Oceans under Threat

Oceans  cover over 70% of the planet’s surface and:

  • drive weather systems,
  • create at least half of the oxygen in our atmosphere,
  • regulate temperatures
  • dominate the global water and carbon cycles
  • is critical in enabling life to exist on Earth

At the Earth System Level, the Ocean and the life within it are the least understood components of our planet.

In the age of the Anthropocene, the Ocean is under the most unprecedented threat in human history. Subjected to multiple human induced stressors such as over-fishing, industrial pollution, ocean acidification and global warming, the Ocean is in a critical condition:

  • Increased temperatures in the Ocean have been detected down to a depth of more than 3,000m.
  • Since 1978, summer sea ice in the Arctic has decreased by 7.4% per decade and may vanish altogether in a few years, with profound impact on life on earth
  • Carbon dioxide absorption has caused a reduction in ocean pH levels, increasing its acidity by 30% since pre-industrial time cause death of critical shell-forming species that are critical to the entire ocean food chain
  • 75% of the global fish stocks that have been assessed are fully exploited, over-exploited or depleted and may have profound effect on ocean fertility and the ability for the ocean to act as a carbon sink
  • Iconic marine species such as sharks and corals are disappearing from the Ocean.
  • Due to human agricultural runoff, ocean ‘dead zones’ are spreading.
  • The tremendous amount of plastic that finds its way to the ocean are creating micro-plastic pollutants affecting oceanic life

(Source: IPSO)


The Oceans Planetary Functions

The Ocean forms one of the key operating systems of our planet. Our oceans:

  • creates more than half our oxygen
  • drives weather systems
  • sinks CO2
  • moderates the climate
  • modulates chemical composition of the atmosphere
  • provides us with vital resources
  • transports huge volumes of water mass globally
The following diagrams illustrate the main functions of our oceans (Source: IPSO)

Figure 1: Photosynthesis: Every second breath of the oxygen we breath is supplied by the ocean (Source: IPSO)

Figure 2: Carbon Cycle (SourceIPSO)

Figure 3: Nutrient Cycle (SourceIPSO)

Figure 4: Water Cycle (SourceIPSO)

Figure 5: Thermohaline Cycle (SourceIPSO)

The Crisis

The oceans are facing multiple threats:

  • We are altering the chemistry of the Ocean and significantly impacting marine life and ecosystems
  • The Ocean has already absorbed more than 80% of the heat added to the climate system
  • The Ocean has already absorbed and around 33% of the carbon dioxide emitted by humans
  • Ecosystems are collapsing as species are pushed to extinction and natural habitats are destroyed

Scientists believe that there is still time to prevent irreversible, catastrophic changes to our marine ecosystems but that this requires drastic action within a decade. Below is a list of the major threats:

Climate change – the biggest threat 

Climate Change is causing temperature increase and acidification

  • Temperature increases are:
    • affecting distribution of marine species
    • affecting the timing of the cycles of life in the Ocean
    • with other factors, causing coral bleaching, devastating large areas of the worlds coral reefs
  • Ocean Acidification is:
    • a direct result of the absorption of carbon dioxide by the Ocean
    • a threat to all marine animals and plants that secrete calcium carbonate as part of their structure
    • believed to already be reducing the size and growth rates of some marine animals

Ocean Acidification 

Our analysis shows that almost every commitment (since Rio Summit in 1992) made by governments to protect the oceans has not been achieved. If these international processes are to be taken seriously, governments must be held accountable and any future commitments must come with clear plans for implementation and a process to evaluation success or failure.

