Light fluctuations are key in modulating plankton trophic dynamics and their impact on primary production

Morison, Françoise; Franzè, Gayantonia; Harvey, Elizabeth L.; Menden‐Deuer, Susanne

doi:10.1002/lol2.10156

Cited by 21 publications

(20 citation statements)

References 42 publications

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“…Last, but not least, this framework ought to be applied to test the predictions of different theories of bloom onset (Verity et al, 1993;Morison et al, 2020;Mojica et al, 2020). While our work pointed out the key role played by the choice of grazing functions in such theories and models, it is important to point out that state of the art Earth System Models often use multispecies ecosystem models (Laufkötter et al, 2015).…”

Section: Discussionmentioning

confidence: 92%

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

Freilich¹,

Mignot

Flierl

et al. 2020

Preprint

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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.

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Section: Discussionmentioning

confidence: 92%

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

Freilich¹,

Mignot

Flierl

et al. 2020

Preprint

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“…New phytoplankton production in the dim sub‐mixed layer following deep mixing is likely underpinned by decreased grazing pressure (Graff and Behrenfeld 2018; Morison et al 2020). The initial consequences of deep mixing are (1) that phytoplankton standing stocks are diluted and separate the grazers from their phytoplankton prey, as posited in the Disturbance‐Recoupling Hypothesis that explains phytoplankton bloom events (Behrenfeld and Boss 2014) and (2) an immediate drop in phytoplankton growth rate (Fig.…”

Section: Discussionmentioning

confidence: 99%

“…S7). This prediction ignores the role of grazers which can quickly establish top‐down control following a disturbance event (Graff and Behrenfeld 2018; Morison et al 2020) and may have prey‐specificities that will impact the phytoplankton composition. Nevertheless, diatoms are often associated with high carbon flux out of the euphotic zone, attributable to their higher sinking rates made possible by the ballast effect of their biomineral frustules and their affinity for aggregation (Klaas and Archer 2002; Moigne et al 2015; Durkin et al 2016).…”

Section: Discussionmentioning

confidence: 99%

“…The ability for phytoplankton to accumulate at depth, following a mixing event, depends on how rapidly the sum of photoacclimation processes (from light harvesting through carbon metabolism) integrate to affect growth in prolonged low light conditions. Recent analyses of a single deep mixing event in the North Atlantic showed that post-mixing plankton communities that were kept in low light increased Chl within about 3 d (Morison et al 2020), but whether those increases in Chl were coupled with growth was less clear (Graff and Behrenfeld 2018).…”

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confidence: 99%

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Rapid photoacclimation during episodic deep mixing augments the biological carbon pump

Penta

Fox

Halsey

2021

Limnology & Oceanography

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Episodic deep mixing events are one component of the biological carbon pump that physically transports organic carbon into the mesopelagic. Episodic deep mixing also disrupts summertime thermal stratification thereby changing the light field and nutrient concentrations available for phytoplankton growth. Phytoplankton survival and growth below the mixed layer following restratification depends on how rapidly cells can employ a variety of photoacclimation processes in response to the environmental changes. To compare the relative timescales of summertime episodic deep mixing events with the timescales of phytoplankton photoacclimation processes, we first analyzed autonomous float data to survey the frequency and magnitude of deep mixing events in the western North Atlantic Ocean. Next, we simulated a sustained deep mixing event in the laboratory and measured rates of acclimation processes ranging from light harvesting to growth in a model diatom and green alga. In both algae increases in chlorophyll (Chl) were coupled to growth, but growth of the green alga lagged the diatom by about a day. In float profiles, significant increases in Chl and phytoplankton carbon (C phyto ) were detected below the mixed layer following episodic deep mixing events. These events pose a previously unrecognized source of new production below the mixed layer that can significantly boost the amount of carbon available for export to the deep ocean.

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“…Vertical fluxes may also be affected by vertical variations of both biological rates and the vertical velocity magnitude (Kahru, 1983). In a multi-species system, the inclusion of cross-fluxes between components will be necessary and will be a source of spatial and temporal variance (Abraham, 1998;Falkowski et al, 1998;Martin and Pondaven, 2003;Morison et al, 2020). Observed variations in community composition may also be a result of ecological interactions but may not alter the net community production (Malone et al, 1993;Giovannoni and Vergin, 2012).…”

Section: Discussionmentioning

confidence: 99%

Vertical fluxes in the upper ocean

Freilich¹

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Oceanic fronts at the mesoscale and submesoscale are associated with enhanced vertical motion, which strengthens their role in global biogeochemical cycling as hotspots of primary production and subduction of carbon from the surface to the interior. Using process study models, theory, and field observations of biogeochemical tracers, this thesis improves understanding of submesoscale vertical tracer fluxes and their influence on carbon cycling. Unlike buoyancy, vertical transport of biogeochemical tracers can occur both due to the movement of isopycnals and due to motion along sloping isopycnals. We decompose the vertical velocity below the mixed layer into two components in a Lagrangian frame: vertical velocity along sloping isopycnal surfaces and the adiabatic vertical velocity of isopycnal surfaces and demonstrate that vertical motion along isopycnal surfaces is particularly important at submesoscales (1-10 km). The vertical flux of nutrient, and consequently the new production of phytoplankton depends not just on the vertical velocity but on the relative time scales of vertical transport and nutrient uptake. Vertical nutrient flux is maximum when the biological timescale of phytoplankton growth matches the vertical velocity frequency. Export of organic matter from the surface and the interior requires water parcels to cross the mixed layer base. Using Lagrangian analysis, we study the dynamics of this process and demonstrate that geostrophic and ageostrophic frontogenesis drive subduction along density surfaces across the mixed layer base. Along-front variability is an important factor in subduction. Both the physical and biological modeling studies described above are used to interpret observations from three research cruises in the Western Mediterranean. We sample intrusions of high chlorophyll and particulate organic carbon below the euphotic zone that are advected downward by 100 meters on timescales of days to weeks. We characterize the community composition in these subsurface intrusions at a lateral resolution of 1–10 km. We observe systematic changes in community composition due to the changing light environment and differential decay of the phytoplankton communities in low-light environments, along with mixing. We conclude that advective fluxes could make a contribution to carbon export in subtropical gyres that is equal to the sinking flux.

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Light fluctuations are key in modulating plankton trophic dynamics and their impact on primary production

Cited by 21 publications

References 42 publications

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

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

Rapid photoacclimation during episodic deep mixing augments the biological carbon pump

Vertical fluxes in the upper ocean

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