Acid on Ice: Present Ocean pH Dynamics and Studies of Antarctic Marine Invertebrates

The Southern Ocean may be particularly vulnerable to ocean acidification and we expect it to be one of the first regions of the global ocean to experience ecological impacts as a result. This is primarily because CO₂ dissolves more readily in colder water.  As a result, calcium carbonate concentrations and pH in high-latitude oceans will decrease more rapidly, making it more difficult for marine species to form shells and other calcium carbonate structures. In the Antarctic, sea urchins are a key member of the invertebrate community and serve as an excellent model to study global change biology such as the impacts of ocean acidification.  In this presentation, I will describe recent research conducted in the Ross Sea, Antarctica that used larval sea urchins and their developmental response to various CO₂ conditions as a means to highlight the resilience of calcifying marine animals in Antarctic waters. We also present the first high-resolution observations of pH from beneath fast sea ice anchored to the Antarctic coast of the southern Ross Sea during the austral spring. pH Sensors called SeaFETs were deployed at our study sites. During these deployments in McMurdo Sound, baseline pH ranged between 8.019-8.045, with low to moderate overall variation (0.043-0.114 units) on the scale of hours to days, a level of variation that is much lower than other parts of the worlds oceans such as coastal regions or coral reefs. These pH data were used to provide a real environmental context for laboratory experiments and set a baseline to compare ambient levels of CO₂ to projected near-future increases. We found that calcifying larval sea urchins were vulnerable to moderately elevated pCO₂, and display smaller body and skeleton sizes. Lowered calcification rates and subtly altered physiology during development may explain the observed changes in size.  Together, data on the natural variability of pH at our study site in the Antarctic and the changes in sea urchin physiology suggest that calcifying invertebrates in the Southern Ocean may be challenged by future ocean conditions. And further, given the large area of the Southern Ocean, any ecological consequences are likely to have a large geographic extent.