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

研究气候在过去如何变化以及为什么变化，是科学努力了解和预测气候未来可能如何变化的一个重要因素。我们可以通过研究一系列记录过去变化的环境来回答一系列关于过去气候的问题。冰芯、树木年轮的不同宽度、洞穴中石笋的生长速度、湖底或泥炭沼泽等沉积物的组成都能为我们的问题提供答案。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，表面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，植物就会做出反应。然后，如果气候变得干燥，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被保存下来，所以我们现在可以站在表面，通过所有的层来分析发生了什么。我们可以用很多方法来做到这一点。我们可以观察植物本身，或者生活在沼泽表面的变形虫。另一种直到最近才被应用于泥炭沼泽研究的方法是观察植物遗骸中捕获的不同同位素比例的变化。同位素是含有相同数量质子但不同数量中子的同一元素的原子。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同位素感兴趣。例如，氧有三种不同的稳定同位素，分别是氧-16、氧-17和氧-18。超过99%的氧是氧-16，它含有8个质子和8个中子。只有大约0.2%是氧-18，它有两个额外的中子，使它比氧-16重。沼泽中的同位素信号来自植物用来构建纤维素的沉淀，纤维素是一种形成细胞结构的有机化合物。我们可以将这些记录与过去的气候联系起来，因为在不同的气候条件下，较轻或较重的氧同位素在降水中更为常见。以前对泥炭沼泽同位素比值变化的研究使用了一种特殊类型的苔藓，称为泥炭藓，从中得出测量结果。这是有效的，但也是有限的，无论是在泥炭藓发生的地理区域，也是一个核心的部分，泥炭藓是存在的;没有人希望在他们的记录空白。我们想解决这两个问题，通过测试的适用性，研究同位素在不同类型的泥炭，发现在地区泥炭藓是不太常见的。在南半球，沼泽通常由高等或维管植物而不是苔藓主导;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广泛分布，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获得过去气候的可靠记录，但要确定，还需要更多的研究。我们将使用新西兰的沼泽，以一种灯心草为主，进行进一步的测试。我们将在一年的时间里研究不同地点的匆忙，以充分了解同位素信号是如何被纳入植物遗骸的。如果我们能够证明同位素方法可以应用于这种泥炭类型，这将是一个很大的进步;该方法将适用于更广泛的地理区域，我们将能够解决有关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.