Éditeur(s) : Yale University
Résumé : Data from a hydrographic section carried out in January-March 1994 offshore from the eastern coast of South America from 50S to 10N, are used to quantify the full-depth exchanges of water between the western boundary currents and the ocean interior. In the upper and intermediate layers, the westward transport associated with the southern branch of the South Equatorial Current was 49 Sv at the time of the cruise. The transports of the central and northern branches in the upper 200 m were 17 Sv and 12 Sv, respectively. After subtraction of the parts that recirculate in the subtropical, subequatorial, and equatorial domains, the fraction of the South Equatorial Current that effectively contributes to the warm water export to the North Atlantic is estimated at 18 Sv. The poleward boundary of the current southern branch is at 31S through the whole thickness of the subtropical gyre, but the latitude of the northern boundary varies from 7 degrees 30'S at the surface to 27S at 1400 m depth. The estimated latitude of its bifurcation into the Brazil Current and North Brazil Undercurrent also varies downward from about 14S at the surface to 28S at a depth of 600 m.In the North Atlantic Deep Water, eastward flows exceeding 10 Sv are observed at 3 degrees -4 degrees of latitude in both hemispheres, at 10S, and at 34S-30S. Between 4S and 17S, a net westward flow with an estimated transport of 19 Sv reinforces the southward deep western boundary current. Cyclonic circulations of Antarctic Bottom Water along the western boundaries of the Argentine and Brazil basins have amplitudes of 15 Sv and 13 Sv, respectively, exceeding those of the interbasin exchanges. The net alongshore transport of this water mass between the hydrographic section and the continental slope reverses to a southward direction from 13S to 27S, probably in relation with an eastward shift of the equatorward near-bottom boundary current at these latitudes.
Journal of Marine Research (0022-2402) (Yale University), 2000-11 , Vol. 58 , N. 6 , P. 1007-1039

Droits : 2000 Yale University
http://archimer.ifremer.fr/doc/2000/publication-803.pdf
DOI:10.1357/002224000763485782
http://archimer.ifremer.fr/doc/00000/803/

Éditeur(s) : American Geophysical Union
Résumé : The origins and fates of the Atlantic salinity maximum water (SMW), formed through excess evaporation in the tropics and subtropics of both hemispheres, are studied using monthly mean outputs of a numerical simulation of the world ocean climatological circulation. After defining formation domains from the surface salinity field and the vertical stratification, a Lagrangian technique is used to estimate the formation rates and main pathways in each hemisphere and the role of this water in the framework of the warm water return flow of the meridional overturning cell. Formation rates around 9 and 11 Sv are found in the Southern and Northern Hemispheres, respectively. While the export of the southern SMW from its formation area is realized by the western boundary currents, that of the northern SMW mainly results from interior subduction. Equatorward of the formation regions, a fraction of each SMW variety is entrained in the subtropical cells that connect the subtropics to the equatorial region. Poleward of them, both varieties are seen to feed the regions of subtropical mode water (STMW) formation around 35degrees of latitude in both hemispheres. The bulk of the transport associated with each variety eventually turns northward: This amounts to similar to6 Sv of southern SMW gathered in the North Brazil Undercurrent (NBUC), and similar to10 Sv of northern SMW found in the Gulf Stream at 35degreesN, of which 8 Sv have gone through the Caribbean Sea. Of the 13.4-Sv northward transport of the meridional overturning cell estimated by the model at 47degreesN, more than 50% (6.9 Sv) is found to have transited through at least one of the SMW regions. This gives an indication of the likely important role of SMW formation in the observed northward salinity increase of the upper Atlantic Ocean.
Journal of Geophysical Union - Research C - Oceans (0148-0227) (American Geophysical Union), 2002-09 , Vol. 107 , N. C10 , P. NIL_610-NIL_624

Droits : 2002 by the American Geophysical Union
http://archimer.ifremer.fr/doc/2002/publication-769.pdf
DOI:10.1029/2002JC001318
http://archimer.ifremer.fr/doc/00000/769/

