Autonomous oceanic primary production through novel chlorophyll fluorometry

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Oceanic phytoplankton are responsible for approximately half the primary production on Earth. These microbes hence constitute both the base of the marine food-chain and a crucial component of the planetary biogeochemical cycles of carbon and nutrients. Phytoplankton primary production varies widely across the oceans from spatial scales of a few km associated with physical phenomena such as fronts and eddies, to the strong gradients observed across whole ocean basins. Moreover, phytoplankton photosynthetic rates respond to environmental forcing in the form of light and nutrient availability at sub-daily through to climatic time scales. However, our understanding of this spatio-temporal variability in phytoplankton photosynthesis is severely hampered by extreme under-sampling of marine systems, which ultimately limits confidence in our best estimates of the magnitude of oceanic productivity. Active chlorophyll fluorometry represents a groundbreaking technology with the potential to overcome this sampling problem through facilitating high quality in situ measurements of photosynthetic rates; especially if such instrumentation can be developed to the point where it can be deployed routinely on autonomous observational platforms. Currently available instrumentation is inadequate for this purpose. This PhD project aims to fill this crucial technological gap, facilitating improved understanding of the variability of oceanic photosynthesis across unprecedented scales.