${\delta }^{13}\mathrm{C}$ records from the mid-depth Atlantic show a pronounced decrease during the Heinrich Stadial 1 (HS1), a deglacial episode of dramatically weakened Atlantic Meridional Ocean Circulation (AMOC). Proposed explanations for this mid-depth decrease include a greater fraction of ${\delta }^{13}\mathrm{C}$-depleted southern sourced water (SSW), a ${\delta }^{13}\mathrm{C}$ decrease in the North Atlantic Deep Water (NADW) end-member, and accumulation of the respired organic carbon. However, the relative importance of these proposed mechanisms cannot be quantitatively constrained from current available observations alone. Here we diagnose the individual contributions to the deglacial Atlantic mid-depth ${\delta }^{13}\mathrm{C}$ change from these mechanisms using a transient simulation with carbon isotopes and idealized tracers. We find that although the fraction of the low-${\delta }^{13}\mathrm{C}$ SSW increases in response to a weaker AMOC during HS1, the water mass mixture change only plays a minor role in the mid-depth Atlantic ${\delta }^{13}\mathrm{C}$ decrease. Instead, increased remineralization due to the AMOC-induced mid-depth ocean ventilation decrease is the dominant cause. In this study, we differentiate between the deep end-members, which are assigned to deep water regions used in previous paleoceanography studies, and the surface end-members, which are from the near-surface water defined from the physical origin of deep water masses. We find that the deep NADW end-member includes additional remineralized material accumulated when sinking from the surface (surface NADW end-member). Therefore, the surface end-members should be used in diagnosing mechanisms of ${\delta }^{13}\mathrm{C}$ changes. Furthermore, our results suggest that remineralization in the surface end-member is more critical than the remineralization along the transport pathway from the near-surface formation region to the deep ocean, especially during the early deglaciation.

${\delta }^{13}\mathrm{C}$来自大西洋中部深度的记录显示，海因里希体育场 1 (HS1) 是大西洋经向海洋环流 (AMOC) 显着减弱的冰消期事件。对这种中间深度减少的拟议解释包括${\delta }^{13}\mathrm{C}$- 枯竭的南方水源 (SSW)， ${\delta }^{13}\mathrm{C}$北大西洋深水 (NADW) 末端成员的减少，以及呼吸有机碳的积累。然而，这些提议机制的相对重要性不能仅从当前可用的观察结果中定量限制。在这里，我们诊断了对冰消期大西洋中深度的个人贡献${\delta }^{13}\mathrm{C}$使用碳同位素和理想化示踪剂的瞬态模拟来改变这些机制。我们发现，虽然低${\delta }^{13}\mathrm{C}$ SSW 增加响应于 HS1 期间较弱的 AMOC，水团混合物的变化仅在大西洋中部深处起次要作用 ${\delta }^{13}\mathrm{C}$减少。相反，由于 AMOC 引起的中深度海洋通风减少而导致的再矿化增加是主要原因。在这项研究中，我们区分了分配给先前古海洋学研究中使用的深水区域的深部端部和来自根据深水团物理起源定义的近地表水的表层端部. 我们发现深层 NADW 端部包括从表面下沉时积累的额外再矿化物质（表面 NADW 端部）。因此，表面端元应该用于诊断${\delta }^{13}\mathrm{C}$变化。此外，我们的研究结果表明，地表端元的再矿化比沿着从近地表地层到深海的运输路径的再矿化更为重要，尤其是在早期冰川消退期间。