Sediment transport by Greenland’s icebergs

Ice-rafted debris (IRD) from Greenland's tidewater glaciers provides key inputs to biogeochemical cycles, sequesters sediment in fjords, and leaves evidence of paleoclimate conditions. Previous work has shown that most IRD is entrained in basal ice, but studies have yet to translate this process knowledge into predictions of IRD export. Here, we combine field data and numerical models to quantify sediment transport in basal ice and estimate IRD fluxes. We present 210 samples of debris-rich icebergs, collected from three fjord systems, showing a long-tailed distribution of sediment concentrations between 0.1% and 45% by mass (3.48% median). Then, we develop a numerical process model of erosion and entrainment to predict the thickness of debris-rich ice layers and the IRD flux from each outlet. Across our selected fjords, we show a first-order relationship between a catchment's ice yield and sediment yield. By extrapolating this relationship across Greenland's marine-terminating outlets, we estimate that icebergs export 454 Mt a^-1 of IRD (with a 95% confidence interval from 292 to 716 Mt a^-1), representing up to one-third of Greenland's total sediment transport. Our results demonstrate the significant role of icebergs in Greenland's sediment budget, improving our understanding of how sediment export from glaciers and ice sheets will change under a warming climate.