Temporal variability of the South Atlantic Meridional Overturning Circulation between 20°S and 35°S

Dong, Shenfu; Goñi, Gustavo; Bringas, Francis

doi:10.1002/2015gl065603

Cited by 58 publications

(136 citation statements)

References 39 publications

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“…The Liu et al (2015) surface-flux-based product suggests higher heat transports in good agreement with UR025.4 and GLORYS2V4 across the South Atlantic basin, although the surface integration method accumulates errors from all higher latitudes. The Liu et al (2015) estimates also reasonably agree with the XBT-AX18 and other South Atlantic observational studies at 35 and 30 • S. However, the observational estimates diverge north of 30 • S, with the transports from Dong et al (2015) and Majumder et al (2016) differing by ∼ 0.7 PW at 20 • S. These discrepancies underscore the uncertainties in observed transports through the South Atlantic. Figure 4a-f show maps of the east-west accumulated volume transports from the surface down to the depth of ψ max (typically ∼ 1000 m) for each latitude, defined hereafter as z max .…”

Section: Time Mean Transportssupporting

confidence: 68%

“…3a-b) suggests that both the SAMOC strength and MHT of the ORAs are more realistic than those of the FRMs. However, even the highest MHTs of UR025.4 and GLORYS2V4 are almost 0.1 PW lower than the lowest observational estimate from Dong et al (2015). The MHT underestimation of the FRMs and ORAs relative to the observations at 35 • S has already been reported by several authors (e.g.…”

Section: Time Mean Transportsmentioning

confidence: 56%

“…For this reason, a SAMOC observing system was already initiated in 2002 with quarterly highdensity expendable bathythermograph (XBT) lines at 35 • S (Garzoli and Baringer, 2007) and more recently with the development of the South Atlantic MOC Basin-wide Array (SAMBA; Ansorge et al, 2014), analogous to the RAPID array in the North Atlantic (Cunningham et al, 2007). However, the lack of long-term measurements in the area still limits our understanding of the South Atlantic state and its variability, reflecting the large disagreement between observational and model studies Dong et al, 2014Dong et al, , 2015Majumder et al, 2016;Stepanov et al, 2016).…”

Section: Introductionmentioning

confidence: 99%

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South Atlantic meridional transports from NEMO-based simulations and reanalyses

2018

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Abstract. The meridional heat transport (MHT) of the South Atlantic plays a key role in the global heat budget: it is the only equatorward basin-scale ocean heat transport and it sets the northward direction of the global cross-equatorial transport. Its strength and variability, however, are not well known. The South Atlantic transports are evaluated for four state-of-the-art global ocean reanalyses (ORAs) and two free-running models (FRMs) in the period 1997-2010. All products employ the Nucleus for European Modelling of the Oceans (NEMO) model, and the ORAs share very similar configurations. Very few previous works have looked at ocean circulation patterns in reanalysis products, but here we show that the ORA basin interior transports are consistently improved by the assimilated in situ and satellite observations relative to the FRMs, especially in the Argo period. The ORAs also exhibit systematically higher meridional transports than the FRMs, which is in closer agreement with observational estimates at 35 and 11 • S. However, the data assimilation impact on the meridional transports still greatly varies among the ORAs, leading to differences up to ∼ 8 Sv and 0.4 PW in the South Atlantic Meridional Overturning Circulation and the MHTs, respectively. We narrow this down to large inter-product discrepancies in the western boundary currents (WBCs) at both upper and deep levels explaining up to ∼ 85 % of the inter-product differences in MHT. We show that meridional velocity differences, rather than temperature differences, in the WBCs drive ∼ 83 % of this MHT spread. These findings show that the present ocean observation network and data assimilation schemes can be used to consistently constrain the South Atlantic interior circulation but not the overturning component, which is dominated by the narrow western boundary currents. This will likely limit the effectiveness of ORA products for climate or decadal prediction studies.

