![]() The drift and decay of icebergs during transit from the calving terminus therefore represents an important mechanism by which nutrients and freshwater are transported into the North Atlantic Ocean however, due to a poor understanding of iceberg-disintegration mechanics, these processes are relatively poorly quantified around Greenland at present 3. Meltwater fluxes sourced from the melting of icebergs and ice mélange within Greenlandic glacial fjords including that of Greenland’s large outlet glacier, Jakobshavn Isbræ 26, may potentially exceed the flux associated with glacier surface and submarine melting 22. In addition to their implications for circulation dynamics within the global ocean 24 and mass-loss feedbacks within the fjords of marine-terminating outlet glaciers 25, elevated meltwater fluxes are likely to increase the input of bioavailable particulate iron into the North Atlantic Ocean 3, potentially affecting marine biological productivity, ecosystem dynamics and the oceanic uptake of CO 2 2. ![]() 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. The Greenland Ice Sheet has experienced persistent and increasing mass loss since the 1990s 18 in a spatially complex pattern driven by rising surface air temperatures 19 and accelerations in outlet glacier velocities 20, 21. Multiple harmonic frequencies with a distinctive ‘chevron’ pattern Hydraulic movement in glacial water channels Impulsive onset and abruptly declining codaĮmergent onset, cigar-shaped envelope, long-duration coda, absence of P- or S-waves, peaks often coincide with ‘Worthington jets’ produced by cavity collapseĥ–30 + (s) (up to 1 hour depending on iceberg dimensions) Seismic methods have also been used to describe flexure and breakage of free-floating tabular icebergs 14, 17, demonstrating their potential to provide insight into the mechanisms responsible for iceberg disintegration. 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. ![]() Over the last four decades 9, passive seismic investigations of glaciological phenomena have revealed that different glaciological processes are characterised by unique and highly distinctive signal properties including dominant spectral frequency, event duration and the shape of the signal onset and coda 10 (Table 1). Although it has been speculated that the lognormal distribution of iceberg sizes observed away from glacial calving fronts is the product of the mechanisms by which icebergs fracture and disintegrate 7, the absence of appropriate methods with which to study free-floating iceberg disintegrations has limited efforts to study the mechanics of this phenomenon. Although iceberg drift-decay models exist 5, our mechanical understanding of iceberg disintegration remains unable to explain the size-frequency distributions of icebergs commonly observed most notably the discrepancy between the power-law distributed icebergs sizes observed at glacial calving fronts 6 and the lognormal iceberg-size distributions observed globally within open waters 7, 8. 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. Consequently, the size-frequency distribution required to model iceberg distributions accurately must vary according to distance from the calving front. 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. ![]() 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. Here we use passive seismic monitoring to examine mechanisms of iceberg disintegration as a function of drift. 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. Although the size-frequency distributions of icebergs can provide insight into how they disintegrate, our understanding of this process is incomplete. ![]()
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