Ocean Acidity

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Photo above shows a large coccolithophore bloom east of New Zealand in an Ocean colour satellite image. Photo: NASA, processed by NIWA.

The Story: The oceans play an important role in reducing the impact of climate change, having absorbed a quarter of the additional carbon dioxide we have added to the atmosphere by burning fossil fuels. However there is a downside to this as the increasing dissolved carbon dioxide is causing a decrease in pH, known as ocean acidification, and a corresponding reduction in dissolved carbonate. Ocean acidity has already increased by ~30% since the late 19th century, and is projected to increase more rapidly than at any time in the past 25 Million years. The resulting changes in water chemistry will be particularly challenging for a range of different marine organisms. Some, such as phytoplankton and seaweeds, may benefit from increased dissolved carbon dioxide, which they use for photosynthesis, whereas other groups that use carbonate for shells and exoskeletons may suffer. In colder sub-Antarctic waters carbonate is lower than in warmer waters, and so some plankton that are important in the food chain, may be under threat as they will have to use more energy to maintain their carbonate shells. Similarly, cold water corals, which provide important habitat for invertebrates and fish larvae in deep water, may be unable to maintain their carbonate exoskeletons.

Coccolithophore phytoplankton that use have an outer layer of carbonate liths Photo: Hoe Chang NIWA

The Scientist: Cliff Law, Principal Scientist, Marine Biogeochemistry, NIWA. Our research involves time-series measurements of pH and carbon dioxide to determine the rate of ocean acidification in open ocean and coastal waters. In addition we carry out experiments on plankton and shellfish under low pH, and collect deep-water corals on the NIWA research vessel, Tangaroa, to examine the impacts of ocean acidification on New Zealand marine ecosystems.

Cliff working beside the Tangaroa Research Vessel.

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