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Effect of Ocean Conveyor Belt on Global Climate

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Published: Thu, 19 Oct 2017

  • Marie Claire Attard Bason

Discuss the ocean conveyor belt system and its implications on global climate

Without the ocean, life on earth will be impossible. When viewed from outer-space, our planet is covered with water; water which is always in constant motion. The ocean covers 71 % of the earth, where 6% of it is covered by sea ice (Siedler, Church, Gould &Griffies, 2001). These mentioned factors make the ocean an important key factor in the transfer of heat energy around the planet. This movement of through ocean currents affect the local weather and temperature to some extremes, which effects also the stabilization of global climatic patterns, the delivery of nutrients and larva to marine ecosystems and many more (Cowan, National Geographic, http://education.nationalgeographic.com/education/media/ocean-currents-and-climate/?ar_a=1, n.d). Moreover, in total, 81 % of the earth’s surface is covered by liquid water including lakes and rivers as well, and covered by solid water which includes snow and land ice (Siedler, Church, Gould & Griffies , 2001). One should first understand some of the major properties of the oceans and the types of circulations and currents that exist, than understand the effect of heat transfer called the Thermohaline Circulation or known as the Conveyor belt, its implications on the climate and anthropogenic influences.

First and foremost, the ocean circulation is generally classified into two parts; a wind-driven circulation that influences the upper part of the ocean system, hundreds of meters up, and the other is a density-driven circulation that influences the bottom part. The major wind currents include the sub-tropical and sub-polar, the Antarctic Circumpolar Current, and the equatorial currents (Grinsted, 2005). Moreover, this system is called the ‘Thermohaline’ circulation, because of its role in heating, cooling and salinification. These roles effect the production of the regional density within the ocean (Toggweiler & Key, 2001). To explain this process in a much better way, the conveyor belt is the ocean circulation system that is driven by changes of heat and freshwater across the sea surface, after the heat and salt are mixed together. This is a driving mechanism (Rahmstrof, 2006).

Secondly, the Thermohaline circulation is seen in the sinking phase, and interestingly enough, there is the formation of new deep water in the North Atlantic and the Southern Ocean. No one exactly knows the whereabouts of the upwelling zones (Rahmstrof, 2006) as the conveyor system has no end (as seen on Fig. 1), but then, in the polar seas near Greenland, there are cold winds from the northern of Canada that cools the surface waters and thus creates sea ice formation (ELF, www.andrill.org/education/…/3A/GlobalOceanConveyWCredits.pdf‎, n,d)

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Fig. 1 Shows the Conveyor Belt pattern and transfer of currents

The process of ice formation is linked to evaporation. With the rising temperature, the sea compresses out the salt from the forming ice. When this process occurs, the surrounding waters become saltier and even more denser. Then, this dense water sinks to the bottom and flows along to the North and South America direction. When this approaches Antarctica, it surrounds the continent and meets with the Antarctic Bottom Water (AABW). This process continues on when then flow flows towards the north into the ocean basins where gradually it mixes with warmer waters present at that site, therefore it rises to the surface in the Pacific Ocean. From there, it makes its way back to the Atlantic and becomes part of the wind driven surface currents eventually returning to the Greenland seas to begin the process again

(ELF, www.andrill.org/education/…/3A/GlobalOceanConveyWCredits.pdf‎, n,d).

In 1751, the first measurement of deep ocean temperatures was recorded by a ship captain of an English trading ship, when he discovered that the water underneath his ship, about a mile below his ship was very cold, despite the location he was at; a sub-tropic location. In 1797, again yet another Englishman named Benjamin Thompson, came up with an accurately explanation on this discovery about cold currents coming from the poles. The difference between Thermohaline and wind driven circulation was distinguished in the 19th-Century, during an argument regarding ocean currents. It was question as well weather or not these two processes happen when the wind pushes along the water or else if they are “convection currents” due to heating and cooling processes. It is important to note that both processes are combined in non-linear way, meaning that both cannot be separated by oceanographic measurements. That is why there are two obvious mechanisms of force, and neither are uniquely separable circulations. Moreover, if changed, the Thermohaline circulation will also change the wind driven currents (Rahmstrof, 2006).

