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”。常见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其生产过程的多样性。例如，海水中的表面活性剂主要是浮游植物在生长以及随后的死亡和分解过程中释放的表面活性剂。这些源自浮游植物的表面活性剂包括多糖（复合糖）、脂质（脂肪和蜡）、脂肪酸和蛋白质等许多其他化合物。这种表面活性剂“池”积聚在所谓的海面微层（SML）中，它是海洋最上面的“皮肤”，厚度仅为十分之一毫米或更小。尽管SML如此薄，但由于多种原因而极其重要，其中之一是它的深度及其化学和物理性质都会极大地影响气候活跃气体（例如海洋和大气之间的二氧化碳）的交换。这很重要，因为海洋目前吸收了化石燃料燃烧过程中释放到空气中的大约四分之一的二氧化碳（大约一半留在大气中，其余四分之一被陆地植被吸收）。因此，了解二氧化碳和其他气体在海面交换的速率非常重要，这主要取决于 SML 的厚度，而 SML 的厚度受风、波浪和其他因素引起的湍流控制。当湍流（例如风速）较高时，SML 较薄，气体交换率较高，但当湍流较低时，SML 较厚，气体交换率下降。 SML中的天然表面活性剂抑制地表水湍流，因此可能非常显着地减慢空气-海洋气体交换的速率。不幸的是，令人惊讶的是，人们对这种表面活性剂对海上气体交换的重要性知之甚少。我们的大部分知识都来自合成化合物的实验室研究。迄今为止，尚无海上天然表面活性剂的详细气体交换数据。海洋浮游植物活动随空间和时间变化，但沿海水域往往最高；迄今为止进行的极少数研究表明，沿着河口向海延伸，直至近海，表面活性剂的浓度急剧下降，成分也发生变化。重要的是，河口和沿海水域是许多气候活跃气体的主要来源地区，因此表面活性剂对气体交换的影响在这些地方最为明显。然而，缺乏相关的测量，因此本研究将研究表面活性剂浓度与沿着河口-近海梯度的表面活性剂浓度和组成的气体交换之间的关系，以更好地了解这种变化与空气-海洋气体交换的关系。表面活性剂池的广泛化学成分方面将能够确定表面活性剂池的整体化学成分是否也在气体交换中发挥作用；迄今为止尚未解决的问题。因此，这项独特的研究将提供推进当前对海气交换的理解所需的宝贵数据，并有助于为基于这项工作的后续项目更明确地确定关键研究目标。这一发展中的研究领域的最终目标是为模型提供数据，这些模型旨在根据大气二氧化碳的增长以及耦合的大气、海洋和陆地系统的气候响应来预测未来的气候变化。