SP1.1 Dynamic enrichment processes of organic matter in the SML

海洋表面微层（SML）是海洋最上层的薄层，是空气和海洋之间任何相互作用的一部分，如气体交换、大气沉积和气溶胶排放。SML中有机质（OM）的富集改变了海气交换过程，但哪些OM成分被选择性富集，以及它们为什么和何时富集，在很大程度上仍然未知（Engel等人，2017）。我们过去的研究表明，来自光自养生产的生物聚合物是SML的重要组成部分，并通过作为生物表面活性剂影响海气交换（Galgani等人，2016；Engel等人，2018）和作为初级有机气溶胶的来源（Trueblood等人，2021）。因此，我们项目的动机是阐明和描述SML中OM的动态丰富过程，特别强调解析OM源。通过我们的建模方法，目标是巩固我们对浮游生物生长条件、生产和生化物质释放（包括潜在的表面活性剂）与SML中OM积累之间联系的机制理解。这样的模型开发将极大地受益于BASS财团的各种子项目的结果和发现。相反，我们的动机是建立一个模型，可以作为一个综合工具，用于解释和整合SML中OM富集的现场、中观和实验室测量。与研究单元BASS - SP1.1的相关性将破译SML中OM的来源、数量和生化组成，从而为所有BASS子项目提供重要信息。海洋表层有机质的主要来源是光合作用产生和新鲜生产的有机质的主要生化成分；即，碳水化合物、氨基酸和脂质受到微生物处理（SP1.2）和SML内的光反应（SP1.3、SP1.4）的影响，并补充溶解有机物（DOM）池（SP1.5）。SP1.1中的模式发展建立了OM的产生与SML内OM的富集之间的联系，旨在通过考虑海洋表层动量通量（SP2.2）和浮力（SP2.3）的变化来解决相应的对海气交换（SP2.1）的影响。建议的SML子模型将根据SP1.4和SP2.3的结果进行细化。模型敏感性分析的结果将提供有关各种OM的表面活性特性及其对海气交换过程影响的补充信息，这些信息将在BASS中进行评估。

The sea-surface microlayer (SML) is the uppermost thin layer of the ocean and part of any interaction between the air and sea, such as gas exchange, atmospheric deposition, and aerosol emission. Organic matter (OM) enrichment in the SML modifies air-sea exchange processes, but which OM components become selectively enriched, as well as why and when they do, has remained largely unknown (Engel et al., 2017). Our past research showed that biopolymers derived from photoautotrophic production are important components of the SML and influence air-sea exchange by acting as biosurfactants (Galgani et al., 2016; Engel et al., 2018) and as a source of primary organic aerosols (Trueblood et al., 2021). Therefore, our project’s motivation is to elucidate and describe the dynamic enrichment processes of OM in the SML, with a particular emphasis on resolving OM sources. With our modelling approach the goal is to consolidate our mechanistic understanding of the linkages between plankton growth conditions, production, and the release of biochemicals, including potential surfactants, and the accumulation of OM within the SML. Such model development will greatly benefit from outcomes and findings of diverse subprojects of the BASS consortium. Conversely, it is our motivation to establish a model that becomes applicable as a synthesis tool for the interpretation and integration of field, mesocosm and laboratory measurements of OM enrichment in the SML. Relevance to the research unit BASS – SP1.1 will decipher the sources, amount, and biochemical composition of OM in the SML and thus, provide important information for all BASS subprojects. The primary origin of OM in the surface ocean is photosynthetic production and the major biochemical components of freshly produced OM; i.e., carbohydrates, amino acids, and lipids are subject to microbial processing (SP1.2) and photoreactions within the SML (SP1.3, SP1.4) and also replenish the pool of dissolved organic matter (DOM) (SP1.5). The model development in SP1.1 establishes a linkage between the production of OM and its enrichment within SML, and aims to resolve the corresponding effects on air-sea gas exchange (SP2.1) by accounting for changes in momentum flux on ocean surface layers (SP2.2) as well as in buoyancy (SP2.3). The proposed SML sub-model will be refined based on results from SP1.4 and SP2.3. Results from model sensitivity analyses will provide complementary information about surface-active properties of various OM and their impacts on air-sea exchange processes, which will be evaluated within BASS.