One of the world’s top scientific research ships which has just finished investigating the Hikurangi subduction zone east of Gisborne will head for Antarctica this weekend to find out how warming oceans will affect the ice sheets, changes to sea level, and global weather systems.
The 140m-long JOIDES Resolution is in New Zealand waters for about 18 months undertaking a series of expeditions to study earthquakes, climate change, and submarine volcanoes.
It operates under the 23-nation International Ocean Discovery Program (IODP), of which New Zealand is a member. Its voyages in New Zealand span the main IODP research themes - climate and ocean change, geological hazards, deep Earth processes, and ocean and subseafloor life.
During its just-completed six-week voyage off the East Coast, the ship drilled between 200m and 750m beneath the seafloor at six locations ranging from 30km to 100km east of Gisborne to obtain information about the physical properties of the Hikurangi subduction zone.
This subduction fault is known internationally for a phenomenon known as slow-slip events. This is a type of creeping behaviour on the fault beneath the seafloor. It involves small bursts of movement on the fault lasting from weeks to months instead of seconds to minutes as in conventional large earthquakes.
First discovered in 2002, slow-slip events occur regularly at 12 to 18-month intervals along the North Island’s east coast and involve up to 35cm of horizontal movement over many weeks. Before their discovery, it was believed large subduction faults were completely locked between big quakes.
Slow-slip events are not felt by humans and can only be detected by permanently positioned GPS instruments that pick up small changes at the surface.
They are poorly understood and scientists want to know what causes them and what relationship they have with large earthquakes.
Understanding the mechanisms behind these ‘tightly coupled’ and ‘loosely coupled’ zones along the length of the subduction fault is not only important for New Zealand, but also the rest of the world.
Co-leader of the just-completed voyage, Phil Barnes of NIWA, said sophisticated instruments obtained valuable information from the boreholes that were drilled into the subduction zone east of Gisborne.
Scientists would spend months analysing this information to better understand the conditions inside the fault zone, Dr Barnes said.
A fresh group of 30 scientists from 11 countries moved onto the ship in the past two days and will set off from Lyttelton on Sunday for the Ross Sea to spend nine weeks drilling holes beneath the seafloor to examine polar climatic conditions going back 20 million years.
Voyage leader, Rob McKay of Victoria University of Wellington, says the aim was to understand how the ocean and the ice sheets interact.
“We want to find out what happens when you put warm water next to the ice sheets. How quickly do they melt? And what’s the impact of that melt on the oceans?"
By drilling down up to 1km beneath the seafloor, the team will be able to get a glimpse into ‘greenhouse worlds’ that existed 20 million years ago when carbon dioxide levels were similar to those currently in our atmosphere.
"Using these geological records to see what the planetary response was to the current carbon dioxide levels means we can better understand what the scale of change could be for us, and what the Earth is capable of in a warmer world," says Dr McKay, an associate professor at Victoria’s Antarctic Research Centre.
He says Antarctica today acts as a giant heat-sink that helps regulate the temperature of the planet.
“If you change that, you’re changing a major part of the global climate system. We’re trying to understand what happened the last time that was changed."
If the West Antarctic Ice Sheet were to melt, as it has in the past, Dr McKay says the global sea level would rise about 3 metres.
The impact from the collapse of the much larger Eastern Antarctic Ice Sheet would be even more dramatic, as it contains enough ice to cause an estimated 20-metre rise in global sea levels.
"The consequences of that for coastal living, globally, are obvious, but we’re also trying to understand the implications for the biosphere in the Southern Ocean. This is one of the largest biological habitats on the planet and we don’t know how it will respond to these changes."
When the JOIDES Resolution returns from the Ross Sea in early March it will stop at Lyttelton again and pick up a fresh crew of scientists and head back to the East Coast for a further probe of the Hikurangi subduction zone east of Gisborne.
New Zealand participates in the IODP through a consortium of research organisations in New Zealand and Australia including GNS Science, NIWA, The University of Auckland, Victoria University of Wellington, and University of Otago.