Dynamics of a stepped carbon-isotope excursion: Ultra high-resolution study of Early Toarcian environmental change
Dynamics of a stepped carbon-isotope excursion: Ultra high-resolution study of Early Toarcian environmental change
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DOI：
10.1016/j.epsl.2011.12.021
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发表时间：
2012-02-15
影响因子：
5.3
通讯作者：
Jenkyns, Hugh C.
中科院分区：
文献类型：
--
作者：
Hermoso, Michael;Minoletti, Fabrice;Jenkyns, Hugh C.
在Toarcian（早侏罗世;类似于1.83亿年前），海洋-大气系统受到最近2.5亿年来碳循环最大的扰动之一，称为Toarcian海洋缺氧事件（T-OAE）。这一事件伴随着-6%的负碳同位素偏移（CIE），这是由于同位素轻碳大量注入海洋-大气系统造成的，可能是由于天然气水合物的不稳定。这项研究揭示了导致CIE和富含有机物的沉积物广泛沉积的事件的节奏和顺序。来自巴黎盆地保存异常完好的碳酸盐和有机物的非常高分辨率的同位素记录使得能够在主要的负CIE之前识别出类似于130 kyr的增加的CO2水平。记录到pCO（2）的加速增加类似于在该负偏移开始之前的25 kyr，并且是如此迅速和如此强烈，以至于它导致巴黎盆地中相对于碳酸钙的水柱不饱和。欠饱和表示为由表面居住的钙化者产生的生物方解石的积累的急剧下降。这些环境扰动，代表CO2注入的前体阶段，早于碳酸盐和有机质中相对较轻的碳同位素的第一步，并暂时归因于Karoo-Ferrar岩浆活动。陆地碳的这种负向变化比海洋碳酸盐的记录稍早。随后的全球变暖被认为是释放同位素轻碳的原因，并最终导致了巴黎盆地的缺氧：这些累积的碳输入对地球系统的反应。同位素和沉积学证据表明，在整个负CIE的第一步不断提高的植物生长素生产力，这表明生物泵加速了过量碳的下降，导致碳酸盐沉积的暂时恢复，类似于CIE的第一步后的45 kyr。在同位素轻碳逐步释放之前，水柱饱和状态的重建只是短暂的。(C)2011 Elsevier By. All rights reserved.
In the Toarcian (Early Jurassic; similar to 183 Myr ago), the ocean-atmosphere system was subject to one of the largest perturbations of the carbon cycle in the last 250 Myr known as the Toarcian Oceanic Anoxic Event (T-OAE). This event was accompanied by a -6% negative carbon-isotope excursion (CIE) caused by massive injection of isotopically light carbon into the ocean-atmosphere system, possibly from destabilisation of gas hydrates. This study reveals the pacing and sequence of events leading up to the CIE and to widespread deposition of organic-rich sediments. The very high-resolution isotopic record from exceptionally well-preserved carbonate and organic matter from the Paris Basin enables recognition of increased CO2 levels similar to 130 kyr in advance of the major negative CIE. An accelerated increase in the pCO(2) is registered similar to 25 kyr before the onset of this negative excursion and was so rapid and so intense that it led to a water column undersaturated with respect to calcium carbonate in the Paris Basin. Undersaturation is expressed as a dramatic drop in the accumulation of the biogenic calcite produced by the surface-dwelling calcifiers. These environmental perturbations, representing precursor phases of CO2 injection, predate the first step towards relatively light carbon isotopes in carbonate and organic matter and are tentatively attributed to Karoo-Ferrar magmatism. This negative shift was registered slightly earlier in terrestrial carbon than marine carbonate. Subsequent global warming is credited with liberating isotopically light carbon, and ultimately fostered anoxia in the Paris Basin: the response of these cumulative inputs of carbon to the Earth system. Isotopic and sedimentological evidence indicates continuously elevated phytoplanktonic productivity throughout the first step of the negative CIE, suggesting that the biological pump accelerated the drawdown of excess carbon leading to temporary recovery of carbonate sedimentation, similar to 45 kyr after the first step of the CIE. This re-establishment of the saturation state of the water column was only fleeting before the later stepwise release of isotopically light carbon. (C) 2011 Elsevier By. All rights reserved.