Controls on iron availability to marine phytoplankton

二氧化碳(CO2)等人为温室气体排放正在导致气候变化、全球变暖和海洋酸化。生活在海洋表层的微型浮游植物可以隔离全球50%的二氧化碳，并提供50%用于初级生产的新氮。除了光和主要营养物质外，浮游植物的生长还受到金属铁(Fe)有效性的强烈影响，因为金属铁是光合作用和固氮所必需的，但在公开海洋中非常稀缺。铁是如此重要，以至于将这种金属播种到缺铁地区被认为是一种可行的方法，可以通过增强浮游植物对大气中二氧化碳的生物吸收来控制气候变化。为了了解铁是如何控制大气二氧化碳水平和海洋生产力的，重要的是首先要试图了解金属对海洋浮游植物有效性的控制。流行的观点是，金属的生物有效性取决于其在周围散装水中的化学形态(即金属形态)；然而，我们最近的研究数据与长期存在的范式不一致。在拟议的项目中，我将挑战这一长期存在的范例，通过使用新的纳米技术和跨学科的方法，研究藻圈中的铁的形态，藻圈是一个微米尺度的空间，直接围绕着浮游植物细胞。浮游植物直接从藻圈吸收包括铁在内的营养物质，而不是直接从散装海水中吸收，然而在这个微尺度空间中的铁的形态以前还没有被研究过。缺乏关于大气层铁形态的知识可能会导致对当前和未来海洋中海洋铁有效性的严重低估或高估，并导致对海洋生态系统如何应对气候变化的错误预测。该跨学科项目将为浮游植物获取铁的基本过程提供一个新的视角，它肯定有助于提高政府间气候变化专门委员会等国际机构评估行星系统对气候变化的敏感性的能力和准确性。

Anthropogenic greenhouse gas emissions such as carbon dioxide (CO2) are causing climate change, global warming, and ocean acidification. Microscopic plants called phytoplankton, living in the surface oceans, sequester 50% of global CO2 and supply >50% of new nitrogen used for primary production. Other than light and major nutrients, phytoplankton growth is strongly influenced by availability of the metal iron (Fe), because the metal is essential for photosynthesis and nitrogen fixation, but is very scarce in the open ocean. Iron is so important that seeding the metal into Fe-poor areas has been proposed as a viable method for controlling climate change by enhancing bio-uptake of atmospheric CO2 by phytoplankton. In order to understand how Fe controls atmospheric CO2 levels and oceanic productivity, it is important to first attempt to understand the controls on availability of the metal to marine phytoplankton. The prevailing view is that metal bioavailability depends upon its chemical forms (i.e., metal speciation) in ambient bulk waters; however, data from our recent studies are inconsistent with the long-standing paradigm. In the proposed project, I will challenge this long-standing paradigm by studying the Fe speciation in the phycosphere, a micrometer scale space which directly surrounds a phytoplankton cell, through the use of novel nano-technologies and inter-disciplinary approaches. Phytoplankton directly take up nutrients including Fe from the phycosphere, rather than directly from bulk seawater, however the Fe speciation in this micro-scale space has not previously been studied. The lack of knowledge on phycosphere Fe speciation would potentially result in serious under or overestimation of oceanic Fe availability in current and future oceans, and lead to erroneous prediction of how ocean ecosystem responds to Climate Change. The interdisciplinary project will provide a new view on the fundamental processes in Fe acquisition by phytoplankton, and it will certainly help improve the capability and accuracy of international agencies such as the Intergovernmental Panel on Climate Change to assess the sensitivity of planetary system to Climate Change.