The Atlantic Ocean is the most powerful Thermohaline circulation in the oceans today. The conveyor belt roughly estimates at 15×106 m3 of upper ocean water into deep water (Toggweiler & Key, 2001) where currents typically extend down up to 1-2km depth, although wind only directly drives between 50m to 200m (Grinsted, 2005). Generally, the flow in the upper part of the conveyor mostly passes through the Florida Straits and up to the east coast of North America, which forms part of the Gulfstream (Toggweiler & Key, 2001). However, one disadvantage may include climate change which is likely to weaken the Thermohaline circulation in the future, with some risk of triggering sudden changes, some of which can be unexpected, that may be irreversible (Rahmstrof, 2006).

In Recent years, there have been numerous newspaper reports, articles on magazines and television documentaries that covered this topic involving concerning threatening scenarios of the Atlantic Thermohaline circulation being breakdown. If this is the case, than this affects and collapses the northern European agriculture and fisheries, and also glaciers will move very fast on Scandinavia and Scotland waters. Irreversible changes are set to be taken very seriously in the discussion on climate change effected by humans. (Rahmstorf, 2000). The Southern Oscillation is the most prominent year to year climate variability that exists in the world. It is associated with many risks such as; fluctuations on atmospheric pressures at sea level point in the tropic regions, a downpour of rainfall, and cold winter circulation over the North of America and other parts of the extra-tropic regions. When this Southern Oscillation was recognized in the late 1960’s, this was related to the oceanic phenomenon- El Nino (Rasmusson & Wallace, 1983). Events concerning El Nino have instances which creates serious consequences for climate and ocean ecosystem. The 1982- 1983 El Nino was perhaps one of the strongest that happened. The El Nino Events, have been documented as far back as 1826 and they are usually followed by professionals that constantly keep and eye on any predictable patter when they occur about once every 4 years (Cane, 1983).

The conveyor belt can be affected by global warming in two different ways; either by warming the surface or else by freshening up the surface. This effect will reduce the density of high-latitude water surfaces waters and therefore inhibits a deep formation in water (Rahmstorf, 2006). Our planet cannot lose all of its water from its surface reservoirs due to sub-duction processes. After an approximate of 1Billion years, only between 25- 30% of the newly generated ocean will be subducted into the mantle. It is also said by many scientists and geographers that in the far future, if the external forces are left separately, than the surface reservoirs will be kept in a steady state. Chances for the Earth’s ocean lie in the faith of external forcing. Unfortunately, all water could disappear as a result of increasing levels the temperature, globally, caused by the total of power generated from the Sun to space (Bounama, Franck & von Bloh, 2001)

How long will it take before the entire Earth dries up from its waters completely? There is still no certain answer to this. Results from studies done by Lovelock & Whitfield (1982) show that liquid water will be always available in surface reservoirs as a result of internal processes, however, the extinction of the biosphere will be caused by other limiting factors caused by external forces.).(Bounama, Franck and von Bloh, 2001)

References

Bounama, C., Franck, S., & Bloh, W. v. (1999). The fate of Earth’s ocean.Hydrology and Earth System Sciences,5(4), 569-576.

Cane, M. A. (1983). Oceanographic events during el nino.Science,222(4629), 1189-1195.

Cowan, A. M. Ocean currents and climate A roller coaster analogy to the ocean conveyor belt Retrieved December, 29th, 2013, fromhttp://education.nationalgeographic.com/education/media/ocean-currents-and-climate/?ar_a=1

Environmental Literacy Framework. (). Global ocean conveyor belt. Message posted towww.andrill.org/education/…/3A/GlobalOceanConveyWCredits.pdf

Grinsted, A. (2005). The thermohaline circulation.

Lovelock, J. E., & Whitfield, M. (1982). Life span of the biosphere.

Rahmstorf, S. (2000). The thermohaline ocean circulation: A system with dangerous thresholds?Climatic Change,46(3), 247-256.

Rahmstorf, S. (2000). The thermohaline ocean circulation: A system with dangerous thresholds?Climatic Change,46(3), 247-256.

Rasmusson, E. M., & Wallace, J. M. (1983). Meteorological aspects of the el Nino/southern oscillation.Science,222(4629), 1195-1202.

Siedler, G., Church, J., Gould, J., & Griffies, S. (2001).Ocean circulation and climate: Observing and modelling the global oceanAccess Online via Elsevier.

Toggweiler, J., & Key, R. M. (2001). Ocean circulation: Thermohaline circulation.Encyclopedia of Atmospheric Sciences,4, 1549-1555.


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