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  • 2005-2009  (4)
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  • 1
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    (Table 2) 230Th, 230Th xs and 232Th concentrations in dissolved, particulate and total (dissolved+small particles) for all KEOPS stations, Marion Dufresne cruise MD145 (2008)
    PANGAEA
    In:  Supplement to: Venchiarutti, Célia; Jeandel, Catherine; Roy-Barman, Matthieu (2008): Particle dynamics study in the wake of Kerguelen Island using thorium isotopes. Deep Sea Research Part I: Oceanographic Research Papers, 55(10), 1343-1363, https://doi.org/10.1016/j.dsr.2008.05.015
    Details
    Publication Date: 2023-10-28
    Description: In the context of the KErguelen Ocean and Plateau compared Study (KEOPS, 19 January-13 February 2005), particle dynamics were investigated using thorium isotope measurements over and off the Kerguelen plateau. Dissolved and particulate 230Th and 232Th samples were collected at nine stations. Dissolved excess 230Th concentrations (230Thxs) vary from 0.5 to 20.8 fg/kg and particulate 230Thxs concentrations from 0.1 to 10.0 fg/kg. Dissolved and particulate 232Th concentration ranges are 16.8-450.2 pg/kg and 3.8-502.8 pg/kg, respectively. The 230Thxs concentrations increase linearly with depth down to the bottom at most of the plateau stations and down to 1000 m at the off-plateau stations. This linear trend is observed down to the bottom (1550 m) at Kerfix, the open-ocean "upstream" station located west of the Kerguelen plateau. A simple reversible scavenging model applied to these data allowed the estimation of adsorption rate constant (k1~=0.2-0.8 per year), desorption rate constant (k-1~=1-8 per year) and partition coefficients (average K=0.16±0.07). Calculated particle settling velocities S deduced from this simple model are ca. 500 m/year at most of the plateau stations and 800 m/year at all the off-plateau stations. The plateau settling velocities are relatively low for such a productive site, compared to the surrounding HNLC areas. The difference might reflect the fact that lateral advection is neglected in this model. Taking this advection into account allows the reconstruction of the observed 230Thxs linear distributions, but only if faster settling velocities are considered. This implies that the 1D model strongly underestimates the settling velocity of the particles. In the deep layers, the occurrence of intense boundary scavenging along the escarpment due to bottom sediment re-suspension and interaction with a nepheloid layer, yielding a removal of ~50% of the Th stock along the northwestward transect, is suggested.
    Keywords: CTD/Rosette; CTD-RO; Date/Time of event; DEPTH, water; Event label; Indian Ocean; Latitude of event; Longitude of event; Marion Dufresne (1995); MD145; MD145_A11; MD145_A3-3; MD145_A3-4; MD145_B1; MD145_B11; MD145_B5; MD145_C1; MD145_C11; MD145_C5; MD145_Kerfix; OISO_12, KEOPS,35MF20050113; Priority Programme 1158 Antarctic Research with Comparable Investigations in Arctic Sea Ice Areas; SPP1158; Thorium-230; Thorium-230, dissolved; Thorium-230, dissolved, standard deviation; Thorium-230, particulate; Thorium-230, particulate, standard deviation; Thorium-230, standard deviation; Thorium-230 excess; Thorium-230 excess, dissolved; Thorium-230 excess, dissolved, standard deviation; Thorium-230 excess, particulate; Thorium-230 excess, particulate, standard deviation; Thorium-230 excess, standard deviation; Thorium-232; Thorium-232, dissolved; Thorium-232, dissolved, standard deviation; Thorium-232, particulate; Thorium-232, particulate, standard deviation; Thorium-232, standard deviation
    Type: Dataset
    Format: text/tab-separated-values, 767 data points
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    DATA PANGAEA
  • 2
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    234Th sorption and export models in the water column: A review (2006)
    Elsevier
    Details
    Publication Date: 2006-08-01
    Print ISSN: 0304-4203
    Electronic ISSN: 1872-7581
    Topics: Geosciences
    Published by Elsevier
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    PAPER CURRENT
  • 3
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    Th-234 sorption and export models in the water column : a review (2006)
    Details
    Publication Date: 2022-05-25
    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): 234-249, doi:10.1016/j.marchem.2005.10.014.
