Previous Group Members
J. Bunbury (Cambridge), E.T. Tipper (Cambridge & ETH), J.A. Becker (Cambridge)
Multiple Controls on Silicate Weathering Rates From a Compilation of Global Catchment Data
West et al. (2002) compiled silicate chemical rates from a global set of small and large catchments. They were able to quantify the separate relationships between silicate chemical weathering and rainfall, temperature and erosion rate. The figure shows silicate chemical weathering rate versus physical erosion rate. A key observation is that in catchments with low erosion rates, chemical weathering is nearly complete (weathering rates in such catchments give a linear relationship with erosion rates) and chemical weathering rates in such ‘transport limited’ catchments do not respond to changes in climate.
Head Waters of the Ganges: Alaknanda River
We have been working in the Alaknanda and Bhagirathi catchments since 1996 with major collecting trips in 1996, 1997, 1998, 2003 and 2004. The major target has been to quantify the Sr inputs from the different geological units and to discriminate between inputs from carbonate and silicate rocks. The very high 87Sr/86Sr ratios of some carbonates (in excess of 1.0!) complicates this. We use the average composition of tributaries draining single geological units to characterise their outputs and the changes in mainstem chemistry to quantify relative inputs (Bickle et al., 2003). We have been attempting to distinguish carbonate from silicate inputs by modelling mixing between carbonate and silicate-derived components in Sr-Ca-Mg-Na space (Bickle et al., 2005) but precipitation of secondary calcite probably compromises these calculations (see results of Marsyandi work below).
Flood Plains of the Ganges and Brahmaputra Rivers
Nepal: Marsyandi River
We have sampled the Marsyandi river catchment in Nepal in April (pre-monsoon) and September (late-monsoon) in 2002 and, in conjunction with Doug Burbank's Geomorphic Himalayan Project in Nepal sampled a number of major tributaries and mainstem sites at two-weekly intervals continuously for two years.
The time-series samples show marked seasonal changes in the ratio of carbonate-derived to silicate-derived chemical fluxes which we think reflects more rapid carbonate dissolution during high runoff during the monsoon. Correlations between the Ca and Mg-isotopic ratios of the dissolved load are thought to relate correlated variations in the extent of weathering of biotite, the main Mg-containing mineral and precipitation of secondary carbonate. Comparison of Sr-Ca-Na ratios between the bedload and dissolved loads suggests that secondary a higher proportion of Ca is lost to secondary calcite during the dry season, and this coupled with the seasonal variations in carbonate to silicate weathering rotates Sr-Ca-Na correlations.
Myanmar: Irrawaddy and Salween Rivers
In conjunction with the Department of Meteorology and Hydrology, Myanmar, we have been sampling and both the Irrawaddy and the Salween at two-weekly intervals since 2004 for analysis of major cations and anions, Sr and Sr-isotopic compositions. We hope to continue this sampling through 2008 to 2011 in collaboration with Ruth Robinson and Michael Bird (St Andrews).
Taiwan: Multiple Catchment Studies
This is a major NERC funded project which started in 2007. The objective is to sample waters from catchments in Taiwan to:
- determine the locations where weathering takes place
- determine the reaction mechanisms which control the weathering process; and
- provide robust (time-averaged) estimates of the silicate and carbonate weathering fluxes.
Taiwan has been chosen for this study because it is accessible, well studied and is one of the few locations in a rapidly eroding, high weathering rate regime where the major controlling parameters on weathering rates (principally temperature, rainfall, and physical erosion rate, but also vegetation, lithology and hydrology) are either well documented or can be determined as part of this study. The project will exploit a collaborative bi-weekly sampling of river waters from 14 catchments in Taiwan initiated in March 2005, the results of past and continuing work on erosion mechanisms and rates in Taiwan, as well as detailed ecological and hydrological work by our Taiwanese colleagues. The project builds on the research by the Earth Surface Processes group.
Our first field season was in September 2007 and currently we are starting analyses of the several hundred water samples collected since 2005.
Himalayan Hot Springs
Rivers extract CO2 from the atmosphere. Metamorphic belts also produce CO2 by decarbonation reactions and in the Himalayas this CO2 is released from numerous hot springs. We (Becker et al., 2007) have quantified the hotspring output of CO2 in the Marsyandi catchment in Nepal by modelling the thermodynamics of the high level degassing and quantifying the flux of hot spring waters by the perturbation of Cl contents in the rivers (cf. Evans et al., 2002).
