Threats from ocean acidification

[Don-Chedi]

Re: Threats from ocean acidification

Carbon dioxide emissions from modern society are turning the ocean more acidic and some sea creatures are already suffering, according to research to be discussed at a major global science conference.
OCEAN ACIDIFICATION

Up to one half of the CO2 released by burning fossil fuels over the past 200 years has been absorbed by world’s oceans
This has lowered its pH by 0.1
pH is the measure of acidity and alkalinity
The vast majority of liquids lie between pH 0 (very acidic) and pH 14 (very alkaline); 7 is neutral
Seawater is mildly alkaline with a “natural” pH of about 8.2
The IPCC forecasts that ocean pH will fall by “between 0.14 and 0.35 units over the 21st Century, adding to the present decrease of 0.1 units since pre-industrial times”

Studies in the Southern Ocean by Australian scientists found that the shells of tiny amoeba-like creatures called foraminifera have become thinner since the Industrial Revolution.
The scientists say this shows that increasing CO2 uptake in the ocean has a direct effect on the ability of micro-organisms to make shells.
The paper, being presented at the University of Copenhagen’s International Scientific Congress on Climate Change, will add to a rising tide of scientific concern over ocean acidification.
Already, ocean acidity has increased about 32% since pre-industrial times. By 2100, it is projected to have increased by perhaps 130%, which scientists fear could have a potentially catastrophic impact on marine life.
In a study published in Nature Geoscience, William Howard, Andrew Moy and colleagues collected the shells of the organisms as they fell towards the sea floor.
They compared the mass of the shells, about the size of a grain of sand, to the mass of older shells on the sea floor.
The modern shells were 30 to 35% lighter than those that formed prior to the industrial period.
The researchers from the University of Tasmania attribute the change to the acidification of the Southern Ocean, which they say is driven by the uptake of CO2 from factories, cars and power stations.
Mussel test
Other scientists are wary of attributing all the blame for the acidification of the Southern Ocean on humans – there is major upwelling of more acidic water from the deep seas.

Dr Steve Widdicombe,
Plymouth Marine Laboratory

Waters from the deep ocean are colder than the surface waters and contain more carbon, which mixes with the seawater to form carbonic acid.
But this will not diminish concern over the problem of ocean acidification in general.
Some of the cutting-edge work in this new field of science is being done at Plymouth Marine Laboratory (PML) in south-west England.
A blustery wind is cutting in from the English Channel when we go to meet the laboratory’s Steve Widdicombe, who is gathering mussels from the estuary of the River Exe.
He will use the molluscs to test how they will respond to increasing acidity as CO2 emissions rise.
The Exe is nearly a mile wide at this point and Steve has to work quickly because the tide is about to turn.
The specimens are taken back to the lab where their blood is sampled with a needle thrust through a gap in their shell.
An enzyme test indicates the strength of their immune system. Then they are placed in tanks where acidity has been increased by bubbling CO2 through the water.

Mussels given health check

This is a long-term test, and Dr Widdicombe suspects it will show that mussels will be seriously compromised by the levels of acidification expected by 2100.
A previous experiment at PML, published in the Proceedings of the Royal Society, showed that starfish would be killed by a pH of 7.7, which may occur by 2100 if CO2 emissions continue to rise.
Ocean pH levels have previously remained roughly constant at 8.2 for at least half a million years.
“We found that relatively small changes in pH (acid/alkali balance) for a long period cause creatures to use up energy trying to respond to the change,” Dr Widdicombe says.
“The more we look at long-term chronic effects of acidification, the more worrying it becomes,” he adds.
“It’s a continuous stress. We can all respond to temporary stress but if we are under continuous stress we get sick.”
The big question with acidification is whether calcifying organisms that need more alkaline conditions to create their shells will be able to adapt to more acidic waters.
“We need to look at evolutionary timescales,” Dr Widdicombe explains.
“No-one has done the studies on what if anything would drive the ability to adapt. “I personally think evolutionary timetables are simply too short to respond to the sort of changes we are making. I really fear the worst.”

[Don-Chedi]

Re: Threats from ocean acidification

Ocean acidification is a term used to describe the changes in the chemistry of the world’s seas, primarily as a result of burning fossil fuels.
Marine scientists are concerned that changes to the oceans’ pH levels will have severe consequences for marine wildlife and ecosystems.

