Surfactant control of air-sea gas exchange in coastal waters

表面活性剂对近海海气气体交换的控制

基本信息

批准号：
NE/I015299/1
负责人：
Robert Upstill-Goddard
金额：
$ 6.36万
依托单位：
Newcastle University
依托单位国家：
英国
项目类别：
Research Grant
财政年份：
2011
资助国家：
英国
起止时间：
2011 至无数据
项目状态：
已结题

来源：
https://gtr.ukri.org/projects?ref=NE%2FI015299%2F1
关键词：
Surfactant control air sea gas

项目摘要

Surfactants are 'wetting agents' that lower the surface tension of water. Familiar everyday surfactants include household detergents but a vast array of natural surfactants reflects a diversity of biological processes responsible for their production. Surfactants in seawater for example are mainly those released by phytoplankton, both during growth and subsequent death and decomposition. These phytoplankton-derived surfactants include, among many other compounds, polysaccharides (complex sugars), lipids (fats and waxes), fatty acids and proteins. This 'pool' of surfactants accumulates in the so-called sea surface microlayer (SML), which is the uppermost 'skin' of the oceans and is of the order of only a tenth of a millimetre thick or less. Despite being so thin the SML is extremely important for a number of reasons, one being that both its depth and its chemical and physical nature can influence greatly the exchange of climate-active gases such as carbon dioxide between the oceans and the atmosphere. This is important because the oceans currently absorb around a quarter of the carbon dioxide that is being released into the air during the burning of fossil fuels (about half stays in the atmosphere and the remaining quarter is absorbed by land vegetation). It is therefore very important to know the rates at which carbon dioxide and other gases exchange across the sea surface and this depends essentially on the thickness of the SML, which is controlled by turbulence due to wind, waves and other agents. When the turbulence (e.g. wind speed) is high the SML is thin and the gas exchange rate is high but when the turbulence is low the SML thickens and the gas exchange rate falls. Natural surfactants in the SML suppress surface water turbulence and so slow down perhaps very significantly, the rate of air-sea gas exchange. Unfortunately surprisingly little is known about the importance of this surfactant effect on gas exchange at sea; most of our knowledge derives from laboratory studies with synthetic compounds. To date there are no detailed gas exchange data for natural surfactants at sea. Marine phytoplankton activity is spatially and temporally variable but tends to be highest in coastal waters; in the very few studies carried out to date surfactants have been shown to strongly decrease in concentration and to change in composition seaward along estuaries, continuing offshore. Importantly, estuaries and coastal waters are major source regions for many climate-active gases and so the surfactant effect on gas exchange will be most pronounced there. However, relevant measurements are lacking and this study will therefore examine the relationship between surfactant concentration and gas exchange along an estuarine-offshore gradient in surfactant concentration and composition to better understand how this variability relates to air-sea gas exchange. Aspects of the broad chemical composition of the surfactant pool will enable determining whether the overall chemical composition of the surfactant pool also plays a role in gas exchange; something that to date has not been addressed. This unique study will thus provide valuable data required to advance current understanding of air-sea gas exchange and help define more clearly key research goals for subsequent projects building on this work. The ultimate goal of this developing research area is to provide data to models designed to predict future climate change based on the growth of atmospheric carbon dioxide and the climate response of the coupled atmospheric, oceanic and terrestrial systems.

表面活性剂是降低水表面张力的“润湿剂”。熟悉的日常表面活性剂包括家用洗涤剂，但大量的天然表面活性剂反映了导致其生产的各种生物过程。例如，海水中的表面活性剂主要是浮游植物在生长和随后的死亡和分解过程中发布的表面活性剂。这些浮游植物衍生的表面活性剂包括许多其他化合物，包括多糖（复杂糖），脂质（脂肪和蜡），脂肪酸和蛋白质。这种表面活性剂的“池”积聚在所谓的海面微层（SML）中，这是海洋上最高的“皮肤”，仅为厚或更小的十分之一。尽管出于多种原因，SML非常重要，但其中一个是其深度以及其化学和物理性质都可以极大地影响气候活性气体在海洋和大气之间的二氧化碳等气候活性。这很重要，因为目前，海洋吸收了大约四分之一的二氧化碳，该二氧化碳在燃烧化石燃料期间被释放到空中（大约一半呆在大气中，其余季度被土地植被吸收）。因此，了解二氧化碳和其他气体在海面上交换的速率非常重要，这实际上取决于SML的厚度，SML的厚度是由风，波浪和其他试剂引起的湍流控制的。当湍流（例如风速）高时，SML很薄，气体汇率很高，但是当湍流低时，SML变厚并且气体汇率下降。 SML中的天然表面活性剂抑制了地表水湍流，并且可能非常明显地放慢了气海气体交换的速度。不幸的是，这种表面活性剂对海上气体交换的重要性知之甚少。我们的大多数知识都来自具有合成化合物的实验室研究。迄今为止，海上天然表面活性剂尚无详细的气体交换数据。海洋浮游植物的活动在空间和时间上是可变的，但在沿海水域往往最高。在迄今为止进行的表面活性剂的少数研究表明，浓度大大降低，并在沿河口沿着河口沿海变化，继续近海。重要的是，河口和沿海水域是许多气候活性气体的主要来源区域，因此在那里最明显的表面活性剂对气体交换的影响最为明显。但是，缺乏相关的测量值，因此这项研究将研究表面活性剂浓度和成分沿河口沿岸梯度的表面活性剂浓度和气体交换之间的关系，以更好地了解这种可变性与空气海气交换的关系。表面活性池的广泛化学成分的各个方面将确定表面活性池的总体化学成分是否在气体交换中起作用；迄今为止尚未解决的问题。因此，这项独特的研究将提供必要的数据，以促进当前对空气气体交换的了解，并帮助定义更明确的关键研究目标，以实现这项工作的后续项目。该发展研究领域的最终目标是为旨在根据大气二氧化碳的生长以及耦合大气，海洋和陆地系统的气候反应来预测气候变化的模型提供数据。