ALBERT

Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Chemical Oceanography at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution May 2022.

Description: Removal of particulate organic carbon (POC) from sunlit surface waters into the deep ocean represents a climatically important sink of atmospheric carbon dioxide (CO2), linking the biogeochemical cycling of POC to CO2-driven climate change. As POC is not well preserved in the sediment record, other proxies, including the chemistry of barium (Ba) in the ocean and through the sedimentary record, offer an avenue to investigate oceanic carbon export through Earth’s history. This thesis seeks to constrain the controls on the formation, cycling, and isotopic signature of the main particulate phase of marine barium, the mineral barite (BaSO4) through its inception in the water column, during deposition, and ultimately into the rock record. To that end, I characterize the depth, spatial region, and general controls on particulate Ba formation in the South Pacific Ocean through shipboard experimentation and find that particulate Ba forms mainly in the surface of the Polar Frontal Zone in the presence of large particles and microbial activity. Next, I characterize the effect of ion exchange on BaSO4, a process previously unstudied under marine conditions, in a laboratory setting. Ion exchange occurs rapidly between dissolved Ba and BaSO4 and imparts a characteristic net offset between the Ba isotope composition of the dissolved and solid phase, which arises through a combination of Ba isotope fractionation during both precipitation and dissolution. Finally, I investigate the role of ion exchange in marine settings using co-located pore fluids and sedimented BaSO4. Modeling constrained by data from natural samples produce results that are consistent with the laboratory study, suggesting that this mode of isotopic fractionation impacts Ba isotopes in the environment and must be accounted for when applying Ba based climate proxies.

Description: Funding for this work was provided by the National Science Foundation (OCE-2023456 & OCE-1827401), the Woods Hole Oceanographic Institution Ocean Ventures Fund, a National Science Foundation Graduate Research Fellowship (2017250048), and Woods Hole Oceanographic Institution.

Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Chemical Oceanography at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution February 2022.

Description: Coastal ecosystems provide key services that benefit human wellbeing yet are undergoing rapid degradation due to natural and anthropogenic pressures. This thesis seeks to understand how disturbances impact salt marsh and estuarine ecosystem functioning in order to refine their role in coastal ecosystem service delivery and predict future resilience. Salt marsh survival relative to sealevel rise increasingly relies on the accumulation and preservation of soil organic carbon (SOC). Firstly, I characterized SOC development and turnover in a New England salt marsh and found that salt marsh soils typically store marsh grass-derived compounds that are reworked over centuries-to-millennia. Next, I assessed how two common marsh disturbances – natural ponding and anthropogenic mosquito ditching – affect salt marsh carbon cycling and storage. Salt marsh ponds deepen through soil erosion and decomposition of long-buried marsh peat. Further, the SOC lost during pond development is not fully recouped once drained ponds are revegetated and virtually indistinguishable from the surrounding marsh. Mosquito ditches, which were installed in ~ 90% of New England salt marshes during the Great Depression, did not significantly alter marsh carbon storage. In Buzzards Bay, Massachusetts, a US National Estuary, we tested relationships among measures of estuarine water quality, recreational activity, and local socioeconomic conditions to understand how the benefits of cultural ecosystem services are affected by shifts in water quality associated with global change and anthropogenic activity. Over a 24-year period, water quality degradation coinciding with increases in Chlorophyll a is associated with declines in fishery abundance and cultural ecosystem service values ($0.08 – 0.67 million USD). In combination, incorporation of both anthropogenic and natural disturbances to coastal ecosystem functioning and service delivery can produce improved estimates of ecosystem service valuation for effective resource decision-making under future climate scenarios.

Description: Funding for this work was provided by John D. and Catherine T. MacArthur Foundation (Grant no. 14-106159-000-CFP), National Science Foundation (OCE1233678), National Oceanic and Atmospheric Administration, National Oceanic and Atmospheric Administration – National Estuaries Research Reserve Collaborative (NA14OAR4170104 and NA- 14NOS4190145), Woods Hole Sea Grant (NA14OAR4170104), MIT Sea Grant (subaward number 5710004045), Ocean Ventures Fund, the Marine Policy Center Johnson Endowment, and Woods Hole Oceanographic Institution.

Description: © The Author(s), 2021. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Farfan, G. A., Apprill, A., Cohen, A., DeCarlo, T. M., Post, J. E., Waller, R. G., & Hansel, C. M. Crystallographic and chemical signatures in coral skeletal aragonite. Coral Reefs. (2121), https://doi.org/10.1007/s00338-021-02198-4.

Description: Corals nucleate and grow aragonite crystals, organizing them into intricate skeletal structures that ultimately build the world’s coral reefs. Crystallography and chemistry have profound influence on the material properties of these skeletal building blocks, yet gaps remain in our knowledge about coral aragonite on the atomic scale. Across a broad diversity of shallow-water and deep-sea scleractinian corals from vastly different environments, coral aragonites are remarkably similar to one another, confirming that corals exert control on the carbonate chemistry of the calcifying space relative to the surrounding seawater. Nuances in coral aragonite structures relate most closely to trace element chemistry and aragonite saturation state, suggesting the primary controls on aragonite structure are ionic strength and trace element chemistry, with growth rate playing a secondary role. We also show how coral aragonites are crystallographically indistinguishable from synthetic abiogenic aragonite analogs precipitated from seawater under conditions mimicking coral calcifying fluid. In contrast, coral aragonites are distinct from geologically formed aragonites, a synthetic aragonite precipitated from a freshwater solution, and mollusk aragonites. Crystallographic signatures have future applications in understanding the material properties of coral aragonite and predicting the persistence of coral reefs in a rapidly changing ocean.

