Accumulation rates and sources of sediments and organic carbon on the Palos Verdes shelf based on radioisotopic tracers (137Cs, 239,240Pu, 210Pb, 234Th, 238U and 14C) |
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| Institution: | 1. A. I. Herzen State Pedagogical University of Russia, 191186 St. Petersburg, Russian Federation;2. Department of Crystallography, St. Petersburg State University, 199034 St. Petersburg, Russian Federation;1. College of Earth and Environmental Sciences, Lanzhou University, Lanzhou 730000, Gansu, China;2. Center for Cancer Prevention and Treatment, School of Public Health, Lanzhou University, Lanzhou 730000, Gansu, China;3. Medical College, Northwest University for Nationalities, Lanzhou 730030, Gansu, China;4. College of Basic Medicine, Lanzhou University, Lanzhou 730000, Gansu, China;5. Cancer Institute and Hospital, Chinese Academy of Medical Sciences, Beijing 100021, China;6. School of Public Health, Yale University, New Haven, CT 06520, United States;7. Jinchuan Worker''s Hospital, Jinchuan Nonferrous Metals Corporation, Jinchang 737103, Gansu, China;1. N. N. Vorozhtsov Novosibirsk Institute of Organic Chemistry, Siberian Branch of the Russian Academy of Sciences, 630090 Novosibirsk, Russian Federation;2. Department of Natural Sciences, Novosibirsk State University, 630090 Novosibirsk, Russian Federation;1. College of Earth and Environmental Sciences, Lanzhou University, Lanzhou 730000, Gansu, China;2. Department of Epidemiology and Statistics, School of Public Health, Lanzhou University, Lanzhou 730000, Gansu, China;3. Center of Medical Laboratory, School of Basic Medical, Lanzhou University, Lanzhou 730000, Gansu, China;4. Workers'' Hospital of Jinchuan Group Co., Ltd., Jinchang 737100, Gansu, China;5. Department of Epidemiology, School of Public Health, Brown University, RI, 02912, USA |
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| Abstract: | We report here bioturbation and sediment accumulation rates determined from replicate sediment cores at four different sampling sites on the Palos Verdes shelf, Southern California, using bomb fallout and natural radionuclides (137Cs, 239,240Pu, 210Pb, 234Th, and 14C), along with supporting measurements of organic carbon (OC), porosity and granulometry. Present-day particle reworking, on time scales of several months, is restricted to the upper 3 cm, with rates ranging from 13 to 200 cm2/year, as deduced from 234Thxs profiles. There is little evidence that particle reworking reached depths significantly greater than 5 cm. Post-1963 (or post-1971) sediment accumulation rates ranged from 0.7 to 1.4 g/cm2/year (equivalent to 1.1–1.8 cm/year for surficial sediments), as calculated from Pu and Cs isotope profiles, with little change over time or distance from the outfall. Lateral transport of older sediment and multiple sediment sources on the Palos Verdes shelf is suggested from radiocarbon measurements on foraminifera and bulk sedimentary organic matter at two sampling sites, which showed variable, old and refractory sources of OC. Pre-1953 sediments accumulated at rates that were at least 0.4 g/cm2/year (≥0.3 cm/year), based on 210Pbxs dating. Given the abundance of sediment sources to the Palos Verdes shelf, the high sedimentation rates, and shallow particle mixed layers, contaminant-enriched layers should continue to move deeper into the sediments. |
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