Pigment packaging and Chl a-specific absorption in high-light oceanic waters

The absorption of light by particles at a single wavelength, a(ph)(lambda) is reduced with increased packaging of the light absorption material within these particles. This reduction can be described by the parameter Q(a)*: Q(a)*(lambda) = a(ph)(lambda)/a(sol)(lambda) = a(ph)(lambda)/S(lambda) x a(om)(lambda), where a(sol)(lambda) is the theoretical maximum light absorption of the cellular material, a(cm), in a completely dissolved state. In practice, the estimations a(sol)(lambda) for living phytoplankton are hampered by the process of removing the chloroplast/thylakoid membranes from the organic matrix of the cell, the destruction of the pigment-protein complexes when an organic solvent is used, and the interference of the excited states of the pigment chromophore by the organic solvent. What is actually being measured by many of the current methods trying to determine a(sol)(lambda) is a(om)(lambda), i.e. the absorption of light by the pigment material in the organic medium of the experiment (methanol, acetone, Triton-X, etc.). The solvation factor, S, in the above equation is the ratio of the true a(sol)(lambda) to the measured a(om)(lambda). We have developed an internally consistent measure of a(ph)(lambda), a(om)(lambda), Chl a concentration, and pheopigment concentration to determine the value of Q(a)* x S. This relationship is used to determine a functional relationship for Chi a absorption for high-light-adapted, natural phytoplankton populations in optically clear waters. The nonlinear packaging effect in these waters is insignificant at the red end of the spectrum. Exclusion of the weight-specific absorption of pheopigments and the assumption of a zero a(ph)(lambda) at a zero pigment (Chl a + pheopigment) concentration produces a misleading Chi aspecific absorption and a false determination of pigment packaging. An algorithm is developed for predicting Chl a concentration from a(ph)(675).