Remineralization dominating the δ13C decrease in the mid-depth Atlantic during the last deglaciation

δ13C records from the mid-depth Atlantic show a pronounced decrease during Heinrich Stadial 1 (HS1), deglacial episode of dramatically weakened Meridional Ocean Circulation (AMOC). Proposed explanations for this include greater fraction δ13C-depleted southern sourced water (SSW), in North Deep Water (NADW) end-member, and accumulation respired organic carbon. However, relative importance these proposed mechanisms cannot be quantitatively constrained current available observations alone. Here we diagnose individual contributions to change using transient simulation with carbon isotopes idealized tracers. We find that although low-δ13C SSW increases response weaker AMOC HS1, mass mixture only plays minor role decrease. Instead, increased remineralization due AMOC-induced ocean ventilation is dominant cause. In study, differentiate between deep end-members, which are assigned regions used previous paleoceanography studies, surface near-surface defined physical origin masses. NADW end-member includes additional remineralized material accumulated when sinking (surface end-member). Therefore, end-members should diagnosing changes. Furthermore, our results suggest more critical than along transport pathway formation region ocean, especially early deglaciation.