A highly advanced ocean sensor is back on land after spending more than a year monitoring the waters of the Labrador Sea.

The SeaCycler was being used in a group venture involving Canadian scientists and teams from Germany and the Scripps Institution of Oceanography in San Diego.

The device has sensors that measure oxygen, carbon dioxide, nutrients, salinity and temperature. 

"It's the only one of its kind in the world so it is a very unique machine and we are very happy to have it back and in perfect condition," said Doug Wallace, a Dalhousie University oceanography professor.

Three on-board computers control the SeaCyler's winch, data handling and transmissions from the ocean surface. When commanded, the sensor — which had been moored 150 metres below the ocean surface — floats up through the water, taking measurements along the way.

Once on the surface, a small antenna transmits the data to a satellite.

A few glitches

Greg Siddall, a Bedford Institute of Oceanography engineer, worked closely with Dalhousie and the rest of the support team on the SeaCycler deployment.

"All of its 29 sensors worked well and collected data from the very surface of the ocean to a depth of 3.4 kilometres below," said Siddall in an email.

He was on board the RV Maria S. Merian when SeaCycler was pulled out of the water in late June.  

"The sensors ... recorded millions of measurements throughout the entire 401-day deployment."

SeaCycler ocean sensor

The latest mission gives the SeaCycler a passing grade. (Oliver Zielinski/University of Oldenburg, Germany)

SeaCycler was expected to transmit every 20 hours over the 14 months but there were a few glitches along the way.

"Sometime in February it stopped reaching the surface for reasons we are still trying to find out, so it didn't send the data back by satellite," said Wallace. "But we have confirmed it did record the data internally until it was recovered."

The latest mission gives the SeaCycler a passing grade.

This was the 14th time it was deployed and it was by far its longest and toughest test to date. The initial deployment in the Labrador Sea failed in September 2015 when a cable malfunctioned.

Device recovered in 'spectacular condition'

This time around, the machine survived the elements, including strong ocean currents and 12-metre waves.

"The equipment was recovered in spectacular condition with minimal corrosion and very little bio-fouling [marine growth], considering its long stay underwater in such a hostile environment," said Siddall in an email.

The Labrador Sea has been described as the "lungs of the ocean."

It is one of the few places in the world's oceans where the deep ocean exchanges oxygen and carbon dioxide directly with the atmosphere. Here, oxygen-rich surface water becomes so dense it sinks into the deep ocean, where it is dispersed.

The data collected will help scientists understand how the deep ocean exchanges carbon dioxide, oxygen and heat with the atmosphere.

'Efficient' use of ship time

Siddall said funding through Dalhousie's Ocean Frontier Institute, German research institutions and the federal Department of Fisheries and Oceans has been approved. It includes money to refurbish the current SeaCycler prototype and build a second unit for deployments in 2018 and 2019.

"Maintaining long time-series measurements is the key to understanding the very complex ocean environment and each SeaCycler research effort really needs a second unit ready to deploy whenever one is recovered," said Siddall.

"Not only is this a good research strategy, it's also an efficient use of expensive ship time."