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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., The 28th IUGG General Assembly (IUGG2023) (Berlin 2023)

The Antarctic continent plays a fundamental role in the global climate system and its role is particularly important in a climate change scenario. Since the '90s, the Ross Sea and the coastal area of Terra Nova Bay have been chosen as specific and peculiar research sites for climatic investigations within the LTER (Long-Term Ecological Research) network. Studies have been conducted by both Italian and international Universities and research centres.This macro-site area is characterized by abundant primary productivity, and zooplankton and benthonic communities. The objective of the research activities is the acquisition of long-term time series related to the biotic communities, the bio-geochemical fluxes and the physico-chemical parameters of the water column in the Ross Sea area. To this aim, four Moorings (A, B, D and H) were deployed to obtain the above-mentioned data, which will be very useful to improve the quality of the existing bio-geochemical models and to provide more precise information on the Antarctic marine ecosystem in relation to global climate change. In the Terra Nova Bay research site, the activities are devoted to the characterization of the relationship between the structure and the dynamic of the pelagic and benthonic communities and the ice cover. Numerous physical, chemical and biological data were collected from the four Moorings, the water samples retrieved at the Terra Nova Bay site and the sediments samples. Such fundamental data allowed establishing an important starting point to better understand the climate change phenomena occurred in the last twenty years, and that will occur in the future, in the Ross Sea Area.

The Antarctic continent plays a fundamental role in the global climate system and its role is particularly important in a climate change scenario. Since the '90s, the Ross Sea and the coastal area of Terra Nova Bay have been chosen as specific and peculiar research sites for climatic investigations within the LTER (Long-Term Ecological Research) network. Studies have been conducted by both Italian and international Universities and research centres.This macro-site area is characterized by abundant primary productivity, and zooplankton and benthonic communities. The objective of the research activities is the acquisition of long-term time series related to the biotic communities, the bio-geochemical fluxes and the physico-chemical parameters of the water column in the Ross Sea area. To this aim, four Moorings (A, B, D and H) were deployed to obtain the above-mentioned data, which will be very useful to improve the quality of the existing bio-geochemical models and to provide more precise information on the Antarctic marine ecosystem in relation to global climate change. In the Terra Nova Bay research site, the activities are devoted to the characterization of the relationship between the structure and the dynamic of the pelagic and benthonic communities and the ice cover. Numerous physical, chemical and biological data were collected from the four Moorings, the water samples retrieved at the Terra Nova Bay site and the sediments samples. Such fundamental data allowed establishing an important starting point to better understand the climate change phenomena occurred in the last twenty years, and that will occur in the future, in the Ross Sea Area.

The Ross Sea exhibits the largest continental shelf and it is considered to be the most productive region in Antarctica, with phytoplankton communities that have so far been considered to be driven by the seasonal dynamics of the polynya, producing the picture of what is considered as the classical Antarctic food web. Nevertheless, the Ross Sea is made up of a complex mosaic of sub-systems, with physical, chemical, and biological features that change on different temporal and spatial scales. Thus, we investigated the phytoplankton community structure of the Ross Sea with a spatial scale, considering the different ecological sub-systems of the region. The total phytoplankton biomass, maximum quantum efficiency (Fv/Fm), size classes, and main functional groups were analyzed in relation to physical–chemical properties of the water column during the austral summer of 2017. Data from our study showed productivity differences between polynyas and other areas, with high values of biomass in Terra Nova Bay (up to 272 mg chl a m–2) and the south-central Ross Sea (up to 177 mg chl a m–2) that contrast with the HNLC nature of the off-shore waters during summer. Diatoms were the dominant group in all the studied subsystems (relative proportion ≥ 50%) except the southern one, where they coexisted with haptophytes with a similar percentage. Additionally, the upper mixed layer depth seemed to influence the level of biomass rather than the dominance of different functional groups. However, relatively high percentages of dinoflagellates (∼30%) were observed in the area near Cape Adare. The temporal variability observed at the repeatedly sampled stations differed among the sub-systems, suggesting the importance of Long-Term Ecological Research (L-TER) sites in monitoring and studying the dynamics of such an important system for the global carbon cycle as the Ross Sea. Our results provide new insights into the spatial distribution and structure of phytoplankton communities, with different sub-systems following alternative pathways for primary production, identifiable by the use of appropriate sampling scales.

The distribution of particulate Fe (pFe), suspended particulate matter (SPM), and other particulate trace metals were investigated in Terra Nova Bay as part of CDW Effects on glaciaL mElting and on Bulk of Fe in the Western Ross sea (CELEBeR) and Plankton biodiversity and functioning of the Ross Sea ecosystems in a changing Southern Ocean (P-ROSE) projects. Variable concentrations of SPM (0.09&ndash, 97 mg L&minus, 1), pFe (0.51&ndash, 8.70 nM) and other trace metals were found in the Antarctic Surface waters (AASW) layer, where the addition of meltwater contributed to the pool with both lithogenic and biogenic forms. The deeper layer of the water column was occupied by High Salinity Shelf Water (HSSW) and Terra Nova Bay Ice Shelf Water (TISW) encompassing glacial water as confirmed by the lightest &delta, 18O measured values. The concentration of pFe in TISW (11.7 &plusmn, 9.2 nM) was higher than in HSSW samples (5.55 &plusmn, 4.43 nM), suggesting that the drainage of material released from glaciers surrounding the area is relevant in terms of pFe contribution. Particulate Fe/Al and Mn/Al ratios were substantially in excess compared with the mean crustal ratios. Microscopic analyses confirmed that more labile Fe oxyhydroxides and authigenic MnO2 phases were present together with biogenic sinking material. Future expected increasing melt rates of these glaciers enlarge Fe input, thus having a greater role in supplying iron and counteracting the reductions in sea ice cover around Terra Nova Bay.

The 0–200 m surface layer of the Ross Sea was studied during summer 2014 to investigate the lability of the particulate organic matter (POM) in response to physical parameters. With the use of satellite information, we selected three zones, characterised by different physical setting: a northern offshore area, crossing the summer-polynya area of the Ross Sea (hereafter called ROME 1), a more coastal area next to the Terra Nova Bay polynya (ROME 2); a southern offshore area, towards the Ross Ice Shelf (ROME 3). Ice-maps showed that the seasonal ice retreat had already occurred in early December for most of the stations. Statistical analysis of the quantitative and qualitative characteristics of the POM pointed to significant differences between the stations, especially in the upper mixed layer (UML). A comparison with previous studies showed that the localised pulses of POM accumulation in the UML were similar to those recorded at the highly productive marginal ice zones, providing notable trophic support to the ecosystem. The UML, although rather thin and easily subjected to alterations, confirmed its pivotal role in the ecosystem dynamics. A POM quality favourable to consumers was highlighted at several stations in ROME 1 and ROME 3. Reduced trophic support was, instead, found in ROME 2. Limited POM consumption where deep-water formation takes place would increase the POM role in the transfer of C to the depths.