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/J005282/1
• 负责人: Neil Mitchell
• 金额: $ 2.48万
• 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: 2012
• 资助国家: 英国
• 起止时间: 2012 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FJ005282%2F1
• 关键词: Comparing; sediment; accumulation; below; unproductive

IODP Expedition 329 cored deep-sea sediments at seven sites along two transects in the center of the South Pacific Gyre (SPG). Before this expedition, the SPG contained the largest portion of the seafloor that was never explored with scientific ocean drilling. Therefore, this expedition and the onshore post-cruise studies 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 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) and I will 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. Grain size data from this remote location can also provide crucial information on eolian inputs and past atmospheric circulation.In addition, the grain size measurements will 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.Due to the unique nature of these sediments, in particular their very low organic matter content, we will also conduct a pilot study to determine the potential for future paleoceanographic and paleoclimatic reconstructions using specific biomarkers (i.e. fossil molecules).This research will deepen our understanding of how pelagic sediments accumulate in the deep ocean. Relatively few precise grain size analyses of pelagic sediments have been reported so far.

IODP探险329在南太平洋环流中心两个断面的七个地点对深海沉积物进行了取芯。在这次探险之前，SPG包含了科学海洋钻探从未探索过的最大部分的海底。因此，这次考察和陆上巡航后的研究将在广泛的战线上促进科学理解。探险329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有时被描述为地球上最大的海洋沙漠。它的中心距离大陆的距离比任何其他环流的中心都要远。该环流的表层叶绿素浓度和初级生产力低于世界海洋的其他区域。在这个纬度，风吹来的沙尘最少。平均沉积速率是地球上最低的沉积速率之一，比赤道太平洋的速率低1-2个数量级。因此，SPG是探索远洋环流极低活动中心沉积性质的理想区域。这项研究将比较低生产力的南太平洋环流之下的沉积物积累与高生产力的赤道中部太平洋的积累。不同的物理环境，以及与SPG之下以粘土为主的沉积物相关的非常不同的颗粒组成和大小，应该会导致有趣的差异。大多数深海沉积研究侧重于相对靠近海岸和主要上升流带之下的地点，在这些地点，生物生产力和进入海底的有机通量一般都很高。与对大陆边缘和斜坡的影响相比，弱底流和相关深水过程对大洋盆地沉积的影响知之甚少。记录海洋底流以下的沉积过程需要进行一系列分析。我将使用地震研究和现场勘测数据(R/V Revelle上的Cruise Knox-02RR)，并进行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，并可以提供相对流动速度的指标。来自这个偏远地点的粒度数据还可以提供有关风沙输入和过去大气环流的关键信息。此外，粒度测量将为探险329的基本目标提供有价值的信息。特别是，它将有助于确定最缺乏有机物质的沉积物中的海底生命是否在很大程度上受到水的原位辐解(水的分子解离，由放射性衰变产生的高能阿尔法粒子造成)的氢的滋养。深海沉积物中的大部分海底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。辐射分解速率将由科学船方根据放射性元素浓度确定，他们需要粒度数据，因为颗粒大小影响水的辐射分解速率。由于富含粘土的沉积物含有比其他深海沉积物高得多的放射性元素，而且在细粒沉积物中，大多数α和β产物发生在孔隙水的冲击范围内，这些深海粘土预计会产生比其他沉积环境高得多的水辐解速率。由于这些沉积物的独特性质，特别是其非常低的有机质含量，我们还将进行一项初步研究，以确定未来利用特定生物标志物(即化石分子)重建古海洋和古气候的可能性。这项研究将加深我们对远洋沉积物如何在深海堆积的理解。到目前为止，关于远洋沉积物的精确粒度分析的报道相对较少。

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

Presence of oxygen and aerobic communities from sea floor to basement in deep-sea sediments

• DOI: 10.1038/ngeo2387
• 发表时间: 2015-04-01
• 期刊: NATURE GEOSCIENCE
• 影响因子: 18.3
• 作者: D'Hondt, Steven;Inagaki, Fumio;Ziebis, Wiebke
• 通讯作者: Ziebis, Wiebke