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  • 2005-2009  (3)
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  • 1
    Publication Date: 2022-05-25
    Description: Author Posting. © The Authors, 2006. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Marine Chemistry 100 (2006): 213-233, doi:10.1016/j.marchem.2005.10.013.
    Description: Thorium-234 is increasingly used as a tracer of ocean particle flux, primarily as a means to estimate particulate organic carbon export from the surface ocean. This requires determination of both the 234Th activity distribution (in order to calculate 234Th fluxes) and an estimate of the C/234Th ratio on sinking particles, to empirically derive C fluxes. In reviewing C/234Th variability, results obtained using a single sampling method show the most predictable behavior. For example, in most studies that employ in situ pumps to collect size fractionated particles, C/234Th either increases or is relatively invariant with increasing particle size (size classes 〉1 to 100’s μm). Observations also suggest that C/234Th decreases with depth and can vary significantly between regions (highest in blooms of large diatoms and highly productive coastal settings). Comparisons of C fluxes derived from 234Th show good agreement with independent estimates of C flux, including mass balances of C and nutrients over appropriate space and time scales (within factors of 2-3). We recommend sampling for C/234Th from a standard depth of 100 m, or at least one depth below the mixed layer using either large volume size fractionated filtration to capture the rarer large particles, or a sediment trap or other device to collect sinking particles. We also recommend collection of multiple 234Th profiles and C/234Th samples during the course of longer observation periods to better sample temporal variations in both 234Th flux and the characteristic of sinking particles. We are encouraged by new technologies which are optimized to more reliably sample truly settling particles, and expect the utility of this tracer to increase, not just for upper ocean C fluxes but for other elements and processes deeper in the water column.
    Description: Individuals and science efforts discussed herein were supported by many national science programs, including the U.S. National Science Foundation and U.S. Department of Energy. S.F. and J.C.M. acknowledge the support provided to the International Atomic Energy Agency (IAEA) Marine Environment Laboratory by the Government of the Principality of Monaco. T.T. acknowledges support from the Australian Antarctic Science Program. K.B. was supported in part by a WHOI Ocean Life Institute Fellowship.
    Repository Name: Woods Hole Open Access Server
    Type: Preprint
    Format: 640962 bytes
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  • 2
    Publication Date: 2022-05-26
    Description: Author Posting. © Sears Foundation for Marine Research, 2007. This article is posted here by permission of Sears Foundation for Marine Research for personal use, not for redistribution. The definitive version was published in Journal of Marine Research 65 (2007): 345–416, doi: 10.1357/002224007781567621
    Description: This review provides an assessment of sediment trap accuracy issues by gathering data to address trap hydrodynamics, the problem of zooplankton "swimmers," and the solubilization of material after collection. For each topic, the problem is identified, its magnitude and causes reviewed using selected examples, and an update on methods to correct for the potential bias or minimize the problem using new technologies is presented. To minimize hydrodynamic biases due to flow over the trap mouth, the use of neutrally buoyant sediment traps is encouraged. The influence of swimmers is best minimized using traps that limit zooplankton access to the sample collection chamber. New data on the impact of different swimmer removal protocols at the US time-series sites HOT and BATS are compared and shown to be important. Recent data on solubilization are compiled and assessed suggesting selective losses from sinking particles to the trap supernatant after collection, which may alter both fluxes and ratios of elements in long term and typically deeper trap deployments. Different methods are needed to assess shallow and short- term trap solubilization effects, but thus far new incubation experiments suggest these impacts to be small for most elements. A discussion of trap calibration methods reviews independent assessments of flux, including elemental budgets, particle abundance and flux modeling, and emphasizes the utility of U-Th radionuclide calibration methods.
    Description: WG meetings and production of this report was partially supported by the U.S. National Science Foundation via grants to the SCOR. Individuals and science efforts discussed herein were supported by many national science programs, including the U.S. National Science Foundation, Swedish Research Council, the International Atomic Energy Agency through its support of the Marine Environmental Laboratory that also receives support from the Government of the Principality of Monaco, and the Australian Antarctic Science Program. K.B. was supported in part by a WHOI Ocean Life Institute Fellowship.
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 3
    Publication Date: 2022-05-26
    Description: Author Posting. © The Authors, 2005. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Marine Chemistry 100 (2006): 190-212, doi:10.1016/j.marchem.2005.10.012.
    Description: The short-lived thorium isotope 234Th (half-life 24.1 days) has been used as a tracer for a variety of transport processes in aquatic systems. Its use as a tracer of oceanic export via sinking particles has stimulated a rapidly increasing number of studies that require analyses of 234Th in both marine and freshwater systems. The original 234Th method is labour intensive. Thus, there has been a quest for simpler techniques that require smaller sample volumes. Here, we review current methodologies in the collection and analysis of 234Th from the water column, discuss their individual strengths and weaknesses, and provide an outlook on possible further improvements and future challenges. Also included in this review are recommendations on calibration procedures and the production of standard reference materials as well as a flow chart designed to help researchers find the most appropriate 234Th analytical technique for a specific aquatic regime and known sampling constraints.
    Description: Individuals and science efforts discussed herein were supported by many national science programs, including the U.S. National Science Foundation and U.S. Department of Energy and the Ministerio de Educación y Ciencia of Spain. The Agency is grateful for the support provided to its Marine Environment Laboratory by the Government of the Principality of Monaco".
    Keywords: Th-234 ; Methodology ; Sampling ; Analytical techniques, ; Export
    Repository Name: Woods Hole Open Access Server
    Type: Preprint
    Format: 327450 bytes
    Format: 289061 bytes
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