Single-Turnover Variable Chlorophyll Fluorescence as a Tool for Assessing Phytoplankton Photosynthesis and Primary Productivity

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

This paper argues 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.

Conclusion: Single-turnover variable chlorophyll fluorescence methods provide a powerful tool for high resolution photo-physiological measurements, with significant potential to examine aquatic productivity and its environmental controls over a range of spatial and temporal scales. Recent advances in instrumentation and data analysis are now beginning to significantly expand the application of ST-ChlF methods to a range of research questions. As the field continues to expand, it is essential to promote global coordination in the development of best practice, using flexible, open-source tools to disseminate information, software, and data products. Through the application of consensus recommendations, and a robust system of documenting user-specific protocols, inter-comparison among emerging datasets will be greatly facilitated. This, in turn, will enable the synthesis of synoptic ST-ChlF observations at global scales, providing new insights into the response of marine productivity to a range of perturbations.

The UN Decade of Ocean Science for Sustainable Development (2021–2030) alongside the UN Sustainable Development Goals 6 and 14 (dealing with clean and productive inland and marine waters, respectively) will provide the opportunity to revolutionize the collection, storage, and analysis of ocean data, leading to better understanding of global-scale patterns in key ocean properties and their response to various environmental factors. ST-ChlF-derived observations are important supplements to existing observations that represent phytoplankton standing stocks. Current advances in automation of measurements will enable data compilations at unprecedented resolution in both time and space. Such data will provide information on physical-biological coupling, including the impacts of localized hydrographic fronts, river plumes, and glacial discharge. At larger scales, regional patterns of phytoplankton physiology can be examined in relation to climate forcing, providing empirical correlations and mechanistic understanding for the improvement of ecosystem models, and remote sensing algorithms. Through concerted international cooperation, we are confident that the expansion of ST-ChlF measurements will significantly advance our understanding of global aquatic ecosystems.

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

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