International audienceRecent increase in Antarctic freshwater release to the Southern Ocean is suggested to contribute to change in water masses and sea ice. However, climate models differ in their representation of the freshwater sources. Recent improvements in altimetry-based detection of small icebergs and in estimates of the mass loss of Antarctica may help better constrain the values of Antarctic freshwater releases. We propose a model-based seasonal climatology of iceberg melt over the Southern Ocean using state-of-the-art observed glaciological estimates of the Antarctic mass loss. An improved version of a Lagrangian iceberg model is coupled with a global, eddy-permitting ocean/sea ice model and compared to small icebergs observations. Iceberg melt increases sea ice cover, about 10% in annual mean sea ice volume, and decreases sea surface temperature over most of the Southern Ocean, but with distinctive regional patterns. Our results underline the importance of improving the representation of Antarctic freshwater sources. This can be achieved by forcing ocean/sea ice models with a climatological iceberg fresh-water flux

Marine ecosystems are under increasing anthropogenic pressures from marine and terrestrial activities. Ship traffic, the major cause of change in the open ocean, and its temporal evolution are still largely unknown because of lack of data. Altimeter data provide a new powerful tool to detect and monitor the ship traffic through a method of analysis of echo waveform. The archive of seven altimeter missions has been processed to create a two decade database of ship locations. The estimated annual density maps compare well with the ones obtained from Automatic Identification System. The ship traffic analysis shows a global fourfold growth between 1992 and 2012, the largest increase being observed in the Indian Ocean and the Chinese seas reflecting the world trade change. Although mainly concentrated along lanes, the traffic has a direct impact on the atmosphere, e.g., on the growth of tropospheric nitrogen dioxide in the Indian Ocean.

Basal melting of floating ice shelves and iceberg calving constitute the two almost equal paths of freshwater flux between the Antarctic ice cap and the Southern Ocean. The largest icebergs (>100 km²) transport most of the ice volume but their basal melting is small compared to their breaking into smaller icebergs that constitute thus the major vector of freshwater. The archives of nine altimeters have been processed to create a database of small icebergs (<8 km²) within open water containing the positions, sizes, and volumes spanning the 1992–2014 period. The intercalibrated monthly ice volumes from the different altimeters have been merged in a homogeneous 23 year climatology. The iceberg size distribution, covering the 0.1–10,000 km² range, estimated by combining small and large icebergs size measurements follows well a power law of slope −1.52 ± 0.32 close to the −3/2 laws observed and modeled for brittle fragmentation. The global volume of ice and its distribution between the ocean basins present a very strong interannual variability only partially explained by the number of large icebergs. Indeed, vast zones of the Southern Ocean free of large icebergs are largely populated by small iceberg drifting over thousands of kilometers. The correlation between the global small and large icebergs volumes shows that small icebergs are mainly generated by large ones breaking. Drifting and trapping by sea ice can transport small icebergs for long period and distances. Small icebergs act as an ice diffuse process along large icebergs trajectories while sea ice trapping acts as a buffer delaying melting.