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Title: The influence of physical dynamics on trophic and biogeochemical processes in Celtic seas
Author: Abram, Lucy Claire
Awarding Body: University of Liverpool
Current Institution: University of Liverpool
Date of Award: 2013
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Shelf seas are small in size (< 10% surface area of the oceans) but are highly productive, where up to 40% of oceanic carbon sequestration takes place. They also have great economic and social importance as they are widely used for fishing, waste disposal and fossil fuel extraction. Fishing resources are economically important and it is estimated that the UK industry is worth £800-1200 million. As a result there is a greater need to understand the dynamics of these systems. This study focuses on the Celtic and Irish Seas of the North West European Continental Shelf and assesses biological and biogeochemical processes across four distinct physical regions. A multidisciplinary approach has been employed to study biological communities across the shelf sea. In this study it has been observed that benthic, pelagic and particulate organic matter (POM) communities appear to adapt in response to different physical environments. Small scale adaptations of organisms were observed between regions of different water column structure. Hence, statistically significant differences in nitrogen isotope values for benthic suspension feeders indicate that these invertebrates are flexible in their feeding, depending on the environment and food availability. Changes in the pelagic community were also observed across the shelf sea. At the shelf break large typically oceanic zooplankton species and larvae were present coinciding with a change in phytoplankton community structure towards larger cells in surface waters when compared to the rest of the shelf sea. The structure of the water column, particularly with respect to mixing and turbulence seems to influence the lability of material sinking through the water column and in turn, the response of heterotrophic communities, which apparently follow the food resource. A change in hydrodynamic setting of a seasonally stratified water column, which led to the partial erosion of the subsurface chlorophyll max (SCM), enabled the impact of a storm-driven mixing event to be determined. The apparent loss of chlorophyll a from the SCM led to the material being redistributed vertically through the water column, as illustrated by the distributions of biological markers (lipids) through the water column before and after the storm. Zooplankton communities also showed evidence of vertical redistribution; prior to the wind event, 80% of the community was in the upper water column, whereas their distribution was even after the wind event. As a result, the storm apparently increased the complexity of the food web dynamic and this change drew more similarities to vertically mixed regions of the shelf than stratified regions.
Supervisor: Sharples, Jonathan; Wolff, George A.; Frid, Chris Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: GE Environmental Sciences