The effects of El Nino on the Galapagos Islands

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What is the el nino effect?

El Nino is the name given to one of the most influential natural climate events in the world. It primarily affects the Pacific ocean by changing the pattern of the Walker weather cell. The Walker circulation is a self-perpetuating cycle stretching the length of the Pacific ocean.  Under normal conditions of the Walker circulation – in the ‘neutral’ years when there is no El Nino or La Nina events – there is a pressure gradient, with high pressure in the east and low pressure in the west. Air rushes from the east to fill the area of low pressure in the west. This creates trade winds. Warm surface water in the first 100 metres or so of the ocean is blown west by the trade winds away from South America to Australia. The water blown away from South America is replaced by upwellings of colder water deeper in the ocean. This is beneficial to ecosystems as nutrients are stirred up from the sea bed with these upwellings.Image result for el nino winds

When the El Nino occurs the trade winds can reverse or even weaken because of pressure changes. The lack of trade winds mean warm water no longer shifts west, and the upwelling considerably weakens as there is relatively little surface water movement due to the lack of constant winds. In severe El Nino years the warmer water flows back towards the east. As a result of this temperature and precipitation patterns change because the evaporation of warm water occurs in different places to normal. Commonly, el nino years lead to wetter stormy weather in America and drier in Australia. 

What causes el nino events? 

It is unknown what exactly triggers El Nino events and whether these events are triggered by changes in the atmosphere or ocean. Scientists detect beginnings of El Nino years through something called a kelvin wave, this is caused by short by strong bursts of westerly winds blowing a stretch of warmer water to east mimicking what happens during El Nino. However, this is not enough to cancel the thermocline and soon conditions return to normal. However,  it is projected, due to climate change, that there will be a more rapid sea surface warming over the eastern equatorial Pacific than in the surrounding ocean waters. so, if sea surface temperatures are warmer than normal in the east this is likely to trigger an El Nino because of a lower sea surface temperature gradient, therefore less differences in pressure over the east and west of the Pacific which reduces trade winds. Therefore the consequences of this is that we are more likely to see an increased frequency of El Nino years because of global warming.

How does the El Nino effect the Galapagos?

The Galapagos archipelago is a tiny cluster of islands that stand right in the middle of the equator have some of the most unique and varied wildlife. Many species are endemic to their individual islands and have had millions of years of evolution to adapt to specific conditions. As the El Nino event is a relatively regular cycle theoretically the wildlife should not be hugely disrupted, but, due to global warming the severity of El Nino events are increasing meaning more severe and long lasting consequences for the islands.

Figure 7

To appreciate the uniqueness of the Galapagos archipelago and fully understand the effects of the El Nino we must first understand the oceanography behind them. This begins with the complex network of ocean currents. Normally the North Equatorial current brings warm tropical waters to the north east side of the galapagos. The South Equatorial current brings cool water from the Antarctic circumpolar current. With this, also comes nutritions upwellings from peru (the humboldt current). The Galapagos also stand right in the way of the equatorial undercurrent which pushes almost 1 billion gallons of water per second. When it hits the islands some water goes around but some travels up causing another source of an upwelling. This is the same effect as hitting a wall with a hose, and the water in the undercurrent spreads up throughout the islands carrying cool nutrient rich waters. During El Nino years the humboldt current is cut off as the lack of trade winds means it does not reach as far as the equator. Galapagos map.PNG

The consequences of this means warmer waters throughout the Galapagos, increased rainfall, and less nutritious waters. Not all the consequences are bad, as the rainfall increases plants thrive. But, because of the delicate balance of the ecosystem this can lead to an overpopulation of some species. Particularly invasive species such as goats, rats and pigs will also increase because of the surplus of food. These animals were introduced to the islands when human settlers first arrived and are associated with the decline and extinction of some species. An example of a heavily affected species is the Galapagos Tortoise. Through rats eating their eggs or pigs destroying the vegetation the tortoises feed on some species have become extinct, 10 of the 15 documented species of tortoise are still alive. 

In the aquatic habitats, El Nino decreases the levels of phytoplankton (the primary producer in the ocean), their optimum conditions consist of cool, nutrient rich waters which the ocean lacks during El Nino years. Phytoplankton is a specialist term for algae and make up many different types. Phytoplankton is essential for all life and they are the primary producers in many food chains along with being responsible for producing oxygen through photosynthesis. The occurrence of El Nino causes algae beds to die which is the diet of iguanas, fish and turtles. In the most recent 2015 El Nino event, thousands of iguanas died of starvation. This is not the only problem for them. It was reported in the 1982 super El Nino event when the red and green algae died it was replaced by a hardier brown algae which iguanas could not survive on, and, in the 1997 El Nino event they suffered up to 90% losses.

Because of the higher ocean temperatures the corals surrounding the islands experience bleaching, and consequently die. It can take decades for coral reefs to return to what they once were after severe El Nino years. This is a major problem as coral reefs are one of the most diverse ecosystems in earth, home to countless species of fish, molluscs and crustaceans.

In terms of organisms in the higher trophic levels, for example birds, sea lions and penguins, they also suffer. There are less fish because the fish have less algae to feed on, this means not as many consumers can be supported leading to a higher competition for food. It has been observed that seabirds, particularly blue footed boobies, abandon nesting sites, lay fewer eggs, and migrate longer distances. Mobile species such as sharks will move offshore to deeper waters in search of food but those who can’t such as iguanas sometimes die in an attempt to find food farther out to shore and die in the process of getting back due to a lack of energy. 

References

“What Are The Trade Winds?”. 2017. Oceanservice.Noaa.Gov. https://oceanservice.noaa.gov/facts/tradewinds.html.

“What Is El Niño?”. 2017. Live Science. https://www.livescience.com/3650-el-nino.html.

Leo, Roger. 2009. “How Does El Nino Affect Climate Change? – Onthesnow”. Onthesnow. http://www.onthesnow.co.uk/news/a/8453/how-does-el-nino-affect-climate-change-.

Cai, Wenju, Simon Borlace, Matthieu Lengaigne, et al. 2014. “Increasing Frequency Of Extreme El Niño Events Due To Greenhouse Warming”. Nature Climate Change 4 (2): 111-116. doi:10.1038/nclimate2100.

McLaughlin, Letisha. 2017. El Nino And Its Effects On The Galapagos Islands. Ebook. http://uncw.edu/phy/documents/McLaughlin_07.pdf.

Haugan Cruises. 2017. “Marine Iguanas Suffer With El Nino – Live Natural Selection”. Haugancruises.Com. http://www.haugancruises.com/news/marine-iguanas-el-nino-near-extinction.html.
Bayer, Brian. 2016. “How The El Niño Phenomenon Affects The Galapagos Islands”. Galapagosisland.Net. http://www.galapagosisland.net/galapagos_islands/el-nino-effects-on-galapagos.html.

Authors note

It has been a busy couple of days for me, and frustratingly I have a number of pieces I am working on but haven’t had the chance to sit down and focus on them yet. They will be uploaded here in due time, but, while that is happening I thought I would upload this essay I wrote a number of years ago. Whilst doing my final year of A-levels if I remember correctly. It is inspired by the effects of the El Nino which I saw first hand, and it encouraged me to learn more about this weather phenomenon. To this day visiting the Galapagos is one of my best memories. Anyway, I thought I would share it as it was really my first science essay that I wrote, unrelated to my studies. Apologies if the article is not particularly clear or concise. As I said, I did write it a few years ago but I also didn’t want to edit it too much. Let it be a reminder of what younger me was capable of achieving and a reminder to always keep improving.

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