Quantification of factors impacting seawater and calcite δ¹⁸O during Heinrich Stadials 1 and 4

We perform idealized experiments of a Heinrich Stadial using an oxygen‐isotope‐enabled Earth System Climate Model. Our results compare relatively well with the planktic and benthic δ 18 O records of Heinrich Stadials 1 and 4. We find that changes in surface can be equally attributed to the “temperature effect” due to fractionation during calcification; the “circulation and climate effect” due to changes in circulation, precipitation, and evaporation; and the “meltwater effect” due to the addition and subsequent advection of depleted fresh water from continental ice sheets. In contrast, the meltwater effect and circulation and climate effect have only a small impact on benthic during the cessation of the Atlantic Meridional Overturning Circulation (AMOC). Significant temperature changes simulated in both the deep Atlantic and Pacific Oceans substantially influence benthic during that time. During the AMOC recovery, however, anomalously low surface waters are advected to the deep Atlantic, thus generating a large (∼0.5‰) decrease in the deep North Atlantic. This is in contrast to a hypothesis that links such depletion seen in Atlantic sediment cores during the last glacial stadials to deepwater formation caused by brine rejection and sea ice formation.