In situ cosmogenic radiocarbon production and 2-D ice flow line modeling for an Antarctic blue ice area

Abstract

Radiocarbon measurements at ice margin sites and blue ice areas can potentially be used for ice dating, ablation rate estimates and paleoclimatic reconstructions. Part of the measured signal comes from in situ cosmogenic 14 C production in ice, and this component must be well understood before useful information can be extracted from 14 C data. We combine cosmic ray scaling and production estimates with a two-dimensional ice flow line model to study cosmogenic 14 C production at Taylor Glacier, Antarctica. We find (1) that 14 C production through thermal neutron capture by nitrogen in air bubbles is negligible; (2) that including ice flow patterns caused by basal topography can lead to a surface 14 C activity that differs by up to 25% from the activity calculated using an ablation-only approximation, which is used in all prior work; and (3) that at high ablation margin sites, solar modulation of the cosmic ray flux may change the strength of the dominant spallogenic production by up to 10%. As part of this effort we model two-dimensional ice flow along the central flow line of Taylor Glacier. We present two methods for parameterizing vertical strain rates, and assess which method is more reliable for Taylor Glacier. Finally, we present a sensitivity study from which we conclude that uncertainties in published cosmogenic production rates are the largest source of potential error. The results presented here can inform ongoing and future 14 C and ice flow studies at ice margin sites, including important paleoclimatic applications such as the reconstruction of paleoatmospheric 14 C content of methane. Copyright 2012 by the American Geophysical Union.