The effect of the diurnal cycle of surfactant-associated bacteria in the sea surface microlayer on SAR imagery

Abstract:

The upper 1 mm of the ocean’s surface, the sea surface microlayer (SML), is occupied by a variety of organisms, including bacterial genera capable of producing surface active agents (surfactants). Bacteria in the subsurface water (SSW) produce organic material containing surfactants, which accumulate in the SML. Surfactant accumulation forms sea surface slicks, which dampen short gravity-capillary waves. Surfactant-associated slicks are visible in Synthetic aperture radar (SAR) imagery. Understanding surfactant producing microbial genera under different environmental conditions may help to implement SAR technology into global marine ecosystem assessment. Our current research is focused on the effect of UV exposure on the abundance of surfactant-associated bacteria within the SML and SSW. We have implemented the sampling approach described in detail in Parks et al. (IJRS Special Issue 2020). The in situ microlayer samples were collected in July-August 2018 and November 2019 at two sites in the Straits of Florida (Looe Key and Fort Lauderdale) during RADARSAT-2 satellite overpasses. The DNA data was analyzed at the Argonne National Laboratory using the Illumina MiSeq. This data indicates a significant difference in the bacterial abundance between day and night in the SML. We hypothesize that the daily UV exposure of the SML results in a lower abundance of UV radiation sensitive, surfactant-associated bacteria. The diurnal variability of the surfactant-associated bacteria in the SML may affect the presence of sea surface slicks visible in airborne SAR.