Fronts and thermohaline structure of the Brazil–Malvinas Confluence System

Severov, D.; Pshennikov, V.; Remeslo, A. V.

doi:10.1016/j.asr.2012.01.024

Cited by 6 publications

(5 citation statements)

References 33 publications

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“…These observations are consistent with sea surface temperatures, which demonstrate that the seismic survey straddles the warmer portion of the confluence during February and March 2013 (Figure 3). Over a 6 week period, the depth of the thermocline remains consistent and its continuity is only disrupted adjacent to the dipping front, most likely the Brazil Current Front whose appearance and disappearance is caused by the observed oscillation of the confluence at this time of year (Olson et al, 1988;Saraceno et al, 2004;Severov et al, 2012;Gunn et al, 2020). The patterns of reflectivity also reveal other transient oceanic processes, including deformation of filaments and lenses, which have previously been interpreted as manifestations of stirring and cross-frontal mixing (Jullion et al, 2010;Gunn et al, 2020).…”

Section: Water Mass Structurementioning

confidence: 67%

Vertical Mixing and Heat Fluxes Conditioned by a Seismically Imaged Oceanic Front

et al. 2021

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The southwest Atlantic gyre connects several distinct water masses, which means that this oceanic region is characterized by a complex frontal system and enhanced water mass modification. Despite its significance, the distribution and variability of vertical mixing rates have yet to be determined for this system. Specifically, potential conditioning of mixing rates by frontal structures, in this location and elsewhere, is poorly understood. Here, we analyze vertical seismic (i.e., acoustic) sections from a three-dimensional survey that straddles a major front along the northern portion of the Brazil-Falkland Confluence. Hydrographic analyses constrain the structure and properties of water masses. By spectrally analyzing seismic reflectivity, we calculate spatial and temporal distributions of the dissipation rate of turbulent kinetic energy, ε, of diapycnal mixing rate, K, and of vertical diffusive heat flux, FH. We show that estimates of ε, K, and FH are elevated compared to regional and global mean values. Notably, cross-sectional mean estimates vary little over a 6 week period whilst smaller scale thermohaline structures appear to have a spatially localized effect upon ε, K, and FH. In contrast, a mesoscale front modifies ε and K to a depth of 1 km, across a region of O(100) km. This front clearly enhances mixing rates, both adjacent to its surface outcrop and beneath the mixed layer, whilst also locally suppressing ε and K to a depth of 1 km. As a result, estimates of FH increase by a factor of two in the vicinity of the surface outcrop of the front. Our results yield estimates of ε, K and FH that can be attributed to identifiable thermohaline structures and they show that fronts can play a significant role in water mass modification to depths of 1 km.

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Section: Water Mass Structurementioning

confidence: 67%

Vertical Mixing and Heat Fluxes Conditioned by a Seismically Imaged Oceanic Front

et al. 2021

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“…Here, MAT and MART are within 1 °C of the proxy data, and onshore precipitation patterns, both in terms of MAP and seasonal phasing, are similar to those inferred from the combined proxy and model results (Figure ; Hirahara et al, ; Schneider et al, ), making this site a good analog for the climate of Seymour Island during the latest Lutetian. This region lies within the confluence system of the subtropical Brazil Current and the subpolar Malvinas (Falkland) Current (Severov et al, ). Interestingly, the position of this confluence oscillates seasonally such that warm equatorial water is delivered during the summer and cold polar water dominates during the winter (Wainer et al, ), increasing the seasonal range of temperatures well above the anticipated zonal MART (Hirahara et al, ).…”

Section: Discussionmentioning

confidence: 99%

Seasonally Resolved Proxy Data From the Antarctic Peninsula Support a Heterogeneous Middle Eocene Southern Ocean

