Description: Interpretations of paleoclimate records from ocean sediment cores rely on age models to provide estimates of age as a function of core depth. As one metric of age model uncertainty, we compare four dating methods using high-resolution data over the last glacial cycle from ten Iberian Margin cores. The first method uses radiocarbon data and the Bayesian statistical software Bacon [Blaauw and Christen, 2011] . The second method aligns benthic δ18O to a target core using the probabilistic alignment algorithm HMM-Match [Lin et al., 2014] . The third and fourth methods are alignment of planktonic δ18O and sea surface temperature (SST), respectively, using the deterministic alignment software Match [Lisiecki and Lisiecki, 2002] . Where three or more age model types overlap in a core, the average range of age estimates is 1.7 kyr, and 90% of age ranges are less than 3 kyr. For the two probabilistic methods, HMM-Match and Bacon, age estimates agree to within uncertainty, and the highest resolution records yield 95% confidence interval widths of 1-2 kyr. However, HMM-Match appears to underestimate alignment uncertainty near benthic δ18O gaps in one core, as indicated by disagreement with the core's planktonic δ18O and SST alignments. Because planktonic δ18O and SST proxies appear to provide reliable alignments on the Iberian Margin, probabilistic alignment algorithms should be developed for these proxies. Ultimately, the most reliable age models would incorporate information from as many proxies as possible.

Description: 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) (17.5e14.6 kyr BP) remains prevalent. Here, we present a new compi- lation of benthic d13C and d18O 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 d13C and d18O 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 d13C signature indicates active deepwater formation in the North Atlantic during HS1. Differences in its d18O 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.

Description: 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. Highlights • Spatial analyses of benthic δ13C and δ18O data from OC3 Atlantic compilation for HS1. • Heavy δ13C, light δ18O waters migrated into deep western North Atlantic basin during HS1. • Active deepwater formation between 30 and 60°N in the North Atlantic during HS1. • New concepts for transport of isotopically light δ18O into deep ocean. • Major contribution of North Atlantic waters to deglacial deep ocean stratification changes.