Some physical and chemical characteristics of bottom sediments in the South China Sea, Area I: Gulf of Thailand and east coast of Peninsular Malaysia

Investigations on horizontal and vertical distribution in levels of total organic matter contents (TOM), acid volatile sulfides contents (AVS), and water contents (WC) of bottom sediments from the eastern and western parts of the Gulf of Thailand and the eastern part of the Peninsular Malaysia have been carried out during 5-28 September 1995 and 24 April to 17 May 1996 by M.V. SEAFDEC. The overall results indicated comparatively low amount of organic matters and sulfides deposited in the sediments. Considering on the vertical profiles, coupled efforts of low rate of sedimentation of the organic matters and high rate of their decomposition should play an important role providing fast diagenesis of their organic substances. Nevertheless, the particulate matters which had settled onto the sea bed and formed the sediments can be remarkably observed to accumulate in two major zones in the Gulf of Thailand; one in the central part of the upper gulf (around Station 7) and another one in the western part of the gulf, near Samui Island (around Station 23). Such an accumulation pattern was considered to be directly controlled by the bottom topography and current effort. The accumulation of organic materials there also implied the mode of biological fishery resources. High abundant of organisms in the benthic community should be observed. Moreover, according to biogeochemical interaction between the sediment-water interface, phytoplankton production in the overlying water column should be enhanced and, consequently, a congregation of organisms in the upper trophic levels especially those of fish species were accordingly expected. Future assessment for development of the fishery resources in the Gulf of Thailand and the eastern part of Peninsular Malaysia has been discussed

Nutrient diagenesis in sediments of the South China Sea, Area II: Sabah, Sarawak, and Brunei Darussalam waters

Study on nutrient diagenesis and physico-chemical characteristics of bottom sediments of the Sabah, Sarawak and Brunei Darussalam waters had been carried out under the ongoing SEAFDEC Collaborative Research Project. The results indicated that organically enriched offshore sediments consisted high levels of pore water nitrate and phosphate concentrations. For the whole study area, the levels of nitrate and phosphate concentrations in pore water were in the ranges of 0.05 to 77.12 µg at NO3--N/L and 0.07 to 13.13 µg at PO43--P/L, respectively. Upward diffusive fluxes of pore water nitrate widely changed in stations. At the nearshore area, the fluxes of pore water nitrate had an average of 26.5 mg at NO3--N/m2/d and were about one order of magnitude higher than those of phopsphate. However, phosphate upward fluxes were apparently high at deep areas off Sabah. Pore water ammonium concentrations were commonly very low but tended to be more accumulated at nearshore organically enriched areas. The ammonium concentrations for the whole study area ranged from non-detected level to 81.76 µg at N/L. The nearshore stations showed very high upward fluxes of ammonium, which were nearly 10 times higher than those of nitrate and phosphate. Sedimentary organic levels were comparatively high in two distinct regions; (I) a shallow nearshore region of Sarawak, and (II) a deep offshore region of Sabah and Brunei Darussalam. The sources of organic materials settled in Regions (I) and (II) were suggested to be derived from different origins. The Northeast monsoon can somewhat enhance organic accumulation in the nearshore region. Overall our results obtained from this study had been used to characterize the bottom sediments into three distinct regions and discussed for further fishery resource development and management

The Catalogue of Core Logging Sheets for Sediments of the Western Gulf of Thailand and Eastern Peninsular Malaysia in April 1996

Oceanographic survey on bottom sediment characteristics has been conducted in the sea areas in the western part of the Gulf of Thailand and the Eastern Peninsular Malaysia as one research program under the collaborative research project between SEAFDEC’s Training Department (TD) in Thailand and the Marine Fishery Resources Development and Management Department (MFRDMD) in Malaysia. This research program was carried out because of the interest in the nature of sea bottom in an area of which only few detail information exist. The information such as vertical distribution of different types of sediments, relationships among sediment physico-chemical process, biological processes in the water column and other fishery resources were of primary interest. The sediment samples surveyed in the Western Gulf of Thailand and Eastern Peninsular Malaysia during April 1996 were immediately recorded for their visible characteristics on board of M.V. SEAFDEC in core logging sheets by using general lithological symbols. The catalogue of core logging sheets here could thus be applicable to easily distinguish the vertical profiles of those bottom sediments. Such visible characteristics could also simply reflect both physic-chemical and biological compositions of bottom deposits in the designated areas

Nutrient Diagenesis in Sediments of the South China Sea, Area II: Sabah, Sarawak, and Brunei Darussalam Waters

Study on nutrient diagenesis and physico-chemical characteristics of bottom sediments of the Sabah, Sarawak and Brunei Darussalum waters had been carried out under the ongoing SEAFDEC Collaborative Research Project. The results indicated that organically enriched offshore sediments consisted high levels of pore water nitrate and phosphate concentrations. For the whole study area, the levels of nitrate and phopsphate concentrations in pore water were in the ranges of 0.05 to 77.12 ?g at NO3--N/L and 0.07 to 13.13 ?g at PO43--P/L, respectively. Upward diffusive fluxes of pore water nitrate widely changed in stations. At the nearshore area, the fluxes of pore water nitrate had an average of 26.5 mg at NO3--N/m2/d and were about one order of magnitude higher than those of phopsphate. However, phosphate upward fluxes were apparently high at deep areas off Sabah. Pore water ammonium concentrations were commonly very low but tended to be more accumulated at nearshore organically enriched areas. The ammonium concentrations for the whole study area ranged from non-detected level to 81.76 ?g at N/L. The nearshore stations showed very high upward fluxes of ammonium, which were nearly 10 times higher than those of nitrate and phosphate. Sedimentary organic levels were comparatively high in two distinct regions; (I) a shallow nearshore region of Sarawak, and (II) a deep offshore region of Sabah amd Brunei Darussalum. The sources of organic materials settled in Regions (I) and (II) were suggested to be derived from different origins. The Northeast monsoon can somewhat enhance organic accumulation in the nearshore region. Overall our results obtained from this study had been used to characterize the bottom sediments into three distinct regions and discussed for further fishery resource development and management