Ocean Currents and Climate Change
Yet ocean currents were surely a main component of the climate system. In , the. NOAA's Ocean Service's Education Professional Development,Oceans, Nautical Charts · Sea Floor Mapping · Corals · Currents · Estuaries · Global Climate Patterns; Precipitation & Energy; Circulation Patterns; Changing Climate Describe the relationship between density of liquids and gases and their temperatures. relationship between the temperature of the ocean current and temperature and The labels on the graphs are not directly on the lines, so the teacher would .
This evaporation-condensation cycle is an important mechanism for transferring heat energy from the Earth's surface to its atmosphere and in moving heat around the Earth.
The areas with the lowest humidity brownish are those that have the weakest circulation and were feared by sailors because of a lack of sustained winds. Water also has a substantially higher heat capacity than rocks by a factor of fiveand therefore the oceans can store much more heat than the land surfaces of the planet.
The bulk of the thermal energy at the Earth surface is stored in the oceans.
Climate Connection: Global Conveyor Belt | promovare-site.info
The large thermal inertia of the oceans is a key factor in stabilizing Earth's climate. Because the oceans are of course also heated more intensely in the equatorial regions, there is abundant warm water near the equator, and cold water in the polar regions.
The atmospheric circulation that is set up between the equator and the poles also influences the redistribution of these water masses. Wind blowing over the ocean surface exerts drag friction and starts to move the surface waters. In addition the currents are influenced by the Coriolis Force and the tides. A general pattern of ocean current is shown in the map below.How Does The Temperature Of Ocean Currents Affect Climate?
The currents are also influenced by the position of landmasses. Whereas in the Pacific we have currents that more or less correspond to the patterns of the surface winds, current patterns look more complex in the Indian Ocean and the Atlantic.
In the North Atlantic, the Gulfstream moves warm equatorial surface waters northward, and a return current of cold arctic water moves southward across the Atlantic seafloor. Decades of research on ocean currents have revealed that there is a large scale oceanic circulation system.
The Gulfstream that moves into the North Atlantic finally sinks as it cools and returns south across the Atlantic seafloor, flows as a bottom current into the South Atlantic, and then rises to the surface again in the Indian Ocean and the Eastern Pacific, only to warm up absorbing heat from overlying air masses and turn west to feed back into the Gulfstream.
Actually, the sinking of the Gulf Stream is not so much a consequence of cooling and density increase, but one of salinity. Equatorial surface waters are more saline high evaporationand the waters of the North Atlantic are less saline because they mix with meltwater [low salinity] from icebergs and from the Greenland ice cap.
Thus, once the Gulfstream cools sufficiently it is heavier that the lower salinity North Atlantic seawater and sinks.
Global Energy Transfer, Atmosphere, Climate
A complete run through this current system is estimated to take about years. At the moment this current system appears very stable, but comparatively minor changes may upset the delicate balance of temperature differences and prevailing winds.
For example, scientists have speculated that melting of the Greenland icecap could introduce so much meltwater of low salinity and low density to the North Atlantic that the Gulfstream is prevented from sinking and returning as a southward flowing bottom current.
This would interrupt the current system and cause equatorial waters and regions to get warmer, and northern Europe to get colder.
Atmospheric and oceanic circulation are closely coupled. Specific examples for this kind of interaction are weather phenomena knows as El Nino and La Nina these will be discussed later. The net result of all these interactions, when averaged over periods of decades to centuries, is the Earth System's overall "condition", a state of dynamic equilibrium.
The global climate is a major expression of this "condition".
3.1 Factors affecting climate
Although circulation of air masses and ocean waters as outlined above plays a significant role in determining global heat exchange and average world temperatures, there are several other, more fundamental, controls on climate.
The basic items that determine Earth climate are: The movement of the continents across Earth's surface modulates the global climate on very long time scales by changing wind patterns, ocean currents, and the ease with which ice can accumulate. Under some configurations of continents and oceans the heat exchange may be severely impeded, leading to hot tropics and ice covered polar regions.
