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

本提案旨在解决关于黑海水柱缺氧的强度和深度分布的争论，并为阐明古代“黑色页岩”古环境的新技术的有效性提供测试。以前的工人们建议,对织物的解释的基础上,从8 ka的沉积物的地球化学特征2 ka,完美层,有机碳(OC)沉积物丰富的第二单元,通常被称为腐泥煤,沉积在一个缺氧的水柱的海侵缺氧的起始时间,早些时候开始更深的水,或产生一个缺氧的水柱高马莲生产率的结果。1988年R/V Knorr考察期间恢复的黑海岩心研究的新结果表明，在大约7.5 ka时，在大约200米至2250米的深度范围内，整个盆地的水柱缺氧几乎是同步发生的，并且缺氧在II单元沉积过程中普遍存在。然而，第2单元上部有机质的浓度、积累速率和保存程度均有所下降，这可能是由于生产力下降和趋化斜带顶部可能受到侵蚀的结果。不同的工作者对各种氧化还原敏感地球化学指标进行了不同的解释。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）大小分布，限制黄铁矿沉淀的位置（水柱与沉积物），另一种是一组有机生物标志物化合物，表明水柱中存在光合硫化物氧化细菌。这些技术将用于分析可获得的黑海重力岩心的深度样带，这些岩心恢复了II单元的完整序列，以便测试黑海全新世演化模型和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.