Another example can be seen in Cytheropteron testudo, a cold-water marine creature, used as a marker for the beginning of the quaternary in Italy (Lowe and Walker 1997).
Terrestrial Evidence
Terrestrial evidence, here including ice sheets are particularly useful as they give a more diverse range of data also on a larger time scale. However, detail may not be as good as with marine evidence, with gaps in the terrestrial record partly due to the effects of climate.
Landforms such as moraines reveal periods of advance, retreat and stand stills (Nesje and Dahl 2000), or where ice has remained stationary for some time. These and glacial deposits such as till can be exposed to the surface for some time, and therefore be subject to weathering and other effects such as uplift, vegetation colonization, soil formation and climate changes (Menzies, J 2002) . This could change the properties of a deposit and or lead to an inaccurate interpretation.
Lowe and Walker (1997) also mention the damaging effects of destruction by melt water, postglacial erosion, weathering or subsequent fluvial activity. It may also be difficult to distinguish landforms which have undergone several periods of glaciation, where the most recent has not destroyed all the evidence of the previous one (Bennett and Glasser 1996). The landforms of the Lake District can be hard to interpret for this reason. It is thus the job of a glacial stratigraphist to establish the relative order of sediments and landforms, and working out what climate conditions were like when they were formed (Bennett and Glasser 1996).
The advantageous thing about landforms is the ability to use mapping techniques to observe the type and distribution of landforms, and any important details about them. Advances in remote sensing techniques have allowed large areas to be mapped quickly (Lowe and Walker 1997), and in a form that reveals most information – infrared and radar monitoring will reveal different details for example.
Lacustrine environments have been ranked as one of the best palaeoclimatic archives (Nesje and Dahl 2000) as lake deposits are directly affected by climatic change. In glacial periods, minerogenic salts and clays dominate, although over all there is a reduced presence of clastic and organic material (Nesje and Dahl 2000). Recorded organism types will vary also, according to climatic conditions.
In lakes, it is the usage of varves (annual deposits that occur annually and in two stages, over two seasons) to date an area. If a full set of varves is retrieved, the date at which the ice retreated exposing bare ground can be calculated (Pacific Institute 2004). This data can be compared with information given in pollen, plankton and diatom records as well as palaeomagnetic variations and geochemical changes taken from the sediments (Nesje and Dahl 2000) to obtain a better view.
Again there may be problems with the data; bioturbation may be encountered by the action of organisms dwelling on the lakebed, and conditions favouring preservation of records may be inhibited due to anoxic bottom waters, causing adverse chemical conditions (Nesje and Dahl 2000). Several cores are usually taken to minimise errors.
Ice coring has become a well-known and trusted form of gathering data about the Quaternary on a global scale, with the most renowned and detailed examples coming from Greenland and Antarctica.
Ice cores can reveal many things about a glacier, including its origin, its basal conditions, climatic circulation conditions and possibly even anthropogenic influences on climate, with the presence of certain human-induced pollutants such as CFCs.
Gasses can be trapped in air bubbles in the ice (Press and Siever 2000). Carbon dioxide concentrations for example, can be calculated, revealing approximate climate temperatures. Oxygen Isotopes, such as those trapped in the shells of marine creatures are also preserved in these air bubbles, again, allowing previous temperatures to be estimated.
Aerosols such as dust can also reveal what was happening globally. If there is a lot of dust, it suggests a large amount of ‘atmospheric aerosol loading’ (Nesje and Dahl 2000), which can be linked to an expansion of deserts, or poorly vegetated areas.
The longest and most useful ice cores come from polar ice sheets, which suffer least from surface melting. The Vostok ice core for example, in the South Pole can date back to the late Glacial Pleistocene maximum and beyond. The longest cores taken from here reach 3623 meters in length (Menzies 2002). Ice cores are limited to a certain extent to the age of preserved ice. This is because the thicker the ice, the lower the temperature required to melt it (at 2200m the basal ice will melt at –1.6oC), thus very early ice accumulation tends to disappear, or be severely deformed in its fluid state (WMR University, 1998).
Comparisons
Because of the wide range of data obtainable from various sources, discrepancies in the accuracy of data, and the spatial limitations that any one data source has information for (e.g. Ice cores are best at giving local rather than global information), it could be said that combining data from as many sources as possible is the best course of action for getting as vivid a picture of quaternary environments as possible. For example terrestrial landforms may be useful in telling us the extent of previous ice sheets and where they moved, but this would be of limited use, without the chronological evidence to tell us when it happened. For example, between the dates 70-115 ka BP, 6 interstadial episodes with probable global significance occurred, as suggested by evidence found in the GRIP (Greenland Ice Core Project) core. Data from the Vostok core as well as North Atlantic marine sediments also suggested this was the case (Lowe and Walker 1997).
Another example of coinciding data from several sources can be seen in oxygen isotope data. A continuous 500,000-year climate record from the isotopes was retrieved from a core at Devils Hole, Nevada. The isotope record correlated strongly with cores taken from Greenland and Vostok cores (Menzies 2002).
The only problem with comparing data is that they are often dated in different ways - for example, ice cores are dated by using ‘ice-layer years’ (Lowe and Walker 1997), whereas radiocarbon dating is used for other areas. For this reason, calibrations for the last glacial – interglacial were created.
To get a full picture of the last quaternary and its climate, it appears that it is very important to look at all the information available to us, and bring it together to get a meaningful overall picture.
It is important to remember that cores taken from marine sediments and glacial ice would mean nothing to scientists if we did not have the technology for radiometric and isotopic dating and analysis that we currently employ (Menzies 2002). Bennett and Glasser (1996) also mention that if we did not have the high-tech computer programmes to interpret and display data in the form of models and graphs replicating such things as ice sheet behaviour and climate patterns, we would have a much more difficult task and probably poorer understanding.
Lowe and Walker (1997) also mention the development of General Circulation models, which are used in the interpretation of Oxygen Isotope records.
Terrestrial and marine evidence has told us a lot about previous climate change – its extent, and patterns of occurrence, which in the long term, will help us better-understand climate patterns of the future, and allow us to better prepare for them. Some areas are still uncertain, but as technologies improve, we can only hope to get as full a picture as the earth is capable of revealing.
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Bibliography
Bennett, M.R and Glasser, N.F (1996), Glacial Geology – Ice sheets and Landforms, Wiley.
Kingdom drilling (2004), Milestones and influences of US offshore history 1940 – 1997. http://www.kingdomdrilling.co.uk/diggin/Milestones%20US%20Oil%20history.pdf
Kleman, J. (1990). On the use of glacial striae for reconstruction of palaeo ice-sheet flow patterns. Geografiska Annaler. 72 A, 217 – 236.
Lowe, J.J and Walker, M.J.C (1997). Reconstructing Quaternary Environments (2nd edition), Longman, Harlow
Menzies, J. (2002) Modern and Post Glacial Environments, Butterworth, Heinemann.
Nesje, A. and Dahl, S.O (2000), Glaciers and Environmental Change. Arnold, Oxford University Press.
Pacific Institute (accessed 20/05/04). Studies in Development, Environment, and Security. Www.globalchange.org/glossall/glossv-z.htm - -. Site now temporarily unavailable, due to web page upgrading.
Press, F. and Siever, R. (2000), Understanding Earth (Third Edition). Freeman.
William Marsh Rice (WMR) University, America – (1998) - Ice – Why do Glaciers Move?
