Distribution Characteristics Of Trace Metals In Pore Water Of The Sediments In The Basin Of Western Pacific Sea Mountain Area

There are abundant iron and manganese nodules in the western Pacific Ocean basin.The study of trace metal geochemistry of pore water in this area will provide an important data base for environmental impact assessment of deep-sea mining in the future.Based on 48 th.Voyage for resources and environment investigation in the western Pacific Ocean,sediment/sediment pore water samples were collected.Trace metal concentrations were measured by using ICP-MS and XRF for porewater and sediment samples respectively.Vertical distribution of trace metals in pore water and sediments,the diffusion flux rate of trace metals between overlaying water and sediments,as well as the potential link between trace metals in pore water and formation of manganese nodules were explored.The results on the three aspects are as follows.1.Both BC1812 and BC1839 stations are in the areas of oxidized sedimentary environments with nodule distribution in the surface layers.The distribution of various trace metals with depth were varied between stations.The contents of most trace metals in pore water samples of station BC1812 were higher and more fluctuating than those of station BC1839.2.According to the vertical distribution,the trace metals in pore water can be roughly divided into three types,i.e.,Redox Sensitive Metals(RSMs,such as Mn,Cu,Co,Cr,Mo,V,U),nutrient type elements(Ni,Zn,Pb,Cd),and conservative type elements(Li,Rb).The element Mn was typical in the RSMs,whose content in pore water metal was enriched in the sub-oxidation surface zone,decreasing with depth.Nutrient type elements,such as Ni,generally has a close relationship between the degradation of nutrient metals and organic matter,but some of them could be also affected by Mn reduction,resulting in two peaks in the vertical profiles.The characteristics of conservative type elements,such as Li,was similar to the vertical distribution of nutrient type elements.Correlation analysis showed significant correlations were found between Cr,Cu,Zn and Mn in BC1812,and between Mo and Mn in BC1839.3.The correlations of trace metal concentrations between solid-phase from sediments and liquid-phase from pore water in BC1812 station demonstrated two trends: negative correlation between solid-and liquid-phase in some metal elements,such as Cr,Mn,Ni,Cu,Pb,,which reflected the interexchange between pore water and sediments;positive correlation between solid-and liquid-phase in others,such as Zn,Rb,Mo,indicating the metals in pore water were mainly released from sediments.4.The calculated diffusion flux rates of metal elements at water-deposition interface showed positive fluxes(Mn and Cu)and negative fluxes(Ni,Pb and V)in both stations.However,opposite diffusion fluxes of Mo,Zn and Co were found in the two stations.Compared with the adjacent sea areas,the diffusion fluxe rates of Mn,Cu and Ni in our study area at the water-sediment interface were greater than those in the CC area of the eastern Pacific Ocean,indicating a potentially better condition for manganese nodules formation.