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Conclusions

So, this blog has tried to explore the issue of ocean acidification. It has been somewhat jumbled and so today I am going to try and bring it all together. 11bn tonnes of carbon dioxide have been absorbed by our oceans in the last 200 years, causing a 30% increase in ocean acidity.  CO₂ dissolves in sea water and forms carbonic acid, this dissociates into HCO₃^- and H⁺, this H⁺ is what’s making our oceans more acidic. I think the most important thing that I have learned from this is that the problem is not that by the end of the century our oceans will be more acidic than they have been in the past 30 million years; it is the rate of the change. This rate is currently 100 times greater than anything we have experienced over the last 650,000 years.  Currently it is expected that by 2100 the pH will have fallen by 0.5 to 7.7.  If oceans acidify slowly, marine species have time to adapt.  At the current rate of change however, species are caught by surprise resulting in many becoming extinct.  The greatest threat is to calcifying organisms due to the shallowing of the aragonite and calcium carbonate saturation horizon, calcification can only occur above this horizon, with dissolution occurring below it. Once corals and other calcium carbonate based species are lost, wide scale extinctions will occur along the food chain.  At the PTB it is thought that the loss of coral and other such marine species was the start of the 5^th mass extinction, this suggests that the losses we are seeing today could cause the initiation of the 6^th mass extinction.  The problem is very real and we can already see the consequences in many of the world’s coral reefs, namely the Great Barrier Reef, and it is believed that all of the world’s reefs will have been lost within 40 years.  I thought it was interesting that even large marine mammals are being affected, and in ways that you would not immediately think of, for example clown fish are finding it much harder to smell the specific anemone that they use as a habitat due to the acidic waters.  The increase in size of lobsters in acidic conditions shows that some species can thrive in these conditions; however they may still be at threat due to changes in the food web.  Boron isotopes work by looking at the ratio of borate ion to boric acid.  The levels of which are affected by ocean pH as borate ion is preferentially incorporated into marine carbonates.  They have been quite successful in helping to reconstruct past pH but in the future further work needs to be done in order to reduce the uncertainty surrounding the isotope fractionation index and to improve the analytical techniques that are used. Towards the end of the blog I have briefly considered if there is any ‘quick-fix’ to improve the health of our oceans, if we are to stop our oceans from becoming undersaturated in aragonite the ocean pH mustn’t fall by more than 0.2 (relative to preindustrial levels).  Iron fertilisation is one of the main theories that has been proposed to combat ocean acidification and it is thought that by dumping large amounts of iron into HNLC areas of the ocean the productivity of phytoplankton will be greatly increased, resulting in algal blooms which will draw large amounts of carbon dioxide out of the atmosphere.  There is much uncertainty surrounding the potential success of iron fertilisation, it is thought that the drop in CO₂ is only found in the surface waters and many studies suggest that only a 10ppm reduction in CO₂ would occur.  There are also possible negative ecological effects that iron fertilisation could have and microbial shifts could cause an increase in other, more harmful, greenhouse gases (For example, methane and DMS).

If I had to try and sum up this blog, the 4 key findings would be:

-          Ocean acidification is a real problem that can’t be ignored, the effects on calcifying organisms is evident and the 30% increase in ocean acidity since preindustrial times is worrying, to say the least.

-          The use of boron isotopes as a proxy needs to be improved further (in terms of the fractionation index and analytical techniques) to increase our understanding of past ocean acidification in order to allow us to see how the current situation varies from past natural variability.

-          Calcifying organisms are most at threat; however some species can thrive in acidic conditions.  More work needs be done to see how the food chain will be affected.

-          Iron fertilisation and other combating schemes need to be improved or drastic cuts in atmospheric carbon dioxide levels need to occur in order to try and slow the rate of change. The unsuccessful Durban climate convention suggests that the latter is unlikely in the near future.

This cartoon shows each countries carbon emissions, China and the USA are by far leading the way.  If China do actually agree to the Durban protocol (when they decide the fine details) then a considerable drop in emissions could occur. This cartoon nicely highlights why Kyoto failed, as the worlds 2nd biggest emitter failed to sign up. Many of the coastal countries that depend heavily on the oceans for food and money have very low emissions yet are at the greatest threat from ocean acidification.  

Will we ever agree on cutting emissions?

So, another climate conference is over and still we are no closer to achieving a successful and viable framework for reducing global carbon emissions. Durban seeked to succeed where Cancun, Kyoto and every other climate convention had failed. Apparently they have drawn up a legally binding deal which will enforce the reduction of carbon emissions in both developed and developing countries, however the deal still has to be agreed and wont come into effect until at least 2020.  The fine details of the deal, for example by how much each country has to cut its emissions, has not yet been decided…..

