Abstract
Warm subtropical-origin Atlantic water flows northward across the Greenland-Scotland Ridge into the Nordic Seas, where it relinquishes heat to the atmosphere and gradually transforms into dense Atlantic-origin water. Returning southward along east Greenland, this water mass is situated beneath a layer of cold, fresh surface water and sea ice. Here we show, using measurements from autonomous ocean gliders, that the Atlantic-origin water was re-ventilated while transiting the western Iceland Sea during winter. This re-ventilation is a recent phenomenon made possible by the retreat of the ice edge toward Greenland. The fresh surface layer that characterises this region in summer is diverted onto the Greenland shelf by enhanced onshore Ekman transport induced by stronger northerly winds in fall and winter. Severe heat loss from the ocean offshore of the ice edge subsequently triggers convection, which further transforms the Atlantic-origin water. This re-ventilation is a counterintuitive occurrence in a warming climate, and highlights the difficulties inherent in predicting the behaviour of the complex coupled climate system.
Highlights
Warm subtropical-origin Atlantic water flows northward across the Greenland-Scotland Ridge into the Nordic Seas, where it relinquishes heat to the atmosphere and gradually transforms into dense Atlantic-origin water
As the ice edge retreats toward Greenland, water masses including the Atlantic-origin water transported by the East Greenland Current that were previously insulated from the atmosphere underneath sea ice are being ventilated
The temperature of the Denmark Strait overflow is minimum in September[27], which, assuming an advective speed of 4–5 cm/s, is consistent with the transport of colder Atlantic-origin water that was re-ventilated the previous winter in the Iceland Sea
Summary
Warm subtropical-origin Atlantic water flows northward across the Greenland-Scotland Ridge into the Nordic Seas, where it relinquishes heat to the atmosphere and gradually transforms into dense Atlantic-origin water. Returning southward along east Greenland, this water mass is situated beneath a layer of cold, fresh surface water and sea ice. Here we show, using measurements from autonomous ocean gliders, that the Atlantic-origin water was reventilated while transiting the western Iceland Sea during winter. Farther to the west (within the region outlined in black in Fig. 1), the influence of fresh, low-density surface water becomes dominant[17,18] The presence of this water mass is known to inhibit convection[19,20], but far a lack of wintertime measurements from the westernmost part of the Iceland Sea has prevented verification[13]. As the ice edge retreats toward Greenland, water masses including the Atlantic-origin water transported by the East Greenland Current that were previously insulated from the atmosphere underneath sea ice are being ventilated
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