scholarly journals Grazing behavior and winter phytoplankton accumulation

2021 ◽  
Vol 18 (20) ◽  
pp. 5595-5607
Author(s):  
Mara Freilich ◽  
Alexandre Mignot ◽  
Glenn Flierl ◽  
Raffaele Ferrari
Keyword(s):  
North Atlantic ◽  
Phytoplankton Biomass ◽  
Phytoplankton Bloom ◽  
Biomass Accumulation ◽  
Grazing Pressure ◽  
Mathematical Framework ◽  
Grazing Behavior ◽  
Phytoplankton Concentration ◽  
The North ◽  
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, mathematical formulations of grazing as a function of phytoplankton concentration that are quadratic at low concentrations (or more generally decrease faster than linearly as phytoplankton concentration decreases) 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 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 Spring bloom onset in the Nordic Seas

2016 ◽  
Vol 13 (11) ◽  
pp. 3485-3502 ◽  
Author(s):  
Alexandre Mignot ◽  
Raffaele Ferrari ◽  
Kjell Arne Mork
Keyword(s):  
North Atlantic ◽  
Spring Bloom ◽  
Large Fraction ◽  
Biomass Accumulation ◽  
Marine Phytoplankton ◽  
The Arctic ◽  
Nordic Seas ◽  
In Situ Data ◽  
The North ◽  
The North Atlantic

Abstract. The North Atlantic spring bloom is a massive annual growth event of marine phytoplankton, tiny free-floating algae that form the base of the ocean's food web and generates a large fraction of the global primary production of organic matter. The conditions that trigger the onset of the spring bloom in the Nordic Seas, at the northern edge of the North Atlantic, are studied using in situ data from six bio-optical floats released north of the Arctic Circle. It is often assumed that spring blooms start as soon as phytoplankton cells daily irradiance is sufficiently abundant that division rates exceed losses. The bio-optical float data instead suggest the tantalizing hypothesis that Nordic Seas blooms start when the photoperiod, the number of daily light hours experienced by phytoplankton, exceeds a critical value, independently of division rates. The photoperiod trigger may have developed at high latitudes where photosynthesis is impossible during polar nights and phytoplankton enters into a dormant stage in winter. While the first accumulation of biomass recorded by the bio-optical floats is consistent with the photoperiod hypothesis, it is possible that some biomass accumulation started before the critical photoperiod but at levels too low to be detected by the fluorometers. More precise observations are needed to test the photoperiod hypothesis.

scholarly journals Basin-wide mechanisms for spring bloom initiation: how typical is the North Atlantic?

2015 ◽  
Vol 72 (6) ◽  
pp. 2029-2040 ◽  
Author(s):  
Harriet S. Cole ◽  
Stephanie Henson ◽  
Adrian P. Martin ◽  
Andrew Yool
Keyword(s):  
Interannual Variability ◽  
Mixed Layer ◽  
North Atlantic ◽  
Spring Bloom ◽  
Phytoplankton Bloom ◽  
Ecosystem Dynamics ◽  
Trophic Levels ◽  
Theoretical Understanding ◽  
The North ◽  
The North Atlantic

Abstract The annual phytoplankton bloom is a key event in pelagic ecosystems. Variability in the timing, or phenology, of these blooms affects ecosystem dynamics with implications for carbon export efficiency and food availability for higher trophic levels. Furthermore, interannual variability in phytoplankton bloom timing may be used to monitor changes in the pelagic ecosystem that are either naturally or anthropogenically forced. The onset of the spring bloom has traditionally been thought to be controlled by the restratification of the water column and shoaling of the mixed layer, as encapsulated in Sverdrup's critical depth hypothesis. However, this has been challenged by recent studies which have put forward different mechanisms. For example, the critical turbulence hypothesis attributes bloom initiation to a reduction in turbulent mixing associated with the onset of positive net heat fluxes (NHFs). To date, the majority of studies on bloom initiation mechanisms have concentrated on North Atlantic datasets leaving their validity in other subpolar regions unknown. Here, we use chlorophyll output from a model that assimilates satellite ocean colour data to calculate bloom initiation timing and examine the basin-wide drivers of spatial and interannual variability. We find that the date that the NHF turns positive is a stronger predictor for the date of bloom initiation, both spatially and interannually, across the North Atlantic than changes in the mixed layer depth. However, results obtained from the North Pacific and Southern Ocean show no such basin-wide coherency. The lack of consistency in the response of the subpolar basins indicates that other drivers are likely responsible for variability in bloom initiation. This disparity between basins suggests that the North Atlantic bloom initiation processes are unique and therefore that this region may not be a suitable model for a global, theoretical understanding of the mechanisms leading to the onset of the spring bloom.

scholarly journals Synoptic-scale analysis of mechanisms driving surface chlorophyll dynamics in the North Atlantic

2015 ◽  
Vol 12 (11) ◽  
pp. 3641-3653 ◽  
Author(s):  
A. S. A. Ferreira ◽  
H. Hátún ◽  
F. Counillon ◽  
M. R. Payne ◽  
A. W. Visser
Keyword(s):  
North Atlantic ◽  
Phytoplankton Bloom ◽  
Initial Increase ◽  
Synoptic Scale ◽  
Spring Phytoplankton Bloom ◽  
Bottom Up ◽  
Common Component ◽  
The North ◽  
The North Atlantic ◽  
Physical Phenomena

