Chemical weathering on the North Island of New Zealand: CO₂ consumption and fluxes of Sr and Os

Abstract

[1] We present Os and Sr isotope ratios and Os, Sr and major/trace element concentrations for river waters, spring waters and rains on the North Island of New Zealand. The Os and Sr data are used to examine whether the NINZ is a significant contributor of unradiogenic Os and Sr to the oceans. Major element chemistry is used to quantify weathering and CO 2 consumption rates on the island to investigate relationships between these processes and Os and Sr behavior. Chemical erosion rates and CO 2 consumption rates across the island range from 44 to 555 km À2 yr À1 and 95 to 1900 Â 10 3 mol CO 2 km À2 yr À1 , respectively. Strontium flux for the island range from 177 to 16,100 mol km À2 yr À1 and the rivers have an average flux normalized 87 Sr/ 86 Sr ratio of 0.7075. In agreement with the previous studies these findings provide further evidence that weathering of arc terrains contributes a disproportionally large amount of Sr to the oceans and consumes very large amounts of CO 2 annually compared to their areal extent. However, the 87 Sr/ 86 Sr from the NINZ is not particularly unradiogenic and it is likely not contributing significant amounts of unradiogenic Sr to the oceans. Repeated Os analyses and bottle leaching experiments revealed extensive and variable sample contamination by Os leaching from rigorously precleaned LDPE bottles. An upper bound on the flux of Os from NINZ can nevertheless be assessed and indicates that island arcs cannot provide significant amounts of unradiogenic Os to the oceans.