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Downwelling
Downwelling is the downward movement of a fluid parcel and its properties (e.g., salinity, temperature, pH) within a larger fluid. It is closely related to upwelling, the upward movement of fluid. While downwelling is most commonly used to describe an oceanic process, it's also used to describe a variety of Earth phenomena. This includes mantle dynamics, air movement, and movement in freshwater systems (e.g., large lakes). This article will focus on oceanic downwelling and its important implications for ocean circulation and biogeochemical cycles. Two primary mechanisms transport water downward: buoyancy forcing and wind-driven Ekman transport (i.e., Ekman pumping). Downwelling has important implications for marine life. Surface water generally has a lower nutrient content compared to deep water due to primary production using nutrients in the photic zone. Surface water is, however, high in oxygen compared to the deep ocean due to photosynthesis and air-sea gas exchange. When ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Langmuir Circulation
In physical oceanography, Langmuir circulation consists of a series of shallow, slow, counter-rotating vortices at the ocean's surface aligned with the wind. These circulations are developed when wind blows steadily over the sea surface. Irving Langmuir discovered this phenomenon after observing windrows of seaweed in the Sargasso Sea in 1927. Langmuir circulations circulate within the mixed layer; however, it is not yet so clear how strongly they can cause mixing at the base of the mixed layer. Theory The driving force of these circulations is an interaction of the mean flow with wave averaged flows of the surface waves. Stokes drift velocity of the waves stretches and tilts the vorticity of the flow near the surface. The production of vorticity in the upper ocean is balanced by downward (often turbulent) diffusion \nu_T. For a flow driven by a wind \tau characterized by friction velocity u_* the ratio of vorticity diffusion and production defines the Langmuir number ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ocean Gyre
In oceanography, a gyre () is any large system of ocean surface currents moving in a circular fashion driven by wind movements. Gyres are caused by the Coriolis effect; planetary vorticity, horizontal friction and vertical friction determine the circulatory patterns from the '' wind stress curl'' (torque). ''Gyre'' can refer to any type of vortex in an atmosphere or a sea, even one that is human-created, but it is most commonly used in terrestrial oceanography to refer to the major ocean systems. Gyre formation The largest ocean gyres are wind-driven, meaning that their locations and dynamics are controlled by the prevailing global wind patterns: easterlies at the tropics and westerlies at the midlatitudes. These wind patterns result in a wind stress curl that drives Ekman pumping in the subtropics (resulting in downwelling) and Ekman suction in subpolar regions (resulting in upwelling). Ekman pumping results in an increased sea surface height at the center of the gyre ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ekman Transport
Ekman transport is part of Ekman motion theory, first investigated in 1902 by Vagn Walfrid Ekman. Winds are the main source of energy for ocean circulation, and Ekman transport is a component of wind-driven ocean current. Ekman transport occurs when ocean surface waters are influenced by the friction force acting on them via the wind. As the wind blows it casts a friction force on the ocean surface that drags the upper 10-100m of the water column with it. However, due to the influence of the Coriolis force, Coriolis effect, as the ocean water moves it is subject to a force at a 90° angle from the direction of motion causing the water to move at an angle to the wind direction. The direction of transport is dependent on the hemisphere: in the Northern Hemisphere, northern hemisphere, transport veers clockwise from wind direction, while in the Southern Hemisphere, southern hemisphere it veers anticlockwise.Colling, pp 42-44 This phenomenon was first noted by Fridtjof Nansen, who reco ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ekman Layer
Ekman transport is part of Ekman motion theory, first investigated in 1902 by Vagn Walfrid Ekman. Winds are the main source of energy for ocean circulation, and Ekman transport is a component of wind-driven ocean current. Ekman transport occurs when ocean surface waters are influenced by the friction force acting on them via the wind. As the wind blows it casts a friction force on the ocean surface that drags the upper 10-100m of the water column with it. However, due to the influence of the Coriolis effect, as the ocean water moves it is subject to a force at a 90° angle from the direction of motion causing the water to move at an angle to the wind direction. The direction of transport is dependent on the hemisphere: in the northern hemisphere, transport veers clockwise from wind direction, while in the southern hemisphere it veers anticlockwise.Colling, pp 42-44 This phenomenon was first noted by Fridtjof Nansen, who recorded that ice transport appeared to occur at an angle ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Upwelling
Upwelling is an physical oceanography, oceanographic phenomenon that involves wind-driven motion of dense, cooler, and usually nutrient-rich water from deep water towards the ocean surface. It replaces the warmer and usually nutrient-depleted surface water. The nutrient-rich upwelled water stimulates the growth and reproduction of primary producers such as phytoplankton. The biomass of phytoplankton and the presence of cool water in those regions allow upwelling zones to be identified by cool sea surface temperatures (SST) and high concentrations of chlorophyll a. The increased availability of nutrients in upwelling regions results in high levels of primary production and thus fishery production. Approximately 25% of the total global marine fish catches come from five upwellings, which occupy only 5% of the total ocean area.Jennings, S., Kaiser, M.J., Reynolds, J.D. (2001) "Marine Fisheries Ecology." Oxford: Blackwell Science Ltd. Upwellings that are driven by coastal ocean curr ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Mixed Layer
