Exploring the roles of ocean circulation and orbital forcing on palaeoceanographic conditions in the southern Tethys during the Late Cretaceous

探索晚白垩世海洋环流和轨道强迫对特提斯南部古海洋条件的作用

• 批准号: NE/R012350/1
• 负责人: Stuart Robinson
• 金额: $ 7.22万
• 依托单位: University of Oxford
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2017
• 资助国家: 英国
• 起止时间: 2017 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FR012350%2F1
• 关键词: Exploring; roles; ocean; circulation; orbital

For much of Earth history atmospheric CO2 levels and average global temperatures are thought to have been much higher than present. These periods of time are known as 'greenhouse' climates. The Cretaceous (145 to 65 million years ago) was an extreme end-member of a greenhouse climate. Then the climate was much warmer than it is today; there was little or no polar ice and sea-levels were high. In polar areas, like Alaska and Antarctica, which are cold today, dinosaurs, crocodiles and tropical plants flourished. The Cretaceous ocean was also sensitive to changes in oxygen concentration, and, at times, became completely devoid of oxygen over widespread areas (so-called 'oceanic anoxic events' or OAEs). The controls on Cretaceous warmth and the links between the greenhouse climate and short-duration events, such as OAEs, are not well understood. Two factors are likely to have been important over different timescales. Over long-timescales (millions of years), changes in atmospheric carbon dioxide and the position of the continents are major drivers of climate. The positions of the continents can affect patterns of ocean circulation, which control the movement of heat around the Earth surface, and the storage of heat in the interior of the ocean. In the modern world, surface water sinks to great depths in the oceans in high-latitude regions and then fills the deepest parts of the ocean basins. This formation of deep-water masses provides oxygen throughout much of the ocean. However, in times of extreme warmth, such as the Cretaceous, it is uncertain whether these processes were operational, with implications for both climate and ocean environments. Using the new deep-sea sediment cores collected during Expedition 369, this project will use an element (neodymium) as a tracer for deep-water masses in the Late Cretaceous, which will allow us to determine where deep-water was coming from (high or low latitudes?), whether these sources changed through time as the continents moved and the relationships between water mass sources and other climatic and environmental phenomena, such as OAEs.On shorter-time scales of 10s to 100s of thousands of years, climate is controlled by variations in Earth's orbit. These variations effect the seasonal and geographic distribution of energy from the sun and the total amount of energy the planet receives, all of which can lead to climatic oscillations. Investigating the signature of these climatic cycles can help understand which processes on Earth were important in controlling regional climates in the past. Furthermore, because each cycle type has a characteristic duration, counting cycles can be used to determine the amount of time represented by a given thickness of sediment on the sea floor. This in turn can help refine the geological time scale by providing accurate estimates of the amount of time that elapsed between key points in the geological record, such as the evolution and extinction of certain organisms. This project will make measurements of the chemical and physical characteristics of the sediment cores from Expedition 369 at extremely high-resolution (more than 50 measurements per m) over 10s to 100s of meters. These data can then be analysed to determine how many cycles are present and of what type.

在地球历史的大部分时间里，大气中的二氧化碳水平和平均全球温度被认为比现在高得多。这些时期被称为“温室”气候。白垩纪（145至6500万年前）是温室气候的极端成员。然后气候比今天温暖得多。几乎没有或没有极地冰，海平面很高。如今，如今寒冷的阿拉斯加和南极，如阿拉斯加和南极，恐龙，鳄鱼和热带植物蓬勃发展。白垩纪海洋也对氧气浓度的变化也很敏感，有时会在广泛的地区完全没有氧气（所谓的“海洋缺氧事件”或OAE）。对白垩纪温暖的控制以及温室气候与短期事件（例如OAES）之间的联系尚不清楚。在不同的时间尺度上，两个因素可能很重要。在长时间（数百万年）的长时间，大气二氧化碳和大陆的位置的变化是气候的主要驱动力。大陆的位置会影响海洋循环的模式，海洋循环的模式控制着地球表面的热量运动，并在海洋内部储存热量。在现代世界中，地表水沉入高纬度地区的海洋深处，然后填充海盆中最深的部分。深水质量的这种形成在整个海洋的大部分地区都提供了氧气。但是，在诸如白垩纪之类的极端温暖时期，尚不确定这些过程是否是运作的，对气候和海洋环境都有影响。使用在Expedition 369期间收集的新的深海沉积物核还是低纬度？），这些来源是否随着大陆的移动而随着时间的流逝而变化，水质量来源与其他气候和环境现象之间的关系，例如OAE.在10至100千年的较短时间范围内，气候是由地球轨道的变化控制。这些变化影响了来自太阳能量的季节性和地理分布以及行星收到的总能量，所有这些能量都可以导致气候振荡。研究这些气候周期的签名可以帮助了解地球上哪些过程对于控制区域气候很重要。此外，由于每种循环类型具有特征持续时间，因此计数周期可用于确定海底上给定的沉积物厚度所代表的时间。反过来，这可以通过提供对地质记录中的关键点之间经过的时间（例如某些生物的演变和灭绝）之间经过的时间的准确估计来帮助完善地质时间尺度。该项目将以极高的高分辨率（每m超过50次测量）在10至100米的米中以极高的高分辨率（超过50次测量）来测量探险369沉积物核的化学和物理特性。然后可以分析这些数据，以确定存在多少个周期以及哪种类型。

项目成果

A lower to middle Eocene astrochronology for the Mentelle Basin (Australia) and its implications for the geologic time scale

• DOI: 10.1016/j.epsl.2019.115865
• 发表时间: 2020-01
• 期刊: Earth and Planetary Science Letters
• 影响因子: 5.3
• 作者: M. Vahlenkamp;D. De Vleeschouwer;S. Batenburg;K. Edgar;E. Hanson;Mathieu Martinez;H. Pälike;K. MacLe