Modelling the terrestrial nitrogen and phosphorus biogeochemical cycles in an intermediate complexity Earth system climate model

De Sisto Lelchitskaya, Makcim Luis (2024) Modelling the terrestrial nitrogen and phosphorus biogeochemical cycles in an intermediate complexity Earth system climate model. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

The application of land nutrient limitation has been shown to improve the accuracy of carbon cycle estimates in Earth system models simulations. As the main limiting nutrients in terrestrial systems nitrogen and phosphorus cycles are crucial for the terrestrial carbon cycle representation. In this thesis a terrestrial nitrogen and phosphorus cycles modules were developed for Earth system models, utilizing the University of Victoria Earth System Climate Model. Both nitrogen and phosphorus cycles were then applied to assess the impact of nutrient limitation on remaining carbon budget estimations. Moreover, the nitrogen cycle representation was used to simulate terrestrial N₂O emissions. After coupling with an existing ocean N₂O emission module, the N₂O dynamics were used to project N₂O concentrations to the end of the 21st century. This represents the first fully coupled terrestrial-ocean N₂O dynamic module in existence. The terrestrial nutrient limitation reduced the capacity of terrestrial vegetation to uptake carbon, decreasing the land primary productivity. This decrease improved the representation of terrestrial productivity in comparison with observations. The remaining carbon budgets were reduced by 19 and 21% for the 1.5°C warming target with the application of nutrient limitation in different Shared Socioeconomic Pathways, re-enforcing the importance of nutrient limitation in the uncertainties of the carbon cycle. As remaining carbon budgets are an important decision-making metric, nutrient limitation is suggested to be taken into account when analyzing or estimating these budgets. The projection of N₂O concentration was between 401 to 418 ppb in the year 2100. These simulations show that N₂O concentrations are insensitive to mitigation efforts currently represented in the Shared Socioeconomic Pathways scenarios, showing similar values in low and high-emission scenarios. Overall, terrestrial nitrogen and phosphorus are an integral part of terrestrial systems and have improved the capacity of the University of Victoria Earth System Climate Model to represent the terrestrial carbon cycle.

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