1. Up to one half of the carbon dioxide (CO2) released by burning fossil fuels over the past 200 years has been absorbed by the world’s oceans
2. Absorbed CO2 in seawater (H2O) forms carbonic acid (H2CO3), lowering the water’s pH level and making it more acidic
3. This raises the hydrogen ion concentration in the water, and limits organisms’ access to carbonate ions, which are needed to form hard parts

Since the Industrial Revolution, there has been a sharp increase in atmospheric CO2 as a result of human activity, primarily from burning fossil fuels. THE pH SCALE
Higher numbers indicate alkalis, while lower numbers signify acidic liquids:
13 – bleach
10 – soap
8.2 – pre-1750 oceans (average)
8.1 – current oceans (average)
7.8 – oceans in 2100 (projected average)
7 – pure water
3 – vinegar
0 – battery acid

(Source: NMEA)

The oceans have absorbed up to half of this excess CO2, which has resulted in changes in the chemistry of surface seawater.
The CO2 in the water, which leads to the formation of carbonic acid, has caused the pH of surface oceans to fall by 0.1 units, and it is projected to fall a further 0.3-0.4 pH units by the end of the century.
The shift in the waters’ chemical make-up not only increases its acidity, but reduces the availability of carbonate ions, which many creatures use to build shells and skeletons out of calcium carbonate.
The decrease in available carbonate ions means that organisms, such as plankton, coral and molluscs, struggle to build or maintain their protective or supportive structures.

The pH of the world’s oceans is not consistent across the globe.
Researchers believe that areas with relatively low pH (the purple areas on the map above), such as the eastern Pacific, could be the result of the upwelling of deeper, colder, CO2-richer waters.
However, no region is expected to escape the impact of falling pH.
As a result, marine biologists say that a number of species and ecosystems face an uncertain future:
Warm-water coral reefs


Evidence suggests that the calcification rates of these corals will be reduced by up to 60%, say US researchers writing in the journal Current Biology.
They say a reduction of this magnitude could adversely affect reef structures, as growth depends on corals’ ability to build faster than the skeleton is eroded.
Weaker structures are likely to be prone to greater degrees of erosion from storms and heavy wave action.
Cold-water corals
Found throughout the world’s oceans, cold-water corals can provide vital habitat for several commercially important fish species.
Forecasts suggest that about 70% of the corals could find themselves under threat by the end of the century.
Plankton
These tiny organisms play an important role in the marine food chain.
Several groups of plankton produce calcium carbonate, and could see their distribution curtailed by ocean acidification.
Scientists agree that more research is required in order to better understand the impact of oceans’ falling pH on the tiny creatures.
Some species, such as coccolithophores (single-celled algae), have shown a marked decrease in calcification rates when exposed to CO2-rich water.
However, others species were largely unaffected.
Invertebrates
Some molluscs, including mussels and oysters, are expected to be adversely affected by ocean acidification.
As with other creatures, the main impact is expected to be thin or deformed shells.
Juveniles have been shown to be more susceptible than adults to limited carbonate ions, which could have long-term consequences as far as viable populations are concerned.
But not all habitats suffer as a result of ocean acidification. For example, sea grasses grow better in CO2-rich waters.
The grass offers a valuable feeding and spawning site for a variety of species, including a number of commercially valuable fish.
However, more research is needed to see if the local benefits from the sea grasses are not outweighed by the wider disruption to the marine food chain.

The Earth’s carbon cycle, the exchange of CO2 between land, sea and air, is generally meant to be in equilibrium.
However, human activities, such as burning fossil fuels and deforestation, mean that an increasing amount of CO2 is being released into the atmosphere.
But not all of the unlocked CO2 remains in the atmosphere. Up to 50% of the emissions are absorbed by the ocean.
The oceans absorb carbon in two main ways – physically and biologically.
Physically, CO2 dissolves into cold ocean water near the poles, and it is carried to the deep ocean by sinking currents, where it stays for hundreds of years.
Over time, thermal mixing brings the water back to the surface and the ocean emits carbon dioxide into the atmosphere in tropical regions.
This natural system helps pump carbon from the atmosphere into the sea for storage.
The biological absorption of CO2 involves phytoplankton, which use sunlight, water and CO2 to produce carbohydrates and oxygen.
When the plankton and the sea animals that eat the plankton die, they sink to the ocean floor.
A small percentage of the carbon in the creatures’ remains is eventually buried and stored in the sediment.
‘Feedback mechanisms’
These natural “carbon pumps” are showing signs of being disrupted, say researchers.
For example, ocean acidification could reduce plankton blooms, resulting in less CO2 being absorbed from the atmosphere.
In theory, the extra CO2 in the atmosphere could lead to an acceleration in global warming, which will warm the oceans.
As a result, the warmer waters will not be able to absorb as much carbon dioxide as cooler seas.
So even less CO2 is taken from the atmosphere, resulting in more of the greenhouse gas being available to warm the planet. The potential of these “feedback” mechanisms to disrupt the planet’s climate system is one of the reasons why marine scientists are calling for urgent action to be taken to stabilise, and eventually reduce, emissions.

[Don-Chedi]

Re: Threats from ocean acidification

Om nog maar een doembericht over de toekomst van de oceanen in het rijtje toe te voegen …

[ROLAND]

Re: Threats from ocean acidification

Kunnen er niet genoeg zijn.