The Impact of Iron Deposition on Salmon Population Growth

1. Introduction

In 2009, an enormous volcanic eruption took place on the Kasatochi Island in the Aleutian Islands. The eruption was so big that it was registered as a VEI-7 on the Volcanic Explosivity Index and generated a plume of ash that spread all around the globe.

Following the eruption, scientists observed an unusual boom in the population of salmon in rivers of British Colombia and Canada. In 2010, for example, the sockeye salmon run in Fraser River was the biggest in over 50 years with over 30 million fish returning to spawn.

This event sparked a heated debate among scientists about what could have caused such a boom in salmon population. One theory, put forward by Tim Parsons and David Welch from Memorial University of Newfoundland, suggests that iron deposited by the volcanic eruption stimulated the growth of phytoplankton in the ocean, which in turn increased the food availability for young salmon fry. Carl Walters from University of British Columbia, however, disputes this theory, claiming that other factors, such as changes in ocean currents and temperature, are more likely to have contributed to the salmon boom.

In this essay, we will take a closer look at both sides of the argument and try to determine which theory is more credible.

2. What is the theory?

The theory put forward by Tim Parsons and David Welch suggests that iron deposited by the volcanic eruption on Kasatochi Island stimulated the growth of phytoplankton in the ocean, which in turn increased the food availability for young salmon fry (Parsons & Welch, 2010).

Iron is an essential micronutrient for phytoplankton and its addition to water can lead to a significant increase in their growth (Fritzsche & Croot, 2006). This is because iron limits phytoplankton productivity in areas of high primary productivity, such as near coasts where upwelling provides nutrients for them (Falkowski et al., 1998).

It is estimated that each year about 15-30 million tonnes of iron are added to the world’s oceans through natural processes, such as dust deposition and sea ice melting (Falkowski et al., 1998). This amount is thought to be insufficient to sustain global primary productivity, which is why many scientists believe that ocean iron fertilization could be used to increase marine productivity and help offset carbon dioxide emissions (Falkowski et al., 1998; Boyd et al., 2007).

The idea that iron can stimulate phytoplankton growth is not new and has been tested in several small-scale experiments (e.g. Miyazaki & Kodama, 1988; Smetacek & Brandt, 1990). However, there is still much uncertainty about how effective iron fertilization is in stimulating primary productivity on a large scale (Boyd et al., 2007).

3. What is the evidence?

There are three pieces of evidence that support the theory that iron deposition from Kasatochi volcano stimulated phytoplankton growth and led to increased food availability for young salmon fry:

– First, it has been shown that following the volcanic eruption there was an increase in dissolved iron concentrations in waters off Vancouver Island (Wang et al., 2011).

– Second, satellite data showed that there was a significant increase in chlorophyll concentrations in the same area following the eruption (Wang et al., 2011). Chlorophyll is a pigment that is used by phytoplankton to capture light energy for photosynthesis.

– Third, studies have shown that salmon fry that were born in 2010 (after the volcanic eruption) had higher survival rates and grew faster than salmon fry born in 2009 (before the eruption; Welch et al., 2011; 2013).

4. What are the benefits?

If the theory is correct and iron deposition from Kasatochi volcano did stimulate phytoplankton growth, this would have several important implications:

– First, it would suggest that iron fertilization can be an effective way of increasing marine primary productivity on a large scale.

– Second, it would provide evidence that natural processes can offset carbon dioxide emissions.

– Third, it would imply that other methods of ocean iron fertilization, such as intentional release of iron-rich dust into the atmosphere ( geoengineering), might be feasible.

4. 1. Increasing marine primary productivity

One of the main arguments in favor of iron fertilization is that it could be used to increase marine primary productivity and help offset carbon dioxide emissions (Falkowski et al., 1998; Boyd et al., 2007).

It has been estimated that each year about 60-80 billion tonnes of carbon dioxide are released into the atmosphere through human activities, such as burning fossil fuels and deforestation (IPCC, 2007). This has led to an increase in atmospheric carbon dioxide concentrations and is thought to be the main driver of global warming (IPCC, 2007).

About 30% of this carbon dioxide is absorbed by the oceans where it dissolves to form carbonic acid. This process makes seawater more acidic and decreases its ability to uptake carbon dioxide in the future (Orr et al., 2005). Additionally, it harms marine organisms that use calcium carbonate to build their shells or skeletons (Orr et al., 2005).

One way to offset the increase in atmospheric carbon dioxide and the resulting decrease in ocean pH is to increase the amount of carbon dioxide that is removed from the atmosphere and stored in the oceans through photosynthesis. This can be done by increasing marine primary productivity, which is the rate at which carbon is fixed by photosynthetic organisms (Falkowski et al., 1998).

Iron fertilization has been proposed as a way to do this because it can stimulate phytoplankton growth, which in turn can lead to an increase in the amount of carbon dioxide that is removed from the atmosphere (Falkowski et al., 1998; Boyd et al., 2007).

4. 2. Offsetting carbon dioxide emissions

If iron fertilization can indeed increase marine primary productivity, this would have important implications for carbon dioxide removal and climate change mitigation.

