Modelling the effect of vertical mixing on bottle incubations for determining in situ phytoplankton dynamics. II. Primary production

Abstract

C) during the incubation period (typically 24 h). One of the main concerns with using fixed-depth bottle incubations is whether stranding samples at fixed depths biases the measured CO 2 fixation relative to the 'true' in situ mixed conditions. Here we employ an individual based turbulence and photosynthesis model, which also accounts for photoacclimation and -inhibition, to examine whether the in vitro productivity estimates obtained from fixed-depth incubations are representative of the in situ productivity in a freely mixing water column. While previous work suggested that in vitro estimates could either over-or underestimate the in situ productivity, we show that the errors due to arresting the incubation bottles at fixed depths are indeed minimal. We present possible explanations for how previous authors could have arrived at contradictory results and discuss whether they might be artefacts related to the particular sampling protocol used. We discuss the errors associated with chlorophyll-based incubation methods for determining in situ phytoplankton growth rates in Ross et al. (2011; Mar Ecol Prog Ser 435:13-31).

An optimality model of photoadaptation in contrasting aquatic light regimes

“…8). Moore et al (2006) suggested high E k indicates acclimation to irradiance above the average growth irradiance, but there has been some debate regarding the depth to which cells in well-mixed regimes are acclimated Moore et al 2006;Ross et al 2011). Our results indicate that in dynamic environments, optimal resource allocation to light harvesting and corresponding Chl : C both decrease with increasing ILD (Figs.…”

“…Resources allocated to carbon fixation influence the capacity of the cell to accumulate energy and carbon reserves in the form of lipid and carbohydrate (Ross and Geider 2009). Energy fixed in reserve polymers can be used to fuel growth in low light or darkness.…”

“…Through their role in carbon fixation, Calvin cycle enzymes are required for storage of energy and carbon in stable organic compounds (e.g., sugars and ultimately starch and lipids) when cells are transiently subjected to optimal and supraoptimal irradiances (Ross and Geider 2009). Solutions to optimal resource allocation models under conditions of constant irradiance do not account for the need to store energy in dynamic light environments.…”

Spectral irradiance dependence of sunlight effects on plankton dimethylsulfide production

“…Due to the spectral dependence of underwater light attenuation, an increase in total irradiance caused by shallow mixing will be accompanied by increasing proportions of shortwave UVR. The dynamic nature of light exposure is still poorly resolved in experimental settings, and its biogeochemical consequences are not well understood (Bertoni et al 2011;Ross et al 2011). Our experimental setup, while not totally realistic, provided a first approximation towards understanding the photobiological bases of some DMS production pathways.…”

Differential response of planktonic primary, bacterial, and dimethylsulfide production rates to static vs. dynamic light exposure in upper mixed-layer summer sea waters

“…The fact that all experiments took place in soft wind conditions, and the relatively high values of the buoyancy (Brunt-Väisälä) frequency within the UML suggest that it was not mixing actively at the time of the CTD casts (Table 1). If we assume that vertical diffusivity (K z ) in the UML interior was in the range 10 −2 -10 −4 m 2 s −1 (Denman and Gargett, 1983;Ross et al, 2011b), it would take ca. 0.25 to 100 h for a population of particles released at a single depth to diffuse across one optical depth in the UML depending on the wavelengths and MLD considered (Gallegos and Platt, 1985).…”