This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).
Recent work by this team shows that geothermal springs in major river valleys near the Main Central Thrust zone of the Himalayan front are significant sources of carbon dioxide. To date we have shown that this source of CO2 exceeds the consumption of CO2 by chemical weathering in the large Narayani basin of central Nepal. Investigators have proposed that the source of this large CO2 flux is metamorphic decarbonation and decarboxylation reactions which take place in the subducted Lesser Himalyan sediments beneath the Himalayan front. In at least this region of the Himalaya, the net flux of CO2 from the carbonate-silicate cycle is strongly positive, in contrast to the widely held view that the Himalaya are an important CO2 sink.
Investigators propose to address two issues: 1) they will sample fluids, gasses and precipitates from geothermal sites and use the combined δ 13C data from DIC, CO2(g), and travertine (CaCO3) to improve constraints on the extent of near-surface degassing. They believe that their current estimates are too low because of our previous inability to constrain this process in low δ13CDIC springs. Their hypothesis is that the extent of degassing in the low δ13CDIC geothermal systems is similar to what they have estimated in the high δ13CDIC springs, i.e. roughly 90%, and that the difference in isotopic composition is caused by different deep sources of CO2. Combined multi-phase δ13C data will allow them to quantitatively test this hypothesis. 2) They only have data from a 200 km-long section of the Himalaya, and it is unclear how representative their data from central Nepal are for the larger region. They hypothesize that geothermal fluxes of heat and CO2 vary with exhumation rate. They will test this hypothesis by developing a similar estimate of geothermal flux in the Sutlej valley of NW India, where thermochronometric data suggests exhumation rates about one half of those in central Nepal. Alternatively they may find that there is no particular relation, and that would suggest CO2 fluxes are more dependent on the overall rate of subduction or local variations in the lithology of sediments undergoing metamorphism in the appropriate P-T window. Regardless of the outcome, data from NW India will allow them to address the issue of along-strike heterogeneity of the CO2 flux in Himalayan geothermal systems and greatly improve estimates of the overall carbon balance.
Scientific merit: the project addresses a major issue in the global carbon cycle: what is the relationship between major orogenic events and the silicate-carbonate cycle. The idea that Himalayan metamorphic fluxes offset or exceed weathering consumption of CO2 is novel and potentially transformative, as directly challenges a widely held paradigm in Earth Sciences.
Broader impacts: this is a collaborative proposal between a major research university (Cornell) and an undergraduate institution (Wheaton College). They will involve undergraduate and graduate students extensively in the field and laboratory work. The project will provide outstanding opportunities for education and training between the two institutions and their international collaborators at the CRPG, France. They will also interact closely with a study program that combines US and Nepali students.
