Effects of ocean acidification on phytoplankton in upwelling areas influenced by river discharges

Barbara Jacob is currently a post-doctoral associate at the Aquatic Ecosystem Functioning Lab (LAFE) under the sponsorship of Dr. Cristian A. Vargas at the Environmental Science Center EULA Chile (Universidad de Concepción), Chile. Her research is focused on understanding the effects of ocean acidification on natural phytoplankton communities as well as on key algal species (flagellates vs. diatom species).

About 48% of carbon dioxide released to the atmosphere in the last 200 years has been caused by man (Raven et al., 2005). The oceans have absorbed nearly half of the fossil-fuel carbon dioxide (CO2) emitted into the atmosphere since pre-industrial times. This capacity causes the reduction in seawater pH and carbonate saturation, a process known as “ocean acidification”. Studies of the effect of ocean acidification on phytoplankton suggest that increasing the concentration of CO2 may stimulate phytoplankton growth rate or efficiency of resource utilization and hence alter the species composition of phytoplankton communities. Recent studies have shown effects of ocean acidification increases the dissolved inorganic carbon consumption of a natural plankton community with rising CO2 (Riebesell et al., 2007). Stoichiometric changes in the C:N ratio of the primary production to high pCO2 levels may affect the availability of labile carbon that could be used by heterotrophic microbial community, in terms of their utilization of the mineral nutrients, which in turn, can limit the primary production due to the reduction of mineral nutrients.

The Humboldt Current System (HCS) is the second most productive eastern boundary current after the Benguela Upwelling Ecosystem (Monteiro 2010). The HCS has shown variability in the pCO2 concentrations due to the CO2 sequestration by photosynthesis and the degassing associated with the upwelling of cold, oxygen-poor and strongly super- saturated CO2. And thus, the biological pump interacts with the physical processes promoting the exchange of CO2 in the ocean- atmosphere interface (Torres et al., 2002). Moreover, these ecosystems are affected by persistent or episodic input of acid water from rivers. The figure 1 shows the coastal upwelling ecosystem close to the Biobío river mouth, in the central-south of Chile. In this area, the favourable winds to the upwelling are present during the spring-summer seasons while, during winter the river freshwater discharges increase. Strong gradients and seasonal variability in the saturation state of the Aragonite (ΩAr) have been observed in the vicinity areas influenced by the Biobío river discharges in this region. During winter period, more acidic and under-saturated with respect to Aragonite waters reached a major longitudinal extension in the studied area, which suggests that regional changes in the carbonate chemical system depends on the interplay between the freshwater river inputs and the upwelling regime.

The main objective of this research is to determine – through field studies and laboratory controlled experimental conditions- the effect of the coastal ocean environmental variability on phytoplankton, in terms of changes in the carbonate system parameters influenced either naturally by river discharge or coastal upwelling. For this purpose, experiments will be designed to represent projections of the future carbonate system and assess the natural response of the key phytoplankton species (diatoms and flagellates), as well as natural phytoplankton communities from different environments.


Monteiro, P.M.S. (2010). The Benguela Current System. Pages 65- 78. In: Liu K-K, Atkinson L, Quiñones R, Mn Manus L (Eds.) Carbon and fluxes in Continental Margins. A global synthesis. The IGBP series Book. Springer-Verlag, New York, pp. 741.
Raven J.A., et al. (2005). Ocean acidification due to increasing atmospheric carbon dioxide. The Royal Society of London, Policy document 12/05, 60 pp.
Riebesell, U., et al. (2007). Enhanced biological carbon consumption in a high CO2 ocean. Nature letters 450: 545- 548.
Torres, R., et al. (2002). CO2 outgassing off central Chile (31- 30°S) and northern Chile (24- 23°S) during austral summer 1997: the effect of wind intensity on the upwelling and ventilation of CO2-rich waters. Deep Sea Research 49: 1413-1429.


This research is supported by FONDECYT (National Fund For Scientific and Technological Development), CONICYT-Chile.

Jacob B. & Vargas C. A., 2013. Effects of ocean acidification on phytoplankton in upwelling areas influenced by river discharges. SOLAS NEWS 15, Summer 2013: 29. Article.

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