    Description: Over the past few decades, the radioisotope pair of 238U/234Th has been widely and increasingly used to describe particle dynamics and particle export fluxes in a variety of aquatic systems. The present paper is one of five review articles dedicated to 234Th. It is focused on the models associated with 234Th whereas the companion papers (same issue) are focused on present and future methodologies and techniques (Rutgers van der Loeff et al.), C/234Th ratios (Buesseler et al.), 234Th speciation (Santschi et al.) and present and future applications of 234Th (Waples et al.). In this paper, we review current 234Th scavenging models and discuss the relative importance of the non steady state and physical terms associated with the most commonly used model to estimate 234Th flux. Based on this discussion we recommend that for future work the use of models should be accompanied by a discussion of the effect that model and data uncertainty have on the model results. We also suggest that future field work incorporate repeat occupations of sample sites on time scales of 1-4 weeks in order to evaluate steady state versus non steady state estimates of 234Th export, especially during high flux events (〉 ca. 800 dpm m-2 d-1). Finally, knowledge of the physical oceanography of the study area is essential, particularly in ocean margins and in areas of established upwelling (e.g. Equatorial Pacific). These suggestions will greatly enhance the application of 234Th as a tracer of particle dynamics and flux in more complicated regimes.
    Description: This paper grew out of discussion held at the “Future Applications of 234Th in Aquatic Systems” workshop held at Woods Hole Oceanographic Institution in August, 2004 (see: http://www.geol.sc.edu/cbnelson/Thmeeting/). We are grateful to the US National Science Foundation Chemical Oceanography Program (OCE 0354757) for its support of the workshop. We thank the US National Science Foundation, the National Oceanic and Atmospheric Administration and the Belgian Science Policy for their support of many of the field and modeling efforts described in this paper.
    Keywords: Th-234 ; Model ; Scavenging ; Export ; Particle dynamics
    Repository Name: Woods Hole Open Access Server
    Type: Preprint
    Format: 2096326 bytes
    Format: application/pdf
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    PAPER (OA)
  • 4
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    Thorium speciation in seawater (2006)
    Details
    Publication Date: 2022-05-26
    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): 250-268, doi:10.1016/j.marchem.2005.10.024.
    Description: Since the 1960’s, thorium isotopes occupy a special place in the oceanographer’s toolbox as tracers for determining rates and mechanisms of oceanic scavenging, particle dynamics, and carbon fluxes. Due to their unique and constant production rates from soluble parent nuclides of uranium and radium, their disequilibrium can be used to calculate rates and time scales of sinking particles. In addition, by ratio-ing particulate 234Th (as well, in principle, other Thnuclides) to carbon (and other elements), and linking this ratio to the parent-daughter disequilibrium in the water column, it is possible to calculate fluxes of carbon and other elements. Most of these applications are possible with little knowledge of the dissolved chemical properties of thorium, other than its oxidation state (IV) and tendency to strongly sorb to surfaces, i.e., its “particle- or surface-activity”. However, the use of any tracer is hindered by a lack of knowledge of its chemical properties. Recent observations in the variability of carbon to 234Th ratios in different particle types, as well as of associations of Th(IV) with various marine organic biomolecules has led to the need for a review of current knowledge and what future endeavors should be taken to understand the marine chemistry of thorium.
    Description: The writing of this paper was supported, in parts by NSF (OCE-0351559; OCE-0350758, and OCE 0354757).
    Keywords: Thorium ; Speciation ; Seawater ; Colloids ; Exopolymeric substances ; Transparent exopolymeric particles ; Amphiphiles ; Biosurfactant ligand
    Repository Name: Woods Hole Open Access Server
    Type: Preprint
    Format: 1607662 bytes
    Format: application/pdf
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