Exploring the oceans

Click here to see a fab graphic of ocean exploration!

Most of the developments in the techniques of exploring the seafloor have been witnessed over the last 150 years. However, it is known that the Vikings – such as Eric the Red, used 'sounding weights'. These were lead weights attached to a rope – or line, which were lowered to the bottom from the side of the boat. Often, the weight had a hollow bottom so a sample of the sediment could be collected. It was a straightforward matter to measure the length of line lowered in order to estimate the depth. The line length was divided up into sections which were equal to a man's arm span from fingertip to fingertip, a length of 1.83m [6 feet], this measurement was called a fathom, a term which is still used today. This method, of taking 'soundings', was used until the mid 1800s. During the mid 19th century governments and scientists launched systematic surveys of the world's oceans.

The ALVIN submersible at WHOI

Deep-sea exploration is a difficult process even with today’s technology.  The great depths that scientists want to learn more about present serious equipment challenges.  To find out what the deep-sea floor looks like, what the current conditions and seawater chemistry are like, and what animals live there requires a range of sophisticated equipment that must be able to withstand the great pressure associated with depth.  Manned and unmanned submersibles, trawls, corers, dredges and towed camera platforms are just some of the equipment used in deep-sea research and can require a whole technical team just to keep them running!

But today’s scientists have it relatively easy.  Deep-sea exploration began in the 19th century when ships were still powered completely under sail.  Compare that to today’s research ships that have enormous engine rooms to keep them going and dynamic positioning systems to make sure the ships stay in position around particular sites!

Deep-sea exploration really started off with a series of expeditions to measure the depth of the ocean using lead sounding lines in the early 19th century.  Thin ropes with a lead weight (called a “plummet”) at the bottom were dropped off ships to estimate the depth of the water.  Sometimes the lead weight had a recess built into it that was filled with a sticky substance called tallow – this would pick up a small sample of the sediment underneath the ship (e.g., mud or sand).  Both the depth and sediment information were used for the ship to navigate safely.

In 1818 Sir John Ross, uncle of Sir James Clark Ross (a famous marine explorer), took part in an expedition to locate the northwest passage in the Arctic Ocean, and, whilst carrying out sounding surveys he pulled up a basket star (a relative of the starfish) from 1.6 km depth.  Years later, on an expedition to the Southern Ocean, his nephew James found lots of animals living at 1.8 km depth on the Antarctic continental slope.  Discoveries like these, including those by Norwegian father and son, Michael and G.O. Sars, of animals living at the bottom of deep Norwegian fjords, filled Victorian scientists with excitement and sent them looking for more deep-sea animals.

However, many scientists at this time believed that the deep sea was an empty, barren place.  They thought that the darkness, cold, and great pressure would prevent life from flourishing, and some studies seemed to confirm this theory.  Scientist Edward Forbes carried out research in the Aegean Sea between 1841-1842, dredging the seabed for deep-sea fauna, but he didn’t find very much.  In 1843 he published his “azoic hypothesis” – that beyond 0.6 km depth there was no life.  We now know that Forbes was just a bit unlucky – this particular area of the Aegean deep sea is quite sparsely populated.  Had he carried out his research somewhere else it might have been a different story.  As it happened, his theory created a lot of controversy amongst scientists, and luckily, fuelled more deep-sea research.  Charles Wyville-Thompson and a contemporary, W.B. Carpenter, went on to carry out research in the deep waters off northwest Britain and the Iberian Peninsula aboard the HMS Lightning (1868) and the HMS Porcupine (1869 and 1870).  They collected sediments from 4.3 km depth, and found that the clay ooze they collected was almost entirely made up of the skeletal remains of plankton.

HMS Challenger

The Challenger expedition was carried out shortly afterwards, between 1872 – 1876, and is perhaps one of the most famous in early deep-sea exploration because it laid the foundations for what we know today.  Prior to the Challenger expedition very little was known about the shape of the deep-sea floor or its fauna.  Charles Wyville-Thompson was part of this expedition as well, in his role as the chief scientist onboard.  On its ~ 130,000 km journey, the HMS Challenger carried out a series of sounding surveys providing the most comprehensive view of the deep-sea floor to date and discovered ~ 4,700 species new to science!  Some of the newly discovered fauna came from trawls taken at over 5 km depth.

Deep-sea scientific research continued to grow after the Challenger expedition, and as technology developed, so did scientist’s view of life in the depths.  Photography, invented in the mid-19th century, soon found its way underwater.  By 1900 a French biologist called L. Boutan had published a book of his underwater photographs.  American scientists M. Ewing and J. Worzel went on to develop the first free-floating remotely operated camera in 1939, and became the first to use underwater photography to investigate underwater environments and processes.  Between 1939-1946 their research group (Woods Hole Oceanographic Institution) invented new features for the camera such as bottom-contact triggering – where the camera would take a photograph when it made contact with the seafloor – and the use of the camera on a platform that could be towed at depth behind the ship.  Photography nowadays plays a large part in deep-sea research, helping scientists to understand everything from how animals use a particular space over time (using “time-lapse” photography) to what the seafloor might be made of.

The last major deep-sea frontier was broken between 1950-1952, when the Danish research ship, the Galathea, collected sediment and animals from 10.19 km depth in the Philippine Trench.  At this depth the pressure is about 7 tons per square inch – that’s equivalent to two elephants sitting on your head!  The expedition proved that animals could survive at this depth – the sample they collected contained mussels, shrimps, and even sea anemones!