Description: This project was funded by the Mineralogical Society of America Edward H. Kraus Crystallographic Research Fund and the WHOI Ocean Ventures Fund. G. Farfan was supported by a National Science Foundation Graduate Research Fellowship Grant No. 1122374 and a Ford Foundation Dissertation Fellowship. Sample collections from R. Waller were funded under NSF Grant Numbers 1245766, 1127582 and NOAA Ocean Exploration Deep Atlantic Stepping Stones. The authors thank Erik Cordes for the samples collected from the Gulf of Mexico, which were supported by NSF BIO-OCE Grant # 1220478. STZC collections from A. Apprill were funded by a Dalio Foundation (now ‘OceanX’) and a KAUST-WHOI Special Academic Partnership Funding Reserve with Christian Voolstra. Research and coral collections in Cuba were conducted under the LH112 AN (25) 2015 license granted by the Cuban Center for Inspection and Environmental Control with the assistance of Patricia Gonzalez and Michael Armenteros. Corals from Western Australia were collected under license number SF009558 obtained by M. McCulloch, and from the Maldives Ministry of Fisheries and Agriculture with collection permits (No. (OTHR)30-D/INDIV/2013/359). Matthew Neave assisted with the collections.

Description: © The Author(s), 2021. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Farrell, U. C., Samawi, R., Anjanappa, S., Klykov, R., Adeboye, O. O., Agic, H., Ahm, A.-S. C., Boag, T. H., Bowyer, F., Brocks, J. J., Brunoir, T. N., Canfield, D. E., Chen, X., Cheng, M., Clarkson, M. O., Cole, D. B., Cordie, D. R., Crockford, P. W., Cui, H., Dahl, T. W., Mouro, L. D., Dewing, K., Dornbos, S. Q., Drabon, N., Dumoulin, J. A., Emmings, J. F., Endriga, C. R., Fraser, T. A., Gaines, R. R., Gaschnig, R. M., Gibson, T. M., Gilleaudeau, G. J., Gill, B. C., Goldberg, K., Guilbaud, R., Halverson, G. P., Hammarlund, E. U., Hantsoo, K. G., Henderson, M. A., Hodgskiss, M. S. W., Horner, Tristan J., Husson, J. M., Johnson, B., Kabanov, P., Brenhin K. C., Kimmig, J., Kipp, M. A., Knoll, A. H., Kreitsmann, T., Kunzmann, M., Kurzweil, F., LeRoy, M. A., Li, C., Lipp, A. G., Loydell, D. K., Lu, X., Macdonald, F. A., Magnall, J. M., Mänd, K., Mehra, A., Melchin, M. J., Miller, A. J., Mills, N. T., Mwinde, C. N., O'Connell, B., Och, L. M., Ossa Ossa, F., Pagès, A., Paiste, K., Partin, C. A., Peters, S. E., Petrov, P., Playter, T. L., Plaza-Torres, S., Porter, Susannah M., Poulton, S. W., Pruss, S. B., Richoz, S., Ritzer, S. R., Rooney, A. D., Sahoo, S. K., Schoepfer, S. D., Sclafani, J. A., Shen, Y., Shorttle, O., Slotznick, S. P., Smith, E. F., Spinks, S., Stockey, R. G., Strauss, J. V., Stüeken, E. E., Tecklenburg, S., Thomson, D., Tosca, N. J., Uhlein, G. J., Vizcaíno, M. N., Wang, H., White, T., Wilby, P. R., Woltz, C. R., Wood, R. A., Xiang, L., Yurchenko, I. A., Zhang, T., Planavsky, N. J., Lau, K. V., Johnston, D. T., Sperling, E. A., The Sedimentary Geochemistry and Paleoenvironments Project. Geobiology. 00, (2021): 1– 12,https://doi.org/10.1111/gbi.12462.

Description: Geobiology explores how Earth's system has changed over the course of geologic history and how living organisms on this planet are impacted by or are indeed causing these changes. For decades, geologists, paleontologists, and geochemists have generated data to investigate these topics. Foundational efforts in sedimentary geochemistry utilized spreadsheets for data storage and analysis, suitable for several thousand samples, but not practical or scalable for larger, more complex datasets. As results have accumulated, researchers have increasingly gravitated toward larger compilations and statistical tools. New data frameworks have become necessary to handle larger sample sets and encourage more sophisticated or even standardized statistical analyses. In this paper, we describe the Sedimentary Geochemistry and Paleoenvironments Project (SGP; Figure 1), which is an open, community-oriented, database-driven research consortium. The goals of SGP are to (1) create a relational database tailored to the needs of the deep-time (millions to billions of years) sedimentary geochemical research community, including assembling and curating published and associated unpublished data; (2) create a website where data can be retrieved in a flexible way; and (3) build a collaborative consortium where researchers are incentivized to contribute data by giving them priority access and the opportunity to work on exciting questions in group papers. Finally, and more idealistically, the goal was to establish a culture of modern data management and data analysis in sedimentary geochemistry. Relative to many other fields, the main emphasis in our field has been on instrument measurement of sedimentary geochemical data rather than data analysis (compared with fields like ecology, for instance, where the post-experiment ANOVA (analysis of variance) is customary). Thus, the longer-term goal was to build a collaborative environment where geobiologists and geologists can work and learn together to assess changes in geochemical signatures through Earth history.

