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

Abstract

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. Show more