DISTRIBUTION AND SOURCES OF ORGANIC MATTER TO THE HAURAKI GULF, NEW ZEALAND USING MOLECULAR CHARACTERIZATION AND CARBON ISOTOPIC ANALYSIS OF SEDIMENTARY LIPIDS

Organic matter in coastal and shelf sediments are derived from both marine and terrestrial sources. Bulk chemical characterization of sedimentary organic matter alone cannot provide a detailed picture of the relative contributions of each source. Molecular level analysis, however, can yield detailed information on sources of organic matter input as chain length and carbon number of marine and terrestrial derived lipids is source-specific. The presence of C27, C29, and C31 n-alkanes and C24, C26, and C28 n-alkanoic acids are indicative of input from land-plant waxes, whereas short chain C12, C14, and C16 n-alkanoic acids are dominant components of algal-derived lipids. Compound-specific isotopic analysis can also be used to determine origins of marine and terrestrial organic matter. Values for marine organic matter are typically enriched relative to values of terrestrial organic matter input from C-3 plants.

Sediment samples were recovered from the Hauraki Gulf of New Zealand during a cruise on the HMS Tangaroa in 1999 using a multi-corer. Sampling sites included near-shore and shelf environments distributed along major currents to investigate the source and distribution of organic matter in the gulf. Total lipids were extracted with hexane and methanol using a Dionex ASE 300 accelerated solvent extractor and saponified. Alkanes and fatty acids were isolated and analyzed by GC-MS.

Initial results from sediment core tops show a predominance of terrestrial organic matter input, especially along near-shore sites. The alkanes are dominated by C21 to C31 chain lengths, with an odd over even predominance. This predominance points to input of cuticular waxes found in higher plants. Carbon isotopic analysis of individual lipids will help resolve sources of these compounds and aid in understanding the contribution of marine and terrestrial organic matter in this complex marine system.