Discovery and quantification of the Atlantic Meridional Overturning Circulation: the importance of 25N

Abstract

Here we present a review of the history of modern understanding of the strength of the Atlantic Meridional Overturning Circulation (MOC), which arguably originates in 1957. This was the year that the Discovery cruises not only observed the Atlantic deep western boundary current for the first time, but also completed a transatlantic section along 24ºN, from which reliable estimates of the size and structure of the MOC were later obtained. It was also the
year Stommel began to publish his estimates of the size of the Atlantic overturning. These key developments are put into the context of early qualitative pictures of the Atlantic MOC which can be traced back to 1798. The early proposals differed significantly from Wüst’s qualitative
picture of layered interhemispheric exchange, published in 1935 but still broadly accepted today, and on which subsequent quantification relied. Early estimates of the Atlantic MOC strength, as by-products of regional circulation schemes, were by today’s standard weak at 6-8 Sv. Stommel’s work from 1957 and later developments in the 1980’s produced much stronger overturning. Recognition of the importance of the MOC’s role in meridional heat transport, necessitating studies dedicated to its quantification, led to a consensus regarding its strength in the early 1980’s. The accepted 16-18 Sv MOC resulting from the 1957 Discovery section analysis supported Stommel’s 1957 work and has since been verified by independent observations. We examine only the steady state MOC here, understanding and quantification of its variability are still very much evolving.

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ORCID for H.L. Bryden: orcid.org/0000-0002-8216-6359

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