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.

IODP Expedition 329将在穿越南太平洋Gyre（SPG）的一系列地点核心深海沉积物。 SPG包含海底最大的一部分，从未通过科学海洋钻井进行探索，因此这种钻井将在广阔的战线中提高科学理解。 Expedition 329的主要目的是记录海洋低生产力心脏下的沉积物中微生物寿命的程度和性质。 SPG有时被描述为地球最大的海洋沙漠。它的中心离大洲要比任何其他回旋的中心更远。在这种回旋中，表面叶绿素浓度和一级生产率低于世界海洋其他地区。在此纬度上，风吹尘的最低水平。 SPG内的平均沉积率是地球上最低的沉积率，比赤道太平洋的速率低1-2个数量级。因此，SPG是探索开放式Gyre极端低活动中心沉积性质的理想区域。这项研究将比较和对比的南太平洋小杂志以下的沉积物积累与高生产力的中央赤道太平洋地区的积累。不同的物理环境以及与SPG下方的粘土为主沉积物相关的非常不同的颗粒组成和大小应导致有趣的差异。大多数深海沉积研究都集中在相对靠近海岸的地点，并在主要上升区域下方，那里的生物生产力和有机通量对海底通常很高。与它们对大陆边缘和斜率的影响相比，对弱底电流和相关深水过程对海洋沉积的影响知之甚少。 SPG下方沉积过程的文档将需要一系列分析。我将使用地震研究和现场调查数据（Cruise Knox-02RR，在R/V Revelle上）以及来自IODP站点的有线记录数据。在地震图像上的初步工作揭示了底部活动的区域，偶尔会导致火山底高于火山底上所有沉积物的局部冲刷。我还将进行Sedigraph晶粒尺寸分析。粒径的变化可以使深海沉积物（包括沉积条件）的许多方面发光，并可以提供相对流速的指标。 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).深海沉积物中的大多数子叶寿命都是由有机物降解产物维持的，因此这将是一个重要发现。辐射分解速率将由科学船上派对从放射性元素浓度确定，他们需要晶粒尺寸数据，因为粒径会影响水辐射溶解的速率。由于富含粘土的沉积物含有比其他深海沉积物的放射性元素浓度要高得多，而且在细粒的沉积物中，大多数α和β产生发生在孔隙水的引人注目的范围内，因此这些深海粘土预计会产生比其他沉积环境更高的水辐射液。这项研究将加深我们对上层沉积物如何在深海中积累的理解。到目前为止，据报道，几乎没有据报道上层沉积物的晶粒尺寸分析。此外，该项目将有助于评估辐射分解对层状沉积物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