scholarly journals Mixing and Phytoplankton Growth in an Upwelling System

2021 ◽  
Vol 8 ◽  
Author(s):  
Antonio Comesaña ◽  
Bieito Fernández-Castro ◽  
Paloma Chouciño ◽  
Emilio Fernández ◽  
Antonio Fuentes-Lema ◽  
...  
Keyword(s):  
Time Scales ◽  
Turbulent Mixing ◽  
Phytoplankton Bloom ◽  
Mixed Layer Depth ◽  
Phytoplankton Growth ◽  
Control Factor ◽  
Upwelling System ◽  
Dissolved Inorganic Nutrients ◽  
Bloom Formation ◽  
Ría De Vigo

Previous studies focused on understanding the role of physical drivers on phytoplankton bloom formation mainly used indirect estimates of turbulent mixing. Here we use weekly observations of microstructure turbulence, dissolved inorganic nutrients, chlorophyll a concentration and primary production carried out in the Ría de Vigo (NW Iberian upwelling system) between March 2017 and May 2018 to investigate the relationship between turbulent mixing and phytoplankton growth at different temporal scales. In order to interpret our results, we used the theoretical framework described by the Critical Turbulent Hypothesis (CTH). According to this conceptual model if turbulence is low enough, the depth of the layer where mixing is active can be shallower than the mixed-layer depth, and phytoplankton may receive enough light to bloom. Our results showed that the coupling between turbulent mixing and phytoplankton growth in this system occurs at seasonal, but also at shorter time scales. In agreement with the CTH, higher phytoplankton growth rates were observed when mixing was low during spring-summer transitional and upwelling periods, whereas low values were described during periods of high mixing (fall-winter transitional and downwelling). However, low mixing conditions were not enough to ensure phytoplankton growth, as low phytoplankton growth was also found under these circumstances. Wavelet spectral analysis revealed that turbulent mixing and phytoplankton growth were also related at shorter time scales. The higher coherence between both variables was found in spring-summer at the ~16–30 d period and in fall-winter at the ~16–90 d period. These results suggest that mixing could act as a control factor on phytoplankton growth over the seasonal cycle, and could be also involved in the formation of occasional short-lived phytoplankton blooms.

scholarly journals Numerical simulations of the competition between wind-driven mixing and surface heating in triggering spring phytoplankton blooms

2015 ◽  
Vol 72 (6) ◽  
pp. 1926-1941 ◽  
Author(s):  
Rica Mae Enriquez ◽  
John R. Taylor
Keyword(s):  
Heat Flux ◽  
Critical Heat Flux ◽  
Mixed Layer ◽  
Turbulent Mixing ◽  
Phytoplankton Bloom ◽  
Mixed Layer Depth ◽  
Phytoplankton Growth ◽  
Surface Heating ◽  
Surface Mixed Layer ◽  
Critical Depth

Abstract About 60 years ago, Sverdrup formalized the critical depth hypothesis to explain the timing of the spring phytoplankton bloom in terms of the depth of the surface mixed layer. In recent years, a number of refinements and alternatives to the critical depth hypothesis have been proposed, including the critical turbulence hypothesis which states that a bloom can occur when turbulent mixing is sufficiently weak, irrespective of the mixed layer depth. Here, we examine the relative influence of wind-driven mixing and net surface heating on phytoplankton growth. Of particular interest is whether wind-driven mixing can delay the spring bloom after winter convection gives way to net surface warming. We address these questions using high-resolution large-eddy simulations (LES) coupled with a simple phytoplankton model. We also describe an analytical phytoplankton model with a formulation for the turbulent mixing based on the LES results. For a constant, prescribed surface heat flux, net phytoplankton growth is seen when the windstress is smaller than a critical value. Similarly, for a constant windstress, a critical heat flux separates cases with growing and decaying phytoplankton populations. Using the LES results, we characterize the critical windstress and critical heat flux in terms of other physical and biological parameters and propose a simple expression for each based on the analysis of the analytical model. Phytoplankton growth begins when the mixing depth shoals above the critical depth, consistent with the critical depth hypothesis. Our results provide a framework to interpret blooms in other conditions where both the depth and the intensity of turbulent mixing might be crucial factors in influencing phytoplankton growth.

scholarly journals Phytoplankton blooms on the western shelf of Tasmania: evidence of a highly productive ecosystem

Ocean Science ◽  
2015 ◽  
Vol 11 (1) ◽  
pp. 1-11 ◽  
Author(s):  
J. Kämpf
Keyword(s):  
Satellite Data ◽  
Coastal Upwelling ◽  
Phytoplankton Bloom ◽  
Hot Spot ◽  
Marine Ecosystem ◽  
Austral Summer ◽  
Phytoplankton Blooms ◽  
Study Region ◽  
Upwelling System ◽  
Fluorescence Line

