【摘要】：海底冷泉活動(dòng)及其伴生的甲烷滲漏，是目前全球變化研究中的熱點(diǎn)問(wèn)題。作為天然氣水合物的賦存標(biāo)志及其分解釋放甲烷的重要途徑，冷泉活動(dòng)在海水-沉積物界面引發(fā)了極為復(fù)雜的生物地球化學(xué)過(guò)程，并對(duì)全球碳循環(huán)和氣候變化產(chǎn)生重要影響。南海是全球重要的甲烷儲(chǔ)庫(kù)之一，其冷泉區(qū)的甲烷滲漏通量與變化過(guò)程無(wú)疑急待評(píng)估和量化。深入開(kāi)展這方面的研究，對(duì)于深入理解天然氣水合物分解釋放對(duì)全球變暖的響應(yīng)及其反饋機(jī)制有重要的科學(xué)意義和應(yīng)用價(jià)值。 本文基于 深海海底邊界層原位環(huán)境觀測(cè)系統(tǒng)（Benvir）‖，于2012年9月在南海北部陸坡中段神狐海域白云凹陷水合物遠(yuǎn)景區(qū)獲得的一系列原位觀測(cè)數(shù)據(jù)，針對(duì)研究區(qū)海底甲烷滲漏強(qiáng)度，疑似冷泉活動(dòng)區(qū)位置，海底甲烷滲漏強(qiáng)度變化及影響，海底生物地球化學(xué)環(huán)境對(duì)海底甲烷滲漏的響應(yīng)等科學(xué)問(wèn)題進(jìn)行了較深入的討論。取得了以下認(rèn)識(shí)。 1.參考世界典型冷泉區(qū)近底層海水溶解甲烷濃度，，將海底甲烷滲漏環(huán)境劃分為背景地區(qū)、低甲烷滲漏區(qū)、中甲烷滲漏區(qū)和高甲烷滲漏區(qū)四種。 2.深入研究了白云凹陷地區(qū)近底層海水中溶解甲烷濃度及其時(shí)序變化特征，認(rèn)為本文研究區(qū)屬于中甲烷滲漏區(qū)。 3.揭示了溫度、壓力和鹽度變化對(duì)溶解甲烷濃度的影響，提出：（1）周期性的壓力變化（潮汐）是控制冷泉活動(dòng)的因素之一，但由于白云凹陷水深較深，壓力對(duì)海底界面的影響較小。（2）溫度的變化會(huì)影響產(chǎn)甲烷菌和甲烷厭氧氧化菌的活性，進(jìn)而影響水體中溶解甲烷濃度的變化。較壓力而言，近底層海水的溫度對(duì)沉積物中水合物穩(wěn)定性的影響較小，但對(duì)海水溶解甲烷濃度的控制更為直接。（3）近底層物理化學(xué)環(huán)境的變化控制溶解甲烷的濃度的同時(shí)，影響了海水中離子濃度，引起了鹽度的變化，因此鹽度和甲烷的變化趨勢(shì)較相似。且鹽度可能會(huì)通過(guò)影響天然氣水合物的穩(wěn)定性來(lái)控制水體中溶解甲烷的濃度。（4）三者都不是影響近底層水體中溶解甲烷濃度變化的主要因素。 4.討論了近底層海水溶解甲烷濃度變化對(duì)生物地球化學(xué)環(huán)境的響應(yīng)，認(rèn)為海流或外來(lái)水團(tuán)引起的二氧化碳、溶解氧濃度和pH值的變化，可能是控制近底層海水中溶解甲烷濃度的主要因素。其中，外源二氧化碳和溶解氧會(huì)引起甲烷氧化還原平衡的變化，從而導(dǎo)致溶解甲烷濃度的變化。pH值的改變會(huì)影響產(chǎn)甲烷菌的活度，從而控制近底層海水中的溶解甲烷濃度。 以上研究將有助于深入理解海底甲烷滲漏及其通量變化及其影響及制約因素，海底環(huán)境和生物地球化學(xué)過(guò)程對(duì)海底甲烷滲漏的通量變化的響應(yīng)機(jī)制。
[Abstract]:Undersea cold spring activity and associated methane leakage are hot issues in global change research. As a sign of gas hydrate occurrence and an important way to decompose and release methane, cold spring activities have triggered a very complex biogeochemical process at the interface between seawater and sediment, and have an important impact on the global carbon cycle and climate change. The South China Sea is one of the most important methane reservoirs in the world. Further research in this field is of great scientific significance and practical value in understanding the response of gas hydrate decomposition and release to global warming and its feedback mechanism. Based on the deep-sea seabed boundary layer in situ environmental observation system (Benvir), a series of in-situ observation data were obtained in September 2012 in the Baiyun Sag Hydrate area of Shenhu Sea in the northern continental slope of the South China Sea. The depth of methane leakage in the study area, the location of the suspected cold spring active area, the variation and influence of methane leakage intensity, and the response of the marine biogeochemical environment to the methane leakage are discussed in depth. The following knowledge has been obtained. 1. Referring to the concentration of dissolved methane near the bottom of sea water in typical cold spring area of the world, the environment of methane leakage is divided into four types: background area, low methane leakage area, middle methane leakage area and high methane leakage area. 2. In this paper, the concentration of dissolved methane in the near bottom sea water and its temporal variation in Baiyun sag are studied, and it is considered that the study area belongs to the middle methane leakage area. 3. The effects of temperature, pressure and salinity on the concentration of dissolved methane are revealed. It is suggested that: (1) the periodic pressure variation (tide) is one of the factors controlling the cold spring activity, but because of the deep water depth in Baiyun depression, Pressure has little effect on the bottom interface. (2) the change of temperature will affect the activity of methanogenic bacteria and methane-anaerobic bacteria, and then affect the concentration of dissolved methane in water. Compared with pressure, the temperature of near-bottom seawater has little effect on the stability of hydrate in sediment, but the concentration of dissolved methane in seawater is controlled more directly. (3) the concentration of dissolved methane is controlled by the change of physical and chemical environment near bottom layer. The change of salinity is similar to that of methane. The salinity may control the concentration of dissolved methane by affecting the stability of natural gas hydrate. (4) none of them is the main factor affecting the concentration of dissolved methane in the near bottom water. 4. The response of dissolved methane concentration to biogeochemical environment in near-bottom seawater is discussed. The change of carbon dioxide, dissolved oxygen concentration and pH value caused by ocean current or foreign water mass is considered. It may be the main factor to control the concentration of dissolved methane in the near-bottom seawater. Exogenous carbon dioxide and dissolved oxygen can change the redox equilibrium of methane and lead to the change of dissolved methane concentration. The change of pH value will affect the activity of methanogenic bacteria and control the concentration of dissolved methane in the near bottom water. The above studies will be helpful to further understand the mechanism of benthic methane leakage and its flux change and its influence and restriction factors, and the response mechanism of seabed environment and biogeochemical process to the flux change of seabed methane leakage.
【學(xué)位授予單位】：中國(guó)海洋大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2014
【分類(lèi)號(hào)】：P734;P744.4

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