The role of sulfides and thiols in the marine copper cycle

铜（Cu）是一种重要的微量营养元素，能促进海洋微生物的许多重要生物地球化学过程，同时也是公认的藻类细胞毒性因子。开阔海洋中的总铜浓度很低（约1 - 3 nM），而在沿海系统中可达到数十nM。据信，只有游离形式的Cu（水合Cu 2+）是生物可利用的形式，浓度低至10 pM的Cu 2+对海洋微生物是一种强效毒物。铜与有机配体的广泛络合（> 99.9%）使游离铜保持在较低的安全水平，随着海洋酸化的持续，预计铜2+的浓度将显著增加。因此，了解铜配体库是最重要的。微生物能够通过产生硫醇来抵消Cu2+浓度的毒性作用。硫醇是含有巯基（S-H）的有机化合物，能够与金属（包括铜）形成高度稳定的络合物。硫醇以多种不同的形式存在，如谷胱甘肽（GSH）、半胱氨酸、巯基乙酸，可能还有更多目前尚未在海洋系统中发现的形式。它们是由表层沃茨中的生物产生的，可能是调节表层沃茨中铜的生物有效性的主要络合剂之一。除了与有机配体形成强络合物外，铜离子还与硫化物物种络合，络合作用在还原环境如热液系统中最主要。在本项目中，我们正在使用伏安法作为一种高灵敏度的分析技术，它可以检测到亚纳米水平的硫醇和/或硫化物化合物，以及确定铜的形态参数（配体浓度和稳定常数）。将进行一系列实验，研究硫醇的生物地球化学行为，探讨它们在有/无光和不同温度下对Cu的稳定性和络合能力。铜络合参数与硫醇络合能力的比较将评估硫醇在控制良好氧化的表面沃茨中铜有机形态方面的作用。我们还希望更好地了解热液系统中可能影响铜与硫化物络合作用的参数，例如温度，并评估这种络合作用可能如何影响铜从喷口向外迁移。这些信息将进一步加深我们对硫醇和硫化物在控制铜地球化学循环中的作用的理解。

Copper (Cu) is an essential micronutrient that facilitates many significant biogeochemical processes in marine microbes and is also a well-recognised toxic agent for algal cells. Total Cu concentrations in open oceans are low (approximately 1-3 nM) while they can reach tens of nM in coastal systems. It is believed that only Cu in its free form, (hydrated Cu2+) is the bioavailable form with concentrations as low as 10pM of Cu2+ being a potent toxicant to marine microbes. Extensive complexation (>99.9%) of Cu with organic ligands maintain free Cu at low safe levels and with on-going ocean acidification, the concentration of Cu2+ is predicted to significantly increase. Understanding of the copper ligand pool is thus of prime importance. Microbes are able to counteract the toxic effects of Cu2+ concentrations by producing thiols. Thiols are organic compounds that contain a sulfhydryl group (S-H) and are able to form highly stable complexes with metals, including copper. Thiols exist in a number of different forms such as glutathione (GSH), cysteine, thioglycolic acid and possibly many more that have not yet currently been identified in the marine system. They are produced by the biology in surface waters and may be one of the main complexing agent regulating the bioavailability of copper in surface waters. In addition to forming strong complexes with organic ligands, copper ions also complex with sulphide species, complexation that is most predominant in reducing environment such as hydrothermal systems .In this project, we are using voltammetry as a highly sensitive analytical technique that allows detection in the sub nM levels of thiols and/or sulfide compounds as well as the determination of Cu speciation parameters (ligand concentrations and stability constants) obtained during titration experiments. A series of experiments will be carried out looking into the biogeochemical behavior of thiols, probing their stability and complexation capability towards Cu in presence/absence of lights and at various temperatures. Comparison of copper complexation parameters with thiols complexing abilities will assess the role of thiols in controlling copper organic speciation in well oxygenated surface waters. We are also interested in better understanding the parameters that might affect the complexation of copper with sulphide, e.g. temperature, in hydrothermal system and assess how this complexation might affect the transport of copper away from the vents. This information will further our understanding on the roles of thiols and sulphide in controlling the copper biogeochemical cycle.