Carbon isotopic measurements on the benthic foraminiferal genus Cibicidoides document that mean deep ocean δ¹³C values were 0.46 ‰ lower during the last glacial maximum than during the Late Holocene. The geographic distribution of δ¹³C was altered by changes in the production rate of nutrient-depleted deep water in the North Atlantic. During the Late Holocene, North Atlantic Deep Water, with high δ¹³C values and low nutrient values, can be found throughout the Atlantic Ocean, and its effects can be traced into the southern ocean where it mixes with recirculated Pacific deep water. During the glaciation, decreased production of North Atlantic Deep Water allowed southern ocean deep water to penetrate farther into the North Atlantic and across low-latitude fracture zones into the eastern Atlantic. Mean southern ocean δ¹³C values during the glaciation are lower than both North Atlantic and Pacific δ¹³C values, suggesting that production of nutrient-depleted water occurred in both oceans during the glaciation. Enriched ¹³C values in shallow cores within the Atlantic Ocean indicate the existence of a nutrient-depleted water mass above 2000 m in this ocean.