Geological evidence indicates large continental‐scale Antarctic ice volume variations during the early and mid‐Miocene. On million‐year timescales, these variations can largely be explained by equilibrium Antarctic ice sheet (AIS) simulations. In contrast, on shorter orbital timescales, the AIS needs not be in equilibrium with the forcing and ice volume variations may be substantially different. Here, we introduce a conceptual model, based on ice dynamical model results, to investigate the difference between transient variability and equilibrium differences of the Miocene AIS. In our model, an ice sheet will grow (shrink) by a specific rate when it is smaller (larger) than its equilibrium size. We show that phases of concurrent ice volume increase and rising CO₂ levels are possible, even though the equilibrium ice volume decreases monotonically with CO₂. When the AIS volume is out of equilibrium with the forcing climate, the ice sheet can still be adapting to a relatively large equilibrium size, although CO₂ is rising after a phase of decrease. A delayed response of Antarctic ice volume to (co‐varying) solar insolation and CO₂ concentrations can cause discrepancies between Miocene solar insolation and benthic δ¹⁸O variability. Increasing forcing frequency leads to a larger disequilibrium, and consequently larger CO₂‐ice volume phase differences. Furthermore, an amplified forcing amplitude cause larger amplitude ice volume variability, because the growth and decay rates depend on the forcing. It also leads to a reduced average ice volume, resulting from the growth rates generally being smaller than the decay rates.

中文翻译：

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南极冰盖瞬变的反相中新世冰量和二氧化碳变化

地质证据表明，在中新世早期和中期，大陆规模的南极冰量变化很大。在百万年的时间尺度上，这些变化很大程度上可以通过南极冰盖平衡（AIS）模拟来解释。相反，在较短的轨道时标上，AIS不必与强迫保持平衡，并且冰量变化可能会大不相同。在此，我们基于冰动力学模型结果介绍一个概念模型，以研究中新世AIS的瞬变和平衡差异之间的差异。在我们的模型中，当冰盖小于（大于）平衡尺寸时，冰盖会以特定速率生长（收缩）。我们显示了同时冰量增加和CO ₂上升的阶段即使平衡冰量随CO ₂单调降低，也可能达到最高水平。当AIS的体积与强迫气候不平衡时，尽管CO ₂在下降阶段之后上升，但冰盖仍可以适应较大的平衡尺寸。南极冰体积对（共变）太阳辐射和CO的延迟响应₂浓度可引起新统太阳辐射和底栖之间的差异δ ¹⁸ ö变性。强制频率增加会导致更大的不平衡，从而导致更大的CO ₂冰体积相位差。此外，放大的强迫幅度会导致更大的幅度冰体积变化，因为增长率和衰减率取决于强迫。这也导致平均冰量减少，这是由于增长率通常小于衰减率。