Assessing offsets between the δ13C of sedimentary components and the global exogenic carbon pool across early Paleogene carbon cycle perturbations
Assessing offsets between the δ13C of sedimentary components and the global exogenic carbon pool across early Paleogene carbon cycle perturbations
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DOI：
10.1029/2011gb004224
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发表时间：
2012-12
影响因子：
5.2
通讯作者：
A. Sluijs;G. Dickens
中科院分区：
文献类型：
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作者：
A. Sluijs;G. Dickens
古新世-始新世热最大值（PETM; ~ 56 Ma）的负稳定碳同位素偏移（CIEs）范围在2‰至7‰之间，即使在截断记录的折现剖面后也是如此。单个碳同位素记录在形状和幅度上与全球外源碳循环的变化不同，这是由于(1)测量底物中不同δ13C混合组分的相对丰度的变化，(2)生理变化引起的同位素分异，以及(3)碳源的同位素组成的变化。这三个因素可能影响许多早古近纪的δ13C记录，特别是在PETM和其他过热事件中。我们将这些概念应用于北冰洋Lomonosov Ridge的晚古新世-早始新世（~ 58-52 Ma）记录。线性回归分析表明，总有机碳(TOC) δ13C与陆相有机组分对沉积物TOC相对贡献的两个指标（支链和类异戊二烯四醚指数和岩相）之间存在相关性。我们利用这些相关性从δ13CTOC中减去陆地分量，计算海相有机质δ13C。结果表明，由于陆生有机碳的增加，整个PETM δ13CTOC的CIE值相对于δ13CMOM的CIE值被放大了~ 3‰。总的来说，贯穿始新世纪的所有碳同位素记录和地球历史上其他主要的气候-碳循环扰动都可能由于上述一个或多个因素而产生偏差。事实上，任何δ13C记录都不太可能显示出全球外源碳循环的CIE的真实形状和大小。对于PETM，我们得出结论，外源碳循环中的CIE可能<4‰，但需要额外的分析和建模来获得该CIE的准确值。
Negative stable carbon isotope excursions (CIEs) across the Paleocene–Eocene thermal maximum (PETM; ∼56 Ma) range between 2‰ and 7‰, even after discounting sections with truncated records. Individual carbon isotope records differ in shape and magnitude from variations in the global exogenic carbon cycle through changes in (1) the relative abundance of mixed components with different δ13C within a measured substrate, (2) isotope fractionation through physiological change, and (3) the isotope composition of the carbon source. All three factors likely influence many early Paleogene δ13C records, especially across the PETM and other hyperthermal events. We apply these concepts to late Paleocene–early Eocene (∼58–52 Ma) records from Lomonosov Ridge, Arctic Ocean. Linear regression analyses show correlations between the δ13C of total organic carbon (TOC) and two proxies for the relative contribution of terrestrial organic components to sediment TOC: the branched and isoprenoid tetraether index and palynomorphs. We use these correlations to subtract the terrestrial component from δ13CTOC and calculate marine organic matter δ13C. The results show that the magnitude of the CIE in δ13CTOC across the PETM is exaggerated relative to the magnitude of the CIE in δ13CMOM by ∼3‰ due to increased contributions of terrestrial organic carbon during the event. Collectively, all carbon isotope records across the PETM and other major climate–carbon cycle perturbations in Earth's history are potentially biased through one or more of the above factors. Indeed, it is highly unlikely that any δ13C record shows the true shape and magnitude of the CIE for the global exogenic carbon cycle. For the PETM, we conclude that CIE in the exogenic carbon cycle is likely <4‰, but it will take additional analyses and modeling to obtain an accurate value for this CIE.