Year: 2026
Type: article
Abstract: Long-term trends in satellite-derived chlorophyll- a (Chl- a ) in optically complex coastal waters may reflect changes in multiple constituents rather than phytoplankton biomass alone. Using satellite Chl- a observations from 1998-2023 and 10 years of in situ hyperspectral remote-sensing reflectance data, \(R_{rs}(\lambda )\) (sr \(^{-1}\) ), together with derived constituent-specific absorption coefficients from the eastern Arabian Sea, we identified coherent positive and negative trends and classified eight optical water types. Positive-trend types generally exhibited greater particulate absorption, whereas negative-trend types showed greater fractional coloured dissolved organic matter (CDOM) absorption at shorter wavelengths. Three-stream radiative-transfer modelling revealed corresponding differences in dimensionless subsurface spectral irradiance reflectance, \(R(z,\lambda )=E_u(z,\lambda )/[E_d(z,\lambda )+E_s(z,\lambda )]\) , euphotic depth, and radiative heating rate. Positive-trend types exhibited mean euphotic depths of 4.0-5.3 m, whereas negative-trend types portrayed shallower values of 3.1-3.6 m and more surface-intensified heating. CDOM-enhanced types exhibited approximately 1.18-fold greater depth-integrated radiative heating within their respective euphotic zones, despite reduced water-leaving reflectance at strongly absorbed wavelengths. These results demonstrated that constituent composition and spectral absorption mediated both the expression of long-term variability in satellite ocean colour and the vertical distribution and transmission of solar irradiance.
Source: Scientific Reports
Language: English
Subfield: Oceanography
Field: Earth and Planetary Sciences
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $2,690
Award: G3874219111
OpenAlex ID: W7216282826