The Antarctic Cold Reversal (ACR) was an important episode of cooling in the

climate Climate is the long-term weather pattern in an area, typically averaged over 30 years. More rigorously, it is the mean and variability of meteorological variables over a time spanning from months to millions of years. Some of the meteorologic ...

history of the Earth during the

deglaciation Deglaciation is the transition from full glacial conditions during ice ages, to warm interglacials, characterized by global warming and sea level rise due to change in continental ice volume. Thus, it refers to the retreat of a glacier, an ice shee ...

at the close of the last

ice age An ice age is a long period of reduction in the temperature of Earth's surface and atmosphere, resulting in the presence or expansion of continental and polar ice sheets and alpine glaciers. Earth's climate alternates between ice ages and gree ...

. It illustrates the complexity of the climate changes at the transition from the

Pleistocene The Pleistocene ( , often referred to as the ''Ice age'') is the geological Epoch (geology), epoch that lasted from about 2,580,000 to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was fina ...

to the

Holocene The Holocene ( ) is the current geological epoch. It began approximately 11,650 cal years Before Present (), after the Last Glacial Period, which concluded with the Holocene glacial retreat. The Holocene and the preceding Pleistocene togethe ...

Epochs. The

Last Glacial Maximum The Last Glacial Maximum (LGM), also referred to as the Late Glacial Maximum, was the most recent time during the Last Glacial Period that ice sheets were at their greatest extent. Ice sheets covered much of Northern North America, Northern Eur ...

and sea-level minimum occurred c. 21,000 years before present ( BP). Antarctic ice cores show gradual warming beginning 3,000 years later. At about 14,700 BP, there was a large pulse of meltwater, identified as

Meltwater pulse 1A Meltwater pulse 1A (MWP1a) is the name used by Quaternary geologists, paleoclimatologists, and oceanographers for a period of rapid post-glacial sea level rise, between 13,500 and 14,700 calendar years ago, during which global sea level rose betw ...

, probably from either the

Antarctic ice sheet The Antarctic ice sheet is one of the two polar ice caps of Earth. It covers about 98% of the Antarctic continent and is the largest single mass of ice on Earth, with an average thickness of over 2 kilometers. It covers an area of almost and ...

or the

Laurentide Ice Sheet The Laurentide Ice Sheet was a massive sheet of ice that covered millions of square miles, including most of Canada and a large portion of the Northern United States, multiple times during the Quaternary glacial epochs, from 2.58 million years a ...

. Meltwater pulse 1A produced a

marine transgression A marine transgression is a geologic event during which sea level rises relative to the land and the shoreline moves toward higher ground, which results in flooding. Transgressions can be caused by the land sinking or by the ocean basins filling ...

that raised global sea level about 20 meters in two to five centuries and is thought to have influenced the start of the Bølling/ Allerød interstadial, the major break with glacial cold in the Northern Hemisphere. Meltwater pulse 1A was followed in

Antarctica Antarctica () is Earth's southernmost and least-populated continent. Situated almost entirely south of the Antarctic Circle and surrounded by the Southern Ocean, it contains the geographic South Pole. Antarctica is the fifth-largest contine ...

and the Southern Hemisphere by a renewed cooling, the Antarctic Cold Reversal, in c. 14,500 BP, which lasted for two millennia—an instance of warming causing cooling. The ACR brought an average cooling of perhaps 3 °C. The

Younger Dryas The Younger Dryas (c. 12,900 to 11,700 years BP) was a return to glacial conditions which temporarily reversed the gradual climatic warming after the Last Glacial Maximum (LGM, c. 27,000 to 20,000 years BP). The Younger Dryas was the last stage ...

cooling, in the Northern Hemisphere, began while the Antarctic Cold Reversal was still ongoing, and the ACR ended in the midst of the Younger Dryas. This pattern of climate decoupling between the Northern and Southern Hemispheres and of "southern lead, northern lag" would manifest in subsequent climate events. The cause or causes of this hemispheric decoupling, of the "lead/lag" pattern and of the specific mechanisms of the warming and cooling trends are still subjects of study and dispute among climate researchers. The specific dating and intensity of the Antarctic Cold Reversal are also under debate.. The onset of the Antarctic Cold Reversal was followed, after about 800 years, by an Oceanic Cold Reversal in the

Southern Ocean The Southern Ocean, also known as the Antarctic Ocean, comprises the southernmost waters of the World Ocean, generally taken to be south of 60° S latitude and encircling Antarctica. With a size of , it is regarded as the second-small ...

Notes and references

Sources

* * * * * *{{cite book , last=Oldfield , first=Frank , title=Environmental Change: Key Issues and Alternative Perspectives , url=https://archive.org/details/environmentalcha0000oldf , url-access=registration , location=Cambridge , publisher=Cambridge University Press , year=2005 , isbn=978-0-521-82936-6 Climate of Antarctica History of climate variability and change Pleistocene events

See also

Notes and references

Sources