Despite intense focus on the ∼190 ‰ drop in atmospheric Δ¹⁴C during Heinrich Stadial 1 at ∼17.4–14.6 ka, the specific mechanisms responsible for the apparent Δ¹⁴C excess in the glacial atmosphere have received considerably less attention. The computationally efficient Bern3D Earth system model of intermediate complexity, designed for long-term climate simulations, allows us to address a very fundamental but still elusive question concerning the atmospheric Δ¹⁴C record: how can we explain the persistence of relatively high Δ¹⁴C values during the millennia after the Laschamp event? Large uncertainties in the pre-Holocene ¹⁴C production rate, as well as in the older portion of the Δ¹⁴C record, complicate our qualitative and quantitative interpretation of the glacial Δ¹⁴C elevation. Here we begin with sensitivity experiments that investigate the controls on atmospheric Δ¹⁴C in idealized settings. We show that the interaction with the ocean sediments may be much more important to the simulation of Δ¹⁴C than had been previously thought. In order to provide a bounded estimate of glacial Δ¹⁴C change, the Bern3D model was integrated with five available estimates of the ¹⁴C production rate as well as reconstructed and hypothetical paleoclimate forcing. Model results demonstrate that none of the available reconstructions of past changes in ¹⁴C production can reproduce the elevated Δ¹⁴C levels during the last glacial. In order to increase atmospheric Δ¹⁴C to glacial levels, a drastic reduction of air–sea exchange efficiency in the polar regions must be assumed, though discrepancies remain for the portion of the record younger than ∼33 ka. We end with an illustration of how the ¹⁴C production rate would have had to evolve to be consistent with the Δ¹⁴C record by combining an atmospheric radiocarbon budget with the Bern3D model. The overall conclusion is that the remaining discrepancies with respect to glacial Δ¹⁴C may be linked to an underestimation of ¹⁴C production and/or a biased-high reconstruction of Δ¹⁴C over the time period of interest. Alternatively, we appear to still be missing an important carbon cycle process for atmospheric Δ¹⁴C.

中文翻译：

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神秘高位 ¹⁴ C的冰川大气：¹⁴ C产生和碳循环变化的影响

尽管强烈关注的了？？¼190 â????了？？°下降大气 我？¹⁴ Ç海因里希StadialÂ1在期间A？？¼17.4 â???? 14.6A ???? ka，负责表观α的具体机制 冰河大气中¹⁴ C过剩的问题很少受到关注。计算效率高的Bern3D地球系统模型，具有中等复杂性，专为长期气候模拟而设计，使我们能够解决有关大气δ的一个非常基本但仍难以捉摸的问题 ¹⁴ C记录：如何解释相对较高的持续性？¹⁴ ℃Laschamp事件发生后的千年中有哪些价值？在预全新世较大的不确定性 ¹⁴ Ç生产速率，以及在较旧的部分 Î?? ¹⁴ C记录，使我们对冰川γ的定性和定量解释变得复杂 ¹⁴ Ç 标高。在这里，我们从敏感性实验开始，研究大气δ的控制。¹⁴ Ç在理想化的设置。我们表明，与海洋沉积物的相互作用可能对模拟η更为重要。¹⁴ ç超过了以前认为。为了提供冰川γ的有界估计 ¹⁴随着C变化，Bern3D模型与¹⁴ C生产率以及重建的和假设的古气候强迫的五个可用估计值集成在一起。模型结果表明，在¹⁴ C生产中的过去变化的可用重建都不能复制升高的 δ？上一次冰期的¹⁴ C水平。为了增加大气α？¹⁴ Ç冰川的水平，必须假定在极地地区AIRA的????海交换效率AA急剧减少，但偏差保持备案年轻的部分比了？？¼33 â???? K a。我们以¹⁴ C生产率将如何演变为与Î一致的最后说明。¹⁴ Ç记录由大气放射性碳预算与Bern3D模型相结合。总的结论是，相对于其余的差异冰川我？¹⁴ C可能链接到低估 ¹⁴ C的生产和/或α的偏高重建 ¹⁴ Ç在感兴趣的时间段。或者，我们似乎仍然缺少大气中的重要碳循环过程？¹⁴ ℃。