Drift-dependent changes in iceberg size-frequency distributions

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.

The Aftermath of Petermann Glacier Calving Events (2008–2012): Ice Island Size Distributions and Meltwater Dispersal

“…In contrast, Kirkham et al (2017) and Tournadre et al (2012) found that the size-frequency distribution of smaller icebergs located further from glacier calving sites was better represented by a log-normal model. .…”

“…The mean slope of the power law distributions that were fit to the temporal and spatial snapshots in our study is very close to that reported for the size‐frequency distribution of Antarctic ice islands (−1.5; Bouhier et al, ; Tournadre et al, ). This suggests that ice islands in both the Arctic and the Antarctic deteriorate through a complex set of fracture and fragmentation mechanisms and that these deterioration processes occur similarly across a range of ice island sizes (Kirkham et al, ; Tournadre et al, ).…”

“…Conversely, larger icebergs (and ice islands) are subject to a more complex set of deterioration processes (e.g., large‐scale fracture, smaller‐scale calving, and ablation). This results in a wide range of ice island surface areas and a situation in which a log‐normal model can display characteristics that are similar to a power law model (Kirkham et al, ; Tournadre et al, ). Mathematically, log‐normal models converge towards power law models as the variation in the variable of interest (i.e., surface area) increases.…”

“…It is likely that freshwater input in these grid cells is overestimated since terminal ice islands were immediately converted to meltwater. Kirkham et al (2017) explain that deterioration is increasingly dominated by a relatively small set of melt processes (e.g., forced convection and wave erosion) as icebergs travel away from source glaciers. Conversely, larger icebergs (and ice islands) are subject to a more complex set of deterioration processes (e.g., large-scale fracture, smaller-scale calving, and ablation).…”

“…While fracturing and fragmentation alter ice island size distributions, they also influence meltwater production. Fracturing causes further dispersal of meltwater as individual ice islands drift apart after a fracture event (Tournadre et al, 2012) and also increases the surface area to volume ratio, which will cause an ice island to be more susceptible to other meltwater-generating deterioration processes (e.g., wave erosion; Kirkham et al, 2017;Stern et al, 2017). The dispersal of meltwater with the drift and deterioration of icebergs and ice islands is often discussed in terms of the impact on fjord dynamics, local ocean properties, and ocean circulation patterns (Enderlin et al, 2016;Stern et al, 2015;Wagner & Eisenman, 2017).…”