scholarly journals Control of oceanic circulation on sediment distribution in the southwestern Atlantic margin (23 to 55° S)

Ocean Science ◽  
2021 ◽  
Vol 17 (5) ◽  
pp. 1213-1229
Author(s):  
Michel Michaelovitch de Mahiques ◽  
Roberto Violante ◽  
Paula Franco-Fraguas ◽  
Leticia Burone ◽  
Cesar Barbedo Rocha ◽  
...  
Keyword(s):  
Ocean Circulation ◽  
Intermediate Water ◽  
Oceanic Circulation ◽  
Southwestern Atlantic ◽  
Sediment Distribution ◽  
Isotopic Signatures ◽  
The North ◽  
Brazil Current ◽  
Lower Circumpolar Deep Water ◽  
Atlantic Margin

Abstract. In this study, we interpret the role played by ocean circulation in sediment distribution on the southwestern Atlantic margin using radiogenic Nd and Pb isotopes. The latitudinal trends for Pb and Nd isotopes reflect the different current systems acting on the margin. The utilization of the sediment fingerprinting method allowed us to associate the isotopic signatures with the main oceanographic features in the area. We recognized differences between Nd and Pb sources to the Argentinean shelf (carried by the flow of Subantarctic Shelf Water) and slopes (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 areas (the upper 1200 m), the transfer of sediments from the Argentinean margin to the north of 35∘ S is limited by the Subtropical Shelf Front and the basin-wide recirculated Antarctic Intermediate Water. On the southern Brazilian inner and middle shelf, it is possible to recognize the northward influence of the Río de la Plata sediments carried by the Plata Plume Water. Another flow responsible for sediment transport and deposition on the outer shelf and slope is the southward flow of the Brazil Current. Finally, we propose that the Brazil–Malvinas Confluence and the Santos Bifurcation act as boundaries of geochemical provinces in the area. A conceptual model of sediment sources and transport is provided for the southwestern Atlantic margin.

scholarly journals 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

2021 ◽  
Author(s):  
Michel Michaelovitch de Mahiques ◽  
Roberto Violante ◽  
Paula Franco-Fraguas ◽  
Leticia Burone ◽  
Cesar Barbedo Rocha ◽  
...  
Keyword(s):  
Ocean Circulation ◽  
Intermediate Water ◽  
Southwestern Atlantic ◽  
Sediment Distribution ◽  
Isotopic Signatures ◽  
The North ◽  
Brazil Current ◽  
Lower Circumpolar Deep Water ◽  
Atlantic Margin ◽  
Current Systems

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.

scholarly journals The influence of the Brazil and Malvinas Currents on the Southwestern Atlantic Shelf circulation

Ocean Science ◽  
2010 ◽  
Vol 6 (4) ◽  
pp. 983-995 ◽  
Author(s):  
R. P. Matano ◽  
E. D. Palma ◽  
A. R. Piola
Keyword(s):  
World Ocean ◽  
Deep Ocean ◽  
Western Boundary ◽  
Oceanic Circulation ◽  
Southwestern Atlantic ◽  
The South ◽  
Wind Speeds ◽  
The North ◽  
Brazil Current ◽  
South Brazil

Abstract. 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.

scholarly journals The influence of the Brazil and Malvinas Currents on the southwestern Atlantic shelf circulation

2010 ◽  
Vol 7 (2) ◽  
pp. 837-871 ◽  
Author(s):  
R. P. Matano ◽  
E. D. Palma ◽  
A. R. Piola
Keyword(s):  
World Ocean ◽  
Deep Ocean ◽  
Western Boundary ◽  
Oceanic Circulation ◽  
Southwestern Atlantic ◽  
The South ◽  
Wind Speeds ◽  
The North ◽  
Brazil Current ◽  
South Brazil

Abstract. 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 describe the dynamical processes controlling the interaction between the shelf 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 no less important. Models and observations indicate that the Malvinas Current not only controls the shelfbreak dynamics and cross-shelf exchanges but also the circulation in the shelf's interior.

