論文

査読有り
2017年8月

Downstream and seasonal changes of lithium isotope ratios in the Ganges-Brahmaputra river system

GEOCHEMISTRY GEOPHYSICS GEOSYSTEMS
  • Takuya Manaka
  • ,
  • Daisuke Araoka
  • ,
  • Toshihiro Yoshimura
  • ,
  • H. M. Zakir Hossain
  • ,
  • Yoshiro Nishio
  • ,
  • Atsushi Suzuki
  • ,
  • Hodaka Kawahata

18
8
開始ページ
3003
終了ページ
3015
記述言語
英語
掲載種別
研究論文(学術雑誌)
DOI
10.1002/2016GC006738
出版者・発行元
AMER GEOPHYSICAL UNION

The Li isotope ratio (Li-7) is expected to be a useful tracer of silicate weathering in river and groundwater systems, which is an important contributor to the seawater compositional changes that accompany the evolution of the Earth's surface environment. To obtain accurate estimates of continental Li fluxes to the ocean, we determined Li-7 values of dissolved Li in the lower Ganges-Brahmaputra river system in both the dry and rainy seasons, and in deep groundwater in the Bengal basin. Dissolved Li and Li-7 values in the lower reaches of the rivers (0.04-0.66 mu mol kg(-1) and +19.1 to +34.2, respectively) were predominantly derived from silicate weathering, as is the case in the upper parts of these rivers. We observed large changes in Li-7 over a distance of more than 1000 km downstream that were due mainly to Rayleigh-type removal of Li from river water. Extremely high Li concentrations (1.15-1.67 mu mol kg(-1)) and low Li-7 values (+5.1 to +11.6) in groundwater samples indicate congruent isotope leaching and dissolution of silicate minerals in the deep aquifer, where the water residence time is long. In the rainy season, Li concentrations and Li-7 values were lower than in the dry season, owing to the shorter residence time of river water and the substantial input of local subsurface flow through lowland alluvium. These results suggest that accurate estimation of continental Li fluxes to the ocean should take account of downstream and seasonal changes, as well as aquifer depth variations, in Li-7 values.

Web of Science ® 被引用回数 : 13

リンク情報
DOI
https://doi.org/10.1002/2016GC006738
Web of Science
https://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=JSTA_CEL&SrcApp=J_Gate_JST&DestLinkType=FullRecord&KeyUT=WOS:000411196000010&DestApp=WOS_CPL
URL
http://www.scopus.com/inward/record.url?eid=2-s2.0-85029702128&partnerID=MN8TOARS
URL
http://orcid.org/0000-0001-5249-4995

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