Single Turnover Active Fluorometry of Enclosed Samples for Autonomous Phytoplankton Productivity (STAFES-APP)

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Primary production by unicellular photosynthetic organisms, collectively called phytoplankton, is a crucial component of oceanic ecosystems and the biogeochemical cycling of carbon in the oceans. Moreover phytoplankton are responsible for around half the photosynthesis on Earth and hence their activity is also a major component of the global carbon cycle. Current techniques and technologies for the measurement of phytoplankton primary production inadequately resolve many of the spatio-temporal scales over which this crucial ecosystem and biogeochemical process varies, limiting our understanding and ability to model the dynamics of this process now and in the future. Moreover all currently available measurement techniques for primary production are prone to considerable methodological errors, including protocol dependent variability (precision) and differences between techniques concerning what precisely they measure and how well the measure it (accuracy). The ability to measure phytoplankton productivity in situ in the ocean using robotic observation platforms, so-called marine autonomous systems (MAS), would represent a step change in our ability to monitor and understand phytoplankton productivity from some of the smallest scales of variability up to the oceanic basin scales which represent some of the largest ecosystems and greatest ecological gradients on the planet. The current proposal thus aims to develop a MAS deployable system for the measurement of phytoplankton primary production. Autonomous measurements of phytoplankton primary production represent a considerable challenge, as the majority of techniques currently available cannot readily be adapted to MAS observational platforms. In this proposal we propose to take advantage of a useful characteristic of phytoplankton to provide the means to measure primary production. Specifically, a proportion of any light shone onto the green pigment chlorophyll, which is a fundamental component of the photosynthetic apparatus, will be re-emitted as fluorescence at a distinct wavelength. The intensity and dynamics of this emitted fluorescence can be quantitatively related to the amount of photosynthesis taking place. Consequently, through the careful design of measurement systems, protocols and data analysis techniques it is possible to derive the rate of photosynthesis using the fluorescence which is emitted as a by-product of the process. Use of such techniques has been investigated for a number of decades. However it is only recently that both enhanced technological capabilities, including reduced power requirements and high quality multi-spectral optics, combined with improved theoretical understanding, including new measurement and data analysis protocols, have combined to put us in a position where we can realistically employ such 'active chlorophyll fluorescence' as a robust autonomous measure of phytoplankton primary production. We thus aim to design, build, test, deploy and verify a novel measurement system which takes advantage of these advances to facilitate new measurements of phytoplankton productivity across multiple platforms and in the address of wide-ranging scientific challenges.