2 rise during Heinrich Stadial 1 (HS1: 14.5–17.5 kyr B.P.) remains elusive. We present a compilation of four paired surface and intermediate-depth foraminiferal δ¹³C records to test whether reduced biological pump efficiency led to the initial CO₂ rise during the last deglaciation. Surface ocean δ¹³C decreased across HS1 while intermediate-depth δ¹³C increased, leading to a reduction in the upper ocean δ¹³C gradient. Our compilation also suggests the δ¹³C gradient increased during the Bølling-Allerød (12.9–14.5 kyr B.P.) and decreased during the Younger Dryas (YD: 11.7–12.9 kyr B.P.). The HS1 and YD data are consistent with reduced biological export of isotopically light carbon from the surface ocean and its remineralization at depth. Our results support the idea that a weaker Atlantic Meridional Overturning Circulation decreased biological pump efficiency by increasing the overall fraction of preformed nutrients in the global ocean, leading to an increase in atmospheric CO₂. The full article is available on the Geophysical Research Letters website at http://onlinelibrary.wiley.com/doi/10.1002/2016GL070723/full  ]]>