SAMI-Alks Used in Inorganic Carbon Study

Graduate student Qipei Shangguan at the DeGrandpre lab at the University of Montana is studying inorganic carbon in the Clark Fork River (CFR), MT, as part of a Montana NSF-EPSCoR grant. Three SAMI-alk and one SAMI-CO₂ instruments were deployed in the CFR for 23 days during September and October of 2019. The data series reveals diel cycles in total alkalinity (TA) of ~80 µmol L-1 and an overall decrease in TA of ~150 µmol L-1 over the time period. The total alkalinity difference between SAMI00 and SAMI02was 1 ± 14 µmol L-1 (n=190), while the difference between SAMI03 and SAMI02 was 8 ± 19 µmol L-1 (n=214), demonstrating good agreement between instruments. Differences between the SAMI-measured TA and benchtop Gran titrations were -4 ± 11, 8 ± 14, and -3 ± 18 µmol L-1 for the three instruments, after calibration to the first bottle sample, demonstrating the accuracy and stability of the measurements over the 3-week period.

The SAMI-CO₂ showed a diel cycle as high as 900 µatm, not typically seen in seawater. Measurement of pCO₂ and TA allowed calculation of DIC and carbonate mineral saturation states. In-depth analysis of the data is the topic of an forthcoming publication.