For the first time ever, China has agreed to be legally binded into cutting its carbon emissions, if this is successful then the total global emissions will be significantly reduced.  However with so few details the deal is unlikely to succeed. One of the largest outcomes of the conference was that Canada withdrew from the only legal treaty committed to reducing greenhouse gas emissions- The Kyoto protocol.  The reasons for their withdrawal are thought to be that they are way off meeting their emissions targets, as in fact their emissions have actually risen.  In order to rectify this they would have to pay billions of dollars in carbon credits yet there would be no effect on the environment.  I think this shows that these legally binding deals are always going to have problems and no one will ever truly agree.  Carbon credits do little to actually help the environment as rich countries will just by credits and continue to pollute.  The fact that countries can pull out if they think they won’t meet their targets makes a mockery of the whole thing. 

Will we ever agree on how to combat climate change? For the health of our oceans I hope so, but somehow I very much doubt it.

Several weeks ago I posted an article which was very sceptical about ocean acidification.  After spending the last term writing this blog and researching ocean acidification, I will now attempt to explore some of their claims and see if there is any truth behind them.

One of their main claims was that ocean biodiversity will flourish under increasingly acidic conditions.  Whilst the last post I wrote suggested that some species of mussel and lobster will be able to survive in acidic oceans there has been no conclusive evidence to suggest that biodiversity will actually prosper.  In fact if you try searching species that will thrive in acidic waters in Google or Web of Science you get very few useful returns. However, if you search species which are threatened by acidifying waters the literature is vast.  As I have said previously, the species most at threat are those which calcify, due to dissolution and a shoaling of the carbonate and aragonite saturation horizon.  These species are often low down in the food chain, and so if they go extinct their predators will also be affected.  The evidence for dissolution is abundant, not only from scientific experiments but also just by looking at some of the world’s coral reefs. I posted this image before which shows how rapidly a shell can deform in acidic water. 

This cartoon shows the deformation of a shell in an acidic ocean over a period of 45 days (NAOO).

Anthony et al. (2011) created a model to see how ocean acidification affected the resilience of coral reefs.  Their main findings were that reefs which suffer from overfishing and eutrophication were more vulnerable to acidic waters.  They also found that as CO₂ levels rise, the resilience and growth rates of coral reefs will fall and mortality will increase.  The Great Barrier Reef has seen a rapid reduction in calcification rates and growth of large corals (Hoegh-Guldberg, 2009).  Hoegh-Guldberg (2009) has also shown that ocean acidification not only reduced the productivity of corals but also made them more sensitive to bleaching.  More recent work by Kurihara et al. (2008) and Mayor et al. (2007) has shown that ocean acidification reduces egg production in marine shrimps and also causes an increase in unsuccessful hatchings in copepods.  Earlier on in this blog I also pointed out larger marine animals were being affected by ocean acidification.  Whale numbers are falling due to an increase in ‘noise’ in acidic waters, which makes communication and navigation trickier.  Clown fish are losing their sense of smell, due to the acidic conditions, which means that they can’t smell their habitats. 

I believe that we cannot deny the fact that ocean acidification is having a detrimental impact on marine organisms.  The effects are most widely felt by calcifying organisms yet larger marine mammals such as Whales are not out of harm’s way.  Caution needs to be given and some people probably over emphasise the effects of ocean acidification, as it is evident that some species can prosper in acidic waters. However, if their prey cannot adapt and goes extinct then they will die too, whether they are adapted to acidification or not.  More work needs to be done to assess the impact of rising CO₂ levels on a wider range of species to see how many other species have been able to adapt.  A significant proportion of ocean species will be affected by ocean acidification but it cannot be claimed that every species will be negatively affected.  Similarly, at the moment the evidence is too large to suggest that creatures are unscathed from rising carbon dioxide levels.

References

Anthony, K, Maynard, J. Diaz-Pulido, G. Mumby, P. Marshalls, P. Cao, L. (2011). ‘Ocean acidification and warming will lower coral reef resilience’, Global change biology, 17, 1798-1808.

Hoegh-Guldberg, O. (2009). ‘Climate change and coral reefs: Trojan horse or false prophecy?’, Coral Reefs, 28, 3, 569-575.

Kurihara, H. Matsui, M. Furukawa, H. Hayashi, M. Ishimatsu, A. (2008). ‘Long-term effects of predicted future seawater CO2 conditions on the survival and growth of the marine shrimp Palaemon pacificus’, J Exp Mar Biol Ecol , 367:41–46.

