Seasonal to interannual variability of water mass characteristics and currents on the Namibian shelf

Junker, Tim; Mohrholz, Volker; Siegfried, Lydia; Plas, Anja van der

doi:10.1016/j.jmarsys.2016.09.003

Cited by 33 publications

(39 citation statements)

References 34 publications

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“…(b) Difference between OGCM and observed (WOA13v2) mean vertical temperature (°C) section at 23°S, with contours every 0.3 °C. (c) OGCM vertical profile of climatological meridional current velocities (m/s) at (14°E, 23°S) to be compared to the ADCP climatology presented in Junker et al (), their Figure a). The monthly mean climatology is computed over the 2003–2015 period.…”

Section: Data Model Methodology and Model Validationmentioning

confidence: 99%

“…Figure c shows the seasonal cycle of the vertical section of meridional current velocities from the OGCM taken at (14°E, 23°S) which has to be compared with the corresponding moored observations presented in Figure a in the study of Junker et al (). There is a good representation of the seasonal cycle of meridional currents between the OGCM and the ADCP currents from Junker et al (). Northward currents (positive values of meridional current velocities) are observed between May and September throughout the water column.…”

Section: Data Model Methodology and Model Validationmentioning

confidence: 99%

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Benguela Niños and Benguela Niñas in Forced Ocean Simulation From 1958 to 2015

et al. 2019

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A systematic study of Benguela Niño and Benguela Niña events during 1958 to 2015 including those that developed before the satellite era (1982) is carried out using an ocean general circulation model in combination with a linear equatorial model. Altogether, 21 strong warm and cold anomalous coastal events are identified among which 6 undocumented extreme coastal events are reported. Results suggest that most of these extreme coastal events including the newly identified ones are linked to remote equatorial forcing via mode 2 equatorial Kelvin waves. The latter propagates after approaching the African coast poleward as coastally trapped waves leading surface temperature anomalies along the Angola‐Benguela current system by one month. One to two months before the peak of Benguela Niños or Niñas usually occurring in March–April, a large‐scale wind stress forcing is observed with both local (variations of alongshore coastal wind stress) and remote forcing developing simultaneously. Results further suggest that surface temperature anomalies off Southern Angola and in the Angola‐Benguela Front are associated with equatorial dynamics and meridional wind stress fluctuations off the southwestern African coast north of 15°S. Similar mechanisms are observed for Northern Namibia in combination with forcing by local meridional wind stress variations.

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Section: Data Model Methodology and Model Validationmentioning

confidence: 99%

Section: Data Model Methodology and Model Validationmentioning

confidence: 99%

Benguela Niños and Benguela Niñas in Forced Ocean Simulation From 1958 to 2015

et al. 2019

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“…Besides equatorial wave forcing, theoretical, modeling, and observational studies have shown that local wind forcing plays an important role in setting the structure and driving the variability of the eastern boundary circulation in upwelling regions, including the Benguela upwelling (McCreary and Chao 1985;Marchesiello et al 2003;Fennel et al 2012;Junker et al 2015;Small et al 2015). In particular, the southern Angola region and the Benguela upwelling to the south are impacted by strong southerly surface winds associated with the Benguela atmospheric low-level coastal jet (e.g., Nicholson 2010; Patricola and Chang 2017).…”

Section: History Of Physical Oceanography In Angolamentioning

confidence: 99%

“…Before it veers offshore, the atmospheric lowlevel coastal jet has a quasi-permanent northern maximum located at about 17.5°S that coincides with the Cunene upwelling cell (Lutjeharms and Meeuwis 1987;Patricola and Chang 2017). This maximum is related to a maximum in negative wind stress curl between 15° and 20°S, which is considered to be the main driving mechanism for poleward flow along the eastern boundaries (e.g., McCreary and Chao 1985;Marchesiello et al 2003;Fennel et al 2012;Junker et al 2015).…”

