Exploring the impact of temperature on dissolved organic matter and life in the deep biosphere off Muroto, Nankai Trough (IODP Expedition 370)

IODP远征370 - Muroto深海生物圈的温度极限(T-Limit) -（2016年9月10日至11月23日），旨在探索深海海底生物圈的生命极限，该生物圈的温度随深度以中等速率上升，超过沉积物/基底界面微生物生命的已知最高温度（~120°C）。在日本Muroto角附近的南开海槽原冲断带，利用DV Chikyu在水深4776 m的ODP站点808和1174附近建立了C0023站点。C0023A孔穿过沉积物/基底界面推进至海底以下1180米的总深度，检索了112个岩心，并开始了长期温度观测（参见：http://www.jamstec.go.jp/chikyu/e/exp370/index.html）。远征370的主要科学目标是：(a)以前所未有的分析灵敏度和精度，探测和调查深海海底生物-非生物过渡过程中生命和生物过程的存在与否；(b)综合研究控制微生物群落生物量、活性和多样性的因素；(c)阐明含有热源和/或地源营养物质和能量基质的流体是否持续或偶然流动支持南开海槽增生复合体的海底微生物群落。本项目将通过深入研究从C0023A孔采集的112个间隙水样中的溶解有机物（DOM）来实现总体考察目标：(1)基于有机代谢物（如醋酸酯和其他挥发性脂肪酸（VFAs）、甲醇和乙醇）的浓度和碳同位素组成的高分辨率深度剖面，我们的目标是深入了解微生物活动和碳流。(2)利用高分辨率深度剖面分析腐殖质样DOM、蛋白质样DOM及其亚群等主要荧光DOM组分，研究沉积物埋藏和加热过程中有机质的生物利用度和变化，及其对微生物丰度和活性的影响。(3)最后，利用超高分辨率傅里叶变换离子回旋共振质谱（FT-ICR-MS）对选定样品进行研究，将使我们能够在分子水平上表征DOM的元素组成，获得埋藏和加热过程中有机质变化途径的机理见解，并利用来自更深、更热来源的流体追踪DOM的放置。

IODP Expedition 370 - Temperature Limit of the Deep Biosphere off Muroto (T-Limit) - (September 10 - November 23, 2016), aimed to explore the limits of life in the deep subseafloor biosphere at a location where temperature increases with depth at an intermediate rate and exceeds the known temperature maximum of microbial life (~120°C) at the sediment/basement interface. Such conditions are met in the protothrust zone of the Nankai Trough off Cape Muroto, Japan, where Site C0023 was established in the vicinity of ODP Sites 808 and 1174 at a water depth of 4776 m using DV Chikyu. Hole C0023A was advanced across the sediment/basement interface down to a total depth of 1180 meters below seafloor, 112 cores were retrieved, and long-term temperature observations were started (see also: http://www.jamstec.go.jp/chikyu/e/exp370/index.html). The primary scientific objectives of Expedition 370 are (a) to detect and investigate the presence or absence of life and biological processes at the biotic-abiotic transition of the deep subseafloor with unprecedented analytical sensitivity and precision; (b) to comprehensively study the factors that control biomass, activity, and diversity of microbial communities; and (c) to elucidate if continuous or episodic flow of fluids containing thermogenic and/or geogenic nutrients and energy substrates support subseafloor microbial communities in the Nankai Trough accretionary complex. This project will address the overarching expedition objectives through in-depth investigation of dissolved organic matter (DOM) in a set of 112 interstitial water samples retrieved from Hole C0023A: (1) Based on high-resolution depth profiles for the concentration and carbon isotopic composition of organic metabolites, such as acetate and other volatile fatty acids (VFAs), methanol and ethanol, we aim to gain insights into microbial activity and carbon flow. (2) Using high-resolution depth profiles for major fluorescent DOM components, such as humic-like DOM, protein-like DOM and subgroups thereof, will seek to investigate the bioavailability and alteration of organic matter during sediment burial and heating, and its impact on microbial abundance and activity. (3) Finally, investigation of selected samples with ultrahigh resolution Fourier Transform Ion Cyclotron Resonance Mass Spectrometry (FT-ICR-MS) will allow us to characterize the elemental composition of DOM on a molecular level, to gain mechanistic insights into pathways of organic matter alteration during burial and heating, and to trace the put of DOM with fluids from deeper, hotter sources.