The Effect of Holocene Climate Change Upon the World's Oceans

Some interesting stuff about the world's oceans:

The world's oceans are an absolutely vital part of the existence of life on Earth, many people underestimate their importance to us and many other forms of life.
There are considered to be five oceans, the Indian, Pacific, Atlantic, Southern and Arctic, together they cover ~362,000,000km² which is equivalent to ~71% of the Earth's surface.
Unsuprisingly, they contain 97% of the planet's water and 99% of the Earth's living space, the majority of which is part of the deep ocean known as the abyss, more than 90% of existing marine life lives or depends on coral reefs. There is even a different kind of life found as hydrothermal vents that are dependent on chemical energy rather than light energy, there is a theory that these vents are actually the origin of life on Earth, although this is not proven as of yet!
It is therefore suprising that less than 10%  of the oceans have actually been explored by man, but as a species we are negatively impacting the oceans at an alarming rate. ... Hello mass extinction.

Here are a few examples:

- Fish is the greatest percentage of protein consumed by man and so most of the world's major fisheries are being fished above their maximum sustainable levels. North Atlantic cod and LEDC reef fish are good examples of overfished species.
- We input a huge amount of plastic waste into the oceans every day, this waste kills up to 1 million sea birds, 100,000 sea mammals (including turtles) and countless fish every year. It is a major problem as plastic stays in marine ecosystems for many years.



- In the past decade, an average of 600,000 barrels of oil has been spilt accidently from ships/oil tankers, this oil has a devastating impact on local marine life and sea birds, the recent oil spill in the Gulf of Mexico, which President Obama was slow to respond to, is a good documented example.
- Nearly 60% of the world's remaining reefs are at significant risk of being lost within the next three decades, and as ~90% of marine life either lives or is directly dependent on coral reefs, this loss would be devastating to marine biodiversity.
- There are 50-75 shark attacks on humans each year (Less than the amount of people killed by elephants, bees, crocodiles and lightning annually), we kill 20,000,000-100,000,000 sharks each year through fishing activities. Collection of shark fins for shark fin soup is a major killer of sharks every year, many have their fins cut off in the water and are then left to die.
- 10,000 years ago at around the start of the Holocene epoch, ocean levels were 110m lower than they are today, Holocene climate change is therefore having a profound effect upon the world's oceans.

Some background on current Holocene climate change:

- Atmospheric C02 concentration is expected to exceed 50 parts per million (ppm) combined with a global temperature rise of 2°C by 2050-2100.
- The concentration of atmosphere C02 currently exceeds 380ppm which is more than 80ppm above the maximum value of the last 740,000 years.
- Currently, approximately 25% of the C02 emitted from all anthropogenic sources enters the world's oceans.

- Some predictions include higher C02 increases of 600-1000ppm and global temperature increases of 3-6°C, any change on this scale would almost certainly be devatstaing.
- The effects of Holocene climate change have been so widespread and complex that some scientists are calling for the start of a new geological epoch known as the 'anthropocene'.

Climate change and the ocean:

There are five main effects that climate change has upon the oceans: (a) warming oceans, (b) melting of the poles, (c) rising sea levels, (d) changes to current systems and (e) ocean acidification.

(a) Warmer oceans are caused by the fact that ~80% of the heat added to Earth's system by climate change has been absorbed by the oceans. This has had many negative effects upon marine life:
- Many species are forced to migrate so that they can maintain the temperature conditions they need to feed and reproduce, species that can't migrate may therefore become extinct.
- Temperature alteration can also directly impact development, age of sexual maturity, timing of spawning and growth. Each of these factors is vitally important in the survival of a species.
- Warmer waters also mean that there will be a decreased upwelling of nutrients from lower in the water column to the surface waters, many marine ecosystems depend on these nutrients, including the Galapagos Islands.

This image demonstrates how the nutrients are mixed normally, the original source of this image can be found here.

