太平洋北部铁锰结核富集区沉积物和间隙水中Fe,Mn,Ca,Mg的地球化学

GEOCHEMISTRY OF Fe, Mn, Ca, Mg IN SEDIMENTS AND INTERSTITIAL WATER OF THE FERROMANGANESE NODULE ENRICHMENT AREA FROM NORTH PACIFIC

本文利用太平洋北部铁锰结核富集区(富集度1.1—22.0kg/m^2)7个柱状样的沉积物和间隙水资料,详细探讨了其Fe,Mn,Ca,Mg的地球化学特征。结果表明:(1)沉积物中Mn明显的比河口、陆架及贫结核洋区富集,而Fe则与河口沉积物相接近;(2)沉积环境不同,沉积物和间隙水中元素的垂直分布和进入间隙水的途径不同;(3)沉积物中Fe,Mg主要来自粘土吸附,Ca来自生物化学作用沉积,而Mn则可能通过河口、陆架及半深海沉积物次表层Mn的迁移、生物化学及附近海底火山作用而富集;(4)由于钙、硅软泥区生物作用强烈,使间隙水中Mn^(2+)/Fe^(2+)比值明显的比钙质软泥和褐色粘土区大,这在某种程度上支持了结核中Mn组元素的沉积物来源。

Geochemistry of Fe, Mn, Ca, Mg in sediments and interstitial water was described in detail based on the data obtained during the first ferromanganese nodule survey in the North Pacific region (167°?00.06'-178°3.58' W, 6°57.16'-10°38.69' N).The average contents of Fe, Mn, Ca, Mg in the surface sediments are 3.02%, 0.60%, 18.87% and 1.43% respectively. Mn content is obviously higher than that in sediments of estuary and continental shelf, but Fe content is similar to that in estuary. The average contents of Fe2+, Mn2+,Ca2+, Mg2+ in interstitial water are 544.4 μg/kg, 117.7 μg/kg and 403.1 μg/g, 1169.3 μg/g respectively. Fe2+ content is obviously higher than that in the estuary interstitial water and -continental shelf, but Mn2+,Ca2+,Mg2+ contents are similar to those in the continental shelf.The vertical distribution of elements and their geochemical nature in the sediment and the plaster stone (CaSO42H2O) in the sediment.In calcsiliceous ooze region, Fe2+ and Mn2+ in interstitial water came mainly from the reduction of iron (Fe3+) and manganese (Mn4+ ) in sediments through the decomposing reaction of some organic carbon under the intermediating action of bacteria, Thus Fe2+ and Mn2+ in 5-10 cm sediments are diffused toward the overlying water, resulting in the decrease of their content.The low Mg2+ content in surface (0-5 cm) interstitial water is due to (1) the reduction of organic carbon by the docomposing action of organic material in sediments, (2) replacement of Fe2+ by Mg2+, in the clay mineral, and the formation of dolomite (CaMg(CO3)2) and the plaster stone (CaSO42H2O) in the sediment.In the brown ooze zone, Fe, Mn in sediments and interstitial water decreased with the in-crease of sediment layer and Fe2+, Mn2+ in interstitial water gathered from mainly the soaking action of high pressure sea water by the sedimentary environment which favoured the exist of the organic material in sediments. Simultaneously, the vertical change of Mg/Ca (Mg2+/ Ca2+) in sediments and interstitial water were not obvious, indicating that Mg, Ca in solution-soil phase has not been redistributed, and Fe2+ Mn2+, Mg2+, Cai+ in interstitial water has not diffused towards the overlying water and moved from surface towards the depth.Fe, Mg in sediments of studing area came mainly from adsorption of clay mineral; Mn in sediments came from the movement of Mn2+ in surface sediment of estuary and continental shelf and the biochemical action and volcanism in oceanic environment; Ca came from the biochemical deposits.In the calcsiliceous ooze zone, owing to the action of organisms and low sedimentary rate compared with that of the calcareous and brown ooze zone, the Mn2+/Fe2+ ratio in interstitial water is higher and Mn/Fe ratio in sediments is smaller than that in the calcareous and brown ooze zones, well in agreement with the higher abundance and faster growth rate of ferromanga-nese nodule in calcsiliceous ooze zone, indicating further the sediment origin of some main elements of ferromanganese nodule.