Éditeur(s) : Springer
Résumé : Interannual variability of subtropical sea-surface-height (SSH) anomalies, estimated by satellite and tide-gauge data, is investigated in relation to wintertime daily North-Atlantic weather regimes. Sea-level anomalies can be viewed as proxies for the subtropical gyre intensity because of the intrinsic baroclinic structure of the circulation. Our results show that the strongest correlation between SSH and weather regimes is found with the so-called Atlantic-Ridge (AR) while no significant values are obtained for the other regimes, including those related to the North Atlantic Oscillation (NAO), known as the primary actor of the Atlantic dynamics. Wintertime AR events are characterized by anticyclonic wind anomalies off Europe leading to a northward shift of the climatological wind-stress curl. The latter affects subtropical SSH annual variability by altered Sverdrup balance and ocean Rossby wave dynamics propagating westward from the African coast towards the Caribbean. The use of a simple linear planetary geostrophic model allows to quantify those effects and confirms the primary importance of the winter season to explain the largest part of SSH interannual variability in the Atlantic subtropical gyre. Our results open new perspectives in the comprehension of North-Atlantic Ocean variability emphasizing the role of AR as a driver of interannual variability at least of comparable importance to NAO.
Climate Dynamics (0930-7575) (Springer), 2013-09 , Vol. 41 , N. 5-6 , P. 1159-1171

Droits : Springer-Verlag Berlin Heidelberg 2012
http://archimer.ifremer.fr/doc/00161/27248/25480.pdf
DOI:10.1007/s00382-012-1578-7
http://archimer.ifremer.fr/doc/00161/27248/

Éditeur(s) : Amer Geophysical Union
Résumé : Sea surface salinity (SSS) measured from space by the Soil Moisture and Ocean Salinity (SMOS) mission is validated in the subtropical North Atlantic Ocean. 39 transects of ships of opportunity equipped with thermosalinographs (TSG) crossed that region from 2010 to 2012, providing a large database of ground truth SSS. SMOS SSS is also compared to Aquarius SSS. Large seasonal biases remain in SMOS and Aquarius SSS. In order to look at the capability of satellite SSS to monitor spatial variability, especially at scales less than 300 km (not monitored with the Argo network), we first apply a monthly bias correction derived from satellite SSS and In Situ Analysis System (ISAS) SSS differences averaged over the studied region. Ship SSS averaged over 25 km is compared with satellite and ISAS SSS. Similar statistics are obtained for SMOS, Aquarius and ISAS products (root mean square error of about 0.15 and global correlation coefficient r of about 0.92). However, in the above statistics, SSS varies due to both large scale and mesoscale (here, for scales around 100 km) variability. In order to focus on mesoscale variability, we consider SSS anomalies with respect to a monthly climatology. SMOS SSS and Aquarius SSS anomalies are more significantly correlated (r > 0.5) to TSG SSS anomaly than ISAS. We show the effective gain of resolution and coverage provided by the satellite products over the interpolated in situ data. We also show the advantage of SMOS (r=0.57) over Aquarius (r=0.52) to reproduce SSS mesoscale features.
Journal Of Geophysical Research-oceans (0148-0027) (Amer Geophysical Union), 2014-12 , Vol. 119 , N. 12 , P. 8878-8896

Droits : 2014. American Geophysical Union. All Rights Reserved.
http://archimer.ifremer.fr/doc/00210/32150/34082.pdf
DOI:10.1002/2013JC009610
http://archimer.ifremer.fr/doc/00210/32150/

