scholarly journals Radium-228-derived ocean mixing and trace element inputs in the South Atlantic

2021 ◽  
Vol 18 (5) ◽  
pp. 1645-1671
Author(s):  
Yu-Te Hsieh ◽  
Walter Geibert ◽  
E. Malcolm S. Woodward ◽  
Neil J. Wyatt ◽  
Maeve C. Lohan ◽  
...  
Keyword(s):  
Trace Elements ◽  
Trace Element ◽  
Vertical Mixing ◽  
South Atlantic ◽  
Open Ocean ◽  
The South ◽  
Horizontal Mixing ◽  
Cape Basin ◽  
Argentine Basin ◽  
Basin Margin

Abstract. Trace elements (TEs) play important roles as micronutrients in modulating marine productivity in the global ocean. The South Atlantic around 40∘ S is a prominent region of high productivity and a transition zone between the nitrate-depleted subtropical gyre and the iron-limited Southern Ocean. However, the sources and fluxes of trace elements to this region remain unclear. In this study, the distribution of the naturally occurring radioisotope 228Ra in the water column of the South Atlantic (Cape Basin and Argentine Basin) has been investigated along a 40∘ S zonal transect to estimate ocean mixing and trace element supply to the surface ocean. Ra-228 profiles have been used to determine the horizontal and vertical mixing rates in the near-surface open ocean. In the Argentine Basin, horizontal mixing from the continental shelf to the open ocean shows an eddy diffusion of Kx=1.8±1.4 (106 cm2 s−1) and an integrated advection velocity w=0.6±0.3 cm s−1. In the Cape Basin, horizontal mixing is Kx=2.7±0.8 (107 cm2 s−1) and vertical mixing Kz = 1.0–1.7 cm2 s−1 in the upper 600 m layer. Three different approaches (228Ra diffusion, 228Ra advection, and 228Ra/TE ratio) have been applied to estimate the dissolved trace element fluxes from the shelf to the open ocean. These approaches bracket the possible range of off-shelf fluxes from the Argentine Basin margin to be 4–21 (×103) nmol Co m−2 d−1, 8–19 (×104) nmol Fe m−2 d−1 and 2.7–6.3 (×104) nmol Zn m−2 d−1. Off-shelf fluxes from the Cape Basin margin are 4.3–6.2 (×103) nmol Co m−2 d−1, 1.2–3.1 (×104) nmol Fe m−2 d−1, and 0.9–1.2 (×104) nmol Zn m−2 d−1. On average, at 40∘ S in the Atlantic, vertical mixing supplies 0.1–1.2 nmol Co m−2 d−1, 6–9 nmol Fe m−2 d−1, and 5–7 nmol Zn m−2 d−1 to the euphotic zone. Compared with atmospheric dust and continental shelf inputs, vertical mixing is a more important source for supplying dissolved trace elements to the surface 40∘ S Atlantic transect. It is insufficient, however, to provide the trace elements removed by biological uptake, particularly for Fe. Other inputs (e.g. particulate or from winter deep mixing) are required to balance the trace element budgets in this region.

scholarly journals Radium-228-derived ocean mixing and trace element inputs in the South Atlantic

2020 ◽  
Author(s):  
Yu-Te Hsieh ◽  
Walter Geibert ◽  
E. Malcolm S. Woodward ◽  
Neil J. Wyatt ◽  
Maeve C. Lohan ◽  
...  
Keyword(s):  
Trace Elements ◽  
Continental Shelf ◽  
Trace Element ◽  
Vertical Mixing ◽  
South Atlantic ◽  
Open Ocean ◽  
The South ◽  
Horizontal Mixing ◽  
Cape Basin ◽  
Argentine Basin

Abstract. Trace elements play important roles as micronutrients in modulating marine productivity in the global ocean. The South Atlantic around 40° S is a prominent region of high productivity and a transition zone between the nitrate-depleted Subtropical Gyre and the iron-limited Southern Ocean. However, the sources and fluxes of trace elements to this region remain unclear. In this study, the distribution of the naturally occurring radioisotope 228Ra in the water column of the South Atlantic (Cape Basin and Argentine Basin) has been investigated along a 40° S zonal transect to estimate ocean mixing and trace element supply to the surface ocean. Ra-228 profiles have been used to determine the horizontal and vertical mixing rates in the near-surface open ocean. In the Argentine Basin, horizontal mixing from the continental shelf to the open ocean shows an eddy diffusion of Kx = 1.7 ± 1.4 (106 cm2 s−1) and an integrated advection velocity w = 0.6 ± 0.3 cm s−1. In the Cape Basin, horizontal mixing is Kx = 2.7 ± 0.8 (107 cm2 s−1) and vertical mixing Kz = 1.0–1.5 cm2 s−1 in the upper 600 m layer. Three different approaches (228Ra-diffusion, 228Ra-advection and 228Ra/TE-ratio) have been applied to estimate the dissolved trace-element fluxes from shelf to open ocean. These approaches bracket the possible range of off-shelf fluxes from the Argentine margin to be: 3.8–22 (× 103) nmol Co m−2 d−1, 7.9–20 (× 104) nmol Fe m−2 d−1 and 2.7–6.5 (× 104) nmol Zn m−2 d−1. Off-shelf fluxes from the Cape margin are: 4.3–6.2 (× 103) nmol Co m−2 d−1, 1.2–3.1 (× 104) nmol Fe m−2 d−1 and 0.9–1.2 (× 104) nmol Zn m−2 d−1. On average, at 40° S in the Atlantic, vertical mixing supplies 0.4–1.2 nmol Co m−2 d−1, 3.6–11 nmol Fe m−2 d−1, and 13–16 nmol Zn m−2 d−1 to the euphotic zone. Compared with atmospheric dust and continental shelf inputs, vertical mixing is a more important source for supplying dissolved trace elements to the surface 40° S Atlantic. It is insufficient, however, to provide the trace elements removed by biological uptake. Other inputs (e.g. particulate, or from winter deep-mixing) are required to balance the trace element budgets in this region.

