Southern Ocean Iron Fertilization near Islands: Fe-Isotope Exchange between Reactive Particles and Seawater

岛屿附近的南大洋铁施肥：反应颗粒与海水之间的铁同位素交换

• 批准号: 504850859
• 负责人: Professor Dr. Michael Staubwasser
• 金额: --
• 依托单位: Institut für Geologie und Mineralogie
• 依托单位国家: 德国
• 项目类别: Research Grants
• 资助国家: 德国
• 项目状态: 未结题
• 来源: https://gepris.dfg.de/gepris/projekt/504850859?language=en
• 关键词: Southern; Ocean; Iron; Fertilization; near

Ocean Fe-fertilization by islands is an important process governing marine phytoplankton production and atmospheric CO2 drawdown. The process is commonly observed in the Southern Ocean, where glacial weathering on islands is believed to supply excess bio-reactive particulate Fe (pFe). Glacial weathering is one aspect particularly sensitive to global warming. Diagenetic recycling of Fe and resuspension from the shelf’s sediments is another mechanism of island ocean fertilization that can be observed throughout the global ocean. Our previous work on King George Island – Antarctic Peninsula – has shown that Fe-isotopes allow for a discrimination between the two sources. However, Fe-isotope data in dissolved Fe (dFe) from throughout the Southern Ocean vary by about 2‰ (δ56Fe) between sites. This suggest either locally different combinations of sources, regionally diverse processes of Fe-cycling with highly variable interaction between dFe and pFe phases, a regionally very dynamic biologic Fe-cycle in the water column, or a variable combination of all three aspects. I propose to use Fe-isotopes to trace the two source types of particulate Fe, and their transformation into bio-reactive dFe from the coast of South Georgia into the open ocean high productivity region during an upcoming FS Polarstern cruise (PS-133), and determine the dissolution and exchange processes between dFe and pFe during Fe-fertilization on the basis of dFe-pFe isotope fractionation. I seek to determine underlying process-based Fe-isotope fractionation factors – which are generally poorly constrained in the marine environment – by a series of laboratory and on-board experiments. Exchange experiments comprise mixtures of pure Fe-oxyhydroxide and Mn-oxide mineral phases with artificial seawater, and mixtures of natural marine particles from the island shelf and slope enriched by crossflow-filtration with crossflow-filtered particle-free seawater from upstream of the island. Likewise, the above mineral phases will be mixed with filtered Southern Ocean seawater. All exchange experiments utilize isotope-spiked water, time-controlled sampling over long intervals, and the three-isotope method that allows for an accurate extrapolation of isotope fractionation factors even when the exchange reaction does not run to incompletion. These experimental fractionation factors serve as the basis for identification of molecular-level dFe-pFe exchange reactions inherent to the natural fertilization process. I anticipate to observe and sample the Fe-fertilization process from the littoral to the open ocean during the PS-133 cruise. Additional samples from an earlier campaign to the littoral and coastal sea off King Georg Island, where isotopic compositions of sediment source endmembers are already known, will be analyzed for comparison.

海洋岛屿铁肥化是控制海洋浮游植物生产和大气CO2下降的重要过程。这一过程通常在南大洋观察到，据信岛屿上的冰川风化提供了过量的生物反应性颗粒铁（pFe）。冰川风化是对全球变暖特别敏感的一个方面。铁的成岩再循环和陆架沉积物的再悬浮是岛屿海洋施肥的另一种机制，可以在全球海洋中观察到。我们以前在南极半岛国王乔治岛的工作表明，铁同位素可以区分两种来源。然而，整个南大洋的溶解铁（dFe）的铁同位素数据在不同地点之间的差异约为2‰（δ 56 Fe）。这表明，无论是本地不同的组合源，区域不同的过程中的铁循环与高度可变的相互作用dFe和pFe相，一个区域非常动态的生物铁循环在水柱，或所有三个方面的变量组合。我建议使用铁同位素示踪两种来源类型的颗粒铁，和他们的转化为生物活性dFe从南格鲁吉亚海岸到公海高生产力区在即将到来的FS Polarstern巡航（PS-133），并确定溶解和交换过程中dFe和pFe在铁施肥的基础上dFe-pFe同位素分馏。我试图确定潜在的过程为基础的铁同位素分馏因素-这是一般在海洋环境中的约束不佳-由一系列的实验室和船上的实验。交换实验包括纯Fe-羟基氧化物和Mn-氧化物矿物相与人工海水的混合物，以及天然海洋颗粒的混合物，从岛架和斜坡丰富的横流过滤与横流过滤的无颗粒海水从上游的岛屿。同样，上述矿物相将与过滤后的南大洋海水混合。所有的交换实验利用同位素加标水，时间控制的采样在很长的时间间隔，和三同位素的方法，允许一个准确的同位素分馏系数外推，即使当交换反应没有运行到不完全。这些实验分馏因素作为识别自然施肥过程中固有的分子水平的dFe-pFe交换反应的基础。我期望在PS-133巡航期间观察和采样从沿岸的到公海的铁施肥过程。将对早些时候在乔治王岛附近的沿岸的和沿海采集的其他样品进行分析，以进行比较，因为那里的沉积物源端元的同位素组成是已知的。