Neodymium isotope constraints on provenance, dispersal, and climate-driven supply of Zambezi sediments along the Mozambique Margin during the past ∼45,000 years

Marine sediments deposited off the Zambezi River that drains a considerable part of the southeast African continent provide continuous records of the continental climatic and environmental conditions. Here we present time series of neodymium (Nd) isotope signatures of the detrital sediment fraction during the past ~45,000 years, to reconstruct climate-driven changes in the provenance of clays deposited along the Mozambique Margin. Coherent with the surface current regime, the Nd isotope distribution in surface sediments reveals mixing of the alongshore flowing Zambezi suspension load with sediments supplied by smaller rivers located further north. To reconstruct past changes in sediment provenances, Nd isotope signatures of clays that are not significantly fractionated during weathering processes have been obtained from core 64PE304-80, which was recovered just north of the Zambezi mouth at 1329 m water depth. Distinctly unradiogenic clay signatures (ENd values <214.2) are found during the Last Glacial Maximum, Heinrich Stadial 1, and Younger Dryas. In contrast, the Nd isotope record shows higher, more radiogenic isotope signatures during Marine Isotope Stage 3 and between ~15 and ~5 ka BP, the latter coinciding with the timing of the northern hemisphere African Humid Period. The clay-sized sediment fraction with the least radiogenic Nd isotope signatures was deposited during the Holocene, when the adjacent Mozambique Shelf became completely flooded. In general, the contribution of the distinctly unradiogenic Zambezi suspension load has followed the intensity of precession-forced monsoonal precipitation and enhanced during periods of increased southern hemisphere insolation and high-latitude northern hemispheric climate variability

Biochemical Study of the Population Heterogeneity and Distribution of the Oval Squid Sepioteuthis Lessoniana Complex in Southwestern Japan

Volume: 12Start Page: 129End Page: 13

TEMPERATURE-DEPENDENCE OF VISCOELASTICITY OF POLYCAPROLACTONE CRITICAL GELS

ABSTRACT A systematic procedure was developed for determining the temperature dependence of critical gel properties. The polymer system was a poly(ccapro1actone) diol (PCL) end-linked with a three-functional isocyanate. Samples varied in prepolymer molecular weight and stoichiometric ratio. Time-temperature superposition was found to apply to the self-similar relaxation modulus G(t) = S P. A prerequisite of time-temperature superposition is that the relaxation exponent n is independent of temperature. As a consequence, criticalgels have theunique property that their loss tangent is independent of temperature. This was confirmed experimentally. The gel stiffness S(T) = S(To)a?/bTshifta with an Arrhenius type temperature dependence. The temperature shift factors for the PCL critical gels seem to be identical with those for the viscosity of the difunctional prepolymer ( t o) and the modulus of the fully cross-linked polymer (G &amp; This suggests that an experimental relationship of S = G,(T)[qo(T)/G,(T)ln is valid for our polymers at the experimental temperatures between 90 and 130 &quot;C