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Home , Glacial period, Last glacial period, Quaternary, Quaternary glaciation

3/23/2020

Quaternary Time and its Significance

There have been periods of intense Glaciation () and Interglaciations (Global warming) in the geological past.

Three major periods of glaciations are recorded at around 600-700 Ma, 280 Ma and during the last 2 Ma. Similarly, there have been periods of Warmer at around 400 Ma and between 240- 20 Ma.

•The (the Quaternary Period) is a • There have been five known ice ages in the 's subdivision of geological time scale. history, with the Earth experiencing the Quaternary •It covers approximately the last two million during the present time. Within ice ages, up to the present day. there exist periods of more severe glacial conditions •The exact duration has been debated: the onset and more temperate referred to as glacial periods and periods, respectively. of the Quaternary Period has previously been placed at 1.8 million years ago; but many workers now favour a longer Quaternary chronology, • The Earth is currently in an interglacial period of the Quaternary Ice Age, with the last of the placing its onset at 2.6 million years ago. Quaternary having ended approximately 10,000 • The Quaternary and the Periods years ago with the start of the . together form the .

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• , also known as the • The Quaternary can be subdivided into glaciation, the current ice age or two epochs: simply the ice age, refers to the period of the • The Pleistocene (up to about 11,500 last few million years (2.58 Ma to present) in which permanent ice sheets were established in years ago) and and perhaps , and • The Holocene (about 11,500 years ago fluctuating ice sheets have occurred elsewhere. to the present day). • The Quaternary Period has witnessed • The entire Quaternary Period (2.58 Ma) is one of extraordinary changes in global referred to as an ice age because at least one environment as well as the period permanent large — Antarctica — during which much of has existed continuously. took place. •

Holocene The Pleistocene is the epoch from 2,588,000 to • The Holocene is a geological epoch which began 11,700 ~12,000 years BP that spans the world's recent period of years ago (around 10 000 14C years ago) continues to the repeated glaciations. The name pleistocene is derived present. from the Greek πλεῖστος (pleistos "most") and καινός • The Holocene is part of the Quaternary period. Its name (kainos "new"). comes from the Greek words ὅλος (holos, whole or entire) and καινός (kainos, new), meaning "entirely recent". It has The Pleistocene Epoch follows the Epoch and is been identified with the current warm period, known as MIS followed by the Holocene Epoch. 1, and can be considered an interglacial in the current ice age. The end of the Pleistocene corresponds with the retreat • All human written history and urban living has occurred of the last continental . It also corresponds with within the Holocene. The word is also used the end of the age used in . for the time period from when have had a significant impact on the Earth's climate and ecosystems to the present.

Thus • The was the most recent glacial period within the current ice age occurring during the • Pleistocene has been a Cooler phase (Periodic build last years of the Pleistocene, from approximately up of Ice Sheets) AND 110,000 to 10,000 years ago. • Holocene has been a Warmer phase • During this period there were several changes between • In general, Quaternary has been marked by major phases glacier advance and retreat. The Last Glacial of cooling ie. Glacial Stages and Shorter Inter glacial Maximum (LGM) refers to the time of maximum Stages. extent of the ice sheets during the last glacial period, • Not only the ice sheets expanded and covered the land, between 26,500 and 19,000–20,000 years ago but there has also been an impact on the • The maximum extent of glaciation was approximately Landscape/Fauna/ Flora -Their and 22,000 years ago. While the general pattern of global modifications. cooling and glacier advance was similar, local • Changes occurred at the scale of few centuries/ differences are present. decades/and even at few scale.

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• Currently, the earth is in an interglacial period, which marked the beginning of the Holocene epoch. Quaternary glaciation /Pleistocene glaciation/ Current • The current interglacial began between 10,000 and 15,000 ice age/ Ice age: years ago, which caused the ice sheets from the last glacial Refers to the period of the last few million years (2.58 Ma to present) period to begin to disappear. Glacial Stages • Remnants of these last , now occupying about 10% of Interglacial Stages the world's land surface, still exist in Himalaya, Greenland and Antarctica etc Last glacial period: Most recent glacial period within • During the glacial periods, what we see as the normal (i.e. the current ice age occurring during the last years of interglacial) hydrologic was completely interrupted the Pleistocene (110,000 to 10,000 years ago). throughout large areas of the world and was considerably modified in others. • Due to the volume of ice on land, was (LGM): Time of maximum approximately 120 meters lower than present. The evidence extent of the ice sheets during the last glacial period, of such an event in the recent past is robust. between 26,500 –20,000 years ago

• Over the last century, extensive field observations have There have been Small scale as well as provided evidence that continental glaciers covered Large scale Temperature fluctuations large parts of , , and . • Even before the theory of worldwide glaciation was generally accepted, many observers recognized that more than a single advance and retreat of the ice had occurred. Extensive evidence now Cenozoic shows that a number of periods of growth and retreat of continental glaciers occurred during the ice age, called glacials and . • The interglacial periods of warm climate are represented by buried soil profiles, beds, and Quaternary and stream deposits separating the unsorted, unstratified deposits of glacial debris.

