Winter Intrusions of Atlantic Water in Kongsfjorden: Oceanic Preconditioning and Atmospheric Triggering

Abstract

AbstractKongsfjorden, an Arctic fjord in Svalbard, is largely influenced by the West Spitsbergen Current (WSC), transporting warm and salty Atlantic Water (AW) into the Arctic region. Despite the geostrophic control preventing AW from entering the fjord in winter, AW intrusions occasionally occur during energetic local wind events in this season. However, recent intrusions remain poorly characterized, and the underlying mechanism(s) and large‐scale precursors are only partly understood. This study uses in‐situ oceanographic and atmospheric measurements, alongside reanalysis data covering 2011–2020, to describe recent wintertime AW intrusions in Kongsfjorden. By discerning common traits in the observed events, the main triggering factors and controls of the phenomenon are described. Our results indicate that AW intrusions are typically triggered by wind reversals over the shelf, consisting of the sudden transition from a strong southerly to a northerly circulation linked to the setup and damping of a high‐pressure anomaly over the Barents Sea. Ocean density is a critical preconditioning factor influencing the nature of the intrusion: when fjord waters exhibit a lower density compared to WSC waters, wind reversals induce AW intrusions by upwelling; in contrast, when fjord waters present higher or similar densities compared to WSC waters, reversals force AW inflows near the surface or at intermediate depths, respectively. Another mechanism was observed only in winter 2014: southerly winds prevailed for 2 months, transporting surface AW from the WSC into the fjord, promoting its intrusion near the surface, on top of denser local waters.