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Volume 12, issue 2 | Copyright
Ocean Sci., 12, 481-493, 2016
https://doi.org/10.5194/os-12-481-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 01 Apr 2016

Research article | 01 Apr 2016

Compensation between meridional flow components of the Atlantic MOC at 26° N

E. Frajka-Williams1, C. S. Meinen2, W. E. Johns3, D. A. Smeed4, A. Duchez4, A. J. Lawrence1, D. A. Cuthbertson1, G. D. McCarthy4, H. L. Bryden1, M. O. Baringer2, B. I. Moat4, and D. Rayner4 E. Frajka-Williams et al.
  • 1Ocean and Earth Science, University of Southampton, National Oceanography Centre Southampton, SO14 3ZH, UK
  • 2Atlantic Oceanographic and Meteorological Laboratory, Physical Oceanography Division, 4301 Rickenbacker Causeway, Miami, FL 33149, USA
  • 3University of Miami, Rosentiel School of Marine and Atmospheric Science, 4600 Rickenbacker Causeway, Miami, FL, USA
  • 4National Oceanography Centre, University of Southampton Waterfront Campus, European Way, Southampton, SO14 3ZH, UK

Abstract. From ten years of observations of the Atlantic meridional overturning circulation (MOC) at 26°N (2004–2014), we revisit the question of flow compensation between components of the circulation. Contrasting with early results from the observations, transport variations of the Florida Current (FC) and upper mid-ocean (UMO) transports (top 1000m east of the Bahamas) are now found to compensate on sub-annual timescales. The observed compensation between the FC and UMO transports is associated with horizontal circulation and means that this part of the correlated variability does not project onto the MOC. A deep baroclinic response to wind-forcing (Ekman transport) is also found in the lower North Atlantic Deep Water (LNADW; 3000–5000m) transport. In contrast, co-variability between Ekman and the LNADW transports does contribute to overturning. On longer timescales, the southward UMO transport has continued to strengthen, resulting in a continued decline of the MOC. Most of this interannual variability of the MOC can be traced to changes in isopycnal displacements on the western boundary, within the top 1000m and below 2000m. Substantial trends are observed in isopycnal displacements in the deep ocean, underscoring the importance of deep boundary measurements to capture the variability of the Atlantic MOC.

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The ocean meridional overturning circulation (MOC) is predicted by climate models to slow down in this century, resulting in reduced transport of heat northward to mid-latitudes. At 26° N, the Atlantic MOC has been measured continuously for the past decade (2004–2014). In this paper, we discuss the 10-year record of variability, identify the origins of the continued weakening of the circulation, and discuss high-frequency (subannual) compensation between transport components.
The ocean meridional overturning circulation (MOC) is predicted by climate models to slow down...
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