北极斯瓦尔巴地区冰川融水中的铁及其同位素向邻近高纬度海水输送的研究

Primary production is limited by iron (Fe) in a large portion of the surface ocean. Marine Fe concentrations control carbon fixation by phytoplankton, thus impacting the global carbon cycle and eventually the global climate. Glacial meltwater has been suggested as a significant source of potentially bioavailable Fe to the oceans. Our previous study in Ny-Ålesund revealed that proglacial process have a large impact on iron concentration. Although our data fall into the range of the data reported by others, iron concentration in meltwater varies up to three orders of magnitude. Thus, the supply of Fe in glacial meltwaters is still poorly constrained, both because only few sites have been studied and because the chemical processing of Fe during transport from glaciers to the adjacent coastal ocean is not well understood. This research project proposes to investigate Kongsforden and Grønfjord and their surrounding glacial meltwaters on Svalbard. The project will apply Fe analysis techniques including size-fractionation and iron stable isotope (δ56Fe), combined with multi-geochemical parameters including major ions, nutrients and dissolved organic carbon, and other hydro-physical-chemical parameters, in order to investigate the transport and reaction of iron from glacial meltwaters into the high latitude ocean. The goal of this project is to understand the biogeochemical cycling of iron in glacial meltwaters, to reveal how iron and its isotopes are transported from meltwater to the fjord, and to present reliable concentration and isotopic data which can eventually be used to establish the role of glacial meltwater in the global ocean iron budget.

大洋的初级生产力受到铁的限制。大洋铁的库存状况能够通过影响浮游植物对碳的固定，影响全球碳循环和气候。近年来，冰川融水的铁被认为可能是大洋生物可利用铁的一个重要来源。我们之前的研究发现冰川前环境会剧烈的改变冰川融水中铁的地球化学过程。虽然我们的数据在前人报道的数据范围内，但冰川融水中铁的含量在不同冰川间可相差3个数量级。目前，对冰川融水中铁的地球化学特征还缺乏认识，其向高纬度海水的输送机制也不明确，很难对这一来源的铁对大洋铁库的贡献进行有效的估算。本项目拟以北极斯瓦尔巴的王湾和盖伦格湾及其周围的冰川融水为研究对象，应用分级和铁稳定同位素技术手段，配合常量离子、营养盐、溶解有机碳等地球化学参数，结合物理、化学和水文等参数，开展冰川融水中铁及其向邻近高纬度海水输送的研究。通过本项目的实施，可望了解冰川融水中铁生物地球化学特征，了解其向邻近高纬度峡湾输送的规律，并有效估算其为大洋铁库存的贡献。

痕量金属铁是海洋中的关键限制因子。大洋铁的库存状况能够通过影响浮游植物对碳的固定，影响全球碳循环和气候。近年来，冰川融水的铁被认为可能是大洋生物可利用铁的一个重要来源。目前冰川融水铁对大洋影响的两个关键问题是：1）冰川风化和环境特征具有差异性，冰川融水中铁的差异性如何；2）冰川融水入海后铁的行为如何，如何向邻近海洋进行铁的输送。针对上述的关键问题，项目执行期间通过调查巴伦支堡和新奥尔松邻近冰川融水水化学，邻近峡湾铁的分布，以及通过分析美国GEOTRACES北冰洋航次铁同位素的数据，展开调查。借助本项目的资助，主要的认识包括：1）巴伦支堡和新奥尔松附近的冰川融水主要体现了碳酸盐和硅酸盐的混合风化，而新奥尔松邻近冰川融水体现了更多的碳酸盐风化特征；2）调查的冰川融水中铁的含量相差2-3个数量级，差异受到风化、冰川前环境等复杂因素影响；3）冰川融水入海后，铁的行为与其他河口类似，都经历了大量的移除过程，但向峡湾外的输出主要受到洋流特征的影响；4）冰川融水向大洋输送的铁同位素指纹特征接近地壳平均组成，并可能通过洋流的远距离输送至开阔大洋。