The biological and physical controls on phytoplankton blooms off the north-east coast of the UK

Hill, Daniel

Abstract

The North Sea is a highly productive temperate coastal shelf sea which contains important fisheries that provides protein to the global market. This study investigated the biological and physical controls on the different spring bloom events in North East coastal waters of the UK in 2022. The study area is situated off the north-east coast of the UK where three distinct hydrodynamic zones were observed. The zones were derived from utilising bathymetry and mixed layer depths, where an inshore / offshore stratified and a permanently mixed zone were outlined. This study uses a range of data collected in situ, remotely sensed data and modelling to assess the physical and biological controls (phytoplankton growth and grazing rates) on varying phytoplankton bloom phenology and primary production in differing hydrodynamic regions along the north-east coast in 2022. Observations showed a north-south gradient whereby increased phytoplankton biomass (blooming) was initiated earliest in stratified waters in the northern latitudes, with delayed blooming in the permanently mixed southern latitudes of the study area. The key drivers in determining temporal and spatial distribution of blooming events were dictated by the onset of stratification and varying light attenuation. Stratification was modelled and estimated to be greatest in the inshore / offshore stratified regions, with significant stratification occurring for approximately 169 days commencing in early spring. This correlated to significant phytoplankton blooms at the initial stages of stratification formation in late March, where high concentration of nutrients and reduced light attenuation, helped facilitate phytoplankton growth. Prolonged stratification within these zones enabled blooming in late Autumn. The permanently mixed region experienced delayed phytoplankton growth, with the initiation of the bloom phase beginning in early June. Blooms correlated to neap-spring tidal cycles where stratification formation occurred on the neap phase of the tidal cycle. The neap phase resulted in lower current speeds, facilitating short periods of stratification formation and potentially aiding in the reduction of light attenuation, enhancing phytoplankton growth in summer and autumn.

Citation

Hill, D. The biological and physical controls on phytoplankton blooms off the north-east coast of the UK. (Thesis). The University of Hull. https://hull-repository.worktribe.com/output/4866477

• Thesis Type: Thesis
• Deposit Date: Oct 15, 2024
• Publicly Available Date: Oct 29, 2024
• Keywords: Biological sciences
• Public URL: https://hull-repository.worktribe.com/output/4866477
• Additional Information: School of Biological and Marine Science; University of Hull
• Award Date: Jun 28, 2024