Earth Science exam Question 1
Q1. Explain the ocean circulation currents and describe the impacts on global climate
Simon Richards

71% of the earth’s surface is covered by water and so has a great effect on the global climate interacting particulary with the atmosphere. The major contributor to the global climate is the sun and its solar energy which warms up the atmosphere, land and water bodies of the planet. The tropics which lie near the equator between 23.50 N latitude and 23.50 S latitude receive the greatest amount of solar radiation as the sun is positioned more directly above this region than any other and the solar energy is available towards the two polar regions as they receive the least amount of solar radiation. The albedo effect also plays a part in the amount of solar radiation that is absorbed by the various surfaces of the planet, the whiter the surface the more solar energy is reflected back into the atmosphere and so the poles covered in snow and ice have a very high albedo effect whereas the dark oceans have a much lower albedo effect and absorb more energy as heat. (Gregory et al; 2002)
Deep water acts as a heat sink absorbing the suns energy and holding it. Generally, the nearer an area of land is to a large body of water, particulary oceans but also large inland lakes, the more moderate the climate is. Since land heats up and cools down much more quickly than large deep areas of water thus a moderating effect on the extremes of temperature of land near to the oceans is produced. During the day the hotter air over land draws in cooler air from over the oceans causing a cooling breeze and this is reversed at night with warmer air rising from the water surface drawing cooler air from the land and replacing it with warmer air.
The circulation of the earth’s ocean currents is the large-scale movement of water around the ocean’s basins. Ocean currents are mainly driven by differences in water temperature which in turn effect the salt concentrations of the water and therefore its density. In the polar regions the water body is cooled in the lower temperatures found in these regions. It is accelerated by the action of melting sea ice sheets and glacier melt which causes the water body to sink. This occurs because water behaves unusually, it becomes less dense as it solidifies and as it freezes it floats. This is due to hydrogen bonding, at temperatures below 4 degrees centigrade the molecules cannot move vigorously enough to break their hydrogen bond and at 0 degrees form a crystalline structure know as ice. This frozen water is approximately 10% less dense than water so floats above it. (Campbell and Reece 2002) Therefore, as ice and snow melt due to global warming the melt water sinks below the ice. This reduces poleward travel of more salty water which further reduces polar salinity creating a positive feedback loop.
This reduction in temperature drives the water down into deep circulation and is especially important particularly in deep oceans below the thermocline where the action of winds on the currents is not an influence as it is in warmer tropical areas of the globe.
The ocean currents flow from high latitudes towards the low latitudes containing warmer water and is called Thermohaline circulation which affects the movement of ocean flow globally. (Curry 1998). The upwelling or mixing caused by this brings essential food and nutrient closer to the surface where it can be used by marine macrophytes who photosynthesize in the diffused sunlight near or on the ocean surface and which are then consumed by marine fauna both micro and macro, greatly enhancing the biodiversity and number of organisms present.
As the cooler waters travel to the tropics they warm up and loop round the continental shelfs leaving the low latitudes to flow up towards the poles again and the process is continuous. The Gulf Stream is a current of warmer water that travels northward from the Caribbean Sea through the North Atlantic Ocean causing a more temperate climate in the UK than its latitude of 53 degrees N would otherwise have.
Winds driven gyres also affect the surface circulation of water but in more limited ways, they are limited in both the depth and latitude and carry warmer upper waters from the tropics near the equator out to the poles. The land mass of the continents greatly affects these movements of these currents as the water follows the contours of the various coastlines.
The earths continual rotation on its axis has a marked effect on the direction of air currents around the earth. This is called the Coriolis effect and as the earth spins faster at the equator than out at the poles  this differing rotational speed  deflects wind to the right in the northern hemisphere creating high pressure when clockwise and low pressure when anticlockwise and to the left in the southern hemisphere, creating high pressure anticlockwise and low pressure clockwise. This system provides the UK with its prevailing south westerly winds which are generated in the sub tropics as high pressure in the south, they travel northwards towards the north pole but are deflected by the Coriolis effect over to the right and pass over the UK. 
