Deepwater circulation significantly changed during the last deglaciation from a shallow to a deepreaching overturning cell. This change went along with a drawdown of isotopically light waters into the abyss and a deep ocean warming that changed deep ocean stratification from a salinity-to a temperature-controlled mode. Yet, the exact mechanisms causing these changes are still unknown. Furthermore, the long-standing idea of a complete shutdown of North Atlantic deepwater formation during Heinrich Stadial 1 (HS1) (17.5e14.6 kyr BP) remains prevalent. Here, we present a new compilation of benthic d 13 C and d 18 O data from the North Atlantic at high temporal resolution with consistent age models, established as part of the international PAGES working group OC3, to investigate deepwater properties in the North Atlantic. The extensive compilation, which includes 105 sediment cores, reveals different water masses during HS1. A water mass with heavy d 13 C and d 18 O signature occupies the Iceland Basin, whereas between 20 and 50 N, a distinct tongue of 18 O depleted, 13 C enriched water reaches down to 4000 m water depths. The heavy d 13 C signature indicates active deepwater formation in the North Atlantic during HS1. Differences in its d 18 O signature indicate either different sources or an alteration of the deepwater on its southward pathway. Based on these results, we discuss concepts of deepwater formation in the North Atlantic that help to explain the deglacial change from a salinity-driven to a temperature-driven circulation mode.