Drift-dependent changes in iceberg size-frequency distributions

James D Kirkham,Nick J Rosser,John Wainwright,David E Hawthorn,Mateusz C Strzelecki,Victoria S Lane,Stuart A Dunning,Emma C Vann Jones,Witold Szczuciński

doi:10.1038/s41598-017-14863-2

Abstract

Although the size-frequency distributions of icebergs can provide insight into how they disintegrate, our understanding of this process is incomplete. Fundamentally, there is a discrepancy between iceberg power-law size-frequency distributions observed at glacial calving fronts and lognormal size-frequency distributions observed globally within open waters that remains unexplained. Here we use passive seismic monitoring to examine mechanisms of iceberg disintegration as a function of drift. Our results indicate that the shift in the size-frequency distribution of iceberg sizes observed is a product of fracture-driven iceberg disintegration and dimensional reductions through melting. We suggest that changes in the characteristic size-frequency scaling of icebergs can be explained by the emergence of a dominant set of driving processes of iceberg degradation towards the open ocean. Consequently, the size-frequency distribution required to model iceberg distributions accurately must vary according to distance from the calving front.

Highlights

The rate at which icebergs drift and disintegrate influences the risk of collisions with high-latitude hydrocarbon infrastructure and shipping[1], the extent of zones of nutrient-enhanced carbon sequestration[2,3], and the interpretation of palaeoclimate indicators such as ice-rafted debris[4]
The application of passive seismic techniques has significantly increased our understanding of inaccessible glaciological processes including crevasse propagation[9,11,12], basal sliding[13,14] and iceberg calving from tidewater glaciers[15,16]
Analysis of satellite imagery demonstrates that the distribution of planform iceberg areas in Vaigat is well fitted by a lognormal distribution except for the likelihood of the very largest icebergs, which are slightly overpredicted (Fig. 3a)

Summary

Introduction

The rate at which icebergs drift and disintegrate influences the risk of collisions with high-latitude hydrocarbon infrastructure and shipping[1], the extent of zones of nutrient-enhanced carbon sequestration[2,3], and the interpretation of palaeoclimate indicators such as ice-rafted debris[4]. The Greenland Ice Sheet has experienced persistent and increasing mass loss since the 1990s18 in a spatially complex pattern driven by rising surface air temperatures[19] and accelerations in outlet glacier velocities[20,21]. During this time, freshwater fluxes into the North Atlantic Ocean sourced from surface and submarine melting of the Greenland Ice Sheet, as well as the melting of icebergs and ice mélange, have been observed to increase[22,23]. Meltwater fluxes sourced from the melting of icebergs and ice www.nature.com/scientificreports/

Methods

Results

Conclusion