The moon and its gravitational pull also affect the oceanic movements with the twice daily tidal range particulary affecting countries like the UK which has very high tidal fluctuations reaching 15m in the Severn estuary, only being surpassed by the greatest tidal range on Earth of 16m in the Bay of Fundy in Canada.
The oceans are a climate regulator as they are slow to heat up and slow to cool down acting like a giant radiator causing land masses near oceans to be more temperate than land masses far from the oceans influence. The ocean is recently being seen not simply a victim of climate change, but a powerful source of solutions as it can produce vast amounts of oxygen O2 and absorb vast amounts of carbon dioxide CO2 and it contains all of the nutrients required for aquatic plant growth which if managed correctly could produce much of the food required for our growing population whilst reducing the carbon dioxide levels of the atmosphere. 
As the earth continues to warm up so does its oceans and with a predicted rise of between 1.5 degrees to 2 degrees C in global temperatures by 2050 compared with pre industrial levels the oxygen capacity of the oceans is compromised as warmer water is able to hold less dissolved oxygen (Greenhalgh, 2015). Dead zones could be created in large parts of the oceans  where thermocline action is decreased due to warmer sea temperatures and the reduced  mixing of deep currents cause stratification of the ocean, the surface layer that traps the O2 would not distribute it into deeper water. If the deeper waters are not oxygenated by being circulated, they will be prevented from absorbing oxygen from the atmosphere and become further depleted leading to marine biodiversity loss. (Altieri and Gedan, 2014). 
Sea level rises caused by global warming melting sea ice are causing global sea levels to increase and low-lying islands and wetland habitats are already being impacted. Wetland habitats are vital as they help prevent eutrophication in the various shallow  intertidal waters by filtering from river systems excess nutrients from run off or leaching of artificial fertilizers off agricultural land or nutrient rich sewage plant outflows, often excessive phosphates and nitrogen which could otherwise cause anoxic conditions as algal blooms caused by very rapid and excessive growth of cyanobacteria. This results in reduction of sunlight reaching other plants and animals in the water body and causing anoxic conditions resulting in dead zones where fish and invertebrates die through lack of oxygen. These are likely to be more serious in the higher latitudes due to these areas experiencing the highest increases in temperatures. (Zielinski, 2014). Declines in wetlands due to sea level rise could therefore result in harmful levels of nutrients reaching coastal areas. Sea level rise is also increasing the total volume of water susceptible to eutrophication because of the expanse in volume of shallow coastal regions 
Over half of the world’s population live near to the coast due to the positive climatic benefits the oceans bring. (Rose 2004). The International Panel of Climate Change IPCC special report on ocean and cryosphere 2019 made clear that as sea levels rise due to global warming hundreds of communities throughout the globe that are in lower lying areas are very vulnerable to massive disruption through flooding causing economic ruin and potential death of millions. 


References
Altieri, A.H. and Gedan, K.B., 2015. Climate change and dead zones. Global change biology, 21(4), pp.1395-1406.
Campbell, N.A., Reece, J.B., Urry, L.A., Cain, M.L., Wasserman, S.A., Minorsky, P.V. and Jackson, R.B., 2002. Biology, Vol.
Curry, J.A. and Webster, P.J., 1998. Thermodynamics of atmospheres and oceans. Elsevier.
Gregory, J.M., Stott, P.A., Cresswell, D.J., Rayner, N.A., Gordon, C. and Sexton, D.M.H., 2002. Recent and future changes in Arctic sea ice simulated by the HadCM3 AOGCM. Geophysical Research Letters, 29(24), pp.28-1.
Hoegh-Guldberg, O., Northrop, E. and Lubchenco, J., 2019. The ocean is key to achieving climate and societal goals. Science, 365(6460), pp.1372-1374.
Zielinski, S., 2015. Ocean dead zones are getting worse globally due to climate change. Acesso em, 21.