Preliminary Results of TErra NOva Bay Polynya High Resolution Experiment (TENORE) Project

The influence of polynya areas on polar oceans is considered significant in both physical and ecological contexts. In latent heat polynyas, such as the one in Terra Nova Bay (TNB), the substantial heat loss causes rapid and continuous sea ice formation. Salt rejection during sea ice formation increases the salinity of the underlying column water. This impacts on the properties of High Salinity Shelf Water (HSSW) which in turn plays a crucial role in the development of Antarctic Bottom Water (AABW) driving the lower branch of the Meridional Overturning Circulation and influencing the climate system. Over recent decades, AABW has experienced warming, freshening, and a volume reduction, with the Ross Sea Bottom Water, the second-largest source of AABW showing the most pronounced freshening. This change has been attributed to a drop in HSSW salinity. Previous studies showed a freshening of 0.05 per decade in TNB between 1995 and 2006, while a more recent study based on long-term mooring data revealed that the salinity decline lasted until 2014, when HSSW salinity sharply increased, with values in 2018 aligning with mid-1990s data. Although this rise in salinity might be already associated to the interannual variability, the available time series is too brief to establish definitive conclusions. This finding emphasizes the need for further in situ observations to better understand the forcings modulating the formation and variability of HSSW in TNB. The TENORE project addresses this topic by expanding conventional in situ measurement capabilities, including CTD profiles and water sampling, through a multi-platform approach that incorporates underwater gliders, unmanned aerial vehicles, drifters and satellite data. TENORE aims at enhancing the understanding of the physical and biochemical processes in TNB and their role in the intricate feedback mechanisms between the ocean and atmosphere in a changing climate. Preliminary results show the success of the sampling strategy in capturing the major signals associated to the investigated processes.