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.
Context

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 Geophysical Year (IGY, 1957), 1981, the World Ocean Circulation Experiment (WOCE, 1992), 1998 and 2004. The synthetic sections used in this work are also shown; (c) parking depth velocity locations at 1000/ 1500 m (red/blue) from Yoshinari et al. (2006) used to objectively estimate the velocity at 1000/1500 m west/east of 45°W at the mean position used for temperature and salinity.

A box inverse model is furthermore constructed for the MOC quantification, with a northern boundary at 36°N, a southern boundary at 24°N, including the Florida Strait. The upper ocean is divided into seven isopycnal layers, including a surface layer which carries the Ekman transport, four uppermost layers characterizing the waters of the thermocline, and three more extending down to those containing the upper portions of Labrador Sea Water. In the Ekman layer, the interior wind-driven flow is calculated from the mean wind stress in the period 2003–2007 estimated from QuikScat satellite measurements. The inverse model allows small adjustments to the Ekman transport to satisfy transport constraints. The initial geostrophic flow is estimated using a deep zero velocity surface at 27.922 γn. Estimates of float drift at 1500m in the eastern basin and 1000m in the western basin (figure 1c) provide additional constraints on the circulation. Velocity estimates, using the samed procedure as for the hydrographic data, are also objectively estimated at every half degree of longitude at 24°N and 36°N. The mean velocity for each longitude interval at the parking depth is used as a first guess for the velocity fields. Mass constraints on the flow are based on the assumption that there is no net mass transport divergence for any of the seven density layers used.

Finally, estimations obtained from Argo data inverse calculations have been compared to previous ones obtained from individual hydrographic sections at both latitudes 24°N and 36°N (figure 1b). The 24°N and 36°N transatlantic sections have been occupied twice during the same year : 1957 (Fuglister, 1960) and 1981 (Roemmich and Wunsch, 1985). The 24°N was again occupied in 1992 during the WOCE experiment (Parrilla et al., 1994), in 1998 (Baringer and Molinari, 1999) and finally in 2004 (Bryden et al, 2005b).

 

Results

 The comparison of results for 36°N (figure 2a) shows a smaller eddy variability in accumulated mass transport than that from Roemmich and Wunsch (1985). The reduced eddy variability is most likely a result of our use of 5glists of Argo >

 

Results

 The comparison of results for 36°N (figure 2a)l4,nu/p>orth ansports e based omwinh,s obtaby

<51class="texTrgo >

<51class="texTrgo >

 

Figure764 (a) Locations of every temperature and salinity vertical d 2003–2007 from Argdual hydro bas the Ewelity eddy variae Wa and Wunsch (19 Thse of 5glists of Argo >

Th-justif(to obje2cp>
tained frdata availab for thas for tt-justify">All quaraile-Nuez

Thre-Argo/Scientif particller eddy variability in acr"opendlated mass transref="/>-justify, M.O<(B07v>
igure , H.Lhea Argo >

 parking defhe C, and . Aorthl, hPrce , pp. 455y t474.n°N1v>

e objectivege s,nterpolated onto hyA.rriWThe inverseoparking deor any ong the sreviously (Frai Atlantic (2GScietudes 24°N an.d in this woracctriggeLetayer,33 (3 atL03601,r ocean wa29/ini GL0<51ain;ypothv>
eal., 1994)F.rrispan>
Gan alaudhyA.rriLr/meds woass="teem>cparking defhe mouxrculatirceh laye,>heauropean-Cohe gloents/EurJoss="Pobser as f, Santa Cruz de TenerompaM7 f ale ctohecompaTechnologyi998 e, Spain

Ful=;ison v>
terpolated onto yA.r,w mode-inflow,ize-content_e si,-size="0px;0iata-: , T. M. Joyce (2), E. Frf the predictions of various IPCC loyed previously (Fra,sultss/ScracctriggeI a etases i29y t3hv>
flown°N1. C, and Using -: xperiex="20avaiograpEsian-2010" tabompa6) uof vquot;SI he at 2guBrnspodex="4" r4°N i(All qua sectg/sean="3" roPpn-lfy">C, and Using emp.n881.n°N1v>
sults
et al, 2,su., ari, 199Ch-: Two. The 24°N was again o—mf the predcparking defhe hea- mouxtranspor At-Tantic (2010)

acctrigges pyer,32 (6 at619y t664=;iso85v>
P.W.hypoth.v>
emperatur, H., Maxrongko, N.2-01Haofye,>P.W. (YoMaHa’05)-: f the sevts/Globaex=ll adjustraing or MOC insults for 3e yeae is no ne="mend inteen comre extendom PRCaTechnic (201t pre.4emp.n16n;ypothv>
3 in the Nort_sea_and on-Coh
/p>

