Weathering processes in the Ganges-Brahmaputra basin and the riverine alkalinity budget

被引:545
作者
Galy, A [1 ]
France-Lanord, C [1 ]
机构
[1] Ctr Rech Petrog & Geochim, CNRS, F-54501 Vandoeuvre Les Nancy, France
关键词
weathering; Himalaya; alkalinity; sulfide; atmospheric CO2; metamorphic CO2;
D O I
10.1016/S0009-2541(99)00033-9
中图分类号
P3 [地球物理学]; P59 [地球化学];
学科分类号
0708 ; 070902 ;
摘要
0We present river chemistry data for a network of rivers draining the western and central Nepal Himalaya. Our sampling locations cover the system from the sources of rivers in Tibet to the Gangetic plain. Water samples were collected throughout the year, including the monsoon season, for rivers in Nepal and for the Ganges and Brahmaputra in Bangladesh. Rivers draining the North Himalaya are characterized by low discharge under a cold and arid climate. Main stream waters have delta(13)C(DIC) near 0 parts per thousand and high [SO42-]/([SO42-]+[HCO3-]) ratios (X-SO4) With values around 40 Eq% and high [Cl-]. Ca is the dominant cation (Ca2+/Sigma cations = 55 to 75 Eq%, after correction of sodium by chloride). Dissolved sulfate is produced in waters from the Tethian Sedimentary Series whereas chlorine is related to thermal waters. Dissolved sulfate is primarily derived from sulfide oxidation rather than evaporite dissolution. delta(13)C(DIC) values of up to 3.9 parts per thousand show that metamorphic CO2 is an important weathering agent. Rivers of the North Himalayan basins have about 50% of their alkalinity derived from carbonate dissolution, 20% from biogenic activity and 30% from metamorphic CO2. On the south flank of the Himalaya, rivers are more depleted in C-13 and have, on average, lower X-SO4. Most rivers have delta(13)C(DIC) and X-SO4 values compatible with a simple mixing between soil CO2 and sulfate derived from sulfide oxidation. During the monsoon, discharge increases by a factor 20 but the total dissolved concentration is only slightly reduced. X-SO4 and delta(13)C decrease while Ca/Sigma cations increases, implying enhanced dissolution of pedogenic calcite. As a whole, the G-B riverine flux of alkalinity derived from silicate weathering is around 2.7 x 10(11) mol/year, modest at the global scale. Sulphuric acid controls 20-30% of the weathering reaction in the Brahmaputra and 6 to 9% in the Ganges. Na+ and K+ balance 60 to 65% of the silicate-derived alkalinity flux, and the long term CO2 consumption by Ganges and Brahmaputra is near 6.4 x 10(10) mol/year. The flux of metamorphic CO2 converted to alkalinity via weathering reactions is ca. 1 x 10(10) mol/year. (C) 1999 Elsevier Science B.V. All rights reserved.
引用
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页码:31 / 60
页数:30
相关论文
共 72 条
[61]  
2.0.CO
[62]  
2
[63]   OXYGEN AND CARBON ISOTOPE STUDIES OF CONTACT METAMORPHISM OF CARBONATE ROCKS [J].
SHIEH, YN ;
TAYLOR, HP .
JOURNAL OF PETROLOGY, 1969, 10 (02) :307-&
[64]   Chemical and strontium, oxygen, and carbon isotopic compositions of carbonates from the Lesser Himalaya: Implications to the strontium isotope composition of the source waters of the Ganga, Ghaghara, and the Indus rivers [J].
Singh, SK ;
Trivedi, JR ;
Pande, K ;
Ramesh, R ;
Krishnaswami, S .
GEOCHIMICA ET COSMOCHIMICA ACTA, 1998, 62 (05) :743-755
[65]   THE ANNUAL CARBON-DIOXIDE CYCLE IN A MONTANE SOIL - OBSERVATIONS, MODELING, AND IMPLICATIONS FOR WEATHERING [J].
SOLOMON, DK ;
CERLING, TE .
WATER RESOURCES RESEARCH, 1987, 23 (12) :2257-2265
[66]  
SUBRAMANIAN V, 1987, J GEOL SOC INDIA, V30, P335
[67]   CHEMICAL COMPOSITION OF OCEANIC AEROSOL [J].
TSUNOGAI, S ;
SAITO, O ;
YAMADA, K ;
NAKAYA, S .
JOURNAL OF GEOPHYSICAL RESEARCH, 1972, 77 (27) :5283-+
[68]  
UPRETI BN, IN PRESS HIMALAYA TI
[69]   EVAPORITE ENCRUSTATIONS AND SULFIDE OXIDATION-PRODUCTS FROM THE SOUTHERN ANTARCTIC PENINSULA [J].
VENNUM, WR .
NEW ZEALAND JOURNAL OF GEOLOGY AND GEOPHYSICS, 1980, 23 (04) :499-505
[70]  
Wake C. P., 1990, ANN GLACIOL, V14, P301, DOI DOI 10.1017/S026030550000879X