Impact of Ocean Acidification on the Air-Sea Exchange of Trace Gases

随着大气中二氧化碳含量的持续上升，海水的pH值将逐渐降低。随着世纪的发展，这种影响几乎肯定会越来越明显。它可能影响从珊瑚到微观浮游生物的海洋生物，特别是那些以碳酸钙为主要成分的结构。对非碳酸盐分泌生物的可能影响更难预测。在这个博士根据这一提议，学生将研究pH值下降对海洋微生物产生微量气体（二甲基硫及其前体二甲基磺基丙酸酯和一系列天然产生的有机卤素气体）的影响。这些化合物是挥发性的，可以穿过海-气界面。在大气中，它们的氧化产物可以导致新的粒子形成或现有粒子增长到云凝结核大小。正因为如此，它们可以影响云的形成，从而影响气候。此外，这些气体在控制大气的氧化能力方面起着重要作用，例如通过破坏臭氧，从而影响空气质量。学生将研究pH值变化对微生物产生气体的影响。为了量化在高CO2条件下变化的气体通量的影响，学生将输入当前排放量的估计，以及未来的排放量到一个国家的最先进的一维模型的大气海洋边界层（MISTRA模型）。这将有助于评估pH值引起的微量气体海气通量变化对微粒形成和大气氧化能力的潜在影响。我们建议研究这个系统的方法是通过使用浮动和固定的生态系统，其中pH值进行调整，以模拟未来的条件和体外研究，使用pH值改变的天然海水和特定生物体的培养物的实地工作的混合物。此外，由于有越来越多的证据表明，海水的pH值降低导致海洋有机物的类型和成分发生显着变化，学生将测试这是否会改变气体在空气-海洋界面的传输速率。这将在围隔生态系统研究中通过加入微量的示踪剂对六氟化硫和3-氦来完成，在实验的时间过程中，其浓度比的变化将给出空气-海洋气体交换率的估计。如果这一效应（以前从未测试过）被证明是重要的，那么其影响将远远超出这里提议研究的气体，例如海洋吸收人造二氧化碳的速率和计算其他气候相关气体的海气通量。最后，学生将使用一个一维模型来评估pH值引起的微量气体的海气交换对颗粒形成和空气质量的重要性。这里提出的建议将为NERC/Defra海洋酸化研究方案增加一个新的层面，不仅研究海水pH值变化对海洋过程的一个重要影响，而且将海洋中的影响与气候和大气化学等更广泛的领域联系起来。

As atmospheric carbon dioxide continues to rise the pH of seawater will get progressively less alkaline. The effect of this will almost certainly become progressively more apparent as the century progresses. It is likely to affect marine organisms from corals to microscopic plankton, particularly those that form their structures with calcium carbonate as a major component. The possible effects on non-carbonate secreting organisms are harder to predict. In this Ph.D. proposal the student will study the effect of decreasing pH on the production of trace gases (dimethyl sulphide and its precursor dimethylsulphoniopropionate and a range of naturally produced organo-halogen gases) by marine microorganisms. These compounds are volatile and can cross the air-sea interface. In the atmosphere their oxidation products can lead to new particle formation or growth of existing particles to cloud condensation nuclei size. Because of this they can affect the formation of clouds and hence climate. In addition, these gases play important roles in controlling the oxidation capacity of the atmosphere by, for example, destruction of ozone and so affect air quality. The student will examine the effect of pH change on the biogenic production of the gases by microbes. In order to quantify the implications of changed gas fluxes under high CO2 conditions, the student will input estimates of current day emissions as well as future emissions into a state-of-the-art one-dimensional model of the atmospheric marine boundary layer (the MISTRA model). This will allow assessment of the potential impact of pH-induced changes in air-sea fluxes of trace gases on particle formation and the oxidation capacity of the atmosphere. The approach we propose to studying this system is by a mixture of field work using floating and fixed mesocosms in which the pH is adjusted to mimic future conditions and in vitro studies using pH-altered natural seawaters and cultures of specific organisms. In addition, since there is growing evidence that lowered pH of seawater leads to significant changes in the type and composition of marine organic matter, the student will test whether this brings about alteration in the rate of transfer of gases across the air-sea interface. This will be done in the mesocosm studies by adding minute amounts of the tracer pair sulphur hexafluoride and 3-helium, changes in whose concentration ratio over the time-course of the experiments will give estimates of air-sea gas exchange rates. If this effect (which has never been tested previously) proves significant then the implications would be far wider than just for the gases proposed for study here, e.g. on rates of man-made carbon dioxide uptake by the oceans and calculation of air-sea fluxes of other climate relevant gases. Finally, the student will use a one-dimensional model to assess the importance of pH-induced changes in the air-sea exchange of trace gases for particle formation and air quality. What is proposed here would add an additional dimension to the NERC/Defra Ocean Acidification research programme by not only studying one important impact of seawater pH change on processes in the oceans but also by linking effects in the oceans to the wider fields of climate and atmospheric chemistry.