5:15 PM - 6:45 PM
[MZZ42-P03] Sediment properties in the Clarion-Clipperton Zone (CCZ) in the eastern Pacific
Keywords:ferromanganese nodules, deep-sea sediments, metals
In Japan, Deep Ocean Resources Development Co.,Ltd. (DORD) contracted with the International Seabed Authority (ISA) on the exploration area for manganese nodules in the Clarion-Clipperton Fracture Zone (CCZ) off southeast Hawaii in 1987, and has conducted environmental baseline surveys in the High Abundance Area (HAA) and the Preservation Reference Zone (PRZ) in the DORD west area since 2001, plus the Area of Particular Environmental Interest-10 (APEI-10) in 2021. This study reports on the sediment characteristics obtained from the 2021 survey.
Sediment samples were collected from seven sites in the PRZ (21PRMC06-21PRMC12), one site in the HAA (21MNMC31), and one site in APEI-10 (21EIMC02) using multiplecorer. Water depths ranged from 5100 to 5400 m and all sediments consisted of pelagic clays. According to the ISA environmental guidelines, core samples were divided into 7 layers (0-1, 1-2, 2-3, 3-5, 5-8, 8-12, 12-20 cm), and for each layer, water content, grain size, total organic carbon (TOC), total nitrogen (TN), carbonate (CaCO3), and biogenic opal were measured. Seven sites in the PRZ were also analyzed for metals.
Comparison of the obtained sediment characteristics showed similar trends for all measured items in the PRZ and HAA, except for 21PRMC11 which was collected from the slope. In contrast, APEI-10 was characterized by slightly higher CaCO3 and slightly lower water content, TOC, TN, and opal. The TOC ranging from 3 to 6 mg/g at all sites, consistent with values previously obtained from the DORD west area. For metals in the PRZ, there was no significant difference in the depth distributions except for 21PRMC11, and the mean values for all sites were Cr=56 µg/g, Mn=4500 µg/g, Ni=170 µg/g, Cu=380 µg/g, Zn=140 µg/g, As=8.3 µg/g, Cd=0.18 µg/g, Pb=24 µg/g, and Hg=30 ng/g. Distribution trends were divided into elements corresponding with manganese oxides (Mn, Ni, Cu, Zn, Cd, REE) and those corresponding with aluminosilicate minerals such as clay (Cr, Fe, As, Pb). The previous surveys showed the PRZ was enriched in Mn, Cu, Zn, and Pb compared to the HAA, which is consistent with the metal concentrations in the PRZ obtained in this study. The concentrations of mercury decreased with depth at all sites and a weak correlation with TOC suggested the distribution corresponding with organic matter.
Sediment samples were collected from seven sites in the PRZ (21PRMC06-21PRMC12), one site in the HAA (21MNMC31), and one site in APEI-10 (21EIMC02) using multiplecorer. Water depths ranged from 5100 to 5400 m and all sediments consisted of pelagic clays. According to the ISA environmental guidelines, core samples were divided into 7 layers (0-1, 1-2, 2-3, 3-5, 5-8, 8-12, 12-20 cm), and for each layer, water content, grain size, total organic carbon (TOC), total nitrogen (TN), carbonate (CaCO3), and biogenic opal were measured. Seven sites in the PRZ were also analyzed for metals.
Comparison of the obtained sediment characteristics showed similar trends for all measured items in the PRZ and HAA, except for 21PRMC11 which was collected from the slope. In contrast, APEI-10 was characterized by slightly higher CaCO3 and slightly lower water content, TOC, TN, and opal. The TOC ranging from 3 to 6 mg/g at all sites, consistent with values previously obtained from the DORD west area. For metals in the PRZ, there was no significant difference in the depth distributions except for 21PRMC11, and the mean values for all sites were Cr=56 µg/g, Mn=4500 µg/g, Ni=170 µg/g, Cu=380 µg/g, Zn=140 µg/g, As=8.3 µg/g, Cd=0.18 µg/g, Pb=24 µg/g, and Hg=30 ng/g. Distribution trends were divided into elements corresponding with manganese oxides (Mn, Ni, Cu, Zn, Cd, REE) and those corresponding with aluminosilicate minerals such as clay (Cr, Fe, As, Pb). The previous surveys showed the PRZ was enriched in Mn, Cu, Zn, and Pb compared to the HAA, which is consistent with the metal concentrations in the PRZ obtained in this study. The concentrations of mercury decreased with depth at all sites and a weak correlation with TOC suggested the distribution corresponding with organic matter.