Retrospective bulk density estimates from southeast Indian Ocean sediments: comparison of waterloss and chlorine-ion methods

Abstract

Knowledge of absolute accumulation rates permits quantitative comparison between and within sediment components from cores of differing age and lithologic character. Dry bulk density is an essential parameter in the calculation of absolute accumulation rates. Dry bulk density measurements require a wet-volume term and are best made when a core is first recovered. Such measurements were not routinely made on Eltanin cores from the southeast Indian Ocean. In an effort to recover this information we have estimated the dry bulk density of sixty samples from five Eltanin cores using a water loss method and a chloride-ion method which is independent of the state of desiccation of the cores. Based on the consistency of the results using these two independent methods we feel confident in our estimation of dry bulk density. Comparison of dry bulk density and %CaCO3 allowed us to develop the following non-linear regression equation for estimating the dry bulk density based on %CaCO3, a more easily and accurately measured property: Dry bulk density = 0.00003104*(%CaCO3)2 + 0.002176*(%CaCO3) + 0.430 This equation can be used to estimate dry bulk density to within ± 0.097 g/cm-3 , thus providing the information needed to reliably calculate absolute accumulation rates. Our Indian Ocean dry bulk density equations are different from those developed by similar techniques for the Pacific and Atlantic Oceans indicating that different lithologies necessitate the development of regional equations.