Abstract. Satellite-derived chlorophyll a data using the standard NASA-OC3 (ocean colour) algorithm are strongly biased by coloured dissolved organic matter and suspended sediment of river discharges, which is a particular problem for the western Tasmanian shelf. This work reconstructs phytoplankton blooms in the study region using a quadratic regression between OC3 data and chlorophyll fluorescence based on the fluorescence line height (FLH) data. This regression is derived from satellite data of the nearby Bonney upwelling region, which is devoid of river influences. To this end, analyses of 10 years of MODIS-aqua satellite data reveal the existence of a highly productive ecosystem on the western Tasmanian shelf. The region normally experiences two phytoplankton blooms per annum. The first bloom occurs during late austral summer months as a consequence of upwelling-favourable coastal winds. Hence, the western Tasmanian shelf forms a previously unknown upwelling centre of the regional upwelling system, known as Great South Australian Coastal Upwelling System. The second phytoplankton bloom is a classical spring bloom also developing in the adjacent Tasman Sea. The author postulates that this region forms another important biological hot spot for the regional marine ecosystem.

scholarly journals Saharan Dust Deposition May Affect Phytoplankton Growth in the Mediterranean Sea at Ecological Time Scales

PLoS ONE ◽  
2014 ◽  
Vol 9 (10) ◽  
pp. e110762 ◽  
Author(s):  
Rachele Gallisai ◽  
Francesc Peters ◽  
Gianluca Volpe ◽  
Sara Basart ◽  
José Maria Baldasano
Keyword(s):  
Mediterranean Sea ◽  
Time Scales ◽  
Phytoplankton Growth ◽  
Saharan Dust ◽  
Dust Deposition ◽  
The Mediterranean

scholarly journals Phytoplankton bloom phenomena in the North Atlantic Ocean and Arabian Sea

2015 ◽  
Vol 72 (6) ◽  
pp. 2021-2028 ◽  
Author(s):  
John F. Marra ◽  
Tommy D. Dickey ◽  
Albert J. Plueddemann ◽  
Robert A. Weller ◽  
Christopher S. Kinkade ◽  
...  
Keyword(s):  
Water Column ◽  
Mixed Layer ◽  
Arabian Sea ◽  
Phytoplankton Bloom ◽  
Mixed Layer Depth ◽  
Ocean Dynamics ◽  
Layer Depth ◽  
Diurnal Variability ◽  
Water Column Stratification ◽  
Iceland Basin

Abstract We review bio-optical and physical data from three mooring experiments, the Marine Light–Mixed Layers programme in spring 1989 and 1991 in the Iceland Basin (59°N/21°W), and the Forced Upper Ocean Dynamics Experiment in the central Arabian Sea from October 1994 to 1995 (15.5°N/61.5°E). In the Iceland Basin, from mid-April to mid-June in 1989, chlorophyll-a concentrations are sensitive to small changes in stratification, with intermittent increases early in the record. The spring increase occurs after 20 May, coincident with persistent water column stratification. In 1991, the bloom occurs 2 weeks earlier than in 1989, with a background of strong short-term and diurnal variability in mixed layer depth and minimal horizontal advection. In the Arabian Sea, the mixing response to the northeast and southwest monsoons, plus the response to mesoscale eddies, produces four blooms over the annual cycle. The mixed layer depth in the Arabian Sea never exceeds the euphotic zone, allowing interactions between phytoplankton and grazer populations to become important. For all three mooring experiments, change in water column stratification is key in producing phytoplankton blooms.

A Model-Based Assessment and Design of a Tropical Indian Ocean Mooring Array

2007 ◽  
Vol 20 (13) ◽  
pp. 3269-3283 ◽  
Author(s):  
Peter R. Oke ◽  
Andreas Schiller
Keyword(s):  
Indian Ocean ◽  
Interannual Variability ◽  
Time Scales ◽  
Ocean Circulation ◽  
Mixed Layer Depth ◽  
Intraseasonal Variability ◽  
Circulation Model ◽  
Tropical Indian Ocean ◽  
Empirical Orthogonal Functions ◽  
Analysis System

