The generation of phytoplankton patchiness by mesoscale current patterns

Abstract

Elken et al. (1994) suggested that phytoplankton patchiness can be generated by mesoscale eddies in light-limited, nutrient-replete environments. This hypothesis is explored using two ecological models of different physical complexity. The model results support the idea that the coupling of mesoscale eddy circulation and phytoplankton growth leads to differential growth rates and thus generates variability in phytoplankton distributions. The specific circulation of a cyclonic eddy isolates a phytoplankton population in its core. Due to the reduced vertical mixing, a higher growth rate is supported in the core, and phytoplankton concentrations increase compared to the surrounding environment. A one-dimensional model is used to explore the hypothesis in general and to perform sensitivity studies. A more realistic simulation uses a coupled threedimensional model for the western Baltic Sea. Starting from vertically and horizontally homogeneous distributions for nutrients and plankton, the models generate patchiness due to the proposed mechanism. The described mechanism may apply for other mesoscale variable environments during light-limited growth periods as well, e.g., the frontal region of the Southern Ocean.

Critical turbulence revisited: The impact of submesoscale vertical mixing on plankton patchiness

“…Both in these simulations and in our simulations at low light intensities, the biomass [66, 1 concentrations became low in regions with deep vertical mixing. However, contrary to our results, Fennel (2001) did not find strips of high biomass adjacent to the regions of deep mixing. This difference can be explained, if we compare the two simulation setups.…”

“…Simulations of light-limited plankton growth in both a three-dimensional flow and a more idealized two-dimensional mixing layer model have been performed earlier by Fennel (2001). Both in these simulations and in our simulations at low light intensities, the biomass [66, 1 concentrations became low in regions with deep vertical mixing.…”

“…Under such nutrient-replete conditions, the plankton growth rate does not depend on the nutrient concentration. In Fennel (2001), the plankton growth rate only depended on the mixing depth and therefore, the plankton concentrations became low in regions with deep mixing, whereas they became high in regions with shallow mixing.…”

“…Hence, strips of high biomass concentrations were found adjacent to regions where the critical turbulence was exceeded, because the nutrient concentration was relatively high at those locations. In the Fennel (2001) simulation, the nutrient concentration was far above the saturation value for plankton everywhere in the domain, a situation that can be considered typical for continental shelf seas. Under such nutrient-replete conditions, the plankton growth rate does not depend on the nutrient concentration.…”

Modeling Of the Phytoplankton Dynamics Considering the Mechanisms of Ectocrine Regulation

“…Данные наблюдений свидетельствуют о том, что на пространственных масштабах от десяти километров и более пятнистость планктонного распределения определяется в основном неоднородностью соответствующих физико-химических полей [15]. Для фитопланктона часто можно установить прямое соответствие между неоднородностью его распределения и физическими (абиотическими) факторами среды как по вертикали (явления в термоклине, конвективный перенос, апвеллинг) [16], так и по горизонтали (воздействие ветра, фронты и синоптические вихри) [17][18][19][20][21].…”