A Kiwi scientist is using coral to measure New Zealand’s ocean currents in one of the largest deep-sea coral reconstruction projects ever undertaken

Dr Dan Sinclair from Victoria University of Wellington’s School of Geography, Environment and Earth Sciences is leading two innovative research projects investigating past environmental changes in Earth’s ocean and rainfall systems.

What makes the projects unusual is the methods Sinclair is using to measure these changes – he is analysing the chemical makeup of long-lived deep-ocean corals and stalagmites to look into Earth’s past.

The use of corals to measure past changes in New Zealand’s ocean currents has its roots in Sinclair’s PhD project, where he used shallow-dwelling tropical corals to track changing land use in Australia. But the use of deep-sea corals is still a new area for Sinclair’s field of palaeoceanography.

“We’re only just scratching the surface of what we can learn from deep-sea corals,” he says. “One of the aims of my research is to show how useful these corals can be in measuring past oceanic changes.”

Sinclair is working with scientists at NIWA to map the changes using information contained in a particular type of coral. The coral they are using lives for thousands of years, giving the scientists a record of past environmental changes that doesn’t exist anywhere else.

“Some of these corals have lived for 4500 years,” says Sinclair. “In contrast, New Zealand’s instrumental and historic records only extend back a few decades to a century at most.”

The ancient corals deposit a tough protein ‘skeleton’ resembling a tree trunk. Just like in human hair and nails, these skeletons contain a chemical record of what the corals ate at different points in their lifetimes. By looking at what chemicals are present in the skeletons over time, Sinclair and his colleagues can determine the chemical makeup of the ocean at that time in history. This changing makeup helps them track nutrients, circulation and other changes in the ocean.   

Using NIWA’s extensive collection of deep-sea corals, Sinclair and his team plan to map ocean changes around the whole of New Zealand – possibly one of the largest deep-sea coral reconstruction projects ever undertaken, according to Sinclair.

“We know that the current changing climate is impacting ocean circulation, but we also know that oceans have naturally varied in the past,” he says. “By creating this map of past changes in New Zealand’s oceans, we can see what portion of current changes are historically normal for this area and what changes we should be concerned about.”

When he’s not looking at ancient corals, Sinclair is dissecting stalagmites to determine rainfall in the Pacific.

“Stalagmites are formed by water dripping into cave systems, so their growth is a useful way to track rainfall changes over time,” he says.

Sinclair can measure the changes in rainfall by analysing the changing ratio of two isotopes of oxygen present in each layer of a stalagmite – the more of a certain oxygen isotope there is, the heavier the rainfall at that time. The layers of the stalagmites are dated using the radioactive decay of naturally present uranium, so Sinclair can determine how old each layer of a particular stalagmite is to a very high precision, and thus how long ago certain changes in rainfall occurred.  

Sinclair is using this method to track the past movements of a weather system called the South Pacific Convergence Zone (SPCZ). This is one of the largest climate systems on the planet and is responsible for the rainfall on most of the Pacific Islands. For many of the islands, this is their only source of fresh water.  

“Climate models have been created that suggest global warming could cause this system to shift up towards the equator, moving completely away from these islands, but the models are still quite uncertain.”

By looking at stalagmite growth on different islands in the Pacific, Sinclair can track the movements of the SPCZ. He can then combine that information with models of past climate to see if these periods of lighter rainfall match movements in the SPCZ and so understand how it responds to rapid climate changes.

“There is currently very little information available about this area of the world, so this data will help us build a more complete picture of global climate systems,” he says. “By gaining a deeper understanding of the processes causing the SPCZ to move, we ultimately hope to be able to provide people in Pacific nations with information to help them better prepare for future climate changes.”

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