Publications From This Work
- Becker, J.A., Bickle, M.J., Galy, A. and Holland, T.J.B. (2007) Himalayan metamorphic CO2 fluxes: Quantitative constraints from hydrothermal springs, Earth Planetary Science Letters. doi:10.1016/j.epsl.2007.10.046
- Tipper, E. T., Galy, A. and Bickle, M. J. (2006a) Riverine evidence for a fractionated reservoir of Ca and Mg on the continents: Implications for the oceanic Ca cycle, Earth and Planetary Science Letters, v. 247, p. 267-279
- Tipper, E. T., Bickle, M. J., Galy, A., West, A. J., Pomies, C. and Chapman, H. J. (2006b) The short term climatic sensitivity of carbonate and silicate weathering fluxes: Insight from seasonal variations in river chemistry, Geochimica et Cosmochimica Acta, v. 70, p. 2737-2754
- Tipper, E. T., Galy, A., Gaillardet, J., Bickle, M. J., Elderfield, H., and Carder, E. A. (2006) The magnesium isotope budget of the modern ocean: Constraints from riverine magnesium isotope ratios, Earth and Planetary Science Letters, v. 250, p. 241-253
- West, A. J., Galy, A. and Bickle, M. J. (2005) Tectonic and climatic controls on silicate weathering, Earth and Planetary Science Letters, v. 235, p. 211-228
- Bickle, M. J., Chapman, H. J., Bunbury, J. M., Harris, N. B. W., Fairchild, I. J., Ahmad, T. and Pomies, C. (2005) Relative contributions of silicate and carbonate rocks to riverine Sr fluxes in the headwaters of the Ganges, Geochimica et Cosmochimica Acta, v. 69 p. 2221-2240
- Bickle, M. J., Bunbury, J. M., Chapman, H. J., Harris, N. B. W., Fairchild, I. J. and Ahmad, T. (2003) Fluxes of Sr into the headwaters of the Ganges, Geochimica et Cosmochimica Acta, v. 67, p. 2567-2584
- Oliver, L., Harris, N., Bickle, M. J., Chapman, H. J., Dise, N. and Horstwood, M. (2003)
- Silicate weathering rates decoupled from the 87Sr/86Sr ratio of the dissolved load during Himalayan erosion, Chemical Geology, v. 201, p. 119-139
- Vance, D., Bickle, M. J., Ivy-Ochs, S. and Kubik, P. W. (2003) Erosion and exhumation in the Himalaya from cosmogenic isotope inventories of river sediments, Earth and Planetary Science Letters, v. 206, p. 273-288
- White, N. M., Pringle, M. S., Garzanti, E., Bickle, M. J., Najman, Y. M. R., Chapman, H. J. and Friend, P. F. (2002) Constraints on the exhumation and erosion of the High Himalayan Slab, NW India, from foreland basin deposits, Earth and Planetary Science Letters, v. 195, p. 29-44
- West, A. J., Bickle, M. J., Collins, R., and Brasington, J. (2002) A small catchment perspective on Himalayan weathering fluxes, Geology, v. 30, p. 355-358
- Bickle, M. J., Harris, N. B. W., Bunbury, J. M., Chapman, H. J., Fairchild, I. J. and Ahmad, T. (2001) Controls on the 87Sr/86Sr ratio of carbonates in the Garhwal Himalaya, headwaters of the Ganges, Journal of Geology, v. 109, p. 737-753
- Najman, Y. M. R., Bickle, M. J. and Chapman, H. J. (2000) Early Himalayan exhumation: isotopic constraints from the Indian foreland basin, Terra Nova, v. 12, p. 28-34
- White, N. M., Najman, Y. M. R., Bickle, M. J., Friend, P. F., Parrish, R. R., Pringle, M. S., Burbank, B. and Maithani, M. (1999) Constraints on Himalayan Eo-metamorphism, post-metamorphic cooling, exhumation and erosion provided by detrital monazite and white mica in the Dharamsala formation, N.W. Indian foreland basin, Terra Nostra, v. 99, p. 168-170
- Harris, N., Bickle, M. J., Chapman, H. J., Fairchild, I. J. and Bunbury, J. M. (1998) The significance of Himalayan rivers for silicate weathering rates: evidence from the Bhote Kosi tributary, Chemical Geology, v. 144, p. 205-220
- Bickle, M. J. (1996) Metamorphic decarbonation, silicate weathering and the long-term carbon cycle, Terra Nova, v. 8, p. 270-276
Last updated on 02-Oct-14 12:35