Description: We thank the donors of The American Chemical Society Petroleum Research Fund for partial support of SGP website development (61017-ND2). EAS is funded by National Science Foundation grant (NSF) EAR-1922966. BGS authors (JE, PW) publish with permission of the Executive Director of the British Geological Survey, UKRI.

Description: In the Rocca Busambra area (mid-west Sicily, Italy), from November 1999 to July 2002, 23 water points including wells and springs were sampled and studied for their chemical and isotopic compositions. Two rain gauges were also installed at different altitudes, and rainwater was collected monthly to determine the isotopic composition. The obtained results revealed the Rocca Busambra carbonate complex as being the main recharge area on account of its high permeability value. From a chemical view point, two main groups of water can be distinguished: calcium– magnesium–bicarbonate-type and calcium–magnesium– chloride–sulphate-type waters. The first group reflects the dissolution of the carbonate rocks; the second group probably originates from circulation within flyschoid sediments. Three water wells differ from the other samples due to their relatively high Na and K content, which probably is to be referred to a marked interaction with the ‘‘Calcareniti di Corleone’’ formation, which is rich in glauconite [(K, Na)(Fe3+, Al, Mg)2(Si, Al)4O10(OH)2]. In accordance with WHO guidelines for drinking water (2004), almost all the samples collected can be considered drinkable, with the exception of four of them, whose NO3 -, F- and Na+ contents exceed the limits. On the contrary, the sampled groundwater studied is basically suitable for irrigation.

Description: Published

Description: 885-898

Description: 2.4. TTC - Laboratori di geochimica dei fluidi

Description: JCR Journal

Description: reserved

Description: Following the 2001 and 2002–2003 flank eruptions, activity resumed at Mt. Etna on 7 September 2004 and lasted for about 6 months. This paper presents new petrographic, major and trace element, and Sr–Nd isotope data from sequential samples collected during the entire 2004–2005 eruption. The progressive change of lava composition allowed defining three phases that correspond to different processes controlling magma dynamics inside the central volcano conduits. The compositional variability of products erupted up to 24 September is well reproduced by a fractional crystallization model that involves magma already stored at shallow depth since the 2002–2003 eruption. The progressive mixing of this magma with a distinct new one rising within the central conduits is clearly revealed by the composition of the products erupted from 24 September to 15 October. After 15 October, the contribution from the new magma gradually becomes predominant, and the efficiency of the mixing process ensures the emission of homogeneous products up to the end of the eruption. Our results give insights into the complex conditions of magma storage and evolution in the shallow plumbing system of Mt. Etna during a flank eruption. Furthermore, they confirm that the 2004–2005 activity at Etna was triggered by regional movements of the eastern flank of the volcano. They caused the opening of a complex fracture zone extending ESE which drained a magma stored at shallow depth since the 2002–2003 eruption. This process favored the ascent of a different magma in the central conduits, which began to be erupted on 24 September without any significant change in eruptive style, deformation, and seismicity until the end of eruption.

Description: Published

Description: 781–793

Description: 2.3. TTC - Laboratori di chimica e fisica delle rocce

Description: JCR Journal

Description: reserved

Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution June 2009

Description: The application of elemental and isotopic metal palaeoredox tracers to the geologic past rests on an understanding of modern metal cycles. This study reevaluates the surface-cycling of Mo and Re in near-surface reservoirs. Revised river averages of Mo and Re are 1.8- and 7.9-fold larger than previous estimates. The river concentrations of 8.0 nmol Mo kg−1 and 11.2 pmol Re kg−1 (pre-anthropogenic), result in shorter seawater response times of 4.4×105 yr (τMo) and 1.3×105 yr (τRe pre-anthropogenic). These metals, especially Re, are more sensitive to changing source and sink fluxes than previously thought. Evaluation of Mo and Re concentrations in high temperature fluids from the Manus Basin indicate that Re is essentially absent from the hydrothermal end member and Mo is present at concentrations considerably lower than ambient seawater. The sink fluxes represented by hydrothermal circulation are negligible in comparison to the revised river source fluxes. Anthropogenic contributions to the Re flux to seawater are seen in the high concentrations of certain impacted water samples such as those associated with mining sites. It may also be seen in a significant, variable, Re enrichment feature in the Hudson River estuary. This Re enrichment feature is not the result of estuarine mixing or the remobilization of sediment-hosted Re. On the basis of a Re - SO2− 4 correlation we are able to quantify and correct for the anthropogenic Re, which corresponds to ~33% of the modern river average. This study documents the development of an analytical method for stable Re isotopes. Though complicated by analyte requirements and 187Re – 187Os decay, Re isotope measurements have a reproducibility of ±0.05h for analyte concentrations of 20 ng Re mL−1. Total Re isotopic variability to date is 0.9h. This includes 0.3h across five commercially available Re products, and 0.5h across a black shale weathering profile. δ187Re variability across the weathering profile was systematic with the most weathered samples showing the most significant 187Re depletions. The Re isotopic weathering profile is well described by both two-component mixing and Rayleigh fractionation. There are currently insufficient data to discriminate between the two models.

Description: We would like to acknowledge financial support from NSF-EAR grant 0519387 and from the WHOI Academic Programs Office as well as support for the WHOI Plasma Mass Spectrometry Facility from NSF-EAR/IF grants 0318137 and 0651366.

