Single-Turnover Variable Chlorophyll Fluorescence as a Tool for Assessing Phytoplankton Photosynthesis and Primary Productivity: Opportunities, Caveats and Recommendations

Phytoplankton photosynthetic physiology can be investigated through single-turnover variable chlorophyll fluorescence (ST-ChlF) approaches, which carry unique potential to autonomously collect data at high spatial and temporal resolution. Over the past decades, significant progress has been made in the development and application of ST-ChlF methods in aquatic ecosystems, and in the interpretation of the resulting observations. At the same time, however, an increasing number of sensor types, sampling protocols, and data processing algorithms have created confusion and uncertainty among potential users, with a growing divergence of practice among different research groups. In this review, we assist the existing and upcoming user community by providing an overview of current approaches and consensus recommendations for the use of ST-ChlF measurements to examine in-situ phytoplankton productivity and photo-physiology. We argue that a consistency of practice and adherence to basic operational and quality control standards is critical to ensuring data inter-comparability. Large datasets of inter-comparable and globally coherent ST-ChlF observations hold the potential to reveal large-scale patterns and trends in phytoplankton photo-physiology, photosynthetic rates and bottom-up controls on primary productivity. As such, they hold great potential to provide invaluable physiological observations on the scales relevant for the development and validation of ecosystem models and remote sensing algorithms

CT-LaSTAF continous FLC from AMT29 in 2019

<p><strong>AMT29 / DY110</strong></p><p><strong>Nov / Dec 2019</strong></p><p><strong>Atlantic Ocean </strong></p><p>See also: <a href="https://www.amt-uk.org/">https://www.amt-uk.org/</a></p><p>AMT29 in Nov/Dec 2019 was the first field deployment of LabSTAF, consequently not all functions were running as they do in the present instrument, most notably there was no automated acquisition of photosynthetic excitation profiles and associated spectral correction of data.</p><p>DWM measurements were run automatically, but no PEC correction applied to the data.</p><p>The instrument was run in continuous FLC mode along the entire transect, the FLC are 'static'.</p><p>The folder <strong>raw_rsf</strong> contains the rsf files acquired with timestamp in UTC.</p><p>Blanks of MQ and 0.2um filtrate were run daily.</p><p>The folder <strong>auxiliary</strong> contains the cruise report, the cruisetrack, the troubleshoot log, the blank measurements, and the setting files used. As outlined in the cruise report, many auxiliary parameters (nutrients, particulate absorption, HPLC pigments, 14C-based and O2-based primary production, in line and above water optics) were measured.</p><p> </p><p> </p&gt

On the light and iron dependent coupling of carbon fixation and photosynthetic electron transport in Arctic and Subarctic marine phytoplankton

Marine phytoplankton primary productivity, the photosynthetic conversion of CO₂ into organic carbon by microscopic photosynthetic algae in the surface ocean, plays a fundamental role in ecosystem dynamics and global biogeochemical cycles. Consequently, the ability to accurately measure, monitor and predict environmental influences on this process over a range of spatial and temporal scales is crucial. The work presented in this thesis evaluates the application of fast repetition rate fluorometry (FRRF) for instantaneous, high resolution estimates of phytoplankton primary productivity. Results from both laboratory experiments and field work in Arctic and Subarctic marine waters show that the conversion factor required to derive carbon-based primary productivity estimates from FRRF-derived rates of electron transport in photosystem II (ETR) varies significantly in response to the interacting effects of iron and light availability (Chapter 2), over diurnal cycles (Chapter 3), and in response to nitrogen and light availability under low temperatures (Chapter 4). At a photo-physiological level, a high conversion factor is observed under conditions of excess excitation energy, where the amount of light energy absorbed in the pigment antenna exceeds the capacity for downstream metabolic processes, i.e. carbon fixation. Phytoplankton employ numerous mechanisms to alleviate excess excitation energy after charge separation, and these processes are postulated to be responsible for the increased de-coupling of ETR and carbon fixation. Consistent with this hypothesis, a strong correlation was observed between the derived conversion factor and the dissipation of excess excitation energy before charge separation, which can be estimated as non-photochemical quenching (NPQ). Because NPQ can be estimated from FRRF measurements, it can be used as a proxy for the magnitude and variability of the conversion factor between carbon fixation and ETR, and this approach holds potential to significantly improve carbon-based primary productivity estimates from FRRF measurements. The work presented in this thesis advances our understanding of the coupling between light absorption, photo-chemistry, and carbon fixation in response to various environmental gradients. The experimental approach taken demonstrates how an appreciation of photo-physiological processes of photosynthesis is critical for improved estimates of phytoplankton primary productivity at regional scales.Science, Faculty ofEarth, Ocean and Atmospheric Sciences, Department ofGraduat

