The influence of surfactants on the mechanisms of ocean bubble generation, and the consequences for air-sea gas transfer.

这个项目将研究天然海洋物质如何影响海洋中气泡的产生。气泡对于发生在海洋顶部几米处的许多过程都很重要。它们大多是由破碎的海浪产生的，尽管较大的气泡很快浮出水面并破裂，但较小的气泡可能会被困在海洋中几分钟。大小气泡对于气体从大气到海洋的转移都很重要，因为它们提供了大量的表面积，在那里气泡中的气体可以接触海洋并可能溶解在海洋中。破碎的海浪会在海洋中产生相当大的背景噪音，因为每个新形成的气泡都会发出声音脉冲。气泡还可以吸收和改变来自其他来源的声音，因此了解气泡的存在对于了解声纳脉冲和其他来自表面以下的声音是如何从海面反弹到海面上很重要的。随着天气模型以及大风和风暴的影响的改善，需要更多的细节来正确理解海洋表面的物理。我们现在了解到，像气泡产生这样的非常小的事件可以对海洋中的气体吸收等更大的过程产生重大影响，所以了解海洋中存在的气泡的数量和大小变得越来越重要。破碎波下的气泡是由于破碎后的头一两秒内存在的强烈湍流而形成的。这种湍流将扭曲气泡，并可能将一个大气泡分解成两个或更多较小的气泡。这些较小的气泡可能会依次破碎，这一过程会继续下去，直到湍流不再强大到足以打破气泡为止。此外，气泡可能会相互碰撞并合并，由两个较小的气泡形成较大的气泡。所有这些过程决定了一个波浪破裂后有多少气泡，以及它们有多大，然后这些固定的气泡数量上升、溶解，并随着时间的推移变化得更慢。气泡的变形取决于湍流的强度和气泡表面的行为方式。表面倾向于减少变形，从而防止气泡破裂。以前的研究已经研究了清洁淡水和咸水中的气泡破裂，但天然海水中含有许多其他物质，这些物质是由水中的小生物体(例如藻类、微小植物和微小动物)产生的。这些物质中的许多会粘在气泡表面上，并可能改变气泡表面的行为，包括分裂和重新连接的可能性。这个奖学金项目将研究单个气泡分裂成两个气泡，以及成对的气泡在湍流中结合在一起形成一个更大的气泡，并比较在存在和没有天然海洋化学品存在的情况下会发生什么。然后，人工波将被产生，并允许在有和没有额外化学品的情况下在波浪槽中破裂，这样我们就可以看到由化学品引起的气泡数量和大小的变化。最后，我们将研究真实海浪中的气泡，以寻找同样的影响。总体结果将有助于我们了解海洋的自然化学物质如何影响海洋和大气的相互作用。海洋化学在海洋的不同区域可能有很大的不同，目前在测量自然气泡数量及其影响时没有考虑到这一点。

This project will examine how natural ocean substances affect the production of bubbles in the ocean. Bubbles are important for many of the processes that happen in the top few metres of the ocean. They are mostly generated by breaking waves, and although the larger ones rise to the surface very quickly and burst, the smaller bubbles can remain trapped in the ocean for several minutes. Both large and small bubbles are important for the transfer of gas from the atmosphere to the ocean, since they provide lots of surface area where the gas inside the bubble can touch the ocean and may dissolve in it. Breaking waves generate a considerable amount of background noise in the ocean, because every newly-formed bubble emits a pulse of sound. Bubbles can also absorb and redirect sound that comes from other sources, and so knowledge of the bubbles present is important for understanding how sonar pulses and other sound from below the surface bounces off the top of the ocean. As modelling of weather and the effect of high winds and storms improves, an increasing level of detail is needed to understand the physics of the ocean surface properly. We now understand that very small events like bubble production can make a significant difference to larger processes in the ocean like gas absorption, so knowledge of the number and size of bubbles that exist in the ocean is becoming increasingly important. Bubbles underneath breaking waves are formed because of the intense turbulence that exists for the first second or two after wave breaking. This turbulence will distort the bubbles and may break a large bubble into two or more smaller bubbles. These smaller bubbles may fragment in turn, and the process continues until the turbulence is no longer strong enough to break the bubbles up. In addition, bubbles may bump into each other and coalesce, making larger bubbles out of two smaller ones. All these processes determine how many bubbles there are just after a wave breaks and how big they are, and then this fixed population of bubbles rises and dissolves and changes more slowly with time. The distortion of a bubble depends on the strength of the turbulence and the way the bubble surface behaves. The surface tends to reduce the distortion and so prevent the bubble breaking up. Previous research has investigated bubble splitting in clean fresh water and salt water, but natural ocean water contains many other substances, which are generated by the small organisms in the water (for example algae, tiny plants and tiny animals). Many of these substances will stick to bubble surfaces and may change how the bubble surface behaves, including the probability of splitting and rejoining. This fellowship project will look at single bubbles splitting into two bubbles and pairs of bubbles joining together to form one bigger bubble in turbulence, and compare what happens with and without the natural ocean chemicals present. Then, artificial waves will be generated and allowed to break in a wave tank with and without the additional chemicals , so that we can see the changes in the number and size of bubbles that are caused by the chemicals. Finally, the bubbles in real breaking waves at sea will be studied to look for the same effects. The overall results will help us understand how the natural chemistry of the ocean could affect how the ocean and the atmosphere interact. Ocean chemistry can be very different in different regions of the ocean, and this is not currently taken into account in the measurement of natural bubble populations and their effects.