Interrogating trees as archives of environmental sulphur variability

‘给我一棵树，我就会读气候历史’是树木年代学的基本前提，在很大程度上也是完全正确的。树内的每一个年轮代表着一年的生长，其中包含了当时环境条件的记录。因此，可以通过年轮宽度分析和化学成分来确定树木的年龄，并将其用作气候变化的记录。然而，对每个环内营养化学的化学解释经常受到许多批评。树木吸收的养分被包裹起来以代表特定年份的环境条件这一基本前提，只有在树木整个宽度范围内被固定而不能进一步生物运输的元素才是正确的。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。考虑到硫磺在调节气候方面的关键作用和作为环境诊断工具的巨大潜力，硫磺应该是固定在年度生长轮内的元素是偶然的。向大气中注入硫气溶胶是通过后向散射和吸收辐射来决定气候的一个关键因素，长期以来一直是陆地生态所关注的问题，在沉积时造成广泛的集水区酸化。排放到大气中的硫气溶胶的两个主要来源是火山排放和工业排放。使用浓度和稳定同位素可以很容易地将这两个来源与背景输入区分开来，这使得古档案的硫同位素含量可能是现有的最重要的诊断元素特征之一。虽然冰芯中的硫同位素含量已经被广泛利用，但更本地化的档案，如洞穴和树轮，在很大程度上仍然超出了气候变化科学家的能力范围，我们还没有发现它们蕴藏的许多秘密。虽然我们已经开始从洞穴中提取硫记录并取得了巨大的成功，但我们相信树木将成为过去千年以来当地大气变化的更敏感、更容易获得的记录。我们相信，我们现在能够进行一项深入的研究方案，以提取树木的硫同位素组成，并推动开发这样一个重要的本地硫磺强迫和大气变化指标。

'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.