Geochemical proxies of sediment core Hz11-PO3 from Lake Hazar in Eastern Anatolia

The elemental composition of lake sediment cores is often the result of several independent processes. In this study we attempt to extract statistically independent climate related signals from µ-XRF multi element data of a core drilled from Lake Hazar in Eastern Anatolia, using the independent component analysis (ICA) method. In addition, we analysed ostracod shells for oxygen and carbon isotopes. The ICA method has advantages over traditional dimension reduction methods, such as principal component analysis or factor analysis, because it is based on maximal statistical independence rather than uncorrelatedness, where independence is a stronger property.
The Hz11-P03 core, which represents the last 17.3 ka, was recovered from Lake Hazar which, at times, formed the headwaters of the Tigris. Applying the ICA method, we selected two out of six independent components by measuring distance correlation similarity. We propose that one of the selected components can be read as a proxy for temperature and the other for precipitation in this region.
Our results indicate that the region was relatively cold and wet during the late glacial, between 17.3 and 14.8 ka BP, and wet and warm during Bølling-Allerød. The lake level dropped below today's level during the Younger Dryas stadial (12.49 and 11.76 ka BP), forming a marked hiatus in the core's stratigraphic record. During the beginning of the Holocene, while precipitation values were high, the temperature gradually increased until 8 ka BP. Between 8 and 5 ka BP, the region was warm but extremely dry. After 5 ka BP, around 3.5 ka BP temperatures suddenly fell, and three abrupt dry phases are observed around 3.5 ka and 2.8 ka and 1.8 ka BP.

湖泊沉积物岩芯的元素组成通常由多种独立的沉积过程共同塑造。本研究采用独立成分分析（independent component analysis, ICA）方法，从安纳托利亚东部哈扎尔湖钻取的沉积物岩芯的µ-XRF多元素数据中，提取与气候相关的统计独立信号。此外，我们还对介形类壳体的氧、碳同位素组成开展了分析测试。相较于主成分分析、因子分析等传统降维方法，独立成分分析（ICA）具备显著优势：其以最大统计独立性为核心依据，而非仅追求变量间的非相关性——独立性是比非相关性更为严格的统计属性。

本次研究所用的Hz11-P03岩芯采自哈扎尔湖，该岩芯完整记录了过去17.3千年的沉积历史，而哈扎尔湖在部分地质时期曾是底格里斯河的源头水系。通过ICA方法，我们基于距离相关相似性从6个独立成分中筛选出2个。我们认为，筛选得到的两个独立成分可分别作为该区域温度与降水的气候代用指标。

研究结果显示，该区域在末次冰消期晚期（距今17.3~14.8 ka BP）整体呈现寒冷湿润的气候特征，在博林-阿勒罗德（Bølling-Allerød）暖期则温暖湿润。在新仙女木冰阶（12.49~11.76 ka BP）期间，哈扎尔湖水位降至现今水位以下，致使岩芯地层记录中出现显著的沉积间断。进入全新世初期，尽管区域降水充沛，但温度仍逐步升高，直至距今8 ka BP。距今8~5 ka BP期间，该区域气候温暖但极端干旱。距今5 ka BP之后，约3.5 ka BP时区域温度突降，且在3.5 ka、2.8 ka及1.8 ka BP前后共出现三次显著的干旱事件。