What do we know about the deep ocean?

The deep ocean – below 200m - is the beating heart of our planet providing food and valuable genetic resources, 97% of our biosphere [1], maintaining a stable climate, and even changing our ideas about life in the universe. Yet it is virtually unknown. We have better maps of Mars than we do of our own seabed and scientists estimate that only 0.0001% has been biologically sampled [2].


The deep ocean is described in three or four zones differing between the water column or pelagic realm and the seabed or the benthic realm:

Benthic

200m – 2,000m: Bathyal zone

2,000m – 6,000m: Abyssal zone

6,000m – 11,000m: Hadal zone

Pelagic

200m - 1,000m: Mesopelagic (Twilight)

1,000m - 4,000m: Bathypelagic (Midnight)

4,000m - 6,000m: Abyssopelagic (Abyssal)

6,000m - 11,000m: Hadopelagic (Hadal)

[The first 200m is referred to as the Epipelagic, Photic or Sunlit zone].

The average depth is around 4,200 meters (2.6 miles) [3], and the deepest known area is the Mariana Trench in the Pacific, plunging to nearly 11,000m (7 miles) deep.  Mount Everest (8,848m) would be submerged beneath the waves with its highest point still one mile below the surface.

Our journey into the diversity and processes of life in the deep ocean has hardly begun. In the mid-nineteenth century, people believed life didn’t exist below 600m (the azoic theory). Research expeditions conducted by HMS Lightning to the North-East Atlantic in 1868, HMS Porcupine to the Mediterranean in 1869 and 1870 and, especially, the global circumnavigation of HMS Challenger between 1872 and 1876 proved for the first time that life was present in the abyssal depths.

We are still catching up today. The 2010 Census of Marine Life estimated that 230,000 marine animal and plant species have been described by science; at least 750,000 species await discovery. We are beginning to realise that the deep ocean may support more species than any other biome on Earth. There are, for example, 10million viruses in one drop of seawater.

An expedition to the Sargasso Sea in 2004 discovered 1,214,207 new genes, leading some researchers to conclude that 99% of the diversity of life in the ocean may as yet to be discovered [4]. Already at least 18,000 products derived from 4,800 ocean species are being used or developed to tackle human diseases and ailments [5]. But imagine for a moment, how all the unknown species can advance medical microbiology, clinical virology, genetics and biotechnology?

Despite too often being out of sight and out of mind, humanity’s future is intertwined with the future of our ocean. How the ocean changes will affect our climate, food security, society, business and even the air we breath. Take just one indicator – the value of oceanic ecosystem services to humankind. They have been valued at a minimum of $24 trillion, whilst the ‘Gross Marine Product’ (e.g. food) is around $2.5 trillion [6], making the ocean the seventh largest economy in the world.

[1] http://www.un.org/sustainabled... 
[2] Delving Deeper, European Marine Board - www.marineboard.eu/file/265/do... 
[3] Ecosystems of the Deep Oceans, edited by P.A. Tyler
[4] http://www.nature.com/nrmicro/... 
[5] http://www.oceanhealthindex.or... 
[6] http://www.worldwildlife.org/p...