(b) Melting of the poles is caused by greenhouse gases increasing atmospheric warming which is one of the factors responsible for the melting of polar ice. This also has many negative effects upon marine life:
- Algae production in polar marine environments is dependent upon the presence of sea ice. Algae are at the base of most of the Arctic food web and support many important species such as Arctic cod. A decrease in one species generally leads to a decrease in another that is dependent, especially in such delicate ecosystems.
- Less sea ice results in the loss of vital habitat for polar marine species and polar mammals such as seals, walruses, polar bears, penguins, whales and other megafauna.
- Sea ice is a vital habitat for Antarctic krill, which is an important source of food for many Southern Ocean seabirds and mammals. A decrease in krill and thus dependent species has already occurred in recent years.

Melting of the poles is already happening at an alarming rate, the original source of this image can be found here.

(c) Rising sea levels are caused by the expansion of ocean water due to warming and by the melting of glaciers and polar ice. Habitats, marine life and humans are affected by this:
- Vital habitats such as coral reefs, mangroves and sea grasses depend on their ability to move into shallower waters, with waters getting deeper slow moving species will be most at risk of extinction.
- Many coastal habitats are lost as sea levels rise, such as turtle nesting beaches, manmade structures such as sea walls and coastal developments, often prevent them from migrating inland.
- Only 2% of the world's land lies at or below 10m of elevation, however, 10% (634 million) of the world's population are directly threatened by rising ocean levels. Pacific island nations such as Kiribati are most at risk, half the population lies within 3m of sea level and two of the islands have already disappeared.

The rising sea levels of Kiribati, the original source of this image can be found here.

(d) Changes to oceanic current systems are caused by changes in ocean temperatures and wind patterns (climate change), these changes affect and alter currents. This effect causes problems for animals, plants and humans:
- The migration patterns of many animals rely on ocean currents, as the currents change so will their migration pattterns, rapid change may cause seriosu problems for individual species.
- Some species depend on ocean currents for nutrients and reproduction, these will also be largely affected and potentially face extinction if they don't adapt or migrate.
- Ocean currents maintain some of Earth's current climates, and so alteration may lead to variations in rainfall and temperature which will in turn affect plants and animals as well as humans. The Gulf Stream is a good example of such a current, it allows the UK to experience a much warmer and wetter climate that than experienced on the same latitiude across the pond, where polar bears can survive.

The world's current thermohaline circulation, red indicates a warm current and blue a cold one, the original source of this image can be found here.

(e) Ocean acidification is caused by the introduction of carbonic acid to the ocean system, this in turn reduces the availability of carbonate to biological systems.
- Availability of calcium carbonate is reduced and thus calcification of organisms such as corals is also reduced causing coral bleaching which ultimately kills the coral.
- It directly harms many ocean plants and animals including: tropical reef building corals, cold water corals, many crustaceans and some plankton that make up the foundation of much of the ocean's food web. Many species in turn are dependent upon such organisms, these become threatened and may face extinction.
- Humans are also affected as many rely on tropical reef fish for food, a decrease in reef coral will lead to a decrease in reef coral feeding fish, disintegration of coral reefs may also lead to a decrease in tourism and sea defence.

This is an example of healthy coral.

Whereas, this is an example of bleached coral, the original source of this image can be found here.

The many effects that climate change has upon the ocean are rapidly changing it from an extremely biodiverse and important resource to the complete opposite. The effects of climate change are unlikely to change or be altered as global warming is not going to stop anytime soon, so i recommend you go out and see these places while you still can!
However, some effects we have upon the oceans can be changed or reduced, such as plastic input, next time you're thinking of dropping plastic onto the beach, buying a plastic bottle when a glass one is available or choosing non bio-degradable products instead of bio-degradable ones, don't! One less plastic bag in the ocean could save many marine animal's lives.

Disclaimer: I do not claim to own the rights to any of the images used in this blog post(except for the last image), links to the original image sources have been given where necessary.