The Pleistocene is the geological epoch that lasted from c. 2.58 million to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was finally confirmed in 2009 by the International Union of Geological Sciences, the cutoff of the Pleistocene and the preceding Pliocene was regarded as being 1.806 million years Before Present (BP). Publications from earlier years may use either definition of the period. The end of the Pleistocene corresponds with the end of the last glacial period and also with the end of the Paleolithic age used in archaeology. The name is a combination of Ancient Greek πλεῖστος (pleîstos), meaning "most", and καινός, meaning "new".
An ice core is a core sample that is typically removed from an ice sheet or a high mountain glacier. Since the ice forms from the incremental buildup of annual layers of snow, lower layers are older than upper ones, and an ice core contains ice formed over a range of years. Cores are drilled with hand augers or powered drills; they can reach depths of over two miles (3.2 km), and contain ice up to 800,000 years old.
In glaciology, an ice sheet, also known as a continental glacier, is a mass of glacial ice that covers surrounding terrain and is greater than 50,000 km2 (19,000 sq mi). The only current ice sheets are the Antarctic ice sheet and the Greenland ice sheet. Ice sheets are bigger than ice shelves or alpine glaciers. Masses of ice covering less than 50,000 km2 are termed an ice cap. An ice cap will typically feed a series of glaciers around its periphery.
The Eemian was the interglacial period which began about 130,000 years ago at the end of the Penultimate Glacial Period and ended about 115,000 years ago at the beginning of the Last Glacial Period. It corresponds to Marine Isotope Stage 5e. Although sometimes referred to as the "last interglacial", it was the second-to-latest interglacial period of the current Ice Age, the most recent being the Holocene which extends to the present day. The prevailing Eemian climate was, on average, around 1 to 2 degrees Celsius warmer than that of the Holocene. During the Eemian, the proportion of CO2 in the atmosphere was about 280 parts per million.
Dansgaard–Oeschger events, named after palaeoclimatologists Willi Dansgaard and Hans Oeschger, are rapid climate fluctuations that occurred 25 times during the last glacial period. Some scientists say that the events occur quasi-periodically with a recurrence time being a multiple of 1,470 years, but this is debated. The comparable climate cyclicity during the Holocene is referred to as Bond events.
The global temperature record shows the fluctuations of the temperature of the atmosphere and the oceans through various spans of time. There are numerous estimates of temperatures since the end of the Pleistocene glaciation, particularly during the current Holocene epoch. Some temperature information is available through geologic evidence, going back millions of years. More recently, information from ice cores covers the period from 800,000 years before the present time until now. A study of the paleoclimate covers the time period from 12,000 years ago to the present. Tree rings and measurements from ice cores can give evidence about the global temperature from 1,000-2,000 years before the present until now. The most detailed information exists since 1850, when methodical thermometer-based records began. Modifications on the Stevenson-type screen were made for uniform instrument measurements around 1880.
The Holocene Climate Optimum (HCO) was a warm period in the first half of the Holocene epoch, that occurred in the interval roughly 9,500 to 5,500 years BP, with a thermal maximum around 8000 years BP. It has also been known by many other names, such as Altithermal, Climatic Optimum, Holocene Megathermal, Holocene Optimum, Holocene Thermal Maximum, Hypsithermal, and Mid-Holocene Warm Period.
The drilling site of the North Greenland Ice Core Project (NGRIP or NorthGRIP) is near the center of Greenland (75.1 N, 42.32 W, 2917 m, ice thickness 3085). Drilling began in 1999 and was completed at bedrock in 2003. The cores are cylinders of ice 11 centimeters in diameter that were brought to the surface in 3.5-meter lengths. The NGRIP site was chosen to extract a long and undisturbed record stretching into the last glacial, and it succeeded. The site was chosen for a flat basal topography to avoid the flow distortions that render the bottom of the GRIP and GISP cores unreliable. Unusually, there is melting at the bottom of the NGRIP core – believed to be due to a high geothermal heat flux locally. This has the advantage that the bottom layers are less compressed by thinning than they would otherwise be: NGRIP annual layers at 10.5 kyr age are 1.1 cm thick, twice the GRIP thicknesses at equal age.
Marine isotope stages (MIS), marine oxygen-isotope stages, or oxygen isotope stages (OIS), are alternating warm and cool periods in the Earth's paleoclimate, deduced from oxygen isotope data derived from deep sea core samples. Working backwards from the present, which is MIS 1 in the scale, stages with even numbers have high levels of oxygen-18 and represent cold glacial periods, while the odd-numbered stages are lows in the oxygen-18 figures, representing warm interglacial intervals. The data are derived from pollen and foraminifera (plankton) remains in drilled marine sediment cores, sapropels, and other data that reflect historic climate; these are called proxies.
An interglacial period is a geological interval of warmer global average temperature lasting thousands of years that separates consecutive glacial periods within an ice age. The current Holocene interglacial began at the end of the Pleistocene, about 11,700 years ago.
The Older Dryas was a stadial (cold) period between the Bølling and Allerød interstadials, about 14,000 years Before Present, towards the end of the Pleistocene. Its date range is not well defined, with estimates varying by 400 years, but its duration is agreed to have been around two centuries.
Dye 3 is an ice core site and previously part of the DYE section of the Distant Early Warning (DEW) line, located at in Greenland. As a DEW line base, it was disbanded in years 1990/1991.
Bond events are North Atlantic ice rafting events that are tentatively linked to climate fluctuations in the Holocene. Eight such events have been identified. Bond events were previously believed to exhibit a roughly c. 1,500-year cycle, but the primary period of variability is now put at c. 1,000 years.
NEEM Camp was a small research facility on the northern Greenland Ice Sheet, used as a base for ice core drilling. It was located about 313 km east of the closest coast, Peabody Bay in northern Greenland, 275 km northwest of the historical ice sheet camp North Ice, and 484 km east-northeast of Siorapaluk, the closest settlement. There was one heavy-duty tent for accommodation of the researchers during summer. Access was by skiway .
Marine Isotope Stage 5 or MIS 5 is a marine isotope stage in the geologic temperature record, between 130,000 and 80,000 years ago. Sub-stage MIS 5e, called the Eemian or Ipswichian, covers the last major interglacial period before the Holocene, which extends to the present day. Interglacial periods which occurred during the Pleistocene are investigated to better understand present and future climate variability. Thus, the present interglacial, the Holocene, is compared with MIS 5 or the interglacials of Marine Isotope Stage 11.
Dorthe Dahl-Jensen is a Danish palaeoclimatology professor and researcher at the Centre for Ice and Climate at the Niels Bohr Institute, University of Copenhagen in Denmark. Her primary field is the study of ice and climate, specifically the reconstruction of climate records from ice cores and borehole data; ice flow models to date ice cores; continuum mechanical properties of anisotropic ice; ice in the solar system; and the history and evolution of the Greenland Ice Sheet.
KumikoGoto-Azuma is an Antarctic palaeoclimatologist and glaciologist and Director of the Ice Core Research Center at the National Institute of Polar Research, Japan.
Siwan Davies FLSW is a Welsh professor of Physical Geography in the department of science at Swansea University.
A geological event is a temporary and spatially heterogeneous and dynamic (diachronous) happening in Earth history that contributes to the transformation of Earth system and the formation of geological strata. Event stratigraphy was first proposed as a system for the recognition, study and correlation of the effects of important physical or biological events on the broader stratigraphical record.
