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Understanding the foraging behavior of marine animals is crucial for assessing their ecological significance and responses to environmental changes. In the context of Antarctica, marine animals face rapid and profound environmental changes related with global warming. However, our understanding of their responses remains limited owing to the formidable challenges inherent in conducting observations, particularly during the harsh austral winter months. In this study, we investigated the influence of changes in seawater properties and light conditions on the seasonal foraging behavior of Weddell seals (Leptonychotes weddellii) in the Ross Sea, Antarctica. We affixed 35 Weddell seals with CTD tags to record their locations and dive profiles, including depth, head acceleration, temperature, and salinity. We found that seals foraged more frequently in modified shelf water and ice shelf water compared to Antarctic surface water. This preference could be connected to greater food availability. Additionally, seals also dove to greater depths and displayed increased activity in capturing prey during daylight hours. This behavior may correspond to the diel vertical migration of pelagic prey in response to varying light conditions. Our findings suggest that Weddell seals have adjusted their foraging behaviors to adapt to spatial and temporal changes in oceanographic conditions. This highlights the importance of extrinsic factors in estimating their seasonal foraging behavior. [ABSTRACT FROM AUTHOR]

The formation of High-Salinity Shelf Water (HSSW), which is the major source of Antarctic bottom water (AABW), has been observed in Terra Nova Bay (TNB) in Antarctica. We believe a description of the spatio-temporal variation of salinity in TNB would help understand the production of HSSW in the region. Hence, the aim of this study is to investigate salinity variations in the Drygalski Basin (DB) and eastern TNB close to Crary Bank of the Ross Sea. For this, we use the moored and profiled hydrographic data, as well as available wind and sea-ice products. We found that deep-ocean salinity in the eastern TNB (~ 660 m) and DB (~ 1200 m) increases each year starting in September, and large amounts of salinity increase (> 0.04) were observed in 2016 and 2017. According to the velocity data observed at the same depths, the increases in salinity from September were due to the advection of HSSW from the coastal region of the Nansen ice shelf (NIS). The significant increases in salinity are related to the formation of active HSSW, evidence of which can be found from the HSSW properties obtained in February 2017 and March 2018. In addition, we show that HSSW can locally formed in the upper layer (< 300 m) of the eastern TNB by wind-driven mixing. HSSW in the upper layer was only detected in 2016 and 2017 when much saltier HSSW was observed below 800 m. This indicates that brine supply related to the development of polynya by winds has contributed to the HSSW formation not only near the NIS, but also in the eastern TNB. Moreover, as compared with historical observations, salinity of HSSW has been increasing since 2016 and, in 2018, it became similar with that in the early 2000. The observation of fluctuations such as this, which contrasts with past freshening, could contribute to estimating properties of recently formed AABW and improving the accuracy of both regional and global climate models. [ABSTRACT FROM AUTHOR]