A recently completed project used the combination of a free-falling microstructure profiler (MSS) and holographic imaging (the holocam) to better understand the dynamics of suspended particles in coastal seas. Surveys were conducted across a single tidal cycle, whereby both instruments were deployed near-simultaneously. The MSS is able to resolve important parameters such as temperature, salinity and optical backscatter (OBS), in addition to its principal function which is to generate an estimate for the rate of turbulent dissipation, ε. The holocam delivers in situ images of suspended particles, allowing identification of both biological and flocculated suspended particulate matter (SPM) (Figure 5). During a survey in September 2010, the combination of enhanced vertical mixing brought about by an increase in wind stress (Figure 5b), and advection of a water mass from the south of the L4 site in the Western English Channel, resulted in marked changes to the phytoplankton population. The data from the holocam allows the user to count individual phytoplankton particles, thus determining how events brought about by the changing conditions may impact the phytoplankton population. The L4 site is dominated by large, chain-forming diatoms. On this basis, phytoplankton > 200μm in size were identified and counted. The counts revealed that far greater numbers of phytoplankton were observed during the period of relative calm. Supporting data from the holocam indicate that a combination of factors contribute to this change. A reduction of particle size, likely a result of the enhanced mixing breaking the diatom chains, and a change in composition as diatoms begin to aggregate with other SPM forming flocs can be directly attributed to the increased turbulence. Further, advection of water from the south is likely to transport water away from the region being sampled, advecting the phytoplankton population with it. Cross, J., W. A. M. Nimmo Smith, R. J. Torres, P. J. Hosegood, 2013. Biological controls on resuspension and the relationship between particle size and the Kolmogorov length scale in a shallow coastal sea. Marine Geology, 343, 29-38, doi:10.1016/j.margeo.2013.06.014. Cross, J., W. A. M. Nimmo Smith, P. J. Hosegood, R. J. Torres, 2013. The dispersal of phytoplankton by enhanced turbulent mixing in a shallow coastal sea. Journal of Marine Systems, submitted. |