Estimation of the global inventory of methane hydrates in marine sediments using transfer functions
Estimation of the global inventory of methane hydrates in marine sediments using transfer functions
复制标题
DOI：
10.5194/bg-10-959-2013
复制
发表时间：
2012-01
期刊：
影响因子：
4.9
通讯作者：
E. Piñero;M. Marquardt;C. Hensen;M. Haeckel;K. Wallmann
中科院分区：
文献类型：
--
作者：
E. Piñero;M. Marquardt;C. Hensen;M. Haeckel;K. Wallmann
海洋沉积物中天然气水合物的聚集主要受微生物转化为甲烷的颗粒有机碳（POC）的聚集、甲烷可被捕获的天然气水合物稳定带（GHSZ）的厚度、控制POC和生成的甲烷在GHSZ内停留时间的沉积速率（SR）以及深层沉积物中甲烷通过上升孔隙流体和气体进入GHSZ的输送控制。最近，Wallmann等人（2012）提出了基于SR、POC和GHSZ厚度的传递函数，用于预测正常和完全压实沉积物两种不同情景下扩散控制地质系统中的天然气水合物储量。我们将这些函数应用于全球深海测量、热流、海底温度、POC输入和SR数据集，根据沉积和压实条件，估计全球海洋甲烷水合物中储存的碳质量为3至455gt碳（GtC）。估计GHSZ大陆边缘全球沉积体积为60 ~ 67 × 1015 m3，孔隙体积为7 × 1015 m3（可用于GH聚集）。然而，已知富甲烷流体的渗流对天然气水合物的聚集有显著的影响。因此，我们用传递-反应代码进行了一组系统模型运行，以推导出明确考虑向上流体平流的扩展传递函数。利用从质量平衡考虑得到的活动边缘的平均流体速度，该扩展传递函数预测了全球大陆边缘天然气水合物聚集的增强。研究了不同的情景，导致全球海底天然气水合物质量约为550 GtC。总体而言，我们的系统方法可以清晰定量地区分POC生物甲烷生成和流体平流对天然气水合物聚集的影响，从而为估计海洋沉积物中大规模和全球天然气水合物储量提供了一个简单的预测工具。
The accumulation of gas hydrates in marine sediments is essentially controlled by the accumulation of particulate organic carbon (POC) which is microbially converted into methane, the thickness of the gas hydrate stability zone (GHSZ) where methane can be trapped, the sedimentation rate (SR) that controls the time that POC and the generated methane stays within the GHSZ, and the delivery of methane from deep-seated sediments by ascending pore fluids and gas into the GHSZ. Recently, Wallmann et al. (2012) presented transfer functions to predict the gas hydrate inventory in diffusion-controlled geological systems based on SR, POC and GHSZ thickness for two different scenarios: normal and full compacting sediments. We apply these functions to global data sets of bathymetry, heat flow, seafloor temperature, POC input and SR, estimating a global mass of carbon stored in marine methane hydrates from 3 to 455 Gt of carbon (GtC) depending on the sedimentation and compaction conditions. The global sediment volume of the GHSZ in continental margins is estimated to be 60–67 × 1015 m3, with a total of 7 × 1015 m3 of pore volume (available for GH accumulation). However, seepage of methane-rich fluids is known to have a pronounced effect on gas hydrate accumulation. Therefore, we carried out a set of systematic model runs with the transport-reaction code in order to derive an extended transfer function explicitly considering upward fluid advection. Using averaged fluid velocities for active margins, which were derived from mass balance considerations, this extended transfer function predicts the enhanced gas hydrate accumulation along the continental margins worldwide. Different scenarios were investigated resulting in a global mass of sub-seafloor gas hydrates of ~ 550 GtC. Overall, our systematic approach allows to clearly and quantitatively distinguish between the effect of biogenic methane generation from POC and fluid advection on the accumulation of gas hydrate, and hence, provides a simple prognostic tool for the estimation of large-scale and global gas hydrate inventories in marine sediments.