Current transport versus continental inputs in the eastern Indian Ocean: Radiogenic isotope signatures of clay size sediments

Analyses of radiogenic neodymium (Nd), strontium (Sr), and lead (Pb) isotope compositions of clay-sized detrital sediments allow detailed tracing of source areas of sediment supply and present and past transport of particles by water masses in the eastern Indian Ocean. Isotope signatures in surface sediments range from −21.5 (ɛNd), 0.8299 (87Sr/86Sr), and 19.89 (206Pb/204Pb) off northwest Australia to +0.7 (ɛNd), 0.7069 (87Sr/86Sr), and 17.44 (206Pb/204Pb) southwest of Java. The radiogenic isotope signatures primarily reflect petrographic characteristics of the surrounding continental bedrocks but are also influenced by weathering-induced grain size effects of Pb and Sr isotope systems with superimposed features that are caused by current transport of clay-sized particles, as evidenced off Australia where a peculiar isotopic signature characterizes sediments underlying the southward flowing Leeuwin Current and the northward flowing West Australian Current (WAC). Gravity core FR10/95-GC17 off west Australia recorded a major isotopic change from Last Glacial Maximum values of −10 (ɛNd), 0.745 (87Sr/86Sr), and 18.8 (206Pb/204Pb) to Holocene values of −22 (ɛNd), 0.8 (87Sr/86Sr), and 19.3 (206Pb/204Pb), which documents major climatically driven changes of the WAC and in local riverine particle supply from Australia during the past 20 kyr. In contrast, gravity core FR10/95-GC5 located below the present-day pathway of the Indonesian throughflow (ITF) shows a much smaller isotopic variability, indicating a relatively stable ITF hydrography over most of the past 92 kyr. Only the surface sediments differ significantly in their isotopic composition, indicating substantial changes in erosional sources attributed to a change of the current regime during the past 5 kyr

Clay mineral distribution in surface sediments between Indonesia and NW Australia - source and transport by ocean currents

The clay mineral distribution in sediments between Indonesia and NW Australia has been assessed on the basis of 166 core-top samples. Clay mineral assemblages are closely related to the geology and weathering regime of the adjacent hinterland and allow the distinction of four clay mineral provinces. Three provinces, Western, Central and Eastern Province are situated along the Indonesian Islands Arc, from Sumatra in the west to Timor in the east. Illite is the major clay mineral of the Western and eastern Province, whereas the Central Province abounds with smectite. The fourth province comprises the NW and West-Australian shelf and slope, as well as offshore plateaus and is dominated by kaolinite. Transport of clays by surface and subsurface ocean currents can be observed within the provinces, e.g. with the Leeuwin and West Australian Current in the NW Australian Province and with the outflow of low-salinity water through the Sunda and Lombok straits in the Central Province. Transport of clays across province boundaries is inhibited by strong salinity fronts, with the exception of the boundary between the Central and Eastern Province