NOAA/WDS Paleoclimatology - Atlantic Ocean 23,000 Year Benthic Foraminifera Stable Isotope Data

Approximately synchronous with the onset of Heinrich Stadial 1 (HS1), d13C decreased throughout most of the upper (~1000-2500 m) Atlantic, and at some deeper North Atlantic sites. This early deglacial d13C decrease has been alternatively attributed to a reduced fraction of high-d13C North Atlantic Deep Water (NADW) or to a decrease in the NADW d13C source value. Here we present new benthic d18O and d13C records from three relatively shallow (~1450-1650 m) subpolar Northeast Atlantic cores. With published data from other cores, these data form a depth transect (~1200-3900 m) in the subpolar Northeast Atlantic. We compare Last Glacial Maximum (LGM) and HS1 data from this transect with data from a depth transect of cores from the Brazil Margin. The largest LGM-to-HS1 decreases in both benthic d13C and d18O occurred in upper waters containing the highest NADW fraction during the LGM. We show that the d13C decrease can be explained entirely by a lower NADW d13C source value, entirely by a decrease in the proportion of NADW relative to Southern Ocean Water, or by a combination of these mechanisms. However, building on insights from model simulations, we hypothesize that reduced ventilation due to a weakened but still active Atlantic Meridional Overturning Circulation also contributed to the low d13C values in the upper North Atlantic. We suggest that the benthic d18O gradients above ~2300 m at both core transects indicate the depth to which heat and North Atlantic deglacial freshwater had mixed into the subsurface ocean by early HS1.