Export of Greenland Sea water across the Mohn Ridge induced by summer storms

The Mohn Ridge separates the Greenland Sea and the Lofoten Basin. Previous studies identified the export across the Mohn Ridge (EMR) from the Greenland Basin into the Lofoten Basin using water mass analysis and the tracer diffusion method, but there is still lack of direct current measurements. A surface mooring with four current meters was deployed on the Mohn Ridge from June 5 to June 18 in 2015, when three cyclones passed in the adjacent area. In the absence of cyclones, the flow on the Mohn Ridge was northeastward, parallel to the ridge. When cyclones appeared, the EMR occurred to transport Greenland Sea water into the Lofoten Basin. The probable mechanism is the sea level height variation caused by the perturbation of the low pressure of cyclones, which yields an outward pressure gradient force to drive the outflow. Our results suggest that the outflow is intermittent and only happens during cyclone activities. The annual mean volume flux of EMR was roughly estimated by the limited data, which is about 3.8×10 6 m 3 /s, a little bit smaller than the estimation based on volume conservation. The results indicate that the contribution of the cyclonic storms to EMR is a greatly important mechanism that potentially influences the global thermohaline circulation through the Greenland-Scotland Ridge overflow.