Simulation of air-sea CO2 flux in an ocean model: understanding processes and using data assimilation
The global ocean is a net sink for atmospheric carbon dioxide (CO2) under present-day climate, as the result of a complex interplay of various drivers which vary spatially and temporally. Global ocean-biogeochemical models are tools to investigate these drivers and can be applied to assess projected...
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University of Exeter
2024
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ftunivexeter:oai:ore.exeter.ac.uk:10871/136054 2024-06-23T07:56:44+00:00 Simulation of air-sea CO2 flux in an ocean model: understanding processes and using data assimilation Rochner, A Sheen, Katy Watson, Andrew Shutler, Jamie Ford, David Meijers, Andrew Brearley, Alexander 2024 http://hdl.handle.net/10871/136054 unknown University of Exeter Physical Geography http://hdl.handle.net/10871/136054 2025-07-31 Under embargo until 31/7/25. Unpublished work http://www.rioxx.net/licenses/all-rights-reserved Thesis or dissertation PhD Doctoral Doctoral Thesis 2024 ftunivexeter 2024-06-04T23:49:40Z The global ocean is a net sink for atmospheric carbon dioxide (CO2) under present-day climate, as the result of a complex interplay of various drivers which vary spatially and temporally. Global ocean-biogeochemical models are tools to investigate these drivers and can be applied to assess projected changes in the ocean CO2 uptake under climate change. However, model-based estimates of the present-day ocean CO$_2$ sink show discrepancies between different models and compared to observation-based estimates, highlighting the uncertainty in the estimates. The work presented in this thesis addresses three themes regarding the discrepancies and uncertainty in the simulated CO2 flux; 1) the skin temperature effect; 2) the drivers of the CO2 flux in the Southern Ocean; and 3) the use of biogeochemical data assimilation to identify and correct model biases. The focus is on one ocean-biogeochemical model, consisting of a physical model (NEMO), coupled to a biogeochemical model (MEDUSA) and a sea ice model (CICE). NEMO-MEDUSA-CICE forms the ocean component of the UK Earth System Model (UKESM1), which contributed to the latest phase of the Coupled Model Intercomparison Project. The analysis comprises runs with the coupled UKESM1 from the ensemble of historical UKESM1 runs and ocean-only runs in which NEMO-MEDUSA-CICE is forced with observation-based atmospheric data. The skin temperature effect describes a temperature gradient, typically a decrease, in the top millimeter of the ocean. When accounted for in observation-based estimates, the skin temperature effect enhances the ocean CO2 uptake, increasing the discrepancy to model-based estimates. In global models, in contrast, the skin temperature effect is typically not included. Here, the impact of including the skin temperature in NEMO-MEDUSA-CICE on the global CO2 uptake is tested in a 35 year ocean-only simulation (1980-2014). Initially, accounting for this effect leads to a transient increase in CO2 uptake. The added CO2 uptake largely accumulates in the mixed layer, ... Doctoral or Postdoctoral Thesis Sea ice Southern Ocean University of Exeter: Open Research Exeter (ORE) Medusa ENVELOPE(157.417,157.417,-79.633,-79.633) Southern Ocean |
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Open Polar |
collection |
University of Exeter: Open Research Exeter (ORE) |
op_collection_id |
ftunivexeter |
language |
unknown |
description |
The global ocean is a net sink for atmospheric carbon dioxide (CO2) under present-day climate, as the result of a complex interplay of various drivers which vary spatially and temporally. Global ocean-biogeochemical models are tools to investigate these drivers and can be applied to assess projected changes in the ocean CO2 uptake under climate change. However, model-based estimates of the present-day ocean CO$_2$ sink show discrepancies between different models and compared to observation-based estimates, highlighting the uncertainty in the estimates. The work presented in this thesis addresses three themes regarding the discrepancies and uncertainty in the simulated CO2 flux; 1) the skin temperature effect; 2) the drivers of the CO2 flux in the Southern Ocean; and 3) the use of biogeochemical data assimilation to identify and correct model biases. The focus is on one ocean-biogeochemical model, consisting of a physical model (NEMO), coupled to a biogeochemical model (MEDUSA) and a sea ice model (CICE). NEMO-MEDUSA-CICE forms the ocean component of the UK Earth System Model (UKESM1), which contributed to the latest phase of the Coupled Model Intercomparison Project. The analysis comprises runs with the coupled UKESM1 from the ensemble of historical UKESM1 runs and ocean-only runs in which NEMO-MEDUSA-CICE is forced with observation-based atmospheric data. The skin temperature effect describes a temperature gradient, typically a decrease, in the top millimeter of the ocean. When accounted for in observation-based estimates, the skin temperature effect enhances the ocean CO2 uptake, increasing the discrepancy to model-based estimates. In global models, in contrast, the skin temperature effect is typically not included. Here, the impact of including the skin temperature in NEMO-MEDUSA-CICE on the global CO2 uptake is tested in a 35 year ocean-only simulation (1980-2014). Initially, accounting for this effect leads to a transient increase in CO2 uptake. The added CO2 uptake largely accumulates in the mixed layer, ... |
author2 |
Sheen, Katy Watson, Andrew Shutler, Jamie Ford, David Meijers, Andrew Brearley, Alexander |
format |
Doctoral or Postdoctoral Thesis |
author |
Rochner, A |
spellingShingle |
Rochner, A Simulation of air-sea CO2 flux in an ocean model: understanding processes and using data assimilation |
author_facet |
Rochner, A |
author_sort |
Rochner, A |
title |
Simulation of air-sea CO2 flux in an ocean model: understanding processes and using data assimilation |
title_short |
Simulation of air-sea CO2 flux in an ocean model: understanding processes and using data assimilation |
title_full |
Simulation of air-sea CO2 flux in an ocean model: understanding processes and using data assimilation |
title_fullStr |
Simulation of air-sea CO2 flux in an ocean model: understanding processes and using data assimilation |
title_full_unstemmed |
Simulation of air-sea CO2 flux in an ocean model: understanding processes and using data assimilation |
title_sort |
simulation of air-sea co2 flux in an ocean model: understanding processes and using data assimilation |
publisher |
University of Exeter |
publishDate |
2024 |
url |
http://hdl.handle.net/10871/136054 |
long_lat |
ENVELOPE(157.417,157.417,-79.633,-79.633) |
geographic |
Medusa Southern Ocean |
geographic_facet |
Medusa Southern Ocean |
genre |
Sea ice Southern Ocean |
genre_facet |
Sea ice Southern Ocean |
op_relation |
http://hdl.handle.net/10871/136054 |
op_rights |
2025-07-31 Under embargo until 31/7/25. Unpublished work http://www.rioxx.net/licenses/all-rights-reserved |
_version_ |
1802650035789234176 |