Mayor, D. Matthews, C. Cook, K. Zuur, A. Hay, S. (2007). ‘CO2-induced acidification affects hatching success in Calanus finmarchicus’, Mar Ecol Prog Ser, 350:91–97.

Attack of the giant lobster?

In an attempt to brighten up an otherwise gloomy blog i have found 2 articles which suggest that some marine species are able to thrive in acidic oceans.  The first article: 

http://news.nationalgeographic.com/news/2009/12/091207-giant-lobsters-acid-oceans/

has found that lobsters, shrimp and crabs are much larger if they grow in acidic waters.  Good news for fish restaurants!

The second article:

http://news.nationalgeographic.com/news/2009/12/091207-giant-lobsters-acid-oceans/

has found a species of mussel which has survived for 40 years along the sides of a submarine volcano, in exceptionally acidic conditions.  They survived in a pH as low as 5.3 (considered to be too acidic for calcifying organisms).  These mussels are able to survive with shells that are half as thick as mussels which live in less acidic waters, proving that adaptations are possible.  These mussels are now thriving as they can survive where many of their predators and competitors cant.

I thought that these two articles were quite interesting and show that there are species which can adapt and thrive, even in acidic waters.  Maybe the future of our oceans isnt as bad as first feared....

Can we do anything to reverse ocean acidification?

Up until now I have spent quite a lot of time looking at what is going on in our oceans and what is likely to happen in the future. The picture hasn’t been too rosy so far, but now I will see if there is anything we can do to combat ocean acidification or if we are just destined to disaster.  Iron fertilisation has been put forward as one of the main mechanisms that could help to reverse the acidifying trend.  Ice cores show that during past glacials iron fertilisation has occurred naturally (for example, dust storms coming from the Sahara towards the Canary islands) and has caused large amounts of CO₂ to be drawn out of the atmosphere (Lampitt et al. 2008). Put simply, it is thought that by adding iron to high nutrient low chlorophyll (HNLC) areas of the ocean it will stimulate the growth of phytoplankton blooms which will take up large amounts of atmospheric carbon dioxide and eventually deposit it into the ocean sediments (Cao and Caldeira, 2010).  There has been quite a large amount of speculation as to whether iron fertilisation will actually cause a reduction in atmospheric and oceanic carbon dioxide levels and several experiments have been run, each reaching different conclusions.  Martin was the first to propose the idea of iron fertilisation and he proposed that 1 ton of carbon added to a HNLC region could cause the sequestration of up to 100,000 tonnes of carbon. More recent, high resolution studies have suggested that iron fertilisation is far less efficient and would only result in a 10ppm reduction in atmospheric CO₂ (Lampitt et al. 2008).  The drop in carbon dioxide is only really found in the surface waters and doesn't extend deeper than about 70m (Cao and Caldeira, 2010).  Cao and Caldeira (2010) also found that even if iron fertilisation was successful by the end of the century it would only reduce the pH change by 0.06.  It is thought that iron fertilisation could produce carbon credits which would be doubly bad news for our oceans as not only would the iron do little to prevent the oceans from becoming acidic, countries would be allowed to increase their carbon dioxide emissions. Many private sector companies are already planning to enrich the ocean in order to gain carbon credits, the moderating of such activities is very difficult, especially away from territorial waters.  There are also several ecological impacts that need to be considered, it is probable that there would be an increase in harmful algae which could cause environments to become toxic.  Microbial shifts could also result in the production of other greenhouse gases such as DMS and methane, both of which are far more potent than carbon dioxide.  Due to monitoring difficulties it is also hard to know if plankton blooms could cause the carbon dioxide to be taken into the deep ocean and sediments.  Iron fertilisation initially sounds like a good idea and some believe that it could cause a large reduction in atmospheric CO₂. There are wide scale ecological effects that could result And the actual reductions in ocean pH and carbon dioxide levels are very low.  More work needs to be done to work out the potential side effects of iron fertilisation and to develop a greater understanding of the movement of carbon dioxide to the ocean sediments.

References

Cao, L. Caldeira, K. (2010). ‘Can ocean iron fertilization mitigate ocean acidification?’, Climatic change, 99, 1-2, 303-311.

Lampitt, R. Achterberg, E. Anderson, T. Hughes, J. Lucas, M. Popova, E. (2008). ‘Ocean fertilisation; a potential means of geoengineering’, Philosophical transactions of the royal society A, 366, 1882, 3919-3945.