HR: 0800h
AN: H31D-1328    [Abstracts]
TI: Geochemical Fluxes and Weathering on High Standing Islands: Taranaki and Manawatu-Wanganui Regions, New Zealand
AU: * Goldsmith, S T
EM: goldsmith.35@osu.edu
AF: Department of Geological Sciences, The Ohio State University, 275 Mendenhall Laboratory, 125 South Oval Mall, Columbus, OH 43210-1398 United States
AU: Carey, A E
EM: carey@geology.ohio-state.edu
AF: Department of Geological Sciences, The Ohio State University, 275 Mendenhall Laboratory, 125 South Oval Mall, Columbus, OH 43210-1398 United States
AU: Lyons, W B
EM: jack.dibb@unh.edu
AF: Byrd Polar Research Center and Dept. of Geological Sciences, 108 Scott Hall, 1090 Carmack Road, Columbus, OH 43210-1002 United States
AU: Hicks, D M
EM: m.hicks@niwa.cri.nz
AF: NIWA, PO Box 8602, Christchurch, 0000 New Zealand
AB: Sediment fluxes from high standing oceanic islands (HSIs) such as New Zealand are some of the highest known. Recent geochemical work has suggested that along with their extremely high physical weathering yields, many New Zealand watersheds also have very high chemical weathering yields. In New Zealand, the magnitude of both the physical and chemical weathering yields is related to the lithology of the watershed. Most of the previous work on this topic has been undertaken in Southern Alps watersheds of schist and greywacke and in East Cape watersheds of semi-consolidated marine sediments and greywacke. We recently sampled North Island watersheds in the Taranaki and Manawatu-Wanganui regions which have been subjected to volcanism since the Miocene. We sampled watersheds that contain both volcanic and sedimentary rocks. A series of water and sediment samples was collected and analyzed for major, minor and trace elements. This was done to quantify the weathering intensities in the watersheds and to establish the relationship between physical and chemical weathering yields in volcanic lithologies. Our results reveal distinct chemical signatures for the different regions. Waters draining the Taranaki region volcanics are significantly enriched in Si and K⁺ and depleted in Ca²⁺, Sr²⁺, and HCO₃^- compared to waters draining the Manawatu-Wanganui region volcanics, which also traverse expanses of sedimentary siltstones and mudstones. The Ca²⁺, Sr²⁺, and HCO₃^- depletions may reflect the relative absence of CaCO₃ in the Taranaki region watersheds. In addition, sediment samples from the Taranaki region show significant enrichment in Ti, Al, Ca, Fe, Mn, Mg, Ca, and P and depletion in Si and Rb compared to those of the Manawatu-Wanganui region. From total dissolved solids concentrations and annual volumetric water discharge, we calculate chemical weathering yields of 60-238 tons km^-2a^-1. These weathering yields fall within the middle to upper range of those previously documented for the Southern Alps (93-480 tons km^-2 a^-1) and East Cape (62-400 tons km^-2 a^-1). Calculated silicate weathering yields of 12-33.6 tons km^-2 a^-1) and CO₂ consumption of 852-2390 x 10³ moles km^-2 a^-1) for the rivers draining the Taranaki volcanic region are higher than those previously reported for watersheds hosted in sedimentary and metamorphosed rock terrains on HSIs. CO₂ consumption is found to be within the range previously measured for the basaltic terrains of the Deccan Traps (580-2450 x10³ moles km^-2 a^-1) and Reunion Island (1300-4400 x10³ moles km^-2 a^-1). Our calculated chemical weathering yields demonstrate the importance of HSIs, particularly those with volcanic terrains, when considering global geochemical fluxes.
DE: 1030 Geochemical cycles (0330)
DE: 1051 Sedimentary geochemistry
DE: 1806 Chemistry of fresh water
DE: 1879 Watershed
DE: 1886 Weathering (0790, 1625)
SC: Hydrology [H]
MN: Fall Meeting 2005