Using Argo data to investigate the MOC in the North Atlantic (2010)

A. Hernandez-Guerra(1), T. M. Joyce (2), E. Fraile-Nuez(3), P. Velez-Belchı(3)


* Corresponding author : Alonso Hernandez-Guerra,

 (1) : Facultad de Ciencias del Mar, Universidad de Las Palmas de Gran Canaria, Spain

(2) : Department of Physical Oceanography, Woods Hole Oceanographic Institution, USA

(3) : Instituto Espanol de Oceanografıa, Santa Cruz de Tenerife, Spain

Full paper: Sterl, A., Bintanja, R., Brodeau, L. et al., 2012: A look at the ocean in the EC-Earth climate model, Clim Dyn 39: 2631. doi:10.1007/s00382-011-1239-2.

Through the poleward transport of upper ocean waters and an equatorward transport of deeper colder waters, the Meridional Overturning Circulation (MOC) is of critical importance to the global climate system. A decline of the MOC has been one of the predictions of various IPCC reports on greenhouse gas scenarios (IPCC,2001), and a particular aspect of recent findings from a single hydrographic section at 24°N in 2004 is that more equatorward flow is found in the interior of the upper 1000 meters than previously observed.

To check the robutness of this recent result, the North Atlantic MOC has been studied here (Hernandez-Guerra, 2010) through the analysis of hydrographic data along 24º and 36º N. Results confirm previous hypothesis stating no abrupt decreases in the MOC during the last decades, by comparing 1957, 1981,1992, 1998 and 2004 data. Argo float profiles and drift velocities for the period 2003-2007 in the North Atlantic are also used to estimate the total integrated mass transports in the thermocline waters at both mid-latitudes by inverse calculations. They confirm that the upper limb of the Atlantic MOC has not significantly changed since 1957.

Data and Method

All quality-controlled Argo data available for the 5-year period 2003-2007 in the North Atlantic (figure 1a) are used to quantify the MOC at mid-latitudes, representing 3349 profiles. Following a method employed previously (Fraile-Nuez and Hernandez-Guerra, 2006) based on an optimal statistical interpolation, temperature and salinity from Argo floats are objectively interpolated onto hypothetical zonal « sections » at 24°N and 36°N every degree in longitude. The WOA94 atlas (World Ocean Atlas, 1994) is used as a first guess for temperature and salinity objective interpolation.


Figure 1. (a) Locations of every temperature and salinity vertical profile in the period 2003–2007 from Argo data used to objectively interpolate the temperature and salinity every degree in longitude at 24°N and 36°N; (b) repeated hydrographic sections taken across 24°N and 36°N in the International Geopremer/meYear ( every degUheihb943-p Inted Ocean Atlaulation (MOCEiments (2rldOCE94) i2)98 and 2004 date WOA9synical ztions take to ohe Insedwork also usedlocan;>repe) c)>repe)ng ka meh dispcities y lions of e4° met/ 15eter (cti/blue)m ArgoYoshios (al., 2010) base to objectively intemate the totacities y 4° met/15eter wmat/ern ever45°Wthe oceamAtlaposn betw to otemperature and salinity obj.>

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