Observations and biogeochemical modeling reveal chlorophyll diel cycle
with near-sunset maxima in the Red Sea
Abstract
The Red Sea is an extremely warm tropical sea that hosts diverse
ecosystems; thus, it is important to understand its ecology in the
context of global warming. Using a coupled physical–biogeochemical
model validated against in situ data, we provide the first report on the
diel cycle (i.e., diel variability) in the Red Sea chlorophyll (CHL)
concentration, revealing near-sunset CHL maxima at 17h ± 1h local time
over the entire basin. This CHL peak time is considerably later than
those reported in most other oceans, suggesting low grazing rates in
this high-irradiance tropical sea. Model-based analyses reveal that CHL
diel cycle is predominantly controlled by irradiance, whereas
longer-timescale (e.g., seasonal) CHL variability is regulated by
nutrient availability, suggesting a light-limited biological production
at diel timescale. The identified CHL diel cycle comprises a fundamental
component of the Red Sea ecology and has implications for CHL remote
sensing and in situ measurements.