Trace elements in New Zealand ferromanganese nodules: implications for deep sea environments

• Main Author: Davies, Andrea
• Format: Thesis
• Language: unknown
• Published: 2018
• Subjects: Inorganic geochemistry; Marine geoscience; Chemical oceanography; Geochemistry; Ferromanganese; Oceanography; School: School of Geography; Environment and Earth Sciences; 040202 Inorganic Geochemistry; 040502 Chemical Oceanography; 040305 Marine Geoscience; 970104 Expanding Knowledge in the Earth Sciences; Degree Discipline: Geology; Degree Level: Masters; Degree Name: Master of Science; Southern Ocean; New Zealand; Campbell Plateau
• Online Access: https://doi.org/10.26686/wgtn.17131868; https://figshare.com/articles/thesis/Trace_elements_in_New_Zealand_ferromanganese_nodules_implications_for_deep_sea_environments/17131868

Ferromanganese nodules are authigenic marine sediments that form over millions of years from the precipitation of Fe oxyhydroxides and Mn oxides from seawater (hydrogenetic-type growth) and sediment pore-water (diagenetic-type growth). Fe-Mn (oxyhydr)oxides grow in layers about nuclei, effectively scavenging minor metals such as Ni, Cu and Co from the waters they grow in. The uptake of different elements into the ferromanganese nodules reflects their environment and mechanism of growth, and these deposits are of interest both as a potential source of metals of economic interest, and as records of changing ocean conditions. This study investigates the composition of 77 ferromanganese nodules from the seafloor around New Zealand. Samples analysed come from locations several thousand kilometres apart under the same water mass (Lower Circumpolar Deep Water – LCDW), but with varying depth, current velocity, and sediment type. The outermost 1 mm rim of each nodule, representing near-modern growth, was sampled to compare with modern environmental parameters including substrate sediment composition and chemical and physical oceanography. Major, minor, and trace element analysis of nodule rims were undertaken, and the authigenic and detrital components examined via leaching experiments to evaluate their relative influence on growth mechanisms. Overall, New Zealand ferromanganese nodules are hydrogenetic in origin. However, there are systematic variations in composition that reflect variable diagenetic influence. Hydrogenetic endmember compositions are defined by samples from two localities in the Southern Ocean that have no evidence for diagenetic influence. Diagenetic influence on nodule composition is exemplified by samples from the two locations in the Tasman Sea, but also include nodules from the Campbell nodule field. Nodules from the Campbell nodule field come from two transects perpendicular to the Campbell Plateau, and the Deep Western Boundary Current (DWBC). Both sediment composition and nodule rim chemistry ...