Understanding modelled sea-air CO2 flux biases in the Southern Ocean through the seasonal cycle
The Southern Ocean forms a vital component of the earth system as a sink of CO2 and heat, taking over 40% of the annual oceanic CO2 uptake (75% of global heat uptake), slowing down the accumulation of CO2 in the atmosphere and thus the rate of climate change. However, recent studies based on the Cou...
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Department of Oceanography
2018
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Online Access: | http://hdl.handle.net/11427/29260 |
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ftunivcapetownir:oai:open.uct.ac.za:11427/29260 2024-09-15T18:37:00+00:00 Understanding modelled sea-air CO2 flux biases in the Southern Ocean through the seasonal cycle Mongwe, Ndunisani Precious Monteiro, Pedro M S Vichi, Marcello 2018 application/pdf http://hdl.handle.net/11427/29260 eng eng Department of Oceanography Faculty of Science University of Cape Town http://hdl.handle.net/11427/29260 Oceanography Doctoral Thesis Doctoral PhD 2018 ftunivcapetownir 2024-06-25T03:25:45Z The Southern Ocean forms a vital component of the earth system as a sink of CO2 and heat, taking over 40% of the annual oceanic CO2 uptake (75% of global heat uptake), slowing down the accumulation of CO2 in the atmosphere and thus the rate of climate change. However, recent studies based on the Coupled Model Intercomparison Project version 5 (CMIP5) Earth System Models (ESMs) show that CMIP5 ESMs disagree on the phasing of the seasonal cycle of the CO2 flux (FCO2) and compare poorly with available observation estimates in the Southern Ocean. Notwithstanding these differences, the seasonal cycle is a dominant mode of CO2 variability in the Southern Ocean, and hence this is an important bias. Previous studies suggest that these biases of FCO2 in ESMs might be a significant limitation to the long-term simulation of CO2 characteristics in the Southern Ocean. Consequently, this study has three primary objectives: first, to develop a process-based diagnostic method to analyze and isolate key biases and their underlaying mechanisms in the model-observations seasonal cycle of FCO2 differences for forced ocean models and ESMs. Second, to use this framework to examine sources of biases responsible for the limited skill of CMIP5 models in simulating the seasonal cycle of FCO2 with respect to observed estimates. Thirdly, to investigate how these present-day biases in the seasonality and drivers of CO2 in CMIP5 ESMs affect modelled longterm changes in the mechanisms of CO2 uptake in the Southern Ocean. In the first part of the dissertation, an objective diagnostic framework was established to analyze model-observation biases in the seasonal scale of FCO2 using the NEMO PISCES ORCA2LP model output, and Takahashi et al. (2009) observed estimates. The diagnostic framework focuses on examining the relative contributions of the competing drivers (SST and DIC) and related processes (solubility, biological and mixing) to instantaneous monthly changes in surface pCO2 (and FCO2) at the seasonal scale. In the second part of the ... Doctoral or Postdoctoral Thesis Southern Ocean University of Cape Town: OpenUCT |
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University of Cape Town: OpenUCT |
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ftunivcapetownir |
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English |
topic |
Oceanography |
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Oceanography Mongwe, Ndunisani Precious Understanding modelled sea-air CO2 flux biases in the Southern Ocean through the seasonal cycle |
topic_facet |
Oceanography |
description |
The Southern Ocean forms a vital component of the earth system as a sink of CO2 and heat, taking over 40% of the annual oceanic CO2 uptake (75% of global heat uptake), slowing down the accumulation of CO2 in the atmosphere and thus the rate of climate change. However, recent studies based on the Coupled Model Intercomparison Project version 5 (CMIP5) Earth System Models (ESMs) show that CMIP5 ESMs disagree on the phasing of the seasonal cycle of the CO2 flux (FCO2) and compare poorly with available observation estimates in the Southern Ocean. Notwithstanding these differences, the seasonal cycle is a dominant mode of CO2 variability in the Southern Ocean, and hence this is an important bias. Previous studies suggest that these biases of FCO2 in ESMs might be a significant limitation to the long-term simulation of CO2 characteristics in the Southern Ocean. Consequently, this study has three primary objectives: first, to develop a process-based diagnostic method to analyze and isolate key biases and their underlaying mechanisms in the model-observations seasonal cycle of FCO2 differences for forced ocean models and ESMs. Second, to use this framework to examine sources of biases responsible for the limited skill of CMIP5 models in simulating the seasonal cycle of FCO2 with respect to observed estimates. Thirdly, to investigate how these present-day biases in the seasonality and drivers of CO2 in CMIP5 ESMs affect modelled longterm changes in the mechanisms of CO2 uptake in the Southern Ocean. In the first part of the dissertation, an objective diagnostic framework was established to analyze model-observation biases in the seasonal scale of FCO2 using the NEMO PISCES ORCA2LP model output, and Takahashi et al. (2009) observed estimates. The diagnostic framework focuses on examining the relative contributions of the competing drivers (SST and DIC) and related processes (solubility, biological and mixing) to instantaneous monthly changes in surface pCO2 (and FCO2) at the seasonal scale. In the second part of the ... |
author2 |
Monteiro, Pedro M S Vichi, Marcello |
format |
Doctoral or Postdoctoral Thesis |
author |
Mongwe, Ndunisani Precious |
author_facet |
Mongwe, Ndunisani Precious |
author_sort |
Mongwe, Ndunisani Precious |
title |
Understanding modelled sea-air CO2 flux biases in the Southern Ocean through the seasonal cycle |
title_short |
Understanding modelled sea-air CO2 flux biases in the Southern Ocean through the seasonal cycle |
title_full |
Understanding modelled sea-air CO2 flux biases in the Southern Ocean through the seasonal cycle |
title_fullStr |
Understanding modelled sea-air CO2 flux biases in the Southern Ocean through the seasonal cycle |
title_full_unstemmed |
Understanding modelled sea-air CO2 flux biases in the Southern Ocean through the seasonal cycle |
title_sort |
understanding modelled sea-air co2 flux biases in the southern ocean through the seasonal cycle |
publisher |
Department of Oceanography |
publishDate |
2018 |
url |
http://hdl.handle.net/11427/29260 |
genre |
Southern Ocean |
genre_facet |
Southern Ocean |
op_relation |
http://hdl.handle.net/11427/29260 |
_version_ |
1810480933257609216 |