International Intercomparison of In Situ Chlorophyll-a Measurements for Data Quality Assurance of the Swedish Monitoring Program

Chlorophyll-a is an essential climate variable. in situ measurements are usually used for the validation of satellite images. Previous intercomparisons have shown that there can be substantial differences between laboratories. In order to shed light on these differences, we arranged international chlorophyll-a with eight participating laboratories during 1–2 July 2021. We performed two dedicated transects through Bråviken bay (NW Baltic proper) and sampled four stations each transect along a gradient. took three surface replicates per laboratory station, i.e., 24 samples laboratory. The were filtered Whatman GF/F filters, filters frozen liquid nitrogen distributed dry ice all together standards. results labs compared quite well. mean normalized bias (MNB) standard ranged −23% +19% −7% Sea high-performance chromatography. MNB −23 +17% (compared median spectrophotometric fluorometric measurements) −2 On average, concentrations measured by method about 13% higher than those spectrophotometry, fluorometry tended more scatter. largest uncertainties seem caused variable storage extraction methods not fully captured this intercomparison. This demonstrated analyzing historical comparisons revealing very large (root square difference (RMSD) up 109% 68%), possibly due too low filtration volumes different methods. Our recommendation flash-freeze store them at −80°C. After storage, they should extracted room temperature within 6–24 h. also indicate ethanol much efficient extracting Chl-a acetone. Last but least, would like point out measuring now range data, as here comparing from study published remote sensing literature.