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 sim ulates the distribution of dissolved inorganic carbon (DIC), alkalinity, ph osphate, dissolved oxygen, and temperature and contains a biological pump w ith production of organic tissue, calcite, and arogonite. Bottom water is c onditioned in one polar domain through interaction with the atmosphere and convective mixing and is injected into the lower portion of the nonpolar do main. Bottom water formed in the downwelling polar domain largely upwells i n the nonpolar domain, although a portion upwells from intermediate depth i nto the other polar domain. In this paper the climate component of the coup led model and its behavior are described, while the carbon cycle component is documented by Harvey [this issue], hereafter referred to as part 2. We d evelop a simple physical basis for determining the relative magnitudes of t he effective vertical diffusion coefficient (k(V)) for different tracers in a one - dimensional (1-D) model and find that kV is smallest for temperatu re, 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 ef fect 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 thermohalin e circulation intensity decreases is significantly different from that of t he classical 1-D upwelling-diffusion model.