Comparing sediment accumulation below the unproductive South Pacific Gyre (IODP expedition 329) with the highly productive central equatorial Pacific

比较贫瘠的南太平洋环流（IODP 第 329 次考察）与高产的赤道中太平洋下方的沉积物积累

• 批准号: NE/I017895/1
• 负责人: Neil Mitchell
• 金额: $ 1.45万
• 依托单位: University of Manchester
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2010
• 资助国家: 英国
• 起止时间: 2010 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FI017895%2F1
• 关键词: Comparing; sediment; accumulation; below; unproductive

IODP Expedition 329 will core deep-sea sediment at a series of sites crossing the South Pacific Gyre (SPG). The SPG contains the largest portion of the seafloor that has never been explored with scientific ocean drilling, so this drilling will advance scientific understanding across a broad front. The primary purpose of Expedition 329 is to document the extent and nature of microbial life in the sediments beneath the low-productivity heart of the ocean. The SPG is sometimes described as Earth's largest oceanic desert. Its center is farther from continents than the center of any other gyre. Surface chlorophyll concentrations and primary productivity are lower in this gyre than in other regions of the world ocean. Wind-blown dust is at a minimum at this latitude. Mean sedimentation rates within the SPG are among the lowest that occur on Earth, 1-2 orders of magnitude lower than rates in the equatorial Pacific. The SPG is thus an ideal region for exploring the nature of sedimentation in the extreme low-activity centre of an open-ocean gyre. This research will compare and contrast sediment accumulation below the unproductive South Pacific Gyre with accumulation in the highly productive central equatorial Pacific. The different physical environment as well as the very different particle compositions and sizes associated with clay-dominated deposits below the SPG should lead to interesting differences. The majority of deep-sea sedimentation studies have focused on sites relatively close to shore and beneath major upwelling zones, where biological productivity and organic flux to the seafloor are generally high. Little is known about the effects of weak bottom currents and related deep-water processes on sedimentation in ocean basins compared with their effects on continental margins and slopes. Documentation of sedimentation processes below the SPG will require a range of analyses. I will use the seismic studies and site survey data (Cruise KNOX-02RR, aboard the R/V Revelle) as well as the wireline logging data from the IODP sites. Preliminary work on the seismic images reveal areas of bottom current activity occasionally resulting in localized scouring of all sediment above volcanic basement. I will also perform SediGraph grain size analyses. Variations in particle size can shed light on many facets of deep-sea sediments including depositional conditions and can provide indicators of relative flow speed. The grain size measurements will also contribute valuable information to the fundamental objectives of Expedition 329. In particular, it will help determine whether subseafloor life in the most organic-poor sediment is nourished to a significant extent by H2 from in situ radiolysis of water (the molecular dissociation of water, H2O, caused by energetic alpha-particles produced by radioactive decay). Most subseafloor life in deep-sea sediments is maintained by products of organic matter degradation so this would be an important finding. Radiolysis rates will be determined from radioactive element concentrations by the scientific shipboard party, who require grain size data because particle size influences the rate of water radiolysis. As clay-rich sediment contains much higher concentrations of radioactive elements than other deep-sea sediment and, in fine-grained sediment, most alpha and beta production occurs within striking range of pore water, these deep-sea clays are anticipated to yield much higher rates of water radiolysis than other sedimentary environments. This research will deepen our understanding of how pelagic sediments accumulate in the deep ocean. Few precise grain size analyses of pelagic sediments have been reported so far. In addition, this project will help to assess the potential importance of water radiolysis to subseafloor sedimentary microbial communities.

国际大洋钻探项目第329次考察将在穿越南太平洋环流的一系列地点采集深海沉积物的岩芯。SPG包含了从未通过科学海洋钻探进行过探索的海底的最大部分，因此这次钻探将在广泛的领域推进科学认识。329号考察队的主要目的是记录海洋低生产力中心下沉积物中微生物生命的范围和性质。SPG有时被称为地球上最大的海洋沙漠。它的中心比其他任何环流的中心都离大陆更远。该环流的表层叶绿素浓度和初级生产力低于世界海洋其他区域。在这个纬度上，风吹尘埃最少。SPG内的平均沉积速率是地球上最低的，比赤道太平洋的沉积速率低1-2个数量级。因此，SPG是探索公海环流极低活动中心沉积性质的理想区域。这项研究将比较和对比非生产性南太平洋环流下的沉积物积累与高生产性赤道太平洋中部的沉积物积累。不同的物理环境，以及非常不同的颗粒组成和大小与粘土为主的存款低于SPG应导致有趣的差异。大多数深海沉积研究都集中在相对靠近海岸和主要上升流区之下的地点，那里的生物生产力和流向海底的有机物通量一般都很高。与对大陆边和大陆坡的影响相比，弱底流和相关深水过程对海洋盆地沉积作用的影响知之甚少。SPG以下的沉积过程的文件将需要一系列的分析。我将使用地震研究和现场勘测数据（R/V Revelle上的Cruise KNOX-02 RR）以及IODP现场的电缆测井数据。对地震图像的初步工作显示，底流活动区偶尔会对火山基底上方的所有沉积物造成局部冲刷。我还将执行SediGraph粒度分析。颗粒大小的变化可以揭示深海沉积物的许多方面，包括沉积条件，并可以提供相对流速的指标。粒度测量也将为329远征的基本目标提供有价值的信息。特别是，它将有助于确定有机物最贫乏的沉积物中的海底生物是否在很大程度上受到水就地辐解（放射性衰变产生的高能α粒子引起的水分子离解，H2O）产生的H2的滋养。深海沉积物中的大多数海底下生命是由有机物降解的产物维持的，因此这将是一个重要的发现。辐解率将由科学船上方根据放射性元素浓度确定，他们需要粒度数据，因为粒度影响水辐解率。由于富含粘土的沉积物所含放射性元素的浓度比其他深海沉积物高得多，而且在细粒沉积物中，大多数α和β产生发生在孔隙水的显著范围内，因此预计这些深海粘土产生的水辐解率比其他沉积环境高得多。这项研究将加深我们对远洋沉积物如何在深海中积累的理解。迄今为止，很少有关于远洋沉积物精确粒度分析的报道。此外，该项目将有助于评估水辐解对海底沉积微生物群落的潜在重要性。

项目成果

Evaluating Cenozoic equatorial sediment deposition anomalies for potential paleoceanographic and Pacific plate motion applications

• DOI: 10.1007/s11001-013-9196-2
• 发表时间: 2014-03
• 期刊: Marine Geophysical Research
• 影响因子: 1.4
• 作者: N. Mitchell;N. Dubois