Different enrichment patterns of pedogenic magnetic particles modulated
by primary iron-phosphorous input
Abstract
Magnetic particles including ferrimagnetic (FM) and antiferromagnetic
(AFM) particles are ubiquitous in the surface of Earth and Mars. The FM
particles dominating soil magnetism usually coexist or compete with AFM
hematite due to their comparable thermodynamic stability. The uncertain
correlation can be modulated by phosphorous (P) absorption during aging
of precursor amorphous iron (Fe) oxides. We investigated two Ferralsol
sequences around a P mining field with comparable content of hematite
but contrasting P/Fe ratio. The FM particles accompanying the formation
of hematite are enriched stably at accelerating rates under high P/Fe
but at unstably even rates under low P/Fe. The FM particles became less
abundant and coarser while the iron oxide crystallinity increased
monotonically as P/Fe decreased. We attribute it to more rapid grain
growth of FM particles and transformation into hematite without P
retarding the crystallization of iron oxides.