Geochemical and Geophysical Evidence for Late Miocene Onset of Tasman Leakage

2020 ◽  
Author(s):  
Beth Christensen ◽  
David DeVleeschouwer ◽  
Jeroen Groeneveld ◽  
Jorijntje Henderiks ◽  
Gerald Auer ◽  
...  
Keyword(s):  
Indian Ocean ◽  
Southern Hemisphere ◽  
Ocean Circulation ◽  
Late Miocene ◽  
Return Flow ◽  
Intermediate Water ◽  
Isotope Data ◽  
The North ◽  
Tasman Sea ◽  
Intermediate Waters

<p>The recent documentation of the southern hemisphere “supergyre”, the coupled subtropical southern hemisphere gyres spanning the 3 ocean basins, leads to questions about its impact on Indian Ocean circulation. The Indonesian Throughflow (ITF) acts as a switchboard directing warm surface waters towards the Agulhas Current (AC) and return flow to the North Atlantic, but Tasman Leakage (TL) is another source of return flow, however, at intermediate water depths. Fed by a complex mixture of South Pacific (SP) western boundary current surface and intermediate waters, and Antarctic Intermediate Water (AAIW), today the topography forces it to flow in a westerly direction. The TL flows over the Broken Ridge towards Madagascar, joining the AC and ultimately Atlantic Meridional Circulation (AMOC).</p><p>Stable isotope data from 4 DSPD/ ODP Indian Ocean sites define the history of TL and constrain the timing of its onset to ~7 Ma.  A simple nannofossil- biostratigraphy age model applied to previously published benthic foraminiferal carbon isotope data ensures the 4 time-series (~11 – 2 Ma) are consistent. All 4 records (Sites 752 Broken Ridge, 590 Tasman Sea, 757 90 East Ridge, 751 Kerguelen Plateau) are similar from ~11 Ma to ~7 Ma, indicating the Tasman Sea intermediate water was sourced from the Southern Ocean (SO). A coeval shift at ~7 Ma at Sites 590 and 752 signals a SP contribution and the onset of TL. We do not observe TL at Sites 757 and 751 and so interpret the post-7 Ma divergence between the TL pair and the KP / 90E Ridge sites as a reflection of different intermediate water masses. The KP / 90E Ridge sites record a more fully SO signal, and these waters are constrained to the region west of the 90 East ridge.</p><p>The isotopic record of TL onset suggests important tectonic changes ~ 7 Ma: 1) opening of the Tasman Sea to the north and 2) Australia’s northward motion allowing westward flow around Tasmania. The former is supported by a change in sedimentation style on the Marion Plateau (ODP Site 1197). The latter is supported by unconformities on the South Australian Bight margin (Leg 182 Sites 1126 (784 m), 1134 (701 m), 1130 (488m) and coeval decreases in mud- sized sediments at the Broken Ridge sites, indicating winnowing associated with the onset of the TL. A divergence is also apparent between Broken Ridge and Mascarene Plateau Site 707 records at this time. These events, coupled with the temporal relationship between the onset of the TL and a change in the character of deposition in the Maldives indicate enhanced Indian Ocean circulation at intermediate depths coincident with the late Miocene global cooling. Combined, these observations suggest the Indian Ocean in general plays a larger role in the global ocean system than previously recognized, and intermediate waters in particular are a critical yet poorly understood component of AMOC.</p>

scholarly journals Mid-depth South Atlantic ocean circulation and chemical stratification during MIS-10 to 12: implications for atmospheric CO<sub>2</sub>

2008 ◽  
Vol 4 (3) ◽  
pp. 667-695 ◽  
Author(s):  
A. J. Dickson ◽  
M. J. Leng ◽  
M. A. Maslin
Keyword(s):  
Southern Ocean ◽  
Ocean Circulation ◽  
North Atlantic ◽  
Sediment Cores ◽  
Convective Cell ◽  
Intermediate Water ◽  
Ocean Ventilation ◽  
Cape Basin ◽  
Glacial Periods ◽  
Atlantic Margin

