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

9628344阿瑟这项建议旨在解决关于黑海水柱中氧缺乏的强度和深度分布的争论，并对阐明古代“黑色页岩”的古环境的新技术的有效性进行测试。以前的工作人员根据对大约8ka至2ka沉积的沉积物的组构和地球化学特征的解释提出，第二单元的富含有机碳的细层状沉积物，通常被称为腐蚀物，要么沉积在缺氧水柱下，对缺氧的启动是时间超越性的，开始于更深的水域，或者是由于地表水生产力高而在缺氧水柱下产生的。对1988年R/V克诺尔探险期间发现的黑海岩心的新研究结果表明，大约7.5ka的水柱缺氧在整个盆地200~2250 m的深度范围内几乎是同步的，并且缺氧贯穿于单元II的整个沉积过程。然而，单元II的上部有机质的浓度、积累速率和保存程度都有所下降，这可能是由于生产力下降和可能的化跃层顶部的侵蚀所致。各种氧化还原敏感的地球化学指标被不同的工作者以不同的方式解释。在拟议的研究中，我们将使用两项新技术，一项涉及限制黄铁矿沉淀位置(水柱与沉积物内)的黄铁矿(框体)粒度分布，另一项涉及一组有机生物标记化合物，表明水柱中存在光合作用硫化物氧化细菌。这些技术将被用于分析恢复了单元II的完整序列的现有黑海重力岩芯的深度剖面，以检验黑海全新世演化模型和总体上富含有机碳的沉积物的起源(S)。

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.