Reconstructing Precipitation Rates from C & H Isotopes in Mangrove Lipids

从 C 重建降水率

基本信息

批准号：
1736222
负责人：
Julian Sachs
金额：
$ 68.19万
依托单位：
University of Washington
依托单位国家：
美国
项目类别：
Standard Grant
财政年份：
2017
资助国家：
美国
起止时间：
2017-10-01 至 2021-09-30
项目状态：
已结题

来源：
https://www.nsf.gov/awardsearch/showAward?AWD_ID=1736222&HistoricalAwards=false
关键词：
Reconstructing Precipitation Rates &amp Isotopes

项目摘要

Global rainfall patterns have changed over the last 35 years, particularly in the tropics, where high-precipitation regions have become wetter, and low-precipitation regions have become drier. In addition, subtropical dry zones have expanded poleward by some 125-250 miles. The underlying causes of these changes are not well understood, owing to the complexity of the climate system and an imperfect understanding of tropical precipitation mechanisms. However, both heuristic arguments and state-of-the-art climate models suggest that these trends will continue if greenhouse gases continue to accumulate in the atmosphere faster than they can be absorbed by the ocean and land biosphere. Confidence in these projections could be improved with a longer precipitation record, particularly over the low-latitude oceans. Unfortunately, the start of the precipitation record over the ocean began just 35 years ago, coinciding with the satellite weather era. Thus the only way to extend the tropical rainfall record back in time is through indirect means. The purpose of this project is to develop a new approach to reconstruct tropical and subtropical rainfall rates from hydrogen and carbon isotope ratios in lipids produced by mangrove trees inhabiting intertidal regions throughout the tropics and subtropics. The research team will continue to engage local government agencies and non-governmental organizations in rapid ecological assessments of pristine and anthrpogenically-impacted systems, and will conduct workshops on mangroves and climate for Micronesian school teachers. Funding also supports education and training of a PhD student and provides research and field experiences for several undergraduates at the University of Washington.This new method for determining rainfall is based on the sensitive biochemical and biophysical responses of mangrove trees to salinity, and the resultant impact on the hydrogen and carbon isotope composition of lipids in mangrove leaves. Recent studies have shown that when salinity increases, 2H/1H fractionation in mangrove lipids systematically increases, and 13C/12C fractionation systematically decreases. From these empirical relationships, salinity and the 2H/1H ratio of growth water can be determined from measurements of the 2H/1H and 13C/12C ratios of taraxerol, a leaf lipid produced by Rhizophora (red) mangroves. Those data will be used to calculate the 2H/1H ratio of precipitation, from which precipitation rates can be determined, owing to the anti-correlation between precipitation 2H/1H ratios and rainfall amount in the tropics. Taraxerol will be extracted from previously-collected mangrove swamp sediments from six US-affiliated Micronesian islands across 2,800 km of ocean that span modern mean annual rainfall rates of 6 to 14 mm d-1. The 2H/1H ratio of precipitation, salinity, and rainfall rates will be determined for: (1) the last 10-20 years from 0-2 cm sediments and compared to instrumental data, (2) the 20th century from 2~10 cm sediments to test whether satellite-derived precipitation since ~1990 is higher than the 20th century mean, and (3) the early (1400-1600 AD) and late (1600-1800 AD) Little Ice Age to test whether precipitation was lower in the western tropical North Pacific during that time.

在过去的35年中，全球降雨模式发生了变化，尤其是在热带地区，在热带地区，高部分地区变得更湿，低沉淀地区变得更干燥。此外，亚热带干燥区域已将极前向125-250英里扩大。由于气候系统的复杂性以及对热带降水机制的不了解，这些变化的根本原因尚不清楚。但是，启发式论点和最先进的气候模型都表明，如果温室气体继续在大气中积累的速度比海洋和土地生物圈吸收的速度更快，这些趋势将继续。通过更长的降水记录，尤其是在低纬度海洋中，对这些预测的信心可以提高。不幸的是，在35年前，降水记录的开始始于卫星天气时代。因此，延长热带降雨记录的唯一方法是通过间接手段。该项目的目的是开发一种新的方法来重建热带和亚热带降雨速率，这些降雨速率是在整个热带和亚热带中居住在潮间带的红树林产生的脂质中的氢和碳同位素比。研究团队将继续与地方政府机构和非政府组织进行对原始和人为影响系统的快速生态评估，并将为Microseian学校老师开展有关红树林和气候的讲习班。资金还支持博士生的教育和培训，并为华盛顿大学的几位大学生提供研究和现场经验。这种确定降雨的新方法基于红树林对盐度的敏感生物化学和生物物理反应，以及对氢和碳同位素的脂肪组成的影响。最近的研究表明，当盐度升高时，有系统增加的红树林脂质分级分级，而13c/12c分级分级会系统地降低。从这些经验关系中，可以通过塔二烯醇的2H/1H和13C/12C比的测量来确定生长水的盐度和2H/1H的比率，含蛋白含量的2H/1H和13C/12C比率，这是由根瘤菌（红色）mangroves产生的叶片脂质。这些数据将用于计算降水量的2H/1H比率，由于降水量2H/1H比与热带的降水量和降雨量之间的抗相关性，可以从中确定降水速率。将从2,800公里的海洋中的六个美国附属的密克罗尼斯群岛中提取塔秒，从前收集的红树林沼泽沉积物中，这些沉积物的现代平均年降雨量为6至14 mm D-1。将确定以下2小时/1小时的降水量，盐度和降雨量的比率：（1）最后10-20年从0-2 cm沉积物和工具性数据相比，（2）20世纪从2〜10 cm沉积物开始测试卫星自1990年以来的卫星降水量是否高于1990年〜20世纪的降水量是否高于20世纪的较高测试。在那个时候，北太平洋西部热带地区的降水是否较低。