The sediment-water interface and shallow-surface sediment are the “factory” for early diagenesis.Research on diagenesis of the Eastern Pacific and Atlantic Ocean suggests that the solid phase metals are enriched above the oxic-suboxic boundary, while the dissolved phase metals are enriched below it. However, there is still limited research of the Northwest Pacific Ocean, especially on the small-scale metal synergistic variations above the boundary and the influence of oligotrophic conditions on metal distribution. This research gives a closer examination into the vertical variations of the two phases metal (Mn、Fe、Co、Ni、Cu、Mo、Cd、Cr、Pb、Zn) from the Western Pacific Intermountain Basin (such as Block M2 in the southern contract area of polymetallic nodules exploration of the Beijing Pioneer Hi-tech. Development Co., Ltd. (the BPC)), and achieves the following scientific knowledge: The boundaries in eutrophic regions such as the Eastern Equatorial Pacific is located at a depth of a few to over ten centimeters in the sediment, while the oligotrophic Western Pacific have relatively deeper boundaries. The relatively weaker biological activity results in smaller amount of metal entering the sediment, as well as the lower content of montmorillonite leads to lower amount of carrier for metal fixation, make the shallow-surface sediment in the study area have lower solid and dissolved metal. Above the boundary, the relatively enriched solid phase metal and the little remaining dissolved phase metal exhibit consistent small-scale vertical variation characteristics. This suggests that similar environmental conditions such as redox conditions, or the simultaneous supply of reactants/ carriers at the same depth, constrain the variations of the two metal phases.
Wang et al. (2026) studied this question.