Also, when we have all the landmasses bunched up in the polar regions the warm ocean current may not get far enough north and we end up with glaciated continents.
Conversely, when we have all the continents hanging around the equator, the polar regions have very good oceanic heat exchange and world temperatures would be more uniform. Item 3 Greenhouse Effect will be discussed at some length later in this lecture. Basically, this is where linkage to the biosphere comes in. Item 1 Astronomical Parameterswill be surveyed now, because we have already set the stage by going over the origin of the solar system.
Earth's rapid rotation about its axis compared to the time for one orbit around the Sun determines day and night, spreads the incoming solar radiation more or less uniformly around circles of latitude, and strongly affects circulation patterns in the oceans and atmosphere. The eccentricity of Earth's orbit modulates the intensity of the incoming solar radiation through the course of the year.
The tilt of Earth's axis with respect to the ecliptic plane results in the seasons. Note, that it is summer in the northern hemisphere when the Earth is closest to the sun perihelion, January 3rd, million kmand winter when it is farthest away aphelion, July 4th, million km. Thus, the tilting of the northern hemisphere towards the sun in summer longer days, more solar energy input and the tilting away from the sun in the winter shorter days, less solar energy input are more important than the actual distance to the sun.
The relationship between the eccentricity of Earth's orbit and the orientation tilt of the planet's axis of rotation vary systematically over time. This causes cyclic shifts of solar energy input that can produce climate modulations repetitive temperature variations. This image shows a tracing of ocean surface temperatures for the pastyears, based on oxygen isotopes of marine microfossils.
We see a very clear periodicity of ca. Fluctuations in the Sun's output apparently with a period of to years may produce small changes in climate over intervals of to years.
A time interval of cooler temperatures that ranged from the midth to the midth century, also known as the "Little Ice Age", may have been caused this way, but this is a tentative interpretation. The Little Ice Age brought an end to an unusually warm era known as the Medieval climate optimum, and brought bitterly cold winters to many parts of the world.
It is most thoroughly documented in Europe and North America. In the midth century, glaciers in the Swiss Alps advanced, gradually engulfing farms and crushing entire villages.
The River Thames and the canals and rivers of the Netherlands often froze over during the winter, and people skated and even held fairs on the ice. Sea ice surrounding Iceland extended for miles in every direction, closing that island nation's harbors to shipping.
The severe winters affected human life in ways large and small. The processes of wind driven surface currents, cold bottom water formation through density effects, and equatorial mixing are commonly referred to as global thermohaline circulation.
Through global thermohaline circulation, heat is transported from the tropics to the poles through surface currents and then cold water is transported back to the equator. By connecting ocean currents, scientists have some evidence to support what is known as the Global Conveyor Belt SF Fig 2. Bottom Water Currents The formation of dense bottom water near the poles forms a cold layer of ocean water on the ocean floor.
Bottom water is constantly being replenished at the poles, while it flows slowly towards the equator. Dense water forms and sinks in the Arctic ocean basin and flows southward between Greenland and Europe into the Atlantic ocean basin.
Because there are no continents to act as barriers, Antarctic Bottom Water flows into all ocean basins. A bottom water current does not form in the Northern Pacific ocean basin because the shallow Bering Strait between Alaska and Russia, which is between 30 and 50m deep, effectively acts like a barrier SF Fig 2.
Equatorial Mixing Surface currents driven by wind, especially those on western boundaries of ocean basins, explain how heat can be transported from the equator to the poles. Thermohaline circulation, through cold bottom water formation, explains how cool water moves back to the equator by traveling along the ocean floor.
Two processes contribute to mixing of cold bottom water and warm surface water near the equator.
The first is tidal mixing. Tides are shallow water waves with very large wavelengths. As tidal waves come into contact with continents and mid-ocean ridges they can cause mixing.