The timing of deglacial circulation changes in the Atlantic

Well‐dated benthic foraminifer oxygen isotopic records (δ18O) from different water depths and locations within the Atlantic Ocean exhibit distinct patterns and significant differences in timing over the last deglaciation. This has two implications: on the one hand, it confirms that benthic δ18O cannot be used as a global correlation tool with millennial‐scale precision, but on the other hand, the combination of benthic isotopic records with independent dating provides a wealth of information on past circulation changes. Comparing new South Atlantic benthic isotopic data with published benthic isotopic records, we show that (1) circulation changes first affected benthic δ18O in the 1000–2200 m range, with marked decreases in benthic δ18O taking place at ∼17.5 cal. kyr B.P. (ka) due to the southward propagation of brine waters generated in the Nordic Seas during Heinrich Stadial 1 (HS1) cold period; (2) the arrival of δ18O‐depleted deglacial meltwater took place later at deeper North Atlantic sites; (3) hydrographic changes recorded in North Atlantic cores below 3000 m during HS1 do not correspond to simple alternations between northern‐ and southern‐sourced water but likely reflect instead the incursion of brine‐generated deep water of northern as well as southern origin; and (4) South Atlantic waters at ∼44°S and ∼3800 m depth remained isolated from better‐ventilated northern‐sourced water masses until after the resumption of North Atlantic Deep Water (NADW) formation at the onset of the Bølling‐Allerod, which led to the propagation of NADW into the South Atlantic. Key Points Benthic d18O can't be used as global correlation tool with millennial‐scale precision Independently dated benthic d18O records provide information on circulation changes Arrival of d18O‐depleted meltwater took place later at deeper North Atlantic sites