Harunur Rashid

Developing a geochemical database on the Bay of Bengal sediments for the assessment of changes in the Ganges-Brahmaputra-Meghna river discharge

Project Summary:

The monsoon climate represents one of the Earth’s most dynamic and synoptic climatic interactions between atmosphere, oceans and continents. Approximately, one half of the humanity depends on the regular return of the monsoon for their livelihood in regions ranging from West Africa through Central to East Asia to Australia. The Indian Ocean monsoon (IOM) is the product of the pressure differences between the land-ocean sensible and the tropospheric latent heating. This pressure gradient sets the stage for the cyclonic summer-monsoon wind and evaporation from the tropical Indian Ocean supplying moisture which intensifies the monsoon. With the threat of increase in greenhouse gases and the ensuing global warming in this century, most of the climate models predict that the future IOM system may turn into early Holocene climate. At present, there are ~15,000 glaciers in the southern margin of the Himalayas hosting ~12,000 km³ of freshwaters. If the IPCC (2007) predictions of the global temperature rise become correct, then the availability of the freshwater resulting from melting of these glaciers and monsoonal rainfall to the agrarian community becomes a serious concern for their livelihood.

In this CWC funded Seed grant project, we wish to provide a geochemical database about the  Indian monsoon intensity from the lower reaches of the Ganges-Brahmaputra-Meghna delta to address the following questions: (a) what are the changes in the Ganges-Brahmaputra-Meghna freshwater outflow fluxes as a result of the warming evident from the receding glaciers in the Himalayas? (b) Were the early Holocene Ganges-Brahmaputra-Meghna rivers discharge fluxes similar to the recent outflow? (c) Are they consistent with the Mount Kilimanjaro or other regional high-resolution hydrological variability records? (d) Are the carbon fluxes increased as a result of increase in the deforestation and hence erosion in the Himalayan foot hills? In this study, we will address these questions by making measurements from the sediment and water samples from the Ganges-Brahmaputra-Meghna rivers basins and the Bay of Bengal. Our preliminary data generated from the CWC Seed Grant will be used to demonstrate the “proof of concept” which will be utilized to seek funds from federal and other funding agencies.

2. Products and Deliverables:

Our CWC Seed Grant was released in late October/early November of 2008. Therefore we had six to eight weeks to work on the project. We will carry out the following measurements to lay the foundation for detailed research: (i) Determination of d¹⁸O, Mg/Ca, Sr/Ca, Li/Ca, Al/Ca, and Ba/Ca values in the planktonic foraminifera from core top and water samples for ground truthing the “modern” values for the freshwater outflow, precipitation, and nutrient content; (ii) measuring the d¹³C from the bulk sediment to assess the carbon sink and sequestration from the terrestrial versus marine sources; and (iii) reconstructing the Ganges-Brahmaputra-Meghna rivers outflow variability for the Holocene period. Part of the sediment samples were given by the Lamont-Doherty Earth Observatory (LDEO) of Columbia University in late November and we have started processing samples. We plan to visit the core repository of the LDEO in March/April 2009 to acquire additional sediment samples for our study. It is worth noting that the LDEO cores are presently the only available in the US sediment cores from these climatically sensitive areas.

 2.A: Subsections with some detail:

Nothing to report for 2008.

2.B: Another Subsection:

Nothing to report for 2008.

3. How the Project Generated New Research or New Funding:

Nothing to report for 2008.

4. Timeline of Accomplishments and Related Costs: Total Funds = $52,677

Our fund was released in late October/early November of 2008. As a result, we have limited time to utilize and pursue the goal of the Seed Grant. We spent $2,400 to acquire 10 ¹⁴C-Accelerator Mass-Spectrometric (AMS) dates from the Keck Carbon Cycle Laboratory of the University of California, Irvine. We have used the dates to constrain the oxygen isotope stratigraphy of an exiting record from the Northern Bay of Bengal to assess the sedimentation rates at the mouth of the Ganges-Brahmaputra-Meghna rivers.