Transport of Deep and Bottom Waters through the Mid-Atlantic Ridge in the Vema Fracture Zone
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NOLOGY
Transport of Deep and Bottom Waters through the Mid-Atlantic Ridge in the Vema Fracture Zone A. N. Demidova,*, A. A. Ivanova, F. N. Gippiusa, and Corresponding Member of the RAS S. A. Dobroliubova Received June 16, 2020; revised July 6, 2020; accepted July 7, 2020
Abstract—This paper addresses changes of Antarctic Bottom Water (AABW) transport through the Vema Fracture Zone based on direct measurements and Glorys12v1 reanalysis. Instrumental measurements of currents and other principal hydrological characteristics were carried out during the 45th cruise of the R/V Akademik Nikolaj Strakhov in November 2019. According to the current velocity measurements in 2019, the transport in the Vema Fracture Zone is 0.9 Sv. Moreover, based on the distribution of dissolved oxygen concentration, it is more correct to consider the isotherm 1.7°С rather than 2°С as the upper boundary of the AABW. The reanalysis showed very good agreement with direct measurements. The average transport of bottom water during the reanalysis period is 0.66 Sv. In general, there is a tendency towards an increase in both transport and temperature over the 25-year period covered by reanalysis. The measurements of the bottom water temperature during twenty successive samplings showed changes from 1.36 to 1.41°С within a day. This interval almost completely covers the entire range of values observed in previous years. Keywords: Vema Fracture Zone, Antarctic Bottom Water (AABW), transport of bottom water, reanalysis, Glorys12v1, 45th cruise of the R/V Akademik Nikolaj Strakhov, water mass transfer DOI: 10.1134/S1028334X20090068
INTRODUCTION The main pathway of the Antarctic Bottom Water (AABW) towards the eastern Atlantic remained incompletely understood for a long time. The AABW reaches the western part practically unhindered and than passes through the Vema, Romanche and Chain Fracture Zones of the Mid-Atlantic Ridge towards the eastern part [2]. Direct measurements of the current velocities in the Romanche and Chain fracture zones [6] revealed a comparable AABW transport of 0.66 and 0.56 Sv, respectively (1 Sv = 106 m3/s). According to most previous studies [1, 7, 9], the transport in the Vema Fracture Zone is 0.5–2 Sv, which is comparable with these values. The AABW transport, including the flux through the Vema Fracture Zone, was recently estimated in oceanic circulation models [3, 11]. Unlike occasional contact measurements, modeling allows the estimation of the transport variations over a long time (up to 20–30 years) by creating retrospective model data arrays, i.e., reanalyses. The disadvantage of this method is insufficient resolution in space and depth (1–3 horizons below 4000 m). At the same time, a aLomonosov
Moscow State University, Moscow, Russia *e-mail: [email protected]
combination of direct measurements and reanalyses provides a more correct determination of AABW transport and the possibility of reconstructing the variations in its parameters for periods when direct measurements were absent. The aim of this work is to determine the
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