Ocean acidification impacts on southern ocean calcifiers

• Main Authors: Howard, W, Roberts, D, Moy, AD, Roberts, JL, Trull, T, Bray, SG, Hopcroft, R
• Format: Conference Object
• Language: English
• Published: IOP Publishing Ltd 2009
• Subjects: Earth Sciences; Atmospheric Sciences; Climate Change Processes; Southern Ocean; Ocean acidification; Planktonic foraminifera
• Online Access: http://journals.iop.org/; http://ecite.utas.edu.au/56382

Adding carbon dioxide (CO2) to the ocean alters the carbonate chemistry and lowers pH, making surfacewaters more acidic and decreasing the carbonate ions available to calcifiers for calcite and aragoniteproduction. Both forms of calcium carbonate dissolve more easily under conditions of higher CO2, lowertemperatures and higher pressures due to depth. As the uptake rate of anthropogenic CO2 is at a maximumin the Southern Ocean we have a unique opportunity to observe marine calcifiers responses to changingcarbonate chemistry. The Southern Ocean provides an excellent setting for the analysis of current and pastocean carbon-cycle changes because it crosses major surface-ocean gradients in carbonate chemistry andcalcium carbonate production and spans the latitudes of maximum oceanic uptake of anthropogenic CO2.Through in situ sustained monitoring sediment traps deployed in the Southern Ocean we infer a reduction incalcification of one morphotype of shelled pteropod of ~ 35% over the past decade, consistent with thecontinuing lowering of aragonite saturation. Through a comparison of surface-sediment foraminifera,representing pre-industrial conditions, and modern foraminifera collected in sediment traps, we estimate a ~38% reduction in calcification since the industrial revolution. Planktonic foraminifera preserved insediments are the same species living in the modern ocean, and provide a pre-industrial baseline to estimatethe effects of acidification on shell formation in the modern high-CO2 ocean. As the magnitude of theanthropogenic CO2 increase is similar to deglacial increases in CO2, the geological record provides a meansof scaling for the ecological response to ocean carbonate chemistry changes. The recent reduction incalcification is similar to deglacial calcification changes during the Late Pleistocene. The responses of theseSouthern Ocean calcifiers represent one of the earliest sets of field evidence of the impacts of CO2 onpelagic ecosystems. Furthermore, as the Southern Ocean contains a disproportionate amount of the oceanicinventory of anthropogenic CO2 it is a biogeochemical harbinger for the impacts of acidification, which willspread throughout the global ocean. Our results point to the importance of field observations on marineecosystems as the ocean continues to absorb CO2 as a means of detecting impacts as early as possible.