Éditeur(s) : Amer Geophysical Union
Résumé : The objective of the paper is to analyze the degree of realism of the Parallel Ocean Program ( POP) model of the Los Alamos Laboratory using the combined TOPEX/Poseidon and ERS-1/2 (TPERS) sea level anomaly (SLA) data sets and to present a detailed study of mesoscale characteristics in the North Atlantic. This description spans 8 years of data from 1993 to 2000. At first, we focus on the analysis of the mean eddy kinetic energy ( EKE) and show that the major characteristics of mesoscale variability are realistically simulated despite an overestimation of the EKE model in the Gulf Stream region. We then describe the SLA space and timescales and propagation velocities at a resolution never achieved before. There is a high level of agreement between the model and altimeter values regarding spatial scales and propagation velocities. POP timescales are, however, significantly longer in the subtropical regions. The westward zonal propagation velocity of both the model and the observations are higher than the speed computed from standard Rossby wave theory. The effect of mean current advection on POP and TPERS propagation velocities is also clearly seen in the Labrador Current and in the Gulf Stream and its recirculations. Finally, a study of the seasonal and interannual variability of the high-frequency (HF) EKE is carried out. The model reproduces accurately most of the HF-EKE seasonal variations in the Caribbean Sea and at high latitudes despite a phase advance. A clear HF-EKE interannual variability is then evidenced. Our hypothesis is that a contraction of the subpolar and subtropical gyres due to the North Atlantic Oscillation (NAO) could explain a reduction of the eddy activity in the North Atlantic Current, in the Newfoundland basin, and in the Azores Current. In the Caribbean Sea, the interannual variability of the EKE for both POP and TPERS seems to be caused by an interannual variability of the wind stress.
Journal Of Geophysical Research-oceans (0148-0227) (Amer Geophysical Union), 2004-12 , Vol. 109 , N. C1205 , P. 16 PP.

Droits : 2004 AGU
http://archimer.ifremer.fr/doc/00087/19841/17491.pdf
DOI:10.1029/2004JC002360
http://archimer.ifremer.fr/doc/00087/19841/

Éditeur(s) : Société Française d'Ichtyologie
Résumé : On the basis of geographical distribution and morphological analysis of the Atlantic Howella , two subspecies of H. brodiei have been established, H. brodiei brodiei for the IndoPacific and H. brodiei atlanlica for the tropical and boreal Atlantic. H. sherborni has been recognized as a separate species, probably distributed circumglobally in southern Ocean but presently recorded only from the South Atlantic, the central South Pacific and from off southern and south-eastern Australia respectively. H. b. atlanlica and H. b. brodiei are distinct by having 3 scale rows between the lateral line and the origin of the second dorsal fin, while H. sherborni has 4 scale rows there. H. sherborni is in geographical contact with the two subspecies while H. b. brodiei and H. b. atlantica are geographically isolated from each other. The new subspecies, H. b. atlantica occurs in the North Atlantic and the tropical South Atlantic. Specimens from 75 mm SL and longer, predominantly occur in the boreal areas, while specimens less than that length occur in the tropical areas respectively. A day and night bathymetric distribution and a size-depth stratification have been observed. NOT CONTROLLED OCR
L'étude de la distribution et l'analyse des caractères méristiques des Howella de l'Atlantique montre la présence dans les régions tempérées nord et tropicales d'une sous-espèce nouvelle, H. brodiei atlantica, et dans la zone tempérée sud de H. sherborni. H. sherborni, caractérisé par 4 rangées d'écailles entre la ligne latérale et l'origine de la seconde dorsale, est au contact, dans l'Atlantique, de H. b. atlantica et, dans les Océans Indien et Pacifique de H. b. brodiei; ces deux sous-espèces, isolées géographiquement, possèdent 3 rangées d'écailles entre la ligne latérale et l'origine de la seconde dorsale. Les exemplaires d'H. b. atlanlica mesurant 75 mm LS ou plus ont été capturés dans la zone tempérée de l'Atlantique nord et ceux de moins de 75 mm principalement dans l'Atlantique tropical et subtropical nord. Les différences de distribution bathymétrique, le jour et la nuit et selon les tailles, sont étudiées chez H. b. atlanlica et H. sherborni. OCR NON CONTRÔLE
Cybium (Société Française d'Ichtyologie), 1991-02 , Vol. 15 , N. 2 , P. 111-128

Droits : 1991 Société Française d'Ichtyologie
http://archimer.ifremer.fr/doc/1991/publication-3769.pdf
http://archimer.ifremer.fr/doc/00000/3769/

