Ferromanganese nodules and crusts (Fe-Mn deposits) are being widely explored for their significant economic potential and paleoenvironmentally significant archives. Fe-Mn deposits contain abundant Fe-bearing minerals including detrital minerals, biogenic Fe-bearing components, but predominantly amorphous Fe hydroxides (AFH). Particularly, the hydrogenetic Fe that is formed in bottom water should be closely related with oceanic environmental and Fe-cycling processes. However, it remains challenging to characterize and quantify the x-ray amorphous AFH component in Fe-Mn deposits. To resolve this problem, we systematically investigated thermally treated hydrogenetic Fe-Mn deposits sampled from the northwestern Pacific Ocean to unravel the AFH component. Our results show that the nanometer-sized AFHs can be transformed into strongly magnetic nanometer-sized (approximately 10-20 nm) magnetite upon heating above 500 °C, which can be feasibly quantified by systematic rock magnetic analyses. Using this novel approach, several Fe-Mn deposits at different water depths from the western Pacific Ocean are investigated. Our results indicate that the abundance of AFH increase at a water depth of ∼5000 m, which can be ascribed to bottom-current stratification. The magnetic approach to indirectly quantify the AFH component in Fe-Mn deposits has a great potential in exploring oceanic paleoenvironment significance.

锰铁结核和地壳（铁锰矿床）因其巨大的经济潜力和古环境重要的档案资料而被广泛研究。Fe-Mn矿床含有丰富的含Fe矿物，包括碎屑矿物，生物成因的Fe组分，但主要是无定形的Fe氢氧化物（AFH）。特别是，在底部水中形成的氢化铁应与海洋环境和铁的循环过程密切相关。然而，表征和定量Fe-Mn沉积物中的X射线非晶态AFH组分仍然具有挑战性。为了解决这个问题，我们系统地研究了从西北太平洋采样的经过热处理的氢化铁锰矿床，以揭示AFH组分。 °C，可以通过系统的岩石磁性分析定量地确定。使用这种新颖的方法，研究了来自西太平洋的不同水深处的几个铁锰矿床。我们的结果表明，AFH的丰度在约5000 m的水深处增加，这可归因于底流分层。磁性方法间接定量铁锰矿床中的AFH成分具有探索海洋古环境意义的巨大潜力。