Characterisation of sedimentary organic matter from three south-eastern Australian estuaries using solid-state 13C-NMR techniques

Abstract

Solid state 13C-nuclear magnetic resonance (NMR) spectroscopy was used to characterise sedimentary organic matter sampled from three estuaries on the central New South Wales coast (Australia). Cross polarisation (CP) and Bloch decay (BD) experiments were used to determine the chemical composition of the samples. These experiments indicated that, although the natural organic matter is predominately terrestrial in origin, the proportion of carbon existing as aromatic carbon, distinctive of vascular plants, decreases towards the mouth of the estuaries. This suggests that the relative contribution of terrestrial and marine source material largely defines the character of estuarine organic matter. Substantial amounts of charcoal were identified in sedimentary organic matter close to recent bushfire activity. Proton-spin relaxation editing (PSRE) was used to probe the physical structure of the sedimentary organic matter at the sub-micron scale. This technique showed that the organic matter was heterogeneous, providing support for a popular model of sedimentary organic matter structure. However, detailed interpretation of the domain structure of the organic matter was hindered by the presence of multiple components from both terrestrial and marine sources.