Andrea Noche Ferreira

• Suessle, Philipp; Taucher, Jan; Goldenberg, Silvan Urs; Baumann, Moritz; Spilling, Kristian & Ferreira, Andrea Noche [Show all 8 contributors for this article] (2025). Particle fluxes by subtropical pelagic communities under ocean alkalinity enhancement. Biogeosciences. ISSN 1726-4170. 22(1), p. 71–86. doi: 10.5194/bg-22-71-2025. Full text in Research Archive Show summary

  Ocean alkalinity enhancement (OAE) has been proposed as a carbon dioxide removal technology (CDR), allowing for long-term storage of carbon dioxide in the ocean. By changing the carbonate speciation in seawater, OAE may potentially alter marine ecosystems with implications for the biological carbon pump. Using mesocosms in the subtropical North Atlantic, we provide first empirical insights into impacts of carbonate-based OAE on the vertical flux and attenuation of sinking particles in an oligotrophic plankton community. We enhanced total alkalinity (TA) in increments of 300 µmol kg−1, reaching up to ΔTA = 2400 µmol kg−1 compared to ambient TA. We applied a pCO2-equilibrated OAE approach; i.e., dissolved inorganic carbon (DIC) was raised simultaneously with TA to maintain seawater pCO2 in equilibrium with the atmosphere, thereby keeping perturbations of seawater carbonate chemistry moderate. The vertical flux of major elements, including carbon, nitrogen, phosphorus, and silicon, as well as their stoichiometric ratios (e.g., carbon-to-nitrogen ratios), remained unaffected over 29 d of OAE. The particle properties controlling the flux attenuation, including sinking velocities and remineralization rates, also remained unaffected by OAE. However, we observed abiotic mineral precipitation at high OAE levels (ΔTA = 1800 µmol kg−1 and higher) that resulted in a substantial increase in particulate inorganic carbon (PIC) formation. The associated consumption of alkalinity reduces the efficiency of CO2 removal and emphasizes the importance of maintaining OAE within a carefully defined operating range. Our findings suggest that carbon export by oligotrophic plankton communities is insensitive to OAE perturbations using a CO2 pre-equilibrated approach. The integrity of ecosystem services is a prerequisite for large-scale application and should be further tested across a variety of nutrient regimes and for less idealized OAE approaches.

• Spilling, Kristian; Heinemann, Malte; Vanharanta, Mari; Baumann, Moritz; Ferreira, Andrea Noche & Suessle, Philipp [Show all 7 contributors for this article] (2023). Respiration rate scales inversely with sinking speed of settling marine aggregates. PLOS ONE. 18(3). doi: 10.1371/journal.pone.0282294. Full text in Research Archive Show summary

  Sinking marine aggregates have been studied for a long time to understand their role in carbon sequestration. Traditionally, sinking speed and respiration rates have been treated as independent variables, but two recent papers suggest that there is a connection albeit in contrasting directions. Here we collected recently formed (<2 days old) aggregates from sediment traps mounted underneath mesocosms during two different experiments. The mesocosms were moored off Gran Canaria, Spain (~ 27.9 N; 15.4 E) in a coastal, sub-tropical and oligotrophic ecosystem. We determined the respiration rates of organisms (mainly heterotrophic prokaryotes) attached to aggregates sinking at different velocities. The average respiration rate of fast sinking aggregates (>100 m d-1) was 0.12 d-1 ± 0.08 d-1 (SD). Slower sinking aggregates (<50 m d-1) had on average higher (p <0.001) and more variable respiration rates (average 0.31 d-1 ± 0.16 d-1, SD). There was evidence that slower sinking aggregates had higher porosity than fast sinking aggregates, and we hypothesize that higher porosity increase the settlement area for bacteria and the respiration rate. These findings provide insights into the efficiency of the biological carbon pump and help resolve the apparent discrepancy in the recent studies of the correlation between respiration and sinking speed.

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