Active North Atlantic deepwater formation during Heinrich Stadial 1

Deepwater circulation significantly changed during the last deglaciation from a shallow to a deep-reaching 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) (17.5–14.6 kyr BP) remains prevalent. Here, we present a new compilation of benthic δ¹³C and δ¹⁸O 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 δ¹³C and δ¹⁸O signature occupies the Iceland Basin, whereas between 20 and 50°N, a distinct tongue of ¹⁸O depleted, ¹³C enriched water reaches down to 4000 m water depths. The heavy δ¹³C signature indicates active deepwater formation in the North Atlantic during HS1. Differences in its δ¹⁸O 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.