Cycles of climatic changes

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Cycles of Climatic Change in Quaternary Period (Glacials and

Interglacials)

By Abdelrhim Eltijani

M.Sc. Applied Geology

2nd semester, roll no. 22

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Outlines

• The Quaternary Period

• Quaternary paleogeography– Definitions

– Background

– The Eemian/Sangamon interglacial, 130-115 ka BP

– The Early-Middle Weichselian/Wisconsin, 115-50 ka BP

– The Last Glacial Maximum (LGM), MIS 2, 20-18 ka BP

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The Quaternary Period

• The Quaternary is the most recent geological period of time in

Earth’s history, spanning the last 2 million years and extending

up to the present day. The Quaternary period is subdivided into

the Pleistocene (“Ice Age”), spanning most of the Quaternary

and the Holocene (present warm interval) epochs, covering the

past 10 000 years.

• The Quaternary is characterized by a series of large-scale

environmental changes that have profoundly affected and

shaped both landscapes and life on Earth. One of the most

distinctive features of the Quaternary the periodic build-up of

major continental ice sheets and mountain ice caps during long

lasting glacial stages, divided by warm episodes (interglacials) of

shorter duration, when temperatures were similar to or higher

than today.

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• There have been shifts in the frequency of climate oscillations and

amplitude of temperatures and glaciations through the Quaternary.

At the onset of the Quaternary, many arctic areas were

comparatively warm, with trees and bushes growing far north of

the present treeline.

• Prior to about 800 000 years ago each interglacial-glacial cycle

lasted for about 40 000 years, but after that the periodicity shifted

to a prevailing rhythm of about 100 000 years.

• Prior to this shift there was a repeated build-up of relatively small-

to-moderate sized ice sheets at high northern latitudes.

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The Quaternary Period• After 800 000 years ago there occurred a major intensification of

glaciations, with repeated growth of continental-scale ice sheets

reaching mid-latitudes and with ice volumes much larger than

during the earlier Quaternary glaciations.

• There have occurred 8-10 major glaciations during the past 800

000 years. Two of the largest Northern Hemisphere glaciations are

the last one (called the Weichselian/Wisconsin glaciation, 20 000

years ago) and the Saalian/Illinoian glaciation, occurring prior to c.

130 000 years ago.

• During the peak of both glaciations, ice sheets covered extensive

areas north of 40-50oN in both Eurasia and N America. The Saalian

glaciation was particularly extensive in the high Eurasian north,

covering vast areas of N Russia, coastal Arctic Ocean and Siberia.

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Global view of

the Last Glacial

Maximum, 18.000

years ago

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• The repeated Northern Hemisphere Quaternary glaciations have

left a complex of landforms, sediments and landscapes that set the

frame for mid-high latitude life and human activities.

• Human societies rely on natural resources that are products of the

Pleistocene glaciations, like sands and gravels for construction

activities, groundwater magazines in ancient fluvial deltas, fertile

glacial till and outwash planes for forestry and agriculture.

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References and further reading

Andersen, B.G. & Borns, H.W.Jr., The Ice Age World, Oslo, Scandinavian University Press,

1994.

Dawson, A., Ice Age Earth, London, Routledge, 1992.

Lowe, J. J. and Walker, M.J.C., Reconstructing Quaternary Environments, Harlow, Longman

Limited, 1997

Nilsson, T., The Pleistocene, Dordrecht, Reidel, 1983.

Williams, M., Dunkerley, D., Decker, P., Kershaw, P. and Chappell, J., Quaternary

Environments, London, Arnolds, 1998.

Wilson, R.C.L., Drury, S.A. and Chapman, J.L., The Great Ice Age: Climate Change and Life,

London, Routledge, 1999.

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Quaternary paleogeography

• Paleogeography deals with reconstructing the physical

geography of past geological times, where the focus is on

physical features such as the shifting locations of shorelines,

rivers and drainage systems, tectonics and mountain-building,

paleolatitude and continental drift, location in time and space of

continental shelf areas and other sedimentary basins.

• The field of Quaternary paleogeography broadly includes all

aspects of paleo-map reconstructions through the Quaternary

Period; ice sheet and sea-level fluctuations in time and space;

the delineation of past topographic or bathymetric contours

….etc.

- Definitions

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• The frame for major global environmental changes is set by

large-scale tectonics and position and configuration of the

continental landmasses. These affect the paths of ocean currents

and air masses and in turn decide the global energy distribution.

• The steady northward drift of Europe, Asia and North America

through the Tertiary Period (65-2 Ma (million years) BP (before

present)) caused the gradual tectonic closing of the connection

between the Pacific Ocean and the Arctic Ocean and reduced

the previously efficient ocean heat transport from equatorial

regions toward the North Pole.

