[A-OS13] Marine ecosystems and biogeochemical cycles: theory, observation and modeling

[AOS13-07] Influence of ENSO on surface chlorophyll-a in the Gulf of Thailand

*Dudsadee Leenawarat¹、Jutarak Luang-on¹、Anukul Buranapratheprat²、Joji Ishizaka³ (1.Graduate School of Environmental Studies, Nagoya University、2.Department of Aquatic Science, Faculty of Science, Burapha University, Thailand、3.Institute for Space-Earth Environmental Research, Nagoya University, Japan)

キーワード：Gulf of Thailand , Chlorophyll-a, ENSO

The Gulf of Thailand (GoT) is a tropical and semi-enclosed sea. This area is surrounded by Vietnam, Cambodia, Thailand, and Malaysia, and connected to the South China Sea via southeastern part. The variation of surface chlorophyll-a (chl-a) in this region was controlled by monsoon system. The large-scale phenomena such as El Niño Southern Oscillation (ENSO) also caused the variation over the monsoon system. These environmental changes caused by ENSO may increase/decrease phytoplankton production. To investigate the impact of ENSO on surface chl-a in each season, monthly chl-a data from MODIS from 2002 to 2018 were used in this study. Environmental parameters including sea surface temperature (SST), wind, precipitation, and discharge were also considered to describe the variability. It was found that the influence of ENSO on chl-a was stronger during the northeast monsoon (NEM; November to February) to the non-monsoon (NON; March to May) than the southwest monsoon (SWM; June to October). In the coastal area, surface chl-a responded to abnormally low/high precipitation and river discharge during El Niño/La Niña in all seasons. In the offshore area, chl-a was affected by changes in wind and water mixing. Weak/strong wind and increased/decreased SST may reduce/enhance in mixing from deep layer water mass that contains higher nutrients. Under El Niño condition, weak/strong wind and increased SST were found during NEM/NON and the opposite condition was found during La Niña condition. Weak in mixing from the deep layer and strong mixing of warm water mass in the upper layer were expected to occur during NEM and NON under El Niño condition. In addition, wind anomaly seems to create the shifting in the high chl-a area near the GoT mouth.