing of the 16S rRNA genes. The data obtained were examined with sediment properties, using statistics and phylogenetics. Bacterial communities changed mainly along the gradients of chemical forms of P and organic matter. Most importantly, sulphate-reducing bacteria correlated with organic and Fe-bound P as well as redox-sensitive iron (Fe). The correlations indicated that sulphate reducers participated in the release of Fe-bound P, indirectly by producing sulphide, which captures Fe, or directly by reducing Fe oxyhydroxides. The predominance of sulphate reducers in most areas suggests that hypoxia has progressed in the phase where bacteria process most of the benthic energy. The phylum Chloroflexi, typical for organic-rich environments, increased downwards and was common throughout the sediment core spanning the 8000-year history of the Baltic Sea. This indicates that these bacteria were important in terminal mineralization and that the Baltic has been relatively organic-rich throughout its history, which makes it sensitive to external nutrient loading. The bacterial communities of the Early and Late Litorina Sea phase were distinguished from the communities of the Litorina Sea phase, which correlated positively with uranium and strontium, used as palaeooxygen and palaeosalinity proxies. Salinity changes also explained a sudden increase in the heterogeneity of the bacterial communities of Litorina Sea layers, which indicates that a salinity maximum occurred in the central Gulf of Finland 6200 6600 years ago. This study showed that bacterial community data may be used as an additional tool e.g. in ocean-drilling projects, which aim to detect historical environmental events from the sedimentary record.Historiansa aikana Itämeri on ollut vuoroin makea- tai murtovetinen ja pohja-alueiden happipitoisuus on vaihdellut. Luonnostaan hapettomat pohja-alueet ovat rehevöitymisen seurauksena laajentuneet ja hapettomuudesta johtuva ravinteiden kuten fosforin ja typen vapautuminen sedimentistä vesipatsaaseen on lisääntynyt, mikä ylläpitää rehevöitymistä. Bakteerit aiheuttavat ravinteiden vapautumista sedimentistä pohjaveteen esimerkiksi hajottaessaan eloperäistä ainetta. Tässä prosessissa aerobit bakteerit kuluttavat happea, mikä lisää esimerkiksi rautaan sitoutuneen fosforin vapautumista. Syvemmällä hapettomissa sedimenteissä eloperäinen aine on pidemmälle hajotettua ja suurin osa bakteereista on horrostilassa tai kuolleena. Syvemmällä menneet bakteeriyhteisöt heijastavat vesipatsaan aiempaa tilaa. Väitöskirjassani tutkin sedimenttien bakteeriyhteisöjen muutosta sedimentin kemiallisten ominaisuuksien ja ympäröivien olosuhteiden kuten pohjaveden happipitoisuuden muuttuessa Suomenlahdella ja Saaristomerellä. Käsittelin tuloksia ravinteiden vapautumisen näkökulmasta, koska vapautuvat ravinteet ylläpitävät Itämeren rehevöitynyttä tilaa. Lisäksi selvitin voiko sedimentin bakteeriyhteisöjä käyttää työkaluna tutkittaessa merien historiaa ja heijastivatko bakteeriyhteisön syvyyssuuntaiset muutokset Itämeren historiallisia vaiheita viimeisten 8000 vuoden ajalta. Määritin bakteeriyhteisön 16S rRNA geenien päätekatkokirjoanalyysillä (T-RFLP) ja sekvensoinnilla. Vertasin yhteisön muutosta sedimentin kemiallisiin, geokemiallisiin ynnä muihin muutoksiin tilastollisilla monimuuttujamenetelmillä. Fosforin käyttökelpoisuus vaikutti eniten sedimentin bakteeriyhteisöihin siirryttäessä maatalouden kuormittamalta Saaristomereltä Suomenlahdelle. Suomenlahdella bakteeriyhteisö muuttui eniten eloperäisen kuormituksen vaikutuksesta. Laajoilla ja erityisesti vähähappisilla pohjilla hallitsivat sulfaattia pelkistävät bakteerit, joiden määrä lisääntyi orgaanisen fosforin ja typen sekä hapetus-pelkistys-olosuhteisiin reagoivan raudan ja tähän rautaan sitoutuneen fosforin lisääntyessä. Sulfaatin pelkistäjät vapauttavat välillisesti rautaan sitoutunutta fosforia, sillä ne tuottavat sulfidia, joka saostuu raudan kanssa ferrosulfideina hapettomissa sedimenteissä. Tästä syystä rautaa ei ole saatavilla sitomaan fosforia hapellisiin sedimenttikerroksiin, jolloin fosfori vapautuu meriveteen. Syvyyssuunnassa lisääntyivät Chloroflexi-pääjaksoon kuuluvat bakteerit, jotka olivat yleisiä keskisen Suomenlahden sedimentissä viimeisten 8000 vuoden aikana. Nämä bakteerit ovat todennäköisesti tärkeitä eloperäisen aineen loppuvaiheen hajotuksessa rehevöityneessä Itämeressä. Ilmeisesti Itämeressä eloperäisen aineen määrä on ollut suuri koko sen noin 8000 vuotisen historian aikana, mikä tekee Itämeren herkästi rehevöityväksi. Suolaisuuden ja hapettomuuden mittareina käytettävät uranium ja strontium selittivät bakteeriyhteisön muutoksen Litorina-merivaiheessa, joka oli Itämeren vaiheista suolaisin. Litorina-vaiheen yhteisöt erottuivat varhaisen ja myöhäisen Litorina-vaiheen yhteisöistä. Suolaisuuden aiheuttamat muutokset pohjan happipitoisuudessa selittivät myös sen, miksi bakteeriyhteisö, joka yksinkertaistui säännöllisesti syvyyssuunnassa, yhtäkkiä monipuolistui noin 6200−6600 vuotta vanhoissa Litorina-sedimenteissä. Keskisellä Suomenlahdella vesi on ollut tuolloin ilmeisesti suolaisimmillaan

