Abstract
Abstract. Horizontal mixing has been found to play a crucial role in the development of spatial plankton structures in the ocean. We study the influence of time and length scales of two different horizontal two-dimensional (2-D) flows on the growth of a single phytoplankton patch. To that end, we use a coupled model consisting of a standard three component ecological NPZ model and a flow model able to mimic the mesoscale structures observed in the ocean. Two hydrodynamic flow models are used: a flow based on Gaussian correlated noise, for which the Eulerian length and time scales can be easily controlled, and a multiscale velocity field derived from altimetry data in the North Atlantic ocean. We find the optimal time and length scales for the Gaussian flow model favouring the plankton spread. These results are used for an analysis of a more realistic altimetry flow. We discuss the findings in terms of the time scale of the NPZ model, the qualitative interaction of the flow with the reaction front and a Finite-Time Lyapunov Exponent analysis.
Highlights
Spatial heterogeneity or “patchiness” in phytoplankton distributions is an old oceanographic observation that dates back to the 12th century (Griffiths, 1939; Bainbridge, 1957) and is still a field of current research
Two hydrodynamic flow models are used: a flow based on Gaussian correlated noise, for which the Eulerian length and time scales can be controlled, and a multiscale velocity field derived from altimetry data in the North Atlantic ocean
The effect of how time and length scales of the flow act on the development of a phytoplankton patch is shown in Fig. 2 for the Gaussian flow model
Summary
Spatial heterogeneity or “patchiness” in phytoplankton distributions is an old oceanographic observation that dates back to the 12th century (Griffiths, 1939; Bainbridge, 1957) and is still a field of current research. Phytoplankton forms the base of the food chain and is responsible for a large amount of the biological primary production in the oceans. It plays an important role for the entire marine ecosystem. A striking feature associated with the dynamics of phytoplankton populations is the occurrence of rapid and extensive bloom formations. Such events are characterised by a sharp rise in algae concentration of up to several orders of magnitude (Beltrami and Carroll, 1994) followed by a sudden collapse, whereby the phytoplankton populations return to their original low level. Given the impact of phytoplankton blooms, it is of interest to understand the dynamics of plankton growth and the conditions for a rapid and wide-spreading plankton patch
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