Drivers of seasonal hydrography in Disko Bay, Greenland

Abstract. This study investigates the seasonal dynamics of Disko Bay in West Greenland. On the eastern side, the hydrography in the bay is driven by ice-ocean interactions and exchange with Ilulissat Icefjord, and on the western side, it exchanges waters with Baffin Bay. Since the mid-1990s, this region has experienced significant changes, including rapid ocean warming, sea-ice decline, and the retreat of Greenland's fastest-flowing marine-terminating glacier. Although West Greenland Irminger Water (WGIW) is known to be a heat source behind many of these changes, it has remained unclear when and how these dense warm waters flow into Disko Bay. We present a 2-year hydrographic record of observations within Disko Bay, determining the key hydrographic seasonality and the processes that drive it. Dense water renewal occurs repeatedly each spring when WGIW crosses the sill between Baffin Bay and Disko Bay. This spring renewal leads to the highest observed temperature and densest waters at depth, which rise high enough in the water column to reach the Ilulissat Icefjord sill. Additionally, we show that renewal may occur in late autumn and winter in the presence of upwelling-favourable winds along the West Greenland shelf. Following the renewal-driven season in spring, the summer and autumn are characterised by a deep-reaching fresh signal that extends over the upper 150 m across large areas of Disko Bay. Spatial analysis reveals an advective path that transports this fresh signal westward from the vicinity of Ilulissat Icefjord, along the northern periphery of the bay. Additional seasonal influence comes from along-isopycnal warming below this fresh layer, which is observed throughout autumn.