Description: In the Rocca Busambra area (mid-west Sicily, Italy), from November 1999 to July 2002, 23 water points including wells and springs were sampled and studied for their chemical and isotopic compositions. Two rain gauges were also installed at different altitudes, and rainwater was collected monthly to determine the isotopic composition. The obtained results revealed the Rocca Busambra carbonate complex as being the main recharge area on account of its high permeability value. From a chemical view point, two main groups of water can be distinguished: calcium– magnesium–bicarbonate-type and calcium–magnesium– chloride–sulphate-type waters. The first group reflects the dissolution of the carbonate rocks; the second group probably originates from circulation within flyschoid sediments. Three water wells differ from the other samples due to their relatively high Na and K content, which probably is to be referred to a marked interaction with the ‘‘Calcareniti di Corleone’’ formation, which is rich in glauconite [(K, Na)(Fe3+, Al, Mg)2(Si, Al)4O10(OH)2]. In accordance with WHO guidelines for drinking water (2004), almost all the samples collected can be considered drinkable, with the exception of four of them, whose NO3 -, F- and Na+ contents exceed the limits. On the contrary, the sampled groundwater studied is basically suitable for irrigation

Description: In press

Description: on line first

Description: 4.5. Degassamento naturale

Description: JCR Journal

Description: reserved

Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution November 1980

Description: Plankton samples have been carefully collected from a variety of marine environments under the rigorous conditions necessary to prevent contamination for major and trace-chemical analysis. Immediately after collection, the samples were subjected to a series of physical and chemical leaching-decomposition experiments designed to identify the major and trace element composition of particulate carrier phases. Elements examined through some or all of these experiments were: C, N, P, Mg, Ca, Si, Fe, Mn, Ni, Cu, Cd, Al, Ba, and Zn. Emphasis was placed on the identification of trace element/major element ratios in the biogenic materials. The majority of the trace elements in the samples were directly associated with the non-skeletal organic phases of the plankton. These associations included a very labile fraction which was rapidly released into seawater and a more refractory fraction which involved specific metal-organic binding. Calcium carbonate and opal were not significant carriers for any of the trace elements studied. A refractory phase containing Al and Fe in terrigenous ratios was present in all samples, even from the more remote marine locations. The concentration of this carrier phase within the plankton samples varied in proportion to the estimated rate of supply of terrigenous matter and in opposition to the rate of production of the biogenic particulate matter. The aluminosilicates contributed insignificant amounts to the other trace elements studied. A trace concentration of particulate Al was identified which was more labile and associated with the organic fractions of the samples. Variations in the surface water concentrations of dissolved Cu, Ni, Cd, and Zn with respect to P are compared to the ratios measured in the plankton samples and their regeneration products. The trace element/major element ratios ,in the residual plankton materials can be combined with estimates of the carrier fluxes to account for the transport of trace elements required to maintain their deep enrichment. A variety of processes determining the geochemical cycles of specific trace elements were identified. As much as 50% of the Cd, Ni, Mn, and P are rapidly released from plankton and recycled within the surface ocean. During this process, the metal/P ratio in the residual particles must decrease by 10-30% for Cd and increase by a factor of 2-4 for Ni and Cu to balance their deep enrichments. Although Mn is taken up and regenerated by plankton, the magnitude of this process is small with respect to other non-biogenic Mn fluxes and has very little influence on its dissolved distribution. The Ba content of all known surface carriers is insufficient to account for the deep enrichment of Ba. A secondary concentration process results in the formation of significant particulate Ba within the upper thermocline.

Description: Portions of the data in this research have been collected under the NSF grant DES 75-03826 and ONR grant N00014-80-C-0273. I have been supported for the last three years on an NSF National Needs Graduate Traineeship to the MIT-WHOI Joint Program. Ship time was generously provided by various principal investigators of the NSF Galapagos Hydrothermal research program and the NSF-IDOE MANOP program.

Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Philosophy and the Woods Hole Oceanographic Institution November 1980

