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Geochemical Journal
Geochemical Journal An open access journal for geochemistry
Published for geochemistry community from Geochemical Society of Japan.

Characteristics of organic matter in lagoonal sediments from the Great Barrier Reef

Masanobu Yamamoto, Hajime Kayanne, Masumi Yamamuro
Geochemical Journal, Vol. 35, No. 6, P. 385-401, 2001


We have applied organic carbon and total nitrogen analyses, Rock-Eval pyrolysis, and gas chromatography-mass spectrometric lipid analysis with in situ methylation with tetramethylammonium hydroxide (TMAH-pyrolysis-GC/MS) to characterize the organic matter in recent lagoonal sediments from the Great Barrier Reef (GBR). On a pyrogram, GBR sediments showed the unique feature that S1 and S3 values were anomalously high. The high S1 value presumably reflects a higher proportion of hydrolyzed lipids, and the high S3 value is due to the degradation of carbonate minerals in a low temperature range. Associated with a CaCO3 increase towards the offshore area, the organic carbon/total nitrogen ratio (C/N ratio) decreased, S1 and S2 values increased, and total fatty acid and phytol concentrations increased. These changes have negative correlations with the branched/total fatty acid ratio, implying that the changes reflect the degree of eubacterial activity. The higher preservations of lipids and lignin phenols in CaCO3-rich sediments are attributable to their higher preservation effect resulting from an impermeable carbonate matrix. The anteiso-/iso-fatty acid ratio has a significant negative correlation with the total fatty acid concentration and a positive correlation with the branched/total fatty acid ratio, indicating that the ratios are closely related to the degree of eubacterial degradation of organic matter.

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