| 南海北部海马冷泉区表层沉积物的AOM生物标志化合物特征及意义 |
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| 引用本文： | 吴一帆,管红香,许兰芳,茅晟懿,刘磊,苏正,刘丽华.南海北部海马冷泉区表层沉积物的AOM生物标志化合物特征及意义[J].地球科学,2022,47(8):3005-3015. |
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| 作者姓名： | 吴一帆 管红香 许兰芳 茅晟懿 刘磊 苏正 刘丽华 |
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| 作者单位： | 1.中国科学院广州能源研究所, 广东广州 510640 |
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| 基金项目： | 国家自然科学基金资助项目91958105国家重点研发项目2018YFC031005广东省基础与应用基础研究重大项目2019B030302004 |
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| 摘 要： | 选取采自南海天然气水合物赋存区海马冷泉，管状蠕虫区（ROV06站位）和贻贝区（HM101站位）的2个表层沉积物柱状样品，提取其中的生物标志化合物，对其种类和稳定碳同位素进行了测定，用以探讨海底表层沉积物中的有机质来源、微生物种群分布及其对冷泉渗漏活动的响应特征. 两个站位的沉积物中均发现了大量与甲烷厌氧氧化古菌（ANME）有关的生物标志物，如2，6，11，15?四甲基十六烷（crocetane）、2，6，10，15，19?五甲基二十烷（PMI）等类异戊二烯烃，古醇（archaeol）、sn2?羟基古醇（sn2?OH?Ar）等，以及来源于硫酸盐还原菌（SRB）的异构/反异构脂肪酸iso?C15和ai?C15等. 这些生物标志物均具有极低的碳同位素特征（古菌生标δ13C值低至-126‰，硫酸盐还原菌生标δ13C值低至?89‰），表明沉积物中发生了甲烷厌氧氧化作用（AOM）. ROV06和HM101站位沉积物中均检测到了crocetane，大多数sn2?羟基古醇/古醇大于1，同时ai?C15/iso?C15脂肪酸比值小于2，这说明两个站位沉积物中的甲烷厌氧氧化古菌主要以ANME?2/DSS为主，指示甲烷渗漏强度较强. ROV06站位的表层沉积物含有crocetane，但sn2?羟基古醇/古醇小于1，且ai?C15/iso?C15脂肪酸比值大于2.1，指示了ANME?1/DSS和ANME?2/DSS混合存在的种群特征，说明ROV06站位顶部甲烷渗漏强度有减小的趋势. 根据古菌种群ANME?2化合物对甲烷的碳同位素分馏（Δ:-50‰）及古菌生物标志物（PMI、古醇、sn2?羟基古醇）的平均δ13C值，计算得到甲烷δ13C值（-58‰~-53‰），显示甲烷为热成因和生物成因混合气. 虽然ROV06和HM101站位的甲烷具有相近的δ13C值，但ROV06站位的SRB生物标志物比HM101站位要更加亏损13C（Δδ13C:18‰），这可能与管状蠕虫的共生菌（硫氧化菌）吸收硫化物并释放出硫酸盐有关，因为其不断释放出的硫酸盐很可能极大地增强了甲烷厌氧氧化作用，使沉积物中含有更多13C亏损的无机碳.
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| 关 键 词： | 冷泉 管状蠕虫 贻贝 甲烷厌氧氧化古菌 硫酸盐还原菌 生物标志化合物 海洋地质 |
| 收稿时间： | 2021-11-03 |
Characteristics and Significance of Biomarkers Related to AOM in Surface Sediments of the Haima Cold Seep in the Northern South China Sea |
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| Abstract: | In this study, two sediment core samples were collected from the tubeworms area (site ROV06) and mussel area (site HM101) of the Haima cold seep, northern South China Sea. We extracted the lipid biomarkers, analyzed the contents and stable carbon isotopic values to study the source of the organic matter in seabed surface sediments, the distribution of microbial communities and their response to the seep leakage intensity. Alarge amount of crocetane, PMI, archaeol and sn2?hydroxyarchaeol (sn2?OH?Ar) related to anaerobic methanotrophic archaea (ANME) and iso?C15 and ai?C15 fatty acids produced by sulfate?reducing bacteria (SRB) were detected. The extremely negative δ13C values of these lipid biomarkers (as low as -126‰ for archaea biomarkers and -89 ‰ for sulfate?reducing bacteria biomarkers) indicated that anaerobic oxidation methane (AOM) occurred in the sediments. Crocetane was detected in the sediments of both ROV06 and HM101 sites, and most of the ratio of sn2?OH?Ar/archaeol was higher than 1, while the ratio of ai?C15/iso?C15fattyacid was lower than 2, indicating dominated community of ANME?2/DSS consortium in both site and a strong methane leakage intensity. The surface sediment of ROV06 site contained crocetane, whereas the low ratio of sn2?OH?Ar/archaeol(less than 1) and high ratio of ai?C15/iso?C15 fatty acid (> 2.1) indicated a mixed communities of ANME?1 /DSS and ANME?2 /DSS and the methane leakage intensity from bottom to surface of ROV06 station with a decreasing trend. The δ13C values of methane (-58‰~-53‰) were calculated based on the carbon isotopic fraction (Δ: -50‰) of ANME?2 and the mean δ13C values of the archaea biomarkers (PMI, archaeol, sn2?OH?Ar), indicating a mixture of thermogenic and biogenic source of methane. Methane at ROV06 and HM101 sites showed similar δ13C values, whereas the δ13C values of the biomarkers derived from SRB at ROV06 was lower than that at HM101 (Δδ13C: 18‰), which may be related to the absorption of sulfide and the release of sulfates by sulfur?oxidizing bacteria, a symbiotic bacterium of the tubeworms. The continuous release of sulfates was likely to greatly enhance AOM progress, resulting in more 13C?depleted inorganic carbon in the sediment. |
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