Turbulence, mixing and biological feedbacks in the ocean mixed layer and their relevence to the coupled ocean-atmosphere system

在热带地区，海表面温度(SST)是决定大气环流的主要因素。因此，海温的微小变化(约1摄氏度)可能会对热带天气和气候产生重大影响。上层海洋(上百米左右)的温度分布，因此海温受通过海洋表面的热通量和海洋中湍流混合量的强烈影响。混合量决定了海面通量分布的洋柱深度(混合层深度)，从而决定了SST的变化率。海洋中的混合主要是由表面的风应力驱动的，但也有其他影响，包括由表面波驱动的混合。温度较高(因此密度较低)的水覆盖在较冷的水上会阻碍混合，而温水上的冷水则会加强混合。表面热通量有四个组成部分：通过吸收太阳辐射加热，通过红外辐射冷却(通常)，风力驱动的蒸发和表面的对流热损失。与表面通量的其他成分不同，太阳辐射通过相当大的海洋深度被吸收，少量辐射甚至可以穿透到100米深。这种加热的准确轮廓由水的清澈程度决定，并对混合量和SST的变化率有很大的影响。决定水透明度的主要因素之一是水中浮游植物的数量。浮游植物是一种小型的自由漂浮的海洋植物，像陆地植物一样，可以吸收太阳辐射和二氧化碳生长(如果有足够的营养物质)。然后浮游植物被浮游动物(小型海洋动物)吃掉。浮游生物是海洋食物链的基础。因为浮游植物需要阳光才能生长，它们在海洋中的水平和垂直分布在很大程度上取决于太阳辐射的可用性以及营养物质的可用性。然而，上层海洋中太阳辐射的垂直分布主要由浮游植物的数量和垂直分布决定。由于浮游植物及其生长所需的营养物质是自由漂浮的，浮游生物和营养物质的垂直分布在很大程度上取决于上层海洋的混合。混合、浮游植物和对太阳辐射的吸收之间的这些强烈相互作用导致了复杂反馈的可能性，这最终可能导致SST、气候和海洋生物生产力的变化。该项目计划通过对海洋混合层进行详细的计算机模拟，包括浮游植物和浮游动物以及营养物的可获得性，来调查这些联系及其在全球气候模型中的再现程度。

In the Tropics, the sea surface temperature (SST) plays the dominant role in determining the atmospheric circulation. As a result, small changes in SST (of about 1 degree centigrade) can have a significant impact on tropical weather and climate. The temperature profile in the upper ocean (the top hundred metres or so), and hence the SST is strongly influenced by the heat flux through the surface of the ocean, and the amount of turbulent mixing in the ocean. The amount of mixing determines the depth of the ocean column through which the surface fluxes are distributed (the mixed layer depth) and hence the rate of change of SST. The mixing in the ocean is driven primarily by the wind stress at the surface, but there are other influences, including mixing driven by surface waves. Mixing is inhibited by warmer (and therefore less dense) water lying on top of colder water, and enhanced by cold water lying on top of warm water. There are four components of the surface heat flux; heating by absorption of solar radiation, cooling (usually) by infrared radiation, wind driven evaporation and convective heat loss from the surface. Unlike the other components of the surface flux, the solar radiation is absorbed through quite a large depth of the ocean, and small amounts can even penetrate as deep as 100m. The exact profile of this heating is determined by how clear the water is, and can have a strong influence on the amount of mixing and the rate of change of SST. One of the major factors determining the clarity of the water is the amount of phytoplankton in the water. Phytoplankton are small free floating marine plants which, like land plants, absorb solar radiation and carbon dioxide to grow (given sufficient nutrients). The phytoplankton are then consumed by zooplankton (small marine animals). The plankton are the base of the marine food chain. Because the phytoplankton need sunlight to grow, their distribution in the oceans, both horizontally and vertically, depends strongly on the availability of solar radiation as well as the availability of nutrients. However, the vertical profile of the solar radiation in the upper ocean is primarily determined by the amount and vertical profile of the phytoplankton. Because the phytoplankton and the nutrients that they need for growth are free floating, the vertical distribution of plankton and nutrients is strongly determined by the mixing in the upper ocean. These strong interactions between the mixing, phytoplankton and the absorption of the solar radiation lead to the potential for complex feedbacks, which can ultimately drive variations in SST, climate and the biological productivity of the ocean. This project plans to investigate these links and the extent to which they can be reproduced in global climate models, by detailed computer modelling of the oceanic mixed layer including the phytoplankton and zooplankton and the availability of nutrients.