The oceanic or limnological mixed layer is a layer in which active turbulence has homogenized some range of depths. The surface mixed layer is a layer where this turbulence is generated by winds, surface heat fluxes, or processes such as evaporation or sea ice formation which result in an increase in salinity. The atmospheric mixed layer is a zone having nearly constant potential temperature and specific humidity with height. The depth of the atmospheric mixed layer is known as the mixing height. Turbulence typically plays a role in the formation of fluid mixed layers. Oceanic mixed layer Importance of the mixed layer The mixed layer plays an important role in the physical climate. Because the specific heat of ocean water is much larger than that of air, the top 2.5 m of the ocean holds as much heat as the entire atmosphere above it. Thus the heat required to change a mixed layer of 2.5 m by 1 °C would be sufficient to raise the temperature of the atmosphere by 1&nbs ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Coastal Downwelling
A coast (coastline, shoreline, seashore) is the land next to the sea or the line that forms the boundary between the land and the ocean or a lake. Coasts are influenced by the topography of the surrounding landscape and by aquatic erosion, such as that caused by waves. The geological composition of rock and soil dictates the type of shore that is created. Earth has about of coastline. Coasts are important zones in natural ecosystems, often home to a wide range of biodiversity. On land, they harbor ecosystems, such as freshwater or estuarine wetlands, that are important for birds and other terrestrial animals. In wave-protected areas, coasts harbor salt marshes, mangroves, and seagrasses, all of which can provide nursery habitat for finfish, shellfish, and other aquatic animals. Rocky shores are usually found along exposed coasts and provide habitat for a wide range of sessile animals (e.g. mussels, starfish, barnacles) and various kinds of seaweeds. In physical oceanography, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Greenland Sea
The Greenland Sea ( Danish: ''Grønlandshavet'') is a body of water that borders Greenland to the west, the Svalbard archipelago to the east, Fram Strait and the Arctic Ocean to the north, and the Norwegian Sea and Iceland to the south. The Greenland Sea is often defined as part of the Arctic Ocean, sometimes as part of the Atlantic Ocean. However, definitions of the Arctic Ocean and its seas tend to be imprecise or arbitrary. In general usage the term "Arctic Ocean" would exclude the Greenland Sea. In oceanographic studies the Greenland Sea is considered part of the Nordic Seas, along with the Norwegian Sea. The Nordic Seas are the main connection between the Arctic and Atlantic oceans and, as such, could be of great significance in a possible shutdown of thermohaline circulation. In oceanography the Arctic Ocean and Nordic Seas are often referred to collectively as the "Arctic Mediterranean Sea", a marginal sea of the Atlantic. The sea has Arctic climate with regular northe ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Mediterranean Sea
The Mediterranean Sea ( ) is a sea connected to the Atlantic Ocean, surrounded by the Mediterranean basin and almost completely enclosed by land: on the east by the Levant in West Asia, on the north by Anatolia in West Asia and Southern Europe, on the south by North Africa, and on the west almost by the Morocco–Spain border. The Mediterranean Sea covers an area of about , representing 0.7% of the global ocean surface, but its connection to the Atlantic via the Strait of Gibraltar—the narrow strait that connects the Atlantic Ocean to the Mediterranean Sea and separates the Iberian Peninsula in Europe from Morocco in Africa—is only wide. Geological evidence indicates that around 5.9 million years ago, the Mediterranean was cut off from the Atlantic and was partly or completely desiccation, desiccated over a period of some 600,000 years during the Messinian salinity crisis before being refilled by the Zanclean flood about 5.3 million years ago. The sea was an important ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Latent Heat
Latent heat (also known as latent energy or heat of transformation) is energy released or absorbed, by a body or a thermodynamic system, during a constant-temperature process—usually a first-order phase transition, like melting or condensation. Latent heat can be understood as hidden energy which is supplied or extracted to change the state of a substance without changing its temperature or pressure. This includes the latent heat of fusion (solid to liquid), the latent heat of vaporization (liquid to gas) and the latent heat of sublimation (solid to gas). The term was introduced around 1762 by Scottish chemist Joseph Black. Black used the term in the context of calorimetry where a heat transfer caused a volume change in a body while its temperature was constant. In contrast to latent heat, sensible heat is energy transferred as heat, with a resultant temperature change in a body. Usage The terms ''sensible heat'' and ''latent heat'' refer to energy transferred between a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sea Ice
Sea ice arises as seawater freezes. Because ice is less density, dense than water, it floats on the ocean's surface (as does fresh water ice). Sea ice covers about 7% of the Earth's surface and about 12% of the world's oceans. Much of the world's sea ice is enclosed within the polar ice packs in the Earth's polar regions: the Arctic ice pack of the Arctic Ocean and the Antarctic ice pack of the Southern Ocean. Polar packs undergo a significant yearly cycling in surface extent, a natural process upon which depends the Arctic ecology, including the Arctic sea ice ecology and history, ocean's ecosystems. Due to the action of winds, currents and temperature fluctuations, sea ice is very dynamic, leading to a wide variety of ice types and features. Sea ice may be contrasted with icebergs, which are chunks of ice shelf, ice shelves or glaciers that Ice calving, calve into the ocean. Depending on location, sea ice expanses may also incorporate icebergs. General features and dynamics ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Westerlies
The westerlies, anti-trades, or prevailing westerlies, are prevailing winds from the west toward the east in the middle latitudes between 30 and 60 degrees latitude. They originate from the high-pressure areas in the horse latitudes (about 30 degrees) and trend towards the poles and steer extratropical cyclones in this general manner. Tropical cyclones which cross the subtropical ridge axis into the westerlies recurve due to the increased westerly flow. The winds are predominantly from the southwest in the Northern Hemisphere and from the northwest in the Southern Hemisphere. The westerlies are strongest in the winter hemisphere and times when the pressure is lower over the poles, while they are weakest in the summer hemisphere and when pressures are higher over the poles. The westerlies are particularly strong, especially in the Southern Hemisphere (called also 'Brave West winds' at striking Chile, Argentina, Tasmania and New Zealand), in areas where land is absent, bec ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
