Iron isotope signatures of recent sedimentary pyrite in the Baltic Sea - Contribution to the development of a Paleoceanograpic proxy

由于环境变化，海洋环境今后很容易受到深刻的改变。沿着海洋酸化，未来几年缺氧情况可能会普遍增加。这些变化将如何在现代海洋中表现出来仍然不确定。波罗的海和黑海的部分底层沃茨目前缺氧，因为与表层沃茨和流入的淡水的交换非常有限。这种情况在目前的海洋中很少见，但在地球历史上更为普遍，而且由于全球气温上升，未来可能会变得更加普遍。波罗的海和黑海的现代缺氧环境类似于古代海洋，并提供了海洋化学如何随时间变化的重要信息。该项目将研究波罗的海的两个地点，即哥得兰深海和兰索尔特深海，以测试和校准一种新的工具-铁同位素，使其能够用于海洋氧含量过去的变化，铁是地壳中第四丰富的元素。它在缺氧条件下比在好氧条件下更易溶解，因此，现代海洋中的铁浓度非常低。铁也是大多数生物体必需的微量元素。海洋浮游植物利用大气中的二氧化碳进行生长。当有更多的铁时，浮游植物生长得更快，因此，铁与全球气候有关。因此，铁是一个重要的研究元素，最近在测量铁同位素方面的进展为研究铁在海洋中的作用提供了一个重要的新工具。对于铁同位素研究，需要使用质谱仪以高精度测量具有略微不同质量（同位素）的铁原子的相对丰度。铁的每种同位素由于其不同的质量而具有略微不同的化学和物理性质，因此在涉及铁的许多过程中表现不同。特别是铁的同位素可以提供有关氧含量变化和生物过程的重要信息。波罗的海是一个独特的环境，可以研究从富氧到缺氧的变化，因为这些变化在过去的几百年里反复发生。这些变化记录在波罗的海的沉积物中，特别是铁硫化物矿物黄铁矿的不同形成机制。黄铁矿是最稳定的铁硫化物矿物，因此得到了广泛的研究。然而，确定黄铁矿的Fe同位素组成的过程还没有得到很好的理解。本项目将研究黄铁矿的铁同位素组成如何随着不同的形成机制和底层水的氧含量而变化。波罗的海存在着与氧化还原条件和铁有关的重金属污染和春季藻华问题。一些蓝绿藻对人类有毒，水华进一步降低了水中的含氧量。拟议中的铁氧化还原循环在波罗的海使用铁同位素的研究将有助于更好地了解在波罗的海造成的环境问题的过程。

The marine environment is vulnerable to profound future modification as a result of environmental change. Along with ocean acidification, a widespread increase of oxygen deficient conditions is likely over the coming years. How these modifications will be manifest in the modern oceans is still uncertain. Parts of the bottom waters of the Baltic Sea and the Black Sea are at present deficient in oxygen since very limited exchange with surface waters and inflowing freshwater occurs. Such conditions are rare in the present ocean, but have been more widespread in the Earth's history and may become more widespread in the future as a result of a global temperature increase. Modern oxygen-deficient environments that are present in the Baltic Sea and Black Sea are analogues for ancient oceans and provide important information on how ocean chemistry has changed over time. This project will study two locations in the Baltic Sea, the Gotland Deep and the Landsort Deep, in order to test and calibrate a new tool, iron isotopes, so that it can be applied to past changes in the oxygen content of the ocean.Iron is the fourth most abundant element in the Earth's crust. It is much more soluble during oxygen-deficient conditions than during oxic conditions and therefore, iron concentrations in modern oceans are very low. Iron is also an essential trace element for most living organisms. Marine phytoplankton use CO2 from the atmosphere for growing. The phytoplankton grows faster when more iron is available and therefore, iron is linked to the global climate. Consequently, iron is an important element to study, and recent developments in measuring iron isotopes provide a critical new tool to study the role of iron in the oceans. For iron isotope studies, the relative abundance of iron atoms that have slightly different masses (isotopes) needs to be measured to high precision using a mass spectrometer. Each isotope of iron has slightly different chemical and physical properties due to their different masses and as a result, behaves differently in many processes that involve iron. In particular, iron isotopes give important information about changes in oxygen contents and biological processes.The Baltic Sea is a unique setting where changes from oxygen-rich to oxygen-deficient conditions can be studied, since these occurred repeatedly over the last few hundreds of years. These changes are recorded in the sediments of the Baltic Sea and result in particular in different formation mechanisms of the iron-sulphide mineral pyrite. Pyrite is the most stable iron sulfide mineral and has therefore been intensively studied. The processes that determine the Fe isotopic composition of pyrite are, however, not well understood. This project will investigate how the iron isotope composition of pyrite changes with different formation mechanisms and oxygen contents of the bottom water.The Baltic Sea has problems with heavy-metal pollution and spring algal blooms that are related to redox conditions and iron. Some species of blue-green algae are toxic to humans and the blooms further reduce the oxygen content of the water. The proposed study of iron-redox cycling in the Baltic Sea using Fe isotopes will contribute to a better understanding of the processes that cause the environmental problems in the Baltic Sea.