Summer hydrography on the shelf off Terre Adélie/George V Land based on the ALBION and CEAMARC observations during the IPY
Résumé
We report on the hydrographic observations collected on the Antarctic continental shelf between 138°E and 146°E as part of the CEAMARC and ALBION projects in December 2007-January 2008. A total of 140 quasi-synoptic CTD (Conductivity-Temperature-Depth) casts were analysed to map the spatial distribution of the summer hydrographic properties. Seven distinct hydrographic regimes were identified based on regional topographic features and the presence of specific water masses. These regimes are associated with spatial contrasts in the distribution of the High Salinity Shelf Water (HSSW) and the Modified Circumpolar Deep Water (MCDW). In particular, the HSSW distribution confirms the unique character of Commonwealth Bay in terms of extreme bottom salinity and dissolved oxygen values. The bay appears to be a preferred region for both dense shelf water formation and storage. The systematic survey of the Adélie Depression shows the ubiquitous presence of HSSW in the depression, and over the Adélie Sill as a 60 m thick layer at the centre of the sill. This water is dense enough to mix down the continental slope and form Antarctic Bottom Water. Upstream of the sill, the HSSW is shown to sit over the topography with indications of recirculation. The D'Urville Trough, another deep basin on the shelf, is filled with warmer and fresher water that is too light to contribute to the formation of AABW. The D'Urville Trough appears to collect MCDW which enters at the shelf break over the Adélie Bank and spreads over the northern slope of the trough. Another branch of MCDW enters in the eastern Adélie Sill and is found almost everywhere in the Adélie Depression with the noticeable exception of the coastal bays. Additional CTD casts collected during the ALBION-2009 experiment in January 2009 suggest that most of the features observed in 2008 in the Adélie Depression should be robust on a year-to-year basis although summer 2009 was characterized by fresher dense shelf waters.