Hydrographic and biogeochemical characterization of Admiralty Bay and the Bransfield Strait connection: insights into Antarctic environmental dynamics

Abstract

The marine systems of Antarctica are among the most sensitive regions on the planet to environmental variability, such as climate change, and play a significant role in global climate regulation. It is expected that waters flowing into Admiralty Bay (AB), Antarctica, from the Bransfield Strait will experience impacts from climate change, such as alterations in temperature, salinity, and sea ice cover—phenomena already observed in other regions of the Antarctic Peninsula and projected by some models. This study aimed to evaluate, based on in situ data, the physical and biogeochemical properties—temperature, salinity, dissolved oxygen, and nutrient levels—of AB over three austral summers (2019, 2022, and 2023) to investigate the impact of climate change on this sensitive marine ecosystem. Water temperature ranged between -1.0 and 0.2°C, while salinity in the study region varied between 34 and 35 PSU across the three campaigns. Despite differences in temperature and salinity observed inside and outside AB, the water masses in both regions displayed characteristics of Transitional Zonal Waters influenced by the Weddell Sea. Additionally, dissolved oxygen ranged from 246 to 342 μmol kg⁻¹ with high saturation (~100%), while Apparent Oxygen Utilization showed positive values (15 to 104 μmol kg⁻¹; with a mean of 43.2±19 μmol kg⁻¹). Observational data were complemented by the exploration of the GLORYS12V1 global assimilative product for the years 2022/2023. The results demonstrated that, despite the Antarctic Peninsula undergoing rapid environmental changes, parameters in AB exhibit remarkable consistency with historical data, indicating a resilient hydrographic regime. However, subtle but significant spatial and temporal variations reflect the complex interplay between local oceanographic processes and broader climatic influences. Notably, the study did not detect major changes in water mass properties, despite evidence of increased freshwater input and declining sea ice cover in the region. This highlights the complex response of the bay to climatic and oceanographic variability, suggesting that local processes, such as intense vertical mixing and cross-shelf exchange mechanisms, may be masking stronger climate change signals. Furthermore, this underscores the importance of continuous and detailed monitoring to uncover the subtle responses of Antarctic coastal systems to ongoing environmental changes. Future research should incorporate high-resolution data and process-oriented physical-biogeochemical numerical modelling experiments to fully capture the dynamics at play.