The effect of temporal variations in the surface mass balance and temperature-inversion strength on the interpretation of ice-core signals

Abstract

The proxy for temperature (δ signal) in ice cores is stored in the snow/ice during precipitation events and hence reflects the temperature at which precipitation is formed (here approximated by the inversion temperature Ti) weighted with the accumulation. Results from a 14 year integration (1980-93) with a regional atmospheric model (RACMO, ΔX = 55 km) show that the annual mean accumulation-weighted inversion temperature (Ti,w and the annual mean Ti are not covariant in time at four out of the five deep-drilling sites considered, mainly due to year-to-year variations in the seasonality of precipitation. As a consequence, the surface temperature (Ts,core) derived from RACMO output, using a method analogous to the retrieval of the surface temperature from ice-core δ signals, deviates from the directly modelled surface temperature Ts on interannual time-scales. Results from a 5 year sensitivity integration, forced with a 2 K temperature increase, show an 18% overestimation of the increase in Ts,core relative to the increase in Ts due to a change in the relationship between the inversion strength and the surface temperature in a different climate regime. Similar errors may occur in deriving the temperature difference between Last Glacial Maximum and present-day climate from δ signals in ice cores.