Comparison of Firn-Model Outputs for Steady-State Climates

Abstract:

With few direct measurements of firn density profiles, pore close-off depth and delta age modeling can further aid the study of polar firn. Model estimates of firn properties can help in planning field campaigns and collecting ice cores. No universally accepted firn-evolution model exists, and modeled firn density profiles can be sensitive to the form of the density equation that is used. We can characterize the subtle differences between firn-evolution models by creating comparisons among a suite of published models. We created a table of temperatures and accumulation-rate values spanning the range of climatic conditions in the dry-snow zone in Greenland and Antarctica. Then, we ran each of seven firn-compaction models for each pair of climate values in the table, producing values of close-off depth, depth-integrated porosity, and delta age for each model. Using gridded temperature and accumulation-rate data from Greenland and Antarctica, we interpolated each gridded pair in our model-output tables to create maps of DIP, COD, and Δage for Greenland and Antarctica for each model. We also computed the mean and variance among the models for each property. By identifying the areas of greatest variance in our parameter space, we can better quantify our confidence in the physical descriptions of firn densification in the models.