Stable carbon and nitrogen isotope ratios of sediment in the gulf of Thailand: Evidence for understanding of marine environment

Sedimental cores from the Gulf of Thailand were collected by core sampler for examination of δ13C and δ15N and organic carbon and nitrogen contents. The δ13C of surface (0–2 cm) sediments from the whole Gulf gave approximately the same value (−21‰) except only one station at the upper Gulf, with an enriched value of −18‰. The δ15N value of sediments at this station was quite low compared to the other stations nearby. The δ15N values of sediments in the upper Gulf were somewhat lower than those in the lower Gulf. High organic carbon content of sediments occurred in the eastern part of the upper Gulf and in the western part near Samui Island. Organic nitrogen contents in the sediment showed almost the same pattern as that of organic carbon contents. The atomic ratios of carbon to nitrogen were high at the most upper part and low in the lower part of the Gulf. Overall, our results can support the idea that the sediments in the Gulf of Thailand were mostly derived from the primary production in the Gulf. Particularly, bottom environments in the upper Gulf receive large inputs of bluegreen algae.