Investigating the use of fast repetition rate fluorometry in understanding algal physiology in optically complex oceans

  • Derek Connor

Student thesis: Doctoral Thesis

Abstract

Increased mechanisation and burning of fossil fuels has resulted in year-on-year increases in the concentration of atmospheric carbon dioxide, a key greenhouse gas. Phytoplankton are photosynthesising organisms that are ubiquitous with water and responsible for approximately 50 % of global primary productivity. These organisms have adapted, evolved, and survived over many millions of years, however, the current rate of change being introduced into the biosphere by anthropogenic climate change raises significant questions about how these organisms will adapt to rapidly changing ocean temperatures and acidity.It is possible to determine the physiological state of phytoplankton using changes in the variable fluorescence output from the photosynthetic pathways present in all phytoplankton. Here this was achieved using a Fast Repetition Rate fluorometer (FRRf). Algal dynamics respond rapidly to changes in environmental conditions making it essential that measurements are made as quickly and accurately as possible.A core aim of this thesis was to conduct a series of characterisation experiments to optimise the use and define the limits of performance of the FRRf with particular focus on the impact of conducting measurements in optically complex Case II waters. In April, 2015, the Marine Optics and Remote Sensing Group here at the University of Strathclyde together with colleagues from the Helmholtz Zentrum Geesthacht (HZG) in Germany, and Wet Labs Inc. (USA) undertook a research cruise around UK coastal waters.During this cruise, FRRf was used to determine the physiological status of phytoplankton in a variety of optically complex waters with support from data produced by a host of in situ and lab-based instruments. Data was analysed to establish if any simple patterns could be observed between the physical, optical, and biogeochemical parameters measured in combination with the FRRf measurements with it being found that temporal variability had the most impact on algal physiology.Subsequently, temporal variability over the course of a single day was investigated using a full day of measurements at a single location in Loch Fyne. A series of six measurements were made over the course of the day providing an opportunity to analyse the impact of overhead conditions on the in situ algal dynamics. Using the inherent optical properties (IOP) data collected at Loch Fyne, it was possible to model the underwater light fields using Hydrolight radiative transfer modelling, which was combined with the FRRf data measured over the day to produce estimates of the daily, column-integrated gross primary productivity (DCIGPP).This DCIGPP model was compared to three existing models for net primary productivity (NPP) from the literature so as to determine how useful an estimate of GPP the DCIGPP model provided. Using a value for the respiration rate of 97 % from the literature, good agreement was found between the DCIGPP-NPP estimates and the estimates of NPP from the VGPM and CbPM models. This suggests that the model of DCIGPP based on FRRf data is potentially useful in estimating the daily gross primary productivity.
Date of Award1 Apr 2017
LanguageEnglish
Awarding Institution
  • University Of Strathclyde
SponsorsNERC (Natural Environment Research Council) & University of Strathclyde
SupervisorDavid McKee (Supervisor) & Gail McConnell (Supervisor)

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