Unit 6.1 Oceans and Climate Flashcards
Describe how warm ocean currents can influence regional climate.
Oceans transport huge amounts of heat, which can exceed the cooling we would expect from increasing latitude. For example, Bergen (Norway) is over 1700km farther from the equator than Halifax (Canada), but is warmer for much of the year. Equally, the South Georgia islands are a similar latitude S to the UK N, but is almost 60% covered in glaciers.
Recognise that oceans cover most of the planet.
Oceans cover approximately 70% of the surface of the Earth.
Describe different methods of measuring the depths of the global ocean.
Sounding: lowering a weight by rope until it reaches the floor. Originally, this was all done by hand, and could take over 2 hours per sounding, during which time the ship had to be stopped. In time, steam powered winches speeded up the process, but it was still slow and inaccurate.
Sonar: emitting a sound pulse and measuring the time until the reflection is recorded. Recordings are much quicker, and from the 1930s knowledge of the ocean floor beneath commercial routes improved, but much of the ocean remained unsurveyed.
Satellite altimetry: measures the ‘bulges’ on the surface which result from the increased local gravity of sea mountains. This allows vast swathes of the ocean to be surveyed, although not to a high resolution, and not below sea ice.
Name areas of the ocean where knowledge of the sea floor may be poor or non-existent.
Altimetry does not work beneath sea ice, and so much polar water can only be surveyed through soundings. However, these are rarely taken, as there are few ships here.
Outline the principle of satellite altimetry.
Satellites can measure the height of the sea surface very accurately, to within a few centimetres.
Local variations in the shape of the sea floor are reflected in the mean shape of the sea surface, that is when the influence of the wind, tides and circulation are removed.
Altimetry is calibrated against areas of the sea floor that have been well surveyed by soundings.
Interpret a hypsometric curve.
E.g. Figure 2.5
A hypsometric curve shows the cumulative frequency of the amount of the Earth’s surface lying at any particular altitude.
Describe the main differences between the ocean basins.
The Pacific Ocean is the largest, and has proportionally the least land area, meaning that wind can flow across the ocean undisturbed. Flow of water above latitudes north of 60o N is blocked by the Bering Straits, but the ocean is virtually open to the south, and the southwest through the Indonesian archipelago.
The Atlantic Ocean is much narrower, yet almost completely open to the north and south. It has a greater proportion of land area, and is split almost equally down the middle by the Mid-Atlantic Ridge.
The Indian Ocean is the smallest of the large oceans, and the least explored. It is roughly triangular, of fairly uniform depth, but divided into deep basins by a mid-ocean ridge. Subject to very strong seasonal influence by the monsoons.
List the sources of different ionic constituents that make up the salts in seawater.
The major components are the products of chemical weathering if rocks, which are washed into the ocean. The exceptions are chlorine and sulfur, which originate as volcanic gases. These are washed out of the atmosphere by rain and are deposited into the oceans.
Describe what is meant by the principle of constancy of composition, and be able to explain why we can measure just one ionic constituent to determine how much salt is in seawater.
The principle of constancy of composition holds that although the total amount of salt varies from place to place, the major elements in seawater are always present in the same relative proportions.
As a consequence, it is possible to only measure a single ionic constituent, and know the total amount of salt, because that constituent will always be a fixed proportion of the total amount of salt. Up to the 1970s, salinity was defined as approximately 1.8 times the amount of chlorine ions present.
Describe how we know that the salinity in the oceans has not changed for the past 10^8 years.
Analysis of marine evaporate deposits and other sediments in the oceans.
Explain why the density of freshwater decreases below a temperature of 3.98 oC.
H2O is a polar molecule: the two hydrogen atoms sit to one side of the molecule. This results in a small net positive charge on the side of the two H atoms, and a small net negative charge on the oxygen side.
As a consequence, H2O molecules are attracted to each other by weak hydrogen bonds, giving an ordered packing of water.
However, when the temperature rises, these hydrogen bonds are broken, and the H2O molecules pack together more closely.
Above 4 oC and the increase in internal energy leads to lower density.
Explain the reasons why a map of sea-surface temperature would not match up with the incoming solar radiation.
The main reason that the SST does not match up with the average incoming solar radiation is that the ocean is not static.
Figs 3.6 and 3.7: Off the coast of Portugal, the cooler waters from the northwest are circulating in a clockwise direction bringing cooler waters south.
Describe the distribution of temperature with depth across the Atlantic Ocean and be able to explain why cooler water is at the sea floor.
Fig 3.9
The range of temperatures in the upper 1000m of the water is much greater than the range of temperatures below 1000m to the sea floor.
Explain how the balance of E - P controls surface salinity of seawater.
E: evaporation increases salinity, by removing water.
P: precipitation decreases salinity, by adding water.
The balance of evaporation and precipitation determines the salinity of saltwater.
Explain why the whole water column in the ocean needs to be cooled before the ocean freezes.
When water at the surface is cooled, its density increases and it sinks. The water which now replaces it at the surface is warmer, and so the cooling process must begin again. However, once this new surface water is cooled, it too sinks due to increased density. This process will continue for as long as there is uncooled water below.
