A quasi-one-dimensional coupled climate-change cycle model 1. Description and behavior of the climate component

A quasi-one-dimensional, coupled climate - carbon cycle model is presented, which consists of two polar domains and one nonpolar domain. The model simulates the distribution of dissolved inorganic carbon (DIC), alkalinity, phosphate, dissolved oxygen, and temperature and contains a biological pump with production of organic tissue, calcite, and arogonite. Bottom water is conditioned in one polar domain through interaction with the atmosphere and convective mixing and is injected into the lower portion of the nonpolar domain. Bottom water formed in the downwelling polar domain largely upwells in the nonpolar domain, although a portion upwells from intermediate depth into the other polar domain. In this paper the climate component of the coupled model and its behavior are described, while the carbon cycle component is documented by Harvey [this issue], hereafter referred to as part 2. We develop a simple physical basis for determining the relative magnitudes of the effective vertical diffusion coefficient (k(V)) for different tracers in a one - dimensional (1-D) model and find that kV is smallest for temperature, intermediate for carbon, and largest for dissolved oxygen. We deduce a substantially smaller kV for temperature in the upper ocean than previously used in 1-D models (similar to0.20 cm(2) s(-2) rather than 0.6-1.0 cm(2) s(-1)) and a smaller peak upwelling velocity (2 m yr(-1) rather than 4 m yr(-1)). The explicit representation of convective mixing has a significant effect on the model surface temperature transient response and sea level rise when the intensity of the thermohaline changes. As a result, the transient temperature response and sea level rise obtained here when the thermohaline circulation intensity decreases is significantly different from that of the classical 1-D upwelling-diffusion model.