There’s a Hole in the Ozone Layer, Dear Liza, Dear Liza

A blog about the human impacts on Antarctica would be incomplete without a post or two concerning the hole in the ozone layer. This is perhaps the most well-known human impact on the continent. Furthermore, this blog has so far considered the human impacts on the ground or on the marine environment. The atmospheric effects are also significant. 

The ozone layer lies between the stratosphere and the troposphere. The reason this layer is useful to us is that ozone molecules absorb ultraviolet (UV) radiation from the Sun and therefore protect us from the harmful effects of excessive UV radiation exposure (Martin and Hine, 2014, in ‘A Dictionary of Biology’).

The hole in the ozone layer was discovered by Farman et al. (1985). The authors collected data at the Halley Bay research station from 1957 to 1984 and, by using spectrophotometers, discovered that the ozone layer was depleting in spring (which is from September to November). The cause of ozone depletion was found to be a chemical reaction that occurs between chlorine and bromine atoms, that originate from chlorofluorocarbons, and ozone (Molina and Rowland, 1974). Chlorofluorocarbons (CFCs) were invented in the 1920s and commercially manufactured in the 1930s (The Ozone Hole, 2014). CFCs were used as cleaning solvents, in fire extinguishers, in aerosols and as refrigerants in air conditioning units (Tsai, 2014:883, in ‘Encyclopedia of Toxicology’). They were desirable because they possessed beneficial properties, including the fact that they were nontoxic and non-flammable. 

Molina and Rowland found that the reaction takes place in the presence of UV radiation. According to the NOAA (2008), during the Antarctic winter, ‘stratospheric ice clouds (PSCs, polar stratospheric clouds) form when temperatures drop below -78C. These clouds are responsible for chemical changes that promote production of chemically active chlorine and bromine’. During the winter, there is no sunlight in Antarctica. Thus, when spring arrives and the sun appears, chlorine and bromine molecules react with ozone molecules, causing it to break down. This is what creates a hole in the ozone layer during the spring. The reason why Antarctica in particular is subject to ozone depletion more than, say, the Arctic, is that cold temperatures are required for the reaction (Solomon, 2004). Figure 1 shows the monthly mean total ozone levels at Halley Bay in October, the middle of spring when ozone depletion occurs, from 1957 to 1984. The figure shows spring ozone depletion starting from the mid-1960s. CFCs have caused the ozone layer to deplete by as much as 50% (Smith et al. 1992) not just in spring, but in the winter as well (Rowland, 1986). The human invention of CFCs has therefore been the sole contribution to ozone depletion. 

Figure 1. Monthly mean total ozone levels at Halley Bay in October from 1957 to 1984. Source: Farman et al. (1985)

Effects

Without the protective shield from the ozone layer, more UV radiation reaches the Earth. For humans, greater exposure to UV can have severe health effects, such as increasing the likelihood of developing skin cancer (Norval et al. 2011), damage to DNA (Herrlich et al. 1992) and eye damage (Longstreth et al. 1995).

But I think it would be more relevant to focus on the effects of ozone depletion on species living in Antarctica. For instance, it has been observed that marine phytoplankton and diatoms have experienced DNA damage due to greater UV exposure (Buma et al. 2001). Furthermore, Smith et al. (1992) discovered that, in the Bellingshausen Sea (for a map of its location, see this post), a greater concentration of UV radiation is hindering photosynthesis which in turn is preventing the growth of phytoplankton. These findings illustrate how the marine ecosystem is negatively affected by the hole in the ozone layer. More specifically, phytoplankton is affected negatively. The importance of phytoplankton is illustrated by the food chain from my post from 29 November. Krill and penguins feed on phytoplankton. This shows how ozone depletion affects the food chain and therefore causes a change in the marine ecology of Antarctica. Additionally, this highlights that although ozone depletion happens in the stratosphere, there are indirect terrestrial effects observed as well.

Figure 2. Marine phytoplankton

I shall end this post with a short video to summarise the hole in the ozone layer, i.e. the key findings, the mechanism, the treaty…etc. It is presented by Shanklin, who co-discovered the hole in the ozone layer.

Next week, I will explore the subsequent regulation that followed from this discovery and its success at restoring the ozone layer. The updated score is 7-4, negative impacts seem to be taking the lead! 

