Collaborative Research: US GEOTRACES GP17-ANT: Iron redox cycling in the Amundsen Sea in the water column and shelf sediments

阿蒙森海是南极海岸变化最快的地区之一，也是南极大陆上冰川融化速度最快的地区之一。铁在控制阿蒙森海初级生产和碳、营养循环中的作用引起了人们的极大兴趣，它可能是南大洋近海富含营养物质但铁含量有限的重要铁来源。这项工作是美国GEOTRACES GP17-ANT在阿蒙森海巡航的一部分，这是一项由多名研究人员参与的微量元素和同位素循环研究。这项工作将研究铁是如何从阿蒙森盆地海底沉积物中动员起来的。这种动员受到与气候变化直接相关的两个因素的影响。冰川融化增加了被称为多冰湖的无冰区域，那里浮游植物大量繁殖。这些水华中的有机物最终到达海底，创造了低氧环境，加速了铁元素向上覆水域的运输。此外，冰川的加速融化将通过冰川/海洋界面的浮力“融水泵”增加铁到地表的运输。这些过程在气候和生物生产力之间产生反馈，必须理解这些反馈，才能开发出具有有用预测能力的模型。更广泛的影响包括与南加州大学联合教育项目和PolarTREC教师合作，创建基于GEOTRACES南极考察的课程，该课程将传播到洛杉矶地区的15所小学，并开发在线数据探索模块，以鼓励海洋学课程中基于数据的学习。该合作项目将通过测定水柱中的铁（II）浓度和氧化还原动力学，以及通过孔隙水测量从海底到水柱的铁和其他元素的通量，研究阿蒙森海沉积物和水柱之间的铁氧化还原循环，以及与南大洋的交换。美国GEOTRACES GP17-ANT巡航的一个主要目标是研究阿蒙森海和南大洋之间的铁交换。拟议的工作对于确定铁的来源和控制来源通量以及将决定其命运的内部转变至关重要。该项目的数据产品将与其他研究人员在巡航后的综合工作中进行整合，包括溶解和颗粒铁和相关金属，如锰，以及重要的沉积物来源示踪剂，如镭同位素。铁（II）在这些冷水中氧化非常缓慢，动力学将与铁（II）底水浓度和底栖生物通量相结合，以评估铁从底栖边界层转移的缓慢氧化动力学的重要性。底栖衍生的碘（表示为“过量碘”）将被用作铁输入的重要半保守示踪剂。碘是一个有用的比较元素，因为铁和碘都在氧化条件下积聚在沉积物中，而在还原条件下释放出来。碘本身就引起了人们的兴趣，因为南极大陆架水域是大气中活性碘的巨大来源。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

The Amundsen Sea is one of the most rapidly changing areas along the Antarctic coast, with some of the fastest rates of glacial melting on the continent. There is great interest in the role of iron in controlling primary production and carbon and nutrient cycling within the Amundsen Sea, and it is probably an important source of iron to offshore waters of the Southern Ocean, which are rich in nutrients but iron limited. The work is part of the US GEOTRACES GP17-ANT cruise to the Amundsen Sea, a multi-investigator study of trace elements and isotope cycling. This work will study how iron is mobilized from sediments at the seafloor of the Amundsen basin. Such mobilization is influenced by two factors directly linked to climate change. Glacial melting increases ice-free areas known as polynyas, which experience large blooms of phytoplankton. Organic matter from these blooms eventually reaches the seafloor, creating low-oxygen conditions that accelerate iron transport into the overlying waters. Moreover, accelerated melting of glaciers will increase the transport of this iron to the surface via the buoyant “meltwater pump” along the glacier/ocean interface. These processes create feedbacks between climate and biological productivity that must be understood to develop models with a useful predictive capability. The broader impacts include partnering with University of Southern California Joint Educational Project and a PolarTREC teacher to create curriculum based on GEOTRACES Antarctic Expedition, which will be disseminated to 15 elementary school in Los Angeles area and develop online data exploration modules to encourage data-based learning in oceanography classes. This collaborative project will investigate iron redox cycling between sediments and water column of the Amundsen Sea and exchange with the Southern Ocean by determining iron (II) concentrations and redox kinetics in the water column as well as fluxes of iron and other elements from the seafloor to the water column from porewater measurements. A major objective of the US GEOTRACES GP17-ANT cruise is to study the exchange of iron between the Amundsen Sea and the Southern Ocean. The proposed work is essential to identifying the sources of iron and controls on source fluxes as well as internal transformations that will determine its fate. The data product from the project will be integrated with the results of other investigators in a synthesis effort after the cruise, including dissolved and particulate iron and related metals like manganese, as well as important tracers of sediment sources like radium isotopes. Iron(II) oxidizes very slowly in these cold waters, and kinetics will be combined with iron(II) bottom water concentrations and benthic fluxes to evaluate the importance of the slow oxidation kinetics on iron transport away from the benthic boundary layer. Benthic-derived iodine (denoted as “excess iodine”), will be utilized as an important semi-conservative tracer of iron inputs. Iodine is a useful comparative element because both iron and iodine accumulate in sediments under oxidizing conditions and are released under reducing conditions. Iodine is of interest in its own right because Antarctic Shelf waters are a massive source of reactive iodine species to the atmosphere.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.