Hydrodynamics of the Bottom-Water Flow from the Arctic to the Atlantic through the Strait of Denmark
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odynamics of the Bottom-Water Flow from the Arctic to the Atlantic through the Strait of Denmark E. G. Morozova, *, D. I. Freya, S. V. Gladysheva, and V. S. Gladysheva aShirshov
Institute of Oceanology, Russian Academy of Sciences, Moscow, 117997 Russia *e-mail: [email protected]
Received January 28, 2020; revised March 11, 2020; accepted April 1, 2020
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. Keywords: Strait of Denmark, bolus, bottom flow, variations of the flow, modeling DOI: 10.1134/S0001433820050096
INTRODUCTION Cold and dense water forms in the Greenland Sea. This water gives rise to North Atlantic Deep Water after it overflows the threshold of the Strait of Denmark into the Atlantic (according to the modern concepts, the densest water in the Strait of Denmark is formed in the Irminger Sea). As a result, the densest lower part of this water mass is formed. In the Western literature, this water is called Denmark Strait Overflow Water (DSOW). Further, this stream flows along the continental slope of America to the south in the form of the Deep Western Boundary Current. Several water masses with different properties are the sources of this water in the Greenland Sea [1–3]. A map of the Strait of Denmark with a scheme of the stations along sections is shown in Fig. 1. The flow of water from the Greenland Sea to the Atlantic is known as a powerful underwater spillway. The depth of the threshold in the strait is about 650 m. Then, the water flows down the slope to the Irminger Sea to a depth exceeding 3000 m. Based on a 20-year series of measurements and model estimates, the water transport with a potential density of σ0 > 27.80 in the Strait of Denmark is estimated at 3.18 ± 0.56 Sv [4–8]. Instrumental observations show that water transport exceeding 6 Sv is often observed in the strait. The flow of Arctic water over the threshold of the Strait of Denmark has been investigated many times. It was shown that the interannual or intra-annual variability is low [9], but strong fluctuations of the flow
and its structure were detected on a time scale of several days. It was
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