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 (εNd), 0.8299 (⁸⁷Sr/⁸⁶Sr), and 19.89 (²⁰⁶Pb/²⁰⁴Pb) off northwest Australia to +0.7 (εNd), 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 (εNd), 0.745 (⁸⁷Sr/ ⁸⁶Sr), and 18.8 (²⁰⁶Pb/²⁰⁴Pb) to Holocene values of -22 (εNd), 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.