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Article Dans Une Revue Marine Geology Année : 1992

Nd isotopes in Indian Ocean sediments used as a tracer of supply to the ocean and circulation paths

Aline Dia
Claude-Jean Allegre
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Résumé

Neodynium isotopic compositions of eighteen sediments from the Indian Ocean were measured. These Quaternary marine sediments were collected in different physiographic provinces, with samples being taken from the abyssal plain, ridge, submarine fan, fracture zone and aseismic ridge environments. The main results is that there are large areas in the Indian Ocean which are isotopically homogeneous, although the results also enforce the idea that in marine sediments the continent-derived material exerts an important control on the Nd budget. The northeastern part of the Indian Ocean is influenced by erosion of the Indonesian arc. The values between ε$_0$ = −7 and ε$_0$ = −8 observed in samples from the Central Indian Ocean are nearly constant both in the eastern and western parts of the Indian Ocean. This was interpreted as mixing between two major inputs: firstly material coming from the erosion of the Indian shield (ε$_0$ = −14 to −17), and secondly from the Indonesian arc (ε0>0). Subsequently all the material is then homogenized by the oceanic circulation. The western Indian Ocean values are more variable perhaps because of the proximity of old continental terrains (i.e. southern Africa) and the influence of Atlantic waters. The highest value (ε$_0$ = 2.93) observed in the southern part of the Indian Ocean may be explained by the influence of the erosion of the Crozet basaltic plateau; indeed, the two samples which exhibit positive Nd isotopic values correspond geographically to the area of erosion of the Crozet, and possibly the Kerguelen, basaltic plateaus. The location of the sample with the lowest isotopic value ε$_0$ = −18.88 (close to Antarctica) implies that this sediment might have included an old continental component (of Precambrian or even Archaen age). This result traces (in the case of particle transport) the circulation of water masses from Antarctica to northern parts of the Indian Ocean (which are known for their deep waters). With the exception of the samples located near the Crozet plateau, where probable destruction of the plateau is occurring, we do not observe any Nd isotopic variations related to the specific physiographic location of any one sample. Consequently, the Nd isotopic variations are principally due to the pathways of water circulation, and possibly winds, over the Indian Ocean.

Dates et versions

hal-04631455 , version 1 (02-07-2024)

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Citer

Aline Dia, Bernard Dupré, Claude-Jean Allegre. Nd isotopes in Indian Ocean sediments used as a tracer of supply to the ocean and circulation paths. Marine Geology, 1992, 103 (1-3), pp.349-359. ⟨10.1016/0025-3227(92)90025-D⟩. ⟨hal-04631455⟩

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