How do deep-ocean turbidity currents behave that form the largest sediment accumulations on Earth?

深海浊流如何形成地球上最大的沉积物堆积？

• 批准号: NE/R001952/1
• 负责人: Peter Talling
• 金额: $ 60.27万
• 依托单位: Durham University
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2019
• 资助国家: 英国
• 起止时间: 2019 至 无数据
• 项目状态: 未结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FR001952%2F1
• 关键词: How; do; deep; ocean; turbidity

Seafloor flows called turbidity currents form the largest sediment accumulations on Earth (submarine fans). They flush globally significant amounts of sediment, organic carbon, nutrients and fresher-water into the deep ocean, and affect its oxygen levels. Only rivers transport comparable volumes of sediment across such large expanses of our planet, although a single turbidity current can transport more sediment than the combined annual flux from all of the World's rivers combined. Here we will make a step change in understanding of turbidity currents, and their wider impacts, by making the first detailed measurements of turbidity current that runout into the deep (2-5 km) ocean. Such direct monitoring of turbidity currents that form major submarine fan systems has been a 'holy grail' for sedimentology, oceanography, and marine geology for decades. It would be broadly comparable to the first detailed measurements of major river systems or other first-order processes for moving sediment across the planet. This project is especially timely due to recent successful tests of new methods and technology for measuring turbidity currents in shallower (less than 2 km) water, which can now be used for deep-water, large-scale submarine fan settings. We choose to study the Congo Canyon off West Africa due to an exceptional set of initial measurements collected in 2010 and 2013. These measurements at 2 km water depth are the deepest yet for turbidity currents. Surprisingly, they showed that individual turbidity currents lasted for almost a week, and occupied 20% of the time. This was surprising because all previously measured oceanic turbidity currents lasted for just a few hours or minutes, and occurred for < 0.1% of the total time. It suggests that turbidity currents that runout into the deep ocean to form major submarine fans may differ from their shallow water cousins in key regards. These preliminary measurements show how monitoring is feasible for the Congo Canyon. They help us to design a project that will now show how these flows runout into the deeper ocean.We will deploy 8 moorings along the Congo Canyon at water depths of 2 to 5 km that will measure frequency, duration, and run-out distance of multiple flows; together with their velocity, turbulence and sediment concentration structures; as well as changes in water, sediment and organic carbon discharge. Our overall aim is to show how deep-sea turbidity current behave using the first direct measurements, and understand causes and wider implications of this behaviour. We will answer the following key questions about flow behaviour:(1) What controls flow duration, and does flow stretching cause near-continuous canyon flushing? We will test a new hypothesis that predicts flows will stretch dramatically as a 'hot spot' of faster moving fluid runs away from the rest of the event, thereby producing near-continuous flushing of submarine canyons. (2) What controls runout and whether flows become more powerful? We will test whether turbidity currents tend towards one of two distinct modes of behaviour, in which they erode and accelerate (a process termed ignition), or deposit sediment and dissipate. (3) How is flow behaviour and character recorded by deposits? This is important because deposits are the only record of most turbidity currents.(4) How does flow behaviour affect the transfer and burial of terrestrial organic carbon in the deep-sea? It was proposed recently that burial of terrestrial organic carbon in the deep sea is very efficient, and an important control on long-term atmospheric CO2 levels. This hypothesis implies little fractionation of terrestrial organic carbon occurs during submarine transport. Composition of organic carbon buried by the offshore flows is similar to that supplied by the river. We will test this hypothesis by analysing amounts and types of organic carbon along the offshore pathway in both flows and deposits.

