Less Remineralized Carbon in the Intermediate-Depth South Atlantic During Heinrich Stadial 1

The last deglaciation (~20–10 kyr BP) was characterized by a major shift in Earth's climate state, when the global mean surface temperature rose ~4 °C and the concentration of atmospheric CO₂ increased ~80 ppmv. Model simulations suggest that the initial 30 ppmv rise in atmospheric CO₂ may have been driven by reduced efficiency of the biological pump or enhanced upwelling of carbon-rich waters from the abyssal ocean. Here we evaluate these hypotheses using benthic foraminiferal B/Ca (a proxy for deep water [CO₃ ²⁻]) from a core collected at 1,100-m water depth in the Southwest Atlantic. Our results imply that [CO₃ ²⁻] increased by 22 ± 2 μmol/kg early in Heinrich Stadial 1, or a decrease in ΣCO₂ of approximately 40 μmol/kg, assuming there were no significant changes in alkalinity. Our data imply that remineralized phosphate declined by approximately 0.3 μmol/kg during Heinrich Stadial 1, equivalent to 40% of the modern remineralized signal at this location. Because tracer inversion results indicate remineralized phosphate at the core site reflects the integrated effect of export production in the sub-Antarctic, our results imply that biological productivity in the Atlantic sector of the Southern Ocean was reduced early in the deglaciation, contributing to the initial rise in atmospheric CO₂.