Abstract. A detailed record of benthic foraminifera carbon isotopes from the South East Atlantic margin shows little glacial-interglacial variability between MIS-12 to MIS-10, suggesting that Glacial North Atlantic Intermediate Water (GNAIW) consistently penetrated to at least 30° S. Millennial-scale increases in either the mass or flux of GNAIW over the core site occur alongside reductions in Lower North Atlantic Deep Water recorded in North Atlantic sediment cores and show that the lower and intermediate limb of the Atlantic deepwater convective cell oscillated in anti-phase during previous glacial periods. In addition, a 500 yr resolution record of the Cape Basin intermediate-deep δ13C gradient shows that a reduction in deep Southern Ocean ventilation at the end of MIS-11 was consistent with a modelled CO2 drawdown of ~21–30 ppm. Further increases in the Southern Ocean chemical divide during the transition into MIS-10 were completed before minimum CO2 levels were reached, suggesting that other mechanisms such as alkalinity changes were responsible for the remaining ~45 ppm drawdown.

scholarly journals Multidecadal-Scale Freshening at the Salinity Minimum in the Western Part of North Pacific: Importance of Wind-Driven Cross-Gyre Transport of Subarctic Water to the Subtropical Gyre

2015 ◽  
Vol 45 (4) ◽  
pp. 988-1008 ◽  
Author(s):  
Takuya Nakanowatari ◽  
Humio Mitsudera ◽  
Tatsuo Motoi ◽  
Ichiro Ishikawa ◽  
Kay I. Ohshima ◽  
...  
Keyword(s):  
Ocean Circulation ◽  
North Pacific ◽  
Model Simulation ◽  
Kuroshio Extension ◽  
Marked Change ◽  
Coupled Model ◽  
Subtropical Gyre ◽  
Intermediate Water ◽  
North Pacific Intermediate Water ◽  
The North

AbstractUsing oceanographic observations and an eddy-resolving ice–ocean coupled model simulation from 1955 to 2004, the effects of the wind-driven ocean circulation change that occurred in the late 1970s during multidecadal-scale freshening of the North Pacific Intermediate Water (NPIW) at salinity minimum density (~26.8 σθ) were investigated. An analysis of the observations revealed that salinity decreased significantly at the density range of 26.6–26.8 σθ in the western subtropical gyre, including the mixed water region (MWR). The temporal variability of the salinity is dominated by the marked change in the late 1970s. With results similar to the observations, the model, selectively forced by the interannual variability of the wind-driven ocean circulation, simulated significant freshening of the intermediate layer over the subtropical gyre. The significant freshening is related to the increase in southward transport of the Oyashio associated with the intensification of the Aleutian low. Accompanying these changes, the intrusion of fresh and low potential vorticity water, originating in the Okhotsk Sea, to the MWR increased, and the freshening signal propagated farther southward in the western subtropical gyre during the subsequent 6 yr, crossing the Kuroshio Extension. These results indicate that the multidecadal-scale freshening of the NPIW is partly caused by intensification of the wind-driven cross-gyre transport of the subarctic water to the subtropical gyre.

scholarly journals Can the North Brazil Current Help Us Understand Atlantic Water Flow?

Eos ◽  
2015 ◽  
Vol 96 ◽  
Author(s):  
David Shultz
Keyword(s):  
Water Flow ◽  
Circulation Pattern ◽  
Atlantic Water ◽  
Oceanic Circulation ◽  
The North ◽  
Brazil Current ◽  
North Brazil ◽  
North Brazil Current ◽  
Northern Brazil

Currents off the coast of northern Brazil can be used to study changes in the larger oceanic circulation pattern in the Atlantic, when variable winds in the regions are properly accounted for.

