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Characterization of “dead-zone” eddies in the eastern tropical North Atlantic (2016)

Abstract.

"Localized open-ocean low-oxygen “dead zones” in the eastern tropical North Atlantic are recently discovered ocean features that can develop in dynamically isolated water masses within cyclonic eddies (CE) and anticyclonic mode-water eddies (ACME). Analysis of a comprehensive oxygen dataset obtained from gliders, moorings, research vessels and Argo floats reveals that “dead-zone” eddies are found in surprisingly high numbers and in a large area from about 4 to 22°N, from the shelf at the eastern boundary to 38°W. [...]"

Source: Biogeosciences
Authors: Florian Schütte et al.
DOI: 10.5194/bg-13-5865-2016

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Subsurface Fine‐Scale Patterns in an Anticyclonic Eddy Off Cap‐Vert Peninsula Observed From Glider Measurements

Abstract.

"Glider measurements acquired along four transects between Cap‐Vert Peninsula and the Cape Verde archipelago in the eastern tropical North Atlantic during March–April 2014 were used to investigate fine‐scale stirring in an anticyclonic eddy. The anticyclone was formed near 12°N off the continental shelf and propagated northwest toward the Cape Verde islands. At depth, between 100 and –400 m, the isolated anticyclone core contained relatively oxygenated, low‐salinity South Atlantic Central Water, while the surrounding water masses were saltier and poorly oxygenated. [...]"

Source: Oceans
Authors: Nicolas Kolodziejczyk et al.
DOI: 10.1029/2018JC014135

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Niche construction by non-diazotrophs for N2 fixers in the eastern tropical North Atlantic Ocean

Abstract.

"Diazotrophic dinitrogen (N2) fixation contributes ~76% to “new” nitrogen inputs to the sunlit open ocean, but environmental factors determining N2 fixation rates are not well constrained. Excess phosphate (phosphate–nitrate/16 > 0) and iron availability control N2 fixation rates in the eastern tropical North Atlantic (ETNA), but it remains an open question how excess phosphate is generated within or supplied to the phosphate-depleted sunlit layer. [...]"

Source: Geophysical Research Letters
Authors: Arvind Singh et al.
DOI: 10.1002/2017GL074218

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Decadal oxygen change in the eastern tropical North Atlantic

Abstract.

"Repeat shipboard and multi-year moored observations obtained in the oxygen minimum zone (OMZ) of the eastern tropical North Atlantic (ETNA) were used to study the decadal change in oxygen for the period 2006–2015. Along 23° W between 6 and 14° N, oxygen decreased with a rate of −5.9 ± 3.5 µmol kg−1 decade−1 within the depth covering the deep oxycline (200–400 m), while below the OMZ core (400–1000 m) oxygen increased by 4.0 ± 1.6 µmol kg−1 decade−1 on average. The inclusion of these decadal oxygen trends in the recently estimated oxygen budget for the ETNA OMZ suggests a weakened ventilation of the upper 400 m, whereas the ventilation strengthened homogeneously below 400 m. [...]"

Source: Ocean Science
Authors: Johannes Hahn, Peter Brandt, Sunke Schmidtko and Gerd Krahmann
DOI: 10.5194/os-13-551-2017

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