Oceans and CO2 Emissions

An important milestone has been reached – atmospheric CO2 concentrations have are now at 400 parts per million (ppm) - see the news story here. This is big news. And it is scary. This is brand new territory for humans – there hasn’t been this much CO2 in the atmosphere for as long as any anatomically modern humans have walked the planet. The difference between 399 and 400ppm isn’t all that much, in the bigger picture it’s a minute change, but the rate at which we have reached this milestone is truly frightening. CO2 concentrations are rising faster than any other time in history, and is caused by humans. The debate is long over, it is now scientific consensus. The major evidence we have for the human induced nature of this rise due to the burning of fossil fuels is the decrease in oxygen levels – not enough for you to panic about though; we’re not running out of oxygen. In the past atmospheric CO2 concentrations have fluctuated, both increasing and decreasing. However, this time the increase has been accompanied by a decline in atmospheric O2 concentrations as the combustion (burning) of organic things like fossil fuels uses up O2 as it releases CO2 (see Shaffer et al, 2009). There are many other well cited papers where evidence for this is verified.

The burning of fossil fuels is changing the planet in ways humans have never had to deal with before (image from moinlucky11 on Deviant Art)

This news is of concern to all who call Earth home. But it is not simply changes to our climate we should be worried about, although these are important. What on earth is going to happen to our oceans? Zeebe et al (2008) published an article in the journal Science asking just that – as CO2 concentrations continue to rise in the atmosphere, what effect will that have on the oceans and the life within them?

Transportation's reliance on oil is a huge source of carbon emissions (image courtesy of e8resources)

Simple chemistry states that as the concentration of CO2 increases in the atmosphere, there will be an overall “drawdown” of CO2 into the ocean to maintain pressure equilibriums. Therefore, it makes sense that the ocean is considered a major “carbon sink”, that has taken up about 40% of all man-made (or anthropogenic) CO2 emissions over the last 200 years. This has slowed the rise in atmospheric CO2 concentrations, and so has somewhat alleviated the changes in climate associated with this rise. However, when that much CO2 is taken up by the ocean, large scale changes in the chemistry of the waters occur. These can have potentially serious consequences for marine life, especially in terms of a change in global ocean pH. This drop in pH (making the waters more acidic) and the lowering of the saturation state for carbonate minerals (the amount of carbonate available for biological processes such as the formation of shells) has been called “Ocean Acidification”

Graph from the IPCC (2007) showing how, over time, the increase in atmospheric CO2 (orange) is closely followed by a decrease in gobal ocean pH (blue). The fluctuations in the curve are due to the seasons - the Northern Hemisphere spring sees the massive northern forsts taking up huge amonts of CO2, making the levels decline, while winter means the trees top photosynthesising and the CO2 levels creep up again.

 Many organisms in the ocean need calcium carbonate to build their shells and skeletons – things like abalone, crusting algae, mussels, oysters and corals. If there is less carbonate in the water, these organisms will be unable to build their shells and the dissolution of calcium carbonate under acidification conditions means that the organisms will literally disappear. In 2012, I conducted a project to test the effects of ocean acidification on baby abalone by looking at the shells with a scanning electron microscope at very high magnification levels. The results were startling, with the erosion of the shells happening right before my eyes (see the pictures below - click on the picture to view a larger version). Although the pH is not going to drop to 7.8 units until 2100, this is still worrying - the shell damage under these conditions and the less calcium carbonate avaliable in the water will mean that the organisms will have to spend more energy forming and replacing their shells than investing in growth.

High magnification images of baby abalone shells under different pH treatments. Far left is the control pH of 8 units; centre is the results of placing the shell in a pHof 7.8 units, and far right is the shell in a treatment on 7.5 pH units. The projected pH for the oceans for 2100 is 7.8 pH units.

 Calcium carbonate is the building block for coral reefs. These ecosystems are already under huge pressure from direct human impacts like overfishing, physical damage and pollution, and ocean acidification may become a more devastating threat in the future as CO2 levels continue to rise. More CO2 dissolving into the water means that the rate of erosion of reefs in this manner could become greater than the rate these reefs are built. Coral reefs are diversity hotspots, supporting a huge range of species and providing food and income through tourism for many people around the world. The loss of these systems will have devastating ecological and humanitarian consequences.

However, most corals occur in warmer waters, and since gases like CO2 dissolve more in cold water than warm, the threat to corals from ocean acidification may not be its most threatening impact. Many other calcifying species are of either direct or indirect importance to humans, and will be under threat due to ocean acidification. Abalone are of economic importance here in South Africa - a huge market exists in the Far East which allows for profitable farming of the species, and economic upliftment and job creation this ensures. Important fish stocks the world over depend on cphytoplankton as food, and the loss of these primary produces at the bottom of the food chain because of ocean acidification will have dramatic ecological, economic and humanitarian issues. For many people, especially the poor, fish is their most important source of protein. Therefore, Zeebe and his fellow authors advocate that carbon emissions must be reduced with immediate effect to avoid these consequences, regardless of climatic considerations.

From left: coral reef (image from NRDC); highly magnified image of coccolithophores (image from the University of Bremen); Atlantic caught herring (image from NOAA)

The scary thing about ocean acidification is that even if we stop all emissions immediately, the ocean will still continue to take up CO2 and the pH will continue to decline. Already the global ocean pH has declined by 0.1 units since the start of preindustrial times. Despite this, the legislation that governs what is deemed an acceptable change in oceanic pH has not been changed –1976 environmental standards of the USA still state that, for marine life, pH should not be changed by 0.2 units outside of the normal range. And since it has been shown in other studies that dropping pH has different effects on different groups of organisms, these standards need to be re-evaluated and CO2 emission limits need to be established in order to prevent future changes in pH that will be beyond those ranges.

