Interrogating trees as archives of environmental sulphur variability

“给我一棵树，我会读气候史”是树木年代学的基本前提，在很大程度上是完全正确的。树的每一轮代表一年的生长，并记录了当时的环境条件。因此，树木可以被确定年龄，并通过年轮宽度分析和化学成分作为气候变化的记录。然而，对每个环内的营养化学的化学解释经常受到很多批评。树吸收的营养素被封装以代表特定年份的环境条件的基本前提，仅适用于那些在树的宽度上被固定而不被进一步生物运输的元素。我们现在认为我们已经发现了这样一种元素，它在生长过程中固定在木质组织中，可以肯定地用于环境重建-这种元素就是硫。硫应该是固定在年轮中的元素，这是偶然的，因为它在调节气候方面发挥着关键作用，并且具有作为环境诊断工具的巨大潜力。硫气溶胶注入大气层，通过辐射的后向散射和吸收，是气候的一个关键决定因素，长期以来一直是陆地生态的一个关切问题，在沉积时造成集水区的广泛酸化。喷入大气的硫气溶胶的两个主要来源是火山和工业排放。这两个来源可以很容易地区分使用浓度和稳定同位素的背景输入，使古档案的硫同位素含量可能是最重要的诊断元素的签名之一。虽然冰芯的硫同位素含量已被广泛利用，但更局部化的档案，如洞穴沉积物和树木年轮，在很大程度上仍然超出了气候变化科学家的范围，我们还没有发现它们所隐藏的许多秘密。虽然我们已经开始并取得了巨大的成功，从洞穴沉积物中提取硫记录，但我们相信树木将成为过去一千年当地大气变化的更敏感，更容易获得的记录。我们相信，我们现在能够进行深入的研究计划，以提取树木的硫同位素组成，并继续开发这种重要的硫强迫和大气变化的本地指标。

'Give me a tree and I'll read climate history' is the basic premise of dendrochronology, and to a large extent is perfectly true. Each ring within a tree represents one year of growth and contains within it a record of the prevailing environmental conditions. Trees can thus be age dated, and used as a record of climate change through ring-width analysis and chemical composition. However, chemical interpretations of the nutrient chemistry within each ring have often been subject to much criticism. The basic premise that nutrients which are taken up by the tree are encapsulated to represent environmental conditions for that particular year, is true only for elements which are immobilised from further biological transport accross the width of the tree. We now think we have found such an element which is fixed within the woody tissues during growth and can be used with certainty for environmental reconstruction - this element is sulphur. That sulphur should be the element which is fixed within the annual growth rings is fortuitous given its key role in modulating climate and fantastic potential as an environmental diagnostic tool. The injection of sulphur aerosol into the atmosphere is a key determinant of climate through backscattering and absorption of radiation, and has long been a concern for terrestrial ecology, causing widespread acidification of catchments upon deposition. Two of the key sources of sulphur aerosol injected into the atmosphere are from volcanic and industrial emissions. Both sources can be readily distinguished from background inputs using concentrations and stable isotopes, rendering the sulphur isotopic content of palaeoarchives to be perhaps one of the most important diagnostic elemental signatures available. Whilst the sulphur isotopic content of ice cores has been extensively exploited, the more localised archives such as speleothems and tree rings have largely remained beyond the reach of climate change scientists and we have yet to discover many of the secrets they harbour. Whilst we have initiated and had excellent success with extracting the sulphur record from speleothems, we believe trees will behave as a much more sensitive, readily available record of local atmospheric change over the past millenium. We believe we are now in a position to conduct an intensive research programme to extract the sulphur isotopic composition of trees and forge ahead with the development of such an important local indicator of sulphur forcing and atmospheric change.