Turbulence as a driver for vertical plankton distribution in the subsurface upper ocean

Diego Macías,Miguel Bruno,Pablo Sangrà,Josep L. Pelegrí,Borja Aguiar-González,Carlos M. García,Ángel Rodríguez-Santana,Eduardo Ramírez-Romero

doi:10.3989/scimar.03854.03a

Abstract

SUMMARY: Vertical distributions of turbulent energy dissipation rates and fluorescence were measured simultaneously with a high-resolution micro-profiler in four different oceanographic regions, from temperate to polar and from coastal to open waters settings. High fluorescence values, forming a deep chlorophyll maximum (DCM), were often located in weakly stratified portions of the upper water column, just below layers with maximum levels of turbulent energy dissipation rate. In the vicinity of the DCM, a significant negative relationship between fluorescence and turbulent energy dissipation rate was found. We discuss the mechanisms that may explain the observed patterns of planktonic biomass distribution within the ocean mixed layer, including a vertically variable diffusion coefficient and the alteration of the cells’ sinking velocity by turbulent motion. These findings provide further insight into the processes controlling the vertical distribution of the pelagic community and position of the DCM.

Highlights

Turbulence is a ubiquitous feature of geophysical fluids that typically arises as a consequence of energy transfer from large to small scales (Kolmogorov 1941).In marine ecosystems, small organisms with little or no motility, such as phytoplankton cells, are immersed in a turbulent environment that influences numerous biological processes, including photosynthesis (Belyaev 1992), nutrient uptake
One of the most common features of the vertical distribution of plankton is the presence of a deep chlorophyll maximum (DCM) (Cullen 1982)
The existence of a DCM may be initially explained by the presence of two vertically opposing gradients of resources that control the vertical distribution of planktonic biomass: light availability from the surface and a high nutrient concentration in deep waters (Longhurst and Harrison 1989)

Summary

Introduction

Turbulence is a ubiquitous feature of geophysical fluids that typically arises as a consequence of energy transfer from large to small scales (Kolmogorov 1941).In marine ecosystems, small organisms with little or no motility, such as phytoplankton cells, are immersed in a turbulent environment that influences numerous biological processes, including photosynthesis (Belyaev 1992), nutrient uptake Turbulence is a ubiquitous feature of geophysical fluids that typically arises as a consequence of energy transfer from large to small scales (Kolmogorov 1941). Small organisms with little or no motility, such as phytoplankton cells, are immersed in a turbulent environment that influences numerous biological processes, including photosynthesis (Belyaev 1992), nutrient uptake One of the most common features of the vertical distribution of plankton is the presence of a deep chlorophyll maximum (DCM) (Cullen 1982). The existence of a DCM may be initially explained by the presence of two vertically opposing gradients of resources that control the vertical distribution of planktonic biomass: light availability from the surface and a high nutrient concentration in deep waters (Longhurst and Harrison 1989). The biomass of photosynthetic plankton organisms is accumulated in a narrow region where there is sufficient light for photosynthetic activity and sufficient inorganic nutrients to allow net positive growth

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