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  • 1
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    Ongoing increase in Eastern Tropical North Pacific denitrification as interpreted through the Santa Barbara Basin sedimentary δ15N record (2019)
    Wiley
    Details
    Publication Date: 2019
    Description: Abstract Decades of observations show that the world's oceans have been losing oxygen, with far‐reaching consequences for ecosystems and biogeochemical cycling. To reconstruct oxygenation beyond the limited scope of instrumental records, proxy records are needed, such as sedimentary δ15N. We combine two δ15N records from the Santa Barbara Basin (SBB), a 24‐year long, biweekly sediment trap time series, and a 114‐year, high‐resolution sediment core together spanning the years 1892‐2017. These records allow for the examination of δ15N variability on seasonal to centennial timescales. Seasonal variability in SBB δ15N is consistent in timing with the poleward advection of a high δ15N signal from the Eastern Tropical North Pacific in the summer and fall. Strong El Niño events result in variable δ15N signatures, reflective of local rainfall, and neither the Pacific Decadal Oscillation nor North Pacific Gyre Oscillation impose strong controls on bulk sedimentary δ15N. Seasonal and interannual variability in sediment trap δ13Corg is consistent with local productivity as a driver, however this signal is not retained in the sediment core. The time series from the sediment trap and core show that bulk sedimentary δ15N in SBB has now exceeded that measured for the past 2000 years. We hypothesize that the change in δ15N reflects the increasing influence of denitrified waters from the Eastern Tropical North Pacific and ongoing deoxygenation of the Eastern Pacific. When juxtaposed with other regional δ15N records our results further suggest that SBB is uniquely situated to record long‐term change in the Eastern Tropical North Pacific.
    Print ISSN: 0883-8305
    Electronic ISSN: 2572-4525
    Topics: Geosciences
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 2
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    Marine polyphosphate: a key player in geologic phosphorus sequestration (2008)
    American Association for the Advancement of Science (AAAS)
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    Publication Date: 2008-05-03
    Description: The in situ or authigenic formation of calcium phosphate minerals in marine sediments is a major sink for the vital nutrient phosphorus. However, because typical sediment chemistry is not kinetically conducive to the precipitation of these minerals, the mechanism behind their formation has remained a fundamental mystery. Here, we present evidence from high-sensitivity x-ray and electrodialysis techniques to describe a mechanism by which abundant diatom-derived polyphosphates play a critical role in the formation of calcium phosphate minerals in marine sediments. This mechanism can explain the puzzlingly dispersed distribution of calcium phosphate minerals observed in marine sediments worldwide.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Diaz, Julia -- Ingall, Ellery -- Benitez-Nelson, Claudia -- Paterson, David -- de Jonge, Martin D -- McNulty, Ian -- Brandes, Jay A -- New York, N.Y. -- Science. 2008 May 2;320(5876):652-5. doi: 10.1126/science.1151751.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, GA 30332-0340, USA.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/18451299" target="_blank"〉PubMed〈/a〉
    Keywords: Apatites/chemistry ; Biomass ; Diatoms/*chemistry ; Geologic Sediments ; Microscopy, Fluorescence ; Pacific Ocean ; Phosphorus/*chemistry ; Polyphosphates/*chemistry ; Spectrometry, Fluorescence
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 3
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    Massive phytoplankton blooms under Arctic sea ice (2012)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2012-06-09
    Description: Phytoplankton blooms over Arctic Ocean continental shelves are thought to be restricted to waters free of sea ice. Here, we document a massive phytoplankton bloom beneath fully consolidated pack ice far from the ice edge in the Chukchi Sea, where light transmission has increased in recent decades because of thinning ice cover and proliferation of melt ponds. The bloom was characterized by high diatom biomass and rates of growth and primary production. Evidence suggests that under-ice phytoplankton blooms may be more widespread over nutrient-rich Arctic continental shelves and that satellite-based estimates of annual primary production in these waters may be underestimated by up to 10-fold.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Arrigo, Kevin R -- Perovich, Donald K -- Pickart, Robert S -- Brown, Zachary W -- van Dijken, Gert L -- Lowry, Kate E -- Mills, Matthew M -- Palmer, Molly A -- Balch, William M -- Bahr, Frank -- Bates, Nicholas R -- Benitez-Nelson, Claudia -- Bowler, Bruce -- Brownlee, Emily -- Ehn, Jens K -- Frey, Karen E -- Garley, Rebecca -- Laney, Samuel R -- Lubelczyk, Laura -- Mathis, Jeremy -- Matsuoka, Atsushi -- Mitchell, B Greg -- Moore, G W K -- Ortega-Retuerta, Eva -- Pal, Sharmila -- Polashenski, Chris M -- Reynolds, Rick A -- Schieber, Brian -- Sosik, Heidi M -- Stephens, Michael -- Swift, James H -- New York, N.Y. -- Science. 2012 Jun 15;336(6087):1408. doi: 10.1126/science.1215065. Epub 2012 Jun 7.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Environmental Earth System Science, Stanford University, Stanford, CA 94305, USA. arrigo@stanford.edu〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/22678359" target="_blank"〉PubMed〈/a〉
