DIMES: Diapycnal and Isopycnal Mixing Experiment in the Southern Ocean

DIMES：南大洋的双重和等重混合实验

• 批准号: NE/E007058/1
• 负责人: Alberto Naveira Garabato
• 金额: $ 169.9万
• 依托单位: University of Southampton
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2008
• 资助国家: 英国
• 起止时间: 2008 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FE007058%2F1
• 关键词: DIMES; Diapycnal; Isopycnal; Mixing; Experiment

The Earth's climate is changing, as it has done in the past. One of the great challenges faced by scientists today is to understand the causes and consequences of these changes. The way many scientists seek this understanding is by running computer-based climate simulations that mimic the complex interactions between the ocean, atmosphere, ice and living beings that are thought to be responsible for driving climate change. It is partly thanks to these simulations that we now know that ocean circulation plays a key role in modulating climate. One of the most important elements of ocean circulation is what scientists know as the 'meridional overturning circulation' (MOC). This term describes the cooling and resulting sinking of surface water masses in high-latitude regions, their journey through the deep ocean and their eventual warming and return to the surface, after many decades or centuries. The MOC is important to climate because the water masses involved in this long circuit through the ocean carry with them heat, CO2 and other significant substances such as plant nutrients, which in this way are distributed around the planet and locked away in the deep ocean for long periods of time. Perhaps the stage of the MOC that puzzles scientists the most, and one of the most serious challenges to the reliability of climate simulations, is the return of deep water masses to the surface. The reason is that the warming of the deep waters that allows this to happen is driven by currents occurring at the smallest spatial and temporal scales at which the ocean flows. Patchy measurements of these so-called 'mixing processes' in the ocean have led some scientists to believe that the surfacing of deep waters is mainly driven by the up-lifiting action of eddies (the weather systems of the ocean, which measure a few or a few tens of kilometres across) in the Southern Ocean. In turn, other scientists contend that the key driving process is small-scale turbulence arising from the breaking of waves (with crest-to-trough distances of tens of metres) travelling through the ocean interior. It is generally agreed amongst scientists that in order to resolve this 'ocean mixing conundrum' we must first understand how eddies and internal waves drive the surfacing of deep water masses in the Southern Ocean. This is so because the Southern Ocean is known to host a large proportion of the global upwelling, and offers the optimal conditions for both upwelling mechanisms to prosper. In order to achieve a breakthrough in this problem, we plan to conduct an experiment in which we will measure mixing processes in the Southern Ocean and their effect on ocean circulation. We will measure mixing directly by releasing a dye in the deep ocean west of Drake Passage and then observing how it spreads in space and time during a series of scientific cruises. In order to determine the extents to which eddies and internal waves are responsible for the observed mixing, we will obtain and analyze sophisticated measurements (many of which will be the first of their kind in the Southern Ocean) of their signatures in the temperature and salinity of the water and the velocity with which it flows. We will do this with a combination of instruments deployed from ships, freely flowing floats tracking water parcels, other floats profiling up and down between the surface and the deep ocean, instruments moored at great depth for 2 years, and satellites measuring sea level. With this unprecedented richness of information, we will be able to answer key questions such as 'What are the physics controlling the upwelling of deep water masses in the Southern Ocean?' and 'How should we represent the important mixing processes in climate simulations?'.

