Specific in vivo absorption coefficient of chlorophyll a at 675 nm1

Abstract

Spectral absorption of phytoplankton from cultures and natural samples was measured by means of an integrating‐sphere photometer. Measurements on suspension yielded specific absorption coefficients for healthy phytoplankton cultures in collimated light at 675 nm between 0.007 and 0.013 m2 (mg Chl a)−1. These values were independent of cell density and cell wall material.Natural samples of Kiel harbor water yielded specific absorption coefficients at 675 nm of 0.009 and 0.017 m2 (mg Chl a)−1. The specific absorption coefficients in suspension were dependent on the optical properties of the individual cells (packaging effect), decreasing (ca. 1/r) with increasing cell size (r radius) and increasing chlorophyll a content per cell as predicted by theory, but are significantly lower than theoretically expected. Comparison with published values shows that specific absorption coefficients of cell suspensions are often overestimated, presumably because of methodological problems.