Determination of sediment accumulation and mixing rates in the gulf of lions, mediterranean-sea

Zuo, Zz; Eisma, D; Berger, Gw

Determination of sediment accumulation and mixing rates in the gulf of lions, mediterranean-sea

1991

Zuo, Zz | Eisma, D | Berger, Gw

Sediment mixing and accumulation rates in the Gulf of Lions were determined, applying the Pb-210 and Cs-137 dating methods to a total of 20 boxcores taken in 1987, 1988 and 1989. The distribution of excess Pb-210 profiles indicated the presence of surface mixed layers in the nearshore sediment cores which ranged from 3 to 15 cm. The apparent Pb-210 accumulation rates varied from 0.02 to 0.63 cm.yr-1 in this study area. Rates were highest near the river mouth of the Rhone and decreased with increasing water depth and increasing distance from the river mouth. Observed depths of Cs-137 penetration within the sediments were compared with depths predicted from the surface mixed layer thickness and the Pb-210 accumulation rate. These showed a general agreement but one station suggests that there are some effects of relatively deep mixing below the intensely mixed surface layer. However, the agreement of Pb-210 and Cs-137 data of most stations indicates a general absence of deep mixing in the Gulf of Lions. Therefore, the apparent accumulation rates calculated from the Pb-210 profiles (below the surface mixed layer) generally reflect the true sedimentation rates. From the sedimentation distribution, the annual amount of sediment deposited in this study area was estimated to be 10.1 x 10(9) kg. yr-1, of which 30 % is biogenic and at least 20 % is contributed by atmospheric input. It is concluded that most of the sediment supplied by the Rhone river was deposited near the river mouth, and the remainder on the continental shelf and the upper slope, only a small amount being transported to the deep-sea basin.

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