- director of conservation at the Zoological Society of London

Ocean acidification is the other “global warming” and centuries of CO2 emissions have brought about fundamental changes in seawater chemistry that threatens life in the ocean.  The ocean absorbs about a quarter of the CO2 we release into the atmosphere every year, so as atmospheric CO2 levels increase, so do the levels in the ocean. Initially, this was seen as a benefit as oceans removed this greenhouse gas from the atmosphere.  When this CO2 dissolves in the ocean, a chemical reaction occurs:

Figure 1: Ocean Acidification Chemical Reaction

  1. CO2 reacts with water to create carbonic acid,  H2CO3:CO2 + H2O ↔ H2CO
  2. The carbonic acid quickly dissociates into H+ ions (an acid) and bicarbonate, HCO3-(a base)
  3. Seawater is naturally saturated with another base, carbonate ion (CO3−2) that acts like an antacid to neutralize the H+, forming more bicarbonate.
  4. The net reaction is: CO+ H2O + CO3−2→ 2HCO3-
  5. As the chemical reaction continues, carbonate ion gets depleted, seawater becomes undersaturated with respect to two calcium carbonate minerals vital for shell-building, aragonite and calcite.

 Scientific models suggest that:

  • the oceans are becoming undersaturated with respect to aragonite at the poles, where the cold and dense waters most readily absorb atmospheric carbon dioxide
  • The Southern Ocean is expected to become undersaturated with respect to aragonite by 2050
  • The problem could extend into the subarctic Pacific Ocean by 2100 (Orr et al., 2005)

The term “ocean acidification” is not entirely accurate. Acid means pH is less than 7.  Since the pH of surface seawater has fallen from 8.2 to 8.1, it has become the oceans are actually becoming less alkaline. It could only become acidic if it dropped below pH=7.  The pH has undergone this shift in a few hundred years, after remaining constant for millions of years.

A decline of 0.1 pH units may not sound like a lot, but on the logarithmic scale of pH it translates to a 30 percent rise in acidity. Seawater pH is projected to drop another .3 to .4 units if carbon dioxide levels reach 800 ppm –one of the scenarios projected by the Intergovernmental Panel on Climate Change by 2100 –raising levels of hydrogen ion, H +, 100 to 150 percent (Orr et al., 2005). It could take “tens of thousands of years” for the chemistry of the oceans to return to pre-industrial levels, the Royal Society of Britain estimates.

A tiny species of zooplankton, the pteropod, called “sea butterflies” for the gelatinous wings they use to swim around, may be in jeopardy. Orr et al. conducted an experiment in 2005 in which the team of researchers  immersed a pteropod in seawater with low aragonite levels. Part of the organism’s shell was eroded in as little as two days. Many creatures depend on the pteropod for food. Any other creatures with shells are at risk of their shell dissolving. The same is true with coral reefs, which are home to a million species of life. Due to the interconnected web of life, this will affect every being in the ocean and may lead to a mass extinction of aquatic life.

Figure 2: Electron micrograph of dissolving damage on shell of zooplankton called the pteropod

Marine Extinction – International Programme on the State of the Ocean (IPSO)

In 2011, a panel of the leading marine scientists met in Oxford and came to a startling conclusion: due to the cumulative impact of a number of severe individual stresses including:

  • climate change causing ocean temperature warming and acidification
  • chemical pollution from manmade sources such as sewage, industrial pollution and agricultural fertilizer runoff
  • gross overfishing

the world’s oceans are faced with an unprecedented loss of species comparable to the great mass extinctions of prehistory. Potential extinction can range from tiny corals all the way to the largest predators in the marine food chain. The conference produced the report Implementing the Global State of the Oceans which concludes that:

  • the oceans of the world are degenerating far faster than anyone had previously predicted
  • many of the negative impacts identified are greater than the worst predictions
  • the first steps to globally significant extinction may have already begun

Dr Alex Rogers, professor of conservation biology at Oxford University and IPSO’s scientific director said that the findings were shocking and “As we considered the cumulative effect of what humankind does to the oceans, the implications became far worse than we had individually realised.

Another participant, Dan Laffoley, the IUCN’s senior adviser on marine science and conservation said “The world’s leading experts on oceans are surprised by the rate and magnitude of changes we are seeing.”

