Quaternary glaciation

Quaternary glaciation
Name	Quaternary glaciation
Caption	Artist's depiction of Earth during a glacial maximum.
Time	c. 2.58 million years ago – present
Duration	Ongoing
Cause	Milankovitch cycles, Atmospheric carbon dioxide, Plate tectonics
Effect	Sea level change, Ecosystem alteration, landform creation

Quaternary glaciation. The Quaternary glaciation, also known as the current ice age, is the geological period of recurring glacial expansion that began approximately 2.58 million years ago and continues to the present. This epoch is characterized by the cyclical advance and retreat of continental ice sheets, primarily in the Northern Hemisphere, profoundly shaping global climates, geographies, and the course of Human evolution. The most recent glacial period ended about 11,700 years ago, giving way to the current interglacial known as the Holocene.

Overview

The onset of the Quaternary glaciation marks the start of the Quaternary period within the Cenozoic era, a time dominated by oscillating cold phases that built massive ice sheets over North America and Eurasia. These glacial cycles are paced by variations in Earth's orbit and influenced by feedbacks involving greenhouse gases and oceanic circulation. Key features of this period include the formation of the Laurentide Ice Sheet over Canada and the northern United States, the Fennoscandian Ice Sheet covering Scandinavia, and significant alpine glaciation in ranges like the Andes and the Himalayas. The intervening warmer interglacials, such as the Eemian, saw ice retreat and sea levels rise.

Causes

The primary astronomical drivers of the glacial cycles are Milankovitch cycles, which describe periodic changes in Earth's orbit and axial tilt, altering the distribution of solar energy received by the planet. These orbital forcings are amplified by critical climatic feedback mechanisms. Declines in atmospheric Carbon dioxide and Methane, as recorded in ice cores from Vostok Station, reinforce cooling, while changes in Ocean circulation patterns, such as the Atlantic meridional overturning circulation, redistribute heat. The positioning of continents, particularly the isolation of Antarctica by the Antarctic Circumpolar Current and the closure of the Isthmus of Panama, established the thermal conditions necessary for sustained polar ice.

Glacial and interglacial periods

The Quaternary is defined by over 50 major glacial-interglacial cycles, as identified in marine sediment records like those from the Lisbon core and isotopic data from Foraminifera. The past 800,000 years, known as the Mid-Pleistocene Transition, saw cycles lengthen and intensify to roughly 100,000-year periods. Notable glacial periods include the Illinoian and Wisconsinan in North America, correlating to the Saale and Weichselian in Europe. The warm Eemian interglacial preceded the last glacial period, which culminated in the Last Glacial Maximum around 26,500 years ago before terminating into the Holocene.

Effects

The glaciation radically reshaped the Earth's surface, with ice sheets eroding bedrock to form landscapes like the Canadian Shield and depositing vast moraines and outwash plains. Global sea levels fell by over 120 meters during glacial maxima, exposing continental shelves such as Beringia, which served as a land bridge for Homo sapiens and Pleistocene megafauna. The changing climates forced major shifts in vegetation belts and faunal migrations, contributing to the Quaternary extinction event. The immense weight of the ice induced isostatic depression of crustal plates, with regions like Scandinavia still experiencing glacial rebound.

Evidence

Extensive physical and chemical evidence documents the glaciation. Landforms like U-shaped valleys in the Alps, cirques in the Rocky Mountains, and drumlin fields in New York provide geomorphological proof. Stratigraphic records from ocean cores, such as those obtained by the JOIDES Resolution, show isotopic shifts in oxygen isotopes within Foraminifera shells, charting ice volume. Direct atmospheric records come from ice cores drilled at Dome C and GRIP, while terrestrial evidence includes loess deposits in China and Poland and fossil assemblages from the La Brea Tar Pits.

Current status and future

The Earth currently resides in the Holocene interglacial, a warm period that began after the Younger Dryas cold reversal. However, the natural orbital forcing suggests a gradual return to glacial conditions over tens of thousands of years. This natural cycle is now being profoundly altered by anthropogenic influences, primarily the rapid increase in Atmospheric carbon dioxide from the combustion of fossil fuels since the Industrial Revolution. Climate models from the Intergovernmental Panel on Climate Change indicate that human activity is likely suppressing the onset of the next glacial period and driving changes that exceed the climatic variability of the past several interglacials, including the Eemian.

Category:Quaternary