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Environment: understanding atmospheric and ocean flows
Environment: understanding atmospheric and ocean flows

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3.4 Ice core going back 800 000 years

Throughout this course so far the focus has been on the Arctic, but because some data from the ice cores tell us about conditions over the entire planet (such as Figure 11), you will now look at data from another core, this time from Antarctica. The Antarctica ice cores go back much further in time than any Greenland ones. The particular core you will look at now is called the EPICA (European Project for Ice Coring in Antarctica) – Dome C core.

Dome C is currently the longest ice core and has snow layers going back almost 800 000 years throughout the Quaternary, and includes the period when Homo sapiens evolved. In fact, the EPICA core can be used to reconstruct Antarctic temperatures more than half a million years before Homo sapiens ever walked the Earth (Figure 13).

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Figure 13 (a) Antarctic temperature changes from the EPICA ice core from 800 000 years before present (BP) up to 1911. The vertical temperature scale has 0 °C for the mean temperature over the past 1000 years, and goes from −10 °C to +5 °C relative to this (Jouzel et al., 2007). (b) Map showing location of Dome C in Antarctica.
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Figure 13(a) is a graph of temperature data inferred from the EPICA ice core going back 800 000 years. The horizontal axis is time measured in years before present (BP) and the minimum is 800 000 BP. The scale is linear and there are ticks every 100 000 years. The maximum on this axis is 0 which is the present day. The vertical axis is temperature change from the present day with a minimum of −10 °C and a maximum of 5 °C. A temperature change of 0 °C refers to the temperature of the present day which is defined as the mean temperature over the past 1000 years. The data on the graph is an irregular orange line which seems to oscillate between two states: one with a temperature close to the present day, and one approximately 8–10 °C colder. At the present day the temperature change is 3 °C, and at around 14 000 years BP the temperature change is about −10 °C. Around 130 000 years BP the temperature change is about 5 °C, but at around 140 000 years BP the temperature change is about −9 °C. At around 250 000 years BP the temperature change is about 3 °C, but at around 275 000 years BP the temperature change is about −9 °C. Around 340 000 years BP the temperature change is about 4 °C, but at around 345 000 years BP the temperature change is about −9 °C. Around 405 000 years BP the temperature change is about 3–4 °C but at around 450 000 years BP the temperature change is about −9 °C . Further back in time the temperature oscillations decrease in magnitude and the warm periods are colder than present by about −1 °C to −2 °C, whilst the cold periods are mostly around −8 °C. The final four cold periods are at times of around 550 000 years BP, 640 000 years BP, 720 000 years BP and 800 000 years BP. Figure 13(b) is an outline map of Antarctica, the landmass is white and a blue dot marks the location of the South Pole. To the South-east of the South Pole is a green dot marking the location of Dome C, the location of the EPICA ice core. The area surrounding Antarctica is shown in blue and represents the oceans: to the top left is the Atlantic Ocean, to the top right the Indian Ocean and the bottom left is the Pacific Ocean. In the bottom right is a scale indicating 1000 kilometres. Dome C is around 1700 km from the South Pole.

Figure 13 (a) Antarctic temperature changes from the EPICA ice core from 800 000 years before present (BP) up to 1911. The vertical ...

Figure 13(a) shows that Antarctic temperatures have varied considerably, but there also appear to be regular cyclical patterns. At the low points, the temperature shown by the core was as much as 10 °C colder than today: colder periods happen about every 100 000 years, with warmer periods between. Four times in the last 450 000 years, the intervening warm periods have been warmer than today (up to 5 °C warmer around 130 000 years ago). During the nine cold periods shown in Figure 13(a), the snow that fell in winter did not melt in the following summer heat, and the ice sheets grew.