POSTER Session 2

TEMPORAL DEVELOPMENT OF A MESOCOSM PHYTOPLANKTON BLOOM ASSESSED BY IOP MEASUREMENTS AND IMAGING

The surface microlayer, the “skin” of the sea, is the thin boundary between the oceans interior and the atmosphere. It constitutes a unique environment in which particulate and dissolved organic matter is enriched, resulting in consequences for light, heat, and gas transfer. The biochemical processes within this layer and their interactions with the underlying bulk water are currently not well understood, amongst other reasons due to a lack in high-frequency observations. We describe the temporal development of a phytoplankton bloom initiated in a mesocosm over the duration of one month by means of phytoplankton imaging and different bio-optical properties. The experiment aimed to evaluate the suitability of optical techniques to detect changes within both surface microlayer and underlying bulk water and assess the effect of the bloom on the microlayer composition. The results show distinct differences in the two compartments in terms of particle composition and optical properties, which varied over the course of the experiment. After initial increase of water transparency due to settling of larger particles, a bloom of small flagellates, identified as the coccolithophore Emiliana huxlei, lead to a rapid increase in water absorption and (back)scattering coefficients in the bulk water. It was followed by a diatom bloom (Cylindrotheca sp.). In the surface layer, the particle concentration was considerably higher, and while it decreased in the bulk with bloom decay, it remained on high levels in the microlayer (flock formation), indicating potential export of particulate material from the bulk water into the surface layer.

Jochen Wollschläger, University of Oldenburg, Institute for Chemistry and Biology of the Marine Environment (ICBM), Germany, https://orcid.org/0000-0001-5399-4414

Michael Novak, Helmholtz Center Hereon, Germany

Rüdiger Röttgers, Helmholtz Center Hereon, Germany

Claudia Thölen, Institute for Chemistry and Biology of the Marine Environment (ICBM), Germany

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