The Ocean’s Elevator: Evolution of interfacial water structure during a marine algal bloom

Abstract:

The composition and lifetime of sea spray aerosols is driven by the molecular and biological complexity at the air-sea interface. The surface properties of marine algal blooms were explored in situ by utilizing surface techniques: vibrational sum frequency generation spectroscopy and Brewster angle microscopy imaging. Over the course of the bloom, the marine algae (Skeletonema marinoi) produced surface active organic and biological species and changed the topmost interfacial waters temporally. Our sum frequency generation spectroscopic results show significant diminishing in the intensity of the “dangling” OH of water consistent with organic molecules partitioning and replacing water molecules at the air-sea interface as the algal bloom progresses. Interestingly, we observe a new broad peak appear between 3500 to 3600 cm^-1 in the late stages of the bloom. This peak is attributed to weakly hydrated waters interacting with surface active biological matter. Brewster angle microscopy images show morphological packing changes with increasing molecular density of surface-active species. Film thickness calculations using our image results quantify the increasing average surface thickness over time. Our work shows the often overlooked but vast potential of tracking changes in the interfacial regime of small-scale laboratory algal blooms. Coupling surface imaging and spectroscopy will lead to a more guided approach to better understand the complex composition of sea spray aerosols and aid climate modelers in their understanding of the radiative budget and global climate change of our planet.