Challenger expedition reveals ocean warming

Apr 8, 2022

By Philip Pearson

Challenger, the great ocean expedition of the 1870s, is now providing evidence to support the UN’s urgent warnings this week (5 April) that ‘It’s now or never’ if the world is to stave off climate disaster. The evidence is brought together for the first time on my website:

The UN report says:

From 1872–76, the research ship HMS Challenger measured global ocean temperature profiles at depths up to 1700 meters along its cruise track… Comparing the HMS Challenger data to data from Argo submersible floats revealed global subsurface ocean warming on the centennial scale.

My book, A Challenger’s Song , tells the story of the Challenger expedition, the greatest scientific voyage of the Victorian era, and the life of its crewman, my ancestor Charlie Collins.

Charlie was one of over 230 crew – officers, six eminent scientists, marines, Able Seamen like Charlie (the leading stoker), and 50 Boy Sailors. The expedition’s mission was to study the oceans from all aspects – temperature, water samples, marine life, ocean depths – using immensely long sounding ropes to lower equipment into the ocean. She was away for over three and a half years, covering 68,980 nautical miles.

Though the voyage was a massive scientific undertaking, ‘The work was too hard and the sea time so long,’ as one sailor wrote home. Yet they would never have been able to anticipate the value today of such work as they undertook on 8 September 1875, as Challenger stood, head to a light breeze, the steam propellers idling gently to hold her still. They’d reached Sounding Station number 272, in the middle of the Pacific Ocean.

Sounding Station 272, mid-Pacific Ocean, one of Challenger’s 354 sounding points. Source: Nature magazine, 2020.

At 4 am the scientists and crew began lowering their equipment into the sea to record the ocean’s depth (2,600 fathoms, or 15,600 feet), trawl the sea floor for marine specimens, and test the water temperature and salinity. Their findings were unique at the time. But today, 150 years later, their simple but pioneering, hand-made measurements have become benchmarks to study changes to the ocean driven by climate change and man-made carbon emissions since the industrial revolution.

To gather samples that day, the crew lowered a cable nearly three miles long to the sea floor. Weights, sampling bottles, thermometers and a trawling bag were attached to the line, with coloured flags at intervals to count out the length of line the crew paid out.

The specimens they reviewed are foraminifera, minute, millimeter-sized single cell organisms with a thin shell usually made from calcium carbonatesuch as these. 

Source: British geological Survey

Ocean acidity

Scientists at the Natural History Museum have compared the Challenger’s collection of minute single-cell specimens (foraminifera) retrieved on that day, 8 September, 1875, and carefully stored, with modern samples of the same species taken from the same part of the Pacific Ocean by the Tara expeditions. 

  • The organisms are now failing to build shells of the same thickness, due to increasing ocean acidity.
  • All modern specimens had up to 76% thinner shells than their historic counterparts, which corresponds to a period of profound change in our oceans.

As CO2 levels continue to rise, more of the gas dissolves into the world’s oceans. As the waters become more acidic, the smallest organisms at the bottom of the food chain are beginning to struggle.

Ocean temperature

The longest interval over which records of ocean temperatures can be compared on a global scale is the 135 years between the voyage of HMS Challenger and the modern data set of the Argo Programme (2004–2010). 

  • The study, the first global-scale comparison of Challenger’s 354 soundings with modern data, showed average warming at the surface waters of the ocean of some 0.6 degrees Centigrade.
  • Warming in the Atlantic Ocean was found to be stronger than in the Pacific Ocean. 

Yet, as The Guardian reports , UN member states are struggling to agree a new binding Treaty to protect the oceans from exploitation, with scientists, environmentalists and conservation organisations blaming states that were ‘dragging their feet’ for the ‘glacial pace’ of talks. One aim is to create vast marine-protected areas. 

It seems that industrial-fishing, deep sea mining and oil interests, along with nations like Iceland and Russia, are obstructing progress towards a global Treaty for the Ocean. Sounds so familiar.

So please help Greenpeace reach 5 million signatures on their petition for a Global Ocean Treaty.