Quantitative Salinity & Water D/H from Paired H & C Isotopes in Mangrove Lipids

在过去的半个世纪里，全球降雨模式一直在变化，影响着全世界人民的生活。对这些变化的全面了解尚未出现，但它们与大气中温室气体积累引起的全球气温变暖有关。在降水量的更广泛的变化中，热带地区发生了变化，潮湿地区变得更加潮湿，干燥地区变得更加干燥。目前还不清楚，在过去30年中观察到的热带降雨量的变化是否在多世纪或多千年的时间尺度上是不寻常的。因此，到目前为止，还不可能说最近的降水趋势是否超出了自然变化的范围。任何这样的结论都需要追溯到一千年或更久以前的热带降雨记录。但目前，在雨量计和卫星出现之前，几乎没有任何方法可以准确地重建地球上大多数地区的降雨量，特别是在海洋热带地区。该项目的目标是开发一种方法，从海洋和湖泊沉积物岩心中提取的红树林脂质的化学性质确定水的盐度和氘氢比，这两个参数与热带地区的降雨量密切相关，红树林是适应盐水生活的非凡树木。它们栖息在全球热带和亚热带的潮间带。拟议研究的方法是基于研究人员最近的观察，即当红树树叶生活的水的盐度发生变化时，红树树叶脂质中氘（2 H）与氢（1H）和碳-13（13 C）与碳-12（12 C）的比例会发生系统性变化。这项研究将通过在实验室中在不同盐度范围内种植红树林来校准多种红树林的反应。然后，调查人员将检验这些校准在应用于栖息在热带岛屿帕劳的盐湖海岸线上的多种红树林物种时是否一致，这些物种的盐度范围很广。由于红树林脂质的氢同位素组成包括红树林生活的水的氘氢比以及该水的盐度，而碳同位素仅对盐度作出反应，因此可以计算沿海水的盐度和氢同位素比。根据这两个参数，人们可以很好地估计降雨量，因为随着降雨量的增加，沿海海水的盐度和氘氢比都会下降。当测量从沿海环境和海洋湖泊的沉积物芯中提取的红树林脂质时，将有可能重建及时的降雨量估计，从而提供所需的长期观点，以得出热带降雨量的近期趋势是否超出自然变化范围的结论，该项目得到NSF海洋科学司海洋地质学和地球物理学方案的联合支持。

Global patterns of rainfall have been changing over the last half-century, impacting the lives of people worldwide. A full understanding of these changes has not yet emerged, but they have been linked to a warming of global temperatures in response to the buildup of greenhouse gases in the atmosphere. Among the more widespread changes in precipitation have occurred in the tropics, where wet regions have been getting wetter and dry regions drier. It remains unknown whether the changes in tropical rainfall observed over the last 30 years are unusual when viewed on a multi-century or multi-millennial time scale. As yet it is therefore not possible to say whether recent precipitation trends are outside the range of natural variability. Any such conclusion will require records of rainfall from the tropics extending back in time a thousand years or more. But at present there are few, if any methods to accurately reconstruct rainfall in most locations on the planet prior to the advent of rain gauges and satellites, especially in the maritime tropics. The goal of this project is to develop a method for determining the salinity and deuterium-to-hydrogen ratio of water, two parameters very closely linked to rainfall in the tropics, from the chemistry of mangrove lipids that can be recovered from ocean and lake sediment cores.Mangroves are remarkable trees that have adapted to living in saltwater. They inhabit the intertidal zones of the global tropics and subtropics. The approach of the proposed study is based upon the investigator's recent observation that the ratio of both deuterium (2H) to hydrogen (1H) and carbon-13 (13C) to carbon-12 (12C) in the lipids of mangrove leaves changes systematically when the salinity of the water in which they live changes. This study will calibrate that response in multiple species of mangroves by growing them in the laboratory at a range of different salinities. The investigator will then test whether those calibrations are consistent when applied to multiple mangrove species inhabiting the shorelines of saline lakes on the tropical island of Palau that span a wide range of salinities. Because the hydrogen isotope composition of mangrove lipids incorporates the deuterium-to-hydrogen ratio of the water in which the mangroves live, as well as the salinity of that water, and the carbon isotopes only respond to the salinity, it is possible to calculate both the salinity and the hydrogen isotope ratio of the coastal water. From these two parameters one can make good estimates of rainfall, since both the salinity and the deuterium-to-hydrogen ratio of coastal water decreases when rainfall increases. When measured on mangrove lipids extracted from sediment cores taken in coastal settings and maritime lakes it will be possible to reconstruct rainfall estimates back in time, thus providing the long-term view needed to conclude whether recent trends in tropical rainfall are outside the range of natural variability.This project is supported jointly by the Marine Geology and Geophysics Program in the NSF Division of Ocean Sciences.