Vivaldi 1991-A study of the formation, circulation and ventilation of Eastern North Atlantic Central Water

R. T. Pollard, M. J. Griffiths, S. A. Cunningham, J. F. Read, F. F. Perez, A. F. Rios

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Abstract

A synoptic, hydrographic data set comprising 32 full depth CTD casts and 2500 CTD/SeaSoar profiles to 500 m is used to describe the theta/S properties and circulation of Central Water east of the mid-Atlantic Ridge and between 39 degrees N and 54 degrees N. Eastward transport of 20 x 10(6) m(3) s(-1) in the North Atlantic Current turns entirely northwards to the west of 54 degrees N, 20 degrees W. This transport consists in the upper layers of Western North Atlantic Water freshened at temperatures below 10 degrees C by mixing with Sub-Arctic Intermediate Water. Northern and Southern branches of the North Atlantic Current are well defined and both turn northwards west of 20 degrees W. A further 10 x 10(6) m(3) s(-1) 1 of Eastern North Atlantic Water forms and recirculates anticyclonicaily to the west of Spain south of the North Atlantic Current and north of 40 degrees N. Eastern North Atlantic Water is most weakly stratified east of 20 degrees W and there is clear correlation between weakly stratified pycnostads and positive salinity anomalies relative to Western North Atlantic Water. Thus Eastern North Atlantic Water is a winter Mode Water in which strong winter cooling has increased the density and hence also the salinity anomaly at a given temperature. Near the southern entrance to the Rockall Trough there is evidence that salinities are also increased by Mediterranean Water influence. Circulation south of the North Atlantic Current is complex. There is no evidence for direct ventilation southwards across 40 degrees N where water properties (theta/S, potential vorticity and CFC-113) and historical data all indicate westward ventilation east of 24 degrees W, with weak southward ventilation occurring further west, in the vicinity of the Azores. The circulation pattern suggested is remarkably similar to that proposed by Helland-Hansen and Nansen in 1926 (The eastern North Atlantic, Geophysiske Publicajoner, 4, 1-76), with anticyclonic circulation of colder Eastern North Atlantic Water north of 40 degrees N meeting warmer water from south of 40 degrees N circulating cyclonically north of the Azores Current. The distribution of pycnostads and theta/S properties between 20 degrees W and 35 degrees W north of the Azores indicates alternate bands of Western and Eastern North Atlantic Water moving eastward and westward respectively, including evidence for westward motion immediately south of the Southern branch of the North Atlantic Current, possibly by westward propagation of anticyclonic eddies containing deep pycnostads. Copyright (C) 1996 Elsevier Science Ltd
Original languageUndefined/Unknown
Pages (from-to)167-192
Number of pages26
JournalProgress in Oceanography
Volume37
Issue number2
DOIs
Publication statusPublished - 1996

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