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  • Adsorption  (1)
  • Aggregation
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  • 1
    Publication Date: 2022-05-25
    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.
    Keywords: GEOTRACES ; Suspended particulate matter ; Adsorption ; Radioactive tracers ; Trace elements
    Repository Name: Woods Hole Open Access Server
    Type: Preprint
    Format: application/pdf
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  • 2
    Publication Date: 2022-05-25
    Description: © The Author(s), 2014. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Deep Sea Research Part II: Topical Studies in Oceanography 116 (2015): 283-302, doi:10.1016/j.dsr2.2014.11.019.
    Description: In this paper, we present, describe, and model the first size-fractionated (0.8–51 µm; 〉51 µm) water-column particulate trace metal results from the US GEOTRACES North Atlantic Zonal Transect in situ pumping survey, with a focus on the lithogenic tracer elements Al, Fe and Ti. This examination of basin-wide, full-depth distributions of particulate elements elucidates many inputs and processes—some for bulk lithogenic material, others element-specific—which are presented via concentration distributions, elemental ratios, size-fractionation dynamics, and steady-state inventories. Key lithogenic inputs from African dust, North American boundary interactions, the Mediterranean outflow, hydrothermal systems, and benthic nepheloid layers are described. Using the refractory lithogenic tracer Ti, we develop a 1-D model for lithogenic particle distributions and test the sensitivities of size-fractionated open-ocean particulate Ti profiles to biotically driven aggregation, disaggregation rates, vertical sinking speeds, and dust input rates. We discuss applications of this lithogenic model to particle cycling in general, and to POC cycling specifically.
    Description: International and US GEOTRACES Offices (OCE-0850963 and OCE-1129603), and fellowship assistance from the Williams College Tyng Fellowship and MIT/WHOI Academic Programs Office to DCO.
    Keywords: Marine particles ; Lithogenic ; Particulate trace metals ; Aluminum ; Iron ; Titanium ; GEOTRACES ; Aeolian dust ; Aggregation ; Disaggregation ; Sinking speed ; Scavenging
    Repository Name: Woods Hole Open Access Server
    Type: Article
    Format: application/pdf
    Format: application/msword
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