    Keywords: Arctic Regions ; Biomass ; Diatoms/growth & development ; *Eutrophication ; *Ice Cover ; Light ; Nitrates/analysis ; Oceans and Seas ; Photosynthesis ; Photosystem II Protein Complex/analysis ; Phytoplankton/*growth & development ; Seawater/chemistry
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 4
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    Ocean chemistry. The missing link in oceanic phosphorus cycling? (2015)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2015-05-16
    Description: 〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Benitez-Nelson, Claudia -- New York, N.Y. -- Science. 2015 May 15;348(6236):759-60. doi: 10.1126/science.aab2801.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Earth and Ocean Sciences and Marine Science Program, University of South Carolina, Columbia, SC 29208, USA. cbnelson@geol.sc.ed.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/25977538" target="_blank"〉PubMed〈/a〉
    Keywords: Cyanobacteria/*metabolism ; *Nitrogen Fixation ; Phosphates/*metabolism ; Phosphorus/*metabolism ; Plankton/*metabolism ; Seawater/*microbiology
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 5
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    Dr. Robert C. Thunell: A 40‐Year Career of Outstanding Science, Service, and Education in Paleoceanography and Paleoclimatology (2019)
    Wiley
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    Publication Date: 2019
    Description: This special issue of Paleoceanography and Paleoclimatology is dedicated to Dr. Robert C. Thunell for his many contributions to the fields of marine geology, micropaleontology, chemical oceanography, and climate system science.Bob was a highly respected researcher and educator whose commitment to service impacted many throughout the community. His scientific contributions resulted in advances that substantively influenced our understanding of how the Earth has changed throughout time and his science, leadership and mentorship has created ripples that will continue to be influential in the years to come. Bob's outstanding 40+‐year career included more than 45 research grants (〉$13 million), which he used to support a diverse and numerous pool of 50 graduate students, postdoctoral scientists, and undergraduates (Appendix A).
    Print ISSN: 0883-8305
    Electronic ISSN: 2572-4525
    Topics: Geosciences
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 6
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    Latitudinal distributions of particulate carbon export across the North Western Atlantic Ocean. (2017)
    PERGAMON-ELSEVIER SCIENCE LTD
    In:  EPIC3Deep-Sea Research Part I-Oceanographic Research Papers, PERGAMON-ELSEVIER SCIENCE LTD, 129, pp. 116-130, ISSN: 0967-0637
    Details
    Publication Date: 2017-11-06
    Description: 234Th-derived carbon export fluxes were measured in the Atlantic Ocean under the GEOTRACES framework to evaluate basin-scale export variability. Here, we present the results from the northern half of the GA02 transect, spanning from the equator to 64°N. As a result of limited site-specific C/234Th ratio measurements, we further combined our data with previous work to develop a basin wide C/234Th ratio depth curve. While the magnitude of organic carbon fluxes varied depending on the C/234Th ratio used, latitudinal trends were similar, with sizeable and variable organic carbon export fluxes occurring at high latitudes and low to negligible fluxes occurring in oligotrophic waters. Our results agree with previous studies, except at the boundaries between domains, where fluxes were relatively enhanced. Three different models were used to obtain satellite-derived net primary production (NPP). In general, NPP estimates had similar trends along the transect, but there were significant differences in the absolute magnitude depending on the model used. Nevertheless, organic carbon export efficiencies were generally 〈 25%, with the exception of a few stations located in the transition area between the riverine and the oligotrophic domains and between the oligotrophic and the temperate domains. Satellite-derived organic carbon export models from Dunne et al. (2005) (D05), Laws et al. (2011) (L11) and Henson et al. (2011) (H11) were also compared to our 234Th-derived carbon exports fluxes. D05 and L11 provided estimates closest to values obtained with the 234Th approach (within a 3-fold difference), but with no clear trends. The H11 model, on the other hand, consistently provided lower export estimates. The large increase in export data in the Atlantic Ocean derived from the GEOTRACES Program, combined with satellite observations and modeling efforts continue to improve the estimates of carbon export in this ocean basin and therefore reduce uncertainty in the global carbon budget. However, our results also suggest that tuning export models and including biological parameters at a regional scale is necessary for improving satellite-modeling efforts and providing export estimates that are more representative of in situ observations.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
