10:45 AM - 11:00 AM
[ACG42-06] Numerical Study on the Mechanisms of Atmospheric and Oceanic Warming in the Arctic Based on the Upper-ocean Heat Budget Analysis
Keywords:Arctic warming, Ocean heat transport
Observations and model simulations have consistently shown that warming in the Arctic is more pronounced than other regions of the world. The role of local climate feedback, such as the albedo feedback, as a contributing factor to this phenomenon has been extensively discussed. There have also been studies on the role of meridional heat transport through the atmosphere and ocean. Many previous studies, however, examined the warming processes of the atmosphere and ocean separately. This study aims to establish an integrative understanding of the atmospheric and oceanic warming in the Arctic through the analyses of ocean heat budget, sea ice mass budget, and heat exchange between the ocean and atmosphere.
Three numerical experiments were performed using an atmosphere-ocean general circulation model, MIROC6: a standard experiment (PI) with a pre-industrial atmospheric CO2 level, a warming experiment (CO2.1pt) with CO2 concentrations increasing by 1% annually from the PI level, and a nudging experiment (CO2.1pt_relax). In the CO2.1pt_relax experiment, sea water temperature and salinity at four Arctic Ocean gateways (Bering Strait, Davis Strait, Barents Sea Opening, and Fram Strait) were nudged to pre-industrial conditions to isolate the effect of reduced ocean heat transport into the Arctic. The CO2.1pt experiment exhibits a significant temperature increase in the Arctic Ocean, predominantly in the upper layers, shallower than 230 m in depth. Seasonal fluctuations of the temperature anomaly are driven by the enhanced absorption of sea surface heat flux in summer and increased heat release to the atmosphere in winter. On the annual average, however, the change in sea surface heat flux contributes to upper ocean cooling, with advection playing a dominant role in the long-term upper ocean warming. This result is consistent with the enhanced ocean heat transport into the Arctic through the Barents Sea Opening. The reduction of sea ice mass is caused by an increase in basal melting and a decrease in bottom growth. These results suggest the importance of the increased summer sea surface heat flux in the sea ice mass budget. Nevertheless, it is possible that advection contributes to suppress ice formation in winter. By comparing the CO2.1pt and CO2.1pt_relax experiments, we isolated the effects of increased ocean heat transport. Ocean heat transport leads to a significant warming near 230 m in depth throughout the Arctic Ocean. In contrast, there is little warming in the Arctic atmosphere. The minimal near-surface atmospheric warming may be due to the advection-induced warming being confined mainly to layers below the strong halocline. Under the identical external forcing, the impact of ocean heat transport change on the atmospheric warming appears to be suppressed without the change in sea ice cover.
Three numerical experiments were performed using an atmosphere-ocean general circulation model, MIROC6: a standard experiment (PI) with a pre-industrial atmospheric CO2 level, a warming experiment (CO2.1pt) with CO2 concentrations increasing by 1% annually from the PI level, and a nudging experiment (CO2.1pt_relax). In the CO2.1pt_relax experiment, sea water temperature and salinity at four Arctic Ocean gateways (Bering Strait, Davis Strait, Barents Sea Opening, and Fram Strait) were nudged to pre-industrial conditions to isolate the effect of reduced ocean heat transport into the Arctic. The CO2.1pt experiment exhibits a significant temperature increase in the Arctic Ocean, predominantly in the upper layers, shallower than 230 m in depth. Seasonal fluctuations of the temperature anomaly are driven by the enhanced absorption of sea surface heat flux in summer and increased heat release to the atmosphere in winter. On the annual average, however, the change in sea surface heat flux contributes to upper ocean cooling, with advection playing a dominant role in the long-term upper ocean warming. This result is consistent with the enhanced ocean heat transport into the Arctic through the Barents Sea Opening. The reduction of sea ice mass is caused by an increase in basal melting and a decrease in bottom growth. These results suggest the importance of the increased summer sea surface heat flux in the sea ice mass budget. Nevertheless, it is possible that advection contributes to suppress ice formation in winter. By comparing the CO2.1pt and CO2.1pt_relax experiments, we isolated the effects of increased ocean heat transport. Ocean heat transport leads to a significant warming near 230 m in depth throughout the Arctic Ocean. In contrast, there is little warming in the Arctic atmosphere. The minimal near-surface atmospheric warming may be due to the advection-induced warming being confined mainly to layers below the strong halocline. Under the identical external forcing, the impact of ocean heat transport change on the atmospheric warming appears to be suppressed without the change in sea ice cover.