William B. Curry

What do benthic δ13C and δ18O data tell us about Atlantic circulation during Heinrich Stadial 1

Approximately synchronous with the onset of Heinrich Stadial 1 (HS1), δ13C decreased throughout most of the upper (~1000–2500 m) Atlantic, and at some deeper North Atlantic sites. This early deglacial δ13C decrease has been alternatively attributed to a reduced fraction of high-δ13C North Atlantic Deep Water (NADW) or to a decrease in the NADW δ13C source value. Here we present new benthic δ18O and δ13C 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 δ13C and δ18O occurred in upper waters containing the highest NADW fraction during the LGM. We show that the δ13C decrease can be explained entirely by a lower NADW δ13C 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 δ13C values in the upper North Atlantic. We suggest that the benthic δ18O 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.

Increased hurricane frequency near Florida during Younger Dryas Atlantic Meridional Overturning Circulation slowdown

15 The risk posed by intensification of North Atlantic hurricane activity remains 16 controversial, in part due to a lack of available storm proxy records that extend beyond 17 the relatively stable climates of the late Holocene. Here we present a record of storm18 triggered turbidite deposition offshore the Dry Tortugas, south Florida, USA, that spans 19 abrupt transitions in North Atlantic sea-surface temperature and Atlantic Meridional 20 Overturning Circulation (AMOC) during the Younger Dryas (12.9–11.7 k.y. B.P.). 21 Despite potentially hostile conditions for cyclogenesis in the tropical North Atlantic at 22