Continental warming preceding the Palaeocene–Eocene thermal maximum
Continental warming preceding the Palaeocene–Eocene thermal maximum
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古新世-始新世热最大值之前的大陆变暖
作者：
Ross Secord;P. Gingerich;K. C. Lohmann;K. MacLeod
海洋和大陆记录显示，在1.558亿年前，碳同位素值出现了突然的负移。这种碳同位素偏移（CIE）与大量同位素轻碳释放到大气中是一致的，并与全球温度急剧上升有关，称为古新世-始新世热最大值（PETM）。CIE期间释放的温室气体，可能包括甲烷，通常被认为是PETM变暖的主要原因。然而，来自海洋记录的一些证据表明，变暖直接先于CIE，这增加了CIE和PETM可能与不同起源的早期变暖有关的可能性。然而，CIE之前的变暖仍然不确定。解开CIE和PETM之前和期间的事件序列对于理解气候突变的原因以及地球系统对气候突变的反应非常重要。在这里，我们表明，大陆变暖约5 °C之前，在大角盆地，怀俄明州的CIE。我们的证据，基于哺乳动物牙齿中的氧同位素（反映温度敏感的分馏过程）和其他代理，揭示了一个显着的温度上升直接低于CIE，并再次在CIE。低于CIE的土壤碳酸盐中δ 13 C值的负放大也支持了前CIE变暖。我们的研究结果表明，至少有两个变暖的来源，其中较早的是不太可能已经甲烷，有助于古埃及新世。
Marine and continental records show an abrupt negative shift in carbon isotope values at ∼55.8 Myr ago. This carbon isotope excursion (CIE) is consistent with the release of a massive amount of isotopically light carbon into the atmosphere and was associated with a dramatic rise in global temperatures termed the Palaeocene–Eocene thermal maximum (PETM). Greenhouse gases released during the CIE, probably including methane, have often been considered the main cause of PETM warming. However, some evidence from the marine record suggests that warming directly preceded the CIE, raising the possibility that the CIE and PETM may have been linked to earlier warming with different origins. Yet pre-CIE warming is still uncertain. Disentangling the sequence of events before and during the CIE and PETM is important for understanding the causes of, and Earth system responses to, abrupt climate change. Here we show that continental warming of about 5 °C preceded the CIE in the Bighorn Basin, Wyoming. Our evidence, based on oxygen isotopes in mammal teeth (which reflect temperature-sensitive fractionation processes) and other proxies, reveals a marked temperature increase directly below the CIE, and again in the CIE. Pre-CIE warming is also supported by a negative amplification of δ13C values in soil carbonates below the CIE. Our results suggest that at least two sources of warming—the earlier of which is unlikely to have been methane—contributed to the PETM.