Hydrodynamics of the Bottom-Water Flow from the Arctic to the Atlantic through the Strait of Denmark

Abstract

The overflow of bottom waters through the Strait of Denmark to the Atlantic has been investigated. A unique physical and hydrodynamic effect of bottom-water overflow has been found. A large volume of cold mixed water overflows as a lens, which is called a bolus. It is shown that the transversal size of the bolus, limited by the 1.028 g/cm3 isopycnal, is approximately 70 km. Its thickness reaches 300 m. This form of overflow over the sill in the form of a bolus alternates with a period of 5 days with the usual overflow. During the bolus overflow, the maximum velocities are found at the leading front, when the water descends down the sill. Minimum velocities are found in the middle of the bolus, which is caused by widening of the bolus after it passes the narrow part of the strait and widens. Velocities increase again in the rear part of the bolus in the narrows of the strait. We suggest a mechanism of a 5-day variation of the overflow regime, which is governed by internal seiches.