被称为浑浊流的海底流形成了地球上最大的沉积物堆积(海底扇)。它们将全球范围内大量的沉积物、有机碳、营养物质和淡水冲入深海，并影响其氧气水平。虽然一股浑浊的水流可以输送的泥沙比世界上所有河流的年流量总和还要多，但只有河流才能在地球上如此广阔的土地上输送相当数量的泥沙。在这里，我们将对流入深海(2-5公里)的浊流进行首次详细测量，从而改变对浊流及其更广泛影响的理解。这种对形成主要海底扇系统的浊流的直接监测，几十年来一直是沉积学、海洋学和海洋地质学的“圣杯”。它将在很大程度上与对主要河流系统的首次详细测量或在地球上移动沉积物的其他一级过程相媲美。由于最近成功测试了测量浅水(不到2公里)水中浑浊流的新方法和技术，该项目尤其及时，现在可以用于深水、大型海底风扇设备。我们之所以选择研究西非的刚果峡谷，是因为我们在2010年和2013年收集了一组特殊的初步测量数据。这些在2千米水深进行的测量是迄今为止对浑浊流进行的最深测量。令人惊讶的是，他们发现单个浑浊洋流持续了近一周，占据了20%的时间。这是令人惊讶的，因为所有以前测量到的海洋浑浊洋流只持续了几个小时或几分钟，并且只发生了总时间的0.1%。这表明，流入深海形成主要海底扇的浑浊洋流可能在关键方面与它们的浅水近亲不同。这些初步测量表明，对刚果峡谷进行监测是可行的。他们帮助我们设计了一个项目，现在将展示这些水流如何流入更深的海洋。我们将沿着刚果峡谷部署8个停泊点，深度为2至5公里，将测量多股水流的频率、持续时间和冲出距离；以及它们的速度、湍流和泥沙浓度结构；以及水、沉积物和有机碳排放的变化。我们的总体目标是使用第一次直接测量来显示深海浑浊流的行为，并了解这种行为的原因和更广泛的影响。我们将回答以下关于水流行为的关键问题：(1)是什么控制了水流的持续时间，以及水流的伸展是否会导致接近连续的峡谷冲刷？我们将检验一个新的假说，该假说预测水流将急剧伸展，因为更快移动的流体的“热点”会离开事件的其余部分，从而产生近乎连续的海底峡谷冲刷。(2)是什么控制了跳跃，流动是否变得更加强大？我们将测试浑浊流是否倾向于两种截然不同的行为模式之一，在这两种模式中，它们被侵蚀和加速(一个称为点火的过程)，或者沉积和消散。(3)沉积物如何记录流动行为和性质？这一点很重要，因为沉积物是大多数浊流的唯一记录。(4)水流行为如何影响深海中陆地有机碳的转移和埋藏？最近有人提出，将陆地有机碳埋藏在深海是非常有效的，是控制长期大气二氧化碳水平的重要因素。这一假说表明，在海底运输过程中，陆地有机碳的分馏作用很小。近海水流埋藏的有机碳的组成与河流提供的有机碳的组成相似。我们将通过分析流动和沉积中沿近海路径的有机碳的数量和类型来检验这一假设。

项目成果

What determines the downstream evolution of turbidity currents?

• DOI: 10.1016/j.epsl.2019.116023
• 发表时间: 2020-02-15
• 期刊: EARTH AND PLANETARY SCIENCE LETTERS
• 影响因子: 5.3
• 作者: Heerema, Catharina J.;Talling, Peter J.;Pope, Edward
• 通讯作者: Pope, Edward

Preconditioning by sediment accumulation can produce powerful turbidity currents without major external triggers

• DOI: 10.1016/j.epsl.2021.116845
• 发表时间: 2021-03-03
• 期刊: EARTH AND PLANETARY SCIENCE LETTERS
• 影响因子: 5.3
• 作者: Bailey, Lewis P.;Clare, Michael A.;Lundsten, Eve
• 通讯作者: Lundsten, Eve

Carbon and sediment fluxes inhibited in the submarine Congo Canyon by landslide-damming

• DOI: 10.1038/s41561-022-01017-x
• 发表时间: 2022-09
• 期刊: Nature Geoscience
• 影响因子: 18.3
• 作者: E. Pope;M. Heijnen;P. Talling;R. Jacinto;A. Gaillot;Megan L. Baker;S. Hage;M. Hasenhündl;C. Heerema;C. McGhee;Sean C. Ruffell;S. Simmons;M. Cartigny;M. Clare;B. Dennielou;D. Parsons;C. Peirce;M. Urlaub

Longest sediment flows yet measured show how major rivers connect efficiently to deep sea.

• DOI: 10.1038/s41467-022-31689-3
• 发表时间: 2022-07-20
• 期刊: Nature communications
• 影响因子: 16.6