How deep are the oceans?
What is the bottom of the deep ocean made of?
Does life exist at the bottom of the ocean?

These were the questions that scientists were asking themselves in the 19th Century and to answer them they organised the first systematic study of the deep seas.

The Challenger Expedition 1872 -1876

In December 1872 the British Navy corvette H.M.S. Challenger left from Portsmouth on the first leg of a three and a half year expedition to explore the deep seas. On loan from the admiralty to the eminent scientific gentlemen of the Royal Society of London, the Challenger had a total ships company of 240, including six civilian scientists led by Prof. Charles Wyville Thompson, F.R.S. The Challenger expedition was the first systematic study of the deep seas and began a new era in marine exploration.

Charles Wyville Thomson, FRS


HMS Challenger

 Thompson described the Challenger (pictured left) as having "the accommodation of a frigate and the handiness and draught of a corvette". Extensive alterations were carried out on the 2,306 ton corvette, all but two of the cannons were removed freeing up space for the storage of sample bottles and sounding cables and two laboratories were fitted out for chemistry and natural history studies.
Before the mid 19th century the deep ocean was an unknown and unreachable environment. Scientists believed that at water depths below 300 fathoms (550metres) the darkness, cold and pressure made life impossible.

In 1841 the British naturalist Edward Forbes sailed on the British Survey ship Beacon. The Beacon had been sent to chart the waters of the Mediterranean and Aegean Sea, and Forbes used this opportunity to dredge up samples from water depths never previously reached. Forbes shared with his fellow scientists of the time the belief that beyond 300 fathoms the mysterious dark depths of the seas was a baren lifeless area and he named this the Azoic (lifeless) zone.


The British naturalist,
Edward Forbes


The natural history laboratory aboard HMS CHallenger
 
Since ancient times mariners had realised that a knowledge of the depth and shape of the seafloor was needed to navigate and explore the oceans. The first measurement ever made at sea was probably the measurement of depth using a rope with a weight on the end.
Things had progressed little by the mid 19th century and the basic principal was much the same. A rope with a weight on the end was still being used but instead of counting knots tied in the rope to give the depth of line out, a mechanical sounding machine lowered the rope and recorded the length on a counting wheel.
Scientists were not only interested in the depth they wanted to know what deposits made up the seafloor. They realised that the sounding weight could be adapted to take and bring back a sample of the seafloor. This led on to the construction of the first simple grab samplers and seafloor coring samplers.
The Challenger scientists had two basic methods of sampling the seafloor. One was the sounding sampler which would bring back a spot sample at the same time as taking a sounding and the other was to dredge the seafloor. The dredge was dragged across the seafloor scraping up material into a net bag, the mouth of which was constructed from strong steel scrapers.
The Baillie Sounder (right) was the sounding sampler used on the Challenger expedition. The sounder acted as a simple sounding weight pulling the sounding rope to the bottom. When the sounder hit the bottom the hollow tube would fill with sediment and the wire holding the weights would release. This would drop the heavy weights and the tube with a small sample of the seafloor would be pulled back to the ship.
These simple sounders were the precursors of the highly specialised and sophisticated coring systems we used today.

The dredge (below) was used to sample areas of hard and irregular seafloor.

Between departure from Sheerness on the 7th of December 1872 and arrival at Spithead on the 24th of May 1876, the Challenger traversed a distance of 68,890 nautical miles and at uniform intervals established 362 observing stations.
At each of these stations the ship stopped and a series of standard observations were made, one of which was to obtain a sample from the seafloor. This was the first time that anyone had sampled the deep seafloor in a systematic manner.

The dredge used on the Challenger

Two crew members empty a dredge haul
onto the Challenger deck




© BOSCORF 2007