General Circulation models Essays

General Circulation models Essays General Circulation models Essay General Circulation models Essay 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.