Judd

Ivany

DeConto

et al. 2019

Paleoceanog and Paleoclimatol

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Understanding conditions at both global and local scales during the greenhouse climate of the Eocene Epoch is critical for making accurate predictions in our rapidly warming world. Despite the wealth of proxy data and modeling studies, fundamental aspects of the climate system still remain uncertain. For example, accurate austral high‐latitude temperatures are necessary to understand the evolution of temperatures during the lead‐up to Antarctic glaciation and determine the meridional temperature gradient during greenhouse warmth, yet records are few and disparate. Here we present seasonally resolved temperature and precipitation data from the latest Lutetian (~42 Ma) from the eastern Antarctic Peninsula. Oxygen isotopes from bivalves indicate a mean temperature of 13.1 °C and a seasonal range of 8.0 °C, slightly (<1 °C) more seasonal than modeled temperatures from high‐obliquity simulations. Carbon isotopes from driftwood suggest that summer accounts for just over half of annual precipitation. When compared with other austral high‐latitude records, the data are consistent with a zonally heterogeneous middle Eocene Southern Ocean. Similar longitudinal variability is observed in the modern boreal high latitudes, where landmasses subdivide the ocean, subjecting basins to their own distinct circulation patterns and coastal processes. With closed Drake and Tasman passages, the middle Eocene Southern Ocean would also have been noncontiguous, resulting in larger variability of sea surface temperatures along individual zonal bands than today. This interpretation resolves inconsistencies among existing high‐austral proxy records and suggests that the large seasonal range of temperatures may be indicative of regional‐scale circulation patterns along the peninsula not captured by low‐resolution climate simulations.

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“…The Southwestern Atlantic margin is characterized by complex hydrography (Matano et al, 2010). It presents two main oceanographic boundaries, the Subtropical Shelf Front (STSF), as the shelf extension of the Brazil -Malvinas Convergence (BMC) (Piola et al, 2000;Severov et al, 2012), and the less-studied Santos Bifurcation (SB) (Boebel et al, 1997;Boebel et al, 1999a). It is also influenced by the Rio de la Plata (RdlP), which discharges freshwater from the second-largest hydrographic basin in South America, with an average value of 22,000 m 3 s -1 (Framiñan and Brown, 1996).…”

Section: Ocean Circulationmentioning

confidence: 99%

New insights of the influence of ocean circulation on the sedimentary distribution in the Southwestern Atlantic margin (23° S to 55° S) based on Nd and Pb isotopic fingerprinting

Mahiques¹,

Violante²,

Franco-Fraguas³

et al. 2021

Preprint

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Abstract. In this work, we provide an extensive inventory of Pb and Nd radiogenic isotopes in surface sediments from the Southwestern Atlantic margin, aiming to interpret the role played by ocean circulation in sediment distribution. There are latitudinal trends for Pb and Nd isotopes, reflecting the different current systems acting on the margin. The utilization of sediment fingerprinting allowed us to associate the isotopic signatures to the main oceanographic forcings in the area. We recognized differences between the Nd and Pb sources for the sediments to the Argentinean shelf, carried by the Subantarctic Shelf Water, and slope, transported by deeper flows. Sediments from Antarctica extend up to the Uruguayan margin, carried by the Upper- and Lower Circumpolar Deep Water. Our data confirm that, for shelf and intermediate (up to 1,200 m water depth) areas, the transfer of sediments from the Argentinean margin to the North of 35° S is limited by the Subtropical Shelf Front and the recirculated Antarctic Intermediate Water. On the southern Brazilian margin, it is possible to recognize the northward influence of the Río de la Plata sediments carried by the Plata Plume Water. This influence is limited by the southward flow of waters transported by the Brazil Current. Finally, we propose that the Subtropical Shelf Front and the Santos Bifurcation act as boundaries of geochemical provinces in the area. Finally, a qualitative model of sediment sources and transport is provided for the Southwestern Atlantic margin.

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Fronts and thermohaline structure of the Brazil–Malvinas Confluence System

Cited by 6 publications

References 33 publications

Vertical Mixing and Heat Fluxes Conditioned by a Seismically Imaged Oceanic Front

Vertical Mixing and Heat Fluxes Conditioned by a Seismically Imaged Oceanic Front

Seasonally Resolved Proxy Data From the Antarctic Peninsula Support a Heterogeneous Middle Eocene Southern Ocean

New insights of the influence of ocean circulation on the sedimentary distribution in the Southwestern Atlantic margin (23° S to 55° S) based on Nd and Pb isotopic fingerprinting

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