Stratification, plankton layers, and mixing measured by airborne lidar in the Chukchi and Beaufort seas

Abstract

A total of 4.9 million vertical profiles of optical backscattering were measured by airborne lidar in July of 2014 and July of 2017 in the Chukchi and Beaufort seas. We found very different ice conditions in the study area between July 2014 and July 2017, but the characteristics of subsurface plankton layers measured by the lidar and their dependence on ice cover were similar for the two years. In both years, the prevalence of subsurface plankton layers exponentially decreased with increasing ice cover. The average depths were similar for both years, with layers in open water deeper than those in the pack ice. The depths of subsurface plankton layers were consistent with mixed layer depth in areas where in situ density profiles were available. A noticeable difference in layer strength (defined as the ratio of the layer signal to the background) was likely caused by higher background phytoplankton concentrations in 2017. Differences in layer thickness were observed, which could be the result of higher current shears in 2017. Turbulent mixing of phytoplankton and zooplankton in Barrow Canyon was inferred from the power spectral density of lidar and acoustic scattering. Lidar measurements suggested that the level of turbulence and its vertical distribution were affected by local upwelling-favorable winds. The vertical distribution of acoustic scattering was different from that of the lidar, which we interpret as different vertical distributions of phytoplankton and zooplankton.