We all used to fantasize about the day when gold would fall directly from the sky so that we could lie flat and touch the fish and sit on the "Tomson Yipin", but reasonable people should be able to think that this is just a beautiful daydream. However, there is such a country in the world, although the sky of their country will not fall real money and silver, but there will be millions of seabirds falling bird droppings of bird droppings can be turned into gold, truly "seeing dung as money".
I believe everyone has heard that Australia is a "country sitting on the back of a sheep" and made a fortune from wool, but this is not the ultimate goal of fish lovers, after all, they also have to feed sheep, trim wool and so on. Peru, an island nation in the Pacific, can "get rich overnight" by picking up and selling guano, and this way of getting rich is also aptly called the "guano economy" by economists.
Bird droppings are quite disliked in the city, and if they are unlucky, they will be uncomfortable for half a day. In agriculture, guano is a treasure, it is an important natural organic fertilizer for the production of crops. Although the feces of other animals also have a fertilizing effect, sea bird droppings are rich in nitrogen and phosphorus, so they are ideal organic fertilizers. In addition, bird droppings rich in nitrogen and phosphorus can be converted into a large amount of phosphate in the high temperature environment of the equator, and under the addition of the environment, various apatites can be formed and converted into phosphate rock, which is also a lot of wealth.
Geographical location of Peru
Peru, a coastal country in the Pacific Ocean
Peru is located in the western part of the South American continent, on the east coast of the Pacific Ocean, because of the Peruvian fishery, one of the world's four largest fisheries, the abundant fish here attracts many seabirds to stop and prey, and these seabirds have left a large amount of guano here. There is a very desolate island off the coast of Peru, the Islas Chincha, which has become a paradise for birds such as cormorants and pelicans due to the lack of human activity. The density of birds here is as high as 2.2 million per square kilometer, and a large number of birds have accumulated hundreds of meters of guano here.
Seabirds that fish for a living
Why is peru rich in fishing grounds and an exaggerated "guano economy"? All this is due to Peru's unique geographical location. As mentioned earlier, Peru is located on the eastern coast of the Pacific Ocean and near the equator, which has contributed to Peru's natural large fisheries and the "guano economy", all of which begin with a mysterious ocean current, the upwelling current.
Bird droppings workers in Peru
We all know that due to the sun's credit, the surface of the seawater is relatively warm, and the deep seawater that cannot be exposed to the sun in the lower part is relatively cold, and a thermocline is formed between them. The upper part of the thermocline is a sea surface mixing layer, the temperature of the mixed layer is relatively uniform, the general thickness is 50-100m, the lower part is the deep cold water, the thermocline is sandwiched between the two temperature changes very sharply in a layer of seawater. In calm winds and waves, the thermocline isolates the nutrient-poor warm seawater in the upper part and the cooler seawater rich in nutrient salts in the lower part, which results in the fish often concentrating in the lower part. But when the wind blows on the shore, the situation is completely different.
Thermocline: Divide the upper warm water and the lower cold water
Speaking of which, you still remember the geodescience deflection force (sometimes called the Coriolis force) that you learned in junior high school geography, when an object moves on the surface of the earth, the geodesic deflection force will drive it to unconsciously change the direction of motion, the southern hemisphere is deflected to the left, and the northern hemisphere is deflected to the right.
Perennial northerly winds along the Peruvian coast, combined with the effects of geodesic deflection forces, drag the surface waters westward. When the surface waters are all moving westward, in order to replenish the balance of the water level, the deep cold water rises, which is the upwelling current mentioned earlier. The cold sea water carries rich nutrient salts to the surface of the Peruvian coast, and the warm sea water and rich nutrition attract a large number of fish to survive and reproduce here, which in turn attracts a large number of fish-for-living birds to inhabit the Peruvian coast, thus driving Peru's fishery economy and guano economy.
Map of upwelling patterns in Peru
Peruvian fisheries
Of course, this kind of behavior of relying on the sky to eat is sometimes unreliable, and when the national economy and people's livelihood of the whole country depend on the strength of the upwelling, this upwelling is likely to have problems. It is not difficult to imagine that the strength of the upwelling depends on the aforementioned thermocline strength. In normal years, southeastern trade winds in the equatorial Pacific Ocean continuously transport warm water from the east to the west, causing warm water to accumulate on the western side of the Pacific Ocean. Under the influence of the Earth's rotation, the water radiating outward on both sides of the equator, coupled with the upwelling of the Peruvian coast, causes the water temperature on the western side of the Pacific Ocean to be significantly higher than that on the eastern side of the Pacific Ocean. This would also keep the thermocline on the eastern shore of the Pacific Ocean, where Peru is located, at a shallower depth and weaker in intensity. At this time, the upwelling will easily break the thermocratic jump and then rise, the intensity will be very large, and it will also bring explosive wealth to Peru.
Pacific SST pattern in normal years
However, Peru's fisheries and guano economy are vulnerable to natural and man-made disasters. El Niño should be heard of by everyone, and the general understanding is only to make it warm when cold, and cold when warm. But in fact, el niño is a manifestation of the imbalance between the ocean and the atmospheric system, and it is the fishermen in Peru, Ecuador and other places who name this phenomenon.
When El Niño occurs, the difference in air pressure between the east and west sea levels near the equator decreases, which leads to a weakening of the strength of the most important southeast trade winds near the equator. As soon as the southeast trade wind weakens, it will cause the warm water in the eastern Pacific Ocean to flow back and flatten the sea level.
Don't look at the calm and waveless surface of the sea, but there has been a huge change below sea level. A large amount of warm water reflux increases and gradually accumulates warm water in the eastern Pacific Ocean, constantly pressing down the thermocline and increasing its strength. The upwelling current off the coast of Peru can no longer be smoothly upwelled, and the nutrient-rich cold water at the bottom cannot be transported to the surface. The loss of rich nutrition, the small fish farmed in Peruvian fisheries have died in large numbers, which not only the fishermen have no income, but the seabirds also have little food, and the dream of falling "gold" in the sky is shattered.
Pacific SST distribution in El Niño years
Of course, there are still many opinions about the mechanism of El Niño, and some scientists believe that it is the cause of the change in the earth's rotation rate, but many scientists believe that it is likely to be the consequence of global warming. Therefore, it is difficult to say whether the collapse of the Peruvian fishing farm economy and the guano economy was a natural or man-made disaster. But in any case, we all know that human beings are still too far away from fully recognizing and using nature.
Note: Image source network and figure worm
1.https://www.washingtonpost.com/graphics/2018/world/in-peru-guano-bird-droppings-are-the-new-gold/
2.https://globalfishingwatch.org/news-views/peruvian-fisheries-covid-19/
Resources
[1] Introduction to Marine Science courseware
Chen Peng, Chen Xinjun, Lei Lin. Effects of Upwelling In Peru on Peruvian Anchovy Fishery[J]. Journal of Fisheries Science, 2018, 42(9):11.
Wang Linhui, Shi Jie, Gao Huiwang. Variation characteristics and influencing factors of Upwelling in Peru in 2014-2016 El Niño[J]. Journal of Ocean University of China:Natural Science Edition, 2020, 50(7):9.
Editor: Zhu Wenxiao
Proofreaders: Li Yuju, Zhao Na