Light-absorbing components in the Great Lakes

•Document magnitude and spectral character of ax for the Great Lakes•The largest component of absorption throughout the system was aCDOM.•Most of aNAP was associated with clay mineral particles.•The distribution of aφ was highly correlated to chlorophyll concentration.•Supports development and preliminary testing of mechanistic retrieval algorithms

Features of light absorption are critical in regulating the optical signal available for remote sensing. The magnitudes, spectral characteristics, spatial patterns, and, to a lesser extent, dynamics of light-absorbing components are documented for the Laurentian Great Lakes. This includes the open waters of each of the five lakes, and selected rivers, embayments and near-shore areas. The absorption coefficient, a(m− 1), is partitioned according to the additive components (ax) of colored dissolved organic matter (aCDOM), non-algal particles (aNAP), phytoplankton (aφ), and water itself (aw; known). Dependencies of ax on various metrics of optically active constituents (OACs), cross-sections, are evaluated. A wide range of magnitudes of ax and a, and contributions of ax to a are documented. For example, the magnitude of a at a wavelength of 440 nm was nearly 10-fold greater in the western basin of Lake Erie than in the open waters of Lake Huron. Rivers, embayments, and near-shore areas generally had higher levels than the open waters. The largest ax throughout the system was aCDOM, originating mostly from terrestrial sources. Most of aNAP was associated with clay mineral particles. The distribution of aφ was highly correlated to chlorophyll concentration. The collected data set is appropriate to support initiatives to develop and preliminarily test mechanistic retrieval algorithms for OACs in the Great Lakes.