Quest for the building blocks of ocean ecosystems: micro-scale fluorescence patchiness

Micro-scale aquatic ecosystems are the engine for earth's biogeochemical cycles. Phytoplankton fix inorganic carbon to organic carbon through the photosynthetic process. Although phytoplankton are single-cell organisms, they often appear in an aggregated form that elevates local fluorescence signal intensity. How intermittent are these features? We have developed a new free-fall microstructure profiler (TurboMAP-L) that carries sensors for turbulent shear and temperature gradient, small-scale fluorescence and turbidity as well as standard hydrographic parameters (conductivity, temperature, depth). The new profiler also carries a new laser fluorescence probe that resolves millimeter scale fluorescence fields, as well as a Digital Still Logger (DSL) CMOS camera system that records a 1024×1280 pixel image at 5Hz time interval with a pixel resolution of 330μm. Fluorescence profiles measured by TurboMAP-L and a conventional fluorescence probe are in good agreement at one-meter scale average. However, the fluorescence signals revealed from the LED fluorescence probe are intermittent at cm scale. Millimeter scale fluorescence signals obtained from the laser probe are even more intermittent than the cm scale LED signals. The source of the millimeter-scale strong signals identified from the DSL images are coagulated discrete material ranging between a few 100 μm and a few millimeters scale. Unfortunately, the DSL images are not focused well, and so the detail of the coagulated matter is not clear. Therefore, a recently developed holographic imaging system is combined with the TurboMAP-L operation in order to identify the detail of the millimeter scale coagulated material. We present the direct comparison results from our recent experiment and discuss the importance of our findings.