- Background

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- Background

An example of Paleogeographical

reconstruction: The Late Weichselian

Barents Sea Ice Sheet (from Forman

et al. 2004)

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- Background• Most Quaternary Paleogeographic reconstructions focus on time

slices through the past ca. 130 ka (kilo-years). That is for the

simple reason that there is ample geological and biological

evidence preserved in the geological record with resolution high

enough to allow for reasonably detailed reconstructions, whereas

evidences of earlier large-scale Quaternary environmental changes

usually are fragmentary.

• During the past 130 ka the climate has changed from interglacial to

glacial and then back to the present-day interglacial, i.e. fluctuated

between end members in the climate-environmental system. It is

assumed that environmental changes through the last interglacial-

glacial cycle have occurred repeatedly through earlier glacial

cycles.

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- The Eemian/Sangamon interglacial, 130-115 ka BP -

• The beginning of the last interglacial is reflected in the marine

records by abrupt shift to lighter isotope values. The preceding

Saalian/Illinoian glaciation was extremely extensive at both high

and middle latitudes, and the onset of the Eemian/Sangamon

interglacial is marked at many Arctic locations by marine

transgression across isostatically depressed coastal areas.

• Deposits from this marine transgression are particularly

pronounced along the northern Russian and Siberian coastal

lowlands. A range of proxy data suggests that the

Eemian/Sangamon climate optimum summer temperatures were

considerably (2-4oC) warmer than that of the present day, and

that vegetation zones on the continents migrated northwards.

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- The Eemian/Sangamon interglacial, 130-115 ka BP -

Figure, demonstrates the

difference between

modern SST and estimated

SST °C at the last

interglaciation, some 120

ka ago. Negative values

mean that the last

interglacial ocean was

colder than today. that

most SST values are

similar to present.

Samples with more than

one estimate reflect use of

more than one proxy

source (F = foram, R =

radiolaria, C = coccolith).

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- The Early-Middle Weichselian/Wisconsin, 115-50 ka BP

• In a Northern Hemisphere and global perspective, this time

interval represents a transition from interglacial to glacial

conditions, with successively falling global sea level as

continental ice volumes increased. Recent research has,

however, increasingly shown that ice sheets in the high arctic

probably reached their maximum extent and volume during the

early stages of ice build-up, during the Early-Middle

Weichselian/Wisconsin.

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- The Early-Middle Weichselian/Wisconsin, 115-50 ka BP

A reconstruction of the Eurasian

ice sheet during the Early

Weichselian glacial maximum (90-

80 ka BP). Figure from Svendsen

et al. 2004.

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-The Last Glacial Maximum (LGM), MIS 2, 20-18 ka BP -

• LGM is defined as the maximum global ice volume as seen in

marine oxygen isotope records and coinciding with the maximum

extension of middle latitudes Northern Hemisphere ice sheets

during the last glacial cycle. It is generally thought to have

occurred around 20-18 ka BP, but it is, however, acknowledged

that the timing, duration and extent of ice cover at LGM differed

considerably in different regions of the Arctic.

• Recent interpretations of the northern Eurasian glacial record

suggest that most of the mainland of N Russia and Siberia

remained ice-free during the LGM.

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-The Last Glacial Maximum (LGM), MIS 2, 20-18 ka BP -

A recent (Svendsen et al. 2004)

reconstruction of the extent of

the Eurasian ice sheet at the

Last Glacial Maximum, 20-18 ka

BP.

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References and suggested further reading:

Elias, S.A. & Brigham-Grette, J. (eds.), Beringian Paleoenvironments. Festschrift

in Honour of D.M. Hopkins. Quaternary Science Reviews, 20(1-3), 2001.

Forman, S.L. et al. 2004: A review of postglacial emergence on Svalbard, Franz

Josef Land and Novaya Zemlya, northern Eurasia. Quaternary Science Reviews

23, 1391–1434

Frenzel, B., Pécsi, M. & Velichko, A. A. (eds.), Atlas of paleoclimates and

paleoenvironments of the Northern Hemisphere: Late Pleistocene – Holocene.

Budapest, Geographical Research Institute, Hungarian Academy of Science, 1992.

Manley, W.F., 2002, Postglacial Flooding of the Bering Land Bridge: A Geospatial

Animation: INSTAAR, University of Colorado, v1,

http://instaar.colorado.edu/QGISL/bering_land_bridge

Svendsen, J.I. et al. 2004: Late Quaternary ice sheet history of northern Eurasia.

Quaternary Science Reviews, 23, 1229-1271.

Documents

Cycles of climatic changes