Plankton Seasonal Dynamics and Carbon Export in a Warming Ocean

Guest, Joanna Kirsty (2024) Plankton Seasonal Dynamics and Carbon Export in a Warming Ocean. Doctoral thesis, University of East Anglia.

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Abstract

Anthropogenic climate change is significantly altering marine ecosystems, with profound implications for oceanic carbon dynamics. This thesis investigates the interplay between phytoplankton phenology and carbon export in marine ecosystems, using the PlankTOM12.2 model and a range of observations. The PlankTOM12.2 model's ability to simulate oceanic carbon fluxes was improved by introducing a representation of bacterial biofilms and updating of the parameterisation for the dissolution of calcite based on recent observations. In addition, the phytoplankton seasonality of PlankTOM12.2 model was shown to reproduce chlorophyll seasonality across 5 latitudinal bands, after improvements to the parameterisation of the growth rates of Plankton Functional Types (PFTs). A comprehensive evaluation against observational data from 1998 to 2020 reveals that the PlankTOM12.2 model effectively captures the phenology of phytoplankton on a regional scale but not at the level of the model grid. Opposing trends in initiation and termination drive global increases in duration of the growing period of 5.1-7.8 days per decade between 1998 and 2020. In addition, the model replicates regional variability in observed trends such as the shortening of growing periods in the tropics and lengthening in high-latitude regions. Temperature, mixed layer depth, and primary production were the primary influence on export production and efficiency. While the effects of growing period duration and initiation on export production are often significant, they are nondominant. However, in the Southern Ocean, the effect of duration and initiation of phytoplankton growth on carbon export is as large as that of mixed layer depth, highlighting the unique environmental dynamics of this region. Under both low- and high- emissions scenarios, primary production decreases by 2100, in line with a decline in phytoplankton biomass; though more variability between regions is observed compared to simpler ecosystem models. Globally, except in the Southern Ocean, particulate organic carbon export production increases despite these declines in primary production. This is driven by increases in export efficiency which increases as primary production declines. This inverse relationship between export efficiency and primary productivity is, at least partially, due to shifts amongst species. The analysis presented here demonstrates that complex ecosystem models are essential for predictions of marine carbon dynamics amidst climate change, underscoring the need for improved model ecosystems and high-resolution observational data for validation. The findings suggest that ecosystem shifts are key drivers in altering phenology and carbon export production, calling for further research to refine our understanding of complex ecosystem interactions.

Item Type:	Thesis (Doctoral)
Faculty \ School:	Faculty of Science > School of Environmental Sciences
Depositing User:	Kitty Laine
Date Deposited:	12 Nov 2024 11:10
Last Modified:	12 Nov 2024 11:10
URI:	https://ueaeprints.uea.ac.uk/id/eprint/97635
DOI:

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