“古新世-始新世極熱” (PETM)是一個(gè)眾所周知的突然變暖事件,，發(fā)生在距今大約5580萬年前,，通常被認(rèn)為是由溫室氣體的大量釋放引起的（很可能來自水合甲烷）,，如在一次碳同位素大幅度偏移（異常）中所記錄到的那樣,。
Ross Secord及其同事通過對(duì)來自美國懷俄明州Bighorn Basin的哺乳動(dòng)物牙齒進(jìn)行同位素分析發(fā)現(xiàn),，在那次同位素異常出現(xiàn)之前大陸氣候變暖大約5 攝氏度,。因此,，PETM似乎是由至少兩個(gè)單獨(dú)的變暖事件引起的,，每個(gè)都是由不同過程造成的。（生物谷Bioon.com）
生物谷推薦英文摘要：
Nature doi:10.1038/nature09441
Continental warming preceding the Palaeocene–Eocene thermal maximum
Ross Secord,[email protected] D. Gingerich,Kyger C. Lohmann& Kenneth G. MacLeod
Marine and continental records1 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 CIE2, 3, 4, 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.
