Anthropogenic changes to seawater buffer capacity combined with natural reef metabolism induce extreme future coral reef CO2 conditions. (26th February 2013)

• Record Type: Journal Article
• Authors: Shaw, Emily C.; McNeil, Ben I.; Tilbrook, Bronte; Matear, Richard; Bates, Michael L.
• Is Part Of: Global change biology. Volume 19:Number 5(2013:May)
• Page Start: 1632
• Page End: 1641
• Publication Date: 2013-02-26
• Subjects: Climatic changes -- Environmental aspects -- Periodicals; Troposphere -- Environmental aspects -- Periodicals; Biodiversity conservation -- Periodicals; Eutrophication -- Periodicals; 551.5
• DOI: 10.1111/gcb.12154
• Languages: English
• ISSNs: 1354-1013

Abstract

<abstract abstract-type="main" xml:lang="en" id="gcb12154-abs-0001"> <title>Abstract</title> <p>Ocean acidification, via an anthropogenic increase in seawater carbon dioxide (CO<sub>2</sub>), is potentially a major threat to coral reefs and other marine ecosystems. However, our understanding of how natural short‐term diurnal CO<sub>2</sub> variability in coral reefs influences longer term anthropogenic ocean acidification remains unclear. Here, we combine observed natural carbonate chemistry variability with future carbonate chemistry predictions for a coral reef flat in the Great Barrier Reef based on the RCP8.5 CO<sub>2</sub> emissions scenario. Rather than observing a linear increase in reef flat partial pressure of CO<sub>2</sub> (<italic>p</italic>CO<sub>2</sub>) in concert with rising atmospheric concentrations, the inclusion of <italic>in situ</italic> diurnal variability results in a highly nonlinear threefold amplification of the <italic>p</italic>CO<sub>2</sub> signal by the end of the century. This significant nonlinear amplification of diurnal <italic>p</italic>CO<sub>2</sub> variability occurs as a result of combining natural diurnal biological CO<sub>2</sub> metabolism with long‐term decreases in seawater buffer capacity, which occurs via increasing anthropogenic CO<sub>2</sub> absorption by the ocean. Under the same benthic community composition, the amplification in the variability in <italic>p</italic>CO<sub>2</sub> is likely to lead to exposure to mean maximum daily <italic>p</italic>CO<sub>2</sub> levels of ca. 2100 μatm, with corrosive conditions with respect to aragonite by end‐century at our study site. Minimum <italic>p</italic>CO<sub>2</sub> levels will become lower relative to the mean offshore value (ca. threefold increase in the difference between offshore and minimum reef flat <italic>p</italic>CO<sub>2</sub>) by end‐century, leading to a further increase in the <italic>p</italic>CO<sub>2</sub> range that organisms are exposed to. The biological consequences of short‐term exposure to these extreme CO<sub>2</sub> conditions, coupled with elevated long‐term mean CO<sub>2</sub> conditions are currently unknown and future laboratory experiments will need to incorporate natural variability to test this. The amplification of <italic>p</italic>CO<sub>2</sub> that we describe here is not unique to our study location, but will occur in all shallow coastal environments where high biological productivity drives large natural variability in carbonate chemistry.</p> </abstract>