Physical and Chemical Weathering Processes and Associated CO₂ Consumption from Small Mountainous Rivers on High-Standing Islands

Studies of chemical weathering have shown that high standing islands (HSIs) have some of the highest yet observed rates of chemical weathering and associated CO₂ consumption. 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 (SMR) on an HSI during an intense storm event; 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. This study, the first comprehensive evaluation of weathering processes on HSIs, provides valuable insights on the relationship of silicate weathering and global CO₂ drawdown on various timescales.

Storm fluxes observed from the Chosui River in Taiwan during Typhoon Mindulle in 2004 revealed the role these events can play in the delivery of sediment, particulate organic carbon (POC) and solutes to the ocean. 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 from silicate weathering, elucidate the important role of these tropical cyclone events on SMRs as a global sink of CO₂.

Carbonate weathering was shown to supply a significant portion of the total cation yields while silicate weathering plays a lesser role. Various relationships were observed between chemical, carbonate, and silicate weathering yields with basin average mean annual rainfall, average basin runoff, annual suspended sediment yields, and post-uplift age of the landscape. Calculated CO₂ consumption from silicate weathering ranges are highly elevated over world average values. Weathering fluxes observed from the sedimentary and metamorphic terrains of Taiwan may represent the upper end of what may have occurred during the early stage collision of the Himalayas.

Geochemical data from the island of Dominca showed the importance of parent material age on the overall delivery of solutes. Observed molar ratios suggest crystallinity of the parent material may also play an important role in determining weathering fluxes. Chemical weathering yields, silicate yields, and associated CO₂ consumption were similar to basalt terrains and amongst the highest determined to date.

Finally, a world-wide composite evaluation of solute fluxes from andesite terrains revealed no discernible relationship with SiO₂ content or age of parent material while runoff and temperature were shown to be the dominant controls. From these relationships and a new highly-detailed lithology map, CO₂ consumption from andesite weathering on HSIs was estimated and found to represent significant portions of values previously calculated from continental silicate weathering thereby confirming the importance of andesite weathering as a CO₂ sink.