Studies of carbon isotopes and cadmium inOn time scales exceeding millennia, the ocean carbon system regulates atmospheric CO 2 levels. The gas trapped as bubbles in polar ice cores shows that CO 2 levels varied between 190 and 280 ppmV during glaciation cycles and, hence, that some aspects of the oceanic carbon system are naturally variable. Several ideas on how the ocean produces these changes in atmospheric CO 2 have been advanced. Although many ideas have merit because they call attention to processes that regulate atmospheric CO 2 , it has proven difficult to come up with a widely accepted model for the dominant cause of glacial͞interglacial CO 2 variability.Despite this persistent sticking point, significant progress has been made concerning the distribution of metabolically regenerated CO 2 throughout the deep ocean. The past state of the oceanic CO 2 distribution is recorded by carbon isotopes and phosphorus-analog Cd as they are incorporated into shells of benthic foraminifera preserved in deep-sea sediments. Marine organic matter is enriched in 12 C and Cd, so that surface waters are depleted in 12 C and Cd because of their removal by plant growth, and deep waters are enriched in 12 C and Cd as debris from those plants (and animals that eat them) decompose in deeper waters. From global data on the distribution of metabolic CO 2 and its analogs, we can infer characteristics of thermohaline spreading patterns. This paper will first briefly review significant aspects of Last Glacial Maximum (LGM) ocean chemical distributions in major ocean basins, emphasizing major areas of agreement and discordance, and then tie this evidence together into a unifying hypothesis for LGM deep-ocean circulation patterns. The paper concludes with new evidence concerning century-scale variability of North Atlantic climate during the past 150,000 years (15 kyr).