Insa Rapp

• PhD
• PostDoc Position at Dalhousie University

The simultaneous limitation of productivity by two or more nutrients, commonly referred to as nutrient co-limitation, affects microbial communities throughout the marine environment and is of profound importance because of its impacts on various biogeochemical cycles. Multiple types of co-limitation have been described, enabling distinctions based...

Following the eruption of the Calbuco volcano in April 2015, an extensive ash plume spread across northern Patagonia and into the southeast Pacific and southwest Atlantic oceans. Here, we report on field surveys conducted in the coastal region receiving the highest ash load following the eruption (Reloncaví Fjord). The fortuitous location of a long...

The eastern boundary region of the southeastern Pacific Ocean hosts one of the world's most dynamic and productive upwelling systems with an associated oxygen minimum zone (OMZ). The variability in downward export fluxes in this region, with strongly varying surface productivity, upwelling intensities and water column oxygen content, is however poo...

Following the April 2015 eruption of the Calbuco volcano, an extensive ash plume spread across northern Patagonia and into the SE Pacific and SW Atlantic Ocean. Here we report the results of field surveys conducted in the marine region receiving the highest ash load following the eruption (Reloncaví Fjord). The fortuitous location of a long-term mo...

Plain Language Summary Some trace metals, including iron, are essential micronutrients for phytoplankton growth. However, the solubility of iron is very low under oxygenated conditions. Consequently, restricted iron availability in oxygen‐rich seawater can limit phytoplankton growth in the ocean, including in the Eastern Tropical South Pacific. Und...

The eastern boundary region of the southeast Pacific Ocean hosts one of the world's most dynamic and productive upwelling systems with an associated oxygen minimum zone (OMZ). The variability in downward export fluxes in this region, with strongly varying surface productivity, upwelling intensities and water column oxygen content, is however poorly...

The availability of the micronutrient iron (Fe) in surface waters determines primary production, N2 fixation, and microbial community structure in large parts of the world's ocean, and thus it plays an important role in ocean carbon and nitrogen cycles. Eastern boundary upwelling systems and the connected oxygen minimum zones (OMZs) are typically a...

The availability of the micronutrient iron (Fe) in surface waters determines primary production, N2 fixation and microbial community structure in large parts of the world's ocean, and thus plays an important role in ocean carbon and nitrogen cycles. Eastern boundary upwelling systems and the connected oxygen minimum zones (OMZs) are typically assoc...

Iron (Fe), cobalt (Co), and vitamin B12 addition experiments were performed in the eastern Equatorial Pacific/Peruvian upwelling zone during the 2015 El Niño event. Near the Peruvian coastline, apparent photosystem II photochemical efficiencies (Fv/Fm) were unchanged by nutrient addition and chlorophyll a tripled in untreated controls over 2 days,...

This thesis discusses sources and cycling of trace metals in tropical oxygen minimum zones. This thesis presents a new developed method for the analysis of a range of trace metals (iron, cadmium, nickel, zinc, copper, lead, cobalt and manganese) at trace levels in seawater. In the following chapters trace metal data from two distinct oxygen minimum...

Nutrient limitation of oceanic primary production exerts a fundamental control on marine food webs and the flux of carbon into the deep ocean. The extensive boundaries of the oligotrophic sub-tropical gyres collectively define the most extreme transition in ocean productivity, but little is known about nutrient limitation in these zones. Here we pr...

Nitrogen (N) is the major limiting nutrient for phytoplankton growth and productivity in large parts of the world's oceans. Differential preferences for specific N substrates may be important in controlling phytoplankton community composition. To date, there is limited information on how specific N substrates influence the composition of naturally...

In certain regions of the predominantly nitrogen limited ocean, microbes can become co-limited by phosphorus. Within such regions, a proportion of the dissolved organic phosphorus pool can be accessed by microbes employing a variety of alkaline phosphatase (APase) enzymes. In contrast to the PhoA family of APases that utilize zinc as a cofactor, th...

Supplementary Discussion, Supplementary Figures, and Supplementary References

A rapid, automated, high-throughput analytical method capable of simultaneous analysis of multiple elements at trace and ultratrace levels is required to investigate the biogeochemical cycle of trace metals in the ocean. Here we present an analytical approach which uses a commercially available automated preconcentration device (SeaFAST) with accur...

Hydrogen peroxide (H2O2) is present ubiquitously in marine surface waters where it is a reactive intermediate in the cycling of many trace elements. Photochemical processes are considered the dominant natural H2O2 source, yet cannot explain nanomolar H2O2 concentrations below the photic zone. Here, we determined the concentration of H2O2 in full de...

This study investigated the effect of intracellular micro-scale mass transfer on microbial carbon isotope fractionation of tetrachloroethene (PCE) and trichloroethene (TCE). Significantly stronger isotope fractionation was observed for crude extracts vs. intact cells of Sulfurospirillum multivorans, Geobacter lovleyi, Desulfuromonas michiganensis,...

Atrazine, propazine, and terbuthylazine are chlorotriazine herbicides that have been frequently used in agriculture and thus are potential drinking water contaminants. Hydroxyl radicals produced by advanced oxidation processes can degrade these persistent compounds. These herbicides are also very reactive with sulfate radicals (2.2-4.3 × 10 9 M - 1...