Every little bit helps – what are you doing to safe guard the future of our oceans?

Bubbles and Whale Strandings

The end of March saw the stranding of 19 adult pilot whales on Noordhoek beach on the western side of the Cape Peninsula, South Africa (see the News24 article). The strandings are the second on this particular beach in recent years, with 55 false killer whales beaching themselves in 2009. There are deep public divisions about what to do in such circumstances. Some want the animals to be “left alone”, and for “nature to take its course”. Others desperately want the animals saved, and bemoan the euthanisation of the whales. Despite this intense public interest (the authorities had to close off the area to keep the fascinated public at bay), the debate as to the causes of cetacean strandings still rages within the global scientific literature.

A stranded pilot whale on Noordhoek Beach, South Africa (see News24)

 The truth is that we simply do not know exactly what causes cetaceans (the scientific term given to whales and dolphins) to strand. Some papers suggest navigational disorientation due to anomalies in the magnetic field of a certain area is the cause of strandings. Because cetaceans utilise the magnetic field of the earth to navigate, a disruption in this system may cause the animals to “get lost” and head towards shore. Another theory is that the tight social groups of whales and dolphins is a cause – if one individual, especially if it is the ‘leader’ of a social group, becomes ill or injured the others will follow it when it beaches. An emerging explanation is that the increased ‘noise pollution’ in the ocean leads to a breakdown in the communication between whales, causing confusion and strandings. A more sinister follow on from that theme is that intense noises created by humans underwater (such as military sonar or underwater mining explosions) results in internal damage to the animals.

A mass stranding of pilot whales (from http://www.smh.com.au/news)

There is no doubt that anthropogenic (man-made) sounds have increased dramatically over the past century, due to the industrialisation of the world’s oceans. Shipping traffic, commercial activity such as oil drilling and exploration, research and military sources have all added to the din below the waves. I have had the privilege to listen to hydrophone recordings taken recently in False Bay of South Africa, and it has stuck me just how noisy it is down there – not just due to natural sounds of the waves and the dolphin dawn chorus, but because of boat traffic. We are particularly sensitive to the effects of pollution we can actually see – a seal entangled and drowned in an old net, an albatross hooked on a long line hook. But we also need to take into account those aspects of pollution we cannot see and how that affects the world around us.

Noise pollution frequencies in the ocean. Note how the noise generated by shipping falls right over the frequency band used by baleen whales to communicate; and how intense the frequencies of sonar are in comparison (from http://www.wired.com)

Sound travels a lot further and faster in water than in air, and marine mammals in particular utilize this very effectively for communication, hunting and orientation. It should be no surprise then that anthropogenic disturbances in the underwater realm have a marked impact on the physiology and behaviour of animals sensitive to sound. The issue needs to become a major conservation concern because it involves human behaviour influencing the behaviour of other organisms and in some cases, harming them. For example, baleen whales communicate by low frequency calls which happen to be on the same frequency band as the increasing ambient noise from shipping traffic (see Tyack, 2008). Does this decrease the range over which the whales communicate? Does it mask their calls or even confuse them? The effects of anthropogenic sounds on cetaceans in particular range from call silencing, displacement and temporary hearing loss to physiological injury of the hearing canal, internal bleeding and stranding. The effect is dependent on the level of noise (the intensity, amplitude and frequency). The most intense anthropogenic sound source comes from seismic exploration and sonar utilised by the military. 

 

An advert by the Whale and Dolphin Conservation Society (see www.wdcs.org/stop/pollution/)

Jepson and his colleagues published a brief communication in Nature in 2003 which discusses the impacts of military sonar on marine mammals. Even though it is not a recent publication, the intense public interest created in light of the recent strandings calls for the examination of the paper. In 2002, fourteen beaked whales were stranded in the Canary Islands (off the coast of Spain) close to where a mid-frequency military sonar exercise had been conducted.  The animals were dissected (as most stranded whales are, including those stranded at Noordhoek), and these autopsies revealed that the animals had not died of illness. However, there was widespread vascular congestion (the overfilling and swelling of the veins with blood as a result of an obstruction in the vessel) as well as prominent, widespread capillary haemorrhages due to the blocking of the blood vessels by blood clots and air bubbles. These bubbles in the blood vessels were also present in several vital organs. These bubbles and the associated damage of organs are usually associated with severe decompression sickness (the bends). If a human diver rises too quickly to the surface, dissolved gases come out of the blood and form bubbles inside the body as the pressure increases again. Cetaceans (deep diving beaked whales in particular) were thought to have physiological adaptations to cope with pressure changes as they dive, such as exhaling before diving or collapsing of lungs. Jepson et al (2003) argue that the formation of these bubbles may be due to changes in the diving behaviour these animals because of the sound disturbance, such as ascending from depth too quickly. It has also been suggested that sonar pulses force dissolved gas in the blood out of solution through changing pressures. These Canary Island strandings are not unique in the presence of bubble-associated tissue injury. Strandings around the world have revealed gas bubbles in blood vessels and gas-filled cavities in the functional parts of the vital organs. The liver was most affected, with gas-filled cavities taking up between 5 and 90% of the volume of the organ. These cavities are not filled with the bacteria associated with the decomposition of a body, and are therefore caused by something before death. 

So, what did cause the strandings of those pilot whales on the beautiful beach in Noordhoek? Necropsies are still taking place, and I look forward to the publication of the results. Until then, we will continue to ponder the deaths of these magnificent creatures. Was it natural? Or was it, once again, the fault of humans?