The dispersal of phytoplankton populations by enhanced turbulent mixing in a shallow coastal sea

Cross, J, Nimmo-Smith, WAM, Hosegood, PJ and Torres, R 2014 The dispersal of phytoplankton populations by enhanced turbulent mixing in a shallow coastal sea. Journal of Marine Systems, 136. 55-64.

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A single tidal cycle survey in a Lagrangian reference frame was conducted in autumn 2010 to evaluate the impact of short-term, episodic and enhanced turbulent mixing on large chain-forming phytoplankton. Observations of turbulence using a free-falling microstructure profiler were undertaken, along with near-simultaneous profiles with an in-line digital holographic camera at station L4 (50° 15′ N 4° 13′ W, depth 50 m) in the Western English Channel. Profiles from each instrument were collected hourly whilst following a drogued drifter. Results from an ADCP attached to the drifter showed pronounced vertical shear, indicating that the water column structure consisted of two layers, restricting interpretation of the Lagrangian experiment to the upper ~ 25 m. Atmospheric conditions deteriorated during the mid-point of the survey, resulting in values of turbulent dissipation reaching a maximum of 10− 4 W kg− 1 toward the surface in the upper 10 m. Chain-forming phytoplankton > 200 μm were counted using the data from the holographic camera for the two periods, before and after the enhanced mixing event. As mixing increased phytoplankton underwent chain breakage, were dispersed by advection through their removal from the upper to lower layer and subjected to aggregation with other suspended material. Depth averaged counts of phytoplankton were reduced from a maximum of around 2050 L− 1 before the increased turbulence, to 1070 L− 1 after, with each of these mechanisms contributing to this reduction. These results demonstrate the sensitivity of phytoplantkon populations to moderate increases in turbulent activity, yielding consequences for accurate forecasting of the role played by phytoplankton in climate studies and also for the ecosystem in general in their role as primary producers.

Item Type: Publication - Article
Additional Keywords: Turbulence; L4; Phytoplankton dispersal; Holographic imaging; Flocculation
Subjects: Biology
Divisions: Plymouth Marine Laboratory > Science Areas > Marine System Modelling
Depositing User: Ricardo Torres
Date made live: 05 Jun 2014 15:59
Last Modified: 13 Dec 2023 12:21

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