17:15 〜 18:45
[AOS12-P03] Seasonal and Interannual variability of Ocean Environment in the Savu Sea
キーワード：Savu Sea, SST, Chlorophyll-a
Monsoon wind is one of the primary forcings of seasonal variability in the Indonesian seas, which includes the ocean environment of the Savu Sea. It is categorized into 3 phases: the Northwest Monsoon season (DJF), the Southeast Monsoon season (JJA), and the transitional period (MAM and SON). This study focuses on local minimum SST and local maximum chlorophyll-a regions that appear during the Southeast monsoon season in the Savu Sea and aims to thoroughly investigate the seasonal and interannual dynamics of those regions. To achieve this goal, the study employs various data from 2011 until 2018; Sea Surface Temperature (SST) data is obtained from high-resolution satellite images provided by GHRSST (Chao et al., 2009) with a spatial resolution of 0.01°. Heat flux data with a resolution of 0.25° is collected from the ERA5 reanalysis (Hersbach et al., 2020). Chl-a concentration data with a resolution of 0.04° is acquired from OC-CCI (Sathyendranath et al., 2019). SLA data with a spatial resolution of 0.25° is estimated by Optimal Interpolation, merging the L3 along-track measurement from the different altimeter missions available (Generated using E.U. Copernicus Marine Service Information; https://doi.org/10.48670/moi-00148). Wind data with a spatial resolution of 0.125° is obtained from the scatterometer satellite, ASCAT MetOp A (Generated using E.U. Copernicus Marine Service Information; https://doi.org/10.48670/moi-00183). The EMT is calculated from the wind speed data and is projected to the coastline of each respective region. The seasonal variability of SST and chlorophyll-a in the Savu Sea are generally influenced by the mixing, Ekman mass transport (EMT), and heat flux seasonal dynamics. During the transition phase (MAM), weak southeasterly winds initiate southward EMT, starting chlorophyll-a growth on the southern coast. In the Southeast monsoon (JJA), strong southeasterly winds induce mixing over the sea and strong southward EMT, resulting in cool SST and abundant chlorophyll-a on the southern coast. In the transition phase (SON), the wind weakens resulting in less mixing and a southward EMT effect. In the Northwest monsoon (DJF), strong northwesterly winds generate northward EMT, resulting in abundant chlorophyll-a on the northern coast and no chlorophyll-a on the southern coast. High heat flux from September to December contributes to a rapid increase in SST. The land topography plays a major role in the distribution of wind speed over the Savu sea, as shown in Fig.1. This topography causes local strong wind regions where the stronger easterly wind, the stronger southward EMT it generates. These stronger southward EMT generate stronger coastal upwellings, bringing more cold-nutrient-rich water to the surface, creating local minimum SST and local maximum chlorophyll-a regions. The identified regions are named: A (119.68°E 8.93°S), B (124.08°E 8.7°S), and C (120.33°E 10.39°S). In 2013 and 2016, these local SST minimums and chlorophyll-a maximums in the southeast monsoon season didn’t appear due to the negative IOD events. These IOD events generated a downwelling Kelvin wave that propagated from the equatorial Indian Ocean to the west coast of Sumatera, the southern Java coast, and the Savu Sea. The downwelling Kelvin wave deepened the thermocline and nutricline depths, counteracting the coastal upwelling forcings in the Southeast monsoon phase that hindered the cold-nutrient-rich water transport to the surface. In contrast, 2015 was the year of a positive IOD event where an upwelling Kelvin wave can be observed. This Kelvin wave enhanced the coastal upwelling forcings by making thermocline and nutricline depths shallower, resulting in more cold-nutrient-rich water transport to the surface.