Jessica Burger

University of Cape Town | UCT · Department of Oceanography

Understanding the transport and accumulation of microplastics is useful to determine the relative risk they pose to global biodiversity. The exact contribution of microplastic sources is hard to elucidate; therefore, investigating the Antarctic Weddell Sea, an area known for its remoteness and little human presence (i.e. limited pollution sources),...

Nitrogen oxides, collectively referred to as NOx (NO + NO2), are an important component of atmospheric chemistry involved in the production and destruction of various oxidants that contribute to the oxidative capacity of the troposphere. The primary sink for NOx is atmospheric nitrate, which has an influence on climate and the biogeochemical cyclin...

Across the Southern Ocean in winter, nitrification is the dominant mixed-layer nitrogen cycle process, with some of the nitrate produced therefrom persisting to fuel productivity during the subsequent growing season. Because this nitrate constitutes a regenerated rather than a new nutrient source to phytoplankton, it will not support the net remova...

In South Africa, the Highveld region and the Johannesburg-Pretoria megacity are known as global NOx (NOx = NO + NO2) “hotspots” identified by satellite-based instruments. The ultimate sink for atmospheric NOx is conversion to aerosol nitrate. However, measurements of aerosol nitrate concentrations do not provide information on which NOx sources ser...

Central to the Southern Ocean's role in setting atmospheric CO 2 is the seasonal alternation between upward mixing of nutrients and their subsequent consumption by phytoplankton. Active nutrient cycling within the mixed layer, including the release of ammonium (NH 4 +) and its removal by phytoplankton and nitrifiers, also affects Southern Ocean CO...

The production and removal of ammonium (NH4+) are essential upper-ocean nitrogen cycle pathways, yet in the Southern Ocean where NH4+ has been observed to accumulate in surface waters, its mixed-layer cycling remains poorly understood. For surface seawater samples collected between Cape Town and the Marginal Ice Zone in winter 2017, we found that N...

Atmospheric nitrate originates from the oxidation of nitrogen oxides (NOx=NO+NO2) and impacts both tropospheric chemistry and climate. NOx sources, cycling and NOx to nitrate formation pathways are poorly constrained in remote marine regions, especially the Southern Ocean, where pristine conditions serve as a useful proxy for the pre-industrial atm...

Across the Southern Ocean in winter, nitrification is the dominant mixed-layer nitrogen cycle process, with some of the nitrate produced therefrom persisting to fuel productivity during the subsequent growing season, potentially weakening the spring/summer biological CO2 sink. To better understand the controls on Southern Ocean nitrification, we co...

The Weddell Sea represents a point of origin in the Southern Ocean where globally important water masses form. Biological activities in Weddell Sea surface waters thus affect large-scale ocean biogeochemistry. During January–February 2019, we measured net primary production (NPP), nitrogen (nitrate, ammonium, urea) uptake, and nitrification in the...

Atmospheric nitrate originates from the oxidation of nitrogen oxides (NOx = NO + NO2) and impacts both tropospheric chemistry and climate. NOx sources, cycling, and NOx to nitrate formation pathways are poorly constrained in remote marine regions, especially the Southern Ocean where pristine conditions serve as a useful proxy for the preindustrial...

The production and consumption of ammonium (NH4+) are essential upper-ocean nitrogen cycle pathways, yet in the Southern Ocean where NH4+ has been observed to accumulate in surface waters, its mixed-layer cycling remains poorly understood. For surface samples collected between Cape Town and the marginal ice zone (MIZ) in winter 2017, we found that...

The Weddell Sea (WS) represents a point of origin in the Southern Ocean where globally-important water masses form. Biological activities in WS surface waters thus affect large-scale ocean biogeochemistry. During summer 2018/2019, we measured net primary production (NPP), nitrogen (nitrate, ammonium, urea) uptake, and nitrification in the western W...

The southern Benguela upwelling system (SBUS) supports high rates of primary productivity that sustain important commercial fisheries. The exceptional fertility of this system is reportedly fuelled not only by upwelled nutrients, but also by nutrients regenerated on the broad and shallow continental shelf. We measured nutrient concentrations and th...

St Helena Bay (SHB), a retention zone in the southern Benguela upwelling system, supports 40–50% of the region's primary productivity. It also experiences harmful algal blooms (HABs) and hypoxic conditions that are difficult to predict given the high sub-seasonal variability. To better understand this variability, net primary production (NPP), nitr...

The elevated levels of primary production associated with eastern boundary currents are driven by nutrient-rich waters upwelled from depth, such that these regions are typically characterised by high rates of nitrate-fuelled phytoplankton growth. Production studies from the southern Benguela upwelling system (SBUS) tend to be biased towards the sum...

Picoplankton (<0.2 - 3µm) found in the marine environment are significant contributors to primary production and phytoplankton biomass. To date, little is known about the community dynamics of picoplankton (archaea, bacteria and picoeukaryotic protists) within St. Helena Bay. This bay is situated on the west coast of South Africa in the productive,...