The Application of a Linked Physical Ocean Circulation–Ecosystem Model to Prediction of Organic-Carbon Sedimentation in Lake Tanganyika, East African Rift System
Published:January 01, 2005
Kunihiro Tsuchida, Akihiko Okui, Yoshinobu Yamade, Noboru Yamazaki, Ryotaro Iwahashi, 2005. "The Application of a Linked Physical Ocean Circulation–Ecosystem Model to Prediction of Organic-Carbon Sedimentation in Lake Tanganyika, East African Rift System", The Deposition of Organic-Carbon-Rich Sediments: Models, Mechanisms, and Consequences, Nicholas B. Harris
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Lake Tanganyika, in the East African Rift System, provides an important modern analog for source-rock deposition in tropical lacustrine environments. In order to test models for source-rock deposition and to improve our understanding of critical processes, we have applied a computer model to simulate deposition of organic carbon in Lake Tanganyika that combines a water-body circulation model with an ecosystem model.
Lake Tanganyika is deep, highly elongated, and subjected to strong southerly winds along the axis of the lake during the dry season, May through August. Our simulations show that deep-water upwelling in the southern lake results from northward wind-driven surface flow during May through August, which causes nutrient enrichment in surface waters and results in strong phytoplankton blooming. During the wet season, weak upwelling, nutrient enrichment, and phytoplankton blooming in the northern lake result from oscillation of the lake. Our simulations suggest that although surface phytoplankton productivity is higher in the southern lake, flux of particulate organic carbon (POC) to the lake bottom is lower than in northern lake. Because the mixing depth is deeper in the southern lake, more oxygen is supplied to the deep part of the lake, which promotes the decomposition of organic matter. In addition, advection of organic matter to the deeper part of the lake was identified as an important process.
Organic-matter flux is relatively insensitive to variation in seasonal wind direction. It is highly sensitive to variation in wind velocity, which affects the strength of lake water circulation, with weaker winds resulting in decreased POC flux to the lake bottom and stronger winds resulting in increased POC flux.
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The Deposition of Organic-Carbon-Rich Sediments: Models, Mechanisms, and Consequences
Depositional models for organic-carbon-rich sediments have been the subjects of both great interest and great controversy for many years. These sediments serve as the ultimate source of virtually all oil and gas. They also represent the interface between biological and geological processes and provide critical evidence for the state of the atmosphere and oceans. Yet despite their importance and decades of research, the origin of these sediments remains the source of vigorous disagreement. The twelve papers in this volume represent the cutting edge of research in this topic. They explore the origin of organic-carbon-rich sediments through a variety of techniques, including sedimentology, geochemistry, paleontology and computer modeling. All papers take multidisciplinary approaches to the topic, and together, they demonstrate the complex interconnected processes that trigger the deposition of organic carbon. This book will appeal to geoscientists in many disciplines, including explorers for petroleum who need models for source rock deposition, organic and inorganic geochemists who study processes in water and sediment, sedimentologists who interpret ancient deposition environments, and climatologists and oceanographers who reconstruct the behavior of the ancient atmosphere and oceans.