Modelling the Deep Biosphere over Deep Geological time at the Nankai Trough, Japan

最近的研究表明，生活在深海沉积岩中的微生物可能是岩石沉积环境中存在的生物的后代。这意味着微生物经历了漫长的地质历史，而且在许多情况下，随着沉积物被掩埋并转化为岩石，微生物在其环境中经历了重大变化。沉积物转化为沉积岩的计算机模型已经被用来模拟单个生物群落在其宿主地质构造中的生与死。然而，到目前为止，这只是在海底的情况下进行的，在这些情况下，地下水或其他流体在地质构造之间几乎没有运动。然而，在许多情况下，流体在地层之间发生转移。例子包括石油和天然气的迁移，以及与地震和构造活动相关的灾难性流体运动。南开海槽就是这样一个地方，这两个过程都可能发生，并且在深度上已经检测到地下微生物。目前，生活在沉积物中的微生物的现有模型不能准确地模拟微生物在地质层之间的转移，这将禁止在这些重要环境中模拟深层地下生物群系。IODP对南开海槽的考察将探索地下，以调查生命的温度极限。这次考察将提供一个获取数据的机会，这些数据将用于开发包含细胞地下运动的深层生物圈的更好模型。为了实现这一目标，有必要获得表征南开海槽中发现的微生物种群的重要数据。记录和描述地质构造之间的边界以及地下微生物的迁移途径也是至关重要的。为了准确地模拟微生物在其宿主沉积物转化为岩石时所经历的过去温度，有必要进行记录过去热蚀变事件的地球化学测量。所需的测量类型取决于所涉及的温度，在这种情况下，测量必须跨越相当大的温度范围，包括近地表的温和温度，以及产生石油和天然气的较高温度。后一组是科学家的常见做法，而前一组则不是。对地质构造边界的观测必须参数化；例如，转换成可以放入模型的数字输入。有两件事需要参数化：1)描述边界如何允许流体通过的基本信息。这些都是很容易做到的常规测量。2)当细胞在岩石中移动时，不同的岩石纹理如何与细胞相互作用。这不是常见的信息，将通过考虑适合南开海槽沉积物的具体情况的实验来确定；例如，气体和流体的存在，以及特定的岩石结构。利用这些数据建立的模型可以用来解决有关地下深处的生命、其他行星上的生命以及地质时期生命演变的基础科学问题。它们还将在预测石油产量、微生物提高石油采收率和污染地面修复的正向建模方面有实际应用。

Recent work has demonstrated that microbes living within deep ocean sedimentary rocks can be descended from the organisms present within the rock's depositional environment. This implies that the microbes experienced a long geological history and in many cases the microbes experienced significant changes in their environment as the sediment was buried and converted to rock.Computer models of the conversion of sediments into sedimentary rock have been adapted to model the life and death of individual biomes within their host geological formations. However, to date, this has only been done for examples of sub-seafloor cases where there is little movement of groundwater or other fluids between geological formations. However, there are many instances where the transfer of fluids between formations occurs. Examples include oil and gas migration, as well as the catastrophic movement of fluids associated with earthquakes and tectonic activity. The Nankai trough is one such place where both process may occur and subsurface microbes have been detected at depth. At the moment current models of microbes living within sediments can not accurately model the transfer of microbes between geological horizons, and this would prohibit the modelling deep subsurface biomes in these important environments.An IODP expedition to the Nankai trough will explore the subsurface to investigate the temperature limits of life. This expedition will provide an opportunity to acquire data that will be used to develop better models of the deep biosphere that incorporate the subsurface movement of cells. To achieve this it is necessary to have access to important data characterizing the microbial populations found in the Nankai trough. It is also essential that the boundaries between geological formations, and migration pathways for microbes within the subsurface are recorded and described. To accurately model past temperatures experienced by microbes as their host sediment is converted into rock, it is necessary to make geochemical measurements that record past episodes of thermal alteration. The type of measurement needed depends on the temperatures concerned, and in this case measurements must span a considerable temperature range including mild temperatures experienced in the near surface, as well as the higher temperatures that generate oil and gas. This later group is common practice for scientists the former is not.Observations of the boundaries between geological formations must be parameterised; e.g. converted into numerical inputs that can be put into a model. Two things need to be parameterised: 1) Basic information describing how the boundaries permit the passage of fluids. These are routine measurements that are easily made. 2) How different rock textures interact with cells as they move through rocks. This is not common information and will be determined by experiments that take account of specific circumstances appropriate to the Nankai trough sediments; e.g. the presence of gases and fluids, and specific rock textures.Models built using this data can then be used for addressing fundamental science questions concerning life in the deep subsurface, life on other planetary bodies and the evolution of life over geological time. They will also have practical applications for predicting petroleum occurrences and forward modelling microbial enhanced oil recovery and contaminated ground remediation.