16.07.2014 - Natural Sciences Sector

Tracking the pulse of the Ocean

Image: LEARNZ. Deployment of a ‘Deep’ Argo by NIWA’s research vessel Tangaroa, east of the Kermadec Trench, June 2014.

The Argo programme is testing new technology that will give us a deeper understanding of the ocean’s role in global processes such as climate change. The National Institute of Water and Atmospheric Research (New Zealand) launched two deep Argo prototypes successfully in an effort tracked for educational purposes. Although monitoring and being able to predict the role played by the ocean is key to understanding – and preparing for – climate change, very little data was available until recently. Initiatives such as the Global Ocean Observation System (GOOS) and one of its key components, the Argo programme, are revolutionizing our understanding of the ocean’s role in our climate, and its response to the greenhouse effect.

Argo allows us to look below the surface, providing a profile of the temperature and salinity of the ocean. A global array of over 3,600 profiling floats are moving up and down in the water column, every 10 days, measuring temperature, salinity, and depth from 2,000 m depth to the sea surface. The array is maintained through international cooperation to sustain observations over time, providing an unprecedented dataset to study variations over periods ranging from days to decades. The data collected is freely available and widely distributed. The Argo mission has transformed our understanding of the ocean's role in climate as well as our weather and climate prediction systems.

The Argo project has already confirmed that the ocean is warming at depth, and that that warming signal is particularly pronounced in the Southern Hemisphere. “There’s been a lot of coverage over the so-called pause” said Dean Roemmich, an oceanographer at the Scripps Institution of Oceanography of the recent apparent slowing of atmospheric warming. “The short story is that the surface temperature of the ocean is highly variable. Whereas when you start looking at the heat content, the average temperature of the ocean down to 2,000 metres, rather than seeing a pause we’ve seen a steady warming continue at the same rate for the last 50 years”. He explained that the ocean has so far buffered us from some impacts of climate change because they have taken up 93% of the excess heat.

But the ocean is deep, and we need to know what happens below 2,000 m, out of the reach of the current floats. In order to expand our knowledge, ‘Deep’ Argo floats are being tested to drop almost to the ocean floor, to almost 6,000 m, equipped with advanced sensors to track temperature and salinity and with an antenna to communicate to a satellite. The floats have been re-designed: unlike their predecessors, they are ball-shaped to withstand higher pressure. They were developed at Scripps Institution of Oceanography in collaboration with the company Sea-bird Electronics, which developed the sensors.

For the first time, two ‘Deep’ Argo floats were deployed by NIWA’s research vessel Tangaroa east of the Kermadec Trench in June 2014; they made their first successful dive, transmitting data collected from a depth of over 5,000m to the surface. "This is really leading-edge emerging technology that will, for the first time, allow us to fill in the gap in data between 2000m and the sea floor," said NIWA oceanographer Phil Sutton.

The LEARNZ platform tracked the launch, taking students on a virtual field trip on the research vessel that included videos each step, interviews and live conversations with the crew. Following this successful mission, the team plans to be back next year to deploy more deep-diving Argo floats in the south-west Pacific.

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