A high-density, high-precision zonal section of nitrate isotopes across the South Indian Ocean

GSTDTAP

项目编号	1851430
	A high-density, high-precision zonal section of nitrate isotopes across the South Indian Ocean
	Daniel Sigman (Principal Investigator)
主持机构	Princeton University
项目开始年	2019
	2019-10-01
项目结束日期	2021-09-30
资助机构	US-NSF
项目类别	Standard Grant
项目经费	296546(USD)
国家	美国
语种	英语
英文摘要	The ocean covers most of the Earth's surface, and its physical, biological, and chemical processes determine many aspects of Earth's climate and the chemistry of the atmosphere. Biologically available nitrogen (or "fixed N") is an essential nutrient for the microscopic plants (phytoplankton) in the ocean. The supply of fixed N can limit the growth of phytoplankton and the capacity of the ocean to absorb carbon dioxide, the most important greenhouse gas. Following the flow and transformation of fixed N is a powerful approach for understanding how the physics, biology, chemistry interact to determine the biological fertility of the ocean and its storage of carbon dioxide away from the atmosphere. With such an understanding, we may be able to predict how the ocean will change in response to human activities and thus affect the conditions for life in the future. Nitrate (NO3-) is the primary form of fixed N in the ocean, and both its nitrogen (N) and oxygen (O) atoms occur in more than one mass, or "isotope": 14N and 15N for N and 16O and 18O for O. The ratios of these isotopes are affected by biological processes, and so isotopic measurements of nitrate reveal processes at work in the ocean that are otherwise hard to disentangle. Moreover, the isotope ratio of N in the ocean through time is recorded in the organic matter of the sediments that accumulate on the seafloor. Thus, the isotopes allow us to reconstruct important features of the past ocean, such as how the sequestration of carbon dioxide by ocean life has changed over past climate changes, which may indicate how this sequestration will change in the future. This project will produce the largest data set so far on the isotopic composition of nitrate in the Indian Ocean. The Indian Ocean is one of the three major basins of the global ocean, the one that has been studied the least, and it may prove to be the best basin for reconstructing past surface ocean conditions because of the abundance of microfossils in its sediments. The measurements of nitrate isotopes generated in this project will serve many purposes. As one example, it will allow for a determination of the circulation path by which nitrate is transferred up from the deep waters to the sunlit surface waters where growing phytoplankton require this nutrient. As a second example, the measurements will help to calibrate new nitrogen isotopic methods for reconstructing past ocean conditions, which utilizes the organic matter trapped in the fossil shells of foraminifera, a type of zooplankton. In order to explain these goals and to spread our understanding of the ocean to educators, each of the two years of the project, a 1-day workshop will be held for the Teachers as Scholars program of the Princeton University Program in Teacher Preparation, which brings middle and high school teachers to Princeton to interact with faculty and learn about important scientific questions and research. The workshop will focus on accessing and visualizing ocean data sets and other oceanographic content for active learning in the classroom. Undergraduates will be involved in the research through summer internships, junior projects, and/or senior theses. This project will produce analyses of the nitrate 15N/14N and 18O/16O ratios in samples collected during the upcoming 2019-2020 GO-SHIP I05 zonal section across the South Indian Ocean from South Africa to Australia at 30-33 deg S. Nitrate 15N/14N and 18O/16O provide critical constraints on the cycle and input/output budget of marine fixed N. The I05 nitrate isotope data will be broadly useful, potentially serving as a cornerstone in the global ocean's nitrate isotope data set. Given the lack of nitrate isotope measurements in the Indian Ocean, especially in the main basin away from the low-[O2] regions to the North, this project will fill a major geographic gap. Moreover, it will provide dense spatial and depth coverage with the highest level of precision currently available, allowing for novel hydrography-based calculations of N fluxes. The nitrate isotope samples will be taken from the same bottles from which the GO-SHIP hydrographic and biogeochemical measurements will be made, maximizing the power of the nitrate isotope data set. The data set will be of use to the growing number of numerical ocean model simulations including biogeochemistry, for identifying regional oceanographic processes, and for ground-truthing paleoceanographic tools. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.
文献类型	项目
条目标识符	http://119.78.100.173/C666/handle/2XK7JSWQ/213257
专题	环境与发展全球科技态势
推荐引用方式 GB/T 7714	Daniel Sigman .A high-density, high-precision zonal section of nitrate isotopes across the South Indian Ocean.2019.