暁新世-始新世温暖化極大事件(PETM)研究の最前線 : 炭素同位体比層序学の貢献(<特集>顕生代の環境擾乱イベントとその解析)  [in Japanese] Forefront researches on Paleocene-Eocene thermal maximum event (PETM) : contribution of carbon isotope stratigraphy(<SPECIAL ISSUE>Organic geochemical analyses in the Phanerozoic environmental disturbance events)  [in Japanese]

The Paleocene-Eocene thermal maximum (PETM) is marked by a large negative carbon isotope excursion (CIE) and massive seafloor carbonate dissolution. Both phenomena are thought to have been caused by a sudden release of a large mass of carbon. The step-like nature of the CIE onset combined with the CIE magnitude has been explained by multiple dissociation of methane clathrate as the primary source of carbon. The natures of onset and the magnitude of CIE, however, are different between marine and terrestrial records implying potential artifacts in either or both records. Recently, the carbon isotope stratigraphy based on various techniques including compound-specific isotope analysis on terrestrial and marine biomarkers, single specimen analysis on surface-dwelling planktonic foraminifera revealed that 'actual' CIE is as large as 4‰ or larger, and the onset of the CIE was geologically instantaneous. These results demonstrated that the CIE magnitude (2-3‰) previously applied to estimate the mass of carbon released during the PETM was considerably underestimated and that abrupt input of ^<13>C-depleted carbon to the ocean-atmosphere system. Forthcoming high-resolution studies on the PETM with precise inter-regional correlation would provide a unique opportunity for comparative research of global warming between PETM period and the present.