Particulate Organic Carbon And Suspended Particle Size Spectra In The Southern Taiwan Strait During Summer

The temporal and spatial distributions of particulate organic carbon (POC), total suspended matter (TSM) , particulate nitrogen (PN) and particle volume concentration were studied in the southern Taiwan Strait. The day-to-day concentrations of POC and TSM were observed in upwelling area. The relationship and variety regulation among POC, TSM and Chl-a, and character of Sheldon size spectra and normalized size spectra were analyzed. The in situ laser particle size analyzer could be regarded as a high-resolution sensor to detect ecosystem structure endowed with POC.In the south of Taiwan Strait in the summer cruises of 2004, 2005 and 2006, high level of surface POC concentration was found near-shore and decreased seaward.Three main patterns in vertical distribution of POC concentration were observed, one showed a downward-decreasing POC profile, the other showed a maximum POC concentration in intermediate layer and then decreased with depth, the third showed a downward-increasing POC profile with maximum POC concentration over near-bed layer. The areas with high value of surface and subsurface POC concentration were located near Dongshan Island and Nan'ao Island. The average concentration of POC was 0.145 mg/L in 2004 cruise and 0.204 mg/L in 2005 cruise and 0.198 mg/L in 2006 cruise.The concentrations of PN were ranged 0.0065~0.0856 mg/L, 0.0114~0.2443 mg/L, 0.0013~0.2269 mg/L respectively for summer cruises of 2004, 2005 and 2006. The ratio of POC to PN was 1.7~16.5, 1.7~10.5 and 1.9～18.4, and the average was 6.8, 5.3 and 5.7 respectively for summer cruises of 2004, 2005 and 2006.There was a positive correlation between POC concentration and Chl-a that implied phytoplankton became the main source of POC. The positive correlation between ratio Chl-a/POC and Chl-a was found for data of all cruises, but ratio Chl-a/POC was small in the high Chl-a area adjacent to upwelling. This may suggest there was high trophic transfer efficiency in food chain of upwelling dominated area or period of southern Taiwan Strait. As revealed by scatter plot for the ratio Chl-a/POC and Chl-a, trophic transfer efficiency was restrained in the summers of 1988, 1998 and 2004, however, it became activity during the summers of 2005 and 2006.The TSM ranged 0.14~4.68mg/L, 1.34~13.28 mg/L, 3.29～36.06 mg/L respectively for the summer cruises of 2004, 2005 and 2006. TSM were enriched during the cruises with strongly alongshore current such as those of 2005 and 2006. For each cruise, there was a positive correlation between POC and TSM, and there was also a positive correlation between ratio Chl-a/POC and TSM. There was negative correlation between POC/TSM and TSM for data of all cruises. Obviously fluctuation in TSM, relative steady POC and steady-going relationship between ratio Chl-a/POC and Chl-a suggested, there was a marine biogenic matter dominated particulate organic carbon system in the southern Taiwan Strait, in despite of the regime with river input particle under strongly alongshore current event.Based on size spectrum theory, field data measured by laser particle size analyzer were used to analyze Sheldon size spectra and normalized size spectra of suspended particle in the southern Taiwan Strait during summer, 2004. The results showed that the patterns of Sheldon size spectra were similar at all stations in transects A and B. In normalized size spectra, the range of slopes was -0.79 to -0.65. Influenced by coastal upwelling of Taiwan Strait and upwelling around the Taiwan Shoal, the slopes were high around the high chlorophyll area or the chlorophyll maximum layer. This indicated that the process of upwelling was in favor of developing locally of biological food chain with high trophic transfer efficiency. The in situ laser particle size analyzer could be regarded as a basic sensor to detect fine structure for trophic transfer efficiency.