Holocene climate variations estimated by means of an ice core

B. Geerts and E. Linacre


Since the early 1980's a deep ice core has been drilled at Vostok, the world's coldest station on the east Antarctic plateau. This ice core, completed in 1998, cover the entire 3,500 m of ice and the bottom layers date back to 400,000 years ago. However snow accumulates only very slowly at Vostok: the annual mean equivalent rainfall is less than 1 cm, and some snow ablates or sublimates.

So the annual layers in the ice core are very thin. Another ice core has been drilled on Taylor Dome, near McMurdo station, which is near the Ross Ice Shelf (Fig 1). This location benefits from the exceptionally high rate of snow accumulation and the relatively low temperature (1). Therefore the core shows seasonal variations unusually clearly, however the bottom of the core dates back only 700 years. Measurements of oxygen isotope ratios give temperatures for each year, and also seasonal variations. The dating of layers in the core is confirmed by the presence of ash from several known volcanic eruptions, as well as by the sunspot cycle.

The data show that most variation occurred in the winter temperatures, except for a time around 1900 AD when there were unusually cool summers. The Medieval Optimum between 1400-1500 AD in the northern hemisphere coincided with warm winters at Taylor Dome, and the northern Little Ice Age of 1750-1850 with cold winters in Antarctica. In other words, the main climate variations during the last 700 years (the Medieval Optimum, the Little Ice Age and the 20th century greenhouse warming) appear to be global events. However it is possible that some fluctuations in the ice core were due to shifts in the paths of weather systems rather than changes of global average temperatures.

Fig 1. Satellite view of Antarctica with the location of Taylor Dome.



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