Why study the Polar regions?
The colder the water, the more CO2 it absorbs, consequently, polar regions will be the first places where surface seawaters will become undersaturated with respect to aragonite, a form of carbonate ion used by marine organisms to make their shells and skeletons, and which decreases as CO2 invades the water. In the figure below, negative values (brown colours) indicate undersaturation, i.e. pure aragonite would dissolve. Figures a and b show the aragonite saturation state of surface waters when atmospheric CO2 reaches 567 ppmv (i.e. twice the pre-industrial value). Figures c and d shows the same combined with the effects of climate change, which intensify the phenomenon, especially in the Arctic where undersaturation will occur 10 to 30 years sooner than in the Antarctic. Ice melting in the Arctic will make wide areas of ocean available to take up atmospheric CO2. There will also be huge amounts of freshwater released which further increase acidification.For millions of years until the present day all surface and near subsurface waters were supersaturated with respect to aragonite. In 2008, we can already observe that near-subsurface waters in the Canada Basin have become undersaturated due to human CO2 emissions. The phenomenon continues at a rapid rate. Recent projections indicate that if CO2 emissions continue to rise as today, 10% of arctic surface waters will be undersaturated already by 2018, 50% by 2050 and 100% by the end of the century.
Arctic Ocean Southern Ocean (Antarctica)(J. Orr, 2008) Negative values (brown colours) indicate undersaturation, i.e. pure aragonite would dissolve. a-b shows the aragonite saturation state of surface waters when atmospheric CO2 reaches 567 ppmv (i.e. twice the pre-industrial value). c-d shows the same combined with the effects of climate change, which intensify the phenomenon, particularly in the Arctic where undersaturation will occur 10 to 30 years sooner and more intensely than in the Antarctic: ice melting in the Arctic will render wide areas of ocean available to take up atmospheric CO2, and release huge amounts of soft waters which also further increase acidification.
What do we want to learn & how?
How will the rapid transition to undersaturated waters affect Arctic calcifiers such as bivalve molluscs and their predators?
All marine calcifiers which are abundant on the Arctic shelf are potentially at risk. They serve as a major food source for walruses, grey whales, bearded seals, and spectacled eiders. In particular we want to find out where are the tipping points: what is the degree of resilience of life for the key species in the food chain? Before waters become permanently corrosive, there will be several years when undersaturation will happen only seasonly. During this key intermediate stage (also corresponding to the time-span where we can hope that policy measures will stop CO2 emissions), to which extent sensitive species will be able to recover when the conditions get back to normal, and for how long can they stand this seasonal stress?
How will changes acidification affect nutrient cycling in between the sediment and the overlying water?
Many marine organisms live in the soft sediment which covers the seafloor. Nutrients such as nitrate, phospate and silicate are important food source for phytoplankton. They can be transferred between the seawater and sediments. The organisms that live in the sediment not only rely on these nutrients as a food source but many also assist in the release or capture of nutreints to/from the seawater. We want to find out if the organisms are affected by ocean acidification, if acidification directly affects nutrient cycling, and if there are indirect affects from impacts on organisms?