SGER: Hydroclimatic History of the Northeastern Pacific Using the DELTA18O from Tree Cellulose

该奖项利用探索性研究小额赠款(SGER)计划资助的资金，对北美西部边缘生长的长寿树木一年生年轮中提取的纤维素的氧同位素组成进行了探索性调查。这项探索性调查旨在确定在美国西部边缘分布的树木的纤维素中是否记录了一致的氧-18变化的氧同位素记录。具体地说，研究人员将测量从加州不同地点的四棵树的年轮中提取的纤维素上的氧同位素。在过去的两个世纪里，对布列松松树纤维素的初步氧同位素研究得出结论，从每年的布列松松树样品中提取的纤维素的氧-18信号表明，19世纪末和20世纪初落在该地点的降水的氧-18有很大的负移(每毫升10个)。氧同位素变化的时间与小冰期的结束相对应，小冰期是北半球大部分地区大气温度较低的时期。研究人员认为，纤维素中记录的氧同位素变化与气候变化有关，并表明这涉及大气湿度来源的变化。然而，他和他的同事们对影响纤维素中氧同位素分馏的生理和环境参数进行了建模，发现每毫升10%的变化既不能用温度的变化解释，也不能用树木部位湿度的变化来解释。研究人员假设，同位素变化似乎要求在20世纪之前，加利福尼亚州怀特山布里斯特莱肯松树遗址的主要水分来源来自亚热带纬度，而在20世纪，主要来源一直来自北纬较高的地区。这项研究将解决的正是这一假设。这项研究可能会对更广泛的科学界产生广泛影响，并通过为古老而棘手的科学问题提供新的视角，催化围绕气候问题的新思维。这些活动非常符合SGER计划潜在的变革性、高风险和探索性。

This award uses funds, under the auspices of the Small Grants for Exploratory Research (SGER) program, to conduct an exploratory investigation of the oxygen isotopic composition of cellulose extracted from annual tree rings from long-lived trees that grow along western margin of North America. This exploratory investigation is intended to determine if there is a coherent oxygen isotope record of oxygen-18 change recorded in the cellulose of trees distributed on the western U.S. margin. Specifically, the researcher will measure oxygen isotopes on the cellulose extracted from the annual rings of four trees at different locations in California. Initial oxygen isotopic work on Bristlecone Pine cellulose, that covers the past two centuries, have concluded that the oxygen-18 signal of cellulose extracted from annual Bristlecone Pine samples indicates there was a large (10 per mil) negative shift in the oxygen-18 of precipitation falling on the site at the end of the 19th century and the early 20th century. The timing of this oxygen isotopic shift corresponds with the end of the Little Ice Age, a period of lower atmospheric temperatures across much of the northern hemisphere. The researcher suggests that the oxygen isotopic shift recorded in the cellulose is related to the climatic changes and suggests that this involved a shift in the source of atmospheric moisture. Yet, he and his colleagues modeled the physiologic and the environmental parameters that influence the fractionation of oxygen isotopes in the cellulose and found that a 10 per mil shift would not be explained by either a change in temperature or a change in humidity at the tree site. The researcher hypothesizes that the isotopic shift would appear to require that prior to the 20th century the primary source of moisture to the Bristlecone Pine site in the White Mountains of California was from subtropical latitudes whereas during the 20th century the primary source has been from higher northerly latitudes. It is this hypothesis, among others, that the research will address.The research could have broad impact on the wider science community and catalyze new thinking in issues surrounding climate by offering a new perspective on old and knotty scientific problems. The activities fit well into the potentially transformative, high risk, and exploratory nature of the SGER program.