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Communication Dans Un Congrès Année : 2012

Submarine groundwater discharge at an active margin: NE Taiwan coast

Niels Hovius
  • Fonction : Auteur
A.J. West
  • Fonction : Auteur
Albert Galy
Douglas Hammond
  • Fonction : Auteur
Shuh-Ji Kao
  • Fonction : Auteur
  • PersonId : 851240

Résumé

Studies of submarine groundwater discharge (SGD) have been focused on passive margins with large floodplains [1]. SGD from active margins without substantial sediment cover remains unknown, but it is in the rapidly eroding highlands along these margins that the feedback between climate and weathering is most effective [2]. In Taiwan, measured erosion and silicate weathering rates are amongst the highest in the world. In a representative section of the northeast coast of Taiwan, at the outlet of the Liwu river, we have explored the possible magnitude and pattern of SGD, and its implications for weathering budgets. The river drains 4 km of emergent mountain relief, with a further 5 km of submarine relief above the Pacific abyssal plain. In the Liwu catchment, 16±1% of the river discharge (averaged over 37 years of record) comes from a deep groundwater reservoir, and deep seated chemical weathering of silicates accounts for 38% of the riverine silicate weathering flux [3]. It is likely that the large inland hydraulic head drives submarine discharge from this deep groundwater reservoir and weathering reactor. We have used the radium quartet (228Ra, 226Ra, 224Ra, 223Ra) along with Temperature-Salinity (T-S) profiles on two 50 km West- East marine transects off the NE coast of Taiwan (<2000m water depth) to search for SGD. Stable isotopes, major elements, and Ra isotopes in water samples were analyzed to constrain the hydrogeology of rivers and two types of groundwater: sandy shallow aquifers (<200 m deep) and a deep bedrock aquifer (~400m deep). Radium activities were measured using RaDeCC. Preliminray results show that the 224Ra and 228Ra activities at the sea surface exceed those in the average deep coastal water column. 228Ra activities are also slightly elevated in some stations at 400-600m depth, below the Kuroshio current. These stations have anomalously low salinity, when compared to regional hydrographic profiles. Given the strong density barrier presented by the Kuroshio current, these Ra and salinity excursions at depth are not likely to result from downward mixing of surface seawater. They may be related to groundwater discharge from submerged mountain bedrock. The T-S and Ra-isotopes data suggest that there may be active SGD across the structural dip of the active margin of East Taiwan. Using both transects and the deep groundwater characteristics, we will add constraints on sediment/water interactions and the occurrence and spatial extent of SGD in the area. [1] Moore (1996) Nature 380, 612-614. [2] West (2005) EPSL 235, 211-228. [3] Calmels (2011) EPSL 303, 48-58.
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Dates et versions

hal-01813463 , version 1 (12-06-2018)

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  • HAL Id : hal-01813463 , version 1

Citer

Julie Gattacceca, Niels Hovius, A.J. West, Albert Galy, Douglas Hammond, et al.. Submarine groundwater discharge at an active margin: NE Taiwan coast. 22nd Goldschmidt Conference, 2012, Jun 2012, Montreal, Canada. pp.1743. ⟨hal-01813463⟩
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