Description: Suspended particulate matter was collected by sediment traps deployed in the Sargasso Sea (Site S2), the north equatorial Atlantic (Site E), the north equatorial Pacific (Site P), and the Panama Basin (STIE Site). Additional samples of suspended particles were obtained by in situ filtration at Site F., at the STIE Site, and in the Guatemala Basin. Concentrations of dissolved Th and Pa were determined by extraction onto manganese dioxide adsorbers at Site P, at a second site in the Sargasso Sea (Site D), at the STIE Site and in the Guatemala Basin. Sediment samples were obtained from cores taken near Sites E and P. Results have shown unequivocally that suspended particulate matter in the open ocean preferentially scavenges Th relative to Pa. This behavior could not have been predicted from the known physical chemistry of Th and Pa. Dissolved 230Th/231Pa activity ratios were 3-5 at Sites P and D and 3-8 at the STIE Site. In contrast, unsupported 230Th/231Pa ratios were 22-35 (average 29.7 for 7 samples) in sediment-trap samples from greater than 2000 m at Sites S2, E and P. Ratios were lower in particulate matter sampled at shallower depths. Particles filtered at 3600 m and 5000 m at Site E had ratios of 50 and 40. In contrast to the open ocean samples described above, samples collected by six sediment traps at depths of 667-3791 m in the Panama Basin had unsupported 230Th/231Pa ratios of 4-8, and the deepest samples had the lowest ratios. Fractionation of Th and Pa that was observed at the three open ocean sites either does not occur or occurs to a very limited extent in the Panama Basin. Particulate 230Th/231Pa ratios were negatively correlated with the concentration of suspended particles. However, variable scavenging rates, as indicated by variable particle concentration, do not completely control the ratio at which Th and Pa are scavenged from solution. Major biogenic and inorganic components of trapped material were found in approximately the same proportions in the STIE samples and in samples from Sites E and S2. Lower 230Th/231Pa ratios found in the STIE samples must therefore result from subtle changes in the chemical properties of the particles. Consideration of 230Th/23lPa ratios in several depositional environments indicates that no single factor controls the ratio at which Th and Pa are adsorbed from seawater. Fluxes of 210Th and 231Pa were less than their rates of production in the overlying water column in every trap at Sites S2, E, and P. In the Panama Basin, fluxes measured with the same traps were greater than or equal to their rates of production. These results are a strong indication that even extremely reactive elements such as Th and Pa are redistributed within the oceans. Redistribution occurs because variable scavenging rates in different environments set up horizontal concentration gradients. Horizontal mixing processes produce a net horizontal transport of Th and Pa from areas of 1ow scavenging rates to areas of high scavenging rates. Protactinium is redistributed to a greater extent than Th. Fluxes of 230Th can be used to set lower limits for horizonttal transport of Pa even when absolute trapping efficiencies of the sediment traps are not known. Less than 50% of the Pa produced at the open ocean sites is removed from the water column by scavenging to settling particles. The remainder is removed by horizontal transport to other environments. At Sites E and P, 230Th/231Pa ratios were identical in the deepest sediment trap sample and in surface sediments. However, 230Th/232Th and 231Pa/232Th ratios were 2.5 times higher in trapped particles than in surface sediments. The 230Th/232Th ratios were 5.5 times higher in particles filtered at 3600 m and 5000 m at Site E than in surface sediments. This observation is best explained by dissolution of most of the 230Th and 231Pa scavenged by settling particles during remineralization of labile biogenic phases. The behaviors of certain other radioisotopes were also studied. 232Th is present only in detrital mineral components of trapped material. Concentrations of 232Th in trapped particles correlate closely with Al and K, at ratios approaching that of average shale or crustal abundances at Site E and P and basalts at the STIE Site. High specifìc activities of 228Th and 239+240Pu were found in sediment trap samples throughout the water column at Sites E and P and in the Panama Basin. The dominant source of these isotopes is near the sea surface and also near the sea floor in the case of 228Th. Thus it appears that the bulk of the trapped material is recently derived from the sea surface where it incorporates these isotopes,with little loss during rapid transit through the water column. A bioauthigenic form of particulate uranium is produced at the sea surface and remineralized in the deep ocean along with its labile carrier phase(s). This flux of uranium to the deep ocean is 0.25-1.0 dpm/cm2103 years, which is insufficient to cause a measurable concentration gradient in the uranium distribution within the mixing time of the oceans. Increased concentrations and fluxes of particulate uranium were not found in the eastern equatorial North Pacific under areas of an intense oxygen minimum. Therefore, reduction of uranium to the tetravalent state with subsequent scavenging to settling particles in oxygen minima is not a mechanism removing uranium from the oceans.

Description: Financial support for parts of this work have come from many sources, including: National Science Foundation Grants OCE-7826318, OCE-7825724, and OCE-7727004; Department of Energy Contract EY-76-S-02-3566; a Cottrell Research Grant from the Research Corporation; the WHOI Ocean Industries Program; a fellowship from the WHOI Education Office, and the Paul Fye Fellowship

Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution June 1982

Description: The concentrations and isotopic compositions of helium have been measured in a number of mantle derived oceanic basalts. The goal of this research is to use the helium isotopic systematics to constrain the nature and origin of mantle heterogeneity in the oceanic mantle. Studies of helium partitioning in mid-ocean ridge basalt (MORB) glass, performed by crushing and melting in vacuo, show that a significant fraction of the helium resides within vesicles. Measured concentrations are therefore a function of original helium content, magmatic history, vesicle size and quantity, and grain size analyzed. The helium solubility inferred from the results is 3.7 x 10-4 cc STP/g-atm), which is significantly higher (by a factor of 5) than the enstatite value (Kirsten, 1968) most often used in the literature. Concentrations obtained from basaltic phenocrysts and glasses suggest that helium behaves as an incompatible element with respect to olivine, clinopyroxene, and plagioclase. Diffusion rates for helium in basaltic glass (in the temperature range 125-400˚C), determined using the method of stepwise heating, yielded an activation energy of 19.9 ± 1 Kcal/mole and 1nDo = -2.7 ± .6 (cgs units). Extrapolation of these results to ocean floor temperatures (0˚C) gives a diffusivity of 1.0 ± .6 x 10-17 cm2/sec, indicating that diffusion is an insignificant mechanism for helium loss from fresh basaltic glasses. The diffusion and partitioning studies suggest that these processes will not alter the helium isotopic ratios in basaltic melts. Therefore, the isotopic composition of the oceanic mantle can be inferred by extracting the helium from basaltic glasses and phenocrysts. A survey of the helium isotopic ratios in MORB glasses from all over the mid-ocean ridge system shows that there is considerable variation; the 3He/4He ratios range from 6.5 to 14.2 x atmospheric. The results from a number of oceanic island basalts show even more variability, with the 3He/4He ratios ranging from 5.0 x atmospheric (for alkali islands such as Gough and Tristan da Cunha) to 31.9 x atmospheric (for Loihi Seamount). The regional variability, and the correlations with 87Sr/86Sr can best be explained by the presence of three distinct reservoirs in the mantle which mix with one another. The three mantle source regions are believed to be 1) the depleted source for normal MORB (with 3He/4He -8.4 x atmospheric), presumed to be in the upper mantle; 2) an undepleted mantle reservoir with 3He/4He 〉 8.4 x atmospheric; and 3) a recycled oceanic crust reservoir with 3He/4He 〈 8.4 x atmospheric. A model for mantle structure that is consistent with the observations is proposed and discussed in light of the geophysical data. 3He concentrations for the different mantle reservoirs are inferred from the measurements, and suggest that the present-day 3He flux, and the 3He in MORB glasses, is ultimately derived from the lower mantle. Consideration of the 3He flux, available 3He/36Ar measurements, and the atmospheric 36Ar inventory, shows that present-day degassing rates are insufficient to generate the atmospheric argon. It is suggested that an episode of more rapid mant1e outgassing occurred in the past.

Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution January 1983

Description: Isotope studies of nitrogen and carbon were undertaken to investigate the fate of particulate organic matter (POM) during its residence in the water column and after deposition on the seafloor. The processes focused on were water-column transformations and sedimentary diagenesis. Sampling sites were chosen to provide POM subject to different specific mineralization processes (nitrification, denitrification, and sulfate reduction), different lengths of water column (duration of the mineralization process), and differences in the size of the organic-matter flux. The δl5N and δ13C of plankton, POM, and sediments from several oceanic sites were related to biological and hydrographic processes identified from nutrient, temperature, and salinity profiles. This was done to determine what effect these processes have on the δ15N of POM. Four stations were studied in the upwelling area off the coast of Peru and one station was studied in the Gulf of Maine. Important factors controlling the δ15N of plankton appear to be the concentration and δl5N of nitrate in the surface waters, and the relative zooplankton and phytoplankton abundances. Plankton from the Peru Upwelling Area are enriched in 15N as compared to plankton from other parts of the world's oceans where denitrification is absent. This enrichment may be due to the assimilation of 15N-enriched nitrate, produced by the selective reduction of 14N during denitrification. Zooplankton are 3 to 4% enriched in 15N as compared with phytoplankton. Production of 14N -enriched fecal pellets is suggested as a mechanism for this trophic enrichment. In the surface waters, the δl5N of POM is similar to that of plankton. In the Peru Upwelling Area, the δ15N of POM from the oxygen-deficient waters decreases with increasing depth. In the Gulf of Maine, below the euphotic zone in the oxic deep waters, the δ15N of POM increases with increasing depth. The difference in isotopic alteration may be due to the effect of different redox conditions on the mechanism and sequence by which specific organic nitrogen compounds, variably enriched in 15M, undergo degradation. Furthermore, bacterial growth on nitrogen-poor particles in the deep waters of the Peru Upwelling Area may contribute to the low δ15N of POM. In contrast to the large range in δ15N (-2 to +17%) of the POM, the range of δ15N in the sediments is small (+5 to +9%). Within a core, the average variation in δ15N was only 1.8%. Temporal variability in the δ15N of sedimenting POM and benthic activity appear to be important in determining the δ15N of the sediments. The large changes in POM concentration and isotope content at the sediment/water interface as compared with the more constant values found down-core, suggest that processes occuring at the sediment/water interface are critical, although bioturbation may also be important in determining the δ15N of oxic sediments. If diagenesis causes a significant loss of organic matter, profiles of organic carbon and nitrogen contents should show decreases with increasing depth and C/N ratios should increase with increasing depth (Reimers, 1981). Since none of the sedimentary profiles exhibited such trends, it is concluded that diagenesis was insufficient to erase the percent carbon, nitrogen and C/N ratio signatures generated by the POM flux and alterations at the sediment/water interface. Temporal variability in the δ15N of bottom-water POM may be caused by changes in deep-water currents which transport POM horizontally and to changes in bacterial and possibly other biological activity in the water column. This thesis work suggests that δ15N may be a useful tool in studying the geochemistry of POM in the marine environment. In addition, this research has shown that interpretation of the sedimentary 15N record must include consideration of isotopic alteration associated with bacterial remineralization of POM and benthic activity.

Description: Funds for this research were provided by the Massachusetts Institute of Technology / Woods Hole Oceanographic Institution Joint Program in Oceanography, the National Science Foundation under Grant No. OCE-8024442, and the Andrew W. Mellon Foundation through the Center for Coastal Research of the Woods Hole Oceanographic Institution.

Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution February 2006

Description: Between 9º-25º E on the ultraslow-spreading Southwest Indian Ridge lie two sharply contrasting supersegments. One 630 km long supersegment erupts N-MORB that is progressively enriched in incompatible element concentrations from east to west. The second 400 km long supersegment contains three separate volcanic centers erupting EMORB and connected by long amagmatic accretionary segments, where mantle is emplaced directly to the seafloor with only scattered N-MORB and E-MORB erupted. Rather than a major break in mantle composition at the discontinuity between the supersegments, this sharp contrast in geometry, physiography, and chemistry reflects “source” versus “process” dominated generation of basalt. Robust along-axis correlation of ridge characteristics (i.e. morphology, upwelling rate, lithospheric thickness), basalt chemistry, and crustal thickness (estimated from gravity) provides a unique opportunity to compare the influence of spreading geometry and rate on MORB generation. What had not been well established until now is the importance of melting processes rather than source at spreading rates 〈 20 mm/yr. Along the orthogonally spreading supersegment (14 mm/yr) moderate degrees of partial melting effectively sample the bulk mantle source, while on the obliquely spreading supersegment (7-14 mm/yr) suppression of mantle melting to low degrees means that the bulk source is not uniformly sampled, and thus “process” rather than “source” dominates melt chemistry.

