Ventilation time scales of the North Atlantic subtropical cell revealed by coral radiocarbon from the Cape Verde Islands

Alvaro Fernandez, Thomas J. Lapen, Rasmus Andreasen, Peter K Swart, Christopher D. White, Brad E. Rosenheim

Research output: Contribution to journalArticle

3 Citations (Scopus)

Abstract

We present coral- and sclerosponge-based reconstructions of the <sup>14</sup>C content in North Atlantic dissolved inorganic carbon (DIC) during the last ∼100 years from the subtropical cells (STCs). These waters are sensitive to the dynamics of the shallow overturning meridional circulation that transports heat and water masses from the subtropics to the tropics. We use these records to investigate the circulation patterns of the off-equatorial upwelling regions of the STCs, which are not well understood. Coral and sclerosponge skeletons provide long time series of ocean DIC <sup>14</sup>C content, a tracer of oceanic circulation, effectively extending the observational record back in time. Sclerosponge data from the Bahamas were used to extend the existing subtropical <sup>14</sup>C time series to the 21st century. Coral <sup>14</sup>C data from the Cape Verde Islands (1890-2002) captured the <sup>14</sup>C signature of water brought to the surface in the off-equatorial regions of the STC present near the West African coast. We observe a unique postbomb trend at Cape Verde that is similar to the upwelling regions in the Pacific, and we interpret this trend as the result of the slow penetration of bomb <sup>14</sup>C into the interior ocean as part of the STC circulation. Using a multibox mixing model we constrain the time history of bomb <sup>14</sup>C in the eastern tropical Atlantic, and we estimate a 20 year time scale for ventilation of the thermocline in this area of the ocean. The similarity between the Atlantic and Pacific <sup>14</sup>C-based records of upwelling suggests that both are caused by bomb <sup>14</sup>C penetration rather than more complex explanations that invoke changes in thermocline depth (e.g., related to El Niño-Southern Oscillation variability) or changes in the strength of the subtropical cells. Our results offer constraints for models of tropical ocean circulation and anthropogenic CO<inf>2</inf> uptake that attempt to reproduce the characteristics of the shallow wind-driven circulation in the Atlantic.

Original languageEnglish (US)
Pages (from-to)938-948
Number of pages11
JournalPaleoceanography
Volume30
Issue number7
DOIs
StatePublished - Jul 1 2015

Fingerprint

ventilation
coral
upwelling
dissolved inorganic carbon
timescale
thermocline
ocean
penetration
time series
wind-driven circulation
oceanic circulation
Southern Oscillation
meridional circulation
twenty first century
skeleton
water mass
tracer
water
coast
history

Keywords

  • Atlantic
  • corals
  • radiocarbon
  • sclerosponges
  • subtropical cells

ASJC Scopus subject areas

  • Oceanography
  • Palaeontology

Cite this

Ventilation time scales of the North Atlantic subtropical cell revealed by coral radiocarbon from the Cape Verde Islands. / Fernandez, Alvaro; Lapen, Thomas J.; Andreasen, Rasmus; Swart, Peter K; White, Christopher D.; Rosenheim, Brad E.

In: Paleoceanography, Vol. 30, No. 7, 01.07.2015, p. 938-948.

Research output: Contribution to journalArticle

Fernandez, Alvaro ; Lapen, Thomas J. ; Andreasen, Rasmus ; Swart, Peter K ; White, Christopher D. ; Rosenheim, Brad E. / Ventilation time scales of the North Atlantic subtropical cell revealed by coral radiocarbon from the Cape Verde Islands. In: Paleoceanography. 2015 ; Vol. 30, No. 7. pp. 938-948.
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abstract = "We present coral- and sclerosponge-based reconstructions of the 14C content in North Atlantic dissolved inorganic carbon (DIC) during the last ∼100 years from the subtropical cells (STCs). These waters are sensitive to the dynamics of the shallow overturning meridional circulation that transports heat and water masses from the subtropics to the tropics. We use these records to investigate the circulation patterns of the off-equatorial upwelling regions of the STCs, which are not well understood. Coral and sclerosponge skeletons provide long time series of ocean DIC 14C content, a tracer of oceanic circulation, effectively extending the observational record back in time. Sclerosponge data from the Bahamas were used to extend the existing subtropical 14C time series to the 21st century. Coral 14C data from the Cape Verde Islands (1890-2002) captured the 14C signature of water brought to the surface in the off-equatorial regions of the STC present near the West African coast. We observe a unique postbomb trend at Cape Verde that is similar to the upwelling regions in the Pacific, and we interpret this trend as the result of the slow penetration of bomb 14C into the interior ocean as part of the STC circulation. Using a multibox mixing model we constrain the time history of bomb 14C in the eastern tropical Atlantic, and we estimate a 20 year time scale for ventilation of the thermocline in this area of the ocean. The similarity between the Atlantic and Pacific 14C-based records of upwelling suggests that both are caused by bomb 14C penetration rather than more complex explanations that invoke changes in thermocline depth (e.g., related to El Ni{\~n}o-Southern Oscillation variability) or changes in the strength of the subtropical cells. Our results offer constraints for models of tropical ocean circulation and anthropogenic CO2 uptake that attempt to reproduce the characteristics of the shallow wind-driven circulation in the Atlantic.",
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AU - Fernandez, Alvaro

AU - Lapen, Thomas J.

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AU - Rosenheim, Brad E.

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AB - We present coral- and sclerosponge-based reconstructions of the 14C content in North Atlantic dissolved inorganic carbon (DIC) during the last ∼100 years from the subtropical cells (STCs). These waters are sensitive to the dynamics of the shallow overturning meridional circulation that transports heat and water masses from the subtropics to the tropics. We use these records to investigate the circulation patterns of the off-equatorial upwelling regions of the STCs, which are not well understood. Coral and sclerosponge skeletons provide long time series of ocean DIC 14C content, a tracer of oceanic circulation, effectively extending the observational record back in time. Sclerosponge data from the Bahamas were used to extend the existing subtropical 14C time series to the 21st century. Coral 14C data from the Cape Verde Islands (1890-2002) captured the 14C signature of water brought to the surface in the off-equatorial regions of the STC present near the West African coast. We observe a unique postbomb trend at Cape Verde that is similar to the upwelling regions in the Pacific, and we interpret this trend as the result of the slow penetration of bomb 14C into the interior ocean as part of the STC circulation. Using a multibox mixing model we constrain the time history of bomb 14C in the eastern tropical Atlantic, and we estimate a 20 year time scale for ventilation of the thermocline in this area of the ocean. The similarity between the Atlantic and Pacific 14C-based records of upwelling suggests that both are caused by bomb 14C penetration rather than more complex explanations that invoke changes in thermocline depth (e.g., related to El Niño-Southern Oscillation variability) or changes in the strength of the subtropical cells. Our results offer constraints for models of tropical ocean circulation and anthropogenic CO2 uptake that attempt to reproduce the characteristics of the shallow wind-driven circulation in the Atlantic.

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