Seasonal particle dynamics in Kongsfjorden during two years of contrasting environmental conditions

Global climate change is particularly pronounced in the Arctic regions, widely recognized as a "climatic hotspot" by the scientific community. This phenomenon, known as Arctic amplification refers to the accelerated increase in Arctic surface temperature compared to the global average. This process drives the ongoing loss of Arctic sea-ice volume and intensifies the ice-albedo feedback mechanism. Key physical drivers include the increased intrusion of warm Atlantic Water into the Arctic Ocean, which profoundly impacts biogeochemical cycles. Over the past decades, the CNR-ISP has developed marine and atmospheric observatories in the Svalbard region. These include three moorings (MDI, KIM, MAP) measuring biogeochemical parameters along the water column in the Kongsfjorden-Krossfjorden fjord system, and the land-based platform, the Amundsen-Nobile Climate Change Tower (CCT), measuring atmospheric parameters. As part of the ITINERIS PNRR project, the moorings were equipped with advanced biogeochemical sensors capable of monitoring Essential Ocean Variables, enablingthe study of seasonal and annual dynamics of suspended marine particles and nutrients. Between 2022 and 2024, contrasting environmental conditions shaped the dynamics of particulate matter and nutrients. One striking difference between the two years was the intrusion of Atlantic water observed at the end of summer in 2023 which extended to the inner Kongfjorden. Additionally, the timing of the spring phytoplankton bloom between 2023 and 2024 shifted, and also the terrestrial input from summer glacier melting exhibited significant variability. The spring phytoplankton bloom begins when PAR increases after the polar night nutrient concentrations are high due to autumn replenishment and winter water convection, and the influence of Atlantic Water on nitrate replenishment rates is evident. The timing of the spring bloom results from a complex interplay of atmospheric and marine factors. In the inner part of the Kongsfjorden, suspended matter concentrations are primary driven by glacial meltwater inputs, which contributes to low-salinity surface waters within the fjord. These findings underscore the intricate relationships between environmental changes, particle dynamics, and nutrient cycling in Svalbard.