Fate of colloids during estuarine mixing in the Arctic

The estuarine behavior of organic carbon (OC) and trace elements (TE) was studied for the largest European sub-Arctic river, which is the Severnaya Dvina; this river has a deltaic estuary covered in ice during several hydrological seasons: summer (July 2010, 2012) and winter (March 2009) baseflow, and the November–December 2011 ice-free period. Colloidal forms of OC and TE were assessed for three pore size cutoffs (1, 10, and 50 kDa) using an in situ dialysis procedure. Conventionally dissolved (< 0.22 μm) fractions demonstrated clear conservative behavior for Li, B, Na, Mg, K, Ca, Sr, Mo, Rb, Cs, and U during the mixing of freshwater with the White Sea; a significant (up to a factor of 10) concentration increase occurs with increases in salinity. Si and OC also displayed conservative behavior but with a pronounced decrease in concentration seawards. Rather conservative behavior, but with much smaller changes in concentration (variation within ±30%) over a full range of salinities, was observed for Ti, Ni, Cr, As, Co, Cu, Ga, Y, and heavy REE. Strong non-conservative behavior with coagulation/removal at low salinities (< 5&permil;) was exhibited by Fe, Al, Zr, Hf, and light REE. Finally, certain divalent metals exhibited non-conservative behavior with a concentration gain at low (~ 2–5&permil;, Ba, Mn) or intermediate (~ 10–15&permil;, Ba, Zn, Pb, Cd) salinities, which is most likely linked to TE desorption from suspended matter or sediment outflux. <br><br> The most important result of this study is the elucidation of the behavior of the "truly" dissolved low molecular weight LMW_{< 1 kDa} fraction containing Fe, OC, and a number of insoluble elements. The concentration of the LMW fraction either remains constant or increases its relative contribution to the overall dissolved (< 0.22 μm) pool as the salinity increases. Similarly, the relative proportion of colloidal (1 kDa–0.22 μm) pool for the OC and insoluble TE bound to ferric colloids systematically decreased seaward, with the largest decrease occurring at low (< 5&permil;) salinities. <br><br> Overall, the observed decrease in the colloidal fraction may be related to the coagulation of organo-ferric colloids at the beginning of the mixing zone and therefore the replacement of the HMW_{1 kDa–0.22 μm} portion by the LMW_{< 1 kDa} fraction. These patterns are highly reproducible across different sampling seasons, suggesting significant enrichment of the mixing zone by the most labile (and potentially bioavailable) fraction of the OC, Fe and insoluble TE. The size fractionation of the colloidal material during estuarine mixing reflects a number of inorganic and biological processes, the relative contribution of which to element speciation varies depending on the hydrological stage and time of year. In particular, LMW_{< 1 kDa} ligand production in the surface horizons of the mixing zone may be linked to heterotrophic mineralization of allochthonous DOM and/or photodestruction. Given the relatively low concentration of particulate versus dissolved load of most trace elements, desorption from the river suspended material was less pronounced than in other rivers in the world. As a result, the majority of dissolved components exhibited either conservative (OC and related elements such as divalent metals) or non-conservative, coagulation-controlled (Fe, Al, and insoluble TE associated with organo-ferric colloids) behavior. The climate warming at high latitudes is likely to intensify the production of LMW_{< 1 kDa} organic ligands and the associated TE; therefore, the delivery of potentially bioavailable trace metal micronutrients from the land to the ocean may increase

