Anja K. Van der Plas

• Senior Researcher at National Marine Information and Research Centre

We conducted sediment trap experiments in the Benguela Upwelling System (BUS) in the southeastern Atlantic Ocean to study the influence of zooplankton on the flux of particulate organic carbon (POC) through the water column and its sedimentation. A total of 2 long-term moored and 16 short-term free-floating sediment trap systems (drifter systems) w...

Bottom-trawl fishery is known to cause major disturbances to marine sediments as the dragging of trawl gears across the seabed fosters sediment resuspension, which can lead to organic particle remineralization and release of benthic CO2 and nutrients into bottom waters. However, its effects on carbon cycling and biological productivity, especially...

We conducted extensive sediment trap experiments in the Benguela Upwelling System (BUS) in the south-eastern Atlantic Ocean to study the influence of zooplankton on the flux of particulate organic carbon (POC) through the water column and its sedimentation. Two long term moored and sixteen short term free-floating sediment trap systems were deploye...

Quantifying greenhouse gas (GHG) emissions is essential for mitigating global warming, and has become the task of individual countries assigned to the Paris agreement in the form of National Greenhouse Gas Inventory Reports (NIR). The NIR informs on GHG emissions and removals over national territory encompassing the 200-mile Exclusive Economic Zone...

The southeastern tropical Atlantic hosts a coastal upwelling system characterized by high biological productivity. Three subregions can be distinguished based on differences in the physical climate: the tropical Angolan and the northern and southern Benguela upwelling systems (tAUS, nBUS, sBUS). The tAUS, which is remotely forced via equatorial and...

Eastern Boundary Upwelling Systems (EBUS) are highly productive ecosystems. However, being poorly sampled and represented in global models, their role as atmospheric CO2 sources and sinks remains elusive. In this work, we present a compilation of shipboard measurements over the past two decades from the Benguela Upwelling System (BUS) in the southe...

The spatial distribution patterns of Merluccius capensis in the Namibian waters were investigated and related to average environmental conditions during 1996-2020. Fisheries-independent data and simultaneously collected water temperature and dissolved oxygen data were used from austral summer surveys. A geostatistical kriging approach was employed...

Due to their lithotrophic metabolisms, morphological complexity and conspicuous appearance, members of the Beggiatoaceae have been extensively studied for more than 100 years. These bacteria are known to be primarily sulfur-oxidizing autotrophs that commonly occur in dense mats at redox interfaces. Their large size and the presence of a mucous shea...

A baseline study on anthropogenic radioactivity in the Namibian marine ecosystem, which is part of the northern Benguela upwelling system, known as one of the most productive ocean areas in the world, has been performed. A scientific cruise carried out in 2014 covering inshore and offshore areas, exhibiting different oceanographic features, has pro...

Climate change is expected to result in a reduction of oceanic oxygen concentration and an expansion of oxygen-minimum zones (OMZs) in the tropical ocean. Oxygen is perhaps the principal environmental variable influencing habitat and health of fish populations. In West Africa, where rich fisheries are essential for supporting the livelihood of coas...

The Global South is a term largely referring to the regions of Latin America, Asia, Africa, and Oceania. Today, the Exclusive Economic Zones of the Global South (GSEEZ) are the most populated and touristic and inhabited marine regions, with much of the world’s population depending on its resources and wealth. Throughout the GSEEZ, megadiverse and p...

The epoch of the Anthropocene, a period during which human activity has been the dominant influence on climate and the environment, has witnessed a decline in oxygen concentrations and an expansion of oxygen depleted environments in both coastal and open ocean systems since the middle of the 20th century. This paper provides a review of system-spec...

The epoch of the Anthropocene, a period during which human activity has been the dominant influence on climate and the environment, has witnessed a decline in oxygen concentrations and an expansion of oxygen-depleted environments in both coastal and open ocean systems since the middle of the 20th century. This paper provides a review of system-spec...

Eastern Boundary Upwelling Systems (EBUS) are well-known for their high productivity and fishery yields. However, being scarcely sampled and poorly represented in global models, their role as CO2 sources and sinks to the atmosphere remains elusive. Here, we present a compilation of shipboard measurements over the past two decades, showing how the B...

Fisheries resources of the Benguela Current Large Marine Ecosystem (BCLME) are critically important to the socio-economic well-being of the people of Angola, Namibia and South Africa. Their high degree of environmental vulnerability underscores the importance of maintaining a healthy ecosystem by increasing its resilience to the impacts of anthropo...

The bearded goby Sufflogobius bibarbatus is an abundant endemic small fish species on the continental shelf of the northern Benguela. The goby habitat is characterised by generally low bottom oxygen concentrations that vary spatially and seasonally. In the present study of population structure, 13 samples of S. bibarbatus from inner and outer shelf...

