Osmium isotope evidence for the regulation of atmospheric CO2 by continental weathering
Osmium isotope evidence for the regulation of atmospheric CO2 by continental weathering
复制标题
DOI：
10.1130/g20158.1
复制
发表时间：
2004-02-01
期刊：
影响因子：
5.8
通讯作者：
Schwark, L
中科院分区：
文献类型：
--
作者：
Cohen, AS;Coe, AL;Schwark, L
地球气候在整个显生界的长期稳定性与在短至几年的时间尺度上发生的剧烈波动形成鲜明对比，反映了通过负反馈进行长期气候调节的高效率。一种基本的机制被认为涉及到通过大陆风化来控制海洋-大气系统中的二氧化碳，尽管到目前为止还没有明确的、高分辨率的数据支持这一假设。来自英国约克郡的富含有机物质的泥岩沉积于托阿尔西亚海洋缺氧事件(约181 Ma，早侏罗世)期间，它包含了同期海水Os-187/Os-188比值异常大的漂移的证据，从类似于0.4到类似于1.0。对这种漂移最有可能的解释是，它是由全球大陆风化速率的短暂增加造成的，类似于400%-800%。Os同位素漂移与全球三角洲(13)C漂移相吻合，其漂移幅度为-6ppm，影响了当时所有主要的生物圈储集层。较高的全球平均气温导致全球化学风化速率大幅增加，而反过来，化学风化又非常有效地将大气中二氧化碳的升高水平和高温降低到漂移前的水平。
The long-term stability of Earth's climate throughout the Phanerozoic stands in marked contrast to the dramatic fluctuations that have taken place on time scales as short as a few years, reflecting the high efficiency of longer-term climate regulation through negative feedbacks. A fundamental mechanism is thought to involve control of CO2 in the ocean-atmosphere system through continental weathering, although unambiguous, high-resolution data supporting this hypothesis have hitherto not been available. Organic-rich mudrocks from Yorkshire, England, which were deposited during the Toarcian oceanic anoxic event (ca. 181 Ma, Early Jurassic), contain evidence of an exceptionally large excursion in the Os-187/Os-188 ratio of contemporaneous seawater, from similar to0.4 to similar to1.0. The most likely explanation for this excursion is that it resulted from a transient increase in global continental weathering rates of similar to400%-800%. The Os isotope excursion coincided with a well-documented global delta(13)C excursion of -6parts per thousand,, that affected all the major biospheric reservoirs of the time. Higher mean global temperatures caused global chemical weathering rates to increase substantially, while, in turn, chemical weathering was very effective in reducing the elevated levels of atmospheric CO2 and the high temperatures to preexcursion levels.