Impact of Extreme Events on Organic Carbon Burial off Southwestern Taiwan
Date Issued
2014
Date
2014
Author(s)
Tsai, Po-Hsuan
Abstract
The tectonically active setting and climatic conditions give Taiwan a high exposure to severe natural hazards. After the Pingtung Earthquake and Morakot Typhoon which occurred in 2006 and 2009, the turbidity currents caused a series of submarine cable breaks along the Gaoping and Fangliao Submarine Canyons off SW Taiwan. Large amounts of terrestrial sediments were fast transported bypass the narrow continental shelf and rapidly moved southward through submarine canyon to the deep sea. This study aims to evaluate the impact of extreme events on the transportation and burial of organic carbon.
Two piston cores which were taken from the Maiden Ridge and its adjacent area (MT7 and MT6) might shed light on understanding the export of terrestrial organic carbon to the abyss by natural geohazards. The 210Pb profile of MT7 in conjunction with the grain size data indicates the existence of the Pingtung Earthquake and Morakot Typhoon related deposits. The sedimentation rate of these two cores which derived from 210Pb is approximately 0.05 cm/yr.
The cores collected from the Gaoping Submarine Canyon, Gaoping Slope and Fangliao Submarine Canyon are used for analyzing TOC, organic C/N and δ13C ratios. The concentrations of total organic carbon are ~0.5%, and C/N rations almost remain between 4 and 8. The high TOC (~1%) and C/N ratio (>10) are observed in the samples with plant debris. The fluctuation of TOC and C/N ratios in near-shore samples is higher than deep sea. In terms of δ13C-values, it progressively decreases with distances from coastal zone to the deep sea. Due to the larger proportions of land-derived organic carbon, the δ13C-values in the surface sediment of upper Gaoping Submarine Canyon, Gaoping Slope, and the turbidite layers at the head of Fangliao Submarine Canyon are lighter.
Furthermore, this study uses the TOC concentrations and δ13C-values to estimate the fractional contributions of terrestrial organic carbon by a simple two component mixing model, and integrate with the 210Pb-derived sediment accumulation rates to evaluate the organic carbon burial between event layers and normal accumulation period. Our results show the extreme natural geohazard events not only fast transported sediments into the deep sea but also delivered large amounts of organic carbon into abyss, and it may play an important role on the global carbon cycling system.
Subjects
鉛-210
總有機碳
穩定碳同位素
海底地質災害
碳埋藏
SDGs
Type
thesis
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