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Section: Time Mean Transportssupporting

confidence: 68%

Section: Time Mean Transportsmentioning

confidence: 56%

Section: Introductionmentioning

confidence: 99%

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South Atlantic meridional transports from NEMO-based simulations and reanalyses

2018

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“…Only in the past few years have observations been collected to study the MOC and/or the DWBC in the South Atlantic region, beginning with repeated upper ocean expendable bathythermograph (XBT) transects (e.g., Garzoli and Baringer, 2007;Dong et al, 2009Dong et al, , 2014 and full-depth hydrographic sections (e.g., Speer 2003, 2007;, and later adding continuous moored observations at a few locations including 11 • S (Hummels et al, 2015) and 34.5 • S (Meinen et al, 2012(Meinen et al, , 2013b. Gridded data sets from Argo float profiles in the upper 2000 m of the water column and satellite altimetry measurements have also been brought to bear on the meridional flows in the South Atlantic (e.g., Schmid, 2014;Dong et al, 2015;Majumder et al, 2016), providing important information about latitudinal variations of the MOC. Note that most of these systems focus only on the volume transport in the upper water column, and do not directly observe the DWBC (e.g.…”

Section: Introductionmentioning

confidence: 99%

Characteristics and causes of Deep Western Boundary Current transport variability at 34.5° S during 2009–2014

et al. 2017

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Abstract. The Deep Western Boundary Current (DWBC) at 34.5 • S in the South Atlantic carries a significant fraction of the cold deep limb of the Meridional Overturning Circulation (MOC), and therefore its variability affects the meridional heat transport and consequently the regional and global climate. Nearly 6 years of observations from a line of pressure-equipped inverted echo sounders (PIESs) have yielded an unprecedented data set for studying the characteristics of the time-varying DWBC volume transport at 34.5 • S. Furthermore, the horizontal resolution of the observing array was greatly improved in December 2012 with the addition of two current-and-pressure-equipped inverted echo sounders (CPIESs) at the midpoints of the two westernmost pairs of PIES moorings. Regular hydrographic sections along the PIES/CPIES line confirm the presence of recently ventilated North Atlantic Deep Water carried by the DWBC. The time-mean absolute geostrophic transport integrated within the DWBC layer, defined between 800-4800 dbar and within longitude bounds of 51.5 to 44.5 • W, is −15 Sv (1 Sv = 10 6 m 3 s −1 ; negative indicates southward flow). The observed peak-to-peak range in volume transport using these integration limits is from −89 to +50 Sv, and the temporal standard deviation is 23 Sv. Testing different vertical integration limits based on time-mean water-mass property levels yields small changes to these values, but no significant alteration to the character of the transport time series. The time-mean southward DWBC flow at this latitude is confined west of 49.5 • W, with recirculations dominating the flow further offshore. As with other latitudes where the DWBC has been observed for multiple years, the time variability greatly exceeds the time mean, suggesting the presence of strong coherent vortices and/or Rossby Wave-like signals propagating to the boundary from the interior.

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“…This extension of the time series is based on the assumption that the relationship between SSH and dynamic height do not change much over time (Dong et al, 2015;Lopez et al, 2017).…”

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confidence: 99%

A Study of the Variability of the Benguela Current

Majumder

Schmid

2017

Preprint

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Abstract. The Benguela Current forms the eastern limb of the subtropical gyre in the South Atlantic and transports a blend of relatively fresh and cool Atlantic water as well as relatively warm and salty Indian Ocean water northward. Therefore, it plays an important role not only for the local freshwater and heat budgets but for the overall meridional heat and freshwater transports in the South Atlantic. Historically, the Benguela Current region is relatively data sparse, especially with respect to long-term observations. A new three dimensional data set of the horizontal velocity in the upper 2000 m that covers the years 2Ocean Sci. Discuss., https://doi

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Temporal variability of the South Atlantic Meridional Overturning Circulation between 20°S and 35°S

Cited by 58 publications

References 39 publications

South Atlantic meridional transports from NEMO-based simulations and reanalyses

South Atlantic meridional transports from NEMO-based simulations and reanalyses

Characteristics and causes of Deep Western Boundary Current transport variability at 34.5° S during 2009–2014

A Study of the Variability of the Benguela Current

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Temporal variability of the South Atlantic Meridional Overturning Circulation between 20°S and 35°S

Cited by 58 publications

References 39 publications

South Atlantic meridional transports from NEMO-based simulations and reanalyses

South Atlantic meridional transports from NEMO-based simulations and reanalyses

Characteristics and causes of Deep Western Boundary Current transport variability at 34.5° S during 2009–2014

A Study of the Variability of the Benguela Current

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Characteristics and causes of Deep Western Boundary Current transport variability at 34.5° S during 2009–2014