Ocean Cooling Pattern at the Last Glacial Maximum

Ocean temperature and ocean heat content change are analyzed based on four PMIP3 model results at the Last Glacial Maximum relative to the prehistorical run. Ocean cooling mostly occurs in the upper 1000？m depth and varies spatially in the tropical and temperate zones. The Atlantic Ocean experiences greater cooling than the rest of the ocean basins. Ocean cooling is closely related to the weakening of meridional overturning circulation and enhanced intrusion of Antarctic Bottom Water into the North Atlantic. 1. Introduction The cooling at the Last Glacial Maximum has been extensively studied geologically and numerically (e.g., [1–5]) where proxy data and numerical modeling were both employed to explore the climate sensitivity and mechanism. The Paleoclimate Modeling Intercomparison Project (PMIP2) presented large-scale features (e.g., [6]). However, the spatial pattern of cooling at that period was little studied previously. In this paper we use the newly released PMIP3 data to study the cooling pattern at the Last Glacial Maximum. 2. Methods We analyze ocean potential temperature anomaly, ocean heat content (OHC) change, and meridional overturning mass stream function based on four available PMIP3 models of IPSL-CM5A-LR, MIROC-ESM, MPI-ESM-P, and MRI-CGCM3 so far (http://cmip-pcmdi.llnl.gov/cmip5/), which follow the PMIP3 21ka experimental design (Table 1; http://pmip3.lsce.ipsl.fr/) and make a comparison between the last 50 years of Last Glacial Maximum (LGM) experiments relative to the base period of the last 50 years of the preindustrial control run. Table 1: PMIP3 LGM models. We calculate the temperature anomaly, meridional overturning mass stream function anomaly, and ocean heat content change of each model by regridding all the temperature data into a common grid. 3. Results 3.1. Geographical Distribution Ocean cooling shows pronounced spatial variations (Figure 1), both horizontally and vertically. The Northern Hemisphere exhibits a stronger cooling than the Southern Hemisphere of IPSL-CM5A-LR, MIROC-ESM, and MPI-ESM-P except MRI-CGCM3 with stronger cooling in the Southern Ocean revealing a notable north-south asymmetry. Figure 1: Geographical distribution of potential temperature anomaly in °C at different water depths. The abscissa is longitude in degrees and the ordinate is latitude in degrees. See text for detailed description. At the surface (Figures 1(a) and 1(b)), significant ocean cooling (<？5°C) occurs in the North Pacific and North Atlantic of the first three models. All these three models have shown the maximum cooling regions in the