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  • 1
    Publication Date: 2017-09-20
    Description: 230Th and 231Pa are produced in sea water by radioactive decay of Uranium isotopes (234U, 235U). Both are particle reactive and are scavenged onto settling particles. As 230Th is more particle reactive than 231Pa, their distribution in the water column and activity ratio give information about particle fluxes and circulation patterns and –intensities. Both particle fluxes and deep water circulation may respond to climatic changes in the Arctic Ocean. This study discusses temporal changes in radionuclide concentration in the context of climate change. We compare results from 1991 [1] 2007 and 2015. We present results of dissolved 231Pa and 230Th activities of samples collected in the Nansen-, Amundsenand Makarov Basins during GEOTRACES sections GIPY11 (2007, 4 stations), GN04 (2015, 10 stations) aboard RV Polarstern. Our discussion of factors controlling the 230Th and 231Pa distribution is supported by, dissolved CFC, dissolved iron and particulate 230Th and 231Pa (3 stations) collected during GEOTRACES section GN04. We find that distributions and concentrations of dissolved 231Pa and 230Th in the central Arctic Ocean have changed significantly since 1991. Dissolved 231Pa concentrations in the Makarov basin decreased by half within less than 20 years. These changes are discussed in the context of environmental changes, such as declining sea ice cover and related increase of particle fluxes or changing deep water circulation. [1] Scholten, J. C., et al. (1995). Deep-Sea Research II 42: 1519- 1531
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , NonPeerReviewed
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  • 2
    Publication Date: 2018-03-26
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed
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  • 3
    Publication Date: 2016-03-21
    Description: Surface water circulation in the Arctic Ocean is known to vary with time in response to the Arctic Oscillation. Clear recent changes have been documented in the freshwater budget (Rabe et al., 2011) and in the penetration of 129I (Karcher et al., 2012). In the Atlantic Water Layer, the penetration of a warming anomaly, first observed 1990 in Fram Strait (Quadfasel et al., 1991) has been well documented. Much less is known of circulation changes at greater depths. We compare new 230Th data collected 2007 in the Eurasian and Makarov Basins up to the Alpha Ridge, and 2007-2009 in the southern Canada Basin with previous data from the Arctic Basins. We observe a decreased 230Th content of mid-depth waters (1000-2250m) at the Alpha Ridge compared to data of 1983, and increasing 230Th activities penetrating southward in the Beaufort Sea over the period 2007-2009 in the upper 1500m coincident with the arrival here of the Atlantic temperature anomaly. We propose that the low-particle flux and high-230Th isolated water mass in the Alpha Ridge region described by Bacon et al. (1989) has been ventilated, resulting in decreased activities in Upper Polar Deep Water here in 2007, and included in an anticyclonic circulation that carried it to the southern regions of the Beaufort Sea. Bacon, M.P, et al., 1989. Vertical profiles of some natural radionuclides over the Alpha Ridge, Arctic Ocean. Earth Planet. Sci. Lett. 95, 15-22. Karcher, M.J, et al., 2012. Recent changes of Arctic Ocean circulation revealed by 129 Iodine observations and modelling. Journal of Geophysical Research 117, C08007. Quadfasel, D., et al., 1991. Warming in the arctic. Nature 350, 385. Rabe, B., et al., 2011. An assessment of Arctic Ocean freshwater content changes from the 1990s to the 2006-2008 period. Deep Sea Research Part I: Oceanographic Research Papers 58, 173-185.
    Repository Name: EPIC Alfred Wegener Institut
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  • 4
    Publication Date: 2016-02-29
    Description: Abstract 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-� 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.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed
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  • 5
    Publication Date: 2018-08-13
    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.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed
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  • 6
    Publication Date: 2018-09-25
    Description: In this study we present dissolved and particulate 230Th and 232Th results, as well as particulate 234Th data, obtained as part of the GEOTRACES central Arctic Ocean sections GN04 (2015) and IPY11 (2007). Samples were analyzed following GEOTRACES methods, and compared to previous results from 1991. We observe significant decreases in 230Th concentrations in the deep waters of the Nansen Basin. We ascribe this non-steady state removal process to a variable release and scavenging of trace metals near an ultra-slow spreading ridge. This finding demonstrates that hydrothermal scavenging in the deep-sea may vary on annual time scales and highlights the importance of repeated GEOTRACES sections
    Repository Name: EPIC Alfred Wegener Institut
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  • 7
    Publication Date: 2018-08-09
    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.
    Keywords: GEOTRACES ; Trace elements ; Isotopes ; Electronic atlas ; IDP2017
    Repository Name: Woods Hole Open Access Server
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  • 8
    Publication Date: 2017-12-14
    Description: © The Author(s), 2016. This is the author's version of the work and is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Deep Sea Research Part I: Oceanographic Research Papers 113 (2016): 57-79, doi:10.1016/j.dsr.2016.03.008.
