(Table 1) Mean sea-ice properties from moored upward looking sonars along the Greenwich meridian

Sea-ice ocean interaction processes are of significant influence on the water mass formation in the Weddell gyre. On the basis of data obtained between 1984 and 2008 from eight repeat hydrographic sections, moored instruments and profiling floats in the Weddell gyre on the Greenwich meridian - almost all of them collected with R.V. Polarstern - we identified variations in the properties of the Winter Water and the sea ice draft. In the Winter Water the salinity was relatively low throughout the 1990s (with a minimum in 1992) and a maximum was observed in 2003. Observations of sea ice draft by moored upward looking sonars are available from 1996 onwards. In the southern part of the transect they display variations on a decadal time scale with a minimum in sea-ice thickness in 1998 and an increase since then. Salinity variations in the Winter Water layer cannot be explained only by variations in sea-ice formation and variable entrainment of underlying Warm Deep Water, but lateral advection of water and sea ice needs to be taken into account as well. Potential sources are melt water from the ice shelves in the western Weddell Sea or transport of water of low salinity entering the Weddell gyre from the east. Accompanying variations of the properties of Warm Deep Water are discussed in detail in a companion paper (Fahrbach et al., 2011, doi:10.1016/j.dsr2.2011.06.007).

Sea ice draft measured by upward looking sonars in the Weddell Sea (Antarctica)

The presented database contains time-referenced sea ice draft values from upward looking sonar (ULS) measurements in the Weddell Sea, Antarctica. The sea ice draft data can be used to infer the thickness of the ice. They were collected during the period 1990-2008. In total, the database includes measurements from 13 locations in the Weddell Sea and was generated from more than 3.7 million measurements of sea ice draft. The files contain uncorrected raw drafts, corrected drafts and the basic parameters measured by the ULS. The measurement principle, the data processing procedure and the quality control are described in detail. To account for the unknown speed of sound in the water column above the ULS, two correction methods were applied to the draft data. The first method is based on defining a reference level from the identification of open water leads. The second method uses a model of sound speed in the oceanic mixed layer and is applied to ice draft in austral winter. Both methods are discussed and their accuracy is estimated. Finally, selected results of the processing are presented.