Melting and fragmentation laws from the evolution of two large Southern Ocean icebergs estimated from satellite data

Abstract. The evolution of the thickness and area of two large Southern Ocean icebergs that have drifted in open water for more than a year is estimated through the combined analysis of altimeter data and visible satellite images. The observed thickness evolution is compared with iceberg melting predictions from two commonly used melting formulations, allowing us to test their validity for large icebergs. The first formulation, based on a fluid dynamics approach, tends to underestimate basal melt rates, while the second formulation, which considers the thermodynamic budget, appears more consistent with observations. Fragmentation is more important than melting for the decay of large icebergs. Despite its importance, fragmentation remains poorly documented. The correlation between the observed volume loss of our two icebergs and environmental parameters highlights factors most likely to promote fragmentation. Using this information, a bulk model of fragmentation is established that depends on ocean temperature and iceberg velocity. The model is effective at reproducing observed volume variations. The size distribution of the calved pieces is estimated using both altimeter data and visible images and is found to be consistent with previous results and typical of brittle fragmentation processes. These results are valuable in accounting for the freshwater flux constrained by large icebergs in models.

[1]  Sveinung Løset,et al.  Thermal energy conservation in icebergs and tracking by temperature , 1993 .

[2]  Rupert Gladstone,et al.  Iceberg trajectory modeling and meltwater injection in the Southern Ocean , 2001 .

[3]  A. Adcroft,et al.  Parameterizing the fresh-water flux from land ice to ocean with interactive icebergs in a coupled climate model , 2010 .

[4]  Jean Tournadre.  Signature of Lighthouses, Ships, and Small Islands in Altimeter Waveforms , 2007 .

[5]  S. Savage.  Aspects of Iceberg Deterioration and Drift , 2001 .

[6]  S. Venkatesh.  On the Deterioration of a Grounded Iceberg , 1986 .

[7]  James C. West,et al.  The radiation characteristics of an arbitrary antenna positioned on a polar ice sheet , 1987 .

[8]  D. Benn,et al.  Calving processes and the dynamics of calving glaciers , 2007 .

[9]  David G. Long,et al.  Tracking large tabular icebergs using the SeaWinds Ku-band microwave scatterometer , 2011 .

[10]  Dirk Olbers,et al.  A two-dimensional model for the thermohaline circulation under an ice shelf , 1989, Antarctic Science.

[11]  J. A. Åström,et al.  Statistical models of brittle fragmentation , 2006 .

[12]  Gaël Durand,et al.  Antarctic icebergs melt over the Southern Ocean: Climatology and impact on sea ice , 2016 .

[13]  Mohamed Sayed,et al.  Size distributions of small ice pieces calved from icebergs , 2000 .

[14]  M. Vernet,et al.  Cooling, dilution and mixing of ocean water by free-drifting icebergs in the Weddell Sea , 2011 .

[15]  Wolfgang Rack,et al.  Basal melting of A-38B: A physical model constrained by satellite observations , 2007 .

[16]  W. Rack,et al.  Model experiments on large tabular iceberg evolution: ablation and strain thinning , 2005, Journal of Glaciology.

[17]  Jean Tournadre,et al.  Antarctic icebergs distributions 1992-2014: ANTARCTIC ICEBERG , 2016 .

[18]  T. Fichefet,et al.  The effect of dynamic-thermodynamic icebergs on the Southern Ocean climate in a three-dimensional model , 2009 .

[19]  M. R. van den Broeke,et al.  An improved semi-empirical model for the densification of Antarctic firn , 2011 .

[20]  Robert Marsh,et al.  NEMO–ICB (v1.0): interactive icebergs in the NEMO ocean model globally configured at eddy-permitting resolution , 2014 .

[21]  Ian Eisenman,et al.  An Analytical Model of Iceberg Drift , 2016, 1610.06403.

[22]  James L. Fastook,et al.  ICESat profiles of tabular iceberg margins and iceberg breakup at low latitudes , 2005 .

[23]  W. Budd,et al.  Antarctic Iceberg Distribution and Dissolution , 1986, Journal of Glaciology.

[24]  David M. Holland,et al.  Modeling Thermodynamic Ice–Ocean Interactions at the Base of an Ice Shelf , 1999 .

[25]  Icebergs , 2020, Gardening in Clay.

[26]  D. J. Goodman,et al.  The Flexural Response of a Tabular Ice Island to Ocean Swell , 1980, Annals of Glaciology.

[27]  Jean Tournadre,et al.  Large icebergs characteristics from altimeter waveforms analysis , 2015 .

[28]  S. Neshyba,et al.  On the Estimation of Antarctic Iceberg Melt Rate , 1980 .

[29]  G. Holdsworth,et al.  Iceberg calving from floating glaciers by a vibrating mechanism , 1978, Nature.

[30]  Ian Allison,et al.  Iceberg calving from the Amery Ice Shelf, East Antarctica , 2002, Annals of Glaciology.

[31]  J. Bassis.  The statistical physics of iceberg calving and the emergence of universal calving laws , 2010, Journal of Glaciology.

[32]  Gerd Rohardt,et al.  Weddell Sea iceberg drift: Five years of observations , 2006 .

[33]  David P. Stevens,et al.  Modelling the dynamics and thermodynamics of icebergs , 1997 .

[34]  Martin Truffer,et al.  A unifying framework for iceberg-calving models , 2010, Journal of Glaciology.

[35]  W. F. Weeks,et al.  Icebergs as a Fresh-Water Source: An Appraisal , 1973, Journal of Glaciology.

[36]  P. Wadhams,et al.  The response of Antarctic icebergs to ocean waves , 1983 .

[37]  Jun Li,et al.  Modeling of firn compaction for estimating ice-sheet mass change from observed ice-sheet elevation change , 2011, Annals of Glaciology.

[38]  W. Cudlip,et al.  Observation of a giant Antarctic tabular iceberg by satellite radar altimetry , 1987, Polar Record.

[39]  P. Wadhams,et al.  Wind‐driven upwelling around grounded tabular icebergs , 2015 .

[40]  E. Okal,et al.  Transoceanic wave propagation links iceberg calving margins of Antarctica with storms in tropics and Northern Hemisphere , 2006 .

[41]  T. H. Jacka,et al.  Antarctic iceberg distribution and dissolution from ship-based observations , 2007 .

[42]  A. Yaglom,et al.  Heat and mass transfer laws for fully turbulent wall flows , 1972 .

[43]  David G. Vaughan,et al.  In situ measurements of Antarctic snow compaction compared with predictions of models , 2010 .

[44]  Tiago H. Silva,et al.  Contribution of giant icebergs to the Southern Ocean freshwater flux , 2006 .

[45]  Niels Reeh,et al.  A nonsteady‐state firn‐densification model for the percolation zone of a glacier , 2008 .

[46]  David G. Long,et al.  A Comprehensive Database for Antarctic Iceberg Tracking Using Scatterometer Data , 2018, IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing.

[47]  Pedro Elosegui,et al.  The “footloose” mechanism: Iceberg decay from hydrostatic stresses , 2014 .

[48]  Edward G. Josberger,et al.  The Melting of Ice in Cold Stratified Water , 1980 .

[49]  Alistair Adcroft,et al.  The effects of Antarctic iceberg calving‐size distribution in a global climate model , 2016 .

[50]  A. Gorban,et al.  A statistical model of aggregate fragmentation , 2011, 1106.2721.

[51]  David G. Long,et al.  Calving and ice-shelf break-up processes investigated by proxy: Antarctic tabular iceberg evolution during northward drift , 2008 .