Report on the Climatology of the Atlantic Basin
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It is well known that climate in different areas is very important for ocean. The temperature of the surface layer, evaporation, salinity, horizontal and vertical circulation of water - all this is in direct or indirect connection with atmospheric processes. The main special feature of Atlantic basin is its large extent and its relatively small width (especially in the North Atlantic), which causes a greater impact on the climate of the ocean and surrounding continents. In addition, the important fact is that the Atlantic seas deeply go into the land. The Atlantic basin borders with vast regions of cooling and formation of high atmospheric pressure: Greenland and the Arctic basin – in the north, Antarctica - in the south. Because of the powerful cooling center - Antarctica, the Southern Hemisphere is largely colder than the northern one, the thermal equator over the Atlantic, as well as for the planet, is shifted to the Northern Hemisphere.
Winds, cyclones and water masses
A special feature is the large seasonal variation of Northern Hemisphere winds in comparison to the low variability of the wind field in the subtropical zone of the Southern Hemisphere. This is similar to the situation in the Pacific Ocean and again caused by the impact of the Siberian and to a lesser extent North American land masses on the air pressure distribution. As a result the subtropical high pressure belt, which in the northern winter runs from the Florida - Bermuda region across the Canary Islands, the Azores, and Madeira and continues across the Sahara and the Eurafrican Mediterranean Sea into central Siberia, is reduced during summer to a cell of high atmospheric pressure with its centre near the Azores.
Azores High dominates European summer weather, bringing winds of moderate strength. During winter, the contrast between cold air over Siberia and air heated by the advection of warm water in the Norwegian Current region leads to the development of the equally well-known Icelandic Low with its strong Westerlies, which follow the isobars between the subtropical high pressure belt and the low pressure to the north. The seasonal disturbance of the subtropical high pressure belt in the Southern Hemisphere is much less developed, and the Westerlies show correspondingly less seasonal variation there.
In the Southern Hemisphere subtropical latitudes, the center of high pressure is the South Atlantic high. In the temperate and subtropical latitudes, it is a zone of reduced pressure, and in Antarctic region it is the area of constantly high pressure, which largely determines the weather in the surrounding areas of the ocean.
The trade winds blow from the subtropical highs to the equator. In the Northern Hemisphere the trade winds have north-east direction and in the Southern Hemisphere they have south-east direction. The stability of these winds direction is up to 80% per year. In the temperate latitudes of both hemispheres western component winds prevail. They are of high speed. In the Southern Hemisphere these winds often turn into the storm - "Roaring Forties". “The Trade Winds are somewhat stronger in winter (Februaryin the north of the equator and August in the south) than in summer on both hemispheres. Seasonal wind reversals of monsoon characteristics are of minor importance in the Atlantic Ocean; their occurrence is limited to two small regions, along the African coastline from Senegal to Ivory Coast and in the Florida - Bermuda area.” (Tomczak, Matthias & Godfrey, 2003) Important seasonal change in wind direction is observed along the east coast of North America, where there are offshore winds during most of the year but warm alongshore winds in summer.
Clouds over the ocean are divided by zones. Tropical and subtropical latitudes are characterized by low cloudiness while temperate and polar latitudes are characterized by high cloudiness. High cloudiness is also observed in the equatorial belt. The average annual precipitation over the Atlantic, in the Northern Hemisphere, is higher than in the same latitudes of the Southern Hemisphere. Near the tropics the difference between western and eastern parts of the ocean is also noticed: the annual precipitation decreases from west to east from 500 to 100 mm. Frequent and dense fogs that are the result of combination of warm air masses and cold water surface are very typical for Atlantic basin. Very thick fog, especially in summer, is formed in the area of the Newfoundland Grand Banks, where warm and cold water mix; the same phenomena occurs in the mouth of the Rio de la Plata.
