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Abstract

We examine how hydraulically-controlled exchange flows in silled fjords affect the relationship between basal glacier melt and features of warm intermediate Atlantic Water (AW) outside the fjords. Using theory and an ocean-circulation model, we show that an exchange flow can be forced to transit into a hydraulic regime if the AW interface height decreases, the AW temperature increases, or the production of glacially modified water is boosted by subglacial discharge. In the hydraulic regime, the heat transport across the sill becomes a rate limiting factor for the basal melt, which is suppressed. An interplay between processes near the ice--ocean boundary and the hydraulically-controlled exchange flow determines the melt dynamics, and the sensitivity of the basal melt to changes of the AW temperature is reduced. The model results are discussed in relation to observations from Ryder, Petermann, and 79$^{\circ}$N glaciers in North Greenland. We also outline how hydraulic suppression of basal melt can be represented in ice sheet modelling.