Measurements of mineral particle absorption properties in turbid estuaries: Intercomparison of methods and implications for optical inversions

We examine optical measurements of total particle absorption and mass specific mineral particle absorption collected from two mineral-rich turbid estuaries. Particle absorptions derived from measurements made with profiling radiometers are compared to those obtained using the Quantitative Filter Technique (QFT). A range of different backscattering ratios and pathlength amplification corrections, used to interpret the radiometer and QFT data respectively, are assessed. We also examine what impact the process of removing organic material from QFT samples by combustion has on the measured absorption properties of mineral particles. Our results show that the process of combustion changes the measured absorption properties of mineral particles retained on filters and we show that if the absorption properties of mineral particles are obtained from combusted QFT samples, significant errors can result in optical inversions that require estimates of mass specific mineral particle absorption. In contrast, using mass specific mineral particle absorption coefficients obtained from a regression technique significantly improves the accuracy of our optical inversion results. A correction for mineral particle absorption measurements derived from combusted QFT samples is presented, and assessed by application to an independent dataset.