scholarly journals First Insight of Meso- and Bentho-Pelagic Fish Dynamics Around Remote Seamounts in the South Atlantic Ocean

2021 ◽  
Vol 8 ◽  
Author(s):  
Fabio Campanella ◽  
Martin A. Collins ◽  
Emma F. Young ◽  
Vladimir Laptikhovsky ◽  
Paul Whomersley ◽  
...  
Keyword(s):  
Atlantic Ocean ◽  
Vertical Mixing ◽  
Pelagic Fish ◽  
South Atlantic ◽  
Open Ocean ◽  
Trophic Levels ◽  
South Atlantic Ocean ◽  
Predatory Fish ◽  
Fish Biomass ◽  
The South

Seamounts have long been recognised as hotspots for pelagic productivity and diversity in the world’s open ocean habitats. Recent studies have suggested that productivity may vary greatly between different seamounts, depending on complex interactions between the bathymetric features and local oceanography. These processes may enhance local primary production which support elevated biomass at higher trophic levels. In addition to enhancing local biomass, seamounts may also act as aggregative features, attracting pelagic species from the surrounding waters. Such characteristics make seamounts attractive targets for fisheries. However, as these unique habitats are localised and relatively small, they are vulnerable to overexploitation, which may have detrimental impact on the wider region. Mapping and quantitative assessments of the fish biomass at different seamounts are crucial prerequisites to identifying vulnerable seamounts and will aid toward understanding the dynamics of these important ecosystems and their vulnerability to fishing pressures. We used fisheries acoustics during two expeditions in 2018 and 2019, to investigate the distribution and abundance of fish and micronekton on and around five little studied seamounts of Tristan da Cunha, a remote archipelago in the South Atlantic Ocean. The results confirmed increased productivity at the seamounts, compared to the surrounding open ocean with higher acoustic backscatter values, a proxy for biomass, particularly at the shallower (~200 m depth) seamounts. Fish largely dominated the backscatter on most of the seamounts especially over the plateau areas where large densities of prey fish, primarily the mesopelagic Maurolicus inventionis, were detected. Very large aggregations, thought to consist of bentho-pelagic fish, were also observed over the slope of McNish Seamount that resulted in very high biomass estimates. Aggregations of this size and magnitude, have, to our knowledge, never been mapped or quantified on seamounts, using acoustic methods. Specific physical processes, such as enhanced retention and vertical mixing that were identified by an oceanographic model, may be some of the drivers of the enhanced fish biomass detected at McNish. The characteristics of the seamounts observed in this work suggest that these habitats are highly suitable for the presence of large predatory fish that can utilise these areas as their primary habitat or as important foraging grounds.

scholarly journals Characteristics and robustness of Agulhas leakage estimates: an inter-comparison study of Lagrangian methods

Ocean Science ◽  
2021 ◽  
Vol 17 (4) ◽  
pp. 1067-1080
Author(s):  
Christina Schmidt ◽  
Franziska U. Schwarzkopf ◽  
Siren Rühs ◽  
Arne Biastoch
Keyword(s):  
Global Climate ◽  
Horizontal Resolution ◽  
South Atlantic ◽  
Comparison Study ◽  
The South ◽  
Agulhas Current ◽  
Cape Basin ◽  
Total Transport ◽  
The Indian Ocean ◽  
Ice Model