High resolution studies indicate Thus, the climate on the Planet earth has been that there has been Centennial and is variable ever since its birth. and decadal level climatic fluctuations in geological past The changes have taken place in the geological past at various scales :

. . . .P .D •At global level .P B A B s s rs r r nt a ea ea e ye y y es 0 00 00 Pr •At regional level 30 22 12 3 •At local level •At different latitudinal and altitudinal positions •At millennial scale •At centennial scale •At decadal scale

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• The major effects of the ice age have been: • The evidences of Glacial and Interglacial • and of material over large parts of the continents periods are preserved in the form of Terrestrial as well as Marine records. • Modification of river systems • Creation of millions of • Terrestrial records (mostly fragmentary) • Changes in sea level – Lake deposits • Development of lakes far from the ice – Ice Cores from Ice sheets margins Vostok Data for 420,000 Years • Isostatic adjustment of the , and abnormal winds. Oxygen Isotope • It affected oceans, flooding, and biological • Marine records (undisturbed) communities. • The spread of ice sheets caused increase in the that effected a major feedback on climate cooling

Climatic changes during Quaternary • The interstadials show up strongly in the Interstadials Greenland ice core records. Between 115,000 • Sudden and short-lived warm events occurred many and 14,000 years ago, 24 of these warm times during the generally colder conditions that events have been recognized in the Greenland prevailed between 115,000 and 14,000 years ago ice cores. (isotope Stages 2-5.4). • Interstadials both began and ended suddenly, though in general the 'jump' in climate at the • First picked up as brief influxes of warm climate start of an interstadial was followed by a more plants and insects into the glacial tundra zone of northern Europe, they are known as interstadials' to gradual decline involving a stepwise series of smaller cooling events. distinguish them from the cold phases or ‘'.

• Heinrich events • . • Opposite in sign to the Interstadials are extreme and short-lived • Heinrich events, occurred during the last cold events during the general colder climatic conditions, known as 'Heinrich events' which were first recognized as glacial period, or "ice age". Scientists drilling through periods with very ice-rafting in the North . These events marine sediments can distinguish six distinct events. occur against the general background of the glacial climate, and represent the brief expression of the most extreme glacial • The last (known as H1) sensu stricto conditions. occurred just after the Last Glacial Maximum and • During such events, broke off from glaciers and traversed seems to mark the extreme cold and aridity that the North Atlantic. The icebergs contained mass eroded by occurs in many parts of the world around 17,000- the glaciers, and as they melted, this matter was dropped onto the sea floor. These deposits are called ice rafted debris (IRD) or ice 15,000 years ago. rafted deposits. • Ice rafting was a primary mechanism of sediment transport during glacial episodes of the Pleistocene when sea levels were very low and much of the land was covered by large masses (sheets) of ice.

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The

• A detailed study suggests that the main Younger Dryas-to-Holocene warming took several decades in the Arctic, but was marked by a series The Younger of warming steps, each taking less than 5 years. About half of the Dryas warming was concentrated into a single period of less than 15 years. • The event at 8200 ka is the most striking sudden cooling event during the Holocene, giving widespread cool, dry conditions lasting perhaps 200 years before a rapid return to warmer and generally moister than the present.

The Younger Dryas cold event at about 12,900-11,500 years ago seems to have had the general features of a Heinrich Event, and may in fact be regarded as the most recent of these. There is sudden onset and ending of the Younger Dryas

Holocene climatic optimum

The Holocene Climate Optimum was a warm period during roughly the interval 9,000 to 5,000 years B.P. • The Medieval Warm Period (MWP) or Medieval Climate Optimum was a time of warm climate lasting from about AD • This event has also been known by many other names, including: 950–1250. Hypsithermal, Altithermal, Climatic Optimum, Holocene • It was followed by a cooler period in the North Atlantic termed Optimum, Holocene Thermal Maximum, and Holocene the (Medieval Climatic Anomaly). Megathermal. • This warm period was followed by a gradual decline until about 2,000 years ago.

• Despite substantial uncertainties, especially Little Ice Age • The Little Ice Age (LIA) was a period of cooling that occurred after the for the period prior to 1600 when data are Medieval Warm Period. While not a true ice age, It is conventionally scarce, the warmest period of the last 2,000 defined as a period extending from the 16th to the 19th centuries. • The temperature has varied according to local conditions. years prior to the 20th century very likely • It is observed that there were three phases of cold intervals between 1550 occurred between 950 and 1100. AD and 1850 AD: • One beginning about 1650 • The heterogeneous of climate during • Another about 1770 the ‘Medieval Warm Period’ is illustrated by • And the last in 1850, • Each of these are separated by intervals of slight warming the wide spread of values exhibited by the individual records.

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• Dansgaard–Oeschger events (often abbreviated D– O events) are rapid climate fluctuations that occurred 25 times during the last glacial period (110,000 – 10,000 Yrs).

• Bond events are North Atlantic climate fluctuations occurring every ≈1,470 ± 500 years throughout the Holocene. • Eight such events have been identified, primarily from fluctuations in ice-rafted debris.

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