The impact of coastal updwellings on air-sea exchange of climatically important gases.

世界气候影响着我们所有人，我们依靠精确的科学测量和模型来预测气候将如何变化，以及我们如何减少或应对这些变化。全球温度、光照和天气模式的变化是由于二氧化碳、甲烷、氧化亚氮和二甲基硫化物等大气成分和气体的增加或变化造成的。这些气体在海水中的浓度可以通过生活在海洋表面的微生物（=病毒、细菌、植物（浮游植物）和动物（浮游动物））的活动而改变。此外，其中一些气体的浓度和改变其浓度的微生物的活动可以被到达海面的光的数量所改变。因此，为了了解这些对气候至关重要的气体的浓度是如何在大气中保持的，科学家必须了解它们是如何在海洋中产生的（通过微生物和光化学反应），以及这些气体是如何在海洋表面和大气之间交换的。在海洋的某些区域，已知这些气体的通量非常高。其中包括东大西洋的一些沿海地区，在那里，由于与海岸平行的持续强风，导致深冷水上升到海岸的表面，以取代被风吹到离岸的地表水。这些“上涌”的深水往往已经远离阳光照射的含氧上层海洋数十年至数百年了，因此主要的微生物活动是产生二氧化碳、甲烷、氧化亚氮和营养物质（如“花园肥料”硝酸盐和磷酸盐）的细菌。这些水还含有溶解的营养化合物，由于其复杂的结构而抵抗细菌分解。当深水到达水面时，高浓度的营养物质刺激藻类大量繁殖，藻类会产生二甲基硫化物，而高浓度的有机营养物质会进一步刺激（但不同的）细菌活动。复杂的营养化合物在黑暗的深海中避免了细菌的分解，可以转化为对气候重要的气体，如二氧化碳和一氧化碳，以及细菌更容易消耗的营养物质，一旦到达表面，相对较高的光可用性。这些相互作用过程（溶解气体的海气交换、气体和微生物营养物质的光化学生产以及微生物调节的气体生产）在海洋中很难测量，特别是在上升流区域，因为水在不断移动和混合。有一种方法可以确保测量结果来自同一块水，这样就可以跟踪微生物和光化学过程的进展，那就是在上涌的水中添加一种惰性化合物，作为特定水域的“标签”。这种惰性化合物（称为六氟化硫）通常以极少量存在于海洋中，因此测量它的仪器必须非常灵敏。通过不断测量表层海水中的这种化合物，我们可以保持科考船在同一水体中的位置。这个独特的项目将标记西北非洲海岸外的上升流，使研究船上经验丰富的化学和生物科学家能够测量光化学，微生物学和物理化学之间的相互作用，在海洋中产生对气候重要的气体并将其输送到大气中。只有了解这些过程是如何发生的，我们才能预测它们在不断变化的环境中会如何变化。该项目的结果将提供给全世界正在研究这个全球重要问题的科学家。

The world's climate affects us all, and we depend upon accurate scientific measurements and models to predict how climate will change and how we might reduce or cope with the changes. changes in global temperature, light and weather patterns are due to increases or changes in atmospheric constituents and gases such as carbon dioxide, methane, nitrous oxide and dimethylsulphide. The concentration of each of these gases in seawater can be changed by the activity of the microbes (= viruses, bacteria, plants (phytoplankton) and animals (zooplankton)) which live in the surface of the ocean. in addition, the concentrations of some of these gases and the activity of the microbes which alter their concentrations can be changed by the amount of light which reaches the sea surface. Therefore, in order to understand how the concentrations of these climatically important gases are maintained in the atmosphere, scientists must understand how they are produced in the ocean (by microbiological and photochemical reactions) and how the gases exchange between the sea surface and the atmosphere. There are certain regions in the ocean where fluxes of these gases are known to be very high. These include some coastal areas of the eastern Atlantic where, due to consistently strong winds parallel to the shore, deep cold water is caused to rise to the surface at the coast to replace surface waters being driven offshore by the wind. These 'upwelling' deep waters tend to have been away from the sunlit oxygenated upper ocean for tens to hundreds of years, and so the predominant microbial activity is of the bacteria which produce carbon dioxide, methane, nitrous oxide and nutrients such as the 'garden fertilizers' nitrate and phosphate. These waters also contain dissolved nutrient compounds which have resisted bacterial breakdown due to their complex structure. When the deep waters reach the surface, the high concentrations of nutrients stimulate blooms of algae which can produce dimethylsulphide and high levels of organic nutrients which stimulate further (but different) bacterial activity. The complex nutrient compounds which avoided bacterial breakdown in the dark deep ocean, can be converted into climatically important gases such as carbon dioxide and carbon monoxide and nutrients more readily consumed by bacteria, by the relatively high light availability once at the surface. These interacting processes (air-sea exchange of dissolved gases, photochemical production of gases and microbial nutrients, and microbially mediated production of gases) are very difficult to measure in the ocean, and particularly in an upwelling region, as the water is continually moving and mixing. One way to make sure that the measurements are taken from the same water mass, so one can follow the progression of microbial and photochemical processes, is to add an inert compound to the upwelling water as a 'label' of that particular patch of water. This inert compound (called sulphur hexafluoride) normally exists in the ocean in vanishingly small amounts and so the instruments which measure it have to be extremely sensitive. By continually measuring this compound in surface seawater we can maintain the position of the research vessel in the same water body. This unique project will label upwelling water off the coast of Northwest Africa, allowing the experienced chemical and biological scientists on the research ship to measure the interplay between photochemistry, microbiology and physical chemistry in producing climatically important gases in the ocean and delivering them to the atmosphere. Only by understanding how these processes occur now can we predict how they might change in a changing environment. Results from the project will be made available to scientists throughout the world who are working on this globally important question.