2.2) Hydrosphere

Question 1

• Describe the PROCESS of the hydrological cycle.

Answer 1

The hydrological cycle is a system composed of inputs, stores, flows or movements and outputs.

1. Solar energy (or insolation) powers the hydrological cycle. By heating the Earth, water is evaporated into the atmosphere.
2. Most of this water vapour comes from the oceans, especially from the tropical regions where the sun’s energy is greatest and heating is most intense.
3. Water is also added to the atmosphere via the process of transpiration (vapour lost through the leaves of plants which have drawn water from the soil) and via sublimation from ice caps and glaciers (from solid ice straight to a gaseous water vapour).
4. All this moisture-laden air is transferred by the system of global winds. Unable to retain all of this water vapour, condensation in the atmosphere results in precipitation (rain or snow) depending on altitude.
5. Precipitation over the sea represents a very quick completion of the cycle, but some water molecules may remain locked in ice caps for thousands of years.
6. Water can make its way back to the ocean by a variety of means. The most noticeable and fastest method is by surface run-off.
7. Major rivers (such as the Amazon and Mississippi) are impressive features and very important locally, but rivers are merely a minor trickle within the vast transfer of water within the hydrological cycle.
8. Water which does not flow over the land surface can seep into the soil and move through it as throughflow.
9. If the underlying rock is permeable (e.g., sedimentary rocks, such as limestone, chalk and sandstone), water will percolate downwards until the rock is saturated, creating subterranean groundwater stores known as aquifers.
10. The saturated rock slowly releases the water allowing it to flow back to the sea via springs and into river systems. The slow release of groundwater allows rivers to continue flowing despite periods of drought.

Question 2

• What is oceanic circulation?

Answer 2

• The world’s oceans play an important role in redistributing energy (heat) around the globe.
• Energy is moved from areas of surplus (high) to those of clear deficit (low), with warm currents transporting warm water polewards and cold currents taking colder water to lower latitudes (towards the Equator).

Question 3

• What is the Global Ocean Conveyor Belt?

Answer 3

• The global ocean conveyor belt is a constantly moving system of deep ocean circulation driven by thermohaline circulation (circulation driven by differences in sewater density, caused by temperature and salinity) and surface wind currents.
• As ocean water in polar regions cools, it forms sea ice, drawing out the freshwater and causing the surrounding water to get saltier.
  ➞ This increases its density and the cold water starts to sink. Surface water is pulled in to replace the sinking water, which then also becomes cold and salty enough to sink. This initiates the deep ocean currents driving the global ocean conveyor belt.
• The Gulf Stream transports warm water away from the Equator.
  ➞ As more warm water is transported north, the cooler water sinks and moves south of the Equator down towards Antarctica.
• Eventually, the cold bottom waters return to the surface through mixing and upwelling, continuing the ocean conveyor belt that encircles the globe.
• The water that returns to the surface through upwelling is usually rich in nutrients. These boost the growth of primary producers, which support marine food webs.

Question 4

• What factors are affecting ocean currents (THERMOHALINE CIRCULATION)?

Answer 4

• Winds drive ocean currents in the upper 100 metres of the oceans surface.
• However, ocean currents also flow thousands of metres below the surface. These deep-ocean currents are driven by differences in the water’s density which is controlled by temperatures (thermo) and salinity (haline).
• This process is known as ‘thermohaline circulation.

Question 5

• What factors are affecting ocean currents (CONTINENTAL LOCATION)?

Answer 5

• The topography and shape of ocean basins and nearby land masses also influence ocean currents.
  ➞ These forces and physical characteristics affect the size, shape, speed, and direction of ocean currents.
• The movement of this heat through local and global ocean currents affects:
  1. the regulation of local weather conditions and temperature extremes (e.g., El Nino/La Nina),
  2. stabilization of global climate patterns,
  3. cycling of gases,
  4. and delivery of nutrients and larva to marine ecosystems.

Question 6

• What factors are affecting ocean currents (SURFACE WINDS)?

Answer 6

• The movement of air produces wind. These wind patterns show how the air moves. It always moves from high to low pressure.
• Surface ocean currents are driven largely by the major wind systems.
• Ocean water circulates in gyres and loops, controlled by the wind systems.
• The waters near the Equator recieve more heat than those near the poles. Therefore, warm water flows outwards from the equatorial regions towards higher latitudes.
  ➞ In consequence, the colder water from the poles flows towards warmer regions creating a circulatory system.

Question 7

• What factors are affecting ocean currents (CORIOLIS FORCE)?

Answer 7

• As the Earth spins, we experience a force known as the Coriolis Force.
• This deflects the direction of the wind to the right in the Northern Hemisphere and to the left in the Southern Hemisphere.

Question 8

• What are ‘ocean gyres’?

Answer 8

• Ocean gyres are large systems of circular ocean currents formed by global wind patterns and forces created by the Earth’s rotation.
• The five major circulation patterns formed by the currents are the world’s five major ocean gyres:
  1. North Atlantic,
  2. South Atlantic,
  3. Indian,
  4. North Pacific,
  5. South Pacific.

Question 9

• What is the PROCESS of ocean gyres?

Answer 9

• Global winds drag on the water’s surface, causing it to move and build up in the direction that the wind is blowing.
• The wind direction is influenced by the Coriolis Effect, resulting in the deflection of major surface ocean currents to the right in a clockwise spiral in the Northen Hemisphere and to the left in an anti-clockwise spiral in the Southern Hemisphere.
• These major spirals of ocean-circulating currents occur north and south of the Equator, but not at the Equator as the Coriolis Effect is absent there.
• The edges of a gyre and its content constantly change with ocean currents and winds, but the circulating nature of ocean gyres traps marine debris and can distribute this over huge surface areas and throughout the top of the water column.