Strength and Variability of the Deep Limb of the North Atlantic Meridional Overturning Circulation from Chlorofluorocarbon Inventories

William M. Smethie, Deborah A. LeBel, Rana A Fine, Monika Rhein, Dagmar Kieke

Research output: Chapter in Book/Report/Conference proceedingChapter

7 Scopus citations

Abstract

The southward flow of North Atlantic Deep Water (NADW) from its origin in the northern North Atlantic Ocean and Nordic Seas forms the deep branch of the North Atlantic meridional overturning circulation. NADW is composed of four water masses, Upper Labrador Sea Water (ULSW), Classical Labrador Sea Water (CLSW), Iceland-Scotland Overflow Water (ISOW) and Denmark Strait Overflow Water (DSOW). These water masses take up anthropogenic chlorofluorocarbon-11 (CFC-11) from the atmosphere in their formation regions. The formation rates of these water masses have been calculated from their CFC-11 inventories measured in the North Atlantic around 1990 and during the World Ocean Circulation Experiment (WOCE) survey from 1996 to 1998. The formation rates from the WOCE survey CFC-11 data, which are averages for the 1970-1997 time period, are 3.5 ± 0.6 Sv for ULSW, 8.2 ± 1.6 Sv for CLSW, 5.7 ± 0.9 Sv for ISOW and 2.2 ± 0.4 Sv for DSOW; these sum to 19.6 ± 2.0 Sv for NADW. From changes in the CFC-11 inventory in ULSW between 1997 and 2003, the rate of formation of ULSW was estimated to increase from a 3-decade average of 3.2 Sv in 1997 to 8 Sv for 1998-1999, and then decrease to 4 Sv for 2000-2001 and 2.5 Sv for 2002- 2003. The sharp increase in ULSW formation rate after 1997 coincided with a shutdown of CLSW formation.

Original languageEnglish (US)
Title of host publicationOcean Circulation: Mechanisms and Impacts - Past and Future Changes of Meridional Overturning
PublisherAmerican Geophysical Union
Pages119-130
Number of pages12
ISBN (Print)9781118666241, 9780875904382
DOIs
StatePublished - Mar 21 2013

Keywords

  • Circulation
  • Meridional
  • Overturning

ASJC Scopus subject areas

  • Earth and Planetary Sciences(all)

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    Smethie, W. M., LeBel, D. A., Fine, R. A., Rhein, M., & Kieke, D. (2013). Strength and Variability of the Deep Limb of the North Atlantic Meridional Overturning Circulation from Chlorofluorocarbon Inventories. In Ocean Circulation: Mechanisms and Impacts - Past and Future Changes of Meridional Overturning (pp. 119-130). American Geophysical Union. https://doi.org/10.1029/173GM09