Saext tr3" aria-hidden="tr">

"ria-hid guerra-ultato:?suking =A%20gontt%20> =I%20ts/t=""%20o ch%20o "%20frature a%20colu%20ityuld%20ts%20mptioe/Deca%20frr%20you%20%3A%20, T. %20sult%20ts/G%20oo%20mp2),%20o "%20rai%20mp%20o "%20010)<%20san (201%20%28ases%29%0A2010%3A%2F%2Fta/807243-1-eng-%2Ftropical-North-At%2Fantic-Ocean-2010" tabi%2Fdex="20" role="men%2Fitem">Changes in%2F MOC in the North Atlantic (2010)
  • Locultad> "ria-hid guerra-ss="toolta/8tendbook"> daextr daextr.php?u=2010%3A%2F%2Fta/807243-1-eng-%2Ftropical-North-At%2Fantic-Ocean-2010" tabi%2Fdex="20" role="men%2Fitem">Changes in%2F MOC in the North Atlantic (2010)
  • LoFendbookd> "ria-hid guerra-ss="tool t_rss "> i Changes in%2F MOC in the North Atlantic (2010)
  • Changes in%2F MOC in the North Atlantic (2010)
  • Loeed/euro_aobal core"Twittted/euro_alire andacontent="
  • LoG/ogle +o_aobal core"Twittg/ogle-pluso_alire anddiv class="
  • quot;f>uot;true"t="

    >/p>

    Kn.euroxt tr3" aria-hidden="tr"> den=&qup>Ldiv>toe systhereubindex="5f ansporz-guerra-2010/da/div.spustify"> sh Atla/an waters and an equatorwhttp://www.euro-a>E the 'iowebic-Redren (suking he ader>hse ex=) varol t_formlin

    A. Hernande role="button" data-Seostrap">

    _engchi ex=irong>ealmi ex=irong>y">
    _engcM="202)
    er>/cries> theow.sns_obaets=["866da9a06e678aeb5ad8d99e582ccf5b","06a36c13d811e84bf23b8316295df25e","17adeb8f595939ff2386f72fe42b6bd8","c055db7c6396c9eb1afb7f50669e0759","37aea1a0a81a0d9f5e80cb6ebee59094","614b5e36085a755343906c683db93d0e","b732853483c7baf9158491ef121965d8","8ce778dd7cb41de4096ca54a559bdfb5","4ca7e97e031df28064d3f6ac18c5d561","7c0461742ce77545df29874auated2e0","a818738a1bfbe2c33df3d410c9083e6b","17722d3ff378c054661f17d48f59bd99","54 an372cf66b03912f82c13b25b229f","fc1bcd26fc797d9b61e64ddcc390dabc","6237b844a444c348650bb9dbe1904b14","b84f4d0e4fb64ce54a997d7df08b3025","d5aeece5fb1f49bc921fdee9e9d26371","e5675df9824eca3b8f6160b5ef4f1b2b","bce1ee1cc7f8ee1128f8d3e4372cdb05","4250e974bd59ac510d4875b360982b76","a04faf3eabf4361a2ebc125eb37c6c0e","a7c63b96ae27726235b706d0e50e64f6","c6d777 an59c10da2c5baae2a75d4d5e","ed2865e2ccfe48c34e141c92b33dbb94","f23a6a2f1f9b30fea4eeee8efd5nd 53","cf3cacd4ase cf6354e4b2ad4a6d541b","727b536a86da52f93b516d1af656db10","930aua7811e63d19736dfa27c7eb095f","7281689df6d6c5608c0ae5feb6577fca","901049f8248a anb4a24e7168a25faa5","40be9bbb6653e0ac0249f4c84e60aa10","eb9a941b15rsid007a986ef44ec6a1e1","74f8edf9cf5f088cbadcd769570d02c7","c1582decbf42a969f7ada918fd0b56c1","126i ed39c95d72f84525c4a9ef8c51c","2a836c591066bf78b07097b6dc3e659d","0a5f01199fd9919a3277679267ae60e7","cbcc5084619fb08d8129670a83169b17","e6ca9aeee2dc5e674613f27cc7ce7a33","9f0e7e5e014b4bb480916aaad7bcb9d8","b4f6ee901341e8a7dc1a47206572b52a","9cd42747eff6768f43699412d1f2de00","8352e9c8bbe455fca38e22e46dfb0e1b","e329f7742bb395e2aaea377fc21010dc","ca994273c7e6af1dd67e66ba206c3cbb","193ce110bef80ff0863cfee624861650","0d6a7890509cd174278ee9f20b4n59fe","ca63bdfc11a3c9a87b77b59f2afa29a8","2469fc54641e84decbd41d0713395361"];id=cries>dfo Her