The Southern Ocean's Iron Cycle through the Cenozoic

铁限制了现代南大洋的初级生产力。这反过来又减少了被高纬度海洋吸收的大气二氧化碳的数量。这些观测提出了一些令人着迷但迄今仍未得到解答的问题，即：南大洋的主要铁源是什么？这些来源的铁在地质时期的供应弹性或变数有多大？铁循环对地球气候的长期变化有何反应？铁循环的变化是否影响了其他营养素的变化，如二氧化硅？该项目将通过多方面的方法研究沉积物的来源、沉积速率和铁源的数量，从而解决这些问题。获得的详细记录将用于研究海洋营养循环的变化与过去6600万年前发生的主要构造、气候和生物地球化学重组的关系。所使用的整体框架将考虑这些主要地球系统过程的相互作用，并量化它们在将铁输送到地球上最大的铁限制生物群方面的个别作用。该项目将根据国际海洋发现计划钻探的富含金属的深海粘土序列的地球化学，量化南大洋的主要铁源及其在空间和时间上的变化。这将通过将粘土来源的统计建模与辐射测量约束的沉积速率和其中铁源的显式量化相结合来实现。由此重建的结果将用于检验下列假设：热液作用产生的铁对新生代高纬度海洋的重要性；构造通道的开放如何重新分配南大洋内的深层来源铁；随着澳大利亚成为沙漠，尘埃产生的铁的供应如何发生变化；以及与硅藻扩散有关的铁循环是否发生了变化。该项目是对作为GEOTRACES计划一部分进行的正在进行的研究的补充，将吸引来自STEM中代表性不足的社区的K-12学生，并将支持两名早期职业研究人员。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Iron limits primary productivity in the modern Southern Ocean. This, in turn, reduces the amount of atmospheric carbon dioxide that is taken up by the high-latitude oceans. These observations raise a number of fascinating and hitherto unanswered questions, namely: what are the major sources of iron to the Southern Ocean? How resilient or variable is the supply of iron from these sources over geologic time? How has the iron cycle responded to long-term changes in Earth's climate? Have changes in the iron cycle influenced those of other nutrients, such as silica? This project will address these questions by means of a multifaceted approach examining the origin of the sediment, deposition rates, and quantification of iron sources therein. The detailed records obtained will be used to examine how changes in ocean nutrient cycles relate to the major tectonic, climatic, and biogeochemical reorganizations that have occurred over the past 66 million years ago. The holistic framework used will consider the interplay of these major Earth system processes and quantify their individual roles in shaping iron delivery to the largest iron-limited biome on Earth. This project will quantify the major sources of iron to the Southern Ocean and how they changed in space and time, based on the geochemistry of metal-rich deep-sea clay sequences drilled by the International Ocean Discovery Program. This will be achieved by combining statistical modeling of the origin of the clay with radiometrically-constrained deposition rates and explicit quantification of iron sources therein. The resultant reconstructions will be used to test hypotheses regarding: the significance of hydrothermally-derived iron to the high-latitude oceans over the Cenozoic; how the opening of tectonic gateways redistributed deeply-sourced iron within the Southern Ocean; how the supply of dust-derived iron changed as Australia became a desert; and, if there were changes in the iron cycle associated with the proliferation of diatoms. This project complements ongoing research conducted as part of the GEOTRACES program, will engage K-12 students from communities underrepresented in STEM, and will support two early-career researchers.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.