R code and data for shifting GICC05 years b2k to intcal20 years BP, used in Matthews et al.

<p dir="ltr">This code is from: Matthews et al. in press. It was used to convert NGRIP GICC05 years to cal. BP years on the Intcal20 timescale. The code was adapted from Engels et al. 2022 as referenced in the main paper. </p>