ALBERT

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: Author Posting. © The Author(s), 2015. This is the author's version of the work. It is posted here by permission of Elsevier for personal use, not for redistribution. The definitive version was published in Marine Chemistry 170 (2015): 49-60, doi:10.1016/j.marchem.2015.01.006.

Description: The natural radionuclides 231Pa and 230Th are incorporated into the marine sediment record by scavenging, or adsorption to various particle types, via chemical reactions that are not fully understood. Because these isotopes have potential value in tracing several oceanographic processes, we investigate the nature of scavenging using trans-Atlantic measurements of dissolved (〈0.45 μm) and particulate (0.8-51 μm) 231Pa and 230Th, together with major particle composition. We find widespread impact of intense scavenging by authigenic Fe/Mn (hydr)oxides, in the form of hydrothermal particles emanating from the Mid-Atlantic ridge and particles resuspended from reducing conditions near the seafloor off the coast of West Africa. Biogenic opal was not found to be a significant scavenging phase for either element in this sample set, essentially because of its low abundance and small dynamic range at the studied sites. Distribution coefficients in shallow (〈 200 m) depths are anomalously low which suggests either the unexpected result of a low scavenging intensity for organic matter or that, in water masses containing abundant organic-rich particles, a greater percentage of radionuclides exist in the colloidal or complexed phase. In addition to particle concentration, the oceanic distribution of particle types likely plays a significant role in the ultimate distribution of sedimentary 230Th and 231Pa.

Description: Cruise management for GA03 was funded by the U. S. National Science Foundation to W. Jenkins (OCE-0926423), E. Boyle (OCE-0926204), and G. Cutter (OCE-0926092). Radionuclide studies were supported by NSF (OCE-0927064 to LDEO, OCE-0926860 to WHOI, OCE- 0927757 to URI, and OCE-0927754 to UMN). Additional support came from the European Research Council (278705) to LFR and the Ford Foundation Predoctoral Fellowship to SMV. Particle studies were supported by NSF OCE-0963026 to PJL.

Description: © The Author(s), 2018. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Chemical Geology 493 (2018): 210-223, doi:10.1016/j.chemgeo.2018.05.040.

Description: The GEOTRACES Intermediate Data Product 2017 (IDP2017) is the second publicly available data product of the international GEOTRACES programme, and contains data measured and quality controlled before the end of 2016. The IDP2017 includes data from the Atlantic, Pacific, Arctic, Southern and Indian oceans, with about twice the data volume of the previous IDP2014. For the first time, the IDP2017 contains data for a large suite of biogeochemical parameters as well as aerosol and rain data characterising atmospheric trace element and isotope (TEI) sources. The TEI data in the IDP2017 are quality controlled by careful assessment of intercalibration results and multi-laboratory data comparisons at crossover stations. The IDP2017 consists of two parts: (1) a compilation of digital data for more than 450 TEIs as well as standard hydrographic parameters, and (2) the eGEOTRACES Electronic Atlas providing an on-line atlas that includes more than 590 section plots and 130 animated 3D scenes. The digital data are provided in several formats, including ASCII, Excel spreadsheet, netCDF, and Ocean Data View collection. Users can download the full data packages or make their own custom selections with a new on-line data extraction service. In addition to the actual data values, the IDP2017 also contains data quality flags and 1-σ data error values where available. Quality flags and error values are useful for data filtering and for statistical analysis. Metadata about data originators, analytical methods and original publications related to the data are linked in an easily accessible way. The eGEOTRACES Electronic Atlas is the visual representation of the IDP2017 as section plots and rotating 3D scenes. The basin-wide 3D scenes combine data from many cruises and provide quick overviews of large-scale tracer distributions. These 3D scenes provide geographical and bathymetric context that is crucial for the interpretation and assessment of tracer plumes near ocean margins or along ridges. The IDP2017 is the result of a truly international effort involving 326 researchers from 25 countries. This publication provides the critical reference for unpublished data, as well as for studies that make use of a large cross-section of data from the IDP2017. This article is part of a special issue entitled: Conway GEOTRACES - edited by Tim M. Conway, Tristan Horner, Yves Plancherel, and Aridane G. González.

Description: We gratefully acknowledge financial support by the Scientific Committee on Oceanic Research (SCOR) through grants from the U.S. National Science Foundation, including grants OCE-0608600, OCE-0938349, OCE-1243377, and OCE-1546580. Financial support was also provided by the UK Natural Environment Research Council (NERC), the Ministry of Earth Science of India, the Centre National de Recherche Scientifique, l'Université Paul Sabatier de Toulouse, the Observatoire Midi-Pyrénées Toulouse, the Universitat Autònoma de Barcelona, the Kiel Excellence Cluster The Future Ocean, the Swedish Museum of Natural History, The University of Tokyo, The University of British Columbia, The Royal Netherlands Institute for Sea Research, the GEOMAR-Helmholtz Centre for Ocean Research Kiel, and the Alfred Wegener Institute.

Description: © The Author(s), 2015. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Marine Chemistry 177 (2015): 1-8, doi:10.1016/j.marchem.2015.04.005.

Description: The GEOTRACES Intermediate Data Product 2014 (IDP2014) is the first publicly available data product of the international GEOTRACES programme, and contains data measured and quality controlled before the end of 2013. It consists of two parts: (1) a compilation of digital data for more than 200 trace elements and isotopes (TEIs) as well as classical hydrographic parameters, and (2) the eGEOTRACES Electronic Atlas providing a strongly inter-linked on-line atlas including more than 300 section plots and 90 animated 3D scenes. The IDP2014 covers the Atlantic, Arctic, and Indian oceans, exhibiting highest data density in the Atlantic. The TEI data in the IDP2014 are quality controlled by careful assessment of intercalibration results and multi-laboratory data comparisons at cross-over stations. The digital data are provided in several formats, including ASCII spreadsheet, Excel spreadsheet, netCDF, and Ocean Data View collection. In addition to the actual data values the IDP2014 also contains data quality flags and 1-σ data error values where available. Quality flags and error values are useful for data filtering. Metadata about data originators, analytical methods and original publications related to the data are linked to the data in an easily accessible way. The eGEOTRACES Electronic Atlas is the visual representation of the IDP2014 data providing section plots and a new kind of animated 3D scenes. The basin-wide 3D scenes allow for viewing of data from many cruises at the same time, thereby providing quick overviews of large-scale tracer distributions. In addition, the 3D scenes provide geographical and bathymetric context that is crucial for the interpretation and assessment of observed tracer plumes, as well as for making inferences about controlling processes.

Description: We gratefully acknowledge financial support by the Scientific Committee on Oceanic Research (SCOR) through grants from the U.S. National Science Foundation, including grants OCE-0608600, OCE-0938349, and OCE-1243377. Financial support was also provided by the UK Natural Environment Research Council, the Ministry of Earth Science of India, the Centre National de Recherche Scientifique, l'Université Paul Sabatier de Toulouse, the Observatoire Midi-Pyrénées Toulouse, the Universitat Autònoma de Barcelona, the Kiel Excellence Cluster The Future Ocean, the Swedish Museum of Natural History, The University of Tokyo, The University of British Columbia, The Royal Netherlands Institute for Sea Research, the GEOMAR-Helmholtz Centre for Ocean Research Kiel, and the Alfred Wegener Institute.