Coral reveals mysteries of the past

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Diagram illustrating coral-coring process and core analysis. Photo courtesy of the Cohen Lab, Woods Hole Oceanographic Institution.

Scientists at the Australian Institute of Marine Science analyzed coral cores to understand how the coral reefs that are native to Western Australia are being affected by changes in water temperature and ocean currents.  The research was published by Nature Communications on April 1st.  The findings provide details about how a climate swing in the tropical Pacific, known as La Niña, affects the Leeuwin current and how our oceans are changing.  The Leeuwin current (LC) is affected by La Niña and often results in strengthened currents as well as high coastal sea levels and unusually warm sea surface temperatures.

There are not many long-term observations of the marine climate so the researchers used long coral cores.  Corals are similar to trees as their growth pattern forms rings which show annual growth, providing a record of the past.  The scientists obtained records of past sea temperatures by measuring the chemical composition of the coral from year to year.  Using this technique, the research team was able to find how changing winds and ocean currents in the Eastern Indian Ocean are driven by climate variability in the western tropical Pacific Ocean.  The long coral records allowed the scientists to look at these patterns of climate variability back to 1795 AD.

Using the long coral records, the team of researchers found that in addition to warming sea surface temperatures, sea-level and LC current strength have increases since 1980.  Another finding suggested that the strong winds and extreme weather of 2011 off Western Australia are highly unusual compared to the past 200 years.

The scientists found that this was clear evidence that global warming and sea-level rise is increasing the severity of these extreme events which impact the diverse coral reefs of Western Australia.  With these conclusions, it is likely that La Nina events will result in more warming and rising sea-level events that could have potential consequences to Western Australia’s unique ocean ecosystem.

 

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Journal Reference:

  1. J. Zinke, A. Rountrey, M. Feng, S.-P. Xie, D. Dissard, K. Rankenburg, J.M. Lough, M.T. McCulloch. Corals record long-term Leeuwin current variability including Ningaloo Niño/Niña since 1795Nature Communications, 2014; 5 DOI: 10.1038/ncomms4607

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