Dynamic Bio-regionalisation of the Southern South China Sea: A Synthesis
from Satellite-Derived Chlorophyll-a Concentration
Abstract
The South China Sea (SCS) is one of the world’s most productive fishing
zones. Regionalising the SCS, particularly the understudied southern
sector (SSCS), is crucial for improving resource management in the SCS.
In this study, we analysed 24 years of satellite-derived chlorophyll-a
concentration (CHL) using a combination of empirical orthogonal function
and Fuzzy C-mean clustering techniques. Our results reveal that the
seasonal variability of CHL can be divided into three distinct regions.
Broadly, these regions separate into the eastern and western basins. The
first region encompasses the eastern boundary of the SSCS, the second
region includes the area off the coast of Vietnam, and the central SSCS,
while the third region extends from Karimata Straits to the Mekong River
mouth. Each region exhibits unique seasonal CHL patterns: the first
region shows a unimodal seasonality, while the second and third regions
display bimodal seasonality. Beyond the climatological occupancy of
these regions, we also demonstrate that their spatial extent is
temporally dynamic. Regions can expand, contract, or shift entirely on
an interannual scale. For instance, during the 1998 El Niño event, CHL
variability in the deep basin experienced a marked changed due to
intense warming. In contrast, during the 2015 El Niño event, despite
similarly intense warming, CHL variability was statistically consistent
with climatological norms. While the modulation of monsoonal winds by El
Niño Southern Oscillation partially explains the interannual variability
in the region. Our findings suggest that this variability is highly
complex, likely due to the dynamic nature of the basin.