Abstract. The inflow of relatively warm and salty water from the Indian Ocean into the South Atlantic via Agulhas leakage is important for the global overturning circulation and the global climate. In this study, we analyse the robustness of Agulhas leakage estimates as well as the thermohaline property modifications of Agulhas leakage south of Africa. Lagrangian experiments with both the newly developed tool Parcels and the well established tool Ariane were performed to simulate Agulhas leakage in the eddy-rich ocean–sea-ice model INALT20 (1/20∘ horizontal resolution) forced by the JRA55-do atmospheric boundary conditions. The average transport, its variability, trend and the transit time from the Agulhas Current to the Cape Basin of Agulhas leakage is simulated comparably with both Lagrangian tools, emphasizing the robustness of our method. Different designs of the Lagrangian experiment alter in particular the total transport of Agulhas leakage by up to 2 Sv, but the variability and trend of the transport are similar across these estimates. During the transit from the Agulhas Current at 32∘ S to the Cape Basin, a cooling and freshening of Agulhas leakage waters occurs especially at the location of the Agulhas Retroflection, resulting in a density increase as the thermal effect dominates. Beyond the strong air–sea exchange around South Africa, Agulhas leakage warms and salinifies the water masses below the thermocline in the South Atlantic.

Bycatch of fish in the South Atlantic krill fishery

1992 ◽  
Vol 4 (4) ◽  
pp. 389-392 ◽  
Author(s):  
Inigo Everson ◽  
Alexei Neyelov ◽  
Yuri E Permitin
Keyword(s):  
South Atlantic ◽  
Open Ocean ◽  
Research Vessel ◽  
The South ◽  
South Georgia

Icefish (Champsocephalus) were taken as bycatch during krill fishing operations from a research vessel. The data indicate that the bycatch of fish in the commercial krill fishery may be significant in some areas of the South Georgia shelf. The problem is thought to be least in open ocean krill fishing.

New species of Neotanais Beddard, 1886 (Crustacea, Tanaidacea) from the deep sea of the tropical and southern East Atlantic Ocean

Zootaxa ◽  
2009 ◽  
Vol 1992 (1) ◽  
pp. 20-36 ◽  
Author(s):  
SIMON WEIGMANN ◽  
JÜRGEN GUERRERO-KOMMRITZ
Keyword(s):  
New Species ◽  
Atlantic Ocean ◽  
Deep Sea ◽  
South Atlantic ◽  
South Atlantic Ocean ◽  
Full Description ◽  
The South ◽  
East Atlantic ◽  
Cape Basin

As part of the sampling efforts during the DIVA-II expedition several Tanaidacea of the genus Neotanais were captured in the Guinea and the Cape Basin in the tropical and southern East Atlantic Ocean. Two different species were sampled, Neotanais rotermundiae sp. n. from the Guinea and Neotanais guskei sp. n. from the Cape Basin. The distribution of both species is limited to these basins. A full description for both species is presented. Neotanais guskei sp. n. is the largest Neotanais reported for the South Atlantic Ocean.

The Greenland Clipper: a fast ocean connection between Greenland and the Southern Ocean

2021 ◽  
Author(s):  
Laurits Andreasen ◽  
Markus Jochum ◽  
Anna von der Heydt ◽  
Guido Vettoretti ◽  
Roman Nuterman
Keyword(s):  
Southern Ocean ◽  
Time Lag ◽  
Vertical Mixing ◽  
Heat Content ◽  
South Atlantic ◽  
Heat Fluxes ◽  
Model Parameters ◽  
The South ◽  
High Northern Latitude ◽  
Adjustment Time

<p>The glacial Dansgaard-Oeschger (DO) events are thought to result in a global reorganization of oceanic heat fluxes and heat content.</p><p>DO events originate in the North Atlantic, but are communicated all the way to the pole of the other hemisphere. This interhemispheric coupling is known as the bipolar seesaw. A striking feature of the bipolar seesaw is the ~100 year time lag between the initial onset at high northern latitudes and the following adjustments at high southern latitudes.</p><p>Here, we focus on this time lag.</p><p>Ultimately high southern latitudes are expected to begin their adjustment, when the sea ice margin in the Southern Ocean (SO) shift position due to cooling/warming in the ocean below. But how is the northern signal propagated into the SO, and what processes control the time it takes the SO to change its state?</p><p>We expect the SO adjustment to have four components: Planetary waves, geostrophic adjustments in the Atlantic, vertical mixing and finally heat fluxes from baroclinic eddies in the SO.</p><p>To investigate the relative importance of these components on the adjustment time in the SO, we apply a fresh water perturbation at high northern latitude in an idealized setup of the Atlantic basin and the Southern Ocean using the newly developed OGCM VEROS. We measure the time it takes the model's Southern Ocean to adjust to the perturbation as a function of different model parameters associated with the components mentioned above.</p><p>We find that the adjustment time - which we believe is related to the bipolar seesaw time lag - is dominated by two components. The first is associated with geostrophic adjustment in the South Atlantic, and the second with the eddy heat fluxes in the Southern Ocean. Interestingly we find that in the limit of a high (realistic) eddy transfer (Gent-McWilliams) coefficient, the geostrophic component constitutes the main part of the the adjustment time and quantitatively matches the observed time lag in the bipolar seesaw.</p><p>This make us suggest that the bipolar seesaw time lag could be caused mainly by adjustments in the South Atlantic.</p>

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