Freshwater Discharges Into Malaysian Coastal Seas

1. Freshwater Discharges Into Malaysian Coastal Seas S. M. Oyop(1), Z.Z. Ibrahim(1) and T. Yanagi(2)(1) Faculty of Environmental Studies, Universiti Putra Malaysia(2) Research Institute for Applied Mechanics, Kyushu Universityemail: (1) zelina@env.upm.edu.my, (2) tyanagi@riam.kyushu-u.ac.jp JSPS MCRP Coastal Marine Science National Coordinators Meeting

2. Rationale • The Southeast Asian regional seas have reduced salinity values • Freshwater discharges from surrounding landmasses • Freshwater discharges bring land-based materials Pacific Ocean South China Sea Andaman Sea Indian Ocean Java Sea JSPS MCRP Coastal Marine Science National Coordinators Meeting

3. Some Questions • How quickly do these materials move out into the deep ocean? • Or do they stay in the area? • Are rivers important nutrient sources? • Or is upwelling more important? JSPS MCRP Coastal Marine Science National Coordinators Meeting

4. Some Flushing Estimates for South China Sea and Malacca Straits • South China Sea • Flushing time about 40 years • Chen and Huang, 1995 • Top 350 m layer about 2.6 (dry season) to 6.8 (wet season) years • Chen et al (2001) • Malacca Strait • Low velocities; low salinities; ... low flushing? • Hii et al 2006 JSPS MCRP Coastal Marine Science National Coordinators Meeting

5. FlushingDefinitions and Method • Turnover Time = Sea Volume/Flux • Tidal Prism Method = Sea Volume/Tidal Volume per Day • Residence Time = (Concentration x Volume)/Flux JSPS MCRP Coastal Marine Science National Coordinators Meeting

6. Data Sources JSPS MCRP Coastal Marine Science National Coordinators Meeting

7. Surface Area=202,422.4 km2 Total Volume=45525.1 km3 1. Volume of the Malacca Strait JSPS MCRP Coastal Marine Science National Coordinators Meeting

8. 2. Annual Rainfall, Runoff, Evaporation • Rainfall = land rainfall x 0.7 x area = 334.5 km3 • Runoff = Peninsular Malaysia x 2 = 93.17 km3 • Evaporation = 3 mm/day x area = 216.2 km3 JSPS MCRP Coastal Marine Science National Coordinators Meeting

9. a. Freshwater Turnover Time • Turnover Time = Volume/flux JSPS MCRP Coastal Marine Science National Coordinators Meeting

10. b. Tidal Prism Volume • Tidal prism per tide (semi-diurnal) = surface area x tide height difference = surface area x 2 m = 404.84 km3 • How much of the water returns on the tide? • % of return flow JSPS MCRP Coastal Marine Science National Coordinators Meeting

11. Tidal Flushing • Tidal prism = volume/(1-return flow)(tidal volume per day) • Assumming % return flow JSPS MCRP Coastal Marine Science National Coordinators Meeting

12. 280 days But there is return flow ... JSPS MCRP Coastal Marine Science National Coordinators Meeting

13. c. Residence Time of Freshwater • Residence Time = Mean Concentration in Strait × Strait Volume / Input per year JSPS MCRP Coastal Marine Science National Coordinators Meeting

14. 3. Salinity Distribution 3. Salinity Variation with Depth JSPS MCRP Coastal Marine Science National Coordinators Meeting

15. Volume of the Upper Layer (0 - 200 m) Volume of 0-200 m = 8298.5 km3 Shallow water volume is 18% of total volume Surface Area=202,422.4 km2 Total Volume=45525.1 km3 JSPS MCRP Coastal Marine Science National Coordinators Meeting

16. Residence Time in the Upper 200 m Layer • We ignore water volume deeper than 200 m JSPS MCRP Coastal Marine Science National Coordinators Meeting

17. Summary JSPS MCRP Coastal Marine Science National Coordinators Meeting

18. North South Some Other Considerations ... • Seasonal variations • Spatial variations Langat JSPS MCRP Coastal Marine Science National Coordinators Meeting