Organic properties of sediments and amino acids in iterstitial waters of ODP Holes 111-677A and 111-678B@en

The basement at Ocean Drilling Program (ODP) Sites 677 and 678 originated from the Galapagos spreading center of the Costa Rica Rift and has moved about 200 km over the last 6 m.y. (Fig. 1) (Shipboard Scientific Party, 1987, 1988; Scientific Drilling Party, 1987). Sediments about 300 m thick cover basement so young that basal sediments at Sites 677 and 678 have been reheated up to 60∞-70∞C at Site 677 and altered to limestone and/or chert (Shipboard Scientific Party, 1988). Sediments from both sites indicate (1) a high sedimentation rate (about 48 m/m.y.) and (2) biogenic silica and carbonate as the main constituents of sediments (Table 1) (Shipboard Scientific Party, 1988). Heatflow observations and measurements of interstitial water chemistry around the sites show that Site 677 is in a lower heatflow zone (166 mW/m**2; 1°12.14'N, 83°44.22'W) whereas Site 678 is located in a zone of higher heat flow (250 mW/m**2; 1°13.01'N, 83°43.39'W) (Langseth et al., 1988; Shipboard Scientific Party, 1988). In the flank hydrothermal systems, circulating solution is moving upward through the sedimentary column in zones of higher heat flow while it is moving downward in zones of lower heat flow (Anderson and Skilbeck, 1981). The chemistry of the interstitial waters is modified by several processes such as (1) diagenetic reactions and (2) advective and (3) diffusive transports of dissolved constituents. Analyses of Ca2+ and Mg2+ in interstitial waters from Sites 677 and 678 show that their profiles are mainly controlled by advective transport (Shipboard Scientific Party, 1988). In contrast, the interstitial-water profiles for NH4+, Si, and PO4[3-] are highly affected by reactions in the sediments. Site 677 offers a good opportunity to investigate amino acids in the interstitial waters because sediments of similar compositions have been deposited at constant rates of sedimentation. There are few previous works on amino acid distributions in interstitial waters (Henrichs and Parrington, 1979; Michaelis et al., 1982; Henrichs et al., 1984; Henrichs and Farrington, 1987; Ishizuka et al., 1988). In this chapter, we report (1) Rock-Eval analysis and (2) the composition of total hydrolyzable and dissolved free amino acids (THAA and DFAA, respectively) in the interstitial waters. Our objectives are to discuss (1) the possible origin of organic materials, (2) the characteristics of THAA and DFAA, and (3) their relationships in interstitial waters.大洋钻探计划（Ocean Drilling Program, ODP）677与678站位的洋壳基底，源自哥斯达黎加裂谷的加拉帕戈斯扩张中心，在过去6百万年（million years, m.y.）间位移了约200公里（图1）（船上科学工作队, 1987, 1988; 科学钻探工作队, 1987）。 约300米厚的沉积物覆盖于如此年轻的洋壳基底之上，致使677与678站位的基底沉积物重新受热：677站位的基底沉积物最高升温可达60℃~70℃，并被蚀变为石灰岩及/或燧石（船上科学工作队, 1988）。 两处站位的沉积物均具备两大特征：(1) 沉积速率较高（约48米/百万年）；(2) 沉积物的主要组分为生物硅与碳酸盐（表1）（船上科学工作队, 1988）。 热流观测与站位周边间隙水化学分析结果显示，677站位处于低热流区（166 mW/m²；1°12.14'N, 83°44.22'W），而678站位则位于高热流区（250 mW/m²；1°13.01'N, 83°43.39'W）（Langseth等, 1988; 船上科学工作队, 1988）。 在侧翼热液系统中，环流溶液在高热流区向上运移穿过沉积柱，而在低热流区则向下运移（Anderson和Skilbeck, 1981）。间隙水的化学组成受多种过程改造，包括(1) 成岩反应；(2) 平流输运；(3) 溶解组分的扩散输运。对677与678站位间隙水中Ca²+与Mg²+的分析结果表明，其浓度剖面主要受平流输运控制（船上科学工作队, 1988）。与之相反，NH4+、Si及PO4³-的间隙水浓度剖面则主要受沉积物内部的反应影响。 677站位为研究间隙水中的氨基酸分布提供了良好契机，因为该区域沉积物组成相似且沉积速率恒定。此前针对间隙水中氨基酸分布的研究相对较少（Henrichs和Parrington, 1979; Michaelis等, 1982; Henrichs等, 1984; Henrichs和Farrington, 1987; Ishizuka等, 1988）。 本章将报道两项内容：(1) Rock-Eval热解分析（Rock-Eval analysis）结果；(2) 间隙水中总水解氨基酸（total hydrolyzable amino acids, THAA）与溶解游离氨基酸（dissolved free amino acids, DFAA）的组成。本文的研究目标为：(1) 探讨有机质的可能来源；(2) 分析THAA与DFAA的组分特征；(3) 阐明二者在间隙水中的相关关系。