Century-Scale Changes in the Seasonality and Drivers of CO2 in CMIP5 ESMs in the Southern Ocean
Abstract
The Southern Ocean is an important sink of CO2 and heat, taking about a third of oceanic CO2 annual uptake and 75% of global heat uptake, thus slowing the rate of climate change. However, its long-term (century-scale) role as a sink of CO2 is still uncertain, and therefore Earth System Models play a crucial role in understanding the mechanisms driving changes in the sink of CO2 and simulating likely long-term scenarios. Nonetheless, it has been shown that CMIP5 ESMs have limited skill in simulating the seasonal cycle of sea-air FCO2 fluxes (FCO2) with respect to observed estimates in the Southern Ocean. Given that the seasonal cycle is the dominant mode for CO2 variability in the Southern Ocean, previous studies have suggested that these seasonal cycle biases might be a significant limitation to ESM's skill in simulating long-term characteristics CO2 in the Southern Ocean. In a previous study, these biases were investigated, it was found that overestimated temperature rates during peak seasons (group-SST models) and exaggerated primary production (group-DIC models) are the two main biases responsible for the limited skill of CMIP5 models to resolving observed comparable seasonal cycle of FCO2. In this study, we used five CMIP5 ESMs from the RCP8.5 scenario to investigate how these present-day biases in the seasonality and drivers of CO2 in CMIP5 ESMs affect our ability to simulate/model long-term changes in the mechanisms of CO2 uptake in the Southern Ocean. The outcome showed that although the analysed models all show increased CO2 uptake at the end of the century, they show important differences in the mechanisms explaining the increased CO2 uptake. For example, the increased CO2 uptake in the present-day temperature biased models (group-SST models) is mainly through surface solubility due to increased anthropogenic atmospheric CO2 and decreased surface CO2 buffering capacity. But they show a weak to a null role of biological activity in the CO2 variability and sink at the seasonal scale at end of the century as is in the present scenario. On the Contrary, increased CO2 uptake in group-DIC models is explained by increased role of biological activity in surface pCO2 variability and CO2 sink and surface solubility driven CO2 uptake during winter.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFMOS31C..03M
- Keywords:
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- 4805 Biogeochemical cycles;
- processes;
- and modeling;
- OCEANOGRAPHY: BIOLOGICAL AND CHEMICALDE: 4806 Carbon cycling;
- OCEANOGRAPHY: BIOLOGICAL AND CHEMICALDE: 4813 Ecological prediction;
- OCEANOGRAPHY: BIOLOGICAL AND CHEMICALDE: 4815 Ecosystems;
- structure;
- dynamics;
- and modeling;
- OCEANOGRAPHY: BIOLOGICAL AND CHEMICAL