Developing a novel proxy for Southern Hemisphere Holocene climate change: stable isotope analysis of restiad peat cellulose

研究过去气候变化的方式和原因，是了解和预测未来气候变化的科学努力的重要组成部分。我们可以通过研究保存着过去气候变化记录的许多环境中的一个来回答一系列关于过去气候的问题。我们的问题在冰芯、树木年轮的不同宽度、洞穴中石笋的生长速度或沉积物(如湖底或泥炭沼泽中的沉积物)中都有答案。泥炭沉积物经过数千年的稳定发展，在我们研究的沼泽类型中，地表植物的生长与当时的气候直接相关。因此，如果气候变得更加潮湿，植物就会相应地发生变化。然后，如果气候变得更加干燥，它们又会发生变化。当沼泽向上生长时，所有这些变化的记录都会被保存下来，所以我们现在可以站在地表上，取一个岩芯穿过所有的层来分析发生了什么。有很多方法可以用来做这件事。我们可以观察植物本身，或者生活在沼泽表面的阿米巴虫。另一种最近才被应用于泥炭沼泽研究的方法是观察在植物残骸中捕获的不同同位素比例的变化。同位素是含有相同元素的原子，含有相同数量的质子，但含有不同数量的中子。同位素既可以是稳定的，也可以是放射性的，但这里我们只对稳定的同位素感兴趣。例如，氧有三种不同的稳定同位素，分别为氧-16、-17和-18。超过99%的氧是氧-16，它包含八个质子和八个中子。只有大约0.2%是氧-18，它有两个额外的中子，使其比氧-16重。沼泽中的同位素信号来自植物用来制造纤维素的降水，纤维素是一种有机化合物，形成了它们的细胞结构。我们可以将这一记录与过去的气候联系起来，因为在不同的气候条件下，更轻或更重的氧同位素在降水中更常见。以前对泥炭沼泽中同位素比率变化的研究使用了一种特殊类型的苔藓，称为泥炭苔藓，从那里得出他们的测量结果。这是有效的，但也是有限的，无论是在出现泥炭的地理区域，还是在存在泥炭的岩心部分；没有人希望他们的记录中存在差距。我们希望通过测试在泥炭中发现的不同类型泥炭中研究同位素的适用性来解决这两个问题，而泥炭是在泥炭不太常见的地区发现的。在南半球，沼泽通常由高等植物或维管束植物主导，而不是苔藓；这些植物可以主动控制其组织中的水分和营养物质的运动。以高等植物为主的沼泽在全球范围内普遍存在，但由于它们与苔藓在生物学上的差异，如果没有严格的测试，我们无法确定同位素方法是否适用。我们的初步结果表明，可以从这些沼泽类型中得出过去气候的可靠记录，但为了确定，还需要更多的研究。我们将使用新西兰的沼泽进行进一步的测试，这些沼泽以一种草甸植物为主。我们将研究一年中不同地点的匆忙情况，以充分了解同位素信号是如何融入植物遗骸的。如果我们能够证明同位素方法可以应用于这种泥炭类型，这将是一大进步；这种方法将适用于更广泛的地理区域，我们将能够比现在更好地解决过去气候变化的紧迫研究问题。

The study of how and why climate has changed in the past is an important element in the scientific drive towards understanding and predicting how it may change in the future. We can answer a range of questions about past climate by studying one of a number of environments that hold a record of past changes. There are answers to our questions in ice cores, the varying width of tree rings, the growth rate of stalagmites in caves or in the make up of sediments such as those at the bottom of lakes or in peat bogs.Peat sediments develop steadily over thousands of years and in the type of bog we study, the growth of plants on the surface is related directly to the prevailing climate. So if the climate gets wetter, the plants change in response. Then, if the climate gets drier, they change again. As the bog grows upwards, a record of all of those changes is preserved, so we can now stand on the surface, take a core back through all the layers and analyse what's been happening.There are many methods we can use to do this. We can look at the plants themselves, or at amoebae that live on the bog surface. Another method that has only recently been applied to studies of peat bogs is to look at changes in the ratios of different isotopes captured in the plant remains.Isotopes are atoms of the same element that contain the same number of protons, but a different number of neutrons. Isotopes can be either stable or radioactive, but here we are just interested in the stable isotopes. Oxygen, for example, has three different stable isotopes known as oxygen-16, -17 and -18. More than 99% of all oxygen is oxygen-16, which contains eight protons and eight neutrons. Only about 0.2% is oxygen-18, which has two extra neutrons, making it heavier than oxygen-16.The isotope signal in bogs comes from the precipitation that plants use to construct cellulose, an organic compound that forms their cell structure. We can relate the record to past climate because, under different climatic conditions, lighter or heavier oxygen isotopes are more common in precipitation.Previous studies of changing isotope ratios from peat bogs have used a particular type of moss, called Sphagnum, from which to derive their measurements. This is effective, but is also limited, both to geographical areas where Sphagnum occurs and also to the parts of a core where Sphagnum is present; nobody wants gaps in their record.We want to address these two issues by testing the applicability of studying isotopes in a different type of peat that is found in regions where Sphagnum is less common. In the Southern Hemisphere, bogs are generally dominated by higher, or vascular, plants rather than mosses; these are plants that can actively control the movement of water and nutrients in their tissue. Bogs dominated by higher plants are widespread globally, but because of the differences in biology between them and mosses, we can't be certain that the isotope method is applicable without rigorous testing. Our initial results suggest that a reliable record of past climate can be derived from these bog types, but to be certain, more research is needed.We will use bogs in New Zealand, dominated by a species of rush, to perform further tests. We will study the rush on different sites over the course of a year to fully understand how the isotope signal is incorporated into the plant remains. If we can demonstrate that the isotope method can be applied to this peat type, it will be a big step forward; the method would be applicable over a much wider geographical area and we will be able to address pressing research questions about past climate change more so than at present.