Are permeable coastal sediments hotspots for the formation of non-volatile dissolved organic sulfur (DOS) in the ocean?

有机硫化合物普遍存在于海洋沉积物中。这些化合物的主要形成途径是无机硫物种与常见生物分子的非生物反应。由于这一过程对全球生物地球化学循环、油田勘探和分子古记录的保存具有重要意义，因此对这一主题进行了大量的研究。然而，对硫化过程中可能形成并最终以溶解有机硫(DOS)形式进入海洋水柱的水溶性化合物的关注很少。根据现有的资料，硫可能是海洋溶解有机物(DOM)中第三丰富的杂元素，仅次于氧和氮。一些硫化物，特别是硫醇，决定了有害元素和必需微量元素的流动性。与气候有关的重要挥发性硫化物来源于DOS。因此，DOS的海洋循环既有大气后果，也有海洋后果。尽管发挥了这一重要作用，但海洋DOS的来源、它在海洋中的循环以及它对海洋生物的作用尚不清楚。此外，DOS的分子组成也难以捉摸。在这个项目中，我们将在海洋生物地球化学的一个新领域进行开创性的研究。我们试图回答有关海洋中非挥发性DOS的形成和分布的基本问题。我们的主要假设：*DOS的形成：(1)硫酸盐还原沉积物是DOS形成的主要场所。(2)形成部位以还原形式的有机硫(主要是硫醇)为主。(3)DOS主要是在早期成岩过程中非生物硫化作用形成的。*DOS在海洋中的运移和去向：(4)DOS从硫酸盐还原的潮间带地下水排放到海洋中。(5)在含氧水柱中，DOS迅速氧化(如生成磺酸)。(6)潮间带沉积物中的DOS以氧化形式在大陆架上长距离运输。除了回答这些假设的科学目标外，该项目将为三名博士生提供在国际项目框架内进行研究生研究的非同寻常的机会，其中一名在德国，两名在巴西。我们将结合两个合作伙伴的力量，应用现场采样、实验室实验以及元素、同位素和分子分析相结合的方法。采样包括德国瓦登海和巴西红树林(里约热内卢和亚马逊)形成鲜明对比的地区，包括大规模的相邻大陆架地区。硫化实验将补充实地研究。对于DOS的定量和分子表征，我们将应用PIS工作组最近建立的新方法，包括超高分辨率质谱学(FT-ICR-MS)以及其他质谱学和色谱学技术。

Organic sulfur compounds are ubiquitous in marine sediments. The main formation pathway of these compounds is the abiotic reaction of inorganic sulfur species with common biomolecules. Because of the importance of this process for global biogeochemical cycles, for the exploration of oil fields, and for the preservation of the molecular paleorecord, there is a wealth of studies on the topic. Very little attention, however, has been paid on water-soluble compounds that may be formed during the process of sulfurization and that may eventually enter the oceanic water column as dissolved organic sulfur (DOS). Based on the little available information, sulfur could be the third most abundant heteroelement in marine dissolved organic matter (DOM), after oxygen and nitrogen. Some sulfur compounds, in particular thiols, determine the mobility of hazardous elements and also essential trace elements. Important climate-relevant volatile sulfur compounds originate from DOS. Thus, the marine cycling of DOS has both atmospheric and oceanic consequences. Despite this important role, the sources of marine DOS, its cycling in the ocean and its function for marine life are unknown. Also the molecular composition of DOS is elusive. In this project we will perform pioneering research in a new field of marine biogeochemistry. We seek to answer fundamental questions with respect to the formation and distribution of non-volatile DOS in the ocean. Our main hypotheses: * Formation of DOS: (1) Sulfate-reducing sediments are prime sites of DOS formation. (2) Reduced forms of organic sulfur (mainly thiols) predominate in the formation sites. (3) DOS is formed primarily via abiotic sulfurization during early diagenesis. * Transport and fate of DOS in the ocean: (4) DOS is discharged from sulfate-reducing intertidal groundwater into the ocean. (5) In the oxic water column, DOS quickly oxidizes (e.g., into sulfonic acids).(6) DOS from intertidal sediments survives transport in an oxidized form over large distances across continental shelves. Aside the scientific objective of answering these hypotheses, this project will provide three PhD students, one in Germany and two in Brazil, with the extraordinary opportunity to perform their graduate research within the framework of an international project. Joining the strength of the two partners, we will apply a combination of field sampling, laboratory experiments and elemental, isotopic and molecular analysis. Sampling includes sharply contrasting regions in the German Wadden Sea and Brazilian mangroves (Rio de Janeiro and Amazonia), including the adjacent shelf regions on a large scale. Sulfurization experiments will complement the field studies. For the quantification and molecular characterization of DOS we will apply novel approaches that were recently established in the PIs working groups, involving ultrahigh-resolution mass spectrometry (FT-ICR-MS), and other mass spectrometry and chromatography techniques.