The scientists found firm evidence that the combined effects of climate change, overfishing, nutrient run-off from farming, pollution and invasion of foreign species have already caused a measurable and dramatic decline in ocean health:

  • some fish species have declined to the point of commercial extinction
  • habitat such as mangrove and seagrass meadows are undergoing “unparalleled” rate of regional extinction
  • entire  marine ecosystem such as coral reefs, may be gone within a generation

They further agreed that the oceans are not resilient enough to withstand the sustained bombardment from multiple attacks. The report cites an example showing the global impact of just one incident in 1998 which has wiped out 16% of the coral reefs in the world. Warning of the conditions of a mass extinction event, the report further says: “Increasing hypoxia [low oxygen levels] and anoxia [absence of oxygen, known as ocean dead zones], combined with warming of the ocean and acidification, are the three factors which have been present in every mass extinction event in Earth’s history. There is strong scientific evidence that these three factors are combining in the ocean again, exacerbated by multiple severe stressors. The scientific panel concluded that a new extinction event was inevitable if the current trajectory of damage continues.”

Ocean Acidification in the Arctic


The International Programme for the State of the Ocean (IPSO) estimates that 75% of the global fish stocks that have been assessed are fully exploited, over-exploited or depleted. We are depleting ocean fauna at a rate of 9,000-10,000 tonnes of fish from the Ocean per hour (based on a catch of 80-90 million tonnes per year). The large industrial The indiscriminant fishing methods used (such as trawling) and enormous scale are devastating both the fish targeted and virtually all other marine creatures, from seabirds to coral. As a result of unsustainable fishing practices, entire industries such as the Cod on the East Coast of Canada have collapsed. In many cases, previously abundant fisheries – such as north-west Atlantic cod – can now produce only a fraction of the food yielded in the past.

New scientific theories are revealing that the damage being done may cause a tipping point in the ocean where large multi-celled creatures may face an uncertain future and where the oceans carbon sinking capability may be at risk.

Habitat Destruction

  1. Human activity such as bottom trawling destroy seabed communities such as coral reefs
  2. Activities which degrade water quality make it unsuitable for marine species
  3. Destruction of coastal vegetation such as mangroves and seagrass where significant amounts of carbon are sequestered

Oil and Gas Subsea Extraction

  • Subsea extraction inevitably creates harmful pollution by releasing hydrocarbons and other contaminants into the Ocean. Castastrophic oil spills like the BP Oilrig disaster in the Gulf of Mexico have an enormous global impact on Oceanic life. Because the ocean is essentially one global body, a catastrophic oil leak in one area can be spread by ocean currents to contaminate the entire global marine ecosystem.
  • The normal process of subsea oil extraction produces fine sediments that are released onto the seabed and which may be contaminated with toxic drilling muds
  • Acoustic surveys of the seabed to prospect for oil may also damage marine ecosystems, through the impacts of sound on marine mammals and fish
  • Mining companies are prospecting for subsea minerals in areas which include habitats such as hydrothermal vents that are home to rare and unique species while O+G companies are planning to drill in sensitive areas such as the Arctic Ocean Oceanic ecosystem


The release of sewage and wastes into coastal ecosystems directly increases microbial activity through the provision of organic matter. This depletes oxygen in the water column and can lead to the development of ‘dead zones’ in coastal waters. In other places, this artificial enrichment of coastal waters causes outbreaks of harmful algal blooms which poison other marine life.

Ocean pollution originates from:

  • industry
  • agriculture
  • domestic sources on land

whether dumped directly into the sea or reaching it via rivers and air currents

Common Pollutants:

  • heavy metals
  • Persistent Organic Pollutants (POPs)
  • plastics
  • petroleum
  • pesticides

Plastic Pollution in the Ocean

 Alien Species

Marine ecosystems are made up of species which interact with each other, and their environments, in ways that have evolved over millions of years. Now, we transport marine species and their larvae over huge distances and introduce them into alien ecosystems. This can happen deliberately, or accidentally (for example when ballast water taken aboard a ship in one region is dumped in another).

Either way, it can put ecosystems under severe stress if alien species overgrow the native species or introduce exotic diseases. In the worst cases – especially when combined with other human stressors, such as over-fishing – the affected ecosystems can collapse completely, as happened in the Black Sea in the 1990s.

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