Silicon Isotopic Fractionation in Lake Tanganyika and Its Main Tributaries |
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| Affiliation: | 1. Pacific Centre for Isotopic and Geochemical Research, Department of Earth, Ocean and Atmospheric Sciences, University of British Columbia (UBC), 6339 Stores Road, Vancouver, BC V6T 1Z4, Canada;2. Soil Science and Environment Geochemistry, Earth and Life Institute, Université catholique de Louvain, Croix du Sud 2/L7.05.10, B-1348 Louvain-la-Neuve, Belgium;3. Soil Science, University of British Columbia (UBC), 127-2357 Main Mall, Vancouver, BC V6T 1Z4, Canada;1. Research Center for Marine Ecology, First Institute of Oceanography, State Oceanic Administration, Qingdao 266061, China;2. Laboratory for Marine Geology, Qingdao National Laboratory for Marine Science and Technology, Qingdao 266237, China;3. Key Laboratory of Marine Chemistry Theory and Technology, Ministry of Education, Ocean University of China, Qingdao 266100, China;4. Tianjin Marine Environmental Monitoring Central Station, State Oceanic Administration, Tianjin 300450, China;1. Ecohydrology Research Group, Department of Earth and Environmental Sciences and The Water Institute, University of Waterloo, Waterloo, ON N2L 3G1, Canada;2. National Key Laboratory of Water Environmental Simulation and Pollution Control, South China Institute of Environmental Sciences, Ministry of Ecology and Environment, No. 18 Ruihe Road, Guangzhou 510530, China;3. Watershed Hydrology and Ecology Research Division, Environment and Climate Change Canada, 867 Lakeshore Road, Burlington, Ontario L7S 1A1, Canada |
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| Abstract: | Silicon isotopic measurements in Lake Tanganyika were performed using multiple-collector inductively coupled plasma mass spectrometry (MC-ICP-MS) in dry plasma condition. Isotopic signatures are reported for dissolved ortho-silicic acid Si(OH)4] collected during a 1-year-long surface waters survey in the southern basin along with several of the major tributaries. Deep-water Si isotopic profiles from a north-south transect cruise conducted in July 2002 are also described. The nutrient-like shape dissolved Si profiles and the isotopic disequilibrium between surface (δ29Si = 0.87±0.08 ‰) and deep waters (0.61 ± 0.05 ‰) suggest the occurrence of biological isotopic discrimination induced by diatoms biomineralisation in a fresh water system. Short-term surface water Si isotopic and diatom biomass variations obtained during the 1-year bi-weekly monitoring (2002–2003) in the south confirms this biological effect. Five epilimnion biogenic opal samples also were analyzed. Their signature (δ29Si of 0.28 ± 0.12‰) compared to those of surrounding waters are consistent with the diatom isotopic fractionation effect measured on marine tropical diatoms. This demonstrates the species and temperature independent character of the silicon isotope fractionations by diatoms. River signatures present variable dissolved Si concentrations which were positively correlated to δ29Si values in the range of previously published world river data. Because of its fast response to climate variability, nutrient dynamics, and limnological changes, δ29Si in siliceous organisms should be very useful in studying environmental changes and particularly the recent decline of diatom Si utilization in Lake Tanganyika. |
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