Compensation of ocean acidification effects in Arctic phytoplankton assemblages

The Arctic and subarctic shelf seas, which sustain large fisheries and contribute to global biogeochemical cycling, are particularly sensitive to ongoing ocean acidification (that is, decreasing seawater pH due to anthropogenic CO2 emissions). Yet, little information is available on the effects of ocean acidification on natural phytoplankton assemblages, which are the main primary producers in high-latitude waters. Here we show that coastal Arctic and subarctic primary production is largely insensitive to ocean acidification over a large range of light and temperature levels in different experimental designs. Out of ten CO2-manipulation treatments, significant ocean acidification effects on primary productivity were observed only once (at temperatures below 2 °C), and shifts in the species composition occurred only three times (without correlation to specific experimental conditions). These results imply a high capacity to compensate for environmental variability, which can be understood in light of the environmental history, tolerance ranges and intraspecific diversity of the dominant phytoplankton species

High latitude Southern Ocean phytoplankton have distinctive bio-optical properties

Abstract: Studying the biogeochemistry of the Southern Ocean using remote sensing relies on accurate interpretation of ocean colour through bio-optical and biogeochemical relationships between quantities and properties of interest. During the Antarctic Circumnavigation Expedition of the 2016/2017Austral Summer,we collected a spatially comprehensive dataset of phytoplankton pigment concentrations, particulate absorption and particle size distribution and compared simple bio-optical and particle property relationships as a function of chlorophyll a. Similar to previous studies we find that the chlorophyll-specific phytoplankton absorption coefficient is significantly lower than in other oceans at comparable chlorophyll concentrations. This appears to be driven in part by lower concentrations of accessory pigments per unit chlorophyll a as well as increased pigment packaging due to relatively larger sized phytoplankton at low chlorophyll a than is typically observed in other oceans. We find that the contribution of microphytoplankton (>20 μm size) to chlorophyll a estimates of phytoplankton biomass is significantly higher than expected for the given chlorophyll a concentration, especially in higher latitudes south of the Southern Antarctic Circumpolar Current Front. Phytoplankton pigments are more packaged in larger cells, which resulted in a flattening of phytoplankton spectra as measured in these samples when compared to other ocean regions with similar chlorophyll a concentration. Additionally, we find that at high latitude locations in the Southern Ocean, pheopigment concentrations can exceed mono-vinyl chlorophyll a concentrations. Finally, we observed very different relationships between particle volume and chlorophyll a concentrations in high and low latitude Southern Ocean waters, driven by differences in phytoplankton community composition and acclimation to environmental conditions and varying contribution of non-algal particles to the particulate matter. Our data confirm that, as previously suggested, the relationships between bio-optical properties and chlorophyll a in the Southern Ocean are different to other oceans. In addition, distinct bio-optical properties were evident between high and low latitude regions of the Southern Ocean basin. Here we provide a region-specific set of power law functions describing the phytoplankton absorption spectrum as a function of chlorophyll a

Diel quenching of Southern Ocean phytoplankton fluorescence is related to iron limitation

Evaluation of photosynthetic competency in time and space is critical for better estimates and models of oceanic primary productivity. This is especially true for areas where the lack of iron (Fe) limits phytoplankton productivity, such as the Southern Ocean. Assessment of photosynthetic competency on large scales remains challenging, but phytoplankton chlorophyll a fluorescence (ChlF) is a signal that holds promise in this respect as it is affected by, and consequently provides information about, the photosynthetic efficiency of the organism. A second process affecting the ChlF signal is heat dissipation of absorbed light energy, referred to as non-photochemical quenching (NPQ). NPQ is triggered when excess energy is absorbed, i.e. when more light is absorbed than can be used directly for photosynthetic carbon fixation. The effect of NPQ on the ChlF signal complicates its interpretation in terms of photosynthetic efficiency, and therefore most approaches relating ChlF parameters to photosynthetic efficiency seek to minimize the influence of NPQ by working under conditions of sub-saturating irradiance. Here, we propose that NPQ itself holds potential as an easily acquired optical signal indicative of phytoplankton physiological state with respect to Fe limitation. We present data from a research voyage to the Subantarctic Zone south of Australia. Incubation experiments confirmed that resident phytoplankton were Fe-limited, as the maximum quantum yield of primary photochemistry, F-v/F-m, measured with a fast repetition rate fluorometer (FRRf), increased significantly with Fe addition. The NPQ "capacity" of the phytoplankton also showed sensitivity to Fe addition, decreasing with increased Fe availability, confirming previous work. The fortuitous presence of a remnant warm-core eddy in the vicinity of the study area allowed comparison of fluorescence behaviour between two distinct water masses, with the colder water showing significantly lower F-v/F-m than the warmer eddy waters, suggesting a difference in Fe limitation status between the two water masses. Again, NPQ capacity measured with the FRRf mirrored the behaviour observed in F-v/F-m, decreasing as F-v/F-m increased in the warmer water mass. We also analysed the diel quenching of underway fluorescence measured with a standard fluorometer, such as is frequently used to monitor ambient chlorophyll a concentrations, and found a significant difference in behaviour between the two water masses. This difference was quantified by defining an NPQ parameter akin to the Stern-Volmer parameterization of NPQ, exploiting the fluorescence quenching induced by diel fluctuations in incident irradiance. We propose that monitoring of this novel NPQ parameter may enable assessment of phytoplankton physiological status (related to Fe availability) based on measurements made with standard fluorometers, as ubiquitously used on moorings, ships, floats and gliders