Did the Ice Age Affect South America?
The ice age, a period marked by the extensive growth of continental ice sheets, has been a subject of extensive research and interpretation. Typically, ice ages are primarily caused or ended by changes in Northern Hemisphere summers due to variations in the Earth's orbit, tilt, and axis (known as the Milankovich cycles). However, the effects of these cycles on the Southern Hemisphere, including South America, have often been overlooked. This article delves into the potential impacts of the ice age on South America, utilizing the Milankovich cycles as a framework.
Understanding the Milankovich Cycles
The Milankovich cycles consist of three key aspects: axial tilt, eccentricity of Earth's orbit, and obliquity (precession). These cycles influence the distribution of solar radiation on Earth, leading to variations in temperature and, consequently, the growth and retreat of glaciers.
Axial Tilt and Glaciations
The axial tilt of the Earth, which ranges between 22.1° and 24.5°, is another crucial factor in the glaciation process. When the axial tilt is at its lowest, it tends to support ice ages, as seen during the last glaciation period. This is because the polar regions receive less solar radiation, leading to the accumulation of snow and ice. Conversely, a peak axial tilt—such as around 10,700 years ago—signals a phase of melting glaciation.
In the Southern Hemisphere, a similar process occurs, but with some nuances. For instance, the peak axial tilt around 10,700 years ago corresponds to a period of glaciation melting in the North. This implies that South America, being less directly impacted by the axial tilt fluctuations, remains relatively stable. However, during the 29,000 to 35,000 years ago range, South America may have experienced the perfect storm of colder summers alongside extensive glaciation in the Northern Hemisphere. This could have resulted in lower sea levels and possibly the expansion of South American glaciers.
Precession and Glaciations
The precession cycle, or axial precession, determines the time of year when Earth's northernmost and southernmost points are directly towards the Sun. A peak in the precession cycle currently occurs in January, making the Northern Hemisphere summers colder and the Southern Hemisphere summers warmer. Conversely, a peak in mid-summer (June) would reverse these effects, making Northern Hemisphere summers warmer and Southern Hemisphere summers cooler.
Given the current alignment of these cycles, the Northern Hemisphere is currently experiencing colder summers, while the Southern Hemisphere enjoys warmer ones. This phenomenon could have significant implications for glacier growth and distribution, particularly in South America. Historical records suggest that during periods of colder summers in the Southern Hemisphere, the African monsoon season might shift northward, bringing rain to previously dry regions such as the Sahara desert, potentially turning them green and fostering the development of lakes and forests.
South American Glaciers and Orbital Variations
Despite the potential for larger glaciers during colder summers, South American glaciers are generally smaller and less studied compared to their counterparts in the Northern Hemisphere. South America's large oceans act as significant temperature buffers, mitigating the effects of the Milankovich cycles. Consequently, the temperature variations in South America are less extreme, with winter and summer temperatures differing by only 5 to 10 degrees Celsius.
Furthermore, South America's predominantly tropical climate, crossed by the equator, makes it less susceptible to glaciation. Glaciers typically occur within the 30-degree latitude band around the poles. During peak glaciation in the Northern Hemisphere, glaciers rarely extend beyond 45 degrees latitude. South America's topography is also a limiting factor, as its highest elevations do not reach the 30-degree latitude line, and only a small portion of the continent is within 45 degrees of the pole.
The focus on South American glaciers and their response to orbital variations would provide valuable insights into how the climatic system operates on a global scale. Further research in this area could enhance our understanding of past and present climate patterns and inform future climate change scenarios.
While detailed historical records of South American glaciers are limited, this article underscores the importance of considering the Milankovich cycles in comprehending the role of glaciations across the globe, including the often-overlooked Southern Hemisphere.
Stay tuned for further updates on the fascinating interplay between climate, glaciers, and Earth's orbital variations.