A review of bioactive iron in global glacier meltwater
Iron (Fe) is an essential nutrient element for biological activities,which can promote the formation of chlorophyll a,and is an important limiting factor for plankton growth in high nutrient salt and low chlorophyll sea area. With the accelerated ablation of glaciers,the erosion of melt water and the abrasion of ice and rock are enhanced,and the rate of chemical weathering is increased,which promotes more Fe elements to transfer from bedrock to melt water. Glaciers transport a large amount of bioactive Fe downstream,which will affect the pri-mary productivity of aquatic ecosystems,thereby affecting the carbon cycle and feedback the evolution of the cli-mate system. The biogeochemical cycle of Fe in glacial meltwater is a hot topic in cryospheric hydrochemistry. At present,some progress has been made in the study of Fe in glacial meltwater,but there are still great deficien-cies in the time and spatial scale. The spatial variation and transport process of Fe in meltwater are still unclear. By reviewing the research results of Fe concentration and flux and its stable isotope ratio (δ56Fe) in glacial melt-water,the concentrations of soluble iron (sFe),colloidal/nanoparticle iron (cnFe),dissolved iron (dFe) and particulate iron (pFe) in glacial meltwater and their spatiotemporal variations of δ56Fe were analyzed at water-shed,regional and global scales. The release rates of various forms of iron from regional and global glaciers were quantified. The annual dFe flux of the glacier is about (403±737) Gg and the production is about (7151±13061) kg·km-2. Concentration of Fe in the meltwater is seasonal,and is affected by factors such as bedrock li-thology and runoff. The amount of iron output from glaciers is mainly affected by the flow rate. In the future,we should strengthen the research on the temporal and spatial evolution of glacier meltwater iron,analyze its source and transport law by using δ56Fe,pay attention to the bioavailable iron,and comprehensively understand the Fe cycle process and its ecological and climatic effects in the glacier environment.
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