Description: The Mediterranean Sea is well-known for its sensitivity to climate change, leading to extensive efforts in monitoring the basin as a whole. However, the Mediterranean is composed of individual sub-basins that exhibit different roles in its conveyor belt’s function. Additionally, impacts on societies and ecosystems have been shown to depend primarily on local manifestation of global-scale changes. Thus, sufficient risk assessment and the development of feasible adaptation strategies require regional studies, especially in sub-basins with high population density along their coastlines. The Tyrrhenian basin, one of the main mixing areas of the Mediterranean, is among the most densely populated semi-enclosed basins, yet it remains the least investigated. This work addresses this issue and provides new regional products, implementing information about the state, long-term variability, and changes in the surface and sub-surface layers of the Tyrrhenian Sea, while considering the potential role of local forcing as well as large-scale climatic patterns. Essential surface monitoring indicators, such as sea surface temperature, sea level anomaly, geostrophic currents, and air-sea interactions, were assessed using satellite, reanalysis, and in-situ data over the last four decades. Corresponding sub-surface indicators, including ocean heat and salt contents and water mass physical properties, were also computed based on more than 750000 hydrographic stations. A dedicated website was created to distribute these indicators, the regional dataset and the corresponding climatologies in order to respond to the increasing needs for directly usable regional products and to provide a reference baseline for the Tyrrhenian Sea.

Description: The production of Antarctic Bottom Water (AABW) is a crucial factor in determining the strength of the Meridional Overturning Circulation, and therefore plays a significant role in the ocean's contribution to the global climate. AABW is primarily formed in the Ross and Weddell Seas, with unique thermohaline characteristics. In recent years, a negative decadal salinity trend has been observed in the Southern Ocean's Pacific sector, related to AABW modification. Correspondingly in the Ross Sea, observations have indicated changes in the thermohaline characteristics of the shelf waters, precursors of the AABW, since 1995. The significant freshening in the western Ross Sea, where AABW is formed and spreads to fill the Pacific Ocean's deep basins, was attributed to the inflow of waters from West Antarctica where a dramatic melting of glaciers is occurring. To determine the freshwater inflow from West Antarctica and the role of these waters in the salinity field variability, a dedicated oceanographic cruise was carried out during austral summer 2020 in the eastern sector of the Ross Sea. Additionally, a section of the same CTD grid was repeated during January 2021. Using physical data from the CTD and LADCP casts, glider deployment and drifters, we estimated water mass characteristics and dynamical features. Eventually, discrete sea water sampling for chemical analyses (nutrients, carbonate system, trace metals, persistent organic compounds) has been carried out to provide new information about the biogeochemistry of the area and origin of the water masses.

Description: The Ross Ice Shelf (RIS) floats over the southern sector of the Ross Sea creating beneath a crucial area for ocean-ice interactions, known as the cavity. This area is characterized by the formation of Ice Shelf Water (ISW) as well as the intrusion of warm water, which is the main driver of basal melting and ice shelf calving. Ocean-driven basal melting and calving are the predominant causes of ice-shelf buttressing losses and the ice discharge that directly affects the global sea level. While the RIS is not considered to be under threat from the on-shelf intrusion of warm Circumpolar Deep Water (CDW), dense High Salinity Shelf Water (HSSW) and seasonally warmed Antarctic Surface Water (AASW) are expected to cause significant basal melting. The RIS northwest sector, which is directly exposed to solar-heated AASW, sees melt rates that nearly triple during the summer months. In this work, we present unprecedented thermohaline observations from Argo floats close to the north-western sector of the RIS during 2020-2022. Data from the floats provide insights into the year-around water mass structure along and even under the RIS. The continuous under-ice profiles made it possible to observe the complete cycle of water column change during seasonal transitions, the formation of HSSW in the RIS polynya as well as the outflow of ISW. Moreover, one Argo float spent 6 months under the RIS, collecting data directly at the sea-ice interface and capturing the intrusion of warm surface waters into the shelf cavity during the summer.

Description: Antarctic Bottom Water (AABW) supplies the lower branch of the global overturning circulation and ventilates the abyssal ocean. Changes in AABW properties and formation rate propagate into the global ocean and affect stratification, sea level, heat content, and the carbon cycle. Approximately 25% of AABW originates from the Dense Shelf Water (DSW) produced on the Ross Sea continental shelf. Understanding the long-term variability of the Ross Sea DSW physical properties and its controlling factors is critical to assessing the AABW variability. Here we use an unprecedented 28 years of current velocity and hydrographic observations collected from a mooring situated in Terra Nova Bay (TNB), where the saltiest DSW is produced. We used these time series to analyze the ocean currents in relation to dense water formation. While recent studies have suggested that the tides are the dominant source of currents close to the Ross Sea shelf break, here we observe a negligible contribution of the tide to the total velocity. We find a strong seasonal variability with a strong barotropic (from 140 m to the bottom) along trough (north-eastward) flow during August to October at the peak of dense water formation, suggesting a correlation between the flow rate at the mooring and the DSW production. Moreover, to investigate the relationship between the dense water production and the AABW outflow from the continental shelf, we have also compared the TNB mooring observations to the time series registered close to the shelf break.