Description: Interocean exchange of heat and salt around South Africa is thought to be a key link in the maintenance of the global overturning circulation of the ocean. It takes place at the Agulhas Retroflection, largely by the intermittent shedding of enormous rings that penetrate into the South Atlantic Ocean. This makes it extremely hard to estimate the inter ocean fluxes. Estimates of direct Agulhas leakage from hydrographic and tracer data range between 2 and 10 Sv (1 Sv = 106 m3 s−1). The average ring shedding frequency, determined from satellite information, is approximately six rings per year. Their associated interocean volume transport is between 0.5 and 1.5 Sv per ring. A number of Agulhas rings have been observed to cross the South Atlantic. They decay exponentially to less than half their initial size (measured by their available potential energy) within 1000 km from the shedding region. Consequently, most of their properties mix into the surroundings of the Benguela region, probably feeding directly into the upper (warm) limb of the global thermohaline circulation. The most recent observations suggest that in the present situation Agulhas water and Antarctic Intermediate Water are about equally important sources for the Benguela Current. Variations in the strength of these may lead to anomalous stratification and stability of the Atlantic at decadal and longer timescales. Modeling studies suggest that the Indian-Atlantic interocean exchange is strongly related to the structure of the wind field over the South Indian Ocean. This leads in the mean to a subtropical supergyre wrapping around the subtropical gyres of the South Indian and Atlantic Oceans. However, local dynamical processes in the highly nonlinear regime around South Africa play a crucial role in inhibiting the connection between the two oceans. The regional bottom topography also seems to play an important role in locking the Agulhas Currents' retroflection. State-of-the-art global and regional “eddy-permitting” models show a reasonably realistic representation of the mean Agulhas system; but the mesoscale variability and the local geometrical and topographic features that determine largely the interocean fluxes still need considerable improvement. In this article we present a review of the above mentioned aspects of the interocean exchange around South Africa: the estimation of the fluxes into the South Atlantic from different types of observations, our present level of understanding of the exchanges dynamics and forcing, its representation in state-of-the-art models, and, finally, the impact of the Indian-Atlantic fluxes on regional and global scale both within the Atlantic Ocean and in interaction with the overlying atmosphere.

Description: Author(s): K. Matano, R. Yatagai, S. Maeda, and Guo-qing Zheng The noncentrosymmetric superconductor Re 6 Zr has attracted much interest for its possible unconventional superconducting state with broken time-reversal symmetry. Here we report Re 185 / 187 nuclear quadrupole resonance measurements on Re 6 Zr ( T c = 6.72 K) and the isostructural compounds Re 27 Zr 5 ( T c = 6.53 K… [Phys. Rev. B 94, 214513] Published Wed Dec 21, 2016

Description: Author(s): S. Maeda, K. Matano, R. Yatagai, T. Oguchi, and Guo-qing Zheng In many cases, unconventional superconductivity are realized by suppressing another order parameter, such as charge density wave (CDW) or spin density wave (SDW). This suggests that the fluctuations of these order parameters play an important role in producing superconductivity. LaPt 2 Ge 2 undergoes a... [Phys. Rev. B 91, 174516] Published Fri May 22, 2015

Description: The oceanic circulation over the southwestern Atlantic shelf is influenced by large tidal amplitudes, substantial freshwater discharges, high wind speeds and – most importantly – by its proximity to two of the largest western boundary currents of the world ocean: the Brazil and Malvinas currents. This review article aims to discriminate the dynamical processes controlling the interaction between this extensive shelf region and the deep-ocean. The discussion is focused on two broad regions: the South Brazil Bight to the north, and Patagonia to the south. The exchanges between the Brazil Current and the South Brazil Bight are characterized by the intermittent development of eddies and meanders of the Brazil Current at the shelfbreak. However, it is argued that this is not the only – nor the most important – influence of the Brazil Current on the shelf. Numerical simulations show that the thermohaline structure of the South Brazil Bight can be entirely ascribed to steady state, bottom boundary layer interactions between the shelf and the Brazil Current. The Malvinas Current does not show the development of eddies and meanders, but its influence on the Patagonian shelf is not less important. Models and observations indicate that the Malvinas Current not only controls the shelfbreak dynamics and cross-shelf exchanges but also influences the circulation in the shelf's interior.

Description: Published

Description: This article presents the results of a high-resolution (1/12°), two-way nested simulation of the oceanic circulation in the southwestern Atlantic region. A comparison between the model results and extant observations indicates that the nested model has skill in reproducing the best-known aspects of the regional circulation, e.g., the volume transport of the ACC, the latitudinal position of the BMC, the shelf break upwelling of Patagonia, and the Zapiola Anticyclone. Sensitivity experiments indicate that the bottom stress parameterization significantly impacts the mean location of the Brazil/Malvinas Confluence and the transport of the Zapiola Anticyclone. The transport of the Brazil Current strengthens during the austral summer and weakens during the austral winter. These variations are driven by the wind stress curl over the southwestern Atlantic. The variations of the transport of the Malvinas Current are out of phase with those of the Brazil Current. Most of the seasonal variability of this current is concentrated in the offshore portion of the jet, the inshore portion has a weak seasonality that modulates the magnitude of the Patagonian shelf break upwelling. Using passive tracers we show that most of the entrainment of deep waters into the shelf occurs in the southernmost portion of the Patagonian shelf and along the inshore boundary of the Brazil Current. Shelf waters are preferentially detrained near the Brazil/Malvinas Confluence. Consistent with previous studies, our simulation also shows that south of ∼42°S the Malvinas Current is composed of two jets, which merge near 42°S to form a single jet farther north.

Description: Published

Description: We compare the oceanic circulation patterns over the Southwestern Atlantic Shelf (SWAS) forced by nine different wind stress climatologies. The largest differences are observed in experiments forced with the Hellerman and Rosenstein [1983, hereafter HR83] and Trenberth et al. [1990, hereafter TR90] winds. HR83 shows a general northeastward flow near the shelf break. The TR90 results shows a bifurcating path south of ~40°S and a poleward flow north of 35°S. The most robust circulation patterns are a broad northward flow and the generation of coastal re-circulation cells in southern Patagonia and the development of a southward jet in the inner portion of the South Brazil Bight.

Description: Published

Description: In this article we use hydrographic data collected in the period 1994-2000 to analyze the summer distributions of temperature and salinity in the southern Patagonian shelf (Argentina). The objective is to infer the circulation patterns of the Patagonian shelf and to relate them to the zooplankton biomass distribution. The vertical structure of the hydrographic variables indicates the existence of two distinct regions. North of 51°S, the water column can be characterized as a two-layer system separated by a thermocline at approximately 50m depth. South of 51°S, the density structure of the water column is nearly homogeneous. The two regions are separated by a front that extends in a northeast direction from the coastal region of the Grande Bay towards the continental slope. The circulation patterns inferred from the observed fields indicates that although the circulation in the southernmost portion of the Patagonian shelf, i.e., from Tierra del Fuego to the Grande Bay front, is towards the north, as predicted by previous studies, this northward flow turns offshore at the location of the Grande Bay front. This frontal region and the associated circulation pattern have not been previously described. The inferred circulation may enhance zooplankton production and accumulation over the coastal area of the Grande Bay - via increased primary production, by favoring both the enrichment and trapping of nutrients, and the retention of organisms

Description: Published