Glacial-Interglacial Variations in d17O of O2 in Ice Cores: Implications for Interactions Between Climate and the Biosphere

[0087999 .本德]该奖项支持一项继续研究冰芯中化石空气中氧的三种同位素组成（O-17和O-18）的项目。这一特性令人感兴趣，因为平流层中的光化学反应会诱导氧和二氧化碳之间的同位素交换，从而使氧的O-17降低与O-18相同的量（“质量无关分馏”）。这个同位素标记是异常的，因为影响氧同位素组成的其他因素对O-17的改变是对O-18的0.5倍。呼吸作用消耗周围（异常）的氧气，光合作用用通常被分解的氧气代替。因此，氧的三种同位素组成可以衡量地球上光合作用的总速率。关注过去6万年的初步结果表明，末次盛冰期全球生物圈的产量约为今天的90%。由于陆地产量比今天少得多，o同位素数据表明海洋总产量比今天大得多。这种增加归因于冰川时期更多的尘埃（和铁）流入海洋。这个项目将把目前对氧的三种同位素组成的测量扩展到40万年以前，以便得出光合作用产氧相对速率随时间的曲线。以1kyr分辨率计算的结果将限制与冰期极大期、间冰期和冰期终止有关的产量变化；具有长间隔事件；轨道日晒周期不伴有冰量的大变化。这项工作将有助于更好地了解生物圈对气候的反应和影响方式。

0087999 BenderThis award supports a project to continue studies of the triple isotope composition (O-17 and O-18) of oxygen in fossil air trapped in ice cores. This property is of interest because photochemical reactions in the stratosphere induce isotope exchange between oxygen and carbon dioxide that lowers the O-17 of oxygen by the same amount as the O-18 ("mass independent fractionation"). This isotopic tag is anomalous in the sense that other factors influencing the isotopic composition of oxygen change O-17 by 0.5 times as much as they change O-18. Respiration consumes ambient (anomalous) oxygen , and photosynthesis replaces it with oxygen which is normally fractionated. Therefore, the triple isotope composition of oxygen give a measure of the gross rate of photosynthesis on the planet. Preliminary results focussing on the last 60,000 years indicate that the production of the global biosphere during the Last Glacial Maximum was about 90% of that today. Because land production was much less than today, the O-isotope data imply that oceanic gross production was much greater than today. This increase has been attributed to a higher glacial flux of dust (and iron) to the oceans. This project will extend current measurements of the triple isotope composition of oxygen back to 400,000 years in order to derive the curve of the relative rate of photosynthetic oxygen production vs. time. The results, at 1 kyr resolution, will constrain changes in production associated with glacial maxima, interglacials and glacial terminations; with long interstadial events; and with orbital insolation cycles unaccompanied by large changes in ice volume. This work will lead to a better understanding of ways in which the biosphere responds to and influences climate.