Periodic Reporting for period 1 - Ocean Glow (Ocean Glow: Controls on ocean productivity using ocean fluorescence detected from space)
Berichtszeitraum: 2022-11-01 bis 2025-04-30
Primary production in the ocean is critically important for human wellbeing—it regulates atmospheric carbon dioxide as well as sustaining almost all ocean life. But models predicting the impacts of climate change do not agree on the sign of ocean primary production in the coming century. Currently, satellite observations tell us how ocean primary productivity is changing, but not the underlying controls. Fieldwork and modelling show nutrient limitation is key, but there is currently no way to observe nutrient limitation at the scales needed to monitor climate change impacts or benchmark the accuracy of models. This project aims to overcome the scaling problem using direct, nutrient-regulated fluorescence signals passively emitted from phytoplankton and detected by satellite sensors in space.
In the Ocean Glow project, we are taking a two-pronged approach to try to break through the current blockage in our understanding of satellite-detected fluorescence signals. In the first prong, a novel laboratory mesocosm facility has been constructed and is being used to quantify the key factors regulating phytoplankton fluorescence emission, in the same way that it is stimulated and detected by satellites. In the second prong we are connecting these experimental results with the real world by undertaking field observations on research cruises through the global ocean. In the final stage of the project we plan to use this ground-based assessment to perform a data-informed deconvolution of the satellite fluorescence signal to observe nutrient limitation at a global, time-resolved scale using the existing, two-decade satellite record. If we are successful in this, it will deliver the tool needed to make important mechanistic assessments of how climate change is impacting ocean productivity.
In the Ocean Glow project, we are taking a two-pronged approach to try to break through the current blockage in our understanding of satellite-detected fluorescence signals. In the first prong, a novel laboratory mesocosm facility has been constructed and is being used to quantify the key factors regulating phytoplankton fluorescence emission, in the same way that it is stimulated and detected by satellites. In the second prong we are connecting these experimental results with the real world by undertaking field observations on research cruises through the global ocean. In the final stage of the project we plan to use this ground-based assessment to perform a data-informed deconvolution of the satellite fluorescence signal to observe nutrient limitation at a global, time-resolved scale using the existing, two-decade satellite record. If we are successful in this, it will deliver the tool needed to make important mechanistic assessments of how climate change is impacting ocean productivity.
A custom-built facility consisting of three replicate mesocosm located in a temperature-controlled laboratory has been constructed to assess in a controlled environment the most important factors regulating sunlight-stimulated phytoplankton fluorescence. These mesocosms are designed to be trace-metal-clean, in order to make assessments of trace nutrient availability on phytoplankton fluorescence characteristics. Light in the mesocosms is provided by a custom-built LED light source with a spectrum mimicking the solar spectrum and intensities replicating the low latitude surface oceans. Each of the mesocosms includes hyperspectral observations of the light field in order to derive upwelled ‘sunlight’-stimulated fluorescence. Multiple tests have been performed and the mesocosms are in a functioning state. At the time of writing, we are planning to start our first experiment manipulating the light, temperature and nutrient limitation environment experienced by a model diatom.
In parallel we have participated in five research cruises with one research cruise underway at the time of writing. The research expeditions have collectively taken place across the global ocean (South Atlantic, high latitude North Atlantic, Equatorial Pacific, Southern Ocean). During these expeditions, radiometric observations of upwelled light from the ocean at hyperspectral resolution has been performed, which allow for derivation of phytoplankton fluorescence in the same way that it is recorded from satellites. We have paired these observations with observations of phytoplankton concentrations and community structure, water column physics and light, as well as the nutrient limitation status of phytoplankton. We plan to use these results to get an assessment of how well sunlight-stimulated fluorescence reflects phytoplankton nutrient limitation over and above other drivers.
In parallel we have participated in five research cruises with one research cruise underway at the time of writing. The research expeditions have collectively taken place across the global ocean (South Atlantic, high latitude North Atlantic, Equatorial Pacific, Southern Ocean). During these expeditions, radiometric observations of upwelled light from the ocean at hyperspectral resolution has been performed, which allow for derivation of phytoplankton fluorescence in the same way that it is recorded from satellites. We have paired these observations with observations of phytoplankton concentrations and community structure, water column physics and light, as well as the nutrient limitation status of phytoplankton. We plan to use these results to get an assessment of how well sunlight-stimulated fluorescence reflects phytoplankton nutrient limitation over and above other drivers.
The mesocosm facility we have developed is state-of-the-art as we can successfully make radiometric observations of phytoplankton growing under trace-metal-clean conditions. To our knowledge this is the first such facility, and will be the tool that we will utilize to understand sunlight-stimulated phytoplankton fluorescence signals in a systematic manner. The field observations are building a state-of-the-art database that will allow us to test to see whether phytoplankton nutrient limitation is reflected in phytoplankton fluorescence signals in the real ocean. At the time of writing (end of first part of the project), the results have not yet been exploited to do this (requiring the lab experiments and field data analysis to be conducted), which is our aim for the middle and later phases of the project.