지구온난화에 따른 해양혼합층 반응: 북태평양 반응

Abstract

This study investigates changes in the mixed layer depth in the North Pacific Ocean in response to global warming by analyzing outputs from Coupled Model Intercomparison Projects phase 3 (CMIP3), as used in the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4). For present climate, we used data from the 20th climate simulation (20C3M) driven by both anthropogenic and natural forcing. Future projections are also assessed for the Special Report on Emissions Scenarios (SRES) A1B scenario which assumes moderate future CO2 emission. The 19 of total 25 IPCC AR4 models were used in this study. Two models (BCC-CM1 & INMCM3_0) were removed simply because of unavailability of temperature and salinity data in PCMDI archives for MLD calculation. Four models (CCCMA-CGCMT47, CCCMA-CGCMT63, NCAR-PCM1, and UKMO-HadGEM1) were additionally excluded because their 1st vertical levels start below 10 m depth that are the reference depth used for MLD estimation in this study. MLD in 21st century decreases in most regions of the North Pacific, while the spatial distribution of the MLD is nearly unchanged. The overall shoaling results in part from intensified upper-ocean stratification caused by both surface warming and freshening. Significant ML decrease (>30 m) is found in two regions: one in the KE, the other in the region centered at 140°W and 30°N. The MLD decrease in the KE is attributable to weakened wind that causes reduced surface cooling. On the other hand, the MLD increases in regions between 40° ~ 45°N and west of 160°W in response to global warming. This deepening results from a northward shift of the KE rather than from intensification of surface cooling or wind stress. Although model configuration (e.g., grid size and sub-grid scale parameterization) varies significantly, the response of the KE MLD to global warming appears to be consistent and robust across the models: all 19 models used in this study show a decreased MLD in the KE, accompa