Physical and chemical weathering processes and associated carbon dioxide consumption from small mountainous rivers on high-standing islands

Recent studies of chemical weathering of on high standing islands (HSIs) have shown these terrains have some of the highest observed rates of chemical weathering and associated CO2 consumption yet reported. However, much remains unknown about controlling process. To determine the role these islands play on climate the following were evaluated: (1) dissolved, particulate and organic carbon fluxes delivered to the ocean from a small-mountainous river on an HSI during an intense storm event (i.e., typhoon) (2) relationship between physical and chemical weathering rates on an HSI characterized by ranges of uplift rates and lithology (3) water and sediment geochemical fluxes and CO2 consumption rates on HSIs with andesitic-dacitic volcanism and (4) the overall chemical weathering fluxes and CO2 consumption rates from andesitic-dacitic terrains on HSIs of the Pacific and the East and Southeast Asia region.Sampling of the Choshui River in Taiwan during Typhoon Mindulle in 2004 revealed a particulate organic carbon (POC) flux of 5.00x105 tons associated with a sediment flux of 61 million tons during a 96 hour period. The linkage of high amounts of POC with sediment concentrations capable of generating a hyperpycnal plume upon reaching the ocean provides the first known evidence for the rapid delivery and burial of POC from the terrestrial system. These fluxes, when combined with storm derived CO2 consumption of 1.65x108 moles from silicate weathering, elucidate the important role of these tropical cyclone events on small mountainous rivers as a global sink of CO2.Geochemical sampling of Taiwan rivers during spring 2004 and summer 2005 revealed carbonate weathering supplies a significant portion of the total cation yields (44--93%) while silicate weathering plays a lesser role. However, absolute silicate weathering rates are so high (5.8--149 tons km-2a-1) that they fall at the upper end of those previously determined from sedimentary and metamorphic terrains of HSIs. Comparisons of chemical weathering yields to potential controlling parameters revealed slightly positive correlations with basin average mean annual rainfall and average basin runoff as well as between silicate weathering rates with annual suspended sediment yields.Sampling and stream gauging of Dominica rivers in July 2006 and March 2008 revealed distinct wet and dry season solute concentrations. A cluster analysis of the stream geochemical data shows the importance of parent material age on the overall delivery of solutes. Observed Ca:Na, HCO3:Na and Mg:Na ratios suggest crystallinity of the parent material may also play an important role in determining weathering fluxes. Observed chemical weathering yields (6--105 t km-2 a-1) were similar to those previously determined for basalt terrains. Silicate yields (3.1--58.4 t km-2 a-1) and associated CO 2 consumption (143--2040 x 103 mol km-2 a-1) are amongst the highest determined to date. These chemical yields confirm the weathering potential of andesitic-dacitic terrains.Chemical weathering yields from two additional andesite terrains, Mt. Pinatubo in the Philippines and Volcan Baru in western Panama are combined with existing datasets in an attempt to calculate a regional CO2 drawdown value for this material. From these relationships and a new highly-detailed lithology map, CO2 consumption from andesite weathering on HSIs of 0.49 x 1012 moles a-1 and for East and Southeast Asia of about 0.59 x 1012 moles a-1 were determined. These values represent between 5.7 and 6.8% of the annual CO2 consumption previously calculated from continental silicate weathering and between 16 and 19% of the value previously calculated from basaltic terrains worldwide thereby confirming the importance of andesite weathering as a CO2 sink. These terrains thus may play an important role on climate evolution over geologic time. (Abstract shortened by UMI.)...