EFFECT OF MIXED LAYER DEPTH ON THE CONDITIONS OF ECOSYSTEM IN MAKASSAR STRAIT

• Main Author: Candra Dewi, Intan
• Format: Theses
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/33843
• Institution: Institut Teknologi Bandung

Makassar Strait is the main inflow channel of Indonesia Throughflow (ITF) where the seasonal variation of water mass transport influences the variation of Mixed Layer Depth (MLD). Changes in the characteristics of MLD have an impact on the ecosystem involving nutrient, phytoplankton, and zooplankton (NPZ). This study discusses the relationship between MLD and ecosystem (NPZ) by applying the NPZ numerical model in the mixed layer. Determination of the study area refers to the Transport, Internal Wave and Mixing in the ITF Region (TIMIT) Cruise in September 2016. Meanwhile, monthly climatological data of nutrient concentration in September from World Ocean Atlas (WOA), and chlorophyll-a concentration from Sea-Viewing Wide Field-of-View Sensor (SeaWiFS) in the middle of September 2016 were used as the model input. The NPZ model used in this study has been able to explain the effect of mixing layer on ecosystem conditions in the Makassar and Lombok Straits. The concentration of nitrate between model and WOA in twelve observation stations had the best fit in July, with Root Mean Square Error (RMSE) of 8.28 mg/m3. Meanwhile, for phytoplankton best fit between model and SeaWiFS data were found in December, with RMSE of 2.10 mg/m3. Then, regarding the stations, the best fit between model and data for phytoplankton were found in station SM01 with RMSE of 2.06 mg/m3, meanwhile, for nitrate, best fits were found in station SM10 with RMSE of 1.02 mg/m3. Results from model show that the thicknesses of MLD during west monsoon tend to decrease southward, from 35 m in the north to 15 m in the south. Conversely, during east monsoon MLD in the southern part tend to increase from 15 m to 35 m. In the northern part of Makassar Strait, the abundance of NPZ reaches its maximum during west monsoon with MLD 35 m. In this location and during this monsoon, the concentrations of nitrate and zooplankton tend to be low, i.e. 26.98 mg/m3 and 43.3 mg/m3, respectively, whereas phytoplankton concentrations tend to be high, i.e. 8.01 mg/m3. These results indicate that thickening of MLD will reduce nitrate concentration due to increased phytoplankton photosynthetic activity that assimilates nitrate, and affects the concentration of zooplankton that depends on the abundance of phytoplankton.