The bearded goby Sufflogobius bibarbatus is an abundant endemic small fish species on the continental shelf of the northern Benguela. The goby habitat is characterised by generally low bottom oxygen concentrations that vary spatially and seasonally. In the present study of population structure, 13 samples of S. bibarbatus from inner and outer shelf...

Multidisciplinary ocean observing activities provide critical ocean information to satisfy ever-changing socioeconomic needs and require coordinated implementation. The upper oxycline (transition between high and low oxygen waters) is fundamentally important for the ecosystem structure and can be a useful proxy for multiple observing objectives con...

Ocean boundary current systems are key components of the climate system, are home to highly productive ecosystems, and have numerous societal impacts. Establishment of a global network of boundary current observing systems is a critical part of ongoing development of the Global Ocean Observing System. The characteristics of boundary current systems...

Coastal trapped waves (CTWs) that propagate poleward along the southwest African shelf potentially leak energy from lower latitudes into the Benguela Upwelling System (BUS). Thus, in addition to local winds, these waves provide an important remote forcing mechanism for the upwelling region. The present study aims at elucidating the nature ofCTWs in...

An investigation of surface phytoplankton communities was undertaken on the shelf of the northern Benguela upwelling ecosystem during austral autumn (May) and spring (September), along latitudinal transects at 20° S and 23° S, from 2 to 70 nautical miles offshore, as well as on a zigzag grid located between these transects. Microscopic identificati...

This paper examines variations in gender-specific body growth, morphology and reproduction of the bearded goby (Sufflogobius bibarbatus) across the Namibian shelf, built on previous work on male reproductive modes. The results indicate a spatial variation in the size composition, condition factor and maturation of gobies across the shelf area. Low...

Biogeochemical cycles of carbon, nutrients, and oxygen transmit mean states, trends and variations of the physical realm in coastal upwelling systems to their food webs and determine their role in regional budgets of greenhouse gases. This contribution focuses on biogeochemical processes in the northern Benguela Upwelling System (NBUS), where low o...

Understanding and validating annual structures in fish otoliths are important for stock assessments and fisheries ecology. Biannual translucent zone formation has been demonstrated for 3-21. months old Namibian shallow-water hake Merluccius capensis. This paper addresses the hypothesis that the pattern continues in older fish. Otolith zone periodic...

In order to study the effects of temperature, oxygen, salinity and time of day on survey trawl catches, we modeled observed catches of juvenile, small, medium and large hakes per station as functions of zenith angle of the sun, geographical position, year, temperature, salinity, oxygen and depth. We used data from summer demersal surveys conducted...

We present long-term current meter records from the Benguela system together with salinity and temperature observations gathered by a mooring on the Namibian shelf across 13 years (2002 - 2015). From this unique data set a climatological mean state is estimated enabling us to investigate seasonal to interannual variations of these variables on the...

Swept-area biomass survey report

The NansClim project (2010-2013) represented a regional collaboration to assess the effects of climate on Benguela dynamics. Based on in situ (since the 1960s in Namibia and South Africa and 1985 in Angola) and satellite (since the 1980s) observations, the project focussed on four subsystems, namely the Angola subtropical, northern Benguela upwelli...

Long-term data sets are essential to understand climate-induced variability in marine ecosystems. This study provides the first comprehensive analysis of longer-term temporal and spatial variations in zooplankton abundance and copepod community structure in the northern Benguela upwelling system from 2005 to 2011. Samples were collected from the up...

On a global scale the ratio of fixed nitrogen (N) and phosphate (P) is characterized by a deficit of N with regard to the classical Redfield ratio of N : P = 16 : 1 reflecting the impact of N loss occurring in the oceanic oxygen minimum zones. The northern Benguela upwelling system (NBUS) is known for losses of N and the accumulation of P in sub- a...

The factors modulating recruitment success of Cape hake Merluccius capensis in Namibian waters are still unresolved. In this study, we used generalised additive models, regression tree analysis and the conventional Ricker model to examine the effect of environmental indices and spawning stock biomass (SSB) on hake recruitment success for the period...

Three scales of LOW variability were found to be amenable to forecasting as well as being suitable to provide information that would be of use to management response plans.u⊙ Short time scale: 7 day lead events linked to local wind variability and "HABs"⊙ Medium Time Scale: 2 month lead events linked to "ETSA" easterly equatorial winds⊙ Decadal Tim...

Dissolved carbon to nutrient ratios in the oceans' interior are remarkably consistent with the classical C : N : P : O2 Redfield ratio of 106 : 16 : 1 : 138 reflecting the mean composition of organic matter photosynthesized in the sunlit surface ocean. Deviations from the Redfield ratio indicate changes in the functioning of the biological carbon p...

