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Publication Details
AFRICAN RESEARCH NEXUS
SHINING A SPOTLIGHT ON AFRICAN RESEARCH
earth and planetary sciences
Noble gases in Lakes Nyos and Monoun, Cameroon
Geochemical Journal, Volume 44, No. 6, Year 2010
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Description
He, Ne and Ar isotopic ratios and concentrations of noble gases in different depths of Lakes Nyos and Monoun in Cameroon, West Africa, were investigated. Samples were collected in November 1999, January 2001 and December 2001. Improved sampling method applied in 2001 enabled us to detect detailed isotopic distribution in the lakes. Concentrations of Ne and Xe in the lake waters were low by factors of-10 and ∼3, respectively, compared with those of air saturated water (ASW), whereas in CO2 gas they were depleted by 2 orders of magnitude compared with those in air. In contrast, He was strongly enriched in lake water by more than three orders of magnitude compared to ASW. 3He/4He ratios of 8 × 10-6 (Lake Nyos) and 5 × 10-6 (Lake Monoun) indicated recharge of magmatic gases of mantle origin to the lakes, though the ratios were lowered by the addition of radiogenic 4He from crustal rocks. A small contribution (<2%) of MORB-like Ne was detected in both lake waters. A simple mixing between two end members, i.e., atmosphere and gases from a deepseated reservoir, can explain the noble gas signatures. Depth profile of He concentration in Lake Nyos showed a clear layered structure with a maximum at 190 m, 20 m above the lake bottom. Below this depth, 3He/4He ratio decreased slightly, suggesting that the fluid from the deep-seated reservoir is supplied to the lake mainly at ca. 190 m. C/3He ratios were 1.5 × 1010 and 0.6 × 1010 in deep and shallow layers of Lake Nyos, respectively. The C/3He ratio was 1.7 × 10 10 at Lake Monoun. A gas recharge model to explain the observed layered structure in Lake Nyos is presented. Copyright © 2010 by The Geochemical Society of Japan.
Authors & Co-Authors
Nagao, Keisuke
Japan, Tokyo
The University of Tokyo
Kusakabe, Minoru
Japan, Toyama
University of Toyama
Yoshida, Yutaka
Japan, Morioka
Yoshida Consulting Engineer Office
Tanyileke, Gregory Z.
Cameroon, Yaounde
Institute for Geological and Mining Research Irgm
Statistics
Citations: 34
Authors: 4
Affiliations: 4
Identifiers
Doi:
10.2343/geochemj.1.0101
ISSN:
00167002
Research Areas
Environmental
Study Locations
Multi-countries
Cameroon