臺灣泥火山的氣體成分及其溫室氣體通量

泥火山是重要的甲烷逸氣管道，但卻一直被視為可忽略的通量。臺灣西南部泥火山氣體主要為甲烷(＞90%)、氮氣(1~10%)與二氧化碳(5%)。嘉義中崙泥火山群噴發氣體含量與其他地區不同，主要成分為二氧化碳(60-85%)、甲烷(10-30%)與氮氣(5-10%)。東部泥火山噴氣中氮氣含量較高，二氧化碳則甚低；分別為甲烷80-95%、氮氣1~10%、二氧化碳0.2%以下。相較於西部的泥火山，東部泥火山二氧化碳的含量低了約一個數量級。同位素的證據顯示古亭坑泥岩區的甲院是生物至混合來源，其他地區則是熱形成來源，觸口斷層區的二氧化碳是無機來源夾雜少量有機來源。與液體資料連結，古亭坑泥岩的流體來源較淺，觸口斷層區流體來源複雜，羅山泥火山群較電光泥火山受到較高度的火成岩影響。臺灣地區陸上泥火山噴口每年排放980-2300公噸甲烷與230-320公噸二氧化碳氣體。若加上土壤逸氣總量可能達到每年1200-2500公噸，因此泥火山是不可忽略的大氣甲烷來源之一。

關鍵字

泥火山；甲烷；溫室氣體；通量；臺灣

並列摘要

Mud volcanoes are important pathways for CH_4 emission from deep buried sediments; however, the importance of gas fluxes has hitherto been neglected in atmospheric source budget considerations , The major gas components of mud volcanoes at southwestern Taiwan are CH_4 (＞90%), N_2 (l - 5%) and CO_2 (1- 5%); the Hsiao-kun-shui mud volcano emits the highest CH_4 concentration (CH_4 ＞97%), On the other hand, the Chung-lun mud volcano shows CO2 up to 85%, and much lower CH4 content (37%). High CH_4 content (＞90 %) with low CO_2 (0.2%) are detected in the mud volcano gases collected in eastern Taiwan. It is suggestive that these gases are mostly of thermogenic origin based on carbon isotope results, with the exception of mud volcanoes situated along the Gu-ting-keng anticline axis showing unique biogenic characteristics . The CO_2 emitted in Chung-Iun shows inorganic origin with few organic CO_2, In Combination of fluid dat a, it is said the fluids at Guting- keng Mudstone mud volcanoes have the shallower origin related to others . Chu -kou Fault mud volcanoes show relatively complex fluid sources. The fluids from Lo-shan mud volcano have carried more igneous signal than Leigong- huo at Longitudinal Valley Fault. Preliminary estimation of CH_4 and CO_2 emission fluxes for mud volcanoes on land in Taiwan fall in a range between 980 to 2300 and 230 to 320 tons annually, respectively. If soil diffusion were taken into account, the total amount of mud volcano CH_4 could contribute up to 0.6% of total natural CH_4 emissions in Taiwan.