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The principal non-water visible-light absorbers can be grouped into phytoplankton pigments, coloured dissolved organic matter (CDOM), and non-algal particles (NAP), including organic detritus and absorbing mineral material. A useful additive decomposition of the absorption coefficient isThe supplied sketch separates the three non-water contributions; its amplitudes are arbitrary and are not concentrations or measured spectra.

Phytoplankton pigments give prominent absorption maxima around $440$ and $675\mathrm{nm}$, associated with chlorophyll a, and a relative minimum in the green. Accessory pigments, including carotenoids and phycobilins, broaden or add absorption bands, so an assemblage is not just a pure chlorophyll-a solution. Intracellular packaging and cell size also modify the shape and absorption per unit pigment.

Coloured dissolved organic matter consists of dissolved light-absorbing organic compounds, often including humic material from terrestrial runoff and marine degradation. Its absorption is strongest at the blue/ultraviolet end and declines approximately exponentially toward red, without the narrow chlorophyll red peak. A common local parameterization is $a_g(\lambda )=a_g({\lambda }_0)e^{-S_g(\lambda -{\lambda }_0)}$ with positive spectral slope $S_g$; here $S_g$ is an optical slope, not gas saturation.

Non-algal particles include nonliving organic detritus, pigment degradation products and absorbing suspended mineral particles. Their aggregate absorption often also decreases approximately exponentially from blue to red, with variable slope and mineral-dependent departures. Suspended sediments can strongly scatter as well as absorb; bright sediment-laden water is not evidence of a red absorption peak. Chlorophyll-containing living cells belong in $a_{\mathrm{ph}}$, so these categories should not be double counted.^[ref]

The photic zone is the illuminated layer supporting photosynthesis; its euphotic depth is conventionally associated with about 1% of surface photosynthetically active radiation, integrated over approximately $400$–$700\mathrm{nm}$. This is a useful convention rather than a universal organism-specific compensation depth. Spectral filtering can be represented locally bywhere $K_d$ is the wavelength-dependent diffuse attenuation coefficient. It includes effects of absorption and scattering and is not simply equal to the absorption coefficient $a$.

In clear, low-chlorophyll water, pure water removes red light strongly, while weak blue pigment and CDOM absorption permits blue light, typically around $450$–$490\mathrm{nm}$, to penetrate furthest. The deepest usable light is consequently dim and blue-rich, and the euphotic zone can extend relatively deep. At high pigment concentrations, phytoplankton pigments preferentially remove blue and red light; associated detritus or CDOM can remove still more blue. The remaining transmission window commonly shifts toward blue-green or green wavelengths, roughly $500$–$570\mathrm{nm}$, and the total light falls off faster, so the euphotic depth is shallower. Exact window and depth depend on the full particle/dissolved mixture, not chlorophyll alone. The diagram normalizes the two deep spectra separately to show their different shapes, not equal absolute light at a common depth.

This confines photosynthetic growth to a thinner illuminated interval in high-chlorophyll water and allows a deeper potential habitat in clear low-chlorophyll water, subject also to nutrient supply, mixing and the organism's compensation requirement. Cells near the base benefit from low-light acclimation and pigment systems that capture the remaining wavelengths. In blue-rich deep ocean water, blue-absorbing pigments and some low-light-adapted picoplankton can be favored; where the surviving light is greener, groups with effective green-absorbing accessory pigments, such as certain phycobilins, gain an advantage. A pigment appears coloured by light it fails to absorb, so green-absorbing accessory pigments need not themselves look green. There is no universal deep species determined by chlorophyll concentration alone. A deep chlorophyll maximum can partly reflect increased pigment per cell rather than a proportional maximum in carbon biomass.^[ref]