Bioluminescence flow visualization in the ocean: an initial strategy based on laboratory experiments

Observations of flow-stimulated bioluminescence have been recorded for centuries throughout the world's oceans. The present study explores, within a laboratory context, the use of naturally occurring bioluminescence as a strategy towards visualizing oceanic flow fields. The response of luminescent plankton to quantifiable levels of flow agitation was investigated in fully developed pipe flow. With two different pipe flow apparatus and freshly collected mixed plankton samples obtained over a year at two separate locations, several repeatable response patterns were identified. Threshold levels for bioluminescence stimulation occurred in laminar flow with wall shear stress levels generally between 1 and 2 dyn cm−2 (0.1–0.2 N m−2), equivalent to energy dissipation per unit mass values of 102–103 cm2 s−3 (10−2–10−1 m2 s−3). In an attempt to account for different concentrations and assemblages of mixed plankton, mean bioluminescence levels were normalized by an index of the corresponding flow-stimulated bioluminescence potential. This procedure generally accounted for variability between turbulent flow experiments, but was not effective for laminar flow. In turbulent flow, mean bioluminescence levels increased approximately linearly with wall shear stress. The magnitude of the flash response of individual cells, however, remained nearly constant throughout high laminar and turbulent flow, even as the energetic length scales of the turbulence became less than the size of the organisms of interest. Threshold flow stimuli levels determined in the laboratory were compared with oceanic measurements taken from the literature and with numerical simulations of ship wakes, one of the few highly turbulent flows to be well studied. Several oceanic flow fields are proposed as candidates for bioluminescence flow visualization.