Antarctic Cold Reversal
Encyclopedia
The Antarctic Cold Reversal (ACR) was an important episode of cooling in the climate
history of the Earth, during the deglaciation at the close of the last ice age
. It illustrates the complexity of the climate changes at the transition from the Pleistocene
to the Holocene
Epoch.
The Last Glacial Maximum
and sea-level minimum occurred c. 21,000 years before the present (BP
). After 18,000 BP, Antarctic ice cores show gradual warming. At about 14,700 BP (or 12,700 BCE), the Antarctic ice sheet
emitted a large pulse of meltwater, identified as "Meltwater pulse 1A
." This meltwater pulse produced a marine transgression that raised global sea level about 20 meters (66 feet) in two centuries, which is thought to have influenced the start of the Bølling
/Allerød interstadial
that was the major break with glacial cold in the Northern Hemisphere. Yet meltwater pulse 1A was followed, in Antarctica and the Southern Hemisphere
, by a renewed cooling, the Antarctic Cold Reversal, which set in c. 14,500 BP (12,500 BCE) and lasted for two millennia — an instance of warming causing cooling. The ACR brought an average cooling of perhaps 3°C. The Younger Dryas
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 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 ACR was followed, after about 800 years, by an Oceanic Cold Reversal in the Southern Ocean
.
Climate
Climate encompasses the statistics of temperature, humidity, atmospheric pressure, wind, rainfall, atmospheric particle count and other meteorological elemental measurements in a given region over long periods...
history of the Earth, during the deglaciation at the close of the last ice age
Ice age
An ice age or, more precisely, glacial age, is a generic geological period of long-term reduction in the temperature of the Earth's surface and atmosphere, resulting in the presence or expansion of continental ice sheets, polar ice sheets and alpine glaciers...
. It illustrates the complexity of the climate changes at the transition from the Pleistocene
Pleistocene
The Pleistocene is the epoch from 2,588,000 to 11,700 years BP that spans the world's recent period of repeated glaciations. The name pleistocene is derived from the Greek and ....
to the Holocene
Holocene
The Holocene is a geological epoch which began at the end of the Pleistocene and continues to the present. The Holocene is part of the Quaternary period. Its name comes from the Greek words and , meaning "entirely recent"...
Epoch.
The Last Glacial Maximum
Last Glacial Maximum
The Last Glacial Maximum refers to a period in the Earth's climate history when ice sheets were at their maximum extension, between 26,500 and 19,000–20,000 years ago, marking the peak of the last glacial period. During this time, vast ice sheets covered much of North America, northern Europe and...
and sea-level minimum occurred c. 21,000 years before the present (BP
Before Present
Before Present years is a time scale used in archaeology, geology, and other scientific disciplines to specify when events in the past occurred. Because the "present" time changes, standard practice is to use AD 1950 as the origin of the age scale, reflecting the fact that radiocarbon...
). After 18,000 BP, Antarctic ice cores show gradual warming. At about 14,700 BP (or 12,700 BCE), the Antarctic ice sheet
Antarctic ice sheet
The Antarctic ice sheet is one of the two polar ice caps of the Earth. It covers about 98% of the Antarctic continent and is the largest single mass of ice on Earth. It covers an area of almost 14 million square km and contains 30 million cubic km of ice...
emitted a large pulse of meltwater, identified as "Meltwater pulse 1A
Meltwater pulse 1A
Meltwater pulse 1A was an instance in the sea level rise of about 20 m in less than 500 years, perhaps just 200 years. The meltwater event occurred in a period of rapid climate change when the Holocene glacial retreat was going on during the end of the last ice age...
." This meltwater pulse produced a marine transgression that raised global sea level about 20 meters (66 feet) in two centuries, which is thought to have influenced the start of the Bølling
Bølling Oscillation
The Bølling oscillation was a warm interstadial period between the Oldest Dryas and Older Dryas stadials, at the end of the last glacial period. It is named after a peat sequence discovered at Bølling lake, central Jutland...
/Allerød interstadial
Allerød Oscillation
The Allerød period was a warm and moist global interstadial that occurred at the end of the last glacial period. The Allerød oscillation raised temperatures , before they declined again in the succeeding Younger Dryas period, which was followed by the present interglacial period.In some regions,...
that was the major break with glacial cold in the Northern Hemisphere. Yet meltwater pulse 1A was followed, in Antarctica and the Southern Hemisphere
Southern Hemisphere
The Southern Hemisphere is the part of Earth that lies south of the equator. The word hemisphere literally means 'half ball' or "half sphere"...
, by a renewed cooling, the Antarctic Cold Reversal, which set in c. 14,500 BP (12,500 BCE) and lasted for two millennia — an instance of warming causing cooling. The ACR brought an average cooling of perhaps 3°C. The Younger Dryas
Younger Dryas
The Younger Dryas stadial, also referred to as the Big Freeze, was a geologically brief period of cold climatic conditions and drought between approximately 12.8 and 11.5 ka BP, or 12,800 and 11,500 years before present...
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 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 ACR was followed, after about 800 years, by an Oceanic Cold Reversal in the Southern Ocean
Southern Ocean
The Southern Ocean comprises the southernmost waters of the World Ocean, generally taken to be south of 60°S latitude and encircling Antarctica. It is usually regarded as the fourth-largest of the five principal oceanic divisions...
.