Impacts of phytoplankton radiant heating on ocean structure and climate

Meng, Siyu (2026) Impacts of phytoplankton radiant heating on ocean structure and climate. Doctoral thesis, University of East Anglia.

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Abstract

Chlorophyll, the primary light-absorbing pigment in phytoplankton, modulates the vertical distribution of solar radiation in the ocean. Despite growing evidence that chlorophyll-induced solar absorption affects ocean physics and climate, this process remains incompletely represented in Earth System Models (ESMs), and its implications for future climate are unclear. This thesis investigates the impacts of chlorophyll-induced solar absorption on ocean structure and climate across multiple spatial and temporal scales.

Contrasting thermal and dynamical responses to chlorophyll-induced solar absorption are found between Pacific and Atlantic eastern boundary coastal upwelling systems, based on an ocean–biogeochemistry coupled model. In the Pacific, shading by high surface chlorophyll reduces solar penetration into the ocean below, leading to colder subsurface waters that are subsequently upwelled and contribute to surface cooling, with enhanced stratification strengthening upwelling. In the Atlantic, solar absorption by a subsurface chlorophyll maximum leads to warmer and weaker upwelling.

Under climate warming, projected future chlorophyll decline reduces solar absorption within the mixed layer, redistributing 0.25Wm−2 of global-mean radiative flux below and delaying anthropogenic surface warming by up to 12 years. The uncertainty arises from inter-model differences in both simulated chlorophyll concentrations and their representation of solar absorption. Such differences also contribute to biases in the mean state of ESMs.

Based on ocean model projections, we further show that future chlorophyll decline leads to significant subsurface warming of 0.05–0.2 ◦C and changes the seasonal cycle of upper-ocean temperature. In addition, chlorophyll decline induces an El Ni˜no–like response in the eastern equatorial Pacific, characterised by thermocline deepening and weakened equatorial circulation.

Overall, this thesis demonstrates that chlorophyll-induced radiative effects play a non-negligible role in regulating mean state and future change of climate, highlighting the need for improved representation of these processes in ESMs.

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Item Type:	Thesis (Doctoral)
Faculty \ School:	Faculty of Science > School of Environmental Sciences
Depositing User:	Kitty Laine
Date Deposited:	06 May 2026 10:45
Last Modified:	06 May 2026 10:45
URI:	https://ueaeprints.uea.ac.uk/id/eprint/102910
DOI:

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