DIMES: Diapycnal and Isopycnal Mixing Experiment in the Southern Ocean

地球的气候正在发生变化，就像过去一样。当今科学家面临的巨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、冰和生物之间复杂的相互作用，这些相互作用被认为是驱动气候变化的原因。部分由于这些模拟，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因素之一是科学家所说的“经向翻转环流”（MOC）。这个术语描述了高纬度地区地表水的冷却和下沉，它们穿过深海，最终在几十年或几个世纪后变暖并返回地面。MOC对气候很重要，因为参与这一漫长海洋循环的水团携带着热量、二氧化碳和其他重要物质，如植物营养物质，这些物质以这种方式分布在地球各地，并长期锁在深海中。也许MOC最让科学家困惑的阶段，也是对气候模拟可靠性最严峻的挑战之一，是深水团返回地表。原因是深海的变暖是由海洋流动的最小空间和时间尺度上的洋流驱动的。对海洋中这些所谓的“混合过程”的不完整测量使一些科学家相信，深海的表面主要是由南大洋的涡流（海洋的天气系统，测量直径几公里或几十公里）的上升作用驱动的。反过来，其他科学家认为，关键的驱动过程是由海浪（波峰到波谷的距离为几十米）在海洋内部的破碎引起的小规模湍流。科学家们普遍认为，为了解决这个“海洋混合难题”，我们必须首先了解涡旋和内波是如何驱动南大洋深水团的表面的。这是因为众所周知，南大洋拥有全球很大一部分上升流，并为这两种上升流机制的繁荣提供了最佳条件。为了在这个问题上取得突破，我们计划进行一个实验，我们将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一种染料来直接测量混合情况，然后在一系列科学巡航中观察它在空间和时间上的传播情况。为了确定漩涡和内波在多大程度上造成了观测到的混合，我们将获得并分析它们在水的温度、盐度和流动速度方面的特征的精密测量结果（其中许多将是在南大洋首次进行此类测量）。我们将结合船上部署的仪器，自由流动的浮子跟踪水域，其他浮子在海面和深海之间上下分析，在深海停泊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，如“控制南大洋深水团上涌的物理原理是什么？”以及“我们应该如何在气候模拟中表现重要的混合过程？”

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?'.