Chemical fluxes from time series sampling of the Irrawaddy and Salween Rivers, Myanmar

Abstract

The Irrawaddy and Salween rivers in Myanmar deliver water fluxes to the ocean equal to~70% of the GangesBrahmaputra river system. Together these systems are thought to deliver about half the dissolved load from the tectonically active Himalayan-Tibetan orogen. Previously very little data was available on the dissolved load and isotopic compositions of these major rivers. Here we present time series data of 171 samples collected fortnightly at intervals throughout 2004 to 2007 from the Irrawaddy and Salween at locations near both the river mouths, the up-stream Irrawaddy at Myitkyina, the Chindwin, a major tributary of the Irrawaddy and a set of 28 small tributaries which rise in the flood plain of the Irrawaddy between Yangon and Mandalay. The samples have been analysed for major cation, anion and 87 Sr/ 86 Sr ratios. The new data indicates that the Irrawaddy has an annual average Na concentration only a third of the widely quoted single previously published analysis. The Irrawaddy and Salween drain about 0.5% of global continental area and deliver about 3.3% of the global silicate-derived dissolved Ca + Mg fluxes and 2.6% of the global Sr riverine fluxes to the oceans. This compares with Ganges and Brahmaputra which deliver about 3.4% of the global silicate-derived dissolved Ca + Mg fluxes and 3.2% of the global Sr riverine fluxes to the oceans from about 1.1% of global continental area. The dischargeweighted mean 87 Sr/ 86 Sr ratio of the Irrawaddy is 0.71024 and the Salween 0.71466. The chemistry of the Salween and the Irrawaddy waters reflects their different bedrock geology. The catchment of the Salween extends across the Shan Plateau in Myanmar through the Eastern syntaxis of the Himalayas and into Tibet. The Irrawaddy flows over the Cretaceous and Tertiary magmatic and metamorphic rocks exposed along the western margin of the Shan Plateau and the Cretaceous to Neogene Indo-Burma ranges. The 87 Sr/ 86 Sr compositions of the Salween and Upper Irrawaddy (between 0.7128 and 0.7176) are significantly higher than the downstream Irrawaddy (0.7095 to 0.7108) and the Chindwin (0.7082 to 0.7095). The Irrawaddy and the Chindwin exhibit lower 87 Sr/ 86 Sr and Na/Ca ratios during and immediately post-monsoon, interpreted to reflect higher weathering of carbonate at high flow. The Salween exhibits higher 87 Sr/ 86 Sr ratios but lower Na/Ca ratios during the monsoon, interpreted to reflect higher inputs from the upper parts of the catchment in the Himalayas.

Sequestration of carbon as carbonate in the critical zone: insights from the Himalayas and Tibetan Plateau

“…In line with the findings in rivers draining the Himalayan region (e.g. Galy et al 1999;Jacobson et al 2002;Tipper et al 2008;Bickle et al 2015;Chapman et al 2015), many more NCHT rivers are affected by secondary calcite precipitation. For instance, based of the chemistry of the dissolved species, around 2/3 of the Ca released in the catchment of the Yellow River by the weathering of rock has precipitated as calcite.…”

“…Although disseminated carbonate compositions in silicate rocks are well constrained in the Himalaya (e.g. Blum et al 1998;Galy et al 1999;Tipper et al 2006;Chapman et al 2015), the composition and variability of carbonate-bearing rocks in the other edges of the TP remain poorly defined. In addition, the determination of the carbonate chemistry and mineralogy in the source rock should improve paleo-reconstruction of this region since proxies derived from soil carbonates, such as 87 Sr/ 86 Sr,…”

Lithology, Monsoon and Sea-Surface Current Control on Provenance, Dispersal and Deposition of Sediments over the Andaman Continental Shelf

“…possible eastern continuation of the Indus Tsangpo Suture Zone, the volcanics from a Cretaceous arc and sediments produced during the collision (Stephenson and Marshall, 1984;Maury et al, 2004;Najman et al, 2004;Szulc et al, 2006;Allen et al, 2008), associated post-collision intrusive igneous rocks (Darbyshire and Swainbank, 1988) and basic/ultrabasic rocks of the eastern syntaxis of the Himalaya. In the middle reaches, the Irrawaddy drains the Mogok Metamorphic Belt containing schists, gneisses, marble, migmatites, and calc-alkaline plutonics (Figure 3; Chapman et al, 2015). Many of the rivers along the Arakan coast and the western tributaries of the Irrawaddy such as the Chindwin River drain the Indo-Burman hills comprising the Neogene and Paleogene sedimentary rocks, ophiolites, serpentinites and metamorphic rocks of Triassic to Cretaceous age (Figure 3).…”

“…The major lithologies these rivers drain are presented in Figure 3. The Irrawaddy River flows, in its upper reaches, through the Gangdese batholith, metamorphic rocks and ophiolites of FIGURE 3 | The lithology map of the drainages of the Irrawaddy, the Salween and the Tanintharyi River basins falling in the Tibet, China, and the Myanmar, modified after (Awasthi et al, 2014;Chapman et al, 2015). possible eastern continuation of the Indus Tsangpo Suture Zone, the volcanics from a Cretaceous arc and sediments produced during the collision (Stephenson and Marshall, 1984;Maury et al, 2004;Najman et al, 2004;Szulc et al, 2006;Allen et al, 2008), associated post-collision intrusive igneous rocks (Darbyshire and Swainbank, 1988) and basic/ultrabasic rocks of the eastern syntaxis of the Himalaya.…”

Projection and Historical Analysis of Hydrological Circulation in Sittaung River Basin, Myanmar

“…Some researchers have been done in the major rivers of Myanmar, such as Irrewaday, Chindwin and Thanlwin [1,2]. However, a few reliable researches have been completed in the Sittaung River basin, the fourth largest river in Myanmar.…”