Abstract A series of observing system simulation experiments (OSSEs) are performed for the tropical Indian Ocean (±15° from the equator) using a simple analysis system. The analysis system projects an array of observations onto the dominant empirical orthogonal functions (EOFs) derived from an intermediate-resolution (2° × 0.5°) ocean circulation model. This system produces maps of the depth of the 20°C isotherm (D20), representing interannual variability, and the high-pass-filtered mixed layer depth (MLD), representing intraseasonal variability. The OSSEs are designed to assess the suitability of the proposed Indian Ocean surface mooring array for resolving intraseasonal to interannual variability. While the proposed array does a reasonable job of resolving the interannual time scales, it may not adequately resolve the intraseasonal time scales. A procedure is developed to rank the importance of observation locations by determining the observation array that best projects onto the EOFs used in the analysis system. OSSEs using an optimal array clearly outperform the OSSEs using the proposed array. The configuration of the optimal array is sensitive to the number of EOFs considered. The optimal array is also different for D20 and MLD, and depends on whether fixed observations are included that represent an idealized Argo array. Therefore, a relative frequency map of observation locations identified in 24 different OSSEs is compiled and a single, albeit less optimal, array that is referred to as a consolidated array is objectively determined. The consolidated array reflects the general features of the individual optimal arrays derived from all OSSEs. It is found that, in general, observations south of 8°S and off of the Indonesian coast are most important for resolving the interannual variability, while observations a few degrees south of the equator, and west of 75°E, and a few degrees north of the equator, and east of 75°E, are important for resolving the intraseasonal variability. In a series of OSSEs, the consolidated array is shown to outperform the proposed array for all configurations of the analysis system for both D20 and MLD.

Modelling the Initiation of Spring Phytoplankton Blooms: a Synthesis of Physical and Biological Interannual Variability off Southwest Nova Scotia, 1983–85

1989 ◽  
Vol 46 (S1) ◽  
pp. s183-s199 ◽  
Author(s):  
R. Ian Perry ◽  
Peter C. F. Hurley ◽  
Peter C. Smith ◽  
J. Anthony Koslow ◽  
Robert O. Fournier
Keyword(s):  
Nova Scotia ◽  
Mixed Layer ◽  
Phytoplankton Bloom ◽  
Mixed Layer Depth ◽  
Critical Value ◽  
Zooplankton Biomass ◽  
Phytoplankton Production ◽  
Spring Phytoplankton Bloom ◽  
Turbulent Dissipation ◽  
Differential Advection

Chlorophyll and nitrate data from monthly surveys off southwest Nova Scotia indicate the spring phytoplankton bloom began near the end of March of each year, occurring early (late) in 1984 (1983). The highest chlorophyll biomass(all months) was found in 1985. Using survey data, the Sverdrup hypothesis for the initiation of the bloom was tested by comparing the critical depth, Zcr, for net phytoplankton production to the observed mixed-layer depth, Zmix. Survey median Zcr/Zmix were consistently less than 1 until May, suggesting that observed blooms were initiated by events outside the specific survey periods. Results of a mixed-layer model incorporating surface heating, differential advection and turbulent dissipation by wind and tide showed reasonable agreement with observed mixed depths, and patterns of the mean (modelled) mixed-layer light intensity are significantly correlated with observed chlorophyll biomass. In 1983 and 1984, mean light intensities first exceeded the critical value for a bloom to occur in late March. In 1985, transient periods of stratification in mid-February and early March produced intensities greater than the critical value. These events, together with higher nitrate concentrations and lower Zooplankton biomass, appear to be responsible for the high chlorophyll biomass observed in 1985.

scholarly journals The importance of phytoplankton trait variability in spring bloom formation

2015 ◽  
Vol 72 (6) ◽  
pp. 1908-1915 ◽  
Author(s):  
Aleksandra M. Lewandowska ◽  
Maren Striebel ◽  
Ulrike Feudel ◽  
Helmut Hillebrand ◽  
Ulrich Sommer
Keyword(s):  
Spring Bloom ◽  
Phytoplankton Bloom ◽  
High Growth ◽  
Phytoplankton Blooms ◽  
Mixing Processes ◽  
Bloom Formation ◽  
Alternative Hypotheses ◽  
Phytoplankton Traits ◽  
Trait Variability

Abstract About 60 years ago, the critical depth hypothesis was proposed to describe the occurrence of spring phytoplankton blooms and emphasized the role of stratification for the timing of onset. Since then, several alternative hypotheses appeared focusing on the role of grazing and mixing processes such as turbulent convection or wind activity. Surprisingly, the role of community composition—and thus the distribution of phytoplankton traits—for bloom formation has not been addressed. Here, we discuss how trait variability between competing species might influence phytoplankton growth during the onset of the spring bloom. We hypothesize that the bloom will only occur if there are species with a combination of traits fitting to the environmental conditions at the respective location and time. The basic traits for formation of the typical spring bloom are high growth rates and photoadaptation to low light conditions, but other traits such as nutrient kinetics and grazing resistance might also be important. We present concise ideas on how to test our theoretical considerations experimentally. Furthermore, we suggest that future models of phytoplankton blooms should include both water column dynamics and variability of phytoplankton traits to make realistic projections instead of treating the phytoplankton bloom as an aggregate community phenomenon.

