太平洋冰川深层的通风
Wallace Broecker1, Stephen Barker, Elizabeth Clark
1Lamont-Doherty Earth Observatory of Columbia University, 61 Route 9W/Post Office Box 1000, Palisades, NY 10964, USA. broecker@ldeo.columbia.edu
Science (New York, N.Y.)
|November 13, 2004
概括
深海核心的放射性碳测年显示,冰川时期的海洋通风率与今天相似. 这挑战了理论,这些理论将较慢的深海循环与冰河时代大气中碳-14水平的增加联系在一起.
科学领域:
- 古代海洋学 古代海洋学 古代海洋学
- 海洋地球化学 海洋地球化学
背景情况:
- 了解过去的海洋循环对于气候建模至关重要.
- 深海通风在冰川时期调节大气中二氧化碳的作用仍在争论中.
- 放射性碳 (14C) 是海洋循环和碳循环的关键标记物.
研究的目的:
- 通过放射性碳测年法,研究在冰川峰值时期的深海通风率.
- 评估海洋循环变化对大气14C/C比率在冰川时期的贡献.
主要方法:
- 从深海核中放射测年共存的盆地和浮游生物.
- 从同一地点共存的木材和浮游生物菌体的放射测年.
- 放射性碳年龄的比较,以重建水质年龄和表面-海洋-大气14C/C差异.
主要成果:
- 在冰川时期的高峰期,深太平洋水域 (2公里深) 的放射性碳年龄并不比现在更老.
- 大气和海洋表面14C/C比率的差异在冰川时期和现代时期是相似的.
- 这些发现表明,在冰川时期,深海通风并没有显著减缓.
结论:
- 深海循环和通风速率在冰川和冰川间时期之间是可比的.
- 深海通风的减速不太可能是冰川时期大气14C/C比率增加的主要驱动因素.
- 过去的海洋学条件可以有效地使用放射性碳测年法对海洋和陆地材料进行重建.
相关概念视频
01:17Steady, Laminar Flow Between Parallel Plates
Understanding steady, laminar flow between parallel plates is essential for analyzing and designing flow in narrow rectangular channels, commonly found in various water conveyance and drainage systems. The Navier-Stokes equations govern fluid motion and are generally challenging to solve due to their nonlinearity. However, simplifications are possible in certain cases, like the steady laminar flow between parallel plates. For this scenario, we assume steady, incompressible, laminar flow.
01:27Laminar Flow
Laminar flow represents a smooth, orderly fluid motion where particles move along parallel paths, resulting in minimal mixing between layers. Streamlined particle paths characterize this flow regime and occur under conditions where viscous forces dominate over inertial forces. The distinction between laminar, transitional, and turbulent flow is primarily determined by the Reynolds number, a dimensionless quantity calculated as:
01:24Laminar Flow: Problem Solving
Laminar flow occurs when a fluid moves smoothly in parallel layers with minimal mixing and turbulence. In fluid mechanics, ensuring laminar flow within a pipe is essential for precise control of flow characteristics, especially in engineering applications. The key factor in determining whether flow remains laminar is the Reynolds number, a dimensionless quantity that depends on the fluid's velocity, density, viscosity, and the pipe's diameter. A Reynolds number of 2100 or lower indicates...
01:26General External Flow Characteristics
The study of external flow is essential for creating structures and objects that interact efficiently and safely with moving fluids, such as air or water. When a body is immersed in a flowing fluid, it experiences two primary forces: drag, which opposes motion along the flow direction, and lift, which acts perpendicular to the flow. The shape, size, and orientation of the object influence these forces.Streamlined and Blunt Bodies in External FlowObjects in fluid flow are classified as...
01:18Boundary Layer Characteristics
When a fluid encounters a solid surface, a boundary layer forms due to the interaction between the fluid's motion and the stationary surface. This phenomenon is characterized by a thin region adjacent to the surface where viscous forces dominate, influencing the fluid's velocity profile. The development of the boundary layer begins at the leading edge of the surface and evolves as the fluid moves downstream.As the fluid flows over the surface, friction between the fluid and the wall slows down...
01:27Uniform Depth Channel Flow
Uniform depth channel flow keeps fluid depth consistent along channels such as irrigation canals. In natural channels, such as rivers, approximate uniform flow is often assumed. This condition occurs when the channel’s bottom slope matches the energy slope, balancing potential energy lost from gravity with head loss due to shear stress. This balance prevents depth changes along the channel length, resulting in a steady, uniform flow.Uniform flow in open channels with a constant cross-section...