Large icebergs characteristics from altimeter waveforms analysis

Large uncertainties exist on the volume of ice transported by the Southern Ocean large icebergs, a key parameter for climate studies, because of the paucity of information, especially on iceberg thickness. Using icebergs tracks from the National Ice Center (NIC) and Brigham Young University (BYU) databases to select altimeter data over icebergs and a method of analysis of altimeter waveforms, a database of 5366 icebergs freeboard elevation, length, and backscatter covering the 2002-2012 period has been created. The database is analyzed in terms of distributions of freeboard, length, and backscatter showing differences as a function of the iceberg's quadrant of origin. The database allows to analyze the temporal evolution of icebergs and to estimate a melt rate of 35-39 m.yr(-1) (neglecting the firn compaction). The total daily volume of ice, estimated by combining the NIC and altimeter sizes and the altimeter freeboards, regularly decreases from 2.2 10(4)km(3) in 2002 to 0.9 10(4)km(3) in 2012. During this decade, the total loss of ice (approximate to 1800 km(3).yr(-1)) is twice as large as than the input (approximate to 960 km(3).yr(-1)) showing that the system is out of equilibrium after a very large input of ice between 1997 and 2002. Breaking into small icebergs represents 80% (approximate to 1500 km(3).yr(-1)) of the total ice loss while basal melting is only 18% (approximate to 320 km(3).yr(-1)). Small icebergs are thus the major vector of freshwater input in the Southern Ocean.