A5060713983- Marine and coastal ecosystems
- Wastewater Treatment and Nitrogen Removal
- Microbial Community Ecology and Physiology
- Oceanographic and Atmospheric Processes
- Marine Biology and Ecology Research
- Isotope Analysis in Ecology
- Atmospheric and Environmental Gas Dynamics
- Age of Information Optimization
- Ocean Acidification Effects and Responses
- Arctic and Antarctic ice dynamics
- Groundwater and Isotope Geochemistry
- Marine and fisheries research
University of Cape Town
2020-2023
Council of Scientific and Industrial Research
2022
Abstract Net primary production (NPP) fueled by nitrate is often equated with carbon export, providing a metric for CO 2 removal to the deep ocean. This “new paradigm” assumes that nitrification, oxidation of regenerated ammonium nitrate, negligible in sunlit upper While surface layer nitrification has been measured other oceanic regions, very few data exist Southern Ocean. We NPP, nitrogen (N) uptake, and 200 m across Atlantic Ocean winter summer. Rates mixed‐layer uptake were low, while...
Abstract. 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 surface waters, its mixed-layer cycling remains poorly understood. For seawater samples collected between Cape Town Marginal Ice Zone winter 2017, we found that concentrations were 5-fold higher than is typical for summer lower north south Subantarctic Front (0.01–0.26 µM versus 0.19–0.70 µM). Our observations confirm...
Abstract Central to the Southern Ocean's role in setting atmospheric CO 2 is seasonal alternation between upward mixing of nutrients and their subsequent consumption by phytoplankton. Active nutrient cycling within mixed layer, including release ammonium (NH 4 + ) its removal phytoplankton nitrifiers, also affects Ocean drawdown, yet remains poorly understood. We conducted kinetics experiments across south Africa investigate dependence NH uptake (summer, winter) oxidation (winter) on...
Abstract. As a key biogeochemical pathway in the marine nitrogen cycle, nitrification (ammonia oxidation and nitrite oxidation) converts most reduced form of – ammonium–ammonia (NH4+–NH3) into oxidized species (NO2-) nitrate (NO3-). In ocean, these processes are mainly performed by ammonia-oxidizing archaea (AOA) bacteria (AOB) nitrite-oxidizing (NOB). By transforming speciation providing substrates for removal, affects microbial community structure; productivity (including chemoautotrophic...
Abstract. Across the Southern Ocean in winter, nitrification is dominant mixed-layer nitrogen cycle process, with some of nitrate produced therefrom persisting to fuel productivity during subsequent growing season. Because this constitutes a regenerated rather than new nutrient source phytoplankton, it will not support net removal atmospheric CO2. To better understand controls on nitrification, we conducted nitrite oxidation kinetics experiments surface waters across western Indian sector...
Abstract. As a key biogeochemical pathway in the marine nitrogen cycle, nitrification (ammonia oxidation and nitrite oxidation) converts most reduced form of – ammonium/ammonia (NH4+/ NH3) into oxidized species (NO2−) nitrate (NO3−). In ocean, these processes are mainly performed by ammonia-oxidizing archaea (AOA) bacteria (AOB), nitrite-oxidizing (NOB). By transforming speciation providing substrates for removal, affects microbial community structure, productivity (including...
Abstract The well‐established importance of Agulhas Current “leakage” for Indian‐Atlantic Ocean exchange heat and salt raises the question relevance eddies carbon nitrogen cycling. We measured net primary production (NPP), nitrate ammonium uptake, nitrification along a transect Cape Basin (CB) in winter 2017, including across an anticyclonic eddy sampled at high‐resolution. Euphotic zone‐integrated rates NPP uptake were more than three‐fold lower center its edges, with intermediate outside...
Abstract. Across the Southern Ocean in winter, nitrification is dominant mixed-layer nitrogen cycle process, with some of nitrate produced therefrom persisting to fuel productivity during subsequent growing season, potentially weakening spring/summer biological CO2 sink. To better understand controls on nitrification, we conducted nitrite oxidation kinetics experiments surface waters across western Indian sector winter. While all (seven total) yielded a Michaelis-Menten relationship...
Abstract. 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 surface waters, its mixed-layer cycling remains poorly understood. For samples collected between Cape Town marginal ice zone (MIZ) winter 2017, we found that concentrations were five-fold higher than is typical for summer, lower north south Subantarctic Front (SAF; 0.01–0.26 µM versus 0.19–0.70 µM). Our...