Shelf–fjord-exchange variability in western Svalbard based on Lagrangian particle tracking

The West Spitsbergen Current transports warm and saline Atlantic Water northward through the eastern Fram Strait, playing a critical role in shaping the hydrographic and climatic conditions of the western Svalbard region. While the core of the West Spitsbergen Current typically follows the shelf break, Atlantic Water can occasionally separate and intrude onto the West Spitsbergen Shelf, where it interacts with colder, fresher Arctic-type water masses. In this study, we use a series of Lagrangian particle tracking experiments forced by a high-resolution regional ocean model to investigate the dominant Atlantic Water pathways across the West Spitsbergen Shelf and into Isfjorden - the largest fjord on the west coast of Spitsbergen - and to assess their temporal variability. Our results show that on average only 15% of surface particles released over the shelf break reach the Isfjorden region, compared to > 50% of particles released on the shelf. Their trajectories are strongly steered by topography in accordance with the Spitsbergen Trough Current. In the mouth of Isfjorden, the location and strength of the density front separating the fjord from the shelf waters determines how far these intruding waters penetrate before recirculating and continuing northward. Surface-layer inflow into the main fjord basin displays a pronounced seasonal cycle, with peak inflow rates of > 50% in late spring and summer, associated with a reversal of the along-fjord wind. Inflow at depth is more episodic and governed by a combination of wind forcing and hydrographic preconditioning. During winter and spring, surface inflow is typically 3–4 °C warmer than the average main fjord temperature. This excess heat flux into the fjord has important implications especially in the surface layer, e.g. for marine-terminating glacier calving rates, local sea ice melt, and the broader marine ecosystem. • AW intrusions are topographically steered from the WSC across the WSS towards Isfjorden. • Hydrography controls the location of a strong recirculation pattern in the mouth of Isfjorden. • Along-fjord winds control the actual surface inflow into Isfjorden proper. • Inflow, especially at depth, warms the fjord interior.