Sains Malaysiana 43(9)(2014): 1389–1396 Variations of Southern South China Sea Characteristics near Pahang (Perubahan Ciri Laut China Selatan Bahagian Selatan Berdekatan Pahang) NUR HIDAYAH ROSELI* & MOHD FADZIL MOHD AKHIR ABSTRACT Oceanographic cruises in Pahang water in October 2003 and April 2004, monsoon transition months, produce data on water characteristics. The temperature in both months showed higher values in nearshore compared to the offshore stations. The nearshore salinity in both months is lower than offshore stations. Comparatively, there were smaller differences in temperature and salinity in October than in April, with very little variation between nearshore and offshore stations. T-S diagram showed signiicant differences between October and April water characteristics. According to the water characteristic observations, the temperature and salinity in October was lower than in April, while dissolved oxygen was higher than in April. The lower temperature and salinity taken during the sampling time in October suggested that during this time, the study area already received the inluences of strong winds due to upcoming monsoon. The warmer and saltier water obtained in April showed that during this time, the study area was inluenced by southwest monsoon. Winds related to rainfall were observed to have impact to the dynamics of water characteristics during both months. Keywords: Current circulation; monsoon transition month; salinity; South China Sea; temperature ABSTRAK Pelayaran oseanograi di kawasan perairan Pahang pada bulan Oktober 2003 dan April 2004, bulan peralihan monsun, menghasilkan data mengenai ciri air. Suhu air pada kedua-dua bulan menunjukkan nilai yang lebih tinggi di kawasan pesisir pantai berbanding dengan stesen luar pesisir. Kemasinan di kawasan pesisir pantai pula adalah lebih rendah daripada stesen luar pesisir bagi kedua-dua bulan. Secara perbandingan, terdapat perbezaan kecil dalam suhu dan kemasinan pada bulan Oktober berbanding bulan April, dengan perubahan yang sangat sedikit di antara stesen berhampiran pantai dan luar pesisir. Gambarajah TS menunjukkan perbezaan yang signiikan antara ciri air pada bulan Oktober dan April. Menurut pemerhatian ciri air, suhu dan kemasinan pada bulan Oktober adalah lebih rendah berbanding pada bulan April, manakala oksigen terlarut adalah lebih tinggi berbanding pada bulan April. Suhu air laut dan kemasinan yang lebih rendah yang diambil pada bulan Oktober memperlihatkan bahawa pada masa ini, kawasan kajian telah menerima pengaruh angin kuat berikutan monsun yang bakal tiba. Suhu laut yang semakin panas dan masin yang diperoleh pada bulan April menunjukkan bahawa pada masa ini, kawasan kajian telah dipengaruhi oleh monsun barat daya. Angin yang turut berkaitan dengan hujan diperhatikan memberi kesan kepada ciri dinamik air pada kedua-dua bulan. Kata kunci: Bulan peralihan monsun; kemasinan; Laut Cina Selatan; peredaran arus; suhu INTRODUCTION Information and knowledge regarding the physical characteristics of seawater at the east coast peninsular Malaysia, especially ~50 km towards the offshore, is very important as it affects local activities. Pahang water is situated in the southern region of the South China Sea (SCS) off the central east coast of peninsular Malaysia. The coastal area of the northern Pahang water was fed by the Pahang River, the largest river in peninsular Malaysia which lows into the SCS (Figure 1). Earlier studies (Hu et al. 2000; Wyrtki 1961) suggested that water properties in the SCS were mainly inluenced by monsoons: the northeast monsoon (October to March) and the southwest monsoon (June to August). Between those seasons, April and October appear to be transition months (Morgan & Valencia 1983; Wyrtki 1961). The monsoon transition periods present special challenges, however, and a deep understanding of the Pahang water is lacking. The last comprehensive study of the Pahang water was done by Mohsin et al. (1986) documented in Ekspedisi Matahari book report. There is only recently, the composite study of datasets collected by INOS between 2002 and 2010 in the SCS and a study on selected regions in Johor were done by Akhir et al. (2011) and Akhir and Yong (2011) respectively. Both studies suggested that during the inter- monsoon period, the coming month, for instance April, will have northeast monsoon characteristics while October will still retain southwest monsoon characteristics. However, those are still unclear and need more on data collection and explanation. Several factors that could affect salinity and temperature at the study area include precipitation,