Grasping the scale of earth's oceans

In the early 1960s my life's heroes were in their prime.
Hans Haas was using military diving gear to film his fabulous shark documentaries. Mike Nelson was up to his neck in Sea Hunt adventures, saving downed jet pilots; and beautiful women were hiring Mike for diving lessons.
And Jacques Cousteau had co-invented Scuba diving, written the Silent World and was exploring the world's seas on the ultimate diving expedition on Calypso.
I had just failed my Eleven Plus, hated school, loved the sea and knew nothing. Except that I wanted to be a diver.
And why not? How can anyone resist the urge to explore our oceans? A glance at some of the facts is all we need:
The oceans contain over 99% of the living space on the planet
Scientists estimate that there are at least a million new species to be discovered in the deep oceans
Oceans cover 71% of our planet and if the land heights and oceans depths were averaged out, the land would be 800m high and the oceans would still be 3,800m deep
It's a vast, almost immeasurable space; and less than 10% has ever been explored by man
These facts alone, not to mention my passion for diving, were the motivation for me to lead our great BBC Oceans team on a series of expeditions, each one rammed full of ambitious, meaningful targets.
We relished the opportunity of revealing the mysteries of our oceans, to observe some of the strangest sea creatures and put the surprising changes that are taking place into a human scale. We thrived on the challenge and all that it entailed:
Eight separate, two-to-three week expeditions
More than 1,000 dives
Over 700 hours underwater
Eight expedition ships, which ranged from a beautiful hand-built yacht to a worn-out converted cargo ship, and a brilliant Norwegian ice-breaker
One ship boarded by the authorities several times and impounded once
Close encounters with African salvage divers
And, of course, the 25 of us travelled the world with around two tonnes of equipment, which we packed, carried, shipped, assembled, repaired, loved and hated
In the Sea of Cortez, we witnessed and filmed rarely seen behaviour in sperm whales - a large male becoming sexually aroused as it socialised with female whales.
We sampled whale breath by the brand-new technique of using a remote-controlled helicopter flying through the whale blow.
With our sperm-whale science-colleagues, Diane Gendron and Karina Acaveda-Whitehouse, this research will provide more information about the question of whale-to-human and human-to-whale lung infections, and help to understand more about the health of the sperm whale population in the Sea of Cortez.
On our Mallorca expedition, we saw the evidence of past climate and sea level changes in the Mediterranean by undertaking technical dives inside one of Europe's greatest underwater cave systems.
On our Red Sea and Indian Ocean expedition, we observed how coral is being grown in nurseries as a way of helping damaged reefs.
Our dive showed how this technique could help revive reefs around the world. You will see also on our Red Sea programme how some coral can possibly adapt to relatively high water temperatures.

In the Atlantic, we went to The Black Hole in the Bahamas. This vertical cave system has only had three scientific expeditions to it before. This is an absolutely one-off, important marine science site. The water in this deep hole appears to mimic what all the world's seas might have been like 3.5 billion years ago.
Later, we dived the stromatolites at Lee Stocking Island, also in the Bahamas. These rock-like objects were the first lifeforms to pump enough oxygen into the sea and atmosphere so that complex lifeforms could develop, helping them become the beautiful, life sustaining waters that we know today.
In the Red Sea, we were the first ever to film the fluorescence in Eritrean corals. The extraordinary phenomenon remains a mystery to scientists who still don't know whether it is part of their survival strategy. And in these rarely dived waters, we found a species of coral which scientists previously didn't know grows off Eritrea's coast.
Our dives underneath the Arctic sea ice revealed the scale of the Arctic Ocean and just how fast it is changing. In our lifetimes, the Arctic Ocean will become unrecognisable to us. On one our dives, we found a previously undescribed species of amphipod - a great find as these tiny creatures provide a crucial link in the entire Arctic Ocean food chain.
Back in the Bahamas, the BBC Oceans team worked with scientists in an experiment to prove that fishing hooks can be made from a metal that repels sharks. It's hoped that this could potentially save millions of sharks being caught as "by-catch".
We had an incredibly rare encounter with a six-gill shark - normally found in 2,000m of water. And we dived with indigenous people using home-built dive-gear of paint-spray compressors and a beer barrel, connected to the diver by 50m of garden hose.
We dived with the world's largest known manta ray population where over 70% have been attacked by sharks.
We even cooked our lunch on underwater thermal vents, placing eggs in the hot waters seeping up from volcanic rocks below the seabed.
Our BBC Oceans expeditions were a tremendous experience and a great success. We even became impervious to sea sickness, air sickness and the daily circuit training.
The oceans are the last true wilderness and we really do know more about the surface of Mars than we do about the depths of our own seas.