Preservation of the Climatic Signal in the Old Ice Layers at the Dome B Area (Antarctica)

In this work we present the results of numerical modeling of the age and temperature distribution in ice layers at the Dome B site (79.02° S, 93.69° E, altitude 3807 m a.s.l., ice thickness about 2.5 km), located 300 km west of the Russian Antarctic station Vostok. Dome B is situated on the onset of the ice flow line passing through the deep 5G borehole, and it is considered one of the most promising places to search for and study the earth’s oldest ice (with an age reaching 1.5 Ma). According to our calculations, all realistic scenarios show the ice age at 60 m above the ice base to be considerably older than 1 Ma, and the glacier base temperature is well below the pressure melting point (–1.8°С for pressure = 23 MPa). For the most likely scenario (accumulation rate 1.8 g/(cm 2 year), effective ice surface temperature –64°С, and geothermal heat flux 60 mW/m 2 ), the ice age is 1.4 Ma and the basal temperature is about –13°С, which is close to the earlier predictions from a 2D model. The maximum estimate of the diffusion length in the old ice (for the scenario in which the basal temperature reaches the melting point and in which 30% of excess diffusion is taken into account) is 5.2 cm. In 1.4-Ma-old ice, a 40-ka climatic cycle is squeezed into a 290-cm-thick ice layer. For this ratio of wavelength and diffusion length, the climatic signal attenuation (ratio between the signal amplitude after and before diffusive smoothing) is 0.6%. Thus, due to the relatively low ice temperature here, we may expect a nearly undisturbed climatic curve in the old ice core that will be drilled one day at Dome B. At the same time, shorter oscillations with wavelengths of <1500 years will be totally erased by diffusion.