Red and black tides: Quantitative analysis of water‐leaving radiance and perceived color for phytoplankton, colored dissolved organic matter, and suspended sediments

Abstract

Using field measurements and quantitative modeling, we demonstrate that red coloration of the sea surface is not associated with any particular group of phytoplankton and is strongly dependent on the physiology of the human visual system. Red or brown surface waters can be produced by high concentrations of most types of algae, colored dissolved organic matter, or suspended sediment. Even though light reflected by red tides commonly peaks in the yellow spectral region (570-580 nm), human color perception requires consideration of the entire spectrum of light relative to receptors within the human eye. The color shift from green to red is not due to any special optical properties of the algae but results from an overlap in spectral response of the eye's red and green cones (centered at 564 and 534 nm, respectively). The spectral peak in light reflected from dense algal blooms coincides with a critical hinge point in color vision (570-580 nm), where fine-scale shifts in the spectral shape of water-leaving radiance due to algal absorption and backscattering properties lead to pronounced variations in the observed color. Of the taxa considered, only Chlorophytes and Prochlorophytes lacked sufficient accessory pigments to produce a red tide. Chlorophyll fluorescence and enhanced near-infrared reflectance (the ''red edge'') contribute negligibly to the perceived color. Black water events are produced when water is highly absorbing but lacks backscattering constituents.

A regional comparison of particle size distributions and the power law approximation in oceanic and estuarine surface waters

“…Today, the tidal range varies over 2 m in amplitude and significantly alters the particle dynamics. The water of Elkhorn Slough was brown in color [Dierssen et al, 2006] and had one of the highest particle concentrations of any water type sampled in this study. Measurements along the shore of Elkhorn Slough at two tidal stages resulted in markedly different particle loads and PSD slopes (Figure 7).…”

“…Normal tidal flow in such a bay would not be sufficient to resuspend sediment beyond a few meters above the seafloor [Fugate and Friedrichs, 2002]. However, after the passage of Tropical Storm Alberto, the water appeared of a brownish color due to the high sediment load [Dierssen et al, 2006] and the median particle concentration was high throughout the shallow and deep portions of the Bay (1740 and 2143 particles L −1 mm −1 , respectively). Moreover, the PSD slopes were not significantly different between the shallow and deep stations (Mean 3.41 and 3.51, respectively).…”

Perspectives on empirical approaches for ocean color remote sensing of chlorophyll in a changing climate

“…Moreover, nutrient fertilization from terrestrial runoff can change phytoplankton dynamics and even produce harmful algal blooms that appear red in color (19). Melting and runoff of glacial sources can increase particle concentrations in the nearshore and change phytoplankton assemblages (20,21).…”

“…Small phytoplankton, like Synechococcus and Prochlorococcus, have enhanced backscattering of blue photons. Larger phytoplankton tend to backscatter light similarly at all wavelengths, or potentially more red photons (19). To assess the sensitivity of empirical ratios to backscattering, the radiative transfer model was run with different magnitudes of spectrally invariant backscattering.…”

Detection technique of Red Tide Using GOCI Level 2 Data

“…최근에는 이러한 한계점을 극복하기 위해 해수의 광학적 특성을 이용하 여 적조를 탐지하는 연구들이 시도되고 있다 (Dierssen et al, 2006;Cannizzaro et al, 2008;Sasaki et al, 2008). 그러 나 이러한 방법들은 상대적으로 용존유기물이나 부유 물질이 적은 해수환경에서 탐지가 용이하다 (Ahn et al, 2006).…”