地球的气候正在发生变化，就像过去一样。今天科学家面临的最大挑战之一是了解这些变化的原因和后果。许多科学家寻求这种理解的方式是通过运行基于计算机的气候模拟，模拟海洋，大气，冰和生物之间的复杂相互作用，这些相互作用被认为是导致气候变化的原因。部分归功于这些模拟，我们现在知道海洋环流在调节气候方面起着关键作用。海洋环流中最重要的元素之一是科学家们所知的“赤道翻转环流”（MOC）。这一术语描述了高纬度地区地表水体的冷却和由此产生的下沉，它们穿过深海的旅程，以及几十年或几个世纪后最终变暖并返回地表。MOC对气候很重要，因为在这条漫长的海洋回路中所涉及的水团携带着热量，二氧化碳和其他重要物质，如植物营养素，这些物质以这种方式分布在地球周围，并长时间锁定在深海中。也许最让科学家困惑的MOC阶段，以及对气候模拟可靠性的最严重挑战之一，是深水质量返回到表面。原因是，导致这种情况发生的深海沃茨变暖是由海洋流动的最小空间和时间尺度上发生的水流驱动的。对海洋中这些所谓的“混合过程”的零星测量使一些科学家相信，深海沃茨的浮出水面主要是由南大洋的漩涡（海洋的天气系统，直径为几公里或几十公里）的上升作用驱动的。另一些科学家则认为，关键的驱动过程是穿过海洋内部的波浪（波峰到波谷的距离为几十米）破碎产生的小规模湍流。科学家们普遍认为，为了解决这个“海洋混合难题”，我们必须首先了解漩涡和内波如何驱动南大洋深水团浮出水面。这是因为南大洋是全球上升流的主要区域，并为两种上升流机制的繁荣提供了最佳条件。为了在这一问题上取得突破，我们计划进行一项实验，测量南大洋的混合过程及其对海洋环流的影响。我们将通过在德雷克海峡以西的深海中释放染料来直接测量混合，然后在一系列科学巡航中观察它如何在空间和时间中传播。为了确定涡旋和内波在多大程度上对观察到的混合负责，我们将获得并分析它们在水的温度和盐度以及流动速度方面的签名的复杂测量（其中许多将是南大洋的第一次）。我们将结合从船上部署的仪器，自由流动的浮标跟踪水包，其他浮标在表面和深海之间上下分布，在很深的地方停泊2年的仪器，以及测量海平面的卫星。有了这些前所未有的丰富信息，我们将能够回答一些关键问题，比如“控制南大洋深水团上涌的物理学是什么？”我们应该如何在气候模拟中表现重要的混合过程？'.

项目成果

Observation of a Large Lee Wave in the Drake Passage

• DOI: 10.1175/jpo-d-16-0153.1
• 发表时间: 2017-03
• 期刊: Journal of Physical Oceanography
• 影响因子: 3.5
• 作者: J. Cusack;A. N. Garabato;D. Smeed;J. Girton

On the Consumption of Antarctic Bottom Water in the Abyssal Ocean

• DOI: 10.1175/jpo-d-14-0201.1
• 发表时间: 2016-02-01
• 期刊: JOURNAL OF PHYSICAL OCEANOGRAPHY
• 影响因子: 3.5
• 作者: de Lavergne, Casimir;Madec, Gurvan;Garabato, Alberto C. Naveira
• 通讯作者: Garabato, Alberto C. Naveira

Forcing of the overturning circulation across a circumpolar channel by internal wave breaking

• DOI: 10.1002/2015jc011597
• 发表时间: 2016-08
• 期刊: Journal of Geophysical Research
• 作者: M. B. Broadbridge;A. N. Garabato;A. Nurser

Deep boundary current disintegration in Drake Passage

• DOI: 10.1002/2013gl058617
• 发表时间: 2014-01
• 期刊: Geophysical Research Letters
• 影响因子: 5.2
• 作者: J. Brearley;K. Sheen;A. N. Naveira Garabato;D. Smeed;K. Speer;A. Thurnherr;M. Meredith;S. Waterman

Stabilization of dense Antarctic water supply to the Atlantic Ocean overturning circulation

• DOI: 10.1038/s41558-019-0561-2
• 发表时间: 2019-10-01
• 期刊: NATURE CLIMATE CHANGE
• 影响因子: 30.7
• 作者: Abrahamsen, E. Povl;Meijers, Andrew J. S.;Meredith, Michael P.
• 通讯作者: Meredith, Michael P.