Temporal variations in primary production have important consequences for carbon transfer, both through the air-sea interface and through pelagic food webs. Coastal waters account for ca. 30% of global primary productivity and long-term biogeochemical time series have greatly improved our understanding of the environmental and phytoplankton community factors that control carbon fixation. For the first time, the temporal and depth-dependent variations in photosynthetic parameters were investigated at station L4 in the western English Channel. From 2009-2010, the highest productivity (1856 mg C m-2 d-l) occurred during August 2009 during a bloom of dinoflagellate Karenia mikimotoi which impacted upon oxygen concentrations. Harmful algal species, K mikimotoi and Phaeocystis poucbetii were shown to account for substantial proportions of the total phytoplankton carbon from 1992-2009 during summer and spring respectively. Persistent summertime rainfall and low-salinity riverine pulses were identified as the key drivers of K mikimotoi blooms, whilst Phaeocystis blooms were related to the North Atlantic Oscillation. An empirical bio-optical model of surface primary production based on phytoplankton light absorption was constructed and validated for use in coastal waters. The model performed better than standard chlorophyll-based algorithms (RMSE < 8%). This approach was successfully extended throughout the water column using characteristic depth-profiles to derive depth-integrated primary production, and subsequently extended to two phytoplankton size groups. Size-fractionated production data revealed that although microplankton contributed much of the total carbon fIxation, smaller phytoplankton had a higher photosynthetic efficiency. The model was further applied to an 8-year time series of absorption measurements, to investigate longer-term temporal dynamics and drivers of productivity at L4. Nano- and picoplankton were found to contribute 48% of primary production at L4. Different driving mechanisms of temporal variability were determined for instantaneous production and seasonal budgets.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:558818 |
| Date | January 2012 |
| Creators | Barnes, Morvan K. |
| Publisher | University of Essex |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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