[1] The northern Benguela upwelling system is a nutrient-replete region with high plankton biomass production and a seasonally changing oxygen minimum zone. Nitrate:phosphate ratios in fresh upwelling water are low due to denitrification in the near-seafloor oxygen minimum zone and phosphate efflux from sediments. This makes the region a candidate...

In this study we investigate the possible reasons for the widespread differences between the seasonal cycles of carbon production and export compared to those of hypoxia in eastern boundary upwelling systems. An idealized model is proposed that qualitatively characterizes the relative roles of physics and biogeochemical fluxes. The model is tested...

Hypoxia has become a world-wide phenomenon in the global coastal ocean and causes a deterioration of the structure and function of ecosystems. Based on the collective contributions of members of SCOR Working Group #128, the present study provides an overview of the major aspects of coastal hypoxia in different biogeochemical provinces, including es...

Hypoxia has become a world-wide phenomenon in the global coastal ocean and causes a deterioration of the structure and function of ecosystems. Based on the collective contributions of members of SCOR Working Group #128, the present study provides an overview of the major aspects of coastal hypoxia in different biogeochemical provinces, including es...

The Benguela system is one of the four major eastern boundary upwelling systems of the world. It is unusual as there are two stratified subtropical or warm temperate boundary regions, on either side of the major wind-driven upwelling region(19–34°S), which itself is subdivided at 26°S by the powerful Luderitz upwelling cell. Important biological co...

Coastal waters support approximately 90 per cent of global fisheries and are therefore an important food reserve for our planet. Eutrophication of these waters, due to human activity, leads to severe oxygen depletion and the episodic occurrence of hydrogen sulphide-toxic to multi-cellular life-with disastrous consequences for coastal ecosytems. Her...

In this study we use multi-year time series to examine the dynamic characteristics of coupled physical–biogeochemical processes that modulate interannual coastal hypoxia in the Benguela upwelling system in the southeast Atlantic. The results confirmed earlier findings on the role of advection to explain much of the seasonal–decadal variability. The...

The seasonal variations in the advection and mixing of water masses in the northern Benguela were studied in relation to the oxygen minimum zone over the Namibian shelf. The used data set consists of hydrographic and current measurements from an oceanographic mooring 20 nm off Walvis Bay, monthly CTD transects from the Namibian 23°S monitoring line...

Data from two cross-shelf sediment sampling cruises were used to explain reasons for the sediment biogeochemical variability in respect of carbon, nitrogen and sulphur, and how the cycling of these elements governs the biogeochemistry of the overlying water through their control of the redox conditions. The spatial extent of this benthic–pelagic fl...

The Namibian Ministry of Fisheries and Marine Resources has the task of collecting and providing relevant oceanographic information for management of their fisheries. However, quality information is difficult to provide because of the complexity of the processes involved in the Namibian marine ecosystem. Nonetheless, there are oceanographic data av...

LOW variability in the Benguela is governed by varying scales of remote and local forcing linked to both Equatorial and Cape Basin systems. The nature of these nonlinea interactions is not clearly understood because scales are large and their elucidation through observational programmes alone is not cost effective. Models are required to characteri...

This chapter focuses on describing, discussing and evaluating the feasibility of forecasting selected shelf processes considered to be of relevance in terms of their impacts on commercially important living marine resources of the BCLME. The impact of shelf processes is examined with regard to both the availability of resources to fishing and their...

Emerging understanding of the variability of natural coastal hypoxia is divided between two main hypotheses: the biogeochemical oxygen demand linked to locally-driven organic matter decay or to supply of low-oxygen waters by physical processes. The precise role of either mechanism in triggering hypoxia has remained elusive. A combined methane and o...

This study investigates the role of internal tides in driving the sedimentation and re-suspension of biogenic POM on the Namibian shelf and give rise to stable 500–800 km long shore alternating bands of high and low POM concentrations. Temperature time series data (September 2000–March 2001) from the benthic boundary layer at three sites are used t...

The BENEFIT programme is a collaborative training and research initiative between Angola, Namibia and South Africa, and donor countries which include Norway, Germany, Iceland and France; it has been described more fully elsewhere in this issue. Seven cruises were planned for 1999, based on discussions, in January 1999 in Cape Town, between German,...

The objective of cruise leg 48-5 was to get a better understanding of the impact of meso-scale physical structures and processes on zooplankton production with reference to fish recruitment. Studies were carried out within the Small Pelagic Fishes and Climate Change (SPACC) programme of GLOBEC and the regional BENEFIT programme and focussed on four...