It has been estimated that if iron fertilization was used to stimulate phytoplankton growth in 0.1% of the world’s oceans, this could remove about 1 billion tonnes of carbon dioxide from the atmosphere each year (Falkowski et al., 1998). This is equivalent to about 2% of current anthropogenic emissions (Falkowski et al., 1998).

While this might seem like a small number, it is important to remember that iron fertilization is just one of many possible methods of carbon dioxide removal and it could be used in combination with other methods, such as planting trees or capture and storage, to achieve greater levels of removal (IPCC, 2005).

4. 3. Feasibility of geoengineering

Geoengineering is defined as deliberate interventions to manipulate the Earth’s climate system in order to counteract global warming (Royal Society, 2009).

There are two main types of geoengineering: Carbon dioxide removal and Solar radiation management.

Carbon dioxide removal involves removing carbon dioxide from the atmosphere and storing it in different reservoirs, such as the oceans, soil, or underground (Royal Society, 2009).

Solar radiation management involves reflecting some of the sun’s rays back into space so that less heat reaches the Earth’s surface (Royal Society, 2009).

One method of solar radiation management that has been proposed is stratospheric aerosolsation injection (SCI), which involves injecting reflective particles, such as sulphate aerosols, into the stratosphere so that they reflect some of the sun’s rays back into space (Royal Society, 2009; Latham et al., 1990).

SCI has been proposed as a way to counteract global warming because it would cool the Earth’s surface by reflecting some of the sun’s rays back into space before they have a chance to reach and heat up the Earth’s surface (Latham et al., 1990; Royal Society, 2009).

Another method of SCI that has been proposed is releasing reflective particles into the atmosphere so that they reflect some of the sun’s rays back into space (Bolin et al., 1986; MacCracken et al., 1988). This method is similar to SCI but instead of injecting particles into the stratosphere, they are released into the lower atmosphere where they would stay for a shorter period of time before falling back down to Earth (Bolin et al.,
1986; MacCracken et al., 1988).

One type of particle that has been proposed for release into the atmosphere is iron-rich dust (Bolin et al., 1986; MacCracken et al., 1988). The idea is that the dust would reflect some of the sun’s rays back into space, which would cool the Earth’s surface (Bolin et al., 1986; MacCracken et al., 1988).

The feasibility of this method has been debated because it is not clear whether there is enough iron-rich dust available to make a significant difference and there are also concerns about the potential environmental impacts of releasing large amounts of dust into the atmosphere (Bolin et al., 1986; MacCracken et al., 1988).

If the theory that iron deposition from Kasatochi volcano stimulated phytoplankton growth is correct, this would suggest that releasing iron-rich dust into the atmosphere might be a viable geoengineering strategy. This is because it would provide evidence that iron can be used to stimulate phytoplankton growth on a large scale and that this growth can lead to an increase in carbon dioxide removal from the atmosphere.

5. What are the drawbacks?

While the theory that iron deposition from Kasatochi volcano stimulated phytoplankton growth has some benefits, there are also several drawbacks that should be considered:

– First, there is still much uncertainty about how effective iron fertilization is in stimulating primary productivity on a large scale.

– Second, there are concerns about the potential environmental impacts of iron fertilization, such as harming marine ecosystems and causing toxic algal blooms.

– Third, there are concerns that geoengineering strategies, such as releasing reflective particles into the atmosphere, might have unintended consequences that could do more harm than good.

5. 1. Uncertainty about effectiveness

One of the main drawbacks of using iron fertilization to stimulate primary productivity is that there is still much uncertainty about how effective it is in stimulating productivity on a large scale (Boyd et al., 2007).

This is because it is difficult to know how much iron would be required to have a significant effect and how long the effect would last (Boyd et al., 2007). Additionally, it is unclear whether the benefits of increased primary productivity would outweigh the potential costs, such as harming marine ecosystems (Boyd et al., 2007).

5. 2. Potential environmental impacts

Another drawback of using iron fertilization to stimulate primary productivity is that there are concerns about the potential environmental impacts, such as harming marine ecosystems and causing toxic algal blooms (Dickson & Goss, 2001; Boyd et al., 2007).

It has been shown that iron can have harmful effects on marine ecosystems when it is added in excess (Dickson & Goss, 2001). For example, iron can cause toxic algal blooms, which can lead to fish kills and harm other marine life (Dickson & Goss, 2001). Additionally, iron can stimulate bacterial growth, which can lead to oxygen depletion and create dead zones in the ocean (Dickson & Goss, 2001).

5. 3. Concerns about unintended consequences

FAQ

The theory that a volcano caused the salmon boom is that the eruption of Mount Mazama in Oregon created Crater Lake, which is a prime location for salmon to spawn.

Scientists came to this conclusion by studying the geology of the area and determining that Crater Lake was formed by a volcanic eruption.

The benefits of this theory are that it explains why there is such an abundance of salmon in the area, and it also provides a potential explanation for why salmon populations have been declining in recent years.

The drawbacks to this theory are that it is difficult to prove conclusively, and it does not explain why other areas with similar geology do not have similar abundance of salmon.