Organic matter composition in sediments of the Oman Margin

Abstract

The quantity and biochemical composition of organic matter (OM) in the sediments underlying and below oxygen minimum zone (OMZ) in the Arabian Sea were studied to provide information on the diagenetic processes of organic carbon under different environmental conditions. Concentrations of total organic carbon (TOC), total nitrogen (TN) and total hydrolysable amino acids (THAA) were significantly higher in sediments within rather than below OMZ, while those of total carbohydrates (TCHO) were slightly lower in the latter, suggesting the presence of a larger supply of labile compounds into the sea bottom at the shallower site (i.e. within OMZ). Hydrolysable amino acid and carbohydrate contribution to TOC were even lower (about 10% in surficial sediments) than the values obtained from the abyssal oligotrophic North Pacific, suggesting that OM food availability in the Oman Margin sediments within OMZ was lower than that observed at abyssal depths. The presence of the highest THAA and TCHO concentrations in the top 40 mm of the sediment core at both sites reflected the presence of bioturbation processes. In contrast with the general view of the deep sea as a stable and constant system, below OMZ in the Arabian Sea sediments, some differences were observed in the two investigated cores indicating the presence of a certain spatial variability in OM content and diagenesis.

Keywords:

• Sediments
• Oxygen minimum zone
• Carbon
• Nitrogen
• Amino acids
• Carbohydrates

Acknowledgements

I would like to thank Prof. G. A. Wolff (University of Liverpool) for samples and kind support and also Mrs P. Houghton, D. Angus and C. Murphy for their assistance in the laboratory (University of Liverpool). I wish to acknowledge the help and encouragement of Dr S. W. A. Naqvi in preparation of this paper. I am grateful to Dr E. Desa (National Institute of Oceanography, Goa) for his support and encouragement and CSIR, India for permission. R. A. was supported by a scholarship from Government of India. Dr. N. B. Bhosle is acknowledged for reading the manuscript and help. Two anonymous reviewers provided helpful comments to improve this manuscript. S. G. Akerkar, A. Mahale and G. S. Michael drafted Figure 1. This paper is dedicated to R. A.'s parents, the Late V. S. M. Rengasamy and Lakshimi. Guru's grace to complete this work is also highly appreciated. This is NIO contribution No. 3846.