Evidence for intense REE scavenging at cold seeps from the Niger Delta margin

International audienceFor many trace elements, continental margins are the location of intense exchange processes between sediment and seawater, which control their distribution in the water column, but have yet to be fully understood. In this study, we have investigated the impact of fluid seepage at cold seeps on the marine cycle of neodymium. We determined dissolved and total dissolvable (TD) concentrations for REE and well-established tracers of fluid seepage (CH4, TDFe, TDMn), and Nd isotopic compositions in seawater samples collected above cold seeps and a reference site (i.e. away from any fluid venting area) from the Niger Delta margin. We also analyzed cold seep authigenic phases and various core-top sediment fractions (pore water, detrital component, easily leachable phases, uncleaned foraminifera) recovered near the hydrocast stations. Methane, TDFe and TDMn concentrations clearly indicate active fluid venting at the studied seeps, with plumes rising up to about 100 m above the seafloor. Depth profiles show pronounced REE enrichments in the non-filtered samples (TD concentrations) within plumes, whereas filtered samples (dissolved concentrations) exhibit slight REE depletion in plumes relative to the overlying water column and display typical seawater REE patterns. These results suggest that the net flux of REE emitted into seawater at cold seeps is controlled by the presence of particulate phases, most probably Fe-Mn oxyhydroxides associated to resuspended sediments. At the reference site, however, our data reveal significant enrichment for dissolved REE in bottom waters, that clearly relates to diffusive benthic fluxes from surface sediments. Neodymium isotopic ratios measured in the water column range from εNd ~−15.7 to − 10.4. Evidence that the εNd values for Antarctic Intermediate waters (AAIW) differed from those reported for the same water mass at open ocean settings shows that sediment/water interactions take place in the Gulf of Guinea. At each site, however, the bottom water εNd signature generally differs from that for cold seep minerals, easily leachable sediment phases, and detrital fractions from local sediments, ruling out the possibility that seepage of methane-rich fluids and sediment dissolution act as a substantial source of dissolved Nd to seawater in the Gulf of Guinea. Taken together, our data hence suggest that co-precipitation of Fe-Mn oxyhydroxide phases in sub-surface sediments leads to quantitative scavenging of dissolved REE at cold seeps, preventing their emission into bottom waters. Most probably, it is likely that diffusion from suboxic surface sediments dominates the exchange processes affecting the marine Nd cycle at the Niger Delta margin

The biogeochemistry of metal cycling

The results of the Planetary Biology and Microbial Ecology's summer 1987 program are summarized. The purpose of the interdisciplinary PBME program is to integrate, via lectures and laboratory work, the contributions of university and NASA scientists and student interns. The 1987 program examined various aspects of the biogeochemistry of metal cycling, and included such areas as limnology, metal chemistry, metal geochemistry, microbial ecology, and interactions with metals. A particular area of focus was the use of remote sensing in the study of biogeochemistry. Abstracts and bibliographies of the lectures and reports of the laboratory projects are presented

A survey of the problem and research needs in the coastal zone

Coastal zone oceanography emphasizing pollution and geological processes - bibliograph