Section: History Of Physical Oceanography In Angolamentioning

confidence: 99%

“…Benguela Niños are marked by a poleward intrusion of warm equatorial water and reduced upwelling (Fig. 3), while SST anomalies of up to 5°C off the coast of Angola and Namibia are observed (e.g., Junker et al 2017). Benguela Niños/Niñas are known to have a strong impact on precipitation variability over adjacent countries (e.g., Rouault et al 2003) as well as on the marine ecosystem and local fisheries (Gammelsrød et al 1998;Boyer and Hampton 2001).…”

Section: History Of Physical Oceanography In Angolamentioning

confidence: 99%

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Eastern Boundary Circulation and Hydrography Off Angola: Building Angolan Oceanographic Capacities

Tchipalanga

Dengler

Brandt

et al. 2018

Bulletin of the American Meteorological Society

123

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The eastern boundary region off Angola encompasses a highly productive ecosystem important for the food security of the coastal population. The fish-stock distribution, however, undergoes large variability on intraseasonal, interannual, and longer time scales. These fluctuations are partly associated with large-scale warm anomalies that are often forced remotely from the equatorial Atlantic and propagate southward, reaching the Benguela upwelling off Namibia. Such warm events, named Benguela Niños, occurred in 1995 and in 2011. Here we present results from an underexplored extensive in situ dataset that was analyzed in the framework of a capacity-strengthening effort. The dataset was acquired within the Nansen Programme executed by the Food and Agriculture Organization of the United Nations and funded by the Norwegian government. It consists of hydrographic and velocity data from the Angolan continental margin acquired biannually during the main downwelling and upwelling seasons over more than 20 years. The mean seasonal changes of the Angola Current from 6° to 17°S are presented. During austral summer the southward Angola Current is concentrated in the upper 150 m. It strengthens from north to south, reaching a velocity maximum just north of the Angola Benguela Front. During austral winter the Angola Current is weaker, but deeper reaching. While the southward strengthening of the Angola Current can be related to the wind forcing, its seasonal variability is most likely explained by coastally trapped waves. On interannual time scales, the hydrographic data reveal remarkable variability in subsurface upper-ocean heat content. In particular, the 2011 Benguela Niño was preceded by a strong subsurface warming of about 2 years’ duration.

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Evidence of nitrification associated with globally distributed pelagic jellyfish

Hubot

Giering

Füssel

et al. 2021

Limnology & Oceanography

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Often considered detrimental to the environment and human activities, jellyfish blooms are increasing in several coastal regions worldwide. Yet, the overall effect of these outbreaks on ecosystem productivity and structure are not fully understood. Here we provide evidence for a so far unanticipated role of jellyfish in marine nitrogen cycling. Pelagic jellyfish release nitrogen as a metabolic waste product in form of ammonium. Yet, we observed high rates of nitrification (NH4+ → NO3−, 5.7–40.8 nM gWW−1 [wet weight] h−1) associated with the scyphomedusae Aurelia aurita, Chrysaora hysoscella, and Chrysaora pacifica and low rates of incomplete nitrification (NH4+ → NO2−, 1.0–2.8 nM gWW−1 h−1) associated with Chrysaora fulgida, C. hysoscella, and C. pacifica. These observations indicate that microbes living in association with these jellyfish thrive by oxidizing the readily available ammonia to nitrite and nitrate. The four studied species have a large geographic distribution and exhibit frequent population outbreaks. We show that, during such outbreaks, jellyfish‐associated release of nitrogen can provide more than 100% of the nitrogen required for primary production. These findings reveal a so far overlooked pathway when assessing pelagic nitrification rates that might be of particular relevance in nitrogen depleted surface waters and at high jellyfish population densities.

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Seasonal to interannual variability of water mass characteristics and currents on the Namibian shelf

Cited by 33 publications

References 34 publications

Benguela Niños and Benguela Niñas in Forced Ocean Simulation From 1958 to 2015

Benguela Niños and Benguela Niñas in Forced Ocean Simulation From 1958 to 2015

Eastern Boundary Circulation and Hydrography Off Angola: Building Angolan Oceanographic Capacities

Evidence of nitrification associated with globally distributed pelagic jellyfish

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