OCE-PRF: Metabolic Contributions to Climate Proxies and Untested Assumptions in the Hydrologic and Ecological Applications of Photoautotrophic Lipids

了解地球的水文和碳循环将如何响应气候变化，无论是由于变暖、海洋酸化还是其他趋势，是海洋学和地球科学界的一项重要任务。人类对这些周期变化的适应取决于对这些变化的准确预测；准确的预测，反过来，需要了解所涉及的机制。辨别这些机制的最好方法之一是通过沉积记录详细调查过去的行为。在这个项目中，该研究员将研究藻类细胞水的氢同位素组成，以检验目前为研究过去气候而开发的有关环境代用物的重要假设。扩大参与的目标包括制作和教学以城市流域的海洋影响为重点的材料。这项工作将与MESA西雅图分会合作进行，MESA是一个致力于改善经济弱势青年、代表性不足的少数民族和妇女的STEM教育的全国性组织。赞助科学家是华盛顿大学环境学院的朱利安·萨克斯。一般认为，单细胞海洋或湖泊光自养生物（藻类和光合细菌）具有与其生长环境同位素相同的内部水池。这激发了许多尝试，从这些生物产生的沉积脂质的氢同位素组成中开发水文代用物，因为这些化合物从细胞内水池中吸收了氢。同样清楚的是，在某些情况下，与水和脂质同位素组成（量化为净分馏因子α）有关的巨大和可变的重要影响可能记录大量对碳循环研究很重要的生态信息。然而，由于最近的研究表明，生长或代谢速率可能对水的细胞内氢同位素组成起着重要的控制作用，因此在进一步开发这些同位素代用物方面，科学界面临着挑战。为了解决这个问题，该研究员将进行一系列实验，以确定光自养生物细胞内水对生长的同位素反应。一系列的恒化培养实验将与新的Kreuzer同位素富集技术相结合，该技术用于以前的代谢水测定。这些实验旨在分离细胞分裂、光照强度、盐度和生长阶段对可用于脂质合成的水的氢同位素组成的影响，并确定任何变化传播成脂质的程度。所提出的工作可能会解决一个重要的开放性问题，即关于一整类有前途的环境代理的保真度。然而，光自养生物中环境水和细胞内水的同位素差异的量化可能为生物学家在许多领域的研究开辟新的途径，因为这些差异可能追踪细胞合成、呼吸和水交换过程。

Understanding how the Earth's hydrologic and carbon cycles will respond to climatic changes, whether as a result of warming, ocean acidification, or other trends, is an important charge of the oceanographic and Earth-sciences communities. Human adaptation to changes in these cycles rests on accurate prediction of those changes; accurate prediction, in turn, requires an understanding of the mechanisms involved. One of the best ways to discern these mechanisms is detailed investigation of past behavior via sedimentary records. In this project, the fellow will investigate the hydrogen isotopic composition of algal cell water in order to test important assumptions regarding environmental proxies currently being developed for such studies of past climate.The participation-broadening goals include producing and teaching material focused on the marine impacts of urban watersheds. This work will occur in collaboration with the Seattle chapter of MESA, a national organization dedicated to improving STEM education for economically disadvantaged youth, under-represented minorities, and women. The sponsoring scientist is Julian Sachs at the University of Washington College of the Environment. Unicellular marine or lacustrine photoautotrophs (both algae and photosynthetic bacteria) have generally been assumed to have internal water pools that are isotopically identical to that of their growth environment. This has spurred numerous attempts to develop hydrologic proxies from thehydrogen isotopic composition of sedimentary lipids produced by these organisms, as these compounds incorporate hydrogen from the intracellular water pool. It has also become clear that, in certain settings, the large and variable vital effects relating water and lipid isotopic compositions (quantified as the net fractionation factor alpha) potentially record a wealth of ecological information important for studies of the carbon cycle. The community faces a challenge in further development of these isotopic proxies, however, as recent work has suggested that growth or metabolic rate may exert significant controls on intracellular hydrogen isotopic composition of water. To address this, the fellow will run a series of experiments to determine the isotopic response of intracellular water in photoautotrophs to growth. A series of chemostat culture experiments will be coupled with the novel Kreuzer isotope enrichment technique employed in previous metabolic water determinations. These experiments are designed to isolate the effects of cell division, light intensity, salinity, and growth phase on the hydrogen isotopic composition of the water available for lipid synthesis, and to determine the degree to which any changes are propagated into lipids. The proposed work may resolve an important open question regarding the fidelity of a whole class of promising environmental proxies. The quantification of isotopic differences between environmental and intracellular water in photoautotrophs may open new avenues of research for biologists across many fields, however, as these differences may trace cellular synthesis, respiration, and water exchange processes.