License to Krill I

Krill are small crustaceans that resemble shrimp and feed of diatoms. They are very abundant in Antarctica, in fact their total global combined weight ranges from 500 to 700 million tonnes (Voytek,1990)! Krill are small creatures as demonstrated by figure 1, which shows their size relative to a paper clip. Despite how small they are, they are essential for life in Antarctica. According to the National Geographic (2014), 'without krill, most of the life forms in the Antarctic would disappear'.

Figure 1. Size of krill relative to a paperclip. Source: The National Geographic (2014)

Why are krill so important?

Krill play an important role in the Antarctic food chain. Krill are at the bottom of the food chain which means that they are important food sources for whales, penguins, seals, fish, copepods and sea birds (Tomaselli, 2012). These animals make up the majority of those found in Antarctica. Because so many animals rely on krill, a change in krill availability may result in starvations among some of these Antarctic animals.

Figure 2 shows which animals feed on krill. Krill are consumed by Emperor penguins, Adélie penguins, crabeater seals, leopard seals, and baleen whales. It’s important to note that the figure does not show all of the animals feeding on krill, only a selection.

Figure 2: Antarctic food chain. Source: Voytek (1990)

Krill population

Given the importance of Antarctic krill in maintaining populations of marine and terrestrial animals, it is desirable to keep krill populations steady. But this not the case. In fact, humans are reducing the levels of krill in Antarctica, both directly and indirectly.

First I’ll explain the direct impacts on krill population. Krill populations are declining due to fishing. The Soviet Union began fishing Antarctic krill in the early 1960s (Aronson et al. 2011). In the 1970s and 1980s, many other countries followed (ibid). Krill are sought after because they are used as fish bait, fish feed in aquaculture and for aquarium trade (ibid). Furthermore, krill can be transformed into krill oil, which is a source of omega-3 and can have beneficial health impacts for us. Krill oil can help protect us against and lower the risk of suffering from health conditions such as rheumatoid arthritis, heart disease, stroke, depression and osteoporosis (University of Maryland Medical Center, 2013; accessed 28 November 2014).

These health benefits incentivise pharmaceutical companies to fish Antarctic krill because there is a market for krill oil products. Below is a video published on YouTube by the pharmaceutical company, BioCeuticals, which catches krill to turn into krill oil. I've posted this video because it gives you a flavour of the use of krill to humans.

What is interesting to note about this video is the way the company justifies its activities. Phrases like “krill is found in great abundance all around the Antarctic continent” and "the estimated biomass of Antarctic krill is twice the biomass of the worldwide human population"  indicates that krill are plentiful anyway so fishing would not create any disastrous ecological impacts. Also, the fact that the company interviewed a WWF Director demonstrates that they care about krill levels in Antarctica and want to engage in fishing in a sustainable manner.

Despite what this company claims about sustainable fishing, Antarctic krill populations have been declining. Figure 3a shows this steady decline. Even though there have been fluctuations since the 1970s, the general trend is a decrease in krill. Figure 3b shows where the krill populations have been declining and to what extent. In figure 3b, the red area indicates where the largest declines have occurred, which has been in the North. This region also happens to be the most accessible for ships because it is close to Argentina, making visits likely. As the video above showed, large ships travel to Antarctica to catch krill and turn them into oil almost immediately (while on the ship).

Figure 3. Krill population decline. 
a) Krill density in Antarctica from 1976 to 2000
b) Krill density across Antarctica
Source: Atkinson et al.(2004)

Indirectly, humans are having an impact on krill populations via climate change. Climate change is causing an increase in sea surface temperatures which is affecting the spawning and nursery areas of krill (Atkinson et al. 2004). According to Hill et al. (2013), sea surface temperatures have been increasing by 0.2^oC every ten years, but this is predicted to increase to warming of between 0.27^oC and 1.08 ^oC by the end of this century. Warmer sea temperatures are causing reduced sea ice extent which is problematic for krill because sea ice forms a large part of krill’s habitat. Atkinson et al. (2004) explains that sea ice also shields krill from predators and fosters sea algae, which are a key food source for krill. Additionally, climate change is exacerbating the destruction of their habitat because winter sea ice duration is reducing due to warmer temperatures and warmer oceans, thus humans are indirectly having a negative impact on krill.

So in this post, hopefully my readers have understood the importance of krill for Antarctic animals that feed on krill and have realised what negative impacts we are having on them, both directly and indirectly. The new scores are negative impacts 4, natural/positive impacts 2. Next week, I will discuss another indirect effect that humans have had on krill population.