    Format: application/pdf
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  • 7
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    An intercomparison of small- and large-volume techniques for thorium-234 in seawater (2001)
    In:  EPIC3Marine Chemistry, 74(1), pp. 15-28
    Details
    Publication Date: 2019-07-16
    Description: AbstractWe conducted an intercomparison of methods for the determination of 234Th in seawater. Samples were collected either from a shore-based 600 m water source, or from standard bottle casts collected in deep waters off Hawaii and in the Southern Ocean. We compared large volume techniques which rely upon Mn cartridges for the collection of dissolved 234Th and its detection via gamma counting (〉200 liter samples) with small volume methods that employed either direct beta counting, or beta counting after radiochemical purification (2-20-Liter samples). Unique to this study are the presentation of a novel 2 and 5 liter 234Th methods. This new method is an adaptation of 20-liter methods which are based on a coprecipitation of thorium with Mn oxides and the direct beta counting of the precipitate. These Mn coprecipitation methods were found to be superior to other methods due to ease of sample collection and processing and low overall analytical uncertainties.
    Repository Name: EPIC Alfred Wegener Institut
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  • 8
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    Testing a new small-volume technique for determining 234Th in seawater (2001)
    In:  EPIC3Journal of radioanalytical and nuclear chemistry, 248(3), pp. 795-799, ISSN: 0236-5731
    Details
    Publication Date: 2019-07-16
    Description: Thorium-234 is a naturally occurring radionuclide that has been widely studied in ocean sciences. These studies use the disequilibrium between the soluble parent uranium-238 (half-life = 4.5 x 109 years), and its particle reactive daughter, 234Th (half-life = 24.1 days), to quantify the in-situ removal rates of 234Th on sinking particles. Here, we present additional experiments that test a new 2-L procedure in which 234Th is co-scavenged with a MnO2 precipitate. Unlike other techniques, this method can be easily applied at-sea with an overall precision and accuracy of £ 5 %. Our experiments have sought to elucidate the effects of delaying reagent addition and precipitate filtration, differences in sample bottle types, and issues related to sample backgrounds and 234Th particulate sampling. Most of these experiments were conducted using water collected on repeated occupations of station ALOHA (22°45.0’N, 158°00.0’W), 100 km North of Oahu, Hawaii.
    Repository Name: EPIC Alfred Wegener Institut
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  • 9
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    An Introduction to the Application and Future Use of 234Th in Aquatic Systems (2005)
    In:  EPIC3Marine chemistry, 100(3), pp. 166-189
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    Publication Date: 2019-07-16
    Description: 234Th is an extremely useful radiotracer of particle dynamics in aquatic systems.Its use, however, is still limited to a relatively small number of investigators. The reasons for this may in part be due to a lack of knowledge of how this nuclide has been used in the past as well as how and where 234Th might be profitably applied in future research. The purpose of this paper, then, is to examine the variety of 234Th applications that have been used to understand natural aquatic processes in four major areas: vertical transport,particle cycling, horizontal transport, and sediment dynamics. We provide a general overview of the possible applications of 234Th in the hopes of provoking an increased interest in the inherent potential and future application of 234Th in these systems. We end this paper with a discussion of future research avenues in the context of three specific regimes: i) the upper 1000 m of the open ocean, ii) coastal sediment/water processes and iii) large freshwater lakes.
    Repository Name: EPIC Alfred Wegener Institut
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  • 10
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    A review of present techniques and methodological advances in analyzing 234Th in aquatic systems (2006)
    In:  EPIC3Marine chemistry, 100(3), pp. 190-212
    Details
    Publication Date: 2016-11-25
    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 on sinking particles has stimulated a rapidly increasing number of studies that require analyses of 234Th, both in marine and in 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 on the production of standard 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.
    Repository Name: EPIC Alfred Wegener Institut
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