Inferring palaeo-accumulation records from ice-core data by an adjoint-based method: application to James Ross Island's ice core

Ice cores contain a record of snow precipitation that includes information about past
atmospheric circulation and mass imbalance in the polar regions. We present a novel
adjoint method to reconstruct a climatic record by both optimally dating an ice-core
and deriving 5 from it a detailed accumulation history. The motivation of our work is the
recent application of phase sensitive radar which measures the vertical velocity of an
ice column. The velocity is dependent on the history of subsequent snow accumulation,
compaction and compression; and in our inverse formulation of this problem, measured
vertical velocity profiles can be utilized directly thereby reducing the uncertainty intro10
duced by ice flow modelling. We first apply our method to synthetic data in order to
study its capability and the effect of noise and gaps in the data on retrieved accumulation
history. The method is then applied to the ice core retrieved from James Ross
Island, Antarctica. We show that the method is robust and that the results depend on
quality of the age-depth observations and the derived flow regime around the core site.
15 The method facilitates the incorporation of increasing detail provided by ice-core analysis
together with observed full-depth velocity in order to construct a complete climatic
record of the polar regions.