Geochemical Characteristics of the Sediment Pore Water in the Northeastern Equatorial Pacific

Abstract

This study investigated dissolved oxygen (DO), nutrients, manganese (Mn) and Iron (Fe) characteristics at the sediment pore water in Northeastern Equatorial Pacific based on the geochemical analyses. The DO concentrations of sediment pore water at the upper sediment ranged 90-136 &#61549 M, drastically decreased with sediment depth increasing, showed that ranged 30-60 &#61549 M. The concentrations of ammonia, nitrate, phosphate and silicate ranged 0.02-16.34 μM, 44.73-229.32 μM, 2.04-2.98 μM and 73.44-405.24 μM, respectively. The vertical profiles of ammonia and nitrate at the sediment pore water showed a contradictory distribution in SD07 and SD16. The concentrations of Mn and Fe ranged 0.1-8.1 μM and 0.3-40.4 μM, respectively. Low concentrations of Mn and Fe are due to the oxic condition at the sediment upper layer. The Mn and Fe reduction zones generally occurs below nitrate reduction zone and at the depth of complete DO removal from the pore water. Manganese reduction in pelagic sediments may be involved in the formation of ferromanganese nodules, since under some circumstances manganese reduction in the sediments and the resulting upward diffusion of dissolved manganese across the sediment-water interface may be an important source of manganese nodules.ater at the upper sediment ranged 90-136 &#61549 M, drastically decreased with sediment depth increasing, showed that ranged 30-60 &#61549 M. The concentrations of ammonia, nitrate, phosphate and silicate ranged 0.02-16.34 μM, 44.73-229.32 μM, 2.04-2.98 μM and 73.44-405.24 μM, respectively. The vertical profiles of ammonia and nitrate at the sediment pore water showed a contradictory distribution in SD07 and SD16. The concentrations of Mn and Fe ranged 0.1-8.1 μM and 0.3-40.4 μM, respectively. Low concentrations of Mn and Fe are due to the oxic condition at the sediment upper layer. The Mn and Fe reduction zones generally occurs below nitrate reduction zone and at the depth of complete DO removal from the pore water. Manganese reduction in pelagic sediments may be involved in the formation of ferromanganese nodules, since under some circumstances manganese reduction in the sediments and the resulting upward diffusion of dissolved manganese across the sediment-water interface may be an important source of manganese nodules.