    Description: Thorium is a highly particle-reactive element that possesses different measurable radio-isotopes in seawater, with well-constrained production rates and very distinct half-lives. As a result, Th has emerged as a key tracer for the cycling of marine particles and of their chemical constituents, including particulate organic carbon. Here two different versions of a model of Th and particle cycling in the ocean are tested using an unprecedented data set from station GT11-22 of the U.S. GEOTRACES North Atlantic Section: (i) 21 228;230;234Th activities of dissolved and particulate fractions, (ii) 228Ra activities, (iii) 234;238U activities estimated from salinity data and an assumed 234U/238U ratio, and (iv) particle concentrations, below a depth of 125 m. The two model versions assume a single class of particles but rely on different assumptions about the rate parameters for sorption reactions and particle processes: a first version (V1) assumes vertically uniform parameters (a popular description), whereas the second (V2) does not. Both versions are tested by fitting to the GT11-22 data using generalized nonlinear least squares and by analyzing residuals normalized to the data errors. We find that model V2 displays a significantly better fit to the data than model V1. Thus, the mere allowance of vertical variations in the rate parameters can lead to a significantly better fit to the data, without the need to modify the structure or add any new processes to the model. To understand how the better fit is achieved we consider two parameters, K = k1=(k-1 + β-1) and K/P, where k1 is the adsorption rate constant, k-1 the desorption rate constant, β-1 the remineralization rate constant, and P the particle concentration. We find that the rate constant ratio K is large (≥0.2) in the upper 1000 m and decreases to a nearly uniform value of ca. 0.12 below 2000 m, implying that the specific rate at which Th attaches to particles relative to that at which it is released from particles is higher in the upper ocean than in the deep ocean. In contrast, K/P increases with depth below 500 m. The parameters K and K/P display significant positive and negative monotonic relationship with P, respectively, which is collectively consistent with a particle concentration effect.
    Description: We acknowledge the U.S. National Science Foundation for providing funding for this study (grant OCE-1232578) and for U.S. GEOTRACES North Atlantic section ship time, sampling, and data analysis.
    Description: 2017-03-31
    Keywords: GEOTRACES ; North Atlantic ; Thorium ; Particles ; Reversible Exchange ; Model ; Inverse Method
    Repository Name: Woods Hole Open Access Server
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  • 9
    Publication Date: 2018-07-06
    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
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  • 10
    Publication Date: 2017-01-04
    Description: Author Posting. © The Author(s), 2014. 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 Deep Sea Research Part II: Topical Studies in Oceanography 116 (2015): 29-41, doi:10.1016/j.dsr2.2014.07.007.
    Description: The long-lived uranium decay products 230Th and 231Pa are widely used as quantitative tracers of adsorption to sinking particles (scavenging) in the ocean by exploiting the principles of radioactive disequilibria. Because of their preservation in the Pleistocene sediment record and through largely untested assumptions about their chemical behavior in the water column, the two radionuclides have also been used as proxies for a variety of chemical fluxes in the past ocean. This includes the vertical flux of particulate matter to the seafloor, the lateral flux of insoluble elements to continental margins (boundary scavenging), and the southward flux of water out of the deep North Atlantic. In a section of unprecedented vertical and zonal resolution, the distributions of 230Th and 231Pa across the North Atlantic shed light on the marine cycling of these radionuclides and further inform their use as tracers of chemical flux. Enhanced scavenging intensities are observed in benthic layers of resuspended sediments on the eastern and western margins and in a hydrothermal plume emanating from the Mid-Atlantic Ridge. Boundary scavenging is clearly expressed in the water column along a transect between Mauritania and Cape Verde which is used to quantify a bias in sediment fluxes calculated using 230Th-normalization and to demonstrate enhanced 231Pa removal from the deep North Atlantic by this mechanism. The influence of deep ocean ventilation that leads to the southward export of 231Pa is apparent. The 231Pa/230Th ratio, however, predominantly reflects spatial variability in scavenging intensity, complicating its applicability as a proxy for the Atlantic meridional overturning circulation.
    Description: Funding for ship time, sampling operations, and hydrographic 552 data was provided by the U. S. National Science Foundation to the US GEOTRACES North Atlantic Transect Management team of W. Jenkins (OCE-0926423), E. Boyle (OCE-0926204), and G. Cutter (OCE-0926092). Radionuclide studies were supported by NSF (OCE-0927064 to L-DEO, OCE-0926860 to WHOI, OCE-0927757 to URI, and OCE-0927754 to UMN). LFR was also supported by Marie Curie Reintegration Grant and the European Research Council.
    Keywords: GEOTRACES ; North Atlantic Ocean ; Thorium ; Protactinium ; Scavenging ; Ventilation
    Repository Name: Woods Hole Open Access Server
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