Description: The main body of work consisting of major element, trace element, and isotopic data acquisition and interpretation (Chapter 2 & 3) was funded by H. Dick’s grant from the National Science Foundation-OCE 9907630. National Science Foundation-OCE 0137325 supported the U-series work described in Chapter 4. The published work of Chapter 5 was funded by National Science Foundation-EAR 9804891, NSF-OCE 9416620, and NSF-OCE 0096634.

Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution August, 1977

Description: In the highly productive coastal surface waters near Walvis Bay, methane is present in concentrations considerably above those which would be predicted from solubility equilibrium with the atmosphere. A one dimensional diffusive model and a one dimensional horizontal advection diffusion model were used to describe the methane distribution. Evaluation of the model fits to the data suggests that both advective supply of methane-rich coastal waters and in situ biological methane production are important sources for the mixed layer methane excess. The complexity of the hydrographic regime near Walvis Bay makes it impossible to make a quantitative estimate of the rate of methane production. In the less productive Murray-Wilkinson Basin in the Gulf of Maine, a mixed layer methane excess is also observed. Methane concentrations are closely correlated with hydrographic parameters and the source of methane at a middepth maximum appears to be the highly anoxic sediments in the adjoining Franklin Basin. Diffusion of methane from the middepth maximum is probably adequate to maintain the surface methane excess against loss across the air-sea interface. Coastal waters are frequently enriched in methane, and it has been shown that advective supply of these methane-rich waters may be a significant source of methane for the mixed layer near the coast. Thus the widespread occurrence of a methane maximum at the base of the mixed layer in the open ocean, coupled with surface waters typically 30-70% supersaturated with respect to solubility equilbrium, suggests that advective supply of methane might be an important methane source for the open ocean as well. However, a study of the western subtropical Atlantic shows that advective transport can probably supply only a fraction of the methane present in the maximum. Also the loss of methane across the air-sea interface was observed to be twenty times greater than the flux from the maximum. Thus in situ methane production must be very important to the open ocean methane distribution. A series of phytoplankton culture experiments demonstrated that cultures of both Coccolithus huxleyi and Thalassiosira pseudonana produce trace amounts of methane during logarithmic growth. (Because the cultures are highly oxygenated, anaerobic methane bacteria can be neglected as methane sources. However heterotrophic bacteria cannot be excluded as possible sources of methane to the cultures.) After three algal generations, the rate of methane increase closely parallels the growth curve suggesting that the methane is in fact coming from the algae. A methane production rate of 2 x 10-10 nmole methane/viable cell/hr was calculated from the data. This rate is three to four orders of magnitude slower than the rates of oxygen consumption and glutamate and glucose uptake measured by other workers. for algae and bacteria. The methane production rate calculated from the culture experiments is the correct order of magnitude to account for the methane production occurring in the open ocean. Methane is present in quite low concentrations in the deep ocean. By calculating water mass ages from GEOSECS and other data, it is possible to estimate methane consumption rates in the deep sea. Methane consumption is rapid at first (probably greater than 0.06 nmole/l/yr). At depth consumption appears extremely slow. This may be due to the fact that the methane concentrations in the deep sea are so low that methane oxidizing bacteria cannot use methane as a substrate, or due to reduced metabolic activity in the bacteria at the high pressures and low temperatures of the sea floor. Methane is present in very high concentrations in anoxic basins, indicating that methanogenic bacteria are active. However, near the anoxic-oxic interface in both the Black Sea and the Cariaco Trench a one dimensional advection diffusion model predicts that methane consumption is occurring in the anoxic zone. In the Black Sea the methane depletion may be indicative of the presence of rapid methane oxidation near the Bosporus overflow. However in the Cariaco Trench the validity of such an explanation is difficult to evaluate since the overflow process is so poorly understood. A box model for the Trench has been developed which incorporates time dependence and supply of chemical species to the water from the sediments at all depths in the Trench. This model can explain the silica and sulfide data quite well, but methane depletion near the interface, relative to the model predictions, still occurs. Thus either anaerobic methane oxidation or decreased methane production in the sediments must be hypothesized.

Description: Financial support was provided by an NSF Graduate Student Fellowship and a research fellowship from Woods Hole Oceanographic Institution. Field and laboratory work were supported by NSF Doctoral Dissertation Support Grant DES75-0273l, ONR Contract NOOOl4-74-C0262, NR 083-004. and the Woods Hole Oceanographic Institution Education Office.

Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution October, 1976

Description: Considerable geological and geophysical evidence now exists to support the hypothesis that seawater circulates through freshly intruded basalt at the mid-ocean ridges. As a consequence of this process, reactions between basalt and seawater take place at elevated temperatures. The mineralogy and chemistry of hydrothermally altered pillow basalts dredged from the Mid-Atlantic Ridge, and belonging to the greenschist facies, have been studied in order to determine the mineralogical changes that result from hyrdrothennal alteration, and to assess the chemical fluxes that result from these reactions in terms of their possible significance in elemental geochemical budgets as potential sources and sinks for elements in seawater. Where possible, pillow basalts were studied that showed varíous degrees of a1teration within a single rock. Such samples provide the best evidence that they have been affected by hydrothermal alteration, rather than regional burial metamorphism, and provide the most useful information for elemental flux calculatìons. During hydrothermal alteration, plagioclase is generally albitised, sometimes with the formation of epidote, and albite may be subsequently a1tered to chlorite. Plagioclase, in association with skeletal clinopyroxene, alters to chlorite and epidote. Olivine is pseudomorphed by chlorite, and clinopyroxene alters to actinolite. The glassy matrix alters to an intergrowth of actinolite and chlorite. Vein minerals irclude chlorite, actinolite, epidote, quartz, and sulphides. On the basis of their minaralogy, the samples may be subdivided into chlorite-rich (〉15% chlorite and 〈15% epidote) and epidote-rich (〉15% epidote and 〈15% chlorite) assemblages. The chlorite-rich assemblages lose CaO and gain MgO, while the epidote-rich samples show very little change in composition compared with their basalt precursor. The epidote-rich samples are more oxidised than their precursors, while the chlorite-rich rocks can be further suhdivided into those that maintain the same proportions of fetrous and ferric iron, and those that show an increase in ferrous iron due to the precipitation of pyrite. The major chemical changes that occur during hydrothermal alteration of pillow basalts are uptake of MgO and H2O, and loss of SiO2 and CaO. The concentrations of Na2O and K2O are apparently not greatly changed, although. they do show some variations in the core-to rim analyses. Consideration of the elemental fluxes in terms of steady-state geochemical mass balances indicates that hydrothermal alteration provides a sink for Mg, which is extremely important in solving the problem of apparent excess magnesium input to the oceans. The amount of calcium that is leached from the rock may be of significance in the geochemical budget of calcium. The concentration of silica in the circulating fluid is probably controlled by the solubility of quartz, and considerable redistribution of silica takes place within the basaltic pile. The changes in the redox conditions during hydrothermal alteration do not affect the present-day oxidation states of the atmosphere and hydrosphere. Trace element analyses indicate that copper and strontium are leached out of the rock and migrate in the circulating fluid, with local precipitation of Cu as sulphides in veins. Li, B, Mn, Ba, Ni and Co show sufficient variation in concentration and location within the altered basalts to indicate that some leaching does take place, and hence hydrothermal alteration of basalts could produce a metal-enriched solution, which may be important in the formation of metalliferous sediments at active mid-ocean ridges.

Description: Most of this work was supported by the National Science Foundation Grants OCE-74-2297l and DES-75-l6596.

Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution April, 1976

Description: The marine geochemical cycles of iron, copper, nickel, and cadmium were studied in order to provide a basis for oceanographic models for trace metals. Copper, nickel, and cadmium can be determined in a 100 ml seawater sample using cobalt pyrrolidine dithioacarbamate chelate coprecipitation and graphite atomizer atomic absorption spectrometry. Concentration ranges likely to be encountered and estimated (1δ) analytical precisions are copper, 1 to 6 nanomole/kg (±0.1); nickel, 3 to 12 nanomole/kg (±0.3); and cadmium, 0. 0 to 1.1 nanomole/kg (±0.1). The technique may be applied to freshwater samples with slight modification. A survey of several east coast U. S. estuaries established that an iron removal process occurs commonly when rivers mix with seawater. Laboratory mixing experiments using water from the Merrimack River (Mass.) and the Mullica River (New Jersey) demonstrated that rapid iron precipitation occurs as negatively-charged iron-organic colloids react with seawater cations and coagulate. This phenomenom was modeled using a synthetic, organic-stabilized colloidal suspension of goethite. The generality of the mechanism suggests that the world-average net river input of iron to the oceans is less than 1 μmole/kg of river water, an order of magnitude below previous estimates. Profiles of cadmium were obtained for 3 GEOSECS stations in the Pacific Ocean. Cadmium shows a consistent linear correlation with phosphate which demonstrates that cadmium is regenerated in a shallow cycle within the water column. The water column correlation is consistent with data on cadmium in marine organisms. Cadmium is enriched in upwelling regions which explains reports of cadmium enrichment in plankton from the Baja California upwelling region. Copper and nickel measurements have been made for three profiles from the Pacific Ocean. Observed copper concentrations range from 1 to 6 nanomole/kg; nickel varies from 3 to 12 nanomole/kg. Copper and nickel are removed from surface waters by uptake into organisms. As noted previously, nickel is regenerated partially in a shallow cycle (like P) and also in a deep cycle (like Ba). Copper is regenerated from biological debris at the bottom but is also scavenged from the mid and deep water column by an undetermined mechanism. The scavenging residence time is 1400 years. An estimate for the continental input of Ni, 7 nanomole/kg of river water, and Cu, 18 nanomole/kg of river water, was derived from measurements in the Amazon estuary. The oceanic residence times for nickel and copper are about 10,000 years. Evidence available on the uptake laws for trace metals by plankton suggests that a consistent relationship between the uptake law and the depth of regeneration may apply.

Description: Money in support of this research came at various times from the ONR, MIT UROP office, and a grant from the Doherty Foundation.