Temporal variability of the Circumpolar Deep Water inflow onto the Ross Sea continental shelf

The Circumpolar Deep Water (CDW) intrusion on the Antarctic continental shelves is the primary source of heat, salt and nutrients playing a major role on the shelf physical and biological processes. Different studies have analyzed the processes responsible for the transport of CDW across the Ross Sea shelf break, but until now, there are no continuous observations that investigate the time of the intrusions. Besides, few works focused on the effect of the tide that controls the intrusion itself. In the Ross Sea, the CDW intrudes onto the shelf in several locations mostly along the troughs, such as the Glomar Challenger, the Joides and the Drygalski. We use hydrographic observations and three moorings placed (one) on the outer shelf in the middle of the Drygalski Trough and (two) on the upper slope at the mouth of the Glomar Challenger basin, in order to characterize the spatial and temporal variability of the CDW inflow onto the shelf. Our data span from 2004 to 2014. In the Drygalski Trough the CDW enters as a thick layer of about 150 m between 250 - 400 m moving upward toward south. At the mooring location, about 50 Km from the shelf break, two main CDW cores can be observed: one on east side of the trough spreading along the west slope of Mawson Bank from about 200 m to the bottom and the other one in the central-west side from 200 m to about 350 m. A signature of this lighter and relatively warm water is detected by the instruments on the mooring at bottom of the Drygalski Trough. The CDW intrusion at the bottom of the trough is strictly related to the diurnal and spring/neap tidal cycles, but a strong seasonal variability of the CDW is clear. A strong inflow of CDW is observed every year at the end of December (after few months that the salinity minimum is registered), while the CDW inflow is at its seasonal minimum during the end of the austral summer in correspondence of the salinity maximum associated with the High Salinity Shelf Water (HSSW). Indeed, the CDW intrusions over the shelf are independent from the HSSW outflow.