Analytical development of sulphur isotope analysis on small (1ug) sulphur samples

硫酸盐是现代海洋中第二丰富的阴离子。硫酸盐进入海洋的主要来源是大陆上含硫矿物的风化，通过河流将硫输送到海洋。海洋硫酸盐的主要汇是各种含硫矿物如黄铁矿和石膏在海洋各部分的埋藏。地球化学家和古海洋学家认为，海洋中的硫酸盐浓度随着时间的推移而变化，是这些通量变化的函数。例如，如果大陆上的硫风化作用增加，我们预计海洋中的硫酸盐浓度将增加。追踪这些变化的一种常用方法是测量各种硫和硫酸盐矿物中硫的同位素比率。例如，硫化物矿物（如黄铁矿）的32 S比34 S多得多，这意味着34 S/32 S的比例非常低。这意味着，在地球历史上，如果有一段时间有更多的黄铁矿被埋在海洋中，那么更多的32 S将被埋在黄铁矿中，从而在海洋中留下更多的34 S-或增加34 S/32 S的比例。因此，如果我们（作为古海洋学家）测量硫酸盐矿物中34 S/32 S的比例，并且我们观察到这个比例迅速增加，我们可能会假设在地球历史的那个时候有更多的黄铁矿被掩埋。准确重建地球历史上硫酸盐中34 S/32 S比率的能力尤为重要，因为海洋硫酸盐对输送到沉积物中的有机碳量的变化非常敏感。这是因为硫循环中最大的汇是硫化物矿物埋藏在富含有机物的沉积物中;硫化物的来源是细菌，它们吃掉最初在海洋表面产生的有机碳。这种有机碳的埋藏反过来又与大气中的氧气直接相关。因此，我们对大气氧历史的重建在很大程度上依赖于我们对地球历史上硫酸盐中34 S/32 S比率的理解。在地球历史上，我们测量硫酸盐中34 S/32 S比率的两种最常见的矿物是硫酸钡（重晶石）和碳酸盐相关硫酸盐。重晶石在1.5亿年前没有得到很好的保存，这意味着古海洋学家在很大程度上依赖于碳酸盐相关的硫酸盐来重建地质历史中关键早期间隔的硫循环。不幸的是，大量的碳酸盐必须溶解，以释放足够的硫酸盐进行同位素分析。我想通过开发在更小的样品上测量硫同位素比率的能力来解决这个问题。我将通过建立一种已经在国际研究小组中使用的技术来做到这一点，使用我们在剑桥大学已经拥有的设备。这将使我能够在更小的样品上测量硫同位素比率。这是一项概念验证研究，我将测量单个碳酸盐壳簇中的硫，并将这些分析与其他硫同位素比分析进行比较，以确定我们可以在小样本上测量硫同位素。

Sulphate is the second most abundant anion in the modern ocean. The main source of sulphate to the ocean is the weathering of sulphur-bearing minerals on the continents, delivering sulphur to the ocean via rivers. The main sink of sulphate from the oceans is the burial of various sulphur bearing minerals such as pyrite and gypsum in various parts of the ocean. Geochemists and paleoceanographers think about sulphate concentrations in the oceans changing over time as a function of changes in these fluxes. For example, should there be more weathering of sulphur from the continents, we would anticipate that sulphate concentrations in the ocean would increase. A common way to track these changes is to measure the ratio of isotopes of sulphur in various sulphur and sulphate minerals. For example, sulphide minerals (such as pyrite) have much more 32S than 34S, meaning the ratio of 34S/32S is very low. This means that if, in Earth history, there was a time when much more pyrite was buried in the ocean, more 32S would be buried in the pyrite, leaving more 34S behind in the ocean - or increasing the ratio of 34S/32S. Thus if we (as paleoceanographers) were measuring the ratio of 34S/32S in sulphate minerals over time and we observed a rapid increase in this ratio, we might hypothesize that there was more pyrite being buried at that point in Earth history. The ability to accurately reconstruct the 34S/32S ratio in sulphate over Earth history is especially important because marine sulphate is very sensitive to changes in the amount of organic carbon that is delivered to the sediments. This is because the largest sink in the sulphur cycle is the burial of sulphide minerals in organic-rich sediments; the source of the sulphide is bacteria, who eat organic-carbon that was originally produced in the surface ocean. The burial of this organic-carbon, in turn, is directly linked to atmospheric oxygen. Thus our reconstructions of the history of atmospheric oxygen rely heavily on our understanding of the 34S/32S ratio in sulphate over Earth history. The two most common minerals on which we measure the 34S/32S ratio in sulphate over Earth history are barium sulphate (barite) and carbonate-associated-sulphate. Barite is not well preserved before 150 million years ago, meaning paleoceanographers have relied heavily on carbonate-associated-sulphate to reconstruct the sulphur cycle over critical earlier intervals in the geologic past. Unfortunately large amounts of carbonate must be dissolved in order to release enough sulphate for isotope analysis. I would like to address this by developing the ability to measure sulphur isotope ratios on much smaller samples. I will do this by establishing a technique that is already used in research groups internationally using equipment we already have at the University of Cambridge. This will allow me to measure sulphur isotope ratios on far smaller samples. This is a proof of concept study in which I will measure sulphur in clusters of individual carbonate shells and compare these analyses with other analyses of sulphur isotope ratios in order to determine that we can measure sulphur isotopes on small samples.