SP 2.3 - Dynamics of convection linking the sea-surface microlayer (SML) with the bulk phase

我们的动机在于，海洋表面微层（SML）与底层散装水之间通过对流的动态联系导致了SML的非均匀性。这反过来又控制了生物光化学反应和海气通量的程度。对流是由蒸发驱动的，蒸发使SML冷却，使其更含盐。因此，SML变得更密集，下沉，并被底层的大块水所取代。然而，在SML和海气交换的研究中，浮力驱动的对流作为大气与海洋之间的动力纽带一直被忽视。我们的主要目标是获得SML和近地表层（NSL）之间动力学的机制理解。我们建议的要点之一是，浮力驱动的对流是SML和海气相互作用的关键组成部分，尽管它的小规模性质。对流的机制理解是必不可少的，因为生物光化学反应和微量气体、能量和动量的海气交换的程度最终将由SML和NSL之间的交换过程决定，并最终与更深层的交换过程决定。我们将开发一个带有多个微电极和光学纹影系统的实验装置来研究不同外力下的对流。我们将研究由于表面张力梯度引起的水平流动的影响（即马兰戈尼效应）。我们还将参与BASS联合介观实验，研究生物源性表面活性剂对SML和NSL之间对流输运机制的影响。在BASS联合野外实验中，我们将研究海洋表面亚中尺度（1 km - 10 km）水动力过程的变率对小尺度对流变化的影响程度。我们将部署两艘研究双体船和一队配备电导率和温度传感器的漂流船，以调查SML和NSL之间的密度异常。我们将监测外部海洋和大气强迫来描述密度异常。最后，我们将利用从实验室实验、中观和实地研究中获得的知识，建立一个数学框架来描述温度和盐度剖面，以及它们在确定的海洋和大气强迫影响下的波动。

Our motivation lies in the fact that the dynamic link between the sea-surface microlayer (SML) and underlying bulk water via convection leads to heterogeneous properties of the SML. This in turn controls the extent of bio-photochemical reactions and air-sea gas fluxes. Convection is driven by evaporation, which cools the SML and makes it more saline. Consequently, the SML becomes denser, sinks, and is replaced by underlying bulk water. However, buoyancy-driven convection has been neglected in the research of the SML and air-sea gas exchange as a dynamic link between the atmosphere and the ocean. Our main objective is to obtain a mechanistic understanding of the dynamics between the SML and the near-surface layer (NSL). One of the main points of our proposal is that buoyancy-driven convection is a key component of the SML and air-sea interaction, despite its small-scaled nature. A mechanistic understanding of convection is essential, as the extent of bio-photochemical reactions and the air-sea exchange of trace gases, energy, and momentum will ultimately be determined by exchange processes between the SML and the NSL, and ultimately with deeper layers. We will develop an experimental setup with multiple profiling microelectrodes and an optical schlieren system to investigate convection under various external forcing. We will investigate the effect of horizontal flow due to gradients of surface tension (i.e. Marangoni effect). We will also participate in the BASS joint mesocosm experiment to investigate the influence of biogenic surfactants on the convective transport mechanism between the SML and the NSL. In the BASS joint field experiment, we will address the question to what extent variations of small-scaled convection are affected by the variability of sub-mesoscale (1 km–10 km) hydrodynamic processes near the ocean’s surface. We will deploy two research catamarans and a fleet of drifters equipped with conductivity and temperature sensors to investigate density anomalies between the SML and NSL. We will monitor external oceanic and atmospheric forcing to describe the density anomalies. Finally, we will use the gained knowledge from the lab experiments, mesocosm, and field study to develop a mathematical framework to describe temperature and salinity profiles, and their fluctuations under the influence of defined oceanic and atmospheric forcing.