Cross shelf hydrographic and hydrochemical conditions and their short term variability at the northern Benguela during a normal upwelling season

Mohrholz, Volker; Eggert, Anja; Junker, Tim; Nausch, Günther; Ohde, Thomas; Schmidt, Martin

doi:10.1016/j.jmarsys.2014.04.019

Cited by 42 publications

(36 citation statements)

References 45 publications

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“…[]), and another one during R/V Maria S. Merian cruise 18/4 (August 2011, Mohrholz et al . []). Note that the extended data set does contain three profiles for December/January; however, these profiles are limited to the upper 200–450 m depth.…”

Section: Methodsmentioning

confidence: 99%

The Angola Current: Flow and hydrographic characteristics as observed at 11°S

Kopte

Brandt

Dengler

et al. 2017

J. Geophys. Res. Oceans

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The eastern boundary circulation off the coast of Angola has been described only sparsely to date, although it is a key element in the understanding of the highly productive tropical marine ecosystem off Angola. Here, we report for the first time direct velocity observations of the Angola Current (AC) at ∼11°S collected between July 2013 and October 2015 in the depth range from 45 to 450 m. The measurements reveal an alongshore flow that is dominated by intraseasonal to seasonal variability with periodically alternating southward and northward velocities in the range of ±40 cm/s. During the observation period, a weak southward mean flow of 5–8 cm/s at 50 m depth is observed, with the southward current extending down to about 200 m depth. Corresponding mean southward transport of the AC is estimated to be 0.32 ± 0.046 Sv. An extensive set of hydrographic measurements is used to investigate the thermal structure and seasonality in the hydrography of the eastern boundary circulation. Within the depth range of the AC, the superposition of annual and semiannual harmonics explains a significant part of the total variability, although salinity in the near surface layer appears to be also impacted by year‐to‐year variability and/or short‐term freshening events. In the central water layer, temperature and salinity on isopycnals vary only weakly on seasonal to annual time scales. The available data set is further used to evaluate different reanalysis products particularly emphasizing the ocean's role in coupled climate model SST biases in the Eastern Tropical Atlantic.

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Section: Methodsmentioning

confidence: 99%

The Angola Current: Flow and hydrographic characteristics as observed at 11°S

Kopte

Brandt

Dengler

et al. 2017

J. Geophys. Res. Oceans

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“…Besides a clear seasonal cycle, biogeochemical processes in the nBUS are strongly influenced by short-term variability due to wind forcing and mesoscale dynamics (Mohrholz et al, 2014). Filaments are "finger-like" features which transport cold waters, tracers, and OM across the frontal zone in coastal upwelling systems (Hösen et al, 2016;Muller et al, 2013).…”

Section: Upwelling Filamentsmentioning

confidence: 99%

N₂O Emissions From the Northern Benguela Upwelling System

Arévalo‐Martínez

Steinhoff

Brandt

et al. 2019

Geophysical Research Letters

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The Benguela Upwelling System (BUS) is the most productive of all eastern boundary upwelling ecosystems and it hosts a well‐developed oxygen minimum zone. As such, the BUS is a potential hotspot for production of N2O, a potent greenhouse gas derived from microbially driven decay of sinking organic matter. Yet, the extent at which near‐surface waters emit N2O to the atmosphere in the BUS is highly uncertain. Here we present the first high‐resolution surface measurements of N2O across the northern part of the BUS (nBUS). We found strong gradients with a threefold increase in N2O concentrations near the coast as compared with open ocean waters. Our observations show enhanced sea‐to‐air fluxes of N2O (up to 1.67 nmol m−2 s−1) in association with local upwelling cells. Based on our data we suggest that the nBUS can account for 13% of the total coastal upwelling source of N2O to the atmosphere.

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“…The Canary upwelling system in the eastern tropical North Atlantic (ETNA; Table ) is among the four major eastern boundary coastal upwelling systems in the world oceans together with the Peruvian (e.g., Brink et al, ) and Californian (e.g., Marchesiello et al, ) upwelling systems in the tropical South and North Pacific, respectively, and the Benguela upwelling system in the tropical South Atlantic (e.g., Mohrholz et al, ). As part of the Canary upwelling, the Mauritanian upwelling region (MUR; Figure ) exhibits a pronounced seasonality (e.g., Lathuilière et al, ; Mittelstaedt, ; Van Camp et al, ).…”

Section: Introductionmentioning

confidence: 99%

Seasonal Variability of the Mauritania Current and Hydrography at 18°N

2018

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Extensive field campaigns in the Mauritanian upwelling region between 2005 and 2016 provide the database for analyzing the seasonal variability of the eastern boundary circulation (EBC) and associated water mass distribution at 18°N. The data set includes shipboard upper ocean current, hydrographic, and oxygen measurements from nine research cruises conducted during upwelling (December to April) and relaxation (May to July) seasons. During the upwelling season, the EBC closely resembles a classical eastern boundary current regime, with a poleward undercurrent flowing beneath an equatorward coastal jet. In contrast, elevated poleward flow exceeding 30 cm/s and extending from the surface down to 250‐m depth is observed during the relaxation season. The pronounced seasonal variability of the across‐shore structure of the EBC can be related to local wind forcing and is in general agreement with Sverdrup balance. The EBC transport is correlated to the wind stress curl leading the transport by 7 days. The short lead time suggests a fast response of locally forced waves adjusting the EBC to wind forcing. The seasonal and vertical water mass distribution is presented based on hydrographic observations. The meridional oxygen distribution and corresponding water mass partitioning into South and North Atlantic Central Water masses reveal a possible northerly ventilation pathway in the deeper layers of the central water stratum. Our results suggest that the poleward surface flow and the poleward undercurrent both are a consequence of the cyclonic wind stress curl forcing and thus propose to name it the Mauritania Current.

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Cross shelf hydrographic and hydrochemical conditions and their short term variability at the northern Benguela during a normal upwelling season

Cited by 42 publications

References 45 publications

The Angola Current: Flow and hydrographic characteristics as observed at 11°S

The Angola Current: Flow and hydrographic characteristics as observed at 11°S

N₂O Emissions From the Northern Benguela Upwelling System

Seasonal Variability of the Mauritania Current and Hydrography at 18°N

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Cross shelf hydrographic and hydrochemical conditions and their short term variability at the northern Benguela during a normal upwelling season

Cited by 42 publications

References 45 publications

The Angola Current: Flow and hydrographic characteristics as observed at 11°S

The Angola Current: Flow and hydrographic characteristics as observed at 11°S

N2O Emissions From the Northern Benguela Upwelling System

Seasonal Variability of the Mauritania Current and Hydrography at 18°N

Contact Info

Product

Resources

About

N₂O Emissions From the Northern Benguela Upwelling System