Scientists predict that a consequence of ocean acidification, where seawater pH is reduced by the invasion of carbon dioxide from human activities, is that marine organisms that produce calcium carbonate shells (e.g. corals, some algae and molluscs) will find it more difficult to survive. A new paper just published in the journal Nature Climate Change (http://www.nature.com/... subscription required) reports that long-term changes in the abundance and distribution of calcifying organisms are more driven by increasing seawater temperature than by the accompanying ocean acidification. The paper highlights the complexity of determining ecosystem response to ongoing climate change where multiple factors (temperature, salinity, pH etc.) conspire to influence important biogeochemical processes in our oceans.
This represents my first contribution to Daily Kos and, so, I wanted to highlight a recent paper published in the scientific journal Nature Climate Change by Gregory Beaugrand of CNRS, Laboratoire d’Océanologie et de Géosciences in France and colleagues. The paper aims to address one of the more pressing questions facing scientists who study ocean chemistry and the physiology of marine microbes: how will ocean acidification, where seawater pH is lowered by the invasion of anthropogenic carbon dioxide, impact the abundance and distribution of calcifying organisms in the sea. Calcifying organisms, like corals, some molluscs and marine algae called coccolithophorids, secrete shells made of calcium carbonate around themselves. The growth and accumulation of the shells of these organisms over geologic time has produced easily recognized limestone formations and landmarks like the White Cliffs of Dover in southwest England. Now as ocean acidification progresses seawater chemistry changes in a way that makes the production of these shells more difficult because calcium carbonate is more soluble in low pH seawater.
This paper reports that changes in the abundance, frequency and distribution of important calcifying plankton in the North Atlantic are primarily driven by increasing oceanic temperature. The authors consider data on organism abundance and distribution collected by the Continuous Plankton Recorder Survey and use principal component analysis to examine how sea surface temperature, seawater pH and the partial pressure of carbon dioxide (pCO2) correlate with long-term (1960-2009) trends in the frequency of occurrence, abundance, and spatial distribution of calcifying organisms. Changes in the abundance and distribution of calcifying plankton will impact the ecology, predator-prey relationships and biogeochemical cycles of the major elements (e.g. carbon). Much attention has been paid to the potential of ocean acidification, where surface seawater pH decreases in response to the invasion of anthropogenic CO2 (a weak acid), to diminish the ability of plankton to precipitate calcium carbonate. The increases solubility of calcium carbonate at low pH, and reduced calcification of some marine plankton, has been demonstrated by a number of acute exposure experiments (where pH is manipulated) with laboratory isolates and natural assemblages.
The authors suggest that the response of calcifiers to levels of acidification presently experienced or expected in the coming decades is weak relative to the over-riding influence of high ocean temperature. Indeed, the frequency and distribution of important planktonic calcifiers like the coccolithophorid Emiliania huxleyi have increased and expanded since a temperature induced regime shift in 1996. The paper highlights the complexity of determining ecosystem response to ongoing climate change where multiple factors (temperature, salinity, pH etc.) conspire to influence important biogeochemical processes.