| Summary: | Our team completed fieldwork in both April and August of 2012, 2013, 2014, and 2015 to collect various measurements and samples along two transects of lakes across Alaskan North Slope. To date, we have analyzed over 300 samples for chromophoric dissolved organic matter (CDOM), chlorophyll-a (and phaeophytin), as well as a suite of cations and anions (F, Cl, SO4, NO3, PO4, Na, NH4, K, Mg, and Ca). Biogeochemical data reveal distinct spatial and seasonal variability in chlorophyll biomass, CDOM, and major cations/anions. In general, waters sampled in April had consistently distinctly higher concentrations of inorganic solutes. Lake waters with the highest total dissolved solid concentrations (~3000 mg/L) were dominated by Na and Cl, indicating a potential seawater influence. The remaining samples grade towards Ca-Mg-HCO3-type waters, reflecting dissolution of carbonate minerals found in underlying rocks and sandstone cements. We also found that chlorophyll concentrations and CDOM absorption were both generally higher during April (compared with August), suggesting significant biological/biogeochemical activity even under lake ice during this early part of the year. By August, primary production may have been limited by the presence of sufficient nutrients and CDOM concentrations may have therefore declined owing to photodegradation processes or bacterial decomposition. One additional striking observation is the latitudinal trend in some biogeochemical constituents, generally increasing from south to north.
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