Hidden erosion on volcanic islands
Hidden erosion on volcanic islands
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DOI：
10.1016/j.epsl.2007.07.019
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发表时间：
2007-10-15
影响因子：
5.3
通讯作者：
Louvat, Pascale
中科院分区：
文献类型：
--
作者：
Rad, Setareh Denise;Allegre, Claude Jean;Louvat, Pascale
(C)我们研究了3个热带火山岛(小安的列斯群岛的瓜德罗普岛和马提尼克岛和留尼汪岛)的河流，以评估化学风化速率。这些岛屿由非常多孔的火山碎屑沉积、安山岩或玄武岩熔岩流组成，允许大量水渗透。根据水文预算，我们估计瓜德罗普岛的渗透率为10%，马提尼克岛为40%。通过将水文收支与取样的地下水的化学成分相结合，量化了地下水向海洋输送的元素通量。这是首次估计火山岛的化学风化速率，其中考虑了高温风化对化学风化速率的贡献。地下水受高温水-岩石相互作用的影响，因此与地表水相比，常量元素和微量元素的浓度更高(4-100倍)，因此分别占马提尼克岛、瓜德罗普岛和留尼汪岛(Martinique)、瓜德罗普岛(Guadeloupe)和留尼汪岛(留尼汪岛)总(地表+地下)风化溶解通量的90%、60%和75%。这表明了这些通量的重要性，到目前为止，玄武岩风化地球化学预算中没有估计到这些通量。地下水的化学风化速率是地表水的2-5倍。计算的总平均化学速率瓜德罗普岛为290吨/公里(2)/年，马提尼克岛为1080吨/公里(2)/年，留尼汪岛为270吨/公里(2)/年。这些价值是世界上最高的。将这一预算外推到全世界所有火山岛的表面，我们估计这些岛屿可以贡献主要河流输送到海洋的溶解负荷的23%到31%，而它们的表面积只占硅酸盐岩石总表面积的9%。(C)2007爱思唯尔B.V保留所有权利。
(c) We have studied rivers from 3 volcanic tropical Islands (Guadeloupe and Martinique in Lesser Antilles and Reunion) in order to evaluate chemical weathering rates. These islands are constituted of very porous pyroclastic deposits, andesitic or basaltic lava flows, allowing significant water infiltration. From hydrological budgets, we estimate that infiltration represents 10% in Guadeloupe and 40% in Martinique. Element fluxes transported by subsurface water to the ocean have been quantified by coupling the hydrological budget with the chemical composition of the sampled subsurface waters. This is the first estimate of chemical weathering rates from volcanic islands, which takes into account the high temperature weathering contribution to the chemical weathering rates. Subsurface waters are impacted by high-temperature water-rock interactions and present therefore higher concentrations (4 to 100 times) of major and trace elements compare to surface waters, representing thus respectively 90%, 60% and 75% of the total (surface+ subsurface) weathering dissolved flux to the ocean for Martinique, Guadeloupe and Reunion. This shows the importance of these fluxes, which until now were not estimated in the basalt weathering geochemical budgets. Chemical weathering rates from subsurface water are 2 to 5 time higher than the rates from surface waters. The total average chemical rates calculated are 290 t/km(2)/yr in Guadeloupe, 1080 t/km(2)/yr in Martinique and 270 t/km(2)/yr in Reunion. These values are among the highest worldwide. Extrapolating this budget to the surface of all volcanic islands world-wide, we estimate that these could contribute between 23% and 31 % of the global flux of dissolved load transported to the oceans by major rivers draining silicate rocks whereas their surface area represent only 9% of the silicate rock total surface area. (c) 2007 Elsevier B.V All rights reserved.