scholarly journals An investigation of grazing behaviors that result in winter phytoplankton biomass accumulation

2020 ◽  
Author(s):  
Mara Freilich ◽  
Alexandre Mignot ◽  
Glenn Flierl ◽  
Raffaele Ferrari
Keyword(s):  
North Atlantic ◽  
Phytoplankton Biomass ◽  
Phytoplankton Bloom ◽  
Biomass Accumulation ◽  
Grazing Pressure ◽  
Mathematical Framework ◽  
Phytoplankton Concentration ◽  
The North ◽  
Bloom Formation ◽  
The North Atlantic

Abstract. Recent observations have shown that phytoplankton biomass increases in the North Atlantic during winter, even when the mixed layer is deepening and light is limited. Current theories suggest that this is due to a release from grazing pressure. Here we demonstrate that the often-used grazing models that are linear at low phytoplankton concentration do not allow for a wintertime increase in phytoplankton biomass. However, certain mathematical formulations of grazing that are quadratic (or more generally non-linear) in phytoplankton concentration at low concentrations can reproduce the fall to spring transition in phytoplankton, including wintertime biomass accumulation. We illustrate this point with a minimal model for the annual cycle of North Atlantic phytoplankton designed to simulate phytoplankton concentration as observed by BioGeoChemical-Argo (BGC-Argo) floats in the North Atlantic. This analysis provides a mathematical framework for assessing hypotheses of phytoplankton bloom formation.

scholarly journals The significance of nitrogen regeneration for new production within a filament of the Mauritanian upwelling system

2015 ◽  
Vol 12 (21) ◽  
pp. 17781-17816
Author(s):  
D. R. Clark ◽  
C. E. Widdicombe ◽  
A. P. Rees ◽  
E. M. S. Woodward
Keyword(s):  
Continental Shelf ◽  
Primary Productivity ◽  
Mixed Layer Depth ◽  
Nutrient Concentrations ◽  
New Production ◽  
Phytoplankton Productivity ◽  
Upwelling System ◽  
Upwelled Water ◽  
Shelf Slope ◽  
N Assimilation

Abstract. The lagrangian progression of biogeochemical processes was followed in a filament of the Mauritanian upwelling system, North West Africa, during offshore advection. Inert duel tracers sulphur hexafluoride and helium-3 labelled a freshly upwelled patch of water that was mapped for 8 days. Changes in biological, physical and chemical characteristics were measured including phytoplankton productivity, nitrogen assimilation and regeneration. Freshly upwelled water contained high nutrient concentrations (NO3− = 9.0 ± 0.1 μmol L−1; PO43− = 0.7 ± 0.1 μmol L−1; Si = 2.7 ± 0.1 μmol L−1) but was depleted in N compared to Redfield stoichiometry (N:P = 13.9:1). A maximum primary productivity rate of 0.7 mol C m−2 d−1 was measured on the continental shelf, associated with N-assimilation rates of 43.8 nmol L−1 h−1 for NO3−, 32.8 nmol L−1 h−1 for NH4+ and a phytoplankton community dominated by diatoms and flagellates. Indicators of phytoplankton abundance and activity decreased as the labelled water mass transited the continental shelf slope into deeper water, possibly linked to the mixed layer depth exceeding the light penetration depth. By the end of the study, primary productivity rates of 0.1 mol C m−2 d−1 were measured, associated with N-assimilation rates of 3.9 nmol L−1 h−1 for NO3−, 6.1 nmol L−1 h−1 for NH4+ and lower nutrient concentrations (NO3− = 4.6 ± 0.3 μmol L−1; PO43− = 0.4 ± 0.1 μmol L−1; Si = 0.9 ± 0.1 μmol L−1). Nitrogen regeneration and assimilation took place simultaneously; NH4+ was regenerated at 9.4–85.0 nmol L−1 h−1; NH4+ was oxidised at 0.30–8.75 nmol L−1 h−1; NO2− was oxidised at 25.55–81.11 nmol L−1 h−1. Results highlight the importance of regenerated NH4+ in sustaining phytoplankton productivity and indicate that the upwelled NO3− pool contained an increasing fraction of regenerated NO3− as it advected offshore. By calculating this fraction and incorporating it into an f ratio formulation we estimated that of the 12.38 Tg C of annual regional production, 4.73 Tg C was exportable.

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