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

我们的动机在于这样一个事实，即海洋表面微层（SML）和下伏散装水通过对流之间的动态联系导致的SML的异质性。这反过来又控制着生物光化学反应和海气通量的程度。对流是由蒸发驱动的，蒸发冷却了SML，使其更咸。因此，SML变得更密集，下沉，并被下面的散装水所取代。然而，浮力驱动的对流作为连接大气和海洋的动力学纽带，在SML和海气交换的研究中一直被忽视。我们的主要目标是获得一个机械的理解之间的动态SML和近地层（NSL）。我们的建议的一个要点是，浮力驱动的对流是SML和海气相互作用的关键组成部分，尽管它的小尺度性质。对流的机械理解是必不可少的，因为生物光化学反应的程度和微量气体，能量和动量的海气交换最终将由SML和NSL之间的交换过程决定，并最终与更深的层。我们将发展一个实验装置，利用多个剖面微电极和光学纹影系统来研究各种外部强迫下的对流。我们将研究由于表面张力梯度（即马兰戈尼效应）而产生的水平流动效应。我们也将参与BASS联合围隔实验，研究生物表面活性剂对SML和NSL之间对流输送机制的影响。在BASS联合现场实验中，我们将解决小尺度对流的变化在多大程度上受到海洋表面附近次中尺度（1公里至10公里）水动力过程变化的影响的问题。我们将部署两艘研究双体船和一支配备电导率和温度传感器的漂流船队，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，我们将使用从实验室实验，围隔生态系统和实地研究中获得的知识来开发一个数学框架来描述温度和盐度剖面，以及它们在定义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.