Arctic more vulnerable to acidification

Research by ACE CRC chemical oceanographer Elizabeth Shadwick serves as a warning against generalisations about how the high-latitude polar environments will respond to climate change. Her work, with ACE Carbon Program leader Tom Trull, Dalhousie University oceanographer Helmuth Thomas and John Gibson from the Australian Antarctic Division, shows significant differences in the underlying characteristics of waters around the Arctic and the Antarctic. The Arctic is likely to experience more rapid changes in pH due to anthropogenic ocean acidification than the Antarctic due to lower alkalinity, warmer waters and nutrient limitation. This natural set-up means that carbonate undersaturation, which may inhibit the ability of organisms to form calcium carbonate shells, is likely to happen earlier in the Arctic than the Antarctic. Dr Shadwick’s research, which has been published in Nature Scientific Reports, compared one full year of data from coastal sites in Amundsen Gulf, in the Arctic, with Prydz Bay, in the Antarctic. “This is instructive because people like to make statements about high latitudes being susceptible, and that’s true, but there are some important differences between the poles,” Dr Shadwick said. She points out that this is not surprising when you look at a map and see the completely different land formations. “The Arctic Ocean is almost entirely surrounded by land - what that means is the Arctic has low salinity and low alkalinity because it has all this river inflow, and the much more open Southern Ocean has relatively higher salinity, even with seasonal ice melt, and correspondingly higher alkalinity.’’ Another notable aspect of the research was that it compared a full 12 months of data from each location. Logistical difficulties mean that polar samples are rarely taken through winter, but while working with the Australian Antarctic Division in 1994-95 Dr John Gibson spent the winter at Prydz Bay and collected samples throughout the year. Dr Shadwick and colleagues scaled that data (with respect to the rise in atmospheric CO2) to 2008 levels and compared it with 12 months of Arctic data collected in 2008 when a the Canadian icebreaker CCGS Amundsen ship spent 12 months in the Amundsen Gulf. “One of the most important things that we need to look at in making projections is the system at its most vulnerable point. Everyone goes in summer because logistically that’s easier, and also that is the period of maximum biological carbon uptake. But if you want to know the vulnerability to changes in CO2 because of anthropogenic emissions, you need the winter conditions because they represent the weak point when CO2 concentrations in the water are at their highest. “In winter it is really hard to make observations and that’s why these two datasets are special - they allow us to project from the period of low pH rather than from the high.” New work on CO2 concentrations at Australia’s Antarctic Davis Station has also just been published as part of the doctoral thesis work of Nick Roden in collaboration with Dr Bronte Tilbrook (CSIRO Marine and Atmospheric Research).

Authorised by the CEO of the Antarctic Climate and Ecosystems Cooperative Research Centre October 2019.

The ACE CRC was established and supported under the Australian Government’s Cooperative Research Centres Program.

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