scholarly journals Millennial changes in North Atlantic oxygen concentrations

2015 ◽  
Vol 12 (15) ◽  
pp. 12947-12973 ◽  
Author(s):  
B. A. A. Hoogakker ◽  
D. J. R. Thornalley ◽  
S. Barker
Keyword(s):  
Ocean Circulation ◽  
North Atlantic ◽  
Bottom Water ◽  
Water Mass ◽  
Intermediate Water ◽  
Northeast Atlantic ◽  
The North ◽  
Cold Events ◽  
The North Atlantic ◽  
Oxygen Concentrations

Abstract. Glacial–interglacial changes in bottom water oxygen concentrations [O2] in the deep Northeast Atlantic have been linked to decreased ventilation relating to changes in ocean circulation and the biological pump (Hoogakker et al., 2015). In this paper we discuss seawater [O2] changes in relation to millennial climate oscillations in the North Atlantic ocean over the last glacial cycle, using bottom water [O2] reconstructions from 2 cores: (1) MD95-2042 from the deep northeast Atlantic (Hoogakker et al., 2015), and (2) ODP 1055 from the intermediate northwest Atlantic. Deep northeast Atlantic core MD95-2042 shows decreased bottom water [O2] during millennial scale cool events, with lowest bottom water [O2] of 170, 144, and 166 ± 17 μmol kg−1 during Heinrich ice rafting events H6, H4 and H1. Importantly, at intermediate core ODP 1055 bottom water [O2] was lower during parts of Marine Isotope Stage 4 and millennial cool events, with lowest values of 179 and 194 μmol kg−1 recorded during millennial cool events C21 and a cool event following Dansgaard–Oeschger event 19. Our reconstructions agree with previous model simulations suggesting that glacial cold events may be associated with lower seawater [O2] across the North Atlantic below ~1 km (Schmittner et al., 2007), although in our reconstructions the changes are less dramatic. The decreases in bottom water [O2] during North Atlantic Heinrich events and earlier cold events at the deep site can be linked to water mass changes in relation to ocean circulation changes, and possibly productivity changes. At the intermediate depth site a strong North Atlantic Intermediate Water cell precludes water mass changes as a cause for decreased bottom water [O2]. Instead we propose that the lower bottom [O2] there can be linked to productivity changes through increased export of organic material from the surface ocean.

scholarly journals Campbell Plateau: A major control on the SW Pacific sector of the Southern Ocean circulation

2017 ◽  
Author(s):  
Aitana Forcén-Vázquez ◽  
Michael J. M. Williams ◽  
Melissa Bowen ◽  
Lionel Carter ◽  
Helen Bostock
Keyword(s):  
Southern Ocean ◽  
Ocean Circulation ◽  
Intermediate Water ◽  
The South ◽  
Mode Water ◽  
The North ◽  
Sw Pacific ◽  
Consistent Picture ◽  
Southward Extension ◽  
Subantarctic Region

Abstract. New Zealand’s subantarctic region is a dynamic oceanographic zone with the Subtropical Front (STF) to the north and the Subantarctic Front (SAF) to the south. Both the fronts and their associated currents are strongly influenced by topography: the South Island of New Zealand and the Chatham Rise for the STF, and Macquarie Ridge and Campbell Plateau for the SAF. Here for the first time we present a consistent picture across the subantarctic region of the relationships between front positions, bathymetry and water mass structure using eight high resolution oceanographic sections that span the region. Our results show that the northwest side of Campbell Plateau is comparatively warm due to a southward extension of the STF over the plateau. The SAF is steered south and east by Macquarie Ridge and Campbell Plateau, with waters originating in the SAF also found north of the plateau in the Bounty Trough. Subantarctic Mode Water (SAMW) formation is confirmed to exist south of the plateau on the northern side of the SAF in winter, while on Campbell Plateau a deep reservoir persists into the following autumn. Antarctic Intermediate Water (AAIW) is observed in the deeper regions around the edges of the plateau, but not on the plateau, confirming that the waters on the plateau are effectively isolated from AAIW and deeper water masses that typify the open Southern Ocean waters.

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