Thermohaline Circulation Studies with an Isopycnic Coordinate Ocean Model

Abstract

The thermohaline circulation (THC) in a 1000-yr near-global numerical simulation using the Miami Isopycnic Coordinate Ocean Model is analyzed and compared to observations. The model, driven by observed monthly atmospheric climatology, uses potential density referenced to 2000 m (σ2) as the vertical coordinate and accounts for compressibility (thermobaricity) effects. Examination of the three-dimensional mass flux field reveals that the model comes fairly close to quantitatively reproducing a number of global and basin-scale circulation features, such as the vertical?meridional overturning rate in the three major basins, the meridional heat flux, and the transport through the major passages. Methods are presented that allow the construction of composite diagrams revealing quantitative regional aspects of the modeled circulation in potential density space. The diagrams reveal many features of the modeled THC that adhere to observations, the most noticeable shortcoming being a weaker-than-observed northward penetration of bottom water into the three major basins caused by insufficient production of Antarctic Bottom Water.