Phytoplankton Concentration Distribution in the Kara Sea According to Aircraft Laser Sounding Data

The spatial distribution of the relative concentration of chlorophyll-a in surface waters was estimated at three sites in the southwestern region of the Kara Sea based on laser-induced fluorescence measurements with an aircraft lidar. The fluorescence intensity was normalized to the simultaneously recorded intensity of Raman scattering signals from water. For two sites in the shelf zone near the western coast of the Yamal Peninsula, the spatial distribution of the normalized fluorescence intensity Cl is quite homogeneous, with variation coefficients of 9 and 15%. The third site in the northern tip of the Yamal Peninsula is strongly affected by river runoff, which is manifested in the presence of sharp frontal zones 5–10 km long. At this site, the Cl variation coefficient attains 40%, and the variations are mainly due to the strong variability of the Raman signals and, to a much lesser extent, to variations in the fluorescence intensity. Factors influencing the variability of Raman signals are considered. Synchronous shipboard in-situ measurements and remote aircraft measurements enabled us to find the calibration coefficient k_Cl = 1.03 ± 0.09 μg/L for the first two sites.