南太平洋东劳扩张中心表层沉积物氨基酸组成所揭示的生物地球化学意义

通过对南太平洋劳盆地东劳扩张中心(ELSC)表层沉积物进行水解氨基酸(THAA)分析、氨基酸对映异构体比值(D/L)分析及总有机碳(TOC)分析,对沉积物中氨基酸含量和来源、有机质降解程度和采样区域生物活动性及温度特征等问题进行了探讨。结果表明,ELSC区域样品中有机质含量较低,TOC含量为0.70～2.15 mg/g(干重),THAA含量为30～511μg/g(干重),热液活动区域原位化能合成作用对沉积物中氨基酸的相对富集有较大的贡献。沉积物中THAA含量和生物群落活动状况与分布范围有关,样品矿物组分对氨基酸的保存亦有一定的影响。由于各采样点热液活动、沉积物类型、生物群落的类型及分布均有所不同,样品中个体氨基酸的组成分布特征有较大差异。以TOC中氨基酸态碳所占百分比TAAC%作为指标对样品有机质活性进行了判别,热液喷口区域样品有机质新鲜程度要普遍高于非热液喷口区域样品,高温热液环境对氨基酸降解途径有一定的影响。样品中个体氨基酸D/L比值变化范围较大,天冬氨酸(Asp)为0.08～0.46,谷氨酸(Glu)为0.06～0.19,丝氨酸(Ser)为0.01～0.81,丙氨酸(Ala)为0.10～0.30。根据样品中THAA含量、TAAC%及个体氨基酸的D/L比值可以粗略判断生物活动性的大小及细菌对THAA的相对贡献,但并不能准确地区分热液活动活跃区域和非活跃区域在温度和生物活动性方面的差异。

Amino acid composition and its biogeochemical significance in sediments from the Eastern Lau Spreading Center, South Pacific Ocean

The total hydrolysable amino acid （THAA）, the ratios between D and L of amino acids （D/L） and the total organic carbon （TOC） were analyzed in surface sediments taken from the Eastern Lau Spreading Center （ELSC）, South Pacific Ocean. The contents, sources and degree of decomposition of the organic matter （OM） in sediments have been investigated. The D/L ratios of amino acids were used to indicate the biological activity and temperature variation in hydrothermal field. The results showed that the contents of TOC and THAA in sediments were in the range of 0.70 2.15 mg/g （dry weight） and 30 511μg/g （dry weight）, respectively. The chemosynthetic-based in-suit community＇s productivity in the hydrothermal systems contributed significant composition to the relative enrichment of THAA. The contents of THAA of the sediments were related to the in-suit community＇s activity and composition, and the mineral composition of the sediments. The compositions of amino acids in sediments were different from each site for different hydrothermal system, because different hydrothermal system exhibits different hydrothermal activity, mineral composition of the sediments, and biological community. The percentage of organic carbon normalized to amino acid carbon （TAAC%） could be used to indicate the degree of degradation of sedimentary OM. The TAAC% showed that activity of OM in the hydrothermal vent fields was higher than those in non-hydrothermal vent fields. Relatively high temperature in the hydrothermal fields might influence the degradation path way of amino acids. The D/L ratios of aspartic acid （Asp）, glutamic acid （Glu）, serine （Ser） and alanine （Ala） in sediments showed a wide range, for example, the D/L ratios of Asp, Glu, Ser and Ala were 0.08 0.46, 0.06 0.19, 0.01 0.81 and 0.10 0.30, respectively. According to the contents of THAA, TAAC% and the D/L ratio of individual amino acid, the biological activity of biomass and the relative contribution of the THAA of bacteria could be assessed. However, it cannot be accurately distinguished between the hydrothermal active fields and non-hydrothermal active fields on the temperature and biological activities just by the composition of the amino acid.