Éditeur(s) : Pergamon-elsevier Science Ltd
Résumé : Quantitative analyses on calcareous nannofossil assemblages on high temporal resolution (600-800 years) have been carried out from Core KC01B in the Ionian Sea (Eastern Mediterranean) throughout Marine Isotope Stage (MIS) 13-9, between 500 and 300 ka. This is an interval of considerable climate changes, known as the Mid-Brunhes event, which includes MIS 11, considered as a possible analogue for future interglacial conditions. In the Mediterranean core, the interval is characterized by the dominance of Gephyrocapsa spp., as also known from ocean records. Calcareous nannofossil abundance fluctuations have been interpreted in terms of modification of sea surface primary productivity/water stratification and temperature. Specifically, the increase in abundance of Gephyrocapsa caribbeanica and small Gephyrocapsa coupled with decreases of Florisphaera profunda, Syracosphaera spp. and Rhabdosphaera spp. suggests enhanced primary productivity/mixed surface waters during interglacial stages and at the Terminations, which can be interpreted in terms of interaction between climate changes and mesoscale oceanographic circulation. On the other hand, distributions of Calciosolenia spp., Oolithotus spp. and Umbilicosphaera sibogae, which are in phase with delta O-18 curve showing higher abundances at the lighter values of the marine isotope record, are considered as warm-water indicators. Biotic proxies point to peculiar climate dynamics through the MIS 12-11 transition (i.e. Termination V). High productive, cool, low salinity and turbid surface waters characterize the early MIS 11(421-408 ka) and likely reflect enhanced continental humidity/monsoon activity over North Africa and increased runoff into the basin. A late surface water warming with respect to Termination V is established at about 403 ka, during a period of low insolation forcing, almost coeval with the deposition of sapropel S11. A climate optimum, lasting about 15 ky (403-389 ka), is then recorded during a period of low insolation forcing centred at 398 ka. The later part of MIS 11 is characterized by climate deterioration at about 389 ka. Comparison with results from subtropical to polar Atlantic records suggests a remarkable relation between Mediterranean and Atlantic climate regimes.
Quaternary International (1040-6182) (Pergamon-elsevier Science Ltd), 2013-03 , Vol. 288 , P. 97-111

Droits : 2011 Elsevier Ltd and INQUA. All rights reserved.
http://archimer.ifremer.fr/doc/00181/29194/27593.pdf
DOI:10.1016/j.quaint.2011.12.007
http://archimer.ifremer.fr/doc/00181/29194/

Éditeur(s) : Amer Geophysical Union
Résumé : The meridional transport of salt in the Atlantic ocean is an important process for climate, controlling the stability of the meridional overturning circulation. The contribution of transient eddies to this transport is quantified in an eddy resolving North Atlantic model at 1/12 degrees resolution (NATL12), and compared with lower resolution North-Atlantic and global 1/4 degrees models. In NATL12 between 10 degrees N and 40 degrees N, there is a volume loss by evaporation of 0.6 Sverdrups (Sv). The divergence of the eddy flux of salt (normalized by a reference salinity of 34.8) is 0.2 Sv over the region, a significant fraction of the total air-seawater exchange, but it is compensated by an opposite convergent transport of salt by the mean flow, so that the total transport of salt is small. The compensation between eddy and mean salt transport is almost complete in a multicentury long global model experiment, but less effective in NATL12 because the short integration time does not allow the salt content to equilibrate and the model drift is large. Eddies arising from baroclinic instability contribute to the meridional salt transports at the northern and southern boundary of the subtropical gyre, where they appear consistent with a lateral diffusion acting on the mean salinity gradient. However, the eddy transport of salt is the sum of two terms: an advective contribution (arising from the correlations of velocity and isopycnal thicknesses) and a diffusion along isopycnals. Both components have the same amplitude at the southern boundary of the subtropical gyre, while diffusion is dominant at the northern boundary.
Journal Of Geophysical Research-oceans (0148-0227) (Amer Geophysical Union), 2012-05 , Vol. 117 , N. C05010 , P. 19 pp.

Droits : 2012 AGU
http://archimer.ifremer.fr/doc/00083/19441/17052.pdf
DOI:10.1029/2012JC007927
http://archimer.ifremer.fr/doc/00083/19441/