Impact of Temperature on Absorption Coefficient of Pure Seawater in the Blue Wavelengths Inferred from Satellite and In Situ Measurements

There has been a long history of interest on how (if) the absorption coefficient of “pure” fresh water ( a fwλ ) and “pure” seawater ( a swλ ) changes with temperature ( T ), yet the impact of T reported in the literature differs significantly in the blue domain. Unlike the previous studies based on laboratory measurements, we took an approach based on ~18 years (2002–2020) of MODIS ocean color and temperature measurements in the oligotrophic oceans, along with field measured chlorophyll concentration and phytoplankton absorption coefficient, to examine the relationship between T and the total absorption coefficient ( a λ ) at 412 and 443 nm. We found that the values of a 412and a 443in the summer are nearly flat (slightly decreasing) for the observed T range of ~19–27 °C. Since there are no detectable changes of chlorophyll during this period, the results suggest that T has a negligible impact ona sw412anda sw443in this T range. As a complement, the impact of salinity ona fwλwas also evaluated using three independent determinations ofa swλanda fwλ , where good agreements were found from these observations.