A Test of Models for the Evolution of Water-Column Anoxia in the Black Sea Over the Past 8.5 Years

小行星9628344亚瑟 这项建议旨在解决关于黑海水体中缺氧的强度和深度分布的辩论，并对阐明古代“黑色页岩”古环境的新技术的效力进行测试。 根据对距今约8 ka ~ 2ka沉积物的组构和地球化学特征的解释，前人认为，单元II的富含有机碳（OC）的细层状沉积物（通常称为腐泥）要么沉积在缺氧水柱下，缺氧的开始是时间海侵的，在较深的水中开始较早，或者是由于地表水的高生产率而在缺氧水柱下产生的。 从1988年R/V Knorr考察期间恢复的黑海岩心研究的新结果表明，在约7.5 ka水柱缺氧的发病几乎是同步的整个盆地的深度范围约200米至2250米，缺氧盛行整个沉积单元II。 然而，浓度，积累率，和保存的有机质的程度都下降了在单元II的上部，也许是由于生产力下降和可能的侵蚀顶部的化跃层。 各种氧化还原敏感的地球化学指标已被不同的工作者以不同的方式解释。 在拟议的研究中，我们将使用两种新技术，一种涉及黄铁矿（framboid）的大小分布，限制黄铁矿沉淀的网站（水柱与沉积物内），和其他一组有机生物标志物化合物指示的存在下，光合作用的硫化物氧化细菌在水柱。 这些技术将用于分析现有黑海重力岩心的深度剖面，这些岩心恢复了第二单元的完整序列，以测试黑海全新世演变模型和一般富含有机碳的沉积物的起源。

9628344 Arthur This proposal seeks to resolve a debate as to the intensity and depth distribution of oxygen deficiencies in the water column of the Black Sea and to provide a test of the efficacy of new techniques for elucidating paleoenvironments of ancient "black shales". Previous workers have suggested, on the basis of interpretation of the fabric and geochemical characteristics of sediments deposited from about 8 ka to 2 ka, that finely laminated, organic-carbon (OC) rich sediments of Unit II, often referred to as sapropels, either were deposited under an anoxic water column for which initiation of anoxia was time transgressive, beginning earlier in deeper water, or were produced under an anoxic water column as the result of high surface-water productivity. New results from the study of Black Sea cores recovered during the 1988 R/V Knorr expedition suggest that the onset of water-column anoxia at about 7.5 ka was virtually synchronous across the basin over a depth range of about 200 m to 2250 m, and that anoxia prevailed throughout deposition of Unit II. However, the concentration, accumulation rate, and degree of preservation of organic matter all decreased in the upper part of Unit II, perhaps as a result of decreasing productivity and possible erosion of the top of the chemocline. Various redox-sensitive geochemical indicators have been interpreted by different workers in contrasting ways. In the proposed study, we will use two new techniques, one involving pyrite (framboid) size distributions that constrain the site of pyrite precipitation (water column vs. within sediment), and the other a set of organic biomarker compounds indicative of the presence of photosynthetic sulfide-oxidizing bacteria in the water column. These techniques will be used in analysis of a depth transect of available Black Sea gravity cores that recovered complete sequences of Unit II in order to test models of the Holocene evolution of the Black Sea and the origin(s) of sediments enriched in organic car bon in general.