기후 변화에 따른 해양 혼합층 변화

Abstract

1. Introduction The mixed layer is the ocean surface zone that responds most quickly and directly to atmospheric fluxes, and it is through the mixed layer that heat and momentum fluxes are transmitted to the deeper ocean and generate longer timescales of variability. Therefore, the ocean's mixed layer depth (hereafter referred to as MLD) is one of the most important quantities in the upper ocean, and is closely associated with physical, chemical and biological systems (Chen et al. 1994, Fasham, 1995, Kara et al., 2003). In spite of a large number of studies on the influence of climate change using Coupled General Circulation Models (CGCMs) (see http://www-pcmdi.llnl.gov/ipcc/subproject_publications.php), there has been little investigation of changes in MLD under climate change projections. The intent of this paper is to examine changes in MLD under atmospheric CO2 doubling in two different CGCMs, focusing on changes in MLD in the tropical Pacific. In order to analyze changes in the MLD under atmospheric CO2 doubling we examinedtwo CGCMs: a control simulation using pre-industrial greenhouse gas concentrations and an experiment simulation using doubled CO2 levels. In the doubled C02 (2xCO2) experiment, CO2 increased at a rate of 1% per year to a level twice that of the present climate. After the 70-year period to C02 doubling, the CGCMs were integrated for an additional 150-year period to examine the climate system's long-term response. In the control experiment, there was no anthropogenic or natural forcing for the entire simulation period. 2. Model We used selected CGCM simulations, namely, MRI_CGCM2_3_2a and GFDL_CM2_0 (hereafter referred to as MRI and GFDL; see Table 1 for references and additional model details). The CGCM simulations were made available by the Program for Climate Model Diagnosis and Intercomparison (PCMDI) on the website http://www-pcmdi.llnl.gov/ipcc/about_ipcc.php. In this study the MLD was obtained from Monterey and Levitus (1997) an