Abstract. Several hypotheses have been proposed for the onset of the spring phytoplankton bloom in the North Atlantic. Our main objective is to examine which bottom-up processes can best predict the annual increase in surface phytoplankton concentration in the North Atlantic by applying novel phenology algorithms to ocean colour data. We construct indicator fields and time series which, in various combinations, provide models consistent with the principle dynamics previously proposed. Using a multimodel inference approach, we investigate the evidence supporting these models and how it varies in space. We show that, in terms of bottom-up processes alone, there is a dominant physical mechanism, namely mixed-layer shoaling, that best predicts the interannual variation in the initial increase in surface chlorophyll across large sectors of the North Atlantic. We further show that different regions are governed by different physical phenomena and that wind-driven mixing is a common component, with either heat flux or light as triggers. We believe these findings to be relevant to the ongoing discussion on North Atlantic bloom onset.

scholarly journals Seasonality of the Microbial Community Composition in the North Atlantic

2021 ◽  
Vol 8 ◽  
Author(s):  
Luis M. Bolaños ◽  
Chang Jae Choi ◽  
Alexandra Z. Worden ◽  
Nicholas Baetge ◽  
Craig A. Carlson ◽  
...  
Keyword(s):  
Water Column ◽  
North Atlantic ◽  
Phytoplankton Bloom ◽  
Microbial Community Composition ◽  
Rrna Gene ◽  
The North ◽  
Biogeographical Distribution ◽  
The North Atlantic ◽  
Plankton Communities ◽  
Planktonic Communities

Planktonic communities constitute the basis of life in marine environments and have profound impacts in geochemical cycles. In the North Atlantic, seasonality drives annual transitions in the ecology of the water column. Phytoplankton bloom annually in spring as a result of these transitions, creating one of the major biological pulses in productivity on earth. The timing and geographical distribution of the spring bloom as well as the resulting biomass accumulation have largely been studied using the global capacity of satellite imaging. However, fine-scale variability in the taxonomic composition, spatial distribution, seasonal shifts, and ecological interactions with heterotrophic bacterioplankton has remained largely uncharacterized. The North Atlantic Aerosols and Marine Ecosystems Study (NAAMES) conducted four meridional transects to characterize plankton ecosystems in the context of the annual bloom cycle. Using 16S rRNA gene-based community profiles we analyzed the temporal and spatial variation in plankton communities. Seasonality in phytoplankton and bacterioplankton composition was apparent throughout the water column, with changes dependent on the hydrographic origin. From winter to spring in the subtropic and subpolar subregions, phytoplankton shifted from the predominance of cyanobacteria and picoeukaryotic green algae to diverse photosynthetic eukaryotes. By autumn, the subtropics were dominated by cyanobacteria, while a diverse array of eukaryotes dominated the subpolar subregions. Bacterioplankton were also strongly influenced by geographical subregions. SAR11, the most abundant bacteria in the surface ocean, displayed higher richness in the subtropics than the subpolar subregions. SAR11 subclades were differentially distributed between the two subregions. Subclades Ia.1 and Ia.3 co-occurred in the subpolar subregion, while Ia.1 dominated the subtropics. In the subtropical subregion during the winter, the relative abundance of SAR11 subclades “II” and 1c.1 were elevated in the upper mesopelagic. In the winter, SAR202 subclades generally prevalent in the bathypelagic were also dominant members in the upper mesopelagic zones. Co-varying network analysis confirmed the large-scale geographical organization of the plankton communities and provided insights into the vertical distribution of bacterioplankton. This study represents the most comprehensive survey of microbial profiles in the western North Atlantic to date, revealing stark seasonal differences in composition and richness delimited by the biogeographical distribution of the planktonic communities.

scholarly journals Sensitivity of phytoplankton distributions to vertical mixing along a North Atlantic transect

Ocean Science ◽  
2014 ◽  
Vol 10 (6) ◽  
pp. 993-1011 ◽  
Author(s):  
L. Hahn-Woernle ◽  
H. A. Dijkstra ◽  
H. J. Van der Woerd
Keyword(s):  
North Atlantic ◽  
Light Attenuation ◽  
Vertical Mixing ◽  
Clear Correlation ◽  
Model Parameters ◽  
Chl A ◽  
Phytoplankton Concentration ◽  
In Situ Data ◽  
The North ◽  
The North Atlantic

Abstract. Using in situ data of upper ocean vertical mixing along a transect in the North Atlantic and a one-dimensional phytoplankton growth model, we study the sensitivity of the surface phytoplankton concentration to vertical mixing distributions. The study is divided into two parts. In the first part, the model is calibrated to the observations. The optical model parameters are determined from measurements of the light attenuation. The biological parameters are calibrated to three different reference stations with observed vertical profiles of the chlorophyll a (Chl a) concentration and the nutrient concentration. In the second part, the sensitivity of the three model calibrations to the vertical mixing is studied. Therefore measured vertical mixing profiles are applied to the model. These mixing profiles are based on the measurements along the transect and are treated as a set of possible mixing situations of the North Atlantic. Results show that shifts in vertical mixing are able to induce a transition from an upper chlorophyll maximum to a deep one and vice versa. Furthermore, a clear correlation between the surface phytoplankton concentration and the mixing induced nutrient flux is found for nutrient-limited cases. This may open up the possibility to extract characteristics of vertical mixing from satellite ocean colour data using data-assimilation methods.

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