Seasonal variation in light penetration and subsurface chlorophyll-α in southern Lake Michigan observed by a glider

The Cooperative Institute for Great Lakes Research (CIGLR) in collaboration with the Observing System and National Oceanic Atmospheric Administration, Environmental Laboratory (NOAA GLERL) deployed an autonomous underwater glider southern Lake Michigan several times per year between 2012 2019 to collect offshore (>30 m depth) limnological measurements, including temperature, photosynthetically active radiation (beginning during 2015), chlorophyll-α fluorescence. From these data, we calculated mixed layer depth, measures of light penetration (diffuse attenuation coefficient, first optical euphotic zone depth), depth subsurface maxima. During summer, mean was typically 10–15 m, Kd PAR 0.1–0.17 m−1, 6–9 35–40 maxima 30–35 m. We also observed substantial spatial temporal variation values across basin within among seasons. Glider-based observations provide a wider horizontal vertical perspective than other methods (e.g., ship- satellite-based observations, buoys, fixed moorings), are therefore valuable, complementary tool limnology. set reported here seasonal basin-scale information that may help identify anomalies useful future glider-assisted investigation into role biophysical processes limnology ecology.