Calcite dissolution driven by benthic mineralization in the deep-sea: in situ measurements of Ca2+, pH,pCO2 and O2 |
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| Institution: | 4. Ocean Science, KIOST School, University of Science & Technology, Daejeon, 34113, Republic of Korea;1. Key Laboratory of Marine Geology and Metallogeny, First Institute of Oceanography, Ministry of Natural Resources, Qingdao 266061, China;2. Laboratory for Marine Geology, Pilot National Laboratory for Marine Science and Technology (Qingdao), Qingdao 266061, China;3. Byrd Polar and Climate Research Center, Ohio State University, Columbus, OH, USA;4. Frontiers Science Center for Deep Ocean Multispheres and Earth System, Key Laboratory of Marine Chemistry Theory and Technology, Ministry of Education,Ocean University of China,Qingdao 266100, China;5. Department of Earth and Environmental Studies, Montclair State University, Montclair, NJ, USA;6. School of Geographic and Oceanographic Sciences, Nanjing University, Nanjing, China;7. College of Marine Geo-sciences, Ocean University of China, Qingdao, China;8. Key Laboratory of Coastal Science and Integrated Management, Ministry of Natural Resources, Qingdao, Shandong Province 266061, China |
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| Abstract: | In situ measured microprofiles of Ca2+, pCO2, pH and O2 were performed to quantify the CaCO3 dissolution and organic matter mineralization in marine sediments in the eastern South Atlantic. A numerical model simulating the organic matter decay with oxygen was used to estimate the calcite dissolution rate. From the oxygen microprofiles measured at four stations along a 1300-m isobath of the eastern African margin and one in front of the river Niger at a water depth of 2200 m the diffusive oxygen uptake (DOU) and oxygen penetration depth (OPD) was calculated. DOU rates were in the range of 0.3 to 3 mmol m?2 d?1 and showed a decrease with increasing water depth, corresponding to an increase in OPD. The calculated amount of degradated organic matter is in the range of 1 to 8.5 gC m?2 a?1. The metabolic CO2, released from mineralization of the organic matter drives calcite dissolution in these sediments overlain by calcite-supersaturated water. Fluxes across the sediment water interface calculated from the in situ Ca2+ microprofiles were 0.6 mmol m?2 d?1 for two stations at a water depth of 1300 m. The ratio of calcite dissolution flux and organic C degradation is 0.53 and 0.97, respectively. The microprofiles indicate that CO2 produced within the upper oxic sediment layer dissolves up to 85% of the calcite rain to the seafloor. Modeling our O2, pH and Ca2+ profiles from one station predicted a calcite dissolution rate constant for this calcite-poor site of 1000 mol kgw?1 a?1 (mol per kg water and year), which equals 95% d?1. This rate constant is at the upper end of reported in situ values. |
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