“Average water temperature at the surface is +16,9 °C, while in the Pacific it is +19,1 °C, Indian it is +17 °C.”(Marshall, Plumb, 2008) The average water column temperature of the Northern and Southern Hemispheres also differs from one another. Due to the Gulf Stream, the average water temperature in the North Atlantic is +6,3 °C and +5,6 °C in the South Atlantic. In general, the temperature of the water surface decreases from the equator to the poles, as well as from west to east. The presence of warm currents keeps the temperature in the west higher than in the east. Also seasonal changes in temperature are well noticed. The lowest temperature recorded in February was in the north and in August in the south, and the highest – vice versa. Daily fluctuations in temperature of the surface layer are not significant. The annual temperature amplitude at the equator is no more than 3 °C, in subtropical and temperate latitudes it is 5-8 °C, and in polar it is - 4 °C. Significant horizontal temperature gradient of the surface layer is in the center of cold and warm currents combination places. For example, “the temperature difference of 7 °Celsius between East Greenland and Irminger within a radius of 20-30 km is a common fact” (Goni, Malanotte, 2003).
Global Warming in the Atlantic Ocean
If the temperature of the Atlantic Ocean increases, it can lead to a stalemate in North America and Europe. That means that if this or that weather will last longer than it should, some places will suffer from flooding and other from drought.
Abnormal weather patterns usually arise from changes in the course of so-called atmospheric jet stream - high-altitude winds, which blow strongly. Because these huge air masses that they had to pick up, remain in one place.
The most interesting fact is that the coincidence of several locks can knock off the usual direction of the Atlantic hurricanes, and this, in turn, will lead to changes in ocean currents, or their speed. If large-scale water circulations slow down, become weaker, the northern part will get an excess of warm and more saline water. Erosion of glaciers base will intensify, the melting of Greenland will accelerate, and the changes in the subpolar ecosystems will take place.
In addition, the melting of ice in the Arctic and the growth of Siberian rivers stock lead to desalination of the Arctic Ocean, which could eventually result in a restructuring of the currents circulation of the Atlantic ocean.
Also the increase in currents speed is noticed in recent years. Scientists have found that the flow speed has become almost two times higher than during the second part of the 19th century. The increase in currents speed leads to the fact that the ice is brought to the southern latitudes faster and in bigger quantities, to the Greenland area, and there it melts. All these factors lead the appearance of "cold screen" on the water surface in North Atlantic, which affects the circulation of currents in the area of the ocean. Some scientists predict that these processes may affect the changes in the Gulf Stream. There is a possibility that the Gulf Stream, which is now being separated from Cape Hatteras, in the form of the North Atlantic current passes through the north of Europe, can get stuck in the form of a ring, the internal circulation in North Atlantic. The result can be a significant cooling in the northern parts of Europe, which are now heated by this current.
Meanwhile, according to the forecasts, the world is predicted to warm up for at least about a century. The models show that the temperature is likely to stabilize for about ten years, after which the warming will continue. The additional heat will be absorbed by ocean during some time, which also results in an ecological problem.
Ocean acidification is one of the most important ecological problems. This problem is directly connected with human activity.
The absorption of CO2 by the ocean is a normal fact and does not damage ocean ecology if the amount does not exceed the natural amount of this gas. However, the absorption of the excessive amounts of carbon dioxide (produced by humans) leads to changes in the chemical composition of sea water, that is, to its acidification. Over the past 200 years, as a result of industrial and agricultural activities on Earth, atmospheric concentration of carbon dioxide rose to its highest level over the past 800,000 years, which caused the planet warming. Oceans have absorbed 525 billion tons of carbon dioxide in the same period. This, in turn, greatly harms all marine life. In particular, various marine organisms as zooplankton, corals, and clams suffer a lot because it becomes harder to build their shells and exoskeletons. Plankton and clams are fish food so the lack of food leads to the disappearance of many species.
The ocean plays an important role in curbing of global warming. According to the scientists’ calculations, the ocean absorbs about one-quarter of carbon dioxide produced by man. If absorption did not take place, the rate of warming of the planet would be accelerated significantly. Scientists estimated that ocean acidity has increased by 0.1 pH, and by the end of the century, they predict the increase of water acidity by 0.3-0.4 pH. (Marshall & Plumb, 2008)
Already, we can see that the fish leave their usual habitat. A good example is the cod, which goes from the south polar seas to the north. But how ocean acidification affects the ability of the water cod to adapt to the temperature is not explored. Also, large colonies of mussels in the northern part of the Mediterranean Sea are influenced by warming. It has already been noticed that this species is on the way of extinction.
Atlantic Ocean is the second largest ocean in the world. The climate of its basin is very interesting; it has its special features and its ecological situation is not a problem of the region but of the whole world. That’s why it is very important to explore this area, learn its nature and improve its ecological situation.